Specific Surface Area Of Product Research Articles

Structural alterations of synthetic allophane under acidic conditions: Implications for understanding the acidification of allophanic Andosols

Acidification of allophanic Andosols has significant effects on their physicochemical properties and productivity. Understanding of the acidification and related effects is limited by the structural changes of allophane – the major mineral composition of allophanic Andosols. In this work, we systematically investigated the structural stability of allophane and the mechanisms of structural changes under different acidic conditions (initial pH 4.0–2.0) by using chemical analysis, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, solid-state magic-angle-spinning nuclear magnetic resonance, and N2 physisorption analysis. The results indicated that the structure of allophane was readily altered in acidic conditions. Acid leaching in conditions with initial pH > 3.0 only dissolved some polymerized silicates from allophane, enlarging the defect pores. By contrast, the dissolution of the imogolite-like local structure was observed in strongly acidic conditions (initial pH < 3.0) and released large amounts of Al and Si, which can further enlarge defect pores or even make hollow spherules collapse followed by the precipitation of amorphous silica. As a result, the microporous parameters increased, reaching maxima in Allo2.2, while the total porosity and specific surface area of products decreased with the decrease of initial pH of the leaching solutions. These changes are supposed to diminish the adsorption and storage capacities of guest species of allophane. These findings suggest that the rapid responsiveness of allophane to acid supposedly plays a crucial role in the acid buffering capacity of allophanic Andosols and that the structural destruction of allophane may significantly contribute to Al toxicity and to breaking the porous structure of acidified allophanic Andosols. For the management of allophanic Andosols, prudent measures should be taken to protect the allophane structure. And it is possible to restore the soil productivity of weakly acidified allophanic Andosols through soil remediation.

Influence of processing on surface morphology and specific surface area for the nickel foam made by electrodeposition

Purpose With the nickel foam made by the technique of electrodeposition on polymer foam, the purpose of this paper is to investigate the influence of several deferent processes on the surface morphology and the specific surface area of this porous product. Design/methodology/approach The surface morphologies of the nickel foam were examined by SEM. The specific surface area of the porous product was measured by gas (N2) permeability method and also calculated by the reported formula. Findings The nickel foam from sintering in NH3 decomposition atmosphere at 850°C will achieve the same specific surface area as that at 980°C, whether this porous structure after electrodeposition comes through direct sintering in NH3 decomposition atmosphere, or through burning in air at 600°C for 4 min beforehand then the same reductive sintering. Originality/value There have been some studies on the preparation and application of nickel foam, but few works focus on the processing influence on the specific surface of this porous product. The present work provides the investigations on the difference of the product made under different producing conditions, and the influence of several deferent processes on the specific surface area of the product.

Synthesis of lamellar mesoporous silica materials using LCs as templates

ABSTRACTThe study focuses on the synthesis of mesoporous silica materials using liquid crystals (LCs) formed in an aqueous mixture of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) as templates and tetrathoxysilane (TEOS) as precursor. For this purpose, the phase behavior and range of LC areas were determined at different temperatures, concentrations, and ratios of CTAB/SDS. It was found that LCs became denser with the increased of concentration of surfactants. The mesoporous materials were synthesized using LCs as templates at various temperatures, surfactant concentrations, and pH values. The mesoporous samples were characterized using SEM and nitrogen sorption analysis. The research results showed that the structure of synthesized samples were lamellar and their surface areas increased significantly with the increase of temperature in the temperature range of LCs, reaching about 900 m2/g at 60°C. The surfactant concentrations affect the thickness of pore wall and thereby the specific surface area of products. The specific surface area and the order of mesoporous sample increased gradually with the decrease of pH.

Effect of construction method and surface area for nano metal−organic framework HKUST-1 upon adsorption and removal of phenazopyridine hydrochloride

Herein, we study adsorption and removal properties of phenazopyridine hydrochloride (PAP) from nano metal−organic framework material HKUST-1 versus bulk compound. The mechanosynthesis of HKUST-1 has been compared to its ultrasonic synthesis. It has been found that by using mechanosynthesis HKUST-1 can be obtained in a much shorter synthesis time with improved adsorption properties. Based on the obtained results for the specific surface area of products, under ultrasound-assisted methods the surface area is decreased, since the amount of the PAP adsorption decreased by this method.

