Ca-La-F Transparent Ceramic Isotropic Thermal Strain
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Solution Overview
Problem
Conventional single crystalline fluorite optical materials suffer from anisotropic thermal strain, limited processability due to temperature changes, and restricted optical applicability due to low refractive index, making it difficult to produce homogeneous Ca—La—F based crystals with high crystallinity for use in optical systems.
Innovation Solution
A Ca—La—F based transparent ceramic is developed using a polycrystalline material with a composition of (Ca1−xLax)F2+x, where x is between 0 and 0.4, produced by mixing and sintering CaF2 and LaF3 particles to achieve a higher refractive index and Abbe's number similar to fluorite, while maintaining isotropic thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single crystalline fluorite is used in optical systems, then high transmittance and high Abbe's number are achieved, but anisotropic thermal strain occurs due to difference in thermal expansion in different crystallographic orientation, causing deterioration of imaging properties
Solution Approach 1:
The patent applies homogeneity by transitioning from single crystal to polycrystalline structure with randomly oriented grains. This uniform distribution of crystal orientations eliminates anisotropic thermal expansion, as the isotropic average of all orientations cancels out directional strain effects, solving the thermal stability problem while maintaining optical performance.
Solution Approach 2:
The patent creates a composite polycrystalline material where multiple small crystallites with different orientations are combined to form a macroscopically isotropic structure. This composite approach allows the material to achieve both the optical properties of fluorite and thermal stability by averaging out anisotropic effects across grain boundaries.
2Reliability
If single crystalline fluorite is used, then high transmittance is achieved, but processability is limited due to cracking easily generated by abrupt change of temperature
Solution Approach 1:
The polycrystalline structure provides homogeneous thermal expansion behavior throughout the material, eliminating the anisotropic stress concentrations that cause cracking in single crystals during temperature changes. This homogeneous structure significantly improves processability while preserving transmittance.
3Reliability
If fluorite is used as optical material, then high Abbe's number is achieved, but refractive index is very low at 1.43, restricting optical applicability
Solution Approach 1:
The patent employs composite materials by incorporating lanthanum fluoride (LaF3) particles into the calcium fluoride matrix. This composite structure enables tuning of the refractive index through composition control while preserving the high Abbe's number characteristic of fluorite-based materials, thereby expanding optical applicability.
Solution Approach 2:
The patent applies parameter changes by modifying the chemical composition from pure CaF2 to (Ca1-xLax)F2+x solid solution. This compositional parameter adjustment allows continuous tuning of refractive index from 1.43 to higher values while maintaining the fluorite crystal structure and high Abbe's number, enhancing optical versatility.
4Reliability
If Ca—La—F based crystal is produced, then refractive index higher than fluorite is achieved, but it is difficult to produce homogeneous crystal of high crystallinity stably
Solution Approach 1:
The patent inverts the conventional approach by abandoning single crystal growth and adopting polycrystalline sintering. This inversion solves the manufacturing difficulty by using powder processing techniques that naturally produce homogeneous composition and high crystallinity without the complex conditions required for single crystal growth, while achieving the desired refractive index through compositional 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
The resulting ceramic exhibits improved optical properties with a higher refractive index and Abbe's number, enhanced transparency, and reduced thermal strain, enabling its use in optical systems for correcting chromatic aberration and providing excellent optical performance.
Implementation Method 1
A sintered body is formed by heating and sintering the calcium fluoride particles at a temperature of not lower than 700° C. and not higher than 1300° C.
Implementation Method 2
By heating the sintered body at a temperature of not lower than 800° C. and not higher than 1300° C. while pressurizing the sintered body by a pressure of not lower than 500Kg/cm2 and not higher than 10000 Kg/cm2 in an inert atmosphere, the sintered body becomes transparent
Implementation Method 3
By heating the sintered body at a temperature of not lower than 800° C. and not higher than 1300° C. while pressurizing the sintered body by a pressure of not lower than 500Kg/cm2 and not higher than 10000 Kg/cm2 in an inert atmosphere, the sintered body becomes transparent
Implementation Method 4
In a single crystalline fluorite which has been conventionally used in optical systems, anisotropic strain is generated due to difference in thermal expansion in different crystallographic orientation at a time of increasing a temperature of the fluorite
Data Source
AI summary
A Ca—La—F based transparent ceramic, including: mixing CaF2 particles and LaF3 particles that are prepared separately from the CaF2 particles to form a mixed body of particles, and sintering the mixed body of particles and making the mixed body transparent, thereby producing a transparent ceramic.