Amorphous Boron Powder Research Articles

Preparation and characterization of amorphous boron powder with high activity

The amorphous boron powders with high activity were prepared by the high-energy ball milling–combustion synthesis method. The effects of the milling rate and milling time on the crystallinity, microscopic morphology and reactivity of amorphous boron powder were studied. The results show that the crystallinity of amorphous nano-boron powder is only 22.5%, and its purity reaches 92.86%. The high-energy ball milling can significantly refine boron powder particle sizes, whose average particle sizes are smaller than 50 nm, and specific surface areas are of up to 70.03 m2/g. When the transmission electron beam irradiates the samples, they rapidly melt. It can be seen that the monomer amorphous boron size is less than 30 nm from the specimen melting traces, which indicates that the samples have high reactivity.

Investigation on the levitation force behaviour of malic acid added bulk MgB2 superconductors

The effects of malic acid addition (from 0 to 15wt% of the total MgB2) on the levitation force properties of bulk MgB2 have been investigated. All samples were prepared from magnesium powder, amorphous boron powder, malic acid (C4H6O5) and toluene (C7H8) by using two-step solid state reaction method. Vertical and lateral levitation force measurements that are under both zero-field-cooled (ZFC) and field-cooled (FC) regimes were carried out at different temperatures of 24, 28 and 32K for samples with various adding level. It was found that the reasonable malic acid adding has a positive impact on the levitation properties. At 24K and 28K, the 4wt% and 6wt% malic acid added samples exhibits a higher levitation force than pure sample. In the case of the optimally additive 4wt% sample, the maximum levitation force corresponds to 18.60N, whereas the pure sample shows 16.95N at 24K for ZFC regime. In this study the enhancing effect of malic acid adding on the levitation force properties of MgB2 has been first time investigated and reported.

The role of various boron precursor on superconducting properties of MgB2/Fe

The superconducting properties of Fe sheathed MgB2 wire has been studied as a function of precursor B powder particle size. The in situ processed MgB2 samples were prepared by means of conventional solid state reaction method with magnesium powder (99.8%, 325 mesh) and three different types of amorphous boron powders (purity; 98.8%, >95% and 91.9%) from two sources, Pavezyum (Turkish supplier) and Sigma Aldrich. The particle sizes of Turkish boron precursor powder were selected between 300 and 800nm. The structural and magnetic properties of the prepared samples were investigated by means of the X-ray powder diffraction (XRD) and ac susceptibility measurements. The XRD patterns showed that the diffraction peaks for our samples belong to the main phase of the MgB2 diffraction patterns. The highest critical temperature, Tc=38.4K was measured for the MgB2 sample which was fabricated by using the 98.8% B. The critical current density of this sample was extracted from the magnetization measurements and Jc=5.4×105Acm−2 at 5K and B=2T. We found that the sample made by using the 98.8% boron showed almost 2 times higher Jc than that of obtained from 91.9% B powder.

Preparation of amorphous nano-boron powder with high activity by combustion synthesis

The preparation process of amorphous nanometer boron powders through combustion synthesis was investigated, and the effects of the reactant ratio, the heating agent and the milling rate on the activity and particle size of amorphous boron powders were studied. The results show that the boron powders exist in the form of an amorphous phase which has the crystallinity lower than 30.4%, and the particle size of boron powder decreases with an increase of the high-energy ball milling rate. The purity of amorphous boron powder is 94.8% and particle sizes are much smaller than 100 nm when the mass ratio of B2O3/Mg/KClO3 is 100:105:17 and the ball milling time is 20 min with the milling rate of 300 r/min. At the same time, the amorphous boron nano-fibers appear in the boron powders.

