High temperature behaviour

The limit to the upper temperature at which a rubber can be used is generally determined by its chemical stability, and will thus vary for different rubbers. Rubbers can be attacked by oxygen or other chemical agents, and because the attack results in a chemical reaction, its potency will increase with temperature. 

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High-temperature behaviour. Consider T much higher than a characteristic temperature like 0q or 9g. Since 3 ha is then small compared to 1, one can expand the exponential to obtain... 

Although the Debye model reproduces the essential features of the low- and high-temperature behaviour of crystals, the model has its limitations. A temperature-dependent Debye temperature, d(F), can be calculated by reproducing the heat capacity at each single temperature using the equation... 

Gas-phase basicities of several substituted benzaldehydes (62 X = o-/m-/p-Me/F, o-j 77 -Cl) have been measured, relative to benzaldehyde or mesitylene as reference bases, over a range of temperatures.101 The tolualdehydes are more basic than benzaldehyde, the halobenzaldehydes less so, following classical aromatic substituent effects. The data also correlate well with solution-based linear-free-energy substituent constants, as well as with theoretical (MNDO) calculations. Some deviations are noteworthy (i) the o-halobenzaldehydes (especially chloro) have higher basicities than predicted, but calculations tend to rale out the hydrogen-bonded isomer (63), which is also contraindicated by a normal A,S value, inconsistent with the expected restriction of— hOH rotation in such a structure (ii) anomalies in the high-temperature behaviour of m-fluorobenzaldehyde in the presence of mesitylene reference base are consistent with a specific catalysed isomerization to the ortho- or para-isomer. 

Pezzotti, G., Tanaka, I. and Okamoto, T. Si3N4/SiC-whisker composites without sintering aids III, High temperature behaviour , J. Am. Ceram. Soc., 74[2] (1991) 326-332. 

If the refractoriness of a material is to be determined, it must be cut or shaped into a cone of the same shape which is then heated at the specified rate together with several standard cones. The high-temperature behaviour of an unknown material is thus compared with that of a known material. The refractoriness is then specified by the number of that standard pyrometric cone whose tip would touch the supporting plaque simultaneously with a cone of the refractory material under investigation (pyrometric cone equivalent, PCE). 

Chemical stability and behaviour at high temperature Behaviour at low temperature Action of light... 

The case of bilinear coupling is important in the description of the high temperature behaviour of albite, and is considered in more detail here. For the case of biquadratic coupling the reader is referred to Salje and Devarajan (1986) and Salje (1990). If we consider two order parameters, Qi and Q2, which are coupled together by a single spontaneous strain, e, the Landau expansion is ... 

Having discussed some of the background to the models that have been used to underpin studies of order-disorder in minerals, let us finally turn to a few of the main results from studies of strain-order-disorder coupling that have been reported for a number of phases. It is worth first considering the case of the high-temperature behaviour of albite (NaAlSi308), as this mineral provides, in many respects, the archetypal example... 

OXYNITRIDE GLASSES EFFECTS OF COMPOSITION ON GLASS FORMATION AND PROPERTIES WITH IMPLICATIONS FOR HIGH TEMPERATURE BEHAVIOUR OF SILICON NITRIDE CERAMICS... 

In the following chapter fundamentals of the high-temperature behaviour of silicon nitrides and silicon nitride-based composites will be presented. Depending on the sintering additive used, silicon nitride materials with different high-temperature properties can be obtained. Some typical materials are chosen from the broad variety of Si3N4 ceramics that exist and summarized in Table 4. 

Significant dehydration does not occur during short time heating from RT to 800 °C (temperature raise of 100 °C/minute and 1 minute for the measurements at each temperature see Section 2). Figure 6 shows high temperature behaviour of type I/II H2O in... 

Fig. 6. High temperature behaviour of beryl from RT to 800 °C for the samples in Fig. 5 (Replotted from Fukuda Shinoda, 2011). (a) under E/ / c-axis. (b) under EXc-axis. The RT spectra after heating at 800 °C are shown as gray lines, showing no significant dehyderation occured during heating.

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