Selective Deposition of Mo2C-Containing Coatings on {100} Facets of Synthetic Diamond Crystals
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-07-31 |
| Journal | International Journal of Molecular Sciences |
| Authors | Arina V. Ukhina, Boris B. Bokhonov, Dina V. Dudina |
| Institutions | Lavrentyev Institute of Hydrodynamics, Institute of Solid State Chemistry and Mechanochemistry |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details a novel, efficient method for selectively depositing molybdenum carbide (Mo2C) coatings on synthetic diamond microcrystals, a critical step for manufacturing high-thermal-conductivity metal-diamond composites.
- Core Value Proposition: Mo2C coatings significantly improve the wettability of diamond surfaces by metal matrices (like copper), minimizing interfacial porosity and maximizing the thermal conductivity of the resulting composites.
- Selective Deposition: The Mo2C coating forms predominantly and selectively on the {100} facets of the diamond crystals during Hot Pressing (HP) and Spark Plasma Sintering (SPS).
- Gas Phase Transport Mechanism: Coating formation is enabled by the sublimation and gas-phase transport of volatile molybdenum dioxide (MoO2), which is present as an oxide impurity in the starting Mo powder.
- Reaction Sequence: MoO2 sublimes, adsorbs selectively onto {100} facets, is reduced to metallic Mo by diamond carbon, and subsequently carbidizes to form the desired Mo2C phase.
- Process Optimization: Increasing treatment time (up to 30 min at 900 °C) drives the carbidization reaction forward, resulting in a higher concentration of Mo2C relative to residual metallic Mo.
- Atmosphere Dependence: Treatment in forevacuum (SPS) yielded a more homogeneous coating than treatment in argon (HP). Conversely, annealing in air resulted in non-selective deposition of MoO3, confirming the need for an inert/reducing environment for carbide formation.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Particle Size (Average) | 100 | ”m | Synthetic diamond (MBD12) starting material. |
| Molybdenum Purity | 99.1 | % | Molybdenum powder (MPCh) starting material. |
| Mo Concentration (Mixture) | 10 or 50 | vol.% | Mo powder mixed with diamond. |
| HP Treatment Temperature Range | 900 to 1000 | °C | Hot Pressing (HP) conditions. |
| SPS Treatment Temperature | 1000 | °C | Spark Plasma Sintering (SPS) conditions. |
| Treatment Time (HP/SPS) | 5, 15, 30 | min | Holding time at peak temperature. |
| HP Atmosphere Pressure | 20 | kPa | Argon atmosphere. |
| SPS Atmosphere Pressure | 10 | Pa | Forevacuum residual pressure. |
| Heating Rate (Constant) | 50 | °C min-1 | Rate used across all experiments. |
| Applied Uniaxial Pressure | 10 | MPa | Pressure applied during HP and SPS. |
| Initial MoO2 Content (Starting Mo) | ~5 | wt.% | Oxide impurity enabling gas transport. |
| Primary Coating Phase | Mo2C | N/A | Molybdenum carbide (desired phase). |
Key Methodologies
Section titled âKey MethodologiesâThe Mo2C coatings were synthesized by treating mixtures of diamond and molybdenum powders using three distinct thermal processing techniques.
- Powder Preparation:
- Synthetic diamond (100 ”m) and Mo powder (99.1%) were mixed in a mortar to achieve 10 vol.% or 50 vol.% Mo concentration.
- Mixtures were loaded into a graphite die (10 mm inner diameter) protected by graphite foil.
- Hot Pressing (HP) Treatment:
- Samples were heated to 900 °C or 1000 °C under a constant uniaxial pressure of 10 MPa.
- Atmosphere: Argon gas maintained at 20 kPa.
- Holding times varied: 5, 15, and 30 min.
- Spark Plasma Sintering (SPS) Treatment:
- Samples (10 vol.% Mo) were heated to 1000 °C under 10 MPa pressure.
- Atmosphere: Forevacuum (residual pressure 10 Pa).
- Holding Time: 15 min. (Note: SPS resulted in more homogeneous coatings due to localized current heating).
- Oxide Precursor Study:
- Molybdenum powder was intentionally pre-oxidized by annealing in air at 400 °C for 30 min to increase the MoOx content (Mo, MoO2, MoO3 phases confirmed).
- This pre-oxidized mixture was then treated in HP (900 °C, 30 min) to study the effect of increased volatile precursor concentration.
- Air Annealing (Control):
- A 50 vol.% Mo mixture was annealed in air at 650 °C for 60 min. This resulted in full oxidation of Mo to MoO3 and non-selective deposition.
- Characterization:
- Phase composition was determined by X-ray Diffraction (XRD) using the Rietveld method.
- Morphology and elemental distribution were analyzed using Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS).
Commercial Applications
Section titled âCommercial ApplicationsâThe selective Mo2C coating technology is highly relevant for industries requiring advanced thermal management and high-performance composite materials.
- High-Power Electronics:
- Manufacturing of high-efficiency heat sinks, heat spreaders, and substrates for high-power density devices (e.g., LEDs, laser diodes, power modules, and RF components).
- Enabling copper-diamond composites with thermal conductivity exceeding 500 W/mK.
- Advanced Composites:
- Production of metal-matrix composites (MMC) using copper or aluminum matrices reinforced with diamond, where strong carbide interfacial layers are essential for load transfer and thermal transport.
- Tooling and Abrasives:
- Improving the performance and longevity of diamond abrasive grits used in metal-bonded cutting and grinding tools by enhancing diamond retention and wear resistance within the matrix.
- Surface Engineering:
- Developing controlled, selective deposition techniques for carbide films on complex geometries, leveraging gas phase transport for uniform coating of powder particles.
- Aerospace and Defense:
- Materials requiring exceptional thermal stability and high specific strength, utilizing Mo2C as a refractory component in cermets or structural composites.
View Original Abstract
An efficient way to improve the properties of metal-diamond composites (mechanical strength, wear resistance, thermal conductivity) is the preliminary modification of the diamond surface to improve its wettability by the metal matrix. In the present work, Mo2C-containing coatings were deposited on the diamond crystals under different conditions: hot pressing (atmosphere of argon), spark plasma sintering (forevacuum), and annealing in air. The influence of the sintering parameters on the morphology and phase composition of the coatings deposited on diamond was studied. Mo2C-containing coatings were selectively deposited on the facets of synthetic diamond microcrystals by annealing of the latter with a molybdenum powder. Experiments were carried out to deposit coatings under different conditions: during hot pressing (argon atmosphere), spark plasma sintering (forevacuum), and annealing in air. The process parameters were the temperature, holding time, and concentration of molybdenum in the initial mixture. Experiments with a pre-oxidized molybdenum powder were also conducted. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The deposition was enabled by the gas phase transport of molybdenum dioxide, MoO2, contained in the starting powder. The following sequence of the coating formation stages was proposed. First, MoO2 sublimes and is adsorbed mainly on the {100} facets of diamond. Then, it is reduced to metallic molybdenum by carbon of the diamond, which further reacts with carbon to form the Mo2C carbide phase. These processes occurred during treatment of the mixtures in the hot press and the spark plasma sintering facility. When the mixture was annealed in air, no selective deposition was observed. During annealing, MoO3 particles adhered to the diamond surface.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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