Solid boron nitride

Given that AH = —254.4 kJ mol-1 and S° = 14.81 J K-1 mol-1 for hexagonal solid boron nitride, use the data of Appendix C to calculate the free energy change for the hydrolysis of one mole of BN (s) by liquid water at 25 °C. Ignore the weak acid-base interaction of the products and the very slight solubility of B(OH)3(s). 

Solid boron nitride is a ceramic material of some consequence that can be formed at high temperatures by the reaction of boron atoms with N2 or NH3. A likely intermediary in its formation is another high-temperature molecule BN, first observed through its electronic emission spectrum nearly 60 years ago but the properties of which have emerged only slowly (14). Identification of the several low-lying electronic states of the molecule is a major problem and only very recently has it become clear that the ground state is not (as with the isoelectronic C2 molecule) but I1 (15). The A n—X Ili transition. 

If solid boron nitride is subjected to u.v. irradiation in the presence of a 4 1 mixture of Fg + O2, NO+BF4 is produced. This is a much simpler process than those involved in earlier synthetic routes to this compound, Fluoroborate equilibria have been examined in 1 molar NaCl solution, measuring [F ] with a LaFg electrode and the pH using a hydrogen electrode. The results may be explained in terms of the following reactions and equilibrium quotients ... 

Elements dissolved in boron influence its crystal structure. Dissolved impurities also influenee the physical and chemical properties of boron, especially the electrical properties, because boron is a semiconductor. Preparation of solid solutions in jS-rh boron requires a careful choice of crucible material. To avoid contamination, boron nitride or a cold, coinage-metal crucible should be used or the levitation or floating-zone melting techniques applied. 

A pellet is pressed of an intimate mixture of finely divided reactants and reaction induced either by arc melting and high-T annealing or by solid-state sintering in an electrical or high-frequency furnace. Isolating the borides from reactive container components can be a problem. The use of boron nitride liners has proved effective. In some cases the protective liner is made of sintered boride containing the same elements as the boride in preparation. 

Molybdenum disulhde (M0S2), graphite, hexagonal boron nitride, and boric acid are examples of lamella materials commonly applied as solid lubricants. The self-lubricating nature of the materials results from the lamella crystalline structure that can shear easily to provide low friction. Some of these materials used to be added to oils and greases in powder forms to enhance their lubricity. Attention has been shifted in recent years to the production and use of nanosize particles of M0S2, WS2, and graphite to be dispersed in liquid lubricants, which yields substantial decreases in friction and wear. 

Miyake, S., Tribology of Carbon Nitride and Boron Nitride Nanoperiod Multilayer Films and Its Application to Nanoscale Processing," Thin Solid Films,Wo. 493,2005, pp. 160-169. 

C21-0047. Boron nitride (BN) is a planar covalent solid analogous to graphite. Write a portion of the Lewis structure and describe the bonding of boron nitride, which has alternating B and N atoms. 

There is great interest in developing molecular precursors for boron-nitrogen polymers and boron nitride solid state materials, and one general procedure is described in this report. Combinations of B-trichloroborazene and hexamethyldisilazane lead to formation of a gel which, upon thermolysis, gives hexagonal boron nitride. The BN has been characterized by infrared spectroscopy, x-ray powder diffraction and transmission electron microscopy. 

A colorless gel formed which was isolated by vacuum evaporation of the volatiles. The resulting colorless glassy solid was pyrolyzed in vacuo at 900°C for 24 hours in a quartz tube and the evolved volatiles identified as NH3 and NH4CI. The remaining solid was briefly (2 hours) heated in air at 1200°C in order to remove minor carbon impurities and to improve crystallinity. This solid was then treated at room temperature with 40% aqueous HF to remove boric acid and silica formed in small quantities. The solid obtained at 900°C was identified as boron nitride however, the majority of the material was amorphous. After treatment at 1200°C, white crystalline boron-nitride was obtained in about 55% yield. 

Evolution did not use this element, only in certain plants is it important as a trace element. The element became well-known because of heat-resistant borosilicate glasses. Boranes are chemically interesting as B-H bonds react very specifically. Perborates are used in laundry detergents (Persil). The hardness of cubic boron nitride approaches that of diamond. Amorphous (brown) boron burns very quickly and gives off much heat and is therefore used in solid-propellant rockets and in igniters in airbags. 

Cubic BC2N. Hetero-diamond B C—N compounds have recently received a great interest because of their possible applications as mechanical and optical devices. The similar properties and structures of carbon and boron nitrides (graphite and hexagonal BN, diamond, and cubic BN) suggested the possible synthesis of dense compounds with all the three elements. Such new materials are expected to combine the best properties of diamond (hardness) and of c-BN (thermal stability and chemical inertness). Several low-density hexagonal phases of B,C, and N have been synthesized [534] while with respect to the high-density phases, different authors report contradictory data [535-538], but the final products are probably solid mixtures of c-BN and dispersed diamonds [539]. 

Samples for solid-state NMR (175-300 mg) were ground with a mortar and pestle and packed into either AI2O3 or boron nitride rotors of cylindrical design. Independent polyester preparations gave identical spectral results. 

The polymers 9.16 were isolated as white solids and characterisation suggested the presence of a significantly branched structure. Pyrolysis at 1200 °C yielded white boron nitride in 85-93% yield. An idealised representation of this process is shown in Scheme 9.10. 

Two forms of boron nitride are known. The ordinary form is a slippery while matenul. The second, formed artificially at high pressures, is the second hardest substance known. Both remain as solids at temperatures approaching 3000 °C. Suggest structures. 

In general, the stable thermodynamic products of ordinary flames have little worth, but many of the uncommon flames have products of value. The chlorination of hydrocarbons may be carried out in a flame process which was recently announced (A4). A most fascinating example is the formation of boron nitride from the flame reaction between diborane and hydrazine, two compounds which are ordinarily thought of as fuels (B2, VI). The stabilization of this flame depends upon the proper preparation of the premixed gases, since a solid adduct between the reactants prevents flame stabilization if the preflame residence time is too great. 

Nitride Boron nitride, BN, white solid, insoluble, reacts wiLh steam Lo form NHj and boric acid, formed by heating anhydrous sodium borate with ammonium chloride, or by burning boron in air. 

When boron is heated to high temperatures with carbon, it forms boron carbide, B12C3, a solid with a high melting point that is almost as hard as diamond. The solid consists of B12 groups that are pinned together by C atoms. When boron is heated to white heat in ammonia, boron nitride, BN, is formed as a fluffy, slippery powder ... 

Boron nitride, BN, is a covalent network solid with a structure similar to that of graphite. Sketch a small portion of the boron nitride structure. 

Sample Preparation. Solid samples were finely powdered and dusted onto mylar tape. In order to minimize thickness effects some model compound samples were diluted with boron nitride. Liquid samples... 

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