Papers by Keyword: Hexagonal Boron Nitride (HBN)

Abstract: Effects of h-BN particles on mechanical properties and adhesion of semi-crystalline poly (ether-ether-ketone) (PEEK) coatings were studied. PEEK powder was mixed with various contents of h-BN nanoparticle in ethanol under ultrasonic mixing. As-mixed powders were sprayed onto low carbon steel substrate with thermal spray technique. The hardness, scratch hardness, specific scratch wear rate, prevailing deformation mechanisms and adhesion were obtained from scratch tests by varying the applied load. The damage geometry on scratched polymer surfaces and scratch wear volume loss were examined using scanning electron microscope (SEM) and surface profilometer, respectively. The results indicated that the addition of h-BN content improved the hardness of the composite. In addition, the specific scratch wear rate and the adhesion between PEEK coatings and substrate decreased with increasing h-BN content. The poor adhesion resulted from the reductions of flow-ability and viscosity between PEEK and substrate caused by heat dissipation from the h-BN particles.

Abstract: Mechanical properties and wear behavior of stainless steel embedded with different solid lubricants were investigated. Hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS₂)-embedded 316L stainless steels (SS316L/h-BN and SS316L/MoS₂) were prepared by powder metallurgy method. Various h-BN and MoS₂ contents (10, 15 and 20 vol%) were mixed with 316L stainless steel powders and then sintered at 1200°C in H₂ atmosphere for 60 min. The experimental results showed that small boride phase and h-BN powder occupied the pores in the microstructure of SS316L/h-BN composite whereas the MoS₂ second phase occupied the pores of the sintered 316L matrix in the microstructure of SS316L/MoS₂ composite. The addition of h-BN decreased the sintered density and hardness whereas that of MoS₂ gave the opposite effect. Dry sliding wear behavior of composites was investigated by using pin-on-disc test rig at the sliding speeds of 0.1 and 0.2 m/s and the applied load of 3 N. The results showed that the MoS₂ composites had higher wear resistance than the h-BN composite but the h-BN composite yielded a better friction reduction.

Abstract: In this article, hexagonal boron nitride nanosheets have been successfully synthesized by the method of solid-phase sintering using boron oxide (B2O3) and sodium azides (NaN3) as the reactants and magnesium powder as catalyst at 450 °C. Results from XRD suggest that the synthesized products be indexed as pure h-BN. The surface morphology of the products was observed by the scanning electron microscope, that the products are constituted of a large number of the structure of nanosheets. And the SEM images show the sheetlike materials with a diameter of about 500-900 nm, and the thickness is about 100 nm. The far-infrared absorption spectrum showed that the typical sp2 hybrid structure of hexagonal boron nitride. The optical properties of the product are observed in the PL spectra, which shows that the prepared BN emits strong visible luminescence at 445 nm (λex = 325 nm).

Abstract: Boron nitride nanotubes attract wide interest because of their unique structures as well as super properties. The structures, properties, synthetic methods and application studies are particularly summarized. Since they were discovered, additionally, the prospects for future research and application are proposed. In this paper, advances in researches on Boron Nitride (BN) nanotubes are reviewed, and some of technologies for preparation of BN nanotubes are described. The tip structures of BN nanotubes produced by different technologies are compared and discussed.

Abstract: Hexagonal boron nitride (HBN), which has the same crystal structure as graphite, has been used as catalytic material for a counter electrode in dye-sensitized solar cells (DSCs) to investigate its potential application. X-ray diffraction (XRD) has been used to confirm the crystal structure of HBN, scanning electron microscopy (SEM) has been used to characterize the morphology of HBN film on counter electrode, and electrochemical workstation has been employed to obtain the electrochemical impedance spectroscopy (EIS) and corresponding impedance parameters. Results show that the HBN film has rough surface and porous structure with pore size of less than 1 μm. When employed the HBN counter electrode to DSCs, the conversion efficiency (η) is only about a tenth of that of graphite based DSCs. Low efficiency of HBN based DSCs is induced by high charge transfer resistance (Rct) of HBN counter electrode, which means that HBN can hardly provide catalytic activity for the reduction of the triiodide ion. Therefore, the crystal structure is not a crucial factor to select the catalytic material for a counter electrode in DSCs. Moreover, the short circuit photocurrent density (Jsc) and the open circuit voltage (Voc) of device also evidently depend on the characteristics of catalytic material.

