Abstract: In the method, a suspension of silica particles in water is provided, the suspension is gelled, the resulting gel is dried under microwaves, the dried gel is fractioned into silica granules having a diameter lying in the range 10 .mu.m to 1000 .mu.m, having an apparent density of about 0.5 g/cm.sup.3 to 0.6 g/cm.sup.3, and a porosity of less than 20%, and the granules are screened in the range 100 .mu.m to 500 .mu.m. The suspension in water of silica particles is made by mixing silica soots having a size of less than 0.1 .mu.m and silica grains having a size greater than 1 .mu.m. Its maximum concentration in total weight is greater than that of a suspension of synthetic soots on their own, thereby making it possible to increase the production capacity of the method. Advantageously, the out-of-range granules rejected by the screening are recycled as silica grains for the aqueous suspension, thereby making it possible to increase the accumulated production efficiency of the method.

Abstract: A three-dimensional composite of silica spheres interconnected by resin is provided having a three-dimensional network structure including silica particles having the following structural and dynamic characteristics and a resin present in the internal pores of said network:(a) three-dimensionally interconnected spherical silica particles having a diameter of 6 to 30 .mu.m;(b) on the surface of said spherical silica particles, a specific surface area of 300 to 400 m.sup.

Abstract: Silica deposits formed during a continuous process for preparing polysilicate microgel are removed and purged form the process by elastically deforming the vessel walls, reducing plugging.

Abstract: A method of manufacturing a silica powder using a sol-gel technique, wherein a suspension consisting of synthetic silica soot, having a specific surface area of less than 80 m.sup.2 /g, is made in water to form a concentration of 50% to 75% by weight of silica; the suspension is gelled; the resulting gel is dried without forming a crust and with microwaves and broken up into silica grains having an apparent density of 0.5 g/cm.sup.3 to 0.6 g/cm.sup.3 ; and screening of the dry gel is performed to provide grains having a desired size.

Abstract: Preparation of inorganic aerogels based on oxides of the metals magnesium, aluminum, silicon, tin, lanthanum, titanium, zirconium, chromium and/or thorium by producing a hydrogel in a sol/gel process, replacing the water in the hydrogel by an organic solvent, and drying the solvent-moist gel, takes place by conducting the drying step by exposing the solvent-moist gel to an ambient temperature which is above the boiling temperature of the solvent and at a pressure which is below the supercritical pressure of the solvent in such a way that the solvent within the gel is heated up very rapidly and evaporates.

Abstract: The specification describes sputtering processes for the deposition of silicon dioxide films doped with high levels of oxides or other materials to alter the optical and/or electrical characteristics of the films. Sol gel methods are used to prepare composite sputtering targets of ultra fine mixtures of materials so the composition of the sputtered films replicate the composition of the target.

Abstract: A process is described to modify the chemical structure of an aerogel under conditions which inhibit plasma formation within the aerogel pores, which process includes; (a) providing an aerogel with a pore size of less than 0.1.mu.; (b) exposing the initial aerogel to at least one gas selected from the group consisting of reducing gas, oxidizing gas, noble gas and combinations thereof, with the proviso that at least one reducing gas or one oxidizing gas is present; and (c) irradiating the combination of step (b) while maintaining the temperature to preserve the structural composition of the aerogel at a pressure of between about 0.1 and 54 Torr for between and about 5 and 960 minutes. This process produces a modified aerogel wherein the pore size does not allow for plasma formation within the pore. Chemical reactions occur within the pores of the aerogel of a nonplasma nature. These modified aerogels have a number of uses, including catalysts, ceramics, composites, chemical sensors, LED's and the like.

Abstract: Silica compatible with flavors, exhibiting, at an RP/DA abrasivity lower than or equal to 10, a compatibility with flavors which is higher than 10% and, at an RP/DA abrasivity higher than 10, a compatibility with flavors of at least 30%. Process for the preparation of flavor-compatible silica by treating the surface of a silica originating from the reaction of an alkali metal silicate with an inorganic or organic acidic agent, the silica being in dry form or in an aqueous suspension, with the aid of an organic compound capable of developing hydrogen bonds or ionic bonds with, respectively, the Si--OH silanol groups or the SiO.sup.- anionic groups at the surface of the said silica to be treated, the said treated silica being subsequently, if necessary, isolated and/or washed and/or dried. Use in dentifrice compositions and dentifrice compositions including the said silica.

