Porous Diamond Research Articles

Porous diamond Co-MOF and polyethylene glycol composites as form-stable phase change materials for thermal energy storage

Porous diamond Co-MOF and polyethylene glycol composites as form-stable phase change materials for thermal energy storage

Convection Heat Transfer and Performance Analysis of a Triply Periodic Minimal Surface (TPMS) for a Novel Heat Exchanger

Heat exchangers are necessary in most engineering systems that move thermal energy from a hot source to a colder location. The development of additive manufacturing technology facilitates the design and optimization of heat exchangers by introducing triply periodic minimal surface (TPMS) structures. TPMSs have shown excellent mechanical and thermal performance, which can improve heat energy transfer efficiency in heat exchangers. This current study intends to design and develop efficient, lightweight heat exchangers for aerospace and space applications. Using the TPMS structure, a porous construction encloses a horizontal tube that circulates heated fluid. Low-temperature water circulates inside a rectangular box that houses the complete system to remove heat from the horizontal pipe. Three porous structures, the gyroid, diamond, and FKS structures, were employed and examined. Porous models with various porosities and surface areas (15 cm2 and 24 cm2) were investigated. The results revealed that the gyroid structure exhibits the highest Nusselt number for heat removal (Nu max = 2250), confirming the highest heat transfer and lowest pressure drop among the three structures under investigation. The maximum Nusselt number obtained for the FKS structure is less than 1000, whereas, for the diamond structure, it is near 1250. A linear variation in the average Nusselt number as a function of the structure surface area was found for the FKS and diamond structures. In contrast, nonlinearity was observed in the gyroid structures.

Enhanced precision lapping techniques for fused quartz optical elements: Synergistic integration of mechanical and mechanochemical processes

Fused silica is a material of great importance in the field of precision optical equipment due to its excellent optical properties, e.g. photolithography, laser fusion devices, etc. However, the material's inherent hardness and brittleness render it a challenging material to process. Therefore, an enhanced precision lapping technique was proposed, i.e., a synergistic integration of mechanical and mechanochemical lapping processes. Firstly, a synergistic lapping tool with an outer layer of porous diamond abrasive and an inner layer of CeO2 abrasive was fabricated by hot press forming method. The reduction of layer thickness due to abrasion and detachment of the porous diamond abrasive layer was analyzed, and the lapping mechanism of porous diamond on fused silica materials was revealed. The surface creation mechanism of the CeO2 abrasive layer on fused silica material was analyzed by molecular dynamics simulation and the results were validated by enhanced precision lapping experiment. The results demonstrated that the surface atoms of fused silica are removed in a ‘remote disordered’ manner by conventional diamond abrasive grains, whereas the surface atoms of fused silica are removed in a ‘proximally ordered’ manner by the fine porous diamond abrasive grains through the micro-multi-flute cutting. Consequently, the grinding of a porous diamond abrasive layer can significantly reduce the processing damage, with the surface roughness of the lapping Ra reaching 199 nm. The lapping of CeO2 induces the formation of an oxygen bridge on the surface of fused silica, which then produces bending vibration. This is followed by the adsorption and diffusion of oxygen atoms, which form the -Ce-O-Si intermediate with the oxygen atoms shared with the fused silica. This process results in the formation of CeSiO3 and CaSiO3 compounds. The final surface quality with a surface roughness of Ra 21 nm was obtained by mechanochemical lapping of the cerium oxide abrasive layer. The single mechanical-mechanochemical composite ultra-precision lapping process provides technical support for the efficient and low-damage processing of hard and brittle components.

Material Removal Mechanism of SiC Ceramic by Porous Diamond Grinding Wheel Using Discrete Element Simulation.

