Effect of aluminum silicate fiber modification on crack-resistance of a ceramic mould

To improve the crack-resistance of the mould for silica sol bonded quartz based ceramic mould casting,aluminum silicate fibers with the diameter ranging from 5 μm to 25 μm and the length about 1 mm were dispersed in the ceramic mould.The effect of the aluminum silicate fibers on the tensile strength,shrinkage rate and the cracking trend of the ceramic mould were investigated.In the ceramic slurry,quartz sand was applied as ceramic aggregate,silica sol containing 30% silicon dioxide as bonder,and the weight ratio of quartz sand to silica sol was 2.69;the dispersed fibers changed from 0 to 0.24vol.%.The mould samples were formed after the slurry was poured and gelled at room temperature,and then sintered at different temperatures ranging from 100 to 800 ℃ to measure the tensile strength and shrinkage rate.The results show that,with the aluminum silicate fiber addition increasing from 0 to 0.24vol.%,the tensile strength increases linearly from 0.175 MPa to 0.236 MPa,and the shrinkage rate decreases linearly from 1.75% to 1.68% for the ceramic mould sintered at 400 ℃,from 1.37% to 1.31% for the ceramic mould at room temperature.As the sintering temperature was raised from 100 ℃ to 800 ℃,the tensile strength increases,and the shrinkage rate decreases at all temperatures,compared with those without fiber dispersion,but their variation patterns remain the same.Furthermore,the cracking trend of the mould and its decreasing proportion were defined and analyzed quantitatively considering both effects of the fiber dispersion on the strength and shrinkage.The cracking trend appears to decrease linearly with increasing fiber content and to reach the maximum reduction of 28.8% when 0.24vol.% fiber was dispersed.Therefore,the investigation proposes a new method to improve the crack-resistance of the ceramic mould,i.e.,inorganic fiber dispersion into the ceramic mould.

Effect of SiO_2 concentration in silica sol on interface reaction during titanium alloy investment casting

Using silica sol as a binder for titanium investment casting is very attractive due to its good stability and reasonable cost as compared with yttrium sol and zirconium sol. However, the mechanism of interface reaction in the related system remains unclear. In this investigation, the interface reaction between Y_2O_3-SiO_2(YSi) shell mold and titanium alloys was studied. A group of shell molds were prepared by using Y_2O_3 sand and silica sol with different contents of SiO_2. Ti-6Al-4V alloy was cast under vacuum by gravity casting through cold crucible induction melting(CCIM) method. Scanning electron microscopy(SEM) and energy dispersive x-ray spectroscopy(EDS) were employed to characterize the micromorphology and composition of the reaction area, respectively X-ray photoelectron spectroscopy(XPS) was used to confirm the valence state of relevant elements. White ligh interferometer(WLI) was used to obtain the surface topography of Y-Si shells. The results show that the thickness of reaction layers is below 3 μm when the SiO_2 content of silica sol is below 20 wt.%. Whereas, when the SiO_2 content increases to 25 wt.%, the thickness of the reaction layer increases sharply to about 15 μm. There is a good balance between chemical inertness and mechanical performance when the SiO_2 content is between 15 and 20 wt.%. Moreover, it was found that the distribution of SiO_2 and the roughness at the surface of the shell are the key factors that determine the level of reaction.

Preparation and Characterization of Hybrid Aqueous Dispersions Composed of Silica Sol and Poly(styrene-co-acrylate)

A stable silica sol with 3-5 nm in diameter, which can form homogeneous film without crack, was prepared and characterized. Then, the inorganic-organic hybrid aqueous dispersion composed of such a silica sol and an emulsion of styrene （St） and acrylate （Ac） copolymer was prepared and the hybrid effect between the silica sol and poly（St-co-Ac） was observed by Fourier transform infra-red （FT-IR） spectroscope. The toughness of the film prepared by this kind of hybrid aqueous dispersion was excellent, as it was enhanced appreciably by commixing with a small amount of poly（St-co-Ac） emulsion. Some amino-polysiloxane modified hybrid aqueous dispersions were also prepared and the properties of the modified dispersions and their films were investigated. The experimental results showed that the film prepared with such an amino-polysiloxane modified hybrid dispersion exhibited excellent hydrophobicity and low surface energy after heat treatment for 1.5 h, during which the formation of the graft copolymer was observed. The surface energy of this film decreases as a result of the enrichment of siloxane segments on the film surface.

