Alumina wear resistance

Other coatings, such as TiAlN (96), TiCN, Zr02, and ZrN (97), and CrN (98) were developed for special appHcations. The last was developed for higher speed machining of titanium alloys. Sometimes a coating is developed not for its wear-resistance but for its heat insulation. The case in point is alumina coating of cBN to reduce the heat conductivity at the surface so that the cBN performance can be enhanced (99). 

Alumina produced by the Bayer process is precipitated and then calcined [Krawczyk, Ceramic Forum International, 67(7-8), 342-8 (1990)]. Aggregates are typically 20 to 70 [Lm, and have to be reduced. The standard product is typically made in continuous dry ball or vibra-toiy mills to give a product d o size of 3-7 [Lm, 98 percent finer than 45 [Lm. The mills are lined with wear-resistant alumina blocks, and balls or cylinders are used with an alumina content of 80-92 percent. The products containing up to 96 percent AI9O3 are used for bricks, kiln furniture, grinding balls and liners, high voltage insulators, catalyst carriers, etc. 

Dense alumina AI2O3 Cutting taals, dies wear-resistant surfaces, bearings ... 

Bearings, liners, seals Wear resistance Alumina, zirconio... 

Engine and turbine ports. Heat and wear resistance SiC, Si3N4, alumina, siolons. 

Artificial bone, teeth, joints Wear resistance, strength Zirconio, alumina... 

Similar materials were used by Skeldon et al to produce a self-lubricating surface film on aluminium. They first produced a porous alumina film on the surface by anodizing, and then re-anodized in an electrolyte containing 0.01 M ammonium tetrathiomolybdate. They then found that the pores of the primary anodized film contained mainly amorphous molybdenum trisulphide, and this was converted by vacuum annealing to hexagonal molybdenum disulphide. The film gave a marked improvement in wear resistance. 

Ceramic materials are also utilized in nuclear reactor components. Applications include insulation of pressure vessels with linings fabricated from silica and alumina-base ceramic bricks or fiber insulation pressure vessels made of prestressed concrete structures that enclose the entire reactor and secondary system wear-resistant surfaces produced by means of coatings such as chromium oxide or chromium carbide and shielding applications, which include materials such as concrete, graphite, and leaded glass ... 

For testing dental restorative materials, many regimes exist that use similar principles to those described for assessing toothpaste abrasivity. These tests may be conducted under conditions of two-body or three-body wear [25], i.e. focussing either on attrition or abrasion. Two-body tests for restorative materials either use human enamel [26] or a hard material, such as alumina [27] or steatite [28], as the abrader. For three-body tests, an abrasive medium, such as toothpaste slurry [29, 30], or an abrasive food, such as rice or millet seeds [31,32], is typically used. These test methods are usually not truly representative of the oral environment rather, they are designed to assess the wear resistance of restorative materials under extreme conditions. 

Extruders are also used in the production of sintered industrial parts. Of special importance is their application for the manufacture of catalyst carriers (Section 6.3.2, Figs. 6.3-20 and 6.3-21). The use of wear-resistant alloys for all parts that come in contact with the material to be extruded make the extruders suitable for the processing of highly abrasive catalysts, other chemicals, and minerals, such as molecular sieves, high-purity aluminas, and kaolin carriers. Interchangeable die plates allow the extrusion of an almost unlimited variety of sizes and shapes on the same basic machine that is then equipped with a variable-speed screw-drive to adjust retention time, pressure, and production rate. 

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