Silicic Acid Gel Research Articles

Preparation and properties investigation of PMMA/silica composites derived from silicic acid

AbstractHybrid materials based on silicic acid and polymethyl methacrylate (PMMA) were prepared by in situ bulk polymerization of a silicic acid sol and MMA mixture. Silicic acid sol was obtained by tetrahydrofuran (THF) extraction of silicic acid from water. Silicic acid was prepared by hydrolysis and condensation of sodium silicate in the presence of 3.6 M HCl. As a comparative study, PMMA composites filled by silica particles, which were derived from calcining the silicic acid gel, were prepared by a comparable in situ polymerization. Each set of PMMA/silica composites was subjected to thermal and mechanical studies. Residual THF in PMMA/silicic acid composites impacted the properties of the polymer composites. With increase in silica content, the PMMA composites filled with silica particles showed improved thermal and mechanical properties, whereas a decrease in thermal stability and mechanical strength was found for PMMA composites filled with silicic acid dissolved in THF. With a better compatibility with polymer matrix, silicic acid sol shows better reinforcement than silica particles in PMMA films prepared via blending of the corresponding THF solutions. Copyright © 2008 John Wiley & Sons, Ltd.

“Spontaneous” growth of fibrous products on the surface of silicic acid gels

We have observed occurrence of fibrous products on gel surface in four-component system of KK (silicic acid sol)–H2O–HCl–NH3, KK–H2O–HCl–NaOH and KK–H2O–HCl–TEA (triethanolamine). Bundles of fibres occur in the system with NH3, sticks and needles in system with NaOH, and finally in the system with TEA we can mostly observe the occurrence of crystalline products. Dependency of product morphology on initial sol composition is occurring in observed systems. In the case of system with NH3, mostly the length of nascent fibres is influenced by the composition, and in the systems with NaOH and TEA it is also final shape of nascent products. Morphology of nascent products in systems with NH3 and NaOH is controlled by quantity of added HCl, but in the system with TEA it is quantity of added TEA. It is characteristic for all observed systems that “spontaneously” occurring products consist of crystalline phase, that is chloride of respective alkali, and amorphous phase, that is SiO2. Beginning of respective chloride crystallization in observed systems probably initializes occurrence of products on gel surface. Further growth of crystals is influenced by present colloid of SiO2 that interacts with surface of growing crystal leading to anisotropy of its growth and therefore to “spontaneous” occurrence of fibrous products.

27Al Multiple-Quantum MAS NMR of Mechanically Treated Bayerite (α-Al(OH)3) and Silica Mixtures

Two-dimensional 27Al multiple-quantum magic angle spinning (MQMAS) NMR experiments are used to study mixtures of bayerite (α-Al(OH)3) with either silicic acid (SiO2.nH2O) or silica gel (SiO2) that have been ground together for varying lengths of time. This mechanical treatment produces changes in the 27Al MAS and MQMAS NMR spectra that correspond to the formation of new Al species. Mean values of the quadrupolar interaction (PQ) and isotropic chemical shift (δCS) are extracted from the two-dimensional 27Al NMR spectra for each of these species. The presence of significant distributions of both 27Al quadrupolar and chemical shift parameters is demonstrated and the effect of grinding duration on the magnitudes of these distributions is discussed.

New application of a traditional analytical method--arsenic removal from water works sludge during iron(III) chloride coagulant production.

The Marsh Test, the original means of determination of arsenic by hydride generation, has been modified to remove arsenic from water works sludge, with iron used instead of zinc as the main agent. Water works sludge (main compound iron(III) oxyhydrate) generated during groundwater treatment can be enriched in arsenic up to several gkg(-1). Acidic dissolution of this sludge to produce FeCl3 coagulant liberates the arsenic. Addition of elemental iron reduces this dissolved As(V) mainly to dispersed elemental As(0) particles, which can be removed by filtration. If the reaction temperature is kept below 50 degrees C, more than 99% of the arsenic can be removed from the coagulant solution and less than 10% will escape as gaseous arsine (AsH3). Severe foaming and silicic acid gel formation occurs during the acidic dissolution, however. For technical and economic reasons the use of the water works sludge for FeCl3 coagulant production is not competitive when compared with other recycling methods.

