GLASS CERAMIC MATERIAL OF A SPINEL TYPE FOR THE PRODUCTION OF FASHION JEWELLERY AND JEWELLERY STONES

Abstract

Glass ceramic material for the production of synthetic stones in fashion jewellery and jewellery, having excellent mechanical properties, chemical and heat resistance, harmless due to absence of lead, arsenic and cadmium compounds, available in a broad scale of colour designs, imitating faithfully natural precious stones thanks to high content of spinel crystalline phase and lowered content of SiO.sub.2, consisting of (in weight %):

20-40% SiO.sub.2,
1.5-10% B.sub.2O.sub.3,
20-35% Al.sub.2O.sub.3,
0.1-20% MgO,
0.1-20% ZnO,
the content of MgO+ZnO being at least 10%,
preferably also
0-15% TiO.sub.2,
0.1-15% ZrO.sub.2,
the content of TiO.sub.2+ZrO.sub.2 being at least 5%,
more preferably also
0-20% of colouring additives in the form of CoO, NiO, CuO, Fe.sub.2O.sub.3, MnO.sub.2, Cr.sub.2O.sub.3, V.sub.2O.sub.5, Pr.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Er.sub.2O.sub.3, AgO and Au.

Claims

1. Glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index (of at least 1.62) and a high heat resistance, characterised in that it is formed by aluminium-boron-silicate glass with the addition of ZnO and MgO oxides, which forms by subsequent heat treatment a homogeneously dispersed nanocrystalline phase consisting of (in weight %): 20-40% SiO.sub.2, 1.5-10% B.sub.2O.sub.3, 20-35% Al.sub.2O.sub.3, 0.1-20% MgO, 0.1-20% ZnO, while the content of MgO+ZnO is at least 10%.

2. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 1, characterised in that it further comprises, as nucleation agents for controlled bulk crystallization: 0.1-15% ZrO.sub.2, 0-15% TiO.sub.2, while the content of TiO.sub.2+ZrO.sub.2 is at least 5%.

3. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 1, characterised in that it comprises 0-20% of colouring additives in the form of CoO, NiO, CuO, Fe.sub.2O.sub.3, MnO.sub.2, Cr.sub.2O.sub.3, V.sub.2O.sub.5, Pr.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Er.sub.2O.sub.3, AgO and Au.

4. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 1, characterised in that it comprises after crystallization ≥20% of the crystalline phase of a spinel type and the crystalline phase related to nucleation agents (ZrO.sub.2, ZrTiO.sub.4).

5. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 4, characterised in that the size of crystalline particles is ≤50 nm and the material is transparent.

6. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 4, characterised in that the size of crystalline particles is je>50 nm and the material is translucent or opaque.

7. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 2, characterised in that it comprises 0-20% of colouring additives in the form of CoO, NiO, CuO, Fe.sub.2O.sub.3, MnO.sub.2, Cr.sub.2O.sub.3, V.sub.2O.sub.5, Pr.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Er.sub.2O.sub.3, AgO and Au.

8. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 2, characterised in that it comprises after crystallization ≥20% of the crystalline phase of a spinel type and the crystalline phase related to nucleation agents (ZrO.sub.2, ZrTiO.sub.4).

9. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 3, characterised in that it comprises after crystallization ≥20% of the crystalline phase of a spinel type and the crystalline phase related to nucleation agents (ZrO.sub.2, ZrTiO.sub.4).

10. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 7, characterised in that it comprises after crystallization ≥20% of the crystalline phase of a spinel type and the crystalline phase related to nucleation agents (ZrO.sub.2, ZrTiO.sub.4).

11. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 8, characterised in that the size of crystalline particles is ≤50 nm and the material is transparent.

12. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 9, characterised in that the size of crystalline particles is ≤50 nm and the material is transparent.

13. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 10, characterised in that the size of crystalline particles is ≤50 nm and the material is transparent.

14. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 8, characterised in that the size of crystalline particles is je>50 nm and the material is translucent or opaque.

15. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 9, characterised in that the size of crystalline particles is je>50 nm and the material is translucent or opaque.

16. The glass ceramic material for the production of fashion jewellery and jewellery stones with a high refractive index and a high heat resistance according to claim 10, characterised in that the size of crystalline particles is je>50 nm and the material is translucent or opaque.

Description

BRIEF DESCRIPTION OF THE FIGURE

[0015] The FIGURE is an X-ray diffractogram with analysed phases that shows that the material contains only the spinel phase and ZrO.sub.2 which was used as the nucleation agent.

