Strength and elasticity of bimodal porous silica prepared from water glass

The bending strength and the Young’s modulus of bimodal porous silica gels having different porosity were evaluated. The porosity of the gel increased by aging the gel under basic conditions, and decreased with increasing the calcination temperature. The mesopores disappeared on calcination at 1,050 °C, whereas continuous macropores retained their morphology up to 1,050 °C for all the samples. Both the bending strength and the Young’s modulus of the bimodal porous silica gels were expressed as power-law functions of the bulk density, and no effect of bimodal pore structures on mechanical properties was observed. We also found linear correlation between the bending strength and the elasticity. The bimodal porous silica had higher strength and elastic modulus compared with other porous materials at the same porosity probably due to the presence of homogeneous micrometer-scale macropores.     

Radiation durability of aluminophosphate glass prepared for the stable storage of high-level nuclear wastes

⁵⁷Fe Mössbauer spectra of 30CaO·15Al₂O₃·5Fe₂O₃·25PbO·25P₂O₅ glass consist of two quadrupole doublets due to distorted Fe(III)O₆ and Fe(II)O₆ octahedra. Mössbauer spectra of the aluminophosphate glass irradiated with⁶⁰Co γ-rays (≈5·10⁴Gy) were essentially the same as those of non-irradiated glass. Mössbauer spectra of γ-ray irradiated aluminophosphate glass, containing 10 stable isotopes (Sr, Y, Zr, Nb, Mo, Ba, La, Ce, Pr, and Nd) as the simulated nuclear waste, were also the same as those of non-irradiated glass. These results indicate that the aluminophosphate glass containing iron and lead has high radiation-durability, in addition to high heat resistivity and high water resistivity.     

Determination of the chemical composition of modified fiber glass silicate materials by differential dissolution

The paper presents the results of application of the stoichiographic method of differential dissolution (DD) to the analysis of modified aluminosilicate and zirconium silicate fiberglass materials (FGM) and related catalysts. Na-Al-Si and Na-Zr-Si FGM have been studied after sodium leaching-out and subsequent modification with Al, Co, and Pt additives. The conditions of detection, identification, and determination of different forms of FGM modifiers and the analysis of the surface of these samples are provided. The DD method has been used for the precise correction of the composition of the fiber glass sample surface.     

Crystallization of X-type zeolite from concentrated sodium silicate and aluminate solutions

Crystallization of an X-type zeolite from concentrated solutions of sodium aluminate (Al₂O₃ 90–330 g l^?1) and silicate (SiO₂ 110–180 g l^?1) was studied.     

Preparation of sodium borosilicates using sodium silicate and boric acid

The gelling behaviour of an aqueous sodium silicate solution with boric acid was investigated for different initial compositions and solid sodium borosilicate samples were obtained by drying the gels at 100°C, 225°C and 450°C. The chemical composition, dissolution, pH, loose-packed bulk density, B.E.T. surface area, moisture, size distribution and XRD/IR patterns of the sodium borosilicate particles were determined. The minimum gelling times were observed at pH values between 9–10 and although no gels were obtained using HCl at pH = 11, the silicate solution was gelled with boric acid suggesting borate ions promote the formation of siloxane network and behave as a crosslinking agent.     

Influence of chemical structure on glass transition temperature of polyimides

A study of the relationship between glass transition temperature of various polyimides and their conformational parameters is presented. The dependence of glass transition temperature on the rigidity of either diamine or dianhydride component is discussed by selecting groups of polymers based each on one diamine and different dianhydrides. The solubility of such polymers is also discussed in connection with the rigidity of their chains.     

Effect of silicate modulus of water glass on the hydration of alkali-activated converter steel slag

Journal of Thermal Analysis and Calorimetry - Converter steel slag, currently underutilized crystalline metallurgical residue, was investigated for use as a precursor for alkali activation. Water...     

XPS characterization of sodium percarbonate granulated with sodium silicate

Granular sodium percarbonate has been characterized by X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The O1s binding energy for the solvating hydrogen peroxide molecules is 535.8 eV. Sodium percarbonate is stabilized by sodium silicate and polyphosphate.     

Effect of chemical structure on combustion and thermal behaviour of polyurethane elastomer layered silicate nanocomposites

The effect of polyol molecular weight and functionality on nanodispersion of clay in PU/clay nanocomposites and the investigation of their thermal and combustion properties are reported and discussed. Lamellar elastomer polyurethane nanocomposites were synthesized using polyols with different molecular weight and functionality and according to these parameters they show several degrees of dispersion which affect their thermal and combustion behaviour. A barrier effect of clay layer is shown in TGA experiments by a delay of thermal degradation products release in nanocomposite materials compared to the virgin polymer; this barrier effect also leads to formation of char during combustion which lowers the peak of rate of heat release in cone calorimeter tests and eliminates fire-induced dripping of the nanocomposite sample during UL 94 test. However, in order to achieve non-burning behaviour nanocomposite technology must be combined with conventional flame retardant technology.     

Optical properties and redox state of silicate glass melts

Advanced experimental techniques to measure the spectral absorption and oxidation state of silicate glass melts are described. Exemplary results of the characterisation of industrial glass melts by these two methods are presented. The technological impact of the high-temperature optical properties and oxidation state of glass melts on radiative heat transfer and on the final glass colour is discussed.     

