制备低团聚掺锑氧化锡超细粉体的新方法

以SnCl4·5H2O和SbCl3为原料,用醇盐水解法制备了纳米掺锑氧化锡(ATO)导电粉体。用正丁醇—二甲苯的混合溶剂共沸蒸馏、有机脱水剂以及其它方法对前驱体胶态沉淀进行脱水处理,以消除粉体团聚。运用XRD、TEM、BET等手段对粉体进行表征,比较了各种脱水处理方法对ATO纳米导电粉体的粒度、团聚度、晶粒生长以及电阻率的影响。结果表明,混合溶剂共沸蒸馏处理以及有机脱水剂是比较有效的脱水方法,可以用来制备比表面积大(85.32m2·g—)、团聚小、电阻率低1的纳米ATO导电粉体。     

Preparation and characterization of nanoscale Y-TZP powder by heterogeneous azeotropic distillation

A heterogeneous azeotropic distillation process was effectively used to dehydrate hydrous zirconia and therefore prevent the formation of hard agglomerates in the preparation of nanoscale zirconia powder. The mechanism of azeotropic distillation to prevent hard agglomerate from forming was studied by investigating the interaction of hydrous zirconia with n-butanol. The prepared powder was sintered to 99.5% of theoretical density by slow-sintering (average grain size of 200 nm), 97.5% by fast-sintering (average grain size of 120 nm) at 1250°C.     

沉淀-共沸蒸馏法合成超细钴蓝颜料的研究

利用沉淀-共沸蒸馏法合成超细钴蓝颜料,并采用扫描电镜(SEM)、X射线衍射(XRD)、荧光反射仪现代分析测试技术对样品性能进行表征.结果表明,用正丁醇共沸蒸馏能有效防止干燥过程中颗粒间的团聚.经1000℃煅烧2h后的钴蓝粉体材料具有良好的分散性、结晶度高、外形规则.其蓝光波段反射率为67 %,红光波段反射率为13 %,达到彩色显象管用钴蓝颜料的要求.为实现性能优异、超细钴蓝的国产化提供了借鉴意义.     

乙酸异戊酯共沸干燥法制备低团聚掺锑氧化锡纳米微粉

以SnCl4·5H2O和SbCl3乙醇溶液为原料,用阴离子树脂交换除氯水解法制备得到无氯离子的前驱体掺锑氢氧化锡胶体沉淀。首次对以含氧官能团为主的系列憎水有机溶剂进行了共沸干燥脱水研究,并对所得粉体团聚程度进行比较。实验发现掺锑氧化锡共沸脱水干燥效果与有机溶剂分子结构之间有密切关系,提出了选择共沸有机溶剂的3个原则,在一系列有机溶剂中选择了最符合的乙酸异戊酯进行干燥实验,与常用的正丁醇共沸溶剂进行了消除粉体团聚效果的比较。运用IR、BET、TEM、XRD等方法对掺锑氢氧化锡粉体的结构、比表面积、形貌、物相进行表征。结果表明,乙酸异戊酯溶剂是理想的共沸干燥有机溶剂,其干燥所得掺锑氢氧化锡蓬松粉体的比表面积为284.44m2/g,比用正丁醇处理的增大了22%。将乙酸异戊酯干燥所得的掺锑氢氧化锡微粉经热处理后得到了低团聚的掺锑氧化锡纳米微粉。     

共沸蒸馏法制备超细氧化铝粉体及其表征

用改进的溶胶－凝胶法（ｓｏｌ－ｇｅｌ）制备了单分散纳米级Ａｌ_２Ｏ_３粉体,研究了不同干燥方法对产品粒子性能的影响．结果表明,共沸蒸馏法能够有效地对氢氧化铝凝胶脱水,防止了硬团聚体的形成．在１１５０℃的温度下煅烧,可制得尺寸分布均匀、呈球形的α－Ａｌ_２Ｏ_３超细粉体,其平均粒径为６８ｎｍ．以透射电镜（ＴＥＭ）、Ｘ射线衍射（ＸＲＤ）、热重（ＴＧ）、差热（ＤＴＡ）、比表面测定（ＢＥＴ）等手段对所得的超细Ａｌ_２Ｏ_３粉体进行了表征．     

共沸蒸馏法合成CeO2纳米颗粒研究

分别以乙醇、正丙醇、异丙醇、正丁醇、异丁醇、仲丁醇及叔丁醇等七种有机醇作为共沸剂,采用液相沉淀法结合共沸蒸馏处理前驱体成功合成了分散性良好、粒子尺寸分布为10-20nm的纳米CeO2颗粒,运用TG／DTA、FI—IR、XRD、TEM等方法对不同有机醇的共沸蒸馏作用以及产品性能进行了分析和表征,探讨了共沸蒸馏法制备纳米CeO2的机理。结果表明：共沸蒸馏能起到有效脱除前驱体凝胶中的水分,防止其干燥和焙烧过程中的硬团聚形成的作用,其中七种醇中以正丁醇的共沸蒸馏效果最佳,所得纳米CeO2颗粒的粒度、均匀及分散性能最好。     