Synthesis of Nanoscale Shell-core Titania Coated Silica Particles in the Presence of Polyether Polyamine and the Phase Transition

The nanoscale titania coated silica was prepared via a two-step precipitating approach, where the nanoscale silica nuclei were first prepared by passing an aqueous solution of sodium silicate through an ion-exchange resin bed, then coated with the precipitation from hydrolyzed butyl titanate in an ethanol-hexane mixture at a low pH value in the presence of poly(ethylene oxide) polyamine salt(PPA) at a high temperature of 90 ℃. In the second-step precipitating process, the spontaneously precipitated titania shell on the silica nuclei was stabilized in the suspension solution with the help of the adsorption of PPA on the particles. A possible precipitating mechanism was suggested. Furthermore, the amorphous titania shell could undergo crystallization from the amorphous to the anatase structure at a high temperature of 650 ℃, and a further phase transition from the anatase to the rutile structure in the different sintering processes at a rising temperature of 750 ℃.

Research on New Silica Sol Matrix Used in Fluid Catalytic Cracking Reaction

A new silica sol binder was obtained by mixing the acid-modified aluminium sulfate and water glass. The effect of SiO2 concentration in sodium silicate, pH value and polymerization was investigated. The new silica sol binder, which possessed abundant pore volume and suitable acid amount, was an ideal component for preparing cracking catalyst. As a result, the corresponding catalyst comprising the new binder showed excellent performance. Compared with the reference sample, the liquefied petroleum gas(LPG) and propylene yield obtained over this catalyst increased by 3.49 and 1.20 percentage points, respectively. The perfect pore structure and suitable Lewis acid amount of new silica sol were the possible reason leading to its outstanding performance.

Laccase biosensor using magnetic multiwalled carbon nanotubes and chitosan/silica hybrid membrane modified magnetic carbon paste electrode

A simple and rapid strategy to construct laccase biosensor for determination of catechol was investigated. Magnetic multiwalled carbon nanotubes (MMCNT) which possess excellent capability of electron transfer were prepared by chemical coprecipitation method. Scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) were used to identify its surfacetopography and magnetization, respectively. Laccase was immobilized on the MMCNT modified magnetic carbon paste electrode by the aid of chitosan/silica (CS) hybrid membrane. Using current-time detection method, the biosensor shows a linear response related to the concentration of catechol in the range from 10-7 to 0.165×10-3 mol/L. The corresponding detection limit is 3.34×10-8 mol/L based on signal-to-noise ratios (S/N) ≥3 under the optimized conditions. In addition, its response current retains 90% of the original after being stored for 45 d. The results indicate that this proposed strategy can be expected to develop other enzyme-based biosensors.

Experiment on the silica sol imbibition of low-permeability rock mass:With silica sol particle sizes and rock permeability considered

It’s a universal engineering problem to seal micro-cracks of low-permeability argillaceous rock mass by grouting in the fields of civil engineering and mining.This paper achieved the grouting sealing of lowpermeability artificial rocks with the permeability of 0.1–40 mD by adopting silica sol imbibition grouting.The variation characteristics of particle size,viscosity,and contact angle of silica sol during solidification and the pore size distribution of low-permeability artificial rocks were measured,and spontaneous imbibition tests of the artificial rocks were carried out.Finally,combined with the imbibition theory,percolation theory,and fracture medium grouting principle,the silica sol imbibition mechanism of lowpermeability rocks and soil was discussed.The results show that:(1)Silica sol can be injected into artificial rocks with the minimum permeability of 0.1 mD through spontaneous imbibition;(2)The particle size increase of silica sol leads to decreased wettability,affinity,and injectability in grouting materials;and(3)In the range of 0.1–40 mD,the grout absorption first increases and then decreases with increased permeability.The number of large pores and fractures in the rock mass is related to injectability,and the number of small and medium pores is related to the internal driving force of imbibition.This study provides a theoretical basis for silica sol grouting sealing of low-permeability argillaceous rocks and is,therefore,an important reference for application.