Preparation of water-soluble sodium deoxycellulosesulfonate from homogeneously prepared tosylcellulose

Water-soluble sodium deoxycellulosesulfonate (DCS-Na) was prepared by nucleophilic substitution of the p-toluenesulfonyl (tosyl) groups of cellulose p-toluenesulfonate (tosylcellulose) by a sulfonate group in aqueous Na2SO3 solution. In the substitution, the yield and degree of substitution (DS) by the sulfonate group (DSsul) were found to increase with increasing reaction temperature and with reaction time, and reached up to 80% and 0.28, respectively, at 100 °C for 72 h. Although the DS of the tosyl group (DStosyl) decreased with increasing reaction temperature and with reaction time, a respectable amount of tosyl group still remained even at 100 °C for 72 h. Furthermore, the intrinsic viscosity, [], of the DCS-Na obtained decreased considerably with increasing reaction temperature and with reaction time. The decreases in DStosyl and [] were very similar to each other in that increasing DSsul was independent of the reaction temperature and the reaction time. The similarity of the decreases suggests that the mechanisms of scission of the cellulose backbone and the leaving of the tosyl groups (from tosylcellulose) in the nucleophilic substitution were closely related to each other. The partial conversion of the tosyl group in the tosylcellulose to the sulfonate group, by the nucleophilic substitution, was also confirmed by the change in the IR absorption spectrum. The product could be considered to be a ter-polymer from the point of view of the AGU (anhydro glucose unit). Thus, we have AGU-co-DAGUS-Na-tosyl AGU as possible options     

The effect of viscosity on nanocrystallization of strontium fluoride from a silicate glass

This paper describes the importance of the viscosity development in the glass-ceramics process with respect to the mechanism of nano crystallization in oxyfluoride glasses. In the glass system under investigation nano crystalline SrF₂ is formed from a silicate glass Na₂O/K₂O/SrF₂/Al₂O₃/SiO₂. The occurring crystallization mechanism is clarified by the variation of the SrF₂ concentration and the resulting structures. As expected, the mechanism shows similarities to other recently described oxyfluoride systems. The feature of the present system is that during cooling of the melt a liquid/liquid phase separation occurs which is not the case in similar systems containing BaF₂. A droplet phase enriched in strontium and fluoride is formed which is embedded in a silicate rich matrix phase. During thermal annealing, nano crystalline cubic SrF₂ is precipitated inside the droplet phase. As a result, the viscosity of the residual glassy phase increases during the course of the crystallization. The crystal sizes do not exceed 8 nm, neither if the annealing time nor if the temperature is increased.     

Predicting glass transition temperatures of linear polymers,random copolymers,and cured reactive oligomers from chemical structure

A reliable semiempirical method for predicting glass transition tempertures of linear polymers, random copolymers, and selected crosslinked networks from knowledge of only their chemical structure is presented. For cases in which new moieties not in the database are encountered, a scaling technique of similar moiety contributions has proven successful. The basic database was composed of 178 linear homopolymers ranging from aliphatic to aromatic heterocyclic polymers and 12 random copolymers. The crosslinked networks investigated in this study involved only diacetylene end-group reactions.     

The three-dimensional structure of water confined in nanoporous vycor glass

Neutron diffraction data, in conjunction with isotopic substitution of deuterium (D) for hydrogen (H), have been analyzed to determine the three-dimensional structure of water confined in vycor, an archetypal hydrophilic porous silica glass containing channels or pores of approximately 40 A diameter. The data have been incorporated into a Monte Carlo computer simulation of the confined water system, and the site-site potentials have been iteratively refined in order to produce a model ensemble which is consistent with both the neutron diffraction data and two possible geometries of the vycor pores (cylindrical and spherical). This approach has allowed us to investigate in detail the contributions to the experimentally accessible partial pair correlation functions, and ascertain whether particular features arise from interactions of the water molecules with the substrate surface, or from purely geometrical confinement effects. We observe a significant decrease in the first shell water oxygen-oxygen co-ordination number, and a decrease in the number of hydrogen bonds per water molecule from approximately 3.6 in bulk water to approximately 2.2 in confinement. In addition, we observe a significant shift inward of the second peak in the water oxygen-water oxygen coordination shell. Overall, we therefore find that the structure of the water in vycor is strongly perturbed relative to the bulk.     

Adhesion of methyl methacrylate copolymers to silicate glass

Adhesion of methyl methacrylate copolymers with acrylic acid, methacrylic acid, and methacrylamide to silicate glass was studied. The copolymers of methyl methacrylate with acrylic and methacrylic acids, compared to poly(methyl methacrylate), are characterized by higher adhesion strength of polymer fi lm-silicate glass joints.     

Adsorption of 1-butanol from water on modified silicate surfaces

The structure and the sorption properties of partially hydrophobized silicates (dodecylammonium and dodecyldiammonium vermiculites) have been investigated in aqueous solutions of 1-butanol. The alcohol is preferentially adsorbed on the surface. The interlayer composition is calculated from adsorption and x-ray diffraction data. In air-dried state the organic cations lie flat on the interlamellar surface. In aqueous butanol solutions, the basal spacing of dodecylammonium vermiculite gradually increases with the extent of butanol adsorption because the chains increasingly point away from the surface. The basal spacing of dodecyldiammonium vermiculite is virtually independent on the interlayer composition because the expansion of the interlayer space is sterically restricted and a relatively rigid structure is formed. The enthalpy of the displacement of water by 1-butanol has been determined by flow sorption microcalorimetry. The displacement process is endothermic.     

Mesostructured silica from amino acid-based surfactant formulations and sodium silicate at neutral pH

We report on the synthesis of hybrid mesostructured silica from aqueous solutions of C₁₂-Glutamic acid and C₁₂-Leucine based surfactant formulations with sodium silicate under neutral pH and atmospheric conditions. The approach shows the challenging task of organizing silica from entirely sustainable sources under environmentally benign conditions.