Talc substances having specific surface properties and method of manufacture

A method for the manufacture of a talc substance comprising:

• heating talc particles in an autoclave at a temperature of at least 150.degree. C. in a reaction medium including water and a water-soluble mineral base,
• holding the reaction medium at temperature in the autoclave for a time sufficient to effect hydrolysis of a proportion of siloxane groups present at the surface of the talc particles,
• after cooling, filtering the reaction medium to separate out a solid phase.

A method for the manufacture of a talc substance comprising:

• heating talc particles in an autoclave at a temperature of at least 150.degree. C. in a reaction medium including an organic base,
• holding the reaction medium at temperature in the autoclave for sufficient time to bring about the hydrolysis of a proportion of siloxane groups present on the surface of the talc particles,
• after cooling, placing the medium in contact with an acid solution and filtering the reaction medium to separate out a solid phase.

A method for the manufacture of a talc substance comprising:

• suspending talc particles in the presence of a free radical initiator in a liquid medium which is a solvent for said initiator and which can be split up by free radicals produced by the initiator under conditions sufficient to break siloxane bonds at the surface of the particles and replace them by hydrophilic groups.

A method for treating a talc substance to confer one or more surface properties upon said talc substance, which comprises:

• fixing onto hydrophilic sites on the surface of the talc substance molecules which have both a group which fixes onto these sites and one or more groups conferring the property or properties.