![]() CSL boundaries are generally low energy configurations since atoms in the two corresponding lattices of the two grains share a certain proportion of common lattice sites, particularly when the boundaries adhere to low energy planes. These boundaries are almost exclusively CSL boundaries, and Σ27 boundaries have been observed in high proportions while other boundaries are also seen, although never of the RAGB type. It is known that dislocation clusters can be traced downwards in the ingot while decreasing in size, and the first point of observation is primarily at a grain boundary. Controlling both these properties is important in order to be able to successfully produce uniform quality high-performance multicrystalline silicon by the advantageous non-seeding method. Furthermore, the density of twins and CSL boundaries depends on the growth mode during initial growth and thus on the degree of supercooling. The ability to generate small grain size material without seeding appears to be correlated to the morphology of the coating, which is generally rougher in the corner positions than in the middle. It appears that both of these grain boundary densities influence the presence of dislocation clusters, and we propose they act as dislocation sinks and sources, respectively. However, the density of CSL boundaries was higher in all the non-seeded than in the seeded ingots. The density of the random angle boundaries in the corner blocks of the non-seeded ingots was similar to the density in the seeded ingots, while the density in the centre blocks was lower. In general, the seeded blocks, both the corner and centre block, have a lower dislocation cluster density than in the non-seeded blocks, which displayed a large variation. It was found that there is a strong correlation between the ratio of the densities of (coincidence site lattice) CSL grain boundaries and high angle grain boundaries in the bottom of a block and the dislocation cluster density higher in the block. Three of the ingots were non-seeded and one ingot was seeded. We will finish this discussion next time.Wafers from three heights and two different lateral positions (corner and centre) of four industrial multicrystalline silicon ingots were analysed with respect to their grain structure and dislocation density. The above comments are based on the use of an endothermically generated atmosphere with a hydrocarbon enrichment gas, as well as with pack carburizing systems. Therefore, the degree of surface oxygen migration into the steel will be dependent on: temperature, time at temperature, presence of oxygen in the form of carbon dioxide, atmosphere carbon potential, alloying elements present in the steel (chemical composition of steel) and grain growth during the atmosphere/pack carb process cycle. Remember that as the steel temperature is increased, the steel grain size will also increase. As temperature is increased from ambient temperature up to the selected carburizing temperature, the speed of the oxygen diffusion will increase.Īnother factor that will affect the amount of oxygen diffusion will be the carburizing-atmosphere carbon potential as well as the grain size. Thus, when atmosphere carburizing at temperatures around 1700☏ and for extended periods of time, the oxygen atom can diffuse into the steel surface and begin the oxidation around the surface grain boundaries. Oxygen has a smaller atomic size, which is about 30% smaller than that of an iron atom. There can be oxygen in the form of surface oxide (hot-rolled scale) if the bar has not been fully machined. For example, if the process is that of pack carburizing or atmosphere carburizing (using and endothermic generator), there will be oxygen present from air, atmospheric moisture or both. In order for the oxidation procedure to commence, oxygen (in some forme) needs to be the present. Grain-boundary oxidation is a phenomenon that is caused by the diffusion of oxygen into the steel surface. ![]()
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