Growth mechanism and ultraviolet-visible property of novel thick-walled boron nitride nanostructures

A novel kind of high quality thick-walled BN nano-tadpoles was successfully synthesized through an effective catalytic chemical vapor deposition combined with a co-precipitation method using Na2SiO3·9H2O, Mg(NO3)2·6H2O and amorphous boron powders as raw materials. SEM, FSEM, EDX, TEM, HRTEM, SAED, XRD, FTIR and Raman spectroscopy were employed for the characterization of the morphology, composition, structure and bonding features of the as-synthesized BN samples. The as-synthesized BN nano-tadpoles revealed a length of 10–15 μm and homogeneously tapered diameter from the head to the tail of the BN tadpole. The head diameter of every BN nano-tadpole was 0.5–1.5 μm and the tail diameter was less than 50 nm. Besides, ultraviolet-visible absorption spectroscopy indicated that the as-synthesized BN nano-tadpoles present a different band gap (5.39 eV) compared with that of BN nanotubes and hBN. Moreover, on the basis of the experimental results, the possible chemical reactions and the base vapor–liquid–solid (VLS) and diffusion association growth mechanism are also proposed to properly interpret the formation of the thick-walled BN nano-tadpoles.

A co-precipitation and annealing route to the large-quantity synthesis of boron nitride nanotubes

A novel co-precipitation and annealing route to the large-quantity synthesis of boron nitride nanotubes (BNNTs), using amorphous boron powder, iron nitrate nonahydrate (Fe(NO3)3·9H2O) and urea (CO(NH2)2) as the raw materials, was demonstrated. An intermediate Fe(OH)3·B was firstly prepared through a co-precipitation process and then annealed in flowing ammonia atmosphere at 1200 °C. It was found that the heat treatment at 800 °C during the annealing process could favor the growth of BNNTs. The BNNTs had an average diameter of 70 nm and possessed bamboo and quasi-cylindrical structures. The annealing temperature greatly affected the formation of BNNTs. Only BN particles could be obtained at lower temperature (e.g. 1100 °C), whereas thorn-like nanosheet-decorated BNNTs were fabricated at higher temperature (e.g. 1300 °C). A combination mechanism of solid–liquid–solid (SLS) and vapor–liquid–solid (VLS) model was suggested to be responsible for the growth of BNNTs.

Preparation and Characterization of Mg1−x B2 Bulk Samples and Cu/Nb Sheathed Wires with Low Grade Amorphous Boron Powder

MgB2 bulk and wire samples were prepared using cheap, low grade amorphous boron powders. Based on chemical analysis performed on the starting reagents, three nominal stoichiometries were studied. It was found that the structural and superconducting properties of the bulk samples were not affected by the composition, but that residual Mg was left in the wires for the nominal MgB2 composition. In contrast, slightly Mg-deficient compositions were free from residual Mg and exhibited higher critical current densities. The MgB2 phase formation kinetics was not influenced by the variations in the nominal powder composition.

Dual-stage ignition of boron particle agglomerates

The ignition characteristics of boron particle agglomerates prepared by drying 2–3mm water slurry droplets of crystalline or amorphous boron powders were investigated by introducing suspended agglomerates into a flow of high temperature oxidizing gases (oxygen/nitrogen/water vapor) obtained by a combination of combustion and electrical heating. Monitoring of the agglomerate luminosity, spectra, and temperature revealed a dual-stage ignition process. The first stage ignition was observed at flow temperatures as low as 715K and was followed by agglomerate quenching if the oxygen concentration in the flow was below some critical value. As the oxygen concentration of the flow was increased beyond this critical value, the second stage ignition leading to full-fledge combustion was observed. The ignition characteristics of boron particle agglomerates were theoretically investigated by developing a numerical model that considers the oxygen concentration gradient inside the agglomerate in order to simulate the ignition process. The model results accurately captured the qualitative behavior of the first stage ignition and quenching as well as the dual-stage ignition processes. The model identified the closure of pores in the agglomerate due to the build-up of the boron oxide layer, which effectively seals off the large interior surface area of the agglomerate from the oxidizer, as being the mechanism responsible for the two-stage ignition phenomenon. The critical flow conditions in terms of flow temperature and ambient oxygen concentration for the second stage ignition were determined by this model. The experimental result for the critical ambient oxygen concentration for the second stage ignition in dry flow was determined to be 70%, which is fairly close to the model prediction of 79%.

