A hollow spherical glass particle, comprising aluminum oxide Al.sub.2O.sub.3, silicon dioxide SiO.sub.2 and at least one metal oxide, wherein the metal oxide is selected from the group consisting of alkali metal oxides and alkaline earth metal oxides, wherein the ratio of aluminum atoms to alkali metal atoms is about 1:1 and the ratio of aluminum atoms to earth alkali atoms is about 2:1, with the proviso that the hollow spherical glass particle is free of boron.

The invention relates to a particulate glass filler wherein glass particles of 0.2 to 1 m mean particle size are connected with other particles, the connection being effected by the glass material itself. More precisely particulate glass filler comprising glass particles, wherein the particles contains centrally located macro glass particles and on the outer surface located micro glass particles wherein the macro and micro glass particles are connected by the material of said particles. Further the invention relates to a method for manufacturing the glass particles and the particulate glass filler comprising said glass particles. It also relates to a composite or dental material comprising the above particulate glass filler.

A method of manufacturing a plurality of expanded microspheres, comprises mixing a plurality of solid particles, at least one binding material capable of binding the plurality of solid particles, and a plurality of reactive expansion components into a batch, forming a plurality of agglomerated particles from the batch, heating the plurality of agglomerated particles in an expansion equipment to above a softening temperature of at least a portion of the plurality of agglomerated particles and activating the plurality of reactive expansion components, and forming a gas and expanding the plurality of agglomerated particles into the plurality of expanded microspheres, the step of activating the plurality of reactive expansion components occurring independently from a chemical composition of an atmosphere surrounding the plurality of agglomerated particles inside the expansion equipment.

A method of manufacturing a plurality of expanded microspheres, comprises mixing a plurality of solid particles, at least one binding material capable of binding the plurality of solid particles, and a plurality of reactive expansion components into a batch, forming a plurality of agglomerated particles from the batch, heating the plurality of agglomerated particles in an expansion equipment to above a softening temperature of at least a portion of the plurality of agglomerated particles and activating the plurality of reactive expansion components, and forming a gas and expanding the plurality of agglomerated particles into the plurality of expanded microspheres, the step of activating the plurality of reactive expansion components occurring independently from a chemical composition of an atmosphere surrounding the plurality of agglomerated particles inside the expansion equipment.

The present disclosure concerns expandable silica particles having a coating comprising talc powder and kaolin powder provided on the outer surface of the expandable silica particle and expandable and expanded silica particles comprising silica fume and/or ultrafine quartz silica sand beneath the surface of the particles. Methods for producing expandable and expanded silica particles are disclosed, including a method using a vibration plate and a furnace having a vibration plate for carrying out that method. The expanded silica particles have high compressive strength, substantially uniform cell size and distribution, low water absorption, and low porosity on the outer surface. They are useful as a filler in matrix materials, like concrete or epoxy, as insulation material with various binder materials, and as water filtration medium.