Electrolytic process to prepare boron powder

The preparation of the element boron is magnesium thermal reduction initially, still the preferred method for large scale preparation of boron powder by metal powder supplier. Amorphous boron powder is mainly used as metallurgical deoxidizer, solid rocket fuel, as well as automotive airbag initiator agent. With the development of electronic industry, high-purity boron powder is widely used as a semiconductor dopant.

The preparation method of the element boron in addition to magnesium thermal reduction method, there are the thermal degradation method, the reduction method of the sodium hydride, boron halide decomposition method, molten salt electrolysis method, etc. Molten salt electrolysis method was considered to be one of the most promising methods. It with high purity of the product, the product is not magnesium and simple process. Scientists have done a lot of research work.. In 1925, the scientists studied the boron trioxide dissolved in various molten salt, molten salt electrolysis prepared by the method of boron powder. In 1949, someone use potassium chloride - potassium fluoroborate system electrolytically prepared 99.51% purity boron powder. Thereafter, the molten salt system of potassium fluoride, potassium hydrogen fluoride, potassium chloride, boron oxide, a fluorine potassium borate based become a boron powder is the main component of the molten salt electrolysis method, In addition to these, borax, boric acid, boron carbide, boron trichloride has been applied to the molten salt electrolysis prepared boron powder.

The device of molten salt electrolysis is prepared boron powder electrolyzer. Due to the high reactivity of the borides, only graphite can be applied to this in the existing materials. The electrolyzers are made of graphite. Cathode commonly used iron electrode also useful, Monel steel electrode corrosion resistance than iron: anode using graphite crucible. Electrolytic power supply with DC voltage, a general in 2.5-3-8.0 volts. The outside of the graphite crucible was heated by an electric furnace, so that the internal molten salt melt, most of the temperature of the system is 650 to 900 ° C. Due to the poor oxidation resistance of graphite, need to pass into the inert gas to prevent the crucible oxidative damage. Electrolysis precipitated boron mostly adhered to the iron on the cathode in the electrolysis is completed, the force can be peeled off. Will remove the boron powder into the boiling dilute hydrochloric acid, to wash away the buildup of molten salt, it can be obtained elemental boron powder.

The device is the biggest problem constraints electrolysis boron powder. Different from electrolytic aluminum, electrolytic boron powder is difficult to achieve continuous production, because when the electrolysis to a certain extent, the composition of the molten salt electrolyte irreversible change occurs, this time only to stop the electrolytic process, and then re-loaded into the material begins electrolysis. Continuous problem not solved make this approach is unlikely to achieve industrial scale production. In an improved method, using a strange idea to solve the carbon residue, which is currently the only viable method. Normal electrolysis process, a graphite crucible as the anode and iron as the cathode, and the boron powder adhered to the iron on the cathode, but in this method, initially iron used as the anode, graphite as a cathode, so that the resulting boron power is deposited on the inner wall of the graphite crucible, play the role of the carbon shield. Then, after a certain time in the electrolysis, the anode reversed, coming graphite crucible as the anode, iron as the cathode, so that the boron powder adhered on the inner wall of the graphite crucible is transferred to the iron on the cathode, thereby obtaining a relatively high purity boron powder.

Source:http://www.mhcmp.com