Synergetic Combination of LIMD With CHPD for the Production of Economical and High Performance $\hbox{MgB}_{2}$ Wires

We propose an economical fabrication concept, the localized internal magnesium diffusion (IMD) method. Instead of using a single magnesium (Mg) rod in the center of a metal sheath tube, we use large-sized Mg particles (20-50 mesh) mixed well with cheap 97% crystalline boron powder to fill the metal sheath tube. After a repeated drawing process, the coarse Mg is elongated along the core wire axis of the metal sheath tube. Textured MgB2 grains are then formed during the sintering process. In the localized IMD process, however, there is still a need to improve the overall density. In order to increase the density of the composite, a modified cold high pressure densification (CHPD) technique has been applied before the reaction. It is found that the critical current density (Jc) of the sample made from large-sized Mg with crystalline boron powder and treated by CHPD is increased significantly, so that it is quite comparable with the Jc values of samples made from expensive small magnesium and nanosized amorphous boron powder. At 4.2 K and 8 T, the Jc value of the wire in this work with the cheapest starting materials reaches 10 000 A/cm2 , which is similar to reported values for samples made by the powder-in-tube and IMD processes with expensive nanosized amorphous boron powder. A possible mechanism is proposed, and the microstructure is analyzed to explain this interesting feature. The main goal of this work is to develop a novel and cost-effective fabrication technique by combining the localized IMD process with CHPD and using cheap crystalline boron powder to manufacture MgB2 superconductor wires with electromagnetic performance superior to that of low-temperature Nb-Ti superconductors.

The use of amorphous boron powder enhances mechanical alloying in soft magnetic FeNbB alloy: A magnetic study

Saturation magnetization and magnetic anisotropy have been studied during mechanical alloying of Fe75Nb10B15 alloys prepared using crystalline and commercial amorphous boron. The evolution of saturation magnetization indicates a more efficient dissolution of boron into the matrix using amorphous boron, particularly for short milling times. The magnetization of the crystalline phase increases as boron is incorporated into this phase. Two milling time regimes can be used to describe the evolution of magnetic anisotropy: a first regime governed by microstrains and a second one mainly governed by crystal size and amorphous fraction.

Spark Plasma Sintering of SuperhardB4C–ZrB2Ceramics by Carbide Boronizing

A carbide boronizing method was first developed to produce dense boron carbide‐ zirconium diboride (“B4C”–ZrB2) composites from zirconium carbide (ZrC) and amorphous boron powders (B) by Spark Plasma Sintering at 1800°C–2000°C. The stoichiometry of “B4C” could be tailored by changing initial boron content, which also has an influence on the processing. The self‐propagating high‐temperature synthesis could be ignited by 1 molZrCand 6 molBat around 1240°C, whereas it was suppressed at a level of 10 molB.B8C–ZrB2ceramics sintered at 1800°C with 1 moleZrCand 10 mole B exhibited super high hardness (40.36 GPa at 2.94 N and 33.4 GPa at 9.8 N). The primary reason for the unusual high hardness ofB8C–ZrB2ceramics was considered to be the formation of nano‐sizedZrB2grains.

Synthesis of nano-sized amorphous boron powders through active dilution self-propagating high-temperature synthesis method

Nano-sized amorphous boron powders were synthesized by active dilution self-propagating high-temperature synthesis (SHS) method at temperatures ranging from 700°C to 850°C in a SHS furnace using Mg, B2O3 and KBH4 as raw materials. Samples were characterized by X-ray powder diffraction (XRD), Laser particle size analyzer, Fourier transform infrared spectra (FTIR), X-ray energy dispersive spectroscopy (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission TEM (HRTEM). The boron powders demonstrated an average particle size of 50nm with a purity of 95.64wt.%. The diluter KBH4 played an important role in the active dilution synthesis of amorphous nano-sized boron powders. The effects of endothermic reaction rate, the possible chemical reaction mechanism and active dilution model for synthesis of the product were also discussed.

