Interaction of boron suboxide with compacted graphite cast iron

The chemical interaction of boron suboxide (B₆O) with compacted graphite cast iron (CGI) was investigated using static interaction diffusion couples between B₆O and CGI at 700 °C, 900 °C and 1100 °C for 1 h. This interaction offers the possibility to evaluate the potential of B₆O as a cutting tool. The microstructures and phase compositions of the interaction zones were investigated. At 700 °C and 900 °C the chemical interaction was minimal. However, at 1100 °C, Fe₂B and SiO₂ were formed at the interface. Hence, machining at 1100 °C is likely to result in chemical wear.     

Hard and tough boron suboxide based composites

Boron suboxide (B₆O) powder was synthesized at temperatures of about 1400 °C from the reaction of amorphous boron powder with boric acid. The synthesized B₆O powders were hot pressed at temperatures up to 1900 °C and at pressures of 50 MPa. Additionally to pure B₆O materials, composites with aluminium were prepared. The microstructure and properties of the sintered compacts were investigated. The addition of aluminium in the composites results in the formation of an additional aluminium borate phase. The composites showed a similar hardness (∼30 GPa) as the pure B₆O samples but increased fracture toughness (∼3.5 MPa m^1/2).     

High pressure modifications in amorphous boron suboxide: An ab initio study

Using constant pressure ab initio calculations, we probe the high-pressure modifications in amorphous boron suboxide (B₆O) consisting of glassy boron trioxide (B₂O₃) and boron (B) domains up to a theoretical pressure of 100 GPa. At this pressure, the structure remains amorphous. We find a steady increase in the average coordination of both B and oxygen (O) atoms. O atoms mostly attain threefold coordination as in B₂O₃ glass at high pressures. On the other hand, the mean coordination number of B-atoms reaches six at high pressures and the structural changes in B-rich regions are perceived to be quite analogous to those of amorphous B. B₁₂ clusters are found to persevere during the pressurizing process and the high-pressure modifications occur predominantly around O-atoms and the regions that connect the pentagonal pyramid-like motifs to each other. Upon pressure release, some high-pressure configurations persist in the model and another noncrystalline structure being about 10% denser than the original state is recovered, suggesting a permanent densification and a possible irreversible amorphous-to-amorphous phase transformation in B₆O. The recovered network shows slightly better mechanical properties than the uncompressed model. During the compression and decompression processes, amorphous B₆O remains semiconducting. The delocalization of some band tail states is seen at high pressures.     

Densification behavior of flash sintered boron suboxide

A study to quantify the flash sintering kinetics of boron suboxide (B₆O) under various electric field strengths and cut‐off amperages is presented. B₆O is conventionally sintered at a prolonged temperature above 1800°C, near its thermal decomposition temperature, with an overpressure >3 atm. By applying a direct current (DC) electric field across a green powder compact, B₆O can be sintered at 1000°C at atmospheric pressure. During the flash sintering process, an intensive radiation was emitted (electroluminescence), which is distinct from the thermal radiation (thermoluminescence) that is expected in conventional sintering. It was observed that the degree of sintering of the large B₆O specimen was heterogeneous due to apparent localization of electrically conducting paths. The material near the surface was sintered, but the core of the specimen was not. It was found that the flash event occurred at a critical temperature, which was obtained by combining external heating via ambient furnace conditions and internal Joule heating. The progressive densification behaviors of the B₆O are also presented.     

Tetrahedral amorphous boron nitride: A hard material

We generate a tetrahedrally coordinated amorphous boron nitride (BN) model by means of first principles molecular dynamics calculations and report its mechanical and electrical properties in detail. The amorphous configuration is almost free from chemical disorder and consists of about 20% coordination defects, similar to tetrahedral (diamond-like) amorphous carbon. Its theoretical band gap energy is about 2.0 eV, less than 4.85 eV estimated for cubic BN. The bulk modulus and Vickers hardness of tetrahedral amorphous BN are computed as 206 GPa and 28-35 GPa, respectively. Based on these findings, we propose that tetrahedral noncrystalline BN can serve as electronic and hard materials as well.     

