DE3415324A1 - METHOD FOR PRODUCING SINTERABLE POWDER FROM (GAMMA) -LIAL0 (DOWN ARROW) 2 (DOWN ARROW) AND THE USE THEREOF - Google Patents

Description

Process for the production of sinterable powder from γ - LiAlO ₀ and its use.

The invention relates to a method for the production of sinterable powder from γ-LiAlO with a phase pure

2
in the order of 99%, in which metallic aluminum is dissolved in an aqueous lithium hydroxide solution.

Lithium-containing, oxidic ceramic materials, for example Lithium aluminate has already been proposed as breeding material for fusion reactors for the production of tritium. For the production of LiAlO- were mostly solid powders of Li ^ CO ,, and Al-O-, finely ground and mixed and either by dry means, for example as pressed pellets, or in the form of aqueous slurries of a heat treatment which included drying and calcining at elevated temperatures. The grinding of the starting substances was carried out over several hours. After that, the ground product was compacted and used for calcination Diffusion annealed for one to two days. Then the reaction product had to be ground again so that the desired sinterable powder could be obtained.

The grinding and crushing not only of the starting substances, but also of the calcined reaction product can be a Be a source of contamination. In addition, there is generally only one portion in these solids reactions 90 to 95% of the desired phase can be expected in the end product. After all, that is for the extraction of tritium required thermal conductivity of the LiAlO "product impaired the presence of other phases.

.3.

3 4-: 5

It was therefore considered desirable to create a simple process for the production of Y-LiAlO ₂ , with which the impurities in the end product, as well as the large amount of time required for the prior art processes (approx. 3 to 4 days) can be avoided . In order to avoid the steps of milling and diffusion annealing, it has been proposed to run as large a part of the process as possible in aqueous solution. It is known that aluminum is dissolved by aqueous LiOH solutions (Gmelin's Handbuch der Inorganischen Chemie, System No. 35, Aluminum, Part A (1934, reprint 1953), page 408, Verlag Chemie GmbH, Weinheim). It is reported there that after boiling such a solution, a sparingly soluble aluminate of the formula LIH (AlO ₂ ) ₂ · 5H ₂ O should precipitate. The production of Y-LiAlO ^ is not addressed there.

The invention is based on the object of creating a simple and improved process for the production of Y-LiAlO ₂ , in which the largest possible proportion of the process takes place in an aqueous solution and a readily sinterable powder of the desired lithium aluminate is obtained in practically pure phases in a short time .

The object is achieved according to the invention in that

a) by the solvent formed during the reaction precipitating suspension formed is spray dried without any intermediate treatment directly with the aid of air at a temperature between 200 ⁰ C and 45O ° C and

b) then the material to be dried is calcined directly at a temperature between 85O ° C. and 1100 ° C. and is converted into the Y-LiAlO ₂ in the process.

The metallic aluminum is advantageously dissolved in the LiOH solution with constant stirring. Although heating the solution is not necessary, the expected precipitation of the lithium hydroxoaluminate will occur according to the reaction equation

2LiOH + 2Al + aq = Li [Al ₂ (OH) ₇ J · nH ₂ O + LiOH + aq

then not too coarse-grained if the solution has been heated to approx. 40 to 50 C beforehand. If the spray drying step is carried out in the range between 350 ° C. and 400 ° C., and the calcination step at the preferred temperature of 900 ° C., powder particles with an outer diameter between 5 and 15 μm are obtained. _{The use of the Y-LiAlO 2} produced by the process according to the invention as a breeding material for fusion reactors has unexpected advantages for the recovery of tritium, since the powder obtained is easily sinterable and it can be processed into molded bodies with densities of up to 95% of the theoretical density.

In the following the invention is based on an implementation example explained in more detail.

S-

Example:

According to the reaction equation

2 LiOH + 2 Al + aq -> - Li [Xl ₂ (OH) _? ] · Η H ₃ O -h LiOH + aq

the approaches compiled in the table were made by dissolving metallic aluminum in an aqueous solution
Lithium hydroxide solution prepared with constant stirring at room temperature.

Table: Approaches for the spray drying of lithium aluminate

No. LiOH Al-Metal HO LiJAl ₂ (OH) ₇ ] Number of (g) (g) (cm ³ ) (g / l) batches

1 23, 95 26th , 98 1000 90 1 2 47, 90 53 , 96 1750 100 1

The No. 2 approach is industrially manufactured
Aluminum sheet, in batch 1, high-purity aluminum tape (MERCK) was used. The LiOH can
both as anhydrous and as containing water of crystallization
Hydroxide (LiOH · ^H ₂ °) ^{for the} preparation of the aqueous
Solution can be used. The spray drying of the resulting suspension, consisting of very finely divided lithium heptahydroxoaluminate in lithium hydroxide solution,
took place in the temperature range of 250-400 C. The yield of spray-dried powder, a stoichiometric mixture of lithium hydroxoaluminate and lithium hydroxide, was more than 90 % in each case. By handling the

of the lithium hydroxide solutions and the suspensions in air, the powders contained up to 5% by weight of carbonate, which were removed during the calcination step.

When the powder was calcined (two hours), the initially present finely dispersed, stoichiometric powder mixture resulted in the desired lithium monoaluminate. Depending on the calcination temperature, mixtures of α- and 3-LiAlO ,, (at 600 _{° C.), α- and Y-LiAlO 2} (at 800 ° C.) and pure γ-LiAlO (above 900 ° C.) were observed. At 900 ⁰ C calcined powder settled by pressing and sintering at about 125O ° C to 80 - 85%, and at about 145 ° ° C in six hours to 90 - condense 95% of the theoretical density. The sintered samples each gave single-phase y-LiAlO_.

Claims (2)

Kernforschungszentrura Karlsruhe, April 1, 1984 Karlsrune GmbH PLA 8420 Gl / hr ANR 1 002 597 patent claims; 1. Process for the production of sinterable powder from -y- -LiAlO ^ with a phase purity of size oranization 99%, in which metallic aluminum is dissolved in an aqueous lithium hydroxide solution, characterized in that a) the suspension formed by the precipitation occurring during the dissolution reaction without any further Intermediate treatment directly with the aid of air at a temperature between 200 ° C. and 45 ° C., spray-dried will and b) then the material to be dried is calcined directly at a temperature between 85O ° C. and 1100 ° C. and is converted into the Y-LiAlO ₂ in the process. 2. Use of the sinterable powder made of pure LiAlO produced according to claim 1 as breeding material for Fusion reactors for the production of tritium.