DD239395B1 - METHOD FOR PRODUCING THORIUM YTTRIUM MIXED OXIDE POWDER - Google Patents

Description

To solve

Mixing Milling Seven

Water soluble. Y Verbinduni

To solve

Mixing I

Co-precipitation I

filtration

desiccation

calcine

Shaping sintering

The powder-ceramic process route has serious disadvantages compared to the chemical process route. These are, above all, the occurrence of abrasion during the grinding of the powder mixture and, in general, a poorer sinterability of the powder due to the low degree of dispersity. Also, for ThOj-based ceramic powders, there is a tendency to produce finely divided powders by a chemical process.

As the water-soluble starting compound for the chemical preparation route nitrates are preferably used. For this purpose, optimum process parameters have become known under which a precipitated thorium-yttrium mixed oxide powder can be obtained which, after shaping, can be sintered to dense bodies even at relatively low temperatures [DD-WP 155060].

Frequently, however, no water-soluble starting compounds of thorium are available, but insoluble oxalate. Thonumoxalate is obtained in the treatment of natural materials, such as monazite sand or in the isolation of technical products, such as thonumhaltigen catalysts

It is already known a method to obtain from Thonumoxalat on the formation of an oxalato-carbonate complex and its decomposition in acidic solution a pure Thonumoxalat which supplies a good sinterable oxide powder with suitable Prozeßfuhrung after calcination [DD-WP 21 7 733 I

For the production of a homogeneous thorium-yttrium oxide, however, this method is not suitable because yttrium precipitates in the carbonated solution as a flaky, insoluble Hydroxidniederschlag Thus, from the Komplexlosung during decomposition no temporally constant ratio of Th to Y is present, resulting in inhomogeneities of Y-distribution in the powder and ultimately in the ceramic leads Daruberhmaus demand and dosage of the hydroxide suspension are more difficult than with clear solutions In principle, the difficulties mentioned to work around, if all the reactants thorium oxalato-Karbonatokomplex,

Acid to decompose the complex,

Yttnumsalzlosung and

Oxalic acid solution to precipitate the Y oxalate

In separate, the desired Th / Y ratio proportional flow to the reaction site were required Here, however, complex and complicated control engineering complex solutions are required.

Object of the invention

The object of the invention is to provide a pure Th on um-Yttnum-IVIischoxid powder produced from throium oxalate and Yttnumsa Iz, which is good sinterable and has a homogeneous Th / Y distribution in the predetermined mixing ratio

Explanation of the essence of the invention

The invention has the object to provide a method by which a precipitate can be obtained from a basic Thonumoxalato-Komplexlosung and a Yttriumsalzlosung containing the two case components in optimal homogeneous distribution and in the predetermined mixing ratio and after calcination a mixed oxide high sinterability supplies.

This object is erfmdungsgemaß solved by the Thoriumoxalato-carbonated complex solution is adjusted to a pH value between 7 and 9 and this solution is added while maintaining the pH mtt oxalations in the amount of 1.5 to 3 times the molar amount of the yttrium used corresponds to the fact that the solution of starch is prepared separately by dissolving the salt in an acid and mixed with the carbonate complex solution so that the pH of the combined solution is always kept between 1 and 3

With the invention, it is possible, by combining only two single-phase solutions and the use of only the pH in the reaction vessel to control the mass flows to achieve a Oxalatgemisch with homogeneous Th / Y distribution, which after calcining a good sinterable, pure and finely dispersed Mixed Oxide Powder Provides The Thorium Oxalato Carbonate Complex Solution is prepared by adding a water soluble carbonate or CO2 to a slurry of thorium oxalate in water

The onset of the loosening process can be accelerated by stirring or increasing the temperature. By adding ammonia, base or acid, a pH value between 7 and 9 is set towards the end of the loosening process. Expediently, both the pH value and the temperature during the loosening process are selected such that no gas evolution occurs, which would lead to an additional carbonate consumption

Instead of the ammonium compounds, it is of course also possible to use the alkali (hydrogen) carbonates. After the end of the loosening process, the solution of insoluble products, such as sparingly soluble carbonates, non-complexed hydroxides or water-insoluble residues, is separated by filtration, which in turn results in a cleaning effect results

Oxalic acid, ammonium oxalate or alkali oxalate is added to the clear solution of carbonatoe If necessary, ammonia solution is added simultaneously to maintain the pH between 7 and 9. The amount of oxalate ions in moles (nox) depends first on the amount of thorium contained in the solution (n _Th ) and the desired molar ratio of yttrium to thorium Χγ / jh in the end product and results from

n <3x = γγ / Th nTh 1.5 a

At stoichiometric conversion, the factor a had the value a = 1 Although it is well known that yttrium oxalate is practically insoluble even in acidic solution [z BH Remy, textbook of inorganic chemistry, Academic publishing Geest & Portig K -G Leipzig, 1954, 7 IS 516 ff], occurs in the inventive method a complete failure u ng the yttrium oxalate only at values a large 1 on Favor has a value of 1.4 <a <2 proved The acid solution is by dissolving an yttrium salt in mineral acid, preferably nitric acid The amount of acid is calculated from the amount of carbonate contained in the complex of carbonatoside (bound in the complex and free from solution) and from the pH of the complex solution. A calculation of the amount of acid required for the decomposition of the carbonate complex and adjustment of a specific pH in the reaction space possible The titrimetric determination of the amount of acid is simpler titration of the complex solution with acid to the desired pH immediately results in the amount of acid required for the entire complex solution. If yttrium oxide is dissolved in the mineral acid instead of the yttrium salt, this must be taken into account when determining the amount of acid required

