Carbon Aluminum Research Articles

A Kinetic-Mechanistic Study of The Hydrogen Evolution Reaction in Sulfuric Acid Solutions with Different Electrode Materials

The hydrogen evolution reaction (HER) has been studied extensively due to the potential application of molecular hydrogen H2as a green fuel. Recently this particular reaction attracted the attention of several electrometallurgical researchers because of another promising application, in which the monoatomic hydrogen species H· (intermediate product of HER) is employed as a reducing agent for copper-sulfide minerals. Consequently, knowledge about the kinetics, mechanisms and rate determining step (rds) of HER in sulfuric acid solutions employing aluminum, copper, Inconel® or glassy carbon(GC) cathodes is necessary to determine the under and overpotential domains where H2 and H· can be generated in a selective manner. Analyses of Tafel plots and the charge transfer coefficients, revealed two electrical potential zones for copper, Inconel and GC, where the monoatomic hydrogen can be recombined chemically or electrochemically to H2 as the rds. On the other hand, with aluminum, only the electrochemical recombination to H2 occurs as the rds. A catalytic effect on the hydrogen recombination reaction was also found when ferrous ion is contained in the solution. Finally, it was determined that aluminum is the most efficient electrocatalyst for producing H· and H2, followed by inconel, copper and GC.

Processing and properties of sol gel derived alumina–carbon nano tube composites

High purity alumina–carbon nano tube (CNT) composites were prepared by an aqueous sol–gel processing route. CNTs were dispersed in alumina sol containing appropriate amount of MgO precursor. Aqueous slurry of alumina was seeded into the sol followed by gelation, drying and calcination at 1000°C for 1h. The calcined powder consisting of alumina-coated CNTs and alumina was milled, sieved, dried, pressed and pressureless sintered at 1400–1600°C for 1h in nitrogen atmosphere. Sintered samples were further isostatically hot pressed at 1300°C and the properties were compared with the pressureless sintered samples. Phase formation was followed by XRD study, CNT retention was confirmed by Raman studies and the samples were further characterized for mechanical and microstructural properties.

Single step hydrothermal synthesis of 3D urchin like structures of AACH and aluminum oxide with thin nano-spikes

3D urchins like ammonium aluminum carbonate hydroxide (AACH) nanostructures with nano-spikes of dia. 20–30nm were synthesized by a simple, single step hydrothermal technique by using aluminum nitrate and urea as precursor materials. It was found that morphology of the produced structure strongly depends upon the urea concentration. With increasing the amount of urea, the AACH particles having embedded rods like surface features transformed into 3D urchins. The added urea decomposed during hydrothermal treatment and increased the pH of the solution, which affected the morphology of the produced nanostructures. SEM, XRD, FTIR and TGA were employed to characterize the produced structures. On heating, the volatile ingredients of AACH were removed, leaving behind the alumina urchins.

Meso/macroporous γ-Al2O3 fabricated by thermal decomposition of nanorods ammonium aluminium carbonate hydroxide

Through exploring the reaction parameters during the synthesis of the AACH, rod-like ammonium aluminium carbonate hydroxide (AACH) with high crystallinity has been successfully prepared via a facile hydrothermal method. The synthesis parameters like time, the molar ratio of NH4HCO3/Al and the properties of starting materials were systematically investigated. The structure was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), IR and transmission electron microscopy (TEM). The experimental results display that the obtained γ-Al2O3 materials possess meso/macroporosity and large pore volume, which are mainly attributed to the removal of gas molecules during the decomposition of AACH. Moreover, using the rod-like AACH as precursor, γ-Al2O3 nanorods were obtained via a low-temperature thermal decomposition method.

Effect of sintering temperature on properties of Al2O3 whisker reinforced 3 mol% Y2O3 stabilized tetragonal ZrO2 (TZ-3Y) nanocomposites

In present study, effect of sintering temperature on density and hardness of 3mol% yttria-stabilized tetragonal zirconia (referred to as TZ-3Y) composite reinforced with alumina whiskers (5, 10, 15 and 20wt.%) has been studied. Initially, Ammonium Aluminum Carbonate Hydroxide (AACH) whiskers were added in TZ-3Y composite and transformed into alumina during sintering performed at different temperatures i.e. 1400, 1500 and 1650°C. Results revealed that for all sintering temperatures, with increase in whisker concentration, sintered density decreased and hardness increased conversely. Maximum hardness of 14.47GPa was achieved with 10wt.% whiskers addition when sintered at 1500°C. However, with addition of CTAB (1wt.%) as deflocculating agent the hardness was further improved to 15.11GPa. While sintering at 1650°C a decrease in hardness was observed. It was mainly due to high temperature morphological change of whiskers i.e. transformation of whiskers into alumina rich grains.

