Sintered aluminum oxide

Sol—Gel Sintered Aluminum Oxide. A new and much more versatile sintered alumina abrasive is now produced from aluminum monohydrate, with or without small additions of modifiers such as magnesia, by the sol—gel process (see Sol-gel technology). The first modified sol—gel abrasive on the market, Cubitron, was patented (27) and produced by the 3M Corporation for products such as coated belts and disks. The success of this material promoted intensive research into sol—gel abrasives. 

The mostly applied porous separator in laboratory cells is sintered glass ( fritted glass ). It can be simply and leakproof mounted by the glassblower into the walls of glass cells and then it is very easy to handle. It is available - like similar ceramic materials, for example, sintered aluminum oxide or unglazed porcelain... 

Manufactured abrasives include silicon carbide, fused aluminum oxide, sintered aluminum oxide, sol-gel sintered aluminum oxide, fused zirco-nia-alumina, synthetic diamond, cubic boron nitride, boron carbide, slags, steel shot, and grit. 

Roberts, R.M. et al.. Hydrogen permeability of sintered aluminum oxide. Journal of the American Ceramic Society, 62, 495 (1979). 

The industrially most important oxide-ceramic material is sintered aluminum oxide. The raw materials used are so-called calcined alumina and melted corundum. 

Sintered aluminum oxides (AljOj) or zirconium oxides (Zr02) are increasingly used as components or as part of an articular endoprosthesis. 

As heated alkalies readily attack stainless steel, it was found necessary to use liners or crucibles in the above bombs. Borosilicate glass was found satisfactory up to about 450 °C. for short periods of time, but it could not be used above this temperature. Various ceramic materials were tried for possible use as containers for the sodium peroxide-superoxide mixtures. Sintered aluminum oxide and magnesium oxide were satisfactory up to 450 °C., but above this temperature the sodium oxides penetrated the sintered material and corroded the stainless steel bomb. Commercial ceramic coatings containing (as the principal components) alumina, magnesia, and titania were also tried without success at a temperature above 450 C. 

Figures 4.179 and 4.180 illustrate two furnaces for TGA for different temperature ranges. The figures are self-explanatory. Several different sample holders are shown in the bottom portions of the figures. The multiple holders can be used for simultaneous thermogravimetry and DTA, the single cmcibles are used for simple thermogravimetry. The major problem for the combined thermogravimetry and DTA technique is to bring the thermocouple wires out of the balance without interference with the weighing process. Even the temperature control of the sample holder may be a major problem in vacuum experiments since the thermocouple does not touch the sample. The cmcibles are made of platinum or sintered aluminum oxide. Typical sample masses may vary from a few to several hundred milUgrams.

An important application for zirconium oxide is as an alloying element in aluminum oxide ceramics. Sintered aluminum oxide is brittle. It has been found that the toughness can be considerably improved by mixing aluminum oxide with 4-15% zirconium oxide and sintering the two together. Then a white ceramic , tough enough for many applications, e.g. tools, is obtained. 

One problem encountered in all experiments on fluid metals is the difficulty of confining samples at high temperatures without contamination from reactions with the cell material. Only a few materials are suitable. For studies of mercury and the alkali metals near their criticeil points, acceptable materials include pure tungsten, molybdenum, and the alloys tungsten-rhenium and tungsten-molybdenum. Sintered aluminum oxide or single crystal sapphire may be used to contain alkali metals up to about 1500 °C and to somewhat higher temperatures for mercury. 

Dispersions of flake aluminum powders having surface oxide up to 14 wt % Al O have been pressed, sintered, and worked to a material known as sintered aluminum powder (SAP). This product exhibits high strength at elevated temperatures. Nickel containing small additions of thoria, known as TD-nickel, is also a high temperature cermet. 

The predominate role of the 2inc and aluminum oxides in the ICI catalyst is to reduce the rate of sintering and loss of metallic copper surface area, which, in addition to poisoning, is one of the modes of activity loss with time for this catalyst. 

Rigid Porous Media These are available in sheets or plates and tubes. Materials used include sintered stainless steel and other metals, graphite, aluminum oxide, silica, porcelain, and some plastics—a gamut that allows a wide range of chemical and temperature resistance. Most applications are for clarification. 

The measures of solid state reactivity to be described include experiments on solid-gas, solid-liquid, and solid-solid chemical reaction, solid-solid structural transitions, and hot pressing-sintering in the solid state. These conditions are achieved in catalytic activity measurements of rutile and zinc oxide, in studies of the dissolution of silicon nitride and rutile, the reaction of lead oxide and zirconia to form lead zirconate, the monoclinic to tetragonal transformation in zirconia, the theta-to-alpha transformation in alumina, and the hot pressing of aluminum nitride and aluminum oxide. 

Figure 5.82 The strength of different dispersion-strengthened alloys relative to the pure metal strength as a function of relative temperature. Preparation techniques include sintered aluminum powder (SAP), internal oxidation, and salt decomposition. Reprinted, by permission, from A. Kelly, Composite Materials, p. 62. Copyright 1966 by American Elsevier, Inc.

J.M. Dynys. Sintering Mechanisms and Surface Diffusion for Aluminum Oxide. PhD thesis, Department of Materials Science and Engineering, Massachusetts Institute of Technology, 1982. 

Aluminum oxide sols are successfully used for application of films [1794, 1793], such as high area films for hybrid circuits [1236]. The same technique was used for the preparation of J-A1203 (NaAlnO,7) in this case alcoholic solutions of NaOR were added to aluminum alkoxide solutions [1795, 1038]. To increase the stability of sols, aluminum alkoxides are frequently modified with acetic acid [1570] or (3-diketones [1659]. Alumina sheets are commercially produced by the sintering of high-purity fine A1203 powders prepared by hydrolysis of modified Al(OPr )3 [1236]. To prepare powders with spherical species from dilute solutions, hydroxopropylcellulose was added to prevent... 

The product is poured into ice water, thoroughly extracted yith benzene, and the benzene solution washed with water. Benzene is then removed by distillation until a volume of 25-50 cc. is reached and the resulting deep-red solution is passed through a 12 by 2 cm. column of aluminum oxide. The column is developed with ordinary, undried benzene, and that portion of the eluate which runs through before the strawberry-red zone reaches the bottom of the tube is discarded. The solution that follows is collected, and a pale yellow crystalline mass is obtained upon removal of the solvent. Recrystallization from ethanol gives 1.24-1.37 g. (60-65%) of pale yellow crystals that sinter at 119° and melt at 122.7-123.2° (cor.). 

The product is then poured into ice water, extracted with benzene, and washed with water, aqueous sodium hydroxide, and finally with water. After removal of the solvent, the residue is sublimed at 1 mm. and a bath temperature of 160-190°. The pale yellow crystals so obtained are dissolved in benzene, and the solution is passed through a short column of aluminum oxide. Removal of the solvent gives 0.2-0.23 g. (40-45%) of white crystals which begin to sinter at 245° and melt at 252-254° (cor.). 

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