Boron Loading Research Articles

Enlargement of a Modular System-Synthesis and Characterization of an s-Triazine-Based Carboxylic Acid Ester Bearing a Galactopyranosyl Moiety and an Enormous Boron Load.

The amount of boron accumulated in tumor tissue plays an important role regarding the success of the boron neutron capture therapy (BNCT). In this article, we report a modular system, combining readily available starting materials, like glycine, 1,3,5-triazine and the well-known 9-mercapto-1,7-dicarba-closo-dodecaborane(12), as well as α-d-galactopyranose for increased hydrophilicity, with a novel boron-rich tris-meta-carboranyl thiol.

On the physical, chemical, and neutron shielding properties of polyethylene/boron carbide composites

Monte Carlo methods are used for solving difficult stochastic problems in radiation shielding applications. The aim of this paper is to show the possibility of using the Monte Carlo code (MCBEND®) for evaluation and optimization of polyethylene with high boron loadings (for up to 40%) to reach better neutron shielding against fast neutrons (Am-Be neutron source). Boron is incorporated in polyethylene as boron carbide (B4C). MCBEND® (Monte Carlo code developed by ANSWERS) is used to simulate neutron transport through the developed borated polyethylene composites. In order to verify the computer simulations, neutron detection and data acquisition systems have been assembled, modified, and thoroughly tested for shielding efficiency. It is shown that borated composite with 10% of boron content showed the highest experimental mass removal cross section. Moreover, composite formulation with 10% of boron shows optimum density, morphology, mechanical attributes, and thermal stability than that of the neat polyethylene matrix. A comparison of experimental and simulation mass removal cross sections shows that the geometry and physics models proposed in this work are in close agreement, with maximum relative difference of not more than 15%.

Hydrogen production from methanol steam reforming over B-modified CuZnAlO catalysts

Abstract In this work, CuZnAlOx (CZA) catalysts prepared by coprecipitation method and a series of yB/CZA catalysts with various boron loadings (y = 0.28%, 0.38%, 0.73%, 0.89% and 4.10%) prepared by impregnation method were used in the methanol steam reforming for hydrogen production. In addition, the B-modified CZA catalysts were deeply characterized by different techniques such as ICP, BET, SEM, N2O chemisorption, TEM, XRD, H2-TPR and XPS to explore the structure-activity relationship. The characterization results revealed that the introduction primarily affected the Cu dispersion, reductibility and the interaction between the boron and copper species. The 0.38B/CZA catalyst revealed the optimum catalytic performance among the researched catalysts, which were due to the presence of highly dispersed Cu particles and the strong interaction between the boron and copper species. The 93% methanol conversion, the CO selectivity as low as 0.3%, and the long-time stability with 102 h time on stream were obtained over it when the reaction conditions were 250°C, n(H2O): n(CH3OH)=3 and GHSV= 9000 mL/(g·h).

Surface modification of B–TiO2 by deposition of Au nanoparticles to increase its photocatalytic activity under simulated sunlight irradiation

Photocatalytic activity of TiO2 under visible light irradiation can be improved by doping with nonmetal atoms. However, inter-band energy states formed upon substitutional or interstitial doping can act as recombination centers, hindering the separation of the charge carriers. In this work, sol–gel synthesized TiO2 was doped with different loadings of boron, namely 0.25, 0.5, 1, 2, and 4 wt. %, and superficially modified by the deposition of Au nanoparticles (0.5, 1.0, and 1.5 wt. %). Particle size of doped TiO2 decreased with the increase of boron loading, while surface area increased accordingly. B2O3 was segregated from TiO2 when boron loading surpassed 1 wt. %. Light absorption of the doped materials was slightly blue shifted as the boron loading increased, more likely because of the quantization effect. Tiny and well dispersed Au nanoparticles were efficiently deposited on the B-TiO2 materials. Au nanoparticle size (3–5 nm) showed no modification as Au loading increased, although deposition rate slightly decreased with the boron loading. The complete mineralization of sulfamethoxazole under UV-A/visible light irradiation was obtained using the (0.5 wt. %) Au/(0.25 wt. %) B-TiO2 material. Electrochemical characterization showed how inter band energetic states increased the separation of the photo-produced charge carriers, while Au nanoparticles hampered the recombination rate via the electron trap effect. Photocatalytic materials displayed high stability. Photoactivity dropped when tap water was tested, because of the dissolved components in the liquid matrix. Some intermediates were identified via LC-MS/MS analysis, which displayed lower antibiotic activity than the parent compound.

