UNIVERSITY of DELAWARE
DEPARTMENT of CHEMISTRY and BIOCHEMISTRY
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June 23, 2008 -- Airplane wings, golf clubs and engine
parts made of glass alloys could be a step closer following new research
into the chaotic structure of glass.
Nature of Glass Remains Anything but Clear
It is well known that panes of stained
glass in old European churches are thicker at the bottom because glass
is a slow-moving liquid that
flows downward over centuries.
Anyone who has looked at the long-term history of human civilizations over the last 50,000 years will notice that one of the most significant transformations took place during the period 1200 to 1850. This transformation affected two of the most important human capacities: the way in which we think and our sense of sight. Compare the nature of painting in Europe in 1200 with that in 1850, or the amount of chemical, physical, and biological knowledge in Europe in 1200 to that in 1850, and one would not hesitate to pronounce that a revolution took place within this 650-year period. This revolution manifested itself not only in the world of art and architecture, but also in transport, housing, energy sources, agriculture, and manufacturing.
We know that all this happened, but after that there is little agreement. We are still uncertain as to why the Renaissance of the 14th, 15th, and 16th centuries, and the scientific and industrial revolutions of the 17th and 18th centuries took place. Nor do we understand why these sweeping changes happened in western Europe, and not in the great Islamic or Chinese civilizations.
The interplay between the availability of more reliable information and the improved manufacture of tools, instruments, and artifacts contributed to the remarkable changes that swept through western Europe. Often in history, we witness the generation of new knowledge through experimentation, which then leads to significant innovations and a richer appreciation of new or improved physical artifacts. These artifacts, if they are useful, in demand, and relatively easy to produce, are often disseminated in large quantities. These objects then change the conditions of everyday life and may fund further theoretical explorations. Such artifacts can do this in two ways: by generating wealth that funds increased efforts to acquire fresh knowledge and by providing better tools for scientific enquiry.
Historically, this triangle of knowledge-innovation-quantification emerged in many spheres of life, most notably in agriculture. The loop is enduring when artifacts are widely disseminated and is a cumulative process. The speed of movement around the triangle and the frequency of its repetition provide a measure of the development of human civilizations. Our analysis of this triangle in the history of glass production and application reveals that glass contributed to the rampant changes that swept through western Europe between 1200 and 1850.*
A Brief History of Glass
The Many Uses of Glass
Another crucial use of glass was for making windows. Until the 20th century, window glass was found mainly in the western regions of Eurasia (principally north of the Alps), appearing rarely in China, Japan, and India. Another application of glass depended on its reflective capacity when silvered. Produced by the Venetians in the 16th century, the use of glass mirrors spread throughout the whole of western Europe, but appeared rarely if at all in Islamic civilizations or in India, China, or Japan. A final critical application of glass was in the production of lenses and prisms. This led to the manufacture of spectacles to improve human sight; eyeglasses first appeared in Europe during the 13th and 14th centuries. The concept of the light-bending and magnifying properties of glass, discovered by the Chinese in the 12th century, was probably known to all Eurasian civilizations. Yet only in western Europe did the practice of making lenses really develop. This coincides precisely with the surge in interest in optics and mathematics during medieval times, which fed into other branches of learning, including architecture and painting.
The reasons for the different uses of glass in different parts of the world may be largely accidental, reflecting variations in climate, drinking habits, availability of pottery, political events, and many othercharacteristics. Intention, planning, individual psychology, superior intellect, or better resources seem to have little to do with it. Yet these accidents instigated the move of western European societies around the knowledge-innovation-quantification triangle. Improvements in glassmaking and the production of more sophisticated glass instruments yielded more accurate information about the natural and physical worlds, which fed back into refinements in glass manufacture and, hence, in glass quality.
Glass and Scientific Knowledge
The list of scientific fields of enquiry that could not have existed without glass instrumentation are legion: histology, pathology, protozoology, bacteriology, and molecular biology to name but a few. Astronomy, the more general biological sciences, physics, mineralogy, engineering, paleontology, vulcanology, and geology would have emerged much more slowly and in a very different form without the help of glass instruments. For example, without clear glass, the gas laws would not have been discovered and so there would have been no steam engine, no internal combustion engine, no electricity, no light bulbs, no cameras, and no television. Without clear glass, Hooke, van Leeuwenhoek, Pasteur, and Koch would not have been able to visualize microorganisms under the microscope, an achievement that led to the birth of germ theory and a new understanding of infectious disease, which launched the medical revolution (see the photograph on page 1407).
Chemistry depends heavily on glass instrumentation. Thanks to glass, European scientists elucidated the chemistry of nitrogen and learned to fix this gas in the form of ammonia to produce artificial nitrogenous fertilizers, a huge step forward in 19th- and 20th-century agriculture. Without glass, there would have been no means of demonstrating the structure of the solar system, no measurement of stellar parallax, no way of substantiating the conjectures of Copernicus and Galileo. The application of glass instruments revolutionized our understanding of the universe and deep space, completely altering our whole concept of cosmology. Furthermore, without glass, we would have no understanding of cell division (or of cells), no detailed understanding of genetics, and certainly no discovery of DNA. Without spectacles, most individuals over the age of 50 would not have been able to read this article. Glass may be an unforeseen accident, but it follows a predictable pattern of movement around the triangle: deeper reliable knowledge enabling the manufacture of innovative artifacts followed by their mass production.
Glass in Everyday Life
Glass, however, is not just a tool to think and perceive with, but also a tool to improve everyday life. The period between the 13th and mid-19th centuries in Europe saw many changes made possible by glass that contributed not only to the intellectual flowering of this era but also to an improved standard of living for many people. For example, glass in the form of windows lengthened the working day and improved conditions for workers. Glass let light into interiors allowing house dirt to become more apparent leading to improvements in hygiene and health. Also, glass is a tough, protective surface that is easy to clean. Glass windows wrought changes not only in private homes, but also in shops with shopkeepers eventually placing much of their produce and merchandise behind glass windows and under glass cabinets.
This clear molten liquid began to transform agriculture and horticulture. The use of glass houses to promote the precocious growth of plants was not an invention of early modern Europe. Indeed, the Romans used forcing houses to promote plant growth and protected their grapes with glass. The Roman idea was revived in the later Middle Ages, when glass pavilions for growing flowers and later fruit and vegetables began to appear. As glass became cheaper and, particularly, flat window glass improved in quality, many more applications appeared. Glass cloches and greenhouses improved the cultivation of fruit and vegetables, bringing a healthier diet to the population. In the 19th century, glass made it possible to bring plants from all over the world to enrich European farms and gardens.
