MXPA00001810A - Tantalum (v) nitride pigments, process for the production thereof and use thereof - Google Patents

Abstract

Tantalum (V) oxide may be nitrided with ammonia at 700 to 1250 C. to yield tantalum (V) nitride. According to the invention, nitriding and consequently pigment quality are improved by adding at least one pulverulent oxide from the series SiO2, GeO2, SnO2, TiO2, ZrO2 and HfO2 or a pulverulent precursor of such an oxide in a quantity of at least 0.1 wt.%, calculated as oxide, to the tantalum (V) oxide to be nitrided and then nitriding the powder mixture.

Description

PIGMENTS OF TANTAL ITRIDE (V), PROCEDURE FOR PREPARING AND USING THEREOF Field of the Invention The invention relates to tantalum nitride or tantalum pigments (v) with improved colorimetric values of the red pigment. Another object relates to the preparation of tantalum nitride pigments (V) based on a nitriding of tantalum oxide (V) with ammonia. Finally, the invention also relates to the use of tantalum nitride pigments (V) with better color. Background of the Invention In the use and also in the disposal of articles pigmented or decorated with oxidic, sulfuric or selenuric heavy metal compounds, toxicologically objectionable constituents such as cadmium and selenium can be released from the red pigments of cadmium sulfoselenide. Therefore, there is a special interest to use pigments with fewer toxicologically objectionable constituents. The tantalum nitride (V) (Ta3N5) is an unobjectionable alternative, however the colorimetric values, especially the brightness, do not always correspond to the pigments obtained by means of the pigments obtainable by means of the methods known up to now. The preparation process hitherto known leads either to unsatisfactory colorimetric values or necessitates the use of compounds of REF .: 32568 special tantalum game. The pentavalent tantalum nitride can be prepared according to H. Moreau and C.H. Ha blet (J. Amer. Che,. Soc. 59, 33-40 (1937)) by means of ammonolysis of TaC15. The nitride thus obtained is not pure, since it contains oxidic constituent parts. In addition, the reaction times are very long. H. Funk and H. Bóhland (Z: anorg. Allg. Chem. 334, 155-62 (1964)) were able to shorten the reaction times by nitriding (NH4) TaF6. Due to the volatility of TaF5 and NH4F the yields of Ta.N5 are reduced and / or the products contain fluorine. The nitriding of tantalum oxide (V) was also presented in the aforementioned document (ta205) at 800 ° C with ammonia; A nitride containing oxide (Ta3N5 (O)) is formed at 800 ° C, the color of which was not characterized in detail. The nitriding of pure tantalum pentoxide with purified ammonia was studied taking as a reference the study by Funk and Bóhland of G. Brauer and J.R. Weidlein (Angew, Chem. 77, 218-9 (1965)); In the presence of titanium chips as a getter or oxygen vacuum tuner, the reaction requires a reaction time of 36 to 120 hours at 860 to 920 ° C. After the re-elaboration of these investigations (see EP-A-0592867) they did not ask to determine the reaction times: first after a reaction time of 150 hours the color formation finished, that is, there were no variations in the color . However, the tantalum nitride (V) was reddish brown and therefore not interesting coloristically. According to the process described in EP-A 0 592 867 it is possible to obtain tantalum nitride (V) with a greater color intensity and simultaneously reduce the reaction time. In this process instead of tantalum oxide (V) a tantalum oxyhydrate (V) of the composition according to the formula Ta205 is used. Aq with a hydrate content (Aq content) in the range of 14 to 1% by weight. To reduce the duration of the nitriding reaction, a flux is added to the tantalum oxyhydrate to nitride. The pigment obtained here showed a variation of red compared to the previously known products, as well as an essentially greater color intensity than the products obtained using tantalum oxide (V). A disadvantage of the process mentioned at the end is that a commercially available tantalum (V) oxide can not be used, but rather a specially prepared tantalum oxyhydrate (V). A disadvantage is that the above procedure using tantalum oxide (V), as mentioned above, leads to products whose colorimetric values prevented its use as a red pigment. The task of the present invention is a process for the preparation of tantalum nitride (V) with improved colorimetric values against the previously known products, which is based on the nitriding of tantalum oxide (V) with ammonia. DETAILED DESCRIPTION OF THE INVENTION The process for the preparation of tantalum nitride pigment (V) was found by nitriding of tantalum oxide (V) in powder form with ammonia at 700 to 1250 ° C which is characterized in that to the tantalum oxide (V) that is nitriding when at least one oxide powder of the group Si02, Ge02, Sn02, Ti02, Zr02 and Hf02 or a powder precursor of these oxides is added in an amount of at least 0.1% in