Thermal reaction characteristics of the boron used in the fuel-rich propellant

High pressure DSC and simultaneous TG/DSC were used to study the different kinds of boron that was used in the fuel-rich propellant and the amorphous boron in different gases and different pressure. Also, some of the samples before the experiment and after the experiment were analyzed by the SEM. The results show that: (1) there is a big exothermic peak between 550 °C and 850 °C for all the samples because the combustion heat of boron is very high, and the exothermic peak appears in advance when the pressure or the oxygen concentration increases. (2) Although the reaction process of all the samples with air or oxygen could be divided into five stages, the reaction characteristics are different from each other. Especially, amorphous boron is much more active than the boron used in the fuel-rich propellant. (3) The exothermic peak at about 700 °C appears in advance, and the percentage conversion of boron decreases when the content of magnesium increases and boron–magnesium compound is used as the raw materials. (4) Some samples start to lose their mass for the sake of the evaporation of the (BO)_n.     

Boron complexes of porphyrins and related polypyrrole ligands: unexpected chemistry for both boron and the porphyrin

The coordination of boron to a range of polypyrrole-containing ligands is explored in this feature article. The boron dipyrromethenes are well-known as laser dyes and fluorescent labels in biology. Subphthalocyanine and subporphyrin macrocycles containing only three pyrrole rings can exist only when templated by a central boron atom. Boron complexes of expanded porphyrins (six or eight pyrroles) can complex boron in dipyrromethene (but not bipyrrole) sites. The primary focus of the article is on boron porphyrin and corrole complexes, where the tight fit of two boron atoms within the very constrained coordination site gives rise to unexpected chemistry at both boron and the porphyrin ligand. These unusual features are described and reasons for their occurrence postulated.     

Boron Separation by the Two—step Ion—Exchange for the Isotopic Measurement of Boron

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Separate vaporisation of boric acid and inorganic boron from tungsten sample cuvette-tungsten boat furnace followed by the detection of boron species by inductively coupled plasma mass spectrometry and atomic emission spectrometry (ICP-MS and ICP-AES)

Utilising extremely different vaporisation properties of boron compounds, the determination procedures of volatile boric acid and total boron using tungsten boat furnace (TBF) ICP-MS and TBF-ICP-AES have been investigated. For the determination of volatile boric acid by TBF-ICP-MS, tetramethylammonium hydroxide (TMAH, Me₄NOH) was used as a chemical modifier to retain it during drying and ashing stages. As for the total boron, not only non-volatile inorganic boron such as boron nitride (BN), boron carbide (B₄C), etc. but also boric acid (B(OH)₃) was decomposed by a furnace-fusion digestion with NaOH to produce sodium salt of boron, a suitable species for the electrothermal vaporisation (ETV) procedure. The proposed method was applied to the analysis of various standard reference materials. The analytical results for various biological and steel samples are described.     

An Examination of the Scope and Stereochemistry of the Ireland–Claisen Rearrangement of Boron Ketene Acetals

The Ireland–Claisen rearrangement of boron ketene acetals is described. The boron ketene acetal intermediates are formed through a soft enolization that obviates the use of strong bases and the intermediacy of alkali metal enolates. Yields and diastereoselectivities of these rearrangements are very sensitive to the choice of boron reagent, even among those that have been shown to effect quantitative formation of boron ketene acetals from esters. The rearrangement occurs at room temperature for all substrates with generally high levels of stereoselectivity. In contrast to previous reports using boron triflates, the use of a commercially available boron iodide reagent allows for a wider substrate scope that extends to propionates and arylacetates, as well as the previously described α‐oxygenated esters. This work also provides insight into the dynamic nature of boron ketene acetals and the ramifications of this behavior for reactions in which they are intermediates.     