Abstract: The method for producing a bulk silica porous material is presented. The obtained material has a large crystal size serving to reduce light scattering, and uniform and adjustable pore size. This can be utilized for optical and electronic functional materials. The method comprises the steps of:forming a silica/surfactant composite by mixing starting materials containing an alkoxysilane, water and a surfactant and allowing to the starting materials to react;maturing said silica/surfactant composite by allowing the same to stand in a closed container to effect the development of a silica network structure and the formation of porous structure in said composite;drying said matured silica/surfactant composite for removing the solvent and for condensation of said matured silica/surfactant composite; and,sintering said condensed silica/surfactant composite to remove the surfactant to obtain a silica porous material.

Abstract: The invention relates to a new process for the preparation of precipitated silica which has a good dispersibility and very satisfactory reinforcing properties. It also relates to new precipitated silicas which are in the form of powder, of substantially spherical beads or of granules, these silicas being characterized by the fact that they have a CTAB specific surface of between 90 and 250 m.sup.2 /g, a BET specific surface of between 90 and 250 m.sup.2 /g, a DOP oil uptake lower than 300 ml/100 g, a zinc content of between 1 and 5% by weight, and by the fact that the number N of stearic acid molecules consumed per nm.sup.2 of silica surface, when stearic acid is reacted with this silica in xylene for 2 hours at 120.degree. C., is at least 1. The invention also relates to the use of the said silicas as reinforcing fillers for elastomers, especially for improving their rheological properties.

Abstract: The present invention is hydrophobic silica gels having a reduced surface area and a method for their preparation under neutral conditions. The method comprises two steps, where in the first step the pH of a mixture comprising a silica hydrosol and colloidal silica is adjusted with a base to within a range of pH 3 to pH 6 to facilitate formation of a silica hydrogel having incorporated therein colloidal silica. In the second step the silica hydrogel is contacted with an organosilicon compound in the presence of a catalytic amount of a strong acid to effect hydrophobing of the silica hydrogel to form a hydrophobic silica gel having a surface area within a range of about 100 m.sup.2 /g to 450 m.sup.2 /g in the dry state. In a preferred process the hydrophobic silica gel is contacted with a sufficient quantity of a water-immiscible organic solvent to convert the hydrophobic silica hydrogel into a hydrophobic silica organogel.

Abstract: A primary object of the present invention is to easily and securely fix a photocatalyst to a substrate. According to the invention, there is provided a process for preparing a photocatalyst material, the process comprising a first step of forming an undercoating containing silica gel on a substrate, a second step of bringing titanium tetrachloride into contact with the undercoating and a third step of heat-treating the coated substrate.

Abstract: A method for preparing a three dimensionally connected silica spheres-resin composite, which comprises hydrolyzing and polymerizing a low molecular weight polyalkoxysilane in the presence of an acid catalyst in a mixed solution of the low molecular weight polyalkoxysilane and a water-soluble polymer in a solvent mixture of water and alcohol to obtain a three dimensional connected silica spheres, impregnating the three dimensional connected silica spheres with at least one material selected from resin-forming monomers and resin-forming prepolymers, and curing the material. The composite obtained by the above method retains its strength even at high temperatures where the organic matter undergoes pyrolysis or burnout.

Abstract: The invention relates to a process for the production of modified SiO.sub.2 aerogels in whicha) a silicatic lyogel is prepared,b) if desired, the lyogel prepared in step a) is subjected to a solvent exchange with another organic solvent,c) the gel obtained in step a) or b) is reacted with at least one chlorine-free silylating agent, andd) the gel obtained in step c) is dried subcritically,wherein the chlorine-free silylating agent is a compound of the formula I ##STR1## wherein each R.sup.1 is identical or different and is selected from a group consisting of linear C.sub.1 -C.sub.6 -alkyl radicals, branched C.sub.1 -C.sub.6 -alkyl radicals, cyclohexyl radicals and phenyl radicals,R.sup.2, R.sup.3 and R.sup.4 are identical or different and are selected from the group consisting of hydrogen atoms, linear C.sub.1 -C.sub.6 -alkyl radicals, branched C.sub.1 -C.sub.6 -alkyl radicals, cyclohexyl radicals and phenyl radicals;and n=1, 2 or 3.

