Degradation sintering mechanisms

What are the principal fundamental mechanisms by which thermal degradation, sintering and redispersion of supported metals occur What factors determine which of these mechanisms predominates or controls the sintering process What do we leam from model catalyst studies regarding these mechanisms ... 

When used as an interlevel dielectric, even greater demands are placed on the polyimide. Because integrated circuit processing includes as a final step a metal sinter at 400 C, the interlevel insulator film must withstand such exposures without degradation of electrical, chemical, or mechanical properties. In addition, the deposition, cure, and etch process must provide for reliable interconnection between the metal layers above and beneath the film (the "via contact") [8]. Issues of ion motion, moisture uptake, and electrical conduction both in bulk and at interfaces must also be considered carefully. 

Materials often exhibit unique properties, processing challenges, and degradation mechanisms that are inherently electrochemical in nature. For example, the sintering of high-technology ceramics is closely related to the behavior of ionic defects in solid electrolytes. 

Raynaud S, Champion E, Bemache-Assolant D (2002b) Calcium phosphate apatites with variable Ca/P atomic ratio II. Calcination and Sintering. Biomaterials 23 1073-1080 Raynaud S, Champion E, Lafon JP, Bemache-Assolant D (2002c) Calcium phosphate apatites with variable Ca/P atomic ratio III. Mechanical properties and degradation in solution of hot pressed ceramics. Biomaterials 23 1081-1089... 

Blends of the recycled HDPE/GRT powder were obtained by mixing in mills and subsequent sintering (Crespo et al., 2010). The influence of the powder on the thermal and mechanical properties of blends and their degradation was investigated by observation of the deformation and fracture using the SEM to analyze the interaction between the GRT powder and HDPE. 

A potential problem with this type of composite system is the possibility of reaction or sintering between matrix partieles and the fibers at points of contact. Exposure tests of UCSB Nextel 610 composite at 1,200°C (2,192°F) for 100 hours shows reasonable mechanical property retention (Figure 6-11). Similar tests have yet to be performed on Nextel 720 eomposites. Therefore, the data on long-term exposure is insufficient to address the issue of matrix-fiber bonding (Levi et al., 1997). Beeause degradation is likely to be kinetically driven, residual fiber strength will be dictated by time at temperature. 

In general, compared with solid state sintering, liquid phase sintering allows easy control of microstructure and reduction in processing cost, but degrades some important properties, for example, mechanical properties. In contrast, many specific products utilize properties of the grain boundary phase and, hence, need to be sintered in the presence of a liquid phase. Zinc oxide varistors and SrTiOs based boundary layer capacitors are two examples. In these cases, the composition and amount of liquid phase are of prime importance in controUing the sintered microstructure and properties. 

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