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A broad effort is underway to improve the sensitivity of NMR through the use of dynamic nuclear polarization. Nitrogen vacancy (NV) centers in diamond offer an appealing platform because these paramagnetic defects can be optically polarized efficiently at room temperature. However, work thus far has been mainly limited to single crystals, because most polarization transfer protocols are sensitive to misalignment between the NV and magnetic field axes. Here we study the spin dynamics of NV–13C pairs in the simultaneous presence of optical excitation and microwave frequency sweeps at low magnetic fields. We show that a subtle interplay between illumination intensity, frequency sweep rate, and hyperfine coupling strength leads to efficient, sweep-direction-dependent 13C spin polarization over a broad range of orientations of the magnetic field. In particular, our results strongly suggest that finely tuned, moderately coupled nuclear spins are key to the hyperpolarization process, which makes this mechanism distinct from other known dynamic polarization channels. These findings pave the route to applications where powders are intrinsically advantageous, including the hyperpolarization of target fluids in contact with the diamond surface or the use of hyperpolarized particles as contrast agents for in vivo imaging.

The synthesis of diamond was performed at a pressure of 8 GPa and a temperature of 1700°C in the Mg–Zn–C system and, after the product was chemically purified, the resulting diamond powder was classified by grain sizes. The effect produced by the ratio between coarse and fine diamond powder fractions and the sintering parameters on the structure and physicomechanical properties of sintered diamond polycrystals was studied. The wear resistance of synthesized samples was investigated when turning a cylindrical X drillability granite core sample from the Korostyshiv deposit. The high-pressure sintering of a mixture of synthesized coarsely and finely dispersed diamond powders was shown to provide a 2.46-fold decrease in the residual porosity as compared to sintering under the same pressure for the diamond powders synthesized in the systems based on iron group metals. Among the resulting polycrystalline samples, the highest hardness determined at a Knoop indenter load of 9.8 N was 66 GPa to attain 87% from the hardness of natural type Ia diamond single crystal (face (100)). Polycrystalline diamond elements sintered in a Toroid 30 high-pressure autoclave at a pressure of 8 GPa and a temperature of 1780°C from the purified product of synthesis in the Mg–Zn–C system with a diameter of 15 mm and a height of 3 mm demonstrated the highest wear resistance, which was 5.6–10.9 times higher than for the reference specimen sintered from the powder synthesized in the Ni–Mn–C system.

There is a considerable demand for microchannels in micro-electro-mechanical systems (MEMS) for heat transfer and biomedical microfluidic system applications. The present paper investigates the machining of microchannels using a twin tool with three dielectric fluids using an in-house micro-electro-discharge machine (μ-EDM). A tailor-made twin-tool setup is fabricated and utilized instead of a single tool to improve the μ-EDM production rate in microchannel machining. Three dielectric fluids (DFs), such as deionized (DI) water, DI water with SiC powder (5 g/l), and DI water with diamond powder (5 g/l), are used to machine microchannels on a copper plate with two tubular copper wires, the size of each Ø300 μm. The input parameters, such as voltage, T on , and T off, are varied at three levels, and the L 9 Taguchi orthogonal array is selected to conduct nine experiments with each dielectric fluid. The output performances, like material removal rate (MRR), tool wear rate (TWR), channel width, depth, and surface roughness (Ra), are analyzed. Each set is optimized individually using gray relational analysis with the entropy weight method (GRA-EWM) to maximize the MRR and channel depth and minimize Ra, channel width, and TWR. The significant parameter of each dielectric fluid is identified using ANOVA. High-resolution scanning electron microscope (HR-SEM) and 3D profilometer are used to obtain machined surface channel images to examine the surface topography and channel characteristics. The output responses of powder-mixed dielectric fluids are compared with plain DI water, and the results are discussed. The experimental investigation shows minimal surface defects and a better surface finish of microchannels achieved through the diamond powder mixed with DI water compared to the other two dielectric fluid media.