ケイ酸塩を用いた木材の無機質複合化（第９報） ケイ酸塩‐ホウ素化合物系による木材無機質複合体のＥＰＭＡ観察と酸素指数法による難燃性評価

The distribution of silicic acid gel and boron compounds in wood-mineral composites made using the silicate-boron compound system was examined by electron probe X-ray microanalysis (EPMA). The fire resistance of the composites was also evaluated by applying both oxygen index and percent weight of residual char. The composites were produced by diffusion-penetrating the water glass-boron compound system (double treatment) and the colloidal silica solution system in the sapwood specimens of Sugi (Cryptomeria japonica). For comparison, the composites were also prepared by impregnating boron compounds only into the wood (single treatment).In the single treatment, most of boron compounds in the composites was located in the cell walls as obvious from boron X-ray maps. However, boron compounds themselves were almost all leached out by the leaching procedure, showing no fixation of them in the composites. On the other hand, in the double treatment having the fixation of 5470% after leaching, silicic acid gel was located mostly in the cell lumina and it was very small in quantity in the cell walls as seen from silicon X-ray maps whereas boron compounds existed in the cell walls besides the lumina even after leaching.In the colloidal silica solution system having the high fixation of 86-94%, most of silicic acid gel was deposited in the cell lumina as an insoluble solid body and it was also very little in the cell walls. In addition, the distribution of boric acid was clearly observed not only in the lumina but also in the walls even after leaching.As a result of fire-resisting test, the oxygen index of the composites trended to increase with an increase in weight percent gain (WPG) and there was a high correlation between the two. The percent weight of residual char was highly correlated to WPG independently of leaching and it increased lineally with an increase in WPG. It may be possible that the percent weight of residual char becomes one way for estimating the fire resistance of the composites because of a high correlation with the oxygen index after leaching.

Modifying Silicic Acid Xerogels and Accelerating Heterogeneous Reactions with Their Participation with the Use of Microwave Radiation

The use of microwave radiation for drying wet silicic acid gels significantly shortens the time of preparation of dry gels, or xerogels. The specific surface area of xerogels increases from 492 to 963 m2/g as the power of microwave radiation is increased from 300 to 1000 W. The effect of microwave radiation on the rate of heterogeneous reactions with the participation of analytical reagents incorporated into silicic acid xerogels was studied. It was found that, in a microwave field of a power of 600 W, the reactions between immobilized Bromobenzothiazo and cadmium, immobilized 1-(2-pyridylazo)-2-naphthol and cobalt(II), and immobilized phosphomolybdic heteropoly acid and hydrazine are essentially accelerated. For the reaction of cobalt(II) with 1-(2-pyridylazo)-2-naphthol incorporated into xerogel, microwave radiation accelerates both the outside and inside diffusion. The use of microwave radiation shortens the time of determining metal ions and hydrazine by solid-phase spectrophotometry.

木質材料 ケイ酸塩を用いた木材の無機質複合化 （第７報） コロイダルシリカ溶液による木材の無機質複合化とその性質

The applicability of colloidal silica for producing a wood-mineral composite by impregnation was investigated, and its properties such as dimensional stability and decay and fire resistances were evaluated.The colloidal silica solution was prepared by mixing silicic acid anhydride (30.4%), boric acid, and chitosan with a low molecular weight (0.3%). Instead of boric acid, metal ions of Cu, Ag, or Ti (1000ppm) were added to the solution. The solution was diffusion-penetrated into the water-saturated specimens of Sugi (Cryptomeria japonica D. Don), followed by drying to solidify the colloidal silica for a combination. The formation of silicic acid gel in the composites made by using the colloidal silica solution system was proved to be mostly insoluble.The composites showed an antiswelling efficiency with the greatest value of 23% due to the bulking effect despite being hygroscopic and a good reduction in water absorptivity. Also, the composites, particularly those by using the colloidal silica-boric acid system, were found to improve greatly the decay and fire resistances.For practical use, the composites were manufactured with boards of yellow poplar (Liriodendron tulipifera L.) applying the colloidal silica-boric acid system. They showed the enhancement of bending strength and modulus of elasticity to some extent of apparent weight percent gains. The absorbed energy in impact bending became greater than that of the untreated wood.

