CH719981A2 - Brightly colored ceramic article and its manufacturing process. - Google Patents

Abstract

The invention relates to a colored article (1) made from a ceramic comprising an oxide-based matrix and a component from the doped or co-doped aluminum garnet family. The present invention also relates to the method of manufacturing said article.

Description

Technical field of the invention

[0001] The present invention relates to a brightly colored ceramic article and in particular to a watch component covering or the movement made from a material based on oxides such as alumina. It also relates to the manufacturing process of said article.

Technology background

[0002] Colored ceramics are commonly produced industrially by mixing a matrix based on metal oxide, for example. Al2O3, ZrO2 and their composites, and a coloring pigment. In certain cases, the ceramic can be colored by doping with different atoms entering the crystal structure. The colors thus obtained are generally pale. For example, the yellow coloring of ceramics is often obtained by doping with praseodymium or by adding pigment based on tungsten oxide and/or vanadium oxide. The color obtained is generally pale yellow or turning orange.

[0003] An alternative was proposed in the watchmaking field in document WO 2018/172428 disclosing the manufacture of a brightly colored ceramic part by incorporating an encapsulated pigment into a metal oxide matrix adapted to allow light to pass through. . More precisely, the process envisages the use of unconventional sintering under pressure with the aim of densifying the material, a complex process to be implemented industrially.

Summary of the invention

The object of the present invention is to propose a new brightly colored ceramic composition making it possible to produce an article using an inexpensive process.

More specifically, the present invention relates to a colored article made from a ceramic comprising a matrix based on oxides and a component from the doped or co-doped aluminum garnet family.

[0006] In more detail, the component of the family of doped or co-doped aluminum garnets, such as yttrium aluminum garnet doped with cerium (YAG:Ce), gives the oxide-based ceramic a bright and shiny color. Such a coloring element not only represents an alternative to conventional coloring pigments but also makes it possible to obtain a more intense shade and significantly expand the range of possible colors. In addition, the development of a composite by adding an oxide-based matrix makes it possible to avoid the use of pure YAG with a significant reduction in costs and a significant improvement in toughness and machinability. .

[0007] When the component from the aluminum garnet family is doped with chromium or with an element from the lanthanide family such as, for example, cerium, neodymium, erbium, holmium and ytterbium, an intense and vivid color is obtained. In particular, when doped with cerium, a yellow color is obtained. This bright color is not achievable by mixing with commercial pigments or by doping with different atoms. When doped with neodymium, a violet coloring is obtained and when doped with chromium a coloring ranging from green to red depending on its oxidation state is obtained. When doped with erbium, a pink color is obtained. When doped with ytterbium, a green color is obtained. Co-doping with one or more additional elements chosen from chromium and an element from the lanthanide family, such as cerium, erbium, ytterbium, holmium and neodymium, makes it possible to modulate these colors and thus to expand the range of colors achievable. The use of a component from the doped or co-doped aluminum garnet family thus makes it possible to obtain bright, brilliant colors with re-emissive properties.

The article thus obtained with these different dopants has a bright color with a component L in the Lab colorimetric space greater than or equal to 80, preferably greater than or equal to 85, more preferably greater than or equal to 90.

It has a hardness greater than or equal to 1000 HV10, preferably greater than or equal to 1200 HV10, more preferably greater than or equal to 1550 HV10.

[0010] It has a toughness KlC of between 1.7 and 6 MPa √m, typically between 2 and 4.5 MPa √m.

[0011] The present invention also relates to the process for manufacturing said article comprising the following steps: – Production of a basic mixture, also called first mixture, with the oxides and the component of the doped aluminum garnet family or co-doped, and this possibly in a liquid medium, – Production of a second mixture comprising the first mixture and an organic binder system, – Granulation of said second mixture, – Formation of a blank having the shape of the article, – Sintering the blank in air at a holding temperature of between 1500 and 1800°C, preferably between 1600 and 1700°C, for a period of between 20 minutes and 20 hours, preferably between 1 hour and 5 hours.

The proposed process, by mixing powders and conventional sintering, is easily industrializable and has a lower economic impact compared to current processes considering manufacturing by SPS (Spark Plasma Sintering) or with a composition comprising pure YAG.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, with reference to the appended drawing.

Brief description of the figure

[0014] Figure 1 represents a timepiece comprising a middle made with the ceramic material according to the invention.

