| Customization: | Available |
|---|---|
| Color: | White |
| Hardness: | 10 |
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| Grade & Type | Room Temp. Thermal Conductivity Range (W/(m·K)) | Typical Grain Size | Key Characteristics & Primary Applications |
|---|---|---|---|
| Optical/Electronic Grade (High Quality) | 1200 - 1800 | 10 - 200+ microns | Large grains, few impurities. Used for high-power laser windows, microwave tube output windows, high-end heat spreader substrates. This is the polycrystalline diamond with performance closest to single-crystal. |
| Thermal Grade (Mainstream) | 800 - 1200 | 5 - 50 microns | The most common industrial-grade product. Offers the best balance among thermal conductivity, mechanical strength, processability, and cost. Widely used in semiconductor laser/power device heat sinks, CPU vapor chambers, aerospace electronics cooling. |
| Mechanical/Tool Grade | 500 - 800 | < 5 microns (nanocrystalline) | Fine grains, high hardness, smooth surface, but numerous grain boundaries cause a significant drop in thermal conductivity. Primarily used for wear-resistant coatings, cutting tools, wire drawing dies. Thermal performance is a secondary consideration. |
Grain Boundary Scattering (Primary Factor)
Phonon Scattering: Heat in diamond is primarily conducted through lattice vibrations (phonons). Grain boundaries strongly scatter phonons, impeding heat flow.
Grain Size Effect: Larger grains mean fewer grain boundaries, longer phonon mean free paths, and higher thermal conductivity. Growing thick films or using post-growth heat treatment to promote grain growth are key processes for improving thermal conductivity. High-quality polycrystalline diamond typically exhibits a columnar structure in cross-section, with small grains at the bottom and large columnar grains at the top. Thermal conductivity is highest when heat flows along the direction of columnar grain growth.
Impurities and Defects
Even in single-crystals without grain boundaries, impurities (e.g., nitrogen, boron, hydrogen, metal inclusions) scatter phonons. In polycrystalline diamond, impurities reside both within grains and tend to concentrate at grain boundaries, causing scattering.
High-purity feedstock gases and optimized deposition processes are fundamental for achieving high thermal conductivity.
Measurement Direction (Anisotropy)
Polycrystalline diamond is anisotropic. Thermal conductivity is highest in the direction perpendicular to the deposition plane (i.e., along the columnar grain growth direction), as phonons can travel along the longer columnar grains.
In directions parallel to the deposition plane, heat flow must frequently cross grain boundaries, resulting in significantly lower thermal conductivity (perhaps only 60%-80% of the perpendicular direction). Product technical data usually specifies the thermal conductivity in the perpendicular direction.
| Property | Polycrystalline CVD Diamond | Single-Crystal CVD Diamond |
|---|---|---|
| Thermal Conductivity | Medium to High (500-1800), depends on grain size & purity | Extremely High (1800-2200+),theoretical limit |
| Uniformity | Anisotropic (Best conductivity perpendicular to surface) | Isotropic (Consistent performance in all directions) |
| Achievable Size | Large (Diameter several inches), significant advantage | Limited by substrate (typically <1 inch), high cost |
| Surface Roughness | As-grown surface usually rough (due to grains) | Atomically smooth, very flat |
| Primary Cost | Relatively lower, can be produced over large areas | Very high, especially for large sizes |
| Core Applications | Heat spreaders, optical windows, wear-resistant tools (Balance of performance & cost) | heat dissipation, quantum sensing, high-pressure physics (Pursuit ofperformance) |
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