Preparation of SiO2 Nanoparticles by Silicon and Their Dispersion Stability

Silicon dioxide sol was synthesized by silicon tn the presence of alkali catalyst. ,SiO2 nanoparticles (size in 8- 15nm) aqueous dispersion was prepared by using dispersion and surface modification in situ. The effects of reaction time, temperature, medium pH value, dispersant and surface-modifier on their diameters, sizes distribution and dispersion stability were also studied. The experimental results show that the preparation method can effectively resolve the dispersion stability of SiO2 nanoparticles in water.     

Preparation of spherical microfine silicon powder

Under certain conditions of proper temperature and pH value, sodium silicate was hydrolyzed in liquid ammonia chloride, and spherical microfine SiO2 powder in micrometer-size was prepared. In this experiment, the relationship between needed time and proper pH value, temperature, density of the solution, and its current capacity were found .The optimum conditions are pH 8.5, 70 ~C, and the concentration of sodium silicate is 0.6 mol/L for the density of the solution. The structure of spherical microfine silicon was characterized by SEM and XRD.     

Process optimization of reaction of acid leaching residue of asbestos tailing and sodium hydroxide aqueous solution

Silica is the major component of the acid leaching residue of asbestos tailing. The waterglass solution can be prepared by the reaction of the residue with sodium hydroxide aqueous solution. Compared to the high temperature reaction method, this process is environmental friendly and low cost. In this paper, the reaction process of the residue and the sodium hydroxide aqueous solution is optimized. The optimum reaction process parameters are as follows: the usage of sodium hydroxide is 26.4 g/100 g acid leaching residue, the reaction temperature is 90℃, the reaction time is 1 h, and the ratio of the liquid/solid is 2.0. The significance sequence of the process parameters to the alkali leaching reaction effect is the usage of sodium hydroxide > the ratio of the liquid/solid > the reaction time > the reaction temperature. The significance sequence to the leaching ratio of SiO2 is the ratio of the liquid/solid > the usage of sodium hydroxide > the reaction time > the reaction temperature. The significance sequence to the modulus of the sodium silicate is the ratio of the liquid/solid > the usage of sodium hydroxide > the reaction time > the reaction temperature. Under the optimum conditions, the leaching ratio of the SiO2 is 77.5%, and the modulus of the sodium silicate is 3.15. The XRD analysis result indicates that the major components of the alkali leaching residue are serpentine, talc, quartz and some albite.     

Synthesis and Microstructure of Doped Alumina Composite Membrane by Sol-Gel Process

1　IntroductionMembranecanbedefinedasasemi permeablebarri erthatpreventsfromintimatecontactbetweentwohomo geneousphases,butallowspreferentialpassageofcertainspeciesacrosstheirsurface .Asamaterialbase,theinor ganicceramicmembranehasexcellentpotentialapplica tionsandadvantages,buttheporesofceramicmembranevarywithacertaincondition,whichhasgreateffectsonthehighselectivity,chemicalandmechanicalstability,andcatalyticproperties.Manyresearcheshavebeencon ductedbyseverallaboratoriestogetabetterporedis …     

Effect of SiO2 on the Preparation and Properties of Pure Carbon Reaction Bonded Silicon Carbide Ceramics

Effect of SiO₂ content and sintering process on the composition and properties of Pure Carbon Reaction Bonded Silicon Carbide (PCRBSC) ceramics prepared with C−SiO₂ green body by infiltrating silicon was presented. The infiltrating mechanism of C−SiO₂ preform was also explored. The experimental results indicate that the shaping pressure increases with the addition of SiO₂ to the preform, and the pore size of the body turned finer and distributed in a narrower range, which is beneficial to decreasing the residual silicon content in the sintered materials and to avoiding shock off, thus increasing the conversion rate of SiC. SiO₂ was deoxidized by carbon at a high temperature and the gaseous SiO and CO produced are the main reason to the crack of the body at an elevated temperature. If the green body is deposited at 1800°C in vacuum before infiltration crack will not be produced in the preform and fully dense RBSC can be obtained. The ultimate material has the following properties: a density of 3.05–3.12 g/cm³, a strength of 580±32MPa and a hardness of (HRA)91–92.3. WU Qi-de: Born in 1949 This work was financially supported by the Key Research Project of the China (No. 96-A10-01-07) and the Key Research Project of the Wuhan (20001001003)     

