Abstract: The invention provides a method for manufacturing boron-free SiO.sub.2 by purification of hexafluorosilicic acid. In this case, an aqueous solution of the boron-containing hexafluorosilicic acid is transferred to the organic phase by treatment with organic compounds immiscible with water and subsequently the organic phase is converted to boron-free hexafluorosilicic acid by means of fluid-fluid extraction in the alkaline or acid medium. Particularly, complex-forming compounds, such as tri-iso-octylamine, and organic solvents, such as xylol, are used as organic compounds. The method produces SiO.sub.2 with a boron content of less than 1 ppm and is usable for manufacturing silicon for solar cells.

Abstract: There are disclosed precipitated silicas which are characterized by the following physical-chemical data:______________________________________ A B C ______________________________________ BET-surface area m.sup.2 /g 400-600 400-600 400-600 according to DIN 66131 DBP-Number % 340-380 320-360 310-360 Bulk density according g/l 180-220 75-120 35-70 to DIN 53194 "ALPINE-Sieve Wt. % 25-60 <0.1 <0.01 Residue" >63 m.mu. ______________________________________Depending on the particle distribution curve, these precipitated silicas can be employed as silica carriers for active materials of all types, as antiblocking agents for polypropylene and polyethylene films, as thickening silica in specific polar systems in which pyrogenic silicas show little thickening capacity, as highly active matting agents for varnishes and as catalyst carriers as well as insulating materials.

Abstract: Dentifrice compositions containing a hydrous silica gel having a water content of from about 20 to about 60 weight percent are disclosed. The abrasiveness of the gel is increased by contacting the gel with an alkaline medium to provide a gel pH of about 6 to about 10 and/or preparing the gel by drying and grinding a silica hydrogel that has been washed with an aqueous acidic solution having a temperature of from about 80.degree. to about 100.degree. F.

Abstract: Process for preparing high mechanical strength pure silicon dioxide suitable for demanding high-grade technical applications including the combination of steps of (a) forming a reaction mixture containing a silicon dioxide precipitate by controllably and gradually admixing with firm agitation an at most 15 weight percent aqueous solution of hexafluorosilicic acid with an about 15 to about 35 weight percent ammonium hydroxide solution at about 25.degree. C. to about 45.degree. C. until the pH is about 8.5 to about 9.2 in the thus formed mixture containing a silicon dioxide precipitate; (b) separating the silicon dioxide precipitate from the mixture; (c) washing the thus separated precipitate; and (d) calcining the thus washed precipitate at about 900.degree. C. to about 1500.degree. C. Silicon dioxide produced in accordance with the present process has better physical properties than commercially available porous alpha-alumina.

Abstract: The specification discloses new and improved processes for forming water-free metal or non-metal oxide materials, which may then be melted and formed into optical components in vitreous or crystal form, which are free of the hydrogen-impurity absorption in the near infrared wavelength range. In one process, a water-free oxide is prepared by reacting a chosen nonpolar compound containing the desired metal or non-metal with an aprotic oxygen-containing compound to form the oxide as a precipitate in a chosen aprotic nonaqueous liquid solvent which provides a water-free environment during the formation of the oxide, to prevent the inclusion of water and water-derived impurities in the oxide as formed.

Abstract: Process for preparing pure silicon dioxide from a hexafluorosilicic acid solution by controllably and vigorously admixing, stirring or blending a hexafluorosilicic acid solution with a quantity of ammonium hydroxide solution amounting to about 40 to about 75 percent by weight of the quantity stoichiometrically required for the converting hexafluorosilicic acid to ammonium fluoride and silicon dioxide to thereby form a reaction mixture and a precipitate therein; separating out this precipitate; treating the precipitate-free liquid with ammonium hydroxide and then recovering the pure silicon dioxide. The silicon dioxide is pure enough to be useful as a catalyst support or as a substitute for quartz.

Abstract: The specification discloses new and improved processes for forming water-free metal or non-metal oxide materials, which may then be melted and formed into optical components in vitreous or crystal form, which are free of the hydrogen-impurity absorption in the near infrared wavelength range. In one process a water-free oxide is prepared by reacting a chosen organic compound containing oxygen bonded to an atom of the metal or non-metal, with a chosen organic acid anhydride to form an intermediate product which is then decomposed to form the desired oxide and to simultaneously regenerate the organic acid anhydride. The regenerated organic acid anhydride reacts with and removes traces of water and water-derived impurities during the formation of the desired oxide and prevents the inclusion of these impurities in the oxide as formed.

