Amount Of Boron Nitride Research Articles

A novel Si3N4/BAS/BN composite synthesized by spark plasma sintering

Based on good thermomechanical and electromagnetic properties of silicon nitride (Si3N4), barium aluminosilicate (BaO–BaTiO3–SiO2 or BAS), and boron nitride (BN), a novel combination of Si3N4/BAS/BN composites was fabricated by spark plasma sintering (SPS) after traditional powder mixing process. The effect of different amounts of BN (3–9 wt%) on the mechanical properties of composite was studied. The phases were observed by X-ray diffraction, and the microstructures were identified by scanning electron microscopy (SEM). The optimal sample is the one containing 3 wt% of BN and is sintered under a final pressure of 50 MPa. This sample has a hardness of 9.03 GPa, a flexural strength of 418.75 MPa, an elastic modulus of 934.46 MPa, and a loss tangent of less than 0.002 in 38% of the X-band frequencies. The optimal sample thickness was determined via the Nicolson-Ross-Weir (NRW) technique considering the mechanical strength limits.

Carbon‐Methanol Based Adsorption Heat Pumps: Identifying Accessible Parameter Space with Carbide‐Derived Carbon Model Materials

AbstractIn adsorption heat pumps, the properties of the porous adsorbent and the refrigerant determine the performance. Major parameters for this working pair are the total uptake of the adsorptive, its kinetics, and the heat transfer characteristics. In the technical application despite powdered adsorbents, thin consolidated layers of the adsorbent can be attractive and obtained by a binder‐based approach but likely result in competing material properties. Thus, for a process optimization, the accessible parameter space and interdependencies have to be known and were deduced in this work for model porous carbons (carbide‐derived carbons derived from TiC and ZrC) and methanol as well as the addition of different amounts of boron nitride, silver, and graphite as heat‐conductive agents and the use of two binders.

Enhancing compressive, tensile, thermal and damping response of pure Al using BN nanoparticles

In the present study, aluminum based metal matrix composites containing various amounts of boron nitride (BN) nanoparticulates (0, 0.5, 1.0 and 1.5 vol.%) were fabricated by using the powder metallurgy (PM) technique involving microwave sintering and hot extrusion process. The microstructure, physical, thermal, mechanical and damping characteristics of the extruded nanocomposites were investigated. Field emission scanning electron microscopy (FE-SEM) study shows the evenly distributed BN particles in Al matrix. Mechanical analysis indicates that the compression, hardness and tensile strength of Al-BN nanocomposites increases with increasing amount of BN content. Particularly, a significant improvement in the tensile strength (∼36%) is achieved in Al-1.5 vol.% BN nanocomposite when compared to the pure aluminum (Al). This improvement strength can be attributed to the dispersion hardening of the Al matrix due to the presence of hard BN nanoparticles. Thermal analysis shows that the coefficient of thermal expansion (CTE) decreases with increasing amount of BN which may be ascribed to inherent low CTE of BN nanoparticles used as reinforcement. The addition of BN nanoparticulates enhanced the damping characteristics of pure Al with Al-1.5 vol.% BN nanocomposite exhibiting the maximum damping capacity and damping loss rate with a minimum change in elastic modulus. The improved combination of properties exhibited by Al-BN nanocomposites make them potential candidates for a wide spectrum of industries especially for weight critical applications.

보론 나이트라이드와 탄소나노튜브로 충전된 실리콘 고무의 열전도도 향상

In order to enhance the thermal conductivity of poly(dimethyl siloxane) (PDMS), boron nitride (BN) and carbon nanotubes (CNTs) were incorporated as the thermally conductive fillers. The amount of BN was increased from 0 to 100 phr (parts per hundred rubber) and the amount of CNTs was increased from 0 to 4 phr at a fixed amount of the boron nitride (100 phr). The thermal conductivity of the composites increased with an increasing concentration of BN, but the incorporation of CNTs had only a slight effect on the enhancement of thermal conductivity. Unexpectedly, the thermal degradation of the composites was accelerated by the addition of CNTs in 100 phr BN filled PDMS. Activation energy for thermal decomposition of the composites was calculated using the Horowitz-Metzger method. The curing behavior, electrical resistivity, and mechanical properties of PDMS filled with BN and CNTs were investigated.

