WO2006043909A1 - Crystal glass free of lead, barium, niobium and of their compounds, and method of its preparation - Google Patents

Crystal glass free of lead, barium, niobium and of their compounds, and method of its preparation Download PDF

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Publication number
WO2006043909A1
WO2006043909A1 PCT/SK2005/000021 SK2005000021W WO2006043909A1 WO 2006043909 A1 WO2006043909 A1 WO 2006043909A1 SK 2005000021 W SK2005000021 W SK 2005000021W WO 2006043909 A1 WO2006043909 A1 WO 2006043909A1
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weight
oxide
content
zirconium
crystal glass
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PCT/SK2005/000021
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French (fr)
Inventor
Peter Simurka
Peter Vrabel
Viera Petruskova
Marek Liska
Vendelin Macho
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Rona, A.S.
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Publication of WO2006043909A1 publication Critical patent/WO2006043909A1/en

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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C4/00—Compositions for glass with special properties
    • C03C4/0028—Compositions for glass with special properties for crystal glass, e.g. lead-free crystal glass
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C1/00—Ingredients generally applicable to manufacture of glasses, glazes, or vitreous enamels
    • C03C1/02—Pretreated ingredients
    • C03C1/022—Purification of silica sand or other minerals
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
    • C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
    • C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
    • C03C3/087—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal containing calcium oxide, e.g. common sheet or container glass

Definitions

  • the invention concerns crystal glass free of lead, barium, niobium and of their compounds, as well as a method of preparation of a glass having refractive index of at least 1.5200, density of at least 2450 kg.m "3 , and for which it holds that the sum of contents of zinc oxide ZnO and potassium oxide K 2 O is at least 10 % by weight, wherein the glass meets demanding technical, aesthetic, ecological and hygienic requirements. It will be prepared from technically available starring raw materials and additives.
  • lead-free crystal glass consisting of (in % by weight) 50 to 65 % of silicon dioxide SiO 2 , 0.5 to 17 % of zirconium dioxide ZrO 2 , 10 to 22 % of potassium oxide K 2 O or sodium oxide Na 2 O, 2 to 10 % of calcium oxide CaO and/or magnesium oxide MgO, further of barium oxide BaO, zinc oxide ZnO, bismuth oxide Bi 2 ⁇ 3 , antimony oxide Sb 2 ⁇ 3 , aluminium oxide Al 2 ⁇ 3 and titanium oxide TiO 2 , as well as of controlled, generally minimum amounts of iron oxide Fe 2 Os, sulfates and chlorides, even utilizing further components, like tin oxide SnO 2 , niobium oxide Nb 2 O 5 and tantalum oxide Ta 2 O 5 [Sasek L., Rada M., Sasek L.: SK 277 737 (1994); WO95/13 993 - C03C3/087,
  • Schott Zwiesel protects crystal glass without lead and barium [Clement M., Brix P., Gaschler L.: SK 280 058 (1993), CZ 286 934(2000)], having high light transmittance, high refractive index and density, but the glass is multi-component, containing among others also niobium oxide Nb 2 Os, while it may contain also strontium oxide SrO, tantalum oxide Ta 2 O 5 , cerium oxide CeO 2 , titanium oxide TiO 2 , as well as fluorides.
  • the lead-free glass according to a further patent [Rytychova K. (Preciosa): CZ 281 030 (1996)] achieves good physico-mechanical parameters, but especially the presence of barium oxide BaO does not meet the most demanding chemical-hygienic parameters; the same holds also for the lead-free glass according to [Halfar J. (Ornela): SK 277744 (1994)]. Also the lead-free glass - o -
  • the aim of the present invention is to provide crystal glass, which eliminates or at least minimizes negative properties of known, especially multi-component glasses, optimally utilizes available starting raw materials, whereby it preserves demanding physico-mechanical, aesthetic and hygienic properties.
  • crystal glass according to the present invention free of lead, barium, niobium and of their compounds, having refractive index of at least 1.5200, density of at least 2450 kg.rn '3 , for which it holds that the sum of contents of zinc oxide ZnO and potassium oxide K 2 O is at least 10 % by weight, the glass being based on ecologically acceptable compounds of elements of the LA, ILA, IV.A, ILB to IV.B subgroups of the periodic element system.
  • the crystal glass contains, in total amount, the compounds of seven selected elements, mainly in the form of oxides, namely of silicon, sodium, potassium, calcium, aluminium, zirconium and zinc, in an amount of at least 99.2 % by weight, where
  • the sum of contents of silicon dioxide SiO 2 and zirconium oxide ZrO 2 as the networking components in crystal glass is 65.11 to 74.0 % by weight, wherein the content of silicon dioxide SiO 2 is 65.10 to 71.90 % by weight, and the content of zirconium oxide ZrO 2 is 0.01 to 2.1 % by weight,
  • aluminium oxide AI 2 O 3 is 0.01 to 3.0 % by weight.
  • the content of silicon, sodium, potassium, calcium, aluminium, zirconium and zinc, especially in the form of oxides is at least 99.3 % by weight.
  • crystal glass in which the sum of contents of silicon dioxide SiO 2 and zirconium oxide ZrO 2 as the networking components in crystal glass is 65.11 to 72.0 % by weight, wherein the content of silicon dioxide SiO 2 is 65.10 to 70.00 % by weight and the content of zirconium oxide ZrO 2 is 0.01 to 2.0 % by weight,
  • the content of zinc oxide ZnO is 1.0 to 3.6 % by weight
  • the content of aluminium oxide AI 2 O 3 is 0.01 to 3.0 % by weight, as well as crystal glass, where the sum of contents of silicon dioxide SiO 2 and zirconium oxide ZrO 2 is 65.11 to 72.0 % by weight, wherein the content of silicon dioxide SiO 2 is 65.1 to 70.0 % by weight and the content of zirconium oxide ZrO 2 is 0.01 to 2.0 % by weight,
  • the content of zinc oxide ZnO is 2.0 to 3.2 % by weight
  • aluminium oxide AI 2 O 3 is 0.2 to 1.5 % by weight.
  • the nature of the invention relates also to crystal glass with the content of silicon dioxide SiO 2 of 66.0 to 70.0 % by weight and the content of zirconium oxide ZrO 2 of 0.5 to 2.0 % by weight.
  • the crystal glass in question contains in the final product metals with variable valency, besides zirconium oxide - -
  • antimony oxides in an amount of at most 0.2 % by weight, more preferably 0.1 % by weight.
  • Further subject matter of the invention consists in a method of preparation of crystal glass free of lead, barium, niobium and of their compounds, having a refractive index of at least 1.5200, density of at least 2450 kg.m '3 , for which it holds that the sum of contents of zinc oxide ZnO and potassium oxide K 2 O is at least 10 % by weight, from starting raw material, like silica dust and/or silica sand, potassium hydrogencarbonate, limestone, sodium sulfate, sodium nitrate, aluminium oxide and/or hydroxide, zinc oxide, sodium carbonate, zirconium oxide and/or zirconium silicate and assistant substances, by modification, thorough homogenization, heating, melting and refining the glass batch, its forming and gradual controlled cooling.
  • starting raw material like silica dust and/or silica sand, potassium hydrogencarbonate, limestone, sodium sulfate, sodium nitrate, aluminium oxide and/or hydroxide, zinc oxide, sodium carbonate, zirconium
  • the nature of this method consists in that the starting raw materials or raw materials and assistant substances are, before their processing, refined to the content of undesirable harmful admixtures, like iron oxide F ⁇ 2 ⁇ 3 in silicon(IV) oxide and/or silica sand, of less than 0.02 % by weight, in limestone to less than 0.035 % by weight, in sodium carbonate to less than 0.002 % by weight, in zirconium(IV) silicate to less than 0.09 % by weight and in aluminium oxide and/or hydroxide to less than 0.01 % by weight, as well as of cadmium(ll) oxide to less than 0.02 % by weight, manganese oxides to less than 0.001 % by weight, copper oxides to less than 0.007 % by weight, lead oxides to less than 0.06 % by weight in zinc oxide ZnO, by treating it with nitric acid HNO 3 and/or hydrochloric acid HCI in any mutual ratio.