A self-propagation high-temperature synthesis and annealing route to synthesis of wave-like boron nitride nanotubes

Large quantities of boron nitride (BN) nanotubes were synthesized by annealing a catalytic boron-containing porous precursor in flowing NH3 gas at 1180°C. The porous precursor was prepared by self-propagation high-temperature synthesis (SHS) method at 800°C using Mg, B2O3 and amorphous boron powder (α-B) as the starting materials. The porous precursor played an important role in large quantities synthesis of BN nanotubes. The as-synthesized product was characterized by X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FTIR), Raman, Scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM). Characterization results indicated that the BN nanotubes displayed wave-like inner structures with diameters in the range of 50–300nm and average lengths of more than 10μm. The possible growth mechanism of the BN nanotubes was also discussed.

Mechanically activated catalyst mixing for high-yield boron nitride nanotube growth

Boron nitride nanotubes (BNNTs) have many fascinating properties and a wide range of applications. An improved ball milling method has been developed for high-yield BNNT synthesis, in which metal nitrate, such as Fe(NO3)3, and amorphous boron powder are milled together to prepare a more effective precursor. The heating of the precursor in nitrogen-containing gas produces a high density of BNNTs with controlled structures. The chemical bonding and structure of the synthesized BNNTs are precisely probed by near-edge X-ray absorption fine structure spectroscopy. The higher efficiency of the precursor containing milling-activated catalyst is revealed by thermogravimetric analyses. Detailed X-ray diffraction and X-ray photoelectron spectroscopy investigations disclose that during ball milling the Fe(NO3)3 decomposes to Fe which greatly accelerates the nitriding reaction and therefore increases the yield of BNNTs. This improved synthesis method brings the large-scale production and application of BNNTs one step closer.

Microwave Synthesis of Nano SiC Doping Mg(B<sub>1-2x</sub>(SiC)<sub>x</sub>)<sub>2</sub> Superconductor and Superconductivity

Superconductor samples Mg(B1-2x(SiC)x)2 (x=0, 5%, 10%) are synthesized from nano SiC, Mg and amorphous boron powders by microwave direct synthesis in a short time. Powder X-ray diffraction (XRD) analysis indicates that the phases of the synthesis sample are MgB2 (major phase) and a small amount of MgO and Mg2Si. The main peaks of MgB2, (100), (101), (002) and (110) are shift to the higher diffraction angle position and the width of half height of the diffraction plane is broaden for the SiC doping Mg(B1-2x(SiC)x)2, which show that the B positions of MgB2 are partly substituted and the grains of MgB2 are fine. Scanning electron microscope (SEM) observation shows that the MgB2 grain size is very small and the sample is tightness (compact). The onset superconducting transition temperature of the Mg(B1-2x(SiC)x)2 (x=0, 5%, 10%) samples measured by magnetization measurement are about 37.6 K, 37.0 K, 36.8 K respectively. The critical current density Jc are calculated according to the Bean model from the magnetization hysteresis loop of the slab Mg(B1-2x(SiC)x)2 (x=0, 5%, 10%) samples. The critical current density Jc of nano SiC doping Mg(B1-2x(SiC)x)2 samples are greatly enhanced. In higher external magnetic field, the Jc of 10% SiC doped sample is the highest; in lower external magnetic field, the Jc of 5% SiC doped sample is the highest; while in the whole external magnetic field, the Jc of undoped sample is the lowest.

Manganese borides synthesized at high pressure and high temperature

We synthesized various kinds of manganese borides by liquid-solid reaction from manganese and amorphous boron powders at high pressure and high temperature. The mixed powders with various atomic ratio of boron to manganese, B/Mn = 0.6, 1.2, 2, 3, 4, 8, were treated at temperature 1100–1350 °C and pressure 4.8-5.5 GPa, for 10–285 min. Typical manganese borides such as Mn4B, Mn2B, MnB, Mn3B4, MnB2, MnB4, and MnBx were synthesized. MnB2 plays an important role in the reaction, which is the middle product and it changes to Mn3B4 and boron with increasing holding time at a mixed atomic ratio of B/Mn = 2 and MnB2 reacted with boron to MnB4 with increasing holding time at a mixed atomic ratio of B/Mn = 8. The preferred orientation of Mn3B4 was also obtained at a mixed atomic ratio B/Mn = 2 and whose growth is highly oriented. The crystalline phases MnB2, Mn3B4, MnB, and Mn2B were prepared with large excess boron content.

