Aluminum Boride Research Articles

Tribological Properties of Aluminum and Silicon Borides at High Temperatures

In our present study, AlB12 and SiB6 plate specimens prepared by spark plasma sintering AlB12 and SiB6 powders, respectively, and their tribological properties were investigated in the temperature range of 25°C to 1000°C in air. Also, the micro Vickers hardness of the AlB12 and SiB6 plate specimens were evaluated in the temperature range of 25°C to 1000°C in an Ar gas atmosphere. It was found that both the steady friction coefficients of the AlB12 and SiB6 plate specimens were as low as 0.07 to 0.08 at 1000°C. According to XPS analyses, it was found that Al2O3 and B2O3 films were observed on the worn surfaces of the AlB12 plate specimens after sliding at 1000°C. On the other hand, SiO2 and B2O3 films were observed on the worn surfaces of the SiB6 plate specimens after sliding at the same temperature. It was also found that both the boride plate specimens exhibited micro Vickers hardness as high as 20 GPa in the temperature range of 25°C to 1000°C.

Efficacy of Borides in Grain Refining Al-Si Alloys

The grain refining efficacy of titanium, aluminum, and niobium borides, as well as niobium aluminides, introduced via commercial and lab made master alloys on Al-Si alloys was investigated. Significant grain refinement is achieved via the introduction of these heterogeneous nuclei regardless of their chemistry, stoichiometry of the master alloy, and addition rate. However, the grain refinement is affected by variable such as contact time, as the inoculating particle may sediment or be poisoned, and cooling rate. Specifically, a faster cooling rate generally leads to finer grains due to the lower time for grain growth. In the case of borides, the chemical inoculation efficiency is greatly affected by their thermodynamic stability in molten Al-Si alloys. Conversely, the grain refining potency of properitectic Al3Nb remains unaffected. The underlying grain refining mechanism was finally investigated using current models based on the growth restriction factor Q to simultaneously consider the effect of nucleant potency and alloy chemistry. Among Ti-, Al-, and Nb-based borides with similar particle size and distribution, the latter are the most efficient to grain refine Al-Si alloys.

Ignition and heterogeneous combustion of aluminum boride and boron–aluminum blend

Adding other metals is an efficient method of breaking through the energy release efficiency limitation of boron-based fuels. A laser ignition testing system was used for investigating the ignition and heterogeneous combustion characteristics of aluminum boride and boron–aluminum blend. The emission spectra and combustion flames of the samples during combustion were recorded by a fiber optic spectrometer and a high-speed camera, respectively. The component, morphology, and distribution features of the condensed combustion products (CCPs) were then analyzed using an X-ray diffractometer, a scanning electron microscope, and an X-ray energy dispersive spectrometer. The emission spectral intensity curves show that the boron–aluminum blend has better ignition feature than aluminum boride (the ignition delay time was 45% shorter). However, the combustion intensity and self-sustaining combustion time of boron–aluminum blend are both inferior to those of aluminum boride. In full wave emission spectra of the samples, the characteristic peaks of combustion intermediate products like BO2, AlO, and AlO2 were found. The combustion flames of the two samples were both yellow green and tapered. The variation trend of the flame size corresponded to that of the emission spectral intensity curves. During the first half of the combustion, large amounts of sparks were ejected from the combustion flame of boron–aluminum blend, which caused the acute fluctuation of combustion intensity. B, Al, B2O3, Al2O3, AlN, and Al5O6N were detected in the CCPs of both samples. In addition, the CCPs of aluminum boride contained unburned AlB2, and those of boron–aluminum blend contained Al4B2O9. Webbed AlN fibers were observed only in the CCPs of boron–aluminum blend, while AlN and Al5O6N whiskers were found in those of both samples. The observed bulks were partially oxidized AlB2 in the CCPs of aluminum boride, or partially oxidized B in those of boron–aluminum blend. As both diffusion and melt-dispersion reactions of aluminum were proceeded during the combustion of boron–aluminum blend, oxidation products of aluminum with different morphology were found in the CCPs of boron–aluminum blend as follows: smooth aluminum spheres with low oxidation degree, rough aluminum oxide spheres with high oxidation degree, empty aluminum oxide shells with hollows or cracks, and fine aluminum oxide particles adhered on the surface of boron bulks.

