Papers by Keyword: Nanocrystallite

Abstract: BaMoO₄ nanocrystallites were synthesized successfully using Sol-gel process with (NH₄)₆Mo₇O₂₄•4H₂O, BaCl₂•2H₂O, citric acid and PEG400 as original materials. The result shows that well-crystallized BaMoO₄ nanoparticles were formed at 600°C with size of ca.50nm. The synthesized BaMoO₄ nanocrystallites were characterized by XRD and IR, and the optical property was studied as well.

Abstract: A novel crystalline precursor for preparing Y₃Al₅O₁₂ (YAG) nanocrystallite was synthesized via a co-precipitation method using (NH₄)₂CO₃ solution as the precipitator. The precursor was characterized by means of powder X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), thermal gravimetry (TG), differential thermal gravimetry (DTG) and differential scanning calorimetry (DSC), respectively. The empirical chemical formula of the crystalline precursor can be expressed as 5[(NH₄)₂Al₆(CO₃)₃(OH)₁₄]×9[Y₂(CO₃)₃×3H₂O] according to the test results. The measured weight loss of 46.7% of the precursor without consideration of the absorbed water is in accord with the calculated value of 47.5% according to the above empirical formula. The phase-pure YAG nanocrystallites were obtained by calcining the above precursors at 900°C for 2 hours in air atmosphere. Transmission electronic microscopy (TEM) result showed that the particle size of YAG nanocrystallites is 40-80 nm. The mechanism of themal decomposition of the crystalline precursor was also presented.

Abstract: Synthesis of CdS/CdCO₃ Core/Shell semiconductor nanocrystals potentially used for solar cell via hydrothermal route is presented. Water-soluble crystallites with wurtzite crystal structure (CdS), hexagonal structure (CdCO₃) with strong photoluminescence are prepared. The synthesis is based on the separation of the nucleation and growth stages of core and shell by controlling some crucial factors such as temperature, pH, ratio and concentration of reactant mixture. Bare wurtzite structural CdS nanocrystallites were synthesized by using cadmium acetate and thiourea as precursors. Ostwald ripening process under high temperature leads to high sample quality. Photoluminescence of nanocrystals with Core/Shell Structure and bare nanocrystals was compared and analysed. Nanocrystals with Core/Shell Structure have stabler performance of photoluminescence than CdS bare nanocrystallites because of the shell. Transmission electron microscopy and X-ray powder diffraction indicate the presence of bulk structural properties in crystallites as small as 5nm in diameter. X-ray Photoelectron Spectroscopy was used to characterize core/shell structure of as-prepared NCs. Ultra-stability and super strong photoluminescence emission of as-prepared CdS/CdCO₃ Core/Shell semiconductor nanocrystallites indicates its potentially practical value in NCs solar cell.

Abstract: The influence of grain size on the lattice constant in some nanocrystallites of perovskite structure was studied in experiment. Some nanometer ultra fine particles of CaMnO3, Nd0.67Sr0.33MnO3 and Nd0.67Sr0.33Mn0.9Cu0.1O3 were prepared by sol-gel method, which were characterized by XRD, thus phase compositions, lattice constants and grain sizes could be obtained. It was found that their lattice constants all decreased with the decreasing grain sizes. In the end, this phenomenon were explained by the binding energy theory.

Abstract: Using zirconium oxychloride hydrate ( ZrOCl₂•8H₂O) and ammonia water (NH₃•H₂O) as raw materials, and ammonium dihydrogen phosphate (NH₄H₂PO₄) as additives, tetragonal zirconia (t-ZrO₂) with size range of 8–12 nm were prepared by coprecipitation method under hydrothermal conditions. The influence factors on phase transformation and the particle size such as phosphor loading, hydrothermal temperature and calcination temperature were studied by X-ray diffraction (XRD), Fourier transform Roman spectra (FT-Roman), the Brunauer-Emmett-Teller (BET) method and X-ray photoelectron spectroscopy (XPS) techniques etc. Research results show that a small amount of phosphor has been incorporated into the framework of ZrO₂ crystals, producing a certain amount of oxygen vacancies. Phosphor can effectively restrain crystal particles growth and improve the thermal stability of metastable t-ZrO₂. The phosphor doped t-ZrO₂ had a high surface area (244.2 m²/g). In contrast to the pure ZrO₂ particles readily aggregating, the phosphor species deposited on the framework of ZrO₂ crystals prevented the agglomeration of the primary particles during calcinations.

Abstract: M-type BaFe12O19 nanocrystalline aggregations were prepared by the citrate sol-gel method, using Fe(NO3)3 and Ba(NO3)2 as raw materials, urea and ethanol as the soft template. The samples were investigated by SEM, TEM, FT-IR, XRD and VSM. SEM and TEM micrographs show the product is hollow nanocrystalline aggregations with microporous. XRD patterns indicate M-type BaFe12O19 aggregations with mesoporous are purity and well crystallinity, the average size of the primary crystals of the aggregations is 48nm. Saturation magnetization and coercivity of the aggregations is 55.3emu/g and 5403Oe, respectively, which are higher than these of previous BaFe12O19 nano-particles reported in the literature.

Abstract: The influence of grain size on the lattice constant in some nanocrystallites was studied by computing the interactive cohesive energy of the nanocrystallites. The relationships of the lattice constant with the grain size in NaCl, CsCl structure ionic crystallites, FCC, BCC structure metal crystallites and FCC, BCC, SCC structure molecular crystallites was studied respectively. The results are in good agreement with the above experimental ones qualitatively.

Abstract: The influence of grain size on the lattice constant in some nanocrystallites was studied by in experiment. It is found that the lattice constant of NaCl, CsCl structure ionic crystallites decreases with the reduction of the grain size. The lattice constant of ultrafine iron and nickel particles increases with the reduction of the grain size. As to the experiment result of g-Fe2O3 nanocrystallites, the lattice constant increases with the decreasing of the grain size. It is opposite to the theoretical result of ionic crystallites, which reason is that the combination of most of atoms in g-Fe2O3 is by the covalent bond other than electrovalent bond.

Abstract: The intermetallic compounds with a skuttedrudite structure were prepared by powder metallurgy methods including mechanical synthesis and pressure sintering. The obtained powders were subjected to milling so as to obtain powders of a nanocrystalline structure. In this work results of phase analysis carried out at particular stages of powders fabrication are presented and the changes in parameters of their crystalline structure are analysed, including the arrangement of X-type atoms within their crystalline lattice which was studied by the Rietveld method.

Abstract: This article concerned with the formation mechanism of the micro-arc oxidization(MAO) coating on magnesium alloys. The micro-arc oxidation ceramic coating on AZ91 magnesium alloy was prepared in a silicate alkaline solution (Na2SiO3:5-30g/l, NaOH: 1-5g/l, KF: 5-8g/l, Na3C6H5O7: 0.5-2g/l, EDTA: 0.5-2g/l). The experiments were carried out in AC current galvanostatic mode with a current density of 20-50A/dm2. The microstructure of the MAO coating was characterized by means of transmission electron microscopy(TEM). Microcrystallite and/or nanocrystallite were found in the MAO coatings, the size of the former was about 50-200nm and the latter was about 20-50nm. Cellular structure was observed in the coatings, which was composed of a lot of micro/nano grains. The grains grew preferentially in some directions during the MAO process, and the cellular structure is formed by the grains growing in a laminar way. The cellular structures also grew and aggregated by laminar way to form the whole MAO coatings.