Showing papers on "Silicic acid published in 1976"

Silicic acid uptake and incorporation by natural marine phytoplankton populations1

Abstract: Germanic acid (/sup 68/Ge) was used as a tracer to study the uptake and incorporation of silicic acid by natural phytoplankton populations in the Gulf of California. The technique was useful in measuring silicic acid incorporation rates as low as 0.5 nM h/sup -1/. The incorporation followed saturation kinetics. K/sub s/ values at two stations were 1.59 and 2.53 ..mu..M. The incorporation was light dependent, maximum rates being achieved at 0.28 x 10/sup 21/ photons cm/sup -2/ d/sup -1/ (0.044 ly min/sup -1/; 9 percent of surface irradiance) and half-maximum rate at 0.02 x 10/sup 21/ photons cm/sup -2/ d/sup -1/ (0.003 ly min/sup -1/; 0.6 percent of surface irradiance); rate of incorporation in the dark was 44 percent of that at light saturation. Enrichment with silicic acid caused stimulation of photosynthetic carbon fixation at two stations.

Kinetics of silicic acid uptake and rates of silica dissolution in the marine diatom thalassiosira pseudonana1,2

Abstract: SUMMARY Tracer techniques using the stable isotope 30Si were used to measure rates of silicic acid uptake and silica dissolution in silicon replete and silicon depleted populations of 2 clones of the marine diatom Thalassiosira pseudonana Hasle & Heimdal. Uptake kinetics were describable using the Michaelis-Menten equation for enzyme kinetics, and no threshold concentration for uptake was evident. The maximum specific uptake rate of the estuarine clone 3H (0.062–0.092 · h−1) was higher than that of the Sargasso Sea clone 13-1 (0.028–0.031 · h−1), but half-saturation constants for uptake by the 2 clones were not measurably different (0.8–2.3 μM for 3H; 1.4–1.5 μM for 13-1). There was little or no light dependence of uptake in populations grown under optimal light conditions prior to the experiment. Exponentially growing populations released silicic acid to the medium by dissolution of cellular silica at rates ranging from 6.5 to 15% of the maximum uptake rate.

DIATOM MINERALIZATION OK SILICIC ACID. I Si(OH)4 TRANSPORT CHARACTERISTICS IN NAVICULA PELLICULOSA

Abstract: SUMMARY Silicic acid transport was studied in the photosynthetic diatom Navicula pelliculosa (Breb.) Hilse using [68Ge] germanic acid (68Ge(OH)4) as a tracer of silicic acid (Si(OH)4). The initial uptake rate of Si(OH)4 was dependent on cell number, pH, temperature, light and was promoted by certain monovalent cations in the medium. Na+ was more effective than K+, whereas Li+ and NH+4 were ineffective at promoting uptake. Uncouplers and inhibitors of oxidative phosphorylation and of photophosphorylation reduced uptake by 40–99% of control values. Uptake was also especially sensitive to the sulfhydryl blocking agents at 10−5 M and to the ionophorous compound valinomycin (10−7 M) which inhibited uptake by 82%. The Si(OH)4 transport system displayed Michaelis-Menten-type saturation kinetics with kinetic parameters of KS= 4.4 p. mol Si(OH)4· 1−1, Vmax= 334 pmol Si(OH)4· 106 cells−1· min−1. Calculations of the acid soluble silicic acid pool size based on 60 s uptake at 20 μM Si(OH)4 suggested that intracellular levels of Si could reach 20 mM and as much as 5 mM could exist as free silicic acid, representing maintenance of a 250-fold concentration gradient compared with the medium. Efflux from preloaded cells was dependent on temperature and the Si(OH)4 concentration of the external medium. In the presence of 100 μMM “cold” Si(OH)4, approximately 30% of the Si(OH)4 in preloaded cells was exchanged in 20 min. The initial uptake rate of Si(OH)4 in logarithmic phase cells was constant, but the uptake rate increased in a linear fashion for 6 h in stationary phase cells. These results suggest that the first step in silica mineralization by diatoms is the active transmembrane transport of Si(OH)4 by an energy dependent, saturable, membrane-carrier mechanism which requires the monovalent cations Na+ and K+ and is sensitive to sulfhydryl blocking agents. Silicic acid transport activity also appears to be regulated during different growth stages of the diatom.