SiC ceramics are typically hard and brittle materials. Serious surface/subsurface damage occurs during the grinding process due to the poor self-sharpening ability of monocrystalline diamond grits. Nevertheless, recent findings have demonstrated that porous diamond grits can achieve high-efficiency and low-damage machining. However, research on the removal mechanism of porous diamond grit while grinding SiC ceramic materials is still in the bottleneck stage. A discrete element simulation model of the porous diamond grit while grinding SiC ceramics was established to optimize the grinding parameters (e.g., grinding wheel speed, undeformed chip thickness) and pore parameters (e.g., cutting edge density) of the porous diamond grit. The influence of these above parameters on the removal and damage of SiC ceramics was explored from a microscopic perspective, comparing with monocrystalline diamond grit. The results show that porous diamond grits cause less damage to SiC ceramics and have better grinding performance than monocrystalline diamond grits. In addition, the optimal cutting edge density and undeformed chip thickness should be controlled at 1-3 and 1-2 um, respectively, and the grinding wheel speed should be greater than 80 m/s. The research results lay a scientific foundation for the efficient and low-damage grinding of hard and brittle materials represented by SiC ceramics, exhibiting theoretical significance and practical value.

Compressive Characteristics and Energy Absorption Capacity of Automobile Energy-Absorbing Box with Filled Porous TPMS Structures

In order to meet the higher requirements of energy-absorbing structures in the lightweight automobile design, the mechanical design and impact energy absorption of porous TPMS structures are studied. Eight kinds of porous TPMS structure elements, Gyroid, Diamond, I-WP, Neovius, Primitive, Fischer-Koch S, F-RD, and PMY, are designed based on Matlab, and the porous structure samples composed of eight elements are printed and molded using SLM. The deformation mechanism, mechanical response, and energy absorption characteristics of different porous TPMS structures are investigated. Gyroid and Primitive elements are selected to fill the internal structure of the energy-absorbing automobile boxes. Traditional thin-walled energy-absorbing boxes served as a control group and were subjected to low-speed impact testing. The results show that the peak load of the energy-absorbing box filled with TPMS porous structures is almost equal to the average load under a 4.4 m/s impact, and the SEA of the energy-absorbing box filled with TPMS porous structures is higher than the traditional thin-walled energy-absorbing box. The problems of excessive peak load and inconsistent load fluctuation of traditional thin-walled energy-absorbing structures are effectively solved by porous TPMS structures with the assurance that the lightweight and energy-absorbing requirements are still met.

Effect of PMMA pore former on mechanical strength and performance of glass fibre metal-bonded porous diamond blocks with Cu–Sn–Ti solder alloys

To develop a metal-bonded diamond tool that does not require frequent dressing during grinding, a novel glass fibre metal-bonded porous diamond block is proposed. The effect of the content percentage and particle size of polymethyl methacrylate (PMMA) pore formers on the porosity of porous diamond blocks was investigated. The Vickers hardness and bending strength of the porous blocks with and without diamonds were tested. Wear tests were performed on the porous diamond blocks. The results show that an increase in the PMMA content (1.75–9.45 wt%) caused an increase in the porosity (2.8 %–22.9 %) and a decrease in the bending strength (8.6 %–71.9 %) and Vickers hardness (22.1 %–54.3 %), compared to those of the blocks without PMMA. An increase of PMMA size (20–40 μm diameter) caused an increase in the porosity (2 %–11.6 %), and a decrease in the bending strength (34.1 %–42.7 %) and Vickers hardness (23.7 %, 40.5 %), compared to those of the blocks without PMMA. However, excessively large PMMA particles (50–70 μm diameter) caused a decrease in the porosity and an increase in the bending strength and Vickers hardness. Increasing the porosity of the diamond blocks appropriately can reduce the need for frequent dressing and enhance the SiC removal rate. However, excessive porosity tends to accelerate diamond wear, leading to a decrease in the SiC removal rate.

