Percolation transitions in porous structure and their effect on physicochemical properties of ceramics

Computer simulation and experimental investigation of zirconia-based ceramics showed that a percolation transition from isolated to communicating pores in this brittle porous material lead to changes in the character of dependence of the elastic properties and structural characteristics on the total porosity.     

The effect of surface modification on physicochemical properties of precipitated silica

The main goal of this study was to obtain hydrophobic silica whose properties would allow their application as plasto- and elastomer fillers. Thus, hydrated silica was modified by silane and titanate coupling agents. The modification procedure and appropriate modification apparatus were developed. The degree of silica surface modification was evaluated by different methods. As grounds for this evaluation, changes in the physicochemical properties, brought about by the condensation reaction of surface silanol groups with alkoxyl or hydroxyl groups of the molecules of coupling agents, were used. The degree of hydrophobicity of the silica surface was determined on the basis of the heat of immersion of this surface, and silanol groups were identified by the infrared spectroscopy. Moreover, changes in the tendency to form agglomerates and aggregates of molecules were studied by microscopy. It was found that modification with silane and titanate coupling agents leads to an increase in silica activity. Application of these agents results in the change of the hydrophilic character to the hydrophobic one. This revised version was published online in November 2006 with corrections to the Cover Date.     

淬火工艺对纳米前驱体三氧化钨功能陶瓷伏安特性的影响

采用自制纳米三氧化钨粉末为原料,以淬火工艺制得纳米基三氧化钨陶瓷.通过I-V特性测量、显微结构和相结构分析,研究了在不同的温度下淬火三氧化钨陶瓷的伏安特性,结果表明较低温度淬火可以使样品的非线性系数提高到10.93,但随着淬火温度(开始淬火温度)的提高,样品的非线性系数急剧下降,当高于900℃淬火时,样品的电学行为转变为线性,非线性系数约为1.对其进行阻抗谱测量,结合相结构与电学行为的关系,认为相结构的不同造成晶界电阻及势垒的不同,改变了电输运特性,从而使其电学行为改变.     

纳米Fe-Cu粉末的制备及其对铁基压坯烧结行为的影响

以化学共沉淀法制备出纳米Fe-Cu复合粉末并对其性能进行了表征,分别以此纳米Fe-Cu粉末和电解Cu粉与铁粉进行混合获得铁基粉末混合料,成形压坯在H2气氛中不同温度下进行烧结,测定基加入不同形态Cu(合金）粉末铁基烧结坯的烧结性能,结果表明,在相同的Cu添加量及烧结条件下,添加纳米Fe-Cu粉末较加入电解Cu粉于铁基压坯中可以明显地提高压坯烧结后的密度,硬度及强度等性能,而添加纳米Fe-Cu粉末压坯在较低温度下烧结可达到添加电解Cu粉压坯在较高温度下烧结后的性能水平,说明采用纳米Fe-Cu粉末形式向铁基压坯中引入Cu有利于制备高密度,高性能的铁基烧结材料。     

The effect of annealing on properties of europium doped ZnO nanopowders obtained by a microwave hydrothermal method

Europium doped ZnO nanopowders made by microwave hydrothermal method are investigated. As zinc oxide precursor zinc nitrate(V) hexahydrate (Zn(NO₃)₂·6H₂O) was used. Two types of nanopowder samples are examined: as grown and annealed at 750 °C in air atmosphere. We investigate the structural, morphological and optical prosperities of europium doped ZnO. Results of scanning electron microscopy, X-ray diffraction, photo- and cathodoluminescence investigations and also CIE1961 chromaticity diagram are presented.     

The gas-sensing properties of thick film based on tetrapod-shaped ZnO nanopowders

Tetrapod-shaped ZnO nanopowders were prepared by the method of vapor-phase oxidation from metallic zinc as raw materials. The gas-sensing properties of thick film based on tetrapod-shaped ZnO nanopowders to volatile organic compounds (VOCs), benzene, toluene, xylene, alcohol and acetone were measured, and compared with that of commercial ZnO powders with granular shape. The results showed that tetrapod-shaped ZnO had the better gas-sensing properties: the maximum sensitivity temperature was reduced, the gas sensitivity was improved and the time of response–recovery was shortened. The differences in gas-sensing properties between the thick films were discussed in according to the morphological characteristics, size and agglomeration of raw powder as well as microstructure of sintered thick films.     

