Papers by Keyword: Boron Nitride

Abstract: Boron Nitride (BN) filler was modified by an ion beam surface treatment to enhance dispersibility to polar solvent and bond strength with epoxy. Surface treatment of the fillers was conducted by Ion Assisted Reaction (IAR), in which Ar⁺ ion beam is irradiated on the filler surface with energy of 1keV, dose varied from 1x10¹⁴ ~ 5x10¹⁶ Ar⁺ ions/cm² by using Cold Hollow Cathode type ion source and oxygen gas 5-10ml/sec. After the surface treatment, the BN powder were spontaneously dispersed into polar solvent in a visual observation which means the modified surface was changed from hydrophobic to hydrophilic, and the powder were easily mixed with a viscous epoxy resin until 40wt% without thinner (a gelation phenomenon with easy blending into the epoxy resin), but the untreated powder exhibits difficulty in mixing with epoxy resin without the thinner. XPS analysis showed oxygen functional groups (B-ON, BN, etc.) were formed on the surface of BN. It was confirmed the surface modification has a high filling ability of the BN filler with binder and better adhesion with epoxy resin compared to the untreated BN filler.

Abstract: Space environment is rich of high energy particles that form the radiation field. Human beings as well as electronic devices are susceptible to their action, even if the exposure time is limited. For this reason, radiation shields are needed to carry out safe space missions. Traditionally, in-space shielding frames are made up of aluminum, but more recent studies have shown that a good shielding efficiency can be achieved by hydrogen (H)-rich materials, as polyethylene (PE). Moreover, it was noticed that small mass atoms as H, boron (B) and nitrogen (N) can reduce secondary emissions. In this work, radiation shields of high-density PE (HDPE) filled with boron nitride (BN) have been manufactured. Since BN particles dispersion into the polymeric matrix strongly affects the composite shielding ability, 2 filling routes have been investigated. The first manufacturing strategy is about melt-mixing: HDPE is melted at 200 °C into a batch-mixer, then BN powder is inserted, and mixing is carried out until the torque exerted by the rollers reaches a plateau. Subsequently, the shield is obtained by molding and machining. The second strategy is about the filler spray deposition; BN is spayed on HDPE plates surface after which stacking occurred and consolidation is carried out at 130 °C for 24 h. At the end, machining is performed. The shields dimensions are 25x25x10 mm³ and 50x46x35 mm³, respectively. Both of them show a good level of agglomeration and a good fillers dispersion, with a final density close to the HDPE nominal value.

Abstract: In this study, the use of boron nitride (BN) foam composites as adsorbents in wastewater treatment using polyvinyl alcohol (PVA), polyvinyl butyral (PVB) and polyester (PE) polymers has been investigated. BN powder has been functionalized by Hummer’s and sodium hydroxide (NaOH) methods to facilitate BN binding with the polymer. Fourier Transform Infrared (FT-IR) results show that hydroxyl (-OH) groups are effectively bounded to the BN structure. Scanning Electron Microscope (SEM) observation demonstrated the 3D interconnected porous structure of the obtained BN foams using different polymers. It is observed that BN and polymer interaction is better in foams formed with PVA and PVB compared to PE polymers. PVA and PVB structure shows a bridge property to link the layers so that a porous network structure is formed. It has been determined that the foam composite modified with Hummer’s method and using PVB as a polymer (h-BN-PVB-H) reaches an adsorption capacity of 8.843 mg/g in 44 hours and provides approximately 18% Crystal Violet (CV) dye removal. h-BN-PVB-H foam composite removes approximately 26% of Reactive Blue 49 (RB 49) dye with an adsorption capacity of 12.313 mg/g in the first 10 minutes. The 3D BN/Polymer foams showed reasonable absorption capacities for olive oil, cyclohexane and toluene from 200-980 wt% relative to the foam’s dry weight. It shows that the produced composite foams can absorb approximately 2-10 times their own weight.

Abstract: Boron nitride (BN) was modified by silane coupling agent (KH560) and used as heat conductive filler to prepare the modified BN (BN560)/epoxy composite. The effect of the BN560 filler content on the thermal conductivity and thermal stability of the epoxy composite was studied. The results show that BN560 can be uniformly dispersed in the epoxy matrix by an ultrasonic disperser. The BN560 added can effectively improve the thermal conductivity of the epoxy composite. With the increase of BN560 content to 20 wt.%, the thermal conductivity of the composite increases accordingly to 0.27 W/(m·K), 50% higher than that of pure epoxy, and a heat conductive network is formed. The BN560 added can improve the thermal stability of the composite. With increasing BN560 content, the thermal decomposition temperature and glass transition temperature of the composite increase. The composite with the BN560 content of 20 wt.% has the weight loss of 10 wt.% at 395.12 °C and the glass transition temperature of 144.59 °C.

Abstract: This paper contributes to the body of knowledge on the efforts to develop nanodielectrics as the next generation of insulation material. The time-to-failure under electrical tree-induced degradation of 1.09-1.35 vol.% hexagonal BN/Epoxy was found to be 3 times longer than in clean epoxy. For 0.31-0.33 vol.% CNS/Epoxy the time-to-failure was 24 times longer than the clean epoxy. The electrical treeing partial discharge behaviour in the BN/Epoxy and CNS/Epoxy showed distinct time-evolution characteristics different from those in the clean epoxy. The improved electrical tree endurance in BN/Epoxy relative to the clean epoxy can be attributed to increased mechanical stiffness. The superiority of the CNS/Epoxy as a nanodielectric is notable. The effect is suggested to be due to the electron affinity properties of the carbon nanospheres at appropriate dispersion levels.

Abstract: The work investigates the properties of lead-free free-machining steel grade A30KhMAR, containing BN inclusions, in comparison with the base Cr-Mo steel 30KhM, lead-bearing AS30KhM, lead-calcium-bearing ASTs30KhM, calcium-bearing ATs30KhM, bismuth-calcium-bearing AVTs30KhM and tin-bearing AО30KhM. Effect of bismuth, calcium, lead, tin and boron nitride inclusions on steel susceptibility to temper brittleness and cold brittleness is studied. Contamination of steels with non-metallic inclusions is estimated. End-quench hardenability curves of the test steel A30KhMAR are obtained. Free-machining Cr-Mo structural steel, containing low-melting elements, has ASTM grain size of the number of 7–8. Hardenability and austenite grain size are satisfactory compared to the base steel 30KhM. Mechanical properties of the test steel in longitudinal direction (ultimate and proof stress, specific elongation, reduction in area, impact toughness, hardness) were also determined. It was found that bismuth, calcium, lead, tin, boron and nitrogen (in the form of boron nitride inclusions) within the studied limits do not have negative effect on mechanical properties of heat-treated ASTs30KhM, ATs30KhM, AVTs30KhM, A30KhMAR and AО30KhM steels, and the values of strength, plasticity and toughness characteristics satisfy the requirements of GOST standards for the base steel 30KhM and lead-bearing steel AS30KhM.

Abstract: Fiber coatings for BN/SiC-and BN/Si₃N₄-bilayer systems were developed for the use in SiC/SiC composites. All coatings were produced with high process velocities of 500 m/h by a continuous roll-to-roll dip-coating process. The fiber surface was fully covered with a homogeneous coating and without fiber bridging. Tensile tests of fiber bundles were used to examine potential degradation of the fiber properties due to the application of the coatings. The coated fiber bundles showed a reduction of the maximum tensile load to 90.0 % for the BN/Si₃N₄ and to 86.7 % for the BN/SiC coating in comparison to the fiber bundle in the as-received state. A thermal treatment of the coated fiber bundles up to 1650 °C led to no reduction of their maximum tensile load. SiC/SiC composites were fabricated by polymer infiltration and pyrolysis. The flexural strength and strain of composites with BN/SiC fiber coating were improved to 467 MPa and 0.42 % in comparison to the composites without fiber coating. The composites with BN/SiC coating showed toughened fracture behavior with fiber pull-out effects.

Abstract: The paper presents theoretical and experimental studies of the formation processes of boron nitride, aluminium nitride, aluminium oxide and manganese sulphide inclusions in a free-cutting steel. Fact Sage software was used to model the behaviour of non-metallic inclusions. Formation temperatures and the amount of key inclusions in steel were calculated. Formation order of inclusions is as follows: aluminium oxide > boron nitride > manganese sulphide > aluminium nitride. The object of study was the A45AR grade steel in 1.1–1.2 kg ingots. It was melted in an induction furnace, and aluminium, nitrided ferrosilicon and ferroboron were added after deoxidation before tapping. Quality estimation included chemical composition, macro-and microstructure, the character and shape of non-metallic inclusions. The finished metal contained fine and uniformly distributed inclusions of boron nitride. Qualitative and quantitative analysis of boron nitrides distribution in metal matrix showed that they were present both as individual and complex compounds, mostly of spherical shape. The size of BN inclusions varied from 0.18 to 6.52 μm. The amount of boron added to steel did not affect the size of MnS non-metallic inclusions.

Abstract: The paper presents theoretical and practical study of formation of non-metallic inclusions in a medium-carbon free-cutting structural steel. FactSage software package was used for thermodynamic modelling of inclusion behaviour. Formation temperature and the amount of aluminium oxides, boron nitrides, manganese sulphides and aluminium nitrides were calculated. Inclusions in the steel form in the sequence Al₂O₃ > BN > MnS > AlN. The object of practical research was a cast billet of A38KhGMAR grade steel. It was melted in a laboratory induction furnace; boron and nitrogen were introduced after deoxidation of the melt with primary aluminium. Quality analysis included determination of chemical composition, macro-and microstructure, type and shape of non-metallic inclusions. Fine and uniformly distributed boron nitride inclusions were obtained throughout the metal matrix; their distribution was studied both qualitatively and quantitatively. Beside isolated particles, boron nitrides are also presented as a component of complex inclusions with manganese sulphides. Inclusion morphology is mostly spherical. The size of BN inclusions varies from 0.41 to 7.23 μm.

Abstract: —Density function theory (DFT) based simulation combined with non-equilibrium green function (NEGF) was used to theoretically investigate electrical properties of symmetrical and asymmetrical boron nitride (BN) passivated graphene nanoribbons. Using density function theory method, it is demonstrated that the band gap of armchair (A) graphene nanoribbon (GNR) can be widened with boron nitride passivation. five symmetrical and five asymmetrical structures were considered, for which we obtained band gaps from 0.45 eV to 2 eV for symmetrical structures and 0.3 eV to 1.5 eV for asymmetrical structures. For the same width of graphene nanoribbon, our results showed that asymmetrical structure has a smaller band gap and almost the same conductance in comparison with the symmetrical one. Finally, comparison between the asymmetrical structure and the hydrogenated armchair graphene (h-AGNR) nanoribbon showed that, hBN-AGNR exhibited a higher conductance compared to an h-AGNR for the same width of GNR.