There are many other useful applications of glass that altered everyday life from the 15th century onward. Among them were storm-proof lanterns, enclosed coaches, watch-glasses, lighthouses, and street lighting. The sextant required glass, and the precision chronometer invented by Harrison in 1714, which provided a solution to calculating longitude at sea, would not have been possible without glass. Thus, glass directly contributed to navigation and travel. Then, there was the contribution of glass bottles, which increasingly revolutionized the distribution and storage of drinks, foods, and medicines. Indeed, glass bottles created a revolution in drinking habits by allowing wine and beer to be more easily stored and transported. First through drinking vessels and windows, then through lanterns, lighthouses, and greenhouses, and finally through cameras, television, and many other glass artifacts, our modern world has emerged from a sea of glass.
The different applications of glass are all interconnected--windows improved working conditions, spectacles lengthened working life, stained glass added to the fascination and mystery of light and, hence, a desire to study optics. The rich set of interconnections of this largely invisible substance have made glass both fascinating and powerful, a molten liquid that has shaped our world.
Enhance the Service: Eliminate the Competition
FUSION, Journal of The American Scientific Glassblowers Society, May
Are you concerned that the glassblowing services you provide could potentially be outsourced? If so, you are not alone. Through discussions with ASGS friends, I have learned that many glassblowers share this apprehension to some extent. While this article focuses mainly on outsourcing concerns facing university and other research glassblowers—the most targeted groups to date—hopefully the information will be helpful to others also. Its purpose is not to create additional anxiety, but rather to promote confidence and strengthen job security.
Within the past couple of years, we have all heard horror stories of a few institutions outsourcing glassblowing services. Fast spreading reports of each incident have ruffled some feathers in the glassblowing community. You may wonder why institutions would elect to make those decisions. You may even ask yourself if those decisions were fair. Surprisingly, I have heard conflicting opinions, not only from case to case, but also from person to person.
Undoubtedly, one reason for institutions to consider outsourcing is a decline in government funding, a situation which has certainly made writing grant proposals more competitive. That situation will probably not change in the near future. Also, floor space is extremely expensive and under constant evaluation for highest priority usage. (This could be the main reason many of us are located in basements or somewhat less sought after areas.) Furthermore, some glassware manufacturers have been forced to consider creative ways to compete with less expensive foreign-made products. As a result, some of these companies have decided that they must offer outsourcing services to survive, even though this is an extremely unpopular practice. They try to appeal to employers by offering to pick up and drop off glassware a couple times a week. Their plan is to work toward being the sole source for all glass needs. Unfortunately, these factors are out of our control.
Outsourcing glassblowing services usually comes into play as an attempt to cut expenses or expand another initiative believed to be a more worthwhile endeavor at that time. However there is another consideration—a very important consideration that employers should evaluate: Are outsiders able to provide services that benefit research efforts, like we can? The answer to that question depends a lot on us and the actions we choose to take. I am thoroughly convinced that we can provide better overall research enhancing services “in-house.” After all, researchers like having us readily available for assisting with design, making changes along the way, or providing immediate support when a problem arises. They greatly appreciate and value our assistance; we definitely provide a nice convenience for them. However, like it or not …we are not a “necessity.”
As I see it, we have only two possible choices. We can offer basic fabrication and repair services, as has been done through the years, and hope to retain our job until retirement. Of course we would be taking a risk that our employers could very well contemplate better uses for our area after we are gone. Or, we can choose to do as some have and include other beneficial services that outside concerns cannot provide. Without question, most of us care about our profession and would choose the more active role, not only to secure our positions but also to enhance research efforts. For those individuals, I offer the following suggestions.
Although it can be difficult at times, the key is to be customer service oriented as much as possible, and also be willing to accept inevitable change. Along with assuring each visitor you can confidently design and fabricate glassware or instruments, be more aggressive in recommending other viable ideas or solutions. Never act as though a job is a lot of trouble or make researchers think they have inconvenienced you unnecessarily. This behavior would create an uncomfortable atmosphere, forcing them to seek assistance elsewhere. They should always feel welcome in your shop, even if they managed to break the same item two or three times. (By the way, if you find this to be a continuous problem you may consider redesigning the glassware so it will be structurally stronger for their particular application.) Also seek to understand what the researchers are trying to achieve and consider how you can help them get results easier, faster or more economically. Go see how the research groups are using your glassware. Make some evaluations: Is it mounted and clamped correctly? Are stopcocks greased and operating properly? Do you notice any vacuum, contamination or other potential problems?
You will discover that most researchers do appreciate a tip that may improve their research efforts or possibly lessen breakage. Now I am not suggesting that you “drive a point home” or make them feel as though you are overstepping your bounds. This behavior would surely lead to poor relations. You want them to feel you are a team player and a useful resource they can depend on. Also, never say, “I don’t know” without following up with “I’ll try to find out and get back to you.” Occasionally a job may come in requiring specialized machining, plating or other service beyond the capability of your shop. In this case, offer to find a reliable resource that can do their job at a reasonable price. Researchers should feel confident knowing that they will leave our shops with a solution, or at the very least, less of a problem than when they came.
In addition, try to maintain an up-to-date technical and material library to assist in locating almost anything that may be needed. Volunteer to go online and track down hard-to-find glass or related equipment. Many Web sources provide new, used or even discontinued items. If time allows, go the extra mile to find out availability or prices. It may take a little extra time, but your effort will be appreciated. In other words, don’t limit yourself to only fabricating and repairing glassware. You may want to offer the service of salvaging glass apparatus and instruments that can be utilized by another department or group. It involves requesting unused items be brought to you, or possibly visiting recently vacated labs to gather them up before they are indiscriminately discarded. These items can then be cleaned, repaired and offered to the research community. Another popular service you may consider is disposal of obsolete glassware or related instruments. Some of these items require strict reclamation or recycling procedures, and may stipulate you work closely with Occupational Health and Safety.
If you haven’t done so already, you might try creating a Web site to show the full capabilities of your glass shop. Depending on information posted, it could prove to be a valuable resource for your research groups. Lastly, you may consider volunteering for or accepting temporary committee positions when asked. Although some may be quite time consuming (and cause a larger backlog), I have actually found they provide rewarding experiences overall. Always take advantage of the opportunity to provide input that may affect the direction and future of your unit.
Most of you are already important assets to your institutions and currently offer many varied services. It is to our benefit--and definitely to the benefit of our colleagues--that we avoid complaisance and maintain a dedicated work ethic and enthusiastic attitude. We should be an easily approachable and useful resource that researchers consider crucial to their team. We can blame others for what seems to be a growing outsourcing trend in our field, or we can concentrate on what we CAN do: We can change our viewpoint, expand our services, and facilitate research in the process. Remember that institutions with strong R&D programs almost always employ at least one in-house glassblower. Therefore, it is certainly in our best interest to help them grow. Of course we do not have the time or energy to solve every problem encountered in an eight hour day. Our services offered must be limited due to individual time constraints and workload. However, we should re-evaluate those restraints periodically to provide realistic services that prove to be most beneficial.
