Thick Boron Carbide Research Articles

An investigation of the ballistic impact behavior of multi-layered armor structure

In this research, a multi-layered composite armor was introduced by combining ceramics, fiber-reinforced composite and metal alloy with the aim of making the armor capable of resisting ballistic impact. A model was developed in ABAQUS/Explicit to predict the impact performance of armor in different scenarios. A thinner version of the proposed structure was manufactured, and experiments were conducted. Data were collected and analyzed including initial and residual velocity and absorbed kinetic energy. The experiments and simulations showed similarities in how the materials response to the ballistic impact. It was found that the thickness of each component contributes to the total ballistic resistance of the whole structure. By putting 20 mm thick Boron carbide layer in front layer, armor structure can absorb more kinetic energy than having 10 mm thick Boron carbide front layer. The sequence order of layers also affected the protection of armor structure. If the front layer is Kevlar/epoxy, armor structure cannot withstand multi-hit attacks because of significant delamination in these layers. Also, the Boron carbide core that had Kevlar/epoxy layer in the front was more shattered than the Boron carbide front layer that had Kevlar/epoxy as the core layer. By applying cohesive layers between Kevlar/epoxy layers, the displacement of fibers in the bonded composite layers was equal to 68% of the displacement of fibers in the unbonded Kevlar/epoxy layers. Also, the multi-layer structure with bonded Kevlar/epoxy layers exerted more stress on projectile after impact compared to structure with unbonded Kevlar/epoxy layers.

Towards robust PICOSEC Micromegas precise timing detectors

The PICOSEC Micromegas (MM) detector is a precise timing gaseous detector consisting of a Cherenkov radiator combined with a photocathode and a MM amplifying structure. A 100-channel PICOSEC MM prototype with 10 × 10 cm2 active area equipped with a Cesium Iodide (CsI) photocathode demonstrated a time resolution below σ = 18 ps. The objective of this work is to improve the PICOSEC MM detector robustness aspects, i.e. integration of resistive MM and carbon-based photocathodes, while maintaining good time resolution. The PICOSEC MM prototypes have been tested in laboratory conditions and successfully characterised with 150 GeV/c muon beams at the CERN SPS H4 beam line. The excellent timing performance below σ = 20 ps for an individual pad obtained with the 10 × 10 cm2 area resistive PICOSEC MM of 20 MΩ/□ showed no significant time resolution degradation as a result of adding a resistive layer. A single-pad prototype equipped with a 12 nm thick Boron Carbide (B4C) photocathode presented a time resolution below σ = 35 ps, opening up new possibilities for detectors with robust photocathodes. The results made the concept more suitable for the experiments in need of robust detectors with good time resolution.

Properties of boron carbide thin films deposited by pulsed laser deposition

Boron carbide (B4C) is the third hardest material known after diamond or ta-C and cubic boron nitride (c-BN). Due to its super-hardness and, moreover, its stability up to high temperatures and chemical stability against ferrous materials , it is an interesting material for use as wear resistant coatings , particularly in applications where diamond or ta-C films are not possible to use. Super-hard boron carbide coatings were produced using Pulsed Laser Deposition (PLD) and their mechanical properties were investigated in dependence of the laser fluence and the substrate temperature during deposition. While substrate temperature was found to have a significant influence on the hardness of the coatings, the influence of the ablation fluence was insignificant. At all fluences used, the indentation hardness increases from some 31 GPa at room temperature up to 47 GPa at 500 °C. The Young's modulus was measured to be in the range of 470 to 600 GPa. The films show good adhesion on tungsten carbide but a poorer adhesion on cold working steel. The surface quality, however, was poor at film thicknesses sufficient for practical applications due to the incorporation of many droplets. In order to improve this, an approach was made using an alternative boron carbide target the results of which also are presented. The target was produced by depositing a several ten microns thick boron carbide film on a steel substrate using PLD. The films deposited using this target were found to have much less and much smaller droplets. • Boron carbide coatings with up to 47 GPa hardness can be prepared by Pulsed Laser Deposition. • The substrate temperature during deposition is crucial for the resulting film hardness. • Super-hard boron carbide coatings show a decrease in wear rate by a factor of 11 compared to uncoated WC hard metal. • The use of denser and more homogeneous targets provides less droplet incorporation.

Fabrication and characterization of silicon based thermal neutron detector with hot wire chemical vapor deposited boron carbide converter

In order to utilize the well established silicon detector technology for neutron detection application, a silicon based thermal neutron detector was fabricated by integrating a thin boron carbide layer as a neutron converter with a silicon PIN detector. Hot wire chemical vapor deposition (HWCVD), which is a low cost, low temperature process for deposition of thin films with precise thickness was explored as a technique for direct deposition of a boron carbide layer over the metalized front surface of the detector chip. The presence of B-C bonding and 10B isotope in the boron carbide film were confirmed by Fourier transform infrared spectroscopy and secondary ion mass spectrometry respectively. The deposition of HWCVD boron carbide layer being a low temperature process was observed not to cause degradation of the PIN detector. The response of the detector with 0.2µm and 0.5µm thick boron carbide layer was examined in a nuclear reactor. The pulse height spectrum shows evidence of thermal neutron response with signature of (n, α) reaction. The results presented in this article indicate that HWCVD boron carbide deposition technique would be suitable for low cost industrial fabrication of PIN based single element or 1D/2D position sensitive thermal neutron detectors.

