Boron In Graphite Research Articles

Determination of boron concentrations at trace level in graphite matrices by AMS

In order to be classified as possible nuclear grade graphite, it is necessary to establish the boron equivalent content in it. The literature offers various but complicated methods for determining the concentration of boron in graphite at the ppm level.In the past, we have developed a preliminary method to measure the trace level of boron in graphite by AMS using a small quantity of material (of the order of mg) without chemical processing. To perform such more accurate measurements, in this study we have developed the preliminary method, by the alternative injection of the isotopes 11B and 12C in the accelerator in an automatic mode.

Using Chemically Active Additives for the Arc Atomic Emission Determination of Boron in Graphite

We studied the effect of chemically reactive additives of AlF3, ZnF2, and SrF2 on the character of boron evaporation from a crater in a DC arc electrode in the analysis of graphite. The introduction of fluorinating additives contributes to a rapid, complete, and stable evaporation of boron. Zinc fluoride is the most effective among the studied compounds. The use of this additive made it possible to lower the limits of quantification of boron in graphite to 5 × 10–6 wt % and to double the reproducibility of the results. The use of zinc fluoride also eliminated the systematic error due to the difference in the evaporation patterns of boron oxide and carbide, which improved the reliability of the determination results.

Theoretical investigation of the catalytic and inhibiting role of boron in graphene oxidation

Boron has been considered as an important promising candidate for oxidation protection in carbon materials. However, the experimental discovery of catalytic effect of boron in graphite makes the role of boron confusing. To better understand the role of boron in carbon materials such as graphite or graphene, we investigate the oxidation behavior of boron-doped stoichiometric and vacancy-defected graphene plane by density functional theory calculations. Boron is found to be a catalyst for oxidation in the stoichiometric surface, while it acts as an inhibitor in the vacancy-defected surface. The electronic properties are calculated to explain why boron behaves differently in different surfaces. We show that the role of boron is closely associated with the redistribution of σ electrons. For instance, the introduction of boron in stoichiometric surface facilitates the delocalized σ electrons transfer from the matrix to oxygen and the adsorption energy increases with the number of transferred σ electrons; while the decrease in reactivity with boron substitution in the vacancy-defected surface is largely attributed to the transition of electrons from delocalized states to localized states, thus suppressing the activity of dangling C atoms. This work helps to provide a theoretical foundation for further investigation of oxidation-resistant carbon materials.

Repelling Polysulfides Using White Graphite Introduced Polymer Membrane as a Shielding Layer in Ambient Temperature Sodium Sulfur Battery

AbstractHerein, a strategy is demonstrated to effectively control the sodium polysulfide dissolution using composite polymer blend membrane. The sufficient interconnected pores in the white graphite introduced polymer blend membrane plays a multifunctional role as an ion selective membrane, evident from the ionic conductivity of 10−3 S cm−1 facilitating the movement of sodium ions and the presence of boron and nitrogen in white graphite acts as an effective absorbent to trap sodium polysulfides. The electrochemical testing reveals significant improvement of about 87.6% in specific capacity when compared to the cell without white graphite@ polymer membrane. Also, the cell exhibits an excellent cycling stability with a capacity retention of 83.1% at the end of 500 cycles. Other than the performance enhancement, the self‐discharge battery is significantly reduced using the developed membrane. The better performance of the room temperature sodium sulfur battery is attributed to the physical and chemical confinement of composite polymer membrane which is also evident from the post analysis study. This is the first attempt of utilizing composite polymer membrane as a blocking layer in room temperature sodium sulfur batteries and is promising for the construction of high performance batteries.

Effective Shielding of Sodium Polysulfides Using Two-Dimensional Ceramic Based Polymer Membrane for Ambient Temperature Sodium Sulfur Battery

The development of high energy density batteries is an essential requirement for the large-scale energy storage applications and the balance between cost as well as performance will drive a way to meet the energy needs. Focusing on low cost energy storage devices, sodium is widely available in the Earth’s crust (23600 ppm). The coupling of low cost sodium anode and sulfur cathode can lead to cost effective high energy density sodium sulfur battery. But the conventional sodium sulfur batteries are operated at a higher temperature of above 300 °C. Since the operating temperature far exceeds the melting points of sodium and sulfur, the problem of corrosion prevails and may bring safety issues. So, the operation of battery at room temperature will turn to improved safety and high energy density. Since solid electrolytes cannot conduct sodium ions at ambient condition, the ambient temperature sodium sulfur battery has to move towards the use of liquid electrolytes. But the dissolution of sodium polysulfides formed during the discharge process is highly soluble in liquid electrolytes and reduces the durability of the battery. Preventing the dissolution of sodium polysulfides by chemical binding towards the cathode is an effective strategy for obtaining the high energy density and durable sodium sulfur battery. This study employs a two-dimensional porous ceramic polymer membrane for suppressing the shuttling effect. The presence of boron and nitrogen in white graphite helps in chemical binding of higher order sodium polysulfides and helps to attain a reversible specific capacity of 1027 mAh g-1 at a current density of 50 mA g-1. The electrochemical impedance study validates the control of polysulfide shuttling using the porous ceramic membrane. This method provides a new technique of controlling the polysulfide shuttling and can lead to the development of room temperature sodium sulfur battery.