I am fortunate to have recently been relocated to a newly renovated shop. I’d like to believe that my efforts and services have helped justify the cost, inconveniences incurred and more importantly the area. My hope is to remain a valuable resource here at the University of Delaware. My goal is the same as many of yours, which is to maintain the need for future scientific glassblowers that will fill our shoes one day.
Submitted to A.S.G.S. by: Doug Nixon
|Did you ever wonder where the odd or interesting names came from for much of our glassware or instruments?|
||This article explains some of them, as well as a few quirky and tragic facts about the individuals themselves....|
Names in Glass Apparatus- By
This paper is the result of a casual
interest in the names of glass apparatus found in catalogues of scientific
glassware. I found myself wondering why a beaker should be a “Berzelius” beaker,
or a gauge a “McLeod” gauge. I wondered
also how long these names had been in use. Eventually, I began to do
a little digging in our library and was amazed at the way these names
seemed to spread over the whole history of science. It was very gratifying
to find that these famous men had so close an association with glass
apparatus, but a little disconcerting to find no mention at all of
the Glassblowers who had manufactured the apparatus.
For about thirty years after the
death of Berzelius, the dominant figure in Chemistry was Baron Justus
Von Liebig (1803-1873). He stared life as an apothecary’s apprentice,
but, through the help of some influential friends, managed to obtain
a position in the laboratories of Gay-Lussac, in Paris. In 1824, when
twenty-one years old, he became Professor of Chemistry at the University
of Geissen. There he introduced a tremendous innovation by setting
up the first laboratory ever for student use. This set a completely
new pattern in the instruction of science students. In collaboration
with Wohler, he was responsible for much of the early work in organic
chemistry, and was also one of the first to experiment with chemical
fertilizers. In appreciation for his work, he was made a Baron in 1842.
To us, he is known as the inventor of the most famous and widely used
of all condensers, the Liebig condenser.
NMR tubes are not 'analytically clean' when delivered to you
Simple Cleaning of NMR Tubes
Removing Water from NMR Tubes
Sponges are the homes of colonies of tiny marine animals, and wonders of miniaturized engineering. They employ complex structural arrangements, the strongest glasses known to man, and even microscopic fiber optics that glow in the dark. Scientists are trying to figure how to reproduce some of their tricks, such as producing glass at low temperatures.
Science behind the news is funded by a generous grant from the NSF
BACKGROUND: Bell Labs researchers have discovered that a sea organism known as the glass sponge uses basic principles much like those found in mechanical engineering textbooks to reinforce its seemingly delicate and brittle structure. Its architecture calls to mind the Eiffel Tower in Paris. Studying such creatures could lead to new concepts in materials science and engineering design.
ABOUT THE GLASS SPONGE: Unlike the squishy, manmade sponges we see all the time in our daily lives, sponges are an ancient group of animals whose presence in the fossil record goes back more than half a billion years. Sponges may be groups of collaborating individual cells rather than one unified animal, since they don't form tissues. This means they don't have hearts, lungs or other organs. But they are capable of creating some of the most complex and diverse systems of skeletons known in nature.
The glass sponge is made entirely of glass, spun into delicate fibers. It can even emit light despite the darkness of deep sea levels, thanks to the presence of fluorescent bacteria embedded in its structure. The intricate glass cages of the sponge have at least seven levels of structural organization. The creatures use fiber-reinforced cements, beams of bundled fibers, and diagonal reinforcement beams running at 45-degree angles to achieve maximum strength and stability. The glass beams, which resemble small needles, are made of alternating layers of glass and glue; the glue between each glass layer prevents cracks from spreading from one layer to the next. Wherever the beams intersect, more glue is added to toughen the connection.
WHAT WE COULD LEARN: By studying the glass sponge, scientists could learn how to create a strong material out of something that seems to be frail. It may also hold the secret to making glass at room temperature, instead of the extremely high temperatures required to do so today. Researchers believe that the individual glass fibers in the sponge are formed by a protein at the center of each glass filament.
The American Society of Civil Engineers contributed to the information contained in the TV portion of this report.
American Society of Civil Engineers
Ten Do’s and Don’ts for Vacuum Systems
UNDERSTANDING GLASS COMPATIBILITY
Bullseye and Moretti glass types are not usually used in research efforts, however the article explains the subject well and in theory is similar to that of all glasses.
These differences in expansion and contraction may not sound like much, but they are very significant on the molecular level. A 10 inch length of Bullseye glass, for example, will shrink about 0.046 inches (about 1 mm) in cooling from around 950 degrees Fahrenheit to room temperature. By contrast, a 10-inch piece of Spectrum glass will shrink about 0.049 inches over the same temperature range. That difference - .003, or three thousandths of an inch - sounds trivial, but its enough to ensure that you cant fuse Bullseye and Spectrum together.
By LIDIA WASOWICZ
Results from space-bound experiments unencumbered by gravity are crystallizing the wondrous possibilities of creating glass that breaks the mold in ways not thought possible on Earth. Space glass could revolutionize fiber optics and other terrestrial technologies and even serve as construction material for erecting structures on other planets. Trailblazers on the cutting-edge of glassmaking envision extraordinarily transparent glass fibers stretching for thousands of miles across continents or super-strong glass glue made of "moon dust" that can cement walls, floors and roads on extraterrestrial worlds. The pioneering craftsmen think they can bring seemingly pie-in-the-sky notions down to Earth. Already, National Aeronautics and Space Administration researchers who have dabbled in making glass in the weightlessness of space have discovered their creation is endowed with some remarkable properties. For one, it has the pristine purity of an object untainted by touch because it lacks the need for a container that must hold the molten precursor of glass -- called the melts -- back on the ground.
"At high temperatures, these glass melts are very corrosive toward any known container," explained Delbert Day, Curators' Professor of Ceramic Engineering and senior research investigator in the Graduate Center for Materials Research at the University of Missouri, Rolla. Day conducted the first U.S. glass melting experiments in near-weightlessness aboard the space shuttle in 1983. As it eats away at the confining crucible, the melt -- and thus the glass -- becomes contaminated by the dissolving particles. In contrast, in gravity-free experiments, the molten glass stayed suspended inside a hot furnace simply by the pressure of sound waves emitted by a special device called an acoustic levitator. Like a trick out of a magician's book of floating gimmicks, acoustic levitation can position and move a tiny sample -- a mere fraction of an inch (a few millimeters) across -- in mid-air. The force from the sound waves suffices to suspend, place and manipulate the test target, eliminating the necessity for containers and the danger of contamination. "The great potential is that we will gain information from experiments in space which will let us better understand materials that we already are making on Earth so that we can make them faster, better and cheaper," predicted Day, whose credits as an inventor include thinner-than-a-human hair glass spheres that deliver high doses of cancer-shattering radiation directly to a disease-riddled organ or tissue. With the newfound availability of space as a one-of-a-kind laboratory, the sky could be the limit in glass research, scientists told United Press International.
"We can't even comprehend what we are missing," Day marveled. For example, his crystal ball points to glass as a major player in the future settling of other worlds, if such comes to pass. "If and when we colonize another planet, we will need to use as much of the material on the planet as possible since we can't transport all of the materials required from Earth," Day projected. Glass made of "moon dust" and native soils melted by solar energy could provide the construction material for floors and walls, he envisioned. "Molten glass could be used to glue the naturally occurring rocks together in much the same way that cement is now used to glue the rocks (aggregate) together to build roads and buildings," Day added. "Might sound a little far-fetched, but everything about living on another planet will be far-fetched." Closer to home, space glass also could have a life-altering impact, scientists proposed. "The key to producing the highly transparent glass fibers used for optical communication, which are revolutionizing our world -- we are now rewiring the world a second time, the first was with copper wires and the second is with glass fibers -- is to develop an entirely new method for melting high purity silica glasses," Day told UPI. "The main idea at this time is to use the information gained from experiments in space to improve our manufacture of glass made on Earth."
On Earth or beyond it, glass -- be it of the ordinary variety used in windows and bottles or of a more exotic form that facilitates optical communication -- follows a fundamental formula. The age-old recipe calls for combining such materials as sand, limestone and soda, boiling the mixture until it glows red-hot, then cooling the incandescent goop with utmost care to avoid the formation of crystals, which would ruin the desired effect. Glass -- a solid with an amorphous internal structure -- can form only if the melt cools quickly enough to preclude the atoms from hooking up into the patterns that typify crystals. When all goes according to plan, the result is a hard, brittle, usually clear or translucent substance that can stand up to wind, rain or sun and serve an ever-expanding range of pragmatic and cosmetic purposes. "While glass is one of the oldest materials made by man (it is thought to have been created by the Phoenicians around 3000 B.C.), we are still discovering new uses and new glasses all the time," Day pointed out. For example, he continued, there are "fibers for optical communication, oven (thermal shock) proof chemical ware and dishes, new glass which barely changes dimensions when heated/cooled that is now used in the Hubble Space Telescope (which couldn't explore the universe without those glass lenses), glass microspheres for treating patients with cancer, et cetera."
Most of the familiar types of glass blend silica obtained from beds of fine sand or from pulverized sandstone, an alkali to lower the melting point, usually a form of soda or, for finer glass, potash, lime as a stabilizer and cullet, or waste glass, to help the mixture melt. Scientists with sights set on more exotic applications, however, strive to break out of the traditional mold. If, as the initial results indicate and Day is convinced, glass melted in zero gravity resists crystallization, then setting up shop in space -- either as a full-force factory or even as an occasional testing ground -- could forever transform glassmaking, scientists said. "Glasses have a wide use in our everyday life, and their use would be even greater if we were able to prevent formation of crystals," noted Tihana Fuss, a doctoral candidate from Zagreb, Croatia, who works with Day's group. "It appears that melting glass in space does exactly that." Taking gravity out of glassmaking could have a two-fold benefit, scientists speculated. "This would not only mean that we would be able to improve properties of present commercially used glasses, but also that we could make new types of glasses," Fuss told UPI. Particularly intriguing to space researchers -- and of exceptional potential value to the fiber optics industry -- is an exotic glass made of metal called ZBLAN, an appellation derived from the chemical names of its components. The blend of fluorine and the metals zirconium, barium, lanthanum, aluminum and sodium (Zr, Ba, La, Al, Na) is 100 times more sheer than silica-based glass. "A fluoride fiber would be so transparent, light shone into one end, say, in New York City, could be seen at the other end as far away as Paris," Day remarked. "With silicon glass fibers, the light signal degrades along the way." To their dismay, scientists found fluoride fibers are difficult to produce on Earth, where the melts tend to crystallize before glass can form. But space-based processing promises to offer tips on overcoming this obstacle, researchers said. In fact, tests conducted in a KC-135, a workhorse four-engine jet aircraft that provides short bursts of near-zero gravity interspersed with periods of high gravity, showed thin fibers of the exotic glass are clearer when made in near-weightlessness than back on the gravity-saddled ground, noted Dennis Tucker, a physicist in the Space Sciences Laboratory of NASA's Marshall Space Flight Center in Huntsville, Ala.
ZBLAN glass fibers carry enormous commercial potential -- to the tune of $2.5 billion a year by some estimates -- for advanced communications, medical and manufacturing technologies using lasers. The biggest payoff could be in optical fiber communications where glass threads carry millions of telephone conversations and video and computer data. Telecommunications companies are investing heavily in optical fiber systems, including a "glass necklace" that will encircle the world, replacing transoceanic cables and eventually entering neighborhood communications. Day points to one crucial missing link that remains: comparison of glasses processed in space and on Earth. He hopes to fill in the blank, and confirm his theory of the superiority of space-based glassmaking, with the next set of experiments -- aboard the International Space Station. "We will measure the number and size of crystals in the glass (produced in space) and compare those numbers with identical glass samples processed on Earth," Day explained. "These data should confirm that glass formation is improved in space." Although the Feb. 1 disintegration of the space shuttle Columbia and the ensuing uncertainty about the future of the shuttle program have played havoc with time schedules, Day and company hope to be conducting their space tests within three years. The realization of practical applications for space-based glass research is still several years away, scientists cautioned. "It depends obviously on funding to perform the basic research, then interest from private companies who see a benefit from producing glass in space for use on Earth," said Tucker, who is working with a private company on the design of an automated fiber producing facility that uses robotics to perform human functions. The plan is to launch the facility into low-Earth orbit and deploy it to produce miles of glass fiber, including ZBLAN, then have it land by parachute and repeat the cycle, Tucker said.Day hopes eventually to bring the lessons learned from space down to Earth.
"(My) ultimate goal," he said, "is to gain knowledge which will improve our life on Earth and which might contribute to our effort and plans to explore the universe."
Bit About Glass
From THE SCORE (# 40), published by Spectrum Glass Company, Inc.
Has anyone ever told you that glass is actually a liquid? That, ever so slowly, everything made of glass is actually flowing, and will eventually reduce itself to a glossy puddle on some futuristic landscape? It's not an uncommon tale, even though it's absolute horsepucky.
