GB2159806A

GB2159806A - Method of producing a sinterable lithium orthosilicate Li4SiO4 powder

Info

Publication number: GB2159806A
Application number: GB08509432A
Authority: GB
Inventors: Dieter Vollath; 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: FR2568866B1; FR2568866A1; DE3415326A1; BE902193A; DE3415326C2; GB8509432D0; GB2159806B

Abstract

A method of producing a sinterable lithium orthosilicate (Li4SiO4) powder having a phase purity of more than 95% comprises a) producing an aqueous lithium hydroxide solution; b) introducing amorphous SiO4 into the solution formed from step a)-thereby forming a suspension-and adding H2O2 to said suspension; c) spray-drying the suspension formed from step b) to form a powdery/pulverulent dry residue; and d) heating the dry residue formed from step c) for reaction and calcination at a temperature in the 500 DEG C to 1000 DEG C. i

Description

SPECIFICATION Method of producing a sinterable lithium orthosilicate Li4SiO4 powder The invention relates to a method of producing a sinterable lithium orthosilicate Li2SiO4 powder having a phase purity of more than 95%.

It has already been proposed to use lithium-containing, oxidic ceramics materials-lithium orthosilicate, for exampic as breeder materials for fusion reactors to obtain tritium. In most of the cases for producing Li4SiO4, solid Li2CO3 and SiO2 powders were finely ground and mixed, and such mixtures were subjected to heat-treatment either when they were in their dry state or when they were in the form of sludges to be dried, said heat-treatment including drying and calcining or melting at high temperatures. Temperatures of 700"C and more were used for these heat-treatment processes which, in the main, were of a long duration (between twenty hours and two days).If, after cooling, the particle size was in the range of from 30 ym to 10 lim, the particles had to be ground for between eight and forty-eight hours in order to obtain the desired size.

Impurities may result from the grinding and pulverising of not only the starting substances, but also the calcined reaction product. In addition, these solids reactions generally only account for between 90%. and 95% of the desired phase in the end product.

The invention seeks to provide a simple method of producing Li4SiO4, so that the impurities in the end product can be eliminated and so that the considerable amount of time and energy needed for the prior art methods can be reduced. The grinding and lengthy diffusion-annealing steps at temperatures higher than 700"C should also be eliminated.

According to the invention, the object is achieved by the following procedural steps: a) producing an aqueous lithium hydroxide solution; b) introducing amorphous SiO2 into the solution formed from step aHthereby forming a suspension-and adding H202 to said suspension; c) spray-drying the suspension formed from step b) to form a powdery dry residue; and d) heating the dry residue formed from step c) for reaction and calcination at a temperature in the range of from 500"C to 1 000 C.

The following reaction takes place in the lithium hydroxide solution: 4LiOH + aq + SiO2 (amorphous) + H202 = Li2SiO1.xH2.O + Li2O2 + aq + H2O2.

The addition of H202 is important for the quality of the powder which results after heattreatment because, if H202 is not present, the powder sticks or coalesces during calcination.

After the spray-drying process, a powdery or pulverulent dry residue is obtained which is composed of the stoichiometric mixture of Li2SiO3.xH2O and Li2O2. Because the subsequent heating of the dry residue, the powder mixture reacts to form Li4SiO4. Reaction and calcination are preferably effected at 600"C for a period of approximately two hours. The product of the method is composed of small, disintegrated spheres having a particle size of from approximately 2 ym to 6 ym. The powder is highly sinterable. Densities higher than 90% of the theoretical density are achieved during the sintering process.

Because of its high degree of purity and its high molecular lithium density, the lithium orthosilicate produced in accordance with the method of the invention is particularly well-suited 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: 4LiOH + SiO2 + aq + H2O2Li2SiO3.xH2O + Li2 02 + aq, an aqueous suspension of amorphous SiO2 (AEROSIL produced by DEGUSSA) was introduced into an aqueous solution of lithium hydroxide with constant stirring, and lithium metasilicate was initially formed within approximately one hour.

In order to improve the subsequent calcination of the dried powder, the surplus LiOH was reacted immediately prior to the spray-drying process in suspension with H202 (in excess) to form Li2O2.

Table: Deposits for spray-drying lithium orthosilicate No. in solution: as suspension: LiOH HO Si02 H20 Li2Si03/Li202 Number 2 of (g) (cm') (9) (cm') (cm') Deposits Deposits 1 63.87 750 40.06 250 "i90 2 The suspension was spray-dried at from 250"C to 350"C, respectiveiy. The yield was more than 90%. 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.

It was possible to calcine the spray-dried, stoichiometric powder mixture at from 500"C to 600"C. By converting the surplus lithium hydroxide into Li202, the possibility of melting occurring here (TM(LiOH) = 450"C) is almost entirely eliminated.

After the powder had been calcined, it could be compressed up to > 90% of the theoretical density by being pressed and sintered at 1 1 00 C for six hours. The sintered samples always produced mono-phase Li4SiO4.

Claims

1. A method of producing a sinterable lithium orthosilicate Li4SiO4 powder having a phase purity of more than 95%, characterised by the following procedural steps: a) producing an aqueous lithium hydroxide solution; b) introducing amorphous SiO2 into the solution formed from step a)-thereby forming a suspension and adding H202 to said suspension; c) spray-drying the suspension formed from step b) to form a powdery dry residue; and d) heating the dry residue formed from step c) for reaction and calcination at a temperature in the range of from 500"C to 1000"C.

2. A method as claimed in claim 1, in which the dry residue is heated at a temperature of 600"C.

3. A method of producing a sinterable lithium orthosilicate Li4SiO4 powder having a phase purity of more than 95%, 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 Li4SiO4 powder produced in accordance with the method as claimed in claim 1, 2 or 3.