Abstract: Amorphous precipitated high structure silica pigment useful in the reinforcement of silicone rubber is described. The silica pigment is treated with an aqueous solution of a metal, e.g., calcium and barium, which forms a relatively water insoluble, white or colorless sulfate salt in amounts sufficient to provide at least an equal molar amount of the metal compared to the amount of alkali metal in the silica. Silicone rubber reinforced with such silica pigment exhibits a water swell of less than 4 volume percent.

Abstract: The specification discloses a process for forming a water-free rare earth oxychloride powder by exposing a water-containing rare earth oxide powder to a reactive atmosphere of chlorine and oxygen at 1000.degree. C. for 24 hours to remove water impurities from the oxide powder and to simultaneously convert the oxide powder to the oxychloride powder.

Abstract: A finely divided silicic acid simultaneously suitable as a filtering auxiliary and as a beer stabilizing agent in the filtration of beer. The acid is particulate, and the particles are of an essentially spherical or spheroidal shape with SiO.sub.2 content of at least 95% and an Na.sub.2 O content of less than 0.25%.

Abstract: A new porous silico-crystal, a method of making same and the use thereof in catalytic conversion of organic compounds. The new product has a composition, expressed in terms of moles of anhydrous oxides per 100 moles of silica as follows:(0 to 15)RN : (0 to 1.5)M.sub.2/n O : (0-2)Al.sub.2 O.sub.3 : (100)SiO.sub.2wherein M is at least one cation having a valence n, RN is a C.sub.1 -C.sub.20 organic compound, having at least one amine functional group of pK.sub.a .gtoreq.7 and wherein the zeolite is characterized by the distinctive X-ray powder diffraction pattern shown in Table I. The new silico-crystal is prepared from a reaction mixture comprising a source of silica, C.sub.1 -C.sub.20 organic compounds, as defined above, with or without a source of alumina, and water.

Abstract: A method for producing a precipitated silicon dioxide having a new combination of physical and chemical properties is disclosed. The pigments are produced by acidulating a solution of an alkali metal silicate with an acid under controlled precipitation conditions. The aqueous reaction medium comprising the precipitated silica is then post-conditioned by introducing a second silicate solution into the reaction vessel and thereafter adding additional acid to react with the said second silicate solution. By varying the amount of the silicate employed in the post-conditioning step, a product is obtained which has a unique combination of physical and chemical properties including reduced wet cake moisture content, high surface areas and oil absorptions, improved surface activity, friability, wetting characteristics, and the like. The product has particular utility for use as a rubber reinforcing agent because of its increased surface activity and oil absorption, etc.

Abstract: Novel precipitated silicon dioxide abrasive compositions which can be incorporated into therapeutic toothpaste compositions containing both soluble fluoride salts and soluble phosphate salts are disclosed. The abrasives comprise low structure precipitated silicon dioxides which have been reacted with about 10 to 300 parts per million alkaline earth metal ion, particularly calcium. Reaction with the alkaline earth metal ion minimizes abrasive interaction with the fluoride ion source in therapeutic toothpaste. Also provided are methods for preparation of the novel silicon dioxide abrasives and resulting toothpaste formulations containing such abrasives.

Abstract: A process for removing sulfur dioxide from effluent gas and for recovering amphoteric components such as alumina from solid inorganic combustion byproducts.

Abstract: Novel precipitated silicon dioxide abrasive compositions which can be incorporated into therapeutic toothpaste compositions containing both soluble fluoride salts and soluble phosphate salts are disclosed. The abrasive comprise low structure precipitated silicon dioxides which have been reacted with about 10 to 300 parts per million alkaline earth metal ion, particularly calcium. Reaction with the alkaline earth metal ion minimizes abrasive interaction with the fluoride ion source in therapeutic toothpaste. Also provided are methods for preparation of the novel silicon dioxide abrasives and resulting toothpaste formulations containing such abrasives.

