Aluminium sintering

Small particles can be introduced into metals or ceramics in other ways. The most obvious is to mix a dispersoid (such as an oxide) into a powdered metal (aluminium and lead are both treated in this way), and then compact and sinter the mixed powders. 

Steam forms a protective white film at temperatures up to about 250°C, but above this temperature steam can, under some conditions, react with aluminium progressively to form aluminium oxide and hydrogen. Sintered aluminium powder (S. A.P.) has relatively good resistance to steam at 500°C, but at about 300°C an addition of 1% nickel to the S.A.P. is needed to prevent rapid disintegration. 

Effects of particle size and pressure on the reactive sintering were studied by Gobran et al. (2004). The synthesis of RuAl was described it was observed that reactive systems containing low-melting constituents such as aluminium are assisted in densification by the formation of a transient liquid phase. Reactive sintering using... 

Hardness of sintered aluminium oxide determined by dynamic abrasion with SiC grain, (after A. Szymaiiski, 1974)... 

Fig. 5.18. Impact abrasion resistance of sintered aluminium oxide.

Vitrified clayware is sintered stoneware which is hardly porous and can withstand chemical and mechanical outside influences. For those reasons vitrified clayware is used for sewers, as a coating for vessels, reactor inlets, pipes, valves and pumps. Plastic clay with a relatively high content of aluminium and alkali metals and a low lime content is used as raw material... 

Many kinds of artificial hip joints are available commercially, but they all consist of the same parts, i.e. a metal stem or shaft, usually made of a titanium alloy and a ceramic head of aluminium or zirconium oxide. The production of the ceramic head starts with a powder and ends with the sintering process. The heat treatment will cause the head to shrink. After production, the head is thoroughly tested, e.g. on its spherical shape and surface roughness. 

Table 5.1 shows an application of XPS to the study of the promoted iron catalyst used in the Haber synthesis of ammonia. The sizes of the various electron intensity peaks allows a modest level of quantitative analysis. This catalyst is prepared by sintering an iron oxide, such as magnetite (Fe304) with small amounts of potassium nitrate, calcium carbonate, aluminium oxide and other trace elements at about 1900 K. The unreduced solid produced on cooling is a mixture of oxides. On exposure to the nitrogen-hydrogen reactant gas mixture in the Haber process, the catalyst is converted to its operative, reduced form containing metallic iron. As shown in Table 5.1, the elemental components of the catalyst exhibit surface enrichment or depletion, and the extent of this differs between unreduced and reduced forms. 

There are two types of tantalum electrolytic capacitor wet and solid . Both varieties consist of a porous anode made by sintering tantalum powder at 1800 °C in vacuum. In the wet type the porous structure is impregnated with sulphuric acid, anodized to form a thin layer of Ta205 and encapsulated in a tantalum container that also serves as the cathode. The use of sulphuric acid gives a lower e.s.r. than that of the aluminium electrolytic and increases the temperature range within which the unit can be run. In the solid type the liquid... 

AIN dissociates into its elements at 2500 °C. It is formed by the reaction of aluminium powder with nitrogen and can be sintered in a nitrogen atmosphere. 

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