Multi-layered X-ray Anode Coating for Thermal Stress Management
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Solution Overview
Problem
Current X-ray anodes in medical imaging scanners face issues with low X-ray production efficiency, thermal stress, and mechanical deterioration due to high rotation speeds, leading to limited power and short lifespan, despite various attempts to address these challenges.
Innovation Solution
A multi-layered anode structure comprising a graphite or carbon-based substrate with intermediate layers of titanium nitride, boron nitride, or silicon carbide, and superimposed sub-layers of rhenium and tungsten alloys, where the sub-layers have different ductilities and elastic moduli, allowing for controlled micro-cracking and enhanced mechanical stress absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the rotation speed of the anode is increased to improve X-ray production power, then the X-ray power increases, but the mechanical stress and thermal load on the anode increase leading to premature deterioration
Solution Approach 1:
The patent uses a composite coating structure consisting of multiple layers with different materials (tungsten, rhenium, and intermediate layers of silicon carbide or titanium nitride) deposited on the graphite substrate. This composite structure combines the high X-ray production capability of tungsten with the thermal stability and stress resistance of intermediate layers, enabling the anode to withstand higher rotation speeds and thermal loads while maintaining reliability.
2Weight of moving object
If a graphite-based substrate is used to reduce anode weight, then the rotation speed can be increased, but carbon migration occurs in the tungsten layer transforming it into brittle tungsten carbide
Solution Approach 1:
The patent introduces intermediate layers composed of silicon carbide or titanium nitride between the graphite substrate and the tungsten layer. These intermediate layers act as barriers that prevent carbon diffusion from the graphite substrate into the tungsten layer, thereby preventing the formation of brittle tungsten carbide while allowing the lightweight graphite substrate to be used for high-speed rotation.
3Power
If the anode is operated at high temperatures to improve X-ray emission, then the X-ray power increases, but large cracks appear in the coating layers due to thermal expansion differences
Solution Approach 1:
The patent modifies the thermal and mechanical parameters of the coating structure by introducing intermediate layers with specific thermal expansion coefficients that are intermediate between those of graphite and tungsten. This gradual transition in material properties reduces thermal stress concentration and prevents crack formation during high-temperature operation, allowing the anode to maintain high X-ray emission power.
4Productivity
If a single-layer tungsten coating is used to produce X-rays, then the X-ray production is efficient, but the layer becomes fragile and brittle especially near the disk
Solution Approach 1:
The patent replaces the single-layer tungsten coating with a multi-layer composite structure that includes tungsten layers for X-ray production, rhenium layers for ductility, and intermediate layers for stress management. This composite structure maintains high X-ray production efficiency while improving the mechanical strength and ductility of the coating, particularly in the region near the disk where stress is highest.
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 enables increased X-ray production power and extended anode lifespan by managing thermal and mechanical stresses, allowing higher rotation speeds and improved image sharpness while reducing exposure times for patients.
Implementation Method 1
the difference between the expansion coefficients of the graphite-based substrate and of the layer capable of producing X-rays causes the appearance of large cracks in this layer
Implementation Method 2
this sub-layer being made of a material different from the materials forming the substrate, the first sub-layer and the second sub-layer
Implementation Method 3
at least one superficial sub-layer being able to produce X-rays under the effect of an incident beam of electrons
Implementation Method 4
a layer formed by a support made of another material, the assembly being called an anode. X-ray production has low efficiency. A large part of the energy of the electrons is transformed into heat in the anode
Implementation Method 5
A large part of the energy of the electrons is transformed into heat in the anode. To limit the thermal load at the point of impact of the electrons, the anode is rotated at high speed
Data Source
Figure 1~2
Figure 3
AI summary
An X-ray emitting anode comprises a substrate and, over a portion of the surface of the substrate, a coating (4) comprising a plurality of superposed or stacked groups (7) of sublayers (8, 9) and an intermediate sublayer (6) between the substrate and the coating, each group comprising at least a first sublayer (8) and a second sublayer (9) that are superposed or stacked, at least one surface sublayer (9n) being capable of producing X-rays under the effect of an incident electron beam. Process for manufacturing this anode in which, for each group, the structure is heated before the sublayers (8, 9) are deposited and cooled after they have been deposited.