The authors studied the volume distribution of particles from ultrafine powders of natural diamond, used as a hardener for a post of diamond tools made on a metal basis by powder metallurgy methods. In [15-17], the authors determined that the addition of ultrafine natural diamond powders to the melt of tin bronze in an amount of 2-3% by weight has a positive effect on the physicomechanical and operational properties of the metal post. It was also determined that the hardening mechanism of the materials under study depends on the nature of the distribution of the hardener particles in the bulk of the matrix. In accordance with previous studies, the authors set the aim - to determine the distribution nature of reinforcing phase particles in the volume of the metal matrix. The studies were carried out using optical metallography, SEM microscopy and Raman spectroscopy. It was established that the particles of the hardener in the volume of the matrix are distributed evenly along the phase boundaries and in the body of the grains and reduce the number of pores formed during sintering compared with the original samples. With the established nature of the distribution of particles, a grain-boundary hardening mechanism is realized, in which dislocations are inhibited by grain boundaries, which are an insurmountable obstacle for them. It is also established that a part of the particles settle directly inside the grains of the material and is distributed throughout the volume uniformly contributing to the dispersion hardening mechanism.

Polymer heat exchangers (HXs) are lightweight and cost-effective due to the affordability of raw polymer materials. However, the inherently low thermal conductivity (TC) of polymers limits their application in HXs. To enhance thermal conductivity polymer composites, two types of diamond powders, with particle sizes of 0.25 µm and 16.7 µm, were used as fillers, while Acrylonitrile Butadiene Styrene (ABS) served as the matrix. Composite polymer samples were fabricated, and their density and thermal conductivity were tested and compared. The results indicate that fillers with larger particle sizes tend to exhibit higher thermal conductivity. A polymer HX based on a Triply Periodic Minimal Surface (TPMS) structure was designed. The factors influencing the efficiency of polymer HXs were analyzed and compared with those of metal HXs. In polymer HXs, the polymer wall is the primary source of heat resistance. Additionally, the mechanical strength of 3D-printed polymer parts was evaluated. Finally, an HX was successfully fabricated using a polymer composite containing 50 wt% diamond powder via 3D printing.

The study is devoted to the electrodynamic properties of composite materials based on AlN–5 wt % C (carbon black) or AlN–5 wt % C (diamond powder) and 5% molybdenum in the frequency range of 1–10 GHz. The materials were obtained by free sintering at a temperature of 1850°C. The results demonstrate that the real and imaginary parts of the relative permittivity of the composites containing carbon black and diamond powder with molybdenum at a frequency of 10 GHz are ɛ' ≈ 16.1, ɛ'' ≈ 4.3 and ɛ' ≈ 9.3, ɛ'' ≈ 0.7.

With the development of miniaturized, highly integrated, and multifunctional electronic devices, the heat flow per unit area has increased dramatically, making heat dissipation a bottleneck in the development of the electronics industry. The purpose of this study is to develop a new inorganic thermal conductive adhesive to overcome the contradiction between the thermal conductivity and mechanical properties of organic thermal conductive adhesives. In this study, an inorganic matrix material, sodium silicate, was used, and diamond powder was modified to become a thermal conductive filler. The influence of the content of diamond powder on the thermal conductive adhesive properties was studied through systematic characterization and testing. In the experiment, diamond powder modified by 3-aminopropyltriethoxysilane coupling agent was selected as the thermal conductive filler and filled into a sodium silicate matrix with a mass fraction of 34% to prepare a series of inorganic thermal conductive adhesives. The thermal conductivity of the diamond powder and its content on the thermal conductivity of the adhesive were studied by testing the thermal conductivity and taking SEM photos. In addition, X-ray diffraction, infrared spectroscopy, and EDS testing were used to analyze the composition of the modified diamond powder surface. Through the study of diamond content, it was found that as the diamond content gradually increases, the adhesive performance of the thermal conductive adhesive first increases and then decreases. The best adhesive performance was achieved when the diamond mass fraction was 60%, with a tensile shear strength of 1.83 MPa. As the diamond content increased, the thermal conductivity of the thermal conductive adhesive first increased and then decreased. The best thermal conductivity was achieved when the diamond mass fraction was 50%, with a thermal conductivity coefficient of 10.32 W/(m·K). The best adhesive performance and thermal conductivity were achieved when the diamond mass fraction was between 50% and 60%. The inorganic thermal conductive adhesive system based on sodium silicate and diamond proposed in this study has outstanding comprehensive performance and is a promising new thermal conductive material that can replace organic thermal conductive adhesives. The results of this study provide new ideas and methods for the development of inorganic thermal conductive adhesives and are expected to promote the application and development of inorganic thermal conductive materials.

