Titanium reduction temperature effects

The dependence of the combustion temperature of the Ti + 0.5 C samples with relative density of 58 2.5% on the PN2 is shown in Figure 11.8. Clearly, the undiluted samples had a high reaction temperature, but this was decreased by a reduction of PN2 or by the addition of diluent. The effect of carbon content on the combustion synthesis of titanium... 

After all other conditions had been optimized, the effect of temperature during the adsorption step was studied again, particularly because the temperature reduction from 150° to 100 °C had no deleterious effect on dispersion stability. Adsorption of the block copolymer onto the titanium dioxide at room temperature would be easy to carry out in practical applications and might be worth even a sacrifice in dispersion stability. Figure 4 shows settling data of dispersions prepared in a Waring... 

The hexagonal close-packed (hep) metals exhibit mechanical properties intermediate between those of the fee and bcc metals. For example, zinc suffers a ductile-to-brittle transition, whereas zirconium and pure titanium do not. The latter and its alloys have an hep structure, remain reasonably ductile at low temperatures, and have been used for many applications where weight reduction and reduced heat leakage through the material have been important. However, small impurities of oxygen, nitrogen, hydrogen, and carbon can have a detrimental effect on the low-temperature ductility properties of titanium and its alloys. 

The hydrogenation of spherical particles of an alloy BT5-1 proceeds without the induction period at 773 K with exothermic effect, therefore a temperature in autoclave raises up to 820 K (sample 1—4). The content of hydrogen in hydrogenation products answers the composition Ti(Al,Sn)Hi 8. On the diffractograms of products of hydrogenation only the reflexes of titanium hydride are observed with the constant of a crystal lattice a = 0.4434-0.4437 nm (for TiHL92 a = 0.4448 nm). The reduction of a diameter of alloy particles results in appreciable decrease of time of sample saturation by hydrogen with 4 h at a diameter of particles of 0.8 mm (sample 4) up to 10 min at a diameter of particles of 0.1 mm (sample 1). At that the density of titanium doped by A1 and Sn in... 

The surface crystal structure and particle size can also influence photoelectro-chemical activity. The mode of pretreatment, for example, dictates whether titanium dioxide exists in the anatase phase (as is likely in samples which have been calcined at temperatures below 500 °C) or in the rutile phase (from calcination temperatures above 600 °C) or as a mixture of the two phases for pretreatments at intermediate temperature ranges. The effect of crystalline phase could be easily demonstrated in the photocatalytic oxidation of 2-propanol and reduction of silver sulfate, where anatase is active for both systems. But when the catalyst was partially covered with platinum black, alcohol oxidation was easy, but silver ion reduction was suppressed. On rutile, redox activity was observed for Ag+, alcohol oxidation was negligible [85]. 

The commonly used MPVO catalysts consist of metal alkoxides, which are easily hydrolysed to inactive oxides in the presence of water. Since the proposed catalytic species for the MPVO reaction also consists of an alkoxide intermediate [6,9] the influence of water and strong Lewis bases on the catalytic activity and selectivity was investigated. As already reported for the liquid-phase reaction [9], Ti-beta has a high tolerance for water due to its hydrophobic interior. As can be seen from Fig. 6a the presence of water is not detrimental to the activity of Ti-beta in the MPV reduction of 4-methylcyclohexanone. The temperature of 110 °C, at which a ketone conversion of 50% is measured, is identical to the temperature required for 50% conversion in the absence of water (Fig. 3), Le. water has no effect whatsoever on the overall MPVO activity of the titanium site. 

Lewis acid catalyzed versions of [4 4- 2] cycloadditions are restricted to functionalized dieno-philes. Nonfunetionalized alkenes and alkynes cannot be activated with Lewis acids and in thermal [4 + 2] cycloadditions these suhstrates usually show low reactivity. It has been reported that intcrmolecular cycloaddition of unactivated alkynes to dienes can be accelerated with low-va-lent titanium, iron or rhodium catalysts via metal-mediated - -complex formation and subsequent reductive elimination39 44. Usually, however, low product selectivities are observed due to side reactions, such as aromatization, isomerization or oligomerization. More effective are nickel-catalyzed intramolecular [4 4- 2]-dienyne cycloadditions which were developed for the synthesis of polycycles containing 1.4-cyclohexadienes45. Thus, treatment of dienyne 1, derived from sorbic acid, with 10mol% of Ni(cod)2 and 30 mol % of tris(o-biphenyl) phosphite in tetrahydrofuran at room temperature affords bicyclic 1,4-dienes 2, via intramolecular [4 + 2] cycloaddition, with excellent yield and moderate to complete diastereocontrol by substituents attached to the substrate. The reaction is sensitive towards variation in the catalyst and the ligand. 

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