Thermal stability and its improvement of the alumina membrane top-layers prepared by sol-gel methods

The thermal stability of unsupported alumina membrane top-layers was studied by determining the pore structure (mainly pore size) change of alumina gels, prepared by sol-gel methods, after sintering at different temperatures ranging from 450 to 1200 °C. The average pore size of the pure alumina membranes and PVA-added membranes increased sharply after sintering at temperatures higher than 1000 °C. Addition of 3% lanthanum, either by mixing lanthanum nitrate in the alumina sol or impregnating lanthanum nitrate into calcined alumina gel, followed by a second heat treatment, can considerably stabilize the pore structure of the alumina membrane top-layers. The pore diameter for the lanthanum-doped membranes was stabilized within 25 nm after sintering at 1200 °C for 30 h, about one-sixth of that for the pure alumina membranes after sintering at 1200 °C for 30 h. The substantial increase in the pore size for the pure alumina membranes at the sintering temperature of 1000 to 1200 °C was accompanied by the phase transformation from -to -alumina. The addition of lanthanum can raise this phase transformation temperature by about 200 °C.     

Solvent effect on ageing of silica gels

The structure of silica gels derived from tetraethoxysilane (TEOS) with molar compositions of TEOSH₂OHNO₃=1100.4 and then aged in various solvents, was studied. The effect of various solvents having different physical properties on the gel structure, as well as the relationship between the solvent properties and the dried gel structure, were investigated. The density, surface area and pore-size distribution were measured. The results of the pore structure and SEM showed the aged gels to have a slit-shaped micropore, narrow pore-size distribution, and homogeneous microstructure. The density, surface area, pore size and pore volume of dried gels changed as the gels were subjected to ageing in various solvents. The surface area could be related to the polarity parameter of the ageing solvent.     

Model for the crystallization and sintering of unseeded and seeded boehmite gels

Boehmite gels crystallize into-alumina with a dendritic morphology and, in thin films, whiskers can be obtained. In bulk gels, vermicular morphologies are observed, their scale depending on the temperature of conversion to-alumina. In seeded gels, where the phase change to occurs at a lower temperature, the scale is much finer than in unseeded gels where a higher-crystallization temperature is required. A model which explains the dendritic morphology is presented; it rests on the hypothesis that the porosity in the gel must be redistributed into the dense-dendrite and the empty interdendritic space at the crystallization front. The dendrite spacing is then determined by the kinetic balance between the rate of crystallization and the rate at which the local porosity is redistributed. Measurements of the crystallization velocity, combined with the model, successfully explain the scale of the dendritic morphologies in the seeded and unseeded bulk gels, and in the seeded gel films. The model predicts that the scale of the dendritic structure should increase rapidly with crystallization temperature, also in agreement with experimental results. The model suggests processing paths for controlling the whisker diameter in seeded films, and for low-temperature sintering of seeded bulk gels.     

Processing effect on structural changes of high acid-catalysed silica gel

The structure of silica gels prepared by hydrolysis of tetraethoxysilane (TEOS) with high acid content has been investigated. The gels were obtained by varying the nitric acid contents at a constant H₂O/TEOS molar ratio of 10. The molar compositions were TEOS: H₂OHNO₃ =110: x(x=0.1–1.0). The effects of acid content and drying temperature on structural changes in the gels were examined. In addition, the surface area, pore volume, pore size distribution, and the microstructure were determined. The results showed that the pore structure changed to larger pore sizes and broader size distributions as a result of increasing the drying temperature. However, at a constant drying temperature, a higher acid content yielded a higher pore volume. The gels dried at lower temperatures had slit-shaped micropores and a narrow pore size distribution; whereas, the gels dried at higher temperatures had ink bottle-shaped pores and a relatively broad size distribution.     

