Gabriella Tranell

Thermodynamic and Kinetic Behavior of B and Na Through the Contact of B-Doped Silicon with Na2O-SiO2 Slags

Boron (B) is the most problematic impurity to be removed in the processes applied for the production of solar grade silicon. Boron removal from liquid silicon by sodium-silicate slags is experimentally studied and it is indicated that B can be rapidly removed within short reaction times. The B removal rate is higher at higher temperatures and higher Na2O concentrations in the slag. Based on the experimental results and thermodynamic calculations, it is proposed that B removal from silicon phase takes place through its oxidation at the slag/Si interfacial area by Na2O and that the oxidized B is further gasified from the slag through the formation of sodium metaborate (Na2B2O4) at the slag/gas interfacial area. The overall rate of B removal is mainly controlled by these two chemical reactions. However, it is further proposed that the B removal rate from silicon depends on the mass transport of Na in the system. Sodium is transferred from slag to the molten silicon through the silicothermic reduction of Na2O at the slag/Si interface and it simultaneously evaporates at the Si/gas interfacial area. This causes a Na concentration rise in silicon and its further decline after reaching a maximum. A major part of the Na loss from the slag is due to its carbothermic reduction and formation of Na gas.

Wavelength and orientation dependent capture of light by diatom frustule nanostructures

The ecological success of diatoms is emphasized by regular blooms of many different species in all aquatic systems, but the reason behind their success is not fully understood. A special feature of the diatom cell is the frustule, a nano-patterned cell encasement made of amorphous biosilica. The optical properties of a cleaned single valve (one half of a frustule) from the diatom Coscinodiscus centralis were studied using confocal micro-spectroscopy. A photonic crystal function in the frustule was observed, and analysis of the hyperspectral mapping revealed an enhancement of transmitted light around 636 and 663 nm. These wavelengths match the absorption maxima of chlorophyll a and c, respectively. Additionally, we demonstrate that a highly efficient light trapping mechanism occurred, resulting from strong asymmetry between the cribrum and foramen pseudo-periodic structures. This effect may prevent transmitted light from being backscattered and in turn enhance the light absorption. Based on our results, we hypothesize that the multi-scaled layered structure of the frustule improves photosynthetic efficiency by these three mechanisms. The optical properties of the frustule described here may contribute to the ecological success of diatoms in both lentic and marine ecosystems, and should be studies further in vivo.

Particle Size Distributions of Particulate Emissions from the Ferroalloy Industry Evaluated by Electrical Low Pressure Impactor (ELPI)

The present article presents a comprehensive evaluation of the potential use of an Electrical Low Pressure Impactor (ELPI) in the ferroalloy industry with respect to indoor air quality and fugitive emission control. The ELPI was used to assess particulate emission properties, particularly of the fine particles (Dp ≤ 1 μm), which in turn may enable more satisfactory risk assessments for the indoor working conditions in the ferroalloy industry. An ELPI has been applied to characterize the fume in two different ferroalloy plants, one producing silicomanganese (SiMn) alloys and one producing ferrosilicon (FeSi) alloys. The impactor classifies the particles according to their aerodynamic diameter and gives real-time particle size distributions (PSD). The PSD based on both number and mass concentrations are shown and compared. Collected particles have also been analyzed by transmission and scanning electron microscopy with energy dispersive spectroscopy. From the ELPI classification, particle size distributions in the range 7 nm – 10 μm have been established for industrial SiMn and FeSi fumes. Due to the extremely low masses of the ultrafine particles, the number and mass concentration PSD are significantly different. The average aerodynamic diameters for the FeSi and the SiMn fume particles were 0.17 and 0.10 μm, respectively. Based on this work, the ELPI is identified as a valuable tool for the evaluation of airborne particulate matter in the indoor air of metallurgical production sites. The method is well suited for real-time assessment of morphology (particle shape), particle size, and particle size distribution of aerosols.

Refining Kinetics of Selected Elements in the Industrial Silicon Process

An industrial oxidative ladle refining process of metallurgical grade silicon has been experimentally examined. An extensive industrial sampling campaign has been performed and samples of silicon and slag have been analyzed by inductively coupled plasma mass spectroscopy (ICP-MS). The elemental concentrations of 45 elements have been evaluated with respect to sampling time during the refining process. Major elements, such as Ca and Al, as well as trace elements are studied. The refining kinetics is discussed and groups of elements with different behaviors are distinguished. For 21 elements, which are responsive to the refining process, kinetic parameters are established. The alkaline and alkaline earth elements are identified as having the highest refining rates, whereas the rare earth elements are slower and most transition metals are quite unresponsive to the oxidative refining operation.

Mechanisms and Kinetics of Boron Removal from Silicon by Humidified Hydrogen

The removal of boron from silicon by top blowing of humidified hydrogen has been studied in the present work through experimental work, thermodynamic calculations, computational fluid dynamic modeling, and quantum chemistry calculations. The effect of process parameters; temperature, lance diameter, lance distance from the melt surface, gas flow rate, and crucible material on the kinetics of boron removal were studied. It has been shown that the rate of boron removal is decreased with increasing temperature due to the competitive reactions between silicon and oxygen as well as boron and oxygen, which can be confirmed with the increases of pSiO/pHBO in the system. The rate of boron removal is increased with increasing the gas flow rate due mainly to the better supply and transport of the gas over the melt surface, as confirmed by the CFD modeling. Moreover, the rate of boron removal in alumina crucible is the highest followed by that in quartz and graphite crucibles, respectively. Faster B removal in quartz crucible than that in graphite crucible can be attributed to more oxygen dissolves in silicon melts. The fastest boron removal in alumina crucible is attributed to the additional boron gasification through aluminum borate (AlBO2) formation on the melt surface. Thermodynamic properties of the AlBO2 species have thus been revised by quantum chemistry calculations, which were more accurate to describe the formation of gaseous AlBO2 than those in the JANAF Thermochemical Tables. The main chemical reactions for boron gasification from silicon melts are proposed as

Effects of 2 ppm Beryllium on the Oxidation of a 5XXX Aluminum Alloy at Temperatures Between 500 and 750 °C

{\text{In graphite, quartz and alumina crucible}}:\quad \underline{\text{B}} + \underline{\text{H}} + \underline{\text{O}} = {\text{ HBO}}\left( {\text{g}} \right)

Diatom frustules as a biomaterial: effects of chemical treatment on organic material removal and mechanical properties in cleaned frustules from two Coscinodiscus species

In graphite, quartz and alumina crucible:B̲+H̲+O̲=HBOg