Coarsening recrystallization

The main structural influences can be described as follows. Any plastic deformation decreases the transition temperature by fining the structure. The higher the degree of deformation, the lower is the DBTT. An as- rolled tungsten sheet shows a DBTT of about 100-200 °C. Fine wires or foils are even ductile at room temperature. Any aimealing increases the transition temperature, and recrystallized samples show a maximum, mainly due to the coarsening of the structure (360 °C). 

In addition to dissolution, the destabilization of carbonate cements may result in recrystallization and replacement by other carbonates. Microcrystalline calcite and dolomite are sensitive to recrystallization at various burial depths. The recrystallization of dolomite has been reviewed by Mazzullo (1992). Burial recrystallization of micritic/microsparitic cements in sandstones may result in the formation of poikilotopic calcite (Saigal Bjorlykke, 1987). However, poikilotopic calcite is also a common primary cement in calcretes (e.g. Knox, 1977 Tan-don Narayan, 1981). Recrystallized calcite and dolomite are recognized as patchily distributed, coarsened crystals. In contrast, precipitational vari-... 

Once coarsening and recrystallization stops, graphite flakes will preserve isotope composition due to slow diffusion. Intracrystalline zoning of 5 C has been detected in some crystals by most studies that have evaluated it. This has been demonstrated by delamination of single flakes at the 20-100 pm-scale (Wada 1988, Arita and Wada 1990, Kitchen and Valley 1995, Satish-Kumar 2000), by ion microprobe (Farquar et al. 1999) or, more simply, by analysis of large vs. small flakes from the same rock (Kitchen and Valley 1995). 

Experimental studies of accessory mineral solubility in aqueous fluids suggests that apatite and monazite solubility in pure H2O is low, and increases with decreasing pH (Ayers and Watson 1991). Ayers et al. (1999), in an experimental study of the coarsening kinetics of monazite in the presence of aqueous fluids, found that monazite either recrystallizes and moves as host grain boundaries migrate, or is trapped as inclusions within the host phase. Inclusion monazites, once isolated from the rock matrix, should record the time of entrapment whereas matrix monazite should record the time of final recrystallization, or, if growth zoned, a complex age spectrum. 

Figure 1. XRD traces of different bioapatite materials from modern and fossil elephants. Fossil dentin, cementum and bone all show a decrease in peak width compared to modem materials, indicating diagenetic recrystallization and coarsening of original apatite. Enamel peaks are essentially unaffected. From Ayliffe et al. (1994).

The recrystallization of ice crystals and the coarsening of air bubbles both lead to deterioration in the texture of ice cream, and a number of methods are employed to slow them down. In contrast, the coalescence of fat droplets is deliberately promoted during ice cream manufacture, and is crucial in making good quality ice cream. The means used to control the coarsening processes of the ice, fat and air dispersions in ice cream are discussed in Chapters 4 and 7. 

Once the product has been packaged, the manufacturing process is complete. The palletized products are sent to the factory cold store, which typically operates at about — 25 C. As well as acting as a hold/ release store, the cold store ensures that the product is at —25 °C prior to distribution. If the product enters the distribution system at or below —25 it can undergo some exposure to warmer temperatures before it reaches a temperature at which it deteriorates rapidly. The purpose of the distribution system, from factory cold store, through the retailer s cold store to the shop freezer is to keep the product cold to prevent a decrease in quality due to recrystallization and coarsening. Care must be taken at each stage to ensure that temperature fluctuations are minimized, as repeated increases and decreases in temperature (for example... 

Recrystallization The coarsening of ice crystals, ie. the increase in mean size at constant ice phase volume. 

An appreciable increase in the utilization efficiency of platinum catalysts in fuel cells was attained when the highly dispersed platinum was deposited not directly onto the conductive electtode base but onto carbon black or other carbon materials serving as an intermediate base for the nanodispersed catalyst. On carbon supports, the nanosized platinum crystallites were less subject to recrystallization and coarsening. In addition, new technical devices such as adding Nafion ionomer to the active mass have helped to considerably improve the contact between catalyst and solid electrolyte (a Nafion-lype membrane). Carbon black was found to be a very convenient support for platinum catalysts. It is readily available and not expensive. Certain blacks (such as furnace black Vulcan XC-72) have special surface properties that have a favorable effect on catalyst activity. 

As seen in Ref 1, the deformation behavior of solder is strongly dependent on the structme of the solder. Sn-Pb, as soldered, consists of large domains that recrystallize due to plastic deformation. This leads to a refinement of the tin phases and to a coarsening of the Pb phases. Once the Sn has recrystallized, enabling GBS, the material is much easier to deform, and creep rates are higher. 

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