Assessment of deterioration in RHA-concrete due to magnesium sulphate attack

The assessment of magnesium sulphate attack on concretes containing rice husk ash (RHA, 20wt% of the cementitious materials) with various average particle sizes was investigated. The total cementitious materials were 390 kg and the water-to-binder ratio (W/B) was 0.53 for all mixtures. Specimens were initially cured in water for 7 d and then immersed in the 3wt% magnesium sulphate solution for up to 111 d of exposure. The specimens were subjected to drying-wetting cycles to accelerate sulphate attack. In addition to the visual monitoring of the specimens, the concrete specimens were subsequently tested for compressive strength, dynamic modulus of elasticity, and length and mass changes. The results show that the specimens exposed to sulphate attack exhibit higher strength and dynamic modulus than those kept in water. The length change is negligible and can be attributed to the normal swelling of concrete. On the other hand, concretes suffers mass loss and surface spalling and softening; the fine RHA-concrete results in a better resistance. For the accelerated sulphate attack method used in this study, mass change and visual monitoring are recommended for assessing the deterioration degree and the effectiveness of supplementary cementitious materials to resist sulphate attack.     

Development of high volume rice husk ash alumino silicate composites

The development of high volume rice husk ash (RHA) alumino silicate composites (ASC) was studied. RHA was used as the source of silica and aluminium in the ASC. The mass ratios of RHA:Al(OH)3 of 70:30 to 99:1 were tested. The results indicate that the obtained ASC mortars are not stable and disintegrate in water. Boric acid was introduced to the mixture to overcome this problem. Stable ASC mortars with high RHA:Al(OH)₃ mass ratios of 90:10 to 97.5:2.5 were obtained with the use of boric acid and 115℃ curing. The compressive strength of the mortar of 20 MPa was gained. The immersion test indicates that high volume RHA ASC mortars show good resistance in 3vol% H₂SO₄ solution, but is slightly less durable in 5wt% MgSO₄ solution.     

Optimization of reaction conditions for the electroleaching of manganese from low-grade pyrolusite

In the present study, a response surface methodology was used to optimize the electroleaching of Mn from low-grade pyrolusite. Ferrous sulfate heptahydrate was used in this reaction as a reducing agent in sulfuric acid solutions. The effect of six process variables, including the mass ratio of ferrous sulfate heptahydrate to pyrolusite, mass ratio of sulfuric acid to pyrolusite, liquid-to-solid ratio, current density, leaching temperature, and leaching time, as well as their binary interactions, were modeled. The results revealed that the order of these factors with respect to their effects on the leaching efficiency were mass ratio of ferrous sulfate heptahydrate to pyrolusite > leaching time > mass ratio of sulfuric acid to pyrolusite > liquid-to-solid ratio > leaching temperature > current density. The optimum conditions were as follows: 1.10:1 mass ratio of ferrous sulfate heptahydrate to pyrolusite, 0.9:1 mass ratio of sulfuric acid to pyrolusite, liquid-to-solid ratio of 0.7:1, current density of 947 A/m2, leaching time of 180 min, and leaching temperature of 73℃. Under these conditions, the predicted leaching efficiency for Mn was 94.1%; the obtained experimental result was 95.7%, which confirmed the validity of the model.     

Cu-Zn-Al_2O_3 nanocomposites:study of microstructure,corrosion,and wear properties

Alumina nanoparticles were added to a Cu-Zn alloy to investigate their effect on the microstructural,tribological,and corrosion properties of the prepared alloys. Alloying was performed using a mixture of copper and zinc powders with 0vol% and 5vol% of α-Al nanopowder in a satellite ball mill. The results showed that the Cu-Zn solid solution formed after 18 h of mechanical alloying. The mechanically alloyed powder was compacted followed by sintering of the obtained green compacts at 750°C for 30 min. Alumina nanoparticles were uniformly distributed in the matrix of the Cu-Zn alloy. The tribological properties were evaluated by pin-on-disk wear tests,which revealed that,upon the addition of alumina nanoparticles,the coefficient of friction and the wear rate were reduced to 20% and 40%,respectively. The corrosion properties of the samples exposed to a 3.5wt% Na Cl solution were studied using the immersion and potentiodynamic polarization methods,which revealed that the addition of alumina nanoparticles reduced the corrosion current of the nanocomposite by 90%.     

