Boron Modification Research Articles

Effect of ammonia and boron modifications on the surface and hydrogen sorption characteristics of activated carbons from coal

In this study, a synthesis procedure was adopted to prepare boron following nitrogen modified activated carbons from coals collected from Kilimli Zonguldak in Turkey. The effects of ammonia and boron modification on the surface and hydrogen sorption characteristics of these coal based activated carbons were investigated. The modification process was carried out by treatment of potassium hydroxide modified activated carbons with ammonia solution, followed by borax decahydrate solutions at various concentrations (0.025–0.1 M). The porous structure of the samples was characterized by using N2 adsorption-desorption data measured at 77.4 K for the relative pressures in the range P/P0 = 0–1. The resulting samples were in irregular structures having high microporosity. The surface area of the sample characterized by the Brunauer-Emmett-Teller model, having a value of 2195 m2/g by ammonia treatment, increased to 3037 and 2661 m2/g after treatments with the 0.075 M and 0.1 M borax decahydrate solutions, respectively. Hydrogen uptake capacities in the range 2.77–4.14 % wt were obtained by borax decahydrate treatments of the ammonia modified samples, whereas the ammonia treated sample had a capacity of 2.35 % wt before boron modifications. 0.075 M borax decahydrate-ammonia treated sample had the highest surface area and total pore volumes among all the other samples obtained. Increasing borax decahydrate concentration in the range 0.025–0.075 M resulted in the increase of hydrogen uptake capacities due to the improvement in surface characteristics including microporous structure and the affinities of nitrogen and boron to hydrogen. The process adopted for boron modification followed by ammonia treatment of the potassium hydroxide activated coal-based carbons yielded improved surface and hydrogen sorption characteristics as compared to the unmodified carbons.

Microstructure characterization and grain morphology of alloy 625 with 0.4 wt% boron modification manufactured by laser wire deposition

Laser wire deposits using Alloy 625 modified with 0.4 wt% B were manufactured on stainless steel 304 substrates. A layer boundary with a thickness of around 250 μm was formed between the layer cores during deposition. Results show that the solidification features in the layer boundary were coarser than the layer core due to the recalescence mechanism. Continuous eutectics were observed segregating the inter-dendritic regions in both the layer boundary and the layer core. The eutectics consisted of mainly Laves phase with a small amount of NbC precipitates. Solidification front velocities (SFV) were calculated from the Kurz-Giovanola-Trivedi (KGT) model. Results showed that they developed in the layer boundary and in the layer core at 0.06 m/s and 0.1 m/s respectively. Electron backscattered diffraction (EBSD) mapping revealed that small equiaxed grains nucleated in the layer boundary, while large columnar grains were prevalent in the layer core. Pole figures showed a strong oriented texture was present along the (100) plane. The columnar to equiaxed transition (CET) model developed by Hunts was considered and the results were in good agreement with the observed grain morphologies.

Catalytic dehydration of ethanol to ethylene and diethyl ether over alumina catalysts containing different phases with boron modification

The catalytic ethanol dehydration of ethanol over the solvothermal-derived alumina catalysts was investigated in this study. First, alumina catalysts were synthesized by the solvothermal methods to obtain three different phase composition of alumina catalysts including γ-phase (G–Al), χ-phase (C–Al) and equally mixed χ–γ phases (M–Al). Then, all catalysts were modified with boron (G–Al–B, C–Al–B and M–Al–B). It was found that the boron modification increased the amounts of total acid sites and the ratio of weak to strong acid sites (WSR). The catalytic activity and product selectivity of six catalysts via catalytic ethanol dehydration at 200, 300, and 400 °C were measured. For all catalysts, it revealed that ethanol conversion increased with increased temperatures from 200 to 400 °C. At 200–300 °C, the unmodified catalysts tended to exhibit the higher catalytic activity than the boron-modified catalysts. However, at high temperature (400 °C), the boron modification tended to increase the catalytic activity, especially for the M–Al–B catalyst (complete ethanol conversion at 400 °C). Considering ethylene production, the M–Al–B exhibited the highest ethylene yield among other catalysts with 92% at 400 °C. For diethyl ether, it was observed that the M–Al catalyst gave the highest diethyl ether yield of 57% at 300 °C. This is because the boron modification increased the amounts of total acid sites, which can promote the production of ethylene, while this is not preferable for diethyl ether production, which is favored by weak acid sites.

