Production and Heat Properties of an X-ray Reflective Anode Based on a Diamond Heat Buffer Layer

At a Glance

Metadata	Details
Publication Date	2020-01-06
Journal	Materials
Authors	Xinwei Li, Xin Wang, Ye Li, Yanyang Liu
Institutions	Changchun University of Science and Technology
Citations	6
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond Heat Buffer Layers for High-Power X-ray Anodes

Executive Summary

This research validates the use of MPCVD diamond as a critical heat buffer layer to significantly enhance the thermal stability and power limits of reflective micro-focus X-ray anodes.

Core Value Proposition: Diamond’s exceptional thermal conductivity (TC) enables rapid vertical and horizontal heat dissipation, preventing localized thermal destruction at the electron beam focal spot.
Material Performance: The fabricated diamond composite anode achieved a measured thermal conductivity of 1893 W/m K for the buffer layer.
Power Limit Doubled: The diamond composite anode demonstrated a working power limit of 73 W, nearly twice the limit of conventional tungsten anodes (37.9 W).
Thermal Stability: The diamond buffer layer reduced the focal spot surface temperature by up to 463 °C compared to a conventional copper-backed anode under identical operating conditions.
Interface Engineering: Robust inter-layer bonding was achieved using a vacuum-evaporation coating process to deposit Titanium (Ti), forming a stable TiC (carbonized alloy) layer for strong adhesion between the diamond and the copper substratum via high-temperature vacuum brazing.
Application: This technology is a breakthrough for high-resolution X-ray imaging systems requiring high intensity and minimized focal spot size (e.g., 20 µm).

Technical Specifications

The following hard data points were extracted from the research paper, detailing the material properties and performance metrics of the diamond composite anode.

Parameter	Value	Unit	Context
Diamond Thermal Conductivity (TC)	1893	W/m K	Measured via Photo-Thermal Deflection (PTD) method.
Diamond Layer Thickness	500 (0.5)	µm (mm)	Optimized thickness for heat buffering.
Tungsten Film Thickness	2.2	µm	X-ray target layer deposited via magnetron sputtering.
Solder Layer Thickness	15	µm	Used for bonding diamond to copper substratum.
Diamond Raman Peak	1330	cm^-1	Characteristic absorption peak confirming diamond structure.
Thermal Stress Coefficient	1.2 x 10^-6	/°C	Parameter used in thermal modeling.
Reference Focal Spot Size	20	µm	Standard spot size for micro-focus X-ray inspections.
Diamond Anode Power Limit	73	W	Determined by the melting point of the Tungsten target (3400 °C).
Conventional Anode Power Limit	37.9	W	Power limit of conventional tungsten anode (Type b).
Surface Temperature Reduction	463	°C	Temperature difference vs. conventional anode at 300 s.
Heat Flux Relationship	q = λ(T1 - T2)/δ	N/A	Heat flux (q) increases directly with thermal conductivity (λ) for similar temperature differences (T1-T2) and thickness (δ).

Key Methodologies

The production of the diamond composite anode required precise MPCVD growth and advanced interface engineering techniques:

Diamond Layer Preparation: A diamond heat buffer layer was prepared on a Molybdenum (Mo) slice using the Plasma Enhanced Chemical Vapor Deposition (PECVD) method, achieving a thickness of 0.5 mm (500 µm).
Layer Separation: The diamond layer was separated from the Mo slice post-deposition.
Surface Metallization (Adhesion Layer): Titanium (Ti) was deposited onto the diamond surface using a vacuum-evaporation coating process. High-temperature annealing followed, causing Ti to react with the diamond to form a stable TiC (carbonized alloy) structure, ensuring robust Ohmic contact and high adhesion.
Brazing: The metallized diamond layer was soldered tightly to a Copper Substratum using a special 15 µm thick solder alloy under high vacuum and high temperature. A gradient temperature profile was used during heating and cooling to mitigate stress caused by differing thermal expansion coefficients.
Target Layer Deposition: A 2.2 µm thick Tungsten (W) film (the X-ray target) was deposited onto the opposite diamond surface using magnetron sputtering.
Thermal Analysis: Performance was verified using Finite Element Analysis (FEA) modeling (ANSYS software) validated by experimental measurements, including Photo-Thermal Deflection (PTD) for thermal diffusion and infrared imaging spectrographs (900-2500 nm range) for indirect surface temperature calculation at the focal spot.

