FR3048693A1 - CERAMICS AND / OR VITROCERAMICS BASED ON TELLUR DIOXIDE, USES AND PROCESS FOR PREPARING THE SAME - Google Patents

Abstract

The present invention relates to a glass-ceramic material and / or ceramic optically translucent and / or transparent in the visible and infrared, characterized in that it comprises a composition of formula (I) below: (A2O3) x (B2O5 y (TeO2) 100-xy (I) where A represents an element selected from Bi and / or Sb, and B represents an element selected from Nb and / or Ta, and x and y independently represent a number from 9 to 13; and in that it is selected from ceramics and glass-ceramics. The present invention also relates to the use of this material for the manufacture of optical materials, as well as products containing it. The present invention furthermore relates to a process for preparing a material as defined in any one of the preceding claims, characterized in that it comprises the following steps: i) preparation of a transparent glass comprising a composition of formula (I), and ii) crystallization of said glass to obtain said material. The present invention finally relates to the use of a glass comprising at least 60% by weight of a composition of formula (I) relative to the total mass of the glass, for the preparation of a ceramic or a glass ceramic optically translucent and / or transparent in the visible and infrared.

Description

CERAMICS AND / OR VITRO CERAMICS BASED ON DIOXIDE DE

TELLURE, USES AND METHOD OF PREPARATION

Technical area

The present invention relates to an optically translucent material and / or transparent in the visible and infrared, and a method for obtaining it and its use. The invention finds applications particularly in the field of optics, active or passive.

In the description below, references in brackets ([]) refer to the list of references at the end of the text. State of the art

Ceramics and vitroceramics are innovative technological materials obtained by crystallization of glass. Because of their crystalline character, ceramics and glass-ceramics have optical properties that make them particularly interesting compared to the corresponding glasses.

The precise control of the crystallization processes involved and influencing the final microstructure of the material can allow the production of transparent or at least translucent glass-ceramics, a characteristic prerequisite for good optical properties. Thus, these ceramics and glass-ceramics have many applications in the field of optics.

However, if it is easy to obtain transparent glasses, obtaining crystallized materials that are transparent or at least completely translucent, such as ceramics, or partially, such as glass-ceramics, is much more difficult.

Compositions of transparent or translucent crystalline materials have been described in the prior art, however these essentially correspond to either monocrystalline ceramics or to polycrystalline ceramics made by sintering powders.

The need for transparent ceramics in the industry is currently met by sintering (nano) -powders or single-crystal synthesis using very slow growth methods, such as the Czochralski process, which requires manufacturing times. ranging from several days to several weeks, and processing temperatures often above 1500 ° C for the oxides usually used. Moreover, the crystals thus obtained have a size of the order of a few centimeters.

Remarkably, the transparency of the glass can be preserved during crystallization (partial or total), leading to the development of highly transparent glass ceramics and ceramics. Vitroceramics are however partially crystallized materials, which limits their photonic properties. In addition, the processes for manufacturing nanocrystallized ceramics generally involve nanometric particles, expensive to manufacture. The particles undergo a pressing step, then a sintering step at a temperature often greater than 1500 ° C during which the growth of the crystals takes place. Control of this step is particularly critical, since it is generally necessary to preserve nanometric-sized crystals, usually less than 100 nm (less than four times the lower limit of the visible wavelength), to maintain transparency. . In the case of birefringent material, excessive crystalline growth implies obtaining opaque ceramics.

Nanocrystallized single crystals and ceramics (obtained from powder sintering), very suitable for high performance applications such as LASER applications, have a manufacturing cost far too high for more usual applications, for example for display, lighting or lenses.

In addition, complex formatting, such as large diameter pieces or atypical forms (eg lens) or "all-ceramic" fibers, are impossible at present. Very expensive and time-consuming techniques such as the Czochralski process, however, make it possible to obtain rods with limited diameters and lengths.

Tellurite-based glasses are known to have many advantages over silica glasses, in particular better infrared clarity of up to 5-6 μm, higher refractive index, better rare earth ion solubility and promising nonlinear optical properties. Thanks to these properties, tellurite-based glasses find applications in many optical devices, such as optical fibers. The major disadvantage of tellurite-based glasses is their poor mechanical properties, which can be overcome by controlled crystallization leading to transparent glass-ceramics. These glass-ceramics can be obtained either by a one-step heat treatment or by a two-stage heat treatment (Bertrand et al .: "New Transparent Glass-Ceramics Based on the Crystallization of" Anti-glass "Spherulites in the BiaOa-NbaOs -TeOa System ", Crystal Growth and Design, September 4, 2015 ([1])). Bertrand et al. describe in this context the preparation of a tellurite-based ceramic. However, this glass-ceramic has a crystallization in the form of spherulites ("crystallized spheres") and quickly loses its transparency when the crystalline fraction increases, which implies the impossibility of obtaining a transparent ceramic.

Glass and glass-ceramics based on tellurium oxide have also been described in the document by Bertrand et al. (A Comprehensive Study of Carbon Contamination in Tellurite Glasses and Glass-Ceramics by Spark Plasma Sintering (SPS) ", J. Am. Ceram Soc., 97 [1] 163-172 (2013) ([2]) ). These materials are obtained by conventional sintering of powder, which is a complex phenomenon and difficult implementation.

The document WO201276527 describes a method of amorphization by mechanosynthesis making it possible to obtain an amorphous powder, which is then sintered to obtain an amorphous solid material (glass) or a glass-ceramic comprising a chalcogenide based on tellurium. However, the product obtained shows only a crystallization on the surface and not in volume.

There is therefore a need for new transparent or translucent ceramics and glass-ceramics to overcome these defects, disadvantages and obstacles of the prior art, in particular of a robust, industrializable process which makes it possible to reduce the costs and improve the optical qualities of the products. ceramics and vitroceramics.

Description of the invention

According to important research, the Applicant has managed to overcome the disadvantages and restrictions of the prior art by preparing new ceramics and glass ceramics, including complete crystallization (or partial in the case of glass-ceramics) and a congruent glass.

The Applicant has in fact developed new vitreous compositions which make it possible to perfectly control the crystallization.

The ceramics and glass-ceramics of the invention can easily be produced by an inexpensive glass-making process, involving a step of annealing a glass of corresponding composition based on tellurium dioxide.

Advantageously, due to its preparation process and its shaping, the ceramics and glass-ceramics of the invention do not present a constraint of shape and size: it is indeed possible to obtain various shapes and large dimensions thanks to the implementation of the process developed by the Applicant. In addition, the chemical compositions of the glasses allow crystallization by volume of the product obtained. The invention involves a simple method of melting a vitrifiable mixture vitrifiable mixture that can be shaped. This first step is followed by a second crystallization step in a furnace (heat treatment adapted). Advantageously, this process is rapid implementation at relatively low temperature (especially less than 900 ° C). In this process, no manipulation of nanopowder is to be listed, unlike the processes of the prior art; as a result, no standards-related constraints are identified.

The technical solution offered by the proposed method makes it possible to overcome the complex phenomena of sintering (such as Spark Plasma Sintering, Hot Uniaxial Pressing, Hit Isostatic Pressing) from nano-powders currently used to obtain transparent ceramics (for example, MgAl204). The invention is particularly interesting for the field of optics, and more particularly for applications requiring materials having a window of transparency between the visible and the infrared. Indeed, the ceramics and glass-ceramics of the invention are advantageously transparent from the visible (500 nm) up to 6 pm and can be formed into solid material or in the form of optical fiber.

According to rare earth ion dopings, which are moreover facilitated, applications as a micro-laser or laser fiber are envisaged.

In addition, another advantage over conventional techniques for obtaining transparent ceramics involving sintering is that no porosity is found in the material obtained.

