The distribution of iron in multicrystalline silicon ingots for solar cells has been studied. A p-and a n-type multicrystalline ingot were intentionally contaminated by adding 53 ppm wt ͑g / g͒ of iron to the silicon feedstock and compared to a reference p-type ingot produced from ultrapure silicon feedstock. The vertical total iron distribution was determined by neutron activation analysis and glow discharge mass spectrometry. For the intentionally Fe-contaminated ingots, the distribution can be described by Scheil's equation with an effective distribution coefficient of 2 ϫ 10 −5. The interstitial iron concentration was measured in the p-type ingots. In the Fe-contaminated ingot, it is almost constant throughout the ingot and constitutes about 50% of the total concentration, which is in conflict with the previous studies. Gettering had a large impact on the interstitial iron levels by reducing the concentration by two orders of magnitude. Considerable trapping was observed at crystal defects on as-cut wafers from the same ingot. The trapping was suppressed by gettering. The back diffusion of iron from the ingot top after complete solidification was modeled and found to affect the iron concentration up to a distance of approximately 17 mm into the ingot. The interstitial as well as the total iron concentration of the reference ingot were extremely low and difficult to measure accurately.

A study has been made of microstructure and hardness of machining chips created from commercially pure iron and carbon steels. Large shear strains imposed during chip formation in machining are found to produce significant microstructure refinement in the chips, resulting in higher hardness compared to the bulk. Transmission electron and scanning electron microscopy have shown the chips to consist entirely of ultra-fine grain structures with ferrite grain sizes in the range of 100-800 nm. With high carbon steels, the microstructure of the bulk material prior to machining is also seen to have a significant influence on the characteristics of the chip.

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