Synthesis of ultrafine single-component oxide particles by the spray-ICP technique

Ultrafine oxide particles were synthesized by introducing aqueous solutions of metal salts into a high-temperature r.f. inductively coupled plasma (the spray-ICP technique). The particles synthesized were spherical for ZrO₂, Y₂O₃, Sm₂O₃, La₂O₃, δ-Al₂O₃, TiO₂ (anatase), β-Bi₂O₃ and CuO, plate-like for Nd₃O₂, Cr₂O₃ and Pr₂O₃, polyhedral for PrO₂, CeO₂ and γ-Fe₂O₃, cubical for NiO, MgO, CaO, Co₃O₄ and Mn₃O₄, bar-like for SnO₂ and ZnO, and foil-like for β-PbO and MoO₃. The products of the alkaline earth group except for magnesium, were hydroxides and/or carbonates, spoiled by atmospheric H₂O and/or CO₂. The particle morphology suggests that particle growth is controlled predominantly by the gas-solid reaction occurring on the surface of nuclei condensed from the gas phase. Some of the oxides revealed a particle morphology characteristic of their crystal structures.     

Crystal growth of tetragonal ZrO2 in the glass system ZrO2-SiO2 prepared by the sol-gel process from metal alkoxides

Glasses in the system ZrO₂-SiO₂ containing 40 to 60 mol % ZrO₂ were prepared by the sol-gel process from metal alkoxides. Tetragonal ZrO₂ was precipitated by heat treatment at 800 and 1200° C, and its crystal growth was measured by differential thermal and X-ray diffraction analyses. At 800 to 900° C, tetragonal ZrO₂ crystals grew three-dimensionally and the activation energy for growth was calculated as about 680 kJ mol⁻¹. On the other hand, the secondary growth of tetragonal ZrO₂ at 1000 to 1200° C followed the cube-root-of-time law. The activation energy for secondary growth was about 380 kJ mol⁻¹. It is suggested that the diffusion of Zr⁴⁺ ions is the rate-limiting process for the secondary crystal growth of tetragonal ZrO₂.     

Toughened glass-ceramics in the ZrO2-Al2O3-SiO2 system prepared by the sol-gel process

Monolithic glass-ceramics containing Al₂O₃ or TiO₂ were prepared in the ZrO₂-SiO₂ system by the sol-gel process from metal alkoxides. Tetragonal ZrO₂ was precipitated by heat treatment at 900–1200 °C and its crystal growth was increased by adding TiO₂ or Al₂O₃. Further heating at higher temperature resulted in the precipitation of zircon and monoclinic ZrO₂ which was transformed from tetragonal ZrO₂. The addition of Al₂O₃ had less effect on both the tetragonal-to-monoclinic ZrO₂ transformation and the precipitation of zircon. The fracture toughness increased as the size of tetragonal ZrO₂ particles increased and then decreased with the appearance of monoclinic ZrO₂ or zircon. The fracture toughness of the glass-ceramics was measured in the glass-forming regions of the ZrO₂-Al₂O₃-SiO₂ system. The fracture toughness was sensitively dependent on both Al₂O₃ and ZrO₂ content, of which the highest value achieved was 9 MPa m^1/2 for the 50ZrO₂·10Al₂O₃·40SiO₂ composition.     

The infrared and Raman spectra of ZrO2-SiO2 glasses prepared by a sol-gel process

Infrared and Raman spectra were measured and interpreted on the basis of structure for various ZrO₂-SiO₂ glasses that were prepared by a sol-gel process involving zirconium nitrate. Interpretation of the spectra indicates the presence of both Zr-O-Si and Si-O-H linkages depending upon heat treatment conditions, and the evidence of zirconium atoms with eight fold coordination for glasses with high ZrO₂ contents. The crystalline products formed during glass devitrification were monitored by vibrational spectra. The formation and detection of tetragonal ZrO₂, zircon, monoclinic ZrO₂ and -cristobalite depended upon the conditions of devitrification.     

Estimation of formation mechanism of spherical fine ZrO2-SiO2 particles by ultrasonic spray pyrolysis

Spherical fine ZrO₂-SiO₂ (11) particles were synthesized from a hydrolysed mix-solution of Si(OC₂H₅)₄ and ZrOCI₂ · 8H₂O by ultrasonic spray pyrolysis, and the formation mechanism of the particles discussed. All of the resultant particles identified as t-ZrO₂ and amorphous SiO₂ with an atomic order dispersion were spherical, and mainly of diameter 0.8 to 1.0m. It was estimated that the three-dimensional ladder siloxane chains containing an equimolar Zr⁴⁺ homogeneously dispersed were formed by hydrolysis, and an atomized droplet itself converted into an isolated ZrO₂-SiO₂ (11) particle without aggregation.     

Deposition of PbTiO3 film by the spray-ICP technique

PbTiO₃ thin films were prepared on various substrates by spraying an ultrasonically atomized aqueous solution of Pb(NO₃)₂ + TiO (NO₃)₂ into an inductively coupled plasma (ICP) under atmospheric pressure. Single-phase PbTiO₃ with perovskite structure was obtained at 500–650 °C. The perovskite obtained below 600 °C showed less tetragonality due to the effect of grain size. The PbTiO₃ films crystallized with preferred (1 1 1) and (0 0 1) orientations on sapphire (0 0 1) and MgO (1 0 0), respectively. Based on the analysis of ICP emission spectra, it is suggested that a reoxidation of titanium preceded that of lead in the plasma, and also that OH in the plasma played an important role in the deposition of PbTiO₃.     

