Adsorption of methane on corn cobs based activated carbon

Activated carbon was prepared with corn cobs and potassium hydroxide under optimized variables. Due to their botanical origin, corn cobs can be an excellent starting material to produce nanoporous carbon for natural gas storage. Samples with different BET surface areas were chosen to perform methane adsorption experiments. Methane adsorptions on corn cob based activated carbon were studied at four different pressures (500, 1000, 1500 and 2000 psi) and two different temperatures (298 K and 323 K) in a volumetric adsorption apparatus. The volume based methane adsorption results specified an ‘increase in the methane adsorption capacities of activated carbon with increasing surface area and showed that adsorption capacity of methane depends on pressure and temperature. The highest methane storage capacity was found to be 160 (v/v) at 298 K and 1500 psi. The applications include use in the transportation of natural gas, natural gas based vehicles, and adsorption of gas from landfills.     

Preparation of high surface area activated carbon from corn by chemical activation using potassium hydroxide

Activated carbons were prepared through chemical activation of corn cob precursor, using potassium hydroxide as the chemical agent. The effect of different parameters, such as particle size, method of mixing, chemical/corn ratio, activation time and activation temperature, on weight loss and BET surface area of the produced activated carbons were discussed. The porosity of the activated carbons was evaluated through nitrogen adsorption. The storage capacity of the activated carbon was evaluated using natural gas. Under the experimental conditions investigated, the optimal conditions for production of high surface area carbons by chemical activation were identified. The results were compared with commercial activated carbons from coal.     

Removal of lead ions from aqueous solutions using powdered corn cobs

This paper is a report on an investigation conducted on adsorption of lead ions (Pb²⁺) onto powdered corn cobs (PCC). Corn cobs were collected from a selected location in Nigeria. The corn cobs were crushed and pulverised into different particle sizes. Its compositions and adsorption properties of Pb²⁺ onto PCC were studied. The effects of pH, particle size of PCC, and initial concentration of Pb²⁺ on the adsorption properties were monitored. The adsorption capacities were analysed by using standard adsorption models. The models were evaluated statistically (total error, coefficient of determination (CD), model of selection criterion (MSC), and root mean square error). The study revealed that PCC contained 2.33%, 86.89%, 10.78%, 0.52%, and 4.56% ash, volatile, moisture, solubility in water, and solubility in 0.25 M of HCl by mass, respectively. Acid digestion of a gram of PCC indicated that PCC contained no chromium and lead, but contained 131 mg Fe, 54.79% carbon, 8.03% hydrogen, 0.41% nitrogen, 0.010 mg of Al, and 1.70 mg calcium. The isotherm models parameters were 28.509 L/mg and 0.141 mg/g; 0.138 mg/g and 11.494 L/mg; 0.142 L/mg and 0.013 mg/g; 0.129 mg/g and 25.641 L/mg, 28.509 L/mg, 3.795 mg/g and 2.336 for Langmuir, Freundlich, Temkin, activated sludge, and Redlich–Peterson. The PCC particle size, initial pH, and initial Pb²⁺ concentration had effects on the adsorption parameters. The statistical evaluations showed that the best model for adsorption of lead ions from raw water onto PCC based on lower errors, high CD (0.88), reliability (97.5%), and MSC (1.86) was Freundlich and followed by activated sludge model. It was concluded that PCC is a good adsorbent like powdered eggshell and other carbon‐based materials.     

Densification of powder compacts by vibration

Various packing methods such as vibration, shaking, etc., in addition to normal gravitational settling, can be often used to density powder compacts. Many issues relevant to this matter are of great importance in advanced ceramic powder processing. In the present work, the relaxation of structure due to vibration is addressed by using a computer experimental model based on Monte Carlo method. Packing structures, diffraction patterns, radial distribution functions are used for the characterization of structures. Bulk properties such as packing fraction and average height of the deposit are examined. The results agree well with those observed in model experiments, even with more implication.     

Densification of nanocrystalline MgO ceramics by hot-pressing

Densification of pure nanocrystalline MgO powder with 10 nm particle size by hot-pressing was investigated in the temperature range 700–800 °C, applied pressure range 100–200 MPa, and for durations of up to 240 min. It was shown that significant densification under the pressure begins above 440 °C. Densities higher than 99.5% with grain size of 73 nm were achieved at 790 °C and 150 MPa for a 30 min duration. Remarkable densification from 90 to 99.5% was observed by temperature change from 700 to 790 °C, for which the grain size was doubled only. The final grain size decreased with increasing the applied pressure. Higher shrinkage rates and cumulative shrinkages were recorded by the application of pressure at 550 °C rather than from room temperature. The temperature at which the pressure was applied is crucial in determining the maximum shrinkage rate in the nanocrystalline compacts. This effect was related to the morphological changes of the particles caused by plastic deformation at lower temperatures. Analysis of the densification rate and its comparison to the literature data was in agreement with Coble creep, where self-diffusion of Mg²⁺ cations along the grain boundaries acts as a main densification mechanism.     