3D gel-printing of phenolic resin-based diamond tool parts

In this study, the phenolic resin-based diamond tool parts were successfully prepared by 3D gel-printing (3DGP), the rheological properties of printing slurries and mechanical properties of the prepared resin-based diamond parts were characterizated. The results show that when the amount of phenolic resin to anhydrous ethanol was 2:1, the slurry was suitable for extrusion printing, and it was also easy to keep the shape of the printed product. When the needle size was 0.60 mm, the layer height was 0.48 mm, and the line width was 0.48 mm, the printed products had superior surface quality. For dense parts, the three-point bending strength of diamond part printed was about 27.0 MPa. The Rockwell hardness values of the dense parts prepared from the two powders were 81.0 for 1.58 μm and 85.1 for 2.61 μm, and their roughness (Ra) was about 6.99 μm and 6.15 μm, respectively. For porous parts, the bending strength of parts prepared from 1.58 μm diamond powder was from 11.8 MPa to 18.2 MPa and that of parts prepared from 2.61 μm diamond powder was from 15.5 MPa to 21.6 MPa when the porosity was 20–50%. The dense and porous resin-based diamond parts with controllable structure and porosity were successfully prepared by 3DGP, which has a promising future application in the field of abrasive materials.

Synthesis of porous single-crystal diamond with boron doping under high temperature and high pressure

In this paper, porous single-crystal diamond with boron doping were synthesized by adding TiB2 to the Fe–Ni–C system at a pressure of 5.6 GPa and a temperature of 1360 °C. The boron and nitrogen impurities were investigated in depth along with the surface defects of the diamonds. The results indicate that when the TiB2 content was within the range of 0–10 wt%, an increase in the doping concentration of TiB2 can lead to a decrease in the nitrogen content and an increase in the boron content in the diamond, causing the crystal color to transition from yellow to pale yellow, pale yellow-blue, and black. When the TiB2 content was within the range of 20–40 wt%, several triangular concave porous structures appeared on the crystal surface. With an increase in the TiB2 addition, the side length of these triangular pits decreased from 2.85 μm to 1.09 μm, while their depth decreased from 590 nm to 50 nm. The roughness of the crystal surface measured by Rq demonstrated values up to 145.302 nm. The results indicate that the size, depth, and density of the triangular defects can be adjusted by the amount of additive TiB2. Our findings provide insights into the surface regulation and functionalization of boron-doped diamond single crystals.

Microstructure Optimization for Design of Porous Tantalum Scaffolds Based on Mechanical Properties and Permeability.

Porous tantalum (Ta) implants have important clinical application prospects due to their appropriate elastic modulus, and their excellent bone growth and bone conduction ability. However, porous Ta microstructure designs generally mimic titanium (Ti) implants commonly used in the clinic, and there is a lack of research on the influence of the microstructure on the mechanical properties and penetration characteristics, which will greatly affect bone integration performance. This study explored the effects of different microstructure parameters, including the fillet radius of the middle plane and top planes, on the mechanics and permeability properties of porous Ta diamond cells through simulation, and put forward an optimization design with a 0.5 mm midplane fillet radius and 0.3 mm top-plane fillet radius in order to significantly decrease the stress concentration effect and improve permeability. On this basis, the porous Ta structures were prepared by Laser Powder Bed Fusion (LPBF) technology and evaluated before and after microstructural optimization. The elastic modulus and the yield strength were increased by 2.31% and 10.39%, respectively. At the same time, the permeability of the optimized structure was also increased by 8.25%. The optimized microstructure design of porous Ta has important medical application value.

Construction of porous diamond film with enhanced electric double-layer capacitance via regrowth of diamond nanoplatelets

The engineering of porous boron-doped diamond (BDD) film has sparked significant interest in improving electric double-layer (EDL) capacitance. However, the presence of disordered and tortuous pores in the BDD film hinders the accessibility of the bottom pore surface area, leading to a decrease in specific EDL capacitance. Herein, a novel porous BDD film with vertically open pore channels is constructed through the overcoating of diamond nanoplatelet template with a BDD layer using chemical vapor deposition. Electrochemical investigations manifest that the specific areal EDL capacitance of the porous BDD is ∼428 times greater than that of the planar BDD film. More impressively, the porous BDD film demonstrates a higher specific volumetric EDL capacitance (39.30 F/cm3) and superior long-term stability (100% capacitance retention after 12,000 cycles), surpassing the performance of most developed porous BDD electrodes. The exceptional performance of the porous BDD film was attributed to the abundant vertically open pore channels, good hydrophilic property, maximized electrochemical available area, and good chemical/mechanical stability. This work benefits the development of the BDD film as an EDL micro-capacitor electrode, and the methodology proposed here shows great potentials to fabricate an ordered porous BDD nanostructure with large specific area for more electrochemical applications.

