Improvements in or relating to the preparation of substantially pure titanium dioxide

Issued February 15, 1973

Date drawing January 16, 1973

PATENT BOARD

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PATENT

No. 136392

THE NETHERLANDS

CLASS I2i 39 b.

int. CI. C04b35/44.

KRONOS TITAN - G. mb II. at Leverkusen, Federal Republic of Germany.

Process for the preparation of finely divided TiO₂, as well as its use in the manufacture of TiO₂- single crystal boules and these boules themselves.

Application No. 286319, filed Dec. 4, 1962, 24 Hours; made available for inspection (art. 22C ROW) February 10, 1965, published (art. 25 ROW) September 15, 1972 under the above-mentioned number in bold, priority invoked from December 4, 1961 onwards, Ver. St. v. Am., No. 157016.

Avg.: Dr. JG Frielink cs in The Hague.

The invention relates to a process for preparing a finely divided TiO₂, by a solution of TiCl₄ reacting in water with oxalic acid in the presence of a chloride and removing the precipitated titanium oxalate from the solution, drying and calcining at a temperature of 600-700°C. It also relates to a method for the production of TiO₂-single crystal boules as well as on these boules themselves.

is applied and, if desired, the obtained anataseTiO₂ is sifted.

Since the TiO . obtained with the invention process₂ is particularly pure, it is well suited to be used as a starting material for the preparation of sintered titanates.

A field of application of the titanium dioxide obtained according to the invention is the use as a starting material in a process for the production of such a process. Thus 10 monocrystals from these, for example in the form of British Pat. No. 378,906, prescribes a process - a so-called TiO₂-boules. This method for converting TiO₂ by making TiO . from an aqueous solution₂-boules by means of an H₂/O₂— ' ' ' ' ' ” . flame is also preferred because it is made of TiCl₄ using oxalic acid and maintaining certain conditions, such as neutralization, manufacture of TiO₂-boules so far only dilution and temperature, basic titanium oxalate down 15 was known with one TiO₂-starting material, which was deposited, filtered off this titanium oxalate and obtained the rutile form from this (U.S. patent by calcining the TiO₂ to prepare. The oxalic acid to be used in this known process must be 2,792,287) and it has been found that the TiO obtained by the process of the invention₂product, which has the analytes in an amount of 0.15-0.3 moles per mole of the ash crystal form/significantly more reactive and of the TiCl₄while the reaction liquid is furthermore more suitable for use as starting material for obtaining a readily filterable basic titanium oxalate for producing monocrystals therefrom.

may contain sodium chloride. Although with these amounts of oxalic acid and ammonium chloride, the process yields TiO₂ excellent pigment qualities to be obtained in the process of the invention is it as a raw material for the consumption are critical, because when using less materials of TiO₂-single crystals from this completely less than 0.5 mol oxalic acid per mol TiCl₄ are suitable for application, because according to this known method it hardens poorly and, moreover, becomes a hard, coarse TiO. obtained TiO₂ is not clean enough for this. ' ” ” ' - - It has now been found that a finely divided TiO₂ _ can prepare, which due to its high purity Amounts of NH₄Cl of less than 0.75 moles per mole is well suited to be used as a starting material for the titanium tetrachloride yielding poor yields and the production of single crystals, if hard product, while yielding amounts greater than 3.0. Amounts of oxalic acid greater than 1.0 mol per mol of TiCl₄ also produce bad results.

one from an aqueous TiCl₄solution with the aid of moles also yield hard coarse products, oxalic acid in an amount of 0.5-1.0 moles per mole De TiCl₄solution, the oxalic acid and the ammonium TiCl₄ in the presence of ammonium chloride in a chloride, amounts of 0.75-3.0 mol NH . can be combined in any way₄C1 per mole TiCl₄ 35 mixed. However, it is preferable first to precipitate the ammonium titanium chloride oxalate and to mix titanium tetrachloride solution and the oxalic acid with this double salt after removal from the solution and only then to this mixture and calcination at 600-700°C. . ammonium chloride solution. Others

