Boron Nitride

We formulate a spin-polarized van Leeuwen and Baerends (vLB) correction to the local density approximation (LDA) exchange potential [P hys. Rev. A 49, 2421 (1994)] that enforces the ion-ization potential (IP) theorem following Stein et al. [P hys. Rev. Lett. 105, 266802 (2010)]. For electronic-structure problems, the vLB-correction replicates the behavior of exact-exchange potentials , with improved scaling and well-behaved asymptotics, but with the computational cost of semi-local functionals. The vLB+IP corrections produces large improvement in the eigenvalues over that from LDA due to correct asymptotic behavior and atomic shell structures, as shown on rare-gas, alkaline-earth, zinc-based oxides, alkali-halides, sulphides, and nitrides. In half-Heusler alloys , this asymptotically-corrected LDA reproduces the spin-polarized properties correctly, including magnetism and half-metallicity. We also considered finite-sized systems [e.g., ringed boron-nitirde (B12N12) and graphene (C24)] to emphasize the wide applicability of the method.

Composites made with boron might be absorbers of low energy neutrons, and could be used for structural materials for spacecraft. Polyethylene/boron nitride composites were fabricated using conventional polymer processing techniques, and were evaluated for mechanical and radiation shielding properties. The boron nitride powder surfaces were also functionalized to improve interfacial adhesion. Addition of neat boron nitride to an injection molding grade HDPE increased the tensile modulus from 588 to 735 MPa with 15 vol % filler. The bonding of a trifunctional alkoxysilane to the powder surface prior to processing increases the composite modulus to 856 MPa at the same loading. Scanning electron microscopy of fracture surfaces verified that the silane-treated powders had improved adhesion at the filler/polymer interface. Radiation shielding measurements of a 2 wt % boron nitride composite were improved over those of the neat polyethylene.

In the last few decades, when travel makes one modest, people prefer air travel instead of car. As such, aircrews and flight passengers are prone to electromagnetic (EM) radiation exposure overtime during flight. Various researches were conducted by the Federal Aviation Agency (FAA) and European Union (EU) in order to understand its details. This paper offers reviews of EM radiation effect to human body in altitude of commercial jet and materials that may provide a convince protection for fuselage structure of aircraft. It was found that Polyethylene (PE) is a convincing material that may absorb EM radiation. NASA has found that lower effective dose toward galactic cosmic rays (GCR) was obtained in PE at 0.1 cSv/day compared to aluminum at 0.125 cSv/day at the same thickness which was 20 g/cm 2 .

In an attempt to investigate the influence of surface coatings on dry running polymer gear wear a number of gears were coated with what was considered to be suitable candidate materials. All the coated gears were made from nylon (PA 6/6) and the coatings were either MoS2, graphite, boron nitride or PTFE. Tests were carried on coated/coated gears running against themselves, coated gears running against a steel counterpart and coated gears running against uncoated gears. Weight loss and running (mesh) temperatures were recorded.
All the coated/coated tests showed that the coatings reduced wear, with PTFE coated gears showing very considerable less wear than any of the other coated gears. Mesh temperatures showed that the lower the temperature the less the wear, with the PTFE gears running at almost half the temperature of the uncoated gears. Coated gears running against steel gears showed that again, the best coating was PTFE, although the wear was higher than for coated/coated gears. For two of the coatings (MoS2 and boron nitride) the wear was higher than for uncoated gears. Temperatures for the PTFE coated gears were around half the temperatures of uncoated, MoS2 and boron nitride gears with the temperatures of the graphite gears falling between the two. For coated gears running against uncoated gears PTFE gears showed the least wear. All the other coatings showed more or less the same wear which was lower than for uncoated gears. The wear for PTFE/PTFE gears was considerably less than for PTFE running against an uncoated gear. In all but one test instead of wear the teeth fractured. None of the gears failed by a loss of adhesion between the coating and the substrate or the substrate and the base polymer.

Li3BN2 is a known lithium ion conductor and has been predicted lately to be a high capacity cathode for Li-ion batteries (Németh, 2014) [4]. In this study, we have investigated the synthesis of Li3BN2 through reactions between Li3N and h-BN powders. Effects of the reaction temperature, holding time and reaction atmosphere on the formation of Li3BN2 have been evaluated. Rietveld refinement of X-ray diffraction patterns of all powders has been performed to quantify the percentage of each phase. The results show that both the reaction temperature and holding time affect strongly the percentage of Li3BN2 in the reaction product. Furthermore, a trace amount of oxygen in the reaction atmosphere can negatively impact the purity of the reaction product because of the high affinity of Li3BN2 towards oxidation.