weight, calculated as oxide, and the powder mixture is nitrided. The dependent process claims refer to preferred embodiments. Surprisingly it was found that the nitriding of tantalum oxide (V) can be substantially improved, when the tantalum oxide (V) powder before nitriding is mixed with an inert oxide of the group Si02, Ge02, Sn02, Ti02, Zr02 and Hf02 or a powdered precursor of those oxides. In the nitriding of the homogeneous powder mixture, red powders are obtained. Under the term "inert" it is understood that the oxides or precursors mentioned under essentially nitriding conditions do not form nitrides. The amount of these oxides or precursors used can vary between wide limits: an amount of use less than 0.1% by weight in relation to tantalum oxide is possible (V), however in these cases, naturally the effect is reduced. Usually, an amount of at least 1% by weight of oxide or an oxide precursor, calculated as oxide, is preferred. It is also possible to use tantalum oxide (V) also in an amount greater than 20% by weight of one or more of the aforementioned oxides or precursors, however it must be taken into account that the pigments used become increasingly clear. Preferably the amount used is from 2 to 15% by weight, 3 to 10% by weight is especially preferred. The effect according to the invention, of improving the nitriding and obtaining products with better colorimetric values, can be obtained using only one of the aforementioned oxides or precursors. Therefore it is also possible to use a combination of two or more compounds of that type. Under the concept "precursors of these oxides" are understood those compounds that are transformed into oxides, below the nitriding temperature, also by heating the powder mixture. Accordingly, they are suitable oxide precursors, especially oxyhydrates, nitrates, carbonate and salts of lower carboxylic acids. According to especially preferred embodiments of the process according to the invention, tantalum oxide (V), silicic acid, zirconium dioxide or a precursor of these oxides, especially basic zirconium carbonate or mixtures of the aforementioned compounds, are added to the oxide. . It was determined that it is especially advantageous to use one or more oxides or precursors thereof, as well as the tantalum oxide (V) to be nitrated in the finest powder form possible. As tantalum oxide (V) commercial products with pigment quality are suitable. To the tantalum oxide (V) to nitride are preferably added those oxides or precursors, whose specific surface (measured according to BET according to DIN 66131 with N2) at least 5 m2 / g. preferably more than 50 m2 / g and in particular about 200 m2 / g is preferred. For example, oxides prepared by means of grinding processes as well as by precipitation processes or by means of flame hydrolysis can be used. Zr02 obtained by means of the thermal dissociation of the zirconium silicate with the subsequent removal of the silicic acid matrix is also suitable. For the preparation of the powder mixture, the devices known to the person skilled in the art can be used: in order to homogenize the powder mixture, the mixing and / or grinding devices are suitable, whereby the tantalum oxide to be nitridized with the oxides or precursors with the which is to be mixed can be carried to a uniform distribution. A good homogenization is also obtained in nitriding rectors, in which the powder mixture moves constantly. Nitriding is advantageously carried out under the trade union of ammonia or an inert gas containing ammonia through a reactor containing the powder mixture at 700 to 1250 ° C, preferably 850 to 950 °. According to a preferred embodiment, the nitriding is carried out in a rotating tube reactor. It was determined that it is advantageous that with the increase of the reaction temperature increase the ammonia flow rate. In this way secondary reactions that worsen the color quality can be avoided. A flow velocity greater than 0.5 m / s in particular is preferred from 1 to 5 m / s. To reduce the nitriding temperature and / or to reduce the required duration of the reaction, the powder mixture can additionally contain a flux. Suitable fluxes are ammonium salts of carbonic acids, minor carboxylic acids or a boric acid; Boric acids or boric acid anhydrides; alkali metal or alkaline earth metal halides. A one or more fluxes in fine powder form can be added to the nitride powder mixes. As long as fluxes are added to the powder mixture, the amount used is advantageously from 1 to 50% by weight and preferably from 5 to 20% by weight, in relation to the powder mixture. As long as this is desired, the water-soluble fluxes can be dissolved after the nitriding of the obtained pigments. The pigments prepared according to the invention are characterized by extraordinarily good colorimetric values L * a * b, in a CIÉ laboratory system (DIN 5033, part 3). The tantalum nitride pigments (V) with these colorimetric values had not been obtainable with the previously