Tungsten Doped ZrB2 Powder Synthesized Synergistically by Co-Precipitation and Solid-State Reaction Methods

Firstly, an amorphous precursor of hydrous nano-ZrO2–WO3 powder was precipitated by a co-precipitation method in alcohol-water mixed solvent using ammonia as a precipitator. Then, a mixture of tungsten doped ZrB2 and W2B5 powder was successfully synthesized via a solid-state reaction by borothermal and carbothermal reduction using nanocarbon, amorphous boron powders and as-synthesized amorphous nano-ZrO2–WO3. Furthermore, thermodynamic calculations clarify the above-mentioned reactions may occur. The mass and heat flow of the samples were monitored by thermal analysis. The crystallographic structure was identified by X-ray diffractometry. The size and morphology of the particles were characterized by TEM microscopy. The combined effects of uniformly distributed tungsten and the complex physicochemical changes effectively improved the solid state reactions.

Interaction of 25% chromium steel with boron powder

Thermochemical treatment of industrial chromium steel (15Kh25T–25% Cr) in amorphous boron powder in the temperature range 850–950°C and reaction times up to 43200 sec (12 h) results in the formation of two boride layers at the steel–boron interface. The microstructure of the outer layer bordering the boron phase consists of elongated crystals of the (Fe,Cr)B and (Cr,Fe)B compounds, while that of the inner layer adjacent to the steel base consists of elongated crystals of the (Fe,Cr)2B and (Cr,Fe)2B compounds. Both layers reveal a pronounced texture. Their diffusional growth kinetics is close to parabolic x 2 = 2k 1 t, where x is the total thickness of both layers (m), k 1 is the layer growth-rate constant (m2 ∙ sec–1), and t is time (sec). The temperature dependence of the growth-rate constant of boride layers on the steel surface is described by a relation of the Arrhenius type k 1 = 1.72 ∙ 10–8 exp (–137.1 kJ · mole–1/RT). Microhardness values are 17.8 GPa for the outer layer, 15.9 GPa for the inner layer, and 1.70 GPa for the steel base. The dry abrasive wear resistance of borided steel samples is more than 250 times greater than that of non-borided ones.

Application of Amorphous Boron Granulated With Hydroxyl‐ Terminated Polybutadiene in Fuel‐Rich Solid Propellant

AbstractAmorphous boron powder granulated with HTPB, whose particle diameter could be controlled, was prepared by mechanical mill method. It was found that amorphous boron powder could be granulated with HTPB binder to form B‐HTPB particles, whose median particle diameter (d50) and specific surface area are in the range of 125.0–431.0 µm and 0.02–0.1 m2 g−1, respectively. The B‐HTPB particles could be dispersed in the HTPB binder with relatively low viscosity compared with direct addition of amorphous boron powder to the HTPB binder. The experimental results showed that the content of boron particles in a fuel‐rich propellant could be increased by addition of B‐HTPB particles and the combustion characteristics of the fuel‐rich solid propellant could be improved.

Nanocarbon-dependent synthesis of ZrB 2 in a binary ZrO 2 and boron system

Thermodynamically, ZrO 2 may react with boron to form B 2O 3/B 2O 2 and ZrB 2 at room temperature. However, this reaction is incomplete at temperatures lower than 1550 °C, even with the use of metastable reactants, i.e., as-synthesized amorphous hydrous nano-ZrO 2 and amorphous boron powders. In this study, a complete disintegration of ZrO 2 was achieved by introducing nanocarbon to the binary system of ZrO 2 and boron at 1550 °C. The metastable reactants affected the temperature required for the solid-state reactions and also strongly affected the kinetics of the transformation. Single crystal and plate-like ZrB 2 particles with a uniform distribution and a size of ca. 1.0 μm in two-dimensions were obtained using 5 wt.% nanocarbon and a B/Zr molar ratio of 4.