Weak superconductivity in the surface layer of a bulk single-crystal boron-doped diamond

We have grown and investigated bulk single-crystal heavily boron-doped diamonds possessing superconductivity with . Only the surface layer with the thickness less than showed the degenerate semiconductor behavior with transition to the superconducting state, while the bulk of the crystal was a typical doped semiconductor. The morphology of the surface layer is dendritic polycrystalline with an average boron content of 2.5–2.9 at.%. The typical Josephson junction current-voltage characteristic was observed. The degenerate semiconductor-superconductor transition as in single-crystal high-temperature superconductors and the structural data analysis of the surface layer indicate the two-dimensional character of superconductivity, and the actual superconducting structure is a set of few-nanometer thick boron carbide layers embedded in a diamond structure.

Time-of-flight neutron detection using PECVD grown boron carbide diode detector

The development of novel neutron detectors requires an understanding of the entire neutron detection process, a process which depends strongly on material properties. Here we present accurate measurements of the neutron detection efficiency of an unenriched 640nm thick boron carbide solid state neutron detector grown by plasma enhanced chemical vapor deposition as a function of the neutron wavelength at a time-of-flight facility. The data were compared to that obtained simultaneously by a calibrated nitrogen detector over the same wavelength range. The measured spectra of both detectors fit a Maxwell–Boltzmann wavelength distribution, thereby indicating that the boron carbide detector can be used as a reliable beam monitor. Measurements of the material properties (density, thickness and elemental composition) of the semiconducting boron carbide enable a precise calculation of the ideal expected neutron detection efficiency. The calculated neutron detection efficiency for the effective moderator temperature (obtained from a fit to the Maxwell–Boltzmann distribution) showed excellent agreement with the experimentally determined neutron detection efficiency of 1.25%. Higher efficiencies may be obtained either by increased film thickness and/or 100% 10B enrichment of the boron carbide source molecule.

Boron carbide based solid state neutron detectors: the effects of bias and time constant on detection efficiency

Neutron detection in thick boron carbide(BC)/n-type Si heterojunction diodes shows a threefold increase in efficiency with applied bias and longer time constants. The improved efficiencies resulting from long time constants have been conclusively linked to the much longer charge collection times in the BC layer. Neutron detection signals from both the p-type BC layer and the n-type Si side of the heterojunction diode are observed, with comparable efficiencies. Collectively, these provide strong evidence that the semiconducting BC layer plays an active role in neutron detection, both in neutron capture and in charge generation and collection.

Research of a condition of shields of the RF-antenna tokamak T-11M after four years of work

In the present paper, the results of the research into the behaviour of protective dielectric elements of the T-11M tokamak RF-antenna after four years of operation in working conditions are presented. In a modernized RF antenna, all its structural plasma facing metal elements are changed by graphite ones with a 40 µm thick boron carbide coating deposited from the gas phase, the lateral metal surfaces are protected by shields, 2 mm thick flat plates made from pyrolytic boron nitride [1] Azizov E. A. Belov A. M. Buzhinskij O. I. et al. Investigations of ion-cyclotron heating in the T-11 M tokamak Fizika Plazmy 20 1060 1064 (1994) (in Russian) [Google Scholar]. For boronization of the vacuum chamber walls, a new manner based on the decomposition of deuterated carborane (C2B10D12) in helium glow discharge was used. After completion of work, the RF-antenna and all dielectric elements were investigated with a standard set of surface diagnostics (scanning electron microscopy, Auger electron spectroscopy, X-ray and neutron diagnostics, profilometer etc.). The analysis has shown that all protective elements after four years of work have kept the coating integrity as well as chemical and phase structure. After four years of operation, the B4C coating thickness has decreased 10 times on the electron side of protective plates and 5 times on the ion side and is, accordingly, 5 and 10 µm.

Structure and mechanical properties of boron carbide coatings formed by electromagnetically accelerated plasma spraying

Structural and mechanical properties are investigated on thick boron carbide (B 4C) coatings, which are formed onto stainless steel substrates by using an electromagnetically accelerated plasma spraying. Hardness, porosity and surface roughness of the coatings show dependences on both the size of raw powder and the substrates distance. Within the coating conditions using two different sized raw powders; 30±10 μm and less than 10 μm in diameters, and different substrates distances ranging from 10 to 50 mm from the gun muzzle, smaller particle and longer substrates distance are found to be more effective in forming a coating with uniform hardness, low porosity and smooth surface. Results of Raman spectroscopy and X-ray diffraction suggest that the crystallite size of original raw B 4C powder is significantly reduced during the process of coating formation.

The 10B( n, αγ) 7Li cross-section between 0.1 and 2.2 MeV

The shape of the excitation function for the standard neutron reaction 10B( n, αγ) 7Li in the energy range from 0.1 to 2.2 MeV has been determined relative to the angular distribution of the neutron source reaction T( p, n) 3He at 1.6, 2.3, and 3.0 MeV proton energy. The 478 keV γ's produced in a 3-mm thick boron carbide sample were observed in a Ge(Li)-detector. The time-of-flight method was used to discriminate against events from neutrons of degraded energy.