Intermetallics electron-poor

The Intermetallic Li-Zn-Ce System, from Electron-poor to Electron-rich Phases 149 9.5... 

A typical crystallisation process in binary alloys can be described, as temperature increases, as follows. In hypoeutectic compositions (where the transition-metal content is greater than the corresponding eutectic composition for a given material), the transition metal crystallises first, until the amorphous phase reaches the eutectic composition, at which both the transition metal and the intermetallic crystallise. In hypereutectic alloys (transition-metal-poor), both phases crystallise simultaneously. Some ternary alloys can also be included in this schematic model, such as Fe-B-Si (Ramanan Fish, 1982) and Ni-B-Si (Baro, Clavaguera and Surinach, 1988). The crystallised phases are a-(Si-Fe) and FejB for the former system, and y-Ni and NijB for the latter. Transmission electron microscopy can be used to study in-situ crystallisation phenomena, identify (Valenzuela et ai, 1982) and evaluate the crystallised fractions (Blanke-Bewersdorff Koster, 1988). 

Non-fused iron catalysts have been studied earlier. The famous Uhde catalyst was KAl (Fe(CN)6), which was used, to be applied in industry. It was abandoned because of its poor stability, and up to now there are still reports about its modifications. Intermetallic compound and alloy catalysts, such as LaNij, FeTi, Fe2Ce and FeZr etc., were also expected to be prospective, but until now they have not been put into practice. In 1970s, the well-known electron donor-acceptor (EDA) catalysts, e.g., phthalocyanine iron-alkali metal, molysite — graphite — potassium and ferrocene-activated carbon-potassium catalyst systems, were found to have the ability to synthesize ammonia under mild conditions in the laboratory. Unfortunately, their activities declined rapidly in the experiments of scale-up. The application of EDA catalysts in industry turned to be a visionary. Therefore, replacement of fused iron catalyst is not an easy thing for a very long time. 

FIG. 8 Scanning electron micrographs (SEM) of the fracture surface of solder joints, (a) A void extends most of the way across the joint and exhibits a smooth interface typical of voids, (b) A joint that, when pulled, separated at the UBM showing the intermetallic compound formed between the Pb-Sn solder joint and the UBM. Such separations are due to poor adhesion usually caused by contamination. Bond pulls and observing the fracture surface is a convenient way to gain insight to the cause of failure of flip-chip solder joints. (Courtesy of IBM Corp.)... 

---