Abstract: Subjects for the invention are to obtain a quartz powder having a high purity and high quality and a process for producing the same and to obtain a glass molding formed by melting and molding the powder and extremely reduced in bubble inclusion. The invention provides a quartz powder, preferably a synthetic quartz powder obtained by the sol-gel method, which, upon heating from room temperature to 1,700° C., generates gases in which the amount of CO is 300 nl/g or smaller and the amount of CO2 is 30 nl/g or smaller.

Abstract: Subjects for the invention are to obtain a quartz powder having a high purity and high quality and a process for producing the same and to obtain a glass molding formed by melting and molding the powder and extremely reduced in bubble inclusion. The invention provides a quartz powder, preferably a synthetic quartz powder obtained by the sol-gel method, which, upon heating from room temperature to 1,700° C., generates gases in which the amount of CO is 300 nl/g or smaller and the amount of CO2 is 30 nl/g or smaller.

Abstract: A method of producing a silica gel by hydrolyzing a silicon alkoxide and subjecting the resulting hydrogel to a hydrothermal treatment substantially without aging it is described. Also described in a silica gel produced by such a method and a silica gel which has the following characteristics: (a) the pore volume is from 0.6 to 1.6 ml/g, (b) the specific surface area is from 300 to 900 m2/g, (c) the mode diameter (Dmax) of pores is less than 20 nm, (d) the volume of pores having diameters within ±20% of Dmax is at least 50% of the total pore volume, (e) it is amorphous, and (f) the content of metal impurities is at most 500 ppm.

Abstract: Subjects for the invention are to obtain a quartz powder having a high purity and high quality and a process for producing the same and to obtain a glass molding formed by melting and molding the powder and extremely reduced in bubble inclusion. The invention provides a quartz powder, preferably a synthetic quartz powder obtained by the sol-gel method, which, upon heating from room temperature to 1,700° C., generates gases in which the amount of CO is 300 nl/g or smaller and the amount of CO2 is 30 nl/g or smaller.

Abstract: A method of producing a silica gel by hydrolyzing a silicon alkoxide and subjecting the resulting hydrogel to a hydrothermal treatment substantially without aging it is described. Also described in a silica gel produced by such a method and a silica gel which has the following characteristics: (a) the pore volume is from 0.6 to 1.6 ml/g, (b) the specific surface area is from 300 to 900 m2/g, (c) the mode diameter (Dmax) of pores is less than 20 nm, (d) the volume of pores having diameters within ±20% of Dmax is at least 50% of the total pore volume, (e) it is amorphous, and (f) the content of metal impurities is at most 500 ppm.

Abstract: A method of producing a silica gel by hydrolyzing a silicon alkoxide and subjecting the resulting hydrogel to a hydrothermal treatment substantially without aging it is described. Also described in a silica gel produced by such a method and a silica gel which has the following characteristics: (a) the pore volume is from 0.6 to 1.6 ml/g, (b) the specific surface area is from 300 to 900 m2/g, (c) the mode diameter (Dmax) of pores is less than 20 nm, (d) the volume of pores having diameters within ±20% of Dmax is at least 50% of the total pore volume, (e) it is amorphous, and (f) the content of metal impurities is at most 500 ppm.

Abstract: Subjects for the invention are to obtain a quartz powder having a high purity and high quality and a process for producing the same and to obtain a glass molding formed by melting and molding the powder and extremely reduced in bubble inclusion.

Abstract: A method of producing a silica gel by hydrolyzing a silicon alkoxide and subjecting the resulting hydrogel to a hydrothermal treatment substantially without aging it is described.

Abstract: A synthetic quartz powder obtained by calcining a powder of silica gel, characterized in that white devitrification spots having sizes of larger than 20 &mgr;m in diameter formed in an ingot obtained by vacuum melting the synthetic quartz powder at a temperature of from 1780 to 1800° C. to form an ingot, followed by maintaining the ingot at a temperature of 1630° C. for 5 hours, are at most 10 spots/50 g.

Abstract: A method for producing a high purity synthetic quartz powder, characterized by using a tetramethoxysilane having a trimethoxymethylsilane content of at most 0.3 wt %, and converting it to a synthetic quartz by a sol-gel method.

Abstract: A process for producing a synthetic quartz powder, which comprises a step of heat-treating a silica gel powder while permitting it to flow in a rotary kiln.

Abstract: A process for producing synthetic quartz powder which comprises calcining silica gel powder to produce a synthetic quartz glass powder, wherein dry air is used in the calcining process at least in the process of cooling from 800.degree. C. to 200.degree. C. This process enables efficient production of synthetic quartz glass powder on an industrial scale.

Abstract: A synthetic quartz glass powder obtained by sol-gel method, wherein the number of black spot particles is at most 5 particles per 50 g, provides a high quality quartz glass shaped product with low bubble content when fused.

Abstract: The disclosure describes a process for producing halogenated phthalic anhydride, which comprises reacting phthalic anhydride with a molecular halogen in vapor phase in the presence of a catalyst containing zeolite as active component.

Abstract: A process for producing a biphenyltetracarboxylic dianhydride which comprises the step of: heating phthalic anhydride at a temperature of from 135.degree. to 300.degree. C. in the presence of a palladium catalyst thereby to allow the phthalic anhydride to undergo a dimerization reaction. According to the process, biphenyltetracarboxylic dianhydride can be synthesized by the direct dimerization of phthalic anhydride.

Abstract: A process for dimerizing an aromatic halogen compound is disclosed, which comprises the step of: subjecting an aromatic halogen compound having at least one halogen atom bonded to an aromatic nucleus carbon to a dehalogenation-dimerization reaction in the presence of a catalyst, water, a reducing agent, and a halogen acceptor, the catalyst comprising a carrier supported thereon palladium and iron.

Abstract: A method of dehalogeno-dimerizing an aromatic halide compound substituted by at least one halogen atom substituted on the aromatic ring using a palladium catalyst on support in the presence of water, a reducing agent and a halogen acceptor is disclosed. The method is characterized by using the palladium catalyst on support immersed in a hydrohalogenic acid prior to the dehalogeno-dimerization reaction.