Cobalt-boron loaded thermal activated Turkish sepiolite composites (Co-B@tSe) as a catalyst for hydrogen delivery

Cobalt-boron loaded thermal activated sepiolite composites ([email protected]) are prepared with an impregnation-chemical reduction method and calcination step for use as a catalyst for sodium borohydride (NaBH4) hydrolysis, solvolysis, and methanolysis. The catalytic activity of [email protected] can be improved by using a thermal-treated raw sepiolite as a catalyst support (Eskişehir, Turkey). The catalysts are analyzed using XRD, XRF, FT-IR, BET, DTA/TG, SEM/EDS and, TEM measurements. The catalytic performance for hydrogen generation is evaluated at room temperature. Research shows that cobalt-impregnated, heat treated, raw sepiolite at 500 °C (Sample B-2) exhibits a high boron loading ability. These conditions, in conjunction with an appropriate calcination treatment, can improve catalytic activity. When the [email protected], in the form of Co3BO5 sized 6 ± 1.8 nm, is dispersed on sepiolite channels, the catalyzed hydrogen generation rate (HGR) shows a trend of more methanolysis than hydrolysis at room temperature.

Microstructural transitions and dielectric properties of boron-doped amorphous alumina thin film

Dielectric Al2−x B x OY thin films were deposited onto Pt (100)/Ti/SiO2/Si substrates via sol–gel and spin-coating technology. The microstructural transition occurred at ~500 °C due to boron loading was confirmed by DSC and XRD. FTIR, 27Al MAS NMR and XPS measurements were employed to investigate the microstructural transition caused by different boron concentrations. The results revealed that Al–O–B bonds and [AlO4] tetrahedrons were produced resulting in the reinforcement of structure with relatively low boron concentrations. With the increase of boron concentration, [BO3] chains and new surfaces crossing over the internal structure gradually produced and disrupted the structural stability. Meanwhile, hydroxyl groups were accumulated in the internal structure owing to the hydrophilic property of boron. According to the reinforced structure with low boron concentrations, the current density decreased and the breakdown strength was enhanced. Typically, the current density was decreased two orders of magnitude at 100 MV m−1 and the breakdown strength of the 0.5 mol% B-doped alumina thin film was increased by 59% (from 293 to 465 MV m−1) in comparison with that of the undoped alumina thin film, whereas the dielectric properties gradually become poor due to the weak structure with the increase of boron concentration. Moreover, the dielectric constant increased owing to hydroxyl groups when the boron doping increased. This work may provide a general strategy for enhancing dielectric properties of the alumina thin film.

Structures of Boron Loaded Turbostratic Graphene with Enhanced Performance in Solid Acid Fuel Cell

