Pervaiz Ahmad

Synthesis of boron nitride nanotubes via chemical vapour deposition: a comprehensive review

Boron nitride nanotubes (BNNTs) have been synthesized by various methods over the last two decades. Among the various growth techniques, chemical vapor deposition (CVD) is one of the best methods for the synthesis of BNNTs in terms of quality and quantity. It offers relatively easy control of different growth parameters such as growth mechanism, experimental set up, precursor variables, catalyst type and temperature, and hence has become very convenient to grow BNNTs with desired size and morphologies leading to various advanced applications. Here, we present a comprehensive review on BNNT growth by CVD techniques ranging from catalytic to plasma assisted CVD. Moreover, the importance of certain variables for an efficient production of BNNTs, and their effects on the size and morphology of the tubes are also discussed elaborately.

Effective Synthesis of Vertically Aligned Boron Nitride Nanotubes via a Simple CCVD

A simple catalytic chemical vapor deposition technique based on the combined logic of previously synthesized vertically aligned carbon nanotubes and pattern growth of boron nitride nanotubes (BNNTs) along with a few simple modifications in the experimental setup is successfully used for the synthesis of vertically aligned BNNTs. Field emission scanning electron microscope images show the top and side view of the as grown pure BNNTs. High-resolution transmission electron microscope images confirm the tubular structure as well as the highly crystalline nature of the tubes. X-ray photon spectroscopy and Raman spectroscopy indicate h-BN as a main constituent of BNNTs synthesized in the present work.

Synthesis of Boron Nitride Microtubes and Formation of Boron Nitride Nanosheets

Boron nitride microtubes are synthesized in a dual zone quartz tube furnace at 1200°C with ammonia as a reaction atmosphere. Field emission scanning electron microscopy (FE-SEM) results show a unique cone-like morphology of the tubes with larger internal space and thin walls structure. The diameters of the tubes were found to be in the range of 1 to ∼2 µm with the walls thickness estimated to be from 10 to 100 nm. XPS survey shows N 1 s and B 1 s peaks at 398.7 and 191 eV, respectively, that represent h-BN in the sample. Raman spectroscopy indicates a high-intensity peak at 1372.53 (cm−1) that corresponds to the E2g mode of h-BN. Along with the novel tubular morphology of boron nitride microtubes, the present work also explains a mechanism for the formation of boron nitride nanosheets (from boron nitride microtubes) found in the FE-SEM results of the current sample.

A simple technique to synthesise vertically aligned boron nitride nanosheets at 1200 C.

Abstract In order to make the synthesis of boron nitride nanosheets (BNNS) easier and safe, a very simple technique is introduced in the present study. In this technique BNNS are synthesised in a conventional horizontal dual zone quartz tube furnace at 1200°C. Field emission scanning electron microscopy image shows the morphology of synthesised BNNS like spread out cotton packs. Transmission electron microscopy (TEM) images show highly crystalline nature of synthesised nanosheets of boron nitride with an interlayer spacing of 0.34 nm. Raman spectrum shows a major peak at 1366 (cm−1) that corresponds to E2g mode of h-BN. X-ray photon spectroscopy survey shows B 1s (at 191 eV) and N 1s (at 398 eV) peaks that verify the boron and nitrogen contents in synthesised nanosheets.

The effect of reaction atmosphere and growth duration on the size and morphology of boron nitride nanotubes

The effect of different reaction atmospheres is analyzed on the size and morphology of boron nitride nanotubes within a single and continuous growth duration of 180 min at 1200 °C. Field emission scanning electron microscopy micrographs show smaller and larger diameter boron nitride nanotubes in the range of 70–700 nm, with straight and curve parts. Some of the larger diameter boron nitride nanotubes have pipe-like morphologies at their top with the diameter in the range of 270–380 nm. High resolution transmission electron microscopy shows the tubular structure of the synthesized nanotubes with a non-uniform diameter. X-ray photoelectron spectroscopy shows B1s and N1s peaks at 190.3 eV and 398 eV for hexagonal boron nitride nature of the synthesized nanotubes. The Raman spectrum reports a higher intensity peak at 1370 (cm−1) that corresponds to E2g mode of vibration in hexagonal boron nitride.

