[Objectives] Diamond, with advantages of high melting point, good insulation, stable chemical properties, and high thermal conductivity, is a promising semiconductor material for high-power devices, sensors, and quantum computing. The best method for producing high-quality single crystal diamonds through microwave plasma chemical vapor deposition (MPCVD) is homoepitaxial growth, which requires expensive single crystal diamond substrates. Therefore, heteroepitaxial growth on foreign substrates is a compromise approach that has to be adopted, where the selection of a proper substrate becomes a major challenge for growing high-quality diamonds. To enhance the quality of heteroepitaxial growth, potassium tantalum niobate (KTa1-xNbxO3, referred to as KTN) crystals are proposed as the substrate. Their lattice parameter (0.3994 nm) is close to that of diamond (0.3567 nm). The structural similarity between them makes it possible to achieve an ideal result with small lattice mismatch and high crystal quality.

[Methods] Diamond thin films were grown on large-size, high-quality KTN single crystals using MPCVD. The effect of different growth times on diamond quality was explored by varying the duration of diamond growth. The surface morphologies, microstructures, and crystalline quality were analyzed using scanning electron microscope (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Diamond samples with different growth times were used to degrade Rhodamine B (RhB) to assess their photocatalytic effect. The absorbance of RhB was measured to evaluate the degradation efficiency of diamond films as catalysts for the pollutant solution.

[Results ] Analysis of plasma diagnostic spectra confirmed the presence of H groups and carbon source groups, while CN groups were absent. The H group exhibited the highest spectral line intensity, higher than that of the C2 group. This indicated that the system was well-sealed and provided sufficient reactive groups for diamond growth. The ratio of peak intensities between Hα and Hβ was high, while the ratio between C2 and Hα was low, both of which were favorable for the deposition of high-quality diamonds. Raman spectroscopy revealed structural changes in diamonds through comparing Isp3/Isp2, the relative intensities of diamond-phase characteristic peaks and non-diamond-phase characteristic peaks. The ratio gradually increased with the extension of growth time, indicating that the quality of diamonds was improving. XRD analysis of diamond films showed characteristic diamond peaks. In the 6h sample, characteristic peaks appeared at 34.8° (111), 40.5° (200), 58.6° (220) and 70.0° (311), consistent with the standard card (JCPDS No. 35-0801) as the characteristic peaks of TaC, indicating the presence of TaC in the 6h sample. However, the TaC characteristic peaks were lower in the 9h sample, and only diamond characteristic peaks were observed in the 12h sample. This indicated that TaC was only a transitional layer formed in the pre-nucleation stage, and TaC was no longer generated with the extension of growth time. From the SEM images of diamond films at different deposition time, it could be seen that the grain size of the 12h sample was much larger and more evenly distributed than those of other samples. The surface of the 12h sample was mostly composed of (100) faceted grains with a high degree of flatness, and the grains growing at the grain boundaries tended to grow significantly larger. Analysis of photocatalytic activity showed that higher diamond purity and lower non-diamond phase proportion led to better photocatalytic activity, more stable photocatalytic performance, and higher reusability.

[Conclusions] A new diamond substrate, potassium tantalum niobate (KTa1-xNbxO3), was successfully used to grow high-quality diamond films using MPCVD technology. The samples were characterized by XRD, SEM and Raman spectroscopy. Results indicate the formation of a TaC transition layer when growing diamond films on the KTN substrate, which is favorable for stable diamond growth. Moreover, with increasing growth time, the diamond grain size increases, the diamond phase content increases, and the sample quality improves. Photocatalytic results show that the sample grown for 12 hours has stronger photocatalytic ability and higher photocatalytic stability, achieving a degradation efficiency of 91.9% for RhB, which is 1.6 times higher than that of the 3h sample. These findings broaden the application of diamond and provide valuable insights for substrate selection in diamond fabrication.

[OBJECTIVES] Low carbon economy and green economy are the strategic direction of sustainable development, in order to reduce the manufacturing cost and energy consumption of diamond grinding tools, this study aims to explore a process of preparing high-performance ceramic bond diamond grinding tools under low energy consumption, to reduce the manufacturing cost and energy consumption of diamond grinding tools. The specific objectives include preparing Ti3SiC2-based diamond composite materials, and studying the effects of combustion-supporting agent Si and diamond particle size on the phase composition, microstructure and grinding performance of the samples.

[METHODS] Ti, Si, graphite powder, and diamond abrasives are selected as raw materials. After proportioning and weighing, they are cold-pressed to prepare green bodies. Ni powder and Al powder are cold-pressed into auxiliary heating green bodies according to the proportion. The material green body is horizontally placed on the auxiliary heating green body and then placed on the graphite block, then placed in a microwave tube furnace, Ar atmosphere is introduced for protection, and the temperature is quickly raised to the thermal explosion temperature point under the condition of 3kW power. After 30 seconds, the microwave source is cut off, and the furnace is cooled to room temperature before the Ar atmosphere input is turned off. At the end of the experiment, Ti3SiC2-based diamond composite material can be obtained.

[RESULTS] Microwave pressureless sintering is more efficient than conventional heating methods below 1000 ℃. High calorific value Ni-Al alloy assistance can shorten the experimental time of sample sintering, and can control the temperature point of inducing SHS reaction below the graphitization temperature of diamond. Under the protection of Ar atmosphere, the Ti-Si-C system undergoes an SHS reaction, which can generate three phases of Ti3SiC2, TiC, and Ti5Si3. Adding a certain amount of Si as a combustion-supporting agent in the experiment will be beneficial to the generation of the target phase of Ti3SiC2. When Ti3SiC2, TiC, and Ti5Si3 are at a certain proportion of equilibrium points, they can stably combine with diamond abrasives to exert the maximum grinding performance. As the Si content increases, the Ti3SiC2 phase first increases and then decreases. When n (Ti): n (Si): n (C) = 3: 1.1: 2, the grinding performance of Ti3SiC2-based diamond composite material is the best, and the diamond particle size is 70/80 mesh. The sample has the highest wear ratio, which can reach 286.53. Through the analysis of the friction wear test section of the composite material, the overall pores of the sample are small and evenly distributed, providing a good grip for the diamond abrasive. The diamond fits tightly with the surrounding matrix, the exposed part of the diamond is slightly higher than the grinding surface of the matrix, and the remaining part is tightly wrapped by the matrix, maximizing the grinding ability of the sample. It is known from the above analysis that the size of the pores, the distribution of the pores, the ratio of the raw materials, and the particle size of the diamond are the keys to the overall grinding performance. The pores are small and evenly distributed, and the matrix is more likely to form a flat grinding plane during the grinding process, which is easy for the diamond to exert good grinding performance. Adding a combustion-supporting agent and increasing the particle size of the diamond can both improve the grinding performance of the sample. When the Si combustion-supporting agent is added to 0.1 mol and the diamond particle size is 180~212 μm, it reaches the highest.

[CONCLUSIONS] By optimizing the raw material ratio and preparation process, using Ni-Al to assist microwave sintering, an SHS reaction is induced at 482 s and 685.5 ℃, preparing a Ti3SiC2-based diamond composite material containing Ti3SiC2, TiC, and Ti5Si3, which has excellent grinding performance. By analyzing the mechanism of the difference in the wear ratio of samples under different raw material ratios, it is found that the small and evenly distributed pore structure in the matrix organization is conducive to producing a flat grinding surface and improving the grinding performance of the composite material samples. This research provides a new method for preparing diamond grinding tools for green and low-carbon circular development, and is expected to reduce energy consumption and improve efficiency in practical applications.