Solid acid fuel cells (SAFC) working at intermediate temperature (250°C) have many advantages compared to the lower temperature proton exchange membrane fuel cell (PEMFC), such as increased catalyst activity and are more resistant to CO poisoning.1, 2 The state-of-the-art cathode is comprised of porous protonic conductor coated by Pt.3, 4 There are two major roles of Pt in the cathode: (1) the oxygen reduction reaction (ORR) catalyst and (2) the electron conductor. To maintain a highly electron conductive network, a high fraction of Pt has to be loaded in ‘conventional’ SAFC electrodes. However, to generate wider application, the cost of the cathode must be reduced significantly. The function of Pt as electron conductor can be replaced by the catalyst support to achieve this reduction in loading. The catalyst support must have high electron conductivity, corrosion-resistance and high surface area. The carbon nanostructures are the common catalyst supports used in the fuel cells. In our previous studies, we demonstrated that multi-wall carbon nanotubes are much more stable during fuel cell testing compared to the single wall carbon structures.5 Indeed, pure single layer or few-layer carbon supports are well known to be particularly vulnerable to corrosion in the present of water. However, previous research showed that substitutional boron can lower the electron density of the reactive carbon, leading to a reduction in the rate of O2 chemisorption.6 Meanwhile, very small amounts of boron (~1%) have been demonstrated to enhance the conductivity of the single carbon structure.7In our recent studies, we synthesize the pure single wall carbon, carbon structures in hydrogen gas and with boron loading. Surprisingly, the boron loading induces the growth of few-layer graphenes (FLGs), which exhibit much better corrosion resistance than the single wall carbon and carbon synthesized in hydrogen gas which consists of multi-wall and single-wall carbon structure. In this research, we focus on the structural investigation of those FLGs. Characterization of the FLGs are performed by high resolution transmission electron microscopy (HRTEM) imaging, monochromated electron energy-loss spectroscopy (EELS), nano-beam electron diffraction (NBED), aberration corrected scanning transmission electron microscopy (STEM) imaging, X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), Raman spectroscopy and X-ray diffraction (XRD). Representative STEM images in a low and high magnification are shown in Figure 1 (a)-(b). A significantly structure deviation compared to pure graphene/graphite is evident due to 1-3% boron loading. Those results indicate the few-layer graphene does not stack in a normal graphitic way in the c direction. The EELS, XPS and NMR show complicated electronic states of the boron in the carbon, implying boron does not have to be in the substitutional site. For example, Figure 1(c) show a representative EELS spectrum taken from a FLG. The featureless boron K-edge looks like to be taken from amorphous boron instead of substitutional boron. This result is also supported by the NBED and XRD, showing a non-flat features of the FLGs. Finally, we used the density functional theory (DFT) to explain the excellent oxygen resistance of FLG with this unique structure. Acknowledgments This work is supported by ARPA-E via cooperative agreement DE-AR0000499. The synthesis science is supported by BES-MSED. We thank JIAM and CNMS for microscopy use. Reference 1. K. Ishiyama, F. Kosaka, I. Shimada, Y. Oshima and J. Otomo, Journal of Power Sources, 2013, 225, 141-149. 2. A. B. Papandrew, R. W. Atkinson Iii, R. R. Unocic and T. A. Zawodzinski, Journal of Materials Chemistry A, 2015, 3, 3984-3987. 3. A. B. Papandrew, C. R. I. Chisholm, R. A. Elgammal, M. M. Özer and S. K. Zecevic, Chemistry of Materials, 2011, 23, 1659-1667. 4. A. B. Papandrew, C. R. I. Chisholm, S. K. Zecevic, G. M. Veith and T. A. Zawodzinski, Journal of The Electrochemical Society, 2013, 160, F175-F182. 5. A. B. Papandrew, R. A. Elgammal, M. Tian, W. D. Tennyson, C. M. Rouleau, A. A. Puretzky, G. M. Veith, D. B. Geohegan and T. A. Zawodzinski, Journal of Power Sources, 2017, 337, 145-151. 6. B. Yuan, W. Xing, Y. Hu, X. Mu, J. Wang, Q. Tai, G. Li, L. Liu, K. M. Liew and Y. Hu, Carbon, 2016, 101, 152-158. 7. M. Harada, T. Inagaki, S. Bandow and S. Iijima, Carbon, 2008, 46, 766-772. Figure 1

Boron-doped activated carbon as efficient and selective adsorbent for ultra-deep desulfurization of 4,6-dimethyldibenzothiophene

Activated carbon was modified with varying concentrations (0.5–10wt.%) of boric acid to make adsorbents with physico-chemical properties that are essential for the removal of bulky and recalcitrant 4,6-dimethyldibenzothiophene (4,6-DMDBT) from the model fuel via adsorptive desulfurization at room temperature. The features of boron-doped activated carbon adsorbents were examined in comparison with unmodified activated carbon using N2 physisorption analysis, inductively coupled plasma-mass spectrometry, Raman spectroscopy, Fourier transform infra-red, temperature programmed desorption and scanning electron microscopy. Boron-doped adsorbents exhibited better adsorption capacity at low boron loadings of 0.5–2.5wt.%, largely due to their preserved surface area compared to those with higher boron loadings (5–10wt.%), and enhanced surface acidity, compared to the unmodified AC. Specifically, the adsorbent containing 1wt.% of boron loading (1BDAC) gave the best adsorption performance of 85% (8.50mg/g) in 100ppmw-S containing 4,6-DMDBT within 5min contact time. Furthermore, for the IBDAC sample, the effect of initial concentration, sorbent dosage, and selectivity were studied in the presence of naphthalene. Remarkable regeneration performance was exhibited by the 1BDAC adsorbent with only 7% loss in adsorption capacity after supplementary five-cycle regenerations. The kinetic studies showed that the adsorption followed a pseudo-second order model while isotherm data were well fitted by Freundlich isotherm. With an optimum boron loading of 1wt.%, the boron-doped AC showed selectivity towards complex refractory organosulfur compound (4,6-DMDBT), which highlights its efficacy for significantly removing the compounds from the model fuel.

