Ultrafine Diamond Research Articles

Centimeter-sized diamond composites with high electrical conductivity and hardness

Achieving high-performance materials with superior mechanical properties and electrical conductivity, especially in large-sized bulk forms, has always been the goal. However, it remains a grand challenge due to the inherent trade-off between these properties. Herein, by employing nanodiamonds as precursors, centimeter-sized diamond/graphene composites were synthesized under moderate pressure and temperature conditions (12 GPa and 1,300 to 1,500 °C), and the composites consisted of ultrafine diamond grains and few-layer graphene domains interconnected through covalently bonded interfaces. The composites exhibit a remarkable electrical conductivity of 2.0 × 104 S m-1 at room temperature, a Vickers hardness of up to ~55.8 GPa, and a toughness of 10.8 to 19.8 MPa m1/2. Theoretical calculations indicate that the transformation energy barrier for the graphitization of diamond surface is lower than that for diamond growth directly from conventional sp2 carbon materials, allowing the synthesis of such diamond composites under mild conditions. The above results pave the way for realizing large-sized diamond-based materials with ultrahigh electrical conductivity and superior mechanical properties simultaneously under moderate synthesis conditions, which will facilitate their large-scale applications in a variety of fields.

Effects of different surface conditioning protocols on shear strength of orthodontic brackets bonded to CAD/CAM materials

The aim of this study was to evaluate the effects of different surface conditioning method combinations on the shear strength of orthodontic brackets bonded various temporary crown materials used in computer aided design and computer aided manufacturing systems. 100 polymethyl methacrylate, 100 bis-acrylic composite and 100 polyetherketoneketone surfaces were prepared from provisional temporary crown blocks. Five different conditioning protocols (etching with 9.6 % hydrofluoric acid, sandblasting with 50 μm Al2O3 particles, roughening with ultrafine diamond bur, Er,Cr:YSGG laser irradiating and priming with methylmethacrylate monomer were applied to the surfaces for each material group. Shear test was performed to half of the bonded samples after 24 hours while the other half 14 days later. The share strengths of the bonded brackets were measured in Newton and Megapascals. In all material groups, the highest share strength values were found in samples sandblasted with Al2O3 particles. For bis-acrylic composite and polymethyl methacrylate groups, the lowest bond strength value were found in samples irradiated with Er,Cr:YSGG laser. The shear bond strengths of the orthodontic brackets bonded to the temporary crown materials produced in CAD/CAM systems vary according to the structure of the material and surface conditioning processes.

Investigation on preparation of composite vitrified bonding ultrafine diamond grinding wheel and machining of PcBN inserts

The grinding of polycrystalline cubic boron nitride (PcBN) is hard owing to its high hardness and superior wear-resistance capacity. Machining of PcBN tools via vitrified diamond grinding wheels with a size above 10 μm may lead to brittle fracture instead of a ductile machining because of the poor toughness of cubic boron nitride. A uniformly dispersed M0.5/1.5 diamond grinding wheel with a composite vitrified bonding was fabricated to improve the surface roughness of PcBN inserts. It is demonstrated that the preparation of composite vitrified bonding with various additions of vitrified bonding produced by the melting-quenching technique (VB-MQ) has little effect on the performance of vitrified bonding, such as bending strength, CTE and phase and achieves the uniform dispersion of M0.5/1.5 diamond as the addition of VB-MQ is no greater than 50%. Both the grinding ratios and the surface roughness of PcBN inserts are enhanced.

