Kinetcis of silicothermic reduction of clacined dolomite in flowing argon atmosphere
The magnesium vapour extracted is removed using vacuum condition to condense as a dense metal. Thermodynamic analysis of this process has been carried out in the past to predict the distribution of the metal impurities in condensed magnesium. The results suggested that a number of impurities in different phases formed in the region between reaction zone and condenser. The thermodynamic results only are not sufficient to describe the process, and the knowledge of the kinetics of the Pidgeon process is required. Kinetics plays important role to give more insight to the process such as for process design and control.
Producing Pure Magnesium Through Silicothermic Under the Atmospheric Pressure
The majority of pure magnesium produced worldwide is made by using silicothermic method (Pidgeon process). However, the Pidgeon process suffers poor efficiency, low industrial concentration, and intermittent production. The main reason is that Pidgeon process requires to keep the reaction chamber in a vacuum state during the entire reduction process. By analyzing the thermodynamic reaction principle, we reveal that it is the low magnesium partial pressure instead of vacuum that is necessary for the silicothermic process. Based on this understanding, we develop a new technique that can produce pure magnesium under the atmospheric pressure by using silicothermic method. Flowing argon is used to carry away the magnesium vapor around the reactants, which reduces the local magnesium partial pressure. The magnesium production efficiency reaches 82.36% that is comparable to the widely used Pidgeon method, and high purity of magnesium with 99.97 wt% after melting is produced directly. The industrialized application of this exciting technique is expected to help the silicothermic to realize high efficiency, automated, and continuous production while at the same time completely change the poor production conditions, and reduce energy consumption and pollution.
Randi Weingarten, the American Federation of Teachers, and the Challenges of Policy Leadership in a Hostile Environment
Randi Weingarten is the president of the most vocal and influential teachers’ union, the American Federation of Teachers. Since rising through the ranks to AFT president in just two years, Weingarten is now a major, if not the most prominent, nongovernmental player in national education policy. She has earned deep respect from many educational policy actors. Likewise, Weingarten elicits withering criticism from others. This fascinating profile explains why, in such a brief period, she has proved to be a fierce, fearless, and effective leader under extraordinarily difficult circumstances. Her experience offers invaluable lessons applicable for others working in similarly intense policy arenas.