Detailed description of the invention

The present invention relates to an article made of a ceramic material based on oxides. The article may be a decorative article such as a constituent element of watches, jewelry, bracelets, etc. or more generally an external part of a portable element such as a shell of a mobile telephone. In the watchmaking field, this article can be a trim component such as a caseband, a back, a bezel, a pusher, a bracelet link, a dial, a hand, a dial index, etc. As an illustration, a middle part made with the ceramic material according to the invention is shown in Figure 1. It can also be a component of the movement such as a plate or an oscillating mass.

[0016] The ceramic material comprises the matrix based on oxides. Examples of oxides include ZrO2, Al2O3, TiO2, SiO2, MgAl2O4 and ZnO or a mixture of these oxides such as Al2O3+ ZrO2. In the presence of zirconia (ZrO2), the latter is generally stabilized with yttrium, cerium, calcium or magnesium. Preferably, the matrix is based on Al2O3. The ceramic material further comprises a phosphorescent coloring component from the doped or co-doped aluminum garnet family. The percentage by weight of the component from the doped or co-doped aluminum garnet family is between 5 and 85%, preferably between 5 and 70%, more preferably between 10 and 60%, relative to the total weight of the material. ceramic. Thus, the ceramic material comprises by weight between 15 and 95%, preferably between 30 and 95%, more preferably between 40 and 90%, of oxides and between 5 and 85%, preferably between 5 and 70%, more preferably between 10 and 60%, of the component of the doped or co-doped aluminum garnet family.

[0017] For aluminum garnets, it may be yttrium aluminum garnet (YAG) or luthenium aluminum garnet (LuAg). Preferably, it is yttrium aluminum garnet. These garnets are doped or co-doped respectively with one or more of the elements of the lanthanide family: cerium, neodymium, holmium, erbium and ytterbium, or with chromium. Preferably, the garnet is doped with cerium. More preferably, it is a yttrium aluminum garnet doped with cerium. Even more preferably, the article comprises a matrix based on alumina (Al2O3) and yttrium aluminum garnet doped with cerium (YAG:Ce). This ceramic may also contain possible impurities with a content less than or equal to 0.2% by weight, or even 0.1% by weight.

Advantageously, the ceramic is made up of the matrix based on oxides, the doped or co-doped component of the garnet family and any impurities. Preferably, the ceramic consists of the alumina-based matrix (Al2O3), the yttrium aluminum garnet doped with cerium (YAG:Ce) and any impurities.

[0019] According to the invention, the component of the garnet family is doped with one of the aforementioned elements and possibly co-doped with one or more other of the aforementioned elements with a total atomic percentage for the dopant and the possible co- dopants relative to this component between 0.1 and 50%. Doping is with cerium when a yellow color is desired. Preferably, for doping with cerium, the atomic percentage relative to the component of the garnet family is between 0.5 and 10%, more preferably between 1 and 5%. Doping is with chromium when a color ranging from green to red depending on the degree of oxidation of the chromium is desired. For doping with chromium, the atomic percentage relative to the component of the garnet family is between 0.1 and 50%. The doping is neodymium when a violet coloring is desired. Preferably, the atomic percentage relative to the component is between 0.9 and 11%. Doping is with erbium when a pink coloring is desired with an atomic percentage relative to the component between 0.1 and 50%. Doping is with ytterbium when a green coloring is desired with an atomic percentage relative to the component between 0.1 and 50%. Adding a co-dopant allows the color to change. It could for example be a component from the garnet family doped with cerium and co-doped with neodymium.

[0020] The article with one or more dopants has a bright color having a component L in the Lab colorimetric space greater than or equal to 80, preferably greater than or equal to 85, more preferably greater than or equal to 90. It has a hardness greater than or equal to 1000 HV10, preferably greater than or equal to 1200 HV10, more preferably greater than or equal to 1550 HV10. For an aluminum oxide matrix with cerium-doped yttrium aluminum garnet, it has a hardness greater than or equal to 1400 HV10, preferably greater than or equal to 1550 HV10. For a matrix of zirconium oxides with yttrium aluminum garnet doped with cerium, it has a hardness greater than or equal to 1250 HV10, preferably greater than or equal to 1400 HV10. Similarly, for a matrix of aluminum oxides and zirconia with cerium-doped yttrium aluminum garnet, it has a hardness greater than or equal to 1250 HV10, preferably 1400 HV10. The article has a toughness KlC of between 1.7 and 6 MPa Vm, preferably between 2 and 4.5 MPa Vm. For an aluminum oxide matrix with cerium-doped yttrium aluminum garnet, it has a KlC toughness greater than or equal to 2 MPa Vm. For a matrix of aluminum oxides and zirconia with cerium-doped yttrium aluminum garnet, it has a KlC toughness greater than or equal to 2.5 MPa Vm. For a matrix of zirconium oxides with cerium-doped yttrium aluminum garnet, it also has a KlC toughness greater than or equal to 2.5 MPa √m. The article has a density greater than or equal to 95%, preferably greater than or equal to 97%, more preferably greater than or equal to 98%.

