WO2011060793A1 - Vitrocéramique aux propriétés de surface améliorées - Google Patents

Vitrocéramique aux propriétés de surface améliorées Download PDF

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Publication number
WO2011060793A1
WO2011060793A1 PCT/DK2010/050314 DK2010050314W WO2011060793A1 WO 2011060793 A1 WO2011060793 A1 WO 2011060793A1 DK 2010050314 W DK2010050314 W DK 2010050314W WO 2011060793 A1 WO2011060793 A1 WO 2011060793A1
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Prior art keywords
glass ceramic
ceramic article
surface region
glass
network
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PCT/DK2010/050314
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English (en)
Inventor
Yuanzheng Yue
Morten Mattrup SMEDSKJÆR
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Aalborg Universitet
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Publication of WO2011060793A1 publication Critical patent/WO2011060793A1/fr

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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
    • C03C23/00—Other surface treatment of glass not in the form of fibres or filaments
    • C03C23/007—Other surface treatment of glass not in the form of fibres or filaments by thermal treatment
    • 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
    • C03C2218/00—Methods for coating glass
    • C03C2218/30—Aspects of methods for coating glass not covered above
    • C03C2218/35—Exuding

Definitions

  • the present invention relates to a glass ceramic article, such as a glass ceramic cook top, with a modified surface region.
  • the modified surface has, among other advantageous properties, an improved chemical durability, an increased hardness, and/or an increased thermal stability, such as thermal shock resistance.
  • the present invention relates to a process for modifying a surface region of a glass ceramic article.
  • the patent application US 3 779 856 discloses a method for preparing glass ceramics of high strength and good thermal shock resistance.
  • the process involves the reduction of a nucleating agent in order to create a high compression stress layer on the surface.
  • the parent glass contains a nucleating agent which can have its valency changed, and such changed valency state is the more effective state for nucleating the glass.
  • the parent glass is subjected to a nucleating temperature while held in a reducing atmosphere for a time sufficient for the nucleation to be substantially complete.
  • the reducing atmosphere in contact with the surface of the glass reduces the valency of the nucleating agent at and just below the surface of the glass resulting in an increased rate of nucleation along that portion of the glass where such reduced nucleating agent is present.
  • the degree of crystallization is greater at the surface than in the interior of the article. This differential crystallization produces a compressive stress layer on the glass ceramic surface.
  • the patent application GB 2 206 878 discloses a process for manufacturing a pyrolytically coated sheet glass product combining a dealkalising (i.e., sodium removing) treatment with a pyrolytic coating treatment to give improved mechanical and chemical stability of the coating.
  • the dealkalising process is achieved by subjecting the glass to an acidic atmosphere at a temperature of 200- 350 °C. Only glasses and not glass-ceramics are considered.
  • the patent application FR 2 696 443 discloses a process for producing a glass surface depleted in alkali and alkaline earth ions. Especially the presence of sodium ions in the surface region is a problem when using glass as a substrate for conducting and semiconducting layers.
  • the disclosed solution to this problem is to subject the glass to a solution of de-ionized water at 96 °C with electrodes being located on both sides of the glass. Hereby, a surface layer is produced that is depleted in alkali and alkaline earth ions. Only glasses and not glass-ceramics are considered.
  • an object of the present invention relates to improving the surface properties of glass ceramic articles.
  • a glass ceramic comprises a crystalline component and a glass component.
  • Inward diffusion of network modifying cations is not expected to occur in glass ceramics, due to strong trapping (or binding) of the ions in the crystalline component, and because the glass component can be isolated in small islands surrounded and/or blocked by the crystalline component.
  • An aspect of the present invention relates to a glass ceramic article comprising a bulk part and a surface region, said glass ceramic article comprises network- modifying cations (NMC); wherein the concentration of the network-modifying cations in the surface region is lower than in the bulk part, wherein the
  • composition in the surface region of the network-modifying cations is a
  • Still another aspect of the present invention relates to a glass ceramic article comprising a bulk part and a surface region, said glass ceramic article comprises network-modifying cations (NMC); wherein the concentration of the network- modifying cations in the surface region is lower than in the bulk part, wherein the composition in the surface region of the network-modifying cations is a
  • Another aspect of the present invention relates to a process for modifying a surface region of a glass ceramic article, said process comprises the step of heat- treating the glass ceramic article in an atmosphere comprising a reducing gas, said process resulting in an inward diffusion of the network-modifying cations (NMC) into deeper regions of the glass ceramic article, whereby the concentration of the network-modifying cations in the surface region is lowered.
  • NMC network-modifying cations
  • Yet another aspect of the present invention relates to a process for modifying a surface region of a glass ceramic article, said process comprises the step of heat- treating the glass ceramic article in an atmosphere comprising a reducing gas, said process resulting in an inward diffusion of the network-modifying cations (NMC) into deeper regions of the glass ceramic article, whereby the concentration of the network-modifying cations in the surface region is lowered, wherein the selection of crystallization degree is at or below the critical value, the critical value referring to the percentage of said crystallization, above which the depth of the surface region drastically drops.