  • undesirable harmful admixtures like iron oxide F ⁇ 2 ⁇
  • the starting raw materials and/or assistant substances are refined to the total content of admixtures, impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum 0.8 % by weight, preferably to the content of impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum 0.2 % by weight, more preferably to the total content of admixtures, impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum 0.7 % by weight, and to the content of impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum 0.1 % by weight.
  • An advantage of the crystal glass according to the present invention is the fact that even though it contains neither lead oxide nor barium oxide, which considerably increase the glass density and refractive index, it has excellent physico-chemical, aesthetic, ecological, chemical and hygienic properties and, simultaneously, it meets the condition of classification of the glass into the group of crystalline: the sum of contents of zinc oxide ZnO, barium oxide BaO, lead oxide PbO and potassium oxide K 2 O is at least 10 % by weight. Besides, it meets the requirements of high refractive index (at least 1.5200) and density (at least 2450 kg.m '3 ).
  • a further important advantage is its relatively high chemical resistance (or stability), expressed by the parameter of water resistance. This parameter classifies it into the hydrolytic class III, wherein it holds: the lower hydrolytic class, the higher chemical resistance of glass.
  • a further unquestionable advantage is that the crystal glass according to the present invention contains low number - only seven - selected components able to form crystal glass of high quality. It is just their well-balanced content, taking into account important influence of each of the components, which participates to a large degree on the properties of the above crystal glass.
  • Silicon oxide SiO 2 decreases density, thermal conductivity and partially also refractive index, but it increases melt viscosity of the glass batch, chemical resistance and mechanical strength of crystal glass.
  • Sodium oxide Na 2 O decreases the melt viscosity, but also chemical resistance, thermal conductivity, density, internal bonds, strength and hardness of glass. Also potassium oxide K 2 O influences the properties in a similar way, however, at lower temperatures (about 740 0 C) it decreases the melt viscosity, but on the contrary, at higher temperatures (about 1300 0 C) it increases viscosity. It decreases also surface tension, liquidus temperature (temperature of the equilibrium between the liquid and crystalline substance), ability to crystallize and density and refractive index.
  • calcium oxide CaO increases the glass strength and hardness, as well as chemical resistance, stability, density, refractive index and bond strength, but simultaneously it decreases dielectric loss of the crystal glass, its thermal and electric conductivity.
  • Aluminium oxide AI 2 O 3 (up to 2 %) improves conditions of melting of glass components, increases viscosity of the melt and chemical resistance of the glass, as well as modulus of elasticity, scratch hardness, surface tension and resistance against temperature changes of the crystal glass.
  • Zinc oxide ZnO increases glass density and viscosity, increases chemical resistance of glass and moderately improves the glass hardness.
  • a further unquestionable advantage of the glass according to the present invention is the fact that possibly present, although nontoxic, but anyway only subsidiary admixtures in the glass, like oxides of titanium, magnesium, antimony, but also unambiguously undesirable admixtures, like oxides of iron, manganese, copper, or even toxic elements, are eliminated to such an amount which has no influence on the decisive properties of the glass.
  • the surprisingly effective combination of amounts and quality of starting raw materials in the batch composition makes it possible to produce more easily crystal glass of high quality, which meets not only the required aesthetic, physical and chemical properties, but unequivocally also hygienically and ecologically faultless utility properties.
  • Quality of the glass according to the present invention, prepared from technical raw materials (when observing permissible limits for admixtures), is surprisingly high - it is very close to properties of glass prepared from raw materials of high purity.
  • admixtures in crystal glass may be formed by controlled amounts mainly of magnesium oxide MgO with antimony oxide Sb 2 ⁇ 3 and possibly by their sulfates. There may still be tolerated trace amounts to micro-amounts of compounds, especially of oxides of lithium, titanium, iron, manganese and copper, and possibly of further nontoxic oxides, coming from less effectively refined starting raw materials.
  • ferric oxide Fe 2 O 3 should be in silica sand under 0.02 % by weight, in limestone under 0.035 % by weight, in sodium carbonate under 0.002 % by weight, in zirconium silicate under 0.09 % by weight, and in aluminium oxide or hydroxide under 0.1 % by weight, and neither in zinc oxide the content of oxides of undesirable metals may exceed 0.1 % by weight.
  • aluminium oxide AI 2 O 3 chloride 0.005; sulfate (as sulfur) 0.1; calcium 0.05; cadmium 0.005; cobalt 0.005; copper 0.005; iron 0.01 ; potassium 0.01; sodium 0.1 ; nickel 0.005, lead 0.005 and zinc 0.005;
  • silicon(IV) oxide sulfate (as sulfur) 0.005; calcium 0.02; cadmium 0.005; cobalt 0.005; copper 0.005; iron 0.02; potassium 0.05; sodium 0.01 ; nickel 0.005, lead 0.005 and zinc 0.005.
  • a laboratory homogenizer was charged with 68.5 g of silicon dioxide (silica sand); 12.1 g of potassium carbonate; 17.6 g of sodium carbonate; 16.7 g of limestone; 2.0 g of zinc oxide; 0.05 g of aluminium oxide and 2.0 g of zirconium oxide.
  • the whole content was transferred into a fusion platinum (Pt) crucible (containing 20 % by weight of Rh) and this was placed into a furnace at room temperature.
  • the crucible content was gradually heated in the furnace to a temperature of 1200 to 1350 0 C, when the crucible content was stirred around.
  • the furnace was further heated up to the melting temperature (1500 to 1600 0 C).
  • the clear melt was poured onto a metal plate and tempered in a muffle furnace at a temperature of 550 to 600 0 C for 1 to 3 hours. In the turned off furnace the glass was left to cool down to room temperature.
  • the obtained crystal glass was analyzed using common chemical methods.
  • the content of metals in it was as follows (in % by weight): 10.26 Na 2 O; 8.16 K 2 O; 9.08 CaO; 1.97 ZnO; 1.93 ZrO 2 ; 0.06 AI 2 O 3 and 68.54 SiO 2 .
  • So multi-component crystal lead-free glass consisting of (in % by weight): 71.0 % of SiO 2 , 11.0 % of K 2 O, 15.5 % of Na 2 O, 2.0 % of CaO, 0.001 % of AI 2 O 3 , 0.001 % of TiO 2 , 0.01 % of ZnO, 0.5 % of MgO, 0.01 % of B 2 O 3 , 0.01 % of Li 2 O, 0.001 % of Sb 2 O 3 , 0.001 % of SrO, 0.008 % of fluorides (F) and 0.0008 % of sulfates (SO 4 2" ), exhibited high transparency, hardness and strength, but the refractive index only of 1.5073.
  • a similar glass except that instead of 0.001 % by weight of Sb 2 O 3 it contained 0.001 % by weight Of As 2 O 3 , had the refractive index only of 1.5075.
  • This glass had, besides its valuable physico-chemical and aesthetic properties, the value of the refractive index only of 1.5053.
  • the refractive index n D of none of them has achieved the declared and required value of 1.52.
  • this lead-free glass had lower number of components.
  • final crystal glass did not meet the required (but otherwise declared) physical properties.
  • crystal glass within the range of "protected" limits of concentrations and number of components containing 74.3 % by weight of SiO 2 , 10.0 % by weight of K 2 O, 12.0 % by weight of Na 2 O, 3.0 % by weight of CaO, 0.4 % by weight of AI 2 O 3 , 0.3 % by weight of TiO 2 , has achieved the value of the refractive index only of 1.5092.
  • Example 2 The procedure was similar to that of Example 1 , thus the crystal glass was prepared from starting raw materials of high purity (p. a.).
  • Example 1 The procedure was similar to that of Example 1 , except that contrary to Example 1 technically or commercially available starting raw materials, or raw materials refined by the methods given in Examples 19 to 21 were used in the batches.
  • Examples 9 and 16 also aluminium hydroxide was used which had been refined by the procedure according to Example 20 to the content (in % by weight): 99.9 of AI(OH) 3 ; 0.005 or 0.001 of Fe 2 O 3 and 0.112 or 0.011 Of Na 2 O, respectively.
