CROSS-REFERENCE TO RELATED APPLICATION

This Application is a 35 USC § 371 US National Stage filing of International Application No. PCT/EP2016/050842 filed on Jan. 15, 2016, and claims priority under the Paris Convention to European Patent Application No. 15151334.8 filed on Jan. 15, 2015.

FIELD OF THE DISCLOSURE

The present invention relates to composite materials comprising ceramics, in particular metal oxide or metalloid based, manufacturing methods therefore and uses thereof.

BACKGROUND OF THE DISCLOSURE

Industrially manufactured colored ceramics are in general aluminum oxides (alumina) or zirconium oxides filled and mixed with a pigment. A pigment is a coloring substance insoluble in the medium that it colors. In particular, pigments are used to color a material in bulk.

In some cases, oxides can also be colored directly by the creation of defects, such as heteroatoms, in the crystalline structure.

The manufacturing of colored ceramic components is well-managed for some colors such as black, white, blue and green, but not for all colors.

For example, despite all the effort applied, it has still never been possible to produce a bright red color ceramic. There are only shades of red/orange or red/brown ceramics.

In fact, the manufacturing method for colored ceramics consists of mixing powdered ceramic with the mineral pigment and then injecting all of it in a mold to get what is called a “green body” bound by a polymer. This green body is next unbound, for example by heating to 600° C., since the polymer binding then sublimates. The green body is finally sintered at a temperature close to the melting point of the ceramic, thus causing densification thereof and resulting in a solid piece.

The rate of pigment used varies according to the desired color but in general several percent by volume, typically of order 3 to 5%, are sufficient for coloring the ceramic. In fact, during the sintering phase, the pigment is in general going to diffuse into the ceramic which is white and which in that way is going to take on the color of the pigment.

However, when the pigment does not diffuse into the ceramic—the ceramic appears white—which reduces the power of the added pigment. The resulting colors are in general pale and lacking in aesthetic interest.

In particular there is no red color pigment which can maintain its color after the sintering step. The resulting colors draw instead on orange, bordeaux or even brown.

The present invention has in particular the goal of proposing a new composite material with which to significantly enlarge the range of possible colors in colored ceramic manufacturing.

The purpose of the present invention is also to propose a new composite material comprising a luminescent pigment.

SUMMARY OF THE DISCLOSURE

For this purpose, the invention relates to a method for manufacturing a composite material combining:a metal oxide or metalloid based matrix, where said matrix is suited for allowing light to pass (after sintering) and has densification temperatures which depend on the pressure to which said matrix is subject;a mineral pigment dispersed in the matrix, having a certain breakdown temperature beyond which said mineral pigment is broken down;
where the densification temperatures of the matrix are greater than the breakdown temperature of the mineral pigment in at least one pressure range below 80 MPa, in particular at atmospheric pressure;
the method comprising the following steps:

a) mixing the mineral pigment in powder form with the matrix in powder form; and

b) sintering of said mixture of powders at some sintering temperature and under a pressure greater than or equal to 80 MPa sufficient in order that the densification temperature of the matrix under said pressure is below the breakdown temperature of the mineral pigment, where the sintering temperature is greater than or equal to the densification temperature of the matrix and below the breakdown temperature of the mineral pigment.

The invention also relates to a method for manufacturing a composite material combining:a metal oxide or metalloid based matrix, where said matrix is suited for allowing light to pass (after sintering) and has densification temperatures which depend on the pressure to which said matrix is subject;a mineral pigment dispersed in the matrix, having a certain breakdown temperature beyond which said mineral pigment is broken down;
where the densification temperatures of the matrix are greater than the breakdown temperature of the mineral pigment in at least one pressure range below 100 MPa, in particular at atmospheric pressure;
the method comprising the following steps:

a) mixing the mineral pigment in powder form with the matrix in powder form; and

b) sintering of said mixture of powders at some sintering temperature and under a pressure greater than or equal to 100 MPa sufficient in order that the densification temperature of the matrix under said pressure is below the breakdown temperature of the mineral pigment, where the sintering temperature is greater than or equal to the densification temperature of the matrix and below the breakdown temperature of the mineral pigment.

Because of these arrangements, it is possible to obtain ceramic composite materials with a very large color palette, in particular including bright red color ceramics. In fact, since the matrix is suited for allowing light to pass, meaning that it is transparent or translucent, it serves to allow the color of the pigment to diffuse to the outside of the material even if the pigment particle is located deep inside the matrix. This has the effect of increasing the pigmentation surface of the material and therefore increasing the vividness of the color thereof.

In preferred embodiments of the method according to the invention, use can also advantageously be made of one and/or the other of the following dispositions:The mineral pigment has an average diameter included between 0.2 μm and 10 μm;The densification temperature of the matrix under said pressure applied during sintering is below 1300° C.;The sintering temperature (temperature applied during sintering) is below 1300° C., even below or equal to 1200° C.;The mineral pigment represents a fraction by volume of said composite material included between 2% and 50%;The mineral pigment is based on cobalt aluminate CoAl2O4;The mineral pigment is in discrete particle form, each comprising a core and a colored coating surrounding the core;The colored coating is an oxide comprising iron, chrome, aluminum, titanium, silicon, zinc, nickel, cobalt, cadmium, copper, vanadium, bismuth and/or manganese;The core of the mineral pigment is suited for allowing light to pass;The core of the mineral pigment is fabricated from a material chosen among mica, alumina, zirconium and titanium dioxide;The formula of the colored coating is KAl2(AlSi3O10)(OH)2;The ceramic matrix is based on magnesium aluminate spinel MgAl2O4;The ceramic matrix is based on zirconium stabilized with yttrium;The pressure applied during sintering is at least equal to 200 MPa;The color of the mineral pigment (and in particular the aforementioned colored coating) is bright red;The mineral pigment is luminescent;The mineral pigment comprises rare earth aluminates and/or rare earth silicates;The mineral pigment is based on strontium aluminate doped with europium;The pressure applied during sintering is at least equal to 600 MPa.

The object of the invention is also a composite material combining:A mineral pigment; andA metal oxide or metalloid based matrix, where said matrix is suited for allowing light to pass and has a densification temperature under pressure that is below a breakdown temperature of the mineral pigment.

In various embodiments of the composite material according to the invention, use can further be made advantageously of one and/or the other of the following dispositions:The mineral pigment represents a fraction by volume of said composite material included between 2% and 50%;The mineral pigment is based on cobalt aluminate CoAl2O4;The mineral pigment may be in discrete particle form, each comprising a core and a colored coating surrounding the core;The colored coating is an oxide comprising iron, chrome, aluminum, titanium, silicon, zinc, nickel, cobalt, cadmium, copper, vanadium, bismuth and/or manganese;The core of the mineral pigment is suited for allowing light to pass;The core of the mineral pigment is fabricated from a material chosen among mica, alumina, zirconium and titanium dioxide;The mineral pigment is luminescent;The mineral pigment comprises rare earth aluminates and/or rare earth silicates;The mineral pigment is based on strontium aluminate doped with europium;The mineral pigment has an average diameter included between 0.2 μm and 10 μm;The densification temperature of the matrix under pressure is below 1300° C.;The matrix is a ceramic, in the sense that it is made up of metal oxides;The matrix is based on magnesium aluminate spinel MgAl2O4.

Finally, a further purpose of the invention is a use of a composite material resulting from the aforementioned method in watch or jewelry making.

