Silicon Hexaboride Research Articles

Investigation of the effect of impurity of precursor materials on Si‐doped boron carbide properties

AbstractBoron carbide is a notable ceramic, with its high hardness and low density. However, it suffers a sudden loss in strength under high shear stress. Doping boron carbide with Si/B is widely used to increase its resistance to amorphization. High purity boron and silicon hexaboride precursor powders are used for doping boron carbide, but these materials have high costs and supply chain constraints. This research investigated the effect of substituting lower purity B or using pure Si powder instead of SiB6 on materials’ properties such as elastic and mechanical properties, microstructure, and amorphization resistances. It was observed that using lower‐purity boron or pure Si powder instead of SiB6 did not significantly affect critical properties, such as fracture toughness, hardness, or amorphization resistance. However, Young's modulus values decreased as B purity decreased and as Si was used instead of SiB6. These findings demonstrate that substituting precursor materials in Si/B co‐doped B4C is possible with little change in the material's properties. This facilitates the use of easier‐to‐access, cheaper production routes to be used for silicon‐doped boron carbide products.

Synthesis, Characterization, and Antibacterial Efficacy of Borosilicate Compound against Escherichia coli

In this study, a glassy borosilicate compound was synthesized using recycled glass and natural clays. Even though glass recycling is the generally accepted standard practice for managing glass waste, fine fractions of container soda-lime glass or cullet of other compositions are still disposed of in landfills. Thus, advanced upcycled products that offer greater economic motivation for implementation in industry may be the key to success, but these are frequently linked to alternative methods of product synthesis. Here, a simple and facile route of borosilicate compound production has been synthesized and characterized. The physicochemical characterization of the compounds was carried out to determine their properties and the antibacterial efficacy of the synthesized compound against Escherichia coli (E. coli) was investigated. The structural and spectroscopic characteristics were identified as a compound that conformed to quartz, cristobalite, and silicon hexaboride (SiB6). For the antibacterial activity, two test types were typically performed; in the first one, the dilutions of the grind were combined with chloramphenicol at a concentration of 20 µg/mL to perform a synergistic action against the bacteria and in the second one, only the amorphous borosilicate compound was tested against E. coli ATCC 25922 strains. The treatments applied considered the dilutions from 8 to 40 µg/mL. The minimum inhibitory concentration (MIC) sensitivity tests began with incubation at 37 °C in the tubes and subsequent seeding in Petri dishes for colony-forming unit (CFU) counting. The results obtained indicated that the samples possessed a productive antibacterial effect, which support their use in various biomedical applications.

Improved mechanical properties of SiB6 reinforced silica-based ceramic cores fabricated by 3D stereolithography printing

Silica-based ceramic core is an extremely critical component in the manufacture of hollow blades during investment casting. However, the traditional preparation methods rely more on the molds, and the manufacturing costs are relatively high. In this study, silica-based ceramics with silicon hexaboride (SiB6) addition were prepared via 3D stereolithography printing. And the effects of the SiB6 content on mechanical properties of the obtained ceramic samples were explored. As the SiB6 content increased to 2.0 wt%, the linear shrinkage gradually decreased, while the room temperature and high temperature flexural strength were enhanced at the SiB6 content from 0 to 1.0 wt% and reduced as the SiB6 content further rose. As the SiB6 content increased to 1.0 wt%, the linear shrinkage was reduced to 1.86% resulting from the oxidation reaction of SiB6. Furthermore, with 1.0 wt% SiB6 addition, the flexural strength of the samples at room temperature was enhanced from 6.75 MPa to 14.63 MPa due to the sintering promotion of oxidation product B2O3, and the flexural strength at 1550 °C was improved from 7.68 MPa to 13.08 MPa because of the enhanced β-cristobalite content, which is suitable for high temperature casting of ceramic cores. Therefore, it demonstrates the capability of fabricating SiB6 reinforced silica-based ceramic cores with high performance via stereolithography.