  • AI(OH) 3 was used with the composition (in % by weight): 99.21 Of AI(OH) 3 ; 0.118 of Fe 2 O 3 ; 0.004 of SiO 2 and 0.668 of Na 2 O.
  • Example 12 and 13 commercially available zirconium silicate ZrSiO 4 was used which had, after refining by the procedure given in Example 21 , the following composition (in % by weight): 66.1 of ZrO 2 ; 33.6 of SiO 2 ; 0.05 of Fe 2 O 3 ; 0.10 Of TiO 2 ; 0.06 Of Y 2 O 3 ; 0.08 of HfO 2 .
  • potassium hydrogencarbonate KHCO 3 having the composition (in % by weight): 94.8 of KHCO 3 ; 5.0 of K 2 CO 3 and 0.1 of KCI; limestone with the composition (in % by weight): 99.15 of CaCO 3 ; 0.94 of MgCO 3 ; 0.03 of SiO 2 ; 0.06 of H 2 O; 0.029 of Fe 2 O 3 ; 0.004 of MnO and 0.03 of AI 2 O 3 ; sodium carbonate with the composition (in % by weight): 99.8 of Na 2 CO 3 ; 0.13 of NaCI; 0.0014 of Fe 2 O 3 ; 0.02 of Na 2 SO 4 ; 0.01 of insoluble part in H 2 O; less than 150 ppm of CaO and less than 120 ppm of MgO; also zinc oxide ZnO containing (in % by weight): 99.53 of ZnO; 0.054 of PbO; 0.01 of CdO; 0.0052 of CuO and
  • Excavated silica sand having the grain size of 0.3 to 1.1 mm contained 92.3 % by weight of silicon dioxide SiO 2 ; 7.22 % by weight of water H 2 O; 0.25 % by weight of aluminium oxide AI 2 O 3 ; 0.14 of iron(lll) oxide or hydroxide Fe 2 O 3 /Fe(OH) 3 and 0.09 % by weight of titanium oxide TiO 2 .
  • Available unrefined powder (grain size of 0.1 to 0.3 mm) aluminium oxide contained 99.21 % by weight Of AI(OH) 3 , 0.004 % by weight of silicon dioxide SiO 2 , 0.668 % by weight of sodium oxide Na 2 O and 0.118 % by weight of ferric oxide Fe 2 O 3 .
  • the refinement, the aim of which was to remove especially iron(lll) hydroxide and oxide, was performed with diluted aqueous solution of hydrochloric acid with the concentration of 10 % by weight, in an amount of 500 mi to 100 g of aluminium hydroxide, under stirring at room temperature for 2 hours.
  • the content of ferric oxide After extraction, filtering aluminium hydroxide off, its drying, burning at a temperature of 400 to 420 0 C for 0.5 hour and subsequent cooling, the content of ferric oxide has decreased to 0.05 % by weight and the content of sodium oxide to 0.112 % by weight.
  • refinement by the method according to the present invention makes possible to replace aluminium oxide by common aluminium hydroxide without negative influence on the required quality of crystal glass.
  • the refinement of powder zirconium(IV) silicate was performed by extraction with aqueous solution of nitric acid with the concentration of 63.5 % by weight. 50 g of the zirconium silicate powder were treated under stirring and tempering at a temperature of 10 to 15 0 C with 100 g of nitric acid solution for 30 min. After drying and burning, the content of ferric oxide was 0.12 % by weight.
  • the content of ferric oxide decreased to 0.05 % by weight, titanium(IV) oxide to 0.10 % by weight, yttrium(lll) oxide to 0.06 % by weight and hafnium(IV) oxide to 0.08 % by weight.
  • the content of zirconium(IV) oxide was 66.1 % by weight and of silicon dioxide 33.6 % by weight - if additionally microwave radiation is used, the same refinement effect is achieved within 10 minutes already.
  • the source of zirconium(IV) oxide as a crystal glass component need not be a compound of high purity, but in the case of the production method according to the present invention, with utilizing chemical refinement, it may be commonly available zirconium(IV) silicate.
  • Crystal glass according to the present invention is designated for manual and machine production of glass rods, plates, illuminating glasses, lustre lamp or even the whole lustres, intermediate products for artificial jewellery and, generally, of a wide assortment of utility glassware products. It can be utilized both in glass industry, and in production of special, especially of aesthetically and hygienically demanding glass, further in artistic and hand-made manufacture.
  • the refinement may be utilized for treatment of starting glass raw materials, both ore and non- metallic raw materials.

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Abstract

The nature of the invention is crystal glass free of lead, barium, niobium and of their compounds, having a refractive index of at least 1.5200, density of at least 2450 kg.m-3, with the content of at least 10 % by weight of zinc oxide and potassium oxide, containing seven selected elements, mainly in the form of oxides, namely of silicon, sodium, potassium, calcium, aluminium, zirconium and zinc, in an amount of at least 99.2 % by weight. The content (in % by weight) of silicon dioxide SiO2 and zirconium oxide ZrO2 is 65.11 to 74.0 %, wherein the content of silicon dioxide SiO2 is 65.10 to 71.90 % and the content of zirconium oxide ZrO2 is 0.01 to 2.1 %. The content of sodium oxide is 8.0 to 14.0 % by weight, the content of potassium oxide is 6.5 to 9.9 % by weight, the content of calcium oxide is 8.6 to 13.0 % by weight, the content of zinc oxide is 0.5 to 3.6 % by weight, and the content of aluminium oxide AI2Ο3 is 0.01 to 3.0 % by weight. It may further contain permissible admixtures of at most 0.6 % by weight and to 100 % by weight impurities and metal compounds, coming from the starting raw materials.

Description

Crystal glass free of lead, barium, niobium and of their compounds, and method of its preparation
Technical Field
The invention concerns crystal glass free of lead, barium, niobium and of their compounds, as well as a method of preparation of a glass having refractive index of at least 1.5200, density of at least 2450 kg.m"3, and for which it holds that the sum of contents of zinc oxide ZnO and potassium oxide K2O is at least 10 % by weight, wherein the glass meets demanding technical, aesthetic, ecological and hygienic requirements. It will be prepared from technically available starring raw materials and additives.
Background Art
Increasing demands on silicate materials [Levender M. D.: Indoor Built Environt., 8 (2), 89-93 (1999)], but especially on crystal glass, lay high demands not only on technical properties (best possible light transmission, high refractive index), but also on ecological and hygienic harmlessness. These demands have led to creation of the so called lead-free crystal glass, consisting of (in % by weight) 50 to 65 % of silicon dioxide SiO2, 0.5 to 17 % of zirconium dioxide ZrO2, 10 to 22 % of potassium oxide K2O or sodium oxide Na2O, 2 to 10 % of calcium oxide CaO and/or magnesium oxide MgO, further of barium oxide BaO, zinc oxide ZnO, bismuth oxide Bi2θ3, antimony oxide Sb2θ3, aluminium oxide Al2θ3 and titanium oxide TiO2, as well as of controlled, generally minimum amounts of iron oxide Fe2Os, sulfates and chlorides, even utilizing further components, like tin oxide SnO2, niobium oxide Nb2O5 and tantalum oxide Ta2O5 [Sasek L., Rada M., Sasek L.: SK 277 737 (1994); WO95/13 993 - C03C3/087, 3/095, 3/11]. However, some of the above oxides are undesirable as crystal glass components, both from the point of view of negative influence on physico-mechanical and aesthetic properties of products of the crystal glass and from the ecological and hygienic point of view, as is the case of barium oxide BaO [Naumann K. et al., (Schott): DE 1985 927 (2000)] and strontium oxide SrO. Moreover, multi-component crystal glass is technically demanding from the point of view of its production, as well as of raw material availability. Moreover, still higher and higher demands on products of crystal glass, especially those coming into contact with food, urgently require avoiding problematic components of crystal glass to greatest possible extent. The situation is similar also in further cases, where also the presence of barium oxide BaO, strontium oxide SrO and fluorides is accented, but also of otherwise suitable components, like magnesium oxide MgO, although calcium oxide CaO and titanium oxide TiO2 are sufficient [Lenhart A.: US 6391810 (2002); Komiya Hidetoshi et al.: EP 0893417 (1997)], and of further admixtures, including niobium oxide Nb2O5 [Sakoske G.: EP 1006088 (2000); Eichholz R.: EP 1306353 (2003)], without significant positive influence on the production and quality of crystal glass. The proposed limits for the component concentrations are often so wide that accepting them one sometimes cannot reach the declared physico-mechanical, aesthetic or even hygienic parameters of the crystal glass.
