Oxide of boron

Safety considerations are paramount in any boron hydride synthesis. The energy yield from the oxidations of boron hydrides is too high for any cavalier treatment of boron hydrides. Exclusion of air is the critical consideration in diborane reactions. Decaborane(14) is less reactive, generally, in a kinetic sense, but the thermodynamic potential is comparable. In addition, all volatile boron hydrides are toxic. The procedures described in the latter two preparations are within our experience non-hazardous. These procedures should be followed in every detail improvisation is not recommended. 

Although most of the fluorine calorimetry has been done with the elements, it has been used to burn oxides, carbides, nitrides, and chal-cogenides and hence determine their heats of formation. In some instances it has proved superior to oxygen bomb calorimetry. Thus the oxidation of boron tends to be incomplete because of oxide coating, whereas fluorination produces gaseous boron trifluoride without surface inhibition. A summary of modem fluorine calorimetry results is assembled in Table III. 

Finally, oxidation of boron-, silicon-, and aluminum-containing materials results in oxide particles. Along with polymers in the oil, these particles can plug lubrication ducts, and cause pump failure (755). An oil filter is often used to remove such particles, thereby extending pump life and increasing the time... 

Alkoxides are usually more difficult to hydrolyze than halides, although hydrolysis can be rapid in activated systems. Pyrimidinethiones can sometimes be hydrolyzed directly to pyrimidinones, but it is often better to convert the thiones into alkylsulfenyl, alkylsulfmyl, or alkylsulfonyl derivatives before hydrolysis <1994HC(52)1, 1996CHEC-II(6)93>. The formation of 5-hydroxypyrimidines is not normally performed using hydrolytic procedures, although it can be achieved by the oxidation of boronate species in aqueous solution <1996CC2719, 2006TL7363>. 

The only important oxide of boron is borou(III) oxide, B2Q3, a tough, high-melting solid which reacts with water to form the important coin-... 

The lower oxides of boron and their derivatives (for example, B202, B4O5) contain boron-to-boron bonds they are much less stable than the borates and far less important at present. The doubtful status of the peroxy borates has already been noted in Chapter 4 (p. 79). 

Boron prepared in this way contains magnesium and oxides of boron as impurities, and the purity ranges from 80% to 95% when the preceding procedure is used. The boron produced... 

Currently there exist no quantitative unclassified rate coefficients for oxidation of boron species. In fact the studies reported in the literature are relatively sparse. A review through 1958 was given by Bauer and Wiberly. The molecule that has received the most attention is diborane, B2Hg. 

OXIDATION OF BORON, SILICON, TIN, MAGNESIUM, AND MERCURY COMPOUNDS... 

Nearly all oxides of nonmetals react with water to give solutions of ternary acids. The Figure 6-9 Sulfur burns in oxygen oxides of boron and silicon, which are insoluble, are two exceptions. to form sulfur dioxide. 

The third patent101 describes a contact mass which may be produced in most various ways" and which consists of oxides of boron or phosphorus or mixtures of these or their salts (not specified) distributed on carriers of other materials (not specified). The oxidation is effected by using pure oxygen or air or compounds such as the oxides of carbon ov nitrogen which are capable of giving off oxygen. An example cites the oxidation of benzyl alcohol to benzaldehyde. 

The principal oxide of boron, B2O3, is obtained as a vitreous solid by dehydration of boric acid at red heat (equation... 

Jacobson, N., S. Farmer, A. Moore, and H. Sayir. 1997. High temperature oxidation of boron nitride. Part 1. monolithic boron nitride, submitted to the Journal of the American Ceramic Society. 

The only important oxide of boron is boric oxide (B2O3). This substance is the anhydride of boric acid, which we may write as H3BO3 or B(OH)3. Boric acid is so weak an acid (Ka = 5.8 X 10 °) that solutions of H3BO3 are used as an eyewash. Upon heating, boric acid loses water by a condensation reaction similar to that described for phosphorus in Section 22.8 ... 

Finally, two other characteristics of hard materials are important their density and their chemical stability. The importance of these properties depends on the application. Oxides are chemically more stable than nitrides, which are in turn more stable than borides or carbides. The susceptibility to oxidation of boron carbide prevents its application at high temperatures, but for ballistic protection, where hardness, rigidity and low density take precedence, boron carbide is unparalleled. Tungsten carbide, on the other hand, is the material of first choice for cutting tools, because of its high hardness and stiffness, and high-temperature oxidation resistance, but is far too dense for application in which weight or inertial forces are important. Its use for ballistic protection is therefore out of the question. 

Corrosion by Hot Gases Boron carbide is mainly used at relatively low temperatures [96], therefore its oxidation has not been studied as thoroughly as that of the Si3N4 and SiC ceramics. There are data on the oxidation of B4C powders [102] and several papers on oxidation of boron carbide materials produced by different methods [103-107]. 

Corrosion by Hot Gases Thermodynamic calculations [108] show that the oxidation of boron nitride at atmospheric and low pressures over the whole temperature range to 2000°C is dominated by... 

The oxidation of boron nitride as well as boron carbide is distinguished by an oxide layer remaining in a liquid state and vaporizing considerably over the whole temperature range. However, the study of the mechanisms of oxidation of boron nitride materials is complicated by the existence of several BN modifications with considerable differences in their structure and properties. The oxidation of a stable hexagonal a-modification of BN with a graphite lattice has been studied most thoroughly [104]. 

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