DE3415323A1 - METHOD FOR PRODUCING SINTERABLE POWDER FROM LITHIUM METASILICATE LI (DOWN ARROW) 2 (DOWN ARROW) SIO (DOWN ARROW) 3 (DOWN ARROW) AND THE USE THEREOF - Google Patents

Description

Nuclear Research Center ti / -> Karlsruhe, April 19, 1984 Karlsruhe GmbH PLA 8422 Gl / hr

ANR 1 002 597

Process for the production of sinterable powder from lithium etasilicate Li ₃ SiO ₃ and its use.

Process for the production of sinterable powder from lithium metasilicate Li ₃ SiO and its use.

The invention relates to a method for producing sinterable powder from lithium metasilicate Li SiO., With a phase purity of the order of 99 %, in which amorphous SiO _{2 is introduced} into an aqueous lithium hydroxide solution and the resulting suspension is exposed to an elevated temperature.

Oxidic ceramic materials containing lithium, for example lithium metasilicate, have already been proposed as breeding materials for fusion reactors for the extraction of tritium. To produce Li ₂ SiO ₃ , solid powders of Li ₂ CO ₃ and SiO ₂ or H ₃ SiO ₃ · ^nH ₂ 0 were usually heated or melted to high temperatures. The temperatures used for the reaction were in the range from more than 700 ° ^C to 1500 ° C and the heat treatment time between 3 to 5 hours at 1400 ° C to 1500 ° C to 8 days at 700 ° C, followed by 3 days at 800 ° C and 4 days at 900 ° C was further heated. Nothing was known about the purity of the products or their particle size. In general, however, the process products have to be ground before they can be further processed. In the solids reactions of the known manufacturing processes at high temperatures or in the melt, impurities are to be expected, so that only 90 to 95 % of the desired phase is present in the end product.

It was considered desirable to create a process for the production of Li ₂ SiO-, with which the impurities in the end product as well as the great expense

time and energy can be avoided with the known methods. At the same time, the process should be more economical than the previously known manufacturing processes. From "Gmelin's Handbuch der Anorganischen Chemie", System No. 20, Lithium, (1927) page 241 it is known that amorphous silica, dried at 100 ° C., is very sparingly soluble in warm LiOH solution, in cold, approximately 2N LiOH solution however, 1 mol of Li ₂ O can dissolve at least 3.4 mol of SiO ₂ . When heated, Li, SiO-, · Hn should precipitate from this solution. The production of sinterable powder from Li ₉ SiO is not indicated there.

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The invention is based on the object of creating a simple and improved process for the production of Li-SiO-, in which the largest possible proportion of the process takes place in an aqueous solution and a well sinterable powder of the with little time and relatively little energy desired Li ₃ SiO is obtained practically in pure phase.

The object is achieved according to the invention in that

a) a stoichiometric amount of SiO to form the Suspension is used, based on the dissolved LiOH,

b, the suspension without further intermediate treatment and is) directly by means of air at a temperature between 200 ⁰ C and 45O ° C spray-dried

c) then the powdery dry residue at a temperature in the range from 500 C to iOÖt> C is heated and calcined.

The following reaction takes place in the lithium hydroxide solution instead of:

2 LiOH + aq + SiO ₂ (amorphous) = ^ Li ₃ SiO ₃ · xH 0 + aq

The resulting suspension is converted into a powder by spray drying without any further intermediate treatment. The spray-dried powder was converted into the desired Li ₂ SiO ₃ ^{within 2 hours by calcination annealing at preferably 600 P C.} With suitable sintering conditions, a density of 95% TD can be achieved.

The lithium metasilicate produced by the process according to the invention is because of its high purity as Breeding material for fusion reactors for the extraction of tritium particularly well suited.

The invention is explained in more detail below with the aid of an implementation example.

Example :

According to the reaction equation

2 LiOH + SiO-, + aa - * - Li ₀ SiO ₀ · xH "0 + aa

an aqueous suspension of amorphous SiO ,, (AEROSIL from DEGUSSSA) is introduced into an aqueous solution of lithium hydroxide with constant stirring. Among other things Constant stirring at room temperature (about 1 hour) was the lithium metasilicate in the suspension

educated. It was assumed that the Li ₉ SiO- was partly present as a monohydrate and partly dissolved.

Table : Approaches for the spray drying of lithium metasilicate

No. in solution: H ₉ O as Suspension: , 18 H ₉ O Li ₂ SiO ₃ number of LiOH 3
(cm) SiO 2-, , 81 (cm " ³ ) (g / i) approaches (G) 1200 (cm ³ ) 800 -v 90 8th 1 95.80 500 120 1000 rO 65 12th 2 53.26 66

For batches no. 1, anhydrous lithium hydroxide was used, for batches of no. 2 lithium hydroxide containing water of crystallization (LiOH · H ₉ O) was used to prepare the LiOH solutions. The suspensions were spray-dried in a temperature range of 200-370 ° C. The yield of spray-dried Li ₉ SiO., · XH ₂ ° ^{t) etru} 5 is more than 90% in each case. The moisture content of the powders varied and was dependent on the temperature of the spray drying. Higher spray temperatures led to slightly lower moisture contents (around 2%). As a result of the handling of the lithium hydroxide solutions and the suspensions in air, the powders contained up to 6% by weight of carbonate components, which were removed during the calcination step.

The powder particles were in the form of small hollow spheres with an average size between 3 and 5 μm.

After calcining at 600 ° C, the powders could be

: n at
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by pressing and sintering at 1100 ° C / 6 hours up to 95%

• f '

compress the theoretical density. The sintered samples each resulted in single-phase Li ₃ SiO ₃ .

Claims (2)

Nuclear Research Center! Karlsruhe, April 19, 1984 Karlsruhe GmbH PLA 8422 Cl / hr ANR 1 002 597 Patent claims: 1. Process for the production of sinterable powder from lithium metasilicate Li ₃ SiO ₃ with a phase purity of the order of 99%, in which amorphous SiO _{2 is introduced} into an aqueous lithium hydroxide solution and the resulting suspension is exposed to an elevated temperature, characterized in that a) a stoichiometric amount of SiO _{9 is used} to form the suspension, based on the dissolved LiOH, b) the suspension without further intermediate treatment directly with the aid of air at a temperature between 200.degree and 450 C is spray-dried and c) then the powdery dry residue at a temperature in the range from 500 ° C to 1000 ° C
is heated and calcined. 2. Use of the sinterable powder prepared according to claim 1 made of pure Li-SiO. As breeding material for fusion reactors for the production of tritium.