Mixture Of Boron Research Articles

B4C ceramics with increased dislocation density fabricated by reactive spark plasma sintering via carbon nanotubes–boron mixture

Boron carbide with high relative density was prepared in situ using spark plasma sintering. Research on the in-situ reaction of boron and carbon nanotubes reveals that the reaction exhibits high reactivity at 1200 °C. Beyond this temperature, increasing the external pressure was beneficial for particle rearrangement, gas release, and dislocation formation. The result of mechanical properties shows that, the flexural strength and fracture toughness of the boron carbides are 656 ± 9 MPa and 5.0 ± 0.3 MPa m1/2, respectively, when sintered at 1750 °C under continuous pressure ramping conditions–an increase of 64.1% and 46.6% compared to that prepared under constant pressure conditions. Increasing the magnitude of the external stress during the in-situ reaction process can also enhance the particle rearrangement efficiency, inducing the formation of twinning and stacking faults in boron carbide ceramics. High–density twinning and stacking faults dominated the toughening mechanisms of ceramic materials.

Synthesis and characterisation of lead-magnesium-boron nanocomposite for radiation shielding application.

There is a need for the replacement of toxic lead with nontoxic materials in radiation shielding applications. Instead of pure lead, lead mixed compounds/mixtures/alloys are considered to be less toxic and hence preferred for radiation shielding purposes. The compounds with magnesium are said to be having good magnetic and mechanical properties. Meanwhile, the boron element avoids secondary radiation and absorbs neutrons. The compound which is a mixture of lead, magnesium and boron is expected to be a good shielding material for radiation for X-rays/gamma rays. Hence in the present study, we have synthesised the lead-magnesium-boron (LMB) nanocomposites (NCs) using the green synthesis approach for the first time. LMB is synthesised by solution combustion method using Aloe vera as a reducing agent. The synthesised NCs are characterised using well-known characterisation techniques. Powder X-ray diffraction confirmed the formation of multi-phase LMB NCs, and average crystal size is found to be 13-15nm. Surface morphology and chemical composition are affirmed by SEM and EDX. The optical energy gap is found to be 1.87eV. FTIR confirmed the functional groups. X-rays/gamma rays, neutrons and bremsstrahlung radiation shielding efficiency are measured by experimental and theoretical, compared with conventional shielding materials. LMB NCs have proved to be efficient. Hence, LMB NCs proved to be potential in X-rays/gamma rays, neutrons and bremsstrahlung radiation shielding.

DIELECTRIC PROPERTIES OF CERAMICS BASED ON BN–ZrB2 AND BN–ZrO2 PRODUCED BY SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS

Dielectric properties of ceramic materials based on BN–ZrB2 and BN–ZrO2 systems synthesized in the mode of self-propagating high-temperature synthesis (SHS) from a mixture of boron B powders, boron nitride BN and zirconium dioxide ZrO2 in an atmosphere of nitrogen N2 have been studied. The experimental results showed that ceramics synthesized from the initial mixture of (30B + 10ZrO2 + 60BN, wt. %) composition have permittivity (?) and tangent of the dielectric loss angle (tg) values of 2.63 and 0.006, respectively, at room temperature.

Structural features of heavily boron-doped graphite and diamond microcrystals synthesized at high pressures

Heavily boron-doped graphite was synthesized from a mixture of adamantane and boron using a high-pressure technique. Ab initio calculations of a carbon cluster of 64 atoms located in two layers of graphene with the inclusion of one boron atom were made. Substitution of boron for carbon in the graphene layer correlates with the experimental data if we consider the change in the cell parameters. The easy transformation of the boron-doped graphite lattice into a diamond one at pressure of about 7.5 GPa may be due to the presence of a small number of boron atoms between graphene layers. Heavily boron-doped diamond crystals in the shape of a five-pointed star were found. The mechanism of their growth includes cyclic twinning and is obviously associated with the presence of a fluid phase in the synthesis medium and facilitated twinning of a diamond lattice containing boron.