共沸蒸馏法制备单分散氧化镍微粉

先采用均匀沉淀法制得单分散的氧化镍前驱体粉末 ,然后用正丁醇进行共沸蒸馏脱水处理。经干燥、煅烧后成功地制成了单分散性相当好的氧化镍微粉。实验证明 ,共沸蒸馏能有效地脱除湿粉末中的水分 ,丁氧基取代了颗粒表面的羟基 ,从而防止了颗粒间Ni—O—Ni的形成 ,消除了硬团聚形成的可能性。     

醇盐水解法制备二氧化钛纳米粉体

利用控制醇盐水解的方法，分析采用正丁醇共沸蒸馏和乙醇洗涤这两种工艺，详细研究了超细二氧化钛粉体的制备过程，采和ＸＲＤ、ＴＥＤ、ＢＥＴ、ＴＧ和ＤＴＡ等方面对用直接沉淀、正丁醇共沸和乙醇洗涤三种方法获得的粉体进行了表征。发现用直接沉淀和乙醇洗涤法均能获得团聚少、颗粒在１５ｎｍ左右的粉体，且乙醇洗涤能进一步减少粉体的团聚，但共沸蒸馏反而增加了粉体的团聚度。     

Formation of silica nanotubes with spring-like pore channels in the walls

A chiral low-molecular-weight amphiphile, l-16Val6PyBr, was synthesized from l-valine, which can cause physical gels in water, benzene and nitrobenzene. Silica nanotubes with spring-like pore channels in the walls were prepared using the self-assemblies of it as templates via a single-templating approach. The morphologies and pore architectures of the silica nanotubes were studied using transmission electron microscopy (TEM), field-emission scanning electron microscopy, powder X-ray diffraction and N₂ sorptions. The TEM images taken after different reaction times indicated a cooperation mechanism. Moreover, nanoworms with concentric circular pore channels and nanoflakes with vertical pore channels were prepared by changing the concentration of the catalyst.     

Mullite formation from ethyl silicate and aluminium chlorides

The formation of mullite via gels prepared from technical ethyl silicate and aluminium chlorides has been studied. Normally, gels prepared specifically with the oxide stoichiometry of mullite (3Al₂O₃·2SiO₂) do not form the mineral mullite on firing to 1200° C in the absence of a mineralizer. However, when the stoichiometric gel is homogeneous (achieved by acidic or neutral catalysts during the gel preparation) firing at 1200° C can lead to an almost quantitative yield of mullite. For a homogeneous gel, the presence of strontium or caesium salts, or an organo-tin compound such as dibutyltin diacetate or dibutyltin oxide during the gel preparation promotes almost quantitative conversion to mullite at about 1000° C. There is a threshold concentration under which conversion to mullite is incomplete, some cristobalite being formed. For the organo-tin compounds, the type of aluminium chloride is unimportant and the way in which water for the hydrolysis step is added is also unimportant. When the gel is non-homogeneous, the product obtained on firing contains cristobalite and-alumina or-alumina, with little mullite, even if strontium or caesium salts, or organ-otin compounds are present. A ceramic bond is formed from alumina and some other refractory grains during firing.     

Preparation of lithium aluminosilicate glass-ceramic monolith from metal alkoxide solution

Glass-ceramic monoliths with a composition of Li₂O·Al₂O₃·4SiO₂ have been synthesized by the sol-gel technique using metal alkoxides as starting materials. Heating dried gel monoliths of about 36 mm diameter and height to appropriate temperatures gave glass-ceramic monoliths of about 20 mm diameter and height without the occurrence of cracks, while a melt-derived glass body of the same composition was cracked or softened on heating. The glass-ceramic monoliths obtained by heating gel monoliths at 1000 C for 40 h were a porous body, whose bulk density and porosity were 1.62 g cm^–3 and 34%, respectively. On heating gel monoliths, -eucryptite crystals were first precipitated around 750 C, followed by precipitation of -spodumene crystals at 830 C. At higher temperatures the latter grew at the expense of the former phase. The crystallized specimens exhibited very low thermal expansion coefficient ranging from –13-12×10^–7 C^–1 at temperatures from room temperature to 700 C depending on the heat-treatment temperature of gels, indicating that a porous glass-ceramic monolith with ultra-low thermal expansion can be prepared using the present sol-gel method.     

Surface free energy components of silica gel determined by the thin layer wicking method for different layer thicknesses of gel

The influence of the thickness of silica gel layer on the penetration rate of selected liquids and, in consequence, on the value of surface free energy components determined by thin layer wicking method was studied. Plates of the following gel thickness were used: 0.25, 0.5, 1.0 and 2.0 mm. Measurements of the penetration rate of apolar liquids, i.e. three alkanes: octane, nonane and decane, diiodomethane, -bromonaphthalene and two polar liquids: water and formamide were made for this purpose. From the obtained relationships x2=f(t) the suitability of Washburns equation in the whole penetration range (9 cm) was confirmed for all thicknesses of porous layers. However, the penetration rate of probe liquids changed with the thickness of the deposited layer, it was mainly dependent on an effective (apparent) radius of the interparticle pores. Using these results and the appropriate form of Washburns equation surface free energy components of silica gel 60 (for four thicknesses of layer) were calculated. It was found that values of apolar Lifshitz–van der Waals (LWs=41.7±0.9 mJ m-2) and polar acid–base (ABs=11.5±0.5 mJ m-2): electron donor (-s=50.8±0.9 mJ m-2) and electron acceptor (+s0.7±0.1 mJ m-2) components of surface free energy were very similar for different layer thicknesses. Even in the case of a 2 mm thick layer reproducible values of both Lifshitz–van der Waals and acid–base component were obtained. It is important when the thin layers are prepared in laboratory conditions, i.e. from suspensions by water evaporating, and the deposited layer is of less controlled thickness. When diiodomethane and -bromonaphthalene are considered as weakly polar liquids, the value of Lifshitz–van der Waals component of silica gel is very close to LWs determined from n-alkanes.     