Hydroxyl-enhanced magnetic chitosan microbeads for boron adsorption: Parameter optimization and selectivity in saline water

Hydroxyl-enhanced materials are considered promising for boron adsorption. But, the use of these materials is hindered by issues of selectivity and separation notably in the presence of co-existing ions. Therefore, magnetic chitosan-based microbeads (MC) were synthesized and functionalized with a glycidol to produce boron-selective adsorbent (MCG). The resulting multi-hydroxyl microbeads were found to be a better substitute to the existing boron adsorbents. The adsorbents were characterized by scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). The BET surface area and vibrating sample magnetometry analyzes confirmed that the functionalized beads had a saturation magnetization, surface area, pore size, and diameter of 46.53Am2/kg, 598m2/g, 2.9nm and ∼150–400μm respectively. Under optimized condition, the MCG showed high adsorption affinity and remarkable selectivity towards boron in the presence of co-existing metal ions (Cu2+, Fe3+, and Ni2+) and salts of Mg2+, Ca2+, Na+ and K+ ions. MCG has 128.5mg/g of boron loading capacity within the first 100min, which is relatively higher than reported values. The spent beads were separated easily from the suspensions by an external magnet and reuse repeatedly.

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.

Tumor targeting, trifunctional dendritic wedge.

We report in vitro and in vivo evaluation of a newly designed trifunctional theranostic agent for targeting solid tumors. This agent combines a dendritic wedge with high boron content for boron neutron capture therapy or boron MRI, a monomethine cyanine dye for visible-light fluorescent imaging, and an integrin ligand for efficient tumor targeting. We report photophysical properties of the new agent, its cellular uptake and in vitro targeting properties. Using live animal imaging and intravital microscopy (IVM) techniques, we observed a rapid accumulation of the agent and its retention for a prolonged period of time (up to 7 days) in fully established animal models of human melanoma and murine mammary adenocarcinoma. This macromolecular theranostic agent can be used for targeted delivery of high boron load into solid tumors for future applications in boron neutron capture therapy.

Optimizing the distribution of aromatic products from catalytic fast pyrolysis of cellulose by ZSM-5 modification with boron and co-feeding of low-density polyethylene

This study investigated the effects of ZSM-5 impregnation with boron on its catalytic properties in catalytic fast pyrolysis (CFP) of cellulose, low-density polyethylene (LDPE), and their mixtures. A series of boron-modified ZSM-5 zeolites were prepared by impregnating a conventional ZSM-5 with different boron loadings (0.5–3wt.%). Due to boron deposition, the acidity and pore size of ZSM-5 decreased with increasing the boron loading. When impregnated with 1wt.% boron, ZSM-5 preserved sufficient catalytic activity for the production of valuable monoaromatic hydrocarbons and decreased the formation of undesired polyaromatic hydrocarbons in CFP of cellulose. In addition, the pore narrowing of ZSM-5 by boron deposition greatly enhanced p-xylene production over m- and o-xylenes in CFP. This result indicates that slightly decreasing the pore size of ZSM-5 can improve aromatic distribution toward more valuable products in CFP. Co-feeding of cellulose with LDPE in CFP further improved the product distribution. As a result of boron modification and co-feeding, the monoaromatic yield increased from 20.0 C% for CFP of cellulose alone with the parent ZSM-5 to 24.6 C% for co-feed CFP of cellulose and LDPE mixture (mixing ratio of 4:1) with the boron-modified ZSM-5, while the polyaromatic yield decreased from 11.3 C% to 6.0 C%. The yield for p-xylene also increased from 2.23 C% to 5.57 C% while the selectivity increased from 47.9% to 75.2%. The results indicate that ZSM-5 modification with boron and co-feeding of plastics have a beneficial effect for improving aromatic product distribution in CFP of biomass.