Some glass buffs think the notion of glass as a liquid got started in Europe a century or so ago, when very old sheet glass was removed from very old buildings under renovation. The workers might have noticed that the sheets were much thicker on one end than the other, and that the thicker end was always down. Drawn by centuries of gravitational pull, they speculated, the bottoms of the windows had become thicker than the tops. Since people were already accustomed to fairly uniform sheet glass by that time, it's no surprise that the ancient hand-blown sheets raised some eyebrows, and possibly, the faulty conjecture.
A more likely explanation for the misconception arises from the definitions of "liquid" and "solid." The truth is, glass exhibits characteristics of each. Webster defines "liquid" as "a substance which exhibits a readiness to flow." Of a "solid" the dictionary says: "of definite shape and volume; not liquid or gas." Clearly, what we call "glass" better fits the latter than the former. But science doesn't look to Webster to draw their distinctions. Science-types will tell you that a material is a solid when its molecules are motionless and lined up in flawless geometric fashion, in perfect little rows and columns, like thousands of tiny soldiers at attention. This molecular configuration is called "crystalline". A liquid, on the other hand, is quite the opposite. Liquid molecules are in a constant state of movement and entirely random in their configuration. Scientifically, then, cold glass is neither liquid nor solid, because its molecules are motionless (like a solid) but random in configuration (like a liquid). This structure is characteristic of all vitreous (glassy) substances.
Many materials, like water and iron, are common in both liquid and solid states. At any given moment, their state depends on their temperature. Water molecules are disorderly and mobile only to a point, which is thirty-two degrees Fahrenheit. There, the water molecules "crystallize" - they line up in perfect lattice-like order and cease moving altogether, until the warmer side of thirty-two shines once again. The liquid has become a solid.
Thirty-two is said to be the "freezing point" of water (or the "melting point", depending on which direction temperature is moving). But this is a "point"only in temperature, not in time. When water reaches thirty-two degrees, it stays at thirty-two degrees until crystallization is complete. This may take a split second (a snowflake) or a great deal of time (Lake Omygoochie). Only when every molecule has taken its place in the lattice and come to a standstill will the temperature continue its decline.
One of the most fascinating things about vitreous substances is the conspicuous absence of any freezing point or melting point. There is no "point" in temperature where glass naturally maintains itself while its molecules reconfigure. As temperature decreases, the free-flowing molecules in molten glass simply move more and more slowly, until they are no longer able to move at all. But theymaintain their random configuration; crystallization does not occur.
If, on the other hand, we hold glass at a given temperature for a long enough time, crystallization, to some degree, will take place. The crystallized areas will no longer be glass, of course, because lack of crystallization is how we define glass. The crystallized areas are non-glass; they are de-vitreous -- devitrification has occurred.
Think about what happens as a piece of cold glass is heated. The randomly configured "frozen" molecules slowly begin to awaken and agitate. As the glass becomes warmer there's more freedom of movement. The higher the temperature, the faster and freer the molecules spin about. What is happening? In a practical sense, the glass is moving through different degrees of viscosity. From cold and hard it becomes warmer and softer, then pliable, then soft enough to slump under its own weight. Eventually it will puddle and finally, become liquidous. There are no such stages or degrees between water and ice; it's either one or the other. Such is the unique magic of vitreous substances.
Glass, then, is really neither a liquid nor a solid; it exhibits definite characteristics of each. In fact, some schools of thought find it more clear and convenient to classify matter into four states instead of the traditional three. So don't be surprised if your kids come home from school one day and tell you the Four states of Matter are liquid, solid, gas, and glass.
I am created of the admixture of
formed by the alchemy of time.
Glass can be covered with a thin coat of silvering and then not covered with the paint used to make an opaque mirror. When this is done, the glass is said to be half-silvered or to be a one-way mirror or one-way glass. Because of these latter names, there are people who believe that a product exists which is always mirrored on one side and always clear on the other side, which is not true. The visibility through such a mirror/glass depends entirely on the lighting - those on the more brightly lit side will see the glass as a mirror and those on the darker side as a more or less transparent window. The silver surface (and reflection) take out much of the light passing through, so the view through the glass is always darkened. If there is any light on the dark side, then it is possible to make out what is going on there from the bright side. Even if the dark side is completely black, some light is present having come through the one-way. Because the reflection is less than perfect, with experience it is easy to spot that a piece of mirror is half-silvered. Normally, because of its expense and fragility, users installing half-silvered do not even disguise the small mirror as being a real mirror - the reflection merely prevents people from easily knowing whether someone is behind the view port. It is now much cheaper to use reflectorized plastic film such as is used on cars.
Front Surface Mirrors
Normally mirror silvering is applied to the back of the glass where it is protected from touching. It is further protected and enhanced by painting over the silvering with opaque paint that reduces further the light passing the silver coating, making the reflection brighter. When silvering is applied to the front of a mirror, it is normally very fragile - it will scratch easily and show fingerprints if touched and if wiped will show smear as tiny scratches, reducing the reflection. It is difficult to put a protective coating on the mirroring, it must be very thin and clear. However, there are uses for front surface mirrors because there is only one reflective surface. Glass makes a very smooth surface for a good mirror, better than metal. If silvering is on the back of the glass, there is some small reflection from the glass front surface and the double image is distortion. The most widely available front surface are the small mirrors sold for use in kaleidoscopes. Astronomical mirrors are front surface silvered and both curved and smaller flat mirrors are sold through astronomy supply firms.
A cancer treatment in which glass microspheres deliver radioactivity directly to diseased areas in the body is currently being tested. Canada already uses the treatment, which shows success for liver cancer, and may be appropriate for other cancers. The treatment is promising, because it replaces the need for external beam radiation, which can cause unnecessary damage to healthy surrounding tissues. In the treatment, 5-10 million glass micro-spheres, 1/3 the diameter of a human hair are injected into an artery. Don't worry - that's only a small fraction of a teaspoon, less than 1/10 cc. Too large to pass outside of the diseased liver, the spheres remain harmlessly in the organ even after their radioactivity has disappeared.
High-Tech Glass: Pure Material Made in Levitation
An experiment originally designed to fly on the International Space Station (ISS) led a team of researchers to develop a completely new type of glass, a material formed while floating in mid-air in a NASA laboratory on Earth. Using static electricity fields to levitate the material, scientists were able to construct a pure glass, free of any contamination typically associated with containers. It could serve as the centerpiece for new medical and industrial lasers, as well as have broadband Internet applications.
"I think there's a lot of potential for this glass," said Rick Weber, director of the Glass Products Division of Containerless Research, Inc., which invented a whole family of the new transparent material. "We've got a wide composition field, so one [glass] can be tuned for a particular use." Weber told SPACE.com that new the glass is currently being put through its paces in several validation projects for applications in high-density lasers, and as the glass components for low-cost, compact broadband devices.