Also important crystal glass producers respond adequately to the requirements. For example, Schott Zwiesel protects crystal glass without lead and barium [Clement M., Brix P., Gaschler L.: SK 280 058 (1993), CZ 286 934(2000)], having high light transmittance, high refractive index and density, but the glass is multi-component, containing among others also niobium oxide Nb2Os, while it may contain also strontium oxide SrO, tantalum oxide Ta2O5, cerium oxide CeO2, titanium oxide TiO2, as well as fluorides. Similarly, lead-free crystal glass having refractive index higher than 1.52 is protected by Rada M., Sasek L., Sasek L.: SK 278 662 (1993), wherein the glass contains besides SiO2, CaO, K2O, Na2O, AI2O3 and ZrO2 also HfO2 and TiO2. From the technical point of view, but especially from the point of view of production and raw material for such glasses, their multi- component composition, as well as the presence of problematic components, like sulfates, chlorides, fluorine and iron, do not meet the most demanding requirements, despite interesting technical properties of such crystal glasses.
Also the lead-free glass according to a further patent [Rytychova K. (Preciosa): CZ 281 030 (1996)] achieves good physico-mechanical parameters, but especially the presence of barium oxide BaO does not meet the most demanding chemical-hygienic parameters; the same holds also for the lead-free glass according to [Halfar J. (Ornela): SK 277744 (1994)]. Also the lead-free glass - o -
[Cornier G., Vasseur D. (Baccarat Cristalleries): EP 553586 (1993)] is a multi- component glass, which, moreover, has too high content of zinc oxide ZnO (16 to 21 % by weight), which fact influences adversely melting, leads to separation to an immiscible phase and formation of striated glass, but also to excessive corrosion of the refractory material.
In many cases, too broad limits for concentrations of components are "protected", which can hardly be utilized for potential industrial production, because they do not make possible production of crystal glass of high quality having the required demanding physico-mechanical, aesthetic and hygienic properties.
The aim of the present invention is to provide crystal glass, which eliminates or at least minimizes negative properties of known, especially multi-component glasses, optimally utilizes available starting raw materials, whereby it preserves demanding physico-mechanical, aesthetic and hygienic properties.
Disclosure of Invention
The raised requirement is solved by crystal glass according to the present invention, free of lead, barium, niobium and of their compounds, having refractive index of at least 1.5200, density of at least 2450 kg.rn'3, for which it holds that the sum of contents of zinc oxide ZnO and potassium oxide K2O is at least 10 % by weight, the glass being based on ecologically acceptable compounds of elements of the LA, ILA, IV.A, ILB to IV.B subgroups of the periodic element system. The nature of the patent consists in that the crystal glass contains, in total amount, the compounds of seven selected elements, mainly in the form of oxides, namely of silicon, sodium, potassium, calcium, aluminium, zirconium and zinc, in an amount of at least 99.2 % by weight, where
- the sum of contents of silicon dioxide SiO2 and zirconium oxide ZrO2 as the networking components in crystal glass is 65.11 to 74.0 % by weight, wherein the content of silicon dioxide SiO2 is 65.10 to 71.90 % by weight, and the content of zirconium oxide ZrO2 is 0.01 to 2.1 % by weight,
- the content of sodium oxide Na2O is 8.0 to 14.0 % by weight,
- the content of potassium oxide K2O is 6.5 to 9.9 % by weight,
- the content of calcium oxide CaO is 8.6 to 13.0 % by weight, - the content of zinc oxide ZnO is 0.5 to 3.6 % by weight, and
- the content of aluminium oxide AI2O3 is 0.01 to 3.0 % by weight.
It may further contain permissible admixtures, like magnesium oxide MgO together with antimony oxide Sb2O3 or with their sulfates in an amount of at most 0.6 % by weight, and the rest to 100 % by weight impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials.
It is preferred, if the content of silicon, sodium, potassium, calcium, aluminium, zirconium and zinc, especially in the form of oxides, is at least 99.3 % by weight.
It has been found that preferred is also crystal glass, in which the sum of contents of silicon dioxide SiO2 and zirconium oxide ZrO2 as the networking components in crystal glass is 65.11 to 72.0 % by weight, wherein the content of silicon dioxide SiO2 is 65.10 to 70.00 % by weight and the content of zirconium oxide ZrO2 is 0.01 to 2.0 % by weight,
- the content of sodium oxide Na2O is 9.9 to 12.5 % by weight,
- the content of potassium oxide K2O is 7.6 to 9.0 % by weight,
- the content of calcium oxide CaO is 8.6 to 11.5 % by weight,
- the content of zinc oxide ZnO is 1.0 to 3.6 % by weight, and
- the content of aluminium oxide AI2O3 is 0.01 to 3.0 % by weight, as well as crystal glass, where the sum of contents of silicon dioxide SiO2 and zirconium oxide ZrO2 is 65.11 to 72.0 % by weight, wherein the content of silicon dioxide SiO2 is 65.1 to 70.0 % by weight and the content of zirconium oxide ZrO2 is 0.01 to 2.0 % by weight,
- the content of sodium oxide Na2O is 8.0 to 11.0 % by weight,
- the content of potassium oxide K2O is 7.5 to 9.8 % by weight,
- the content of calcium oxide CaO is 8.6 to 11.0 % by weight,
- the content of zinc oxide ZnO is 2.0 to 3.2 % by weight, and
- the content of aluminium oxide AI2O3 is 0.2 to 1.5 % by weight.
The nature of the invention relates also to crystal glass with the content of silicon dioxide SiO2 of 66.0 to 70.0 % by weight and the content of zirconium oxide ZrO2 of 0.5 to 2.0 % by weight.
It has also been found that it is preferred, if the crystal glass in question contains in the final product metals with variable valency, besides zirconium oxide - -
and antimony oxides, in an amount of at most 0.2 % by weight, more preferably 0.1 % by weight.
Further subject matter of the invention consists in a method of preparation of crystal glass free of lead, barium, niobium and of their compounds, having a refractive index of at least 1.5200, density of at least 2450 kg.m'3, for which it holds that the sum of contents of zinc oxide ZnO and potassium oxide K2O is at least 10 % by weight, from starting raw material, like silica dust and/or silica sand, potassium hydrogencarbonate, limestone, sodium sulfate, sodium nitrate, aluminium oxide and/or hydroxide, zinc oxide, sodium carbonate, zirconium oxide and/or zirconium silicate and assistant substances, by modification, thorough homogenization, heating, melting and refining the glass batch, its forming and gradual controlled cooling. The nature of this method consists in that the starting raw materials or raw materials and assistant substances are, before their processing, refined to the content of undesirable harmful admixtures, like iron oxide Fβ2θ3 in silicon(IV) oxide and/or silica sand, of less than 0.02 % by weight, in limestone to less than 0.035 % by weight, in sodium carbonate to less than 0.002 % by weight, in zirconium(IV) silicate to less than 0.09 % by weight and in aluminium oxide and/or hydroxide to less than 0.01 % by weight, as well as of cadmium(ll) oxide to less than 0.02 % by weight, manganese oxides to less than 0.001 % by weight, copper oxides to less than 0.007 % by weight, lead oxides to less than 0.06 % by weight in zinc oxide ZnO, by treating it with nitric acid HNO3 and/or hydrochloric acid HCI in any mutual ratio.
The starting raw materials and/or assistant substances are refined to the total content of admixtures, impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum 0.8 % by weight, preferably to the content of impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum 0.2 % by weight, more preferably to the total content of admixtures, impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum 0.7 % by weight, and to the content of impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum 0.1 % by weight. It has been found that it is advantageous, if pure nitric acid HNO3 having concentration of 20 to 65 % by weight and hydrochloric acid HCI having concentration of 5 to 35 % by weight are used for the refining of starting materials and/or assistance substances, and if the refinement is performed at a temperature of 10 to 50 0C. It is even more preferred, if the refinement is performed under co- action of microwave radiation.