Ignition and Combustion of Condensed Systems with Energy Fillers

This paper describes the results of an experimental study of ignition and combustion of condensed systems, containing energy fillers, i.e., powders of aluminum, boron, aluminum borides, and titanium. Compositions on a hydrocarbon or active fuel binder with a combined oxidizer (ammonium perchlorate and/or ammonium nitrate) are considered. Thermodynamic estimates for the ballistic characteristics of the compositions under study are given. It is shown that a unit pulse increases by 3.5% with the replacement of aluminum by boron in the compositions considered. It is experimentally determined that the time delay of ignition of boron-containing compositions decreases in conductive and radiant heat transfer and that the stationary burning rate of boron and aluminum boride containing compositions increases. The efficiency of the impact of energy fillers on the characteristics of condensed systems as a function of the composition of a combined oxidizer is determined.

Mechanochemical synthesis of nanocrystalline aluminium boride (AlB12)

Low-temperature synthesis of aluminium boride (AlB12) powders by mechanochemical synthesis of Al and B powder blend has been carried out. The influence of milling time on the phase formation temperature and annealing time of AlB12 was investigated. X-ray diffraction of the milled and annealed powder samples revealed the formation of AlB2 without any oxide phases. AlB12 powder was synthesized at a significantly low temperature of 1030 K. The processed AlB12 powder was nanocrystalline in nature confirmed by transmission electron microscopy investigations. It has been shown that mechanochemical synthesis could be an attractive route for the synthesis of borides at low temperatures.

Systematic investigation of structural, electronic, optical and thermal properties of ternary MoAlB; an ab initio approach

Structural, electronic, optical and thermal properties of molybdenum aluminum boride (MoAlB) have been analyzed systematically using the full potential linearized augmented plane wave method based on density functional theory at ambient condition as well as high pressure and high temperature. Density of states and band structure calculation reflect the metallic character of MoAlB. In addition to this, the electron charge density calculation reveals the strong covalent bonding, in between ‘B’ atoms as well as ‘Mo’ and ‘B’ atoms. Optical parameters exhibit anisotropic nature and MoAlB become transparent in ultraviolet region for the radiation of energy above 25 eV. The thermal properties were investigated by using the quasi-harmonic Debye model at high temperature and high pressure.

Optimization for Turning of Aluminium and Titanium Di Boride Cast Composites Using Response Surface Methodology

In present work an effort has been set up to orchestrate aluminum metal matrix composite to study its machining properties. Status of aluminum metal matrix composite was set up by reinforcing Titanium di boride (TiB2). The cast composite samples were carefully machined. The outcome of machining components like cutting speed, feed and depth of cut on surface roughness were explored through turning operation. For modeling and optimizes the impact on surface roughness for input parameters of aluminum metal composites, the Response Surface Methodology was utilized. The adequacy of numerical model was finished using ANOVA. The deliberate and anticipated qualities were sensibly close, which verify that the numerical model can be adequately used. Response surface curve lines were made for formative the greatest conditions for a basic surface roughness. The anticipated condition delineates that the feed is the key variable taken after by cutting speed controls the surface roughness. The surface roughness was begin to decrease with reduce the feed and lift the cutting speed and depth of cut

Powders of metal borides obtained by the SHS method and low-temperature plasma

This paper introduces principle possibility of producing aluminum and titanium boride predetermined morphology using the SHS method and plasma processing. Thermal analysis data for synthesized boride powders in comparison with boron powder and nano-sized aluminum are presented It was found that the synthesized metal borides, according to the thermal analysis data, are promising as a fuel in high-energy materials: the oxidation state of AlB2 is ~ 80%, at a degree of boron oxidation ~ 20%, aluminum ~ 67%.

