Optimization of sol-gel synthesized preceramic polymer precursors for fabrication of high purity boron carbide (B4C) powders

Boron Carbide (B4C), due to its high hardness and elastic modulus, superior chemical stability, low density and high neutron absorption cross section, is well suited to a variety of industrial applications such as blasting nozzles, wire-drawing dies, powdered metal and ceramic forming dies, vehicle armour, bulletproof vest, nuclear reactor control rods and neutron absorbing shielding. The current fabrication techniques of boron carbide powders such as carbothermal reduction, direct synthesis from elements, vapour-phase reduction, and magnesiothermic reduction require expensive equipment and starting materials. For this reason, in recent years studies focused on the development of low-temperature synthesis techniques to reduce the production cost of boron carbide as well as to get better control over composition and particle morphology

Low temperature synthesis and characterization of high purity nano boron carbide (B4C) structures

Boron carbide (B4C) is accepted as an important engineering material due to its high melting point, high hardness, high Young's modulus, excellent radiation (neutron) absorption properties and low thermal conductivity. Although different methods, such as high temperature carbothermic reduction and chemical vapor decomposition, have been used to synthesize boron carbide, a low cost technique that provides high purity B4C with no residual carbon, is required by industry. Therefore, in the present study, synthesis of high purity, high crystallinity nanostructured boron carbide particles with various morphologies, is proposed using a modified low-temperature sol gel process. The effects of starting chemicals, calcination and sintering temperature/time on the formation of B4C structures, morphology and stoichiometry were reported. Detail characterization studies including TEM, XRD, NMR and DTA were used to support the results on the formation of stoichiometric boron carbide with high crystallinity at low temperatures

Processing of surface modified nano boron carbide (B4C) containing flexible composites as shielding materials

Aims: The main aim of the work is to synthesize nano boron carbide using cost effective modified sol-gel technique and then functionalize the obtained nanoparticles surface so that they can be homogeneously distributed within flexible polymeric matrices for radiation shielding purposes. Methods: Different starting chemicals were used in sol gel technique to obtain nano boron carbide (B4C) particles with controlled size and morphology. Surface modification with various functional groups was conducted on the synthesized particles and final coated B4C particles were embedded within the polymers using high shear mixing process in the form of thin sheets and plates. Results: It was shown first that nano boron carbide particles can be obtained by a novel modified sol gel technique using nano elemental boron which results in obtaining stoichiometric boron carbide. Surface modified B4C with functional groups resulted in the excellent distribution within polymeric matrices leading to the improvement in both mechanical and shielding properties. Conclusions: Size and morphology controlled B4C can improve the mechanical and shielding properties of polymer based composites. The final obtained composite materials are considered to be suitable candidate for lightweight radiation shielding materials

Processing of nano boron carbide reinforced flexible polymer composites with improved shielding properties

Aims: The main objective of the current research is to develop light-weight and flexible electromagnetic shielding materials with improved properties using nano/mikro boron carbide dispersed into polymer based matrices after surface modification. Methods: Nano/micro boron carbide particles with various morphologies were synthesized by sol-gel techniques and the obtained particles were surface modified with different functional groups. After mixing the particles with different polymers using high shear mixer, shielding composite plates were shaped using injection moulding and warm pressing. Results: It was shown that sol-gel technique was able to produce boron carbide particles with controlled morphology and better shielding properties could be obtained using these particles within polymeric matrices leading to the formation of flexible composites. Conclusions: Overall, it was found that light-weight and effective shielding materials could be obtained using boron carbide particles dispersed within polymeric matrices. Surface modification of the particles is critical for good dispersion and hence to get better final properties. The concentration of the reinforcing particles also affects the properties in terms of energy absorption and shielding

Processing and properties of new generation radiation shielding nano composites

Electromagnetic radiation from equipments in medical diagnostic centers or nuclear reactors causes ionization including gamma rays and x-rays that are well known to be very harmful to human health. Therefore, flexible, light-weighed and environmentally friendly shielding materials that can replace toxic and very heavy Pb based materials are required. In the present work, synthesized and surface modified micro/nano B4C particles are distributed within polymeric matrices in order to obtain flexible shielding materials. The effect of surface functionalization and concentration of boron carbide on the distribution characteristics of boron carbide and the final properties of the composites are examined