The new material, known as REAl glass -- short for Rare Earth Aluminum oxide -- was first developed at NASA's Electrostatic Levitator (ESL) laboratory at Marshall Space Flight Center in Huntsville, Alabama. Scientists there routinely use static electricity to allow their experiments to defy gravity inside a vacuum chamber, then zap them with lasers to turn them into floating molten balls of material that can later cool without any interference from a crucible or container. "The ESL is a very pure way to look at what a material does," said Jan Rogers, a facility scientist for the ESL. "In an oven or container of any sort you have contact with the container wall, and at high temperatures a sample can interact with those walls, absorbing specks of dust and having a chemical reaction with the container." By melting and cooling a levitated material, scientists can understand not just its formation, but its inherent physical properties. Surface tensions keeps molten samples together which, when cool, coalesce into tiny spheres. At the most fundamental level, making REAl glass uses the same method used by glass-makers for centuries, namely mixing materials together, melting them, then cooling them into a solid. But its the levitation that gives REAl glass its kick. The process allowed researchers to imbue their glass with a number of attractive properties, such as chemical stability, infrared transmission and laser activity.
"Other glasses tend to have just one of those properties, and at least one weakness," Weber said. "They could be really good at infrared transmission, but dissolve in water so you wouldn't want a window made out of it." Laser applications are key for REAl glass, since the material could serve as the "gain medium," a component that amplifies light into a concentrated beam capable of cutting metal for car assembly or human tissue during surgery. REAl glass laser gain mediums could provide a range of available wavelengths to give surgeons more control of beam intensity, depending on tissue type and surgery, he added.
Once Containerless Research scientists understood the basics of REAl glass formation, they were able to adapt the technology away from its dependency on electrostatic levitation. The step was a crucial one for commercial purposes, since NASA's ESL facility is only powerful enough to levitate tiny sample materials up to three millimeters wide and 70 milligrams in weight. "So we're not talking about golf balls and pineapples here," Weber said of the ESL's production capabilities. "For commercial purposes, we needed at least rods and plates of the glass." Weber's team was able to devise a small-scale production plan that uses platinum crucibles to melt REAl glass and cooling forms that shape into commercial rods and plates, all without taking away the materials positive properties.
A glassy side project
Containerless Research scientists did not originally seek to develop REAl glass outright when they approached NASA with a proposed space station experiment. That proposal, which used the Marshall lab as a proving ground before reaching the orbiting outpost, sought to explore the properties of molten oxides and aluminates. "Most of my customers are space flight candidates," said Rogers of the researchers who use the ESL facility. "Some of them have experiments for the ISS, where they would be using the next generation levitator." That instrument, an electromagnetic levitator for space-based material science studies, is being developed for the European Space Agency's Material Science Laboratory aboard the Columbis module of the ISS. The module was scheduled to be launched via space shuttle in October 2004, though NASA does not expect another shuttle flight until at least March 2005.
"When the appropriate instrumentation is available,
we still hope to conduct that flight experiment," Weber said. Other
scientists have used some form of levitation, though not exactly Weber's
for glass making, both on Earth and in space. Delbert
Day, a NASA-funded researcher at the University of Missouri-Rolla, for
example, used sound waves to levitate glass samples in order to study
higher-quality glasses. He also designed microgravity experiments for
the space shuttle.
Researchers: Evidence of ancient Egyptian glassmaking
What may be one of the earliest glassmaking sites in ancient Egypt has been uncovered in the eastern Nile Delta. Evidence at Qantir-Piramesses indicates that glass was made there out of raw materials as early as 1250 B.C., researchers from England and Germany report in Friday's issue of the journal Science. The reworking of already made glass into finished goods has been documented at ancient sites in the Middle East and Egypt, but the new report adds evidence for primary glass production at this location. Thilo Rehren of University College, London, and Edgar B. Pusch of Pelizaeus Museum in Hildesheim, Germany, report finding a large number of crucibles with remains of glass inside.
Glass was made using finely crushed quartz powder which was melted with other materials inside the ceramic crucibles, which then were broken to get the glass out, they reported. The glass ingots "would then have been transported to other, artistic workshops where they were re-melted and worked into objects," Pusch and Rehren reported. Much of the glass produced at Qantir-Piramesses was red, produced using copper in a complex process, and some of it was blue or colorless.A large shipment of glass ingots has been found in an ancient shipwreck off the coast of Turkey. The wreck predates the materials found at Qantir-Piramesses, but the ingots are similar in size and shape to the crucibles found at the Egyptian site.
Fragments of similar crucibles have also been found in Egypt at el-Amarna and Lisht, Rehren and Pusch noted. Caroline M. Jackson of the University of Sheffield in England called the new report "highly significant." Jackson, who was not part of the research team, said, "Rehren and Pusch convincingly show that the Egyptians were making their own glass in large, specialized facilities." In a commentary accompanying their report, Jackson says their analysis reinforces the role of glass in Egypt "as an elite material that was exported from Egypt to the Mediterranean world." Rehren and Pusch's research was funded by the German Research Council and the British Academy.
reference pasted as printed from CNN.com 6-16-05
History of Glass
Early Times | Middle Ages | Early American Glass | Modern Glass Making
Before people learned to make glass, they had found two forms of natural glass. When lightning strikes sand, the heat sometimes fuses the sand into long, slender glass tubes called fulgurites, which are commonly called petrified lightning. The terrific heat of a volcanic eruption also sometimes fuses rocks and sand into a glass called obsidian. In early times, people shaped obsidian into knives, arrowheads, jewelry, and money. We do not know exactly when, where, or how people first learned to make glass. It is generally believed that the first manufactured glass was in the form of a glaze on ceramic vessels, about 3000 B.C. The first glass vessels were produced about 1500 B.C. in Egypt and Mesopotamia. The glass industry was extremely successful for the next 300 years, and then declined. It was revived in Mesopotamia in the 700's B.C. and in Egypt in the 500's B.C. For the next 500 years, Egypt, Syria, and the other countries along the eastern shore of the Mediterranean Sea were glassmaking centers.
Early glassmaking was slow and costly, and it required hard work. Glass blowing and glass pressing were unknown, furnaces were small, the clay pots were of poor quality, and the heat was hardly sufficient for melting. But glassmakers eventually learned how to make colored glass jewelry, cosmetics cases, and tiny jugs and jars. People who could afford them—the priests and the ruling classes—considered glass objects as valuable as jewels. Soon merchants learned that wines, honey, and oils could be carried and preserved far better in glass than in wood or clay containers.
