DE102007005118A1 - Synthetic crystal and process for its preparation - Google Patents

Abstract

The present invention provides a method for producing a synthetic crystal, in particular a synthetic sapphire or ruby, wherein the method comprises a matrix substance comprising Al <SUB> 2 </ SUB> O <SUB> 3 </ SUB> at least one oxide additive is mixed.

Description

The The present invention relates to a synthetic crystal and a method for its production, in particular relates The invention relates to a method for producing synthetic Sapphire or ruby.

in the The state of the art becomes synthetic sapphire, for example made by a Verneuil process of alumina (Al2O3).

One such artificial Sapphire, which consists only of Al2O3, points parallel and perpendicular different degrees of hardness to its c-axis. The c-axis is doing one of the spatial Coordinate axes of the crystal lattice, each consisting of one a, b and c axes.

The hardness have the known in the art synthetic sapphires while Knoop 2200 parallel to the c-axis and Knoop 1800 perpendicular to the c-axis. The name Knoop refers to a hardness test (DIN EN ISO 4545) for determining the degree of hardness of materials. To determine the degree of hardness of a material a rhombic diamond tip is used, which is pressed into the material becomes. Depending on how deep the tip penetrates into the material, Different degrees of hardness result.

at later Grinding or polishing processes of the artificial Sapphires or rubies are due to the different degrees of hardness in the vertical and parallel direction of the c-axis of the crystal to a non-uniform material removal on the surface of the crystal. This results, for example, a non-uniform roundness of balls made of artificial Sapphire exist.

task It is therefore an object of the present invention to provide a method which allows to produce synthetic sapphire whose degrees of hardness both parallel and perpendicular to the c-axis of the crystal of are comparable size, resulting in a later Processing of the artificial Kristalls a uniform material removal and thus a uniform roundness of synthetic sapphire produced balls.

These The object is achieved by the method according to the invention 1 solved.

Further advantageous embodiments of the invention are specified in the dependent claims.

According to a first aspect of the present invention, a method is preferred for producing a synthetic spherical crystal, in particular a synthetic sapphire, wherein in the method a base substance which comprises Al ₂ O ₃ , with at least one oxide additive, in particular an oxide additive of lower hardness, is mixed. In this way, a better roundness of the ball is achieved.

Under A synthetic crystal is a crystal that is based on artificial Way under certain conditions (temperature, pressure) produced becomes. examples for artificial Crystals are artificial sapphire (Al2O3) or artificial Ruby (Al2O3 + CrO2).

Appropriate Method with which such an artificial crystal, in particular a sphere can be made, for example, the Verneuil method, the Czochralski process, neck Kyropoulos process, Tammann-Stöber process, Bridgman-Stockberger method, zone melting method, pedestal method, Cold crucible method, Hydrothermal process, HPHT process, CVD process, MOCVD process, plasma process, Photon plasmatron method and molecular beam epitaxy.

Under A synthetic sapphire is a natural one or synthetic or artificial crystal, which has the chemical composition Al2O3 and a purity of 99.99% has. The crystal structure of synthetic sapphire, the Also called colorless corundum is hexagonal. The degree of hardness parallel to its c-axis, one of the three coordinate axes (a, b, c) of the crystal Knoop 2200, perpendicular to the c-axis is the hardness Knoop 1800. The crystal is colorless.

Under a mixture is understood to mean that in the process according to the invention two or more substances are mixed together. The real one Mixture of the basic substance and the oxide additive takes place in molten state in the crystal growing, preferably in a Verneuil method.

Under A basic substance is understood to be a first substance which is preferred percentage of the majority on the mixture. The proportion of the matrix substance is preferred between 99% and 99.999%

Under Al 2 O 3 is understood to mean an oxygen compound of the element aluminum, Al2O3 is also present as clay and in mineral form as well Corundum is called.

Under An oxide additive is understood as meaning chemical compounds which Have oxygen. Preferably, the process according to the invention is understood under an oxide additive metal oxides from the group nickel oxide (NiO), iron oxide (Fe2O3), titanium oxide (TiO3), vanadium oxide (V2O5) or cobalt oxide (CoO). The oxide additive is preferred in a quantitative ratio from 0.001% to 1.00% to the ground substance containing at least Al2O3 includes, attached. This additive has a lower hardness than Al2O3.

