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PubMed2004

Fracture of silicate glasses: ductile or brittle?

Atomic force microscopy is used to investigate the possibility of cavity formation during crack growth in silicate glasses. Matching areas on both fracture surfaces were mapped and then compared. For silica glass, and soda-lime-silicate glass, the fracture surfaces matched to a resolution of better than 0.3 nm normal to the surface and 5 nm parallel to the surface. We could find no evidence for cavity formation in our study and suggest that completely brittle fracture occurs in glass.

Journal Article↗
PubMed2005

In situ Brillouin spectroscopy of a pressure-induced apparent second-order transition in a silicate glass.

Brillouin scattering measurements of a silicate glass, carried out at high pressures in the diamond anvil cell, show a dramatic increase in the pressure dependence of longitudinal velocity, and a discontinuity in the compressibility of the glass at about 6 GPa. While a first-order phase transition has been documented under pressure within amorphous ice, we demonstrate that an apparent second-order transition to a new, structurally distinct amorphous phase can occur via the abrupt onset of a new compressional mechanism, which may be triggered by a shift in polymerization of the glass or an onset of a change in coordination of silicon, within pressurized amorphous silicates.

Journal Article↗
PubMed2006

Interfacial reactions and silicate formation in highly dispersed Lu2O3-SiO2 system.

Solid state interface reactions in highly dispersed Lu2O3-SiO2 binary oxide system were studied at 600-1100 degrees C with X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared spectroscopy (FTIR). The results show that at 600-900 degrees C an amorphous, nanometer thick Lu-O-Si layer covering SiO2 particles exists in the system. At higher temperatures the breakage of the layer into amorphous islands occurs and crystalline silicates with various structures are formed. In particular, Lu4[Si3O10][SiO4] silicate, analogue of B-type Dy-Tm disilicates, forms at 1000 degrees C.

Journal Article↗
PubMed2004

Mesoporous silicates prepared using preorganized templates in supercritical fluids.

Well-ordered mesoporous silicate films were prepared by infusion and selective condensation of silicon alkoxides within microphase-separated block copolymer templates dilated with supercritical carbon dioxide. Confinement of metal oxide deposition to specific subdomains of the preorganized template yields high-fidelity, three-dimensional replication of the copolymer morphology, enabling the preparation of structures with multiscale order in a process that closely resembles biomineralization. Ordered mesoporous silicate films were synthesized with dielectric constants as low as 1.8 and excellent mechanical properties. The films survive the chemical-mechanical polishing step required for device manufacturing.

Journal Article↗
PubMed1967

Siliceous urinary calculi in calves: prevention by addition of sodium chloride to the diet.

Urinary calculi were found in all but one of 14 calves given a ration associated with the formation of siliceous calculi. No calculi were found in a similar group of 14 calves given the same ration with sodium chloride added (4 percent). It is suggested that sodium chloride prevented calculus formation by in creasing water intake and urine volume, with a consequent reduction in the con-centration of silicic acid in the urine

Animals↗
PubMed2000

[Coordination and local structure of Si and Al in silicate glasses and melts: X-ray absorption spectroscopic study].

The coordination and local structure of Si and Al in silicate glasses and melts have been studied using Si and Al K-edge X-ray absorption spectroscopy for the first time. It has been verified that in SiO2-P2O5 and Na2O-SiO2-P2O5 join phosphate silicate glasses, Si atoms remains tetrahedrally coordinated with oxygen when the content of P2O5 is below 32 mol%, but partial Si atoms become octahedrally coordinated with oxygen when the content of P2O5 increases above 32 mol%, and the proportion of the octahedrally coordinated Si atoms increases with the increasing content of P2O5. It has also been demonstrated that Al remains four-fold coordinated with oxygen in ambient NaAlSi2O6-NaAlSi3O8 glasses, but in the same composition glasses quenched at 4.4 GPa and 1,575 degrees C, partial Al atoms becomes five- and six-fold coordinated with oxygen, and at the same pressure and temperature, the proportions of five- and six-fold coordinated Al atoms increases with the increasing content of NaAlSi2O6 in the glasses. Thus, the pressure-induced coordination change of Al in aluminosilicate glasses and melts has been observed for the first time by Al K-edge X-ray absorption spectroscopy.

English Abstract↗
PubMedDate not supplied

[Structural research on silicate dental materials].

Comparative studies of the structural features of Gamma porcelain, Sikor glass ceramic, and Cast Glass Ceramic (CGC) by x-ray structural analysis and IR spectroscopy have revealed that improvement of the physical characteristics of stomatological silicate material in transition to glass ceramic is explained by similarity of their composition with lithium disilicate. CGC structure due to convergence of the composition of the major areas of chemical heterogeneities is the most compact as compared to Sikor structure and more so us. Gamma. As evidenced by IR spectroscopy, super microhardness of CGC, observed in practice, appears to be related to their higher solidity in contrast to that of Gamma porcelain, structurally similar to amorphous silica, and that of Sikor characterized by a poorly crystallized tridymite structure. Higher physical characteristics of CGC distinguish it among the known silicate materials used in dentistry and recommend it for wide practice.