Abstract: The present invention relates to particulate compositions having improved thermal conductivity values. An embodiment of the present invention is a particulate composition which under a 103421 Pa load, at 20.degree. C., and at a pressure (P) within the range of 133.322-13332.2 Pa, in Nitrogen, has: a packing density of less than or equal to 160 kg/m3, and a Thermal Conductivity (TC) at 133.322-1333.22 Pa of less than or equal to (0.260 lnP+4.53) milliWatt/meterK (mW/m.multidot.K) and a TC at 1333.22-13332.2 Pa of less than or equal to (0.824 lnP+0.47) mW/m.multidot.K. A preferred particulate composition is a gel composition. Also disclosed are insulation bodies comprising the particulate compositions.

Abstract: This invention relates to a process for the preparation of an inorganic oxide gel comprising contacting at least one fluorinated inorganic oxide precursor with a fluorinated gelling agent in the presence of at least one fluorinated solvent to form a solution; allowing sufficient time for gelation to occur; and isolating the inorganic oxide gel. Gels made by this process are useful as coatings and as components in inorganic/organic hybrid materials.

Abstract: The invention relates to a new process for the preparation of precipitated silica which has a very good dispersibility and very satisfactory reinforcing properties. It also relates to new precipitated silicas which are in the form of powder, of substantially spherical beads or of granules, these silicas being characterized by the fact that they have a CTAB specific surface of between 100 and 240 m.sup.2 /g, a DOP oil uptake lower than 300 ml/100 g, a pore distribution such that the pore volume consisting of the pores whose diameter is between 175 and 275 .ANG. represents less than 50% of the pore volume consisting of the pores of diameters which are smaller than or equal to 400 .ANG., a median diameter, after disintegration with ultrasound, smaller than 5 .mu.m and an aluminium content of at least 0.35% by weight. The invention also relates to the use of the said silicas as reinforcing fillers for elastomers.

Abstract: A method for production of high specific surface area silica gel by hydrolysis of silicon tetrahalide, wherein a solution of silicon tetrahalide in a non-reactive solvent such as alcohol is mixed with water to produce silica gel having a high surface area and narrow pore diameter distribution especially suited for use as normal phase packing material in high performance chromatography columns. The water contains fluoride ions if the halide is chloride. Reverse phase packing material can be prepared by reacting the normal phase silica gel with organochlorosilanes to prepare bonded reverse phase material for use in high performance liquid chromotagraphy systems.

Abstract: Siliceous oxides having a combination of low total volatiles content and basic pH are useful as odor control agents in organic resin systems, especially polyolefin-based systems. These modified siliceous oxides advantageously reduce odor and off-trade while minimizing discoloration of the resin. The adsorbents are especially useful for resin systems containing fatty acid amide slip aids.

Abstract: System for thermal and/or acoustic insulation of a tube intended, for example, to allow the outflow of hydrocarbons originating from an oil deposit, consisting of a sleeve surrounding the tube over at least a part of its length. According to the invention, the sleeve consists of an aerogel. A method for thermal and/or acoustic insulation of a tube is also described.

Abstract: A precipitated silica with the following physicochemical properties:______________________________________ BET surface area 35 to 350 m.sup.2 /g BET/CTAB surface area ratio 0.8 to 1.1 Pore volume, PV 1.6 to 3.4 ml/g Silanol group density (V2 = 6 to 20 ml NaOH consumption) Average aggregate size 250 to 1500 nm CTAB surface area 30 to 350 m.sup.2 /g DBP value 150 to 300 ml/100 g V.sub.2 /V.sub.1 by Hg porosimetry 0.19 to 0.46 DBP/CTAB 1.2 to 2.4. ______________________________________is produced by reacting alkali silicate with mineral acids at temperatures of 60.degree. to 95.degree. C. while maintaining a pH of 7.5 to 10.5 and continuously stirring, continuing the reaction to a solids concentration in the precipitation suspension of 90 to 120 g/l, adjusting the pH value to a value of less than or equal to 5, filtering out, washing, drying and optionally grinding or granulating the precipitated silica. The precipitated silica is used as a filler in vulcanizable rubber compounds and vulcanizates.