Densification mechanism and microstructure characteristics of nano- and micro- crystalline alumina by high-pressure and low temperature sintering

Fully dense ceramics with retarded grain growth can be attained effectively at relatively low temperatures using a high-pressure sintering method. However, there is a paucity of in-depth research on the densification mechanism, grain growth process, grain boundary characterization, and residual stress. Using a strong, reliable die made from a carbon-fiber-reinforced carbon (C_f/C) composite for spark plasma sintering, two kinds of commercially pure α-Al₂O₃ powders, with average particle sizes of 220 nm and 3 μm, were sintered at relatively low temperatures and under high pressures of up to 200 MPa. The sintering densification temperature and the starting threshold temperature of grain growth (T_sg) were determined by the applied pressure and the surface energy relative to grain size, as they were both observed to increase with grain size and to decrease with applied pressure. Densification with limited grain coarsening occurred under an applied pressure of 200 MPa at 1050 °C for the 220 nm Al₂O₃ powder and 1400 °C for the 3 μm Al₂O₃ powder. The grain boundary energy, residual stress, and dislocation density of the ceramics sintered under high pressure and low temperature were higher than those of the samples sintered without additional pressure. Plastic deformation occurring at the contact area of the adjacent particles was proved to be the dominant mechanism for sintering under high pressure, and a mathematical model based on the plasticity mechanics and close packing of equal spheres was established. Based on the mathematical model, the predicted relative density of an Al₂O₃ compact can reach ～80 % via the plastic deformation mechanism, which fits well with experimental observations. The densification kinetics were investigated from the sintering parameters, i.e., the holding temperature, dwell time, and applied pressure. Diffusion, grain boundary sliding, and dislocation motion were assistant mechanisms in the final stage of sintering, as indicated by the stress exponent and the microstructural evolution. During the sintering of the 220 nm alumina at 1125 °C and 100 MPa, the deformation tends to increase defects and vacancies generation, both of which accelerate lattice diffusion and thus enhance grain growth.     

Densification of oxides via cold sintering of hydrate precursors

A generalized cold sintering densification strategy based on a hydroxide precursor transformation route is proposed for oxides. The densification of MgO, CuO, ZnO and WO₃ was achieved via cold sintering by using their corresponding hydroxides at temperatures not exceeding 450 °C. Nano-oxides formed by the decomposition of the hydroxides exhibited good low-temperature sinterability. The densification mechanisms mainly involved particle rearrangement promoted by in situ released water and intergranular diffusion accelerated by surface defects of the oxide particles generated from hydroxide decomposition. During the cold sintering process, the oxides with relatively higher solubility in a water vapor environment are more likely to form surface defects, which promoted water-aided densification. Owing to the possibility of obtaining the corresponding hydroxides for almost all oxides, this strategy renders cold sintering feasible for a wide range of materials.     

Al2O3-TiAl复合材料的致密化过程分析

借助Origin软件分析了Ti—Al-TiO2-Nb2O5系混合粉末在热压过程的致密化变化行为，并获得了在保温过程的压头一时间关系。结果表明烧结过程大致分为3个阶段：慢收缩阶段、剧烈收缩阶段和保温阶段。保温60min的复合材料在保温阶段压头位移变化曲线划分为3个阶段：初期、中期和后期，其各时期的压头位移随时间的变化关系分别为：L=-4．85×10^-4t^2＋0．209t＋27．4，L=48．875＋0．005t和L=49．564＋0．002t，并与致密化过程有很好的拟合。物相分析认为非晶相的生成影响了力学性能，恰当的保温时间在40～50min之间。     

Densification,microstructure, and mechanical properties of V-substituted HfB2-based ceramics

This study firstly developed Hf_1-xV_xB₂ (x = 0, 0.01, 0.02, 0.05) powders, which were derived from borothermal reduction of HfO₂ and V₂O₅ with boron. The results revealed that significantly refined Hf_1-xV_xB₂ powders (0.51 μm) could be obtained by solid solution of VB₂, and x ≥ 0.05 was a premise. However, as the content of V-substitution for Hf increased, Hf_1-xV_xB₂ ceramics sintered by spark plasma sintering at 2000 °C only displayed a slight densification improvement, which was attributed to the grain coarsening effect induced by the solid solution of VB₂. By incorporating 20 vol% SiC, fully dense Hf_1-xV_xB₂-SiC ceramics were successfully fabricated using the same sintering parameters. Compared with HfB₂-SiC ceramics, Hf_0.95V_0.05B₂-20 vol% SiC ceramics exhibited an elevated and comparable value of Vickers hardness (23.64 GPa), but lower fracture toughness (4.09 MPa m^1/2).     

