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Properties Of Borosilicate (PYREX 7740) Glass
Chemical Resistance
Borosilicate glass is inert to almost
all materials with the exception of hydrofluoric acid, hot phosphoric
acid and hot alkalies. Of these, hydrofluoric acid has the most serious
effect and, even when a solution contains a few parts per million,
attack will occur.
Phosphoric acid and caustic solutions
cause no problems when cold but at elevated temperatures corrosion
occurs. Caustic solutions up to 30% concentration can be handled safely
at ambient temperatures.
Physical Properties:
Composition
Low-expansion borosilicate glass has
the following approximate chemical composition:
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SiO2
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81%
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Na2O
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4.0%
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K2O
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0.5
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B2O3
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13.0%
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Al2O3
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2.0%
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For further details please refer to
ASTM E 438, "Standard Specification for Glasses in Laboratory Apparatus."
Linear Coefficient of Expansion:
Between 32°F and 572°F [0°C and 300°C], per ASTM Method E 228)
18.1 x 10-7 in/in/7°F
32.5x10-7 cm/cm/°C
Annealing:
All fittings and all straight lengths are annealed to reduce internal
stress. This also makes the pipe easier to field fabricate.
Thermal Conductivity:
0.73 Btu/hr-ft2-°F/ft
0.0035 cal/sec-cm2-°C/cm
Specific Heat:
0.20 Btu/lb-°F
0.20 cal/gm-°C
Dialectric Constant:
at 23°C and 1M Hz per ASTM Method D 150: 4.6 ±-0.2
Density:
Approximately 139 lb/ft3 (2.23 gm/cm3)
Young's Modulus:
per ASTM Method C215: in the range of 9 x 106 to 10 x 106 psi.
Mechanical Strength:
The mechanical properties of glass differ from those of metals. The
lack of ductility of glass prevents the equalization of stresses at
local irregularities or flaws and the breaking strength varies considerably
about a mean value. This latter is commonly found to occur at a tensile
strength of about 70 kg/cm2 (1000 psi). The glass should be adequately
supported and appropriate allowance should be made for special conditions
such as high temperatures, dense liquids, etc. Subject to the above,
maximum working pressures are as specified in the following table.
Working Temperatures
Borosilicate glass retains its mechanical
strength and will deform only at temperatures which approach its strain
point. The practical upper limit for operating temperatures Is much
lower and is controlled by the temperature ditterentials in the glass,
which depend on the relative temperatures of the contents of the equipment
and the external surroundings.
Provided borosilicate glass is not subjected to rapid change in temperature,
creating undue thermal shock, it can be operated safely at temperatures
up to 450°F (232°C). The normal limiting factor is actually the gasket
material. The degree of thermal shock (usually defined as sudden chilling)
which it can withstand depends on many factors, for example: stresses
due to operating conditions; stresses imposed in supporting the equipment;
the wall thickness of the glass, etc. It is therefore undesirable to
give an overall figure but, as a general guide, sudden temperature changes
of up to about 216°F (120°C) can be accommodated
At sub-zero temperatures, the tensile
strength of borosilicate glass tends to increase and equipment can
be used with safety at cryogenic temperatures.
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