The blowpipe was invented about 30 B.C., probably along the eastern Mediterranean coast. This invention made glass production easier, faster, and cheaper. As a result, glass became available to the common people for the first time. Glass manufacture became important in all countries under Roman rule. In fact, the first four centuries of the Christian Era may justly be called the First Golden Age of Glass. The glassmakers of this time knew how to make a transparent glass, and they did offhand glass blowing, painting, and gilding (application of gold leaf). They knew how to build up layers of glass of different colors and then cut out designs in high relief. The celebrated Portland vase, which was probably made in Rome about the beginning of the Christian Era, is an excellent example of this art. This vase is considered one of the most valuable glass art objects in the world.
The Middle Ages.
Little is known about the glass industry between the decline of the Roman Empire and the 1200's. Glass manufacture had developed in Venice by the time of the Crusades (A.D. 1096-1270), and by the 1290's an elaborate guild system of glassworkers had been set up. Equipment was transferred to the Venetian island of Murano, and the Second Golden Age of Glass began. Venetian glass blowers created some of the most delicate and graceful glass the world has ever seen. They perfected Cristallo glass, a nearly colorless, transparent glass, which could be blown to extreme thinness in almost any shape. From Cristallo, they made intricate lacework patterns in goblets, jars, bowls, cups, and vases. In the 1100's and 1200's, the art of making stained-glass windows reached its height throughout Europe.
By the late 1400's and early 1500's, glassmaking had become important in Germany and other northern European countries. Manufacturers there chiefly produced containers and drinking vessels. Northern forms were heavier, sturdier, and less clear than Venice's Cristallo. During the late 1500's, many Venetians went to northern Europe, hoping to earn a better living. They established factories there and made glass in the Venetian fashion. A new type of glass that worked well for copper-wheel engraving was perfected in Bohemia (now part of the Czech Republic) and Germany in the mid-1600's, and a flourishing industry developed.
Glassmaking became important in England during the 1500's. By 1575, English glassmakers were producing Venetian-style glass. In 1674, an English glassmaker named George Ravenscroft patented a new type of glass in which he had changed the usual ingredients. This glass, called lead glass, contains a large amount of lead oxide. Lead glass, which is especially suitable for optical instruments, caused English glassmaking to prosper.
Early American glass.
The first factory in what is now the United States was a glass plant built at Jamestown, Virginia, in 1608. The venture failed within a year because of a famine that took the lives of many colonists. The Jamestown colonists tried glassmaking again in 1621, but an Indian attack in 1622 and the scarcity of workers ended this attempt in 1624. The industry was reestablished in America in 1739, when Caspar Wistar built a glassmaking plant in what is now Salem County, New Jersey. This plant operated until 1780.
Wistar is one of the great names of early American glass. The second great American glassmaker was Henry William Stiegel, also known by his nickname, "Baron" Stiegel. Stiegel made clear and colored glass, engraved and enameled glass, and the first lead glass produced in North America. A third important American glassmaker was John F. Amelung, who became best known for his elegant engraved glass.
Another important early American glass, Sandwich glass, was made by the Boston and Sandwich Glass Company, founded by Deming Jarves in 1825. It was long believed to be the first company in America to produce pressed glass. But the first was actually the Bakewell, Page, and Bakewell Company of Pittsburgh, Pennsylvania, which began to make pressed glass earlier in 1825. These two companies and many others soon made large quantities of inexpensive glass, both pressed and blown. Every effort was made to produce a “poor man's cut glass.” In lacy Sandwich, for example, glassmakers decorated molds with elaborate designs to give the objects a complex, lacelike effect.
In the early 1800's, the type of glass in greatest demand was window glass. At that time, window glass was called crown glass. Glassmakers made it by blowing a bubble of glass, then spinning it until it was flat. This process left a sheet of glass with a bump called a crown in the center. By 1825, the cylinder process had replaced the crown method. In this process, molten glass was blown into the shape of a cylinder. After the cylinder cooled, it was sliced down one side. When reheated, it opened up to form a large sheet of thin, clear window glass. In the 1850's, plate glass was developed for mirrors and other products requiring a high quality of flat glass. This glass was made by casting a large quantity of molten glass onto a round or square plate. After the glass was cooled, it was polished on both sides.
Bottles and flasks were first used chiefly for whiskey, but the patent-medicine industry soon used large numbers of bottles. The screw-top Mason jar for home canning appeared in 1858. By 1880, commercial food packers began to use glass containers. Glass tableware was used in steadily increasing quantities. The discovery of petroleum and the appearance of the kerosene lamp in the early 1860's led to a demand for millions of glass lamp chimneys. All these developments helped to expand the market for glass.
Changes in the fuel used by the glass industry affected the location of glass factories. In the early days when wood was used as fuel, glassworks were built near forests. By 1880, coal had become the most widely used fuel for glassmaking, and glassmaking operations were near large coal deposits. After 1880, natural gas became accepted as the perfect fuel for melting glass. Today, most glass manufacturing plants are near the major sales markets. Pipelines carry petroleum and natural gas to the glass plants.
After 1890, the development, manufacture, and use of glass increased rapidly. The science and engineering of glass as a material are now so much better understood that glass can be tailored to meet an exact need. Any one of thousands of compositions may be used. Machinery has been developed for precise, continuous manufacture of sheet glass, tubing, containers, bulbs, and a host of other products.
New methods of cutting, welding, sealing, and tempering, as well as better glass at lower cost, have led to new uses of glass. Glass is now used to make pipelines, cookware, building blocks, and heat insulation.
Ordinary glass turns brown when exposed to nuclear radiation, so glass companies developed a special nonbrowning glass for use in observation windows in nuclear power plants. More than 10 tons (9 metric tons) of this glass are used in windows in one nuclear power plant. In 1953, automobile manufacturers introduced fiberglass-plastic bodies. Today, such materials are used in architectural panels to sheathe the walls of buildings. They are also used to make boat hulls and such products as missile radomes (housings for radar antennas). Other types of glass have been developed that turn dark when exposed to light and clear up when the light source is removed. These photochromic glasses are used in eyeglasses that change from clear glasses to sunglasses when worn in sunlight.
During the late 1960's, glass manufacturers established collection centers where people could return empty bottles, jars, and other types of glass containers. The used containers are recycled—that is, broken up and then melted with silica sand, limestone, and soda ash to make glass for new containers. Glass can be recycled easily because it does not deteriorate with use or age. In addition to the collection centers, some communities have set up systems to sort glass and other reusable materials from regular waste pickups.
In the 1970's, optical fibers were developed for use as "light pipes" in laser communication systems. These pipes maintain the brightness and intensity of light being transmitted over long distances. Types of glass that can store radioactive wastes safely for thousands of years were also developed during the 1970's.
The late 1900's brought important new specialty glasses. Among the new specialty glasses were transparent glass ceramics, which are used to make cookware, and chalcogenide glass, an infrared-transmitting glass that can be used to make lenses for night vision goggles.