Co-precipitation synthesis of Nd:YAG nanopowders II: The effect of Nd dopant addition on luminescence properties

Nanopowders of Yttrium Aluminium Garnet (Y₃Al₅O₁₂, YAG) doped with neodymium (Nd:YAG, 0.2–24.0 at.%) were prepared using the co-precipitation method followed by an annealing treatment up to 950 °C. For a concentration of neodymium lower than 3.2 at.% the materials were found constituted by the garnet phase according to X-ray diffraction investigations. However, at higher neodymium loading the hexagonal and monoclinic forms of yttrium aluminium oxides were found together with the garnet phase.For Nd quantity lower than 0.8% the luminescence emission spectra appear to be nearly the same, indicating that in the examined range of composition the immediate surrounding of the emitting Nd³⁺ ions is independent of its concentration. For Nd quantity higher than 0.8%, the emission lines have nearly the same peak position, but the band-widths are larger and the relative line intensity increases with neodymium content. A dramatic decrease of two magnitude orders of the luminescence lifetimes occurs with the Nd quantity increase. This behaviour is ascribable to the presence of a secondary phase together with the quenching effects.     

The effect of polyvinyl alcohol addition on the physicochemical properties of ZnO synthesized by ethylene glycol-hydrothermal method

The effect of the addition of very small amount of polyvinyl alcohol (PVA) on the resulting physicochemical properties of ZnO synthesized by ethylene glycol-hydrothermal method was studied. Significant change in particle size distribution and specific surface area can be observed even only 0.02% PVA (w/w) was added into the ethylene glycol (EG) solution, in which the median particle size distribution increased from 5 to 8 nm and at the same time the specific surface area is also increased to nearly 50%. Further addition of PVA resulted in the decrease of the specific surface area due to the formation of agglomeration and aggregation of particles as observed by FESEM study. This study shows that the presence of minute amount of polymer, PVA plays very crucial role in determining the resulting properties of the synthesized ZnO by EG-hydrothermal method.     

制备方法对石墨烯电化学性能的影响

石墨烯处于当今电化学纳米材料研究的前沿,因制备方法多种多样,得到的石墨烯材料性能也存在相当大差异。综述了通过目前流行的制备方法获得的石墨烯的电化学性能研究成果,分析了制备方法间、制备条件间的不同对石墨烯电化学性能的影响。     

The effect of silicon dioxide content of natural stones on their strength properties,material removal rate and power consumption in diamond grinding

The paper addresses the influence of silicon dioxide content of natural stones on their Mohs hardness, ultimate uniaxial compression strength, microhardness as well as on the removal rate and power consumption in diamond grinding of these materials. An increase in the amount of this constituent in natural stones is demonstrated to have an effect on strength properties and power consumption in grinding and a considerable effect on removal rate in diamond grinding.     

微米及纳米金刚石薄膜的制备及其组织性能研究.

采用微波等离子体化学气相沉积(MPCVD)方法在铜衬底上沉积了微米和纳米两种金刚石薄膜,过渡层均为钛一铝一钼.用场发射扫描电子显微镜(FESEM)观察薄膜的表面及断面形貌,用拉曼(Raman)光谱测量所得金刚石薄膜的质量,利用压痕法测试了所得薄膜的附着性能,研究结果表明:过渡层可有效提高微米金刚石薄膜在铜衬底上的附着力,反应气氛中Ar的存在可促使纳米金刚石薄膜的形成,改善薄膜表面的粗糙度.     

The effect of pH on the physicochemical properties of silica aerogels prepared by an ambient pressure drying method

Hydrophobic silica aerogels were successfully synthesized by an ambient pressure drying method from various silicic acids with different pH values which were prepared from water glass. In this study, we selected xylene as the solvent and performed the surface modification in a TMCS (trimethylchlorosilane)/xylene solution, in order to improve the reproducibility of the aerogels. The densities of the aerogels were about 0.10–0.14 g/cm³ and the apparent porosities were in the range of 94.5–96%, depending on the processing conditions. Their specific surface area was in the range of 700–750 m²/g and their average pore size was around 20 nm. The transparency of the as-dried aerogels was enhanced as the pH value was increased. The transmittance of the heat-treated aerogels was slightly decreased with increasing heat-treatment temperature. On the other hand, an abrupt increase in the transmittance was observed when the temperature exceeded 400 °C and this phenomenon might be related to the change in the surface structure caused by the desorption of the methyl groups.     