Abstract: hBN-TiN Binary Composite Was Fabricated Using Spark Plasma Sintering (SPS) at Temperatures between 1973 and 2273 K. With Increasing TiN Content from 10 to 90 Vol%, the Relative Density Increased from 75.7 to 96.4%. The Maximum Relative Density of 96.4% Was Achieved in the hBN-TiN Containing 90 Vol%TiN Sintered at 2273 K. hBN and TiN Was Stably Coexisted at 1973 K without TiB₂ Formation.

Abstract: When filling liquid’s temperature is over 300 degrees centigrade, the internal high pressure forming process is easy to be decomposed and metamorphosed, therefore, as the pressure transmission medium, the important limited factor for the further development of the temperature state internal high pressure forming process is the heat-resistant limit. This paper analyzes the physical properties of the composite powder between micro silica and hexagonal boron nitride, and on the basis of it, discusses its pressure-transmitting properties under the static pressure condition. The researcher uses the pressing machine to force the press on different quality of the mixed powder in the different temperature, and measures the wall pressure distribution by using the high temperature resistant pressure sensor. The experimental results demonstrate that when the hexagonal boron nitride comes to 2 percents of the composite powder, the effect of the pressure transmission performance are the best, meanwhile it is not a significant factor for the temperature to influence the pressure transmission properties of the composite powder, and it will keep stable on the high temperature. In the 500 degrees centigrade, as the pressure transmission medium, the warm state internal high pressure forming research has been done through adding axial force and internal pressure to the 40Cr steel pipe fittings. The research results prove that the pressure transmission medium can not only overcome the traditional medium in high pressure forming filling liquid under high temperature, but also fully improve the plasticity deformation of metal workpieces. It helps to the bulging of complex, high hard metal pieces, and it is also helpful for simplified forming technology.

Abstract: Using ring compression tests, the interfacial friction and flow stress of 3Y-TZP/Al₂O₃ composite at elevated temperatures were investigated. Theoretical calibration curves of the friction factor and the relative average pressure curves for the ring compression tests of 6:3:2 standard rings were drawn based on a velocity field capable of describing the bulge phenomena. The lubricant was the boron nitride (hexagonal). The tests were adopted at temperature range of 1400°C-1600°C. Results indicate that the interfacial friction factor has the value in the range of 0.34-0.49, so that boron nitride lubricant can be used effectively in present temperatures. As two extremely important parameters, the temperature and strain rate have no significant effect on the fraction factor. It is proved reliable that the ring-compression test at 1400°C and even higher is used to evaluate the performance of boron nitride lubricant.

Abstract: Hexagonal boron nitride (h-BN)/polyetheretherketone (PEEK) composite powders were deposited on carbon steel substrate via the flame spray coating technique. The content of hexagonal boron nitride with a mean particle size of 0.5 micrometer was varied from 2 to 8 wt% in this work. Tribological properties, namely specific wear rate and friction coefficient, at room temperature, 100 °C and 200°C were performed using Ball-on-Disc sliding wear test. At elevated temperature, h-BN could result in marked decrease in the friction coefficients and specific wear rates.

Abstract: In this work, the three compositions of hexagonal boron nitride (10, 15 and 20 vol. %)-embedded 316L stainless steel (SS316L/h-BN) composites were prepared by a conventional powder metallurgy technique and then sintered at varying temperatures of 1100 to 1250°C for 60 min in H₂ atmosphere. The h-BN content and sintering temperature were found to affect the microstructure and hardness of the composites. The hardness decreased with increasing h-BN content and was improved by increasing the sintering temperature. Microstructure results revealed that the boride phase was formed at the grain boundary at the sintering temperature higher than 1150°C and the boride phase formation was observed to transform the h-BN in the composites.