Properties of binary TiO2-SiO2 composite particles with various structures prepared by vapor phase hydrolysis

Various TiO₂/SiO₂ composite nanoparticles were prepared by vapor phase hydrolysis of Titanium Tetraisopropoxide (TTIP) and Tetraethylorthosilicate (TEOS) in a tubular reactor heated by electrical furnace by changing the methods of reactant mixing, the molar ratio of the precursors and the set temperature of the furnace. These variables affected the average size and the bulk composition of the particles as well as their morphological and crystalline structures. The morphological structures of the particles were reconfirmed as T-S, S-T and T/S as in the previous study. Various correlations were obtained between the molar ratio of the precursors, and the size, the composition and the TiO₂ main peak intensity of the particles as a parameter of the mode of reactant mixing. In general, it was found that high content of silicon constituent showed translucent envelopes surrounding primary particles, which increased the dispersion diameter of the particles, reduced the thermal stability, retarded the anatase-to-rutile transformation and the initial photocatalytic degradation of phenol in an aqueous solution.     

Microstructure of plasma dissociated zircon and liquid immiscibility in the ZrO2-SiO2 system

The foam texture developed in plasma-dissociated zircon consists of plane surfaced interlocking grains which contain crystallites of dendritic zirconia embedded in amorphous silica. In the interstices of these grains silica has been segregated. This segregation appears to have come about mainly as the result of supercooling and liquid immiscibility. This accounts for the development of the almost pure silica phase and the formation of a zirconia-rich phase which crystallized to yield dendrites consisting of monoclinic zirconia at ambient temperature. Clear envelopes on the grains were found to consist of amorphous silica-rich material containing zirconia spherulites whose density of development is proportional to the zirconia content of the envelopes.     

化学修饰法制备的ZrO2-SiO2系凝胶薄膜的感光特性研究

本研究采用溶胶-凝胶与化学修饰相结合的方法制备了xZrO2@(100-x)SiO2系薄膜,进一步研究了这种薄膜的紫外光谱特性,发现了当x＞30时,这种凝胶薄膜在335nm附近有较强的吸收峰,这一吸收峰对应于与Zr形成配位体的BzAcH的π-π*迁移.当紫外光照射薄膜后,随着含Zr螯合物的分解,吸收峰也消失,并引起薄膜在有机溶剂中的溶解特性的显著变化,表现出明显的感光特性.这种薄膜经400℃、30min热处理以后,薄膜中的有机物消失,可获得非晶质的ZrO2-SiO2系薄膜,依据这一特性可以用紫外光对这类薄膜进行微细加工.     

Ultrafine ZrO2 powder by Laser Evaporation: Preparation and properties

Ultrafine oxide powders were produced by CO₂ laser evaporation of coarse ZrO₂ powder or compact stabilized ZrO₂ material The 10.6μm radiation in the power range 1–4kW was generated by a transversal flow Co₂ laser which can oscillate in cw and pw operation The vaporization rate depends on the relative position of the focal plane to the surface of the ZrO₂ powder, the laser intensity and the supplied energy input. At a laser intensity of 4.2 · 10⁵ Wcm⁻² the optimum vaporization rate is 130 g · h⁻¹ (cw-operation of the laser). The produced powders consist of spherical particles; their diameters vary in the range from 5 to 200 nm can be controlled by the process conditions. The surface area (BET) is adjustable from 10 to 30 m² · g⁻¹. The powders of unstabilized zirconia show an unusual high content of the tetragonal phase. In case of chemically stabilized zirconia the composition can change during the process of evaporation and recondensation.     

ZrO2-SiO2膜的制备和结构研究

以正硅酸乙酯和氧氯化锆为原料,用溶胶－数胶法制备了无支撑ＺｒＯ２－ＳｉＯ２膜。应用ＤＴＡ－ＴＧ、ＸＲＤ－ＳＥＭ和ＢＥＴ等测试技术对无支撑ＺｒＯ２－ＳｉＯ２膜结构、表面形貌和孔径进行了表征,结果ＺｒＯ２－ＳｉＯ２凝胶膜虽在４６７℃开始出现少量单斜ＺｒＯ２,但在５００℃和１２００℃热处理后的晶相均为四方ＺｒＯ２显然ＳｉＯ２的存在的ＺｒＯ２－ＳｉＯ２膜具有比ＺｒＯ２膜同的热稳定性,在９５０℃欧下发人头发     

Luminescence of nanostructured SnO2-SiO2 glass-ceramics prepared by sol-gel method

Nanostructured silica based glass-ceramics samples of composition (100 - x)SiO2-xSnO2, with x from 1 to 10, have been synthesized by thermal treatment of precursor sol-gel glasses. The average size of the obtained SnO2 nanocrystals, calculated by using the X-ray diffraction, can be predetermined by using well-controlled concentration of tin precursor. The mean radius ranging from 1.6 to 5.5 nm, is comparable to the exciton Bohr radius, corresponding to wide band-gap semiconductor quantum-dots in an insulator SiO2 glass. A spectroscopy study in terms of optical absorption and photoluminescence spectra has been carried out as a function of SnO2 concentration. Size-dependent red-shifts of excitation and emission bands, with increasing of tin precursor concentration, point to the quantum confinement effect. The nanocrystal sizes have been obtained and compared by using the Brus and Scherrer equations. The band gap increase is in agreement with results, based on the effective mass model. The recombination of conduction band electron with oxygen vacancies is proposed to explain the luminescence red-shift.     

溶胶凝胶快速热解法制备ZrO_2超细粉体

采用溶胶凝胶快速热解法制备了ZrO2 超细粉体 ,详细考察了各种制备参数对胶凝时间以及样品性质的影响规律。结果表明 :胶凝时间受溶液中脲含量及胶凝温度影响显著 ;而热解温度、胶溶剂用量、胶凝温度和溶液组成对样品的性状、比表面积、孔分布及粒径均有不同程度的影响