YTTRIUM AND/OR RARE EARTHS ALUMINATES HAVING PEROVSKITE STRUCTURE, PREPARATION THEREOF AND USE AS PIGMENTS

Abstract: Yttrium and/or rare earths aluminates having perovskite structure and particular brillance especially in tones from red to yellow are described.

Description: YTTRIUM AND/OR RARE EARTHS ALUMINATES HAVING PEROVSKITE STRUCTURE, PREPARATION THEREOF AND USE AS PIGMENTS. Field of the Invention This invention relates to yttrium and/or rare earths aluminates having perovskite structure, useful as pigments, in ceramic applications, having particular brilliance, even after baking, particularly in tones from red to yellow. Prior Art It is known that pigments are used for coloration of a wide range of products, from varnishes to glasses, from plastics to ceramic products. For products which undergo processes of preparation including heat-treatment, often at elevated temperature, (as, for example, in the case ceramic products) , there is the problem of providing pigments which maintain their tone and brilliance, even after such processes which, on the contrary, often tend to alter qualities and therefore the final appearance of the pigment itself. In particular, pigments for colorations from yellow to red seem to be very sensible to the effects of temperature and, after baking, they show undesired color changes, as, for example, colors based on cadmium sulfoselenides. Multiple solutions have been studied in order to find pigments able to overcome said drawbacks. The pigments studied by the applicant tend to limit the use of toxic components and are comprised in the group of 0-perovskite structure pigments. Pigments having known 0-perovskite structure (with respect to this. see the following Patents: EP - 5^5 7~5; EP - 5^5757; FR - 2 667 536 and FR - 2553 7^9) are not comprised in the range of colorations that we have reported. Detailed Description of the Invention This invention permits to solve said problems by means of yttrium and/or rare earths alummates of perovskite type which gave unexpected results of unaltered tone and color intensity, even after heat treating, particularly in the tone from red to yellow. Pigments according to the present invention have perovskite structure and contain Aluminium, Yttrium and/or rare earths and doping metals, as Chromium, Vanadium. Nichei, Tungsten, Iron, Copper. Pigments according to the present invention can be chemically expressed by the Formula: A1 (2-x-y) (Y.Ln) χ 0 3 : yM wherein M = Cr 2 0 , 2 0 5 , NiO , WO CuO , FeO , Re 2 0-, Ln = Er , La . Yb , Sm , Gd or mixtures thereof . 0.48≤x≤1 .51 0.007≤y≤0.2 Analogously , the chemical composition of pigments according to the present invention can be represented as follows, by expressing the different metals as the corresponding oxides: A1 2 0 3 = 10 - 44% Ln ? 0 = 0 - 86% [wherein Ln = Er, La, \ b , Sm, Gd or mixtures thereof] Z 0 = 0 - 10% [wherein Z is an alkali metal or an alkaline-earth metal and s is 1 or 2. respectively] F = 0 - 5% Q = 0 - 5% [wherein Q = Cr. , Ni. Fe. Cu, W] The possible presence of F ana Z 0 in the final product is due to the possible use of %hιch are generally utilized in the processes of preparation of the pigments (as indicated hereinafter). Pigments according to the present invention are prepared according to known procedures. The metal compounds are mixed in order to yield a homogeneous mixture which is then sintered in furnace, at a temperature comprised between 1200° and 1600° C over a period of time from about 10 to 20 hours. As metal compounds to be used as starting products the following can be considered: all salts able to provide the cation of interest, for example hydroxides, oxides, carbonates, sulfates or nitrates of the correspondent metals, oxides and hydroxides are generally preferred. As doping metals, those which are known in ceramic applications can be used, among which, those which gave the best results are: Chromium, Vanadium, Nickel, Tungsten, Copper and Iron. The possible use of catalysts, as indicated above, permits to perform the sintering reaction at the lowest temperatures of the said range. As catalysts, halides, fluosilicates, carbonates or double caroonates cf alkali metals or alkaline-earth metals can be used; metal fluorides are preferred and more particularly, sodium fluoride is preferred. Products according to the present invention can be obtained according t- the normal processes of sintering. The quantities of the starting products used for the preparation of the mixture to be smtereα. are preferably equal to the stoichiometric quantities in order to avoid tne presence of unreacted products in the final compound. Λ ccordιng to the starting raw materials, the sintering can proceed in oxidizing atmosphere or reducing atmosphere. ^fter sintering, the products can be subjected to grinding and. if necessary, they are finally dried and chemically modified so tnat the final granulometry is the preferred one according to their next use. Pigments according to the present invention can be used in varnish applications, plastic applications and particularly as ceramic pigments. Compounds according to the invention, in which yttrium is present and in which the doping metals are Chromium or Vanadium, are particularly preferred for their intense coloration from red to yellow, respectively, and for the particular stability and brilliance after treating at elevated temperatures. This invention will be more and better clarified by the following examples herein reported for illustrative and not limiting purpose. Example 1 A mixer is charged with Aluminium hydroxide (36.8 g) , Yttrium oxide (55-5 g) - Sodium fluoride (2.5 g) . Calcium carbonate (1.0 g) , Dolomite (3 g) . Chromium oxide (1.2 g) and mixing is carried out to yield a homogeneous mixture. The mixture is baked in furnace at a temperature of 1300°-l4θO° C up to the complete color generation 15 hours, approximately). 85 g of red pigment of the following Formula: A1 0.964 Y 1.004°3 : 0.032Cr 2 0 3 are obtained. Example 2 According to Example 1, the following compounds are mixed: Aluminium hydroxide g 32 Yttrium oxide g 30 Erbium g 30 Sodium fluoride g 3 Calcium carbonate g 1.5 Dolomite g 2 Chromium oxide g 1.5 87 g of a red pigment of the following Formula: A1 0.962 v 0.623 Er 0.367°3 : = 0 - o46Cr 2°3 are obtained. Example 3 According to Example 1. the following compounds are mixed: Aluminium hydroxide g 29 Erbium g 63 Sodium fluoride g 3 Calcium carbonate g 1.5 Dolomite g 2 Chromium oxide g 1.5 88 g of a red pigment of the following Formula: Al lι031 Er 0 _ 9li| 0 3 : 0.05 Cr 2 0 3 are obtained. Example 4 According to Example 1, the following compounds are mixed: Aluminium hydroxide g 32 Yttrium oxide g 55 Sodium fluoride g 2 Calcium carbonate g 3 Ammonium metavanadate g 3 Dolomite g 5 84 g of a yellow pigment of the following Formula: A1 0.895 Y 1.062°3 :0 - 0itV 2 0 5 are obtained.