Application of cycloaddition reactions to the syntheses of novel boron compounds

This review covers the application of cycloaddition reactions in forming the boron-containing compounds such as symmetric star-shaped boron-enriched dendritic molecules, nano-structured boron materials and aromatic boronic esters. The resulting boron compounds are potentially important reagents for both materials science and medical applications such as in boron neutron capture therapy (BNCT) in cancer treatment and as drug delivery agents and synthetic intermediates for carbon-carbon cross-coupling reactions. In addition, the use of boron cage compounds in a number of cycloaddition reactions to synthesize unique aromatic species will be reviewed briefly.     

A FT-IR Study of the Synthesis of Boron Ormosils by Means of the Sol-Gel Process

Borosilicon ormosil materials can be prepared by using the sol-gel method. The precursors used for the synthesis were TEOS (tetraethylorthosilicate), TEB (triethylborate) and PDMS (silanol terminated polydimethylsiloxane). Four samples containing different boron amounts were prepared and reactions were studied by FT-IR spectroscopy. The spectra were deconvoluted and the time evolution of the most important bands was analysed in order to know the role of the boron in the reaction process. Different plots show that boron affects the self-condensation process of the hydrolysed TEOS molecules but does not have much influence in the way of the co-polymerization.     

Determination of Phase Stability of Elemental Boron

Boron is an important element, used in applications from superhard materials to superconductors. Boron exists in several forms (allotropes) and, surprisingly, it was not known which form (α or β) is stable at ambient conditions. Through experiment, we quantify the relative stability of α‐boron and β‐boron as a function of temperature. The ground‐state energies of α‐boron and β‐boron are nearly identical. For all temperatures up to 2000 K, the complicated β‐boron structure is more stable than the simpler α‐boron structure at ambient pressure. Below 1000 K, β‐boron is entropically stabilized with respect to α‐boron owing to its partially occupied sites, whereas at higher temperatures β‐boron is enthalpically stabilized with respect to α‐boron. We show that α‐boron only becomes stable on application of pressure.     

Dramatic Substituent Effects on the Photoluminescence of Boron Complexes of 2-(Benzothiazol-2-yl)phenols

Substituents can induce dramatic changes in the photoluminescence properties of N,O-chelated boron complexes. Specifically, the boron complexes of 2-(benzothiazol-2-yl)phenols become bright deep blue- and orange-red-emitting materials depending on amino substituents at the 5- and 4-positions of 2-(benzothiazol-2-yl)phenol, respectively. Absorption and emission data show that the resulting boron complexes have little or small overlap between the absorption and emission spectra and, furthermore, X-ray crystal structures for both the blue and orange-red complexes indicate the absence of π-π stacking interaction in the crystal-packing structures. These features endow the boron complexes with bright and strong photoluminescence in the solid state, which distinguishes itself from the typical boron complexes of dipyrromethenes (BODIPYs). A preliminary study indicates that the blue complexes have promising electro-optical characteristics as dopant in an organic light-emitting diode (OLED) device and show chromaticity close to an ideal deep blue. The substituent effects on the photoluminescent properties may be used to tune the desired emission wavelength of related boron or other metal complexes.     

A Preliminary experimental study of the boron concentration in vapor and the isotopic A preliminary experimental study of the boron concentrationin vapor and the isotopic fractionation of boron betweenseawater and vapor during evaporation of seawater

A laboratory experiment was undertaken to investigate the behaviour of boron at theseawater-air interface under air flow conditions. Dried air at 25 and 35℃ was passed over or bub-bled through seawater at the same temperature. A combination of ice-chilled condensers and KOHimpregnated cellulose fibre filters was used to collect boron from the reacted air. When air strippedof boron was passed over the seawater, boron was found in the reacted air, and its concentrationwas higher in the higher temperature test. In the tests where air was bubbled through seawater theconcentration of boron in the reacted air was directly proportional to the air flow rate. In this situa-tion the boron in the reacted air was mainly introduced as a spray of microdroplets. Isotopic analy-sis of the collected boron in the non-bubbled tests yields fractionation factors which demonstratethat the lighter isotope, 10B, is enriched in the reacted air. The size of the fractionation changeswith temperature, ruling out a purely kinetic effect.     

