Abstract: The invention relates to high-porosity silica xerogels and a process for their preparation consisting of subjecting silica alcogels to thermal treatment in the presence of organic compounds containing amino and hydroxyl groups.The xerogels are characterised by a total pore volume .gtoreq.2 cc/g and a mean pore diameter .gtoreq.100 .ANG..

Abstract: A process for producing the precursor of a precipitated catalyst for the sub.3 synthesis, based on Fe, Al, Co and K oxides, which comprises the steps of:(A) preparing an aqueous solution of water-soluble compounds of Fe, Al and Co--adding iron as a water-soluble ferrous salt of an organic acid--and causing, by addition of an alkaline precipitating solution, the co-precipitation of the corresponding (Fe, Al and Co) hydroxides, which still contain iron in the ferrous form;(B) oxidizing the hydroxide suspension prepared according to point (A) until divalent iron and trivalent iron are in a ratio to each other which ranges from 0.20 to 0.50;(C) operating an alkaline doping with a potassium compound and heating in an inert atmosphere up to above 850.degree. C.

Abstract: Mixed oxides of alumina and zirconia having a controlled granulometric distribution, consisting essentially of spherical, submicronic particles, wherein zirconia is distributed uniformly in alumina and may reach 38% by weight, said zirconia being in the stabilized form at room temperature in the tetragonal phase, after having subjected the amorphous hydrated composite oxides to thermal treatments, wherein occurs the transition of zirconia to the tetragonal phase.

Abstract: A process for preparing hydrated alumina consisting essentially of spherical particles having a narrow granulometric distribution (polydispersion index dw/dn.ltoreq.2) starting from aqueous solution of aluminum sulphate, the molar ratio SO.sub.4.sup.= /Al.sup.3+ being greater than 1, by homogeneous precipitation in the presence of cationic polyelectrolytes, which are soluble under the reaction conditions and have a mean molecular weight higher than one million and an ionicity, deriving from the cationic groups present in the polyelectrolyte, of at least 3 milliequivalents/gram.

Abstract: A process for preparing titanium dioxide in the form of spherical particles having the particle size distribution indicated by dw/dn.ltoreq.2, by hydrolysis of strongly acid solutions of Ti(IV), wherein the molar ratio SO.sub.4.sup.= /Ti(IV) is at least 1.5, and in the presence of cationic polyelectrolytes having a molecular weight higher than 1 million and a ionicity of at least 3 milliequivalents per gram.

Abstract: This invention relates to a process for stabilizing ferromagnetic chromium dioxide in respect of water and oxidizable organic compounds which it may contact in magnetic tapes. The process is applicable to a starting CrO.sub.2 having good magnetic properties, i.e. a coercive force not lower than about 400 Oersted, a maximum magnetic induction B.sub.m not lower than about 2500 gauss, and a magnetic induction B.sub.r not lower than about 1600 gauss. The CrO.sub.2 is subjected to a heat treatment at a temperature ranging from 300.degree. to 390.degree. C. in the presence of a gas stream not exerting any oxidizing or reducing action on the compounds of trivalent, tetravalent and hexavalent chromium. Suitable gases are, for example, nitrogen, helium and argon.

Abstract: A process is disclosed for obtaining acicular magnetic particles of .gamma.-Fe.sub.2 O.sub.3 modified with Fe.sup.++ and Co.sup.++ ions. The product thus obtained and magnetic tapes containing said product are also disclosed. A suspension of acicular .gamma.-Fe.sub.2 O.sub.3 in an aqueous solution of soluble Fe.sup.++ and Co.sup.++ salts is prepared. NH.sub.3 is then added in such quantity that the molar ratioNH.sub.3 /(Fe.sup.++ +Co.sup.++)is between 2.1 and 3, and the whole mass is then heated up to 100.degree.-200.degree. C. When the molar ratio Fe.sup.++ /Co.sup.++ is greater than about 2.5, it is necessary to operate in the presence of a metered quantity of oxygen or of an oxygen-containing gas; when the ratio is smaller or equal to about 2.5, the presence of a metered quantity of oxygen is optional.

Abstract: A process is disclosed for preparing silver powders with a controlled apparent density wherein an aqueous silver oxide suspension is treated with hydrogen at a temperature between 60.degree. and 115.degree. and under a partial hydrogen pressure of between 5 and 25 atmospheres. The aqueous silver oxide suspension may be additioned with one or more alkali metal, alkaline earth metal, or silver sulphides. Further the aqueous silver oxide suspension may be additioned with one or more silver salts soluble in water or made soluble by complexing with ammonia, such as ammoniacal silver sulphate, silver nitrate or ammoniacal silver nitrate.

Abstract: A process is disclosed for producing magnetite having an equiaxial morphology in the state of a hyperfine powder, starting from a solution of a bivalent iron solution, characterized in that:A. an aqueous suspension of Fe(OH).sub.2 is prepared by reacting an aqueous solution of a ferrous salt with alkali;B. said aqueous suspension of Fe(OH).sub.2 is fed into an autoclave into which is also introduced a quantity of air corresponding to 4-15 normal liters per 100 g of bivalent Fe; andC. the autoclave is then brought to a temperature between 150.degree. and 200.degree. C and maintained at this temperature until the inside pressure has stabilized itself at a constant level, thereby bringing about the formation of the desired magnetite which, once discharged from the autoclave, is washed and dried. The aqueous suspension of Fe(OH).sub.2 subjected to thermal decomposition in the autoclave may have present therein Cu.sup.+.sup.+ion, in a quantity between 0.3 and 1.4% by weight of the bivalent Fe. When Cu.sup.+.sup.