Mechanical characterization of Mg-B_4C nanocomposite fabricated at different strain rates

Magnesium has wide application in industry. The main purpose of this investigation was to improve the properties of magnesium by reinforcing it using B_4C nanoparticles. The reinforced nanocomposites were fabricated using a powder compaction technique for 0, 1.5 vol%, 3 vol%,5 vol%, and 10 vol% of B_4C. Powder compaction was conducted using a split Hopkinson bar(SHB), drop hammer(DH), and Instron to reach different compaction loading rates. The compressive stress–strain curves of the samples were captured from quasi-static and dynamic tests carried out using an Instron and split Hopkinson pressure bar, respectively. Results revealed that, to achieve the highest improvement in ultimate strength, the contents of B_4C were 1.5 vol%, 3 vol%, and 3 vol% for Instron, DH, and SHB, respectively. These results also indicated that the effect of compaction type on the quasi-static strength of the samples was not as significant, although its effect on the dynamic strength of the samples was remarkable. The improvement in ultimate strength obtained from the quasi-static stress–strain curves of the samples(compared to pure Mg) varied from9.9% for DH to 24% for SHB. The dynamic strength of the samples was improved(with respect to pure Mg) by 73%, 116%, and 141% for the specimens compacted by Instron, DH, and SHB, respectively. The improvement in strength was believed to be due to strengthening mechanisms,friction, adiabatic heating, and shock waves.     

不同应变速率下Mg?B4C纳米复合材料的力学性能表征

Magnesium has wide application in industry. The main purpose of this investigation was to improve the properties of magnesium by reinforcing it using B₄C nanoparticles. The reinforced nanocomposites were fabricated using a powder compaction technique for 0, 1.5vol%, 3vol%, 5vol%, and 10vol% of B₄C. Powder compaction was conducted using a split Hopkinson bar (SHB), drop hammer (DH), and Instron to reach different compaction loading rates. The compressive stress–strain curves of the samples were captured from quasi-static and dynamic tests carried out using an Instron and split Hopkinson pressure bar, respectively. Results revealed that, to achieve the highest improvement in ultimate strength, the contents of B₄C were 1.5vol%, 3vol%, and 3vol% for Instron, DH, and SHB, respectively. These results also indicated that the effect of compaction type on the quasi-static strength of the samples was not as significant, although its effect on the dynamic strength of the samples was remarkable. The improvement in ultimate strength obtained from the quasi-static stress–strain curves of the samples (compared to pure Mg) varied from 9.9% for DH to 24% for SHB. The dynamic strength of the samples was improved (with respect to pure Mg) by 73%, 116%, and 141% for the specimens compacted by Instron, DH, and SHB, respectively. The improvement in strength was believed to be due to strengthening mechanisms, friction, adiabatic heating, and shock waves.     

Cu-Zn-Al2O3 nanocomposites:study of microstructure,corrosion,and wear properties

Alumina nanoparticles were added to a Cu-Zn alloy to investigate their effect on the microstructural, tribological, and corrosion properties of the prepared alloys. Alloying was performed using a mixture of copper and zinc powders with 0vol% and 5vol% of α-Al nanopowder in a satellite ball mill. The results showed that the Cu-Zn solid solution formed after 18 h of mechanical alloying. The mechanically alloyed powder was compacted followed by sintering of the obtained green compacts at 750℃ for 30 min. Alumina nanoparticles were uniformly distributed in the matrix of the Cu-Zn alloy. The tribological properties were evaluated by pin-on-disk wear tests, which revealed that, upon the addition of alumina nanoparticles, the coefficient of friction and the wear rate were reduced to 20% and 40%, respectively. The corrosion properties of the samples exposed to a 3.5wt% NaCl solution were studied using the immersion and potentiodynamic polarization methods, which revealed that the addition of alumina nanoparticles reduced the corrosion current of the nanocomposite by 90%.     