Characterization of Spent Prebaked Aluminium Carbon Anode as a Source of Fuel for Foundrymen

Small scale foundries in Ghana are in search of a suitable coke for their foundry operations since there is no coal mine in Ghana. Two grades of spent prebaked aluminium carbon anodes (herein referred to as grade P and grade K), which are remnants from the aluminium electrolysis at Volta Aluminum Company (VALCO), an aluminium smelting company in Ghana, have been characterized to assess their quality and use as foundry coke. Proximate analysis and X-ray diffraction techniques have been used for their quality assessments. Coke grade P had lower moisture content, volatile matter and ash content compared to grade K. In both grades, sulphur and phosphorus contents were within requirements of a quality foundry coke. However, the volatile matter and ash contents of both grades were not satisfactory. Fixed carbon contents in both grades were below that of a quality foundry coke. Carbon structure of coke found in both grades is crystalline in nature. The crystalline width, Lc, was calculated to be 4.05 A and 5.12 A for grade K and P, respectively.

High adsorption capacity and the key role of carbonate groups for heavy metal ion removal by basic aluminum carbonate porous nanospheres

A fast, low-cost and scalable method was developed to prepare basic aluminum carbonate (Al(OH)CO3) porous nanospheres via a microwave-assisted solvothermal process in 5 min. All chemicals used were low-cost and environmentally benign. These Al(OH)CO3 nanospheres had an extremely large surface area (484 m2 g−1), abundant carbonate groups, and showed superb adsorption properties with maximum capacities of 170 mg g−1 and 60 mg g−1 for As(V) and Cr(VI) at pH 7, respectively. These values were obviously higher than that of many other nanomaterials. In addition, for practical applications, 5 mg Al(OH)CO3 nanospheres could purify 6 kg As(V) contaminated water, reducing the As(V) concentration from 100 ppb to less than 10 ppb. A new adsorption mechanism involving ion exchange between carbonate groups and As(V) or Cr(VI) species was proposed and confirmed.

Statistical Optimization for the Adsorption of Acid Fuchsin onto the Surface of Carbon Alumina Composite Pellet: An Application of Response Surface Methodology

Statistical Optimization for the Adsorption of Acid Fuchsin onto the Surface of Carbon Alumina Composite Pellet: An Application of Response Surface Methodology

Facile Synthesis of Ammonium Aluminum Carbonate Hydroxide Multilayered Nanofiber by Using Solid State Reaction

In this paper, we make systematical investigation for the new synthesis pathway of AACH multilayered nanofiber, which has been prepared by a low-temperature solid-state reaction. The phase transformation sequence of AACH on heating is found that the precursor converts into γ-Al2O3at 700-900°C and elevated temperature results in the θ-Al2O3and α- Al2O3crystal phase formation at 1000°C. With a higher calcination temperature at 1100°C, α- Al2O3pattern appears. The specific surface area (SBET) of aluminum oxide specie calcined at 500°C for 4h is still in 420.2m2/g. Meanwhile, it suggests a partial change in particle sizes and morphology of sample calcined at 500°C for 4h.

A simple hydrothermal route to bimodal mesoporous nanorod γ-alumina with high thermal stability

AbstractIn the presence of polyethylene glycol, bimodal mesoporous nanorod γ-alumina was successfully synthesized via the thermal decomposition of ammonium aluminium carbonate hydroxide precursor which was prepared via hydrothermal processing with inorganic aluminium salt. The alumina exhibits high surface area (494 m2g–1), large porosity (1.1 m3g–1) and a particular double-pore structure after calcination at 500 °C. The smaller pore diameter is concentrated on about 3 nm and the larger one is exhibited in the range of 10 – 38 nm. The scaffold-like aggregation of γ-alumina nanorods endows this novel material with excellent thermal stability. A possible formation mechanism of bimodal mesoporous structure is also proposed in this study.

Effect of Barium Aluminates on Acid Resistance of Fracturing Proppants

In order to explore the effect of removing siliceous components on acid resistance of fracturing proppants, acid resistance of fracturing proppants in a new silicon-free system was studied in this paper. The fracturing proppants were made by pressureless sintering using high-purity alumina and barium carbonate as the basic raw material. Acid resistance test was carried out in 12 wt% HCl + 3 wt% HF at 65 oC for 30 minutes according to The Petroleum and Gas Industrial Standards of China (SY/T5108-2006) and morphology, structure and chemical analysis of the samples were investigated using X-ray diffraction and scanning electron microscopy. Experiments show that fracturing proppants that contain barium aluminates have better acid resistance. The acid solubility of the samples is less than 3%, especially when the content of barium carbonate is about 10% (mass fraction, the same below), the acid solubility of the sample reaches 0.52% which is far beyond the demands (5%) of the Standards of SY/T5108-2006. Results prove that the removal of siliceous components of raw materials can prominently improve the acid resistance of fracturing proppants. It can provide a new referential thought for improving the acid resistance of fracturing proppants.

