SiO2 Precipitation Research Articles

A method for finding critical stresses of dislocation movement

A method is presented which makes possible the determination of the critical resolved shear stress, τc, for dislocation movement in a crystal. The method is based on the analysis of dislocation rosettes which are generated either by microindentation, or by precipitates of a second phase. The method does not require a knowledge of the indentation (or precipitate) stress field; it requires only information on the positions of a set of leading dislocation loops. At once one can also obtain the effective indentation stress field and, for the first time, the precipitate stress field. For illustration, the method is applied to the determination of τc in silicon, using both indentation and precipitate dislocation rosettes. The value of τc thus obtained varies from a low of 3×107 dyn/cm2 in oxygen-free samples to a high of 5.5×108 dyn/cm2 in a sample containing ∼2×1018 atoms/cm3 of oxygen with clustering. The SiO2 precipitate stress field in the present case was found to vary as x−1, suggesting that the precipitate is probably a thin plate.

The effect of oxygen on the electrical properties of silicon

Interstitial oxygen present in solution, as detected by the 9 μ absorption band, increases the Hall mobility of electrons in n-type silicon crystals but decreases the Hall mobility of holes in p-type. These results are explained by the lattice strain produced via dissolved interstitial oxygen impurities. Results on samples saturated with oxygen and heat treated to cause precipitation of SiO 2 in the temperature range of 950–1250°C show that the SiO 2 particles decrease the values of Hall mobility compared to the initial values on samples without precipitates. Re-annealing causes the dissolution of the precipitates and recovery nearly to the initial values of the Hall coefficient.

Zur geochemie der diagenese

The changes, not caused by weathering, in a sediment between its sedimentation and metamorphism are characterized by the word diagenesis. The borderline between diagenesis and metamorphism is arbitrary and a matter of usage of language. It is questionable whether metasomatic changes are to be included. The discussion of solution and precipitation of SiO 2 and CaCO 3 in the sediment is based on the solubility curves of SiO 2-Gel and CaCO 3 in pure water at 17°C and in sea water at 20°C. Where CaCO 3 is dissolved SiO 2 can be precipitated and vice versa. Silification of wood is also caused by the precipitation of SiO 2 due to the formation of CO 2 in course of the decomposition of wood. The chemical character of the reaction between SiO 2 and CaCO 3 in aquatic solutions, for which the participation of H 2CO 3 is necessary, is briefly discussed.