Abstract: The invention relates to a new process for the preparation of precipitated silica which has a good dispersibility and very satisfactory reinforcing properties. It also relates to new precipitated silicas which are in the form of powder, of substantially spherical beads or of granules, these silicas being characterized by the fact that they have a CTAB specific surface of between 90 and 250 m.sup.2 /g, a DOP oil uptake lower than 300 ml/100 g, a pore distribution such that the pore volume consisting of the pores whose diameter is between 175 and 275 .ANG. represents less than 50% of the pore volume consisting of the pores of diameters smaller than or equal to 400 .ANG., a zinc content of between 1 and 5% by weight and by the fact that the number N of molecules of stearic acid consumed per nm.sup.2 of silica surface, when stearic acid is reacted with the said silica in xylene for 2 hours at 120.degree. C., is at least 1.

Abstract: Mesoporous desigels are fabricated as nitrides, carbides, borides, and silicides of metals, particularly transition metals, and most particularly early transition metals. The desigels are prepared by forming a gel of a metallic compound, and removing solvent from the gel. In some instances, the thus produced desigel may be further reacted to change its composition, while preserving its mesoporous structure. The materials are particularly suited as electrodes for capacitors, including ultracapacitors, and for batteries.

Abstract: A hydrophobic aerogel is fabricated by reacting a polymer having a skeleton structure of (SiO.sub.2).sub.n with a hydrophobic agent having hydrophobic groups as well as functional groups reactive to silanol groups to obtain a denatured polymer, forming a gel consisting of two phase of a dispersing medium and the denatured polymer which was performed a hydrophobic treatment, and then, supercritically drying the gel at temperature and pressure above a critical point of the dispersing medium. The hydrophobic aerogel has improved characteristics free from deterioration in light transmissivity as well as lowered thermal resistance and also free from a dimensional variation such as shrinkage which would otherwise occur by contact with moisture, so that it can maintain the excellent characteristics for long time periods. Particularly, the aerogel is useful as a material having excellent light transmissivity and thermal resistance.

Abstract: Process for the preparation of aerogels by subcritical drying of inorganic and organic hydrogels and lyogels to give aerogels, dielectric drying methods being used.

Abstract: Colloidal compositions based on fillers, sol oxides, poly silicates, and, optionally, pigmenting agents, and their method of production the solid disperse phase not only operates to cross-link but also as an overmatrix incorporating macroparticles therein. The dispersant is finally chemically set with excess setting agent so that the preliminary product can be finalized to the desired material. For this purpose a matrix-like substance of filler-like macroparticles and sol oxide (crosslinling substance) and a buffer are brought together for assisting the formation of the overmatrix and are processed. This substance is pigmentable by introducing a variation mixture into the substance, so that a wide range of characteristics can be obtained. The substance directed at the desired material, namely a hydration and balancing process stage and a subsequent setting and stabilizing process stage.

Abstract: A suspension containing a novel reactive ultrafine particulate silica having a radius of gyration of at most 10 .ANG., has an excellent storage stability, and provides excellent various properties as a hard coating composition.

Abstract: A process for the preparation of a silica aerogel that includes subjecting a mixture that includes an organosilicon compound and ethyl acetoacetate to hydrolysis and polycondensation in an acidic medium to obtain a transparent gel. The organic solvent is substituted by liquid carbon dioxide and the carbon dioxide is evacuated under supercritical conditions of the carbon dioxide to obtain an aerogel.

Abstract: Xerogels and a process for their preparation involving acidifying an aqueous waterglass solution, polycondensing the resulting silica by addition of a base, removing most of the water from the gel by washing the gel with an organic solvent, reacting the resulting gel with a silylation agent and then drying the silylated gel under subcritical conditions.

Abstract: A method of removing silica or silicates from solids results from the acid hydrolysis of materials containing cellulose and hemicellulose is disclosed. The method includes the steps of treating the solids with a metal hydroxide solution to produce an extract, reducing the pH of the extract to produce silicic acid, and removing the silicic acid from the extract.

Abstract: A process for the preparation of mixed silica-zirconia sols and mixed oxides in spherical form, comprising mixing a silicon alkoxide with a solution of an inorganic zirconium salt in a low molecular weight polyol and subjecting the intermediate thus formed to acid hydrolysis in a water medium.