When preparing the glass melt for crystal glass, it is very important to provide for the purity of the applied assistant substances and to prevent by technical means its contamination, especially by oxides of metals with variable valency, either at its refining by refining mixtures or at de-colorization also by de¬ coloring agents.
An advantage of the crystal glass according to the present invention is the fact that even though it contains neither lead oxide nor barium oxide, which considerably increase the glass density and refractive index, it has excellent physico-chemical, aesthetic, ecological, chemical and hygienic properties and, simultaneously, it meets the condition of classification of the glass into the group of crystalline: the sum of contents of zinc oxide ZnO, barium oxide BaO, lead oxide PbO and potassium oxide K2O is at least 10 % by weight. Besides, it meets the requirements of high refractive index (at least 1.5200) and density (at least 2450 kg.m'3). A further important advantage is its relatively high chemical resistance (or stability), expressed by the parameter of water resistance. This parameter classifies it into the hydrolytic class III, wherein it holds: the lower hydrolytic class, the higher chemical resistance of glass.
A further unquestionable advantage is that the crystal glass according to the present invention contains low number - only seven - selected components able to form crystal glass of high quality. It is just their well-balanced content, taking into account important influence of each of the components, which participates to a large degree on the properties of the above crystal glass.
Silicon oxide SiO2 decreases density, thermal conductivity and partially also refractive index, but it increases melt viscosity of the glass batch, chemical resistance and mechanical strength of crystal glass.
Sodium oxide Na2O decreases the melt viscosity, but also chemical resistance, thermal conductivity, density, internal bonds, strength and hardness of glass. Also potassium oxide K2O influences the properties in a similar way, however, at lower temperatures (about 740 0C) it decreases the melt viscosity, but on the contrary, at higher temperatures (about 1300 0C) it increases viscosity. It decreases also surface tension, liquidus temperature (temperature of the equilibrium between the liquid and crystalline substance), ability to crystallize and density and refractive index.
On the contrary, calcium oxide CaO increases the glass strength and hardness, as well as chemical resistance, stability, density, refractive index and bond strength, but simultaneously it decreases dielectric loss of the crystal glass, its thermal and electric conductivity.
Aluminium oxide AI2O3 (up to 2 %) improves conditions of melting of glass components, increases viscosity of the melt and chemical resistance of the glass, as well as modulus of elasticity, scratch hardness, surface tension and resistance against temperature changes of the crystal glass.
Zinc oxide ZnO (up to 4 %) increases glass density and viscosity, increases chemical resistance of glass and moderately improves the glass hardness.
A further unquestionable advantage of the glass according to the present invention is the fact that possibly present, although nontoxic, but anyway only subsidiary admixtures in the glass, like oxides of titanium, magnesium, antimony, but also unambiguously undesirable admixtures, like oxides of iron, manganese, copper, or even toxic elements, are eliminated to such an amount which has no influence on the decisive properties of the glass.
It has been just the utilization of the above, but also of further new effects of individual components of the glass, which made possible to minimize their number in the crystal glass according to the present invention to a combination of seven selected of them, which have not only made possible to obtain aesthetic crystal glass having a refractive index of at least 1.5200 and a density of at least 2450 kg.m"3, free of lead, barium, niobium and of their compounds, but they have also removed the necessity of technically demanding "fortification" by niobium oxide ND2O5, tantalum oxide Ta2θs (niobium(V) oxide in combination with tantalum(V) oxide acts as conditionally glass-forming oxide), hafnium oxide HfO2, neodymium oxide Nd2θ3, or possibly by other oxides of transitional metals. The required properties of glass have been achieved by a suitable combination of ZrO2 with other components. ~ O ~
In this way, the surprisingly effective combination of amounts and quality of starting raw materials in the batch composition makes it possible to produce more easily crystal glass of high quality, which meets not only the required aesthetic, physical and chemical properties, but unequivocally also hygienically and ecologically faultless utility properties. Quality of the glass according to the present invention, prepared from technical raw materials (when observing permissible limits for admixtures), is surprisingly high - it is very close to properties of glass prepared from raw materials of high purity.
Nevertheless, it is necessary to minimize to highest possible degree undesirable admixtures, like compounds of iron, manganese, copper, arsenic and further transitional elements, especially oxides of metals with variable valency, both in starting raw materials and in technological stages, including refining and de-colorization, to prevent contamination of the melt.
Lowering the number of compounds of selected elements (glass components) to seven, as well as effective refinement of starting materials or assistant substances by the method according to the present invention, which lowers the amount of subsidiary admixtures, considerably simplify the process of glass preparation. For example, it is not necessary to add usual modifying additives, like boron oxide B2O3 and lithium oxide U2O, which improve melting temperature and liquidus temperature.
Although permissible, but not necessary admixtures in crystal glass may be formed by controlled amounts mainly of magnesium oxide MgO with antimony oxide Sb2θ3 and possibly by their sulfates. There may still be tolerated trace amounts to micro-amounts of compounds, especially of oxides of lithium, titanium, iron, manganese and copper, and possibly of further nontoxic oxides, coming from less effectively refined starting raw materials.
It is obvious that one must take care of highest possible purity of starting raw materials, especially as undesirable admixtures of compounds of metals with variable valency are concerned. It has been found that permissible amounts of ferric oxide Fe2O3 should be in silica sand under 0.02 % by weight, in limestone under 0.035 % by weight, in sodium carbonate under 0.002 % by weight, in zirconium silicate under 0.09 % by weight, and in aluminium oxide or hydroxide under 0.1 % by weight, and neither in zinc oxide the content of oxides of undesirable metals may exceed 0.1 % by weight. In the case of higher concentrations, there is necessary treatment to the above values by the method according to the present invention, especially refinement from oxides of undesirable metals by extraction with acids, especially diluted nitric acid having concentration of 20 to 65 % by weight and/or hydrochloric acid having concentration of 5 to 35 % by weight, at a temperature of 10 to 50 0C, preferably under co-action of microwave radiation to accelerate selective extraction.
Further more detailed data on composition of the crystal glass and formulation of its components, methods of its preparation, as well as on the achieved high quality of the glass when observing the limits for the abundance of its components, both in comparison with a glass prepared from raw materials of high purity on one hand and with a glass prepared from technical raw materials for industrial use on the other hand, will be apparent from the examples. Nevertheless, the examples serve merely as illustrative examples and do not restrict the invention scope as given in the claims in any way.
Examples of invention embodiments
Example 1 (from raw materials of high purity)
Starting chemicals of high purity - raw materials of nearly 100 % purity (nearly p. a. purity), which are not used at an industrial scale because of high costs
- have been used for crystal glass preparation. The amounts of admixtures are low and they are (in % by weight):
- in sodium carbonate Na2CO3 the total nitrogen: 0.0005; sulfate (as sulfur) 0.003; chloride 0.0005; phosphates with silicates 0.002; calcium 0.002; cadmium 0.0005; cobalt 0.0005; copper 0.0005; iron 0.0002; potassium 0.005; nickel 0.0005; lead 0.0005; aluminium 0.0005; manganese 0.0005; chromium 0.0005 and magnesium 0.0002;
- in potassium carbonate K2CO3 the total nitrogen 0.001 ; sulfate (as sulfur) 0.004; chloride 0.003; phosphates 0.001 ; silicates 0.005; calcium 0.001 ; cadmium 0.005; cobalt 0.005; copper 0.005; iron 0.005; silver 0.0005; arsenic 0.00005; barium 0.0005; aluminium 0.005; bismuth 0.0005; magnesium 0.005 and lithium 0.005; - in calcium carbonate CaCU3 chloride 0.03; sulfate (as sulfur) 0.05; cadmium 0.005; cobalt 0.005; copper 0.005; iron 0.005; potassium 0.01 ; sodium 0.01 ; nickel 0.005; lead 0.005 and zinc 0.005;
- in zinc oxide ZnO chloride 0.005; sulfate (as sulfur) 0.005; calcium 0.005; cadmium 0.005; cobalt 0.005; copper 0.005; iron 0.005; potassium 0.01 ; sodium 0.01 ; nickel 0.005 and lead 0.005;
- in aluminium oxide AI2O3 chloride 0.005; sulfate (as sulfur) 0.1; calcium 0.05; cadmium 0.005; cobalt 0.005; copper 0.005; iron 0.01 ; potassium 0.01; sodium 0.1 ; nickel 0.005, lead 0.005 and zinc 0.005;
- in zirconium oxide ZrO2 hafnium(IV) oxide 0.01 and silicon(IV) oxide 0.01 ;
- in silicon(IV) oxide sulfate (as sulfur) 0.005; calcium 0.02; cadmium 0.005; cobalt 0.005; copper 0.005; iron 0.02; potassium 0.05; sodium 0.01 ; nickel 0.005, lead 0.005 and zinc 0.005.
