Abstract: The invention relates to the use of synthetic (synthetically produced) iron raw materials to prepare iron oxide pigments in the Penniman process and other iron-dissolution processes.

Abstract: Non-silking iron oxide yellow pigments with high color density.Iron oxide yellow pigments in the .alpha.-FeOOH modification with a silking index of less than 5 were obtained in whicha) .alpha.-FeOOH seeds are produced by precipitation from an Fe(II)-containing solution with an alkaline precipitating agent in the presence of soluble aluminium salts in an amount of 3 to 9 wt. %. calculated as Al.sub.2 O.sub.3, with respect to precipitated .alpha.-FeOOH, and subsequent oxidation to .alpha.-FeOOH andb) pigment growth is performed by precipitating further iron with simultaneous oxidation, wherein the seed/time yield is less than 0.3 h.sup.-1 and the pH value is less than 3.9 over the entire period of pigment growth andc) pigment growth is terminated at a reproduction factor between 3 and 20.

Abstract: The present invention relates to a process for the production of yellow, highly transparent iron oxide pigments of elevated chemical purity, to yellow iron oxide pigments obtainable in this manner and to the use thereof to color lacquers and plastics.

Abstract: The invention relates to very highly transparent iron oxide pigments with high color saturation, to a process for their production and to their use for pigmenting paints and plastics.

Abstract: The invention relates to the use of synthetic (synthetically produced) iron raw materials to prepare iron oxide pigments in the Penniman process and other iron-dissolution processes.

Abstract: The present invention relates to a process for the production of red, transparent iron oxide pigments of elevated chemical purity, to iron oxide pigments obtainable in this manner and to the use thereof to color lacquers and plastics.

Abstract: The invention relates to transparent iron oxide pigments having an average particle size, based on the longest needle axis, of less than 0.1 .mu.m, to processes for their production and to their use for pigmenting lacquers and plastics.

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.