利用回收磷青铜片经热挤压法制备的磷青铜/铝两相材料及其组织和力学性能的研究

Despite the existence of conventional methods for recycling chips, solid-state techniques have become popular, whereby waste metals are directly recycled into consolidated products with the desired shapes and designs. We investigated the feasibility of recycling phosphor bronze chips through a hot extrusion process using aluminum powder as a metal binder for the fabrication of a metal-fiber-reinforced aluminum matrix composite. To do so, mixtures containing 20vol%–50vol% of chips were prepared, cold-compacted, and extruded. The quality of the consolidated samples was evaluated by determining the density of the fabricated composites and studying their microstructures. In addition, we performed tensile and hardness tests to evaluate the mechanical properties of the fabricated composites. We also analyzed the fracture surfaces of the samples to study the fracture mechanism as a function of the volume fraction of phosphor bronze chips in the fabricated composite. The results indicated that the most effective consolidation occurred in the sample containing 20vol% of chips extruded at 465°C in which the chips serve as ideal fibers for improving the mechanical properties, especially the ultimate tensile strength, in comparison with those of Al matrixes that contain no chips but are produced under the same conditions.     

Fabrication of phosphor bronze/Al two-phase material by recycling phosphor bronze chips using hot extrusion process and investigation of their microstructural and mechanical properties

Despite the existence of conventional methods for recycling chips, solid-state techniques have become popular, whereby waste metals are directly recycled into consolidated products with the desired shapes and designs. We investigated the feasibility of recycling phosphor bronze chips through a hot extrusion process using aluminum powder as a metal binder for the fabrication of a metal-fiber-reinforced aluminum matrix composite. To do so, mixtures containing 20 vol%–50 vol% of chips were prepared, cold-compacted, and extruded. The quality of the consolidated samples was evaluated by determining the density of the fabricated composites and studying their microstructures. In addition, we performed tensile and hardness tests to evaluate the mechanical properties of the fabricated composites. We also analyzed the fracture surfaces of the samples to study the fracture mechanism as a function of the volume fraction of phosphor bronze chips in the fabricated composite. The results indicated that the most effective consolidation occurred in the sample containing 20 vol% of chips extruded at 465°C in which the chips serve as ideal fibers for improving the mechanical properties, especially the ultimate tensile strength, in comparison with those of Al matrixes that contain no chips but are produced under the same conditions.     

Effects of process parameters on nonaqueous gelcasting for copper powder

An approach to fabricate sintered copper with high green strength and high sintered density using nonaqueous gelcasting technology is presented in this study. The effects of various gelcasting processing parameters such as monomer content, monomer/crosslinker ratio, initiator content, dispersant dosage, and temperature on the flexural strength of dried green bodies and the relative density of sintered bodies were studied to obtain better microstructures and properties. The appropriate process parameters obtained for copper gelcasting are as follows: monomer content, 20vol%–30vol% (based on the total volume of reagents); monomer/crosslinker ratio, 10:1 to 20:1; initiator content, 3vol%–4vol% (based on the volume of the monomer); dispersant dosage, 1.5wt%–2.5wt% (based on the mass of the copper powder); and reaction temperature, 65–75℃.     

Effects of cellulose nanocrystals on the acid resistance of cementitious composites

Acid mine drainage presents an important threat to cementitious structures. This study is aimed at investigating the effect of cellulose nanocrystals(CNCs) on the acid resistance of cementitious composites. CNCs were added to mortar mixtures as additives at cement volume ratios of 0.2 vol%, 0.4 vol%, 1.0 vol%, and 1.5 vol%. After 28 d of standard curing, the samples were immersed in a sulfuric acid with a p H value of 2 for 75 d. The unconfined compressive strength(UCS) test, the density, water absorption, void volume test, and thermogravimetric analysis were carried out to investigate the properties of CNC mixtures before sulfuric acid immersion. It was found that the addition of CNC reduced the volume of permeable voids and increased the hydration degree and mechanical strength of the samples. Changes in mass and length were monitored during immersion to evaluate the acid resistance of mixtures. The mixture with 0.4 vol% CNC showed a reduced mass change and length change indicating its improved acid resistance.     