Abstract: A process for stabilizing silica-rich geothermal brine to prevent silica scaling comprises selectively providing a supply of ferric ions, allowing the silica-rich brine to combine with the ferric ions to form insoluble, iron-rich siliceous material and separating the insoluble siliceous material from the brine to form a brine having a silica content which is reduced below the saturation level required for substantially scale-free handling of the brine. In one embodiment of the process in which the brine contains sufficient dissolved ferrous ions, the process comprises selectively contacting the brine with an oxidizing agent, preferably by aerating the brine, to oxidize a selected portion of the ferrous ions to ferric ions, which then combine with silica to form the insoluble iron-rich siliceous material. The ferric ion content of an iron-deficient brine may be augmented by adding ferric and/or ferrous ions to the brine.

Abstract: A method for preparing synthetic cristobalite comprises (1) preparing a mixture containing sources for an oxide of silicon and for an oxide of boron, a base of an alkali or alkaline earth metal or precursor of such base, a polyhydric alcohol, and water; and (2) maintaining the mixture at suitable reaction conditions to effect formulation of the cristobalite, said reaction conditions comprising a reaction temperature within the range of about 30.degree. C. to about 300.degree. C., a pressure of at least the vapor pressure of water at the reaction temperature, and a reaction time that is sufficient to effect crystallization.

Abstract: A crystalline silicate suitable for use in preparing an aromatic alkylation or isomerization catalyst is prepared by hydrothermally crystallizing said crystalline silicate from a silicate solution containing an organic agent, in combination with a base solution, and an acid solution. Crystallization is effected utilizing high shear mixing.

Abstract: Process for the production of silica fibers of the type in which alkali water glass is dry spun into water-containing alkali silicate fibers which are then contacted with solutions containing hydrogen ions for transforming into silica fibers, the improvement being dry-spinning glass free from non-alkaline compounds having a molar ratio of alkaline oxide to silic dry dioxide of from about 1:3 to 1:1.9 and a viscosity of about 10-700 Pa measured at 30.degree. C., at 10.degree.-50.degree. C. in a drying funnel of a temperature of more than 100.degree. C., at a discharge velocity of minimum 5 m/min.

Abstract: A silica polymorph suitable for use in preparing an aromatic alkylation or isomerization catalyst is prepared by hydrothermally crystallizing said silica polymorph from a silicate solution containing an organic agent, in combination with a base solution, and an acid solution. Crystallization is effected utilizing high shear mixing followed by an unagitated period during the crystallization of said silica polymorph.

Abstract: A new silica is formed by hydrothermally reacting an aqueous dispersion of silica and sodium hydroxide, under certain conditions, to form a partly polymerized silicate; spray drying the mixture to form spheres of polysilicate; reacting the polysilicate with sulfuric acid to form a synthetic amorphous silica; and filtering, washing and drying the synthetic silica. This silica is useful as an adsorbent in polyol purification. When milled and air classified to the proper particle size, it is useful as a polishing agent in dentrifrices and as a flatting pigment in paints.

Abstract: Hydrofluoric acid and/or other fluorine compounds are recovered by reacting fluosilicic acid with a sodium-containing compound to form an alkaline aqueous slurry comprising precipitated amorphous silica and dissolved sodium fluoride. The precipitated amorphous silica is separated from the alkaline aqueous slurry leaving an aqueous solution of sodium fluoride. The sodium fluoride solution can be used as such or reacted with other substances (such as alumina, to form synthetic cryolite). Sodium fluoride is recovered from the aqueous solution (as by evaporation or extraction) and used per se or reacted with sulfuric acid to produce hydrogen fluoride.

Abstract: Dentifrice compositions containing a hydrous silica gel having a water content of from about 20 to about 60 weight percent are disclosed. The abrasiveness of the gel is increased by contacting the gel with an alkaline medium to provide a gel pH of about 6 to about 10 and/or preparing the gel by drying and grinding a silica hydrogel that has been washed with an aqueous acidic solution having a temperature of from about 80.degree. to about 100.degree. F.

Abstract: A crystalline SiO.sub.2 --modification, which is characterized by an X-ray diffraction diagram having certain diffraction lines, and a process for the preparation of this crystalline SiO.sub.2 --modification by crystallizing reactive amorphous SiO.sub.2 under hydrothermal conditions in the presence of hexamethylenediamine. Sodium ions, phosphate ions and/or sulfate ions may be added for the crystallization.

Abstract: Hydrofluoric acid is recovered from fluosilicic acid by reacting fluosilicic acid with sodium sulfate to form sodium fluosilicate. The sodium fluosilicate is reacted with a sodium-containing compound to form an alkaline aqueous slurry comprising silica and dissolved sodium fluoride. The reaction occurs under such conditions that the slurry contains precipitated amorphous silica. The precipitated amorphous silica is separated from the alkaline aqueous slurry leaving an aqueous solution of sodium fluoride. Sodium fluoride is recovered from the aqueous solution and reacted with sulfuric acid to produce hydrogen fluoride.