Comparative effects of tungsten, diamond burs and laser for residual adhesive removal after orthodontic debonding on flexural strength, surface roughness and phase transformation of high-translucent zirconia: An in vitro study

ObjectivesInformation regarding the effects of orthodontic bracket debonding on zirconia restorations, and the preferred method for residual adhesive removal from the zirconia restoration surface is lacking. Thus, this study aimed to assess the effects of different methods of residual adhesive removal after orthodontic bracket debonding on flexural strength, surface roughness, and phase transformation of high-translucent (HT) zirconia. Materials and methodsThis in vitro study evaluated 72 bar-shaped HT zirconia specimens; 18 specimens were assigned to the control group. Metal brackets were bonded to the remaining specimens by resin cement. After bracket debonding, the residual adhesive on the surface of specimens was removed by three methods (n=18): a 30-flute tungsten-carbide (TC) bur at low speed, an ultrafine diamond bur at high speed, and Er:YAG laser irradiation. The surface roughness (Ra and Rz) was measured. X-ray diffraction (XRD) analysis was carried out, and the flexural strength was measured as well. Data were statistically analyzed (α=0.05). ResultsBefore polishing, all methods increased the Ra and Rz values (P<0.05) except for the diamond bur yielding a Rz value comparable to that of the control group. The Ra values of the test groups were comparable after polishing, and still higher than that of the control group (P<0.05). The flexural strength of all three test groups was comparable (P>0.05), and significantly lower than that of the control group (P<0.001). The monoclinic phase was not observed in any group. ConclusionsOrthodontic bracket debonding adversely affects the surface roughness and flexural strength of zirconia despite polishing.

Fabrication and application of CNT fiber-ultra-fine diamond composites via electrophoretic deposition and instantaneous Joule-heating method

One-dimensional carbon nanotube (CNT) fibers combined with three-dimensional ultra-fine diamond have a synergistic effect that can be used in a variety of applications. The current challenge is how to combine the two materials quickly and efficiently. To actualize the combination of the two materials, a two-step method is adopted in this study. The electrophoretic deposition method, which allows ultra-fine diamond particles to adhere uniformly and controllably to the surface of carbon nanotube fibers. The instantaneous Joule-heating method can realize the instantaneous high-temperature recombination of diamond and CNT fibers. CNT fibers' flexibility and thermal conductivity are combined with ultra-fine diamond's high hardness in this composite. A polishing tool was made by knitting ultra-fine diamond/CNT fiber threads on non-woven fabric and used to dry polish potassium dihydrogen phosphate (KDP) crystals. CNT fibers were examined for wear, surface morphology, and KDP surface roughness before and after processing. The results reveal that the composite material-prepared tool has greater wear resistance and machining efficiency.

Effect of surfactants on vitrified bond diamond composites prepared by sol-gel and dispersibility of diamond

Vitrified ultrafine diamond grinding wheels are ideal for machining next-generation semiconductor power device material, such as SiC etc. However, a crucial problem limiting the application of ultrafine diamond originates from the dispersion of aggregates in vitrified bond. In this study, in can be confirmed that the preparation of uniformly dispersed diamond/vitrified bond composites using sol-gel technique is feasible. Surfactants with various types and additions interactively promote the dispersion of diamond, which make both the bending strength and diamond dispersion of the composites are suitable for precision grinding. The results are valuable for the preparation of vitrified grinding wheels with ultrafine diamond for precision machining of semiconductor.

Lapping performance of mixed-size agglomerated diamond abrasives in fixed abrasives pads

Ultra-fine diamond grains are used to prepare agglomerated diamond (AD) abrasives that are, in turn, applied to make fixed agglomerated diamond abrasive (FADA) pads. The as-prepared pads demonstrated very low removal efficiency along with a poor processing stability，which limits the applicability of ultra-fine diamond grains in fixed abrasive tools. In this reported research, mixed-size agglomerated diamond (MAD) abrasives with a combination of ultra-fine diamond grains and coarser diamond grains were employed to make FADA pads for lapping BK7 glass. Three types of FADA pads were manufactured with ultra-fine AD abrasives, coarser AD abrasives and MAD abrasives, respectively, for maximizing the process efficiency and stability of fixed abrasive pads consisting of ultra-fine diamond abrasives while improving the surface quality of the lapped glass substrates. The results showed that a FADA pad with MAD abrasives exhibited higher material removal rate (MRR) than a pad with AD abrasives of ultra-fine diamond grains only and lower surface roughness Ra and better surface microstructure than a pad with AD abrasives of coarser diamond grains. The distinct lapping feature of MAD abrasives was that the coarser diamond grains mainly accelerate the lapping efficiency while the ultra-fine diamond grains improved the surface quality of workpiece.