Ultra-precision lapping of H2O(g) plasma-treated CaF2 by porous diamond grits

The calcium fluoride (CaF2) component has excellent light transmission and a high laser damage threshold in the UV band, and thus is a potentially ideal material for high-power laser facility. However, the low-damage surface is difficult to attain via the existing processing technologies due to its brittleness, especially the dissociation property of the (111) surface. We innovatively propose H2O(g) plasma-assisted porous diamond abrasive lapping technology to achieve low-damage and high-precision surface processing of CaF2 component, which means that the CaF2 component is modified first and then the softened modified layer is removed by the porous diamond abrasive lapping. The H2O(g) plasma modification mechanism was elucidated through a combination of molecular dynamics simulation and experiment and comparison with H2O(g) plasma etching. The modification layer including an oxide layer and a phase change layer was produced by adjusting the plasma processing process (power of 25 W and H2O(g) content of 10 ml). Then the modified CaF2 component was lapped by the porous diamond abrasive tool on the ductile domain layer which is more than the modified layer and less than the sum of the modified layer and plastic domain. When the lapping process parameters were 200 rpm platen rotation speed and 20 N lapping pressure, a surface accuracy of 15.34 nm PV, 2.29 nm RMS (φ1 mm) was obtained. This study provides technical support for the low-damage processing of CaF2 component.

The Influence of Heat Treatment Temperature on Tensile Properties of Metal-Bonded Diamond Composites Fabricated via Selective Laser Melting.

Selective Laser Melting (SLM) is an effective technology for fabricating new types of porous metal-bonded diamond tools with complex geometries. However, due to the high cooling rate and internal stresses during SLM fabrication, defects such as high porosities and interface gaps still need to be resolved before it can be considered for use in other applications. The influence of heat treatment temperature on internal characterization, interface microstructures, and tensile properties of AlSi7Mg-bonded diamond composites fabricated by SLM were investigated in this work. From experimental results, the porosities of HT-200, HT-350, and HT-500 specimens were 12.19%, 11.37%, and 11.14%, respectively, showing a slightly lower percentage than that of the No-HT specimen (13.34%). Here, HT represents "Heat Treatment". For No-HT specimens, an obvious un-bonding area can be seen in the interface between AlSi7Mg and diamond, whereas a relative closer interface can be observed for HT-500 specimens. After heat treatment, the elastic modulus of specimens showed a relative stable value (16.77 ± 2.79~18.23 ± 1.72 GPa), while the value of yield strength decreased from 97.24 ± 4.48 to 44.94 ± 7.06 MPa and the value of elongation increased from 1.98 ± 0.05 to 6.62 ± 0.51%. This difference can be attributed mainly to the disappearance of the solid-solution hardening effect due to the increase of Si content after heat treatment.

Sound absorption performance of micro-perforated plate sandwich structure based on triply periodic minimal surface

The sandwich structure based on Triply periodic minimal surface (TPMS) is a lightweight and high-strength multifunctional composite material that combines the versatility of heat exchange, impact resistance, and energy absorption, and has been widely used in various fields such as aviation and aerospace. However, its sound absorption performance has not meant fully studied. In this paper, a Micro-perforated plate Diamond sandwich structure (MPP-DSS) was designed based on TPMS method, which was composed of aluminum alloy solid panel, aluminum alloy macroscopically ordered porous Diamond structure and aluminum alloy micro-perforated plate. The acoustic absorption performance in low and medium frequency band was studied by impedance tube method. The results show that MPP-DSS has higher absorption coefficient and bandwidth than traditional perforated plate structure with the same structural parameters. Increasing the thickness of micro-perforated plate can improve the sound absorption capacity of MPP-DSS in the low frequency range, but the width of the sound absorption band will be narrowed accordingly. Different from the resonant sound absorption mechanism of the traditional perforated plate structure, the sound absorption mechanism of MPP-DSS is the combined effect of resonant sound absorption and friction loss sound absorption. This study broadens the versatility of the TPMS structure and can serve as a reference for the design of integrated load-bearing and sound-absorbing structures.