Phase transformation and grain coarsening of zirconia/mullite composites

ZrO 2/mullite composites (ZMC) with homogeneously dispersed ZrO 2 grains were prepared from colloidal or sol-gel processes of the precursors, which were a mixture of colloidal pseudo-boehmite (γ-AlOOH), zirconia and silicic acid gel, or prepared from dissociated zircon with alumina powder. After pressureless sintering of the ZMCs, their microstructure was examined by means of X-ray diffractometry, scanning electron microscopy and analytical transmission electron microscopy techniques. The microstructure of the ZMCs showed a difference in scale. ZrO 2 and mullite grains grown in the gel matrix were formed at temperatures as low as 1100 and 1300 °C, respectively. Experimental results indicated that heat treatment from 1300 to 1600 °C influences the growth of mullite and fine ZrO 2 grains in ZMCs, especially for the composite prepared from sol-gel methods in which the ZrO 2 grew from tens of nanometres to micrometre size. The effects of the presence of ultra-fine ZrO 2 on retarding the grain growth of mullite and the increase of metastable t-phase ZrO 2 are also discussed. The growth of fine ZrO 2 grains in a mullite matrix belongs to a mechanism of coalescence.

Freeze formed ceramic fibres: effect of pre-ageing the gel

Preparation of silica fibres by unidirectional freezing of a silicic acid gel was first reported by Mahler and Bechtold [1]. During freezing, the polysilicic acid phase separates from water. If the conditions are right, the water freezes as long columnar crystals and polysilicic acid is expelled into the intercolumnar space where it polymerizes further. On thawing the frozen mass, amorphous fibres of silica are obtained. Subsequently to this first report, fibres of zirconia [2, 3] and alumina [4, 5] have also been grown by unidirectional freezing of gels. Kokubo et al. [2, 3] studied in some detail the conditions for fibre formation from a gel prepared from ZrOC12.8H20. They found that the ratio G/R,, where G is the temperature gradient at the frozen gel front and R is the freezing rate, has to be within narrow limits (2 to 8 °C h cm -2) for obtaining fibres longer than 20 mm. At larger values of G/R, columnar crystals of ice grow as a plane front with no intercolumnar space. At small G/R values, the ice crystals grow in radial form and zirconia is expelled randomly. Only at intermediate G/R values is a suitable geometry for fibre formation, consisting of long ice crystals with fine spaces between them, obtained. The other factors besides G/R which are important for the formation of fibres by this process are concentrations of the starting sol and the time of ageing of the gel. Kokubo et al. [:2] found that sols with low concentrations either do not gel or do not yield fibres while higher concentration result in longer fibres. The third process variable, namely pre-ageing of the gel before freezing, has not been investigated. In the present work some interesting effects of pre-ageing were observed and are reported below. Aqueous solution of concentration 2 ~ ZrOC12 was prepared using ZrOC12"8H20. 5 ml of this solution was transferred to a 8ram diameter x 120 mm cellulose acetate membrane tube made in the laboratory. Dialysis was carried out against distilled water to obtain clear hydrogels. The gels were aged in distilled water for ageing times ranging from 96 to 720 h with renewal of water once every 24 h. The gel cylinders were wrapped with a 3 mm thick polyeurethane foam and placed in a plastic tube. The plastic tube was then lowered into a liquid Na bath at rates between 1.7 to 2.5 cmh -1. Some experiments were also conducted I:o determine the effect of the ratio G/R. In these experiments, the rate of freezing of the gel interface at distances between 4 and 6 cm from the bottom of the gel cylinder were measured by inserting thermocouples as described in [3]. The frozen gelLs were removed

Diffusion of a dispersed solute in a polymeric matrix

A theoretical model for the diffusion study of a molecule in suspension in a continuous medium is presented. This model provides a realistic representation of the release by diffusion of a drug in a polymeric matrix at a concentration C 0 above its solubility C s in the medium, in the case where the molecule diffuses into the receptor, similar to what occurs with the donor. The release kinetics is a function of t 1 2 . It contains a numerical parameter β which is a function of the ratio C 0/C s. The table of values of β is g variant of the method of analysis is also presented which has the advantage of not requiring knowledge of the solubility of the molecule in the system, which is often hard to measure in practice. In the experimental section, the theoretical models are validated using the diffusion of testosterone in suspension in a silicic acid gel.