SUMMARY

[0016] The subject matter of the invention is a material for jewellery and fashion jewellery use—transparent, translucent or opaque glass ceramic of a spinel type with the refractive index of at least 1.62, with high mechanical toughness and very good heat resistance, not containing compounds of lead, arsenic, cadmium and lithium, ensuring maximum health safety. Due to the high content of spinel crystalline phase and a reduced content of SiO.sub.2, this material can be coloured by the addition of various oxides so that it faithfully imitates colours of natural precious stones (namely spinel and gahnite).

[0017] The invention relates to a material for jewellery and fashion jewellery stone, which consists (in weight %) of:

20-40% SiO.SUB.2.,

[0018] 1.5-10% B.sub.2O.sub.3
20-35% Al.sub.2O.sub.3,

0.1-20% MgO

0.1-20% ZnO

[0019] while the content of MgO+ZnO is at least 10%,
preferably also of

0-15% TiO.SUB.2

0.1-15% ZrO.SUB.2

[0020] while the content of TiO.sub.2+ZrO.sub.2 is at least 5%
and more preferably also of
0-20% of colouring additives in the form of CoO, NiO, CuO, Fe.sub.2O.sub.3, MnO.sub.2, Cr.sub.2O.sub.3, V.sub.2O.sub.5, Pr.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Er.sub.2O.sub.3, AgO and Au.

[0021] The invention thus relates to a glass ceramic material with a reduced content of SiO.sub.2 comprising only the spinel crystalline phase and crystalline phases connected with nucleation agents (ZrO.sub.2, ZrTiO.sub.4), with a high heat, mechanical and chemical resistance.

[0022] Parameters of the material according to the invention are mentioned in Table 1.

TABLE-US-00001 TABLE 1 Selected properties of the new material Parameter Unit Value Refractive index ≥1.62 Density [g.cm.sup.−3] ≥3.1 Young modulus of elasticity [GPa] ≥110 Hardness by Vickers ≥900 Melting temperature [° C.] ≥1550 Transformation temperature Tg [° C.] ≥745 Crystalline phase share [%] ≥20 Coefficient of thermal expansion [.Math.10.sup.−7 K.sup.−1] 35-55

[0023] The base glasses were prepared by homogenization of the initial components and by melting in a platinum or SiO.sub.2 crucible at temperatures between 1550° C. a 1700° C. The molten glass was homogenized by means of platinum or SiO.sub.2 stirrer and subsequently cast into a pre-heated mould and transferred into a cooling furnace heated to the temperature of 600-650° C. in order to relax the inner tension and then cooled down in a controlled way to room temperature. The cooled blocks were cut into slices or prisms of suitable dimensions, which were subsequently subjected to controlled crystallization.

[0024] The crystallization of glass was conducted in two stages at temperatures optimized by DSC analysis. By selecting nucleation temperature (Tn), crystallization temperature (Tc), the heating rate and the holding time at the selected temperature, the crystallization process can be controlled in terms of size and amount of crystalline phase (Z. Strnad, Skelně krystalické materiály, 1983). In order to achieve a transparent material, it is necessary (in case of the cubic spinel phase) to keep the size of the crystalline particles at most 50 nm. By increasing the size of the crystallites above this value, first opalescent colouration of the material occurs and consequently, with further crystal growth, transparency is lost totally. Nucleation temperatures according to the detected transformation temperatures Tg ranged between 600° C. and 700° C., temperatures of subsequent crystallization for transparent material ranged between 750° C. and 950° C., temperatures of subsequent crystallization for opaque material ranged between 950° C. and 1100° C. The specific temperature regimes are mentioned in Table 2 in connection with examples of embodiment. An example of X-ray diffractogram with analysed phases is on the FIGURE. The diffractogram shows that the material contains only the spinel phase and ZrO.sub.2 which was used as the nucleation agent.

[0025] The material prepared in this way may be processed by cutting, grinding and polishing into the desired shape of fashion jewellery or jewellery stone.

[0026] The base of the new glass ceramic material is aluminium-boron-silicate glass matrix with ZnO and MgO, which is toxically harmless. During the process of heterogeneous bulk nucleation, separated areas of solid solutions ZrO.sub.2—TiO.sub.2 and/or ZrO.sub.2 and/or ZrTiO.sub.4 nanocrystals are formed in the matrix. The reduced content of SiO.sub.2, the optimised amount and ratio of MgO and ZnO and namely the addition of B.sub.2O.sub.3 contribute to the fact that during the subsequent crystallization process only spinel phases are formed and the generation of other undesirable phases (for example quartz, sapphirine, enstatite, willemite, mullite, petalite, cordierite) is suppressed. This distinguishes the new material from the materials disclosed in the patents mentioned above, in particular U.S. Pat. No. 9,801,435. In addition, it does not contain lithium, lead or other undesirable compounds. The addition of B.sub.2O.sub.3 changes the kinetics of the crystallization, broadens the temperature range for the formation of the spinel phase and, moreover, reduces the melting point of the primary glass. This makes it possible to melt the material in conventional electric furnace in a platinum or quartz crucible.