Grain boundary segregation in Si-doped B-based ceramics and its effect on grain boundary cohesion

Boron carbide and boron suboxide are attractive for their low densities and ultrahigh hardness values, yet they exhibit poor fracture resistance. Strategies to improve mechanical performance aim to control bulk microstructures and properties by incorporating Si-based additives. A related approach to toughen boron carbide is tailoring the phase-like states of grain boundaries by applying the concept of grain boundary complexion engineering. This work directly investigates the potential of grain boundary complexion engineering to improve fracture resistance by systematically evaluating grain boundary segregation behavior of a polycrystalline silicon hexaboride / boron carbide diffusion couple using aberration-corrected scanning transmission electron microscopy and ζ-factor microanalysis. A main result was that all grain boundaries in the diffusion couple exhibited Si segregation that, depending on the bulk Si concentration, approached up to 3 monolayers of coverage, thereby resulting in nanolayer complexions (oftentimes known as intergranular films). Furthermore, upon analyzing 110 distinct grain boundaries throughout the diffusion zone and an impurity boron suboxide region, free energies of Si segregation in boron carbide and boron suboxide were experimentally determined using the Brunauer, Emmett and Teller (BET) multilayer grain boundary segregation theory. Subsequently, changes in grain boundary energy due to Si segregation were quantified and a maximum energy reduction of 51% and 81% were observed in boron carbide and boron suboxide, respectively, which led to decreases in works of adhesion of 18% and 17%, respectively. In summary, this work uncovers grain boundary processing-structure-property relationships that can be used to improve the fracture resistance in icosahedral boron-based ceramics.

Structure Prediction and Mechanical Properties of Silicon Hexaboride on Ab Initio Level.

Silicon borides represent very appealing industrial materials for research owing to their remarkable features, and, together with other boride and carbide-based materials, have very wide applications. Various Si–B phases have been investigated in the past, however a limited number of studies have been done on the pristine SiB6 compound. Structure prediction using a data mining ab initio approach has been performed in pure silicon hexaboride. Several novel structures, for which there are no previous experimental or theoretical data, have been discovered. Each of the structure candidates were locally optimized on the DFT level, employing the LDA-PZ and the GGA-PBE functional. Mechanical and elastic properties for each of the predicted and experimentally observed modifications have been investigated in great detail. In particular, the ductility/brittleness relationship, the character of the bonding, Young’s modulus E, bulk modulus B, and shear modulus K, including anisotropy, have been calculated and analyzed.

Research of properties of protective coating applied to the surface of reaction-sintered ceramic materials

The study describes the properties of the protective coating deposited on the surface of the reaction-sintered silicon carbide and molybdenum disilicide. The technology of increasing the protective ability of the coating of products deposited on the surface on the basis of reactive sintered carbide of silicon and molybdenum disilicide, which operate in an oxidizing environment at high temperature and a sharp change of thermal regime, is investigated. The obtained results showed that the presence of a protective slip layer significantly increases the stability of the deposited silicoboride coating, thus blocking the interaction of silicon hexaboride with the environment, slowing down almost all diffusion processes at the transition of the interaction of diffusion. It has been established that the simultaneous use of both diffusion and slurry coatings enables maximum protection of reaction-sintered ceramic materials based on silicon carbide and molybdenum disilicide against high-temperature gas corrosion. The developed coating ensures maximum resistance to repeated changes in temperature conditions, while cyclic changes destroy products of silicon carbide and molybdenum disilicide without applied protective coating. The proposed protective coating can be recommended for the protection of reaction-sintered ceramic materials operated in high temperatures.

Amorphous silicon hexaboride at high pressure

ABSTRACT We investigate the pressure-induced structural phase transformation of amorphous silicon hexaboride (a-SiB6) using a constant pressure first principles approach. a-SiB6 is found to undergo a gradual phase transformation to a high-density amorphous phase (HDA) in which the average coordination number of both B and Si atoms is about 6. The HDA phase consists of differently coordinated motifs ranging from 4 to 8. B12 icosahedra are found to persist during compression of a-SiB6 and the structural modifications primarily occur around Si atoms and in the regions linking pentagonal pyramid-like configurations to each other. Upon pressure release, an amorphous structure, similar to the uncompressed one, is recovered, indicating a reversible amorphous-to-amorphous phase change in a-SiB6. When the electronic structure is considered, the HDA phase is perceived to have a wider forbidden band gap than the uncompressed one.

Effect of Oxygen Partial Pressure and Temperature on the Oxidation Behavior of SiB6

The oxidation kinetics of silicon hexaboride (SiB6) was studied at different partial pressures of oxygen. The specific weight gain was measured at 1173 K, 1223 K, and 1273 K for $$ P_{{{\text{O}}_{2} }} $$ = 0.1, 0.23, and 0.33 atm using thermogravimetric analysis. The conventional empirical expressions for oxidation were observed at all selected oxygen partial pressures and temperatures. The structural characterization of the oxidation product was characterized using XRD and FT-IR, with SiB6, SiO2, B, and amorphous B2O3 observed after oxidation for 25 hours. The oxidation surface morphology was also characterized to obtain the oxidation product size, ranging from 4.54 to 24.69 µm with increasing $$ P_{{{\text{O}}_{2} }} $$ and temperature. The diffusional activation energy for the oxidation process was also calculated from the empirical constant, obtained from the mathematical fitting of the specific weight gain with time. The oxidation activation energies for SiB6 are 250.72, 235.64, and 232.65 kJ/mol at $$ P_{{{\text{O}}_{2} }} $$ = 0.1, 0.23, and 0.33 atm, respectively.

