GB2159807A

GB2159807A - Method of producing a sinterable lithium metasilicate Li2SiO3 powder

Info

Publication number: GB2159807A
Application number: GB08509433A
Authority: GB
Inventors: Dr Dieter Vollath; Dr Horst Wedemeyer; Elmar Gunther
Original assignee: Kernforschungszentrum Karlsruhe GmbH
Current assignee: Forschungszentrum Karlsruhe GmbH
Priority date: 1984-04-25
Filing date: 1985-04-12
Publication date: 1985-12-11
Also published as: GB2159807B; FR2563510A1; DE3415323A1; FR2563510B1; BE902192A; GB8509433D0; DE3415323C2

Abstract

A method of producing a sinterable lithium metasilicate Li2SiO3 powder having a 99% phase purity, whereby amorphous SiO2 is introduced into an aqueous lithium hydroxide solution, a) a stoichiometric amount of SiO2 is used to form the suspension, relative to the dissolved LiOH; b) the suspension is directly spray-dried by means of air at a temperature of from 200 DEG C to 450 DEG C without any additional, intermediate treatment; and c) the powdery dry residue is then heated at a temperature in the range of from 500 DEG C to 1000 DEG C and calcined. i

Description

SPECIFICATION Method of producing a sinterable lithium metasilicate Li2SiO3 powder and use thereof The invention relates to a method of producing a sinterable lithium metasilicate Li2SiO3 powder having a 99% phase purity, whereby amorphous SiO2 is introduced into an aqueous lithium hydroxide solution, and the resultant suspension is subjected to a high temperature.

It has already been proposed to use lithium-containing oxidic ceramics materials-lithium metasilicate, for example-as breeder materials for fusion reactors to obtain tritium. In most of the cases for producing Li2SiO3, solid Li2CO3 and SiO2 or H2SiO3. nH2O powders were heated to high temperatures or melted. The temperatures used for the reaction were in the region of more than 700"C to 1500"C, and the heat-treatment period lasted from three to five hours at from 1400"C to 1500"C and eight days at 700"C, then heating was continued for three days at 800"C and for four days at 900"C. No details were known about the purity of the products and about the particle size of such products.Generally, however, it is necessary to grind the products of the method prior to their being further processed. Impurities result from the solids reactions of the known production methods at the high temperatures or in the molten mass, so that only 90% to 95% of the desired phase is present in the end product.

It was considered desirable to provide a method of producing Li2SiO3 so that the impurities in the end product can be eliminated and so that the considetable amount of time and energy needed for the known methods can be reduced. At the same time, the method should be more economical than the hitherto-known production methods. It is known, from Gmelin's "Handbuch der Anorganischen Chemie", System No. 20, Lithium (1927), Page 241, that amorphous silicic acid, which has been dried at 100"C, is very poorly soluble in a hot LiOH solution, but 1 mol Li2O can dissolve at least 3.4 mols SiO2 in a cold solution of, for example, 2N LiOH.

Heating should precipitate Li2SiO3.H2O from this solution. The production of a sinterable Li2SiO3 powder is not mentioned there.

The invention seeks to provide a simple, improved method of producing Li2SiO3, whereby as much of the method as possible is effected in an aqueous solution and whereby only a short period of time relatively little energy are required to obtain a highly sinterable powder of the desired Li2SiO3 in an almost phase-pure manner.

According to the invention, the object is achieved in that: a) a stoichiometric amount of SiO2 is used to form the suspension, relative to the dissolved LiOH; b) the suspension is directly spray-dried by means of air at a temperature of from 200"C to 450"C without any additional, intermediate treatment; and c) the powdery dry residue is then heated at a temperature in the range of from 500"C to 1000"C and calcined.

The following reaction takes place in the lithium hydroxide solution: 2LiOH + aq + SiO2 (amorphous) = Li,SiO,. x H2O + aq.

The resultant suspension is converted into a powder by spray-drying without any additional intermediate treatment. The spray-dried powder was converted into the desired Li28i03 by calcination-annealing at 600"C, preferably, within two hours. Under suitable sintering conditions, a density of 95% of the theoretical density can be achieved.

Because of its high degree of purity, the lithium metasilicate produced in accordance with the method of the invention is particularly highly suitable for use as a breeder material for fusion reactors to obtain tritium.

The invention is explained more fully hereinafter with reference to one operational example.

Example In accordance with the reaction equation:

an aqueous suspension of amorphous SiO2 (AEROSIL produced by DEGUSA) was introduced into an aqueous solution of lithium hydroxide with constant stirring. By continuing to stir constantly at room temperature (for approximately one hour), lithium metasilicate was thereby formed in the suspension. It was assumed that some of the Li2SIO3 was present as a monohydrate and that some of the Li2SiO3 was dissolved.

Table: Deposits for spray-drying lithium metasilicate No. in solution: as suspension: LiOH H20 SiO2 H20 Li2SiO3 Number of (9) (cm3) (cma) (cma) (g/l) Deposits 1 95.80 1200 120.18 800 ,-,-'90 8 2 53.26 500 66.81 1000 65 12 Anhydrous lithium hydroxide was used for the deposits of No. 1, and lithium hydroxide containing crystal water (LiOH .H2O) was used for the deposits of No. 2 to produce the LiOH solutions. The suspensions were spray-dried in the temperature range of from 200"C to 370"C.

The yield of spray-dried Li2SiO3. X H2O was always more than 90%. The moisture content in the powders varied and depended on the spray-drying temperature. Higher spraying temperatures resulted in slightly smaller moisture contents (approximately 2%). By air-treating the lithium hydroxide solutions and the suspensions, the powders contained up to 6% by weight of carbonate components which were removed during the calcining step.

The powder particles were in the form of small hollow spheres having an average size of between 3 pm and 5 ym.

After the powders had been calcined at 600"C, they could be compressed up to 95% of the theoretical density by being pressed and sintered at 1100 C for six hours. The sintered samples always produced single-phase Li28i03.

Claims

1. A method of producing a sinterable lithium metasilsicate Li2SiO3 powder having a 99% phase purity, whereby amorphous SiO2 is introduced into an aqueous lithium hydroxide solution, and the resultant suspension is subjected to a high temperature, in which: a) a stiochiometric amount of SiO2 is used to form the suspension, relative to the dissolved LiOH; b) the suspension is directly spray-dried by means of air at a temperature of from 200"C to 450"C without any additional, intermediate treatment; and c) the powdery dry residue is then heated at a temperature in the range of from 500"C to 1000"C and calcined.

2. A method as claimed in claim 1, in which the spray-drying is effected at 200"C to 370"C, and the dry residue is heated at 600"C.

3. A method of producing a sinterable lithium metasilicate Li28i03 powder having a 99% phase purity, as claimed in claim 1 or 2, substantially as hereinbefore described and exemplified.

4. A breeder material for a fusion reactor for producing tritium, comprising sinterable, pure Li28i03 powder produced in accordance with the method as claimed in claim 1, 2 or 3.