Effect of BN filler on thermal properties of HDPE matrix composites

The effects of boron nitride (BN) content and particle size on the thermal properties of BN/high density polyethylene (HDPE) composites were investigated. The thermal conductivities and thermal diffusivities of the composites were dependent on the BN content. For composites with same amount of BN, the thermal conductivity and thermal diffusivity increased with an increase in the size of the BN particles. Composites with a mixture of different-sized BN particles exhibited higher thermal conductivities than those of composites with single-sized BN particles. The specific heat capacities of the composites were also affected by the BN content and particle size. Several theoretical models were employed to predict the effective thermal conductivities of the composites, and the predicted values were compared with those obtained experimentally.

Effect of Boron Nitride (BN) on Luminescent Properties of Y3Al5O12:Ce Phosphors and their White Light‐Emitting Diode Characteristics

This article reports a low‐cost yellow‐emitting Y3Al5‐xBxO12‐xNx:Ce3+ phosphor with an enhanced luminescent intensity and excellent thermal stability for white light‐emitting diodes (LEDs). It was synthesized by a simple gas‐pressure sintering (GPS) process. The effect of B3+–N3− incorporation on the optical properties of Y3Al5O12:Ce3+ phosphor was investigated. The addition of appropriate amounts of boron nitride (BN) leads to a marked increase in photoluminescent intensity and a slight shift of its emission spectra toward the blue region, which is assigned to the improved crystallinity and increased particle size. Especially, the prepared oxynitride phosphor does not exhibit any thermal quenching under high temperature, and the emission intensity at 250°C even increases up to 175% of that measured at 20°C. Finally, the white LED flat lamp with luminous efficiency as high as 101 lm/W, color rendering index of 72, and correlated color temperature of about 6600 K is successfully realized by using YAG:Ce3+ phosphor doped with 0.5 molar ratio BN, which is acceptable and promising for general indoor illuminations to replace fluorescent or incandescent lamps.

Synthesis of zirconium diboride–zirconium nitride composite powders by self-propagating high-temperature synthesis

Formation of zirconium diboride–zirconium nitride composite powders by self propagating high temperature reaction of zirconium, boron and hexagonal boron nitride powders was investigated. Zirconium diboride–zirconium nitride powder mixtures with varying proportions were produced by changing the amount of boron nitride in the reactants. Products were subjected to powder X-ray diffraction analysis; and grain size and morphology was examined by scanning electron microscope. It was seen that the velocity of the wave front, adiabatic temperature of the reaction and grain size of the products decreased by increasing the boron nitride amount in the reactants. It was deduced from the scanning electron microscope examinations and crystal size calculations performed from the broadening of the peaks on the X-ray diffractions patterns that zirconium nitride grains were much finer than zirconium diboride grains.

Generation of BN in the Combustion Residue of Boron-Containing Propellant

Residue analysis of boron-containing propellant burned in the primary and aft-mixing combustors of a solid propellant ramjet (SPRJ) indicated that a considerable amount of boron nitride (BN) was created in addition to the main product of B 2 O 3 . The formation heat of BN is far less than that of B 2 O 3 , which brings some disadvantage to the heat release of boron. Ignition and combustion of boron are carried out in an oxygen bomb Calorimeter. Thermoanalysis, X-ray diffraction, elementary analysis, and X-ray photoelectron spectroscopy are adopted to investigate the source of BN, the effect of air pressure, and the effect of oxidizers. The results show that the output of BN increases with the rising of air pressure, N 2 is proved to be the main origin of elemental nitrogen in forming BN, and a competition effect exists between the oxidation and nitrification of boron.

Effect of boron nitride on melt fracture phenomena and processability of lldpe during extrusion

AbstractMelt fractures related to processing instabilities limit processing rates in many commercially important polymer processing operations, such as fiber spinning, film blowing, extrusion, and various coating flows. Therefore, melt fracture is responsible for deteriorating the quality and the mechanical properties of final products for rates greater than a critical processing one at which melt fracture occurs. In this study, a commercial linear low‐density polyethylene (LLDPE) was modified by adding a small amount of boron nitride (BN) during extrusion in order to improve processability. Capillary rheometry was used to assess processability at various temperatures, levels of applied shear rate, and the length‐to‐diameter (L/D) ratio for both the pure resin and resins containing boron nitride. Also, parallel‐plate rheometry was used to evaluate the dynamic rheological properties of these resins. The relationship between the characteristic relaxation time and the critical shear rate for the onset of melt fracture and slip is discussed.

Interface reactions between quaternary cobalt alloys and carbon coating in thin film disk media

A study of interface reactions between the magnetic layer and the protective carbon coating, and the influence of these interactions on magnetic properties of rigid disk media for magnetic data storage is presented. Quaternary CoPtCrB and CoPtCrTa alloy films and protective hydrogenated or nitrogenated carbon coatings were deposited by dc magnetron sputtering onto metal hard disks (AlMg substrate/electroplated NiP layer/Cr underlayer). Core level x-ray photoelectron spectroscopy of nitrogenated carbon films on B-containing alloys showed the formation of boron nitride and small amounts of chromium nitride at the interface, and also indicated the likely presence of chromium carbide. The amount of boron nitride at the interface varied depending on substrate bias voltage and temperature during deposition of the carbon coating. From a quantitative analysis of the x-ray photoelectron spectra it was inferred that boron nitride formation was controlled by the diffusion of boron from deeper regions of the magnetic layer to the interface. Surprisingly, compared to disks using the same magnetic alloy but with a hydrogenated or pure carbon coating, no effects of these interface reactions on the magnetic properties of the disks could be detected. In contrast, for a Ta-containing alloy the same comparison revealed a drop in the coercivity of up to 200 Oe in disks with nitrogenated carbon overcoats. Strong evidence for the formation of tantalum nitride as well as small amounts of chromium nitride was found in the photoelectron spectra. Thus, while the formation of boron nitride at the interface of CoPtCrB media and protective carbon coating does not affect the magnetic properties of the disks in the range of boron and nitrogen concentrations investigated here, small changes in the chemical environment of Ta and/or Cr can lead to significant changes in the magnetic properties of the CoPtCrTa media.

Properties of plasma-deposited composite metal-boron nitride coatings

By altering the processing parameters of plasma spray-deposition of composite metal-boron nitride materials, it is possible to vary within wide ranges the physicomechanical properties of soft sealing deposits of these materials. The strength, porosity, hardness, and solid lubricant content of metal-boron nitride sealing coatings are determined primarily by the physicomechanical properties of the metal and the amount of boron nitride in the composite being deposited and also by the particle size analysis of the charge. The effect of jet parameters on the properties of coatings varies depending on the nature of the composite material, which is mainly due to differences in the energetic levels and degrees of spheroidization of charge particles.

Friction characteristics of tungsten-boron nitride alloys

1. Materials of the tungsten-boron nitride type may prove to be quite promising for use in sliding bearings intended to operate under special conditions. We base this prediction on the high wear resistance of such materials at all the sliding speeds and pressures investigated. 2. We established the sliding speeds and pressures that produce the minimum coefficient of friction. In establishing the causes of this phenomenon, we will seek ways to further improve the friction characteristics of these materials. 3. An increase in the amount of boron nitride introduced into the powder mixture does not lead to a reduction in the coefficient of friction, apparently because of formation of a large amount of hard phases during hot pressing of the specimens.