Glasses linear thermal expansion

Glass Linear thermal expansion coefficient x10 /°C References... 

Thermal Properties. Many commercial glass-ceramics have capitalized on thek superior thermal properties, particularly low or zero thermal expansion coupled with high thermal stabiUty and thermal shock resistance properties that are not readily achievable in glasses or ceramics. Linear thermal expansion coefficients ranging from —60 to 200 x 10 j° C can be obtained. Near-zero expansion materials are used in apphcations such as telescope mirror blanks, cookware, and stove cooktops, while high expansion frits are used for sealing metals. 

Thermal Expansion. The averaged value of the coefficient of linear thermal expansion of diamond over the range 20 to 100°C is 1.34 X 10 cm/cm/ C and 3.14 x 10 from 20 to 800°C. At room temperature the values for sihca glass and diamond ate 0.5 X 10 and 0.8 X 10 , respectively. The relatively low expansion combined with the low reactivity of diamonds, except for carbide formation, leads to some challenges in making strong bonds between diamond and other materials. 

Thermal expansion Glasses having coefficients of linear thermal expansion... 

An additional check is the almost coincidence of the linear thermal expansion coefficients of the composite in the glassy region. Theory yields acl = 48.20 x 10-6 °C whereas experiment gives ac, = 48.00x 10 6 °C 1. This coincidence does not hold beyond glass transition. Indeed it was found that ot = 122.90 x 10-6 °C, whereas the experiment gave a 2 = 158 x 10"6 °C 1. 

The coefficient of linear thermal expansion is almost constant, for most types of glass, for temperatures up to 400-600°C. The actual value depends on the chemical constitution of the glass. It then increases rapidly above a certain temperature, often called the... 

Modern temperature scale proposed by G. Fahrenheit, defined by a thermometer, a law and three fixed points. Fahrenheit s thermometer was a mercury-in-glass one. Thermal expansion versus temperature was assumed linear. Three fixed points were defined 0°F temperature of a mixture of water, ice and ammonium chloride 32°F temperature of melting ice 96°F temperature of human body... 

ISO 11359-2, Plastics - Thermomechanical analysis (TMA) - Part 2 Determination of coefficient of linear thermal expansion and glass transition, 1999. 

Aj3th is the jump of the linear thermal expansion coefficient at the glass transition temperature. As Fig. 1 lb shows, da is proportional to the rate (1 — a) of the flowing units, that is to the molecular arrangements, which can form some confer-... 

Glass-ceramics based on the LijO-AljC -SiC can be tailored, principally through varying the alumina content, to have linear thermal expansivities in the range from close to zero to approximately 18 MK-1. The low expansion materials have excellent resistance to thermal shock whilst those with the higher expansivities can be successfully joined to a range of metals. 

Fig. 3.7 Stages in the fabrication of a glass-ceramic, gas-tight, high current switch housing (a) the formed glass shape, (b) 18% Cr stainless steel (linear thermal expansivity 13 p.p.m. K ) flanges bonded to glass, (c) finished glass-ceramic component. The transparency of the disc (d) results from a very small grain size. (Courtesy of Advanced Ceramics Limited, UK.)...

Compared to glass, glass-ceramics are mechanically stronger, more resistant to chemical attack and have a wider range of thermal expansion coefficients. Complex non-linear thermal expansion characteristics can be achieved, resulting in very close thermal expansion matching to a variety of metals and alloys, including those with non-linear behaviour [24],... 

The coefficient of linear thermal expansion. If a piece of straight glass rod of any diameter and of length L cm is heated uniformly through At°C, it will expand by some amount /cm. We can now say that the increase in length/unit length/°C rise in temperature is a, and... 

TABLE 20. Linear thermal expansion coefficients of metals and of corresponding sealing glasses... 

Most industrial glasses have linear thermal expansion coefficients between 30 10 /K (thermal shock resistant borosilicate gla.ss) and 80 to 90 lO /K (window gla.ss). In composite systems, such as used in the electronics industry for fusing (soldering) glasses to metal conductors or casing components, the thermal expansion coefficients of the glass and the metal have to be precisely matched. 

Many RIM formulated systems also incorporate milled glass fibers, or other kinds of fillers to bring about a reduction in linear thermal expansion and contraction, and increase part rigidity. 

Studies of the effects of various types of fiber and particulate fillers have shown that milled glass fibers are in the near term the most suitable means to achieve part stiffness and the required reduction in the coefficient of linear thermal expansion to allow practical mating of RIM polyurethane panels with steel. 

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