SiO2 Sol Research Articles

ChemInform Abstract: Preparation and Properties of Clays Pillared with SiO2-TiO2 Sol Particles.

The silicate layers of montmorillonite clay were pillared with SiO2–TiO2 sol particles. Although only the SiO2 sols were negatively charged, the SiO2–TiO2 mixed oxide sols were positively charged and could be ion-exchanged with the interlayer cations of montmorillonite. The resulting pillared clays had a basal spacing expanded to more than 40 A; the spacing was maintained during calcination up to 773 K. The adsorption properties of the calcined samples were studied for nitrogen as well as organic vapors. A structural model for the arrangement of the intercalated sol particles is proposed in which small SiO2–TiO2 sol particles are packed between the silicate layers. Micropores with a slit width of 10–12 A are formed in the interstices between the sol particles and the silicate layers.

Preparation and Properties of Clays Pillared with SiO2–TiO2 Sol Particles

Abstract The silicate layers of montmorillonite clay were pillared with SiO2–TiO2 sol particles. Although only the SiO2 sols were negatively charged, the SiO2–TiO2 mixed oxide sols were positively charged and could be ion-exchanged with the interlayer cations of montmorillonite. The resulting pillared clays had a basal spacing expanded to more than 40 Å; the spacing was maintained during calcination up to 773 K. The adsorption properties of the calcined samples were studied for nitrogen as well as organic vapors. A structural model for the arrangement of the intercalated sol particles is proposed in which small SiO2–TiO2 sol particles are packed between the silicate layers. Micropores with a slit width of 10–12 Å are formed in the interstices between the sol particles and the silicate layers.

Preparation and Thermal Expansion Behavior of Excess SiO<sub>2</sub> Pollucite Powders

Pollucite powders of single phase containing excess SiO2 have been prepared from CsNO3, Al2O3 sol and SiO2 sol by a sol-gel processing. Behaviors of the thermal expansion of these powders have been also studied. As a result of the research for synthesis of the pollucite powders (Cs2O:SiO2:Al2O3 (molar ratio)=1:4.5-5:1), the two-stage heat treatment was the most effective: after the dried samples prepared by the solgel process were heated at 600°C for 24h and were subsequently heated at 750°C for 10h, then the powders were calcined at 1000°C for 50h. The synthesized pollucite powders of single phase containing excess SiO2 showed a low thermal expansion from room temperature to 200°C. Furthermore, it is revealed that the range of temperature showing the thermal expansion less than 0.1% was extended up to 600°C.

Structure and associated properties of concentrated SiO2 sols in dilute salt solutions

Using the Verwey-Overbeek potential (VO) function the various liquid-state properties of SiO2 sols in dilute salt solutions have been evaluated under the mean spherical model approximation (MSMA). The structure factors of these SiO2 sols predicted by this model are compared with results obtained from small-angle neutron scattering experiments by Ramsay et al. Fourier transformation of these structure factors have been performed to obtain the radial distribution functions (RDF), and from these RDF's we computed coordination numbers of the sol particles. The interparticle distancedc of sol particles has been obtained from the peak position in structure factorS(k) by using the Bragg's equation. The surface potential Ψs of the oxide sols has been determined from the amplitude (A) of the VO potential. The present calculations clearly indicate some sort of ordering in the sols system. It is gratifying to note that the present theoretical calculations could reproduce the available observed results very satisfactorily with respect to structure factor and other data.

Contributions to the mechanism of water glass hardening by using thermal analysis methods and X-ray diffractometry

Thermal analysis methods and X-ray diffractometry provided data on and permitted practical use of the eutectic mixture between Na2O·2SiO2 and SiO2, which melts at 790°C. Based on this, water glass was used as a binder to obtain artificial cluster granules, ceramically hardened by heating at 800°C. The process of water glass hardening in the presence of hardening reagents such as Na2SiF6, NH4Cl, silica gel and ultra-fine silica was studied by thermal analysis. In the first stage, gelification of the SiO2 sol takes place by neutralization of the NaOH deflocculant, while the second stage involves tridimensional cross-linking by polycondensation, promoted by powders rich in SiO2.

Alumina as a Matrix for Fixation of Fission Products

ABSTRACTFission products and α-emitters from reprocessing plants ( HAW ) are incorporatedinto a ceramic matrix consisting of 90 w/o α-AI2O3 The amount of HAW in the product is 10 w/o. The matrix is produced by a sol-gel technique using a boehmite powder and a SiO2 sol as starting materials. To reduce the sintering temperature seeding with α-AI2O3 particlesis applied. The first step of the process is mixing of the starting materials with the nitric acid containing HAW. This results in the production of a gel. The gel is extruded and subsequently dried at 105ºC. Calcination is carried out in a hydrogen containing atmosphere. Finally, the material is sintered at 1300ºC. During heat treatment only minor volatilization is observed. Even cesium is almost completely retained sinceit forms an aluminosilicate (Cs2O. xSiO2. yAI2O3; feldspar type). The waste product has a total leach rate of 4 * 10-7g * cm-2 d-1 at 97ºC as determined in a Soxhlet apparatus. Under the same conditions, specific leaching rates of radiologically important nuclides, such as cesium and strontium, are approximately 10-6 g * cm-2 d-1. The process has the advantage that commercially available starting materialscan be used. In addition, only a moderate sintering temperature is required and pressingbefore or during sintering is not necessary.