  • NMC network-modifying cations
  • Figure 1 show a schematic representation of the proposed mechanism of surface modification, for explaining the present invention
  • Figure 2 shows a schematic representation of the quantitative link between the extent of diffusion and the crystallization degree
  • FIG. 3 shows heat flow ( ⁇ ) as a function of temperature (T) for the Diop-Fel glass.
  • the DSC upscan is carried out in argon at a rate of 20 K/min.
  • the enthalpy of crystallization ( ⁇ ) is determined from the DSC upscan.
  • Figure 4 shows SNMS depth profiles of glasses and glass-ceramics heat-treated in H2/N2 (1/99) at 995 K for 2 h.
  • (c) Diop- Fel sample crystallized at 1210 K for 30 min in argon (a 93.3 %).
  • (d) Diop-Fel sample crystallized at 1223 K for 30 min in argon (a 100 %).
  • a g lassy state of matter results if crystallization (nucleation and crystal g rowth) is avoided upon cooling of a melt. Controlled crystallization of a glass can result in a partially crystallized material (glass ceramic) that may possess superior properties useful for various technical applications rang ing from cookware to architectural materials and bone implants.
  • a g lass ceramic can therefore be defined as described by Varshneya (2006) p. 94 : "...when a glass is g iven a particular nucleation treatment to confine the nucleation to within a certain time interval, and such nuclei are allowed to grow till they reach a desired size, then the resulting composite can have valuable thermal and mechanical properties.
  • glass ceramics contain both glassy and crystalline components.
  • the crystalline and glassy components might have the same composition, but they d iffer in structure as crystals have a more ordered structure than g lasses.
  • SRO short-range order
  • LRO long-range order
  • the SRO existing in a g iven glass is ideally identical to that found in the
  • Crystals are defined to be solids with perfect LRO which implies perfect periodicity of the atomic arrangement.
  • LRO perfect periodicity of the atomic arrangement.
  • the atoms in a glass form a continuous random network where SRO exists.
  • the conditions for the formation of a continuous three-dimensional network are (Zachariasen, 1932) : 1) An oxygen atom is linked to not more than two cations.
  • At least three corners in each oxygen polyhedra must be shared in order to form a three-dimensional network.
  • the chemical components in an oxide glass can be divided into different categories according to their role in the structural arrangement of the glass.
  • the oxides are classified according to the fractional ionic character of the cation-anion bond as the anion is oxygen in every case. If the cation forms bonds with oxygen with a fractional ionic character near or below 50%, the cation will act as a network former (Shelby, 2005). All glasses contain at least one network former as it is the primary source of the structure.
  • silicon acts as the network former and it exists as silicon-oxygen tetrahedrai that are linked by bridging oxygen (BO) atoms.
  • BO bridging oxygen
  • the tetrahedrai themselves are very ordered.
  • the required lack of LRO is introduced by variability in the Si-O-Si angle, rotation of adjacent tetrahedrai around the point occupied by the oxygen atom linking the tetrahedrai, and rotation of the tetrahedrai around the line connecting the linking oxygen with one of the silicon atoms (Shelby, 2005).
  • Cations which form highly ionic bonds with oxygen are termed network modifiers as they only serve to modify/interfere with the network structure without becoming part of the primary network (Shelby, 2005).
  • Network modifiers provide non-bridging oxygen (NBO) atoms with a negative charge as they are introduced as oxides and have coordination number > 6.
  • NBO non-bridging oxygen
  • Both alkali (e.g., Na + and K + ) and alkaline earth (e.g., Ca 2+ and Mg 2+ ) ions can act as modifiers. Every alkali ion has one neighbouring NBO, while every alkaline earth ion has two neighbouring NBOs.
  • the strength of the network is dependent on the amount of network formers and modifiers. An increase in the amount of network modifiers results in an increase in the amount of NBOs which decreases the connectivity (or the degree of polymerization) of the composition. This lowers the melting temperature and several other properties of the glass (Shelby, 2005).
  • Diffusion of mobile ions is an important process in glasses since it affects several properties such as electrical conductivity, thermal expansion, dielectric loss, and chemical durability.
  • An important type of diffusion is the so-called inward cationic diffusion. This diffusion occurs due to a reduction of a polyvalent element (e.g., Fe 3+ to Fe 2+ ) at temperatures around T g (glass transition temperature).
  • the glass transition temperature (7 g ) is defined as the onset of change of heat capacity due to the glass transition when heating a glass as defined in Shelby (2005).
  • the reduction drives an inward diffusion (from the surface toward the interior) of network modifying cations, which in turn leads to the formation of a network forming cation-rich layer (e.g. a Si0 2 -rich surface layer).
  • a network forming cation-rich layer e.g. a Si0 2 -rich surface layer.
  • the reduction proceeds via two simultaneous processes: gaseous permeation and outward flux of electron holes. To maintain charge neutrality, the latter process requires an inward diffusion of mobile network modifying cations.
  • the inward diffusion approach can be used to create hard and durable surface due to the formation of a network forming cation-rich layer (e.g. a Si0 2 -rich surface layer).
  • polyvalent element can be found in numerous articles in the field of glass science and technology. In the present context this term will refer to an element which may exist in different redox states. The best direct definition one may find in Pye et al. (2005) p. 28 : “7n this chapter, all those elements will be considered to be polyvalent, which may occur in a glass melt in at least two different oxidation states, even if extreme oxidizing or reducing conditions are necessary.” Surface modification of glass ceramics by inward infusion
  • a glass ceramic comprises a crystalline component and a glass component.
  • Inward diffusion of network modifying cations is not expected to occur in glass ceramics, due to strong trapping (or binding) of the ions in the crystalline component, and because the glass component can be isolated in small islands surrounded and/or blocked by the crystalline component.
  • Figure 1 shows a schematic representation of the proposed mechanism of a surface modification of a silicate glass ceramic article, for explaining the present invention.
  • the figure shows a mechanism according to the present invention for the formation of a network forming cation-rich layer (e.g. a Si0 2 -rich layer) in the surface region 3.
  • the schematic representation is a still shoot of a dynamic process.
  • the Fe 3+ ions are converted to Fe 2+ ions (network modifying cations) and electron holes (h * ).
  • the extremely low partial oxygen pressure in the atmosphere provides a large driving force for the removal of oxygen from the glass ceramic article 1.
  • oxygen anions surrender two electrons to fill the h * and are subsequently released from the free surface 6 via reaction with H 2 to form H 2 0.
  • the diffusion of h * towards the surface is charge-balanced by an inward migration of the divalent cations (including Fe 2+ ). Hence, the inward diffusion is driven by reduction of the high valence to the low valence state of the polyvalent element.
  • the network modifying cations in this example Mg 2+ , Ca 2+ and Fe 2+
  • a network forming cation-rich layer e.g . a Si0 2 -rich surface surface layer
  • one aspect of the invention relates to a process for modifying a surface region of a glass ceramic article, said process comprises the step of heat-treating the glass ceramic article in an atmosphere comprising a reducing gas, said process resulting in an inward diffusion of the network-mod ifying cations (NMC) into deeper regions of the glass ceramic article, whereby the concentration of the network-mod ifying cations in the surface region is lowered .
  • NMC network-mod ifying cations
  • Another aspect of the present invention relates to a process for modifying a surface region of a glass ceramic article, said process comprises the step of heat- treating the glass ceramic article in an atmosphere comprising a reducing gas, said process resulting in an inward d iffusion of the network-mod ifying cations (NMC) into deeper regions of the glass ceramic article, whereby the concentration of the network-mod ifying cations in the surface region is lowered, wherein the selection of crystallization degree is at or below the critical value, the critical value referring to the percentage of said crystallization, above which the depth of the surface region drastically d rops.
  • the deg ree of crystallization of the untreated glass ceramic type is below the critical value, the critical value referring to the percentage of said crystallization, above which the depth of the surface region drastically d rops.
  • composition in the surface region of the network- mod ifying cations is a consequence of above-mentioned inward d iffusion .
  • the network mod ifying cations occupy interstitial positions within the network and thereby create non-bridging oxygens.
  • NMC network modifying cations
  • a network forming cation-rich layer could e.g . be a Si0 2 -rich surface layer, a B 2 0 3 -rich surface layer, a P 2 0 5 -rich surface layer, a Ge0 2 -rich surface layer, or a Te0 2 -rich surface layer, or a mixture of such network forming cation oxides.
  • Another aspect of the invention relates to said process, wherein the selection of crystallization degree and inward diffusion depth is at or around the critical value, the critical value refers to the percentage of said crystallization, above which the depth of the surface region drastically drops.
  • Yet another aspect of the invention relates to said process, wherein the selection of crystallization degree and inward diffusion depth is above the critical value, the critical value refers to the percentage of said crystallization, above which the depth of the surface region drastically drops.
  • Yet another aspect of the invention relates to said process, wherein the reducing gas is a mixture of one or more reducing gasses.
  • Still another aspect of the invention relates to said process, wherein the reducing gas is further mixed with one or more inert gasses.
  • Another aspect of the invention relates to said process, wherein the atmosphere comprises a mixture of nitrogen gas and hydrogen gas.
  • Yet another aspect of the invention relates to said process, wherein the
  • atmosphere comprises a mixture of carbon monoxide gas and carbon dioxide gas.
  • Still another aspect of the invention relates to said process, wherein the atmosphere comprises a mixture of gasses selected from a group consisting of: SbH 3 , AsH 3 , B 2 H 6 , CH 4 , PH 3 , SeH 2 , SiH 4 , SH 2 , SnH 4 , Cl 2 , NO, N 2 0, CO, H 2 , N 2 0 4 , S0 2 , C 2 H 4 , and NH 3 .
  • Another aspect of the invention relates to said process, wherein the reducing gas is substantially impermeable in the untreated glass ceramic.
  • a preferred aspect of the invention relates to said process, wherein the reducing gas is substantially impermeable in the untreated glass ceramic. It could be an advantage, in addition to the increased connectivity of the surface region or layer, to increase the thickness of said surface region to further improve the chemical durability, to increase the hardness, and/or to increase the thermal stability.
  • Yet another aspect of the invention relates to said process, wherein the heat- treatment is performed so as to obtain a thickness of said surface region of at least 100 nm, 200 nm, 400 nm, 500 nm, 600 nm, or 700 nm.
  • a preferred aspect of the invention relates to said process, wherein the heat-treatment is performed so as to obtain a thickness of said surface region of at least 100 nm, 200 nm, 400 nm, 500 nm, 600 nm, 700 nm, 1000 nm, 1500 nm, or 3000 nm.
  • the thickness of the silica-rich layer can be controlled by tuning the temperature and duration of the heat-treatment.
  • Another aspect of the invention relates to said process, wherein the heat- treatment is performed at 0.1-3.0 times the glass transition temperature (T g ) of the original glass in Kelvin.
  • a preferred aspect of the invention relates to said process, wherein the heat-treatment is performed at e.g. 0.1-3.0, 0.5-3.0, 0.6-3.0, 0.7-3.0, 0.8-2.0, or 0.9-2.0 times the glass transition temperature (T g ) of the original glass in Kelvin.
  • Still another aspect of the invention relates to said process, wherein the heat- treatment period is performed for 0.01-36 hours.
  • Another aspect of the invention relates to said process, wherein the heat- treatment is performed in the interval of 0.001-36, 0.01-36, 0.1-36, 0.1-30, 0.1- 24, 0.2-36, 0.2-34, 0.2-20, 0.3-36, 0.3-25, 0.3-18, 0.4-36, 0.4-27, 0.4-12, 0.5- 36, 0.5-15, 1-5, 1-4, or 1-3 hours. Even shorter or longer times are within the teaching of the invention. Regulating the pressure of the surrounding atmosphere in said process has an important impact on the temperature and/or duration of heat-treatment.
  • Yet another aspect of the invention relates to said process, wherein the pressure of the said atmosphere is 0.001-20 atm.
  • the diffusion mechanism of the present invention is characterized by chemical diffusion.
  • kinetic analysis will challenge this assumption and the diffusion coefficients for the divalent cations will be calculated. Therefore, in yet another embodiment according to the invention, the diffusion is characterized by chemical diffusion.
  • the diffusion is rate-limited by the reduction kinetics in a manner where the diffusion is parabolic with time.
  • the polyvalent element should in certain embodiments of the invention have a redox state that is relatively easy to reduce in a weak reducing atmosphere, e.g. in about 0.001, 0.01, 0.02, 0.03, 0.07, or 0.09 atm. H 2 .
  • the inventors of the present invention have found that the inward diffusion depth is not linearly correlated over the whole range with the crystallization degree, but instead seems to be following two different paths or mechanisms. Both paths show an approximated linear relation between the inward diffusion depth and the crystallization degree, but with different inclinations.
  • a graphical representation e.g. figure 2
  • the two lines representing the two linear relations intercept in a point defined by the inventors as the critical degree of crystallization/critical value.
  • the critical degree of crystallization/critical value refers to the percentage of crystallization above which the diffusion coefficient drastically drops. The existence of a critical degree of crystallization could indicate a sudden drop in the degree of interconnection between the islands of the glass component.
  • the inward diffusion is perceived by the inventors mainly to occur in the glass component since no inward diffusion was observed for fully crystalline samples (figure 2). It is contemplated by the inventors that at low crystallization degrees, the islands of the glass component remain interconnected allowing a relatively fast cationic diffusion . At a certain critical degree of crystallization, the g lass component seems to become disconnected, resulting in the formation of isolated g lassy islands. It has been found by the inventors that the critical degree depends on the content of the polyvalent ions in g lass ceramics.
  • Fig ure 2 shows a schematic representation of the quantitative link between the extent of diffusion and crystallization degree, for explaining the present invention .
  • Iron-bearing d iopside (CaMgSi 2 0 6 ) systems have been studied as examples.
  • the extent of diffusion is quantified by the diffusion depth of the Mg 2+ ions ( ⁇ ) .
  • Similar results are obtained for the d iffusion of calcium and iron ions.
  • ⁇ decreases with increasing deg ree of crystallization (a) .
  • the decrease of ⁇ is especially pronounced in the range from about 80% to 100% . No noticeable diffusion occurs in the fully crystalline samples. The results may be explained as follows.
  • the d iffusing ions are more strong ly bound in the crystalline state than in the g lassy state. Thus, a larger potential energy barrier needs to be overcome to initiate diffusion .
  • the more ordered structure of crystals causes the molar volume of a glass to be larger than that of the corresponding crystal . This is macroscopically observed as an increase in density when a glass is crystallized (Shelby, 2005) . Hence, a glass has a large fraction of interstitial sites within the network which are
  • the inward d iffusion of cations is driven by the red uction of Fe 3+ to Fe 2+ .
  • the reducing H 2 gas must first penetrate into the uppermost surface layer, subseq uently be dissolved in the structure, and simultaneously contact and reduce the Fe 3+ ions in the glass structure. The penetration, and hence, red uction process is easier in the more open glass structure (Shelby, 1996) .
  • another aspect of the invention relates to said process, wherein the depth of the surface region, as a function of the degree of crystallization, has a critical value separating two regimes; a high-level regime below the critical value with relative slowly changing depth, and a low-level regime higher than the critical 5 value with relative fast changing depth.
  • Both regimens show an approximated linear relation between the inward diffusion depth and the crystallization degree, but with different inclinations.
  • the difference between the inclinations is at least a factor of 2, such as at least 5, preferably at least 7, such as at least 10, preferably at least 20, such as at least 30, preferably at least 40, such as at least 60, 10 preferably at least a factor of 100.
  • Another aspect of the invention relates to said process, wherein the depth of the surface region is a function of the degree of crystallization, said function
  • the critical value refers to the
  • the term "drastically drop” refers to a difference between the two inclinations of at least a factor of 2, such as at least 5, preferably at least 7, such as at least 10, preferably at least 20, such as at least 30, preferably at least
  • 25 40 such as at least 60, preferably at least a factor of 100.
  • the invention is particularly, but not exclusively, advantageous for obtaining an 30 improved glass ceramic article having improved chemical durability, an increased hardness, and/or an increased thermal stability.
  • a preferred aspect of the present invention relates to a glass ceramic article, wherein the selection of crystallization degree and inward diffusion depth is at or about or around the critical value.
  • the critical value refers to the percentage of said crystallization, above which the depth of the surface region drastically drops.
  • Such selection could deviate from the critical value by 20%, such as in the interval of 0%-19%, such as 1%-15%, such as 1%-12%, such as 1%-11%, preferably such as 1%-10%, such as in the interval of l%-5%, such as 4% from the critical value.
  • the network modifying cations occupy interstitial positions within the network and thereby create non-bridging oxygens.
  • NMC network modifying cations
  • a network forming cation-rich layer could e.g. be a Si0 2 -rich surface layer, a B 2 0 3 -rich surface layer, a P 2 0 5 -rich surface layer, a Te0 2 -rich surface layer, a Ge0 2 -rich surface layer, or a mixture of such network forming cation oxides.
  • one aspect of the invention relates to a glass ceramic article comprising a bulk part and a surface region, said glass ceramic article comprises network modifying cations (NMC); wherein the concentration of the network modifying cations in the surface region is lower than in the bulk part, wherein the
  • composition in the surface region of the network modifying cations is a
  • Yet another aspect of the present invention relates to a glass ceramic article comprising a bulk part and a surface region, said glass ceramic article comprises network-modifying cations (NMC); wherein the concentration of the network- modifying cations in the surface region is lower than in the bulk part, wherein the composition in the surface region of the network-modifying cations is a
  • the selection of crystallization degree is below the critical value, the critical value referring to the percentage of said crystallization, above which the depth of the surface reg ion drastically d rops.
  • the mechanical properties e.g . the hard ness
  • the mechanical properties are augmented due to the increased network connectivity (i .e., polymerization degree) of the surface layer resulting in an increased effective concentration of network forming cations in the said surface layer.
  • the present invention relates to a glass ceramic article, wherein the bridging-oxygen content of the corresponding oxide of the network forming cation is substantially higher in the surface reg ion than in the bulk region .
  • the present invention relates to a glass ceramic article, wherein the silicate, borate, germanate, tellurite or phosphate bridg ing-oxygen content is substantially higher in the surface reg ion than in the bulk region .
  • the present invention relates to a glass ceramic article, wherein the concentration of Si0 2 , B 2 C>3, Ge0 2 , Te0 2 , P 2 0 5 , or mixtures thereof in the surface reg ion is substantially higher than in the bulk part. It could be an advantage, in add ition to the increased connectivity of the surface region, to increase the thickness of said surface region to further improve the chemical durability, to increase the hardness, and/or to increase the thermal stability. To obtain a relatively high concentration of network forming cations in the surface region, it may be contemplated that the glass ceramic type comprises a relatively large weight percentage of their corresponding oxides (e.g .
  • the glass ceramic article according to the invention has a weight percentage of network forming cations of at least 10-35%, preferably at least 30-49%, and even more preferably at least 50%.
  • Other components than network forming cations may be comprised in the glass ceramic article, such as alkali oxides, alkaline earth oxides and polyvalent metal oxides.
  • the glass ceramic article according to the invention has a weight percentage of alkali oxides of at least 0-90%, such as 0.5-85%, preferably at least 1-80%, such as 3-75%, preferably at least 5-50%, such as 7-30%, preferably at least 10-20%.
  • the glass ceramic article according to the invention has a weight percentage of alkaline earth oxides of at least 0-90%, such as 0.5- 85%, preferably at least 1-80%, such as 3-75%, preferably at least 5-50%, such as 7-30%, preferably at least 10-20%.