[0021] The ceramic article with the alumina matrix and the yttrium aluminum garnet doped with cerium has a yellow color with in the CIELAB colorimetric space (compliant with CIE standards n°15, ISO 7724/1, DIN 5033 Teil 7, ASTM E-1164) an L* component greater than or equal to 85, preferably greater than or equal to 90, an a* component between -5 and 15, preferably between -5 and 12 and a b* component between 65 and 110, preferably between 70 and 97.

[0022] The ceramic article with the alumina and zirconia matrix and the yttrium aluminum garnet doped with cerium also has a yellow color with in the CIELAB colorimetric space (compliant with CIE standards no. 15, ISO 7724 /1, DIN 5033 Teil 7, ASTM E-1164) an L* component greater than or equal to 85, preferably greater than or equal to 90, an a* component between -5 and 5, preferably between -5 and 2 and a component b* between 45 and 80, preferably between 50 and 70.

[0023] The article is manufactured by sintering with the process consisting of: – Making the basic mixture, also called the first mixture, with the various compounds mentioned above and possibly in a liquid medium, – Making a second mixture comprising the first mixture and an organic binder system (paraffin, polyethylene, polyvinyl acetate, etc.), – Granulate and, where appropriate, dry said second mixture, for example, in an atomizer. Preferably, the aggregates have a size d50 of between 10 and 100 µm, and, preferably, between 40 and 60 µm, – Form a blank by giving this second granulated mixture the shape of the desired article, for example, by injection or pressing. Preferably, shaping is carried out by uniaxial pressing and/or cold isostatic pressing (CIP), – Sinter the blank in air at a holding temperature of between 1500 and 1800°C, preferably between 1600 and 1700° C, for a period of between 20 minutes and 20 hours, preferably between 1 hour and 5 hours. This step makes it possible to achieve a densification greater than 97% compared to the theoretical density. This step can be preceded by a thermal debinding step in a temperature range between 200 and 1200°C. It could also be a solvent debinding in the case of shaping by injection, – Optionally, press the blank with hot isostatic pressing (HIP) at a temperature which is from 50°C to 150 °C lower than the sintering temperature in order to improve the final density of the blank.

The blank thus obtained is cooled. It can then be machined, polished and decorated if necessary to obtain the desired item. The color being present in the mass of the blank, these finishing operations do not alter the final color of the article.

[0025] Tests were carried out for ceramics comprising alumina and yttrium aluminum garnet doped with cerium with percentages for yttrium aluminum garnet doped with cerium (YAG:3Ce) of between 10 and 60% in weight. Tests were also carried out for ceramics comprising a yttrium-stabilized alumina-zirconia matrix and cerium-doped yttrium aluminum garnet with a percentage for cerium-doped yttrium aluminum garnet (YAG:3Ce ) of 50% by weight. Tests were also carried out for ceramics comprising a zirconia matrix and yttrium aluminum garnet doped with cerium with a percentage of 20% by weight for the latter. In all these tests, the doping is 3 atomic% compared to the garnet and the zirconia is stabilized. The results are given in table 1 below. Hardness measurements are HV10 hardnesses. The toughness was determined based on measurements of the lengths of the cracks at the four ends of the diagonals of the hardness imprint according to the formula: with P which is the applied load (N), a which is the half-diagonal (m) and / which is the length of the measured crack (m).

[0026] The Lab colorimetric values were measured on the polished samples with a CM-3610A spectrophotometer under the following conditions: SCI measurements (specular reflection included) and SCE (specular reflection excluded), inclination of 8°, MAV measurement zone of 4mm in diameter.

The samples were sintered in air at a temperature of between 1600°C and 1700°C with a stage of between 2 and 4 hours. All samples obtained have a yellow color. Colorimetry measurements show a very high brightness with L* values greater than 90 compared to L* values of around 80 in the case of zirconia colored by the addition of praseodymium oxide. Also, colorimetry measurements show a very high yellow tint with b* values greater than 75 for an alumina matrix, compared to b* values of around 30 in the case of zirconia colored by the addition of oxide. of praseodymium. This yellow component intensifies with the increase in the content of yttrium aluminum garnet doped with cerium. On the other hand, toughness and hardness decrease with this increase in content. Depending on the content of yttrium aluminum garnet doped with cerium, it is thus possible to modulate the properties and color according to the needs of the application.