A Prospective Way to Reduce Emissions in Secondary Steel Making Metallurgy by Application of Functionalized Doloma Carbon Refractories

Doloma and doloma carbon refractories are the standard refractory systems applied in AOD (argon oxygen decarburization) and VOD (vacuum oxygen decarburization) vessels in the secondary metallurgy to produce stainless steel. This refractory system is connected with metallurgical benefits such as high oxidic stability of its oxides, and the ability to bond sulfur from the hot metal. Production and application of carbon-bonded refractories is directly linked with environmental harmful emissions in the broadest sense. In the center of this work is the aspect of increased residual carbon content of the binder resin due to TiO2 addition. Furthermore, this work has observed the applicability of TiO2-treated bricks in AOD converter. The increased residual carbon content of the binder resin connected with improved mechanical, physical, and thermomechanical properties due to sub-micro scaled TiO2 and metallic antioxidant addition offers the feasibility to reduce the total carbon content without downgrading the brick properties. This aspect has not been observed yet, and is of high interest with respect to reduced emissions and environmental friendly refractories. Previous works have investigated the influence of TiO2 on other carbon-bonded refractory systems, such as alumina carbon and magnesia carbon. As illustrated in this work and previous work, TiO2 is working completely different in the doloma carbon system when compared with other systems.

Effect of Calcination and Reduction Process on MWCNT Growth during Synthesizing MWCNT-Alumina Hybrid as Composite Reinforcement

Multiwall carbon nanotube (MWCNT) and alumina hybrid compound prepared via chemical vapour deposition (CVD). The CVD process always reported that the catalyst must undergo calcinations and reduction process before growing the carbon nanotube (CNT). In this work, MWCNT-alumina hybrid was successfully synthesized via simple CVD method. The morphologies study showed that the MWCNT-alumina hybrid with calcination and reduction, and calcination without reduction has been successfully synthesized.

Methylation of methyltrichlorosilane with methyl chloride over active metals and activated carbon

Gas phase methylation of methyltrichlorosilane with methyl chloride to high-valued dimethyldichlorosilane was carried out by using metallic aluminum as a chlorine acceptor in the co-presence of activated carbon, tin, and zinc. The addition of activated carbon in metallic aluminum significantly enhanced the methylation of methyltrichlorosilane, and dimethyldichlorosilane was dominantly produced. Activated carbon played a catalyst role in the methylation reaction. When active metals, such as tin and zinc, were added in the mixture of aluminum and activated carbon, the active metals and activated carbon synergistically catalyzed the methylation of methyltrichlorosilane with methyl chloride toward the formation of dimethyldichlorosilane.

Advance in preparation of magnetic nanowires and its application in biosensors

Magnetic nanowires not only have nanometer properties, but also have magnetic property of giant magnetoresistance. Recently, nanowires were applied widely in high density hard disk slider, super magnetic storage element, micro-sensors, micro-engine, biomedical engineering, etc. This artical reviews the current preparation method of nanowires, the template synthesis, including several general templates such as track-etched porous polycarbonate membrane, porous anodic aluminum oxide membrane and carbon nanotubes, as well asgrowth patterns of nanowires in the templates. The applications of nanowires in several biosensors are introduced.The applications will greatly improve current ways of sensor detection, which will open up new areas of the field of biosensor study. Key words: Magnetic nanowires; Biosensors; Giant magnetoresistance; Anodic aluminum oxide; Electrochemical deposition

Preparation of porous alumina–carbon nanotube composites via direct growth of carbon nanotubes

A simple approach is reported for the in situ growth of carbon nanotube-containing porous alumina structures by a thermal pyrolysis method. The composite was created by direct on-site growth of carbon nanotubes inside the porous alumina matrix, after introducing both a catalyst (Ni(NO 3) 2) and a carbon source (camphor) into the cavities of the large matrix brick. Pyrolysis was carried out when the pre-treated brick was heated in a furnace at 850 °C under a H 2–Ar atmosphere. The resulting multi-walled carbon nanotubes with average diameters of 30–70 nm and lengths up to several micrometers are dispersed uniformly at each section of the alumina matrix. An improvement in the compression strength of the composites has been obtained, due to the inclusion of carbon nanotubes.

