Self-assembled SnO<Subscript>2</Subscript> colloidal particles and their gas sensing performance to H<Subscript>2</Subscript>, C<Subscript>2</Subscript>H<Subscript>5</Subscript>OH and LPG

Using organo-tin Sn(OC4H9)4 as precursor, sodium dodecyl sulfonate (SDS) and SDS-gelatin (SDS-G) complex as template, two tin dioxide colloidal particles were prepared by a self-assembly method. Both SnO2 products were respectively labelled SnO2-B particles with SDS and SnO2-C particles with SDS-G, which are applied in fabricating SnO2 gas sensors corresponding to SnO2-B’ and SnO2-C’ sensors. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermo-gravimetry and different thermal analysis (TG/DTA) were used for characterizations. The experimental results show that SnO2-B colloidal particles are composed of mesoporous piece-like particles, while SnO2-C particles mainly consist of spherical particles. Gas sensing measurements show that SnO2-B’ sensor performs the best sensing response to all target gases, including H2, C2H5OH and liquid petroleum gas (LPG). In particular, the sensing response of SnO2-B’ sensor is achieved at 32 in H2 atmosphere at the concentration of 1000×10-6 M. The gas sensing mechanism was purposely discussed from the electron transfer process and the microstructures of the as-prepared SnO2 products. It is found that serious agglomerations in SnO2-B’ particles facilitate the high gas sensing performance of SnO2-B’ sensor, while mesoporous structures in SnO2-C’ particles decrease the gas sensing response of SnO2-C’ sensor.     

Effects of Nitrogen Doping on Microstructure and Photocatalytic Activity of Nanocrystalline TiO2 Powders

Nitrogen-doped TiO2 nanocrystalline powders were prepared by hydrolysis of tetrachloride titanium （TiCl4） in a mixed solution of ethanol and ammonium nitrate （NH4NO3） at ambient temperature and atmosphere followed by calcination at 400 ℃ for 2 h in air. FTIR spectra demonstrate that amine group in original gel is eliminated by calcination, and the TiO2 powder is liable to absorb water onto its surface and into its capillary pore. XRD and SEM results show that the average size of nanocrystalline TiO2 particles is no more than 60 nm and with increasing the calcination temperature, the size of particles increases. XPS studies indicate the nitrogen atom enters into the TiO2 lattice and occupies the position of oxygen atom. The nitrogen doping not only depresses the grain growth of TiO2 particles, but also reduces the phase transformation temperature of anatase to futile. The photocatalytic activity of the nitrogen-doped TiO2 powders has been evaluated by experiments of photocatalytic degradation aqueous methylene blue.     

Preparation and characterization of CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript>:Sb films deposited on glass substrates by R.F. sputtering

CeO2-TiO2 films and CeO2-TiO/SnO2：Sb （6 mol%） double films were deposited on glass substrates by radio-frequency magnetron sputtering （R.F. Sputtering）, using SnO2：Sb（6 mol%） target, and CeO2- TiO2 targets with different molar ratio of CeO2 to TiO2 （CeO2：TiO2-0：1.0; 0.1：0.9; 0.2：0.8; 0.3：0.7; 0.4：0.6; 0.5：0.5; 0.6：0.4; 0.7：0.3; 0.8：0.2; 0.9：0.1; 1.0：0）. The films are characterized by UV-visible transmission and infrared reflection spectra, scanning electron microscopy （SEM）, Raman spectroscopy, X-ray photoelectron spectroscopy （XPS） and X-ray diffraction （XRD）, respectively. The obtained results show that the amorphous phases composed of CeO2-TiO2 play an important role in absorbing UV, there are Ce^3-, Ce^4- and Ti^4- on the surface of the films; the glass substrates coated with CeO2-TiO2 （Ce/Ti=0.5：0.5; 0.6：0.4）/SnO2：Sb（6 mol%） double films show high absorbing UV（〉99）, high visible light transmission （75%） and good infrared reflection （〉70%）. The sheet resistance of the films is 30-50 Ω/□. The glass substrates coated with the double functional films can be used as window glass of buildings, automobile and so on.     