Abstract: A wet silica gel can be prepared by a process comprising the steps of contacting a stable, aqueous, fluid, silica system having a pH greater than 7.5 with an ion exchange resin which removes metal ions and replaces them with H+ ions and thereby reduces the pH to less than 5.0, adding an organic liquid to the aqueous silica system, providing, however, that the organic liquid added stays in one phase with the aqueous, silica, system, and does not cause the silica to precipitate, and adding a base to the silica system so that the pH of the silica system is in the range of from about 5.0 to about 7.5, and allowing the wet silica gel to form. The wet silica gel formed by this process is characterized by its high organic solvent content and the low concentration of basic metal ions.

Abstract: The invention relates to a process for preparing modified SiO.sub.2 gels, in which the gel is aged using a solution of a condensable alkyl and/or aryl orthosilicate, or using an aqueous silicic acid solution, in order to strengthen the structure of the gel.

Abstract: This invention describes an acoustic transducer, either speaker or microphone, that uses an aerogel diaphragm or an aerogel acoustic interface made of magnetic aerogel or conductive aerogel or both. In the case of a speaker, the aerogel diaphragm is directly driven either by electromagnetic or electrostatic means to reproduce high fidelity sound. In the case of a microphone, the aerogel diaphragm is modulated by acoustic energy, and in turn, the aerogel diaphragm electromagnetically or electrostatically modulates a field detection element resulting in a high fidelity electrical audio signal output.

Abstract: Liquid comprising from 93 to 100 percent by weight alcohol is removed from silica alcogel at subcritical temperature to produce silica aerogel. The silica aerogel produced by the method of the present invention not only has high porosity, but in most instances it also has a narrow distribution of small pore sizes. The silica aerogel is preferably reduced in size so as to form particulate silica aerogel.

Abstract: A statistically large population of particles of amorphous precipitated silica comprising pigmentary phase particles and glassy phase particles and having a glassy phase fraction in the range of from 0.3 to 30 area percent is useful as an abrasive for dentifrice compositions, especially toothpaste.

Abstract: Novel silica particulates adopted for formulation into dentifrice compositions have a unique surface chemistry as to be at least 50% compatible with zinc values, and have a number of OH functions, expressed as OH/nm.sup.2, of at most 15 and a zero charge point (PZC) of from 3 to 6.5.

Abstract: A process for producing zinc oxide-containing spherical silica, which comprises emulsifying, in an organic solvent containing a surfactant, a dispersion having zinc oxide with a particle size of from 0.005 to 0.5 .mu.m dispersed in an aqueous alkali metal silicate solution in an amount of from 10 to 70 wt % based on the total amount of zinc oxide and SiO.sub.2 in the aqueous alkali metal silicate solution, followed by gelation of the resulting emulsion with carbon dioxide gas.

Abstract: Hydrophobic silica aerogels obtainable by reacting a waterglass solution with an acid at a pH of from 7.5 to 11, substantially removing ionic constituents from the resulting silica hydrogels by washing with water or dilute aqueous solutions of inorganic bases, while the pH of the hydrogels is kept in the range from 7.5 to 11, displacing the aqueous phase contained in the hydrogel by an alcohol, and subsequent supercritical drying of the resulting alcogels.

Abstract: Process for the preparation of aerogels by subcritical drying of inorganic and organic hydrogels and lyogels to give aerogels, dielectric drying methods being used.

Abstract: A temperature-activated polysilicic acid is prepared by heating an acidified aqueous alkali metal silicate. The temperature-activated polysilicic acid is used in the production of paper for improvement of retention and water removal.

Abstract: A method for forming a low temperature cofired ceramic package which is made using a multi-layered densified spherical powder formed via a sol-gel process. This densified powder is formed from layers of SiO.sub.2 reacted with trimethyl borate. The spherical powder has a preselected particle size and boron content sufficient to render the low temperature cofired ceramic package fully dense, even in the presence of a second phase filler ceramic, at a sintering temperature below 1000.degree. C. Binder material is added to the spherical powder and ceramic filler to form a plurality of tapes. A ceramic assembly is then formed by layering the plurality of tapes upon one another and firing the ceramic assembly at a temperature below 1025.degree. C. to form a fully dense cofired ceramic package. In order to form the multi-layered densified spherical powder, a silica core, which is formed using a sol-gel process, is reacted with trimethyl borate.