Thus, a first subject of the invention relates to an optically translucent and / or transparent material in the visible and the infrared, characterized in that it comprises a composition of following formula (I): (A2O3) x (B2O5 wherein A represents an element selected from Bi and Sb, and B represents a member selected from Nb and Ta, and X and y independently represent a number from 9 to 13, and that the material is selected from a ceramic and a glass ceramic.

For the purposes of the present invention, the term "glass" means an amorphous inorganic solid, such as a solid, which can be obtained in solid form or in pulverulent form (glass frit), depending on the quenching conditions.

For the purposes of the present invention, the term "ceramic" means a polycrystalline inorganic material consisting of crystals, with a degree of crystallization of between 98% and 100%, ie between 98% and 100% by weight. crystalline material. Advantageously, this material is not obtained in the form of powder, which makes it possible to overcome the sintering phenomenon to obtain a solid material.

For the purposes of the present invention, the term "glass-ceramic" means an inorganic material consisting of a mixture of glass and crystals, with a crystallization rate of between 5 and 98%, ie between 5% and 98% by weight of the crystalline material. The crystals are embedded in a glass matrix and this material is not obtained in the form of powder, which makes it possible to overcome the sintering phenomenon to obtain a solid material.

For the purposes of the present invention, "transparent" is understood to mean the fact that it can be seen through the material (in the visible range). This qualitative notion of transparency can be specified quantitatively, if necessary, by a specular light transmission measurement (http://www.perkinelmer.com/product/lambda-950-uv-vis-nir-spectrophotometer-1950). This measurement consists of measuring the light intensity along the axis of the incident light beam. A material may be considered transparent when its specular light transmission is greater than or equal to 30%, for example greater than 40%, or greater than 50%, or greater than 60%.

For the purposes of the present invention, the term "translucent" means that the material transmits light but that it is not possible to see the objects through the material. The translucent materials exhibit a significant diffusion phenomenon that can be measured by means of a spectrophotometer equipped with an integrating sphere.

For the purposes of the present invention, the term "visible domain" is intended to mean that part of the electromagnetic spectrum visible to the human eye, that is to say a representation of all the monochromatic components of the visible light. The International Commission on Illumination (CIE) defines the view of the reference observer between a wavelength in vacuum of 380 nm, perceived as a violet, and that of 780 nm, corresponding to a red.

For the purposes of the present invention, the term "infrared domain" is used to mean a wavelength greater than that of visible light but less than that of microwaves. This may include a wavelength of between about 0.7 pm and about 1 mm.

According to the present invention, in formula (I), the numbers x and y represent molar proportions. The numbers x and y can independently represent 9, or 10, or 11, or 12, or 13.

For example, x can be 9, and y can be 9, 10, 11, 12, or 13.

For example, x may be 10, and y may be 9, 10, 11, 12, or 13.

For example, x may be equal to 11, and y may be 9, 10, 11, 12, or 13.

For example, x may be 12, and y may be 9, 10, 11, 12, or 13.

For example, x may be 13, and y may be 9, 10, 11, 12, or 13.

The numbers x and y can be equal.

For example, x and y can be equal to 12.5 each.

According to the invention, the material may comprise at least 60% by weight of the composition of formula (I) relative to the total mass of said material. For example, the material may comprise 60%, or at least 70%, or at least 75%, or at least 80%, or at least 90%, or at least 95% or at least 100% by weight of the formula (I) with respect to the total mass of said material. Advantageously, the material may comprise at least about 75% by weight relative to the total mass of the material, 75% being included. Alternatively, the material may comprise 100% by weight of the composition of formula (I) relative to the total mass of said material, that is to say be composed of the composition of formula (I).

The material of the present invention may comprise, in addition to the composition of formula (I), where appropriate, additive elements conventionally used in the technical field. It may be for example dopants such as transition metal ions or rare earths. The amount of additive elements may be sufficient to achieve 100% by weight of the material. For example, the material may comprise up to 40% by weight of additive elements relative to the total mass of the material, i.e. between 0 and 40%. For example, if the material comprises 75% of composition of formula (I), then it comprises 25% of additive elements.

