Thermal conductivity fillers

Thermal conductivity range, W/K-m Filler (thermal conductivity given in parentheses)... 

In addition to the type of filler, thermal conductivity depends on many other factors including the amount of filler used, whether it is by weight or by volume, its form and size, the surface treatment of the filler particles, the completeness of cure, and the test conditions used for measurement. Test methods are described in MIL-STD-883, Method 1012.1 and in ASTM C518. ... 

N/A 90°C min. Non-reinforced film, inorganic fillers, thermal conductivity... 

D= — the matrix /filler thermal conductivity ratio ( m matrix,/ filler)... 

One have calculated temperature in the computing cell with a finite element software Comsol using a steady state heat conduction model. Using eq.(l), ETC values are deduced (fig. 5). For simple cubic arrangement of particles, it is shown that the ETC increase cannot be more than 14 times higher than the matrix conductivity and that having a matrix /filler thermal conductivity ratio smaller than 10 is not worth for ETC improvment. 

Other results concern the relative weight, on ETC values, of the thermal contact resistance (parameter C), the thickness of matrix layer between two particles (parameter B) and matrix/filler thermal conductivity ratio (parameter Z>) [7]. It is shown that thermal contact resistance is a factor of great importance for high ETC values. 

Carbon—graphite materials do not gall or weld even when mbbed under excessive load and speed. Early carbon materials contained metal fillers to provide strength and high thermal conductivity, but these desirable properties can now be obtained ia tme carboa—graphite materials that completely eliminate the galling teadeacy and other disadvantages of metals. 

Fillers are used in tooling and casting application. Not only do they reduce cost but in diluting the resin content they also reduce curing shrinkage, lower the coefficient of expansion, reduce exotherms and may increase thermal conductivity. Sand is frequently used in inner cores whereas metal powders and metal oxide fillers are used in surface layers. Wire wool and asbestos are sometimes used to improve impact strength. 

The choice of filler depends on the end use. Metal fillers will improve machineability, hardness and thermal conductivity but may in some cases inhibit cure. 

Plastics are high-molecular-weight organic compounds of natural or mostly artificial origin. In fabrication, plastics are added with fillers, plasticizers, dyestuffs and other additives, wliich are necessary to lower the price of the material, and give it the desired properties of strength, elasticity, color, point of softening, thermal conductivity, etc. 

Filler or Reinforcement Chcmicul Resistance i 8 u i i Electrical Insulation Impact Strength Tensile Strength Dimensional Stability Stiffness Hardness Lubricity Electrical Conductivity Thermal Conductivity 1 8 C s TS 1 X I I h 11... 

For certain products, skill is required to estimate a product s performance under steady-state heat-flow conditions, especially those made of RPs (Fig. 7-19). The method and repeatability of the processing technique can have a significant effect. In general, thermal conductivity is low for plastics and the plastic s structure does not alter its value significantly. To increase it the usual approach is to add metallic fillers, glass fibers, or electrically insulating fillers such as alumina. Foaming can be used to decrease thermal conductivity. 

An activator in rubber compounds containing organic accelerators. In polychloroprene, zinc oxide is considered to be the accelerator rather than the activator. The use of zinc oxide as a reinforcing agent and as a white colouring agent is obsolescent. Zinc oxide is manufactured by either the French (or indirect) process or by the American (or direct) process. It can be used as a filler to impart high thermal conductivity. 

Properties of peroxide cross-linked polyethylene foams manufactured by a nitrogen solution process, were examined for thermal conductivity, cellular structure and matrix polymer morphology. Theoretical models were used to determine the relative contributions of each heat transfer mechanism to the total thermal conductivity. Thermal radiation was found to contribute some 22-34% of the total and this was related to the foam s mean cell structure and the presence of any carbon black filler. There was no clear trend of thermal conductivity with density, but mainly by cell size. 27 refs. 

Due to the dependence on mean free path as described in Eq. (4.40), the thermal conductivity of heterogeneous systems is impossible to predict on heat capacity alone. As in previous sections, we do know that disorder tends to decrease thermal conductivity due to mean free path considerations, and this is indeed the case for fillers with high thermal conductivities, such as copper and aluminum in epoxy matrices (see Table 4.12). The thermal conductivity of the epoxy matrix increases only modestly due to the addition of even high percentages of thermally conductive fillers. 

This is also important in determining processing behaviour. The thermal conductivity of most mineral fillers is about one order of magnitude higher than that of thermoplastics and their incorporation considerably increases the conductivity of a composite. This effect is beneficial in processing as mouldings can be expected to heat up and cool down more rapidly, leading to shorter cycle times [68]. 

The coefficient of linear expansion of unfilled polymers is approximately 10 X 10 5 cm/cm K. These values are reduced by the presence of fillers or reinforcements. The thermal conductivity of the polymers is about 5 X 10 4 cal/sec cm K. These values are increased by the incorporation of metal flake fillers. The specific heat is about 0.4 cal/g K, and these values are slightly lower for crystalline polymers than for amorphous polymers. 

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