Fused corundum

The purity meets the requirements of most ceramic technologies with the exception of special oxide ceramics, where the purity requirements are much more demanding. In the case of fused corundum, the composition is similar to that specified above however, the grinding frequently brings about some contamination. 

Selective oxidation of benzene to maleic anhydride vanadium molybdenum oxide on fused corundum (catal5Uically inactive support without pores)... 

Corundum, when pure, is also known as the gemstone white sapphire. Certain other gemstones consist of corundum with small amounts of transition metal ions as impurities Cr in ruby and Fe and Ti in blue sapphire, for example. Artificial gemstones are made by fusing corundum with carefully controlled amounts of other oxides. 

Corundum is an aluminum oxide that possesses a hexagonal crystal structure, The compound is extremely hard (2000 on the Knoop scale), sp gr 3.95, and is widely used in abrasives and refractories. Corundum is manufactured by fusing alumina or bauxite in an electric arc furnace operated at about SIOO C. 

It is difficult to achieve a gas-tight seal to the anode current connections, which must also be electrically insulated against the cover of the electrolyzer, to which the cathodes are attached. Formerly, fused calcium fluoride was used as sealing material. This is, however, brittle and sometimes even porous recently sintered corundum has been used and for the external packing teflone (polymerized tetrafluoro-ethylene), buna, and polyvinylchloride. 

White bauxites are chiefly used for the production of aluminium sulphate and the alums. Red bauxites form the raw material for the preparation of alumina, and therefore of aluminium. Intermediate or refractory bauxites, fused in an electric furnace, give artificial corundum. 

Duclaux, Ann. Chim., 1872, 25, 433 Duclaux and Errera, J. de Phys., 1925, 6, 202 for compressible liquids, see Muskat, Physics, 1934, 5, 71 for flow through short capillaries (porous masses, cracks, filter paper, etc.), see Bell and Cameron, J. Phys. Chem., 1906, 10, 658 Washburn, Phys. Rev., 1921, 17, 374 Bull and Wronski, J. Phys. Chem., 1931, 41, 463 (bibl.) the results may be affected by adsorption Wentworth, Amer. J. Sci., 1944,242,478 the method was used for fused metals with a sintered corundum plug by Schanze and Sauer-wald, Sci. Rep. Tohoku Imp. Univ., 1936, Honda Annivers. Vol., 510 Barrer, Diffusion in and through Solids, Cambridge, 1941. ... 

The clear solutions in 1 or 2 are slowly evaporated to dryness by using a heating plate or an infrared lamp. The residue is then transferred to a corundum crucible (size 10 X 60 mm), and this is inserted into a fused quartz tube in the center of a tubular furnace. (To prepare larger quantities, e.g., 10 mmole, a 100 X 15 X 10-mm Alundum boat is more convenient.) The sizes of the tubular furnace and the fused quartz tube should be sufficient that the sample can be... 

A sample of Gag03 is triturated with excess fused Ga. The mixture is placed in a corundum boat and heated under vacuum in a quartz apparatus provided with a cold finger, according to the... 

Direct synthesis from Ga and S is impossible. Thus, excess fused Ga is triturated with GaS, mixed with GagSg to promote better wetting, according to the method of Klemm andVon Vogel, developed by Brukl and Ortner. The mixture is placed in a corundum boat inserted in a quartz apparatus, equipped with a cold finger, in high vacuum. The boat contents are heated to 700-720°C. If these temperatures are exceeded, the sublimed GagS has too low a sulfur content. 

The phosphide forms when stoichiometric quantities of Na and red P are fused under a protective Ar blsinket in a Tamman crucible. The latter is made of sintered corundum and is hermetically sealed in an outer iron crucible. 

L. Blanc found that the oxide calcined from 500° to 800° has a sp. gr. 5-033 at 820°, 5-110 at 1080°, 5-130 and when fused, 6-145. H. P. Walmsley gave 5-238 for the sp. gr. of the dispersed oxide and W. H. Zachariasen, 5-25, calculated from the X-radiogram data. W. Biltz and co-workers found the mol. vol. of chromic oxide in the spinels to be 28-9. F. Wohler found that crystalline chromic oxide has a hardness great enough for it to scratch quartz, topaz, and hyacinth and G. Rose, and W. P. Blake found that it is as hard as corundum. 0. Ruff and A. Riebeth discussed the plasticity of mixtures of the oxide with water, etc. 

Figure 14.15 The dispersion of (a) fused silica glass and (b) corundum...

Figure 11. Comparison of the grinding performance of known (fused and sol/gel derived) grinding materials on the basis of AI2O3 with a new single phase corundum grit produced by a powder...

The flame fusion technique (see Figure 7.20b) was originally devised in 1904 by Verneuil for the manufacture of artificial gemstones, such as corundum (white sapphire) and ruby. This method is now used for the mass production of jewels for watches and scientific instruments. A trickle of fine alumina powder plus traces of colouring oxides is fed at a controlled rate into an oxyhydrogen flame. Fusion occurs and the molten droplets fall on to a ceramic collecting rod. A seed crystal cemented to the rod is fused in the flame and the rod is lowered at a rate that allows the top of the growing crystal (known as a boule) to remain just molten. Renewed interest has recently been shown in this method for the production of rubies for lasers. 

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