Application of Vacuum Drying to Silica Sol Ceramic Mold

Silica sol ceramic mold was made at room temperature with JN-30 silica sol, silica powder and NH4Cl. It is found that the harden time of silica sol ceramic mold is only 0.5 to 1.5 h under the amount of NH4Cl solution of 7% to 8% with 15% concentration, and less surface cracks occur by using vacuum drying. The proper vacuum drying process parameters： vacuum drying temperature is 80 to 100℃, drying time is 5 h and vacuum is 0.06 to 0.07MPa. The harden mechanics, vacuum drying mechanics and the reason of less surface cracks of silica sol ceramic mold by vacuum drying： were also analyzed in this paper.

Facile and Controlled Synthesis of Silica Sol Nanospheres Through a Modifi ed Sol-Gel Process

An effective and reproducible preparation of silica sol nanospheres via a modified sol-gel process has been described. Monodisperse and stable silica sol nanospheres with uniformsize were successfully obtained through the optimized synthesis in which the mixture of tetraethyl orthosilicate （TEOS） and ethanol was followed by the addition of water and ammonium hydroxide （NH3） separately, and the size of silica sol spheres was strictly controlled in the range of 25-119 nm with a narrow size distribution by fine adjustment of several reaction parameters. Results showed that in the presence of low concentration of TEOS, spheres size rose first and reached maximum when H2O concentration was up to 66 g/L. However, the diameter of silica sol spheres decreased above 66 g/L of H2O concentration. Furthermore, it was also found that the size and size distribution of silica sol nanospheres were affected by NH3 concentration. As NH3 concentration increased from 15 to 35 g/L, the diameter declined from 83 to 64 nm. Nevertheless, higher NH3 concentration would result in relatively broad size distribution, and gelation occurred when NH3 concentration reached 44 g/L. In addition, the effect of the different feed rates ofNH3 on the size growth of silica sol nanospheres was also discussed.

Synthesis and Characterization of Polystyrene/Nanosilica Organic-Inorganic Hybrid

A polystyrene（PS）/nanosilica organic-inorganic hybrid material was prepared from styrene monomer and commercial aqueous silica sol containing large amounts of Si-OH by means of emulsion polymerization. The nanosilica sol was modified by the addition of the reactive coupling agent methacrylexy propyltrimethoxysilane （ MPS）, and the resulting latex particles were protected by surfactants such as sodium dodecyl sulphonate（ SDS）, hydroxypropyl methyl cellulose （ HMPC）, and poly （vinylpyrrolidone） （PVP）. The effects of the type of surfactant, the amount of surfactant, and the coupling agent on the shape and stability of the resulting latex particles were investigated. The TEM observation indicates that among SDS, HMPC, and PVP, SDS is the best surfactant. When the content of SDS is 0. 5% and the amount of MPS is 7% in the system, the latex with obvious core-shell structure could be obtained. The average diameters of the monodispersed particles range from 182 to 278 nm, and the average number of silica beads for each composite are 1325 and 4409, respectively. The FrIR analysis shows that PS was chemically linked to silica through MPS. The thermal gravimetric analysis shows that when there is a higher silica content, the hybrid composites have a better heat resistance.

Silica-Dominated Matrix Platform and Its Application in FCC Catalysts

An advanced silica-dominated matrix technology platform and its application were introduced in this paper. Through novel proprietary processing,the advanced silica-dominated matrix was prepared from the unique silica sol and pseudo-boehmite.The matrix pore size distribution and acidity can be tailored to provide optimal coke-selectivity and bottoms-cracking ability matched to feedstock characteristics.A novel FCC catalyst(RSC-2006) for reducing coke and slurry yields was developed based on the silica-dominated matrix technology platform.The results of commercial application of the said technology indicated that the RSC-2006 catalyst exhibited excellent performance on bottoms cracking,coke selectivity and high value products yields.