All the chemicals were from renowned firms (Fluka, Aldrich, Merck), and they were commercially available chemicals of high purity, designated as of p. a. purity.
A laboratory homogenizer was charged with 68.5 g of silicon dioxide (silica sand); 12.1 g of potassium carbonate; 17.6 g of sodium carbonate; 16.7 g of limestone; 2.0 g of zinc oxide; 0.05 g of aluminium oxide and 2.0 g of zirconium oxide.
After thorough homogenization the whole content was transferred into a fusion platinum (Pt) crucible (containing 20 % by weight of Rh) and this was placed into a furnace at room temperature. The crucible content was gradually heated in the furnace to a temperature of 1200 to 1350 0C, when the crucible content was stirred around. The furnace was further heated up to the melting temperature (1500 to 1600 0C). After the melting was finished, the clear melt was poured onto a metal plate and tempered in a muffle furnace at a temperature of 550 to 600 0C for 1 to 3 hours. In the turned off furnace the glass was left to cool down to room temperature.
The obtained crystal glass was analyzed using common chemical methods. The content of metals in it was as follows (in % by weight): 10.26 Na2O; 8.16 K2O; 9.08 CaO; 1.97 ZnO; 1.93 ZrO2; 0.06 AI2O3 and 68.54 SiO2.
There were further determined: _
refractive index at a temperature of 20 0C, nD = 1.5291 ; density at 20 0C p = 2542.9 kg.m'3; the sum of contents of the oxides ZnO + PbO + BaO + K2O = 10.13 % by weight; hydrolytic class = III; mean relative molecular weight M(r) = 62.76 g.mol"1; mole refraction R(m) = 7.60 cm3.mol"1; transformation temperature T9 = 540.4 0C; linear coefficient of thermal expansion of the glass in the temperature interval of 350 to 450 0C α(g) = 1.12.10"5 0C"1; linear coefficient of thermal expansion of metastable melt in the temperature interval of 560 to 600 0C a(\) = 3.82.10"5 0C"1; points of viscosity curve: at η = 102 dPa.s t = 1413 0C; at η = 103 dPa.s t = 1181 0C; at η = 104 dPa.s t = 1026 0C; at η = 105 dPa.s t = 914 0C; at η = 106 dPa.s t = 830 0C; at η = 107 dPa.s t = 762 0C; at η = 108 dPa.s t = 710 0C; at η = 109 dPa.s t = 668 0C; at η = 1010 dPa.s t = 631 0C; at η = 1011 dPa.s t = 602 0C; at η = 1012 dPa.s t = 575 0C; at η = 1013 dPa.s t = 555 0C and at η = 1014 dPa.s t = 531 0C.
From the results, there are apparent not only high refractive index and high density of the crystal glass, but also good chemical resistance (hydrolytic class III - glass, which is suitable also for dishwashers).
Example 2 (comparative, according to the known state of the art)
In preparation of crystal glass, components and amounts according to crystal glasses, cited also in the prior art of the description in this application have been used.
So multi-component crystal lead-free glass consisting of (in % by weight): 71.0 % of SiO2, 11.0 % of K2O, 15.5 % of Na2O, 2.0 % of CaO, 0.001 % of AI2O3, 0.001 % of TiO2, 0.01 % of ZnO, 0.5 % of MgO, 0.01 % of B2O3, 0.01 % of Li2O, 0.001 % of Sb2O3, 0.001 % of SrO, 0.008 % of fluorides (F) and 0.0008 % of sulfates (SO4 2"), exhibited high transparency, hardness and strength, but the refractive index only of 1.5073.
A similar glass, except that instead of 0.001 % by weight of Sb2O3 it contained 0.001 % by weight Of As2O3, had the refractive index only of 1.5075.
Similar situation occurred with a further multi-component crystal glass, prepared with "protected" abundance of components, namely (in % by weight): 72.0 % of SiO2, 10.0 % of K2O, 16.0 % of Na2O, 2.0 % of CaO, 0.05 % of AI2O3, 0.001 % of TiO2, 0.05 % of ZnO, 0.05 % of ZrO2, 0.05 % of Sb2O3, 0.001 % of - -
HfO2, 0.005 % of Fe2O3, 0.001 % of sulfates (SO4 2") and chlorides (Cl"). This glass had, besides its valuable physico-chemical and aesthetic properties, the value of the refractive index only of 1.5053.
Despite the fact that the crystal glasses contained 14 or 13 defined metal oxides in concentrations protected by patents, the refractive index nD of none of them has achieved the declared and required value of 1.52.
Example 3 (comparative)
Unlike the multi-component crystal glasses according to Example 2, this lead-free glass had lower number of components. As their mutual influence has not been respected, final crystal glass did not meet the required (but otherwise declared) physical properties. For example, crystal glass within the range of "protected" limits of concentrations and number of components, containing 74.3 % by weight of SiO2, 10.0 % by weight of K2O, 12.0 % by weight of Na2O, 3.0 % by weight of CaO, 0.4 % by weight of AI2O3, 0.3 % by weight of TiO2, has achieved the value of the refractive index only of 1.5092.
It is obvious that neither this crystal glass achieves the declared and required refractive index of 1.52. From the above it follows that some of the limits declared in the documents of the state of the art are not real and they do not make possible to obtain glass having declared properties.
Examples 4 to 8 (from raw materials of high purity)
The procedure was similar to that of Example 1 , thus the crystal glass was prepared from starting raw materials of high purity (p. a.).
The charges used in Examples 1 and 4 to 8 are summarized in Table 1.
Table 1
Figure imgf000013_0001
- -
Figure imgf000014_0001
Some achieved physico-chemical parameters of representative crystal glasses are given in Table 2. All crystal glasses prepared from the starting raw materials of high purity (p.a.) have, similarly as the glass prepared according to Example 1 , high refractive index, density and chemical resistance.
Table 2
Figure imgf000014_0002
* After 24 hours of sample tempering in the temperature range of 880 to 1050 0C no crystals have been observed. From the above one can conclude that the crystallization rate of the samples is low.
Examples 9 to 18 - -
The procedure was similar to that of Example 1 , except that contrary to Example 1 technically or commercially available starting raw materials, or raw materials refined by the methods given in Examples 19 to 21 were used in the batches.
So in Examples 9 and 16, sand refined by the procedure given in Example 19, having the composition (in % by weight): 99.8 of SiO2; 0.09 or 0.011 to 0.006 of Fe2O3; 0.08 of AI2O3 and 0.02 of TiO2, was used. In the rest of the Examples it had the composition (in % by weight): 99.7 of SiO2, 0.012 of Fe2O3; 0.15 Of AI2O3 and 0.04 of TiO2.
In Examples 9 and 16 also aluminium hydroxide was used which had been refined by the procedure according to Example 20 to the content (in % by weight): 99.9 of AI(OH)3; 0.005 or 0.001 of Fe2O3 and 0.112 or 0.011 Of Na2O, respectively. In the rest of Examples technical AI(OH)3 was used with the composition (in % by weight): 99.21 Of AI(OH)3; 0.118 of Fe2O3; 0.004 of SiO2 and 0.668 of Na2O.
In Examples 12 and 13 commercially available zirconium silicate ZrSiO4 was used which had, after refining by the procedure given in Example 21 , the following composition (in % by weight): 66.1 of ZrO2; 33.6 of SiO2; 0.05 of Fe2O3; 0.10 Of TiO2; 0.06 Of Y2O3; 0.08 of HfO2.