Synthesis of Submicron Boron Carbide by the Non-Vacuum Method with Indirect Supply of the Thermal Energy of a DC Arc Discharge

The results of experimental studies demonstrating the possibility of obtaining boron-carbide powder by treating a mixture of carbon and amorphous boron containing a small amount of boron oxide with DC arc discharge plasma are presented. A feature of the applied nonvacuum electric-arc method for the synthesis of boron carbide is its implementation in an open air environment due to achievement of the effect of screening the reaction zone with gaseous oxide and carbon dioxide. In this case, the initial reagents are heated to the required temperatures by a DC arc discharge plasma burning in the immediate vicinity of the initial-material mixture in the cavity of the graphite crucible. The resulting material contains particles of boron carbide with a size in the submicron range, which are characterized by the “shell–core” type structure. The scheme of the discharge circuit of a laboratory reactor with horizontal arrangement of electrodes and an indirect supply of thermal energy to the initial reagents described in the paper makes it possible to significantly increase the content of the boron-carbide phase and reduce the content of the graphite impurity phase.

High-Pressure Synthesis of Light Lanthanide Dodecaborides (PrB12 and CeB12): Effects of Valence Fluctuation on Volume and Formation Pressure.

Light lanthanide dodecaborides, RB12 (R = Pr and Ce), were synthesized from a stoichiometric mixture of hexaborides and boron using a laser-heated diamond anvil cell under high-pressure and high-temperature conditions. Contrary to the expectation that lighter lanthanide elements require higher pressure to crystallize RB12, in situ X-ray diffraction experiments reveal that cerium dodecaboride crystallizes at 26 GPa, which is significantly lower than that required to form the heavier praseodymium dodecaboride (35 GPa). In addition to the lower formation pressure, an anomalous volume reduction is also observed in CeB12, which can be explained by a valence fluctuation between Ce3+ and Ce4+ indicated by X-ray absorption near-edge structure measurements. A polyhedral coordination change from a truncated cube in RB6 to a truncated octahedron in RB12 and associated shortening of the R-B bond length result in an increase in bulk modulus and hardness.

Investigation of the effect of boron additive to lubricating oil on engine performance, exhaust, and emissions

In this study, the effect of adding doped boron to lubricating oil on engine performance and emissions, in the cases of using gasoline and natural gas as fuel, was investigated in a spark ignition engine. The engine was initially run on a mixture of undoped boron lubricating oil, gasoline, and natural gas. Subsequently, engine performance and emission values were measured in the work, after the engine was run for 50 h. The same measurements were repeated for both the initial values and the values after 50 h with gasoline and natural gas by adding boron to the lubricating oil. Experimental results revealed that using boron-doped lubricating oil causes an average of 2.4–8% reduction in specific fuel consumption when using gasoline and natural gas as fuel in the engine. It was found that the use of boron in the lubricating oil did not make a significant change in C2, CO, and HC emissions, but caused a significant 11.4–12.9% reduction in NOX emissions. As a result, it was observed that adding boron-doped lubricating oil in a gasoline engine provides a relative improvement in engine performance and emissions.

A Study of Thermal Decomposition and Kinetic Evaluation of Boron Blended Flash Powder Composition

Abstract Herein, the thermal characteristics of flash powders of different combinations of potassium nitrate, sulfur, aluminum, and boron are reported. From the literature, it is identified that boron implements lack of sensitiveness to flash powder mixture, which promotes safety during the manufacturing process. But the thermal behavior of the boron blended compositions remains a mystery. Hence, various combinations of flash powder compositions are prepared by keeping the % of KNO3 and % of S constant, and gradually 23% of aluminum is reduced (23% to 0) by increasing the quantity of boron (0% to 23%) in 19 trials and are subjected to thermogravimetric analysis (TGA)/differential scanning calorimetric (DSC) analysis individually. The TGA and the DSC analysis reveals that the 65.65% replacement of aluminum with boron mixture shows predominant characteristics which is suitable for fireworks. Also, the reaction kinetics and the critical ignition temperature are calculated for the optimum composition. The performance of the fireworks product is checked with varying quantities to meet out the optimum quality.