Preparation of BN／SiO2 ceramics by PIP method

The precursor infiltration and pyrolysis(PIP) method for preparation of BN/SiO2 composites was used to improve mechanical properties, dielectric properties and feasibility of high temperature dielectric parts with large dimensions and complex shapes. In the processing procedure, the porous BN ceramic matrix was first successfully prepared by compacting the mixed powders of B and BN and then sintering them at a certain temperature under normal pressure of N2. The polycarbosilane(PCS) solution was vacuum infiltrated into porous BN ceramics at the room temperature and then at 800℃ in the air to depolimerize out amorphous SiO2, and sintered further at 1 300℃ in N2 to get BN/SiO2 composites. The microstructure of materials was studied by means of X-ray diffraction and electron probe micro analysis. The thermo-decomposition mechanism of PCS was investigated by a TG-DTA and infrared (IR) spectrum analysis. The flexural strengths were measured by the three-point bending method. The dielectric constant and the loss tangent were measured by the wave-guide method. The results show BN/SiO2 composites were fabricated. The obtained composites posses a flexural strength of 61.96 - 93.31 MPa, the dielectric constant in the range of 3.50 - 3.78 and the order of magnitude of the loss tangent at 10^-3 , which are good for the high tempera turedielectric parts with large size and complex shapes.     

Experimental investigation on viscosity of Cu-H2O nanofluids

A procedure for preparing a nanofluid that a solid-liquid composite material consists of solid nanoparticles with sizes typically of 1–100 nm suspended in liquid was proposed. By means of the procedure, Cu-H₂O nanofluids with and without dispersant were prepared, whose sediment photographs and particle size distribution were given to illustrate the stability and evenness of suspension with dispersant. The viscosity of Cu-H₂O nanofluid was measured using capillary viscometers. The mass fractions(w) of copper nanoparticles in the experiment varied between 0.04% and 0.16% with the temperature range of 30–70 °C. The experimental results show that the temperature and SDBS concentration are the major factors affecting the viscosity of the nano-copper suspensions, while the effect of the mass fraction of Cu on the viscosity is not as obvious as that of the temperature and SDBS dispersant for the mass fraction chosen in the experiment. The apparent viscosity of the copper nano-suspensions decreases with the temperature increase, and increases slightly with the increase of the mass fraction of SDBS dispersant, and almost keeps invariability with increasing the mass fraction of Cu. The influence of SDBS concentration on the viscosity of nano-suspension was relatively large comparing with that of the nanoparticle concentration. Funded by Guangdong Provincial Natural Science Foundation (No. 04105950), Specialized Research Fund for the Doctoral Program of Higher Education (No. 20050561017), and Program for New Century Excellent Talents in University (No. NCET-04-0826)     

Preparation and thermoelectric properties of SiO<Subscript>2</Subscript>/<Emphasis Type="Italic">β</Emphasis>-Zn<Subscript>4</Subscript>Sb<Subscript>3</Subscript> nanocomposite materials

A series of SiO₂/β-Zn₄Sb₃ core-shell composite particles with 3, 6, 9, and 12 nm of SiO₂ shell in thickness were prepared by coating β-Zn₄Sb₃ microparticles with SiO₂ nanoparticles formed by hydrolyzing the tetraethoxysilane in alcohol-alkali-water solution. SiO₂/β-Zn₄Sb₃ nanocomposite thermoelectric materials were fabricated with these core-shell composite particles by spark plasma sintering (SPS) method. Microstructure, phase composition, and thermoelectric properties of SiO₂/β-Zn₄Sb₃ nanocomposite thermoelectric materials were systemically investigated. The results show that β-Zn₄Sb₃ microparticles are uniformly coated by SiO₂ nanoparticles, and no any phase transformation reaction takes place during SPS process. The electrical and thermal conductivity gradually decreases, and the Seebeck coefficient increases compared to that of β-Zn₄Sb₃ bulk material, but the increment of Seebeck coefficient in high temperature range remarkably increases. The thermal conductivity of SiO₂/β-Zn₄Sb₃ nanocomposite material with 12 nm of SiO₂ shell is the lowest and only 0.56 W·m⁻¹·K⁻¹ at 460 K. As a result, the ZT value of the SiO₂/β-Zn₄Sb₃ nanocomposite material reaches 0.87 at 700 K and increases by 30%.     

Micaceous iron oxide prepared from pyrite cinders by hydrothermal method

Micaceous iron oxide (MIO) with a hexagonal flaky shape was prepared by hydrothermal method. The ferric hydroxide used as precursor was obtained by an acidic leaching solution of pyrite cinders reacting with ammonia solution. The optimal experimental conditions for preparing micaceous iron oxide were investigated by orthogonal experiments. Micaceous iron oxide can be successfully prepared when optimal parameters of total iron concentration of 2.0 mol/L, pH value of 8, n(Fe²⁺)/n(Fe³⁺) of 0.1, mass of seed crystal of 1 g, reaction temperature of 260 °C and reaction time of 30 min are applied. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffractometry (SAEM) were adopted to characterize the hydrothermal products prepared under optimal conditions. The results indicate that highly crystallized α-Fe₂O₃ hexagonal flakes, about 1.0–1.5 μm in diameter and 0.1 μm in thickness, are prepared. Furthermore, the quality of micaceous iron oxide prepared can meet the required characteristics of micaceous iron oxide pigments for paints (ISO10601—2007).     