Preparation of Magnesia Insulation Materials by Walnut Shell Powder Impregnated with Silica Sol

In order to reduce the thermal energy loss of high temperature kilns and furnaces and lower the surface temperature of the kiln body,magnesia insulation materials were prepared using self-made magnesia porous aggregates(using high purity magnesia powder as starting material and potassium oleate as the foaming agent),middle grade magnesia powder,calcium aluminate cement,and SiO_(2) micropowder as starting materials,introducing walnut shell powder impregnated with silica sol(short for Sws)as a pore-forming agent.The effects of the Sws addition(0,10%,15%,and 20%,by mass)and the sintering temperature(1300,1350,1400,and 1480℃)on the properties of magnesia insulation materials were studied.The results show that(1)for the specimens fired at 1480℃,when the Sws addition is 10%,the cold compressive strength is 22 MPa;when the Sws addition is 20%,the thermal conductivity is 0.368 W·m^(-1)·K^(-1)(350℃);(2)nano-silica in the silica sol reacts with MgO in the matrix to form forsterite,which encapsulates the pores volatilized from the walnut shell powder and forms closed pores.

The preparation of high concentration alkaline silica sol with the method of vacuum distillation

High concentration alkaline silica sol has been prepared by the method of vacuum distillation, which shows that the stable and high concentration silica sol can be obtained under conditions as follows： 70℃, vacuum degree of 0.095Mpa and dispersant of SDS. The experimental results show that the sol particles size decreases with mass concentration first and then increase, sol viscosity increases with mass concentration during the concentrating process. The TEM method was used to study the dispersion behavior of sol particles, its result showed that sol particles dispersed more uniformly after concentrating process than before concentrating distinctly. It could be concluded that the disperse degree of alkaline silica sol could be increased by addition of right dispersant. The dispersion mechanism of dispersant in alkaline silica sol was also discussed.

Attrition resistant catalyst for dimethyl ether synthesis in fluidized-bed reactor

Fluidized-bed reactor is a candidate for dimethyl ether （DME） synthesis from syngas because of its excellent heat removal capability. In order to improve the attrition resistance of catalyst, an amount of silica sol as binder was added to the catalyst composed of methanol synthesis component CuO/ZnO/Al2O3 and methanol dehydration component HZSM-5, which was prepared by coprecipitation and shaped by spray drying to get spherical particles. The effect of silica sol on the catalytic activity was investigated in a fixed-bed flow microreactor. Based on the experiment results, silica sol in the range of 0-20wt% had small effect on the catalytic activity. Generally, the CO conversion and DME yield decreased with the increase in concentration of silica sol, while the attrition resistance of catalysts increased with increasing silica sol, indicating that it was feasible to improve the attrition resistance without greatly sacrificing the activity of catalyst. In addition, the characterizations of catalysts were carried out using Brunauer-Emmett-Teller （BET）, X-ray powder diffraction （XRD） and temperature programmed reduction （TPR）.

Influencing Factors of Properties of Castables for Hot Blast Stove Pipes

In order to prolong the service life of castables for hot blast stove pipes,effects of SiO2 micropowder addition and aggregate kind on properties of castables for hot blast stove pipes,and properties of silica sol bonded castables were researched using homogenized bauxite,andalusite particles,andalusite fines,white fused corundum fines,α-Al2O3 micropowder,pure calcium aluminate cement,SiO2 micropowder,and silica sol as starting materials. The results show that：（1） as SiO2 micropowder addition increases,the shrinkage rate of fired specimens increases; BD increases firstly,reaches the highest at 4 mass%,and then decreases; CMOR and CCS of all specimens increase gradually; so the appropriate SiO2 micropowder addition is 4 mass%;（2） the specimens with bauxite aggregate have better CCS and volume stability,but specimens with andalusite aggregate have better thermal shock resistance;（ 3） for castables for hot blast stoves using silica sol as binder,the addition of pure calcium aluminate cement can decrease the linear change rate after treatment at 1 400℃ and can slightly enhance CCS and CMOR,but has very little influence on AP and BD; and the introduction of citric acid worsens the thermal shock resistance of specimens.