Fabrication and Application of Gel Forming Ultrafine Diamond Abrasive Tools

To solve the problem of phase agglomeration and microstructure inconsistency in the conventional powder pressing method of ultrafine diamond abrasive tool, a fabrication method of ultrafine diamond abrasive tool based on gel forming was proposed. The gel experiments of polyvinyl alcohol (PVA) and phenolic resin (PF) were carried out, and the basic physicochemical properties of the gel were tested by SEM, IR and TGA. The mechanical properties of gel forming and hot pressing forming abrasive tools were Compared. The polishing experiments of the gel abrasive tool and the hot-pressing abrasive tool were carried out. The results showed that when the PF/PVA ratio was between 5:1 and 10:1, the porous network gel structure was formed. The IR and TGA analysis indicated that the molecular crosslinking of PF and PVA occurred after gel. Compared with hot pressing abrasive samples, the abrasive distributions of gel abrasive samples were more uniform. The supersmooth surface of the SiC flat mirror with surface roughness Ra below 3 nm was obtained by the gel abrasive tool, which was better than by hot pressing abrasive tool. The surface flatness value PV 0.213 μm could be obtained by using the gel abrasive tool with low PVA content.

Modeling the relationship between the hardness and wear resistance of materials during their comparative testing by the "block-on-ring" method

The authors propose a novel model accounting for the hardness of materials in a simplified algorithm in order to evaluate their wear resistance by the “block-on-ring” method during tests on a friction machine. This work is relevant for the study of the factors influencing wear and continues to improve this method based on the Taylor series and the testing results for a number of materials in a wide range of hardness. The problem is solved by correlation analysis of the dependence of the hardness of materials on the Mohs scale on the experimental wear parameters, including the volumetric wear resistance of these materials. A complete software that has been developed implements a simplified version of the “block-on-ring” method for wear testing of materials, taking into account their hardness. The high correctness and efficiency of the proposed model is confirmed by the increasing hardness of a polytetrafluoroethylene composite filled with ultrafine diamond. Practical significance. The model of the relationship between the wear resistance and the hardness of materials proposed and justified in the paper is ready for use in their tests by the “block-on-ring” method in production conditions.

The Effect of Matrix and Processed Material Properties on the Performance of Diamond Drills

The results of laboratory tests for drilling of corundum, chamotte, and porcelain with diamond tubular drills in running water, as well as the friction of cylindrical samples of the matrix against these materials, have been described. Bronze containing ultrafine ASM 1/0 diamond powders and molybdenum, as well as bronze without this reinforcement, served as the matrix for the drills and cylindrical samples. The speed of processing corundum, chamotte, and porcelain with diamond drills constantly increased when the concentration of diamond powders raised to 11 wt.%. At the same time, the tool wear significantly reduced, reaching the minimum at 5–9 wt.% of ASM 1/0 concentration (depending on the choice of the test material). The wear of diamond powder increased binsignificantly when the concentration of diamond powders grew to 11 wt.%. Similar results were obtained for the matrix of samples. Thus, the wear of the matrix samples decreased with an increase in the ASM 1/0 concentration. Such a decrease was observed even at 11 wt.% for friction against corundum. During friction against chamotte and porcelain, the wear of the samples reached the minimum at 7 wt.% diamond powders. As in the case with drills, a further increase in the content of ASM 1/0 in the reinforcement led to an increase in wear of the samples. High wear of the drills and samples at a relatively high content (11 wt.%) of ultrafine diamond powders was explained by the porosity that occurred in the matrix. The studies performed allowed concluding that reinforcement containing ultrafine ASM 1/0 diamond and molybdenum powders should be introduced into the matrix of diamond drills to improve their performance and decrease the consumption of abrasive material. The matrix samples containing up to 7 wt.% of ultrafine diamond powders can be successfully used as an abrasive tool for finishing (polishing) a series of nonmetallic materials, in particular, semiprecious and precious stones in jewelry production.

