Boronic chemical stability

The refractory-metal borides have a structure which is dominated by the boron configuration. This clearly favors the metallic properties, such as high electrical and thermal conductivities and high hardness. Chemical stability, which is related to the electronic... 

The boron-doped diamond film electrode is the newest of the voltammetric indicator electrodes. It is promising because of its high chemical stability, low background currents, and wide potential windows (high overpoten-... 

Borosilicate glass and ceramics are inert materials and have great chemical stability the weak point about glass, however, is its fragility. Glass can be used for both organics and inorganics, but one should be mindful of the fact that it is a potential source of boron and silicon and cannot be used if these elements are to be determined. 

There is obviously a particular need to develop materials which can function at high temperatures. Due to their strong covalent bonding, boron cluster compounds generally possess attractive mechanical properties as materials, e.g. stability under high temperature due to their high melting points (typically >2300 K), chemical stability, resistance to acidic conditions, and small compressibility. Furthermore, importantly, the B12 icosahedra compounds have also been found to have intrinsic low thermal conductivity, as will be discussed in detail in later sections, and which is desirable for thermoelectric applications. 

Most attention has been devoted to an exploration of the chemistry of the borazaromatics. In these compounds, two neighboring carbon atoms of an aromatic system are replaced by the isoelectronic boron-nitrogen groups as illustrated by the 2,1-borazaronaphthalene, 7 2>3>. Their great chemical stability is a distinct feature of heteroaromatic materials and several reviews of their chemistry have been published 4 6>. 

Owing to its extraordinary chemical stability, diamond is a prospective electrode material for use in theoretical and applied electrochemistry. In this work studies performed during the last decade on boron-doped diamond electrochemistry are reviewed. Depending on the doping level, diamond exhibits properties either of a superwide-gap semiconductor or a semimetal. In the first case, electrochemical, photoelectrochemical and impedance-spectroscopy studies make the determination of properties of the semiconductor diamond possible. Among them are the resistivity, the acceptor concentration, the minority carrier diffusion length, the flat-band potential, electron phototransition energies, etc. In the second case, the metal-like diamond appears to be a corrosion-stable electrode that is efficient in the electrosyntheses (e.g., in the electroreduction of hard to reduce compounds) and electroanalysis. Kinetic characteristics of many outer-sphere... 

Stronger van der Waals forces hold the sheets in line with each other so that boron nitride is not as good a lubricant as graphite. However, research is being conducted on the use of boron nitride as a high-temperature lubricant because of its chemical stability. 

Cubic boron nitride has high thermal conductivity, high dielectric constant, great hardness, and good chemical stability. The material can be doped n-type with Si and p-type with Be to form p-n junctions. While cubic boron nitride (c-BN) has been successfully doped p- and n-type to produce the first UV-LEDs, it is an indirect bandgap semiconductor which will ultimately limit emission efficiency. Relatively few studies have been performed on this material system. ECR-LPCVD techniques [23, 24] and LPCVD [25] have had the most success informing BN films. As with other specialty materials there is a lack of BN substrates. In order to produce the c-BN phase, high deposition temperatures often are combined with assisted techniques. 

The reduction of PhsB is known to result in a radical anion PhsB that is in equilibrium with the dimeric species [PhsB-BPhs] ". However, if bulky substituents as in MessB are present and thus prevent attack of nucleophiles or dimerization, a blue-colored stable radical anion can readily be identified. While arylboranes are also known to form purple-colored dianions, the second reduction of simple triarylboranes is typically irreversible. In a recent study, Okada and Oda reported the formation of purple-colored solutions of dimesitylphenylborane dianions [Mes2BAr] (146 Ar = Ph, 4-Me3SiC6H4, biphenyl) upon extended reaction of Mes2BAr with Na-K alloy in THE (Scheme 21). Formation of dianions was confirmed by multinuclear NMR spectroscopy. While the bulky mesityl groups provide chemical stability to the dianions and thus prevent further chemical reactions, the presence of the unsubstituted phenyl group is believed to allow for effective tt-interactions with the jC>-orbital on boron. 

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. 

The distinguishing characteristics of boron phosphide are its high melting point, which exceeds 2500 C [1], and its high chemical stability [2]. It cannot be dissolved in mineral acids or in boiling aqueous solutions of alkalies. When heated in air, boron phosphide remains stable up to 800-1000 0. 

Boron compounds have low solubility relative to some cadmium, gadolinium, or europium compounds in nitric acid solutions, and would be more likely to precipitate from solution if high concentrations are required. Cadmium is a desirable poison however, it may be volatile at temperatures encountered in the waste conversion proqess and would therefore require an additional process for recovery. Additional requirements for, soluble poisons Include chemical stability in the solution and processing behavior similar to the fissile material. Each poison s neutron absorption rate is uniquely dependent on the neutron energy spectra of the system hence, the relative neutronic effectiveness of each poison varies from one system to another. Consequently, a mixture of poisons in a solution may be more effective than dither poison alone. ... 

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