Abstract: Calcium-iron oxide composite particles of the present invention have a BET specific surface area of 1 to 100 m2/g and containing iron atom in an amount of 1 to 50 moles based on 100 moles of calcium atom, the iron atom of not less than 50% based on the total amount of iron atom contained in said calcium-iron oxide composite particles being bonded with calcium atom for forming a calcium-iron ferrite phase. A hydrogen chloride-scavenger comprising the calcium-iron oxide composite particles, is capable of effectively capturing harmful hydrogen chloride generated by thermal decomposition or combustion of chorine-containing resin molded products upon fire or incineration thereof, and fixing the hydrogen chloride as stable calcium chloride or the like.

Abstract: Calcium-iron oxide composite particles of the present invention have a BET specific surface area of 1 to 100 m2/g and containing iron atom in an amount of 1 to 50 moles based on 100 moles of calcium atom,

Abstract: Calcium-iron oxide composite particles of the present invention have a BET specific surface area of 0.1 to 100 m2/g and containing iron atom in an amount of 1 to 500 moles based on 100 moles of calcium atom, the iron atom of not less than 50% based on the total amount of iron atom contained in said calcium-iron oxide composite particles being bonded with calcium atom for forming a calcium-iron ferrite phase. A hydrogen chloride-scavenger comprising the calcium-iron oxide composite particles, is capable of effectively capturing harmful hydrogen chloride generated by thermal decomposition or combustion of chorine-containing resin molded products upon fire or incineration thereof, and fixing the hydrogen chloride as stable calcium chloride or the like.

Abstract: A method of decoloring a colored concrete, comprises adding to the colored concrete, a decoloring pigment comprising a titanium oxide pigment, or a titanium oxide pigment and a pigment having a complementary color relative to color of the colored concrete. Such method can decolore the color of the colored concrete residue which attaches to or remains in production facilities in order to return a color thereof to that of an ordinary plain concrete, without works or treatments for washing-out or removing the colored concrete residue which attaches to or remains in the production facilities, in which the works or treatments are required in the case where the production facilities are used for the production of an ordinary plain concrete after the colored concrete has been produced therein, and without works or treatments for purifying a waste water generated upon washing-out or removing the residue and for making the waste water harmless; and a pigment used therefor.

Abstract: Disclosed herein are non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium, comprising acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles coated with at least one selected from the group consisting of an A1 compound, a silane coupling agent, a titanate coupling agent, an aluminate coupling agent and a zirconate coupling agent; a non-magnetic undercoating layer containing such non-magnetic particles; and magnetic recording medium having such an undercoating layer.

Abstract: Disclosed herein are magnetic iron oxide particles which have a spindle shape and a substantially uniform particle size and shape, and are substantially free of dendrites and have a large axial ratio (major axial diameter/minor axial diameter) and an excellent print-through characteristic, and a method of producing the same.

Abstract: Disclosed herein are a process for producing acicular goethite particles comprising the step off: blowing an oxygen-containing gas into a ferrous salt reaction solution containing colloidal ferrous hydroxide or iron-containing colloidal precipitates which is obtained by reacting an aqueous ferrous salt solution with less than one equivalent of an aqueous alkali hydroxide solution, an aqueous alkali carbonate solution, or an aqueous alkali hydroxide and alkali carbonate solution based on Fe.sup.

Abstract: Disclosed herein are a process for producing acicular goethite particles comprising the step of: blowing an oxygen-containing gas into a ferrous salt reaction solution containing colloidal ferrous hydroxide or iron-containing colloidal precipitates which is obtained by reacting an aqueous ferrous salt solution with less than one equivalent of an aqueous alkali hydroxide solution, an aqueous alkali carbonate solution, or an aqueous alkali hydroxide and alkali carbonate solution based on Fe.sup.

Abstract: Disclosed herein are magnetic iron oxide particles which have a spindle shape and a substantially uniform particle size and shape, and are substantially free of dendrites and have a large axial ratio (major axial diameter/minor axial diameter) and an excellent print-through characteristic, and a method of producing the same.

Abstract: Disclosed herein are magnetic iron oxide particles comprising spindle-like magnetite or maghemite particles having an aspect ratio(major:minor) of less than 4:1 and containing 0.1 to 20 atomic % of Si to Fe, and a process for producing the same.