Under The term "mixed" means that the basic substance, so Al2O3, and the oxide additive, so at least one of the compounds from the group of nickel oxide, iron oxide, titanium oxide, Vanadium oxide or cobalt oxide are mixed together in such a way that the oxide additive uniformly distributed in the ground substance so that at the later preferred method for producing an artificial crystal, preferred a Verneuil process, the resulting synthetic crystal has uniform material properties.

According to one Another aspect of the present invention, it is preferred that the basic substance further in addition Chromium oxide comprises CrO2. By adding CrO2 to Al2O3 can with the method according to the invention preferably synthetic ruby can be produced. The synthetic one Ruby shows a light pink to dark pink color. chromium has an even greater hardness than Al2O3 on, bringing even in the case of synthetic sapphire comparable differences in the degrees of hardness parallel and vertical to the c-axis of the crystal.

The Compound Al2O3 or Al2O3 + CrO2 can be used as the basic substance or base, to which later preferably at least one added oxide additive becomes. Al2O3 and CrO2 are present in such a way that the two compounds preferably in powder form can be mixed together.

According to another aspect of the present invention, it is preferable that the oxide additive is a metal oxide derived from the group consisting of nickel oxide (Ni), iron oxide (Fe ₂ O ₃ ), titanium oxide (TiO ₂ ), vanadium oxide (V ₂ O ₅ ), cobalt oxide (CoO) or a combination thereof.

By the addition of metal oxides that have a lower hardness than Aluminum oxide Al2O3 and chromium oxide CrO2, the result Advantage that the difference in the degrees of hardness parallel (Knoop 2200) and perpendicular (Knoop 1800) to the c-axis of the crystal structure can be. is the difference in the degrees of hardness parallel and perpendicular to the c-axis The crystal structure has a difference of 400 Knoop, so can after an addition of oxide additive a difference of about 350 to 399 Knoop, depending on the percentage Proportion of the oxide additive can be achieved.

By the reduction of the difference in the degrees of hardness parallel and perpendicular to the c-axis of the artificial Crystal is a uniform Material removal of the crystal in a grinding or polishing possible. at the grinding or polishing processes is made with appropriate abrasives or polishing agents of synthetic Diamond, which is the largest occurring temper has ground or polished. Because the crystal is both parallel as well as perpendicular to the c-axis equal degrees of hardness, the degree of hardness on the surface a ball, for example, to be ground or polished uniformly is, it comes to a uniform Material removal on the sphere surface. Thus, with the grinding and polishing processes a sphere with uniform roundness are produced.

In the case of an artificial sapphire or pure ruby, however, which consists of Al2O3 or Al2O3 + CrO2, therefore, see places where the crystal has a lower hardness than elsewhere 1 , a larger material removal than at locations where the crystal has a greater hardness. In the case of a ball, therefore, results in a non-uniform Abschliff or removal of the crystal after a correspondingly ongoing grinding or polishing period. Therefore, the ball has no spherical ideal shape, but is increasingly oval. By adding at least one metal oxide to the basic substance of Al 2 O 3 or Al 2 O 3 + CrO 2, this nonuniform material removal can thus be avoided and it comes to a uniform roundness of the preferred ball of artificial sapphire or ruby.

One Metal oxide is a chemical compound that is made up of one metallic element, such as nickel (Ni), iron (Fe), titanium (Ti), vanadium (V) or cobalt (Co) and oxygen.

Under Nickel oxide, NiO, is the oxygen compound with nickel. By adding of nickel oxide to Al2O3, the one with the inventive method Synthetic crystal made a pale yellow color. Further indicates by adding from nickel oxide to Al 2 O 3 + CrO 2 of the process according to the invention Synthetic crystal made a yellow orange, topaz or orange color, with different color gradation by the amount of added Nickel oxide results. The more nickel oxide added, the more it tends to be the color of the crystal towards yellow-orange.