Carbon nanofibers modified with heteroatoms as metal-free catalysts for the oxidative dehydrogenation of propane.

Carbon nanofibres (CNFs) were modified with B and P by an ex situ approach. In addition, CNFs doped with N were prepared in situ using ethylenediamine as the N and C source. After calcination, the doped CNFs were used as catalysts for the oxidative dehydrogenation of propane. For B-CNFs, the effects of boron loading and calcination temperature on B speciation and catalytic conversion were studied. For the same reaction temperatures and conversions, B- and P-doped CNFs exhibited higher selectivities to propene than pristine CNFs. The N-CNFs were the most active but the least selective of the catalysts tested here. Our results also show that the type of P precursor affects the selectivity to propene and that CNFs modified using triphenylphosphine as the precursor provided the highest selectivity at isoconversion.

Boron-loaded plastic scintillator with neutron-γ pulse shape discrimination capability

Development of the plastic scintillator with neutron sensitivity from thermal to multi-MeV and pulse shape discrimination (PSD) has been demonstrated. Incorporation of 10B-containing compounds into the plastic scintillator with PSD capability leads to detector improvement in regard to neutron detection efficiency while preserving the discrimination between neutrons and γ-rays. Effects of boron loading on scintillation and pulse shape discrimination properties are discussed. A PSD figure-of-merit value of 1.4±0.03 has been achieved for events in a thermal neutron energy domain, 50–100keVee, for PSD plastic loaded with 5wt.% of m-carborane.

Effect of modification of the alumina acidity on the properties of supported Mo and CoMo sulfide catalysts

Aluminas with different boron loadings were prepared by impregnation with H3BO3 solutions and then used to prepare pure Mo and CoMo catalysts. According to infrared (IR) spectroscopy of 2,6-dimethylpyridine, the acid properties of the alumina have been finely tuned by boron addition. The effect of alumina acidity change on the properties of sulfided Mo and CoMo has been characterized using transmission electron microscope, X-ray photoelectron spectroscopy, and IR spectroscopy of CO-adsorption as well as model compound reactions as thiophene hydrodesulfurization (HDS), 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS and 2,6-dimethylaniline (DMA) hydrodenitrogenation (HDN). The acidity change of alumina has a direct influence on the electronic properties of MoS2 and CoMoS sites but not substantially modifies the morphology and dispersion of the sulfide phase. The results point out a relationship between the Brønsted acidity of the support and the electronic properties of the MoS2 and CoMoS phase. The change of the electronic properties of the active sites has a marked positive influence on the hydrogenation activity of the active phase. The performances of the Mo and CoMo catalysts in the reactions of HDS of thiophene and 4,6-DMDBT and HDN of DMA have been related to the variations of the structural and electronic properties resulted from boron addition.

Solid tethered imino-bis-propanediol and quaternary amine functional copolymer brushes for rapid extraction of trace boron

A synthesis strategy is described for designing new, more efficient and reusable boron specific resin material which is able to remove trace boron from aqueous solutions within less than a minute. This strategy involves generation of dense N-vinyl formamide (NVF)-diallyldimethylammonium chloride (DADMAC) copolymer brushes (up to 1510% w/w) on PS-DVB (10%) microspheres by surface initiated polymerization (SIP) of the monomer mixture from dithiocarbamate surface groups, using photo-iniferter technique. Hydrolysis of the formamido groups and followed reaction with glycidol yield hairy grafts with boron chelating imino-bis-propanediol (IBP) functions and chain expanding quaternary amino groups. Experiments revealed that, the materials built up of hairy grafts with 0%, 10% and 20% of DADMAC contents show boron loading capacities 2.9–4.0mmolg−1, the latter being the highest capacity reported so far. Moreover the increasing DADMAC content provides even faster boron uptakes from non-buffered solutions. New boron chelating resins presented seem to be promising for practical uses, due to their easy regeneration with 10% HCl and unchanged boron sorption capacities after 10 times of recycling.

