Alumina: electrical conductivity

Other important properties of Cr02 when used as a magnetic pigment are its black color, electrical conductivity (2.5-400 O-1 cm-1 [5.27]) and relatively high crystal hardness (Mohs hardness 8-9 [5.20]). Therefore, coating formulations based on Cr02 require less or even no additives such as carbon black (good conductivity, black color) or refractory oxides such as alumina. 

Figure 5-6. Frequency dependence of electrical conductivity of Na-/ -alumina at different temperatures [U. Strom, K. L. Ngai (t98l) D. P. Almond et al. (1982)]. Calculation [K. Funke (1984)] with the following parameters v0 = 20 GHz, CAB(0) = k-800 K, CBA(0) = k- 200 K.

In the previous section, /1-aluminas were discussed. If one replaces Na+ by H30+ or NH4 in these oxide compounds by, for example, electrolysis, then proton conducting materials can be obtained. Their ionic conductivity, however, is relatively low (10—5 Q-1 cm-1) because of the strong interactions between the small H+ ions and O2- ions in the conduction plane (OH ). The electrical conductivity is markedly higher in crystals of NH4 -/ -Ga203. 

The vast majority of metal complexes in the solid state are insulators and do not exhibit any interesting electrical conduction properties because the metal atoms are surrounded by insulating ligands which prevent the passage of carriers from one site to another. This review will be limited to a discussion of the electrical conduction properties of coordination compounds, and will not include simple inorganic compounds with high electrical conductivity such as mixed metal oxides, (3-alumina and TaSe3. 

As the electrolytes, alkali metal sulfates(M=Li, Na, and K)(l-ll), 3-Alumina(12), and NASIC0N(13, 14) have been examined. Alkali metal sulfates are cation conductors at elevated temperature(>700 C). However, they have several disadvantages. One is the phase transformation of the sulfates(15-18). By this transformation, cracks occur in the electrolyte body and result in the permeation of the ambient gases. The other disadvantage is their low electrical conductivity. Mono, di, or tri-valent cations(19-24) have been doped so as to enhance their conductivity. Furthermore, they become ductile at a tem-... 

Upon discharge sodium ions diffuse through the sodium-conducting /J- or -alumina or NASICON -> solid electrolyte. On the outer surface of the solid electrolyte they react with molten sulfur and/or low valency sulfide anions forming negatively charged polysulfide anions. The rather low electric conductivity of molten sulfur is improved by addition of tetracyanoethylene... 

Although it is perhaps not used as extensively as aluminum chloride, aluminum bromide is also widely used as a Lewis acid catalyst. Aluminum fluoride is used in the preparation of cryolite, Na3AlF6, which is added to alumina to reduce its melting point and increase its electrical conductivity in the electrolytic production of aluminum. One reaction that can be employed to produce the fluoride is... 

There are several important hydrated forms of alumina corresponding to the stoichiometries A1(0)0H and Al(OH)3. Addition of ammonia to a boiling solution of an aluminum salt produces a form of A1(0)0H known as boehmite, which may be prepared in other ways also. A second form of A1(0)0H occurs in Nature as the mineral diaspore. The true hydroxide Al(OH)3 is obtained as a crystalline white precipitate when carbon dioxide is passed into alkaline aluminate solutions. It occurs in Nature as the mineral gibbsite. Materials sometimes referred to as /1-aluminas have other ions such as Na+ and Mg2+ present. They possess the idealized composition Na2011Al203. They can act as ion exchangers, have high electrical conductivity, and are potential solid state electrolytes for batteries. 

It should be noted that reinforcement applications are not limited to organic polymers. Though ceramics are already hard and chemically/thermally resistant, these materials may also be doped with CNTs to improve their inherent brittleness. This has already been proven for the incorporation of 5-10% of CNTs within an alumina matrix. The resultant material exhibits five times the fracture toughness and seven times greater electrical conductivity relative to undoped AI2O3, with an added property of unidirectional heat conductivity,... 

Calcium Carbonate, Calcium Silicate, Powdered Aluminium, Copper Alumina, Flint Powder, Carborundum, Silica, Molybdenum Disulphide Chopped Glass Mica, Silica, Powdered or flaked Glass Metallic Filler or Alumina Colloidal Silica, Bentonite Clay Improved Thermal Conductivity Improved Machinability Improved Abrasion Resistance Improved Impact Strength Improved Electrical Conductivity Improved Thixotropic Response... 

Table 2 shows electrical conductivity data of the catalysts and the support. A is the electrical conductivity of alumina. B is the electrical conductivity of Sn and alkali metals promoted alumina. C is the electrical conductivity of Pt catalyst while D is the electrical conductivity of Pt-Sn catalyst. E is the electrical conductivity of Pt-Sn-Alkali metals catalyst. The data shows that the addition of metal to alumina increases electrical conductivity. The addition of Sn to Pt catalyst augments electrical conductivity approximately three times. Further incorporation of the alkali metals results in an order of magnitude further increases. 

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