Claims: CLAIMS 1 . Yttrium and/or rare-earth aluminates of the chemical Formula: A1 ( 2-x-y ) ■ ( Y . Lπ ) χ 0 3 : yM wherein : M = Cr 2 0 3 , V 2 0 5 , NiO. W0 3 . CuO. FeO. Fe 2 0 3 Ln = Er, La, Yb, Sm, Gd and blends thereof. 0.48≤x≤1.51 0.007≤y≤0.2 2. Aluminates according to claim 1 having the following composition (wherein the different metals are expressed as oxides): Y 2 0 3 = 0 - 81% A1 2 0 3 = 10 - 44% Ln 2 0 3 = 0 - 86% [wherein Ln = Er. La. Yb. Sm. Gd or blends thereof] Z g 0 = 0 - 10% [wherein Z is an alkali metal or an alkaline-earth metal and s is 1 or 2, respectively] F = 0 - 5% Q = 0 - 5% [wherein Q = Cr. V. Ni. Fe, Cu, W] 3- Aluminates according to claim 1 of the Formula: A1 (2-x-y) ' Y x°3 : yM wherein x and y are as defined above. 4. Aluminates according to claim 1 of the Formula: A1 (2-x-y) ' Ln x°3 : yM wherein x, y and Ln are as defined above. 5- Aluminates according to claim 3 of the Formula: A1 (2-x-y) ' Y x°3 : ~ vCr 2°3 wherein x and y are as defined above. 6. Aluminates according to claim 3 of the Formula: A1 (2-x-y) Y x°3 : - vV 2°5 wherein x and y are as defined above. 7- Aluminates according to claim 4 of the Formula: A1 (2-x-y) Ln x°3 : yCr 2°3 wherein x, y and Ln are as defined above. 8. Aluminates according to claim 4 of the Formula: A1 (2-x-y) Ln x°3 : - vV 2°5 wherein x, y and Ln are as defined above. - Aluminates according to claim 1 of the Formula: A1 (2-x-y) Y x°3 : y Cu0; A1 (2-x-y) Y x°3 : 'Nl0: A1 (2-x-y) Y x°3 : yW0 3 ; Al (2 _ χ . y) Ln χ 0 3 : yCuO; Al (2 . χ _ y) Ln χ 0 3 : yNiO; Al (2 . χ . y) Ln χ 0 3 : yW0 3 ; Al (2 . χ . y) Y χ 0 3 : yFeO; Al (2 _ χ _ y) Y χ 0 3 : yFe 2 0 3 ; Al (2 . χ . y) Ln χ 0 3 : yFeO; Al {2 _ χ _ y) Ln χ 0 3 : yFe^; wherein x, y and Ln are as defined above. 10. Aluminates according claim 1 of the Formula: A1 0.964 .004°3 : °-°3 2 Cr 2 0 3 ; Al 0>962 Y 0t623 Er 0 . 36? 0 3 : 0.046 Cr 2 0 3 : A1 1.031 Er 0.9l4°3 : °-°55 r 2 0 3 ; Al 0#895 Y 1 #o62 0 3 • 0.04 2 0 5 11. Process for preparation of compounds accorαing to claim 1 wherein metal compounds, possibly in the presence of catalysts, are mixed in order to achieve a homogeneous mixture which is then sintered at a temperature between 1200° and 1600° C over a time from 10 to 20 hours. 12. Process according to claim 11 wherein said metal compounds used as starting products are fluorides, hydroxides, oxides, carbonates, sulfates and nitrates of the correspondent metals. 13 - Process according to claim 12 wherein fluorides of alkali metals or alkaline-earth metals , f luosilicates , carbonates or double carbonates of alkali or alkaline-earth metals are used as catalysts . 14 . Process according to claim 13 wherein the catalys t is sodium fluoride. 15- Use of the compounds according to claims 1 and 2, as pigments. 16. Use according to claim 15 in the industry of varnishes, plastics and ceiaiuic. 17- Use according to claim 16 of the red pigment: 18. Use according to claim 16 of the yellow pigment: Al (2 _ χ _ y) • Y χ 0 3 : yV 2 0 5

Inventors: BALDI GIOVANNI, BITTOSSI MARCO, DEL CONTE VITTORIANO, BALDI, GIOVANNI, BITTOSSI, MARCO, DEL CONTE, VITTORIANO
Applicants: BALDI GIOVANNI, BITTOSSI MARCO, COLOROBBIA ITALIANA SPA, DEL CONTE VITTORIANO, BALDI, GIOVANNI, BITTOSSI, MARCO, COLOROBBIA ITALIA S.P.A., DEL CONTE, VITTORIANO
Application year: 1996
Main classification: C01F17
IPC codes: C01F17, C01G31, C01G37, C04B35, C08K3, C09C1