Abstract: Novel crystalline silicas and their use as alkylation catalysts, e.g., methylation of toluene. The performance of the catalysts can be improved by selected promoters.

Abstract: Detergent compositions comprised of conventional detergent ingredients and additives include a non-abrasive silica scouring agent having a B.E.T. surface area of between 80 and 150 m.sup.2 /g, and desirably a C.T.A.B. surface area below 45 m.sup.2 /g and a porosity on the mercury porosimeter below 20 cm.sup.3 /g.

Abstract: A synthetic precipitated silicon dioxide is provided which is an abrasive agent for use in toothpaste or other dentifrice compositions wherein the precipitated silicon dioxide has a controlled particle size, narrow size distribution and controlled functional properties including very low structure and an oil absorption of less than about 60 cc/100 g. The precipitated silicon dioxide provides a product which is more economical to produce than silica xerogels now used in dentifrices, and provides a precipitated silicon dioxide which gives excellent clarity in clear gel dentifrice compositions.

Abstract: A process is herein described for the manufacture of high purity, granular silicic acid from aqueous alkali metal silicate solutions by acidification thereof, freezing and subsequently thawing the reaction mixture, and filtering, washing and drying the insoluble residue formed, in which the alkali metal silicate solutions have a molar ratio of SiO.sub.2 :Me.sub.2 O of from about 2:1 to 20:1, Me representing an alkali metal, and before freezing the aqueous alkali metal silicate solutions are adjusted to a pH value in the range of from about 2.5 to 6 and to a SiO.sub.2 content of from about 1 to 10 percent by weight by means of one or more aqueous solutions or suspensions of organic acids which complex aluminum, titanium, and iron ions and which form soluble alkali metal salts under the conditions of the process.

Abstract: A synthetic amorphous silica having a CTAB surface area of from about 80 to about 125 m.sup.2 /g and a structure index of at least 0.80 is disclosed as adapted for the reinforcement of elastomeric materials, as well as methods for the preparation thereof.

Abstract: A method of producing silica compositions from hydrogels in which the hydrogel is washed in a first water-soluble organic liquid to remove a principal portion of the water. The washed composition is then washed in at least one second water-soluble organic liquid and the second organic liquid is removed from the composition by venting the second organic liquid from the composition at a temperature above the critical temperature of the second organic liquid to produce a silica composition.

Abstract: Process for the manufacturing of silicas having a specific surface area ranging between 100 and 600 sq m/g, which does not vary upon drying, due to the action of a strong acid on an alkaline silicate, characterized by the fact that the addition of strong acid to the alkaline silicate is interrupted one to three times.

Abstract: Amorphous silicas having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500.mu. and a thickness of about 50 A to about 1.mu., the length being at least about 10 times the thickness, the amorphous silicas being in the form of primary particles, secondary particles, aqueous dispersions of the particles and shaped bodies.

Abstract: A finely divided silicic acid having a pH>6 is prepared by spray drying, in the presence of a base or basic-reacting substance, a highly concentrated silicic acid suspension having excess, unwanted acidity.

Abstract: Hydrofluoric acid is recovered from fluosilicic acid by reacting fluosilicic acid with sodium hydroxide to form a first slurry having a pH of from about 11 to about 14, the first slurry containing sodium metasilicate and precipitated sodium fluoride. Sodium fluoride is recovered from the first slurry leaving a first solution which is reacted with sodium fluosilicate or fluosilicic acid or both to form a second slurry comprising silica and dissolved sodium fluoride. The reaction occurs under such conditions that the second slurry contains precipitated amorphous silica. The precipitated amorphous silica is separated from the second slurry leaving a second solution of sodium fluoride. Sodium fluoride is recovered from the second solution. Recovered sodium fluoride is reacted with sulfuric acid to produce hydrogen fluoride.