Hydration Mechanism of Cement-based Materials with Different Si-rich Mineral Admixtures

Early hydration mechanism of cement-based materials with silica fume, nano-SiO2 and silica sol of different contents was investigated, and the detailed effect of these Si-rich mineral admixtures in three stages of early hydration（NG, I, D） using kinetics model was focused. The results showed that silica fume, nano-SiO2, and silica sol have significant effect on kinetic parameters n, k1, k2 and k3, the fineness and existing form of SiO2 particles in these Si-rich mineral admixtures are two important factors to affect the hydration process and on the parameters. Through integrated use of methods of hydration heat-Krstulovic-Dabic Modelsynthetical thermal analysis, data of hydration heat were collected, hydration degree was characterized, as well as the resulting crystallization behavior of early hydration, to build a numerical relationship between parameter n and CH contents that n decreases with increasing CH, and thus, a direct connection between hydration heat release behavior and crystallization behavior has been established.

Preparation and Processing Properties of Nozzle Plate for Aluminum Continuous Strip Casting

The currently used ceramic nozzles for aluminum deep processing continuous hot rolled strips are featured with good integrity, high strength, good processing prop- erty, but non-uniform structure caused by the migration of silica sol. In this work, nozzle materials were prepared with aluminum silicate ceramic fiber, kaolin, and alumi- num tripolyphosphate as starting materials, silica sol or silica sol -epoxy resin as the binder. After pulping, cast- ing, curing at different temperatures and hot treatment, the prepared materials were analyzed in terms of migra- tion layer thickness, cold modulus of rupture, and micro- structure morphology. The results show that （1） with the same curing temperature, the migration layer thickness of specimens bonded by different binders all decreases with the curing time prolonging; with the same curing time, the migration thickness declines first and climbs then as the curing temperature increases; overall, the specimen cured at 40 ~C for 120 min has the thinnest migration layer; from the comparison, it is found that the silica sol -epoxy resin bonded specimen has slightly thinner mi- gration layer than the specimen bonded by silica sol only; （2） the specimen bonded by silica sol and epoxy resin has thinner migration layer, lower cold modulus of rupture and obvious lower bulk density than the silica sol bonded specimen; （3）the material introduced with epoxy resin has better processing property but slightly lower strength than the material bonded by silica sol.

Synthesis of Si3N4 Powder Using Sawdust as Carbon Source

Si3N4 powder was synthesized by carbothermal re- duction nitridation reaction using sawdust as carbon source and introducing SiO2 by silica sol immersion. Effects of SiO2 content of silica sol, molding pressure, reaction temperature, reaction duration, and N2 flow rate on phase compositions and microstructure of result- ants were studied. The results show that using 7. 5 mass% SiO2 containing silica sol immersed sawdust as raw materials, the prepared Si3N4 powder is featured with high α-Si3N4 content, few impurities, etc. in the conditions of 1 450 ℃ of reaction temperature, 9 h of reaction duration, 400 mL ·min- 1 of N2 flow rate and 10 MPa of molding pressure.

Effect of Variant Counterions on Stability and Particle Size of Silica Sol

The effects of variant counterions with ionic strength of 0.05, 0.10, 0.20 and 0.25 mol·kg^-1 on the stability and particle size of silica sols have been studied using the traditional methods of Ubbelohde viscosity measurement, TEM and titration respectively, finding that the stability and particle size of the silica sols are all concerned with the acidic, positively electric properties and the sizes of the counterions, as well as the attraction between the counterions and surface silicon hydroxyl groups of the silica sols. The small positively charged counterions lead to the decrease in particle sizes, making the silica sol the most stable. But the larger weakly acidic counterions can restrict the particle sizes of the silica sols and easily make the sols coagulate. It was also found that there existed a linear relationship between log r and log η, which has not ever been reported. The effect of temperature on the stability and particle sizes was also discussed.

Electrocrystallizations of copper on glassy carbon in CuCl_2 silica sol and aqueous solutions

Electrocrystallizations of copper from both CuCl_2 silica sol and aqueous solutions were studied by the chronoamperometry technique.It was found that current density contributions of the double-layer charging（iDL） in current-time transients（CTTs） from both of the solutions were large.An adsorption-nucleation based model was proposed to analyze quantitatively the CTTs,by which copper electrocrystallization mechanism was characterized as progressive nucleation with 3D growth（3DP） under diffusion control.The diffusion coefficient of copper ions and the AN_∞products in aqueous solutions were larger than that in silica sols, which indicated that copper nucleation was inhibited in sol solution.The large iDL may be resulted from the adsorption of chloride ions on the electrode surface.