In the rest of Examples technical zirconium silicate ZrSiO4 was used having the composition (in % by weight): 67.0 of ZrO2; 32.3 of SiO2; 0.14 of Fe2O3; 0.21 of TiO2; 0.14 Of Y2O3 and 0.21 of HfO2.
In Examples 9 to 18, there were in the batches further used: potassium hydrogencarbonate KHCO3 having the composition (in % by weight): 94.8 of KHCO3; 5.0 of K2CO3 and 0.1 of KCI; limestone with the composition (in % by weight): 99.15 of CaCO3; 0.94 of MgCO3; 0.03 of SiO2; 0.06 of H2O; 0.029 of Fe2O3; 0.004 of MnO and 0.03 of AI2O3; sodium carbonate with the composition (in % by weight): 99.8 of Na2CO3; 0.13 of NaCI; 0.0014 of Fe2O3; 0.02 of Na2SO4; 0.01 of insoluble part in H2O; less than 150 ppm of CaO and less than 120 ppm of MgO; also zinc oxide ZnO containing (in % by weight): 99.53 of ZnO; 0.054 of PbO; 0.01 of CdO; 0.0052 of CuO and 0.0001 of Mn.
Composition of the batches using the above, thus industrially available raw materials, for preparation of crystal glass according to Examples 9 to 18 is given in Table 3. - -
Table 3
Figure imgf000016_0001
Chemical composition (in % by weight, determined by chemical and physico-chemical methods) of crystal glasses according to Examples 9 to 18 is given in Table 4.
Table 4
Figure imgf000016_0002
It is obvious that while at a low content of zirconium(IV) oxide and high content of silicon(IV) oxide the meltableness of the glass batch is better, the values of the refractive index exceed the minimal specified value of the refractive index only by a very small part. In Example 16 it is other way round: though melting is more complicated (necessity to reach higher melting temperature), . - _
values of the refractive index, density and chemical resistance significantly exceed the defined limits.
In Table 5, there are summarized selected physical, chemical, as well as some aesthetic and mechanical parameters of the prepared crystal glasses having composition (in % by weight) according to Table 4.
It follows from the table that all melted glasses of Examples 9 to 18, though prepared from technical raw materials, but with observing maximum values for the content of oxides of the seven selected metals, as well as with observing maximum values for the subsidiary admixtures, have the refractive index over 1.5200, density over 2450 kg.m"3 and also good chemical resistance.
Table 5
Figure imgf000018_0001
* After 24 hours of sample tempering in the temperature range of 880 to 1050 0C no crystals have been observed. From the above one can conclude that the crystallization rate of the samples is low.
Example 19
Excavated silica sand having the grain size of 0.3 to 1.1 mm contained 92.3 % by weight of silicon dioxide SiO2; 7.22 % by weight of water H2O; 0.25 % by weight of aluminium oxide AI2O3; 0.14 of iron(lll) oxide or hydroxide Fe2O3/Fe(OH)3 and 0.09 % by weight of titanium oxide TiO2.
After sieving a sand fraction with the grain size of 0.3 to 0.5 mm was separated. 100 g of this sand were poured in 500 g of aqueous solution of hydrochloric acid with the concentration of 6 % by weight and under occasional stirring extraction was performed at a temperature of 30 ± 2 0C for 3 hours. After separation of the sand by filtration, drying and careful firing the content of iron(lll) oxide or hydroxide was 0.09 % by weight.
Under the same conditions, but using aqueous solution of hydrochloric acid of p. a. purity with the concentration of 31.5 % by weight, refined sand was obtained having the content of 0.011 % by weight of iron(lll) oxide or hydroxide; using a mixture of 20 % by weight of hydrochloric acid with 11.5 % by weight of nitric acid instead of the aqueous solution of hydrochloric acid alone, refined sand was obtained, containing only 0.006 % by weight of iron(lll) oxide, 0.08 % by weight of aluminium oxide and 0.02 % by weight of titanium(IV) oxide.
If using microwave radiation for heating, the same results were achieved in a considerably shorter time (refining only 0.3 to 0.5 hours instead of 3 hours).
The above given results confirm that the method of preparation with refinement according to the present invention makes it possible to utilize technical available raw materials (sand) for preparing crystal glass of high quality with the required properties.
Example 20
Available unrefined powder (grain size of 0.1 to 0.3 mm) aluminium oxide contained 99.21 % by weight Of AI(OH)3, 0.004 % by weight of silicon dioxide SiO2, 0.668 % by weight of sodium oxide Na2O and 0.118 % by weight of ferric oxide Fe2O3. The refinement, the aim of which was to remove especially iron(lll) hydroxide and oxide, was performed with diluted aqueous solution of hydrochloric acid with the concentration of 10 % by weight, in an amount of 500 mi to 100 g of aluminium hydroxide, under stirring at room temperature for 2 hours. After extraction, filtering aluminium hydroxide off, its drying, burning at a temperature of 400 to 420 0C for 0.5 hour and subsequent cooling, the content of ferric oxide has decreased to 0.05 % by weight and the content of sodium oxide to 0.112 % by weight.
By increasing the concentration of hydrochloric acid to 25 % by weight, otherwise under the same conditions, the content of ferric oxide in aluminium oxide decreased to 0.001 % by weight and the content of sodium oxide to 0.011 % by weight.
Similar effect, but already within 40 minutes of extraction, was achieved at a temperature of 25 to 28 0C under the action of microwave radiation.
At a temperature of 40 to 45 0C the same refining effect was achieved within 15 minutes and at a temperature of 45 to 50 0C already within 10 min.
It has been confirmed that refinement by the method according to the present invention makes possible to replace aluminium oxide by common aluminium hydroxide without negative influence on the required quality of crystal glass.
Example 21
Technical zirconium(IV) silicate containing 67.3 % by weight of zirconium(IV) silicate, 32.3 % by weight of silicon dioxide, 0.14 % by weight of iron(lll) oxide, 0.21 % by weight of titanium(IV) oxide, 0.14 % by weight of yttrium(lll) oxide and 0.21 % by weight of hafnium(IV) oxide was subjected to refinement.
The refinement of powder zirconium(IV) silicate was performed by extraction with aqueous solution of nitric acid with the concentration of 63.5 % by weight. 50 g of the zirconium silicate powder were treated under stirring and tempering at a temperature of 10 to 15 0C with 100 g of nitric acid solution for 30 min. After drying and burning, the content of ferric oxide was 0.12 % by weight. After adding another 5 % by weight of hydrochloric acid to the aqueous solution of nitric acid, otherwise under the same conditions, the content of ferric oxide decreased to 0.05 % by weight, titanium(IV) oxide to 0.10 % by weight, yttrium(lll) oxide to 0.06 % by weight and hafnium(IV) oxide to 0.08 % by weight. The content of zirconium(IV) oxide was 66.1 % by weight and of silicon dioxide 33.6 % by weight - if additionally microwave radiation is used, the same refinement effect is achieved within 10 minutes already.
It has been proved that the source of zirconium(IV) oxide as a crystal glass component need not be a compound of high purity, but in the case of the production method according to the present invention, with utilizing chemical refinement, it may be commonly available zirconium(IV) silicate.
Industrial applicability
Crystal glass according to the present invention is designated for manual and machine production of glass rods, plates, illuminating glasses, lustre lamp or even the whole lustres, intermediate products for artificial jewellery and, generally, of a wide assortment of utility glassware products. It can be utilized both in glass industry, and in production of special, especially of aesthetically and hygienically demanding glass, further in artistic and hand-made manufacture. The refinement may be utilized for treatment of starting glass raw materials, both ore and non- metallic raw materials.

