UNIVERSITY of DELAWARE
DEPARTMENT of CHEMISTRY and BIOCHEMISTRY

 

Physical Properties

 


The four most common glass types utilized by UD research groups are:

Quartz and Vycor are used mostly where purity, greater chemical resistance or high temperature are required. It is extremely important that special care be taken to clean properly. Even a single finger print can easily start the onset of devitrification. In most cases neither can be fused to other glass types without the use of graded seals or transition tapes. In limited cases a chemical (HF) process may be used on other glasses which would allow them to be directly fused to Quartz or Vycor.

Soda lime has limited applications for reasons stated below. It can be used as an intermediate glass and also wets and seals to certain metals.

Borosilicate is the most common and preferred glass to work with. It can handle higher heat than Soda Lime , but not the extreme temperatures of Quartz and Vycor. It is resistant to most chemicals and able to handle large temperature fluctuations.

The composition of glasses mentioned above are sometimes modified to meet special industrial needs or requirements. There are also many different glass types available that are engineered for specific uses such as alumino silicate, lead, nonex, uranium, etc. Most are not readily compatible with one another and must be taken into consideration during the designing phase.

Below are the basic physical properties of each

 

Borosilicate Glass
 

(Pyrex, Kimax KG-33, Duran) - Low Expansion Glass

 

With proper care, it will withstand most temperatures used in normal laboratory use. It is highly resistant to chemical attack. The low coefficient of expansion also allows manufacturing it with heavy walls giving it mechanical strength, while retaining reasonable heat resistance.It is a glass that can be fabricated more easily than most other glasses, thus making it more economical. Borosilicate is by far the most widely used, and prefered, glass for laboratory apparatus.

 

Note: There are some borosilicate glasses (usually foreign made) that are not compatible with standard US maunfacturers mentioned above. If in doubt bring item to the

Glass Shop to be tested.

 

The information below gives basic compositions. Each US manufacturer's "recipe" may vary slightly, but they should be compatible.

 

Chemical Composition

Composition

(percent approx.)

SiO2

80.6%

B2O3

13.0%

Na2O

4.0%

A12O3

2.3%

Miscellaneous Traces

0.1%

Physical Properties

Coeff. of Exp.

32.5 x 10-7cm/cm/C

Strain Point

510C

Anneal Point

560C

Soften Point

821C

Density

2.23 g/cm3

Youngs Mod.

6.4 x 103 Kg/mm2

Refract. Index

1.474 @ Sodium D Line

Temp. Limits

490C (Extreme Service)

230C (Normal Service)

Max. Thermal Shock

160C

Applications
Designed for use in all products requiring very high resistance to strong acids, alkalis and products intended for use in heat applications such as autoclaves, hot plates and open flame.

Warnings

Thick-walled ware, such as bottles, jars and desiccators, should not be heated by flame, hot plate, or other comparable source of heat.

Do not use hydrofluoric or hot phosphoric acid in glass.

Do not use scratched or abraded glassware.

Hot alkalines will etch glass.

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Fused Quartz
 

Quartz is found as colorless transparent crystals which are practically pure silica. It is both difficult and expensive to produce in any form. It has good mechanical strength and almost perfect elasticity. Because its coefficient of expansion and contraction is near zero, it is it can be ground and polished into one of the flattest surfaces in the world. It can also be melted into solid ingot form from which rod is drawn or into hollow "fused quartz" ingots for tubing fabrication. It can be processed into some of the finest optical devices available. Quartz products can be used continuously at 900C, and intermittently to 1200C provided it is not in contact with contaminating materials which can cause the onset of divitrification. Because of its extremely low coefficients, like vycor, it can be used for very precise analytical work.

 

Property

Typical Values

 

 

Density

2.2x10 3 kg/m3

 

Hardness

5.5 - 6.5 Mohs' Scale 570 KHN 100

Design Tensile Strength

4.8x10 7 Pa (N/m2) (7000 psi)

 

Design Compressive Strength

Greater than 1.1 x l0 9 Pa (160,000 psi)

Bulk Modulus

3.7x10 10 Pa (5.3x10 6 psi)

Rigidity Modulus

3.1x10 10 Pa (4.5x10 6 psi)

Young's Modulus

7.2x1 -10 Pa (10.5x10 6 psi)

 

Poisson's Ratio

.17

 

 

 

Coefficient of Thermal Expansion

5.5x10 -7 cm/cm . C (20C-320C)

 

Thermal Conductivity

1.4 W/m . C

 

Specific Heat

670 J/kg . C

 

 

 

Softening Point

1683C

 

Annealing Point

1215C

 

Strain Point

1120 C

 

 

Electrical Resistivity

7x10 7 ohm cm (350C)

 

Dielectric Properties

(20C and 1 MHz)

 

 

Constant

3.75

 

 

Strength

5x10 7 V/m

 

 

Loss Factor

Less than 4x10 -4

 

 

Dissipation Factor

Less than 1x10 -4

 

 

 

 

Index of Refraction

1.4585

 

Manufacture

Quartz is one of the many forms of silicon dioxide and sand is its best known source for manufacture.