玉米芯氨水预处理及酶解工艺研究

为有效提高木质纤维素酶解转化率,文中以玉米芯为研究对象,在常压中温下采用氨水浸泡工艺处理原料,考察了预处理条件对木质素脱除率和纤维素、半纤维素酶解转化率的影响规律。确定了最适预处理条件:氨水质量分数为15%、固液质量体积比为1∶6 g/mL、反应温度为60℃和预处理时间为12 h。该条件下纤维素、半纤维素回收率和木质素脱除率分别为94.5%,86.7%和48.1%;在每g葡聚糖加入30 FPU纤维素酶和60 CBUβ-葡萄糖苷酶条件下,酶解24 h后纤维素和半纤维素酶解转化率分别可达83.0%和81.6%。     

Adsorption kinetics of cadmium ions onto powdered corn cobs

Environmental pollution caused by the presence of toxic materials such as cadmium is becoming global problem and concern. This paper presents a report on kinetics of Cd²⁺ removal from aqueous solutions through adsorption using powdered corn cobs (PCC). Corn cobs were collected from a selected location, washed to remove sand, air dried, ground and sieved into different particle sizes. The selected properties of PCC were determined using acid digestion method. Adsorption capacities through kinetics of Cd²⁺ removal from synthetic solutions, typical raw water and domestic‐institutional wastewater were studied. Effects of pH, PCC particle size, initial concentration of Cd²⁺ and temperature on adsorption capacities were monitored through pseudo first‐ and second‐order models, Elovich and intraparticle diffusion models to present adsorption rate parameters. The study revealed that PCC contained 86.89% volatile solids, had 4.56% acid solubility, 0.52 water solubility and 2.33% ash content. PCC removed Cd²⁺ from aqueous solutions (synthetic, raw water, and wastewater). The relationship between time and concentration of Cd²⁺ remaining in the solution followed exponential functions with squared correlation coefficient ranging from 0.9928 to 0.9993, 0.8701 to 0.9284, and 0.8514 to 0.9290 for synthetic solution, raw water, and typical domestic‐institutional wastewater, respectively. Mechanism of cadmium adsorption onto PCC was in two separate stages linear portions in the first parts, while the final parts are curves indicating intraparticle diffusion. It was concluded that PCC is an effective adsorbent for Cd²⁺ removal. The estimated production cost was 0.068 USD as against 0.50, 2.12, and 3.12 USD for producing adsorbents from empty fruit bunches; pencom shell and sugar cane based activated carbons, respectively.     

Densification mechanism during reactive hot pressing of B4C-ZrO2 mixtures

The densification behaviors of pure B₄C and B₄C-ZrO₂ mixtures were compared during hot pressing. The results showed that in-situ formed ZrB₂ effectively enhanced the densification process of B₄C-ZrO₂ mixtures, more significantly during the intermediate stage. Within the relative density ranging from 0.75 to 0.90, the B₄C-15?wt%ZrO₂ mixture (B15Z) achieved the maximum densification rate as twice much as that of pure B₄C. The stress exponent n>3 indicated plastic deformation was the dominant densification mechanism of B15Z. The viscosities of plastic flow were evaluated using Murray-Rodger-William equation and the viscosity of B15Z was only a quarter of that in pure B₄C. The sintering activation energy was calculated to be 305.9?kJ/mol for pure B₄C and 197?kJ/mol for B15Z, respectively. It was proposed that the lower viscosity of plastic flow and activation energy accelerated the sliding and propagating motions of plastic flow, by which underlain the enhanced densification behaviors of B₄C-ZrO₂ mixtures.     

Densification and grain growth behaviour of high-purity MgO ceramics by hot-pressing

High-purity MgO ceramics with a relative density higher than 99.60% and a mean grain size of 8.1 µm were prepared by hot-pressing at 1450 °C and 35 MPa for 120 min. The MgO ceramic was 130 mm in diameter and 10 mm in height. The densification mechanism and grain growth of MgO powder during the sintering process were investigated based on the principles of general deformation and classical phenomenological kinetic theory. The threshold pressure of plastic deformation at the initial sintering stage was also analysed. The results suggest that plastic deformation is the dominant densification mechanism during the initial period and that an applied pressure of 20 MPa is sufficient for the deformation. During the final period, Mg²⁺ diffusion along the grain boundaries controls the densification process, and the grain growth activation energy at the final stage is estimated as 336.38±2.35 kJ mol⁻¹.     