Synthesis and characterization of aluminum diboride products using 27Al, 11B NMR and ab initio studies

Understanding different bonding environments in various metal borides provides insight into their structures and physical properties. Polycrystalline aluminum diboride (AlB2) samples have been synthesized and compared both with a commercial sample and with the literature. One issue that arose is the relative ease with which boron-rich and aluminum deficient phases of aluminum borides can be presented in AlB2. Here, we report 27Al, 11B nuclear magnetic resonance (NMR) spectroscopy and first-principles calculations on AlB2 in order to shed light on these different bonding environments at the atomic level and compare the structural and electronic properties of the products of different preparations. Along with the aforementioned, the present study also takes an in-depth look at the nature of the 11B and 27Al nuclear spin–lattice relaxation recovery data for the AlB2 and other superhard materials. The nuclear spin–lattice relaxation has been measured for a static sample and with magic-angle spinning. The combination of NMR and band structure calculations highlights the synthetic challenges with superhard materials.

Producing of aluminum boride in plasma of high-current impulse arc discharge

The experimental investigations were conducted on producing ultradisperse materials in a beam of electrodischarge plasma that contained aluminum and boron. A beam is generated by a high-current impulse accelerator of plasma and flows into an inert atmosphere (argon). According to the quality X-ray diffraction analysis, the produced powder material consists of aluminum and aluminum boride α-AlB12.

Keywords

Polycrystalline cubic boron nitride (PcBN) composites were sintered around 6 GPa/1200 °C in a cubic multi anvil press: aluminium in the starting mixture reacts with cubic boron nitride (cBN) and forms aluminium boride (AlB2) and nitride (AlN) bonding among cBN grains during high pressure high temperature (HPHT) sintering. X-ray diffraction (XRD), Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy were utilized to analyse different phases, micro-structure, morphology, and compositions of the composites material. The dense structure of superhard cBN grains bonded together with light AlB2/AlN offers superior hardness, high strength, and X-ray transparency; PcBN anvils (12 mm height × 12 mm diameter × 5 mm culet) were built for rotational anvil cell for in-situ synchrotron high pressure experiments on Zirconium, and these PcBN anvils survived up to 32 GPa after initial tests.

Laser ignition of high-energy materials containing AlB2and AlB12powders

Boron-containing substances are known to have high gravimetric and volumetric heats of oxidation in comparison with any metals that make them promising for using in high-energy materials. This work is aimed to study ignition characteristics of ammonium perchlorate and nitrate-based composite solid propellants containing aluminium borides by means of radiative heating by CO 2 -laser. It was found that the effect upon laser ignition (ignitability) at full replacement of ASD-4 aluminum powder by aluminium diboride and dodecaboride is close. The ignition time of HEM is reduced by 2.0–2.5 times compared with ASD-4 HEM sample in the heat flux density range of 90–200 W/cm 2 .

In situ development of AlBx/AA6060 and AA5083 alloys cast composites

Abstract Al – AlBx (x = 2,12), AA6060 – AlBx (x = 2,12) and AA5083 – AlBx (x = 2,12) composites with 3 wt % AlBx particles were developed by in-situ reaction of molten aluminium and alloys (AA5083 and AA6060) with inorganic salt KBF4 at a temperature of 900 °C. The chemical reaction produces boron, which dissolves into the molten alloy and subsequently forms aluminium borides (AlB2 and AlB12). The thermodynamic properties of the reactions are calculated by HSC Chemistry 6.0 software. In the case of aluminium matrix the melt solidified in the crucible, between 980 °C and 200 °C, in order to develop the peritectic reaction AlB12 + 5Al(l) = 6AlB2. It was found that both in the case of aluminium and aluminium alloys the peritectic reaction occurs partially. The composites were characterised by SEM and XRD analysis. The stress-strain measurement showed 8% improvement towards the matrix alloys. The fracture features of composites were examined using SEM analysis. Ductile and brittle locally fractography is revealed. Composites exhibited a higher resistance to crack initiation than the matrix alloys. The results obtained in the experiments and analysis helps to clarify the mechanism of interaction between liquid aluminium and KBF4 at high temperatures.