Advantageously, the ceramic or glass-ceramic material may be comprised of doping agents, such as rare earth ions, for example Er 2+, Nd 2+ or Yb 2+ ions, or transition metal ions, for example ions. ## STR1 ## or Ni 2+. The doping element, its concentration and its degree of oxidation are chosen according to the optical properties sought for the material. This doping may in particular be particularly advantageous for various applications in the field of optics, in particular by conferring optical properties on the specific material, for example luminescence.

The material according to the invention can be a solid material. Alternatively, it may be a thin layer, for example a material whose thickness is between about 1 nm and about 10 pm or a fiber.

Another subject of the invention relates to a process for preparing a material as defined above, characterized in that it comprises the following steps: i) preparation of a transparent glass comprising a composition of formula (I) and ii) crystallization by heat treatment of said glass to obtain said material.

Advantageously, the transparent or translucent ceramics and glass-ceramics of the present invention obtained by the process of the invention therefore have the same constitution as the glass from which they derive. Step i) of preparing a transparent glass is a conventional step and the skilled person can use any method of preparing a glass suitable for the object of the invention. Step i) may for example comprise a melting step of the elements entering into its composition leading to a liquid, followed by a step of solidification of this liquid. The elements used in the composition of the glass may be mixed in powder form at the beginning of step i). The elements used in the composition of the glass may be, for example, oxide powders. The melting may be, for example, a fusion of these oxide powders. The skilled person can adapt the melting temperature required to obtain the glass in the light of his technical knowledge. Whatever the embodiment, the melting temperature may be, for example, from about 700 ° C to about 1000 ° C, for example about 850 ° C.

The melting temperature can be obtained by any heating method known to those skilled in the art, for example heating in a conventional oven.

Advantageously, the molten mixture is then poured into a mold of desired shape and then cooled in order to obtain a solid material of the desired shape. Casting in a mold advantageously allows to obtain pieces of very varied shapes and large dimensions. By way of example, the piece obtained may have a pellet or lens shape. The thickness of the part may be between 500 μm and 100 mm. The piece can have a diameter of between 1 mm and 100 mm. Using other methods (fiber drawing, spraying), the part can be in the form of fiber or thin layer.

It is difficult to obtain such a variety of shapes by the techniques of the prior art for producing monocrystals or nanoscale polycrystalline ceramics ultra-dense for optics, obtained by sintering under high pressure and high temperature. Indeed, the shape of the single crystals is constrained by the synthesis process. In the case of transparent polycrystalline ceramics, the sintering process used requires a pressing step (under high pressure), which is incompatible with obtaining various shapes (the conventional shapes obtained in press being of cylindrical or parallelepipedic type). The step of solidifying the liquid may be or include cooling the liquid. Preferably, the method according to the invention does not involve a nucleation step. It does not require two-stage annealing or the use of nucleating agents.

Advantageously, the transparent glass may comprise at least 60% by weight, for example at least 70%, or at least 75%, or at least 80%, or at least 90% or 100% by weight relative to the total mass of the glass, of a composition of formula (I). Preferably, the transparent glass may comprise at least 75% by weight relative to the total mass of the glass, of a composition of formula (I). The crystallization step ii) may be a congruent crystallization in volume. For the purposes of the present invention, the term "congruent crystallization" means a crystallization in which the chemical composition of the crystals of cubic symmetry is identical to that of the base glass from which it is made.

It may for example be performed by heat treatment of the glass.