known methods. According to this, the tantalum nitride pigments (V) according to the invention are characterized by a content of at least one oxide of the group Si02, Ge02, Sn02, Ti02, Zr02 and Hf02 in an amount of at least 0.1% in weigh . The tantalum nitride pigments (V) according to the invention can also be obtained by means of the process according to the invention, also by the nitriding of other tantalum compounds (V), in particular tantalum oxyhydrates (V) or tantalum oxynitrides (V). Considering the following test criteria, the pigments according to the invention present the following colorimetric values L * a * b *: L * less than 40; a * greater than 35, especially 40 to 45; b * 40 to 50. The colorimetric measurement was performed with PVC plastisol stained with the pigment, mixing 0.7 g of pigment and 2 g of Plastisol and dispersing in a paint stripper machine; Applications of the pastes with a thickness of 300 μm were gelled for 10 minutes at 140 ° C. As the colorimetric values show, the pigments are characterized by high values of red, high brightness and high heat intensity. Another advantage of the oxides contained in the pigments according to the invention is the improvement of the dispersibility of the pigments. The pigments according to the invention can be used for the preparation of vitreous paints as well as for dyeing bakeable glazes at less than 800 ° C as well as for plastics, lacquers and cosmetic articles. The vitreous colors are obtained by mixing the pigments with fluxes, especially glass frits. For application, or decoration of substrates with direct printing or for the manufacture of decals, the mixture and flux are first dispersed in a liquid to pastey printing medium. The advantages of the invention are that a commercially available tantalum oxide (V) can be used in nitriding and still obtain very bright pigments. The oxides contained in the pigment, as long as they are present in an amount of approximately / less than 10% by weight in the nitride powder mixture, lead to a reduced clarification of the shade, but also to an increase in the brilliance and the dispersibility. The oxides or precursors to be mixed in the tantalum oxide (V) to nitrate, lead to an acceleration of the reaction. The invention will be clarified with the help of the following examples and comparative examples. Preparation of the pigments: Example 1 (Bl) 300 g of commercially available tantalum oxide (V) (purity> 99.9%, d50 = 0.5 μm) were mixed with 6% silicon dioxide (F 500 from Quare Frechen, D50 = 3.4 μm) and homogenized. The mixture was then heated at 910 ° C with ammonia (13001 / h) for 12 hours in a rotating tube (d .. = 14 cm, 1 = 50 cm) of quartz glass (rotation speed 1 rpm). A red powder was obtained as a product. Example 2 (B2) 300 g of commercially available tantalum oxide (V) (purity > 99.9%) were mixed with 9% silicon dioxide F 500 and homogenized. The mixture was then heated at 910 ° C with ammonia (13001 / h) for 12 hours in a rotating quartz glass tube (rotation speed 1 rpm). A red powder was obtained as a product. Example 3 (B3) 300 g of commercially available tantalum (V) oxide (purity> 99.9%) were mixed with 4% precipitated silica (Sipernat 22S from Degussa) and homogenized. The mixture was then heated at 910 ° C with ammonia (1300 1 / h) for 12 hours in a rotating quartz glass tube (rotation speed 1 rpm). A red powder was obtained as a product. Example 4 (B4) 300 g of commercially available tantalum oxide (V) (purity > 99.9%) were mixed with 3% precipitated silica (Sipernatr 22S) and homogenized. The mixture was then heated at 910 ° C with ammonia (13001 / h) for 12 hours in a rotating quartz glass tube (rotation speed 1 rpm). A red powder was obtained as a product. Example 5 (B5) 300 g of commercially available tantalum oxide (V) (purity> 99.9%) were mixed with 10% zirconium dioxide with a mean grain diameter of 2.5 μm and homogenized. The mixture was then heated at 910 ° C with ammonia (1300 1 / h) for 12 hours in a rotating quartz glass tube (rotation speed 1 rpm). A red powder was obtained as a product. Ejenflo 6 (B6) 300 g of commercially available tantalum oxide (V) (purity > 99.9%) were mixed with 5% basic zirconium carbonate (Kynoch Kaapstreek) and 6% by weight of precipitated silica (Sipernat 22S) and homogenized. The mixture was then heated at 910 ° C with ammonia (1300 1 / h) for 12 hours in a rotating quartz glass tube (rotation speed 1 rpm). A red powder was obtained as a product. Comparative Example 1 (VB1) 300 g of commercially available tantalum oxide (V) (purity> 99.9%) were poured into a rotating quartz glass tube. The oxide was then heated at 910 ° C with ammonia (1300 1 / h) for 12 hours in a rotating quartz glass tube (rotation speed i rpm). A red-brown powder was obtained as a product. Comparative Example 2 (VB2) a) Preparation of tantalum oxide hydrate: 10 g of tantalum chloride (V) are dissolved in 400 ml of concentrated hydrochloric acid under boiling heat.