Effect of Metal Additives on the Combustion Characteristics of High-Energy Materials

Thermodynamic calculation of combustion parameters and equilibrium composition of HEMs combustion products showed, that at the increase of aluminum powder dispersity the specific impulse and combustion temperature of solid propellants are reduced due to the decrease of the mass fraction of active aluminum in particles. Partial or complete replacement of aluminum by metal powder (B, Mg, AlB 2 , Al\Mg alloy, Fe, Ti and Zr) in HEMs composition leads to the reduce of the specific impulse and combustion temperature. Replacement of aluminum powder by boron and magnesium in HEM reduces the mass fraction of condensed products in the combustion chamber of solid rocket motor. So, for compositions HEMs with boron and aluminum boride the mass fraction in chamber is reduced by 24 and 36 %, respectively, with respect to the composition HEMs with Al powder. But the mass fraction of CCPs in the nozzle exit increases by 13 % for HEMs with aluminum boride due to the formation of boron oxide in the condensed combustion products. Partial replacement of 2 wt. % aluminum powder by iron and copper additives in HEM leads to the reduce of CCPs mass fraction in chamber by 4–10 % depending on the aluminum powder dispersity duo to these metals are not formed condensed products at the HEMs combustion in chamber.

Nanodispersive aluminum boride prepared by a plasma recondensation of aluminum and boron micron powders

This work presents investigations into the composition and some properties of nanodispersive powders of aluminum boride prepared by the plasma-recondensation technique. It is shown that, under a strictly determined aluminum: boron ratio in the starting mixture and with the complete observance of technological processing parameters, aluminum boride (n-AB) nanopowders of the required composition and dispersivity can be obtained. SEM investigations of the aluminum boride samples reveal that aluminum boride powders are mixtures of spherical particles of different sizes and a significant agglomeration of the particles is observed. In general, the sizes of particles are varied from several dozens of nanometers up to 500 nm and more. Investigations into the thermal-oxidative activity of synthesized aluminum boride using thermogravimetric and differential thermal analysis show that these compounds are more active towards air than nanodispersive aluminum. The highest rate of oxidation of aluminum borides was observed in the temperature range of 680–700°C.

Sintering of polycrystalline boron nitride composites for in-situ synchrotron high pressure research

Polycrystalline cubic boron nitride (PcBN) composites were sintered around 6GPa/1200°C in a cubic multi anvil press: aluminium in the starting mixture reacts with cubic boron nitride (cBN) and forms aluminium boride (AlB2) and nitride (AlN) bonding among cBN grains during high pressure high temperature (HPHT) sintering. X-ray diffraction (XRD), Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy were utilized to analyse different phases, micro-structure, morphology, and compositions of the composites material. The dense structure of superhard cBN grains bonded together with light AlB2/AlN offers superior hardness, high strength, and X-ray transparency; PcBN anvils (12mm height×12mm diameter×5mm culet) were built for rotational anvil cell for in-situ synchrotron high pressure experiments on Zirconium, and these PcBN anvils survived up to 32GPa after initial tests.

Modification of aluminium and aluminium alloys by AL-B master alloy

Chemical compositions and microstructures affect on mechanical – physical and working properties of aluminium and aluminum alloys. Transition elements, such as Ti, V, Cr, Zr in solid solution greatly reduce the electrical conductivity of aluminium and its alloys. For reduction of detrimental effects of transition elements, Al-B master alloys are added into molten aluminium to occur reactions of boron and transition elements to form diborides of titanium, vanadium, chromium and zirconium, which are markedly insoluble in molten aluminium, then these transition elements have an insignificant effects on conductivity. In addition, Al-B master alloys is also used as a grain refiner of aluminium and aluminium alloys. Aluminium borides particles in Al-B master alloys act as substrates for heterogeneous nucleation of aluminium and its alloys. Al-B master alloys are prepared from low cost materials, such as boric acid H3BO3 and cryolite Na3AlF6, by simple melting method, easily realize in electrical wire and cable factories.