[0027] The base glass ceramic material can be, by modification of its composition, coloured into colour hues faithfully imitating the colours of natural precious stones, namely spinels and gahnites, but also sapphires, amethysts, emeralds, rubies, etc. The new material is especially suitable for deep blue, green and blue-green hues. The change in colouring may be achieved by the addition of one or more components selected from the group of oxides CoO, NiO, CuO, Fe.sub.2O.sub.3, MnO.sub.2, Cr.sub.2O.sub.3, V.sub.2O.sub.5, Pr.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Er.sub.2O.sub.3, AgO and/or Au in the amount of 0-20 weight %.

[0028] The material has suitable mechanical properties, which is the hardness greater than 6.5 according to Mohs scale ((≥900 according to Vickers) guaranteeing to products good resistance against damage caused by dust particles, and it is still well processable with conventional abrasive materials. It has also suitable thermal properties, namely low coefficient of thermal expansion, which is lower than in case of natural spinels and corundum, and which enables to process products of this material by the productive jewellery technology of lost wax casting.

[0029] The glass ceramic according to the present invention contains a certain minimum amount of Na.sub.2O, which is introduced into it as an impurity from used initial components, namely from glass sand.

[0030] The glass ceramic according to the present invention contains a certain minimum amount of Fe.sub.2O.sub.3, which is introduced into it as an impurity from used initial components. In some cases Fe.sub.2O.sub.3 is purposefully added to the stem in order to colour the resulting material.

EXAMPLES

[0031] The examples of embodiment of the invention, together with the selected parameters of glass/glass ceramic, are mentioned in Table 2. The composition according to example 1 is a glass ceramic, which is blue, transparent, has the refractive index of 1.63, imitating the colour of sapphire. The compositions according to examples 2 and 3 are glass ceramics, which are transparent: yellow-green, imitating the colour of peridot, and green, imitating the colour of emerald, with the refractive index in the range from 1.62 to 1.67. The composition according to example 4 is a glass ceramic of non-transparent, blue-green (turquoise) colour. All these materials have a high heat resistance (colour and shape stability) and are suitable to be processed by the lost wax casting method.

TABLE-US-00002 TABLE 2 Examples of embodiments of the invention and selected parameters (in weight %) Oxide/Example 1 2 3 4 Al.sub.2O.sub.3 27.51 25.48 24.61 28.13 SiO.sub.2 32.4 30.03 29.01 33.16 ZnO 13.17 12.2 11.79 MgO 4.35 4.03 3.89 11.12 B.sub.2O.sub.3 8.35 7.72 7.46 8.53 TiO.sub.2 4.85 ZrO.sub.2 9.15 15.39 14.87 17.00 CoO 0.08 NiO 0.14 1.42 2.06 Pr.sub.2O.sub.3 5.15 4.86 MnO.sub.2 2.08 CuO Fe.sub.2O.sub.3 Cr.sub.2O.sub.3 V.sub.2O.sub.5 Nd.sub.2O.sub.3 Er.sub.2O.sub.3 AgO Au Examples of the technology of the crystallization process Melting 1570° C. 1585° C. 1600° C. 1620° C. temperature Nucleation 660° C., 5 h  710° C., 5 h  680° C., 5  730° C., 5 h  Crystallization 830° C., 25 h 890° C., 15 h 870° C., 20 950° C., 15 h Selected detected parameters Refractive 1.63 1.65 1.62 — index n.sub.d Colour blue yellow-green green turquoise Tg 751 757 753 752

INDUSTRIAL APPLICABILITY

[0032] The present glass ceramic material is harmless (it does not contain compounds of Pb, Cd or As) and it is intended for use namely as a synthetic stone in fashion jewellery and jewellery industry. Thanks to the high content of spinel crystalline phase, it imitates faithfully the colours and optical-aesthetic properties of natural precious and semi-precious stones, namely spinel. Thanks to its excellent thermal properties (the shape and colour stability) and a low coefficient of thermal expansion, it may be preferably used in production of jewels by the lost wax casting method.

[0033] Obviously, the material may be used anywhere else, where it is convenient due to its properties.

[0034] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0035] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0036] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.