Intrinsic hardness of boron carbide: Influence of polymorphism and stoichiometry

Boron carbide comprises of polymorphs that differ in crystallographic arrangement and stoichiometry. Consequently, specimens extracted from the same batch can exhibit variability in mechanical properties depending on the constituent mixture of polymorphs. In this work, density functional theory simulations and estimates from three models (bond resistance model, bond strength model, and electronegativity model) are utilized to (i) investigate the influence of polymorphism and stoichiometry on the intrinsic hardness of boron carbide, (ii) reveal the sensitivity of the estimates to the model used, and (iii) test their conformance to experimental data. The study finds intrinsic hardness of boron carbide to be primarily a function of stoichiometry, with polymorphism having a lower influence. Furthermore, hardness estimates are shown to exhibit substantial sensitivity to the model used, differing by as much as 9 GPa for the same polymorph. Thus, the search for new superhard materials should be guided by more than just one model. Our analysis finds bond resistance model to offer the best conformance to experimental data, indicating that bond length is a much stronger influencer of intrinsic hardness in covalent crystals than coordination numbers and electronegativities of bonding atoms.     

Ab initio study of boron-rich amorphous boron carbides

Amorphous boron carbide compositions having high B contents (B_xC_1−x, 0.50 ≤ x ≤ 0.95) are systematically created by way of ab initio molecular dynamics calculations, and their structural, electrical, and mechanical characteristics are inclusively investigated. The coordination number of both B and C atoms increases progressively with increasing B/C ratio and more close-packed materials having pentagonal pyramid motifs form. An amorphous diamond-like local arrangement is found to be dominant up to 65% B content, and beyond this content, a mixed state of amorphous diamond– and B-like structures is perceived in the models because sp³ hybridization around C atoms is still leading one for all compositions. The pentagonal pyramid motifs around C atoms are anticipated to appear beyond 65% content. The intericosahedral linear C–B–C chains do not form in any model. All amorphous boron carbides are semiconducting materials. The mechanical properties gradually increase with increasing B concentration, and some amorphous compositions are proposed to be hard materials on the basis of their Vickers hardness estimation.     

Doping effects on the electro-degradation of phenol on doped titanium suboxide anodes

Titanium suboxide is an excellent electrode material for many oxidization reactions.In this article,the electrodes of pure Ti_4O_7,doped Ti_4O_7and the mixed-crystal of Ti_4O_7and Ti_5O_9were prepared to evaluate their activities and doping effects in the electro-degradation of phenol.It was revealed by the HPLC analysis results that the degradation intermediates and routes were significantly affected by the doping element.On the pure Ti_4O_7anode,a series of classic intermediates were obtained from benzoquinone and hydroquinone to various carboxylic acids.These intermediates were degraded gradually to the final organic intermediate of oxalate in all experiments.At last,oxalate was oxidized to CO_2and H_2O.Distinctively,the Y-doped Ti_4O_7 anode directly broke phenol toα-ketoglutaric acid without the intermediates of benzoquinone and hydroquinone.The strong oxidization ability of the Y-doped Ti_4O_7 anode might be responsible for the highest COD removal ratio.In contrast,the Ga-doped Ti_4O_7 anode showed the worst degradation activity in this article.Three intermediates of benzoquinone,hydroquinone and maleic acid were found during the degradation.Benefiting from the weak ability,oxalate was efficiently accumulated with a very high yield of 74.6%.The results demonstrated promising applications from electrochemical preparation to wastewater degradation by adjusting the doping reagent of Ti_4O_7 electrodes.     

The influence of the hydrogen origin at the surface of Mo suboxide during the deoxygenation of carboxylic acid

This work investigates the reactivity of a molybdenum suboxide in the deoxygenation of benzoic acid in the presence of hydrogen or propylene. Major differences are highlighted with Mo₈O₂₃ as the active phase. When the reaction is performed in the presence of hydrogen as the reductant, benzoic acid is converted to benzaldehyde, toluene and benzene. If molecular hydrogen is replaced by propylene as a weaker reductant, the only product formed during the reaction is benzaldehyde. It is demonstrated that, in absence of molecular hydrogen in the reaction mixture, a large amount of benzoic acid remains irreversibly adsorbed on the catalyst surface. The comparison of the two series of catalytic tests allows to somehow discriminate how the nature and the mobility of the hydrogen atoms involved in the reaction dictate the behaviour of the catalyst.     