Abstract: Hydrofluoric acid is recovered from fluosilicic acid by reacting fluosilicic acid with sodium sulfate to form sodium fluosilicate. The sodium fluosilicate is reacted with sodium hydroxide to form a first slurry having a pH of from about 11 to about 14, the first slurry containing sodium metasilicate and precipitated sodium fluoride. Sodium fluoride is recovered from the first slurry leaving a first solution which is reacted with sodium fluosilicate or fluosilicic acid or both to form a second slurry comprising silica and dissolved sodium fluoride. The reaction occurs under such conditions that the second slurry contains precipitated amorphous silica. The precipitated amorphous silica is separated from the second slurry leaving a second solution of sodium fluoride. Sodium fluoride is recovered from the second solution. Recovered sodium fluoride is reacted with sulfuric acid to produce hydrogen fluoride.

Abstract: A polymerization catalyst and method which produces substantially pure silica that is uncontaminated with alkali metal or alkaline earth metal ions before associating with the resulting support silica the chromium compound which is either a chromium oxide or a chromium compound convertible to the oxide in the heat activating of the catalyst. In general, the catalyst is prepared by hydrolyzing an organosilicate ester to form suspended silica with the hydrolyzing being catalyzed with an aqueous acid solution containing mixed solvents. Next the resulting liquid is neutralized with an alkali free basic solution such as ammonium hydroxide at controlled low temperature. Then sufficient water is added to permit stirring the resulting gel and this is stirred and heated forming a suspended silica. The silica is then separated and dried, associated with the chromium compound and the mixture then heat activated in the presence of oxygen.

Abstract: A method for producing a precipitated silicon dioxide having a new combination of physical and chemical properties is disclosed. The pigments are produced by acidulating a solution of an alkali metal silicate with an acid under controlled precipitation conditions. The aqueous reaction medium comprising the precipitated silica is then post-conditioned by introducing a second silicate solution into the reaction vessel and thereafter adding additional acid to react with the said second silicate solution. By varying the amount of the silicate employed in the post-conditioning step, a product is obtained which has a unique combination of physical and chemical properties including reduced wet cake moisture content, high surface areas and oil absorptions, improved surface activity, friability, wetting characteristics, and the like. The product has particular utility for use as a rubber reinforcing agent because of its increased surface activity and oil absorption, etc.

Abstract: In the purification of an ammonium fluoride solution containing silicic acid by adding iron (III) ions and precipitating the iron (III) ions at a pH above 8.5 and a concentration of free ammonia in the solution of more than about 1% by weight, the silicic acid being carried with the iron (III) ion precipitate, the improvement which comprises adding the iron (III) ions to the ammonium fluoride solution at a temperature below about 30.degree. C. and, before removal of the precipitate, to the solution a salt of at least one of the alkali metals, alkaline earth metals, zinc, aluminum and lead in such quantity that the solution becomes saturated with such salt.

Abstract: A method for producing precipitated silica products having a unique combination of physical and chemical properties is disclosed. The products are produced by acidulating a solution of an alkali metal silicate with an acid under carefully controlled precipitation conditions. In accordance with the method, at least a portion of the alkali metal silicate solution theoretically required to react with said acid is initially charged to the reaction vessel. Thereafter, the remaining silicate solution and the acid are simultaneously added to the reaction vessel in a manner to control the alkalinity of the reaction medium. By controlling the percent of the silicate solution initially charged to the reaction vessel, silicas having predetermined properties can be obtained. Properties of the products include low wet cake moisture content, low structure, low oil absorption, high abrasiveness, and low void volume. The products can be used as abrasive and polishing agents in dentifrice compositions.

Abstract: There is provided a process for treating air-borne dust containing silicon dioxide in order to form a silicic acid or a silicate. The air-borne dust is dissolved in an alkali metal hydroxide solution to form an alkali metal silicate solution. The alkali metal silicate solution is purified by treating it with activated charcoal and/or oxidation agents. Non-decomposable substances remaining after the purification step are removed from the alkali metal silicate solution. The alkali metal silicate solution is then reacted with acids and/or salts of aluminum, magnesium and calcium. The resulting product is then filtered, washed and dried, and then comminuted to form a finely divided, amorphous, substantially pure, precipitated, silicic acid or silicate having a whiteness according to Berger at a wave length of 460 m.mu. of about 90 to about 95% and a specific surface area of about 30 to about 800 m.sup.2 /g BET.

Abstract: Free flowing, finely divided precipitated silicic acid granules of reduced dust content and reduced abrasion are obtained by a process including the step of subjecting a silicic acid suspension to intensive shearing action. Rubber compositions containing the precipitated silica produced in this way are also disclosed.