New Approach for the Application of Functional Ceramic Material in Carbon Bonded Doloma Refractories to Reduce Emissions

AbstractDoloma carbon bricks with graphite contents of approximately 2 wt% are widely used in the production of stainless steels in argon oxygen decarburisation (AOD) or in vacuum oxygen decarburisation (VOD) vessels as lining material. The application of doloma refractories is connected with metallurgical benefits such as high oxidic stability of its oxides, and the ability to bond sulphur from the hot metal. The production and application of carbon bonded refractories is linked with environmental harmful emissions in the broadest sense. Amongst the aspect of environmental friendly refractory systems this work has observed and shown the interaction of functional ceramic material TiO2 with the organic binder system. In the centre of this work is the aspect of increased residual carbon content of the binder resin due to TiO2 addition. The increased residual carbon content of the binder resin connected with improved mechanical, physical and thermomechanical properties due to sub‐micro scaled TiO2 addition offers the feasibility to reduce the total carbon content without downgrading the brick properties. This aspect has not been observed yet and is of high interest with respect to reduced emissions and environmental friendly refractories. Previous works have investigated the influence of TiO2 on other carbon bonded refractory systems such as alumina carbon and magnesia carbon. As illustrated in this work and previous work, TiO2 is working completely different in the Doloma Carbon system from other systems.

Quantitative investigation in the influence of oxalic impurities on photoluminescence properties of porous AAOs

Anodic alumina oxides (AAOs) prepared in oxalic acid (H 2C 2O 4) solution at a constant voltage of 40 V were investigated by the techniques of temperature programmed desorption combined mass spectrograph (TPD-MS), thermogravimetric analysis (TGA), differential thermal analysis (DTA) and photoluminescence (PL). The results indicate that the desorption of H 2O, CO and CO 2 and the decomposition of H 2C 2O 4 which led to the weight loss of AAOs samples occurred below 400 °C, while the water desorption was the main reason for weight loss. In the temperature range of 400–900 °C, a small quantity of aluminum oxalate (Al 2(C 2O 4) 3) decomposed and gave birth to CO and CO 2, during this process CO became the major product. The drastic decompositions of aluminum carbonate (Al 2(CO 3) 3) and Al 2(C 2O 4) 3 took place near 930 °C, which produced a large amount of CO 2. The amount of (C 2O 4) 2− embedded in bulk AAOs was calculated versus the total weight of AAOs film, and the PL intensity of AAOs was correlated to the doping of oxalic acid radical. The above results may have great significance in the better application of AAOs as matrix of photonic crystals.

Preparation of Alumina from Heated Kaolin Leached by Citric Acid with AACH as an Intermediate

Because the supply of bauxite ores in many countries is becoming deficient, a process of preparing alumina from an alternative resource, namely, kaolin, is proposed in this work. First, kaolin was heated at 600 °C for 2 h before being leached with 1 M citric acid solution, about 75% of the Al in kaolin entered the leachate as aluminum citrate (AlCit) solution. Then, about 50% of the Al(III) in the leachate could be precipitated as ammonium aluminum carbonate hydroxide (AACH) by addition of NH4HCO3 at pH 9.00 ± 0.50. The morphology of AACH characterized by SEM and TEM was spherical particles composed of many nanorods with sizes of about 500 × 25 nm. Finally, mesoporous γ-Al2O3 was obtained by roasting AACH at 700 °C. The Fe and Na contents in the obtained γ-Al2O3 product determined by XRD and ICP-AES were 2 and 0.1 ppm, respectively. The obtained γ-Al2O3 had a morphology similar to that of AACH, and its BET surface area was as high as 235.2 m2/g.

Alumina–Carbon Nanofibers Nanocomposites Obtained by Spark Plasma Sintering for Proton Exchange Membrane Fuel Cell Bipolar Plates

AbstractThere is an increasing demand of multifunctional materials for a wide variety of technological developments. Bipolar plates for proton exchange membrane fuel cells are an example of complex functionality components that must show among other properties high mechanical strength, electrical, and thermal conductivity. The present research explored the possibility of using alumina–carbon nanofibers (CNFs) nanocomposites for this purpose. In this study, it was studied for the first time the whole range of powder compositions in this system. Homogeneous powders mixtures were prepared and subsequently sintered by spark plasma sintering. The materials obtained were thoroughly characterized and compared in terms of properties required to be used as bipolar plates. The control on material microstructure and composition allows designing materials where mechanical or electrical performances are enhanced. A 50/50 vol.% alumina–CNFs composite appears to be a very promising material for this kind of application.