Boron Carbide as an Electrode Material: Tailoring Particle Morphology to Control Capacitive Behaviour

In this study, boron carbide powders consisting mainly of nano/micro fibers or polyhedral-equiaxed particles were synthesized via the sol–gel technique, and the influence of particle morphology on electrochemical performance of boron carbide electrodes was investigated. Thermal decomposition duration of the precursors played a determinant role in the final morphology of the synthesized boron carbide powders. The morphology of boron carbide powders successfully tuned from polyhedral-equiaxed (with ~3 µm average particle size) to nano/micro fibers by adjusting the thermal decomposition duration of precursors. The length and thickness of fibers were in the range of 30 to 200 µm and sub-micron to 5 µm, respectively. The electrochemical performance analysis of boron carbide powders has shown that the particle morphology has a considerable impact on the boron carbide electrodes electrochemical performance. It was found that the synergetic effects of polyhedral-equiaxed and nano/micro fiber morphologies exhibited the best electrochemical performance in supercapacitor devices, resulting in the power and energy density of 34.9 W/kg and 0.016 Wh/kg, respectively

Non-catalytic synthesis of boron carbide (B4C) nano structures with various morphologies by sol-gel process

Non-catalytic synthesis of boron carbide (B4C) powders with various morphologies is presented by sol-gel technique using boric acid, glycerol, and citric acid as starting materials. The effect of composition and processing conditions on the phase assembly, particle size and morphology of boron carbide powders were investigated. The formation of nanobelt, needle like, and polyhedral-equiaxed boron carbide particles with a wide-ranged particle size distribution in between 50 nm and 100 mm were observed after heat treatment at 1300 degrees C for 5 h in argon atmosphere. Furthermore, rod, plate and rhomboid-flake like boron carbide structures were produced by using relatively higher heat treatment temperature of 1500 degrees C

Boron Carbide as an Electrode Material: Tailoring Particle Morphology to Control Capacitive Behaviour

In this study, boron carbide powders consisting mainly of nano/micro fibers or polyhedral-equiaxed particles were synthesized via the sol–gel technique, and the influence of particle morphology on electrochemical performance of boron carbide electrodes was investigated. Thermal decomposition duration of the precursors played a determinant role in the final morphology of the synthesized boron carbide powders. The morphology of boron carbide powders successfully tuned from polyhedral-equiaxed (with ~3 µm average particle size) to nano/micro fibers by adjusting the thermal decomposition duration of precursors. The length and thickness of fibers were in the range of 30 to 200 µm and sub-micron to 5 µm, respectively. The electrochemical performance analysis of boron carbide powders has shown that the particle morphology has a considerable impact on the boron carbide electrodes electrochemical performance. It was found that the synergetic effects of polyhedral-equiaxed and nano/micro fiber morphologies exhibited the best electrochemical performance in supercapacitor devices, resulting in the power and energy density of 34.9 W/kg and 0.016 Wh/kg, respectively

Processing and properties of boron carbide (B4C) reinforced LDPE composites for radiation shielding

In the present work, boron carbide (B4C) particles were synthesized with sol-gel technique following with heat treatment at 1500 °C in an argon atmosphere. 3-(Triethoxysilyl)-propylamine, a silane coupling agent, was doped on to the surface of synthesized B4C particles. The surface modified B4C particles were embedded in LDPE matrix in order to obtain flexible, lightweight and environmentally friendly shielding materials. The effect of surface functionalization and concentration of boron carbide on its distribution characteristics in the polymer matrix and its effects on the mechanical and neutron shielding properties of the composites are examined. The results showed that high purity-fully crystalline B4C powders with polyhedral-equiaxed morphology in the size range of 20 nm–500 nm were produced. It was found that even the very low amount (0.6–1.7 wt%) of incorporated nano/sub-micron B4C particles in LDPE matrix improved the neutron shielding (up to 39%), tensile strength (9.3%) and impact resistance (8%) of the composites