Effect of surface modification of Grewia optiva fibres on their physicochemical and thermal properties

This paper deals with the surface modification of Grewia optiva fibre through benzoylation and graft copolymerization process. Benzoylation of Grewia optiva fibre has been carried out on mercerized fibre with varying concentrations of benzoyl chloride solution. Graft copolymerization of acrylonitrile (AN) onto Grewia optiva fibre was carried out with ceric ammonium nitrate as the redox initiator in aqueous medium under the influence of microwave radiation. Raw, graft copolymerized and benzoylated fibres were subjected to evaluation of some of their properties like swelling behaviour, moisture absorbance and chemical resistance behaviour. It has been observed that 5% benzoyl chloride treated and graft copolymerized Grewia optiva show more resistance towards moisture, water and chemicals when compared with that of raw fibre. Further morphological, structural changes, thermal stability and crystallinity of raw, graft copolymerized, pretreated and benzoylated fibres have also been studied by SEM, FTIR, TGA and XRD techniques.     

The effect of Tb doping on the structure and spectroscopic properties of MgAl2O4 nanopowders

In this paper, a modified sol-gel method was employed to prepare nanostructured MgAl₂O₄ spinel powders doped with Tb³⁺ ions and thermally treated at 700 and 1000 °C for 3 h. The structural properties of the prepared at 700 and 1000 °C powders where characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). According to obtained XRD patterns the formation of single-phase spinels after calcination was confirmed. The XRD analyses demonstrated that the powders were single-phase spinel nanopowders with high crystallite dispersion. The Rietveld method was applied to calculate lattice parameters. The averaged spinel particle size was determined to be ∼10 nm for calcination at 700 °C and ∼20 nm at 1000 °C. The emission and excitation spectra measured at room and low temperature (77 K) for the samples calcined at 700 and 1000 °C demonstrated characteristic spectra of Tb³⁺ ions. The effect of MgAl₂O₄:Tb³⁺ grain sizes on luminescence properties was noticed.     

Effect of processing methods on physicochemical properties of titania nanoparticles produced from natural rutile sand

Titania (TiO₂) nanoparticles were produced from natural rutile sand using different approaches such as sol–gel, sonication and spray pyrolysis. The inexpensive titanium sulphate precursor was extracted from rutile sand by employing simple chemical method and used for the production of TiO₂ nanoparticles. Particle size, crystalline structure, surface area, morphology and band gap of the produced nanoparticles are discussed and compared with the different production methods such as sol–gel, sonication and spray pyrolysis. Mean size distribution (d₅₀) of obtained particles is 76 ± 3, 68 ± 3 and 38 ± 3 nm, respectively, for sol–gel, sonication and spray pyrolysis techniques. The band gap (3.168 < 3.215 < 3.240 eV) and surface area (36 < 60 < 103 m² g^?1) of particles are increased with decreasing particle size (76 > 68 > 38 nm), when the process methodology is changed from sol–gel to sonication and sonication to the spray pyrolysis. Among the three methods, spray pyrolysis yields high-surface particles with active semiconductor bandgap energy. The effects of concentration of the precursor, pressure and working temperature are less significant for large-scale production of TiO₂ nanoparticles from natural minerals.     

系列功能化离子液体的合成表征及其性质研究

通过两步法合成了含不同阴离子的系列含酯基官能团的咪唑类离子液体,用核磁共振、红外光谱、元素分析对其进行了结构表征,证明了该合成方法的可靠性;对功能化离子液体的基本物化性质及热稳定性等进行了全面研究,并选择了含有相同烷基的未功能化离子液体1-丁基-3-甲基咪唑四氟硼酸盐进行对比,发现酯基官能团的引入,使烷基咪唑类离子液体展现出不同的物化特性。所合成的含酯基功能化离子液体为进一步开展离子液体的各方面研究提供了全新的材料并打下了一定基础。     

Effect of Nd-doping on the optical properties of yttrium aluminum garnet nanopowders

Nd-doped and Nd/Si-codoped yttrium aluminum garnet powders were synthesized via a solvothermal method using ethanol as the solvent. The photoluminescence spectra of the powders revealed that the intensity of the emission increased with Nd-doping concentration initially and then decreased with further increase in Nd concentration. The powder containing 3.5 atm% Nd exhibited the highest light emission intensity. The fluorescence lifetime of the yttrium aluminum garnet powders was also measured as a function of Nd-doping concentration. The results were fitted with an empirical equation.