Simple and low‐cost synthetic route for SiBCN ceramic powder from a boron‐modified cyclotrisilazane

AbstractThis study reports a simple and low‐cost synthetic route for preparing SiBCN ceramic powder via pyrolysis of boron‐modified cyclotrisilazane (BCTS). BCTS resins were synthesized by reacting boric acid with 1, 3, 5‐trimethyl‐1′, 3′, 5′‐trivinylcyclotrisilazane (CTS) in the molar ratio of 1:1, 1:3, and 1:5. The boron modification in CTS resin resulted in optimum properties for preceramic polymers such as solubility in common solvents, processable viscosity (<20 cps) and high ceramic yield (>80 wt. %). The polymer to ceramic conversion was carried out at 1450 and 1650°C under a nitrogen atmosphere. The study demonstrated that the changes in CTS concentration and pyrolysis temperature significantly affected the evolution of ceramic phases, morphology, and elemental composition which were thoroughly investigated through XRD, SEM, and HRTEM techniques. The results revealed the formation of β‐SiC, β‐Si3N4, and oxide ceramic phases with BCTS in the molar ratio of 1:1 and 1:3; whereas, β‐SiC, β‐Si3N4, and turbostratic BN(C) ceramic phases were obtained with BCTS in the molar ratio of 1:5.

Influence of boron modification and cooling conditions during solidification on structural and phase state of heat- and wear-resistant white cast iron

Influence of boron modification and cooling conditions during solidification on structural and phase state of heat- and wear-resistant white cast iron

Effect of heat treatments on microstructure evolution and grain morphology of alloy 625 with 0.4 wt% boron modification fabricated by laser wire deposition

Alloy 625 modified with 0.4 wt% B was deposited on stainless steel 304 substrate by laser wire deposition. The microstructure was characterized and grain morphology was analyzed in the as-deposited and two post heat-treated conditions. In the as-deposited condition, continuous eutectics were observed to segregate in the inter-dendritic regions. The eutectics mainly consist of Laves phase and small amount of NbC precipitates. It was also found that the solidification features in the layer boundary were coarser than the layer core due to the recalescence mechanism. Small equiaxed grains nucleated in the layer boundary and eliminated the epitaxial growth which is normally formed during the additive manufacturing process. In the two-step aging condition, the eutectics were almost fully dissolved in the layer boundary. This has been associated with the layer boundary's larger elemental diffusion path when compared to the layer core. Partial recrystallization occurred in the layer core and led to nucleation of equiaxed grains. The grain size in both the layer boundary and the layer core coarsened during heat treatment. In the annealed and aged condition, the eutectics observed in the as-deposited condition were fully re-melted, resulting in the formation of large sized M5B3 borides during re-solidification. The fraction of borides in the layer boundary was lower, with smaller sized precipitates than those in the layer core. Similarly, to the two-step aged condition, partial recrystallization and grain growth developed during annealing and aging treatment.

Enhancing the vanadium dispersion on V-MCM-41 by boron modification for efficient iso-butane dehydrogenation

A series of boron modified V-MCM-41 catalysts were in situ synthesized. The modification effect of boron to the vanadium species and catalytic performances were systematically studied. The catalysts could still maintain mesoporous structure and relatively large specific surface area after boron modification. Boron species were mainly in the form of triangular [BO3]3− units on the surface and the pores of the catalysts. The introduction of boron could effectively enhance the dispersion of vanadium species and increase the amount of surface vanadium sites. The catalysts showed high activity towards iso-butane dehydrogenation. The results of catalytic tests showed that both the iso-butane conversion and iso-butene selectivity improved with the presence of boron species. The best catalytic performance was obtained on the sample with the maximum vanadium sites. The performance of the catalyst still remained stable after several cycles of tests and regenerations, which was promising for industrial application in moving bed or fluidized bed reactor in the future.

Effects of boron and fluorine modified γ-Al2O3 with tailored surface acidity on catalytic ethanol dehydration to ethylene

The effect of boron and fluorine modified γ-Al2O3 was investigated during ethanol dehydration to ethylene. The conventional and modified γ-Al2O3 were prepared by a sol–gel method and characterized by various techniques. The results showed that boron modified γ-Al2O3 possessed decreased amount of Lewis acid sites by increasing the boron content. Fluorine modified γ-Al2O3 created new Bronsted acid sites with increasing the fluorine content, which resulted in the coexistence of Bronsted and Lewis acid sites, at the same time, strong acid sites appeared. Boron modified γ-Al2O3 catalyst (Al-B1) at 340 °C exhibited excellent catalytic stability and good selectivity for ethanol conversion to ethylene. The improvement in the catalytic stability could be attributed to the lower acidity after boron modification. The results indicated that on γ-Al2O3 catalyst, strong acid sites especially Bronsted acid sites were responsible for coking deactivation and unfavorable to ethanol dehydration to ethylene.