Combustion of Transition Metal–Boron Mixtures in Argon Gas

Combustion of Transition Metal–Boron Mixtures in Argon Gas

Diborides of transition metals: Properties, application and production. review. Part 2. Chromium and zirconium diborides

The second part of the review considers properties, application and methods for producing chromium and zirconium diborides. These diborides are oxygen-free refractory metal-like compounds. As a result, they are characterized by high values of thermal and electrical conductivity. Their hardness is relatively high. Chromium and zirconium diborides exhibit significant chemical resistance in aggressive environments. They have found application in modern technology because of these reasons. Chromium diboride is used as a sintering additive to improve the properties of ceramics based on boron carbide and titanium diboride. Zirconium diboride is a component of advanced ultra-high temperature ceramics (UHTC) ZrB2–SiC used in supersonic aircrafts and in gas turbine assemblies. Ceramics B4C–CrB2and B4C–ZrB2have high-quality performance characteristics, in particular, increased crack resistance. The properties of refractory compounds depend on the content of impurities and dispersion. Therefore, to solve a specific problem associated with the use of refractory compounds, it is important to choose the method of their preparation correctly, to determine the admissible content of impurities in the starting components. This leads to the presence of different methods for the borides synthesis. The main methods for their preparation are:a) synthesis from elements;b) borothermal reduction of oxides;c) carbothermal reduction (reduction of mixtures of metal oxides and boron with carbon;d) metallothermal reduction of metal oxides and boron mixtures;e) boron-carbide reduction. Plasma-chemical synthesis (deposition from the vapor-gas phase) is also used to obtain diboride nanopowders. Each of these methods is described.

Synthesis of boron carbide from its elements up to 13 GPa

The synthesis of boron carbide from its elements (boron and carbon) has been studied under pressures up to 13 GPa and optimum parameters have been determined by varying the (P, T, reactants) conditions. Stoichiometric mixtures of amorphous boron and amorphous carbon have been subjected to a range of temperatures from 1673 K to 2273 K at the pressure values of 2 GPa and 5 GPa. The formation temperatures have been compared to those obtained from mixtures of β rhombohedral boron and graphite, and β rhombohedral boron and amorphous carbon at 2 GPa and 5 GPa. The formation temperature is thus shown to be affected by the pressure and the choice of the reactants. The carbon concentration of boron carbide is also shown to be affected by the pressure at which it is synthesised from elements, and we propose pressure as a means to control the carbon content. Temperature cycling has also been shown to reduce the formation temperature of boron carbide at 13 GPa. The formation of α rhombohedral boron as an intermediate phase is seen at 5 GPa before the formation of boron carbide.

Characteristics of Cr-B Coatings Produced on Vanadis® 6 Tool Steel Using Laser Processing.

The paper presents the results of a study of the microstructure, chemical composition, microhardness and corrosion resistance of Cr-B coatings produced on Vanadis 6 tool steel. In this study, chromium and boron were added to the steel surface using a laser alloying process. The main purpose of the study was to determine the impact of those chemical elements on surface properties. Chromium and boron as well as their mixtures were prepared in various proportions and then were applied on steel substrate in the form of precoat of 100 µm thickness. Depending on the type of precoat used and laser processing parameters, changes in microstructure and properties were observed. Coatings produced using precoat containing chromium and boron mixture were characterized by high microhardness (900 HV0.05–1300 HV0.005) while maintaining good corrosion resistance. It was also found that too low laser beam power contributed to the formation of cracks and porosity.

Luminescent properties of Ce3+-activated lithium borosilicate glasses tuned by various ratios of lithium to boron

Motivated by the urgent practical requirement of neutron detection, Ce3+-activated lithium borosilicate glasses consisting of 80 mol% lithium and boron mixtures with high neutron capture cross-section were synthesized by melt quenching method in air. The structures of lithium borosilicate glasses were revealed by both FTIR and Raman spectra. The effects of Li/B ratios on the optical properties, such as optical transmittance, photoluminescence, decay lifetime and radioluminescence (RL) were investigated in detail. It is found that the integrated emission intensity of Ce3+ ions can be enhanced by a factor of 13.5 and 1.2 under UV light and X-ray excitation, respectively. The developed Ce3+-activated lithium borosilicate glass is featured with the emission band centered at 350 nm and the lifetime within 25–30 ns, which shows promising application for thermal neutron detection.