Strengthening boron carbide by doping Si into grain boundaries

Grain boundaries, ubiquitous in real materials, play an important role in the mechanical properties of ceramics. Using boron carbide as a typical superhard but brittle material under hypervelocity impact, we report atomistic reactive molecular dynamics simulations using the ReaxFF reactive force field fitted to quantum mechanics to examine grain-boundary engineering strategies aimed at improving the mechanical properties. In particular, we examine the dynamical mechanical response of two grain-boundary models with or without doped Si as a function of finite shear deformation. Our simulations show that doping Si into the grain boundary significantly increases the shear strength and stress threshold for amorphization and failure for both grain-boundary structures. These results provide validation of our suggestions that Si doping provides a promising approach to mitigate amorphous band formation and failure in superhard boron carbide.     

Hard boron rich boron nitride nanoglasses

Boron‐rich amorphous boron nitride (B_xN_1?x, 0.55 ≤ x ≤ 0.95) alloys are generated by means of ab initio molecular dynamics simulations and their local structure, mechanical properties and electronic structure are exposed. BN:B phase separations are perceived in all amorphous networks, suggesting that these materials can serve as nanoglass ceramics. The sp² hybridization is the main building unit in the BN‐rich regions for low boron concentrations, and the models carry locally the signature of the two‐dimensional hexagonal BN structure. The amorphous states having both sp² and sp³ hybridizations form for boron contents between 70% and 80%. At higher boron concentrations, sp³ hybridization with a fraction of ~90%‐98% is detected as seen in the cubic or wurtize BN crystals. In the boron rich regions, the ideal and defective pentagonal pyramids emerge at 60% boron content, and the first complete B₁₂ molecule develops at 70% boron concentration. In addition to the B₁₂ icosahedron, the formation of a cage‐like B₁₆ molecule is, for the first time, discovered in some amorphous alloys. The isolated B₁₆ molecule is, however, found to be unstable. The Vickers harness calculations reveal that some of these amorphous alloys can serve as hard materials. When their electron properties are considered, all amorphous materials are predicted to be semiconducting.     

Impact of impregnation with boron compounds on the surface hardness and abrasion resistance of some varnished woods

This study was performed to determine the impact of impregnation with boron compounds on the surface hardness and abrasion resistance of some varnished woods. For this purpose, test specimens prepared from Oriental beech, White oak, Scotch pine, and Uludag fir, which met the requirements of ASTM D 358, were impregnated according to ASTM D 1413‐99 with boric acid (Ba), borax (Bx), and boric acid + borax (Ba+Bx) by the vacuum technique. After impregnation, the surfaces are coated with synthetic (Sn), water‐borne (Wb) and acid hardening (Ah) varnishes in accordance with ASTM D 3023. the surface hardness of specimens after the varnishing process was determined in accordance with ASTM D 4366. The abrasion resistance of specimens after the varnishing process was determined in accordance with TS 4755. According to the wood type, impregnation material and varnish type, the surface hardness was the highest for Oriental beech impregnated with borax + boric acid and acid hardening varnish and the lowest for Uludag fir impregnated with borax + boric acid and synthetic varnish. According to the wood type, impregnation material and varnish type, the abrasion resistance was the highest for Oriental beech impregnated with borax + boric acid and acid hardening varnish and the lowest for Scotch pine impregnated with borax + boric acid and synthetic varnish. Those results should be taken into account for applications like parquet, flooring etc., where the surface hardness and abrasion resistance values are very important. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

NiB／SiO2非品态合金催化剂用于合成3-苄氨基-4-甲氧基-乙酰苯胺

以3-氨基-4-甲氧基乙酰苯胺（AMA）、苯甲醛（BAD）为原料，采用负载型NiB/SiO2非晶合金催化剂，缩合加氢制备3-苄氨基-4-甲氧基乙酰苯胺（BAMA）。考察不同条件对催化剂活性的影响，同时对制备的催化剂和产物进行相关表征。优化工艺条件为：催化剂中Ni2＋：BH4-=1：2．5，n（AMA）：n（BAD）=1：1,1，m（cat）：m（AMA）=2.5％，反应温度55～600C，反应压力1．2MPa，BAMA收率可达92．7％。     

三氟化硼苯甲醚体系分离硼的影响因素

利用三氟化硼和苯甲醚进行硼同位素的分离相对于其他方法有较高的优越性,结合实验研究的过程,研究了温度、压力、杂质对于实验过程的影响,由实验数据和文献中的结论,得出要保持好络合塔身温度在10℃,就可以络合比较完全.测得络合塔身各点温度随测温位置的变化趋势,在络合塔身存在一个温度最高的点,可以达到60℃左右,讨论了该点的形成...     

