Fine Diamond Particles Research Articles

Diamond reinforced reaction-bonded boron carbide composites: Fabrication, microstructure, mechanical and tribological properties

Reaction-bonded boron carbide composites were fabricated by molten silicon infiltration of diamond-containing boron carbide preforms. The effects of diamond particle size on the microstructure, mechanical and tribological properties of reaction-bonded boron carbide composites were investigated. Fine diamond particles (≤7.7 µm) completely reacted with silicon generating nano silicon carbide particles, which bonded the boron carbide particles forming a 3-D ceramic skeleton and improving the flexural strength of the composites. Coarser diamond (≥24 µm) particles were retained protected by a dense SiC layer generated from the reaction of diamond and molten silicon. A “core-shell” structure with the retained diamond as the “core” and with the reaction formed silicon carbide as the “shell” formed. Relief structures were established on the composites’ surface during the wear process, greatly reducing the friction coefficient and improving the wear resistance.

Improvement of dispersion of nanometer-sized diamond particles for precise polishing by ultrasound exposure

A novel acoustic dispersion method for fine diamond particles was investigated by our group. Nanometer-sized diamond particles for abrasive agents should be dispersed sufficiently in water without aggregation. The particles usually aggregate immediately after their manufacture. The dispersants and dispersion equipment are used for dispersion of the particles. However, these dispersion methods present problems in their dispersion characteristics and reaggregation because such methods do not improve the essential surface characteristics. We suggested the acoustic dispersion method. We reported in 2005 at the IEEE Conference in Rotterdam that nanometer-sized diamond particles with 5-nm primary particle size were dispersed using ultrasound. The particles with 5-nm primary particle size are anticipated for use as future abrasive agents. Particles with 50-nm primary particle size are actually used at present as abrasive agents. Therefore, in this study, we investigated the dispersion of particles with primary particle sizes of 20, 50, 80, and 150 nm. Results show that the aggregated particles were disaggregated to nanometer-sized particles. Zeta potentials of the diamond particles were increased by ultrasound. These results suggest the improvement of dispersion of nanometer-sized diamond particles in water.

Improving dispersion of nanometer-size diamond particles by acoustic cavitation

A novel acoustic-dispersion method for fine diamond particles was developed. Two samples of nanometer-sized diamond particles were used. They had primary particle sizes of 5 nm (ND5) and 150 nm (ND150). Disaggregation of agglomerated particles using ultrasound and surface modification of ND5 and ND150 were investigated. The ND5 and ND150 particles aggregated to secondary particles, having sizes on the order of micrometers. The surfaces of ND5 and ND150 particle were modified due to chemical reactions and the particles were disaggregated by acoustic cavitation. The ND5 particles were disaggregated to give an average particle size of about 100 nm by ultrasound exposure with average acoustic intensities higher than 800 W/m 2. The agglomerated ND150 particles with size of 15 μm were disaggregated to reach an average particle size of about 300 nm by ultrasound exposure with an average acoustic intensity higher than 2000 W/m 2. The surfaces of ND5 and ND150 particles were found to be modified with hydroxyl groups resulting from acoustic cavitation. This could lead to a well dispersed solution of nanometer-sized diamond particles in water.

Diamond nucleation in low electron temperature CH 4/H 2 plasma

Nucleation of diamond crystal is observed on a surface of fine diamond particles of micron meters attached to a nickel plate placed in methane–hydrogen plasma. The electron temperature T e in the plasma is quite important for the nucleation. When T e is reduced to ∼0.4 eV, we observed an appearance of nanometer diamond nucleation on the surface of the fine diamond particles. The size and the number of nucleation cite increase with the deposition time with average growth rate of ∼10 nm/h.