The yttrium-containing acid solution prepared in this way is now combined in a reaction vessel with the oxalic acid-containing thorium oxalato-carbonatocomplex solution with vigorous mixing ζ B by means of a stirrer so that the pH value is always between 1 and 3. In this process, the carbonate complex decomposes with the deposition of thorium oxalate Yttrium to poorly soluble yttrium oxalate The pH below 1 [DD WP 21 7 7 ~ - 3] recommended for the preparation of pure thorium oxalate via the thorium oxalato carbonate complex surprisingly leads to the precipitation of Th Y mixed oxalate products which are poorly sinterable after calcination On the other hand, the best sintering ability of the resulting oxide powder mixture is obtained at pH values of about 2. The concentration ratios of protons and yttrium set in the acid solution ensure that the deposition of thorium and yttrium oxalate always takes place in the same ratio

The case process can be carried out either continuously or intermittently, the temperature in the reaction chamber greatly affects the particle size distribution of both the oxalate and the prepared therefrom oxide pul ve rs For obtaining a good si nterf ah owned mixed oxide powder is to maintain the reaction temperature below 50 ⁰ C. After completion the precipitation, the oxalates ζ B are separated by filtration from the solution, washed and dried The calcination is expediently carried out at temperatures between 600 and 1 200 ⁰ C in air

exemplary

An exemplary embodiment for the production of a mixed oxide powder with 7.5% by weight of Y.sub.2 O.sub.3 is intended to explain the general procedure further.

1 000g of thorium oxalate (impurity content 2%) are slurried in 2 l of water. To this suspension are added 460 g of ammonium bicarbonate and 450 ml of concentrated ammonia solution (25% strength). The batch process is terminated after 5 hours by repeated stirring. The solution is brought to pH with a small amount of ammonia solution Value of 8 3 was adjusted and sucked through a medium-hard filter. To the clear filtrate, 144 g of ammomum oxalate dissolved in water are added, the total amount of solution is increased to 5 μl by addition of water and the pH is corrected again to the value of 8.3

25 ml of the total solution are then titrated with concentrated nitric acid to a pH of 2.0. Therefore, 3.6 ml of concentrated acid are required. Thus 720 ml of co-centered hydrochloric acid yttrium nitrate are dissolved corresponding to a quantity of 39.3 g of Y ₂ O ₃ Both solutions are simultaneously added to the reaction vessel at room temperature in such a way that approx

The reaction vessel is equipped with a stirrer and a glass electrode. The quantity of acid contained is always adjusted so that the glass electrode always displays values around pH-2. After approx. 2 hours, the precipitation process is complete; both solutions are completely combined and the pH of the solution is reached at 2.0 After settling of precipitate and decantation of the supernatant clear solution is filtered through a medium-hard filter The precipitate is washed with 21% distilled water and finally with 200 ml of alcohol After drying (12 h at 8O ⁰ C, then 8h at 200 ⁰ C) and calcination (2h in air at 800 ° C in sintered shells) is a pure finely dispersed mixed oxide powder obtained, which can be compacted without addition of auxiliaries at a pressure of 150 MPa by cold pressing and sintering in hydrogen at 1700 ⁰ C and 2 h temperature retention time provides a shaped body of more than 95% of the theoretical density

Claims (1)

Invention claim: Process for the preparation of thorium-yttrium mixed oxide powder by co-precipitation of an oxalate mixture of triumchlorium and yttrium compounds in solution and subsequent calcination, starting from a triumoxalato-carbonate complex solution and an yttrium salt solution, characterized in that the thorium oxalato-carbonate complex solution is admitted to a pH between 7 and 9 and this solution is added while maintaining the pH with oxalate ions in the amount corresponding to 1.5 to 3 times the molar amount of yttrium used that the yttrium solution by dissolving the salt in an acid is prepared separately and mixed with the carbonate complex solution so that the pH of the combined solution is always kept between 1 and 3. Field of application of the invention The invention relates to a process for the preparation of thorium-yttrium mixed oxide powder. Thorium-Yttnum mixed oxide powder is the starting material for the production of yttrium-doped thorium oxide ceramics. Because of its special electrical properties, this ceramic is mainly used as a solid electrolyte material in measuring probes for determining the oxygen potential under strongly reducing conditions. In addition, applications in laser technology and high-temperature technology are emerging. Characteristic of the known technical solutions For the production of thorium-yttrium mixed oxide powder, two principal process routes are known: powder ceramic way chemical way ThO ₂ powder Water soluble. Th bond