具有结构色的生物质纳米纤维的制备与表征

 采用硫酸水解联合高压均质化,制备了生物质纳米纤维素晶体（CNC）,经超声波处理诱导自组装形成手性排列,并研究了其自组装膜的结构色特征。扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察显示,纤维素纳米晶体尺寸均一,多呈短棒状,具备形成手性排列的结构基础。表面电势、流变性能及偏光特性研究表明,水解时硫酸浓度越高,生成的CNC表面Zeta电位绝对值越大,黏度越大,越利于形成手性排列,从而产生良好的偏光性;CNC经超声波处理有助于自组装成“光子晶体”,显示出较好的结构色。     

酸性环境中富水充填材料腐蚀及劣化机理

为了研究酸性环境对富水充填材料的影响,通过强度检测、扫描电镜、能谱分析及X射线衍射( XRD)等实验手段,分析富水充填材料在酸性环境中浸泡后的宏观性能及微观结构变化,并探讨其腐蚀及劣化机理.结果表明：富水充填材料在pH值为1和3的盐酸溶液中浸泡180 d后抗压强度比标养28 d的强度分别降低88.8%和58%,在pH值为3的硫酸溶液中浸泡后降低68%,pH值为1的硫酸溶液中浸泡后强度降为零;微观实验结果显示随着富水充填材料在硫酸溶液中浸泡时间的延长,试件内部有二水石膏生成,盐酸溶液中试件仅在pH值为1的溶液中浸泡180 d后产生二水石膏;盐酸溶液对富水充填材料的腐蚀主要为H+中和作用下硬化体结构的溶解腐蚀,硫酸溶液对材料的腐蚀为硬化体结构的溶解腐蚀和石膏的膨胀腐蚀;硫酸溶液对富水充填材料的腐蚀作用强于盐酸溶液.     

复合胶凝材料的抗硫酸性能与腐蚀动力学分析

通过硫酸浸泡腐蚀试验,研究矿粉单掺、硅灰-矿粉双掺2种复合胶凝材料体系的抗硫酸腐蚀性能.以质量损失、酸消耗量和腐蚀深度等为测试指标,研究了硬化水泥石在硫酸溶液中的劣化性能.结果表明,硫酸溶蚀水泥石形成的疏松腐蚀层可避免内部水泥石与酸直接接触,具有减缓酸腐蚀的作用.根据不同腐蚀时间的腐蚀深度建立了硬化水泥石的酸腐蚀动力学方程d=Ktn,d和t分别为腐蚀深度和腐蚀时间,K和n为试验拟合指数.据此可推算水泥石一定腐蚀时期的腐蚀深度,为混凝土结构设计、维修和防护等提供参考.     

硫酸溶液对水泥土强度影响的试验研究

通过由硫酸污染土配制成的水泥土室内模拟试验,对不同硫酸质量比条件下,一定水泥掺量的水泥土试件外观特征及无侧限抗压强度进行实时观测和记录,得到硫酸水泥污染土试件表观特征照片和抗压强度变化曲线;试验结果分析表明,硫酸对水泥土外表形态影响不大,没有出现开裂、起皮等现象,但是对水泥土外表颜色和力学强度产生了明显影响,由污染土配制成的水泥土颜色较干净土配制成的水泥土颜色有了明显变化;硫酸质量比不同,水泥土强度存在很大差异,得出除硫酸质量比为9 000 mg/kg外,其他硫酸质量比条件下的水泥土强度在90 d龄期时均有不同程度的降低,并且探索性地讨论了硫酸导致强度发生变化的原因,文章对水泥土在硫酸污染条件下的应用及工程设计具有一定参考价值.     