Improving the operating performance of superhard composites is an important and urgent task, due to a continuing industrial need. In this work, diamond composites with high wear resistance were obtained by sintering fluorinated mixtures of micron-sized diamonds with nanodiamonds at high pressures and temperatures (7–8 GPa, 1550–1700 °C). Aluminum and cobalt powders were added to the diamond mixture to activate the process. The external infiltration of nickel into the diamond layer was carried out additionally during the sintering process, and the effects of nickel infiltration on the structure and properties of composites were studied. The metal melt ensured the mass transfer of carbon within a volume, and the formation of a strong diamond framework. The composition of the additives was selected in such a way that the binding phase became ultimately composed of the intermetallic AlNixCo1−x(x ≤ 1). The Young’s modulus of composites synthesized in this way had a value of 850 GPa, and their wear resistance when turning white granite was more than twice as high as that of premium commercial PDC. The obtained results thus demonstrate that by using nickel to increase melt infiltration into diamond-based composites, the mechanical properties of Al/Co/fluorinated diamond compositions, studied previously, can be further improved.

In order to improve the automatic level for laser-cladding repair of high value industrial equipment, such as polycrystalline diamond compact bit (PDC bit) applied in oil industry, a universal scheme of integrated automatic system for repairing is proposed in this paper, and the basic functional modules together with the executing order according to which each module runs are defined. There are two main technical points, i.e.,inspection and repairing, that need to be realized for such integrated automatic system. Therefore, according to the proposed scheme and the existing instruments, a dual-robot system, which includes two KUKA industrial robots, is adopted as the technological implementation, where one robot is used to carry a 3D scanner to reconstruct the PDC bit to realize inspection while the other is used to hold the laser to melt the special powder flowing to the damaged region of the bit to complete cladding. To realize automatic running of the whole integrated system, a hand-eye calibration method, namely three-point calibration, is then proposed, by which coordinates of point cloud of the damaged PDC bit detected by 3D scanner can be transformed to those of the coordinate system of the robot with the laser, so that the cladding path planned via cutting slice of the damaged region of the PDC bit in the upper computer software, the key of the integrated system developed by QT programming tool, can be tracked by laser head and then the damaged part of the PDC bit can be repaired. Finally, a laser-cladding experiment for repairing PDC bit is carried out and the feasibility of the proposed scheme of the integrated automatic system and the effectiveness of the dual-robot system implemented via KUKA robots are verified, According to existing literature, no papers about such integrated system for automatic laser cladding repair have been published.

A system of boron-doped diamond (BDD) anode combined with a gas diffusion electrode (GDE) as a cathode is an attractive kind of electrolysis system to treat wastewater to remove organic pollutants. Depending on the operating parameters and water matrix, the kinetics of the electrochemical reaction must be defined to calculate the reaction rate constant, which enables designing the treatment reactor in a continuous process. In this work, synthetic wastewater simulating the vacuum toilet sewage on trains was treated via a BDD-GDE reactor, where the kinetics was presented as the abatement of chemical oxygen demand (COD) over time. By investigating three different initial COD concentrations (C0,1 ≈ 2 × C0,2 ≈ 4 × C0,3), the kinetics was presented and the observed reaction rate constant kobs. was derived at different current densities (20, 50, 100 mA/cm2). Accordingly, a mathematical model has derived kobs. as a function of the cell potential Ecell. Ranging from 1 × 10−5 to 7.4 × 10−5 s−1, the kobs. is readily calculated when Ecell varies in a range of 2.5–21 V. Furthermore, it was experimentally stated that the highest economic removal of COD was achieved at 20 mA/cm2 demanding the lowest specific charge (~7 Ah/gCOD) and acquiring the highest current efficiency (up to ~48%).