For the purposes of the present invention, the term "heat treatment of a glass" means a heat treatment of the glass making it possible to crystallize it in a controlled manner. Those skilled in the art can adapt the annealing time and temperature so as to obtain transparent or translucent ceramics and glass-ceramics according to his general knowledge. The annealing may for example be carried out at a temperature between the glass transition temperature of the glass and its crystallization temperature. It may be for example a temperature between 350 ° C and 650 ° C, for example between 450 ° C and 550 ° C. It can be carried out for a time of between 15 minutes and 48 hours, for example between 15 minutes and 6 hours, or preferably between 30 minutes and 2 hours. Generally, the crystallization step is longer for obtaining ceramics than for the production of glass-ceramics. In fact, during the manufacture of glass-ceramics, the glass is not allowed to reach a cure rate of 98%. The annealing step may be carried out by any heating method known to those skilled in the art, for example heating in a conventional oven, for example a convection oven and / or equipped with heating resistors.

The ceramics and glass-ceramics of the invention being prepared by a heat treatment of the glass, they therefore advantageously have the same composition as the glass from which they are derived.

A method of preparing ceramics and / or glass-ceramics including a step of crystallizing a glass may be referred to as the "glassmaking process".

In addition, transparent ceramics and glass-ceramics prepared by a glass-making process can be shaped easily. Indeed, the glass process used for their manufacture makes it possible, by casting in a mold, pieces of very varied shapes and large dimensions.

Preferably, the glasses, ceramics and glass-ceramics of the present invention do not include fluorides, oxyfluorides or sulphides, but only oxides. Advantageously, this makes it possible to synthesize under air and not in a controlled atmosphere as necessary for fluorides or sulfides. Advantageously, the ceramics based on oxides thus have better chemical durability.

Another subject of the invention relates to a ceramic and / or a glass-ceramic which can be obtained by the implementation of the method of the invention.

Another subject of the invention relates to the use of a glass comprising at least 60% by weight of a composition of formula (I) relative to the total mass of the glass, for the preparation of a ceramic or an optically translucent and / or transparent glass ceramic in the visible and the infrared.

Advantageously, the transparent glass may comprise at least 60% by weight, for example at least 70%, or at least 75%, or at least 80%, or at least 90% or 100% by weight relative to the total mass of the glass, of a composition of formula (I). Preferably, the transparent glass may comprise at least 75% by weight relative to the total mass of the glass, of a composition of formula (I).

Another object of the invention relates to a product comprising an optically translucent and / or transparent material in the visible and infrared domains of the invention. The product may be chosen from an optical fiber, a lens, a laser fiber, in particular a micro-laser, an opto-electronic system, such as a signal amplifier or an optical waveguide, and a scitillator.

Another object of the invention relates to the use of a material according to the invention, for the manufacture of optical materials. It may be, for example, active or passive optical components. This may include materials used in medical imaging, lighting, laser marking or as a lens, this list is not limiting. Other advantages may still appear to those skilled in the art on reading the examples below, illustrated by the appended figures, given for illustrative purposes.

Brief description of the figures

FIG. 1 represents the optical transmission curve of a glass of composition 75 TeO 2 - 12.5Bi 2 O 3 - 12.5Nb 2 O 5 heated for 1 h 30 at 510 ° C. The abscissa axis represents the wavelength in nm, and the ordinate axis represents the transmittance expressed in%. The photograph of this ceramic is represented in insert.

FIG. 2 shows the differential scanning calorimetry thermogram of a glass of composition 75 TeO 2 - 12.5Bi 2 O 3 - 12.5Nb 2 O 5 with heating kinetics at 10 ° C / min. The x-axis represents the temperature (in degrees Celsius) and the y-axis represents the heat flux (u.a.).

FIG. 3 represents the X-ray diffractograms of a glass of composition 75 TeO 2 - 12.5Bi 2 O 3 - 12.5Nb 2 O 5 treated at different temperatures (30 ° C., 380 ° C., 400 ×, 420 ° C., 440 ° C., 460 ° C. , 480X, 500X, 520 ° C, 540 ° C, 560 ° C).

FIG. 4 represents the observation by scanning electron microscopy of the surface of a ceramic of composition 75 TeO 2 -12.5Bi 2 O 3 -12.5Nb 2 O.sub.2, heated for 1h30 to 51O.sup.-1.