Valence electron structure and properties of the ZrO<Subscript>2</Subscript>

To reveal the properties of ZrO₂ at the atom and electron levels, the valence electron structures of three ZrO₂ phases were analyzed on the basis of the empirical electron theory of solids and molecules. The results showed that the hybridization levels of Zr and O atoms in the m-ZrO₂ were the same as those in the t-ZrO₂, while those in the c-ZrO₂ rose markedly. The electron numbers and bond energies on the strongest covalent bonds in the m-ZrO₂ phase were the greatest, the values were 0.901106 and 157.5933 kJ/mol, respectively. Those in the t-ZrO₂ phase took second place, which were 0.722182 and 123.9304 kJ/mol, and those in the c-ZrO₂ phase were the smallest, which were 0.469323 and 79.0289 kJ/mol. According to the product of the bond energy on the strongest covalent bond and equivalent bond number (this value reflected the crystal cohesive energy), the order from the greatness to smallness was the c-ZrO₂> t-ZrO₂ > m-ZrO₂. This showed that the m-phase bonds were the tightest, their energy was the smallest, the crystal cohesive energy of the m-phase was the largest, and the m-phase existed most stably at room temperature. So it must need energy or higher temperature to take apart the stronger covalent bonds to form a new phase. Supported by the Major Project of the National Natural Science Foundation of China (Grant No. 90505015)     

Microstructure and mechanical properties of TiB<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites

Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing TiB2-30%Al2O3 can be attained due to the plate-like TiB2 particle and its random orientation and excessive Al2O3 grain growth. When sintering temperature is higher than 1 700 ℃, TiB2 grain growth can be found, which obvious improves flexural strength of TiB2 matrix but decreases toughness. It seems that mechanical properties of TiB2-Al2O3 composites are mainly depended on relative density besides grain growth. otherwise, they will be determined by relative density and TiB2 matrix strength together. Anyway, Al2O3 addition can weaken the grain boundary and thus improve the toughness of the materials. A flexural strength of 529 MPa, Vickers hardness of 24.8 GPa and indentation toughness of 4.56 MPa·m1/2 can be achieved inTiB2-30vol% Al2O3.     

The Mechanism of Sol-Gel Synthesis of Normal Spinel LiMn2O4 with Chelation of Citric Acid

The sol-gel process of citric acid chelating with metal cations for the synthesis of normol spinel LiMn2O4 and the reaction mechanion mechavism were investigated by means of XRD,TG-DTA,and SEM ,the results show that at the beginning lithium citrate and chelate compound of citic acid with manganese ions formed ,and then with heating the esterification and condensation reacions occured between them and glyol ,The products obtained are polymers in which metal cations are distibuted homogeneously on atomic scale that ensur hight reacivity to cations of Li^ and Mn^2 ,Firing the gel grepared by this process ,the lattice diffusions of solid reactant ions caused by non-homogeneity of reactants are elinimated and avoided .At 400℃ phase-pure LiMn2O4 with nanometer scale crystallization having precise stoichiometry and perfect crystallization can be obtained ,The model of chelate coordinated of double -molecule between citric acid and Mn^2 in the gel network is proosed ,It is important for explaining the dispersion state of Mn^2 and the formaiton process of gel by this model.     

Synthesis and photocatalytic property of the ZrO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> pillared laponite

The ZrO2/TiO2 pillared laponite (Ti-Zr-lap) photocatalysts were prepared with intercalation reaction by supercritical fluid drying (SCFD),and characterized by XRD,TEM,SEM and BET surface area analysis,and the photocatalytic properties of Ti-Zr-lap were investigated by degradation of azo dye acid red B (ARB).The results showed that the ZrO2/TiO2 pillared structures in laponite could be formed,with the mass fraction of (Zr4++Ti4+)/laponite (Xm) increasing,the basal spacing and the BET surface area of Ti-Zr-lap significantly increased.The Ti-Zr-lap used as photocatalyst had the advantages of stable and porous layered structure,large surface area with the anatase type TiO2.Compared with the Ti-Zr-lap dried by air drying,the Ti-Zr-lap dried by SCFD showed better photocatalytic property which was very close to that of P25 TiO2.Using the Ti-Zr-lap as photocatalyst with the optimum Xm of 0.16 and the calcination temperature of 500 ℃,under the conditions of the initial concentration of ARB 20 mg/L,photocatalyst concentration of 1.5 g/L and irradiation time 60 min,the decoloring rate of ARB could achieve 98.3%,indicating that the Ti-Zr-lap had excellent photocatalytic property.     