Abstract: A fluorescent substance of which main component is comprised from 32 mol % to 35 mol % of silicon element and from 68 mol % to 65 mol % of oxygen element, and in which includes from 10 ppm to 1 wt % of silicon carbide and silicon nitride as an activator. And, a manufacturing method of the fluorescent substance by hydrolyzing silicon alkoxide by using alkali or acid catalyzer under the presence of carbon, and by heat treating the obtained precursor at the temperature of 500.degree. C. to 900.degree. C.

Abstract: A method for preparing inorganic oxide-based materials of spherical form with substantially monomodal distribution, consisting of forming a sol of at least one of the inorganic oxides of interest, adding to said sol a solvent immiscible with the sol, finely dispersing the obtained two-phase mixture into a dispersion of particles of equal diameter, growing said particles by limited coalescence to the desired diameter, gelling said mixture by adding a second solvent containing a gelling agent, and removing the solvent.

Abstract: The invention relates to modified SiO.sub.2 gels (xerogels), the preparation thereof and the use thereof as thermal insulators. The xerogels are prepared by acidifying an aqueous waterglass solution, polycondensing the silicic acid produced thereby, by adding a base, to an SiO.sub.2 gel, removing the water from the resulting gel by extractive distillation with an organic solvent which forms with water an azeotrope which separates on cooling into two phases, reacting the gel with a silylating agent, and then drying at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used for removing the water.

Abstract: Precipitated silicas having wet cake moisture values in excess of 85%, BET surface areas of 600-700 m.sup.2 /g, oil absorption values of 50 to 60 cc/100 g, total intruded volume of about 1.2 to 0.8 cc/g, and a median pore radius of 50 .ANG. to 20 .ANG. are produced by a low temperature silica precipitation process. The silicas have unique flatting characteristics and are additionally useful as conditioning agents for food and salt and in dentifrice compositions.

Abstract: An amorphous silica has a pore size distribution wherein 90% of the pores have a diameter above 15 nanometers, and less than 20% of the pore volume is in pores having a pore diameter between 10 and 20 nanometers, the amorphous silica having a CTAB surface area of less than 100 m.sup.2 /g, the amorphous silica having a matting efficiency of below 20 gloss units at an incidence angle of 60.degree. and a loading of 5% by weight. It can be prepared by a precipitation route. It is used in thixotropic paints and lacquers.

Abstract: Novel precipitated silica particulates, well suited for conditioning/sorbing a wide variety of liquid active agents thereon, e.g., the vitamins, have (i) a BET surface area of at least 170 m.sup.2 /g; (ii) an oil absorption (DOP) ranging from 220 to 300 ml/g; (iii) a fill density in the packed state of at least 0.29; (iv) a mean particle diameter ranging from 80 to 150 .mu.m; and (v) a maximum grain size distribution index of 0.70.

Abstract: A stabilizing agent for beer comprising a particular amorphous silica exhibiting a large negative zeta-potential in the pH region of the beer. The amorphous silica is of the xerogel type and has a specific surface area of from 100 to 600 m.sup.2 /g, a porous volume of 1 to 2 cc/g, and OH groups in a number of not larger than 7/nm.sup.2 on the silica surface, and an aqueous suspension thereof exhibits a pH of from 4 to 6.2 and a zeta-potential of negative polarity, the absolute value thereof being not smaller than 20 mV. When used as a stabilizing agent for beer, the amorphous particulate silica effectively removes the haze since the aqueous suspension thereof exhibits a weakly acidic pH which is close to that of the beer and a large negative zeta-potential, and helps improve froth-holding property and fragrance-retaining property of the beer.

Abstract: Novel silica particulates especially adapted for formulation to dentifrice compositions exhibit unique physical and chemical properties. In one embodiment, silica particulates have a unique surface chemistry as to be at least 50% compatible with zinc values, and have a number of OH functions, expressed as OH/nm.sup.2, of at most 15 and a zero charge point (PZC) of from 3 to 6.5. In a second embodiment, particulates have a surface chemistry as to be at least 65%, and preferably at least 90% compatible with guanidine values, notably chlorhexidine, and acidity function thereof, Ho, of at least 3.3. In a third embodiment, silica particulates are compatible with organic amines, and have a pH, in aqueous suspension, which varies according to the equations pH.ltoreq.7.5-0.7 log(C) and pH.gtoreq.5.0-0.5 log(C) and which also varies as a function of the electrical conductivity thereof, according to the equations pH.ltoreq.8.5-0.4 log(D) and pH.gtoreq.7.0-0.