Beta-boron

Indeed, focusing on this low thermal conductivity, Slack et al. have investigated boron cluster compounds like beta boron, YB66 among others, as possible embodiments of the "electron crystal phonon glass" systems that they have proposed (Slack et al., 1971 Cahill et al., 1989). 

To a limited degree, the fill-gas will determine what type of radiation the proportional counter will be able to detect. Argon and helium are the most frequently used fill gases and allow for the detection of alpha, beta, and gamma radiation. When detection of neutrons is necessary, the detectors are usually filled with boron-triflouride gas. 

The aluminosilicate versions of SSZ-31 and NCL-1 have been prepared with Si/Al ratios from 20 to The borosilicate was most conveniently prepared by using zeolite boron Beta as the source of boron. Recently, it was shown that a sodium borate source could be used with boron Beta seeds if the crystallization was conducted in sealed quartz tubes (39). In related work, a high silica Beta was converted... 

A comparative study with various types of zeolite showed that Cs-exchanged X and Y zeolites were active for toluene alkylation but primarily catalyzed the decomposition of methanol to CO.431 L and Beta zeolites, in turn, were less active and required higher reaction temperature but were much more selective, providing only very little CO. Adding boron to Cs-exchanged zeolites promotes the alkylation reaction 432 It appears that boron reduces the decomposition of methanol to CO without inhibiting active sites for side-chain alkylation. 

Post-synthesis gas-solid isomorphous substitution methods are also known [61]. Ti-beta essentially free of trivalent metals can be prepared from boron-beta. However, the gas-phase method is not efficient for Ti incorporation and could have some disadvantages such as the deposition of Ti02 [62],... 

Turan, S. and Knowles, K.M., (1997), Interphase boundaries between hexagonal boron nitride and beta silicon nitride in silicon nitride-silicon carbide particulate composites , J. Eur. Ceram. Soc., 17 (15/16), 1849-1854. 

Tritium is also one of the products obtained by bombardment of fluorine, beryllium, antimony, copper, or silver with deuterons, or the bombardment of boron and nitrogen with neutrons. Tritium is the simplest known radioactive isotope. It decays by emission of beta particles to form an isotope of helium and has a half-life of about 12 years. 

The aluminium atom is not the only non-silicious metal that can be incorporated in the Beta framework. So far the boron,26 iron,27 gallium28 and titanium21,29 containing materials have been reported. Especially the Ti-containing analogue has received a lot of attention due to its potential in oxidation chemistry using aqueous hydroperoxide as the oxidant (qui vivre). The synthesis of Ti-beta is quite difficult compared to the aluminum analogue... 

AIPO4-24, AIPO4- pollucite, aluminosilicophosphate analcime, Cs heryUosilicate pollucite, Cs, Fe silicate poUucite, gaUosilicate analcime, Cs2CuSi50i2 Boron-beta... 

The significance of this finding lies in the greater sensitivity to differences in the substitution pattern at the beta rather than alpha carbon of the trgnt, double bond undergoing hydroboration. Thus, the (fos, aw, Mg orientation of the a-CHMe (/. e. C-2 ) is reversed in cis vs. trans alkenes and the opposite relative configuration is obtained for these isomers after the boron adds to this center. Consistent with this e/ — ... 

Titanium Silicalite-2 (TS-2), structurally similar to TS-1, could be prepared likewise using tetrabutylammonium hydroxide as the template [13, 14]. Titanium aluminum Beta (Ti,Al-[3) was prepared by hydrothermal synthesis from amorphous silica, sodium aluminate, tetraethyltitanate and tetraethylammonium hydroxide [15]. The presence of A1 was necessary for the crystallization of the product. Al-free Titanium Beta (Ti-[3) could be obtained in the presence of particular templates, such as dibenzyldimethylammonium hydroxide [16]. Titanium Mordenite (Ti-MOR), conversely, was obtained by post-synthesis insertion of Ti to dealuminated Mordenite [17]. Ti-MWW (Ti-MCM-22) was obtained by the synthesis of the lamellar precursor of Ti,B-MCM-22 followed by acid treatment to remove most of the boron and extra-framework Ti and finally calcination to burn out the template and bring about the condensation of lamellae into the three-dimensional MWW structure [18]. Ti is present in a number of different environ-... 

The acidity of zeolites can be reduced by the incorporation of boron in the zeolite framework [162,163] and therefore B-substitut ZSM-5, ZSM-11 and Beta were teaed [158,164]. Al " " free boron zeolites are inactive, but these zeolites with low levels of Al " " ions which can be obtained by adding AI2O3 binder to the Al free boron zeohte have weak acidity and are moderately active at 500 - 600°C and isobutene selectivities of up to 50 % have been reported. At these conditions the observed activity and selectivity of B/Al-ZSM-5, B/Al-ZSM-11 and B/Al-Beta were. similar and therefore it was concluded that the pore aructure did not play a decisive role in the converaon of n-butene into isobutene [164]. However, A1 which migrates into the pores not only modifies the acidity but also modifies the effective pore diameter. 

M.S. Rigutto, R. de Ruiter, J.P.M. Niederer, and H. Van Bekkum, Titanium-Containing Large Pore Molecular Sieves from Boron-Beta Preparation, Characterization and Catalysis. Stud. Surf. Sci. Catal., 1994, 84C, 2245-2252. 

The susceptor materials used in high-temperature processing include zirconia, boron nitride, graphite, carbon black, sodium-beta alumina, zinc oxide, and silicon carbide. While each of these susceptor materials has relatively high dielectric losses at room temperature, silicon carbide is also refractory with a relatively good resistance to oxidation at temperatures up to roughly 1500°C.t ° ... 

Production of alpha-terpinyl alkyl ethers Beta Excellent yields in continuous reactor Eliminates use of HCl, H2SO4, AICI3, toluene, sulfonic acid, boron trifluoride etherate, and acidic cation resins as catalysts... 

In some cases, the stcric constraints of the zeolite pores can enable or impede secondary reactions. A good example is found in the rearrangement of benzyl allyl ethers over 11-Beta zeolites. In the normal course of this reaction, catalyzed by H-Bcta or boron trifluoride etherate, the benzyl allyl ether is transformed to a 4- arylbutanal, probably via a five- membered ring intermediate e.g. methallyl 2,5-dimethoxybenzyl ether ... 

Boron and aluminium compete In the crystallization of zeolite beta. Aluminium Incorporation is faster than boron Incorporation. Non-llnear effects of the B/Al ratio on the (B+A1)/S1 ratio are observed. The particle size Is affected by the composition of the synthesis gel, the bigger crystals being formed frcmi highly boric gels. 

Zeolite beta was among the first zeolites which underwent successful replacaaoent of boixrn for aluminium (1). The main grx>und for inserting boron in zeolitic frameworks is the modulation of the strength of the acid sites (2-5), but structural boron proved to be less stable than aluminium In the activation treatments, especially in hydrothermal conditions (6, 7). Ihis drawback may be turned into advantage Wien a network quite unstable under dealuminating conditions is concerned, as in the case of zeolite beta (8). The milder conditions required for deboration are likely to affect to a lesser extent the lattice stability. B-beta could then represent a suitable precursor of the activated form of the zeolite (9). Moreover the different kinetics of incorporation of boron and aluminium are likely to influence other properties of the solid, like the size and habit of the crystals and the defect patterns (10-12). 

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