高温浓硫酸中氟离子掺入对不锈钢耐蚀性能的影响

采用浸泡法和电化学测试方法结合扫描电镜和能谱仪研究了高温浓硫酸中氟离子的掺入对304、2507以及904L三种不锈钢耐蚀性能的影响.结果表明:氟离子的掺入对三种不锈钢在浓硫酸中的腐蚀具有抑制作用,综合来看,904L具有更为稳定的耐蚀性能;三种不锈钢在高温浓硫酸中由于生成了热力学不稳定的硫化镍而产生了活化转钝化现象,而掺入氟离子会和硫离子发生竞争使其排挤出电极表面,氟离子与镍离子结合形成另外一种更稳定的阻挡层使不锈钢耐蚀性提高.     

硫酸中香蕉皮还原低品位锰矿的浸出行为及动力学模型

Manganese was leached from a low-grade manganese ore (LGMO) using banana peel as the reductant in a dilute sulfuric acid medium. The effects of banana peel amount, H₂SO₄ concentration, reaction temperature, and time on Mn leaching from the complex LGMO were studied. A leaching efficiency of ~98% was achieved at a leaching time of 2 h, banana peel amount of 4 g, leaching temperature of 120°C, manganese ore amount of 5 g, and sulfuric acid concentration of 15vol%. The phase, microstructural, and chemical analyses of LGMO samples before and after the leaching process confirmed the successful leaching of manganese. Furthermore, the leaching process followed the shrinking core model and the leaching rate was controlled by a surface chemical reaction (1 ? (1 ? x)1/3 = kt) mechanism with an apparent activation energy of 40.19 kJ·mol?1.     

纳米纤维素丙烯腈-丁二烯-苯乙烯复合材料的特性

为了改善纳米纤维素晶须(CNC)在非亲水性树脂中应用时分散困难、热分解温度低、与基体相容性较差等缺点,将冷冻干燥的纳米纤维素在高聚物的有机溶液中预先包覆,然后与苯乙烯-丁二烯-丙烯腈树脂(ABS)、马来酸酐接枝聚乙烯在挤出机内熔融共混制成ABS/CNC复合材料。通过扫描电镜(SEM)、热重分析测试(TGA)、拉伸性能测试等手段对复合材料进行性能表征。SEM观察发现CNC是以层状纳米片的形式均匀地与ABS复合; 力学性能测试表明,接枝聚乙烯的加入有利于改进CNC与ABS的界面相容性,与纯ABS相比,添加0.7%CNC的复合材料其拉伸强度提高了15.6%,弹性模量提高了52%。TGA测试结果表明,CNC的热分解温度由211 ℃提高到263 ℃,大大改善了CNC在聚合物加工过程中的温度适应性。     

不同化学结合剂对铜氧化物的团聚和浸出行为

The chemical binder is one of the critical factors affecting ore agglomeration behavior and leaching efficiency. In this study, we investigated the effect of the type of binder and mass fraction of the H₂SO₄ solution used on the curing, soaking, and leaching behavior of agglomerations. The results revealed that Portland cement (3CaO·SiO₂, 2CaO·SiO₂, and 3CaO·Al₂O₃) was the optimal binder for obtaining a well-shaped, stable agglomeration structure. A higher extraction rate was achieved when using Portland cement than that obtained using sodium silicate, gypsum, or acid-proof cement. An excessive geometric mean size is not conducive to obtaining well-shaped agglomerations and desirable porosity. Using computed tomography (CT) and MATLAB, the porosity of two-dimensional CT images in sample concentrations L1–L3 was observed to increase at least 4.5vol% after acid leaching. Ore agglomerations began to be heavily destroyed and even to disintegrate when the sulfuric acid solution concentration was higher than 30 g/L, which was caused by the excessive accumulation of reaction products and residuals.