Expandable silica particles and methods for making and using the same
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.
1 . An expanded silica particle obtained by coating an expandable silica particle with talc powder and kaolin powder, wherein the expandable silica particle comprises a sintered or heat-pressed mixture comprising silica powder and at least one expanding agent, and then expanding the coated expandable silica particle by application of heat to the coated expandable silica particle at a temperature above the activation temperature of the at least one expanding agent in the range from 800° C. to 950° C. to form the expanded silica particle.
2 . The expanded silica particle according to claim 1 , wherein the expanded silica particle has a water adsorption determined according to UNI EN 1097-6:2013 (appendix C—adsorption after 5 minutes) of less than 20 weight-percent.
3 . The expanded silica particle according to claim 1 , wherein the open porosity of the expanded silica particles, when measured according to ISO 5017, is not greater than 12 percent.
4 . The expanded silica particle according to claim 1 , wherein the expanded silica particle has a particle size of at least 2 mm and a compressive strength of at least 7 MPa.
5 . The expanded silica particle according to claim 1 , wherein the silica powder is recycled glass.
6 . The expanded silica particle according to claim 1 , wherein the at least one expanding agent comprises silicon carbide powder.
7 . The expanded silica particle according to claim 1 , wherein the expandable silica particle further comprises silica fume and/or ultrafine quartz sand.
8 . The expanded silica particle according to claim 1 , wherein the silica powder is recycled glass, the expanding agent comprises silicon carbide and the expandable silica particle further comprises silica fume and/or ultrafine quartz sand.
9 . The expanded silica particle according to claim 1 , wherein the coated expandable silica particle is coated with at least 1 wt.-% and up to 10 wt.-% kaolin powder and at least 1 wt.-% and up to 4 wt.-% talc powder, wherein the wt.-% is based on the total weight of the expandable silica particle with the coating.
10 . The expanded silica particle according to claim 9 , wherein the weight ratio of talc powder to kaolin powder is at least 1:2 and up to 1:1.
11 . The expanded silica particle according to claim 1 , wherein the expandable silica particle is coated with the talc powder and the kaolin powder by dry-coating an outer surface of the expandable silica particle with the talc powder and the kaolin powder.
12 . The expanded silica particle according to claim 11 , wherein the talc powder is applied to the outer surface of the expandable silica particle before applying the kaolin powder to the outer surface of the expandable silica particle.
13 . The expanded silica particle according to claim 1 , wherein the expandable silica particle is expanded by heating the expandable silica particle to a temperature in the range from 850° C. to 900° C.
14 . The expanded silica particle according to claim 1 , wherein the expandable silica particle is expanded by feeding the expandable silica particles to at least one vibration plate while heating the expandable silica particles to a temperature above the activation temperature of the expanding agent at a temperature in the range from 800° C. to 950° C. to form expanded silica particles.