A novel metallic silicon hexaboride, Cmca-B6Si

Using first-principles calculations, we propose a novel metallic silicon hexaboride, Cmca-B6Si. This structure is dynamically and mechanically stable at ambient pressure. Furthermore, the formation energy of Cmca-B6Si is lower than those of synthesized Pnnm-SiB6 and SiB4, indicating that Cmca-B6Si is thermodynamically stable. The calculations of thermodynamic stability and structural inheritance indicate that Cmca-B6Si may be obtained by removing Li from the synthesized LiB6Si, that is, by imitating the preparation of Si24 and T-Graphene C4. The structure of Cmca-B6Si is a covalent three dimensional framework linked by B12 icosahedrons and Si atoms. The analysis of band structure and density of states reveals that Cmca-B6Si is metallic because of the partially occupied 2p and 3p electrons of B and Si atoms, respectively. The electron orbitals reveal that Cmca-B6Si has a novel two-dimensional metallicity. This study gives a fundamental investigation on the structural, phonon, and electronic properties of Cmca-B6Si.

Oxidation kinetics and thermophysical properties of gamma irradiated silicon hexaboride

Silicide hexaboride (SiB6) compound with a purity of 99.5% was irradiated using 60Co gamma radioisotope under the atmospheric pressure with a dose rate (D) of 0.27 Gy/s at the 9.7, 48.6, 97.2, 145.8 and 194.4 kGy doses at room temperature. The oxidation kinetics, diffusion velocity, and depth of oxidation of the SiB6 compound were determined by using a differential scanning calorimetry (DSC) in the temperature range of 920 ≤ T ≤ 1270K. The maximum thickness of the B2O3 and SiO2 oxide layers was determined on the surface of SiB6 from the caloritmetric analyzes. The thickness of the formed oxide layers was found in the range of 10 nm and 60 nm. The activation energy of oxide layers formed on the surface as observed from Arrhenius plots was found to increase up to 49.8 kJ mol−1 with respect to absorption dose of SiB6 samples in the temperature range between 950 K and 1270 K. The results have revealed that it has been observed a change in thermodynamic functions (ΔS, ΔH, and ΔG) from room temperature up to 1270 K.

Extending ζ-factor microanalysis to boron-rich ceramics: Quantification of bulk stoichiometry and grain boundary composition

Accurate quantification of light elements which produce only soft X-ray lines via X-ray energy dispersive spectrometry (XEDS) has been traditionally difficult due to poor X-ray emission and detector efficiencies at low energies and significant X-ray absorption effects. The ζ-factor microanalysis method enables one to correct for these shortcomings; however, ζ-factor microanalysis has not yet been thoroughly applied to inorganic materials which are entirely or mostly composed of light elements such as boron carbide, boron nitride, or boron suboxide. This work successfully extended ζ-factor microanalysis to boron-rich ceramics and accurately determined stoichiometries of multiple boron carbides and measured grain boundary compositions of a boron carbide mixed with additives consisting of rare-earth ions. Various strategies were employed to experimentally determine a full range of ζ-factors and measurements were validated using materials of known composition including silicon hexaboride and silicon carbide. Overall, this work has shown that XEDS is a viable technique for light element quantification in (scanning) transmission electron microscopy, in terms of both the accuracy and precision, which is comparable or superior to the complementary electron energy loss spectrometry.

ζ–Factor Development and Quantification of a Boron Carbide and Silicon Hexaboride Diffusion Couple

ζ–Factor Development and Quantification of a Boron Carbide and Silicon Hexaboride Diffusion Couple

Amorphous silicon hexaboride: a first-principles study

ABSTRACTWe report for the first time the atomic structure, electronic structure and mechanical properties of amorphous silicon hexaboride (a-SiB6) based on first-principles molecular dynamics simulation. The a-SiB6 model is generated from the melt and predominantly consists of pentagonal pyramid-like configurations and B12 icosahedral molecules, similar to what has been observed in most boron-rich materials. The mean coordination number of B and Si atoms are 5.47 and 4.55, respectively. The model shows a semiconducting behaviour with a theoretical bandgap energy of 0.3 eV. The conduction tail states are found to be highly localised and hence the n-type doping is suggested to be more difficult than the p-type doping for a-SiB6. The bulk modulus and Vickers hardness of a-SiB6 are estimated to be about 118 and 13–17 GPa, respectively.

