Other Intermetallic Compounds

Another Example AuSn.—From among the many other intermetallic compounds which might be used as a second illustration, AuSn is chosen to show how the consideration of metallic valence and use of the radii contribute to the explanation of the choice of a suitable structure by a compound. 

Ni3Al is one of a very few intermetallic compounds that is ductile at room temperature. Additionally, it has the interesting property that between 25 and 550 °C it gets harder rather than softer. This anomalous yielding is not unique to this compound. Several other intermetallic compounds behave similarly. 

Titanium iron hydrides are among the materials which, at the present time, appear to have potential for practical applications as an energy-storage medium (7). The formation and properties of titanium iron hydride have been studied by Reilly and Wiswall (3), who found that the reaction proceeds in two steps as indicated by Reactions 5 and 6. Both hydrides have dissociation pressures above 1 atm at room temperature in contrast to TiH2 which is very stable. Titanium iron is representative of intermetallic compounds that consist of an element (titanium) capable of forming a stable hydride and another element (iron) that is not a hydride former or at best, forms a hydride with great difficulty. Iron presumably plays a role in destabilizing the hydrides. Titanium also forms a 1 1 compound with copper (there are other intermetallic compounds in the titanium-copper system) and this fact, coupled with the observation that copper... 

Under conditions of diffusion control, the TiAl3 layer, known to be the first to occur between titanium and aluminium, consumes all the aluminium atoms diffusing across its bulk exclusively for its own growth, not sharing them with the other intermetallic compound layers. Therefore, those or at least one of them can grow only at the expense of diffusion of the titanium atoms. 

The electrode substrates typically considered for potentiometric stripping analysis are -> glassy carbon and wax-impregnated graphite. Application of metal substrates is usually limited due to the possibility of contamination of mercury by amalgamation. Also other intermetallic compounds can be formed. Very careful polishing is essential to obtain good results. 

A.2.2 Nonpolar Binary Intermetallic Phases. Zintl phases are characterized by the presence of markedly heteropolar bonding between the Zintl ions (electronegative polyatomic clusters) and the more electropositive metal atoms. By contrast, the bonding between heteronuclear atoms within other intermetallic compounds is primarily covalent or metallic. A number of different structure types exist for any given... 

Many of the intermetallic compounds are very difficult to process into thin sheets because they exhibit very low ductility at ambient temperatures. Powder metallurgical techniques coupled with tape casting have been employed to process these materials into continuous thin sheets which, after removal of the polymer binder and plasticizer, can be sintered and rolled to full density with a sequence of cold work and annealing steps. The use of tape casting has recently been reported for the production of iron aluminide (FeAl) thin sheets with excellent properties. We believe that this processing technology can be used for other intermetallic compounds, especially for the production of continuous thin sheets. 

In the case of beryllium, the phase diagrams contain at least one intermetallic compound which has the same stoichiometry (RBeu and AnBen) and the same structure (prototype NaZnu). In the Sc-Be system other intermetallic compounds have been detected. 

NMR work on the magnetically ordered state of other intermetallic compounds is summarized in table 18.11. Many of these compounds have the CsCl structure, and in general a major objective has been to understand the dependence of the s-f exchange interaction on conduction electron concentration. 

The third class of refractory compounds comprises compounds of metals with each other—intermetallic compounds. A special branch of chemistry which has arisen in the last few years, metal chemistry, is devoted to the study of these compounds. 

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