Solid solutions thermal conductivity

The temperature dependence of electrical conductivity has been used [365] to distinguish between the possible structural modifications of the Mn02 yielded by the thermal decomposition of KMn04. In studies involving additives, it is possible to investigate solid-solution formation, since plots of electrical conductivity against concentration of additive have a characteristic V-shape [366]. 

Measurements of photoconductivity and of the Hall potential [367] are accurate and unambiguous methods of detecting electronic conduction in ionic solids. Kabanov [351] emphasizes, however, that the absence of such effects is not conclusive proof to the contrary. From measurements of thermal potential [368], it is possible to detect solid-solution formation, to distinguish between electronic and positive hole conductivity in semi-conductors and between interstitial and vacancy conductivity in ionic conductors. 

In a number of general properties, such as viscosity and thermal conductivity, melts differ little from solutions. Their surface tensions are two to three times higher than those of aqueous solutions. This leads to poorer wetting of many solids, including important electrode materials such as carbon and graphite, by the ionic liquids. 

That boiling produces bubbles of vapor creates an additional problem for performing the experiment. If a bubble of gas forms at the bottom of a capillary tube, its expansion and rise to the top of the capillary will expel the rest of the liquid. This is due to the fact that the surface tension of most liquids combined with the narrow bore of the capillary will not allow fluid to drain around the bubble as it rises. The solution is that a larger sample tube and sample is required for the experiment. One advantage of the boiling point experiment is that the thermal conductivity of a liquid is higher than its solid because of the mobility of the molecules. 

Elemental composition Ba 69.58%, C 6.09%, O 24.32%. The compound is digested with nitric acid under heating and the solution is analyzed for barium by atomic absorption or emission spectrometry (see Barium). Carbon dioxide may be determined by treating a small amount of the solid with dilute HCl and analyzing the evolved gas by GC using a thermal conductivity detector or a mass spectrometer. The characteristic mass of CO2 is 44. 

Figure 4.31 Thermal conductivity in the solid solution system MgO-NiO. Multiply by 418.7 to obtain k in units of W/m K. From W. D. Kingery, H. K. Bowen, and D. R. Uhlmann, Introduction to Ceramics. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

The thermal conductance of materials depends on temperature and decreases as the latter increases. It also depends on the density of a solid, increasing with density. The presence of foreign atoms in solid solutions contributes to growth of thermal resistance, i.e., to reduction of thermal conductance (Pampuch, 1971). 

The carbides and nitrides of vanadium and titanium crystallize in the same face centered cubic (fee) system, and because of the closeness of their cell parameters (Table 15.1) form solid solutions. These ceramic materials exhibit interesting mechanical, thermal, chemical and conductive properties.1,2 Their high melting point, hardness and wide range of composition have therefore attracted considerable attention in the last decade. Moreover, their good abrasion resistance and low friction also make these ceramics attractive for protective coating applications.3-5 Chemical vapor deposition (CVD) is a commonly used technique for the production of such materials. In the conventional thermally activated process, a mixture of gases is used.6-9 In the case of TiC, TiN, VC and VN, this mixture is... 

Cryoinjury to the specimen is caused directly by extra- or intracellular ice crystal formation as well as by ice-induced solution effects during cryopreservation. Ice crystals seriously deform cell components. Another disadvantage of the formation of ice crystals near the specimen surface is slowing the cooling rate in areas below the surface because their thermal conductivity is about half that of solid water in a noncrystalline state. Furthermore, ice crystal formation is accompanied by the generation of latent heat, which also slows down the freezing rate. 

A satisfactory theory of metallic bonding must account for the characteristic properties of high electrical and thermal conductivity, metallic lustre, ductility and the complex magnetic properties of metals which imply the presence of unpaired electrons. The theory should also rationalise the enthalpies of atomisation A/f tom of metallic elemental substances. A/f tom is a measure of the cohesive energy within the solid, and we saw in Chapter 5 how it plays an important part in the thermochemistry of ions in solids and solutions. The atomisation enthalpies of elemental substances (metallic and nonmetallic) are collected in Table 7.1. There is a fair correlation between A/Z tom an(J physical properties such as hardness and melting/boiling points. 

The salt monomer method was successfully applied to the preparation of the electrically-conducting polyimide-carbon black composites [62]. The composites are prepared as follows An aqueous solution of salt monomer 9PMA was mixed with carbon black, giving a suspension. This was evaporated to dryness under reduced pressure to afford a homogeneously-mixed powder composed of the salt monomer and carbon black. The powder was subjected to solid-state thermal polycondensation in the form of a pellet at 240 °C for 1 h under atmospheric pressure. The semiconducting aliphatic polyimides (P-9PM, Tm=315 °C) having electric conductivity of about 10"6 S/cm was readily obtained by mixing only 1 wt% of carbon black based on the polyimide. 

The simplest technique is to use separate numerical solvers for the fluid and solid phases and to exchange information through the boundary conditions. The use of separate solvers allows a flexible gridding inside the solid phase, which is required because of the three orders of magnitude difference in thermal conductivities between the solid and gas. It is also easy to include various physical phenomena such as charring and moisture transfer. Quite often, ID solution of the heat conduction equation on each wall cell is sufficiently accurate. This technique is implemented as an internal subroutine in FDS. 

As seen from Figure 10, the autowave solution of equation (2) exists only at G < G0 0.64. Physically this implies that in a system described by this model the autowave mode of the reaction propagation over a solid reactant mixture becomes impossible at a definite increase in the strength of the sample, decrease in the thermal effect and reaction velocity, and increase in the thermal conductivity. 

The thermal conductivity of a pure metal is lowered by alloying, whether the alloy formed is a single phase (solid solution) or multiphase mixture. There are several reasons for this. First, electrons are scattered by crystal imperfections and solute atoms (electron-defect scattering). Second, a substantial portion of the thermal conductivity in alloys, in contrast to that of pure metals, is by phonons, Kph (phonons are the sole contribution in electrically insulating solids) and phonons are also scattered by defects. Finally, electron-phonon interactions limit both Kei and Kp. ... 

MuUite is another important crystalline ceramic that is an oxide It is a solid solution of alumina and silica in the compositional range 71-75 wt% alumina. Mullite is represented by the formula, 3 Al203.2Si02. It has excellent strength and creep resistance as well as low thermal expansion and conductivity. For more detailed information on the structure and properties of mullite the reader is referred to Schneider et al. (1994). Table 6.2 provides a summary of the properties of mullite. 

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