"Glass," Discovery Channel School, original content provided by World Book Online
Quartz belongs to the rhombohedral crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end. In nature quartz crystals are often twinned, distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. Well-formed crystals typically form in a 'bed' that has unconstrained growth into a void, but because the crystals must be attached at the other end to a matrix, only one termination pyramid is present. A quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward.
Quartz goes by an array of different names. The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). Chalcedony is a generic term for cryptocrystalline quartz. The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline.
Although many of the varietal names
historically arose from the colour of the mineral, current scientific
naming schemes refer primarily to the microstructure of the mineral.
Colour is a secondary identifier for the cryptocrystalline minerals,
although it is a primary identifier for the macrocrystalline varieties.
This does not always hold true.
Not all varieties of quartz are naturally occurring. Prasiolite, an olive coloured material, is produced by heat treatment; natural prasiolite has also been observed in Lower Silesia in Poland. Although citrine occurs naturally, the majority is the result of heat-treated amethyst. Carnelian is widely heat-treated to deepen its colour.
Because natural quartz is so often twinned, much quartz used in industry is synthesized. Large, flawless and untwinned crystals are produced in an autoclave via the hydrothermal process: emeralds are also synthesized in this fashion.
Quartz occurs in hydrothermal veins and pegmatites. Well-formed crystals may reach several metres in length and weigh hundreds of kilograms. These veins may bear precious metals such as gold or silver, and form the quartz ores sought in mining. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals."
Quartz is a common constituent of granite, sandstone, limestone, and many other igneous, sedimentary, and metamorphic rocks.
Quartz is the most common material identified as the mystical substance maban in Australian Aboriginal mythology. It is found regularly in passage tomb cemeteries in Europe in a burial context, eg. Newgrange or Carrowmore in Ireland. The Irish word for quartz is grian cloch, which means 'stone of the sun'.
Roman naturalist Pliny the Elder believed quartz to be permanently frozen ice. He supported this idea by saying that quartz is found near glaciers in the Alps and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of the ability of quartz to split light into a spectrum.
Nicolas Steno's study of quartz paved the way for modern crystallography. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60 degree angle.
Charles Sawyer invented the commercial quartz crystal manufacturing process in Cleveland, OH. This initiated the transition from mined and cut quartz for electrical appliances to manufactured quartz.
The quartz oscillator or resonator was first developed by Walter Guyton Cady in 1921 . George Washington Pierce designed and patented quartz crystal oscillators in 1923 . Warren Marrison created the first quartz oscillator clock based on the work of Cady and Pierce in 1927 .
Quartz crystals are rotary polar (see rotary polarization) and have the ability to rotate the plane of polarization of light passing through them. They are also highly piezoelectric, becoming polarized with a negative charge on one end and a positive charge on the other when subjected to pressure. They will vibrate if an alternating electric current is applied to them. This proves them to be highly important in commerce for making pressure gauges, oscillators, resonators and watches.What is Fused quartz?
From Wikipedia, the free encyclopedia
Fused quartz and fused silica are types of glass containing primarily silica in amorphous (non-crystalline) form. They are manufactured using several different processes.
Fused quartz is made by melting high-purity naturally occurring quartz crystal at around 2000°C using either an electrically heated furnace (electrically fused) or a gas/oxygen-fuelled furnace (flame fused). Fused quartz is normally transparent.
Fused quartz can also form naturally. The naturally occurring form of fused quartz is usually referrred to as Metaquartzite and is formed under metamorphic conditions. Due to increased heat the crystals within the quartz become fused together.
Fused silica is produced using high purity silica sand as the feedstock, and is normally melted using an electric furnace, resulting in a material that is translucent or opaque. (This opacity is caused by very small air bubbles trapped within the material.)
Synthetic fused silica is made from a silicon-rich chemical precursor usually using a continuous flame hydrolysis process which involves chemical gasification of silicon, oxidation of this gas to silicon dioxide, and thermal fusion of the resulting dust (although there are alternative processes). This results in a transparent glass with an ultra-high purity and improved optical transmission in the deep ultraviolet. One common method involves adding silicon tetrachloride to a hydrogen-oxygen flame.
Fumed silica is manufactured by a similar flame hydrolysis process to synthetic fused silica, however it is in the form of a fine powder/dust and is typically used in applications such as fillers for rubbers and plastics, coatings, adhesives, cements, sealants, cosmetics, pharmaceuticals, inks and abrasives.
The optical and thermal properties are superior to those of other types of glass due to its purity (or rather, its lack of impurities). For these reasons, it finds use in situations such as semiconductor fabrication and laboratory equipment. It has better ultraviolet transmission than most other glasses, and so is used to make lenses and other optics for the ultraviolet spectrum. Its low coefficient of thermal expansion also makes it a useful material for precision mirror substrates.
Heat Induced Stress in Glass
Scientific Glassblowers fabricate simple to complex
glass apparatus to be used under laboratory conditions - which can mean
harsh chemical exposure, high and/or low pressures, and a host of other
environments hostile to people and facilities. An awareness of product
design is essential as well as the integrity of the glass structure
itself. An element in product safety is the fabrication of stress or
strain-free glass apparatus and systems. This is a very basic introduction
to glass stress and annealing. Blowing glass in the fabrication of scientific
glassware involves the use of a torch or burner. The flame is adjusted
to varying degrees of sharpness, ranging from a pinpoint for precision
work, to a large bushy flame used for heating and forming broad areas.
This process of heating, forming and cooling will introduce stress (often
referred to as strain) into the glassware. Invisible to the naked eye,
the strain never- the-less is present and is a potential point of failure
in the glass apparatus unless relieved. The amount of strain present
will be determined by a number of factors including the intensity and
size of the torch flame, glass wall thickness and the complexity of
the seal itself. The severity of the stresses may be enough to cause
glass failure.....sometimes while the glass piece is under construction!
Many glassblower's hand anneal the work during the fabrication process,
with full furnace annealing prior to customer receipt.
Manual of Scientific Glassblowing
Another hidden type of stress.....yet can be just as damaging
Many people don't realize the stress put on their vacuum systems from improper assembly and clamping of glassware. It is VERY important that manifolds and all attached pieces are hung as straight as possible and that clamps are tightened evenly for both sides. If this is not done properly the glass is being "torqued" and can fail at any time. Since this strain is not visable except under polarized lights, it is not realized until you come in one day and find it broken or have it fail at a crucial time. If you find this to be a problem in your lab let me know and I will show the correct way of clamping. I can also "heat relieve" your system if your clamping method doesn't allow proper adjustment.
Contact me if you'd like to understand more about the dangers of heat induced (or physically induced) stresses in your glassware and what you can do to eliminate them.