Gaseous Fluorides Formation Mechanism in the Roasting Process of the Fluorite-Bearing Iron Concentrate

The gaseous fluorides formation mechanism in the roasting process of the fluorite-bearing iron concentrate was studied by thermodynamic calculation, differential thermal analysis (DTA) and chemical analysis. The results show that fluorine in the fluorite-bearing iron concentrate begins to escape since 400~500°C, and the emission rate of fluorine significantly increases when the temperature is above 1100°C; in the roasting process of fluorite-bearing iron concentrate, SiO2, K2O, Na2O, MgO, Al2O3 in the gangue and water vapor in roasting atmospher react with CaF2 in fluorite to generate such gaseous fluorides as SiF4, KF, NaF, MgF2, AlF3 and HF; with the increase of roasting temperature, the emission rate of fluorine increases obviously; and the water vapor in roasting atmosphere can improve escaping of fluorine.The results provide a theoretical basis for the improvement of roasting technology to reduce fluorine emission in the roasting or sintering process of Baiyanobo iron concentrate.

Investigation of Dry Plasma Etching of Silicon

Meso-scale structures are formed on a silicon surface using a sulphur hexafluoride (SF6) based dry etching process. Etched feature parameters, including etch rate, trench profile, and selectivity are explored using an optical emission spectroscopy and a resonance hairpin probe. With increasing process power, the etch rate was observed to increase, which was correlated with an observed increase in intensity of fluorine emission. Damage of the photoresist with increasing power was observed and a marked increase in hydrogen (H) emission was found to indicate this fault. The electron density and the sidewall roughness were also found to increase with higher reactor power. The e-SF6 collisions contribute to the production of atomic fluorine, which etches the silicon by the dissociative ionization (SF+5 and F or SF+3 and F) and electron impact dissociation (SF5 and F).

Mechanical and Physicochemical Properties of Tetric EvoCeram® - Dental Composite Material

This work presents results of research of fluoride release, microhardness and surface roughness and wear of the Tetric EvoCeram material. Wear tests were carried out by means of special tribotester for tooth analysis and by pin-on-disc tribometer. The wear of composite material and counterface (human enamel) were measured. Finally, investigations showed that fluoride ions from commerce material were slightly released. However, the amount of fluoride ions release was depended on pH and temperature of agent solution. Fluorine emission from composite material changed its surface roughness and microhardness. The using method of wear process influenced on friction coefficient value. During friction process the wear layer on composite surface was formed.