Purity boron carbides

There is no metal contamination introduced when a high purity boron carbide coating is introduced as the new chamber wall coating. 

Research-grade material may be prepared by reaction of pelleted mixtures of titanium dioxide and boron at 1700°C in a vacuum furnace. Under these conditions, the oxygen is eliminated as a volatile boron oxide (17). Technical grade (purity > 98%) material may be made by the carbothermal reduction of titanium dioxide in the presence of boron or boron carbide. The endothermic reaction is carried out by heating briquettes made from a mixture of the reactants in electric furnaces at 2000°C (11,18,19). 

Boron Triiodide. Boron ttiiodide is not manufactured on a large scale. Small-scale production of BI from boron and iodine is possible in the temperature range 700—900°C (70—72). Excess I2 can be removed as Snl by reaction with Sn, followed by distillation (71). The reaction of metal tetrahydroborates and I2 is convenient for laboratory preparation of BI (73,74). BI can also by synthesized from B2H and HI in a furnace at 250°C (75), or by the reaction of B with excess Agl or Cul between 450—700°C, under vacuum (76). High purity BI has been prepared by the reaction of I2 with mixtures of boron carbide and calcium carbide at elevated temperatures. 

Uses. Amorphous boron is used as an addictive in pyrotechnic mixtures, solid rockets propellants, explosives, etc. Refractory metal borides are used as addic-tives to cemented carbides. High purity boron is used in electronics as a dopant to... 

The SSMS samples are reground with a boron carbide mortar and pestle and diluted with two parts of high purity graphite. The samples with graphite are placed in polystyrene vials with two or three %-in. 

A breakthrough discovery was reported by Sabatini (ARDEC) in the area of green illuminants. Formulations without any heavy metal can be based on boron carbide (B4C, fuel) with a suitable oxidizer (e.g. Iboron carbide (B4C) in pyrotechnical compositions. It can be seen that flares with 100% boron carbide as fuel show longer burn times and higher luminous intensity than the control barium nitrate based flare (M125 Al) while the spectral (color) purity is slightly lower. 

As it was mentioned, boron carbide containing enriched elemental boron ( B 65 at%) can serve as the control rod material in fast breeder nuclear reactors. Because boron carbide is fabricated by reacting elemental boron with carbon and the elemental boron in turn is produced by electro-winning process, Jain et al. (2011) have carried out studies to explore the viability of a high-temperature molten salt electro-winning process for the large-scale production of °B isotopically enriched elemental boron. It was established that elemental boron powder with a purity of better than 95 wt% could be produced. 

The furnace is usually cooled externally to limit the toss of volatile materials and hence the outer mantle stays unreacted. The core contains blocky boron carbide of relatively high purity (total metallic impurities <0.5 mass-%), reproducible stoichiometry (B/C ratio = 4.3) [50], and several percent of residual graphite. The chunks are crushed and milled to the final grain size. 

In laboratory-scale production, boron carbide can also be synthesized in the form of high-purity powders or coatings (e.g., [165]) ... 

High-purity fine boron carbide powder with an average particle size of 0.5-5 pm has been synthesized by the reaction of boric add with a carbon-containing compound in a vented tube furnace [134]. 

After the detail study through a thorough process qualification, the new boron carbide coated chamber wall is used to replace the previously anodized aluminum surface. The new ceramic material such as YAG or Y2O3 is used to replace original high purity alumina. This configuration was introduced to semiconductor wafer fabrication for evaluation. Excellent etch performance, enhanced defect and particle reduction, and 50 to 100 times chamber lifetime improvement are reported. The production yield of the wafer fabrication also improved about 7% in production at the customer site (see Fig.l9) [41]. The following data provide some of the information. The sequence of the data collection is as follows ... 

Because the solubility coefficients of carbon in the solid and the liquid phase are almost the same, zone melting, which is used to prepare high-purity crystals of many other elements, is not suitable in the case of boron. Technical boron, which is often taken as the ingredient for the preparation of boron compounds, contains up to about 0.5% carbon. However, in several preparative methods for boron compounds the carbon content may be reduced by secondary chemical or physical reactions. The purest P-rhombohedral boron crystals that have become available up to now were produced by Wacker-Chemie, Munich, FRG. Despite the claimed purity of 99.9999% with respect to other elements, even this high-purity boron contains carbon in concentrations of typically 30 to 80 ppm. Therefore, apart from boron carbide containing carbon as a determining bonding partner, in the assessment of the properties of boron and boron compounds attention must be paid to the fact that a certain, usually unknown carbon content could have influenced the properties determined. 

A powder with good characteristics (high purity, good homogeneity, fine particle size, narrow particle size distribution, absence of hard agglomerates) is a must to get the desired properties and microstructure in the final component and thus synthesis of high quality powder is extremely important. Powders of ZrB and HfB are synthesized by (a) reaction between elements (Brochu et al., 2008 Tamburini et al., 2008) (b) borothermic reduction of metal oxide (Peshev et al., 1968), (c) boron carbide reduction of metal oxide in presence of carbon (Sonber et al, 2010 2011) (d) carbothermic reduction of metal oxide and B Oj (Fahrenholtz et al., 2007) (e) Metallothermic reduction of metal oxide and B Oj (Setoudeh et al., 2006 Kobayashi et al., 1993),(f) molten salt electrolysis (Frazer et al.,1975) (g) solution based techniques (Yan et al., 2006) and (h) s3mthesis from polymer precursors (Suetal., 1991). 

It is possible to make electrolithically deposited coatings in special cells and in the cells under operation [123, 124]. Thermodynamically, it is possible to receive the deposited coatings, combining the addition of titanium compounds in electrolyte, and boron oxides to the carbon anode material. Metal oxides dissolve in electrolyte the ions of metals discharge at the cathode and deposit on the cathode as titanium boride and titanium carbide. The problem involves the poor controllability of the process and the need to fulfill the required purity of aluminium (in titanium and boron content). Once small amounts of boron oxide and titanium (in the form of oxide of salt) are added, it is possible to obtain the metal of required purity and quality, but the coating process lasts for a long time and is poorly ccmtroUed. 

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