Gd2O2S Fluorescent Ceramic Grain Size Optimization
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Solution Overview
Problem
Existing methods for manufacturing fluorescent ceramics using powders with grain sizes between 10 nm to 100 nm are chemically unstable when stored in air, leading to surface oxidation and the formation of undesirable phases that decrease light output and scattering within the ceramics, and the use of a reducing atmosphere during hot pressing limits the formation of an optimal microstructure.
Innovation Solution
A method involving single-axis hot pressing of Gd2O2S doped with elements like Eu, Tb, Yb, Dy, Sm, Ho, using powders with grain sizes of 1 μm to 20 μm at temperatures of 1000° C. to 1400° C. and pressures of 100 MPa to 300 MPa, followed by air annealing and optional vacuum annealing, which enhances the chemical stability and optical properties of the ceramics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If powders with grain sizes of 10 nm to 100 nm are used for manufacturing fluorescent ceramics, then the surface area and reactivity are increased, but the chemical stability decreases leading to surface oxidation and formation of undesirable phases
Solution Approach 1:
The patent changes the critical parameter of powder grain size from the conventional 10-100 nm range to a coarser 1-20 μm range. This parameter change fundamentally alters the surface-to-volume ratio, reducing surface oxidation while maintaining manufacturing effectiveness. The coarser grains provide sufficient surface area for reaction while offering inherent chemical stability against oxidation during storage and handling.
2Stability of the object's composition
If a reducing atmosphere is used during hot pressing to prevent oxidation, then the chemical stability is improved, but the compaction efficiency decreases due to gas pressure counteracting the pressing force
Solution Approach 1:
The patent performs preliminary action by selecting coarser-grained powders (1-20 μm) that are inherently chemically stable before the hot pressing process begins. This preliminary selection eliminates the need for a reducing atmosphere during pressing, allowing the full pressing force to be applied without gas pressure counteraction, thereby achieving both chemical stability and high compaction efficiency.
3Volume of stationary object
If powders with grain sizes of 10 nm to 100 nm are used, then the density and fine microstructure are achieved, but the light scattering increases due to surface oxidation and second phase formation
Solution Approach 1:
The patent changes the grain size parameter to 1-20 μm, which fundamentally alters the microstructure characteristics. The coarser grains reduce light scattering by eliminating surface oxidation and unwanted secondary phases, while the hot pressing process still achieves sufficient density through the combination of temperature (1000-1400°C) and pressure (100-300 MPa).
Solution Approach 2:
The patent converts the potential disadvantage of coarser grain size (which might be perceived as reducing density) into a benefit by demonstrating that the coarser grains (1-20 μm) actually improve optical properties by eliminating light scattering from oxidation. The high density is achieved through optimized hot pressing parameters rather than fine powder size, turning the grain size characteristic from a potential harm into a beneficial feature.
4Stability of the object's composition
If the grain size of powder is increased to improve chemical stability, then the handling and storage stability are improved, but the sintering and densification may be affected
Solution Approach 1:
The patent changes multiple parameters simultaneously: grain size (1-20 μm), temperature (1000-1400°C), and pressure (100-300 MPa). The higher temperature and pressure compensate for the coarser grain size, enabling effective sintering and densification while maintaining the chemical stability benefits of larger grains.
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 results in fluorescent ceramics with improved light output, reduced afterglow, and increased transparency, with a relative light yield up to 2.3 times higher than cadmium tungstate crystals, and a significant decrease in afterglow, making them suitable for medical imaging applications like computer tomographs.
Implementation Method 1
hot pressing of Gd2O2S doped with M... at a temperature of 1000° C. to 1400° C. and a pressure of 100 MPa to 300 MPa
Implementation Method 2
air annealing at a temperature of 700° C. to 1200° C. for a time period of 0.5 hours to 30 hours
Implementation Method 3
Fluorescent members for detecting high-energy radiation contain a phosphor that can absorb the radiation and convert it into visible light
Data Source
AI summary
The present invention relates to a fluorescent ceramic having the general formula Gd2O2S doped with M, whereby M represents at least one element selected form the group Ce, Pr, Eu, Tb, Yb, Dy, Sm and/or Ho, whereby said fluorescent ceramic comprises a single phase in its volume; to a method for manufacturing a fluorescent ceramic using single-axis hot pressing; a detector for detecting ionizing radiation and to a use of said detector for detecting ionizing radiation. The method for manufacture of a fluorescent ceramic material using a single-axis hot pressing, comprises the steps: a) selecting a pigment powder of Gd2O2S doped with M, and M represents at least one element selected from the group of Eu, Tb, Yb, Dy, Sm, Ho, Ce and/or Pr, whereby the grain size of said powder used for hot-pressing is of 1 μm, and said hot-pressing is carried out at—a temperature of 1000° C. to 1400° C.; and/or—a pressure of 100 Mpa to 300 MPa; air annealing at a temperature of 700° C. to 1200° for a time period of 0.5 hours to 30 hours.