Lithium Silicate Glass Ceramic Strength via Ion Exchange
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Solution Overview
Problem
Current methods for enhancing the strength of lithium silicate glass ceramics in dental applications, such as bridges and crowns, face limitations in achieving both high strength and translucency, particularly due to the heat expansion coefficient issues with rubidium oxide and the lack of effective strength increase when replacing lithium ions with sodium ions in conventional processes.
Innovation Solution
A method involving the replacement of lithium ions in lithium silicate glass ceramic form bodies with alkali metal ions of greater diameter, such as sodium or potassium, through a coating process with a paste containing these ions, followed by heat treatment, to create surface compressive stress and increase strength, while maintaining biocompatibility and optical qualities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If lithium ions are replaced by rubidium ions to increase strength, then the flexural strength increases by up to 80%, but the heat expansion coefficient of the ceramics is increased
Solution Approach 1:
The patent changes the ion exchange parameters by selecting potassium ions instead of rubidium ions, and by controlling the exchange temperature and duration to achieve the desired balance between strength increase and heat expansion coefficient control
Solution Approach 2:
The patent applies ion exchange only to the surface layer of the ceramic, creating a compressed surface layer with increased strength while maintaining the bulk material's original properties including heat expansion coefficient
2Strength
If lithium ions are replaced by sodium ions through conventional processes, then the strength enhancement is attempted, but the effect is insufficient to achieve high strength levels
Solution Approach 1:
The patent changes the ion exchange parameters by using potassium ions instead of sodium ions, and by optimizing the exchange temperature (200-400°C) and duration to achieve superior strength enhancement (flexural strength >800 MPa) compared to conventional sodium ion exchange
Solution Approach 2:
The patent creates a composite structure with a compressed surface layer (potassium-rich) and an uncompressed core (lithium-rich), combining the benefits of surface hardening with the retention of original bulk material properties
3Strength
If a paste coating process with alkali metals is applied to increase strength, then the flexural strength exceeds 800 MPa with shorter annealing times, but the process complexity increases
Solution Approach 1:
The patent applies a paste coating containing alkali metal salts to the ceramic surface before the ion exchange process, preparing the surface in advance to facilitate controlled ion exchange and achieve uniform compressed layer formation
Solution Approach 2:
The patent uses a paste coating as an intermediary medium that delivers alkali metal ions to the ceramic surface in a controlled manner, enabling uniform ion exchange and compressed layer formation while simplifying process control
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
This method effectively increases the flexural strength of lithium silicate glass ceramic form bodies beyond conventional levels, achieving values over 800 MPa with shorter annealing times and maintaining the desired optical and chemical stability, suitable for dental restorations like bridges and crowns.
Implementation Method 1
replacement of lithium ions by alkali metal ions of greater diameter
Implementation Method 2
the at least portion of the form body is in contact with the paste for a time t at a temperature T
Data Source
AI summary
The invention relates to a method to produce a medical form body of lithium silicate glass ceramic. To increase its strength it is proposed that a surface compressive stress is created in a form body of lithium silicate glass, or containing lithium silicate glass, through the replacement of lithium ions by alkali metal ions of greater diameter. For this purpose the form body is covered with a paste that contains alkali metal.