硼吸附树脂的研究进展

硼是一种重要的战略资源,开发与利用过程中容易流失大量硼导致环境的污染与资源的浪费,从环境溶液体系中提取与回收硼资源成为研究热点.介绍了硼溶液的基本性质,探讨了使用硼吸附树脂富集溶液中的硼或去除含硼废水中的硼的各种方法,综述了硼吸附树脂的发展过程性能和研究现状.     

Synthesis of ultrafine nano-polycrystalline cubic boron nitride by direct transformation under ultrahigh pressure

Using a turbostratic pyrolytic boron nitride as a starting material, we synthesized a variety of ultrahard polycrystalline cubic boron nitride (PcBN) as a function of the heating duration changing from 1 to 60?min under a constant temperature and pressure conditions (1950?°C and 25?GPa) using a multi-anvil apparatus. When the heating duration was less than 13?min, ultrafine nano-polycrystalline cBN (U-NPcBN) with the mean grain size of <50?nm was produced. Among these U-NPcBNs those synthesized with 11–13?min were found to have a uniform texture composed purely of cBN (i.e. with no wurzite BN residue) and a Knoop hardness of >53?GPa, which is 20% higher than that of the hardest conventional binderless PcBN in practical use. Furthermore, the PcBNs synthesized with 18–20?min showed a unique nanocrystalline texture composed of relatively coarse grains dispersed in a fine grained matrix and even higher Knoop hardness (54.5–55.2?GPa).     

NaHCO3溶液浸出硼精矿中硼的工艺

研究了NaHCO3溶液提取硼精矿熟料中硼的工艺,考察了液固比、NaHCO3用量、浸出温度、浸出时间和搅拌速率对硼提取率的影响. 结果表明,最佳提取工艺条件为液固质量比2.1:1,NaHCO3用量为理论用量的150%,反应温度100℃,反应时间1 h,搅拌速率400 r/min,该条件下硼浸出率达92.88%. 硼精矿熟料的晶形大多是柱状和扁平状,并有微小颗粒附着其表面;终硼泥为很多小晶体堆叠在一起,与硼精矿熟料相比,终硼泥颗粒变小,因此可用收缩核模型描述硼精矿熟料中硼在NaHCO3溶液中的浸出过程. 金云母、遂安石、利蛇纹石和橄榄石是硼精矿熟料的主要物相,而终硼泥出现了MgCO3和Na2Mg(CO3)2物相,遂安石消失.     

Ultrafine-grained B6O–diamond composites with superb mechanical properties

We report here the high-pressure and high-temperature (HPHT) synthesis of well-sintered B₆O–diamond composites from B₆O and carbon black nanopowders. The carbon black was transformed into diamond nanograins at HPHT conditions, and simultaneously formed high-strength B₆O–diamond interfaces. The ultrafine B₆O and diamond nanograins and the high-strength B₆O–diamond interfaces synergistically construct excellent mechanical properties for the synthesized composites. The B₆O–diamond composites possess a hardness (avg. 52 GPa) comparable to that of polycrystalline diamond (40–60 GPa), whereas the fracture toughness (avg. 7.2 MPa m^1/2) is increased several times compared to previously synthesized polycrystalline B₆O ceramics (1.7–3.1 MPa m^1/2) and B₆O-based composites (3–4 MPa m^1/2). Fracture behavior analysis demonstrates that the main toughening mechanisms in this B₆O–diamond composite are nanotwin toughening, crack deflection, and crack bridging.     

粉状三氧化二硼的制备

将尿素添加到偏硼酸中，放入马弗炉内逐步升温室300℃，可制得粉状三氧化二硼，此法特别适宜于高纯三氧化二硼的制备。     

High‐Temperature Strength of Boron Suboxide Ceramic Consolidated by Spark Plasma Sintering

The spark plasma sintering (SPS) of B₆O ceramics using a highly crystalline boron suboxide powder with a low oxygen deficiency level is reported. The monolithic boron suboxide ceramic exhibited a room‐temperature strength of 300 ± 20 MPa, which is comparable to the strength of monolithic boron carbide. With increasing flexural test temperature, the strength of the boron suboxide ceramics increased to 450 MPa at 1400°C. The increase in strength with the temperature is associated with the unique microstructure of boron suboxide grains, which allows intergranular “brittle” fracture along subgrains even at 1400°C. This suggests that even higher strengths can be achieved.