EXAMPLES

Example 1 Manufacture of a Glass of Composition (Bi203) 12.5 (Nb20s) 12.5 (TeO2) 75

This glass is prepared by melting the raw materials used in its composition leading to a liquid, followed by solidification of this liquid by cooling.

For this, the different materials are weighed in stoichiometric proportions and intimately mixed by manual grinding with a mortar and pestle. This mixture is then placed in a platinum crucible and then melted at a temperature of 850 ° C for 1 hour in an oven equipped with heating resistors.

The liquid thus obtained is cast in a brass mold preheated to 300 ° C. This rapid cooling (quenching) allows the solidification of the liquid.

The glass thus obtained is placed in an annealing furnace at a temperature Tg-10 ° C (with Tg the glass transition temperature) for 2 hours and then the temperature is reduced to 20 ° C in 5 hours in order to be able to release the mechanical stresses. contained in the glass during its quenching. Thus the glass can be cut and polished for possible characterizations (optical, mechanical, thermal).

Example 2: Manufacture of transparent ceramic composition (Bi203) 12.5 (Nb205) 12.5 (TeO2) 75

The previously synthesized glass is crystallized during a heat treatment of 1H30 at 510 ° C in a conventional oven. The material thus obtained is optically polished so as to have surfaces free from defects and thus has a high transparency.

FIG. 1 represents the optical transmission curve of the ceramic thus obtained (thickness of the sample: 1.7 mm).

Figure 4 shows the observation by scanning electron microscopy of the surface of the ceramic heated 1h30 to 510 ° C. The surface of this ceramic was previously chemically treated with acid to reveal the grain boundaries.

List of references 1. Bertrand et al. : "New Transparent Glass-Ceramics Based on the Crystallization of" Anti-glass "Spherulites in the Bi203-Nb205-Te02 System", Crystal Growth and Design, September 4, 2015. 2. Bertrand et al. (A) Comprehensive Study of the Carbon Contamination in Tellurite Glasses and Glass-Ceramics by Spark Plasma Sintering (SPS) ", J. Am., Ceram Soc., 97 [1] 163-172 (2013) 3. WO201276527.

Claims (12)

1. Glass-ceramic material and / or ceramic optically translucent and / or transparent in the visible and infrared, characterized in that it comprises a composition of formula (I) below: (A2O3) x (B2O5) y (TeO2) 100 wherein A represents an element selected from Bi and / or Sb, and B represents an element selected from Nb and / or Ta, and X and y independently represent a number from 9 to 13. 2. Material according to claim 1, comprising at least 60% by weight of said composition of formula (I) relative to the total mass of said material. 3. Material according to claim 1, consisting of said composition of formula (I). 4. Material according to one of the preceding claims, wherein said material is a solid material. 5. Process for the preparation of a material as defined in any one of the preceding claims, characterized in that it comprises the following steps: i) preparation of a transparent glass comprising a composition of formula (I), and ii) crystallizing said glass to obtain said material. 6. The method of claim 5, wherein the step i) of preparing a transparent glass comprises a step of melting the elements entering into its composition leading to a liquid, followed by a step of solidification of the liquid. 7. Method according to any one of claims 5 or 6, wherein the crystallization step ii) is carried out by annealing said glass. 8. The method of claim 7, wherein the crystallization step ii) is congruent crystallization at a temperature between 350 ° C and 650 ° C, for a time between 15 minutes and 48 hours. 9. Use of a glass comprising at least 60% by weight of a composition of formula (I) relative to the total mass of the glass, for the preparation of an optically translucent and / or transparent ceramic or glass-ceramic in the visible and the infrared. 10. Product comprising a material as defined in any one of claims 1 to 4. 11. The product of claim 10, said product being selected from an optical fiber, a lens, a thin layer, a micro-laser and a thin layer. 12. Use of a material as defined in any one of claims 1 to 4 for the manufacture of optical materials.