Manufacture of olefin polymers

Abstract: This invention relates to a process for the manufacture of olefin polymers by polymerization of monoolefins with the aid of a silicic xerogel/chromium trioxide catalyst obtained by (1) synthesizing a particulate silicic xerogel, (2) doping this xerogel with chromium trioxide or a chromium compound which converts to chromium trioxide under conditions of stage (3) and (3) maintaining the resulting product at an elevated temperature in a water-free oxygen-containing stream of gas. The characteristic feature of the process of the invention is that the silicic xerogel/chromium trioxide catalyst used is one obtained by (1) synthesizing the silicic xerogel in the first stage as follows: (1.1) taking an aqueous solution of a sodium silicate, (1.2) substituting substantially all of the sodium ions contained in said solution by hydrogen ions by means of an ion exchanger, (1.3) introducing a water-soluble aluminum salt into the resulting aqueous silicic acid solution, (1.4) adjusting the pH of the solution obtained in stage (1.3) to from 0.1 to 3.5, if necessary, (1.5) adjusting the solution obtained in (1.3) or (1.4) to a pH of from 4 to 12 by means of a nitrogen-base compound, (1.6) extracting the product forming the solid phase in stage (1.5) (silicic hydrogel) by means of an alkanol and/or alkanone until the organic liquid absorbs no more water and, finally, (1.7) drying the dehydrated gel saturated with organic liquid resulting from stage (1.6) (xerogel formation). This process makes it possible to obtain polymers having a satisfactory particle size distribution and a favorable melt index.

3-Hydroxy-4,5-dimethyl-2(5H)-furanone, a Burnt Flavoring Compound from Aged Sake

Abstract: A burnt flavoring compound, which imparts to aged sake its characteristic and dominant flavor, was isolated by Diaion HP–20, silicic acid and Dowex 1–X8 (CH3COO−) column chromatography and chloroform extraction. Based on thin-layer and gas liquid chromatography, UV and GC–MS spectral data, it was identified as 3-hydroxy-4,5-dimethyl-2 (5H)-furanone and its structure was also confirmed by synthesis. It was suggested that this compound was formed by the condensation of a-ketobutyric acid with acetaldehyde which occurred from degradation of threonine.

Method for preparation of perfectly spherical particles of silicagel with controlled size and controlled pore dimensions

Abstract: The invention relates to a method for preparation of perfectly spherical particles of silicagel with controlled particle size and controlled pore diameter, which are suitable as packings for high-speed liquid chromatography and gel permeation chromatography. Free liquid silicic acid is obtained by acidifying of solutions of alkaline metal silicates in organic solvents by organic acids miscible with water in the presence of higher amine as an emulsifier and polymerized to hydrogel in the form of spherical particles. These are isolated and partially hardened by heating above 100° C in a neutral organic medium, e.g. amyl acetate or dibutyl sebacate, to remove a part of water by distillation, then subjected to hydrothermal processing with water under pressure at a temperature above 150° C and eventually stabilized. Chromatographic beds of silicagel particles prepared in this way may be used both with aqueous and organic eluants and exhibit very low spreading of zones and high separation efficiency comparable with commercial styrene-divinyl-benzene gels.

Studies on the biochemistry and fine structure of silica shell formation in diatoms : Division cycle and chemical composition of Navicula pelliculosa during light-dark synchronized growth.

Abstract: Cell division in Navicula pelliculosa (Breb.) Hilse, strain 668 was synchronized with an alternating regime of 5 h light and 7 h dark. Cell volume and dry weight increased only during the light period. DNA synthesis, which began during the third h of light, was followed sequentially by mitosis, cytokinesis, silicic acid uptake, cell wall formation, and cell separation. Silicification and a small amount of net synthesis of DNA, RNA and protein occurred during the dark at the expense of carbohydrate reserves accumulated during the light period. Cells kept in continuous light, after synchronization with the light-dark regime, remained synchronized through a second division cycle; the sequence of morphological events was the same as that in the light-dark division cycle, but the biosynthesis of macromolecular components changed from a stepwise to a linear pattern. The silicon-starvation synchrony was improved by depriving light-dark synchronized cells of silicic acid at the beginning of their division cycle, then resupplying silicic acid to cells blocked at wall formation.

Toothpaste compositions containing improved amorphous precipitated silicas

Abstract: A method for producing precipitated silicic acid products and silicates having a unique combination of physical and chemical properties is disclosed. The products are produced by acidulating a solution of an akali metal silicate with an acid until precipitation just begins. At this point the reaction mass is aged for a period of time and thereafter the acid addition is continued until the precipitated product is obtained. Products produced in accordance with the invention exhibit lower wet cake moisture (or higher percent solids) and are characterized by their low structure, low oil absorption, high abrasiveness and high pack density. The products can be used as abrasive and polishing agents in dentifrice compositions, in the production of molecular sieves, in paints and the like. In a particularly advantageous embodiment, an adduct material, such as aluminum, is added to control the refractive index of the precipitated silica. Products produced in this manner have particular utility for use as abrasion and gelling agents in clear toothpaste compositions.