ВЛИЯНИЕ ПРЕДВАРИТЕЛЬНОЙ ВОДНОЙ ОБРАБОТКИ СОСНОВЫХ ОПИЛОК НА СТРУКТУРНЫЕ ИЗМЕНЕНИЯ ДРЕВЕСИНЫ И СВОЙСТВА УГЛЕРОДНОГО ПРОДУКТА НА ЕЕ ОСНОВЕ

The effect of long-term water extract of pine sawdust on the structure of wood and its carbon product. It is found that such a timber processing increases the fraction of the amorphous phase and the content of hydrogen in its composition. Using X-ray diffraction is determined that the processing of wood after water decreases the crystallinity of cellulose and increases the width of the crystallite size. It is revealed that an increased content of amorphous component in the timber after the water processing is stored in the structure of the carbon product based on it, compared with an untreated timber and its product.The possibility of producing porous carbon materials from sawdust pine subjected to long exposure to water. Carbonation of these chips, up to 800 °C leads to the formation of a porous carbon product, specific surface of which is 400 times higher than the specific surface area of product obtained from conventional chips in the same conditions. It is assumed that the disclosure of the porous structure of the carbon product from the timber after the water treatment due to the change of its structure, including the expansion of the crystal lattice of cellulose, and removing formed during carbonization of low molecular weight fragments.

Porosity of starch–proteins extrudates determined from nitrogen adsorption data

Extrudates of potato starch with selected proteins (concentrate of soybean proteins, whey proteins and acidic casein) were produced at 22% raw material moisture, and at various process temperatures and extruder screw speeds. Increase of screw speed and temperature had a significant effect on changes in the specific surface area and porosity of products which were tested with the use of low-temperature sorption of nitrogen. The nitrogen adsorption isotherms plotted are of types II and III according to IUPAC, both for the raw material and for the product. Equation BJH was used to determine the surface area (SBJH), volume (VBJH) and average pore diameter (DBJH). For diameters from 35 Å to 74 Å, the calculated pore volumes assumed values within the range of 23·10−5 cm3/g −55·10−5 cm3/g. Curves of pore size distribution based on average pore diameter within the range of 19.7–23.2 Å indicate a large cumulative volume of pores.Extrusion caused a decrease in the specific surface area of the product, from 0.19 m2/g to 0.32 m2/g. A high correlation was noted between increase in porosity and expansion, and the optimum screw speed and temperature profile.

Continuous Ammonium Silicofluoride Ammonification for SiO2 Nanoparticles Preparation in a Microchemical System

The ammonium silicofluoride ammonification process is a potential atomic economical process for nanosized silica preparation. In this work, this process was continuously conducted in a micropores dispersion microreactor and specially investigated. The exploration on the evolution of the yield and the specific surface area of product with reaction proceeding under various feeding conditions indicated that both of two consequent stages of fast precipitation and precipitate aging may occur remarkably in the microchemical system. However, their overlap could be reduced by enhancing mixing and strictly controlling the residence time. Correspondingly, this process could stably preparing high-quality SiO2 nanoparticles (specific surface area >400 m2/g) at equilibrium yield. Furthermore, optimization on reaction temperature was discussed, and the adaptability of high concentration (NH4)2SiF6 as feed was tested as well. This research provided fundamentals and a guide for developing and designing an industrial production technology of nanosized silica based on the ammonium silicofluoride ammonification process.

A nanocomposite precursor strategy to mixed-metal oxides with excellent catalytic activity for thermal decomposition of ammonium perchlorate

NiAl-layered double hydroxide/carbon (LDH/C) nanocomposites were prepared by a hydrothermal process simultaneously involving the crystallization of LDH and carbonization of glucose. The nanocomposites calcined in air lead to porous NiAl-mixed-metal oxides with tunable surface areas. The porosity of resultants is ascribed to the templating effect, resulting from the depletion of carbonaceous products with the elevating temperature under air atmosphere. The specific surface areas of products are sensitive to carbonaceous product content in the composite precursor, Ni/Al ratio and as well the calcination temperature. The specific surface area reaches a maximum under medium carbon content in the precursor and decreases with the increasing calcination temperature. On a basis of the nature of metal oxides and their high surface areas, the mixed-metal oxides are utilized for catalytic thermal decomposition of ammonium perchlorate (AP) and exhibit excellent catalytic activity. The peak temperature of AP decomposition was greatly decreased compared to that of pure AP. And the temperature is strongly dependent on the surface areas of mixed oxides. Furthermore, the decomposition activation energy of AP with the mixed oxide additives was calculated to be 74.6 and 80.4kJmol−1 by two methods of kinetics, respectively, both of which are smaller than that of pure AP.

Synthesis of Activated Carbon from Rice Chaff by Microwave Hydrothermal Method

Rice chaff can be converted into activated carbon by alkaline treatment at high temperature. In this study, we tried to synthesize activated carbon from rice chaff by microwave hydrothermal treatment with NaOH solution. Rice chaff was heated at 700°C for 1 h in N2 after HCl treatment to remove impurity, such as alkali metals, resulting in the formation of charcoal. The charcoal was mixed with NaOH aqueous solution, and then heated at 100°C under microwave irradiation. After heating, the product was separated by filtration, washed with deionized water and dried at 50°C. The specific surface area of product was 1060 m2/g under microwave irradiation and 690 m2/g by conventional heating with autoclave, which indicates that microwave hydrothermal treatment is effective for activation of charcoal.

