Minimum Aeration in Acidithiobacillus ferrooxidans Cultures Required to Maintain Substrate Oxidation without Oxygen Limitation

The volumetric oxygen transfer coefficient (kLa) was used to define the conditions necessary for minimum aeration and to eliminate potential oxygen limitation in bioleaching cultures ofAcidithiobacillus ferrooxidans. The Michaelis constants for oxygen were 1.07 and 0.71 μmol O2l-1for the oxidation of ferrous iron and elemental sulphur, respectively. The critical oxygen concentration, below which oxygen limitation occurred, was determined to be 6.25 and 3.125 μmol O2l-1for the oxidation of ferrous iron and elemental sulphur, respectively. The (kLa)critvalues required to maintain oxygen-unlimited substrate oxidation for ferrous iron and elemental sulphur were 7.70 and 4.88 h-1, respectively.

Critical Concentrations of Atmospheric Contaminants in a-Si:H and μc-Si:H Solar Cells

We report on a direct comparison of the effect of the atmospheric contaminants on a-Si:H and μc-Si:H p-i-n solar cells deposited by plasma-enhanced chemical vapor deposition (PECVD) at 13.56 MHz. Nitrogen and oxygen were inserted by two types of controllable contamination sources: (i) directly into the plasma through a leak at the deposition chamber wall or (ii) into the process gas supply line. Similar critical concentrations in the range of 4-6×1018 cm-3 for nitrogen and 1.2-5×1019 cm-3 for oxygen were observed for both a-Si:H and μc-Si:H cells for the chamber wall leak. Above these critical concentrations the solar cell efficiency decreases for a-Si:H solar cells due to losses in the fill factor under red light illumination (FFred). For μc-Si:H cells the losses in FFred and in short-circuit current density deteriorate the device performance. Only for a-Si:H the critical oxygen concentration is found to depend on the contamination source. Conductivity measurements suggest that at the critical oxygen concentration the Fermi level is located about 0.05 eV above midgap for both a-Si:H and μc-Si:H.