High thermal coefficient of expansion

The larger the thermal coefficient of expansion number, the less radical a temperature change the glass can withstand and vice versa. However, a thin piece of glass with a high thermal coefficient of expansion will be able to withstand a more radical temperature change than a very thick piece of glass with the same or lower thermal coefficient of expansion. 

Inadequate ullage in the container. This is especially relevant where ingredients either exert high vapour pressures or have high thermal coefficients of expansion (e.g. alcohol). 

Kyocera has been conducting research and development on AIN and LTCC for more than 10 years, and has produced many kinds of AlN and LTCC products, such as Cer-Quad and multilayer packages, in addition to thin film substrates. Now, we have developed three materials for packages. The first is a novel AlN material (AN75W) that can co-fired at low temperature to reduce cost. The second is a novel LTCC that has a high thermal coefficient of expansion close to that for FR-4. The third is also a novel LTCC that has low permittivity... 

LTCC WITH HIGH THERMAL COEFFICIENT OF EXPANSION... 

When standard tridymite is cooled below 380 C, several phase inversions occur with various changes in symmetry. These tend to produce a large shrinki e and therefore a high thermal coefficient of expansion between 0 -200 C, almost 400 X lO K-h... 

High thermal coefficient of expansion High degree of smoke Uberation in a fire May be sensitive to UV light degradation Slow curing... 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

Several problems arise in the preparation of solutions in nonaqueous solvents. The large thermal coefficient of expansion of many solvents necessitates the use of weight methods to establish concentrations, with subsequent calculation of molarities from weight concentrations. Also, solutions must be prepared and maintained under strictly anhydrous conditions during the course of the experiment. Further, since the preparation of quantities of highly pure solvent is difficult, the use of minimum amounts is desirable. Finally, salts sometimes dissolve very slowly in certain solvents, which makes efficient stirring to hasten dissolution important. 

The successful operation of SOFCs requires individual cell components that are thermally compatible so that stable interfaces are established at 1000°C (1832°F), i.e., thermal expansion coefficients for cell components must be closely matched to reduce stresses arising from differential thermal expansion between components. Fortunately, the electrolyte, interconnection, and cathode listed in Table 8-1 have reasonably close thermal expansion coefficients [i.e., 10 cm/cm°C from room temperature to 1000°C (1832°F)]. An anode made of 100 mol% nickel would have excellent electrical conductivity. However, the thermal expansion coefficient of 100 mol% nickel would be 50% greater than the ceramic electrolyte, or the cathode tube, which causes a thermal mismatch. This thermal mismatch has been resolved by mixing ceramic powders with Ni or NiO. The trade-off of the amount of Ni (to achieve high conductivity) and amount of ceramic (to better match the other component thermal coefficients of expansion) is Ni/YSZ 30/70, by volume (1). 

The adhesive is manufactured in tape form by a hot-melt process. It is a tacky solid at room temperature. The integrity is maintained by using a finely woven glass fabric scrim as the carrier. This process is an excellent example of the compromises required in the technology of formulation. Some of the high-temperature performance that is expected from the phenolic resole is sacrificed for the improved bond strength and toughness afforded from the epoxy resin. The filler is added to make the thermal coefficient of expansion of the cured adhesive more metallic in nature. Dicyandiamide is the... 

The prospects of widespread apphcation of amorphous Si/B/N/C ceramics are rather promising. These expectations are not only based on the attractive properties (low density, low thermal coefficient of expansion, low thermal conductivity, high thermal shock resistivity, and good mechanical performance, in particular at high temperatures) but also on the broad choice in ways of processing. Many of the precursor syntheses as worked out in the laboratory have the potential for being scaled up to technical dimensions, which has been already demonstrated for the TADB-based route. 

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