Boron-stabilized crystallization

The DTA measurements exhibit the stability of c-BN at standard conditions. Influences of grain size and purity (oxide content) of the cubic boron nitride crystals on the conversion temperature become obvious. Fine grained samples containing boron oxide show a significantly lower conversion temperature than coarse material (conversion at 900 °C for 1.5-pm c-BN containing boron oxide and 1500 °C for 600-pm pure c-BN). 

Boron nitride (0.5 wt%) was used as nucleating agent in melt-spun fiber from poly-3-hydroxybutyrate. The nucleating agent controlled and stabilized crystallization. Secondary crystallization was suppressed, which otherwise woirld have lead to brittleness and poor mechanical performance. ... 

The most interesting results of the computational data, however, concern the addition of the second electron which is strongly endothermic in all cases. In other words, these dianions are predicted to dissociate an electron in the gas phase spontaneously. In solution or the solid state, it is possible that the ions could be stabilized by the effects of counter cations. This stabilization has been accomplished for the boron dianions which crystallized as contact ion pairs [47-50]. However, as indicated above, no success has been achieved so far in... 

Thermodynamic considerations postulate BjH to be a better boron source than BCl, in CVD of TaB2Using reaction (f) at < 1200 K deposits with extremely small crystal sizes are obtained on graphite substrates . They contain amorphous B at deposition temperatures < 873 K and are substoichiometric in B above this T. Carbon from the substrate substitutes for B, thereby stabilizing the diboride structure at high deposition T... 

It is very difficult to cool pure metals and other pure elements fast enough to form glasses. However, metallic alloys can often be converted into glasses, particularly if they contain a mixture of small and large atoms such as iron and boron, or they are multi-component mixtures of metals that crystallize into more than one intermetallic compound (i.e., eutectic compositions). Thus, covalent chemical interactions of the atoms are important because they stabilize liquids and thereby inhibit crystallization. 

Cubic Phase of Boron Nitride c-BN. The cubic phase of boron nitride (c-BN) is one of the hardest materials, second only to diamond and with similar crystal structure. It is the first example of a new material theoretically predicted and then synthesized in laboratory. From automated synthesis a microcrystalline phase of cubic boron nitride is recovered at ambient conditions in a metastable state, providing the basic material for a wide range of cutting and grinding applications. Synthetic polycrystalline diamonds and nitrides are principally used as abrasives but in spite of the greater hardness of diamond, its employment as a superabrasive is limited by a relatively low chemical and thermal stability. Cubic boron nitride, on the contrary, has only half the hardness of diamond but an extremely high thermal stability and inertness. 

We would like to remind that all tubular structures are composed of 96 boron atoms, the same number of atoms in the elemental a-boron unit cell of boron crystals. The purpose is simply having clusters of the same size, in order to be energetically comparable. On one hand, a-boron is a real component existing in nature, and on the other hand, single-wall nanotubes so far have been predicted and also synthesized [15]. In this case we calculated the total B3LYP energies and determined the structure stability as follows = (nEi - E ) / n = Ei - E / n, where E is the... 

The more stable boron chelates can be isolated even from aqueous solution, whereas those of lower stabilities are only accessible from non-aqueous media. Catechol- and inositol-borates (3, 5 and 6) possesses a well-defined monomeric structure,75 whereas those obtained from monosaccharides and alditols are polymeric.121 A crystal structure determination122 has been carried out for sodium scyUo-inositol diborate (6). 

It is well known that the elements in framework of zeolite molecular sieves greatly influence the properties and behaviors of these materials [1-3], The introduction of heteroatoms into the framework has become one of most active fields in study of zeolites. The investigations were mostly focused on the methods to introduce heteroatoms into the framework (for examples, hydrothermal synthesis and post-synthesis), the mechanisms for incorporations, the effect of heteroatoms on the acid-base properties and the catalytic features of modified samples [1-10]. Relatively less attention was paid to the effect of treatment process on the porous properties of samples although the incorporation of heteroatoms, especially by the so-called post-synthesis, frequently changes the distribution of pore size. Recently, we incorporated Al, Ga and B atoms into zeolites (3 by the post-synthesis in an alkaline medium named alumination, galliation and boronation, respectively. It was found that different trivalent elements inserted into the [3 framework at quite different level. The heteroatoms with unsuitable atom size and poor stability in framework were less introduced, leading to that a considerable amount of framework silicon were dissolved under the action of base and the mesopores in zeolite crystal were developed. As a typical case, the boronation of zeolites (3 and the accompanied formation of mesopores are reported in the present paper. 

Cmde diketene obtained from the dimerization of ketene is dark brown and contains up to 10% higher ketene oligomers but can be used without further purification. In the cmde form, however, diketene has only limited stability. Therefore, especially if it has to be stored for some time, the cmde diketene is distilled to > 99.5% purity (124). The tarry distillation residue, containing triketene (5) and other oligomers, tends to undergo violent spontaneous decomposition and is neutralized immediately with water or a low alcohol. Ultrapure diketene (99.99%) can be obtained by crystallization (125,126). Diketene can be stabilized to some extent with agents such as alcohols and even small quantities of water [7732-18-5] (127), phenols, boron oxides, sulfur [7704-34-9] (128) and sulfate salts, eg, anhydrous copper sulfate [7758-98-7]. 

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