电感耦合等离子体原子发射光谱(ICP-AES)法测定钢中硼时样品溶解损失及空白控制研究

用电感耦合等离子体原子发射光谱(ICP-AES)法研究了钢中硼的测定。实验发现,分析线在硼182.64nm处无硼铁基体空白值低于纯试剂(无铁)空白值。样品分析时,应进行无硼铁基空白实验,结果计算只能用此空白值。对普通玻璃烧杯和聚四氟乙烯烧杯的酸溶样品测定结果进行了比较,结果表明,测定结果和空白值相近且都很低,无硼普通玻璃烧杯也能满足钢中低含量硼的测定需要。通过对实验与报道结果比较分析表明,硝酸或王水加热溶解样品得到的溶液中硼没有损失,此溶液可测定钢中酸溶硼;用高氯酸发烟处理后,样品中酸不溶硼可能会溶解,但硼会挥发损失。因此,高氯酸发烟处理不能测定硼。     

Predicting two-dimensional boron-carbon compounds by the global optimization method

We adopt a global optimization method to predict two-dimensional (2D) nanostructures through the particle-swarm optimization (PSO) algorithm. By performing PSO simulations, we predict new stable structures of 2D boron-carbon (B-C) compounds for a wide range of boron concentrations. Our calculations show that: (1) All 2D B-C compounds are metallic except for BC(3) which is a magic case where the isolation of carbon six-membered ring by boron atoms results in a semi-conducting behavior. (2) For C-rich B-C compounds, the most stable 2D structures can be viewed as boron doped graphene structures, where boron atoms typically form 1D zigzag chains except for BC(3) in which boron atoms are uniformly distributed. (3) The most stable 2D structure of BC has alternative carbon and boron ribbons with strong in-between B-C bonds, which possesses a high thermal stability above 2000 K. (4) For B-rich 2D B-C compounds, there is a novel planar-tetracoordinate carbon motif with an approximate C(2)(v) symmetry.     

The effect of the sintering atmosphere on the densification of B4C ceramics

Densification of boron carbide during sintering may be improved by a two-stage process, namely heating to 2000°C under vacuum and sintering at 2190°C under argon. This sintering regime allows achieving a relative density of the ceramic bodies fabricated from a fine powder higher than 95%. The nitrogen treatment of the boron carbide phase at 1900°C leads to the formation of the BN phase and precipitation of graphite. Vacuum treatment of these samples at 2000°C leads to decomposition of the boron nitride phase. The liberated free boron may again react with graphite to form in situ boron carbide particles. The experimental investigations of the sintering behavior of the boron carbide phase under various atmospheres supported the thermodynamic predictions regarding the phase transformation. No evidence, however, was found for enhanced sintering under a nitrogen atmosphere.     

Fitting the boron peak and resolving interferences in the 450–490 keV region of PGAA spectra

Prompt gamma activation analysis (PGAA) is one of the most powerful analytical methods for the determination of boron because of its very large neutron capture cross section. The peak of boron in the PGAA spectra is highly broadened due to the Doppler-effect. An improved method is presented to fit the boron peak, and to resolve interference with the gamma-rays of sodium and other matrix components. The method has been checked on test samples and on geological samples as well.     

连续浸提-分光光度法测定硼泥中不同形态的硼

采用连续浸提法将硼泥中的硼划分为七种物理形态,即:水溶态、醇溶态、盐溶态、络合态、硫酸盐等结合态、Fe-Mn结合态及残渣态。用分光光度法测定各形态硼的含量。测定结果的相对标准偏差为4.4%(n=4),回收率为91.7%~102.4%。     

Phase diagram of the B-B2O3 system at 5 GPa: experimental and theoretical studies

X-ray diffraction with synchrotron radiation has been used to study in situ the chemical interaction of beta-rhombohedral boron with boron (III) oxide and phase relations in the B-B2O3 system at pressures up to 6 GPa in the temperature range from 300 to 2800 K. The B-B2O3 system has been thermodynamically analyzed, and its equilibrium phase diagram at 5 GPa has been constructed. Only one thermodynamically stable boron suboxide, B6O, exists in the system. It forms eutectic equilibria with boron and B2O3.     

