Ball-milled Boron Research Articles

Insight into the key role of oxygen dopants over ball-milled boron nitride for efficient degradation of PFOS alternative 6:2 fluorotelomer sulfonic acid.

6:2 Fluorotelomer sulfonic acid (6:2 FTS) has been identified as an alternative to perfluorooctane sulfonic acid but has been proven to cause potential threats to humans and the environment. In this study, boron nitride (BN) photocatalysis was explored for 6:2 FTS degradation with 100% removal (kobs=1.8h-1) and desulfurization rate of 100% as well as the defluorination rate of 57.3%. The superior performance of BN was primarily related to oxygen dopants defects (O-dopants). In addition, O-dopants contribution was confirmed by ball-milled BN (B-BN), which introduced more O-dopants and exhibited an increased 6:2 FTS degradation rate of 2.88h-1. The decomposition of 6:2 FTS was attributed to holes (h+), hydroxyl radicals (•OH), and superoxide (•O2-) and proceeded via two pathways, the hydrogen abstraction from ethyl carbons by •OH and the C-S bond activation by h+ and •OH. To the best of our knowledge, this is the first study demonstrating that h+, •OH, and •O2- played significant roles in the heterogeneous photocatalytic degradation of 6:2 FTS.

Effects of post-thermal treatments of ball-milled boron nitrides on solid base catalysis

Abstract Ball-milled hexagonal boron nitride was investigated as a solid base catalyst. The ball-milled boron nitrides were heated in a vacuum or air and used for Knoevenagel condensation. Measurements by X-ray diffraction, nitrogen adsorption, thermogravimetry-mass spectrometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy indicated that the heat treatment under vacuum hardly changed the physicochemical properties including crystal structure and surface composition whereas the heat treatment in air significantly altered the properties due to the formation of B2O3. The number of basic sites increased with the increase of the evacuation temperature. The boron nitrides after evacuation gave moderate product yield for Knoevenagel condensation of benzaldehyde with malononitrile at 40 °C. The boron nitrides after calcination showed different activity, dependent on the calcination temperature. The boron nitride after ball-milling, followed by calcination at 300 °C exhibited the highest activity. The catalytic activity was not directly related to the base amount and the surface areas, suggesting that acid-base bifunctionality plays an important role in Knoevenagel condensation using the ball-milled boron nitride catalysts.

Influence of milling time and glycerin treatment for boron powder on the superconducting properties of MgB 2 bulk

A correlation between the ball milling time and glycerin treatment of boron powder on the superconducting properties of MgB 2 was elucidated. The aim of the planetary ball milling was to enhance the high field critical current density ( J c) by controlling the particle size of the boron powder. The boron powder was ball-milled for 1, 2, 5 and 7 h at 200 rpm in toluene. Each of the different ball-milled boron powders were then treated with glycerin as a source for carbon doping. The results showed that by combining mechanical milling and glycerin treatment for the boron powder, the J c increased significantly over the entire range of magnetic fields as compared to the pure MgB 2 sample. The optimum level of milling time + glycerin treatment was found to be 2 h, and further milling decreased the J c due to substantial decreased in T c.

A correlation between transport current density and grain connectivity in MgB2/Fe wire made from ball-milled boron

Studies of the magnetic field dependence of the transport critical current density (Jct) and the grain connectivity of MgB2/Fe wires fabricated from ball-milled boron have been conducted in detail, and strong correlations have been found, as evidenced by differences in grain size, critical transition temperature, and resistivity. It was observed that the samples fabricated by ball milling had relatively small grain sizes, resulting in a strong field dependence of the Jct in the high field region. On the other hand, the ball-milled boron was associated with poor connectivity between adjacent grains. It is clearly shown that the observed reduction in low field Jct is related to the reduction in the superconducting area fraction (AF) that is reflected by the connectivity factor. Even if high temperature sintering in all the samples can compensate for the degradation of the Jct in the low field region, the subsequent grain growth is mainly responsible for the degradation of Jct in the high field region.

Influence of Nanocrystalline Boron Precursor Powder on Superconductivity in MgB2 Bulk

In this report, high-purity nanocrystalline boron powders processed by ball-milling were used as the precursor powders to fabricate MgB2 superconductor. The transport properties and the critical current density in the samples made from ball-milled boron powders and as-supplied boron powders were investigated. It was found that the ball-milled boron powders led to a significant enhancement of the critical current density in MgB2 sintered at 650 degrees C. The reason can be attributed to the small MgB2 grain size caused by the ball-milled boron precursor powders. The resistivity of the samples made from the ball-milled boron powder was lower than that of the sample from as-supplied boron powder. As the sintering temperature increased, both resistivity and upper critical field decreased in the samples using the ball-milled boron powders as a precursor. Poor connectivity and large strain are responsible for the high resistivity.

Superconducting properties of MgB2 prepared from attrition ball-milled boron powder

Abstract We report superconducting properties of the MgB 2 pellets prepared from the attrition ball-milled boron, in order to control the grain size of the MgB 2 that is formed from it. We observed that the semi-crystalline peaks in the ball-milled boron became broader when the ball-milling time was further increased, indicating that the boron powders had lost their crystalline. In addition, the B 2 O 3 peak was appeared in the ball-milled powders, resulting in an increase in the amount of MgO. However, the sample prepared from boron that was ball milled for 5 h showed an improvement of critical current density ( J c ), even with increased MgO phase, under an external magnetic field at 5 K and 20 K.

Mechanosynthesis of Boron Nitride Nanotubes

Boron nitride nanotubes (BN-NTs) with pure hexagonal BN phase have been synthesized by heating ball-milled boron powders in flowing ammonia gas at a temperature of 1200°C. The as-synthesized products were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and electron energy loss spectroscopy (EELS). The diameters of nanotubes are in the rage of 40–120nm and the lengths are more than 10μm. EELS result identifies that the ratio of boron and nitrogen is almost 1:1. The growth temperature is a crucial growth parameter in controlling the structure and crystalline of BN-NTs. The nanotubes grown at 1100°C possesses of a bamboo-like structure, while as the temperature increased to 1200°C, most of the nanotubes exhibited a cylindrical structure. In addition, changing the heating time can control the size of the nanotubes. The gas atmosphere has influence on the yield of BN-NTs during heating process. When heating atmosphere was replaced by nitrogen, the yield of nanotubes was remarkably decreased.

Boron nitride nanotubes synthesized in the temperature range 1000–1200 °C

Boron nitride nanotubes were synthesized on the iron-deposited alumina substrates by a catalytic reaction of the ball-milled boron and boron nitride powder mixture with ammonia in the temperature range 1000–1200 °C. The diameter of nanotubes is in the range of 40–100 nm. The nanotubes grown below 1100 °C possess exclusively a bamboo-like structure. As the temperature increases to 1200 °C, almost all nanotubes show a cylindrical structure in which the boron nitride sheets are tilted to the tube axis by an angle of about 25°. Electron energy-loss spectroscopy identifies that the ratio of boron and nitrogen is almost one. The Raman scattering peak associated with the E 2g mode shifts to the higher frequency and narrows as the growth temperature increases. The results indicate that the growth temperature can be a crucial growth parameter in controlling the structure and crystallinity of boron nitride nanotubes. On the basis of the structural features, we suggest a base-growth mechanism for both bamboo-like and cylindrical boron nitride nanotubes.