Removal of trace boron from aqueous solution using iminobis-(propylene glycol) modified chitosan beads

In this paper, a new boron chelating chitosan based polymer with multi-hydroxyl iminobis (propylene glycol) (IBPG) functions was prepared. A cross-linked chitosan (CCTS) with 2.70mmolg−1 amine content was modified with excess amount of glycidol at pH 7 and boron chelating resin with IBPG functions (4.60mmolg−1) was obtained. The boron chelating ability of the resulting resin was investigated under different experimental conditions (pH, foreign ions). This prepared material was evaluated by FT–IR spectra and UV spectra analysis. The IBPG modified CCTS resin was demonstrated to have a boron loading capacity of 2.2±0.05mmolg−1 within 45min. Desorption and resin regeneration studies were carried out to determine the effectiveness of the synthesized resin with HCl and NaOH respectively. The adsorption test indicated that the chitosan based chelating resin with IBPG functions exhibited higher selectivity of boron (2.05mmolg−1) in the presence of foreign ions especially Fe(III).

COMBUSTION OF PTFE-BORON COMPOSITIONS FOR PROPULSION APPLICATIONS

An experimental study was conducted to evaluate the potential of solid fuels based on PTFE and boron mixtures for hybrid rocket motor applications. Specifically, a processing technique based on sintering was studied to determine the viability of these fuels. Sintering of the fuels provided reasonable mechanical properties to allow for exploration of these fuels without the addition of performance-robbing ingredients. Linear regression rates of sintered and unsintered fuels were collected in a diffusion flame setting with gaseous oxygen as the oxidizing component demonstrating that the sintering process had no effect. This family of fuels has shown that they will not combust at atmospheric pressure unless pure oxygen is present. However, sintered fuels with boron loadings greater than or equal to 25% by weight do self-propagate at atmospheric pressure once ignited in the presence of oxygen, whereas unsintered fuels do not self-propagate unless they have boron loadings greater than or equal to 30% by weight. At pressures up to 12 MPa, fuels containing 10% by weight boron would not self-propagate in a nitrogen atmosphere, whereas fuels containing 20% boron would self-propagate at pressures greater than about 5.7 MPa. Preliminary lab-scale rocket motor firings demonstrate the viability of a hybrid rocket based on PTFE and boron mixtures. In addition, they demonstrate that the regression rates of these fuels show dependencies on pressure and possibly oxidizer flow rate as well. Thermochemical analysis suggests that these fuels offer a significant performance benefit in terms of density impulse, while also presenting a significant technological challenge due to excessively high flame temperatures for some mixtures.

Evaluation of boron loading to soil profile for basin-scale by using TETrans in irrigated areas

The research study was carried out in an area of 1500 ha located in Ankara-Kesikkopru Plain left river bank irrigation area. TETrans computer model which is a one dimensional solution transfer model was used in order to determine boron content of the soil profile and groundwater. Boron content which has accumulated in the soil profile between in 2000 to 2002 was estimated in order to determine the potential risk that may occur in the next 10 years. Measured soil boron levels and boron levels estimated from the model were statistically compared. It was seen that the relationship between the estimated levels and measured levels is significant. Results obtained were used as a database in Geographical Information System and alteration maps were prepared for soils that may be formed in time. According to research study results, it was seen that, as long as the present conditions throughout the plain continue, there would be a boron problem to a significant level in the future. Pollution maps that are obtained will help executive and decision-making units in displaying more clearly the problem which may occur in the future and preparing action plans. Key words: Trace element transport computer, geographical information system, soil and water resources, socio-economical development.

Characterisation of boron-doped coal-derived carbon foams and their oxidation behaviour

Carbon foams with improved resistance to oxidation were obtained from a bituminous coal and different boron precursors (boron oxide, boron carbide and pyridine–borane complex), by controlled carbonisation under the pressure derived from the release of the volatile matter, which also acts as the foaming agent. The foams were subsequently carbonised at 1100°C and the presence of boron gives rise to an increasing disorder in the carbon structure. After heat treatment at 2400°C, it is confirmed that boron occupies substitutional positions in the graphitic layers, and at high boron loadings (>2.5%), boron clusters, boron carbide and BC2O structures are also observed. The presence of boron has two opposite effects on the oxidation behaviour of the foams. At low B loadings, the foams obtained with boron carbide display lower oxidation temperatures. In the other foams, increases in the temperature of oxidation and the amount of residue remaining after the oxidation tests are observed.