Preparation and uses of titanium and zirconium chloroalkoxides

The preparation of titanium and zirconium chloroalkoxides by the treatment of titanium tetrachloride with ethylene oxide vapour and zirconium tetrachloride with either ethylene oxide vapour or 1,2-propylene oxide is described. Under the reaction conditions used, ethylene oxide gives mainly the tetra-(2-chloroethoxide). Zirconium tetrachloride and 1,2-propylene oxide give the tetra-(chloropropoxide). Titanium and zirconium chloroalkoxides, particularly the tetra-(2-chloroethoxides), can be used to bind suitably graded refractory powders. In admixture with diethanolamine, both titanium and zirconium tetra-(chloroethoxide) are good thixotropy developers for aqueous emulsion paints.     

Catalytic graphitization of carbon using titanium and zirconium

The role of titanium and zirconium as graphitization catalysts was studied using anisotropic carbons prepared from Gilsonite pitch and acenaphthylene (HHT 1173°K), and an isotropic carbon prepared from a phenol-hexamine resin (HTT 1273°K). Heat-treated mixtures of metal and carbon, HTT 2673 and 3073°K were examined by polarized-light optical microscopy, line-broadening analyses of X-ray diffraction profiles and electron probe measurements. Both metals are effective as catalysts, producing crystallites with dimensions of about 200 nm at 3073°K. The extent of graphitization increases with metal content to about 10% of metal. Diffusion of titanium and zirconium within the carbon matrix is significant. Graphitic material is precipitated from solution of carbon in titanium and zirconium. There is no evidence of carbide formation.     

Hydrogenolysis of alkanes and olefin polymerization on the silica-supported zirconium hydrides: A comparative DFT study

The model reactions of ethylene polymerization and hydrogenolysis of linear alkanes (propane, n-butane, and n-pentane) on the silica-supported zirconium hydrides (Si–O)₃Zr^IVH, (Si–O)₂Zr^IVH₂, and (Si–O)₂Zr^IIIH were studied using the DFT approach. Catalytic processes under study were shown to occur involving different surface hydrides. The ethylene polymerization was found to proceed at comparable rates on the zirconium monohydrides, (Si–O)₃ZrH, and dihydrides, (Si–O)₂ZrH₂. Cleavage of linear alkanes on the monohydrides (Si–O)₃ZrH is thermodynamically unfavorable; however, the dihydrides (Si–O)₂ZrH₂ can act as catalysts of the process under mild conditions. Hydrides of the trivalent zirconium, (Si–O)₂Zr^IIIH, can also contribute to the hydrogenolysis reaction. A feature of all the systems studied is low regioselectivity of the corresponding processes.     

Single-event microkinetics for coke formation during the catalytic cracking of (cyclo)alkane/1-octene mixtures

A single-event microkinetic model (SEMK) is applied to model initial coking rates during the catalytic cracking of (cyclo)alkane/1-octene mixtures at 693–753 K and (cyclo)alkane and 1-octene inlet partial pressures of 26.6 and 4.8 kPa on a REUSY equilibrium catalyst. Three types of irreversible alkylations involving both gas phase and surface coke precursors, viz., alkylation of phenyl substituted carbenium ions with C₃–C₅ alkenes, alkylation of the nucleus of monoaromatics with C₃–C₅ alkylcarbenium ions, and alkylation of C₈–C₁₀ alkylcarbenium ions with C₃–C₅ alkenes, have been considered as rate-determining steps in coke formation. The bulky alkylated species formed out of these alkylations are considered as coke. The activation energies for these alkylations obtained via non-isothermal regression are independent of the feedstock within the parameters confidence limits reflecting the fundamental character of the SEMK. The negative effect of temperature on the experimentally observed coking rates is qualitatively described and is explained in terms of an overcompensation of the increase of the rate coefficient by a lower surface coke precursor concentration.     

羊皮无铬鞣制过程锆钛含量分布研究

以绵羊浸酸原皮为原材料,研究不同鞣制时间鞣液和羊皮中的锆钛含量变化.采用微波消解法处理皮样,电感耦合等离子体原子发射光谱法测定结果表明,锆钛在肉面层的含量最高,其次是粒面层,中间层含量最低.随着鞣制时间增加,锫钛在3层中含量趋于均匀.提碱之前,无铬鞣剂以渗透为主.提碱后,皮革中金属元素含量急剧升高.扫描电子显微镜观察显...     

Parameter studies of the synthesis of titanium dioxide nanoparticles: Effect on particle formation and size

The large scale synthesis of TiO₂ nanoparticles in the nonaqueous benzyl alcohol route was investigated with respect to the influence of process parameters, like temperature, pressure, reactor filling ratio, agitator speed and precursor concentration, on the induction time of particle formation and particle size. A coherence of the varied process parameters and the molecular reaction mechanism was found that supports the suggested mechanism of particle formation, representing an important step toward a controllable and predictable particle synthesis.     

Copolymerization of ethylene and 2-vinylnaphtalene with titanium and zirconium catalysts

Copolymerization of ethylene and 2-vinylnaphtalene (VN) has been investigated with dimethylsilylene(tetramethylcyclopentadienyl)(N-tert-butyl)titanium dichloride (1) and rac-isopropylidenebis(indenyl)zirconium dichloride (2) using methylaluminoxane as a cocatalyst. The copolymerization gave the corresponding copolymer in good yield. The catalyst 1 showed higher incorporation of VN than the catalyst 2. Thermal properties of the resulting copolymers were investigated by DSC in comparison with those of poly(ethylene-co-styrene), and poly(ethylene-co-VN) showed higher T_g than poly(ethylene-co-styrene).     

