Systems, boron-free

Since boron trichloride reacts with many lubricants to form hydrogen chloride, the diboron tetrachloride synthesis is carried out in a grease-free system. A mercury float-valve vacuum system4 depicted in Fig. 15 is employed here. The U-traps have a capacity of 50 ml. without plugging and tubes A and B have... 

Caution. The boron hydride derivatives encountered in this preparation are extremely air sensitive and can inflame violently in the atmosphere. They are also very toxic, or believed to be so. The preparation should be carried out in a vacuum line in a well-ventilated area. A grease-free system should be used. ... 

Some Boron-Free Nido and Arachno Systems... 

The initial step in the program is the development of a characterization project to assess the effect of a number of primary variables on the performance of laminates under irradiation and at 4 K. Typical variables are reinforcement type, resin system, and cure cycle. The materials will represent a cross section of the existing commercial laminate production. Several laminates will be specially fabricated to provide increased radiation resistance. They will utilize commercial, boron-free glass for reinforcement and epoxy systems cured with aromatic amines. All test laminates will be made by a commercial producer under conditions dupli-... 

In boron-containing systems the initial Si3N4-crystallization without decomposition may indicate that the carbon is not present in the form of a reactive free carbon boron may keep carbon in some other (amorphous ) form to suppress or to retard... 

An electrolyte-free system for ozone generation using heavily boron-doped diamond electrodes. Diamond Relat. Mater., 40, 7-11. 

The selection of boron-free core leads to a considerable simplification of the auxiliary systems related to boron management, which in turns leads to a significant reduction in investment and maintenance costs. Reactivity control in accidents may be backed-up by the injection of borated water. 

FIORINI, G.L., GAUTIER, G.-M., BERGAMASCHI, Y., Feasibility studies of a soluble boron-free 900-MWe PWR, Safety Systems Consequences of the partial or total elimination of soluble boron on plant safety and plant systems architecture. Nuclear Technology, Vol. 127 (1999), p 239-258. 

The amount of solid, liquid and gas waste from the equipment and systems is reduced by a boron-free design, and simplification of the primary system helps reduce waste generated during maintenance. 

Despite many controversial arguments regarding the definition and physical origin of aromaticity [1,15-17], the concept of aromaticity has crossed the boundary of benzenoid hydrocarbons [with (4n + 2)ji -electrons] to include heterosystems [50] like pyridine, thiophine, cations such as tropylium [12] and cyclopropenium [13], anions like cyclopentadienyl [51], organometallic systems, namely ferrocene [52], purely carbon-free systems [53,54], namely Pj, [(P5)2Ti]. The three-dimensional aromaticity of boron-based clusters [55] and of fullerenes [56], the homoaromaticity of cationic systems [57], aromaticity of triplet state annulenes [58], and pericyclic transition states [59] has enlarged the concept of aromaticity. Extension of aromaticity... 

Brown proposed a mechanism where the enolate radical resulting from the radical addition reacts with the trialkylborane to give a boron enolate and a new alkyl radical that can propagate the chain (Scheme 24) [61]. The formation of the intermediate boron enolate was confirmed by H NMR spectroscopy [66,67]. The role of water present in the system is to hydrolyze the boron enolate and to prevent its degradation by undesired free-radical processes. This hydrolysis step is essential when alkynones [68] and acrylonitrile [58] are used as radical traps since the resulting allenes or keteneimines respectively, react readily with radical species. Maillard and Walton have shown by nB NMR, ll NMR und IR spectroscopy, that tri-ethylborane does complex methyl vinyl ketone, acrolein and 3-methylbut-3-en-2-one. They proposed that the reaction of triethylborane with these traps involves complexation of the trap by the Lewis acidic borane prior to conjugate addition [69]. 

Figure 4.22 Schematic diagram of a field effect transistor. The silicon-silicon dioxide system exhibits good semiconductor characteristics for use in FETs. The free charge carrier concentration, and hence the conductivity, of silicon can be increased by doping with impurities such as boron. This results in p-type silicon, the p describing the presence of excess positive mobile charges present. Silicon can also be doped with other impurities to form n-type silicon with an excess of negative mobile charges.

In systems derived from PH3 BH3, changes in the coupling constant, /pH, are found which are similar to those seen in compounds derived from PH3, i.e. compounds with phosphorus in coordination number 3. The observation that the alteration does not correspond to that seen for derivatives of PHi suggests that the very weak donor-acceptor bond in PH3 BH3 does not affect the hybridisation of phosphorus, as compared with that in free PH3, as much as might at first be expected. A small increase in the electron withdrawing action by halogen substitution of the hydrogen atoms bonded to boron causes an increase in the s character of the P-H bonds. 

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