Gelatin-assisted porous expansion of mesoporous silica

In this study, we report the pore expansion effect of gelatin, a common amphoteric biological protein, on the hexagonal mesoporous silica materials. Tetraethyl orthosilicate (TEOS) was used as silica source and the nonionic surfactant P123 (EO20PO70EO20) as template. The microstructure characters of products were investigated by low-angle X-ray diffraction (LAXRD), transmission electron microscope (TEM), and N2 adsorption–desorption measurements. The results show that the products prepared with gelatin have the mild expansion ratios of 29–39% and 5–22% in pore diameter and pore volume, respectively. The specific surface area of products ranges from 445 to 590 m2 g−1. Moreover, it is revealed that the presence of gelatin did not change the intact 2D-hexagonal mesoporous structure of materials. The ultraviolet–visible absorption spectroscopy (UV–Vis) analysis indicates that there is an interaction between the oxygen atoms of P123 and gelatin molecules. The pore expansion may be because the gelatin can interact with the hydrophilic sides of P123 micelles via hydrogen bonds interaction, which is different from the reported pore expansion mechanisms for other systems.

Synthesis of High-Purity Boron Nitride Nanocrystal at Low Temperatures

High-purity nanocrystalline boron nitride has been successfully synthesized by a simple synthesis method using amorphous B powder and NaN3 as the reactants and anhydrous CH3CN as the solvent at 380 °C. Results from XRD, FT-IR, EELS, and BET absorption measurements suggest that the synthesized product can be indexed as pure hexagonal BN with lattice constants of a = 2.497 Å and c = 6.678 Å, and the specific surface area of product is 52.19 m2/g. The TEM images show the multiplex belt spherelike, fiberlike, sheetlike, and tubelike morphologies of the products. Here, the multiplex belt spherelike and sheetlike structures are reported for the first time. When the temperature of reaction and the solvent are controlled, BN products with particular morphologies can be selectively produced. The optical properties of the product are observed in the PL spectra, which shows that the as-prepared BN emits strong visible luminescence at 580 nm (λex = 325 nm).

アルミナの超微粉砕における液体添加物の助剤効果とアルミナ粉体の挙動

The effect of liquid additives of grinding aid on the ultrafine grinding of alumina was studied by using a vibration rod mill. Liquid additives studied were five alcohols and two glycols with different alkyl groups. Experiments were carried out by batch operation, and the changes in specific surface area of products with grinding were measured by BET adsorption method. The behavior of alumina powder during grinding was also investigated by monitoring the temprature change of the grinding vessel. The results showed that alcohols and glycols had a significant effect on the ultrafine grinding of alumina as a grinding aid. The maximum specific surface area of alumina obtained with an additive was found to increase proportionally with the amount of additive. The thermal analysis of ground products suggested that three molecular layer of the additive molecules existed on the product surface when the specific surface area reached the maximum value. It was found that the monitoring of the temperature change of grinding vessel would be useful in understanding the grinding status.

The effect of liquid additives on dry ultrafine grinding of quartz

The dry ultrafine grinding of quartz with liquid additives was carried out using a vibration rod mill with a laboratory scale. Liquid additives used were mainly seven alcohols and three glycols with different alkyl groups. All of the experiments were carried out by batch operation, and the variations of specific surface areas of products with grinding time were measured by BET adsorption method. The results showed that alcohol and glycol additives were satisfactorily effective for the ultrafine grinding of quartz. The maximum specific surface area of quartz obtained with an additive was found to increase in proportion to the amount of the additive. The additive molecules of multimolecular layers were supposed to adsorb on the quartz surface when the specific surface area reached the maximum value. The principal effect of additives in ultrafine grinding is considered to be the increase in flowability and the control of reagglomeration of quartz powder due to the alkoxylation of hydroxyl groups on the quartz surface.

Niobium Carbide Synthesis from Niobium Oxide: Study of the Synthesis Conditions, Kinetics, and Solid-State Transformation Mechanism

The carburization of B-niobium oxide (B-Nb2O5) to niobium carbide (NbC) in 20% (v/v) CH4/H2was studied at temperature-programmed conditions. The reaction required high temperatures, greater than 1370 K, and variations of heating rate (0.04–0.17 K s−1) and molar space velocity (400–1600 h−1) had only a minor effect on the product specific surface area (Sg). In the course of the transformationSgincreased from 1 m2g−1to about 20 m2g−1, and scanning electron microscopy showed the development of macropores of about 100 nm. The progress of the reaction was followed by mass spectroscopic analysis of the gaseous products, which identified two distinct stages. X-ray diffraction analysis of reaction intermediates showed that in the first stage B-Nb2O5was reduced to NbO2, and in the second stage NbO2was simultaneously reduced and carburized to NbC. The first reduction occurred by a nucleation mechanism with an activation energy of 100 kJ mol−1. Independent experiments with NbO indicated that it was not involved in the reaction pathway. However, X-ray photoelectron spectroscopy revealed the presence of an oxycarbide phase which was probably the intermediate in the final transformation. Overall the reaction took place by the following steps:[formula]The oxycarbide phase transformed rapidly to the product NbC and was not observable as a bulk phase by XRD.

