Process for the production of a zirconia-based, coloured, in particular grey, article and a zirconia-based coloured decorative article obtained using this process

Abstract

A process for the production of a grey zirconia-based article wherein a first mixture includes a zirconia powder forming the base constituent, 4% to 15% by weight of at least one stabilizer selected from among the group of oxides including yttrium oxide, magnesium oxide and calcium oxide alone or in combination, 0.1% to 1% by weight of a vanadium oxide powder (V.sub.2O.sub.5), 0.1% to 1% by weight of a chromium oxide powder (Cr.sub.2O.sub.3) and 0.1% to 1% by weight of a silicon oxide powder (SiO.sub.2); making a second mixture including the first mixture and a binder; making a granulated mixture by conducting a granulation of the second mixture; forming a blank by giving this second granulated mixture the shape of the desired article; sintering the blank in air for at least thirty minutes at a temperature in the range of between 1250 and 1550 C.

Claims

1. A process for producing a zirconia-based article, the method comprising: a) making a first mixture comprising: a zirconia powder as a base constituent, 4% to 15% by weight of at least one stabiliser selected from the group consisting of yttrium oxide, magnesium oxide, and calcium oxide, 0.1% to 1% by weight of a vanadium oxide powder (V.sub.2O.sub.5), 0.1% to 1% by weight of a chromium oxide powder (Cr.sub.2O.sub.3), and 0.1% to 1% by weight of a silicon oxide powder (SiO.sub.2); b) making a second mixture comprising said first mixture and a binder; c) making a granulated mixture by conducting a granulation of said second mixture; d) forming a blank by giving the granulated mixture a desired shape of the article; and e) sintering said blank in air for at least thirty minutes at a temperature ranging from 1250 to 1550 C. to obtain a grey zirconia-based article.

2. The process according to claim 1, wherein the first mixture comprises: 0.4% to 0.7% by weight of the vanadium oxide powder (V.sub.2O.sub.5), 0.2% to 0.3% by weight of the chromium oxide powder (Cr.sub.2O.sub.3), and 0.2% to 0.3% by weight of the silicon oxide powder (SiO.sub.2).

3. The process according to claim 1, wherein the first mixture further comprises: 0.1% to 1% by weight of a manganese oxide powder (MnO.sub.2).

4. The process according to claim 1, wherein the first mixture further comprises: 0.1% to 5% by weight of an aluminium oxide powder (Al.sub.2O.sub.3).

5. The process according to claim 1, wherein the first mixture further comprises: 0.1% to 1% by weight of an iron oxide powder (Fe.sub.2O.sub.3).

6. The process according to claim 1, wherein the stabiliser is yttrium oxide.

7. The process according to claim 1, further comprising: polishing the article after said sintering e) to obtain a polished grey zirconia-based article.

8. The process according to claim 1, wherein the binder is a polyvinyl alcohol.

9. The process according to claim 1, wherein said making c) is performed by subjecting the second mixture to a screening to obtain particles that have a grain size of less than 200 m.

10. The process according to claim 1, wherein the obtained zirconia-based article is in a solid grey color.

11. The process according to claim 1, wherein the first mixture further comprises: 0.2% to 0.3% by weight of a manganese oxide powder (MnO.sub.2).

Description

(1) Other features and advantages of the invention shall become evident in light of the following description explaining non-restrictive practical examples of the invention given solely for illustration purposes.

(2) A first example of the production process of the invention that will now be described in detail enables the formation of a grey sintered zirconia-based article, the appearance and mechanical properties of which are particularly well suited to the formation of component parts of wristwatches or to the formation of any other decorative and/or functional article.

(3) The grey zirconia article obtained in accordance with this first example comprises 98.8% by weight of stabilised zirconia and the remainder in weight of 0.5% by weight of a vanadium oxide powder (V.sub.2O.sub.5), 0.2% by weight of a silicon oxide powder (SiO.sub.2) and 0.5% by weight of a chromium oxide powder (Cr.sub.2O.sub.3).

(4) The zirconia is stabilised in the tetragonal phase in the classic manner by at least one stabiliser selected from among the group of oxides comprising yttrium oxide, magnesium oxide and calcium oxide alone or in combination, this stabiliser amounting in quantity to 5% by weight in relation to the zirconia.

(5) To form this article the procedure using this practical example of the process of the invention is as follows:

(6) 2470 grams of zirconia powder stabilised with 5% by weight of yttrium oxide are weighed. The powder used has an average grain size in the micrometer or submicrometer range of typically 0.5 micrometers. Such a powder is sold under the reference TZ-3Y by the Tosoh Corporation, Japan.

(7) 30 grams of a mixture of silicon oxide, vanadium oxide and chromium oxide powder are then weighed.