Compacts of Boron-Doped Synthetic Diamond: Lowering of Synthesis Temperature and Its Effect on the Doping Level and Electrochemical Behavior

Substituting of metal (Co, Ni) borides for boron carbide in the boron carbide–graphite growth system for the process of diamond growth in the region of diamond thermodynamic stability allowed lowering the synthesis temperature for the electrodes of this new electrode material―boron-doped diamond compacts―significantly (by ~1000°C) without any deterioration of their electrochemical properties. On the other hand, using of amorphous boron with finer grain as compared with the boron carbide, mixed with graphite, results in a marked increase of the electrodes’ electrochemical efficiency, due to increase in their roughness after the chemical removing of boron-containing inclusions from their surfaces. Thus obtained compact electrodes have wide potential window and low background current in supporting electrolytes, they are well reproducible. Special features of their electrochemical impedance spectroscopy are similar to those of the recently studied compacts synthesized on the basis of boron carbide.     

Continuous flow system for the determination of trace boron in iron and steel utilizing in-line preconcentration/separation by Sephadex column coupled with fluorimetric detection

A simple, rapid and sensitive system for the determination of trace boron in iron and steels is presented, in which in-line separation/preconcentration of boron from iron matrix is directly coupled with fluorimetric detection in a continuous flow system. Boron was adsorbed on a small column packed with Sephadex G-25 gel, followed by elution with a small volume of dilute hydrochloric acid. The formation of boron complex with 1,8-dihydroxy-3,6-naphthalenedisulphonic acid in a continuous flow system was used for the sensitive determination of boron by fluorescence detection(lambda(ex)=314 nm and lambda(em)=355 nm). The present FIA system offers many advantages over existing methods, especially with respect to simplicity and sensitivity, permitting semi-automated determination of boron with a short analysis time (about 10 min), low limit of determination (0.1 ppm in steels) and good reproducibility (rsd<3% for 1-18 mug g(-1) boron in steels).The present FIA system can be readily applied to the steel samples.     

Electrochemical Determination of Boric Acid Using the Boric Acid–Tiron Complexation System

For monitoring the boron concentration in reverse osmosis (RO) water produced by desalination plants, a voltammetric determination method for the amount of electrochemically inactive boron has been developed by using the complexation with 4,5‐dihydroxybenzene‐1,3‐disulfonic acid (Tiron). Cyclic voltammetric measurements showed the oxidation peak of boric acid–Tiron 1 : 1 complex at 920 mV. This peak was successfully applied to the determination of boron in RO water with the LOD of 0.1 mg B dm^?3 by using differential pulse voltammetry. The redox and acid–dissociation behaviors of Tiron and its boron complex are found to depend on the properties of pH buffer reagent.     

Dramatic Substituent Effects on the Photoluminescence of Boron Complexes of 2‐(Benzothiazol‐2‐yl)phenols

Substituents can induce dramatic changes in the photoluminescence properties of N,O‐chelated boron complexes. Specifically, the boron complexes of 2‐(benzothiazol‐2‐yl)phenols become bright deep blue‐ and orange‐red‐emitting materials depending on amino substituents at the 5‐ and 4‐positions of 2‐(benzothiazol‐2‐yl)phenol, respectively. Absorption and emission data show that the resulting boron complexes have little or small overlap between the absorption and emission spectra and, furthermore, X‐ray crystal structures for both the blue and orange‐red complexes indicate the absence of π–π stacking interaction in the crystal‐packing structures. These features endow the boron complexes with bright and strong photoluminescence in the solid state, which distinguishes itself from the typical boron complexes of dipyrromethenes (BODIPYs). A preliminary study indicates that the blue complexes have promising electro‐optical characteristics as dopant in an organic light‐emitting diode (OLED) device and show chromaticity close to an ideal deep blue. The substituent effects on the photoluminescent properties may be used to tune the desired emission wavelength of related boron or other metal complexes.