Apparatus for preparation of a sprayable precipitated silicic acid suspension

Abstract: A silicic acid filter cake and suspension agent are fed to a container equipped with a stirrer having a peripheral speed of about 20-30 m/sec. The ratio of container diameter to stirrer diameter is about 3:1. The ratio of container diameter to level of filling is a maximum of about 1:2. The container contains at least about 1.5 to about 2 kg of silicic acid suspension, for each 1 kg of silicic acid filter cake which is added to the container. The contents of the container is mixed while maintaining a pH of at most about 4. A portion of the resulting silicic acid suspension is drawn off from the zone of highest turbulence in the container. An apparatus for carrying out the process is provided.

Purification of nutritive oils

Abstract: Parenterally administrable oil-in-water emulsions formed from nutritive oils, such as soybean and sunflower oils, are improved first by treating the nutritive oil with silicic acid to remove undesirable components such as peroxides, pigments, thermal and oxidative decomposition products, certain unsaponifiable matter such as sterols, and polymers. Purification is effected by treating the oil with silicic acid or silica gel either directly, or as a solution thereof in a suitable solvent, such as hexane. Autoxidation of the purified oil is prevented by adding to the purified oil a tocopherol antioxidant, γ-tocopherol being preferred. There is also added a metal scavenging agent such as ascorbyl palmitate.

Process for the production of epoxy silicate compounds and polymers

Abstract: Silicic acid and epoxy compounds are reacted to produce epoxy silicate compounds, and polymers, when mixed together in the presence of a suitable catalyst.

Preparation of aqueous silica sols free of alkali metal oxides

Abstract: A process for preparing silica sols substantially free of alkali metal ions which comprises A. adding to a boiling aqueous solution of a lower alkanol amine a 2-10% by weight aqueous solution of silicic acid, the mole ratio of SiO 2 to lower alkanol amine being in the range of from 1:1 to 100:1; B. evaporating water during the addition of the silicic acid to the aqueous solution of the lower alkanol amine so as to maintain a constant volume; C. recovering the aqueous colloidal silica sol which is substantially free of alkali metal ions, said sol having a mole ratio of SiO 2 to alkanol amine in the range of 1:1 to 100:1; and then if desired, D. treating this sol with both a cation and anion ion exchange resin so as to further deionize the resulting alkaline metal-free silica sol, as well as to remove substantial quantities of the alkanol amine. Then if an alkaline sol is desired, adjusting the pH of the resulting acid sol of Step D to between 9 and 10 with an aqueous solution of ammonia.

Process for the production of poly(urethane silicate) resin and foams

Abstract: Silicic acid is reacted with a suitable polyalcohol by using heat and an alkali catalyst to produce a polyalcohol silicate. The polyalcohol silicate is then reacted with a suitable isocyanate to produce a poly(urethane silicate) resin. An activator, such as water, may be mixed with the said resin to cause foaming and/or cross linking of the polymer.

Photoluminescent building material - contg. photoluminescent substances, silicic acid derivs. and binding agent

Abstract: A matl. which possesses sufficient strength as a building matl. and is luminescent, as it contains photoluminescent substances, such as ZnS crystals, and also transparent matls. so chosen that they allow sufficient penetration of U. V. radiation to the photoluminescent matl. and at the same time allow transmission of light emitted by the photoluminiescent substances from the inside of the matl. The light transparent matls. are pref. derived from silicic acid, and the matl. contains also a synthetic resin binding agent and/or hydraulic binding agent, e.g. cement, mortar, gypsum. Suitable silicic acid derivs. are ground quartz glass, ground quartz, silicic acid gel, silica gel, and silicic acid anhydride. Pref. at least a part is in the form of a U. V.-permeable colloid. Pref. the transparent components are bound together by a synthetic resin which can wholly or partly replace the hydraulic binding agent, e.g. the cement of concrete. Such synthetic resins are heat-hardenable resins or thermoplasts, e.g. polyurethanes, polyesters, epoxy, resins, acrylic resins or vinyl resins. The building matl. can also contain "cascade" substances which absorb excitation energy in specific frequency ranges and give it up at a different frequency range in which the photoluminiscent centres can be excited. The cascade substance is pref. an aromatic substance in which the synthetic resin dissolves.

Treatment of waste

Abstract: OF THE DISCLOSURE Process for the treatment of toxic waste by means of a silicate, in the presence of water, in such a way as to form a solid aggregate includes treatment of the silicate in an acid medium, for the purpose of obtaining silicic acid of low molecul-ar weight; mixing the silicic acid with the waste to be treated, in the presence of water and in a sufficiently acid medium to cause the waste to undergo at least partial solution; precipita-tion of a gel of high molecular weight from the resultant aqueous mixture; addition thereto of a mixture which reacts with the gel of high molecular weight to form a silicate, possible in the presence of a cementation agent, in such a way as to produce a sludge, and the hardening of the sludge into a solid aggregate.