Mechano-radicals produced from ground quartz and quartz glass

Electron spin resonance spectroscopy (ESR) measurements of the mechano-radicals produced from ground quartz and quartz glass were studied. Three mechano-radical types were produced: E'center, non-bridging oxygen hole center (NBOHC) and peroxy radical. The ESR spectrum was found to vary with the type of atmosphere during grinding. The concentration of mechano-radicals was approximately proportional to the specific surface area of product. Adjacent E'center and NBOHC radicals recombined with each other. The life time of mechano-radicals was found to be longer than about 3800 h in a vacuum.

Synthesis of high surface area vanadium nitride

Fine vanadium nitride powders (particle size 11 nm) have been prepared by temperature programmed reduction and nitridation of V 2O 5 by gaseous ammonia. The reaction was followed by monitoring gas phase reaction products by on-line mass spectroscopy. X-ray diffraction and elemental analysis were used to identify various solid-state reaction intermediates, V 6O 13, V 2O 4, VO 2, V 2O 3, and VO, and to establish that the final reaction step was the nitridation of VO to VN. Heating rate had a substantial effect on product specific surface area and a rate of 0.083 K sec −1 resulted in an optimal value of 90 m 2g −1. The activation energy for nitridation was not constant, but rose from 203 to 243 kJ mol −1 as the extent of reaction increased from 0.25 to 0.75. The transformation was limited by the bulk diffusion of oxygen and nitrogen and not by a surface process.

Effect of mill diameter on the rate of initial grinding in vibration ball mills

Vibration ball milling was carried out using three kinds of mills with the same internal volume but different diameters. The variations of specific surface area produced with time were investigated at a constant vibration intensity using feldspar with an initial size range of 74 – 149 μm. As a result, it was found that the specific surface area of product was markedly influenced by the difference in mill diameter even at the same vibrating conditions. According to an empirical equation proposed in a previous paper, the rate of initial grinding was also found to vary by a factor of 1.4 to 2.0, depending upon the mill used. The dependence of the rate of grinding on mill diameter can be explained by considering an effective area of mill shell capable of colliding with balls and a motion of balls in each mill. An available suggestion for designing a mill pot was obtained from this work.

Experimental investigation of the decrease of grinding rate in planetary ball milling.

Dry grinding experiments were carried out with a planetary ball mill. Layer particles adhering to the mill wall and freely movable particles in the mill were separated from each other and changes in their weight fractions, size distributions and specific surface areas with grinding time were measured for various balls, feed sizes and powder fillings. Certain correlation between the decrease of grinding rate and the increase of coating particles was confirmed and a new empirical equation for expressing the change of specific surface area of product in batch grinding were derived.

The K-absorption edge of vanadium in some vanadium compounds

Fine vanadium nitride powders (particle size 11 nm) have been prepared by temperature programmed reduction and nitridation of V2O5 by gaseous ammonia. The reaction was followed by monitoring gas phase reaction products by on-line mass spectroscopy. X-ray diffraction and elemental analysis were used to identify various solid-state reaction intermediates, V6O13, V2O4, VO2, V2O3, and VO, and to establish that the final reaction step was the nitridation of VO to VN. Heating rate had a substantial effect on product specific surface area and a rate of 0.083 K sec−1 resulted in an optimal value of 90 m2g−1. The activation energy for nitridation was not constant, but rose from 203 to 243 kJ mol−1 as the extent of reaction increased from 0.25 to 0.75. The transformation was limited by the bulk diffusion of oxygen and nitrogen and not by a surface process.

Studies in fluid energy grinding

The results of 239 experimental runs on grinding calcite of particle size range 0.15–1.70 mm in an experimental jet mill of 20 mm diameter, using feed rates of 5–150 g/min and air pressure of 3–6 kg/cm 2 G are reported. The effects of (1) solids feed rate, feed size and grinding nozzle pressure on product size distribution, specific surface area produced, grinding ratio, holdup, residence time and grinding rate, (2) injector nozzle pressure on product size distribution and product specific surface area and (3) grinding nozzle diameter on product size distribution are indicated. Observations are made on the efficiency of grinding and choking conditions. Correlations for grinding ratio, specific surface area produced and optimum feed rate are presented. The present work seems to be the first attempt to bring together the variables involved in jet milling, to suggest conditions for optimum feed and choking and to develop quantitative relationships within the range of experimental work investigated.