Permanent sintered

Barium carbonate of finely controlled particle size reacts in the soHd state when heated with iron oxide to form barium ferrites. Magnetically aligned barium ferrite [11138-11-7] powder can be pressed and sintered into a hard-core permanent magnet which is used in many types of small motors. Alternatively, ground up magnetic powder can be compounded into plastic strips which are used in a variety of appHances as part of the closure mechanism. 

The high melting point and reactivity of tantalum with the permanent gases at high temperatures prevents conventional consolidation by melting and casting in air. The metal is in fact consolidated by vacuum sinter-... 

The additional problems which arise in heterogeneous reactors, where hot spots may cause permanent damage to the catalyst by sintering, will be examined in Chap. 4. 

In different forms (bar, casting such as sand, centrifugal, die, permanent mould, etc., extrusion, forging, impact extrusion, pressing, sintered, powder pressing)... 

In the fall of 1934, Dr. Grosse reduced this pure oxide by two methods and obtained from it the metal protactinium, which is even rarer than radium, but much more permanent in air. In die first method, he bombarded the oxide on a copper target, in a high vacuum, with a stream of electrons. After a few hours, he obtained a shiny, partly sintered, metallic mass, stable in air. In his second method, he converted the oxide to the iodide (or chloride or bromide) and cracked it in a high vacuum on an electrically heated tungsten filament, according to the reaction ... 

Interesting are attempts to design dynamic hardness testers with a higher level of automation. Among these, we should mention the Equotip hardness tester manufactured by Proceq of Switzerland and the Sonodur A probe manufactured by Branson-Krautkramer. In the former, the sampler in the shape of a ball of sintered carbide is mounted in a beater weighing 5.5 g, which is also fitted out with a permanent magnet. This enables measurement of the speed of impulse and rebound by proportional current induction in the measuring coil. The quotient of rebound and impulse speed multiplied by 1000 is defined as hardness L (after the name of the method s author—Leeb). The hardness measurement result L can be converted to HKC, Hb or Hv with the aid of tables. 

Sintered samples of Sm2Fe17Xy with sufficient mechanical strength for use as the permanent magnetic materials are obtained by high-pressure... 

The copper catalysts preserved their activity up to temperatures of 400° for some hours (except for a poisoning effect traced to the products of reaction, which was not appreciable below 280°), so that it is clear that the active centres are not appreciably destroyed by thermal agitation and mobility of the atoms, below this temperature. Above 400°, sintering occurs, with permanent loss of activity. 

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