Process for the production of silicon dioxide particles

Abstract

The present invention relates to a process for producing spherical submicron particles of amorphous silicon dioxide, in which silicon dioxide and a reducing agent is injected into a reaction vessel of zirconium oxide in molten state, said zirconium oxide is serving as a heat reservoir, in which silicon dioxide reacts with the reducing agent producing a silicon-sub-oxide vapor, said silicon-sub-oxide vapor is oxidized into said spherical submicron silicon oxide particles.

Claims

1. A process for producing spherical submicron particles of amorphous silicon dioxide comprising injecting silicon dioxide and a reducing agent into a reaction vessel, the reaction vessel comprising a molten pool of zirconium oxide based material, wherein said molten pool of zirconium oxide based material is serving as a heat reservoir, in which silicon dioxide reacts with the reducing agent producing a silicon-sub-oxide vapour, SiO; oxidizing the produced silicon-sub-oxide vapour into spherical submicron particles of amorphous silicon dioxide.

2. The process according to any of the preceding claim 1, wherein the temperature of the zirconium oxide based material comprised in the vessel is at least at the melting point of the material.

3. The process according to claim 1, wherein the temperature of the zirconium oxide based molten pool is selected from the group consisting of the following ranges: 2650-2800 C., 2700-2710 C., 2710-2720 C., 2720-2800 C., 2800-2900 C., and 2900-3000 C.

4. The process according to claim 1, wherein said obtained spherical silicon dioxide particles possess a size selected from the group consisting of the following ranges: 10.sup.9-10.sup.6 m, 10.sup.9-10.sup.8 m, 10.sup.8-10.sup.7 m, and 10.sup.7-10.sup.6 m.

5. The process according to claim 1, wherein the reducing agent is carbon.

6. The process according to claim 1, wherein a gas is injected into the zirconium oxide.

7. The process according to claim 6, wherein the gas is an inert gas or nitrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The process of the present invention may also comprise the production of microsilica or spherical submicron particles of amorphous silicon dioxide, SiO.sub.2, whereby a mixture of silicon dioxide and the reducing agent carbon are added zirconium oxide based molten pool in a vessel.

(2) The main reaction for preparing the silicon sub-oxide vapour silicon oxide, SiO, is as follows:
SiO.sub.2+CSiO(g)+CO(g)

(3) Thus, the process of the present invention is a carbothermic process.

(4) The pool of molten zirconium oxide based molten pool is kept at temperatures above 2650 C. and preferably above the melting point of pure zirconium oxide. The molten zirconium oxide based material can also be kept at a temperature interval of 2710-2720 C. The vapour pressure of the produced silicon sub-oxide, the SiO vapour pressure, reaches 1 Atmosphere at approximately at 1800 C. In this embodiment the temperature above 2650 C. is much higher than the temperature of approximately 1800 C. required for producing SiO vapour. Thus the molten pool will serve as a heat reservoir. However at the high temperatures as mentioned above, the surface area of the resulting silicon dioxide particles will be modified towards lower surface areas while still being essentially sub-micron. The produced silicon sub-oxide vapour, SiO-gas, is oxidised to SiO.sub.2 particles immediately above the bath and recovered in filters such as among others bag house filters.

(5) The molten pool of the zirconium oxide based material of the present invention will serve as a heat reservoir as mentioned above thus stabilizing and accelerating the process for producing spherical submicron particles of an amorphous silicon dioxide. In the present invention zirconium oxide will serve as an almost inert heat reservoir thus the produced spherical submicron particles of silicon dioxide will obtain high purity. In the present invention the obtained purity of the spherical submicron producing spherical submicron particles of amorphous silicon dioxide is at least 99% by weight.

(6) Having described preferred embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples of the invention illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims.