Transparent Lithium Glass-Ceramic with Amorphous Surface Zone
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Solution Overview
Problem
Existing methods for producing transparent glass-ceramic materials with low thermal expansion and high strength are costly, complex, and require specialty nucleating agents, often resulting in uneven lithium distribution and surface roughness, which affects their coatability and transparency.
Innovation Solution
A lithium-containing, transparent glass-ceramic material with a thick, amorphous, lithium-depleted vitreous surface zone and a crystalline interior is produced using a method that involves specific temperature and residence time controls, along with a support plate with air or gas supply lines to ensure uniform lithium depletion on all sides, resulting in high transparency and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional methods are used to produce transparent glass-ceramic materials with low thermal expansion and high strength, then the materials achieve the required mechanical properties, but the production process becomes costly and complex, and specialty nucleating agents are required
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the glass-ceramic material, specifically incorporating lithium oxide (Li2O) at 0.5-5.0 wt% and aluminum oxide (Al2O3) at 10-30 wt%, along with specific ratios of other oxides. This compositional parameter adjustment enables the material to achieve high strength and low thermal expansion without requiring complex production processes or specialty nucleating agents, thereby resolving the contradiction between mechanical strength and production complexity
Solution Approach 2:
The patent creates a composite glass-ceramic material system combining multiple oxide components (SiO2, Al2O3, Li2O, B2O3, MgO, CaO, SrO, BaO, TiO2, ZrO2, Nb2O5, Ta2O5, SnO2, PbO, ZnO) in specific proportions. This composite approach allows the material to simultaneously achieve the required mechanical strength, low thermal expansion, and high transparency without relying on complex production methods or expensive specialty nucleating agents
2Ease of manufacture
If conventional methods are used to produce transparent glass-ceramic materials, then the materials can be manufactured, but they exhibit uneven lithium distribution and surface roughness, which affects coatability and transparency
Solution Approach 1:
The patent employs parameter changes by precisely controlling the chemical composition parameters, particularly lithium oxide (Li2O) at 0.5-5.0 wt% and aluminum oxide (Al2O3) at 10-30 wt%, along with the ratios of other oxides. This compositional parameter optimization ensures uniform lithium distribution throughout the material and produces a smooth surface finish, thereby improving manufacturing precision while maintaining ease of manufacture
Solution Approach 2:
The patent applies local quality by creating a specific microstructure with a vitreous surface zone (0.1-5.0 wt% crystals) that is distinct from the crystalline interior. This localized difference in crystal content creates a smooth surface layer that enhances coatability and transparency, while the interior maintains the necessary crystalline structure for strength, thus resolving the contradiction between ease of manufacture and manufacturing precision
3Strength
If the surface of glass-ceramic material is placed under compressive stress to enhance strength, then shattering is prevented, but the production method becomes more complex
Solution Approach 1:
The patent uses parameter changes in the chemical composition, specifically incorporating lithium oxide (Li2O) at 0.5-5.0 wt% and aluminum oxide (Al2O3) at 10-30 wt%, which inherently generates surface compressive stress during the crystallization process. This compositional parameter adjustment allows the material to achieve enhanced surface strength and shatter resistance without requiring additional complex production steps or external stress application methods
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves high transparency and strength in glass-ceramic articles with a sharp transition between the vitreous surface and crystalline interior, reducing scattering and refractive index differences, and allows for the production of glass-ceramic sheets suitable for vehicle glazing and other applications without the need for costly adaptations.
Implementation Method 1
The above-described compressive stress in the surface can be generated by a wide variety of methods. Presented hereinafter are some of the prior-art methods similar to the present invention.
Implementation Method 2
the nucleating agent is reduced at and directly beneath the surface of the glass and hence exhibits an increased efficacy. Then, in the course of the subsequent crystallizing step, the degree of crystallization at the surface of the article is greater than in the interior.
Implementation Method 3
the nucleating agent with the changed valence exhibiting an increased nucleation efficacy. Accordingly, the nucleating step in ceramicization takes place under a reducing atmosphere which is in direct contact with the surface of the starting glass
Implementation Method 4
U.S. Pat. No. 4,391,314 discloses a method which, for the purpose of generating the compressive stress in the surface of a glass-ceramic, makes use of differences in thermal expansion coefficient between crystal phase (lithium aluminum silicate crystal phase) and residual glass phase (borosilicate or boroaluminosilicate).
Data Source
AI summary
A lithium-containing, transparent glass-ceramic material is provided. The material has low thermal expansion and has an amorphous, lithium-depleted, vitreous surface zone. The zone is at least 50 nm thick on all sides and encloses a crystalline interior, which has high transmission. The material includes a transition region connecting the zone and the interior.