Magnetic phase transition and lattice dynamic features in ErB2C borocarbide

A sample of erbium borocarbide ErB2C was synthesized from a stoichiometric mixture of erbium, boron, and pyrographite hydride. Temperature dependent magnetic susceptibility, heat capacity and lattice parameters of borocarbide at 2–300 K were experimentally investigated, the Raman spectrum was determined and analyzed. Sharp anomalies in the heat capacity and magnetic properties of ErB2C near T = 16.3 K, caused by the transition to the antiferromagnetic state, as well as diffuse anomalies at a higher temperature, caused by the effect of the crystal field (Schottky anomalies) were revealed. It was found that the magnetic phase transition does not cause measurable anomalies in the lattice parameters of borocarbide due to the weak coupling between the Er3+ ion subsystem and the B–C layers. Almost zero thermal expansion of erbium borocarbide in the basal plane (along a and b axes) (anisotropic invar effect) as well as an unusual character of the c-axis thermal expansion were observed. The first of these features is due to the high bonding energy in the B–C layers and the weak bond between the layers in the borocarbide crystal lattice. It was found that the anomalous expansion along the c axis is a consequence of the action of the crystal field. The splitting scheme for the ground level of Er3+ ions by crystal field was determined from the analysis of the Schottky anomaly of the heat capacity.

Diborides of transition metals: Properties, application and production. Review. Part 1. Titanium and vanadium diborides

The properties, applications and methods for producing titanium and vanadium diborides are considered. These diborides are oxygen-free refractory metal-like compounds. As a result, they are characterized by high values of thermal and electrical conductivity. Their hardness is relatively high. Titanium and vanadium diborides exhibit significant chemical resistance in aggressive environments. For these reasons, they have found application in modern technics. So, they are used as surfacing materials when applying wear-resistant coatings on steel products. It is also possible to use vanadium diboride as a catalyst in organic synthesis and the anode in renewable electrochemical current sources. Perspective are ceramics B4C – TiB2and B4C – VB2, which make it possible to obtain products based on boron carbide with high-quality performance characteristics, in particular, with increased crack resistance. Such composite ceramics are obtained by means of hot pressing, spark plasma sintering and pressureless sintering. The properties of refractory compounds depend on the content of impurities and dispersion. Therefore, to solve a specific problem associated with the use of refractory compounds, it is important to choose the method of their preparation correctly, to determine the admissible content of impurities in the starting components. This leads to the presence of different methods for the synthesis of borides. The main methods for their preparation are: synthesis from simple substances (metals and boron); borothermal reduction of oxides; carbothermal reduction (reduction of mixtures of metal oxides and boron with carbon; metallothermal reduction of mixtures of metal oxides and boron; carbide-boron reduction. Plasma-chemical synthesis (deposition from the vapor-gas phase) is also used to obtain diboride nanopowders. Each of these methods is characterized in the article.

Augmentation of Aluminum and Boron Ignition

Effect of K2CO3 and KCl additives on the process of high-temperature oxidation and ignition of conglomerates of powdered boron and aluminum particles and on the critical conditions for the ignition of particle–gas mixtures of these metals is studied experimentally. It is revealed that the mixtures of boron and aluminum particles covered (encapsulated) with salts ignite at temperatures lower than the ignition temperatures of mechanical mixtures of metals with these salts in appropriate proportions and significantly lower ignition temperatures of pure boron and aluminum. This indicates the active role of salts in the process of heterogeneous ignition. It is established that, for boron conglomerates, the accelerating effect of salt additives on the oxidation of conglomerates is noticeable at all investigated concentrations and compositions starting from 1% (by weight). For aluminum, an increase in the reaction rate is noticeable only for KCl additives at concentrations of 3% and above.