It is then diluted with 80 ml of water and tantalum oxyhydrate with concentrated ammonia solution at pH 7. The precipitate is washed until it is free of chlorine, washed with ethanol and dried at 120 ° C. The amorphous product under X-rays has a residual water content of 14.9% by weight (after calcining at 1000 ° C). b) Nitriding: Then the g of that product is poured into a corundum wafer and heated in a stream to ammonia (9 1 / h) for 80 hours at 820 ° C. You get a red product. c) Colorimetric values: The colorimetric values are the plastics usually dyed with the same amounts (0.7 g pigment and 2 g PVC-Plastisol) are the following: L + 35.21, a * 38.03; b * 41.44. Coloristic test of the powder obtained: The powder prepared according to the given indications was mixed with PVC-Plastisol and examined coloristically. For this, 0.7 g of the sample and 2 g of Plastisol were mixed and dispersed in a paint stripper machine. The paste with a thickness of 300 μm was applied with a spatula. The gelation was carried out by heating at 140 ° C in the course of 10 minutes. With a spectrophotometer, color values L * a * b * were measured and transformed to the system value (DIN 5033, part 3). The color values can be found in the following table.

Table: By comparing the examples with Comparative Example 1 it was shown that the addition of oxides improves color formation significantly. By comparing examples 3, 4, and 6 according to the invention with comparative example 2, it has been shown that with the optimal selection of the oxide or precursor greater values a (value of red) are obtained than when they are not present. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (8)

1. CLAIMS Having described the invention as above, it is claimed as property that contained in the following: 1. - Procedure for the preparation of tantalum nitride pigment (V) by means of the nitriding of tantalum oxide (V) in the form of powder with ammonia to 700 to 1250 ° C which is characterized because of tantalum oxide (V) that will be nitriding when at least one oxide powder of the group Si02, Ge02, Sn02, Ti02, Zr02 and Hf02 or a powder precursor of these oxides is added in an amount of at least 0.1% by weight, calculated as oxide, and the powder mixture becomes nitride.
2. 2. Method according to claim 1, characterized in that the tantalum oxide (V) is added one or more oxides in powder form from the group of Si02 and Z: j: 02 or precursors of Si02 and Zr02 in an amount from 1 to 20% by weight, especially 2 to 15% by weight.
3. 3. Process according to claim 1 or 2, characterized in that the oxide of tantalum (V) is mixed with oxide and / or precursors thereof with a specific surface area of at least 10 m2 / g.
4. 4. - Procedure according to the claims 1 to 3, characterized in that the nitriding is carried out at 850 to 950 ° C.
5. 5. - Process according to claims 4, characterized in that, to the tantalum oxide (V) to nitrure is added 2 to 10% by weight of a pyrogenic silica or precipitate with a specific surface BET, N2) in the range of 150 to 700 m / g.
6. 6. Process according to one of claims 1 to 5, characterized in that zirconium carbonate is used as Zr 02 source.
7. 7. Process according to one of claims 1 to 6, characterized in that the nitride powder mixture contains one or more fluxes from the group of ammonium salts of carbonic acids, minor carboxylic acids or a boric acid; Boric acids or boric acid anhydrides; alkali metal or alkaline earth metal halides.
8. 8. Method according to one of claims 1 to 6, characterized in that the nitriding is carried out in a rotating tube. 9.- Tantalum nitride pigment (V) characterized by a content of at least one oxide of the Si02 group, Ge02, Sn02, Ti02, Zr02 and Hf02 in an amount of at least

   0. 1% by weight 10. - Use of tantalum nitride pigments (V) according to claim 9 and obtained according to one of claims 1 to 8, for the preparation of vitreous paints as well as for dyeing bakeable glazes at less than 800 ° C as well as for plastics, lacquers and cosmetic articles. TANK NITRIDE PIGMENTS (V), PROCESS FOR PREPARING AND USING SUMMARY OF THE INVENTION Tantalum oxide (V) can be nitrated with ammonia at 700 to 1250 ° C to form tantalum nitride (V) According to the invention nitriding is improved and with this also the quality of the pigments, wherein the tantalum oxide (V) which is to be nitridized when at least one oxide powder of the Si02 group, Ge02 / SnO_, is added, Ti02, Zr02 and Hf02 or a powder precursor of these oxides in an amount of at least 0.1% by weight, calculated as oxide, and the powder mixture is nitrided.