Ceramics↗
PubMed1994

Polyclonal human T-cell activation by silicate in vitro.

Silica (SiO2) or related substances such as silicone ([-R2Si-O-]n), which is used in plastic surgery, or asbestos (e.g. chrysotile; 3MgO.2SiO2.H2O) have 'adjuvant effects'. In a study of scleroderma patients in Germany more than 78% had experienced exposure to silicate dust. T-cell receptor (TcR) V beta gene analysis on CD4- CD8- double-negative alpha beta T cells from scleroderma patients, using polymerase chain reaction (PCR), showed that certain V beta genes, V beta 5, V beta 7 and V beta 17, were predominantly expressed in the cells. We found that certain V beta repertoires, V beta 5.3 and V beta 6.7, were predominantly expressed on fractionated T cells with a high Ca2+ level that had been stimulated by chrysotile in vitro. The intracellular Ca2+ level in human peripheral blood mononuclear cells (PBMC) increased after incubation with silica or chrysotile. Interleukin-2 (IL-2) release from PMBC also rose significantly with chrysotile stimulation, but no change was observed when major histocompatibility complex (MHC) class II DP/DR positive cells were depleted. Therefore, our results support the possibility that silicate acts as a superantigen.

Adult↗
PubMed1994

An optical biosensor based upon glucose oxidase immobilized in sol-gel silicate matrix.

Glucose oxidase immobilized in a transparent silicate gel prepared by a sol-gel method was used as a simple solid-state optical biosensor for glucose. The sensor was based upon the measurement of initial rates of reduction of the FAD prosthetic group of the enzyme in the presence of various concentrations of glucose. The analytical range of the sensor was 1-100 mM, and the measurement time was 2 min. The enzyme was considerably protected by the silicate matrix against leaching, thermal inactivation and even H2O2-dependent inactivation. The sensor was stable in daily use for 6 months.

Aspergillus niger↗
PubMed1985

In vivo corrosion of sodium silicate glasses.

Square-shaped implants of various sodium silicate glasses were weighed and implanted intraperitoneally in rat for periods ranging from 8 to about 60 days. The implants were then removed and their aspect was compared to their aspect before exposure to physiological environment. The corrosion products were studied by x-ray diffraction and electron microprobe analysis. Weight changes were also measured to calculate a biodegradation rate. The glass 66 SO (66.6 SiO2-33.3 Na2O) was strongly corroded, as early as after the first week. The nonsoluble degradation products formed a cocoon encapsulating the now smaller specimen. The analysis of the cocoon showed that it was made of a silica-rich layer containing also calcium and phosphorus. In this layer the ratio Ca/P could correspond to that of an apatite. The biodegradation rate reached 71 x 10(-4) g . cm-2 . day-1. The glass 75 SO (75 SiO2-25 Na2O) was not so quickly corroded: Cracks appeared at the surface and progressively reached the center of the implants. There was no removable shell but a white deposit, adherent to the surface. This deposit contained silica and also calcium and phosphorus at the periphery. The biodegradation rate was only 2.6 x 10(-4) g . cm-2 . day-1.

Animals↗
PubMed1988

Further experiences in the treatment of cystic craniopharyngeomas with yttrium 90 silicate colloid.

20 patients suffering from cystic craniopharyngioma were treated with intracavitary irradiation on 25 occasions. The beta emitting radionuclide 90Y silicate colloid was instilled into the cyst or cystic part of the tumour. 17 patients on 22 occasions underwent follow-up CT and ophthalmological examinations 1 to 144 (average: 34) months after the intracavitary radioisotope therapy. An 23 occasions there was an average of 82 to 90% volume decrease of the craniopharyngioma cysts. On two occasions the volume has remained unchanged and the result of the 90Y therapy cannot be evaluated yet. The neuroophthalmological prognosis was good only when a relatively intact optic disc was seen; when the disc was atrophic the visual deterioration proved to be irreversible. Pathologically, it is the fibrotic tissue that is responsible for the shrinkage of the cyst.

Brain Neoplasms↗
PubMed1985

Lead silicate toxicity: a comparison among different compounds.

The aim of this report is to point out the relative toxicity of different commercial products containing lead silicates by studying their in vitro solubility and rate of absorption via the respiratory and digestive systems, compared with those of red lead (lead tetroxide). In vitro solubility was tested, by a modified Brimsdown method, with bidistilled water, saline, blood serum, pleural fluid, and dilute hydrochloric and acetic acids as solvents. Experimental animals were administered 25 mg equivalent mean doses using an intragastric tube or endotracheal intubation. Results showed that in vitro solubility gradually increases from distilled water, through saline and biological fluids, to acidic media. Lead absorption via the respiratory system is rapid and persistent, with small differences among the tested compounds. Less information can be gained from intragastric experiments. No correlation was found between in vitro solubility and in vivo absorption. On the other hand, in vitro studies must be strictly standardized. The relative absorption of the different materials, compared with red lead showed that all of them have to be regarded as equally toxic.

Absorption↗
PubMed1986

Adsorption thermodynamics of carbofuran on antimony (V) silicate cation exchanger.