In situ determination of the diffusion coefficient of a solute in a gel system using a radiotracer

The study of diffusion in polymeric gels often poses difficult experimental problems, notably when the rate of release is determined in a liquid receptor phase which can interact with the gel. In this publication, we propose an accurate method to determine the diffusion coefficient by a gel-gel kinetic release study. The method is based on the use of a multi-channel radioactivity counter to obtain the in situ concentration profile of the diffusing molecule in the gel where a concentration gradient has been determined initially. In the first part, the theoretical interpretations of such profiles are given. In the second part, an experimental example of the method applied to the diffusion of testosterone in a silicic acid gel is presented.

ChemInform Abstract: Degradation of Silicic Acid Sols, Silicic Acid Gel, and Aerosil in Aqueous Tetramethylammonium Hydroxide Solutions.

AbstractWith the aid of the trimethylsilylation and molybdate methods it is shown that the degradation rate of silicic acid sols in tetramethylammonium (TMA) hydroxide solution depends on the average particle size.

Development of zeolite for non-phosphated detergents in Japan

Abstract

Effects of induction of general and regional anesthesia for cesarean section on maternal plasma β-endorphin levels

Plasma β-endorphin was measured in 40 healthy pregnant women undergoing cesarean section. Group 1 patients (N = 14) received general anesthesia by rapid-sequence induction and endotracheal intubation with curare, thiopental, and succinylcholine. Anesthesia was maintained with nitrous oxide, oxygen, and muscle relaxant until delivery. Group 2 patients (N = 26) received regional anesthesia (spinal, 14, and epidural, 12). Maternal blood samples were drawn from indwelling venous catheters prior to and after induction of either general or regional anesthesia. Plasma β-endorphin was determined by radioimmunoassay following silicic acid extraction and gel chromatography. In the 14 patients who underwent general anesthesia, the mean (±SEM) plasma β-endorphin increased significantly (p < 0.025) from 46 ± 7.4 to 111.6 ± 8.9 fmol/ml. There was no significant change in plasma β-endorphin level of the 26 patients who underwent regional anesthesia; β-endorphin levels averaged 44.5 ± 5.1 and 47.6 ± 4.8 fmol/ml prior to and after induction of anesthesia, respectively. These data demonstrate that plasma β-endorphin concentrations are elevated following induction of general anesthesia but not with induction of regional anesthesia, which suggests that less stress is associated with regional than with general anesthesia induction in patients undergoing cesarean section.

Different patterns of central and peripheral βEP, βLPH and ACTH throughout life

The aim of the present study was to evaluate the relationship between central and peripheral concentrations of proopiocortin-related peptides in different periods of life. One hundred and eighty-nine plasma samples from normal subjects (18–87 years) obtained in basal conditions, and 20 cerebrospinal fluid (CSF) samples obtained by lumbar puncture from healthy volunteers (18–75 years) were studied. βLipotropin (βLPH), βendorphin (βEP) and ACTH were measured by specific RIA after silicic acid plasma extraction and gel chromatography (βLPH and βEP). No sex differences were found in the patterns of the three peptides either in the plasma or in CSF. In the plasma samples, both βLPH and βEP concentrations showed a pattern throughout life which was expressed by a paraboloid function with the lowest values found in young and old subjects and with peaks at 51.3 and 48.2 years, respectively. On the contrary, ACTH values failed to be represented by a significant linear or curvilinear regression and presented only a slight decrease in subjects over 75 years of age. CSF levels of βLPH were significantly lower in 45–76 year old subjects ( 18.8±12.6 fmol/ml , M± SD ) than in 18–44 year old subjects ( 34.5±15.8; p<0.05), as were those of βEP (elderly: 41.2±19.7; young: 94.2±36.7; p<0.05), which showed a significantly linear inverse correlation with age ( r=0.6062 , p<0.01). These CSF samples did not show any ACTH variations connected with age. In conclusion, ACTH levels in basal conditions are not correlated to those of βLPH or βEP, either in the plasma or in CSF, while the two opioids show parallel changes. Moreover, the differences in the age-related changes of βLPH and βEP in plasma and CSF markedly sustain the existence of two different compartments in which proopiocortin-related peptides are subject to different forms of control.

