Process for the production of coloured articles, in particular orange articles, made of zirconia; and coloured ornamental articles made of zirconia obtained according to the process

Abstract

The present invention relates to a process for manufacturing orange zirconia based articles, characterized in that it comprises a series of steps, in that: a first mixture comprising the following components: zirconia powder, 3-20% by weight of at least one stabilizer selected from the group of oxides comprising yttria, magnesia and calcia, alone or in combination, 0.1% to 5% by weight of at least one element intended to form a glass phase and selected from the group comprising silica, alumina, lithium oxide and yttria, alone or in combination, 1% to 6% by weight of ceria powder; a second mixture comprising the first mixture and a binder is produced; a granulated mixture is produced by granulating the second mixture; a green body is formed by imparting the shape of the desired article to the second granulated mixture; air sintering at a temperature of 1,250-1,500°C for at least 30 minutes and annealing the desired article in a reducing atmosphere at a temperature of 700°C to 1,350°C for 30 minutes to 20 hours, and polishing the sintered green body.

Description

[0001] This invention relates to the manufacture of colored zirconia-based articles, particularly articles exhibiting colors ranging from bright orange to copper brown achieved by sintering. For convenience, such articles are referred to as "orange articles" in the following description.

[0002] The present invention also relates to decorative zirconia-based orange articles obtained specifically according to the method described below.

[0003] It is known to incorporate colorants or pigments such as cadmium sulfide (CdSe), cadmium selenide, and cadmium sulfide selenide into ceramic materials to obtain, for example, orange / red ceramic products used to produce enamels, glazes, and containers for household or floor use.

[0004] The use of such colorants has many drawbacks when they need to be incorporated into industrial ceramics, especially sintered zirconia-based ceramics.

[0005] In reality, these colorants are unstable at high temperatures and exhibit their coloring properties at 1,000 or 2,000°C. This greatly limits the use of such colorants, and in particular, they are not permitted for the production of sintered zirconia products, since the sintering temperature of zirconia is above 1,100°C in any case.

[0006] Furthermore, the use of such colorants containing heavy metals in objects intended to come into contact with the user's skin, such as watch cases, is at least strongly discouraged if not prohibited by law.

[0007] In addition, commercially available colorants of this type have large particle sizes, which is incompatible with obtaining a homogeneous mixture with zirconium oxide powder.

[0008] Therefore, the main objective of this invention is, on the one hand, to provide a method for manufacturing bright orange sintered zirconia-based articles, and on the other hand, to provide such articles obtained according to the method, which have satisfactory mechanical properties and exhibit a bright orange color at a depth of at least 5 mm from the surface.

[0009] Therefore, the present invention relates to a method for manufacturing bright orange zirconia-based articles, characterized by comprising a series of steps, wherein:

[0010] A first mixture comprising the following components is produced:

[0011] ●Zirconium oxide powder,

[0012] ● 3-20% by weight of at least one stabilizer, said stabilizer being selected, alone or in combination, from the group consisting of oxides including yttrium oxide, magnesium oxide, and calcium oxide.

[0013] ● 0.1% to 5% by weight of at least one element intended to produce a glassy phase and selected alone or in combination from the group consisting of silicon dioxide, aluminum oxide, lithium oxide and yttrium oxide.

[0014] ●1% to 6% by weight of cerium oxide powder;

[0015] A second mixture comprising the first mixture and the adhesive is produced.

[0016] A granular mixture is produced by granulating the second mixture;

[0017] A green body is formed by giving the desired shape to the second granular mixture;

[0018] Air sintering at 1,250-1,500°C for at least 30 minutes, and

[0019] The desired product is placed in an area with 10 -6 Up to 10 -1 Annealing at a reducing atmosphere with an oxygen partial pressure of atmospheric pressure for 30 minutes to 20 hours at a temperature of 700°C to 1,350°C, and

[0020] Polish the sintered green blank.

[0021] The method of this invention allows for a reduction in sintering temperature by incorporating cerium oxide powder (CeO2) into the mixture to be sintered. Cerium oxide also acts as one of the determining elements for imparting the desired orange color to the product.

[0022] In practice, after sintering in the presence of CeO2, the product is ivory white. Then, in a subsequent step of the method of the present invention, during the so-called annealing step, it is reduced to Ce2O3 (+3 oxidation state) using the presence of CeO2 (+4 oxidation state). After this annealing step, the product has a color ranging from yellowish-orange to bright orange, depending on the amount of cerium in both the +4 and +3 oxidation states present at the particle boundaries. The color of cerium oxide in the +4 oxidation state (CeO2) is ivory white, and the color of cerium oxide in the +3 oxidation state (Ce2O3) is bright orange.