Synthesis and luminescence of nano fluorescent powder of Y<Subscript>4</Subscript>Al<Subscript>2</Subscript>O<Subscript>9</Subscript>: Eu<Superscript>3+</Superscript>

Nano fluorescent powder of Y₄Al₂O₉: Eu³⁺ was synthesized by sol-gel method. The XRD shows that the product prepared at 900°C is pure-phase Y₄Al₂O₉: Eu³⁺. The Y₄Al₂O₉ powder is nano-size crystal testified by BF and ED analysis of TEM. The grain diameter of Y₄Al₂O₉ is in the range between 20 and 50nm, and its average is 30 nm. The luminescent spectra show that Eu³⁺ ious occupy two kinds of sites in Y₄Al₂O₉ crystal lattice. One is in the strict inversion center, and the other is in off lying inversion center. When excited with UV light (λ=254nm), Y₄Al₂O₉: Eu³⁺ exhibits an orange emission bond at λ=590 nm due to the⁵D_o→⁷F₁ transition and a red emission band at λ=610 nm due to⁵D_o→⁷F₂ transition. YUAN Xi-ming: Born in 1951 Funded by Key Scientific and Technological Project of Hubei Province (2001 AA102A03)     

A Modified Co-precipitation Method to Prepare Cu/ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst and Its Application in Low Temperature Water-gas Shift (LT-WGS) Reaction

A modified co-precipitation method for the production of Cu/ZnO/Al₂O₃ complex was studied. The modification was that part of Al was introduced by adding Al³⁺ into Cu²⁺/Zn²⁺ solution, and the rest of Al was added after co-precipitation step in the form of pseudo-boehmite. The prepared samples were characterized by different techniques such as X-ray diffraction, N₂ adsorption, H₂-N₂O titration, temperature programmed reduction and scanning electron microscopy. X-ray diffraction characterizations revealed that Al³⁺ can be doped in aurichalcite lattice, and the maximum doping amount of Al³⁺ was 5.0% of total Cu and Zn atoms. The Cu/ZnO/Al₂O₃ sample produced by the modified method, in which co-precipitated Al³⁺ was 2.5% of total Cu and Zn atoms showed much better activity and stability in water-gas shift reaction than commercial sample. The high Cu surface area (26.1 m²/g) obtained by decompositon of doped aurichalcite is believed to be responsible for the activity enhancement. The stability was enhanced mainly because of the support effect of γ-Al₂O₃, which was decomposed from pseudo-boehmite in the calcination step.     

Investigation on the electrocatalytic characteristics of SnO<Subscript>2</Subscript> electrodes with nanocoating prepared by electrodeposition method

SnO₂ electrodes have many advantages in the degradation of toxic or bio-refractory organic wastewater, and SnO₂ is a kind of anode material which has the potential to be widely used. Electrocatalytic efficiency and service life of TiSnO₂ electrodes are key factors that can influence its applications. In order to enhance the electrocatalytic characteristics of TiSnO₂ electrodes, a type of electrocatalytic electrode with nanocoating was prepared by direct current (DC) electrodeposition method and thermal oxidation technique. With phenol as the model pollutant, the electrochemical degradation efficiencies of electrodes with nanocoating and non-nanocoating were investigated. It was demonstrated that the electrodes with nanocoating have higher efficiency than that of electrodes with non-nanocoating. The degradation time was decreased 33.3% for the same amount of phenol’s degradation. The crystal structure of surface coating, the micrograph of electrode surface and the chemical environment of Sn and Sb in the electrode surface were analyzed with the help of XRD, SEM and XPS. The results showed that the surface of electrode was mainly SnO₂ crystal with rutile structure and that much adsorbed oxygen in nanocoating was the dominant factor for enhancing the electrocatalytic characteristics. Supported by the Excellence Young Teacher Foundation of China Education Ministry and Research Foundation for Outstanding Young Scholars of Heilongjiang Province (Grant No. JC-02-04)     

Synthesis Mechanism and Material Characterization of C<Subscript>4</Subscript>AF Obtained by the Self-propagating Combustion Reaction Method

To investigate the influence of preparation process on the properties of synthesized C₄AF, the powder was prepared via the self-propagating combustion reaction (SPCR) method using urea as fuel and metal nitrates as cation precursors. Synthesis mechanism of the SPCR method, calculation and adjusting principles of urea dosage were detailedly introduced. Material characterization of synthesized C₄AF was performed with the aid of X-ray diffractometry, Fourier transform infrared spectrometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, ²⁷Al nuclear magnetic resonance and isothermal microcalorimetric technique. Remaining content of transition phase of calcium carbonate in synthesized C₄AF was determined by quantitative analysis of X-ray diffractometry. It was found that there was no difference in the hydration behavior of C₄AF synthesized by the SPCR method and the traditional solid-state reaction (SSR) method. C3AH6 and amorphous iron (III) hydroxide (Fe(OH)₃) would be formed during the hydration of C4AF while CH not. Crystallite size of synthesized C₄AF was 16.1 Å and the apparent activation energy was 36.2 kJ/mol. Coordinated condition of Al in C₄AF can be detected by ²⁷Al NMR technique, but the peaks were broadened and the intensities were relatively low, supporting the use of ²⁷Al NMR for the quantitative analysis of C₃A in Portland cements.     