Applications
Designed for use in all products that must withstand very high temperatures or thermal shock. Can only be sealed to borosilicate glass with graded seals.
Because of its properties and extremely low coefficient of expansion and contraction, its optical qualities are unmatched.

 

Cleaning

For applications in which cleanliness is important, The following procedure is recommended: The product, particularly tubing, should be washed in deionized or distilled water with a degreasing agent added to the water. The fused quartz should then be placed in a 7% (maximum) solution of ammonium bifluoride for no more than ten minutes, or a 10 vol % (maximum) solution of hydrofluoric acid for no more than five minutes. Etching of the surface will remove a small amount of fused quartz material as well as any surface contaminants. To avoid water spotting which may attract dirt and cause devitrification upon subsequent heating, the fused quartz should be rinsed several times in de-ionized or distilled water and dried rapidly. To further reduce the possibility of contamination, care should be used in handling fused quartz. The use of clean cotton gloves at all times is essential. Washing of translucent tubing is not recommended because the water or acid solution tends to enter the many capillaries in the material. This may cause the quartz to burst if the pieces are subsequently heated rapidly to very high temperatures.

Warnings
Do not use hydrofluoric acid (or hot phosphoric acid).
Alkaline solutions attack slowly at room temperature , but much faster at elevated temperatures.

 

Soda Lime Glass
 
 

Soda lime is not as chemical resistant as borosilicate glass. Its lower melting point and higher coefficient or expansion and contraction make it ideal for certain glass to metal operations as well as inexpensive glassware such as pipettes or plate glass. However those same coefficients make it unusable where high heat or great temperature fluctuations are necessary. Because its characteristics it is not recommended that soda lime "apparatus" be purchased in many cases. It is much more difficult (or sometimes impossible) to repair if damaged.


Chemical Composition

Composition

(percent approx.)

SiO2

73%

Na2O

14%

CaO

7%

MgO

4%

Al2O3

2%


Physical Properties

Coeff. of Exp.

89 x 10-7cm/cm/C

Strain Point

511C

Anneal Point

545C

Soften Point

724C

Density

2.40 g/cm3

Youngs Mod.

Not available

Refract. Index

1.515 @ Sodium D Line

 

Warnings
Do not use hydrofluoric or phosphoric acid on soda lime glass.

Alkalines will etch glass.

 

Vycor
 

 

Vycor labware has several exceptional properties and is similar to fused quartz in its nature. Unlike quartz, vycor is man-made from borosilicate glass through a special leaching process to form its characteristics. It may be used at much higher temperatures than borosilicate glass and will withstand considerably more thermal shock. Vycor products can be used continuously at 900C, and intermittently to 1200C provided it is not in contact with contaminating materials which can cause the onset of divitrification. Being of a very simple composition and extremely low coefficient of expansion and contraction,like quartz, it can be used for very precise analytical work. There are roughly 7 types of vycor that allow for many uses. They were created to allow, higher heat ranges, infrared transmission, varying UV transmission ranges, specific porous properties (thirsty glass), and to absorb most visable light from a tungsten filiment while transmitting infrared radiations.

 

Chemical Composition

Composition

(percent approx.)

SiO2

96.4%

B2O3

3.0%

A12O3

0.5%

Misc. Traces

0.1%

Physical Properties

Coeff. of Exp.

7.5 x 10-7cm/cm/C

Strain Point

890C

Anneal Point

1020C

Soften Point

1530C

Density

2.18 g/cm3

Youngs Mod.

6.7 3 103 Kg/mm2

Refract. Index

1.458 @ Sodium D Line

Temp. Limits

1200C (Extreme Service)

900C (Normal Service)

Manufacture
Vycor is formed as a borosilicate type glass. It is then subjected to a chemical treatment that removes most of the elements in the glass except silica (SiO2). Glass is then reheated to eliminate the microscopic holes caused by the chemical treatment. Only quartz has a higher silica content.

Applications
Designed for use in all products that must withstand very high temperatures or thermal shock. Can only be sealed to borosilicate glass with graded seals.

Cleaning

For applications in which cleanliness is important, The following procedure is recommended: The product, particularly tubing, should be washed in deionized or distilled water with a degreasing agent added to the water. The fused quartz should then be placed in a 7% (maximum) solution of ammonium bifluoride for no more than ten minutes, or a 10 vol % (maximum) solution of hydrofluoric acid for no more than five minutes. Etching of the surface will remove a small amount of fused quartz material as well as any surface contaminants. To avoid water spotting which may attract dirt and cause devitrification upon subsequent heating, the fused quartz should be rinsed several times in de-ionized or distilled water and dried rapidly. To further reduce the possibility of contamination, care should be used in handling fused quartz. The use of clean cotton gloves at all times is essential. Washing of translucent tubing is not recommended because the water or acid solution tends to enter the many capillaries in the material. This may cause the quartz to burst if the pieces are subsequently heated rapidly to very high temperatures.

Warnings
Do not use hydrofluoric acid (or hot phosphoric acid).
Alkaline solutions attack slowly at room temperature , but much faster at elevated temperatures.

 

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