Volume Distribution of Reinforce Particles in a Metal Matrix

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.

Nanodiamonds: unique nanoparticles for use in biomedicine and biotechnology

Nanodiamonds are ultra-fine diamond particles, which due to their nano-scale size, unique physico-chemical properties, and a large ratio of easily chemically modifiable surface to volume, are of interest to biologists, chemists and physicists. This work is a review of the literature on their preparation, properties and perspectives related to the possibility of their use in biomedical sciences. The high biocompatibility of nanodiamonds, confirmed by a number of in vivo and in vitro studies, distinguishes them from other nanoparticles and allows their use as a neutral system for transporting biologically active compounds. Such nanoparticles can be used as carriers of peptides, proteins, nucleic acids, drugs or other synthetic compounds that will cause the intended biological effect in the body, in bioimaging and tissue engineering. Promising results of studies on different biological models suggest practical applications of nanotechnological solutions based on nanodiamonds.

Wear Resistance of Bronze-Matrix Samples of Diamond Tubular Drills with Ultrafine Diamond and Molybdenum Powder Reinforcement

The paper examines the abrasive wear rate of samples produced by vacuum impregnation of ultrafine diamond (ASM 1/0) and molybdenum powders with tin bronze. The tests were performed using a SiC-based abrasive wheel in the presence of cooling water. The introduction of and increase in the ultrafine diamond powder in the samples substantially decrease their wear rate (by a factor of 78). The hardness of the samples first increases when diamond powder content rises to 5 wt.% and then decreases when ASM 1/0 content further rises to 11 wt.% because of small porosity that appears in the samples. The use of a bronze matrix containing more than 15 wt.% Sn does not decrease the wear rate of the test samples and, hence, of the associated diamond tools, in spite of increase in their hardness.

The effect of nano-additives on the processes of electrodeposition of nickel precipitation

The article presents the results of investigates of the effect of ultrafine additives (zirconium diboride, silicon carbide, diamond) on the physical and mechanical properties of composite electrochemical nickel deposits obtained from colloid-electrolyte baths. It was revealed that the most effective nanostructured additives are zirconium diboride and ultrafine diamond. Current efficiency and potentiostatic researches shew mutual participation of finely dispersed nickel hydroxide compounds in the formation of a composite electrochemical deposits and dispersed phase of zirconium diboride or ultrafine diamond that are attendant in the solution or formed during electrolysis and introduced into the electrolyte. It is shown that the optimal values of internal tensions and microhardness are associated with the hardening of the nickel matrix together with various nano-dispersed additives that are included in the deposit. These deposits can be used as an alternative to chrome deposits on parts of machinery.

Conical support for double-stage diamond anvil apparatus

ABSTRACTBoth micro-paired and conical support type double-stage diamond anvil cells (ds-DAC) were tested using a newly synthesized ultra-fine nano-polycrystalline diamond (NPD). Well-focused X-ray sub-micron beam and the conically supported 2nd stage anvils (micro-anvils) with 10 μm culet enable us to obtain good quality X-ray diffraction peaks from the sample at around 400 GPa. The relationship between confining pressure and sample pressure depends heavily on the initial height (thickness) of micro-anvils, the difference of a few micrometers leads to a quite different compression path. The conical support type is a solution to retain both enough thickness and strength of micro-anvils at higher confining pressure conditions. All conical support ds-DAC experiments terminated by the failure of the 1st stage anvil instead of 2nd one. The combination of ultra-fine NPD 2nd stage anvil and NPD 1st stage anvil opens a new frontier for measurement of the X-ray absorption spectrum above 300 GPa.