Density functional theory investigation of oxygen interaction with boron-doped graphite

Boron inserted as impurity by substitution of carbon atoms in graphite is known to change (improve or deteriorate) oxidation resistance of nuclear graphite, but the reason for both catalytic and inhibiting oxidation is still uncertain. As a first step, this work is more specially devoted to the adsorption and diffusion of oxygen atoms on the surface and related to the problem of oxygen retention on the pure and boron-containing graphite surfaces. Adsorption energies and energy barriers associated to the diffusion for molecular oxygen recombination are calculated in the density functional theory framework. The existence of boron modifies the electronic structure of the surface, which results in an increase of the adsorption energy for O. However, low boron loading makes it easier for the recombination into molecular oxygen. For high boron concentration, it induces a better O retention capability in graphite because the presence of B-B bonds decreases recombination of the adsorbed oxygen atoms. A possible explanation for both catalytic and inhibiting effects of boron in graphite is proposed.

AMS measurements of trace levels of boron in graphite

The accelerator mass spectrometry analyzing method has been applied to measure low boron concentrations in graphite for nuclear reactors. The detection limits were found to be between 5 × 10−6 (upper limit) and 3 × 10−12 (lower limit) for the B/C mass ratio.

Raman Spectroscopy of Boron-Doped Single-Layer Graphene

The introduction of foreign atoms, such as nitrogen, into the hexagonal network of an sp(2)-hybridized carbon atom monolayer has been demonstrated and constitutes an effective tool for tailoring the intrinsic properties of graphene. Here, we report that boron atoms can be efficiently substituted for carbon in graphene. Single-layer graphene substitutionally doped with boron was prepared by the mechanical exfoliation of boron-doped graphite. X-ray photoelectron spectroscopy demonstrated that the amount of substitutional boron in graphite was ~0.22 atom %. Raman spectroscopy demonstrated that the boron atoms were spaced 4.76 nm apart in single-layer graphene. The 7-fold higher intensity of the D-band when compared to the G-band was explained by the elastically scattered photoexcited electrons by boron atoms before emitting a phonon. The frequency of the G-band in single-layer substitutionally boron-doped graphene was unchanged, which could be explained by the p-type boron doping (stiffening) counteracting the tensile strain effect of the larger carbon-boron bond length (softening). Boron-doped graphene appears to be a useful tool for engineering the physical and chemical properties of graphene.

First-Principles Simulations of Boron Diffusion in Graphite

Boron strongly modifies electronic and diffusion properties of graphite. We report the first ab initio study of boron interaction with the point defects in graphite, which includes structures, thermodynamics, and diffusion. A number of possible diffusion mechanisms of boron in graphite are suggested. We conclude that boron diffuses in graphite by a kick-out mechanism. This mechanism explains the common activation energy, but large magnitude difference, for the rate of boron diffusion parallel and perpendicular to the basal plane.

Water formation in graphite and boron-doped graphite under simultaneous O + and H + irradiation

When graphite is exposed to simultaneous irradiation by H + and O +, in addition to the H +-induced hydrocarbon and O +-induced CO and CO 2 formation, water is also formed. The present investigation explores the effect of the presence of boron in graphite on water formation. The results show that B-doped graphite specimens (∼15 at.% B) exposed to simultaneous O + and H + irradiation produce less water when compared to pure graphite under similar irradiation. The concept of the formation of ‘water-precursors’ at the end of the O + range is proposed to explain the observed effect.

Evidence for the solubility of boron in graphite by electron energy loss spectroscopy

We present the results of transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS) studies on two carbon–boron alloys both prepared by chemical vapour deposition at ca. 1000°C and differing in their [Boron]/[Carbon] atomic ratio as well as in their morphology. In both samples, impurity concentrations, principally oxygen and nitrogen, were found to be low relative to boron dopant levels. For low boron contents, typically around 5–10 at.%, the sample consisted of onion-like spherical particles approximately 10 nm in diameter which exhibited a non-homogeneous distribution of boron, concentrated at a level of 5–6 at.% in the centre. For this sample, studies of the B–K- and C–K-ELNES (electron energy loss near-edge structure) together with associated modelling of the unoccupied density of electronic states, indicate a substitution of boron atoms on threefold coordinated sp2-sites within the graphite network. For higher boron doping levels, typically 25 at.%, the sample consisted of homogeneous thin films. In this case, the change in shape of the B–K-ELNES indicates that boron has higher coordinations than planar trigonal together with possibly some residual sp2 sites. This study unambiguously demonstrates the presence of boron substitution solely within an sp2-bonded graphite network in the case of low boron contents and, when combined with other studies, gives an indication of the solubility limit for boron in graphite for the chemical vapour deposition (CVD) process.

