DE3415324C2 - Process for the preparation of sinterable powder from γ-LiAl0? 2? and its use - Google Patents

Abstract

The invention relates to a method for producing sinterable powder from γ-LiAlO2 with a phase purity of the order of 99%, in which metallic aluminum is dissolved in an aqueous lithium hydroxide solution. The aim is to create an improved process for the production of γ-LiAlO2, 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) the suspension formed by the precipitation occurring during the dissolution reaction is spray-dried directly with the aid of air at a temperature between 200 ° C. and 450 ° C. without further intermediate treatment and b) then the material to be dried is added directly a temperature between 850 ° C and 1100 ° C, preferably at 900 ° C, calcined and thereby converted into the γ-LiAlO2.

Description

The invention relates to a process for the production of sinterable powder from / -LiAlO ₂ with a phase purity of 99% by dissolving metallic aluminum in an aqueous lithium hydroxide solution with the formation of a precipitation.
Oxidic ceramic materials containing lithium, for example lithium aluminate, have already been proposed as breeding materials for fusion reactors for the production of tritium. For the production of LiAlO ₂ , solid powders of Li ₂ CO3 and A1 ₂ O3 were usually finely ground and mixed and either subjected to a heat treatment in a dry way, for example as pressed pellets, or in the form of aqueous slurries, which included drying and calcination at elevated temperatures ( DJ Suiter: "Lithium-Based Oxide Ceramics for Tritium-Breeding Applications", June 1983, Report MDC E2677 [McDonnel Douglas Astronautics Co, St Louis MO, USA], pages 2-4 to 2-6). The grinding of the starting substances was carried out over several hours. The malt product was then compacted and diffusion annealed for one to two days for calcination. The reaction product then had to be ground again so that the desired sinterable powder could be obtained.
Milling and crushing of not only the starting materials but also the calcined reaction product can be a source of impurities. In addition, in these solids reactions, only 90 to 95% of the desired phase is generally to be expected in the end product. Finally, the thermal conductivity of the LiAlOr product required for the extraction of tritium is impaired by the presence of other phases
It was therefore considered desirable to create a simple process for the production of / -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 J ₂ - 5 H ₂ O is said to be precipitated (Am. Formerly J. 24 [1900], p. 309)) / -LiAlO ₂ is not addressed there.

The invention is based on the object of creating a simple and improved process for the production of / -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 the suspension obtained is ^{spray-dried with the aid of air at a temperature between 20O 0} C and 450 ⁰ C without further intermediate treatment and the material to be dried is then calcined ^{directly at a temperature between 850 0} C and 1100 ^{0 C.}

The dissolution of the metallic aluminum in the LiOH solution is advantageously non-permanent Stir. Although heating the solution is not necessary, the expected precipitation of the lithium hydroxoaluminate will occur according to the reaction equation

2 LiOH + 2 Al + aq = Li [Al ₂ (OH) ₇ ] · π H ₂ O + LiOH + aq

then not too coarse-grained if the solution was previously heated ^{to approx. 40 to 50 ° C.} Is carried out of the spray-drying step is in the range between 350 ⁰ C and 400 ⁰ C, and the calcination step at the preferred temperature of 90O ⁰ C, then powder particles are obtained μπι having an outer diameter 5 to 15 The use of the sinterable powder of pure LiAlO ₂ produced by the process according to the invention as breeding material for fusion reactors has unexpected advantages for the recovery of tritium, since the powder obtained can be processed into molded bodies with densities of up to 95% of the theoretical density.

example

According to the reaction equation
2 LiOH + 2 Al + aq - Li [Af ₂ (OH) ₇ ] ■ η H ₂ O + LiOH + aq

were the approaches compiled in the table by dissolving metallic aluminum in a aqueous lithium hydroxide solution prepared with constant stirring at room temperature

Tabel:
Approaches to the spray drying of lithium aluminate UOH
fe) Al metal
(G) H ₂ O
(cm ³ ) Li [Al ₂ (OH) ₇ ]
(g / i) number of
approaches No. 23.95
47.90 2638
53S6 1000
1750 90
100 1
1 1
2

In batch no. 2, industrially manufactured aluminum sheet was used, and in batch 1, high-purity aluminum tape was used. The LiOH can be used both as an anhydrous hydroxide and as a hydroxide containing water of crystallization (LiOH - H ₂ O) for the preparation of the aqueous solvents. Spray-drying the resultant suspension 15, consisting of very finely divided Lieiiumheptahydroxoaluminafin lithium hydroxide solution was carried out in the temperature range of 250-400 ⁰ C. The yield of spray dried powder, a stoichiometric mixture of Lithiumhydroxoaluminat and lithium hydroxide were respectively more than 90%. As a result of the handling of the lithium hydroxide solutions and the suspensions in air, the powders contained up to 5% by weight of carbonate components, which were removed during the calcination step. 20th

Direction When Calcinienf powder (two hours) was finely dispersed in the first vorliegeaden stoichiometric powder mixture the desired LithiummonoaiuminaL depending on the calcination temperature in this case were mixtures of AC and / IiAlO _2-2 (at 600 ⁰ C), "- and ^ -LiAlO ₂ ( at 800 ⁰ C) and pure LiAIO ^ ₂ (above 900 ⁰ C) observed at 900 ⁰ C calcined powder settled by pressing and sintering at about 1250 ⁰ C to 80-85% and at about 1450 ⁰ C in six hours at 90 - Compress 95% of the theoretical density. The sintering samples each gave single-phase ^ -LiAlO ₂ .

Claims (2)

Patent claims: 1. A process for the production of sinterable powder from / -LiAlO ₂ with a phase purity of 99% by dissolving metallic aluminum in an aqueous lithium hydroxide solution with the formation of a precipitation, characterized in that the suspension obtained without further intermediate treatment with hooves of air a temperature between 200 ⁰ C and 450 ⁰ C is spray-dried and the material to be dried is then calcined directly at a temperature between 850 ° C and 1100 ° C. 2. Use of the sinterable powder produced according to claim 1 from pure IiAlO ₂ as breeding material for fusion reactors for the production of tritium.