Preparation and Thermal Expansion Behavior of Pollucite Powders by Sol-Gel Processing

Pollucite (Cs2O⋅Al2O3⋅4SiO2) powders were prepared from a combination of Al2O3 sol, SiO2 sol and CsNO3 starting materials by sol-gel processing, and a stable region of single phase pollucite was investigated. The pollucite powders of single phase were synthesized when Cs2O:SiO2 and Al2O3:SiO2 molar ratios were 0.91-1.02:4 and 0.96-2.38:4, respectively, by standerdizing SiO2 molar ratio. The lattice parameters at room temperature were affected mainly by the Cs2O/SiO2 ratio. It was confirmed by a high temperature X-ray diffractometry that the thermal expansion for the pollucite powders is greatly affected by the change of compositions: The thermal expansion coefficient decreased with decreasing Cs2O/SiO2 ratio from room temperature to 200°C, and increased with increasing Al2O3/SiO2 ratio above 600°C. An increasing tendency of the latter has turned out to be caused by a slight amount of α-Al2O3 formed in the course of calcination. However, such behavior was not observed at the Cs2O/Al2O3 ratio of less than 1.

電解鉄箔を支持体としたＰＳ版の特性

A study was conducted on the effects of treatment conditions on the plate-making properties and printability of pre-sensitized plates having an electroformed iron foil support. This iron foil support had excellent bending properties when electroformed at 90-95°C in a bath containing 800g/L ferrous chloride. The surface roughness of the iron foil increased linearly with foil thickness, which needed to be at least 15μm in order to be used as the presensitized plate. The amount of chromium deposited on the iron foil required to improve its corrosion resistance was 5mg/dm2. When these chromium-plated iron foils were cathodically treated in a suspension consisting of Al2O3 sol and SiO2 sol, their hydrophilic properties and their adhesion to light-sensitive resins were improved. The amount of aluminum deposit required was 1.0-2.0mg/dm2 and the silicon deposit requirement was 0.4-1.0mg/dm2. The structure of the hydrophilic film was examined by ESCA and X-ray diffraction and was found to consist mainly of Al(OH)3 and SiO2, which are appeared to be amorphous. Pre-sensitized plates supported by these treated iron foil supports were capable of printing 50, 000 sheets without problems of staining, spotting, or scumming.

Mechanical Properties of High Purity Sintered ZrSiO<sub>4</sub>

Mechanical properties of ZrSiO4 sintered bodies, fabricated from a synthesized high purity ZrSiO4 powder, were studied at various Si/Zr atomic ratios of ZrSiO4 by the observation of microstructures, The ZrSiO4 powder was prepared by calcining a homogeneous mixture of ZrO2 and SiO2 sols containing ZrSiO4 seed particles, When fired at 1600° to 1700°C, ZrSiO4 sintered bodies had densities of more than 95% of the theoretical density and the grain size was about 2-4μm. The mechanical strength was 320MPa from room temperature to 1400°C. This mechanical property depended on the Si/Zr atomic ratio, and showed the best results at the equimolar composition, Sintered ZrSiO4 bodies had a thermal shock resistance superior to those of mullite sintered bodies or alumina sintered bodies having high stabilities at high temperature.

Microstructure and Mechanical Properties of Mullite Ceramics

Microstructural effects on the mechanical and thermomechancical properties of mullite ceramics have been investigated. The mullite ceramics were fabricated by reaction-sintering of mixture of kaolin and Al2O3(M-1) and by pressureless-sintering of a powder prepered from Al2O3 and SiO2 sols (M-2) and Al2O3 sol-ethylsilicate (M-3) system from the sol-gel method. Transmission electron microscopic observation revealed that samples M-1 and M-2 contained foreign phases, but that they were much less in M-2. These showed different temperature dependence in mechanical properties such as hardness, Young's modules, fracture toughness and strength. These differences were explained by the amount of grain boundary impurity phases. Thermal shock fracture behavior was also discussed.

Preparation of ZrSiO<sub>4</sub> Powder Using Sol-Gel Process (Part 1)

The effect of temperature, heating rate and addition of ZrSiO4 seed crystals on the preparation of ZrSiO4 powders by the sol-gel process was studied using X-ray powder diffractometry. ZrSiO4 powders have been prepared by different precursors in Zr(OPri)4-Si(OEt)4, Zr(OPri)4-SiO2 sol, ZrOCl2⋅8H2O-Si(OEt)4 and ZrOCl2⋅8H2O-SiO2 sol groups. The formation rate of ZrSiO4 was higher in Si(OEt)4 than in SiO2 sol. The formation rate was influenced by heating rate, and, in particular, increased remarkably below 2.5K/min. When a small amount of commercial ZrSiO4 was added to the powder of precursor composition as seed crystals, ZrSiO4 powder with a purity of 94-96% was formed at 1600°-1650°C. It was found that the addition of seeds results in lowering of the formation temperature of ZrSiO4 by about 100°C. On the other hand, a ZrSiO4 powder of 94-96% purity was obtained by heating the powder of precursor composition at 1300°C for 1h, followed by re-heating at 1600°C for 1h. The results have suggested that the preparation of ZrSiO4 powder of nearly single phase is possible using the sol-gel process by controlling the seedings and/or the two-stage heating.