Low-Lithium LAS Glass Ceramic for Stable Cooking Surfaces
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Solution Overview
Problem
Current glass ceramics for cooking surfaces face challenges in achieving low thermal expansion, chemical resistance, and cost-effectiveness while maintaining optimal melting properties and optical transmission, often requiring high lithium content and expensive color oxides.
Innovation Solution
A transparent, colored glass ceramic with high quartz mixed crystal as the main phase, reduced lithium oxide content, and the use of molybdenum oxide as a color oxide, along with controlled additions of magnesium and zinc oxides to manage thermal expansion and melting temperature, while avoiding costly colorants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high lithium content (4-5% by weight) is used in glass ceramics, then low thermal expansion and good chemical resistance are achieved, but raw material costs increase
Solution Approach 1:
The patent reduces the lithium oxide content from the conventional 4-5% by weight to 3.0-3.6% by weight, specifically optimizing the lithium content parameter to lower raw material costs while maintaining the required thermal expansion stability through compensated composition adjustments
Solution Approach 2:
The patent employs a composite glass ceramic system combining lithium aluminosilicate base glass with high quartz mixed crystal phase (HQMK) and controlled additions of magnesium oxide and zinc oxide, creating a multi-phase composite material that achieves low thermal expansion without requiring high lithium content
2Illumination intensity
If expensive color oxides (CoO, NiO, Nd2O3, CuO) are used to color glass ceramics, then desired optical properties are achieved, but production costs significantly increase
Solution Approach 1:
The patent replaces expensive color oxides with cheaper alternative colorants, specifically using iron oxide (Fe2O3) and/or manganese oxide (MnO2) which are significantly less costly while achieving the required optical transmission properties for cooking surface applications
Solution Approach 2:
The patent optimizes the composition parameters by limiting expensive color oxides to trace amounts (CoO, NiO, Cr2O3, CuO, or Nd2O3: each less than 0.01% by weight) while using cost-effective alternatives, thereby changing the colorant composition parameters to reduce raw material costs
3Quantity of substance
If lithium content is reduced to lower costs, then raw material expenses decrease, but thermal expansion control and crystal phase formation become difficult
Solution Approach 1:
The patent compensates for reduced lithium content by precisely adjusting other composition parameters: aluminum oxide (19-22% by weight), silicon dioxide (64-68% by weight), magnesium oxide (0.1-1% by weight), and zinc oxide (1-3% by weight), thereby maintaining thermal expansion stability despite lower lithium content
Solution Approach 2:
The patent creates a high quartz mixed crystal phase (HQMK) with specific local crystalline structure and composition characteristics, where the crystal phase forms with optimized local chemistry that provides negative thermal expansion to compensate for the reduced lithium content in the overall composition
4Reliability
If high crystal phase content (>60%) is used to achieve low thermal expansion, then thermal stability is improved, but melting properties and processing become more difficult
Solution Approach 1:
The patent optimizes the base glass composition parameters, specifically the ratio of network formers (SiO2, Al2O3) to modifiers (Li2O, MgO, ZnO), to facilitate crystal phase formation during controlled cooling while maintaining good melting properties at conventional processing temperatures
Solution Approach 2:
The patent incorporates nucleating agents (TiO2: 0.1-1% by weight, ZrO2: 0.1-1% by weight) in the initial glass composition that prepare the melt for subsequent crystal phase formation during cooling, enabling high crystal content to be achieved without excessive difficulty in processing
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 solution provides a cost-effective glass ceramic with low thermal expansion, excellent chemical resistance, and adapted optical transmission, suitable for cooking surfaces with improved melting properties and reduced raw material costs.
Implementation Method 1
The property of these materials, which is essential for use as a cooking surface, of having a very low thermal expansion in the range from room temperature to 700 ° C and above, is obtained through the combination of crystal phases with negative thermal expansion and an amorphous residual glass phase with positive thermal expansion.
Implementation Method 2
0.003 to 0.25 percent by weight of molybdenum oxide (MoO 3 ) is used as color oxide for the glass ceramic according to the invention
Implementation Method 3
While previously mainly the refining agents arsenic and antimony oxide known from the glass industry were used, today other, less toxic alternatives such as tin oxide (SnO 2 ) are preferred as refining agents for reasons of environmental and occupational safety.
Data Source
Figure 1
AI summary
The invention relates to a transparent, colored glass ceramic, in particular a LAS glass ceramic, suitable for use as a cooking surface, with high quartz mixed crystal (HQMK) as the main crystal phase and a thermal expansion in the range of 20°C to 700°C of -0.5 to +0.5 ppm/K, wherein the glass ceramic contains as components 3.0 to 3.6 wt% lithium oxide (Li2O) and is either colored with 0.003 to 0.05 wt% vanadium oxide (V2O5) or colored with 0.003 to 0.25 wt% molybdenum oxide (MoO3).