Profile analysis of surfaces lapped with diamond particles of several shapes

Mechanical lapping is still used widely as one of fine finishings of material surfaces in spite of increasing applications of chemical polishing. In the mechanical operation, fine diamond particles play an important role because of their high lapping performance except for the presence of occasional scratching which should be solved or mitigated by investigating particle characteristics and lapping procedures. On the other hand, the approach to comprehensive analysis of surface profiles recorded during lapping process needs to be considered in addition to the statistical standards such as average surface roughness, maximum peak height, 10-point height, etc. It is a useful trial to apply wave analyses aided with functional transformation for identification of the characteristic parameters of lapped surfaces. Hence, the profiles were analyzed for surfaces prepared under several differently shaped diamond particles within narrow size ranges. In this report, the results of the mathematical analysis of the profiles obtained from 2D scanning of lapped surfaces, which include the directional roughness, are discussed in terms of surface uniformity, asymmetricity, waviness evaluation, etc. These surface characteristics are closely related with the shape parameters of grinds (diamond particles) such as elongation, polygonality, irregularity, etc.

Diamond-particles levitated in a reactive plasma

Dynamic behaviors of fine diamond-particles levitated in low-pressure plasmas are investigated. Fine diamond-particles injected into the plasma are charged up negatively and confined electrically above a radio frequency (RF) powered electrode at some vertical position where the gravity force acting on the particles balances with the electric force in the sheath region in front of the RF electrode. The average size of the diamond particles employed here is ∼2 μm. We observed that the diamond particles reveal strong motions in the lower-pressure discharge plasma. These motions are quite random and the equivalent kinetic temperature attained is ∼10 eV which is higher than the thermal level of the particles. The motion is gradually suppressed in the higher-pressure regime. The mechanisms of the diamond particle behaviors are discussed.

Atom force microscopy study on HTHP as-grown diamond single crystals

For understanding the mechanism of diamond growth at high temperature–high pressure (HTHP) from a metallic catalyst–graphite system, it is of great interest to perform atomic force microscopy (AFM) experiments, which provide a unique technique different from that of normal optical and electronic microscopy studies, to study the topography of HTHP as-grown diamond single crystals. In the present paper, we report first AFM results on diamond single crystals grown from a Fe-Ni-C system at HTHP to reveal the growth mechanism of diamond single crystals at HTHP. AFM images for as-grown diamond samples show dark etch pits on the (111) surface, indicating dislocations. Some fine particles about 100–300 nm in dimension were directly observed on the (100) diamond surface. These particles are believed to have been formed through transition of graphite to diamond under the effect of the catalyst and to have been transported to the growing diamond surface through a metallic thin film by diffusion. The roughness of the (100) diamond surface is found to be about several tens of nanometers through profile analysis. The diamond growth at HTHP, in a sense, could be considered as a process of unification of these fine diamond particles or of carbon-atom-cluster recombination on the growing diamond crystal surface. Successive growth interlayer steps on the (111) diamond surface were systemically examined. The heights of the growth interlayer steps were measured by sectional analysis. It was shown that the heights of the growth interlayer steps are quite different and range from about 10 to 25 nm. The source of the interlayer steps might be dislocations. The diamond-growth mechanism at HTHP could be indicated by the AFM topography of the fine diamond particles and the train-growth interlayer steps on the as-grown diamond surfaces.

Lapping performance guide of poly-crystal diamond particles through morphological analysis

Morphological properties of fine diamond particles are intimately related to applications for fine processing such as wearing and polishing of advanced industrial materials and products. The authors are improving and refining particles of poly-crystal diamonds made by an explosive method through size-sorting and shape classification. Obtained products, of micron sizes, have been tested on the lapping rates with the peripheral morphology aided by the parameters of Fourier transformation, where this new method of transforming peripheral functions is presented by the authors. The results will be useful to indicate the direction of better productivity with quantitative parametric characterization instead of the previous qualitative shape descriptions. The relationship between sizes and shapes of particles in conjunction with the mechanical lapping conditions must carefully be taken into account to evaluate the state of polished surfaces. The ordinary standard examines either statistical values from several representatively selected points or mean roughness from the wavy polished surfaces. It is certain that a faster polishing rate, with particles of optimum shape and/or larger size, creates rather rough surfaces, however, statistical averages are likely to be less accurate. For particles with higher lapping rates but fewer scratches, surface profiles (waviness) are evaluated by the Fourier transformation (FFT) method (averages of power spectra) in this report.