Under Iron oxide, Fe2O3, is the stable iron (III) oxide that forms on contact produced by metallic iron and oxygen. Rust exists, for example from Fe2O3. By adding from Fe 2 O 3 to Al 2 O 3, that with the inventive method Synthetic crystal made a blue color. Further points by adding from Fe 2 O 3 to Al 2 O 3 + CrO 2 produced by the process according to the invention synthetic crystal to a gray-green or violet color, wherein the different color gradation by the amount of of added Fe2O3 yields. The more iron oxide added to the mixture, the better more the color of the crystal tends towards violet.

Under Titanium oxide is understood to mean the substance group of titanium-oxygen compounds. TiO2, too referred to as titanium (IV) oxide, has a white color. By adding TiO 2 to Al 2 O 3 has the synthetic produced by the process according to the invention Crystal a blue color. Continue by adding TiO 2 to Al 2 O 3 + CrO 2 of the synthetic crystal produced by the process according to the invention a gray-green or violet color, with different color gradation by the amount of added Titanium oxide results. The more TiO2 is added to the mixture Al2O3 + CrO2, the more the color of the crystal tends to violet.

vanadium oxide V2O5 is also referred to as vanadium pentoxide because the vanadium with five Oxygen atoms is bound. By adding V2O5 to Al2O3 + CrO2 has the with the inventive method Synthetic crystal made a gray-green color.

Under Cobalt oxide CoO, cobalt (II) oxide is dyed olive green to reddish brown. The Crystals have a structure like common salt. By adding Cobalt oxide to Al2O3 has the method according to the invention Synthetic crystal made a dark green color. Further points by adding Nickel oxide to Al2O3 + CrO2 of the inventive method Synthetic crystal made a bright green color.

at the method according to the invention becomes the oxide additive as a powdery material to the ground substance added which also in powdered Form is present.

By The addition at least one oxide additive, as previously described was, the degrees of hardness can be parallel and perpendicular to the c-axis of the later during the process of the invention control growing crystals so that they are no longer so vary greatly, as in the case of the pure synthetic sapphire (Al2O3) or ruby (Al2O3 + CrO2) Case is. Likewise leaves by adding, As previously described, the coloring of the synthetic Determine the crystal. Depending on which oxide additive is selected, For example, a color spectrum can be from light yellow to blue, purple to dark green become.

As well it is preferred that a plurality of oxidic additives, that is several metal oxides mixed together and a total mixing ratio of 0.001% to 1% compared to the ground substance. Thus, the concerning the chemical properties of the individual metal oxides later resulting degree of hardness of the synthetic crystal combined and optimized become.

According to one Another aspect of the present invention, it is preferred that 0.001% to 1.00% of the oxidic additive is added to the ground substance. By the corresponding percentage share, so preferred 0.001% to 1.00% can be both appropriate material properties (Hardness parallel and perpendicular to the c-axis of the crystal) as well as color properties achieve.

According to another aspect of the present invention, it is preferred that the erfindungsge method further comprises a Verneuil method. The Verneuil process is a process for producing artificial crystals. It is also referred to as flame fusion and was developed between 1890 and 1892. The basic principle in the production of an artificial crystal according to the Verneuil principle is that one brings an ammonium aluminum alum with or without at least one oxidic additive by means of a blast gas blower to melt. The ammonium aluminum alum and the oxide additive are contained in a container having a passage to a fuel nozzle, which is fired with hydrogen. A downward flame heats a crest of a growing crystal and the steady supply of ammonium aluminum alum and oxide additive from the firing nozzle creates a thin melt film on the synthetic crystal, on the underside of which crystallization occurs. At a temperature of more than 2000 ° C, the crystal grows drop by drop like a stalagmite.

In Modification to this is in the Pereuil method of the present Invention instead of the ammonium aluminum alum the basic substance, So Al2O3 or Al2O3 + CrO2 used. The further process steps take place as in the classic Verneuil process.

By the procedure leaves create a kind of "crystal pear", which, after she cooled down is in cubes is cut. These dice are ground in appropriate steps to balls, the Al2O3 and at least one oxide additive, ie artificial Sapphire with 0.001% to 1% addition of at least one oxidic Have additional. On the other hand, CrO2 is additionally added to the process added to Al2O3, the result is an artificial ruby with 0.001% to 1% addition of at least one oxide additive.