[0023] The amounts of cerium oxide in the +4 and +3 oxidation states present at the particle boundaries are determined by the annealing conditions, and more specifically by changing the oxygen partial pressure in the oven environment in which the annealing is performed.

[0024] According to one embodiment, the first mixture comprises 0.1-1% by weight of oxide powder for the glass phase, preferably 4-5% by weight of cerium oxide powder (Ce). +4 O2).

[0025] The present invention also relates to a decorative bright orange zirconia-based article obtained according to the above method, characterized in that it is formed from a sintered part made from a molded part, the molded part substantially comprising a zirconia matrix, 3-20 wt% of at least one stabilizer selected from the group consisting of oxides including yttrium oxide, magnesium oxide and calcium oxide alone or in combination, 0.1 wt% to 5 wt% of a glass phase comprising at least one element selected from the group consisting of silicon dioxide, aluminum oxide, lithium oxide and yttrium oxide alone or in combination, and 1 wt% to 6 wt% of cerium oxide.

[0026] The advantage of the product is that it exhibits a strong gloss after polishing, making it particularly suitable for manufacturing decorative products such as watch case components, jewelry, bracelets, brooches, tie pins, necklaces, handbags, telephones, furniture, or household appliances.

[0027] Other features and advantages of the invention will become apparent from the following description of an example of the implementation of the method of the invention.

[0028] The manufacturing method of the present invention, which is now described in detail, is a method for producing bright orange sintered zirconia-based articles, the appearance and mechanical properties of which are particularly suitable for the manufacture of watch components or any other decorative articles.

[0029] The bright orange zirconia article obtained according to the method comprises 89% to 98.9% by weight of stabilized zirconia and the remainder by weight, namely 0.1% to 5% by weight of a glass phase formed alone or in combination of silica, alumina, yttrium oxide and lithium oxide, and 1% to 6% by weight of cerium oxide.

[0030] Zirconia is typically stabilized to a tetragonal phase by at least one stabilizer selected from the group consisting of yttrium oxide, magnesium oxide, and calcium oxide, either alone or in combination, in an amount of 3% to 20% by weight relative to the zirconium oxide.

[0031] To prepare the article, an example of the method according to the present invention is carried out, one method being as follows:

[0032] 943g of stabilized zirconium powder containing 3% yttrium oxide was used. The powder used had an average particle size in the micrometer range, typically 0.1-0.5 μm. This powder was sold under the reference name TZ-3 Y by the Tosoh Corporation, Japan.

[0033] Then weigh a mixture of 7g of silicon dioxide, aluminum oxide and lithium oxide powders, which is expected to form a glassy phase during the subsequent sintering.

[0034] Preferably, the glass phase comprises, by weight, 47%, 40%, and 13% of a mixture or combination of silica, alumina, and lithium oxide, respectively.

[0035] The silicon powder used has an average particle size of less than 1 μm, typically 40 nm, and is sold by Cerdec, Germany, under the name Aerosil OX50.

[0036] The aluminum powder used has a micron or submicron scale, typically with an average particle size of 0.5 μm, and is sold by Baikowski, France, under the name CR30.

[0037] The lithium powder used has a micron or submicron scale, typically with an average particle size of 2.4 μm, and is sold by Sigma-Aldrich Chemicals, Switzerland, under reference number 374725. The powder may be ground to achieve the desired particle size if necessary.

[0038] Finally, weigh 50g of cerium oxide (Ce) 4+ O); The powder used has a particle size of micron or submicron, typically 0.5 μm, and is sold by Sigma-Aldrich Chemicals, Switzerland, under reference number 202975.

[0039] It should be noted that these powders should preferably have a purity of more than 95%.

[0040] When weighing the powder, all of the powder is mixed and homogenized in a wet medium. In the final stage of homogenization, approximately 50g of a binder, such as polyvinyl alcohol, is added.

[0041] The mixture is then dried, for example, in a conventional atomizer.

[0042] The resulting particles are then sieved to maintain particles with a size of less than 200 μm.

[0043] The sieved particles are then pressed into a mold with the desired shape of the product to form its green body.

[0044] The article, to which it is now almost its final, typical shape, is placed in a sintering furnace. In this respect, it should be noted that sintering can be carried out in air. The article is then heated to approximately 1,000°C in a first stage at a rate of 30°C / hour, and then to 1,250°C in a second stage at a rate of 50°C / hour. The article is held at this temperature for at least 30 minutes, preferably 1 hour.

[0045] It should be noted that sintering can of course be carried out at any other temperature above or equal to 1,100°C and below 1,600°C.

[0046] During sintering, silica, alumina, yttrium oxide, and lithium oxide combine with cerium oxide in the +4 oxidation state at the particle boundaries to form a concentrated glassy phase, which imparts an ivory color to the finished product after sintering.