Porous Natural Diamond with Embedded Metal (Pt0.50–Co0.50)

Natural diamond crystals with a highly porous surface were used as substrates for synthesizing single-phase bimetallic Pt–Co nanoparticles at temperatures of 500 °C and 800 °C. The metal nanoparticles inside the pores were determined to take the form of single-phase Pt0.50Co0.50 solid solutions with different degrees of superstructure ordering. A detailed characterization of both nanoalloys revealed a tetragonal symmetry with a space group, P4/mmm. For the sample obtained at 500 °C, the lattice parameters were a = 2.673(2), c = 3.735(3) Å, and c/a = 1.397(1); for the samples obtained at 800 °C, the parameters were—a = 2.688(2), c = 3.697(3) Å, and c/a = 1.375(1). Within the experimental parameters, no significant chemical interaction of the diamond with the Pt–Co particles was identified. The results demonstrate a strong anchoring effect of the metallic material within the etching pores. The successful synthesis of bimetallic Pt–Co particles embedded inside the caverns can facilitate a study of their magnetic properties. The presence of Pt–Co in specific diamond compositions can also be used for marking diamond crystals as a means for their subtle identification, as well as confirming the possibility of capturing significant amounts of metal along with diamonds during their dissolution in the deep Earth.

Effect of Diamond Phase Dispersion on the Properties of Diamond-SiC-Si Composites

The research aimed at the composition optimization for diamond-SiC-Si composites. The effect of a porous diamond workpiece was studied on the properties (porosity, density, modulus of elasticity, phase composition) of the product of its siliconization with molten silicon. The lowest porosity and highest modulus of elasticity were observed in the case of using mixed matrices with the maximum size of diamond grains of 250/200 μm for siliconization. The best results in terms of the sound speed (16,600 m/s) and elasticity modulus (860 GPa) were achieved by microwave processing of a composite containing detonation nanodiamonds.

Combination of porous structure and MnO2 modification for improving capacitance of planar BDD electrode

Wearable electronic devices have become a preferred choice for health monitoring, but suffer from low capacitance of planar electrodes. This work aims to improve the capacitive performance through the combination of porous boron-doped diamond (BDD) and MnO2 modification. BDD film was deposited on the substrate of titanium foam using hot-filament chemical vapor deposition (HFCVD). Constant-voltage deposition was then employed to deposit MnO2 on the BDD, and the deposition time was adjusted to evaluate the influence of MnO2 modification on the electrode capacitance. Porous structure formed by titanium foam enables BDD electrode to exhibit larger specific surface area, and reach a capacitance of 67.9 mF/cm2. Porous BDD/MnO2 film (MnO2 deposited for 1500 s) shows pea-like morphology and has optimal capacitive performance. BDD/MnO2-1500 s electrode displays a maximum capacitance of 1383.6 mF/cm2 at a current density of 2 mA/cm2, which is about 195 times that of the planar BDD electrode (7.1 mF/cm2 at a current density of 2 mA/cm2) along with a minimum Rct value of 2 Ω. This allows us to see the fact that improvement mechanism of combining porous structure and MnO2 modification may result from common effect of three following aspects: (1) Porous structure gives BDD superior specific surface area and favorable ion transport channels than planar electrode; (2) Pseudocapacitance effect of MnO2 increases the capacitance density; (3) Pea structure of MnO2 may markedly increase the specific surface area of the film and shorten ion/electronic diffusion distances.