Densification and Mechanical Properties of Boron Carbide Ceramics with Addition of Silicon Hexaboride

Boron carbide(B_4C)ceramics were fabricated by hot-pressing at 2000℃for 1h with 2wt% and 5wt% SiB_6 additives respectively.The effect of addition of SiB_6 on sinterability and mechanical properties of B_4C ceramics was studied.The results show that B_4C ceramics can be fully densified by the addition of SiB_6 and thus the mechanical properties of the sintered samples are effectively improved. When 2wt% SiB_6 is added,the bulk density of B_4C ceramics reaches 2.515g/cm~3 which is about 99.5% of the theoretical density,while hardness and flexural strength of the sintered sample are 31.2GPa and 426.6MPa respectively.With the amount of SiB_6 increase to 5wt%,the density,hardness and flexural strength of B_4C ceramics are reduced to 2.500g/cm~3,29.7GPa and 387MPa respectively.On the other hand,the adding amount of SiB_6 does not make a remarkable effect on fracture toughness of B_4C samples since the K_(1c)values in both cases are around 3.2MPa.m~(1/2).The phase assemblages and the reasons induced the changes in mechanical properties of the sintered samples with addtion of SiB_6 are also discussed.

High temperature oxidation of silicon hexaboride ceramics

Isothermal oxidation of silicon hexaboride (SiB 6) ceramic powder at high temperature was investigated. The SiB 6 powder samples were heated from room temperature to 1273K for 25 hours in air, and weight changes were measured to estimate the oxidation resistance and nature of the oxide layers on the SiB 6 ceramics. The samples oxidized in the temperature range of 673 to 1273 K for 25 hours exhibited increasing weight gain with increasing oxidation temperature. The oxidation proceeded in accordance with the parabolic law during the initial oxidation stage. The weight gain increased with increasing oxidation temperature. Based on the results of X-ray diffraction analysis, silicon oxide (SiO 2) and boron oxide (B 2O 3) were present on the surface of samples oxidized in the temperature range of 873 to 1273 K.

Preparation and electrical properties of silicon hexaboride composites containing carbon.

In this study, SiB6 and SiB6-10wt%C prepared by hot pressing. The influence of temperature on the electrical conductivity of SiB6 and SiB6-10wt%C sintered body was investigated. The sample was sintered at 1973K for 3.6ks in vacuum under a pressure of 25MPa. The relative density of sintered body at 1373K was approximately 99%. The high temperature electrical conductivity measured using a D.C. four-terminal method.

Low temperature growth of silicon-boron layer by ultrahigh vacuum chemical vapor deposition

A polycrystalline silicon-boron (Si-B) layer with a thickness of 180 nm was grown on recrystallized amorphous silicon in an ultrahigh vacuum chemical vapor deposition (UHV/CVD) system using pure SiH4 and B2H6 (1% in H2). The growth temperature was as low as 550 °C. Auger electron spectroscopy and secondary ion mass spectroscopy showed that the boron concentration is extraordinarily high (2×1022 cm−3). From the analysis of transmission electron diffraction patterns, the phase of silicon hexaboride (SiB6) was found to be present in the as-deposited Si-B layer. After thermal annealing, most of the boron atoms in the Si-B layer were found to be immobile. The presence of SiB6 in the Si-B layer may lead to the reduction of boron diffusivity in the Si-B layer during thermal annealing.

Reaction between boron carbide and silicon

This article examines the high-temperature reaction between boron carbide and silicon and confirms the assumption that silicon carbide and silicon hexaboride are the reaction products by calculating the isobaric-isothermal potential of the reaction at temperatures above the melting point of silicon and as high as the temperature of decomposition of silicon hexaboride. X-ray diffraction and crystallographic results are presented for the solution and crystallization behavior of the reaction participants.

An Investigation of the Compound Silicon Boride (SiB6)

Single crystals of the compound silicon hexaboride have been prepared. Laue, rotation, and Weissenberg photographs indicate an orthorhombic cell with lattice parameters , , and . The pycnometer density is 2.43 g/cm3. The average electrical resistivity of single crystals, based on a probe technique, is 0.2 ohm‐cm. The melting point is 1950°C. has a Knoop hardness, with a 100‐g load, of 1910 kg/mm2.