[0047] It should be noted that the presence of lithium oxide advantageously lowers the sintering temperature and limits the color change of cerium oxide, thereby allowing for a bright orange color.

[0048] After the sintering step, the product is placed in an annealing furnace with a selectable atmosphere. The desired product is annealed in a hydrogen atmosphere (H2), or in an atmosphere containing a mixture of nitrogen and hydrogen (N2 / H2) or a mixture of argon and hydrogen.

[0049] During this annealing operation, the oxygen partial pressure in the furnace is 10. -6 Up to 10 -1 Atmospheric pressure, annealing temperature is 700℃ to 1250℃, and annealing time is usually 30 minutes to 20 hours.

[0050] According to a preferred embodiment of the method of the present invention, the atmosphere in the annealing furnace is hydrogen, and the oxygen partial pressure is 10. -4 Up to 10 -1 Atmospheric pressure, annealing temperature 900-1,150℃, and annealing time 4-6 hours. It should be understood that the color depth inside the product changes proportionally with the annealing time.

[0051] Depending on the annealing conditions, the color of the product obtained after annealing is bright orange or a shade between orange and copper brown.

[0052] The article is then cooled and machined to obtain a shape suitable for its end use. It should be noted that the color is applied deep inside the article so that the machined article never changes its color.

[0053] Finally, the product is polished, for example, using diamond polishing paste, so that the resulting product has a glossy appearance in a bright orange or shades between the above colors, depending on the annealing conditions, giving it an attractive and meaningful aesthetic feature, especially for applications in the watchmaking industry.

[0054] In another example of the method according to the invention, the above-described operation was performed to produce a circular watch bezel with a diameter of 45 mm and a thickness of 4 mm. This example uses a combination of SiO2 (47%), Al2O3 (40%), and Li2O (13%) to form a compound with a total composition weight percentage of 0.7%, the mixture forming a glassy phase, 6 wt% CeO2, and the remainder, i.e., 93.3 wt% stabilized ZrO2. When constructed to its desired final shape, the bezel was sintered in air at 1,450 °C for 2 hours. These bezels were then annealed at 1,000 °C for 12 hours in an atmosphere containing 5% hydrogen and 95% argon. The bezel was then cooled and mirror-polished. The resulting bezel has a bright orange luster appearance. After breaking the bezel, coloring was also observed to be achieved deep within the article.

Claims

1. A method for manufacturing bright orange zirconia-based products, characterized in that... It includes a series of steps, namely: A first mixture comprising the following components is produced: ● Zirconia powder, ● 3-20% by weight of at least one stabilizer, said stabilizer being selected from the group consisting of oxides comprising yttrium oxide, magnesium oxide, and calcium oxide, alone or in combination. ● 0.1% to 5% by weight of at least one element intended to produce a glassy phase and selected from the group consisting of silica, alumina, lithium oxide and yttrium oxide, alone or in combination. ● 1% to 6% by weight of cerium oxide powder; A second mixture comprising the first mixture and the adhesive is produced; A granular mixture is produced by granulating the second mixture; A green body is formed by giving the desired shape to the second granular mixture; Air sintering at 1,250–1,500°C for at least 30 minutes, and The article is annealed in a reducing atmosphere at a temperature of 700°C to 1,350°C for 30 minutes to 20 hours, and Polish the product.

2. The method of claim 1, wherein the first mixture comprises 0.1% to 1% by weight of a powder intended to form a glass phase.

3. The method of claim 1 or 2, wherein the powder intended to form the glass phase comprises, in decreasing amounts by weight, silicon dioxide, aluminum oxide, lithium oxide and yttrium oxide.

4. The method of claim 1 or 2, wherein the powder intended to form the glass phase comprises 47% silica, 40% alumina and 13% lithium oxide by weight.

5. The method according to claim 1 or 2, characterized in that... The first mixture contains 4-5% by weight of cerium oxide powder.

6. The method according to claim 1 or 2, characterized in that... The stabilizer is yttrium oxide.

7. The method according to claim 1 or 2, characterized in that... The annealing temperature is 700-1,350°C and the reducing atmosphere has a 10 -6 Up to 10 -1 The partial pressure of oxygen at atmospheric pressure.

8. The decorative bright orange zirconia-based article obtained by the method according to claim 1, characterized in that... The article is formed from a sintered component, which is made from a molded component, the molded component comprising: Zirconia matrix, At least one stabilizer, comprising 3-20% by weight, wherein the stabilizer is selected from the group consisting of oxides including yttrium oxide, magnesium oxide, and calcium oxide, and mixtures thereof. 0.1% to 5% by weight of a glass phase, said glass phase comprising at least one of silica, alumina, lithium oxide, and yttrium oxide, and 1% to 6% by weight of cerium oxide.