(8) The silicon powder used has a grain size of 2 microns APS and is sold under the reference No. 13024 by Alfa Aesar, Germany. The vanadium oxide powder used has an average grain size on the micrometer or submicrometer scale of typically 22 mesh and is sold under the reference No. 10904 by Alfa Aesar, Germany.

(9) The chromium oxide powder used has an average grain size on the micrometer or submicrometer scale of typically 2.4 micrometers and is sold under the reference No. 374725 by Sigma Aldrich Chemie, Switzerland. If necessary, the powder is ground to obtain the desired grain size.

(10) It will be noted that all these powders must preferably have a purity of above 95%.

(11) Once weighing of the powders has been concluded, all these powders are mixed and blended in a wet medium. About 50 grams of a binder, e.g. a polyvinyl alcohol, are added in the final blending phase.

(12) The mixture is then dried, e.g. in a classic atomiser.

(13) The granulate obtained is screened to retain particles that have a grain size of less than 200 micrometers.

(14) The screened granulate is then pressed into a mould that has the configuration of the desired article in order to form a blank of the latter.

(15) In its almost final general form the article is placed in a sintering furnace. It will be noted in this regard that the sintering can be conducted in air. The article is then heated in a first phase at a rate of 30 degrees per hour to about 1000 C., then in a second phase at a rate of 50 degrees per hour to a temperature of 1450 C. The article is kept at this temperature for at least thirty minutes and preferably for one hour.

(16) It will be noted that the sintering can, of course, be conducted at any other temperature higher than or equal to 1100 and lower than 1600 C.

(17) The colour of the article obtained after the sintering operation is a pure grey.

(18) The article is then cooled, then machined to obtain a shape suitable for its final use. It will be noted that the colouration achieved is a solid colouration such that a machining operation on the article does not impair its colour in any way.

(19) The article is then polished, e.g. using a diamond paste, and the article thus obtained has a light grey glossy appearance, so that it exhibits attractive and interesting aesthetic characteristics, in particular for applications in the watchmaking domain.

(20) According to another embodiment of the process of the invention the mode of operation described above was followed to make circular watch bezels 45 mm in diameter and 4 mm thick. In this example a combination of V.sub.2O.sub.5 (0.63%), Cr.sub.2O.sub.3 (0.25%), SiO.sub.2 (0.25%), MnO.sub.2 (0.25%) and Al.sub.2O.sub.3 (0.25%) was used to form a compound, of which the proportion by weight of the total composition is 1.63%, and the balance is 98.37% by weight of stabilised ZrO.sub.2. Once configured in their desired final form, the bezels and watch cases were sintered in air for 2 hours at 1450 C. The bezels and watch cases were cooled and then mirror polished. The bezels and watch cases obtained had a dark grey glossy appearance. The colouration was also found to be solid after breakage of a case.

(21) According to a still further embodiment of the process of the invention the mode of operation described above was followed to make circular watch bezels 45 mm in diameter and 4 mm thick. In this example a combination of V.sub.2O.sub.5 (0.75%), Cr.sub.2O.sub.3 (0.5%), SiO.sub.2 (0.30%), MnO.sub.2 (0.10%), Al.sub.2O.sub.3 (0.25%) and Fe.sub.2O.sub.3 (0.25%) was used to form a compound, of which the proportion by weight of the total composition is 2.15%, and the balance is 97.85% by weight of stabilised ZrO.sub.2. Once configured in their desired final form, the bezels were sintered in air for 2 hours at 1450 C. The bezels were cooled and then mirror polished. The bezels obtained had a slightly brownish grey glossy appearance. The colouration was also found to be solid after breakage of a bezel.

(22) The following table shows other examples of articles made in accordance with the invention with the colours obtained according to their composition.

(23) TABLE-US-00001 % EXAMPLES constituents 1 2 3 4 5 6 7 8 9 10 11 stabilised 95.10 95.60 96.30 97.10 97.85 97.95 97.95 98.13 98.38 98.55 98.8 ZrO.sub.2 V.sub.2O.sub.5 1.00 1.00 0.50 1.00 1.00 0.75 0.75 0.63 0.63 0.50 0.50 Cr.sub.2O.sub.3 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.25 0.25 0.25 0.50 SiO.sub.2 0.40 0.40 0.20 0.40 0.40 0.30 0.30 0.25 0.25 0.20 0.20 MnO.sub.2 0.50 0.50 0.25 0.25 Al.sub.2O.sub.3 2.50 2.50 2.50 1.00 0.25 0.25 0.25 0.25 0.25 Fe.sub.2O.sub.3 0.25 0.25 0.25 Colour Pinkish Grey Battleship Pure Dark Pure Dark Light Pure Light Grey grey bordering grey grey grey grey grey grey dark grey bordering on green grey on green