Zero thermal expansion

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. 

Li20-Si02 (LAS). The trade names of such glass-ceramic matrix materials are Corningware, Zerodur and Ceran. This type of glass-ceramic matrix material has nearly zero thermal expansion and high thermal shock resistance. It is used for the production of optical and telescopic mirrors. 

Sol-gel methods are used to prepare a heterogeneous, nanometer composite of calcium zirconium phosphate and strontium zirconium phosphate, Cao.sSro.sZrsOn. In this composite, individual domains both expand and contract upon heating, leading to a material with virtually zero thermal expansion over the range 0-500 °C. 

Usefiil zero thermal expansion composites are made by combining materials that show the unusual property of negative thermal expansion (i.e. contraction) with normal (positive) expansion materials. Examples of phosphates showing negative thermal expansion are the diphosphate-divanadate solid solutions ZrP2- V Oy and the microporous aluminophosphate AIPO-17 which shows a particularly large effect. ... 

Winkler HGF (1948) Synthese und Kristallstruktur des Eukiyptits, LiAlSi04. Acta Ciystallogr 1 27-34 Xu H, Heaney PJ (1997) Memory effects of domain structures during displacive phase transitions a high-temperature TEM study of quartz and anorthite. Am Mineral 82 99-108 Xu H, Heaney PJ, Yates DM, Von Dreele RB, Bourke MA (1999a) Structural mechanisms underlying near-zero thermal expansion in p-eucryptite a combined synchrotron X-ray and neutron Rietveld analysis. J Mat Res 14 3138-3151... 

Note that in general the nitrides and carbides of Si, with their lower thermal expansion coefficients, are more resistant to thermal shock than oxides. In theory, a material with zero thermal expansion would not be susceptible to thermal shock. In practice, a number of such materials do actually exist commercially, including some glass-ceramics that have been developed which, as a result of thermal expansion anisotropy, have extremely low a s (see Ch. 4). Another good example is fused silica which also has an extremely low a and thus is not prone to thermal shock. 

In the case of a positive expansion coeflhcient with increasing pressure a rise in temperature is predicted, in the case of a negative expansion coefficient, the temperature decreases, and in the case of a zero thermal expansion coefficient the temperature does not change at all. All these three cases are realized in the case of water. The thermal expansion coefficient is 0 at 4 °C. At 2 °C, the thermal expansion coefficient is —1.6 and at 6 °C the thermal expansion coefficient is 1.6The... 

Tauch, D., Russel, C. Glass-ceramics with zero thermal expansion in the system bao/al2o3/b2o3. J. Non-Cryst. Solids 351(27-29), 2294-2298 (2005)... 

The expansion of chemical bonds with increasing temperature leads the vast majority of known solids to expand with heating (positive thermal expansion, PTE), a property once thought to be an immutable law of nature. A relatively small number of materials are known that defy this expectation and contract upon heating i.e. display negative thermal expansion, NTE) or are temperature-invariant i.e. display zero thermal expansion, ZTE). These novel behaviours arise due to a range of physical mechanisms that include magnetostriction and, most... 

It can be shown theoretically, as well as by experiment, that multilayer angle-ply laminates have negative or zero thermal expansion coefficients at... 

Materials that do not expand at all as the temperature rises, zero thermal expansion (ZTE) materials, would be of value for many purposes, especially in microelectronic devices that may become warm due to power consumption. For this reason, materials that show ZTE are being actively sought. In the past, a ZTE solid could be constructed by using a composite of two materials, one showing thermal contraction and one showing thermal expansion. However, composite materials often have accompanying drawbacks in use, and a number of solids have now been fabricated that show virtually no expansion at all as the temperature rises. 

Glass matrix composites, in particular with carbon fibre reinforcement, have been also proposed for a variety of applications which require thermal dimensional stability, i.e. materials with multidimensional near zero thermal expansion coefficients such as support structures for laser mirrors [21, 22]. 

Lightweight and isotropic near-zero thermal expansion materials can be obtained by adding metallic particles to a negative thermal expansion glass-ceramic matrix [95]. These materials find applications in mirrors and general optics, sensors, microwave components and antennae because of their impressive thermal and dimensional stability. 

Zirconyl pyrophosphate, (ZrO)2P207, mp = 2070°C, p = 3.88 g/cc, is stable up to about 1600 C, and calcium orthophosphate, Ca3(P04)2 which melts at 1820°C, can be used for some purposes at temperatures up to 1600°C. The zirconyl compound, which loses P2O5 above 1600°C, has potential use as a low-expansion ceramic, although its strength is rather limited [3]. Up to llOO C the net expansion is <1.7 x 10 C (Table 12.27). Zirconyl pyrophosphate is a good electrical insulator and its dielectric constant is similar to that of alumina [4]. Solid solutions of composition Ca Sr,. Zr4(P04)g and Zr 2-Nx i show almost zero thermal expansion over a considerable temperature range, and are promising materials for future application (see below). 

Hyde [180] at GEC Engineering Research Centre, Stafford describes how a continuous ceramic fiber preform is impregnated with a sol, which then sohdifies into a gel. Carbon fiber reinforced silica made in this way has non-zero thermal expansion, but much higher strength than a zero-expansion glass ceramic. 

Loop Tackle markets relatively cheap compression molded chopped carbon fiber fly reels, which are lightweight, with virtually zero thermal expansion and water absorption and excellent corrosion resistance to sea water. 

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