Amniotic fluid β-endorphin and β-lipotropin concentrations during the second and third trimesters

Amniotic fluid β-endorphin (β-EP) and β-lipotropin (β-LPH) were measured by radioimmunoassay after silicic acid extraction and gel chromatographic separation of the two peptides in uncomplicated second-trimester and term pregnancies, in diabetic patients at term, and in pregnancies complicated by Rh-isoimmunization, premature labor, and intrauterine growth retardation. Furthermore, the lecithin/sphingomyelin (LS) ratios as well as the dehydroepiandrosterone sulfate (DHEA-S) and cortisol levels were determined in most of the amniotic fluid specimens. Both the mean (±SE) β-EP (65.3 ± 9.1 fmol/ml) and β-LPH (150 ± 15.8 fmol/ml) concentrations were significantly higher in the 20 patients with normal pregnancies of 16 to 21 weeks' duration than those found in 21 patients with uncomplicated term pregnancies of 38 weeks' gestation, averaging 42.6 ± 6.0 and 80.1 ± 10.7 fmol/ml, respectively. The mean amniotic fluid β-EP and β-LPH concentrations measured in the latter subjects were similar to those observed in 23 diabetic patients with otherwise uncomplicated term pregnancies. The mean amniotic fluid β-EP and β-LPH levels found in the limited number of patients with Rh-isoimmunization (N = 9), premature labor (n = 8), and intrauterine growth retardation (n = 5) with pregnancies of 24 to 36, 24 to 36, and 34 to 38 weeks' gestation, respectively, were not significantly different from the mean amniotic fluid β-EP and β-LPH concentrations of uncomplicated term pregnancies. In all patients but those with Rh-isoimmunization, β-EP concentrations exhibited a positive correlation with β-LPH levels. However, the molar β-LPH: β-EP ratio was significantly lower at term than during the early second trimester. Neither β-EP nor β-LPH correlated with the amniotic fluid LS ratio and only β-LPH exhibited a significant inverse correlation with amniotic fluid DHEA-S. The latter was significantly higher in uncomplicated term than second-trimester pregnancies. These results confirm that immunoassayable β-EP is present in amniotic fluid and declines toward term. These data demonstrate that immunoassayable β-LPH is present in amniotic fluid and show a more pronounced decrease toward the end of pregnancy than β-EP. Neither peptide, at least on account of the amniotic fluid levels, appears to be associated with fetal maturation. The physiologic significance of amniotic fluid β-EP and β-LPH and their possible role as markers of fetal response to stress remain to be elucidated.

Formation of silica microplates by freezing dilute silicic acid solutions

Abstract Formation of noncrystalline silica flakes (1, 2) and fibers (3) by freezing silicic acid sols and gels (0.1-1 M Si02) has been studied. This phenomenon is interesting from both the inorganic and geochemical viewpoints although the data on the products formed by freezing dilute silicic acid solutions are not available in the literature. We froze and thawed monomeric silicic acid solutions (0.05-2 mM) and observed the formation of polygonal, circular, elliptical, and annular silica microplates with diameters of 0.5 to 20 ,μm. The circular, elliptical, and annular microplates were similar to laminar opaline silica (LOS) in soils (4-7), suggesting that soil LOS can be formed when the soil solution containing silicic acid is frozen.