  • the glass ceramic article according to the invention has a weight percentage of polyvalent metal oxides of at least 0.001-90%, such as 0.5-85%, preferably at least 1-80%, such as 3-75%, preferably at least 5- 50%, such as 7-30%, preferably at least 10-20%.
  • the thickness of the network forming cation-rich surface layer can be controlled by the content of the polyvalent element.
  • the composition in the surface region of the network-modifying cations is a consequence of inward diffusion, wherein the inward diffusion is caused by reduction of a polyvalent element.
  • the present invention relates to a glass ceramic article, wherein the inward diffusion is caused by reduction by a reducing gas and/or a reducing liquid.
  • the present invention relates to a glass ceramic article, wherein the depth of the surface region is a function of the inward diffusion process.
  • the thickness of the network forming cation-rich layer can also be controlled by tuning the temperature and duration of the heat-treatment in the reducing atmosphere.
  • the present invention relates to a glass ceramic article, wherein the depth of the surface region is a function of time, temperature, field strength of diffusing ions, partial pressure of the reducing gas, concentration and redox ratio of a polyvalent element, and/or type of untreated glass ceramic.
  • the inventors of the present invention have found that the inward diffusion depth is not linearly related over the whole range to the crystallization degree, but seem to be following two different paths or mechanisms. Both paths show an
  • the present invention relates to a glass ceramic article, wherein the depth of the surface region is a function of the degree of crystallization of the untreated glass ceramic type.
  • the function is nonlinear.
  • the present invention relates to a glass ceramic article, wherein said function comprises two approximated linear relations separated by a critical value; a first linear relation below the critical value with a lower inclination than a second linear relation above the critical value, said critical value refers to the percentage of said crystallization, above which the depth of the surface region drastically drop.
  • the present invention relates to a glass ceramic article, wherein the degree of crystallization of the untreated glass ceramic type is above the critical value. In another embodiment, the present invention relates to a glass ceramic article, wherein said diffusion is characterized by chemical diffusion.
  • the surface layer exerts a strong impact on the surface properties of the glass ceramic due to the increased connectivity. In particular, it considerably enhances the chemical durability (in both acid and alkali solutions) and the hardness of the glass ceramic.
  • the glass ceramic article according to the invention has a silicate bridging oxygen content that is substantially higher in the surface region than in the bulk region, i.e. the network connectivity of the surface region is higher than that of the bulk region.
  • the glass ceramic article according to the invention has a decrease in the number of non-bridging oxygen atoms per tetrahedron, NBO/T, in the surface region of at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.
  • TEC thermal expansion coefficient
  • the crystalline component of thermal glass ceramics has a negative coefficient of thermal expansion, which contrasts with the positive coefficient of the glass.
  • glass ceramics When an interface between materials will be subject to thermal fatigue, glass ceramics can be adjusted to match the coefficient of the material they will be bonded to. At a certain point, generally between 70% and 78% crystal I inity, the two coefficients balance such that the glass ceramic as a whole has a thermal expansion coefficient that is very close to zero. Glass ceramic is a mechanically strong material and can sustain repeated and quick temperature changes up to 800-1000 °C. At the same time, it has a very low heat conduction coefficient and can be made nearly transparent (15-20% loss in a typical cooktop) for radiation in the infrared wavelengths.
  • the present invention relates to a glass ceramic article, wherein the hardness of the glass ceramic is substantially higher in the said surface region than in the corresponding surface region of untreated glass ceramic.
  • the present invention relates to a glass ceramic article, wherein the chemical durability of the glass ceramic in the said surface region is substantially higher than in the corresponding surface region of untreated glass ceramic.
  • the present invention relates to a glass ceramic article, wherein the thermal shock resistance of the glass ceramic is substantially higher than corresponding untreated glass ceramic.
  • the thickness of the network forming cation-rich layer may be controlled by the content and reduction of the polyvalent element.
  • the present invention relates to a glass ceramic article, wherein the glass ceramic comprises transition metallic cations. In yet another embodiment, the present invention relates to a glass ceramic article, wherein at least some of the transition metallic cations are network- modifying cations (NMC) .
  • NMC network- modifying cations
  • the present invention relates to a glass ceramic article, wherein the polyvalent element is selected from a group consisting of: Au, Ir, Pt, Pd, Ni, Rh, Co, Mn, Ag, Se, Ce, Cr, Sb, Cu, U, Fe, As, Te, V, Bi, Eu, Ti, Sn, Zn, and Cd .
  • the present invention relates to a glass ceramic article, wherein the transition metallic cations are selected from a g roup consisting of: Ti 4+ , Ti 3+ , V 5+ , V 4+ , V 3+ , Cr 6+ , Cr 5+ , Cr 3+ , Mn 7+ , Mn 6+ , Mn 5+ , Mn 4+ , Mn 3+ , Fe 5+ , Fe 4+ , Fe 3+ , Co 4+ , Co 3+ and Ni 3+ .
  • the present invention relates to a glass ceramic article, wherein the transition metallic cations are selected from a g roup consisting of: Ti 2+ , V 2+ , Cr 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , , Zr 2+ , Nb 2+ , Mo 2+ , Ru 2+ , Rh 2+ , Pd 2+ , Ag 2+ , Cd 2+ , Ta 2+ , W 2+ , Re 2+ , Os 2+ , Ir 2+ , Pt 2+ , Hg 2+ and Ra 2+ .
  • the transition metallic cations are selected from a g roup consisting of: Ti 2+ , V 2+ , Cr 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , , Zr 2+ , Nb 2+ , Mo
  • the present invention relates to a glass ceramic article, wherein at least some of the network-modifying cations (NMC) are from Group Ila in the Periodic Table, e.g . Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , and Ra 2+ .
  • NMC network-modifying cations
  • the present invention relates to a glass ceramic article being : a glass ceramic cook top, glass ceramic cookware, bone implants, glass ceramic bakeware, a telescope mirror, or a building material .
  • the element and the redox state may determine the color of the glass ceramic article depending on the glass ceramic application, e.g . transparency of glass or a specific color for a specific application .
  • the present invention relates to a glass ceramic article, said glass ceramic article being : a glass ceramic cook top, glass ceramic cookware, bone implants or glass ceramic bakeware, or telescope mirror for astronomical observatory, or build ing materials.
  • the glass ceramic is transparent in the optical range of 10- 1200 nm, preferably in the visible range of 380-750 nm .
  • the glass ceramic is capable of absorbing UV-light in the range of between 400-10 nm, 400-315 nm, 315-280 nm, or 280-100 nm, preferably in the range of between 400-100 nm.
  • the Vickers hardness (H v ) test has been developed as a method to measure the hardness of materials. In the present invention, the Vickers hardness
  • the hardness increases with duration and temperature of the heat- treatment, i.e., the hardness increases when the thickness of the modified layer increases.
  • the glass ceramic article has a hardness of the glass ceramic that is substantially higher in said surface region than in the corresponding surface region of untreated glass ceramic, e.g. at least + 10%, +20%, +30%, +40%, +50%, + 100%, +200%, + 300%, + 1000% higher H v .
  • the said surface layer exerts a strong impact on the surface properties due to an increase in the connectivity. In particular, it may considerably enhance the chemical durability in both acid and alkali solutions. In acid solutions, leaching of alkali ions from the glass ceramic is the dominant dissolution mechanism.
  • the glass ceramic article has a chemical durability in the said surface region that is substantially higher than in the corresponding surface region of untreated glass, e.g. at least 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 3, 5, 10, 30, 50, 100, 1000 times better than in the corresponding surface region of untreated glass ceramic.
  • the modified surface has, among other advantageous properties, an increased thermal stability, such as thermal shock resistance.
  • the glass ceramic article has a thermal shock resistance that is substantially higher than the thermal shock resistance of the corresponding untreated glass, e.g. at least 1.5, 2, 3, 5, 10, 30, 50, 100, 1000 times better than the thermal shock resistance of the corresponding untreated glass ceramic.
  • the invention creates an improved glass ceramic article, having improved chemical durability, an increased hardness, and/or an increased thermal stability, without using the extrinsic coating technology that requires additionally expensive raw materials.
  • the reduced element has lower mobility than the earth alkaline ions in the glass network.
  • the layer thickness can be tuned according to specific requirements.
  • the glasses are first crystallized to various extents and these samples are then heat-treated in a reducing atmosphere to induce the diffusion. Finally, the diffusion profiles are measured and compared with the degree of crystallization.
  • the glass compositions used in this work are given in Table I.
  • Mixtures of reagent- grade Si0 2 , CaC0 3 , MgO, and Fe 2 0 3 powders were melted in a Pt90RhlO crucible at 1803 K for 3 hours.
  • the glass samples were obtained by quenching the melts on a brass plate and they were then annealed at 998 K for 15 min.
  • Cylindrical glass samples (diameter: ⁇ 8 cm; height: ⁇ 5 mm) were prepared and the glass- ceramics samples were obtained by heat-treating the cylindrical samples for 30 min at various temperatures in argon. These samples were polished according to the procedure described elsewhere (Smedskjaer et al., JPC-B).
  • the crystalline component in the diopside glass system is diopside 5 (CaMgSi20 6 ) .
  • augite is the crystalline component in the diopside glass system.
  • a is determined 10 from the area of the crystallization peak in the DSC scan, i.e., the enthalpy of crystallization ( ⁇ ) .
  • the maximum enthalpy is obtained from an untreated glass sample (AHuntreated) .
  • a can be calculated by Eq . (1) :
  • the inset of Figure 3 shows the crystallization peaks of the Diop-Fel samples that have been crystallized before the DSC measurement for 30 min at various temperatures T h .
  • AH sam pie decreases with increasing T h , and hence, a increases with T h .
  • Figure 4 shows SNMS depth profiles of four different samples. No inward diffusion is observed when the amorphous diopside system is heat-treated in H2/N2 (1/99) since no reduction of Fe 3+ can take place [Fig . 4(a)] . In contrast, surface depletion of calcium, magnesium, and iron is observed in the reduced Diop-Fel glass [Fig . 4(b)] . This inward diffusion leads to the formation of a silica-rich surface layer. When this g lass is partly crystallized, the extent of the inward d iffusion is lower [Fig . 4(c)] . No d iffusion occurs when the sample is fully crystalline [Fig . 4(d)] .
  • FIG. 1 shows the quantitative link between the extent of diffusion
  • H 2 will be more or less soluble. Hence, different cone, of H 2 will result in inward diffusion (probably: when H 2 is more soluble, a lower H 2 cone, is needed to obtain inward diffusion). ⁇ Characterizing the nanostructured layer more precisely.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Glass Compositions (AREA)

Abstract

La présente invention concerne un article vitrocéramique, tel qu'un dessus vitrocéramique de table de cuisson, dont une partie de la surface est modifiée. Cette surface modifiée dispose, parmi d'autres propriétés avantageuses, d'une meilleure durabilité chimique, d'une dureté accrue, et/ou d'une stabilité thermique accrue, notamment en ce qui concerne la résistance aux chocs thermiques. L'invention concerne plus particulièrement un procédé de modification d'une zone de surface d'un article vitrocéramique par traitement thermique à température de transition gazeuse Tg sous atmosphère de gaz réducteur tel que H2/N2 (1/99). La concentration des cations modificateurs de réseau ou "NMC" (Network-Modifying Cations) dans la région de surface de l'article vitrocéramique est inférieure à celle dans l'épaisseur de l'article, la composition de la région de surface des cations modificateurs de réseau résultant d'une diffusion vers l'intérieur.
PCT/DK2010/050314 2009-11-23 2010-11-19 Vitrocéramique aux propriétés de surface améliorées WO2011060793A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3779856A (en) 1971-07-23 1973-12-18 Owens Illinois Inc Glass-ceramic and method for making same
GB2206878A (en) 1987-07-11 1989-01-18 Glaverbel Pyrolytically coated sheet glass and process of manufacfuring same
FR2696443A1 (fr) 1992-10-02 1994-04-08 Saint Gobain Vitrage Int Substrat en verre, obtenu par désalcalinisation, utilisé dans le domaine électronique.

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3779856A (en) 1971-07-23 1973-12-18 Owens Illinois Inc Glass-ceramic and method for making same
GB2206878A (en) 1987-07-11 1989-01-18 Glaverbel Pyrolytically coated sheet glass and process of manufacfuring same
FR2696443A1 (fr) 1992-10-02 1994-04-08 Saint Gobain Vitrage Int Substrat en verre, obtenu par désalcalinisation, utilisé dans le domaine électronique.

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GAILLARD F.; SCHMIDT B.; MACKWELL S.; MCCAMMON C.: "Rate of hydrogen-iron redox exchange in silicate melts and glasses", GEOCHIMICA ET COSMOCHIMICA ACTA, vol. 67, 2003, pages 2427 - 2441
GERSTEN J. I.; SMITH F. W.: "The Physics and Chemistry of Materials", 2001, JOHN WILEY & SONS
J. E. SHELBY: "Handbook of Gas Diffusion in Solids and Melts, ASM International", 1996, MATERIALS PARK
J. E. SHELBY: "Introduction to Glass Science and Technology", 2005, THE ROYAL SOCIETY OF CHEMISTRY
L. D. PYE; A. MONTENERO; I. JOSEPH: "Properties of Glass-Forming Melts", 2005, CRC PRESS
MOESGAARD ET AL., J. NON-CRYST. SOLIDS, vol. 353, 2007, pages 1101
PYE ET AL., IN THIS CHAPTER, ALL THOSE ELEMENTS WILL BE CONSIDERED TO BE POLYVALENT, WHICH MAY OCCUR IN A GLASS MELT IN AT LEAST TWO DIFFERENT OXIDATION STATES, EVEN IF EXTREME OXIDIZING OR REDUCING CONDITIONS ARE NECESSARY, 2005, pages 28
SMEDSKJAER ET AL., J. PHYS. CHEM. B, vol. 113, 2009, pages 11194
SMEDSKJAER M M ET AL: "Inward cationic diffusion and formation of silica-rich surface nanolayer of glass", CHEMISTRY OF MATERIALS, AMERICAN CHEMICAL SOCIETY, WASHINGTON, US LNKD- DOI:10.1021/CM802513R, vol. 21, no. 7, 14 April 2007 (2007-04-14), pages 1242 - 1247, XP008115833, ISSN: 0897-4756, [retrieved on 20090303] *
SMEDSKJAER M M ET AL: "Inward cationic diffusion in glass", JOURNAL OF NON-CRYSTALLINE SOLIDS, NORTH-HOLLAND PHYSICS PUBLISHING. AMSTERDAM, NL LNKD- DOI:10.1016/J.JNONCRYSOL.2009.04.008, vol. 355, no. 14-15, 1 June 2009 (2009-06-01), pages 908 - 912, XP026103283, ISSN: 0022-3093, [retrieved on 20090504] *
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