Determination of boron in graphite by a wet oxidation decomposition/curcumin photometric method.

Determination of boron in graphite by a wet oxidation decomposition/curcumin photometric method.

Ordering in BxC1-x compounds with the graphite structure.

We present a theoretical study of the structural stability of ordered configurations of ${\mathrm{B}}_{\mathit{x}}$${\mathrm{C}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ solid solutions with the graphite structure. The calculations were carried out self-consistently using norm-conserving pseudopotentials in the local-density approximation. The cohesive energies of a number of ordered structures at different compositions x have been subjected to a cluster expansion, which enables us to predict the cohesive energy of the random alloy at the corresponding compositions and to gain insight on the tendency of the system towards ordering. We find that, at T=0 K, some ordered configurations have a cohesive energy higher than the corresponding random distribution at the same compositions. The inspection of the cluster interactions leads moreover to the conclusion that segregation of boron in graphite is highly discouraged and long-range order is likely to occur.

Boron in graphite: Content, speciation, and significance

The mean boron content of syngenetic graphite in metasedimentary rocks is significantly higher than that of epigenetic vein graphite or igneous graphite. The boron commonly found in chemical analyses of natural graphites does not occur in solid solution with the carbon but rather is contained in a mechanically included borosilicate phase.

Potentiometric determination of boron in graphite microspheres for nuclear engineering

The well-known acidimetric determination of boron via the boric acid-mannitol complex is applied to the analysis of boron-loaded graphite microspheres used in nuclear engineering. After the sample is accurately ground, it is fused with an oxidizing alkaline flux. The melt is dissolved with warm water, the solution is acidified to completely remove carbon dioxide and the boric acid is titrated potentiometrically with carbonate-free sodium hydroxide after its complexing with mannitol. The determination of at least 0.2% boron in graphite is carried out with an average error of less than 1%.

Evaluation of energy band parameters of carbons

The systematic dependence of the Hall effect of carbons on the electronic band parameters has analytically been studied on the basis of Yazawa's band model which takes into account in a simple way the interlayer perturbation. Many experimental results on the magnetic-field dependence of the Hall effect of carbons can be satisfactorily explained by adjusting the band parameters. The change in the Hall voltage with the band parameters is so drastic as to provide a powerful tool for evaluating these parameters of carbons. The evaluation procedures are described in detail and some examples of the application to experimental results presented. It is concluded that as-deposited pyrolytic graphite has a high concentration of acceptors with small activation energy (~ l0 meV), which may probably originate from the structural defects. On the other hand, the activation energy of boron in graphite is found to exceed 100 meV.

An emission-spectrographic method for the determination of boron in nuclear-grade graphite

A rapid, highly sensitive method is described for the spectrographic determination of boron in nuclear-grade graphite. Boron, present in the sample in the form of boron carbide (B4C), is volatilised as the trifluoride by the addition of 1 per cent. of Kel-F powder (polychlorotrifluoroethylene) to the samples. The samples, containing 500 p.p.m. of silicon as the internal standard, are excited by a 10-A d.c. arc in the presence of an argon-controlled atmosphere. A linear relationship between the intensity ratio of the lines boron 249·773 nm and silicon 245·214 nm and the boron concentration is established in the boron concentration range 0·1 to 5 p.p.m. The relative standard deviation, calculated from twelve determinations on each sample, ranges from ±8 per cent. (at 5 p.p.m. of boron) to ±11 per cent. (at 0·1 p.p.m. of boron).

Solid Solution of Boron in Graphite

The solubility of boron in graphite was determined in the temperature interval of 1800° to 2500°C. The maximum solubility was 2.35 at. % at 2350°C; the solution was shown to be substitutional.

Spectrographic determination of boron in nuclear graphite

A spectrographic method is described for the determination of boron (0.2–1.0 p.p.m.) in nuclear graphite and for the estimation of 0.1–0.2 p.p.m. of boron. Neither boron-free graphite electrodes nor additional foreign substances as internal standard are required. Both the electrodes consist of sample powder, properly bakelite-processed. The standard deviation is 10%.

原子炉用黒鉛中の微量ホウ素の分光分析

Two procedures are described for the sensitive spectrographic determination of 0.023 ppm of boron in graphite for nuclear reactor. In the first method, preliminary concentration is carried out by the removal of the graphite by ashing in the presence of La2O3. Then the contents of boron in La2O3 are determined by the carrier-distillation method. In the second method, the sample in the form of powder is compressed into pellets with the aid of a phenol-formaldehyde resin as binding medium, and these are arced at 7 A (d.c.). By means of display microphotometry, the peak height of B at 2497.73 Å is compared with that of the NO(γ) band component at 2497.14 Å.