Synthesis of Highly Crystalline Multilayered Boron Niride Microflakes

Boron niride microflakes of 2–5 μm in diameter and greater than 40 μm in length with multilayer structure and highly crystalline nature are synthesized in two states of catalysts and dual role of nitrogen at 1100 °C. Most of the microflakes are flat, smooth and vertically aligned with a wall-like view from the top. Transmission electron microscopy shows overlapped layers of microflakes with an interlayer spacing of 0.34 nm. The h-BN components of the synthesized microflakes are verified from B 1s and N1 s peaks at 190. 7 and 397.9 eV. Raman shift at 1370 (cm−1) and sharp peaks in the XRD pattern further confirm the h-BN phase and crystalline nature of the synthesized microflakes. Microflakes of h-BN with the above characteristics are highly desirable for the development of a solid state neutron detector with higher detection efficiency.

Experimental investigation on momentum and drag reduction of Malaysian crop suspensions in closed conduit flow

The study of frictional losses in fiber suspension flow is one of the significant scientific interests as the characteristics of suspension flow considerably changes with shear stress, fiber source, and treatments applied on fibers. Pressure drop measurements were obtained for different Malaysian crop fiber suspensions flowing through a closed conduit. The generated data were gathered over a range of flow rates and suspension concentrations. It was found that the magnitude of the pressure drop of the fiber suspensions is dependent on the concentration, characteristics, and fiber source. Considerable drag reduction is obtained for concentration of 0.6 wt. % at high flow rates. Such a reduction of pressure drop at the particular concentrations and the flow rates is interesting and useful as these data can be used for design and optimization of fiber handling equipment and piping systems. Furthermore, the effect of different fibers, fiber properties and flexibility on pressure drop were studied.

Boron nitride nanowires synthesis via a simple chemical vapor deposition at 1200 °C

A very simple chemical vapor deposition technique is used to synthesize high quality boron nitride nanowires at 1200 ˚C within a short growth duration of 30 min. FESEM micrograph shows that the as-synthesized boron nitride nanowires have a clear wire like morphology with diameter in the range of ∼20 to 150 nm. HR-TEM confirmed the wire-like structure of boron nitride nanowires, whereas XPS and Raman spectroscopy are used to find out the elemental composition and phase of the synthesized material. The synthesized boron nitride nanowires have potential applications as a sensing element in solid state neutron detector, neutron capture therapy and microelectronic devices with uniform electronic properties.

The effect of particle size on the dispersion and wear protection ability of MoS2 particles in polyalphaolefin and trimethylolpropane ester

The effect of particle size and surfactant on dispersion stability and wear protection ability was experimentally evaluated for polyalphaolefin (PAO 10) and bio-based base oil (palm trimethylolpropane ester) added with molybdenum disulfide (MoS2) particles. Nanolubricants were developed by adding 1 wt% of MoS2 particles that varied in size. In addition to the variation in particle size, an anionic surfactant was also used to analyze its interaction with both types of nanoparticles for stable suspensions and for the related effects on the antiwear characteristics. The wear protection characteristics of the formulations were evaluated by four-ball extreme pressure tests and piston ring on cylinder sliding wear tests. The wear surfaces were analyzed by scanning electron microscopy along with an energy-dispersive X-ray and an atomic force microscopy. The MoS2 nanoparticles with a nominal size of 20 nm exhibited a better load-carrying capacity, while better sliding wear protection was provided by nanoparticles with a nominal size of 50 nm.

Ionic liquid as a potential solvent for preparation of collagen-alginate-hydroxyapatite beads as bone filler

Abstract In this study, collagen/alginate/hydroxyapatite beads having different proportions were prepared as bone fillers for the restoration of osteological defects. Ionic liquid was used to dissolve the collagen and subsequently the solution was mixed with sodium alginate solution. Hydroxyapatite was added in different proportions, with the rationale to enhance mechanical as well as biological properties. The prepared solutions were given characteristic bead shapes by dropwise addition into calcium chloride solution. The prepared beads were characterized using FTIR, XRD, TGA and SEM analysis. Microhardness testing was used to evaluate the mechanical properties. The prepared beads were investigated for water adsorption behavior to ascertain its ability for body fluid uptake and adjusted accordingly to the bone cavity. Drug loading and subsequently the antibacterial activity was investigated for the prepared beads. The biocompatibility was assessed using the hemolysis testing and cell proliferation assay. The prepared collagen-alginate-HA beads, having biocompatibility and good mechanical properties, have showed an option of promising biologically active bone fillers for bone regeneration.