Influence of thickness on the properties of solution-derived LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> thin films

LiMn₂O₄ thin films of different thickness were derived from solution deposition and heat treated by rapid thermal annealing. The phase identification and surface morphology were studied by X-ray diffraction and scanning electron microscopy. The electrochemical properties of the films were examined by galvanostatic charge-discharge experiments and electrochemical impedance spectroscopy. LiMn₂O₄ thin films of different thickness derived from solution deposition and rapid thermal annealing are homogeneous and crack free with the grain size between 20 nm and 50 nm. The specific capacity of these films is between 42 and 47 μAh·cm²·μm⁻¹. The capacity decreases with the increase of discharge current density. The capacity loss per cycle increases from 0.012% to 0.16% after being cycled 50 times as the film thickness increases from 0.18 μm to 1.04 μm. The lithium diffusion coefficients of these films are in the same order of 10⁻¹¹ cm²·s⁻¹.     

Tensile properties of an aluminum matrix composite reinforced by SnO<Subscript>2</Subscript>-coated Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript> whisker

Al18B4O33 whisker was coated by SnO2 particles using a chemical precipitation method, and an aluminum matrix composite reinforced by the coated whisker was fabricated by squeeze casting technique. It is found that the SnO2 coating can react with aluminum matrix during squeeze casting process, and Sn particles are induced near the interface between Al18B4O33 whisker and matrix. The tensile test at room temperature indicated that the tensile strength of Al18B4O33 whisker reinforced aluminum matrix composite can be enhanced by suitable content of SnO2 coating. The composites with various whisker coating contents exhibit maximum tensile plasticity at about 300 ℃, and the composite with a suitable whisker coating content could enhance its tensile plasticity evidently, which suggest that an Al18B4O33 whisker-Al composite with both high strength at room temperature and high formability at elevated temperature can be designed.     

Controlled preparation of monodisperse CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by a facile method

CoFe2O4 nanoparticles (NPs) were synthesized by coprecipitation method using FeCl3·6H2O and CoCl2·6H2O as precursors.The synthesized conditions were optimized,such as added means of precipitator,quantity of precipitator,the mol ratio of Fe 3+ to Co2+,reaction temperature and pH value.The synthesized material was characterized by XRD,TEM,FTIR,EDS,Raman and its magnetic properties were studied by VSM.The experimental results confirm that the sample is cubic spinel structure CoFe2O4 with a narrow size distribution and a good dispersion feature.CoFe2O4 NPs with well-controlled shape and size was obtained at 70℃.The magnetic properties indicate superparamagnetic behavior and good saturated magnetization.     

Preparation and characterization of nanocomposite MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

Nanocomposites MgFe₂O₄/SiO₂ were successfully synthesized by the sol-gel method in the presence of N, N-dimethylformamide (DMF). The formation of pure MgFe₂O₄ was confirmed by powder X-ray diffraction (XRD) and electron diffraction. The structural evolution of MgFe₂O₄ nanocrystals was followed by powder X-ray diffraction and IR absorption spectroscopy. The formation of spinel structure of MgFe₂O₄ started at 800 °C, and completed at 900 °C. The transmission electron microscopy (TEM) measurements suggest that the particle sizes increase with the increasing annealing temperature, and the mean particle sizes of the spherical samples annealed at 800 °C, 900 °C and 1 050 °C are ca. 3 nm, 8 nm and 11 nm, respectively. Magnetization measurements at room temperature and 78 K indicate superparamagnetic nature of these MgFe₂O₄ nanocrystals. Funded by the National Natural Science Foundation of China(No. 30771676), the Natural Science Foundation of Jiangsu Province (No. BK20081842), and the Foundation of Nanjing Bureau of Personal for the Returned Overseas Chinese Excellent Scholars     

Preparation and Upeonversion Lumineseenee ofNanoerystailine Gd2O3： Er^3＋, Yb^3＋

Nanocrystalline Gd1.77Yb0.2Er0.03O3 samples were prepared by combustion and precipitation methods. Structures and upconversion luminescence properties of samples were studied. The results of XRD show that all samples are cubic structure, the average crystallite size could be calculated as 23 nm and 39 nm, respectively. The lattice constants were obtained. The FT-IR spectra were measured to investigate the vibrational feature of the samples. Upconversion luminescence spectra of samples under 980 nm laser excitation were investigated. The strong red emission of samples were observed, and attributed to 4F9/2→4I152 transitions of Er^3＋ ions, the emission intensity for sample synthesized by precipitation method is stronger compared to that of combustion method. The possible upconversion luminescence mechanisms in nanocrystalline Gd1.77Yb0.2Er0.03O3 were discussed.     