Claims

P AT E N T C L A I M S
1. Crystal glass, free of lead, barium, niobium and of their compounds, having a refractive index of at least 1.5200, density of at least 2450 kg.m"3, for which it holds that the sum of contents of zinc oxide ZnO and potassium oxide K2O is at least 10 % by weight, based on ecologically acceptable compounds of elements of the I .A, 11. A, IV.A, II. B to IV.B subgroups of the periodic element system, ch a racterized i n th at it, as a whole, contains seven selected elements, mainly in the form of oxides, namely of silicon, sodium, potassium, calcium, aluminium, zirconium and zinc, in an amount of at least 99.2 % by weight, where
- the sum of contents of silicon dioxide Siθ2 and zirconium oxide Zrθ2 as the networking components in crystal glass, is 65.11 to 74.0 % by weight, wherein the content of silicon dioxide SiO2 is 65.10 to 71.90 % by weight and the content of zirconium oxide ZrO2 is 0.01 to 2.1 % by weight,
- the content of sodium oxide Na2O is 8.0 to 14.0 % by weight,
- the content of potassium oxide K2O is 6.5 to 9.9 % by weight,
- the content of calcium oxide CaO is 8.6 to 13.0 % by weight,
- the content of zinc oxide ZnO is 0.5 to 3.6 % by weight, and
- the content of aluminium oxide AI2O3 is 0.01 to 3.0 % by weight, while it may further contain permissible admixtures, like magnesium oxide MgO together with antimony oxide Sb2O3 or with their sulfates, in an amount of at most 0.6 % by weight, and the rest to 100 % by weight impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials.
2. Crystal glass according to claim 1, characterized in that the content of silicon, sodium, potassium, calcium, aluminium, zirconium and zinc, especially in the form of oxides, is at least 99.3 % by weight.
3. Crystal glass according to claim 1 or2, c h a ra cte rize d i n that - the sum of contents of silicon dioxide SiO2 and zirconium oxide Zrθ2 as the networking components in crystal glass, is 65.11 to 72.0 % by weight, wherein the content of silicon dioxide SiO2 is 65.10 to 70.00 % by weight and the content of zirconium oxide ZrO2 is 0.01 to 2.0 % by weight,
- the content of sodium oxide Na2O is 9.9 to 12.5 % by weight,
- the content of potassium oxide K2O is 7.6 to 9.0 % by weight,
- the content of calcium oxide CaO is 8.6 to 11.5 % by weight,
- the content of zinc oxide ZnO is 1.0 to 3.6 % by weight, and
- the content of aluminium oxide AI2O3 is 0.01 to 3.0 % by weight.
4. Crystal glass according to claim 1 or2, c h a ra cte rize d i n that
- the sum of contents of silicon dioxide SiO2 and zirconium oxide ZrO2 is 65.11 to 72.0 % by weight, wherein the content of silicon dioxide SiO2 is 65.1 to 70.0 % by weight and the content of zirconium oxide ZrO2 is 0.01 to 2.0 % by weight,
- the content of sodium oxide Na2O is 8.0 to 11.0 % by weight,
- the content of potassium oxide K2O is 7.5 to 9.8 % by weight,
- the content of calcium oxide CaO is 8.6 to 11.0 % by weight,
- the content of zinc oxide ZnO is 2.0 to 3.2 % by weight, and
- the content of aluminium oxide AI2O3 is 0.2 to 1.5 % by weight.
5. Crystal glass according to claim 1,2, 3 or 4, characterized in t h at the content of silicon dioxide SiO2 is 66.0 to 70.0 % by weight and the content of zirconium oxide ZrO2 is 0.5 to 2.0 % by weight.
6. Crystal glass according to claims 1 to5, cha racterized i n th at the content of metals with variable valency, besides zirconium(IV) oxide and antimony oxides, in the final crystal glass product is at most 0.2 % by weight.
7. Crystal glass according to claims 2 to 5, characterized in th at the content of metals with variable valency, besides zirconium(IV) oxide and antimony oxides, in the final crystal glass product is at most 0.1 % by weight. _
8. Method of preparation of crystal glass, free of lead, barium, niobium and of their compounds, having a refractive index of at least 1.5200, density of at least 2450 kg.m"3, for which it holds that the sum of contents of zinc oxide ZnO and potassium oxide K2O is at least 10 % by weight, according to any of claims 1 to 7, from starting raw materials, like silica dust and/or silica sand, potassium hydrogencarbonate, limestone, sodium sulfate, sodium nitrate, aluminium(lll) oxide and/or hydroxide, zinc oxide, sodium carbonate, zirconium(IV) oxide and/or zirconium silicate and assistant substances by modification, thorough homogenization, heating, melting and refining the glass batch, its forming and gradual controlled cooling, characterized in that the starting raw materials are, before processing them to glass batch, refined to the content of undesirable harmful admixtures, like ferric oxide Fβ2θ3 in silicon(IV) oxide and/or silica sand to less than 0.02 % by weight, in limestone to less than 0.035 % by weight, in sodium carbonate to less than 0.002 % by weight, in zirconium(IV) silicate to less than 0.09 % by weight and in aluminium(lll) oxide and/or hydroxide to less than 0.01 % by weight, as well as of cadmium(ll) oxide to less than 0.02 % by weight, manganese oxides to less than 0.001 % by weight, copper oxides to less than 0.007 % by weight, lead oxides to less than 0.06 % by weight in zinc oxide ZnO, by treating them with nitric acid HNO3 and/or hydrochloric acid HCI.
9. Method of preparation according to claim 8, characterized in t h a t the starting raw materials and/or assistant substances are refined to a content of admixtures, impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum of 0.8 % by weight.
10. Method of preparation according to claim 8 or 9, characterized in that the starting raw materials and/or assistant substances are refined to a content of admixtures, impurities and metal compounds, including metal oxides with variable valency, coming from the starting raw materials, of maximum of 0.2 % by weight.
11. Method of preparation according to claim 8, 9 or 10, characteri¬ zed in t h a t the starting materials and/or assistance substances are refined by treatment with pure nitric acid HNO3 having concentration of 20 to 65 % by weight and/or hydrochloric acid HCI having concentration of 5 to 35 % by weight.
12. Method of preparation according to claim 8, 9, 10 or 11, characte¬ rize d i n th at the starting materials and/or assistance substances are refined at a temperature of 10 to 500C.
13. Method of preparation according to claim 12, c h a ra cte ri zed i n th at the starting materials and/or assistance substances are refined at a temperature of 10 to 500C under co-action of microwave radiation.
PCT/SK2005/000021 2004-10-19 2005-10-19 Crystal glass free of lead, barium, niobium and of their compounds, and method of its preparation WO2006043909A1 (en)

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WO2012156707A1 (en) * 2011-05-13 2012-11-22 Nazeing Glass Works Limited Improvements in crystal glass
CZ303762B6 (en) * 2012-01-30 2013-04-24 Vysoká skola chemicko - technologická v Praze Optical sodium-aluminiumsilicate glass for photonic components
CN103553330A (en) * 2008-05-02 2014-02-05 东洋佐佐木玻璃株式会社 Glass object
US10364176B1 (en) 2016-10-03 2019-07-30 Owens-Brockway Glass Container Inc. Glass precursor gel and methods to treat with microwave energy
US10427970B1 (en) 2016-10-03 2019-10-01 Owens-Brockway Glass Container Inc. Glass coatings and methods to deposit same
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FR2921357A1 (en) * 2007-09-21 2009-03-27 Saint Gobain SILICO-SODO-CALCIUM GLASS COMPOSITION
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CN103553330A (en) * 2008-05-02 2014-02-05 东洋佐佐木玻璃株式会社 Glass object
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WO2012156707A1 (en) * 2011-05-13 2012-11-22 Nazeing Glass Works Limited Improvements in crystal glass
CZ303762B6 (en) * 2012-01-30 2013-04-24 Vysoká skola chemicko - technologická v Praze Optical sodium-aluminiumsilicate glass for photonic components
US10364176B1 (en) 2016-10-03 2019-07-30 Owens-Brockway Glass Container Inc. Glass precursor gel and methods to treat with microwave energy
US10427970B1 (en) 2016-10-03 2019-10-01 Owens-Brockway Glass Container Inc. Glass coatings and methods to deposit same
US10479717B1 (en) 2016-10-03 2019-11-19 Owens-Brockway Glass Container Inc. Glass foam
CN112624608A (en) * 2020-12-18 2021-04-09 中国建筑材料科学研究总院有限公司 Borosilicate glass curing substrate and preparation method and application thereof

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