6CCVD Solutions & Capabilities

6CCVD specializes in providing the high-quality, custom MPCVD diamond materials and precision fabrication services necessary to replicate and advance this critical X-ray anode technology.

Applicable Materials

To replicate or extend this research, the primary material required is high-purity, high-thermal conductivity Polycrystalline Diamond (PCD).

Recommended Material: Optical Grade PCD (Polycrystalline Diamond).
Justification: The paper explicitly notes the diamond layer was prepared via PECVD and possesses a polycrystalline structure with a TC of 1893 W/m K. 6CCVD’s MPCVD-grown PCD routinely achieves and exceeds this thermal performance, ensuring maximum heat diffusion and thermal stability required for high-power applications.

Customization Potential

The successful fabrication of the composite anode relies on precise dimensional control and advanced interface engineering, both core competencies of 6CCVD.

Requirement from Paper	6CCVD Capability	Benefit to Customer
Thickness (0.5 mm / 500 µm)	PCD plates available from 0.1 µm up to 500 µm, and substrates up to 10 mm.	Exact thickness matching for optimal thermal modeling and performance.
Metallization (Ti/TiC Adhesion Layer)	In-house deposition of Ti, Pt, Au, Pd, W, Cu.	We provide custom Ti deposition and controlled annealing processes to form the critical TiC adhesion layer required for robust diamond-to-metal brazing.
Polishing (Surface Quality)	PCD polishing to Ra < 5 nm (inch-size wafers).	Ensures smooth, high-quality interfaces for uniform target layer deposition (Tungsten) and reliable thermal contact.
Dimensions (Custom Anode Size)	Plates/wafers up to 125 mm (PCD).	Ability to scale up successful micro-focus designs to larger, high-power X-ray systems.
Shipping	Global shipping (DDU default, DDP available).	Reliable, worldwide delivery of sensitive materials.

Engineering Support

The successful integration of diamond into X-ray anodes relies heavily on precise material selection, thermal modeling, and interface engineering (brazing, metallization). 6CCVD’s in-house PhD team can assist with material selection, thermal modeling, and interface optimization for similar High-Power Micro-Focus X-ray Anode projects, ensuring optimal thermal stability and power limits.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

This paper introduces an X-ray reflective anode with a diamond heat buffer layer, so as to improve heat dissipation of micro-focus X-ray sources. This also aids in avoiding the destruction of the anode target surface caused by the accumulation of heat generated by the electron beam bombardment in the focal spot area. In addition to the description of the production process of the new reflective anode, this study focuses more on the research of the thermal conductivity and compounding ability. This paper also introduces a method that combines finite element analysis (FEA) in conjunction with thermal conductivity experiments, and subsequently demonstrates the credibility of this method. It was found that due to diamonds having a high thermal conductivity and melting point, high heat flux produced in the micro-focus spot region of the anode could be conducted and removed rapidly, which ensured the thermal stability of the anode. Experiments with the power parameters of the radiation source were also completed and showed an improvement in the power limit twice that of the original.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma13010241

References

2006 - Experimental system for high resolution X-ray transmission radiography [Crossref]
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2004 - Superminiature X-ray tube [Crossref]
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2018 - Thermal Analysis of the Focal Spot of Anodes of Powerful X-ray Tubes [Crossref]
2017 - X-ray tubes for projection X-ray radiography of new Generation [Crossref]
2003 - Liquid-metal-jet anode electron-impact X-ray source [Crossref]