Abstract: Inorganic hydrogels, e.g., silica-containing hydrogels, are contacted with contacting agents comprising oxygen-containing organic compounds and then dried to remove the liquid components therefrom. The contacting agent can also be an oxygen-containing organic compound in combination with a liquid hydrocarbon or an oxygen-containing compound in combination with a liquid hydrocarbon and a surfactant. The hydrogel can be treated with a catalytic metal compound prior to or during the contacting with the contacting agents in order to produce a composition after drying and calcining that is catalytically active for olefin polymerization. The treated hydrogel can also, after drying, be treated anhydrously with a catalytic metal compound to produce a composition that is active for 1-olefin polymerization upon calcination.

Abstract: A method for producing a precipitated silicon dioxide having a new combination of physical and chemical properties is disclosed. The pigments are produced by acidulating a solution of an alkali metal silicate with an acid under controlled precipitation conditions. The aqueous reaction medium comprising the precipitated silica is then post-conditioned by introducing a second silicate solution into the reaction vessel and thereafter adding additional acid to react with the said second silicate solution. By varying the amount of the silicate employed in the post-conditioning step, a product is obtained which has a unique combination of physical and chemical properties including reduced wet cake moisture content, high surface areas and oil absorptions, improved surface activity, friability, wetting characteristics, and the like. The product has particular utility for use as a rubber reinforcing agent because of its increased surface activity and oil absorption, etc.

Abstract: A method for producing a precipitated silicon dioxide having a new combination of physical and chemical properties is disclosed. The pigments are produced by acidulating a solution of an alkali metal silicate with an acid under controlled precipitation conditions. The aqueous reaction medium comprising the precipitated silica is then post-conditioned by introducing a second silicate solution into the reaction vessel and thereafter adding additional acid to react with the said second silicate solution. By varying the amount of the silicate employed in the post-conditioning step, a product is obtained which has a unique combination of physical and chemical properties including reduced wet cake moisture content, high surface areas and oil absorptions, improved surface activity, friability, wetting characteristics, and the like. The product has particular utility for use as a rubber reinforcing agent because of its increased surface activity and oil absorption, etc.

Abstract: Silica products having very high structure as defined by the ability of the silica material to hold water in its wet cake, high oil absorption, and very high surface area can be produced by controlling the rate of acidulation during their production and maintaining the same at a very low rate during the course of the addition of acid to the solution of alkali metal silicate. The control of the index of refraction of the silica so produced is achieved by introduction of controlled amounts of adduct material such as aluminum sulfate to the acid prior to its introduction to the silicate solution.

Abstract: A method is provided for treating a hydrogel with a saturated, aliphatic alcohol selected from the group consisting of 1-pentanol, 2-pentanol, 3-methyl-1-butanol, 4-methyl-2-pentanol, 2,2-dimethyl-1-propanol and 1-hexanol to remove water thereby producing a dried product that retains a porous structure and is particularly suitable upon impregnation with a polymerization catalyst for use in promoting the production of ethylene polymers of melt index in excess of about 6.6.

Abstract: Aluminosilicate zeolites are prepared containing an outer aluminum-free shell. The outer shell is essentially SiO.sub.2 that has crystallized on the zeolite surface in the ZSM-5 type configuration, leading to a more selective catalyst.

Abstract: A hydrometallurgical process for the treatment of a soluble silicate-bearing material for the recovery of its valuable metal content by leaching the silicate-bearing material at an elevated temperature with an aqueous solution of a mineral acid, precipitating silicic acid during the same stage in an easily settling and filtering form, the silicate-bearing material being added at such a rate that its concentration calculated as SiO.sub.2 corresponds to the simultaneously precipitating silicic acid quantity, and by finally separating the solid material from the valuable-metal-bearing solution.

Abstract: A new method for producing precipitated silicas having a unique combination of physical and chemical properties is disclosed. The silicas are produced by acidulating a solution of an alkali metal silicate having a specific SiO.sub.2 /Na.sub.2 O mol ratio with an acid until precipitation just beings. 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 and are characterized by their low structure, low oil absorption, high abrasiveness and high pack density, and as such are distinctly different from silicas used as reinforcing fillers in rubber. In a particularly advantageous embodiment, an adduct material, such as aluminum, is added to control the refractive index of the precipitated pigment. Products produced in this manner have particular utility for use as abrasion and gelling agents in clear toothpaste compositions.