A study on the wear resistance of electroless Ni–P/Diamond composite coatings

The ability to co-deposit particulate matter in a matrix of electroless nickel has led to a new generation of composite coatings. Polycrystalline diamond is one of the many varieties of particulate matter that can be co-deposited. Composite diamond coating is a regenerative layer of fine diamond particles dispersed in a hard electroless nickel matrix. In this work, experiments have been carried out to study the effect of heat treatment, particle size and phosphorus content on the wear characteristics of the composite electroless coating containing diamond particles. The results indicate substantial increase in wear resistance after the coated sample containing 9–10 wt.%. P content having fine diamond particle size is annealed around 350°C.

ABRASIVE MACHINING OF GLASS-CERAMICS WITH A DENTAL HANDPIECE

Dental restorations are commonly prepared from machinable glass-ceramics using modern dental CAD/CAM systems. Unfortunately, little is understood about the influence of machining parameters on material removal rates and any damage which could be introduced into the restoration during the abrasive machining processes employed with these systems. These effects are investigated for three experimental machinable glass-ceramics with varying microstructure and one closely related commercial material. Abrasive machining is performed with dental burs containing coarse and fine diamond particles. The results show that the microstructure of the glass-ceramic, the size of diamond grit in the burs, and the load applied to the burs during machining have significant effects on the machining behavior. By increasing the size of the mica platelets within the glass-ceramics or by increasing the load on the burs, material removal rate increases. However, chipping damage at groove edges increases as either the load is increased or as the size of the mica platelets is decreased. The use of coarse burs does not necessarily result in high material removal rates but increases the extent of chipping damage. Surface roughness is found to be relatively independent of the microstructure or applied load but is strongly dependent upon coarseness of the diamond particles in the burs.

The effects of particle pollution on the mechanical behaviour of multilayered systems

The mechanical stability of multilayered structures depends on the intrinsic properties of its layers, as on the external applied solicitations (thermal and/or mechanical). Moreover, the structural imperfections, as the ones generated during the deposition process of the layers, may also play an important role in the mechanical stability of the multilayers. For example, a continuous or a sequential laser irradiation on a multilayered mirror, can produce mechanical damage, which is nucleated at the imperfections of the multilayer. With the aim to study the mechanical damage associated to the imperfections of a multilayered structure, the response to an external stress on multilayered samples, with and without imperfections was analysed. The imperfections were obtained by the dispersion of fine diamond particles on polished substrates, before the deposition of the layers. The mechanically damage was progressively induced by pulling the samples in tension in a SEM. The critical parameters, characterising the behaviour and describing the damage are compared and discussed.

Reaction Sintering of Si Coated-Diamond Fine Particles under Ultrahigh Pressure.

Fine diamond particles (from 0. 5 to 2μm) were successfully coated with silicon of 6. 6, 13. 8 and 20. 0vol% by PVD method. These coated particles were sintered under 5. 5GPa at 1723K for 0. 5h with a cubic type ultrahigh pressure apparatus. Silicon carbide in each sintered diamond compact was formed between the diamond particles during sintering and acted as a bonding material for the diamonds. The obtained sinter having silicon carbide of 21. 8vol% was fully densified and showed very high hardness (about 9700 HV 1. 0) as high as the diamond sinter produced for industrial usage.

微粒子の表面処理 超微粒ダイヤモンド

微粒子の表面処理 超微粒ダイヤモンド

Formation of diamond during passage of a shock wave in a copper/graphite powder: Formation process and numerical simulation

A powder mixture of copper and graphite was dynamically shock-compressed by a rod-in-cylinder method. Structural characterization of the recovered specimen by transmission electron microscopy (TEM) showed the development of fine spherical diamond particles through shock-induced nuclei formation in the high pressure state and shock-assisted nuclei growth during unloading to ambient pressure via a solid–liquid–solid (SLS) phase transformation. A 2 μm large diamond particle was formed via a shock-induced martensitic path. Quantitative numerical simulation applying the two-dimensional computation code AUTODYN 2D was conducted to evaluate the pressure conditions during shock loading.