Structure and mechanical properties of ZrO2-mullite nano-ceramics in SiO2-Al2O3-ZrO2 system

ZrO2-mullite nano-ceramics were fabricated by in-situ controlled crystallizing from SiO2-Al2O3-ZrO2 amorphous bulk. The thermal transformation sequences of the SiO2-Al2O3-ZrO2 amorphous bulk were investigated by X-ray diffraction, infrared spectrum, scanning electron microscope and differential scanning calorimetric. And the mechanical properties of the nano-ceramics were studied. The results show that the bulks are still in amorphous state at 900 ℃ and the t-ZrO2 forms at about 950 ℃ with a faint spinel-like phase which changes into mullite on further heating. ZrO2 and mullite become major phases at 1 100 ℃ and an amount of m-ZrO2 occur at the same time. The sample heated at 950 ℃ for 2 h and then at 1 100 ℃ for 1 h shows very dense and homogenous microstructure with ball-like grains in size of 20-50 nm. With the increase of crystallization temperature up to 1 350 ℃, the grains grow quickly and some grow into lath-shaped grains with major diameter of 5 μm. After two-step treatment the highest micro-hardness, flexural strength and fracture toughness of the samples are 13.72 GPa, 520 MPa and 5.13 MPa·m1/2, respectively.     

Fabrication and characterization of nano silver powder prepared by spray pyrolysis

Silver powder was fabricated by spray pyrolysis, using 2%–20% AgNO₃ solution, 336–500 mL/h flux of AgNO₃ solution, 0.28–0.32 MPa flux of carrier gas and in the 620–820 °C temperature range. The effects of furnace set temperature, concentration of AgNO₃ aqueous solution, flux of AgNO₃ aqueous solution as well as carrier gas on the morphology and particle size distribution of silver powder, were investigated. The experimental results showed that with the high concentration of AgNO₃ aqueous solution, the average grain size of silver decreased with the increasing of furnace set temperature. But the gain size distribution was not homogenous, the discontinuous grain growth occurred. With the low concentration of AgNO₃ aqueous solution, the higher furnace set temperature made the nano sliver grains sintered together to grow. Nano silver powder about 100 nm was fabricated by spray pyrolysis, using 2wt% AgNO₃ solutions, 336 mL/h flux of AgNO₃ aqueous solution, 0.32 MPa flux of carrier gas at 720 °C furnace set temperature.     

Screening, identification and desilication of a silicate bacterium

The strain Lv（1- z） isolated from the Henan bauxite was characterized by morphological observation, biochemical and physiological identification, and 16S rDNA sequence analysis. The influences of temperature, initial pH value, the volume of medium, shaking speed and illite concentration on the desilicating ability of the strain Lv（1- z） were investigated. The results show that the bacterium is a Gram-negative rod-shaped bacterium with oval endspores and thick capsule, but without flagellum. The biochemical and physiological tests indicate that the strain Lv（1- z） is similar to Bacillus rnucilaginosus. In GenBank the 16S rDNA sequence similarity of the strain Lv（1- z） and the B. rnucilaginosus YNUCC0001（AY571332） is more than 99%. Based on the above results, the strain Lv（1- z） is identified as B. rnucilaginosus. The optimum conditions for the strain L（1- z） to remove silicon from illite are as follows., temperature is 30℃ ;initial pH value is 7.5; medium volume in 200 mL bottle is 60 mL; shaking speed of rotary shaker is 220 r/m ; illite concentration is 1%.     

Flotation de-silicating from diasporic-bauxite with cetyl trimethylammonium bromide

1　INTRODUCTIONTheZetapotentialsofkaolinite ,illiteandchlo riteweremeasuredforthecoalflotation ,allthesethreeclaymineralswerenegativelychargedinthepHrangeof 2 .5 11.0 [1] .Theadsorptionofsodiumdode cylsulfateanddodecyltrimethylammoniumchlorideontokaolinitewasstudiedintheabsenceandpresenceofsodiumhexametaphosphate .Itwasfoundthatthepresenceofthelongchainphosphatedecreasedad sorptionoftheanionicsurfactantbutincreasedthead sorptionofthecationicsurfactant[2 ] .Acommercialmonoetheramineandac…     

Effect of Electron Beam on the Structure and Crystallization Features of BaO-SrO-TiO2-SiO2 Glass

Glasses of BaO-SrO-TiO2-SiO2 after electronic radiation treatment of 50-1000 kgy were studied by means of IR spectra, DTA and visible light absorption method. The result shows that the glass structure is changed due to the formation of structue defect from oxygen vacancy and E‘color center, which resultsd in the crystallization process and new precursors, and decreasement of Tg temperature and crystallization peaks by 20 -50℃.     