Boron substitution in aluminum cluster anions: magic clusters and reactivity with oxygen.

We have studied the size-selective reactivity of AlnBm(-) clusters m = 1,2 with O2 to investigate the effect of congener substitution in energetic aluminum clusters. Mixed-metal clusters offer an additional strategy for tuning the electronic and geometric structure of clusters and by substituting an atom with a congener; we may investigate the effect of structural changes in clusters with similar electronic structures. Using a fast-flow tube mass spectrometer, we formed aluminum boride cluster anions and exposed them to molecular oxygen. We found multiple stable species with Al12B(-) and Al11B2(-) being highly resistant to reactivity with oxygen. These clusters behave in a similar manner as Al13(-), which has previously been found to be stable in oxygen because of its icosahedral geometry and its filled electronic shell. Al13(-) and Al12B(-) have icosahedral structures, while Al11B2(-) forms a distorted icosahedron. All three of these clusters have filled electronic shells, and Al12B(-) has a larger HOMO-LUMO gap due to its compact geometry. Other cluster sizes are investigated, and the structures of the AlnB(-) series are found to have endohedrally doped B atoms, as do many of the AlnB2(-) clusters. The primary etching products are found to be a loss of two Al2O molecules, with boron likely to remain in the cluster.

The Effect of Reinforcement Ratio on the Wear Behaviour of AlB2Flake Reinforced Metal Matrix Composites

Aluminium boride composites (Al AlB2) having two di erent volume fractions of reinforcing (AlB2), namely 4.0 and 10.0 per cent have been produced through synthesizing boron by reaction of boron oxide (B2O3) with liquid aluminium. Friction and wear characteristic of the composites have been investigated under dry sliding condition and results compared with pure aluminium. The wear rate increases with normal load and sliding speed and is signi cantly lower with the composites when compared to that of monolithic material. The coe cient of friction increased with increasing volume fraction of AlB2 reinforcement phase. The wear rate, however, decreased with increasing volume fraction of AlB2.

The Efficiency of the Centrifuge is Force Action on the Propagation Mechanism of SHS-Wave

Adiabatic wave (AW) is generated by the effect of two forces, namely centrifugal and Coriolis forces, caused on the reaction of the self-propagating high-temperature synthesis (SHS). The synthesis occurs in the aluminothermic oxide system placed inside the heat insulated cylindrical reactor rotating around a vertical<br />axis. Actually there take place two processes during the SH synthesis: 1. separation of the reaction products, in particular aluminum (corundum) oxide concentrated on a quartz wall of the reactor and forming a tube; 2. formation of a coherent flow of liquid metal particles accelerating in the reactor axis direction according to its rotation speed and co-ordinates of Rх particle in the reactor. The size of the cluster representing particles practically does not change from the very moment of their generation as a result of the reaction due to their motion coherency. Considering the motion speed particles get inside a fresh combustible mixture deeper and deeper and, thus, initiate ignition of the accumulating reaction mixture. This provides growth of the heat release rate and transition of the process to the adiabatic mode. Metal clusters bearing kinetic energy and heat energy of the reaction (T = 2.8-3.5 thousand K) actually have a high energy potential that can increase according to growth of the rotation speed and longitudinal size of the reactor. So, if any highly endothermic reaction mixture takes place within a reactor co-ordinate with exponential growth of the moving clusters energy this reaction can be initiated and consequently will give start to numerous research capabilities. A real possibility of such rare and new materials synthesis technology is illustrated using as an example a reaction of the boron and aluminum oxides attacked by 92 m/s speed moving tungsten clusters with formation of a product from the intermediate boron and aluminum oxides and also tungsten and aluminum borides. The results of the synthesized oxide material study using a radio spectrometer has been presented and presence of free valency in it has been identified. Production of free valency materials is of interest in terms of their mixture with nanomaterilas and their compaction at ultrahigh pressure with the purpose to receive new materials with original mechanical, electric, photo-electric, and other properties. The references given below contain data on this technology studied previously.