Effect of heat treatment on microstructure evolution and mechanical properties of Inconel 625 with 0.4 wt% boron modification fabricated by gas tungsten arc deposition

Microstructure evolution and mechanical properties of IN625 wires modified with 0.4wt% B deposited by gas tungsten arc in shielding argon were studied in both as-deposited and heat treated condition. In the as-deposited condition, hardness heterogeneity was observed along the build. The upper section had higher hardness than the lower section. From SEM and EDS observation, this high hardness was attributed to the continuous eutectics (mainly Laves phase with few NbC) at the inter-dendritic regions. These eutectics in the lower section that were partially re-melted during the multi-pass process had formed non-continuous features contributing to a lower hardness. Moreover, fine isolated M5B3 borides that confirmed by TEM with SAD patterns precipitated out from the γ matrix in lower section as a result of the multiple thermal cycles. The Laves phases were totally re-melted during heat treatment, resulting in the formation of large size M5B3 borides from SEM and TEM analysis during heat treatment solidification. This led to elimination of hardness heterogeneity by homogenizing microstructure along the build after annealing and aging treatment. This microstructure evolution also eradicated the risk of strain-age cracks during heat treatment. A large amount of zigzag grain boundaries were formed attributed to the pinning effect of M5B3 and NbC. The tensile properties of heat treated IN625B deposits were tested at both ambient and elevated temperature. The results indicated that the ultimate tensile strength and yield strength of gas tungsten arc IN625B deposits were superior to the conventional IN625 in the solution annealed condition.

Microstructure evolution of Inconel 625 with 0.4 wt% boron modification during gas tungsten arc deposition

Gas tungsten arc deposits were made on substrate of stainless steel 304 using IN625 wires modified with 0.4 wt% B in shielding argon. The temperature profiles were simulated by the modified Rosenthal 3D equation. The re-melting boundary correlated well with the hardness profile and corresponding microstructure evolution along the as-manufactured sample. The upper section had higher hardness than the lower section. This high hardness was attributed to the existence of continuous eutectics (Laves phase and NbC) in the inter-dendritic regions. These eutectics in the lower section partially re-melted in this multi-pass process to form non-continuous features contributing to a lower hardness. Moreover, fine isolated borides precipitated out from the γ matrix in lower section as a result of the multiple thermal cycles. The eutectic phases were identified to be Laves phase with few NbC. The isolated borides were confirmed as M5B3 type of boride by TEM. Modeling of the segregation behavior of the major alloying elements according to Clyne-Kurz equations was conducted and the results were in good agreement with chemical concentration profiles.

Effect of Boron Modifications of Palladium Catalysts for the Production of Hydrogen from Formic Acid

In this study, we explore the effect of light nonmetal dopants (e.g., boron, carbon, and nitrogen) on the catalytic properties of transition-metal surfaces using the recently discovered boron-doped palladium catalyst for formic acid decomposition as an example. We use periodic density functional theory (DFT) calculations to derive an understanding of how subsurface boron modifies the palladium catalyst to be more active, and we find that the effect of the boron modification of palladium is different depending on the class of an adsorbate. Our DFT calculation results are also coupled to the microkinetic model of formic acid decomposition published previously to show that the catalytic properties of boron-doped palladium can be analyzed within the same conceptual framework used for understanding the catalytic trends of (undoped) transition-metal and alloy catalysts.

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.

ChemInform Abstract: Structure and Bonding of γ‐B28: Is the High Pressure Form of Elemental Boron Ionic?

AbstractThe recently characterized crystal structure of metastable γ‐B28 is analyzed from a crystal chemical point of view and compared with that of α‐B12, the simplest boron modification.

Structure and Bonding of γ-B28: Is the High Pressure Form of Elemental Boron Ionic?

The recently characterized crystal structure of metastable γ-B(28) is analyzed from a crystal chemical point of view, and the electron requirement of its building units and that of their linkage is determined. The structure consists of unique B(2) dumbbells and B(12) icosahedra, which are connected through two-center and three-center, two-electron bonds. The different bonding motifs are ascertained by theoretical calculations of difference charge distributions. Chemical bonding in high pressure γ-B(28) bears great resemblance to α-B(12) which is the simplest boron modification. The previously made description of γ-B(28) as ionic in terms of (B(2))(δ+) and (B(12))(δ-) is not supported.

In-situ nitrogen doping and boron modification of nanocrystalline titania powders by chemical vapour synthesis

During the chemical vapour synthesis (CVS) of nanocrystalline titania doping and/or modification can be directly carried out in-situ by using an additional precursor. In this study, nitrogen doped nanocrystalline titania powders and boron modified nanocrystalline titania powders were synthesised by CVS. The resultant powders were characterised by X-ray diffraction (XRD) and UV-vis spectroscopy. In both cases, a red shift in the band gap of titania was seen. Electron paramagnetic resonance spectroscopy (EPR) showed the presence of nitrogen in the titania lattice. Solid state nuclear magnetic resonance (NMR) spectroscopy showed that boron in titania was present in BO4 coordination with the oxygen atoms.

