Abstract: The invention relates to a reducing agent for the soluble chromate content of cement and to methods for the production thereof, which comprise concentrating an used sulfuric acid, containing iron (II) sulfate, and separating the sulfuric acid from the obtained precipitate which contains iron (II) sulfate.

Abstract: The invention relates to a reducing agent for the soluble chromate content of cement and to methods for the production thereof, which comprise concentrating an used sulfuric acid, containing iron (II) sulfate, and separating the sulfuric acid from the obtained precipitate which contains iron (II) sulfate.

Abstract: The invention concerns a method for processing heavy metal-laden spent sulfuric acid. For this, iron-laden spent sulfuric acid or iron-laden sulfuric materials obtained therefrom are reacted with a material that contains iron chloride and optionally other metal chlorides, producing iron (II) sulfate. The spent sulfuric acid preferably derives from titanium dioxide production.

Abstract: The invention concerns a method for processing heavy metal-laden spent sulfuric acid. For this, iron-laden spent sulfuric acid or iron-laden sulfuric materials obtained therefrom are reacted with a material that contains iron chloride and optionally other metal chlorides, producing iron (II) sulfate. The spent sulfuric acid preferably derives from titanium dioxide production.

Abstract: The invention relates to a reducing agent for the soluble chromate content of cement and to methods for the production thereof, which comprise concentrating an used sulfuric acid, containing iron(II) sulfate, and separating the sulfuric acid from the obtained precipitate which contains iron(II) sulfate.

Abstract: A process for preparing finely-divided oxides of metals of metalloids of the elements of main groups III and IV and sub-groups III, IV, V and VI of the Periodic System of Elements, comprising reacting compounds of these elements with a polymerizable hydrocarbon compound or mixture to form a polymer product, which is then thermally treated to yield the oxide product.

Abstract: Silicon nitride powder having a total oxygen content of less than 1.8% by weight and an isoelectric point in 0.001M aqueous KNO.sub.3 solution of below pH 4 is prepared by calcining Si.sub.3 N.sub.4 powder having an oxygen content of 0.4% by weight or less in an oxygen containing atmosphere at temperatures between 700.degree. and 1200.degree. C. for 15 to 90 minutes or by grinding such as Si.sub.3 N.sub.4 powder in water, lower alcohol or a water/alcohol mixture for 15 to 120 minutes.

Abstract: Si.sub.3 N.sub.4 powders having a total oxygen content of less than 1.8% by weight with the proportion of surface oxygen content of more than 65% of the total oxygen content, and having a fluorine content of less than 35 ppm are prepared by annealing Si.sub.3 N.sub.4 powders having a total oxygen content of less than or equal to 0.4% by weight in an oxygen-containing atmosphere at temperatures of 700.degree. C. to 1200.degree. C. for 15 to 90 minutes or by grinding Si.sub.3 N.sub.4 powders having a total oxygen content of less than or equal to 0.4% by weight in water, alcohol or aqueous alcohol 15 to 120 minutes.

Abstract: Si.sub.3 N.sub.4 powder wherein the total oxygen content of the powder is 0.4% by weight or less is produced by preparing an amorphous Si.sub.3 N.sub.4 intermediate by reacting a Si-containing compound with an N-containing compound and the intermediate is then crystallized wherein "P", multiplication product of(i) the specific surface of the amorphous intermediate (BET in m.sup.2 /g),(ii) the moisture content C.sub.H.sbsb.2.sub.O (in volume ppm) of the atmosphere during handling and(iii) the time t in hours required for handling the amorphous intermediate,is kept smaller than the limit value product P.sub.G of 1000 in accordance with the following equation:"P"=BET (m.sup.2 /g).times.C.sub.H.sbsb.2.sub.O (vol ppm).times.t(h)<P.sub.G.

Abstract: Sinterable Si.sub.3 N.sub.4 powder containing Si.sub.3 N.sub.4 particles and sintering additives wherein Si.sub.3 N.sub.4 particles have an average particle size of less than 1 .mu.m, contain no particle having a diameter greater than 100 .mu.m, have a total content of metallic impurities less than 1000 ppm and an iron content of less than 200 ppm, and wherein the sintering additives are uniformly distributed throughout the powder is prepared by co-grinding pulverulent sintering additive and Si.sub.3 N.sub.4 containing less than 1000 ppm metallic impurities in a spiral jet mill.

Abstract: Carbides, nitrides or carbonitrides of elements from the main groups III and IV and sub-groups III, IV, V and VI of the periodic system of elements are prepared by(i) reacting compounds of the formula MX.sub.m or R.sub.n MX.sub.m-n with a reactive hydrocarbon-containing compound or a mixture of compounds which is polymerizable and which contains a reactive compound with one C--OH-group in whichM is an element of the main group III or IV or sub-group of III, IV, V or VI of the periodic system of elements,X is a halogen,R is hydrogen or alkyl or aryl,m is an integer corresponding to the valency stage of M,n is an integer from 1 to one less than the velency stage of M, and(ii) thermally decomposing the resulting product from (i) to the corresponding carbide or to the corresponding nitrides or carbonitrides with further nitridation.

Abstract: Sinterable Si.sub.3 N.sub.4 powder having an average particle size of less than 1 .mu.m, wherein no individual particle has a diameter greater than 100 .mu.m, the total content of metallic impurities of the powder is less than 1000 ppm and the iron content is less than 200 ppm is produced by grinding agglomerated Si.sub.3 N.sub.4 in a spiral jet mill.