Preparation of micro and nanoparticles from corn cobs xylan

Summary Xylan, a hemicelllulose extracted from corn cobs, was used to prepare micro and nanoparticles. First, a chemical evaluation of xylan extract was performed. Then, particles were prepared by a coacervation method based on neutralization of an alkaline solution with an acid solution. The influence of polymer content (2.85 to 100 mg/ml) and surfactant presence (0.6 to 1.8%_(v/v)) on the manufacturing process was evaluated. It was demonstrated that neutralization of the xylan solution with HCl or acetic acid was able to generate micro and nanoparticles and that surfactant concentration influences both the particle size stability and morphology. Therefore, the optimal concentration of surfactant was 1.5%_(v/v). Received: 16 January 2001/Revised version: 16 May 2001/Accepted: 16 May 2001     

The angle of repose of bulk corn stover particles

Lignocellulosic biomass feedstock such as corn stover, the residues left on the field after corn grain harvest, has been studied as one of the renewable feedstocks to be used for fuel ethanol conversion in the near future. The primary objective of this work was to determine the angle of repose (AoR) of bulk corn stover particles prepared to four particle sizes (chopped and particles screened through 6.4, 3.2 and 1.6 mm) at two moisture contents (dry, < 10% and wet, > 20%). The results show that particles size and feedstock moisture content were important variables that affected the angle of repose for all three angle of repose methods (piling AoR loose-base, piling AoR fixed-base and sliding AoR) investigated. In general, increasing moisture content and particle size increased the piling AoR (loose-base), piling AoR (fixed-base) and sliding angle of repose. Characterization of the flow behavior of bulk corn stover particles using the piling AoR (loose-base) and comparison with three granular bulk solids of biological origin (corn, soybean and distillers dried grains with solubles, DDGS) indicated that dry and wet stover particles of the particle size ranges tested in this study have a poor flow behavior.     

Densification and microstructure evolution of reactively sintered transparent spinel ceramics

Reactive sintering is an effective and simple method to prepare transparent spinel ceramics. In this research, transparent MgO·nAl₂O₃ (0.98?≤ n?≤?2) spinel ceramics were prepared via reactive sintering in air followed by hot isostatic press (HIP), using MgO and γ-Al₂O₃ powders as raw materials. The influence of composition on densification and microstructure evolution was systemically investigated. More importantly, the relationship between microstructure of presintered samples and final properties of transparent ceramics was singled out. Thermodynamically stable large pores were easily generated in magnesia-rich and stoichiometric samples after presintering in air, causing severe abnormal grain growth during the HIP treatment and poor optical quality of the resulting samples. The presintering temperature of alumina-rich samples widely varied with composition. No large pores were observed in the presintered sample, which was beneficial for the elimination of residual pores in the following HIP process. Highly transparent spinel ceramics with n?=?1.1 and 1.3 were successfully fabricated with the transmittance above 84% even at the short wavelength of 400?nm, close to the theoretical value.     

醋酸水解玉米芯中木聚糖的动力学

利用醋酸作为催化剂水解玉米芯中半纤维素来制备还原糖,测定了温度在160-200℃、固液质量比为1∶15、搅拌速度为500 r/min下,不同水解时间水解液中还原糖的收率以及副产物糠醛的收率.利用半纤维素高温液态水的Garrote模型拟合还原糖生成过程.实验表明,该模型能够较好地描述还原糖生成过程以及副产物糠醛的产生过程...     

In-situ solid solution of Mo or Cr in WB2: Densification,microstructure, and properties

Pure tungsten diboride (WB₂) ceramic prepared by the boro/carbothermal reduction combined with spark plasma sintering (SPS) of WB₂ can reach a relative density >90%. However, the final sintered density still needs further improvement to meet the application requirement. In this study, the WB₂ ceramics doped with Mo or Cr (W_0.95Mo_0.05B₂ and W_0.95Cr_0.05B₂) were prepared and the effects of Mo or Cr doping on powder characters, sintering behavior, microstructure, mechanical and physical properties of WB₂ were systematically investigated. The results showed that the average particle size of the WB₂ powders was increased significantly after adding either dopant, and the relative density of WB₂ ceramics was improved from ～93% to ～95% and 96% with Cr and Mo addition, respectively. However, the Vickers hardness of WB₂ with either dopant was reduced. On the other hand, the W_0.95Mo_0.05B₂ solid solution exhibited slight improvement on both of the thermal and electrical conductivity as compared with WB₂. But, both of the thermal and electrical conductivity of W_0.95Cr_0.05B₂ solid solution decreased significantly to about 50% of the values obtained for WB_2. The decrease in thermal and electrical conductivity of W_0.95Cr_0.05B₂ solid solution was mainly attributed to the formation of high concentration of atomic defects, i.e. dislocations.