Heat-conducting properties of thermobarically-sintered detonation nanodiamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-12-01 |
| Journal | Letters on Materials |
| Authors | В. А. Плотников, Denis Bogdanov, Alexander Bogdanov, А. А. Чепуров, С. В. Макаров |
| Institutions | V.S. Sobolev Institute of Geology and Mineralogy, Altai State University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research investigates the thermal conductivity (TC) properties of composite materials synthesized by thermobaric sintering of detonation nanodiamond (DND) powder. The findings highlight a significant departure from the thermal behavior of bulk diamond, emphasizing the dominant role of nanoscale effects.
- Low Thermal Conductivity: The DND composite exhibits extremely low TC, ranging from 7 to 19 W/(mK). This is approximately two orders of magnitude lower than high-quality diamond monocrystals (up to 2100 W/(mK)).
- Anomalous Temperature Dependence: Unlike classical diamond monocrystals, which show monotone TC growth with rising temperature, the DND composite TC remains practically constant (10-17 W/(mK)) across the measured range of 50-300°C.
- Dominant Scattering Mechanism: The low TC is attributed primarily to interfacial phonon scattering, resulting from the quasi-ballistic motion of phonons within the small (approx. 4.5 nm) nanocrystals.
- Phonon Confinement Effect: The temperature independence of TC is explained by the features of the phonon spectrum in nanocrystals, where the geometric size limits the excitation of higher-frequency phonon modes.
- Synthesis Conditions: Composites were successfully sintered under extreme conditions: 5 GPa pressure and temperatures between 1100°C and 1500°C using a BARS high-pressure apparatus.
- Structural Confirmation: Raman analysis confirmed the absence of the characteristic diamond line (1322 cm-1) in the sintered composite, indicating structural changes and the presence of non-diamond carbon phases (graphite G-line and disordered graphite D-line).
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sintering Pressure | 5 | GPa | DND composite synthesis. |
| Sintering Temperature Range | 1100 - 1500 | °C | DND composite synthesis. |
| DND Nanocrystal Size (L) | 4.5 | nm | Limits phonon wave vector (q < 1/L). |
| DND Composite TC (50°C) | 7 - 19 | W/(mK) | Measured thermal conductivity range. |
| DND Composite TC (300°C) | 10 - 17 | W/(mK) | Measured thermal conductivity range (anomalous stability). |
| High-Quality Monocrystal TC (50°C) | 2089 | W/(mK) | Comparison (Fe-Al-C system). |
| Synthesized Monocrystal TC (50°C) | 606.7 | W/(mK) | Comparison (Fe-Ni-C system). |
| Micron Powder Metal-Diamond Composite TC | 485.6 | W/(mK) | Comparison material. |
| Diamond Hardness (Typical) | 80 - 130 | GPa | General property of diamond materials. |
| DND Specific Surface Area | 300 | m2/g | Contributes to high interfacial scattering. |
| Raman Diamond Line (Initial Powder) | 1322 | cm-1 | Characteristic diamond peak. |
| Raman Graphite Line (Sintered Composite) | 1600 | cm-1 | G-line (non-diamond carbon phase). |
Key Methodologies
Section titled “Key Methodologies”The DND composites were synthesized and characterized using high-pressure sintering and spectroscopic analysis:
- Sample Preparation: Detonation nanodiamond powder was pressed into 8 mm diameter disks and placed into refractory MgO oxide capsules.
- Thermobaric Sintering: Experiments were conducted using a high-pressure multi-anvil “split-sphere” apparatus (BARS).
- Pressure and Temperature Control: Sintering was performed at a constant pressure of 5 GPa, with temperatures varied across five points: 1100°C, 1200°C, 1300°C, 1400°C, and 1500°C.
- Thermal Cycle: Samples were held at peak temperature for 60 seconds, followed by rapid quenching (2-3 seconds) via effective water cooling.
- Thermal Conductivity Measurement: The TC coefficient was measured using the TM-X-400 apparatus in a monotonous heating mode, assessing dependence on temperature from 50°C to 300°C. Copper was used for calibration.
- Raman Spectroscopy: Confocal Raman microspectrometry (LabRAM HR800) was used at room temperature with He-Cd (325 nm) and Nd:YAG (532 nm) lasers to analyze the carbon phase structure and phonon modes.
Commercial Applications
Section titled “Commercial Applications”While the primary goal of high-TC diamond research is heat dissipation, the specific findings regarding the low, stable TC of sintered DND composites suggest applications where thermal isolation or specialized nanostructure properties are required.
- Thermal Isolation/Barrier Coatings: The stable, low thermal conductivity (10-17 W/(mK)) across the 50-300°C range makes this material potentially useful for thermal barrier applications where temperature stability is critical.
- Nanocomposite Reinforcement: DND is a robust, ultra-hard filler. The material can be used in composites where mechanical strength is prioritized over thermal conduction, or where the matrix material dictates the overall thermal performance.
- Advanced Abrasives and Polishing: Detonation nanodiamonds are commercially utilized for their extreme hardness and small size, particularly in precision polishing slurries and superhard coatings.
- Biomedical and Drug Delivery: Nanodiamonds are widely researched for their biocompatibility, high surface area, and ability to functionalize for targeted drug delivery and bio-imaging applications, independent of their thermal properties.
- High-Performance Heat Sinks (Indirectly): The research provides critical data contrasting nanodiamond performance against micron-sized diamond composites (which achieved up to 485.6 W/(mK)). This informs material selection, confirming that achieving high TC requires controlling particle size to the micron scale and promoting diamond scaffold formation (e.g., using Si or carbide-promoting binders).
View Original Abstract
The research was conducted to study the thermal conductivity of detonation nanodiamonds-based composites. Composite nanodiamond materials were obtained in the course of thermobaric sintering at the press-free high-pressure apparatus (BARS) under 5 GPa and at temperatures within the range of 1100 -1500°С. It was ascertained that unlike diamond monocrystals with their thermal conductivity reaching up to 2100 W / (mK), the thermal conductivity of a nanodiamond composite is considerably lower and does not go beyond 18 W / (mK). Specifically, the temperature dependence of the thermal conductivity coefficient of a nanodiamond composite is anomalous as compared to a similar dependence in diamond monocrystals. The thermal conductivity coefficient in diamond monocrystals grows in compliance with the rising temperature, whereas it shows practically no changes in a nanodiamond composite in the temperature range of 50 - 300°С. Such a temperature dependence of the thermal-conductivity coefficient is apparently related to the features of the phonon spectrum of diamond monocrystals. This feature is stipulated by the dependence of the phonon spectrum of nanocrystals on their size, represented by a set of phonon modes in the range of the wave vector 0 < q <1 / L, i.e., the size of a diamond nanocrystal of 4.5 nm is alleged to limit the excitation of harmonics during nanodiamond composite heating, as opposed to macroscopic crystals that demonstrate the excitation of higher-frequency phonon modes during temperature growing.