Boron oxide preparation

Hafnium Boride. Hafnium diboride [12007-23-7] HfB2, is a gray crystalline soHd. It is usually prepared by the reaction of hafnium oxide with carbon and either boron oxide or boron carbide, but it can also be prepared from mixtures of hafnium tetrachloride, boron trichloride, and hydrogen above 2000°C, or by direct synthesis from the elements. Hafnium diboride is attacked by hydrofluoric acid but is resistant to nearly all other reagents at room temperature. Hafnium dodecaboride [32342-52-2] has been prepared by direct synthesis from the elements (56). 

The reaction of methyl propionate and formaldehyde in the gas phase proceeds with reasonable selectivity to MMA and MAA (ca 90%), but with conversions of only 30%. A variety of catalysts such as V—Sb on siUca-alumina (109), P—Zr, Al, boron oxide (110), and supported Fe—P (111) have been used. Methjial (dimethoxymethane) or methanol itself may be used in place of formaldehyde and often result in improved yields. Methyl propionate may be prepared in excellent yield by the reaction of ethylene and carbon monoxide in methanol over a mthenium acetylacetonate catalyst or by utilizing a palladium—phosphine ligand catalyst (112,113). 

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). 

Preparation. The simplest method of preparation is a combination of the elements at a suitable temperature, usually ia the range of 1100—2000°C. On a commercial scale, borides are prepared by the reduction of mixtures of metallic and boron oxides usiag aluminum, magnesium, carbon, boron, or boron carbide, followed by purification. Borides can also be synthesized by vapor-phase reaction or electrolysis. 

Na2B0402 10H2O, and cmde oil residue (41) in a rotary kiln heated to 1038°C. Borax is fed at the rate of 1360 kg/h and sprayed with 635 kg/h of 17% residue cmde oil. The heated mixture then reacts with CI2 at 760°C in a separate reactor to yield BCl. On a smaller scale, BCl can be prepared by the reaction of CI2 and a mixture of boron oxide [1303-86-2] 2 3 coke, and lampblack in a fluidized bed (42). Other methods for the preparation... 

Boron may be prepared by several methods, such as chemical reduction of boron compounds, electrolytic reduction in nonaqueous phase, or by thermal decomposition. Many boron compounds including boron oxides, borates, boron halides, borohydrides, and fluoroborates can be reduced to boron by a reactive metal or hydrogen at high temperatures ... 

Passing back to the boron group, if it is desired to form anhydrous chloride, it is necessary either to heat the element, or its oxide mixed with charcoal, in a current of chlorine, or, except in the case of boron, to prepare a double salt of the chloride with ammonium chloride, and to volatilise the latter after driving off the water the aqueous chlorides are formed by dissolving the oxides or hydroxides in hydrochloric acid. Thallium forms monohalides, sparingly soluble in cold water, and thereby attaches itself to the copper group. 

Hexane (99% n-hexane) was obtained from Aldrich. Silica was obtained as a 30% Colloid (LUDOX-HS, 30 wt% SiOj) from DuPont. Aluminum hydroxide, boron oxide, and sodium metaborate were obtained from Alfa Products. Boric acid was obtained from J. T. Baker. Commercial samples of mordenite and zeolite Y were obtained from the Norton and Union Carbide Companies, respectively. A specific example which illustrates the typical procedure used for preparing mordenite and zeolite Y from gels is given below. 

Zeolite Y was dealuminated with EDTA according to a published procedure (4). Boron oxide (0.15 g) was dissolved in 140 mL of 0.22 H KOH. Zeolite Y (5 g, Si/Al = 9.1) was suspended in the solution. The suspension was heated at 80°C for 24 h in a Teflon vessel. Products were washed thoroughly with deionized water and dried at 120°C. The chemical composition of products prepared by direct synthesis and by post-synthetic methods are listed in Table 1. 

C , which is prepared mainly by deuteron bombardment of a boron oxide target, emits positrons as well as 7-rays and can be readily measured with an outside Geiger counter. Its short half life, however, limits its use (Table I). 

It is separable in two allotropic modificationa Amorphous boron is prepared by decomposition of the oxide, by heating with metallic potassium or sodium. It is a greenish-brown powder sparingly soluble in H,0 ittfusible and capable of direct union with 01, Br, O, S and N. 

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