Patterning of CVD diamond films by seeding and their field emission properties

Selective seeding for growing diamond on Si substrates was performed by conventional lithography using photoresist mixed with fine diamond particles. The selectivity was improved by filtering the diamond powder-photoresist mixture and carrying out reactive ion etching of patterned substrates. As a result, a selectivity up to 2.0 × 10 2 or higher was achieved. The resolution was of the order of 1 μm. Field emission from diamonds prepared using this selective growth method was observed without any postgrowth treatment. The measured current vs. voltage plot of a diode showed a rectifying characteristic. Under a forward bias, a current of about 15 μA was obtained at about 570 V, with a turn-on voltage of about 480 V. The emission current was comparable with that which had been observed for Si field emitter tips.

The effect of pretreatment in a fluidized bed upon diamond synthesis on particles by chemical vapour deposition

Diamond synthesis was carried out on non-diamond particles (single- and poly-crystal silicon, quartz and SiC) by microwave plasma-enhanced chemical vapour deposition. Fine diamond particles were deposited on the non-diamond particle surface. The particle deposition density on the untreated particle substrates was strongly dependent on the surface characteristics of the particle substrates. The value ranged from 10–105 mm−2 for each particle. Particle substrates were pretreated in a gas-solid fluidized bed, and these were then used for the deposition of diamond. The pretreatment of the surface of the particle substrate in the fluidized bed greatly enhanced the nucleation of diamond. A deposition density of about 107 mm−2 was obtained on single-crystal silicon particles pretreated for 15 h. The effectiveness of the fluidized bed pretreatment on the deposition density was observed to be appreciable for the four kinds of particle examined.

Techniques for Patterning of CVD Diamond Films on Non‐Diamond Substrates

Three techniques for patterning of CVD diamond films are developed. First, predeposition patterning is performed by standard lithography using photoresist mixed with fine diamond particles to act as seed crystals. Second, substrates are masked either before ultrasonic treatment with diamond powder (which promotes nucleation), and the mask removed before diamond growth, or masked after treatment but before diamond deposition. Third, patterning of continuous diamond thin films by selective etching in oxygen at 700°C has been performed in a rapid thermal processor using or as masking layer. The selectivity and resolution was found to be good in all cases.

IR spectra of small molecules adsorbed on carbon films. Adsorption potentials and spectral shifts

IR spectra of CO, NO and CH 3F adsorbed on graphite-like and diamond powder films were studied at low temperatures. The graphite-like films were prepared by laser evaporation of graphite in He atmosphere. The diamond films were obtained by sedimentation of fine diamond particles from a suspension. In a11 cases physical adsorption was observed. The spectrum of adsorbed NO showed clearly the presence of dimers. For CO, the adsorption potential and the shift in frequency from the gas phase were calculated for both adsorbents, and compared with the experimental values.

Abrasive wear with fine diamond particles of carbide-containing aluminum and titanium alloy surfaces

Abrasive wear testing with 3 and 30 μm diamond particles demon-strated that the wear resistance of aluminum and titanium alloys can be significantly increased by introducing tungsten carbide or titanium carbide particles into their surfaces. Carbide particles ranging in size from about 20 to 200 μm were incorporated into the surface of the alloys by a laser processing technique which can produce hardened surfaces about 0.5–3.0 mm thick. The testing showed that the wear resistance of aluminum-base alloys was improved by as much as a factor of 30 in samples containing TiC. Less dramatic improvements were found for Ti-6Al-4V containing TiC and WC, the largest improvement being by a factor of 3.8. The test results are discussed in terms of the type of carbide particle used, the volume fraction of carbide in the test samples and the microstructures of the laserprocessed surface.