Coefficient of thermal endurance

The ability to withstand thermal shock resulting from sudden changes in temperature is important for technical applications of glass. The thermal endurance of inorganic glass, studied mainly by Schott and Winkelmann [24] (see also refs. [1] and [25]), is a very complex property. The investigations have led to the definition of a coefficient of thermal endurance F ... 

The coefficient of thermal endurance for selected materials is shown in Table 4.10. The phenomenally high coefficient of tiiermal endurance of BN is primarily a result of the high ratio of its tensile strength to modulus of elasticity as compared to other materials. Diamond also has a high coefficient primarily because of its high tensile strength, high thermal conductivity, and low TCE. 

Flexibilizers generally cannot be used to counteract internal stress in high temperature adhesive because of their relatively low glass transition temperature and thermal endurance properties. However, most high-temperature adhesive systems incorporate metallic fillers (generally aluminum powder) to reduce the coefficient of thermal expansion and degree of shrinkage. 

The ability of a substrate to withstand thermal shock is a function of several variables, including the thermal conductivity, the coefficient of thermal expansion, and the specific heat. AAtinkleman and Schott [6] developed a parameter called the confident of thermal endurance that qualitatively measures the ability of a substrate to withstand thermal stress ... 

These characteristics can be further enhanced and their applications widened by fillers, additives, and reinforcements. Compounding properly will yield an almost limitless combination of an increased loadcarrying capacity, a reduced coefficient of friction, improved wear resistance, higher mechanical strengths, improved thermal properties, greater fatigue endurance and creep resistance, excellent dimensional stability and reproducibility, and the like. 

Boric oxide in the glass composition has been found to increase both the impact and tensile strength of glass containers. It also decreases the coefficient of expansion and increases rate of heat transfer and strength, all of which play important roles in thermal endurance. The use of 1% BjOj often results in a better distribution and less checking in machine-made ware, besides the other advantageous properties mentioned above. 

Very high strength and rigidity, almost constant up to 140 °C Processable up to 250 °C, in the short nm up to 300 °C Very low creep tendency High endurance under completely reversed stress High abrasion resistance up to 250 °C, favottrable sliding behaviour Low thermal expansion coefficient Low absorption of water... 

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