Solid Solution Characteristics of Pb（B1/3Nb2/3）O3-bascd Composite Ceramics

The solid solution characteristics of Pb（B1/3Nb2/3）O3-based （B=Zn^2＋, Mg^2＋, Ni^2＋） composite ceramics prepared by two-phase mixed-sintering method were developed based on dielectric measurements. Results show that there are double dielectric peaks for PZN-based composite ceramic, implying two phases coexist. However single dielectric peak was presented in PMN- and PNN-based composite ceramics, respectively. It is indicated that obvious solid solution reaction exists during the sintering process of these two systems. The effects of B-site ion difference on the solid solution characteristics were discussed by crystal chemistry. SEM was employed to investigated the microstructures of composite ceramics. The influences of solid solution reaction on grain growth were discussed.     

Devitrification behaviour of rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy prepared by melt spinning method

Rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy was prepared by using melt spinning. Its calorimetric behavior was characterized by using differential scanning calorimeter in a continuous or isothermal heating mode. phase transformation was investigated, with a special interest in primary crystallization, by using an in-situ examination of X-ray diffractometry （XRD） and high resolution transmission electron microscopy （HRTEM）. The results show that, the whole devitrification of rapidly solidified Al87NiyCu3Nd3 amorphous alloy involves two main processes of primary crystallization and secondary crystallization that consist mainly of two reactions. For primary crystallization, the apparent activation energies, EIso and EKis and growth activation energies Eg are about 153, 166 and 288 kJ/mol, respectively. The interdiffusion of Al atoms is a rate-controlled step of formation of the a（Al） particles, but slow diffusion of Ni and Nd atoms plays a significant role in retarding growth of the α （Al） particles. For secondary crystallization, EIso, EKis and Eg of the first reaction are about 291,208 and 290 kJ/mol, and those of the second reaction are about 367, 269 and 372 kJ/mol. The two reactions of secondary crystallization are controlled mainly in an interface-controlled three-dimensional mode, depending mainly on slow diffusion of Ni and Nd atoms.     

Study on the isothermal oxidation behavior in air of Ti3AlC2 sintered by hot pressing

The isothermal oxidation behavior at 900–1300°C for 20 h in air of bulk Ti₃AlC₂ with 2.8 wt% TiC sintered by means of hot pressing was investigated in the work. The isothermal oxidation behavior generally followed a parabolic rate law. The parabolic rate constants increased from 1.39×10⁻¹⁰ kg²·m⁻⁴·s⁻¹ at 900°C to 5.56×10⁻⁹ kg²·m⁻⁴·s⁻¹ at 1300°C. The calculated activation energy was 136.45 kJ/mol. It was demonstrated that Ti₃AlC₂ had excellent oxidation resistance due to the continuous, dense and adhesive protect scales consisted of a mass of α-Al₂O₃ and a little of TiO₂ and/or Al₂TiO₅. In principle, the oxide scale was grown by the inward diffusion of O²⁻ and the outward diffusion of Ti⁴⁺ and Al³⁺. The rapid outward diffusion of cations usually resulted in the formation of cracks, gaps, and holes.     

Thermochemical Study of Mixed Ligand Complexes of Rare Earths with Glycine and L-alanine

In order to obtain the standard molar enthalpies of formation of Rare-Earth amino acid coordination compounds, precise isothermal solution-reaction calorimetric method was used. The value of Δ_rH _m ^Θ of two coordination reactions was determined at T=298.2 K. From the experimental results and other auxiliary values, the standard molar enthalpies of formation of Ln(Gly)_5/2(Ala)_3/2(ClO₄)₃·H₂O(s) [Ln=La, Yb] at T=298.2 K were obtained. The values of them is to be Δ_rH _m ^Θ [La(Gly)_5/2(Ala)_3/2(ClO₄)₃·H₂O(s)]=−3545.45 kJ/mol and Δ_rH _m ^Θ [Yb(Gly)_5/2(Ala)_3/2)(ClO₄)₃·H₂O(s)]=−3793.81 kJ/mol, respectively. QU Jing-nian: Born in 1954 Funded by the Teaching and Research Award Program for Outstanding Young Professors in High Education Institute, Ministry of Education, P. R. China