β-Endorphin and β-lipotropin concentrations in umbilical cord blood

Antisera suitable for human β-endorphin and β-lipotropin radioimmunoassay were developed, and radioimmunoassays were established to measure these peptides in umbilical cord plasma, with silicic acid extraction and gel chromatography used to separate the β-endorphin from the β-lipotropin fraction. These two peptides were determined in umbilical venous plasma from 64 newborn infants. Umbilical vein β-endorphin and β-lipotropin concentrations averaged 38.5 ± 3.2 and 50.4 ± 4.1 (± SE) fmoles/ml in the 54 newborn infants without and 115 ± 18 and 110 ± 25 fmoles/ml in the 10 newborn infants with apparent fetal distress. Neither the presence or absence of labor nor the route or mode of delivery was found to affect umbilical vein β-endorphin or β-lipotropin concentrations. However, cord plasma levels of both peptides were significantly elevated in conjunction with fetal distress, as evidenced by prolonged bradycardia, late and prolonged variable fetal heart rate decelerations, or fetal acidosis. In 18 of 22 pairs of simultaneously measured umbilical venous and arterial β-endorphin and β-lipotropin concentrations in newborn infants without apparent intrapartum distress, the venous β-endorphin concentrations, which averaged 40.4 ± 3.5 fmoles/ml, were significantly higher than the arterial β-endorphin levels, with a mean of 28.5 ± 4.2 fmoles/ml. No significant umiblical arteriovenous concentration difference could be observed for β-lipotropin. This suggests that at least a portion of the cord plasma β-endorphin is derived from the placenta. The ratio of umbilical arterial to venous β-endorphin concentrations rose as the absolute cord plasma β-endorphin levels increased. Furthermore, both the molar umbilical venous and arterial β-lipotropin to β-endorphin ratios decreased significantly in association with intrapartum fetal distress. These data indicate that the stress-related increase in umbilical plasma β-endorphin exceeds that of β-lipotropin and may be, at least in part, of fetal origin. Umbilical venous β-endorphin and β-lipotropin levels of neonates whose mothers did not receive meperidine or other narcotic agents did not differ from those of neonates whose mothers were given meperidine or other narcotics during labor. Our data, in conjunction with those of others, are consistent with the hypothesis that fetal hypoxia causes the release of neurotransmitters such as β-endorphin, which may modulate the regulation of fetal heart rate patterns.

Critical study of the interference of silicic derivatives on fluoride determination

Several physical properties of various silicic derivatives are examined in order to elucidate an interference with fluoride during codistillation of hexafluorosilicic acid with superheated steam.The stated interference cannot be explained by the granulometry or by the specific surface area of the interfering derivatives but their porous structure: a nonporous adsorbent (silica) does not interfere; a porous adsorbent (silicic acid and silica gel) is liable to interfere when its pores reach a definite size, approximately a diameter of 50 Å.The occurrence of imprisonment of some fluoride anions in the pores of the interfering silicic derivatives is suggested.

A specific homologous radioimmunoassay for human beta-endorphin: direct measurement in biological fluids.

A highly sensitive and specific homologous RIA for direct measurement of human β-endorphin (βh-EP) has been developed. This RIA can detect as little as 5 pg/tube and cross-reacts with human β-lipotropin (βh-LPH) by only 5% on a molar basis and 2% by mass. Although the inhibition of binding of [125I]βh-EP in the RIA by βh-LPH was parallel to the inhibition curve produced by the addition of unlabeled βh-EP, the curves obtained by the addition of ovine and porcine β-endorphins and ovine β-LPH were not parallel to the βh-EP curve. This indicates that the antiserum against βh-EP recognizes different antigenic determinants in the βh-EP molecule compared to the corresponding animal peptides. Assay cross-reaction with ovine β-EP (10%), porcine β-EP (5%), and ovine β-LPH (16%) was small. No cross-reaction with 22 other peptides was found. Quantitative recovery of βh-EP was obtained after addition of the peptide to human plasma, cerebrospinal fluid, and amniotic fluid. Control experiments in which increasing quantities of βh-LPH up to 1.6 ng/ml were added to plasma revealed no significant alteration of β-EP immunoreactivity. The ability of the present RIA to discriminate between βh-EP and βh-LPH was further validated by column chromatography. The plasma concentrations of βh-EP in normal men and women determined by direct RIA were found to be 115 ± 9 pg/ml (n = 27) and 112 ± 5 pg/ml (n = 25), respectively. The βh-EP concentration in normal human plasma measured by direct RIA was comparable to that found after silicic acid extraction and gel chromatography (107 pg/ml). βh-EP concentrations in paired maternal (248 ± 28 pg/ml; n = 6) and cord (250 ± 54 pg/ml; n = 6) plasma were significantly higher (P < 0.05) than those in nonpregnant subjects. βh-EP concentration in term amniotic fluid was 104 ± 6 pg/ml (n = 6). The administration of metyrapone produced a rise in plasma βh-EP concentration of 37–155%. βh-EP was not detectable in cerebrospinal fluid samples obtained by lumbar puncture (n = 19). The present RIA system is sufficiently sensitive and specific to permit direct measurement of βh-EP in human biological fluids.