Optical and magnetic properties of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> nano-composite films

Fe₂O₃/SiO₂ nano-composite films were prepared by sol-gel technique combining heat treatment in the range of 100–900 °C. The particle size was observed by FE-SEM. Optical properties of the films were investigated by UV-visible spectra. Structural and magnetic characteristics were investigated through FT-IR and VSM. The transparency of the Fe₂O₃/SiO₂ nano-composite films decreased with the content of the Fe₂O₃. Water and organic solvent in the films were evaporated with heat treatment, so the transparency of the films was enhanced under high temperature. It is also found that the saturation magnetization (M _s) of the films increases with the temperature. As the content of the Fe₂O₃ increases, when the content of the Fe₂O₃ is around 30wt%, the M _s of the films has a maximum value.     

Preparation and characterization of Bi4Ti3O12 platelets by a novel low-temperature molten salt system

Bismuth titanate (Bi₄Ti₃O₁₂) platelets were prepared by molten salt method in a new salt system of CaC_l2-NaCl at 650–750 °C, using bismuth nitrate pentahydrate (Bi(NO₃)₃―H₂O) and titanium butoxide (Ti (OC₄H₉)₄) as raw materials. The synthesis temperature of Bi₄Ti₃O₁₂ platelets was decreased to 650 °C from 900–1100 °C. The phase compositions and crystalline morphology of Bi₄Ti₃O₁₂ platelets were investigated by XRD and SEM. The experimental results indicate that Bi₄Ti₃O₁₂ platelets containing tetragonal and orthorhombic phase with the size of 1–3 μm can be synthesized at 650 °C for 2 h, and the orthorhombic phase becomes the dominant phase at 750 °C for 5 h. The size and proportion of Bi₄Ti₃O₁₂ platelets increase with the increment of the calcining temperature and holding time. The proportion of platelets increases to about ninety percent, and the platelets grow up to about 3–10 μm at 750 °C for 5 h from 1–2 μm at 650 °C for 2 h. This technical route provides a new low-temperature molten salt system for preparing platelets by molten salt methods.     

Effect of temperature on polishing and flatting time of float-formed Li<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass

Li₂O-Al₂O₃-SiO₂ glass prepared from traditional melting and cooling process was investigated. The surface characteristic of LAS glass was studied by simulating tin bath with different temperature and time, and the effect of surface tension/viscosity ratio on flatting time was analyzed. The results demonstrated that LAS glass can polish effectively when polishing at 1 300 for 8 °C min, and the optimum flatting and polishing temperature was 1 250–1 300 °C.     

Preparation of ITO nano-powders by hydrothermal-calcining process

1 INTRODUCTIONSn-doped In2O3(ITO) is one kind of n-typesemiconductor material[1].It has excellent electro-optical properties , such as electrical conductivityand high transparency under visible light[2],andiswidely used in electronic , transparent electrode ,solar cells and electro-irradiance , especially inscreen display[3 ,4].Recently nearly half of the met-al indium has been used to prepare ITO materialsin the developed countries[5], such as Japan, A-merica ,France and so on.So the…     

Preparation of Bauxite Ceramic Microsphere

Ceramic microspheres were prepared by using Chinese bauxite as raw materials through the centrifugal spray drying method. The control technology of microsphere size, degree of sphericity was researched. The ceramic microspheres were sintered by a double sintering process. The microstructure and composition of ceramic microsphere were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and X-ray energy spectroscopy. The results show that the degree of sphericity of the ceramic microsphere was good and the particle size was 10-100 μm. The XRD analysis reveals that the main crystalline phase of the ceramic microsphere was a-Al2O3 and mullite （3Al2O3·2SiO2）. The product can be used as reinforced material for composite material, especially for antiskid and hard wearing aluminum alloy coating.     

Pozzolanic Activity of Burned Coal Gangue and Its Effects on Structure of Cement Mortar

The pozzolanic activity of coal gangue burned at different burning temperatures was investigated. The burned coal gangue was mixed with portland cement in different proportions （ 20% - 60% ）. The pozzolanic activity of coal gangue burned and the hydration products were examined, the compressive strengths of the pastes of the mixtures were tested, and the mechanism of the reaction was discussed. The experimental results slum, that the coal gangue burned at 750 ℃ has the optimum pozzolanic activity, and the burned coal ganguc with SiO2 and Al2 O3 is in an active form. When the coal gangue burned at 750℃ is mixed into portland cement, the content of calcium hydroxide in paste is significantly reduced, while the contents of hydrated calcium silk.ate and hydrated calcium aluminate are increased accordingly, hence resulting in the improvement of the microstructure of mortar. The compressive strength of cement paste decreases with increasing the content of burncd coal gangue. The decease in strength is small in the range of 20% - 30% coal gangue substitution and significant in 30%- 60% substitution.