The invention therefore relates to a method of addition, which can also be used, however, a method for the preparation of finely divided TiO₂ through a 40 such as for example mixing the oxalic acid with a solution of TiCl₄ reacting in water with oxalic acid at the ammonium chloride and the subsequent addition of a chloride and removing the gene of the titanium tetrachloride solution and the mixed titanium oxalate from the solution.

heating, drying and at a temperature of 600-700°C. The solutions can be calcined at temperatures from 30°C to 30°C and are characterized in that the chloride is reacted with each other as chloride from 45 to 80°C.

ammonium chloride used in an amount of 0.75–3.0 mole NH₄C1 per mole TiCl₄, while it. oxal- are added, after which the precipitate can be allowed to acidify in an amount of 0.5-1.0 mol per mol of TiCl₄ settle before being filtered off. The precipitation

Available at the Industrial Property Office in The Hague — Price per copy ƒ 3,—

4 is then dried and calcined at a temperature of dioxide having a bulk density of 0.40 kg per liter which is from 600 DEG to 700 DEG C. in order to have the ammonium chloride crystal structure of the anatase.

and to remove oxalate residues and form the titanium dioxide. The calcined titanium dioxide product of the anatase of the anatase modification. After annealing modification - - - - the product is usually ground and sieved, 5 analysis:

for example over a sieve with openings of 0.149 mm. The screened product is soft, free flowing and has a bulk density of 0.35 to 0.46 kg per liter.

The invention is further elucidated with reference to the following example. 10

Example.

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&lt;0,01 %

SiO₂Fe₂O₃A1₂O₃sb₂O₃snO₂Mg Nb

An aqueous titanium tetrachloride solution is prepared in the following manner: 14 kg of titanium tetrachloride 15 From this anatase feedstock, a unit is slowly added to a water-cooled crystal boule of the rutile modification prepared below the container containing 28 liters of demineralized water, using the protocol of the US. The water is stirred rapidly and the titanium tetrachloride patent 2,792,287, by which prescription it is added at such a small rate, that the anatase feedstock is not passed through an oxygen/hydrogen temperature of the mixture during mixing, where it is melted and rises above 35°E. ' on a support member crystallized in the

The oxalic acid solution is prepared by mixing 400 cm³ form of a single crystal boule of the rutile modification. demineralized water at a temperature of 70° O. In connection with the anatase crystal structure of the material to be heated and subsequently stirred thereto with 126 g of food material according to the invention, this chemically pure oxalic acid (H₂C₂O₄.2 H₂O) is added faster and the feeding is more even and smooth. After the oxalic acid is added, the solution is used more easily than with the rutile feedstocks, which have been adjusted to a temperature of 60°C.

The ammonium chloride solution is prepared by From the above description and the explanatory 400 cm³ demineralized water at a temperature in the example mentioned clearly shows that a gentle heating of 50 DEG C. and adding 80.2 g of free-flowing titanium dioxide feedstock with the chemically pure ammonium chloride to it with stirring is added. The crystal structure of anatase can be prepared at full temperature of the solution is maintained at 40° O by the simple method of the present invention. invention and that a titanium dioxide material with the

In order to carry out the conversion of the above opanatase modification as feedstock, which is according to releases, the oxalic acid solution in the process of the present invention is first stirred and 445 mls of solution are added to this solution.³ of Reid, has a high purity and as boule-fed the cut titanium tetrachloride solution (which has 180 g material nutritional properties, which are better TiO₂ per liter), which is prepared in the above-described manner than the hitherto used food materials. The ammonium chloride solution is the rutile modification. is then added to the mixture of titanium tetrachloride and oxalic acid, whereupon a precipitate begins to form almost immediately. The mixture is then stirred for at least 2 hours to complete the precipitation, after which the precipitate is allowed to leave 1. Process for preparing finely divided IÏO₂ settle and then filter, wash and rinse several 45 through a solution of TiCl₄ in water with oxalic acid dried in vacuo for hours. The precipitate shows the following chemical analysis: