Voids carbides

Compounds isotypic with the k phases arc found among intcrmetallics, borides, carbides and oxides and also with silicides, germanides, arsenides, sulfides and sclcnides no nitrides, however, are found. The mode of filling the various voids in the metal host lattice of the k phases follows the schemein Ref. 4 and is presented in Table 1 for all those compounds for which the atom distribution is well known from x-ray or neutron diffraction. Accordingly, B atoms in tc-borides, Zr, Mo, W, Re)4B and Hfy(Mo, W, Re, Os)4B , occupy the trigonal prismatic interstices within the parent metal framework of a Mn, Aln,-type structure (see Table 1 see also ref. 48). Extended solid solutions are found for (Hf, Al)[Pg.140]

When Acheson found the hexagonal crystals in the voids, he sent some to B.W. Frazier, a professor at Lehigh University. Professor Frazier found that although the crystals were all silicon carbide, they differed in their crystalline structure. He had discovered the polytypism of SiC [18]. Polytypism will be explained in Section 1.3.2. 

Figure 2.26 Replicas prepared from fracture surfaces and viewed in TEM. (a) River patterns of a brittle failure of a steel fastener (b) fine, equiaxed ductile dimples on the surface of a tensile fracture of high-strength steel. The small carbide particles where local rupture and void formation initiated are apparent. (Reprinted with permission from ASM International. All rights reserved www.asminternational.org)...

Having now some notion of how a patent specification should be drawn, let us apply our knowledge to an actual patent. The patent I wish to discuss—Jones, Kennedy, and Rotermund (9) — issued on June 9, 1936, originally to Union Carbide Carbon Corp. An examination of the reports reveals that this patent has the distinction of being the last one to have been sustained by the U. S. Supreme Court. To be sure, since the Union Carbide case, the high court has taken a number of patent cases for consideration, but save for the so-called A P case (/), in which the patent was held void, none required consideration of the issues of validity and infringment. 

A small amount of Ar was trapped in the boron carbide preform. The number of moles was estimated from the ideal gas law using the melting temperature of the metal and the void volume in a typical boron carbide preform. 

A curious compromise is reached in many ionic crystals. The crystal NaCl,f or example, is based on two interpenetrating close-packed (fee) lattices. The positions of one lattice are occupied by positive ions, while those of the other are occupied by negative ions. Consider the unit cube of the fee structure in Fig. 27.7(a). There is a void, or hole, outlined by the octahedron, at the center of the cube. An identical octahedral hole is centered on each edge of the unit cube (Fig. 27.7b). Each hole is at the center of an octahedron, which has atoms at each of the six apices. The centers of the octahedral holes occupy the positions of an fee lattice, which interpenetrates the lattice on which the atoms are located. Small foreign atoms, such as H, B, C, N, can occupy these holes. Many carbides, hydrides, borides, and nitrides of the metals are interstitial compounds formed in this way. 

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