Modified gel casting technique to fabricate honeycomb structured vitrified-bonded ultrafine diamond grinding wheels

To avoid agglomeration of ultrafine diamond particles and to improve machining precision of silicon (Si) wafers, a combination of gel casting and pore-forming agent is introduced to fabricate vitrified-bonded ultrafine diamond grinding wheel with ultrahigh porosity (~75%), honeycomb structure, and homogeneous microstructure. Moreover, the as-prepared grinding wheel possesses uniformly distributed closed pores, which are highly desirable for chip removal, heat dissipation and extended service life. In addition, influences of sintering schedules on microstructure, porosity and bending strength of the as-prepared grinding wheel are systematically investigated. Because of the honeycomb structure, the as-fabricated grinding wheel renders superior self-sharpness, which is required for continuous grinding of Si wafers without dressing, and this subsequently enhances the working efficiency. Results reveal that the surface roughness and damaged layer of the ground Si wafers are approximately 5.0 nm and 0.21 μm, respectively. The current study provides a novel pathway for efficiently processing high-quality silicon wafers.

Controllable distribution of ultrafine diamond particles by electrostatic spray deposition

Electrostatic spray deposition (ESD) is a technique with characteristics of uniform atomization and ultrafine powder distribution due to the stable formation of controllable small droplets. Based on this advantage, we demonstrated uniformly distributed ultrafine diamond particles for fabricating thin grinding layer by ESD technique. The atomization spray process of the charged droplets enclosed ultrafine diamond particles in the electrostatic field was revealed. The average number and standard deviation of particles were analyzed to meet satisfactory atomization effect in single droplet. The number, distribution uniformity, and distribution density, distribution range of particles were evaluated quantitatively by regulating electrode voltage, liquid flow, and receiving height. The corresponding optimum values of 781, 88%, 10.4 × 10−3 μm−2 and 5 mm were obtained. Thin diamond abrasive layers at different injection times were formed to preliminarily fabricate ultrafine grinding tool. Results indicate that the distribution of particles on the cross-section of the thin layer was better, with a distribution uniformity of 84.52%.

High pressure generation using double-stage diamond anvil technique: problems and equations of state of rhenium

ABSTRACTWe have developed a double stage diamond anvil cell (ds-DAC) technique for reproducible pressure by precisely fabricating 2nd stage anvils using a focused ion beam system. We used 2nd stage micro-anvils made of ultra-fine (< 10 nm) nano-polycrystalline diamond with various shapes and dimensions synthesized from glassy carbon at high pressure and temperature. The X-ray diffraction patterns from the rhenium sample always showed very broad peaks due to large pressure gradients in the culet of the micro-anvils. Deconvolution of the broad 101 diffraction peak results in compression of rhenium to V/V0 = 0.633 for the smallest d-spacing. The calculated pressure for this minimum volume varies from 430 to 630 GPa, depending on the choice of the equation of state of rhenium. We conclude that the most likely pressure achieved for the minimum volume of rhenium is in a range of 430–460 GPa based on a calibration using the platinum pressure scale to 280 GPa and the latter value of 630 GPa is unreasonably high, suggesting that the pressures in an earlier study for the equation of state of rhenium would have been significantly overestimated.

Effects of Different Stain Removal Protocols on Bonding Orthodontic Brackets to Enamel