According to one Another aspect of the present invention, it is preferred that the synthetic crystal, in particular synthetic sapphire or synthetic ruby, which by the method according to the invention is produced, a difference in hardness parallel to the c-axis and the degree of hardness perpendicular to a c-axis of the synthetic sapphire of less as Knoop 400 has.

The name Knoop refers to a hardness test (DIN EN ISO 4545) for determining the degree of hardness of materials. To determine the hardness of a material, a rhombic diamond tip is used, which is pressed into the material. Depending on how deep the tip penetrates into the material, different degrees of hardness result. The addition of at least one oxide additive, which is in the range of 0.001% to 1%, results in a reduction in the degree of hardness of the synthetic crystal. Thus, the hardness parallel to the c-axis of the crystal less than 2200 Knoop and perpendicular to the c-axis less than 1800 Knoop. In addition, the degrees of hardness parallel and perpendicular to the c-axis no longer differ as much from each other as is the case in pure synthetic sapphire. This results in the advantage that with the aid of the method according to the invention preferably spheres can be produced which have a uniform roundness (see 2 ).

Furthermore In the present invention it is preferred that the synthetic Crystal a maximum deviation from an ideal spherical shape of less than 130 nm, preferably less than 100 nm, in particular from 5 to 15 nm, preferably from 3 to 10 nm, more preferably from 1 to 2 nm. Below a maximum deviation of one Ideal spherical shape is the distance between the ideal shape a ball and the actual one surface geometry of the synthetic crystal. The maximum deviation from an ideal Ball shape or the maximum shape error is thus defined as the Difference from the largest distance the actual surface geometry to the center and the smallest distance to the actual surface geometry to the center. It is the difference of the Center of the actual synthetic crystal measured maximum and minimum distance, which in the ideal sphere is always constant the radius. has the synthetic crystal is an increase or depression in comparison to the ideal shape of a ball, so there is a corresponding Distance, which is between 5 to 15 nm, preferably between 3 to 10 nm, more preferably between 1 to 2 nm from the ideal form the ball deviates or a maximum deviation of less than 130 nm. Due to the maximum deviation in the aforementioned Areas results in the advantage that the inventive synthetic crystal a surface geometry which corresponds to almost an ideal sphere.

preferred embodiments The invention will be described below with reference to the accompanying drawings explained in more detail.

1 shows a measuring profile of a ball of pure synthetic sapphire (Al2O3).

2 shows a measuring profile of a ball of synthetic sapphire, which with an oxide additive (Fe2O3) was provided.

In 1 is the measuring profile ( 2 ) of a synthetic sapphire ball, wherein the synthetic sapphire is a 99.99% pure Al2O3 synthetic sapphire.

Next is the ideal form ( 1 ) of a ball having a uniform roundness, in the form of a circle.

Such a measurement profile ( 2 ) comes from the fact that one measures the surface of the object to be measured, here a ball, with a suitable measuring device (not shown) once by 360 °. Such a measuring device has, for example, a measuring pin, which is fixedly mounted in the measuring device. The ball to be measured is also mounted in a corresponding device. Subsequently, either the measuring pin is moved one or more times around the equator or any other degree of latitude of the ball or the ball moves with respect to the measuring device. Once the measuring pin has moved once around the ball or ball around the measuring pin by 360 °, the measuring profile ( 2 ) in front.

Unevenness or irregularities of the surface are expressed by the fact that there are more or less pronounced deviations outwards or inwards in relation to the ideal shape (FIG. 1 ) of the sphere shown comes.

The in the 1 shown distances correspond to 50 nm intervals.

In the profile it can be seen that at approx. 45 ° and 225 ° the measuring profile ( 2 ) the ball the largest deviation from the ideal shape ( 1 ) has a ball. This is due to the hardness of Knoop 2200 synthetic sapphire parallel to the c-axis. The maximum deviations amount to about 50 to 75 nm from the ideal form ( 1 ) the ball.