Grain wear properties and grinding performance of porous diamond grinding wheels

Conventional diamond grinding wheels present challenges such as poor self-sharpening and difficulties in achieving ductile domain machining when processing hard and brittle materials, reducing machining quality and efficiency. This paper introduces a novel grinding wheel composed of porous diamond abrasive grains for better ultra-precision machining. Thermochemical etching is used to produce porous diamond grains of varying corrosion levels, and the cutting and wear mechanisms of these grains are investigated through molecular dynamics simulations and single-grain scratch tests. Compared to conventional diamond grains, the increased "micro-edge" and "multi-edge" features of porous diamond grains effectively reduce cutting force and heat. Notably, corrosion pore sizes ranging from 2 μm to 5 μm reduce cutting damage. Conventional diamond abrasive grains primarily incur damage through crystal surface dissociation and block crushing, whereas porous diamond abrasive grains experience damage mainly due to micro-crushing and micro-fracture. Ultra-precision grinding tests on 4H–SiC revealed that conventional abrasives produced cracks and pits on the grinding surface. In contrast, abrasives with a 2 μm eroded aperture exhibited predominantly ductile removal with minimal cracks and pits present. Abrasives with a 5 μm eroded aperture displayed desirable characteristics. This research offers valuable technical insights for enhancing the grinding performance of diamond wheels.

Facile Preparation of Porous Diamond Films via Microwave Plasma Based on Metal Particles Heterogeneous Catalysis Etching

The porous diamond film was fabricated via a self-developed microwave plasma chemical vapor deposition (MPCVD) system in H2/Ar plasma by utilizing micrometer-sized diamond films coated with nickel as starting material. SEM and Raman spectroscopy were used to evaluate the evolution of the morphology and sp3 phase of porous diamond with changes in the surface treatment process parameters, including the etching temperature and time. The results indicate that once the etching temperature exceeds 700 °C, the pitting etching phenomenon can be observed on the surface of diamond film. In a certain range, increasing the etching time increases the depth of surface holes on diamond film, whereas the microporous density exhibits an inverted parabolic change pattern. The porous diamond films with uniform pores structure can be obtained by adopting optimal etching process parameter when the H2/Ar plasma temperature is determined at 900 °C for 30 min. The porous formation mechanism of diamond film is attributed to the nickel particles’ heterogeneous catalysis behavior, which promotes the transition route from diamond phase to graphite phase, followed by the preferential etching of graphite phase by H2/Ar plasma.

Permeability design and assessment of the additively manufactured metal-bonded diamond grinding wheel based on TPMS structures

The development of porous metal-bonded diamond grinding wheel with excellent permeability and satisfying mechanical properties is a huge challenge for traditional manufacturing process. In this paper, a novel design and fabrication method of metal-bonded diamond grinding wheel with human-designed open porous structure is proposed based on triply periodic minimal surfaces (TPMS) and additive manufacturing (AM) process. Darcy’ law and Kozeny-Carman equation are used to calculate the permeability coefficient for the porous grinding wheel. The optimal design method of grinding wheel porous structure is proposed comprehensively considering the geometric characteristic, permeability and mechanical properties. The grinding performance of AM porous grinding wheel is evaluated by BK7 glass grinding experiment. The permeability test result proves the effectiveness of permeability design method for the novel diamond grinding wheel. The grinding test result proves the advantages of the novel diamond grinding wheel.

Microporous poly- and monocrystalline diamond films produced from chemical vapor deposited diamond-germanium composites.

We report on a novel method for porous diamond fabrication, which is based on the synthesis of diamond-germanium composite films followed by etching of the Ge component. The composites were grown by microwave plasma assisted CVD in CH4-H2-GeH4 mixtures on (100) silicon, and microcrystalline- and single-crystal diamond substrates. The structure and the phase composition of the films before and after etching were analyzed with scanning electron microscopy and Raman spectroscopy. The films revealed a bright emission of GeV color centers due to diamond doping with Ge, as evidenced by photoluminescence spectroscopy. The possible applications of the porous diamond films include thermal management, surfaces with superhydrophobic properties, chromatography, supercapacitors, etc.