Dynamic synthesis of zirconium dioxide powders

We investigated the process of zirconium dioxide powder synthesis by shock wave loading of a porous metal and the subsequent dispersion. The synthesized powder consists of hollow spherical shells and highly porous conglomerates with a 500 μm mean dimension. The specific surface of the powder is independent of the particle size and is 1.25±0.35 m²/g. The tetragonal modification predominates for large dimensions, while the monoclinic is more common in the small. The possibility of stabilizing the oxides in the high-temperature phase is investigated. Deceased. Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences, 660036 Krasnoyarsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 6, pp. 78–81, November–December, 1993.     

Kinetic aspects of the formation of lead zirconium titanate

The kinetics of the second calcination step in the formation of PZT solid solution (with perovskite ABO₃ lattice) has been investigated by using two different particle sizes of the B-site precursor (1.91 and 5.08 μm), the finer size being obtained by prolonged milling. In-situ analysis performed by high-temperature X-ray diffractometry in a non-isothermal mode (20–800 °C) revealed a reduction of the calcination temperature by 100 °C with a decrease in particle size of the precursor. In order to clarify the mechanism of the solid-state reaction to PZT, isothermal heat treatment of the mixtures was performed in the temperature range 540–700 °C. The activation energies for the fine and the coarse powders were estimated as 150 and 210 kJ mol⁻¹ respectively, and the reaction was found to follow the Jander model for diffusion-controlled solid-state reaction kinetics.     

Phase formation in titanium glazes

Phase formation in titanium-containing systems is examined. The results of studies of phase formation under crystallization are reported for the SiO₂−TiO₂−CaO−Al₂O₃−B₂O₃−Na₂O system. The principal phases in the compositions studied were found to be sphere, anorthite, and rutile. Translated from Steklo i Keramika, No. 1, pp. 17–20, January, 1997.     

钛,锆,铪取代的膦叶立德的合成及应用

简介了ⅣＢ族金属－钛、锆和铪取代的膦叶立德的各种合成方法及它们与酮、醇和一氧化碳的反应。     

Structure formation and degradation of partially stabilized zirconium dioxide

The process of structure formation of partially stabilized zirconium dioxide powders during the heat treatment of precipitated zirconium and yttrium hydroxides and structure degradation in time depending on hydroxide precipitation method (mutual and sequential precipitation) has been investigated. During calcination, the t→m-ZrO₂ transition takes place in sequentially precipitated hydroxides, and the m→t-ZrO₂ transition takes place in coprecipitated hydroxides. It was noted that soft readily destroyable aggregates are formed during the heat treatment of sequentially precipitated hydroxides. This makes it possible to produce fine ZrO₂ powders (d=50–100 nm) avoiding disaggregation and/or milling. It has been found that the zirconium dioxide degradation process, which is due to the t→m-ZrO₂ transformation, decreases with increasing amount of Y₂O₃ and cubic modification of ZrO₂ in heat treatment products and in the case of coprecipitation of hydroxides     

Experimental study of wave formation in a flame front

Kazan. Translated from Fizika Goreniya i Vzryva, Vol. 24, No. 5, pp. 77–79, September–October, 1988.     

Mechanism of the formation of precursors for the Cu/ZnO methanol synthesis catalysts by a coprecipitation method

Precursors of Cu/ZnO catalysts with various Cu/Zn molar ratios were prepared by a coprecipitation method. It was found that amorphous copper hydroxycarbonate and sodium zinc carbonate were intermediates for the formation of various precursors such as hydrozincite, malachite and aurichalcite. Aurichalcite having a high Cu/Zn ratio was prepared from a mechanical mixture of these intermediates.     

Cluster formation mechanisms of titanium dioxide during combustion synthesis: Observation with an APi-TOF

Few studies reported the formation of Ti-containing clusters in the initial stages of TiO₂ flame synthesis. The conversion from synthesis precursor to TiO₂ monomers was commonly assumed to take place through global reaction such as thermal decomposition and/or hydrolysis at high temperatures. More recent studies have been able to identify stable intermediates of Ti-containing monomers, most commonly Ti(OH)₄, as the final step before the formation of TiO₂. However, no larger Ti-containing cluster formation mechanisms or interactions between these monomers have been tracked. To investigate cluster formation pathways of TiO₂ during flame synthesis, Charged clusters were measured in an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer. TiO₂ nanoparticles were synthesized by adding titanium tetraisopropoxide (TTIP) precursor to a premixed CH₄/O₂/N₂ flat flame aerosol reactor. Pure TiO₂ clusters were not detected by the APi-TOF. Results from measured mass spectra and mass defect plots show that for positively charged clusters, the abstraction of CH₂ groups occurs simultaneously with the clustering of larger intermediate organometallic species. For negatively charged clusters, NO_x formation pathways in the flame may play a role during the initial stages of TiO₂ formation, since a lot of Ti-containing clusters were attached with nitrate-related species. These research findings provide insights on quantum dot synthesis and molecular doping where rapid dilution of the flame synthesized nanoparticles is needed to better control the particle size and chemical composition. The possible influences of and potential artifacts brought by the dilution system on observing the incipient particle formation in flames were also discussed.

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Composition of the combustion products of mixtures of aluminum nanopowders with titanium and zirconium dioxides in air

The combustion products of mixtures of aluminum nanopowder with titanium and zirconium dioxides in air were studied. The products were found to contain stabilized crystalline phases of TiN and ZrN. Maximum weight content of TiN (29.4%) was observed in the combustion products of a starting mixture containing 52% aluminum nanopowder, and the maximum content of ZrN (28.6%) was observed in the combustion products of a starting mixture with 35% aluminum nanopowder.