A study of the color stability of commercial oleic acid

Abstract: Commercial oleic acid has a tendency to develop a dark color during heating. It has been found that this discoloration is partially due to oxidation and partially due to the presence of minor constituents. Their characterization as oxidized and polymerized fatty acids will be reported in a separate paper. The effects of the two factors are synergistic to each other and thus accentuate the darkening of the commercial oleic acid when it is heated under air. Removal of the minor constituents from commercial oleic acid by silicic acid treatment drastically improved its color stability. The generally acknowledged concept that the higher the polyunsaturated fatty acid content in the commercial oleic acid, the lower its color stability, is not correct. The color stability of commercial oleic acid is more predominantly dependent upon the content of minor constituents than that of polyunsaturated fatty acid.

Metal-requiring and non-metal - requiring catalysts in the autoxidation of methyl linoleate

Abstract: During the autoxidation of methyl linoleate, peroxide-containing substances are formed which, when added to unoxidized methyl linoleate, will catalyze oxygen uptake. Materials active only in the presence of added metal ions (MCs) were not inactivated during aerobic thin-layer chromatography on silicic acid or alumina but were selectively inactivated by treatment with triphenylphosphine. Catalysts not requiring added metal ions for activity (NCs) are not affected by triphenylphosphine, but the catalytic activity is lost during aerobic thin-layer chromatography. Autoxidized methyl linoleate was separated into four peroxide-containing fractions by elution from a silicic acid column with hexane-diethyl ether mixtures. Each fraction was found to contain both MCs and NCs.

Novel thermosetting resins and process for preparing the same

Abstract: A novel thermosetting resin, the thermoset resin obtained therefrom having such a thermal resistance that the temperature at which the thermoset resin is caused to show a weight loss of 6% by heating at a temperature elevation rate of 10° C. per minute is at least 400° C., is prepared by reacting a specific phenolic resin with a member selected from the group consisting of a silicic acid ester of the formula Si(OR) 4 wherein R represents alkyl or aryl and a mixture of a silicic acid ester of the formula as defined above and a titanic acid ester of the formula Ti(OR) 4 wherein R has the same meaning as defined above in the presence of an alkaline catalyst while keeping the reaction system in a molten state, to an extent that 20- 70 mole %, based on the phenol present in the starting system to be reacted with said member, of phenolic hydroxyl groups in terms of the amount of phenol, remain unreacted. The thus obtained novel resins of the present invention can be easily set or hardened in accordance with the ordinary manner; namely by mixing with a thermohardening agent such as hexamethylenetetramine and then heating, to give thermoset resins having a superior thermal resistance as compared with the conventional phenolic resins. In addition, the thermoset resins obtained from the novel resins of this invention are excellent in mechanical strength, electrical properties and luster of molded articles.

Process for preparing calcium fluoride from hexafluoro silicic acid and production of silicic acid gel or active silicic acid from said calcium fluoride

Abstract: Disclosed is a process for the preparation of calcium fluoride comprising reacting hexafluoro silicic acid with calcium carbonate in the presence of sulfate or aluminum ions within a pH range of between about 2 and 6 and separating the calcium fluoride precipitate from the resulting aqueous silica sol.

Silica beads prepn. - from aq silicate soln dispersed in water-immiscible solvent, and hardener

Abstract: Beads consisting mainly of silicic acid are prepd. by (1) dispersing aq. silicate solns. pref. Na water-glass solns. in a water-immiscible org. solvent, pref. toluene, opt. with addn. of dispersant, to form a water-in-oil emulsion, (2) introducing a hardener for silicate soln. which is more soluble in org. solvent than in aq. phase and (3) stirring, up to hardening of the silicate soln. The beads are used as catalyst supports but esp. fillers, absorbents and drying agents. Quick hardening takes place inwards from particle surface, whereby bead structure is stabilised and pore channels are partic. uniform.

Duplex org.-inorg. coating in conducting materials - surface being covered with inorg. coating over which coating is applied by electrophoresis

Abstract: Conducting materials are provided with two coatings, the surface being covered first with an organic coating based on silicic acid and/or metal phosphate over which is applied by electrophoresis an organic coating of a material which is either anion active or cation active. For coating metals and metal surfaces which are made conducting by applying an electrodeposit, or a metal powder, or graphite.

Hydrophobing process for silicic acid and silicate by organosilane

Abstract: Finely divided hydrophobic silica or silicate is produced by treating the dry, moving particles with an organic silane at elevated temperature. The silica or silicate which had been prepared by wet precipitation or pyrogenically and which is in powdered form is heated to a temperature of about 200 DEG to 300 DEG C. with agitation and is brought to a fluidized condition and then is treated dropwise with an organosilane which is stable and boils below 300 DEG C.