Conversely, it is about 135 ° and 315 °, where the smallest deviations of the measuring profile ( 2 ) of the ideal form ( 1 ) occur. This is due to the hardness of Knoop 1800 synthetic sapphire perpendicular to the c-axis. The maximum deviations amount thereby approx. 5 to 20 nm of the ideal form ( 1 ) the ball.

These Deviations are caused by the fact that it is in areas where the Ball a lower degree of hardness has, ie at 135 ° and 315 °, a stronger Material removal takes place. This can be explained by the fact that the degree of hardness the grinding or polishing agent used, much greater than the degree of hardness of Ball is in this area.

On the other hand It comes in areas where the ball has a higher degree of hardness, ie to the Knoop 2200, at 45 ° and 225 °, too a weaker one Material removal. This leaves explain themselves by that the degree of hardness of the grinding or polishing agent used, less than or equal to the degree of hardness the ball is in this area. Due to the different material removal in different areas of the ball gets the ball thus after a certain number of grinding or polishing cycles one oval shape, with the deviations in the nm range and with the naked eye are not detectable. For precision balls, the deviations of only a few nanometers are balls with such Material properties can not be used.

In 2 is the measuring profile ( 2 ) of a sphere made of synthetic sapphire, to which synthetic sapphire was added an oxidic addition of 1% Fe 2 O 3 to the ground substance Al 2 O 3.

As in 1 is here also the ideal form ( 1 ) of a sphere represented by a circle.

The in the 2 Distances shown correspond to 50 nm intervals.

Unlike the in 1 shown profile falls in 2 on that the deviations from the ideal form ( 1 ) at about 45 ° and 225 °, originally in 1 are still about 50 to 75 nm, in a range of about 5 to 10 nm.

Further one recognizes that in the ranges from approx. 135 ° and 315 °, where also in 1 the smallest deviations of the measuring profile ( 2 ) of the ideal form ( 1 ) have occurred, these deviations at all are no longer recognizable. The deviations are approximately in the 1-2 nm range.

The reduction of deviations from the ideal form ( 1 ) of a ball are due to the reduction in the difference in the degrees of hardness parallel and perpendicular to the c-axis.

Thus, it comes to a uniform grinding or polishing of the ball, since the surface of the ball has a nearly uniform degree of hardness, as from 2 is recognizable.

The Grinding or polishing agent has a hardness comparable to the ball of artificial Crystal on. Thus it comes in the course of a certain number of Grinding or polishing cycles, a uniform grinding or removal material of the artificial Crystal and thus to a nearly uniform roundness of the ball.

The finally Table 1 shows which colors by addition of metal oxides to the ground substance (Al 2 O 3 or Al 2 O 3 + CrO 2). The crystals thus obtained have a smaller deviation of degree of hardness parallel and perpendicular to the c-axis, making it rounder Balls are obtained with less deviation than in an Al2O3.

In this way, it is possible to produce balls, in particular for scanning elements, with a higher accuracy than was previously the case. The precision balls produced in this way from cut cubes have smaller deviations than was the case with the previous materials. Table 1

1

ideal form the ball

2

measuring profile the ball

Claims (7)

A process for producing a synthetic crystal, in particular a synthetic sapphire, wherein in the process a base substance comprising Al ₂ O ₃ is mixed with at least one oxide additive. The method of claim 1, wherein the matrix further comprises CrO ₂ additionally. The method according to claim 1 or claim 2, wherein the oxide additive is a metal oxide derived from the group consisting of nickel oxide (NiO), iron oxide (Fe ₂ O 3), titanium oxide (TiO ₂ ), vanadium oxide (V ₂ O ₅ ), cobalt oxide (CoO) or a combination thereof. Method according to one of the preceding claims, wherein 0.001% to 1.00% of the oxidic additive of the ground substance added become. Method according to one of the preceding claims, the method further comprising a Verneuil method. Synthetic crystal, which after the preceding method claims wherein the synthetic sapphire is a difference in temper parallel and in the degree of hardness perpendicular to a c-axis of the synthetic sapphire of less than Knoop 400 has. A synthetic crystal according to claim 6, wherein the synthetic crystal a maximum deviation from an ideal Spherical shape less than 130 nm, preferably less than 100 nm.