Impact of Boron Modification on MCM-41-Supported Cobalt Catalysts for Hydrogenation of Carbon Monoxide

Boron modification on MCM-41-supported cobalt (Co) catalysts was found to decrease the catalyst activity during CO hydrogenation. The decreased activities were due to stronger support interaction between Co oxide species and the support with the presence of boron resulting in lower reducibility. However, based on methanation the selectivity to C2–C4 products slightly increased with low loading of boron.

Effect of fluorine and boron modification on the HDS, HDN and HDA activity of hydrotreating catalysts

A series of fluorine- and/or boron-modified catalysts were studied, among which the catalysts simultaneously modified with fluorine and boron were prepared and studied for the first time. The hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatics (HDA) activities of all the catalysts were evaluated with model compounds, 4,6-DMDBT, pyridine and 1-methylnathphlene. The catalysts were also characterized by FT-IR, BET, X-ray photoelectron spectroscopy (XPS), and thermogravity/differential thermal analysis (TG/DTA) for acid type and acidity, pore structure, metal distribution on the surface of catalysts, existing state of hydrogenation metals, and decomposition of fluorine, boric and hydrogenation metal compounds. The experimental results showed that the catalyst simultaneously modified with borane isoproxyl and ammonium fluoride had the best HDN and HDA activities and good HDS activity, though the lowest acidity among the catalysts. The excellent hydrogenation activity of this catalyst may attribute to its highest dispersed active nickel and its large pore volume and surface area. The catalyst modified with NH 4F and H 3BO 3 showed a similar performance to the catalyst modified with H 3BO 3 only. The incorporation of boron led to a greater increase in hydrogenation activity than the addition of fluorine which presents a detrimental effect on the HDN reaction.

Beta Phase Superplasticity in Titanium Alloys by Boron Modification

Addition of boron to titanium alloys produces fine TiB whiskers in situ with excellent thermal stability and good chemical compatibility with the matrix. These whiskers stabilize a fine-grain microstructure by restricting grain growth at high temperatures in the β phase field. The hot deformation behavior in the β phase field (temperature range 1050–1200 °C) of Ti-6Al-4V alloys modified with two different levels of B additions (1.6 and 2.9 wt.%) produced by powder metallurgy was investigated using hot compression tests in the strain rate range of 10−3 to 10−1 s−1 and hot tensile tests at a nominal strain rate of 6×10−4 s−1. The β phase exhibits superplasticity, which occurs due to stabilization of a fine-grain microstructure by the TiB. Matrix grain boundary sliding and β/TiB interface sliding appear to contribute to the β superplasticity. The ability to achieve superplasticity at higher temperatures enable lower flow stresses, improved chemical homogeneity, and high strain rate capability due to enhanced accommodation processes.

Catalyst deactivation of high-silica HZSM-5 in the Beckmann rearrangement reaction of cyclohexanone oxime

The Beckmann rearrangement of cyclohexanone oxime was carried out over high-silica HZSM-5 zeolites and boron-modified HZSM-5 to elucidate the effects of silica alumina ratio and boron modification on the catalyst deactivation rate. The relationship between cyclohexanone oxime conversion and time on stream could be represented by the equation x( t) = x(0)·exp(− b· t) where x( t) and x(0) are conversions at a time on stream t and at the initial stage t = 0, respectively, and b is the deactivation coefficient. The deactivation coefficient increased with increasing concentration of strong acid sites. When the deactivated zeolites were evacuated under a pressure of 1 Torr at 573 K for 5 h, the catalytic activity was recovered up to 50% of the initial activity. The deactivation of the ZSM-5-type zeolite was mainly due to the adsorption of volatile material on the acid sites.

The effect of boron modification of Pt/Al 2O 3 on hydrogen chemisorption

The effect of boron modification of Pt/Al 2O 3 on hydrogen chemisorption has been studied by the temperature-programmed desorption method. The X-ray diffraction technique was also used to investigate the crystal phase of alumina support and Pt metal particle size upon boron modification. The TPD spectra revealed a major peak accompanied by an unresolved high-temperature shoulder. The major peak is assigned to adsorption of hydrogen on a Pt metal site. The upward shift of this peak upon boron modification indicates a stronger Pt-H interaction. The high-temperature shoulder can be attributed to hydrogen spillover from the metal onto the support. The peak area of this high-temperature shoulder is increased upon boron modification, indicating that boron can enhance the spillover of hydrogen.