Chemically Strengthened Glass with Metal Oxide Gradient
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Solution Overview
Problem
Thermally tempered glass is limited to thick articles, and chemically strengthened glass lacks the desired stress profile and exhibits undesired weight and dimension changes, making it impractical for thin, lightweight applications requiring superior fracture resistance.
Innovation Solution
A method of forming chemically strengthened glass with a non-zero alkali metal oxide concentration gradient along its thickness using a molten salt bath comprising at least 90% potassium salt and 10% sodium salt, optimized for thin glass articles, which minimizes weight gain and warp while achieving high central tension and compressive stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermal tempering is used to achieve large compressive stress layers for improved fracture resistance, then fracture resistance is improved, but the glass article thickness must be 3 millimeters or greater
Solution Approach 1:
The patent changes the fundamental parameter of stress distribution within the glass by creating a metal oxide concentration gradient through chemical strengthening. This gradient produces a tailored stress profile with high central tension that achieves superior fracture resistance in thin glass articles without requiring the minimum thickness constraint of thermal tempering processes.
2Length of moving object
If chemical strengthening is used to strengthen thin glass articles, then thickness limitation is removed, but the stress profile exhibits a substantially flat CT region with lower maximum central tension value
Solution Approach 1:
The patent applies local quality by creating a non-uniform metal oxide concentration distribution within the glass thickness. The concentration gradient is specifically tailored to produce varying stress levels at different depths, with enhanced central tension in the middle region while maintaining compressive stress at surfaces, thereby achieving superior fracture resistance compared to uniform chemical strengthening.
3Strength
If ion exchange process is used to chemically strengthen glass, then glass can be strengthened, but undesired increases in weight and dimensions occur
Solution Approach 1:
The patent optimizes the ion exchange parameters by controlling the metal oxide concentration gradient to vary along the thickness rather than being uniform. This tailored concentration distribution achieves the necessary strengthening effect while minimizing the total amount of metal oxide incorporated, thereby reducing undesired weight gain and dimensional changes compared to conventional uniform ion exchange processes.
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 provides thin glass articles with improved fracture resistance and reduced warp and weight gain, achieving stress profiles similar to thermally tempered glass without the thickness limitations, suitable for various applications including mobile devices and architectural uses.
Implementation Method 1
ion exchanging a plurality of alkali ions into the glass-based substrate to form a glass-based article with a non-zero alkali metal oxide concentration that varies along at least a substantial portion of the thickness (t) of the glass-based article
Data Source
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AI summary
Provided are methods of forming a chemically strengthened glass-based article. Certain methods comprise: providing a glass-based substrate comprising a first surface and a second surface opposing the first surface defining a thickness (t), a length dimension, a width, and a weight; and ion exchanging a plurality of alkali ions into the glass-based substrate to form a non-zero alkali metal oxide concentration that varies along at least a substantial portion of the thickness (t). The ion exchanging comprises immersing a glass-based substrate in a molten salt bath comprising at least about 90% by weight KNO3, and less than about 10% by weight NaNO3 for a time in the range of 70% to 130% of the ion exchange time that produces a peak central tension (CT) with the same molten salt bath composition and temperature. Also provided are ion exchanged glass-based articles prepared by said methods.