To evaluate the effect of different stain removal protocols with or without topical fluoride application on the bond strength of orthodontic brackets to enamel. Eighty extracted premolars were randomly assigned into four groups according to the stain removal protocol. The stain removal protocols were (1) using rubber cup with prophylaxis paste in (G1, n = 20), (2) air-abrasion with prophy-jet polishing system (G2, n = 20), (3) micro-abrasion with opalusture polishing paste (G3, n = 20), and (4) macro-abrasion with ultrafine diamond finishing tips (G4, n = 20). Ten teeth in each group (SG1, n = 10) had no topical fluoride treatment after stain removal protocol, while the rest (SG2, n = 10) were subjected to topical fluoride application. After bonding the orthodontic brackets, all specimens were thermocycled before testing their bracket-enamel bond strength. The debonded bracket and enamel surfaces of each specimen were also assessed to determine the adhesive remnant index (ARI) for each subgroup. Specimens in G2, G3, and G4 recorded lower shear bond strength as compared with G1 (p < 0.05). For all groups, specimens in SG2 demonstrated lower bond strength than their counterpart in SG1 (p < 0.05). No significant differences were detected between the ARIs of different subgroups (p > 0.05). Bonding orthodontic brackets is affected by the protocol of removing enamel stains. The use of the rubber cup with prophylaxis paste provided the highest bracket-enamel bond strength. Topical fluoride application usually complicates the bonding process of orthodontic brackets to cleaned enamel surfaces. The results of the current study indicate higher bracket bond strength to enamel surfaces treated with different stain removal protocols than the clinically acceptable values (5.9-7.8 MPa). However, the more aggressive enamel pretreatment methods should not be considered unless the clinical situation necessitates such action. Postponing the topical fluoride application is advisable to follow the bracket bonding procedure. This action would prevent the negative effect of topical fluorides on bracket-enamel bond strength.

EFFECT OF DIFFERENT POLISHING SYSTEMS ON PROPERTIES OF CONTEMPORARY COMPOSITE RESINS

Objectives: This study aimed to evaluate the effects of different polishing systems on the surface roughness and surface micro-hardness of three types of composites. Materials and Methods: One hundred and eighty samples were prepared in disc-shaped stainless steel molds with a uniform size of 6 mm in diameter and 4 mm in thickness. The samples were divided according to the materials used into three groups of 60 samples for each material, and each group was then subdivided into subgroups according to the polishing instruments with 20 samples in each subgroup: Group I (control group) (Mylar’s strip) with no finishing and polishing. Group II, polishing with Spiral polishing wheels and Group III, polishing with Sof-lex Pop-on discs. Each subgroup was divided into two groups according to measurements of surface roughness and microhardness (n=10). Restorative materials were handled according to the manufacturers’ instructions. The molds were placed on flat glass plates covered with Mylar’s strips and then were filled with restorative materials. The materials were covered with Mylar’s strips, and a glass slide was pressed against the mold to adapt the materials completely to the inner portions of the molds. The excess material was removed, and the samples were photo-activated for 40 sec at the top surface using high intensity Elipar TM LED light curing unit, all samples were light cured following the manufacturers’ instructions. The specimens’ surfaces in groups II and III were finished with an ultrafine diamond finishing. After finishing the group II specimens were polished using Spiral polishing wheel. Group III specimens were polished using Sof-Lex Pop-on discs, strictly following the manufacturer’s instructions. All of the groups were stored in saline for 24 hr. All of the specimens were equally subdivided for both the surface roughness and micro-hardness test. The data were analyzed using one-way ANOVA at a significance level of 0.05 for both the surface roughness and microhardness tests, followed by Tukey,s post hoc test, using SAS software. Results: Comparing between the three polishing techniques, the Mylar’s strips (control group) exhibited significantly lower roughness values (smoothest surface) than the polishing systems (p <0.0001). Nanocomposite had the lowest surface roughness comparing to other materials. Comparing between the three materials, the greatest microhardness mean value was recorded with Sonic bulkfill, using Mylar’s strips or Spiral wheel or Solfex disc polishing techniques(p <0.0001). Conclusions: The control group had the lowest surface roughness and microhardness values compared to the polishing groups. No significant difference on surface roughness between Spiral wheel disc values and Soflex disc. The lowest surface roughness material was Nano-composite in each of the used techniques and Sonic bulkfill had the highest mic-ohardness than bulkfill and nanocomposite