Systematic bias in the measurement of water in oils by tubular oven evaporation and azeotropic distillation.

Water in oil has been measured by tubular oven evaporation and by azeotropic distillation into a coulometric moisture analyzer. The results of these measurements were compared to the results obtained by volumetric titration of water in oil. The volumetric measurements were consistently higher than the measurements made by tubular oven evaporation or azeotropic distillation. A mass balance study was performed by volumetric Karl Fischer titration of the water in the oil that remained in the tubular oven and in the distillation apparatus. This study indicated that measurable amounts of water were not removed after exhaustive evaporation or distillation. The sum of the water removed by distillation from toluene and that remaining in the distillation chamber was equal to the amount of water measured in the oil by the volumetric method. The data are consistent with the existence of an oil-water azeotrope that does not release water upon evaporation at 160 degrees C or upon dissolution in toluene and distillation of the water-toluene azeotrope. These results were obtained for oils varying in viscosity from 8 to 850 m2/s, and the amount of water remaining associated with the oil appears to be dependent upon the composition of the oil and the method of analysis.     

Preparation and properties of alumina-baria nano-composites

Barium doped alumina was prepared by calcination of gels obtained from metal chloride solutions by homogeneous precipitation with urea. The gels were either air-dried, oven-dried, microwave-dried or autoclave treated. The materials were analysed by SAXS, XRD, DTA/TG and TEM. The phase composition of the calcined products depended on the gel drying procedure. Barium aluminates formed directly at low temperatures in the microwave treated gel because of the uniform distribution of barium in the dried gel. After calcination at 1200 °C the aluminates were uniformly distributed as nanoscale particles within an -Al₂O₃ matrix. In contrast, autoclave treated samples initially consisted of boehmite crystals coated with barium carbonate which reacted on calcination to form a surface layer of BaAl₂O₄. The autoclaved material withstood 1 h at 1400 °C in air without transformation to -Al₂O₃. This increased thermal stability of transition alumina (-Al₂O₃) is attributed to the presence of the BaAl₂O₄ surface layer. The final transformation to -Al₂O₃ was associated with the transformation of a surface layer of BaAl₂O₄ to nanoscale particles of BaAl_9.2O_14.8.     

Preparation and electromagnetic characteristics of silica coated Fe–Ni–Mo alloy flakes

The Fe–Ni–Mo alloy flakes were firstly prepared from water atomized powders. Subsequently, by a facile sol–gel technique using tetraethylorthosilicate (Si(OC₂H₅)₄) as a precursor, we successfully synthesized silica coated Fe–Ni–Mo alloy flakes. These products were characterized by Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Furthermore, their electromagnetic parameters, complex permittivity and complex permeability within 2–12 GHz were measured. The results show that both and values of the silica coated flakes substantially decrease with the increase of coating times. Meanwhile, the μ′ values of silica coated samples are larger than those of the as-milled sample at the high frequencies. However, the maximum μ′ exhibits a decline while resonance frequency shifts to high values with the increase of coating times. The calculated reflection loss (RL) curve reveals that a proper thickness of coating can redound to improve the absorbing performances of silica coated Fe–Ni–Mo alloy flakes in high frequency range.     

Preparation and properties of borosilicate gels by the reaction of tetraacetoxysilane with boron tri-n-butoxide

The preparation and properties of gels via borosiloxane polymers formed by the reaction of tetraacetoxysilane (TAS) with boron tri-n-butoxide (BTB) in tetrahydrofuran (THF) was investigated. The reaction formed polyborosiloxanes which underwent further condensation to give heterogeneous gels at room temperature and homogeneous gels with (TAS/BTB 2) or without (TAS/BTB = 1) cracks at 60 °C. The addition of ethanol to the reaction mixture formed homogeneous gels under milder conditions. In the presence of hydrochloric acid as a catalyst, transparent round gel plates of B₂O₃ contents up to 34 mol % were obtained by the reaction in the molar ratios of TAS/BTB = 9/2–1/2. Polyborosiloxanes of molecular weight around 1000 were found to be formed. It was found that the consisted of borosiloxanes incorporated with well cross-linked borosiloxane networks, which provided borosilicates containing B₂O₃ up to 30 mol % on heat treatment.