[0028] For matrices comprising zirconia, the yellow is a little less intense with values of b* of the order of 50 but nevertheless always greater than the values of 30 in the case of zirconia colored by addition of oxide of praseodymium. In terms of hardness, values above 1250 HV10 are obtained. For toughness, values greater than 2.5 MPa √m are obtained. 10 90 / 94.8 -3.5 76.7 1698 3.4 98.8 20 80 / 93.8 3.2 86.1 1680 4 99 40 60 / 95.3 6.9 92.5 1612 2.7 97.2 60 40 / 94.3 10.3 93.6 1600 2.3 99.5 20 / 80 ** ** ** 1460 ** 98 50 40 10 91 -1.2 56.95 >1250 2.95 ** **not measured

Table 1

[0029]

Claims (18)

1. Colored article made from a ceramic comprising an oxide-based matrix and a component from the doped or co-doped aluminum garnet family. 2. Article according to claim 1, characterized in that the ceramic comprises the matrix based on oxides with a weight content of between 15 and 95% and the component from the aluminum garnet family doped or co-doped with a content by weight of between 5 and 85%. 3. Article according to one of the preceding claims, characterized in that the ceramic comprises the matrix based on oxides with a weight content of between 30 and 95%, preferably between 40 and 90%, and the component of the family of doped or co-doped aluminum garnets with a weight content of between 5 and 70%, preferably between 10 and 60%. 4. Article according to one of the preceding claims, characterized in that the component of the aluminum garnet family is doped or co-doped with one or more elements with a total atomic percentage for all of the element(s) included between 0.1 and 50% compared to the component of the aluminum garnet family. 5. Article according to one of the preceding claims, characterized in that the family of doped or co-doped aluminum garnets includes luthenium aluminum garnet and yttrium aluminum garnet and in that the doping element or co-dopant is chosen from chromium or an element from the lanthanide family. 6. Article according to the preceding claim, characterized in that the element of the lanthanide family is chosen from cerium, neodymium, erbium, holmium and ytterbium. 7. Article according to the preceding claim, characterized in that for doping with cerium, the atomic percentage relative to the component of the aluminum garnet family is between 0.5 and 10%, preferably between 1 and 5%. 8. Article according to claim 6, characterized in that for doping with neodymium, the atomic percentage relative to the component of the aluminum garnet family is between 0.9 and 11%. 9. Article according to one of the preceding claims, characterized in that the ceramic comprises a matrix based on aluminum oxides, zirconium oxides or stabilized zirconium oxides or a mixture of these oxides. 10. Article according to claim 6, characterized in that the ceramic comprises a matrix based on aluminum oxides and a yttrium aluminum garnet doped with cerium with possibly a co-doping element. 11. Article according to one of the preceding claims, characterized in that the ceramic consists of the matrix based on oxides and a component from the family of doped or co-doped aluminum garnets and possible impurities . 12. Article according to one of the preceding claims, characterized in that the ceramic has in the CIELAB colorimetric space a component L* greater than or equal to 80, preferably greater than or equal to 85, more preferably greater than or equal to 90. 13. Article according to claim 10, characterized in that the ceramic has in the CIELAB colorimetric space a component a* between -5 and 15, preferably between -5 and 12 and a component b* between 65 and 110, preferably between 70 and 97. 14. Article according to one of the preceding claims, characterized in that the ceramic has a hardness greater than or equal to 1000 HV10, preferably greater than or equal to 1200 HV10, more preferably greater than or equal to 1550 HV10. 15. Article according to one of the preceding claims, characterized in that the ceramic has a toughness KlC between 1.7 and 6 MPa √m, preferably between 2 and 4.5 MPa √m. 16. Article according to one of the preceding claims, characterized in that it is a covering component or a watch movement, or a jewelry component. 17. Method for manufacturing an article according to one of the preceding claims, comprising the following steps: – Production of a basic mixture, also called a first mixture, with the oxides and the component of the doped or co-doped aluminum garnet family, according to one of claims 1 to 11, and this possibly in a liquid medium , – Production of a second mixture comprising the first mixture and an organic binder system, – Granulation of said second mixture, – Formation of a draft having the shape of the article, – Sintering of the blank in air at a holding temperature of between 1500 and 1800°C, preferably between 1600 and 1700°C, for a period of between 20 minutes and 20 hours, preferably between 1 hour and 5 hours. 18. Manufacturing method according to the preceding claim, characterized in that it comprises, after the sintering step, a hot isostatic pressing (HIP) step at a temperature which is 50°C to 150°C lower than the temperature sintering.