Hypergravity-Induced Accumulation: A New, Efficient, and Simple Strategy to Improve the Thermal Conductivity of Boron Nitride Filled Polymer Composites.

Thermal conductive polymer composites (filled type) consisting of thermal conductive fillers and a polymer matrix have been widely used in a range of areas. More than 10 strategies have been developed to improve the thermal conductivity of polymer composites. Here we report a new “hypergravity accumulation” strategy. Raw material mixtures of boron nitride/silicone rubber composites were treated in hypergravity fields (800–20,000 g, relative gravity acceleration) before heat-curing. A series of comparison studies were made. It was found that hypergravity treatments could efficiently improve the microstructures and thermal conductivity of the composites. When the hypergravity was about 20,000 g (relative gravity acceleration), the obtained spherical boron nitride/silicone rubber composites had highly compacted microstructures and high and isotropic thermal conductivity. The highest thermal conductivity reached 4.0 W/mK. Thermal interface application study showed that the composites could help to decrease the temperature on a light-emitting diode (LED) chip by 5 °C. The mechanism of the improved microstructure increased thermal conductivity, and the high viscosity problem in the preparation of boron nitride/silicone rubber composites, and the advantages and disadvantages of the hypergravity accumulation strategy, were discussed. Overall, this work has provided a new, efficient, and simple strategy to improve the thermal conductivity of boron nitride/silicone rubber and other polymer composites (filled type).

Influence of Chromium Concentration on Corrosion Resistance of Surface Layers of Stainless Steel

Phase transformations occurring during the non-vacuum electron-beam surfacing using a mixture of amorphous boron and chromium powder (from 5 to 30 wt%) as well as the effect of the resulting structure on the corrosion resistance of the surface layers of chromium-nickel austenitic steel have been investigated. It has been found that when processing a powder mixture with a minimum chromium content (5 and 10 wt%), layers with a dense arrangement of borides are formed. Further increase in chromium concentration (20 and 30 wt%) leads to the formation of solid solutions in the modified layer. It has been shown that an increase in the concentration of chromium in the surface layer leads to a twofold increase in the corrosion resistance of the 12Х18Н9T (AISI 302) steel surface.

Высокоборированный дисперсный алюминий: экспериментальная оценка его нейтронно-экранирующих свойств

By the method of mechanical alloying, compaction and thermosynthesis of a mixture of amorphous boron and aluminum powders, a prototype of highly borated (~50 wt.%) dispersed boron-aluminum was obtained. A comparative assessment of the neutron-shielding properties of borated dispersed aluminum and fibrous boron-aluminum VKM Al-B under irradiation with neutrons with a flux density of 1.4·106 n/cm²·s with a fluence of 3·109 n/cm2 was carried out. Using optical and scanning electron microscopy, a morphological analysis of samples of dispersed-borated powdered aluminum and fibrous-composite boron-aluminum was carried out. It was found that in both materials the level of absorption of neutrons with energies of 0.02-0.05 eV is up to 99.5-99.95%. It is concluded that highly borated dispersed boron-aluminum supplements the line of known boron-containing neutron-absorbing materials with the possibility of using it up to temperatures of 500-700°C.

Numerical study of boron diffusion in CMT and related thermal fatigue near cold legs of an AP1000 nuclear power unit

AP1000 adapts Passive Core Cooling System to improve the safety. However, it is found that static diffusion under the difference of the boron concentration and sampling lead to boron loss, which makes the boron concentration in core makeup tank lower than the specification limits. Corresponding to this problem, replenishing high concentration boron water is a way to meet the requirements for boron concentration. Under this circumstance, this study numerically investigates the effect of static boron diffusion, sampling and replenishing on boron concentration. The results show that static diffusion and sampling have a slight impact on boron dilution, but in different ways. A larger replenishing flow rate is useful to enhance the boron mixture. However, that will result in a heavy heat load on the “T" connection of reactor coolant system and core makeup tank.