The adsorption thermodynamics of carbofuran has been studied on antimony (V) silicate cation exchanger at 30 and 50 degrees C. The adsorption isotherms of carbofuran have been found to follow the Freundlich adsorption model and yield "S" class isotherms. The order of adsorption of carbofuran is in accordance with the partial molal free-energy changes in the exchanger. The thermodynamic equilibrium constant (K0), standard free energy (delta G degrees), enthalpy (delta H degrees), and entropy (delta S degrees) changes have also been calculated for predicting the nature of adsorption.

Adsorption↗
PubMed2003

A hybrid zinc-calcium-silicate polyalkenoate bone cement.

A novel bone cement composed of sintered zinc-calcium-silicate phosphate and hybrid polyalkenoates has been developed. Synthesis and formulation of glass fillers, monomers and polymers as well as formulation of the cement were described. The effects of sintering, polymer content, glass powder/polymer liquid (P/L) ratio and comonomer on compressive strength (CS) and curing time (CT) were investigated. The effects of P/L ratio and comonomers on shrinkage as well as exotherm were also studied. Results show that the experimental cement was 61% higher in CS, 10% lower in diametral tensile strength, 35% lower in flexural strength, 62% less in exotherm, and 68% less in shrinkage, compared to conventional polymethylmethacrylate cement. With increasing polymer content and P/L ratio in the cement formulation CS of the cement increased but CT decreased. Curing time, shrinkage and exotherm of the cement decreased with increasing P/L ratio. It appears that this novel cement may be a potential candidate for orthopedic restoration if its biological performance is good and formulation is optimized.

Biocompatible Materials↗
PubMed1985

Interaction of type I collagen with sepiolite (magnesium silicate).

Type I collagen from calf skin interacts with magnesium silicate (sepiolite) resulting in a collagen-clay complex which is separated by centrifugation. The interaction primarily occurs with high molecular weight aggregates of the protein as indicated by the fact that collagen from the skin of lathyritic rats interacts to a lesser extent. Thus, when calf skin collagen is fully retained, 45% of protein from lathyritic animals remains in solution. Monomeric forms of collagen remain soluble after short periods of interaction with sepiolite; at 5 minutes, 34% of the calf skin collagen preparation is recovered in apparently monomeric form. In contrast protein-protein interaction produces the complete retention of the total collagen with longer periods of time.

Animals↗
PubMed1993

Role of microenvironmental deterioration of the bone marrow in the development of bone atrophy in magnesium silicate-treated rats.

The role of microenvironmental deterioration of the bone marrow in the development of bone atrophy was examined in rats with bone atrophy induced by magnesium silicate. In the tibial metaphyses, proliferation of myelocytic elements of haematopoietic tissue was prominent and caused narrowing of sinusoids, increased distance between sinusoids and trabecular bone and atrophy of trabecular bone. There was a significant correlation in volume percentage between haematopoietic cells and trabecular bone, between haematopoietic cells and sinusoids and between sinusoids and trabecular bone. These results imply that atrophy of trabecular bone is related to microenvironmental deterioration of the bone marrow, that is, a decrease in efficiency of exchange of nutrients and waste products between sinusoids and trabecular bone due to the proliferation of haematopoietic cells and a deficiency of nutrient supply to the bone marrow due to the narrowing of sinusoids.

Animals↗
PubMed1993

Long term follow up of radiosynovectomy with yttrium-90 silicate in haemophilic haemarthrosis.

OBJECTIVES: The aim of this study was to evaluate the long term effect of radiation synovectomy with yttrium-90 silicate in haemophiliac patients with recurrent haemarthrosis. METHODS: The bleeding frequency and the mobility of the joint were recorded in 16 joints of 14 patients 1 year before radiosynovectomy and during follow up, which ranged from 3 to 6 years. Patients evaluated the effect of their own treatment by completing a questionnaire. Radiographs of the joints were scored by an independent radiologist before treatment. RESULTS: A satisfactory reduction of the frequency of haemorrhage was achieved in 94% of joints during the first year after treatment and was maintained in 63% until the end of the follow up period. In general there was no decrease in mobility attributable to radiosynovectomy, and the patients' own evaluations agreed with the evaluations based on the frequencies of haemarthrosis in 75%. Patients who had only minor, or no, radiological abnormalities of the joints before treatment showed the best results. One patient developed synovitis as a complication of the radiosynovectomy. CONCLUSION: Radiosynovectomy is an effective and safe treatment for recurrent haemarthrosis in haemophiliac patients, especially in those who have joints with no or minor radiological damage.

Adolescent↗
PubMed1984

In vitro macrophage cytotoxicity of five calcium silicates.

Five calcium silicate minerals (two naturally occurring and three synthetic compounds) with defined morphology and chemical composition were compared for their cytotoxic and lysosomal enzyme releasing effects on unstimulated mouse peritoneal macrophages in vitro. One synthetic material, a fibrous tobermorite, was cytotoxic towards the cells, and two naturally occurring wollastonites induced selective release of beta-glucuronidase from the cells.

Animals↗