Dissolution processes,hydrolysis and condensation reactions during geopolymer synthesis: Part I—Low Si/Al ratio systems

Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial charge model (PCM). For metakaolin powders activated with 5.0 M NaOH, solid-state nuclear magnetic resonance (NMR) spectra disclose the existence of monomeric [Al(OH)₄]⁻ species after two hours of dissolution, consistent with PCM predictions. However, no equivalent monomeric silicate species were observed for 5.0–10.0 M NaOH activator solutions characteristic of systems with nominal Si/Al ≤ 1. The apparent absence of monomeric silicate species suggest rapid condensation of silicate units with [Al(OH)₄]⁻ to generate aluminosilicate species, as indicated by the evolution of the shoulder at around −87 ppm in the ²⁹Si NMR spectra. Of the two possible stable silicate species [SiO₂(OH)₂]²⁻ and [SiO(OH)₃]⁻, the latter appears most likely to condense with [Al(OH)₄]⁻ to produce aluminosilicate oligomers, from which larger oligomers subsequently form through further condensation with [Al(OH)₄]⁻ leading to a gradual build up of aluminosilicate networks and a lowering of system alkalinity. This dissolution and hydrolysis sequence at the early stages of synthesis suggests a reaction path wholly consistent with predictions of the partial charge model.     

Dissolution processes,hydrolysis and condensation reactions during geopolymer synthesis: Part II. High Si/Al ratio systems

The mechanisms of speciation of aluminate and silicate phases during dissolution and condensation stages of alumino-silicate geopolymer reactions characterised by Si/Al ≥ 3, have been investigated and the results compared to predictions of the partial charge model. Solid-state nuclear magnetic resonance (NMR) traces indicate that free [Al(OH)₄]⁻ species, present in lower silicate formulations such as Si/Al ≤ 1, do not occur in the present systems, suggesting that the condensation reaction between [Al(OH)₄]⁻ and silicate species is fairly quick and is consumed as soon as it is formed. This observation is also consistent with both calorimetric measurements and model predictions, as the condensation time increased exponentially with increased Si/Al ratio in the geopolymeric phase, indicating again that the high content of Al species in the gel phase greatly enhanced the condensation rate. The experimental observations suggest that the condensation process in these systems occurs in two stages: (a) quick condensation between aluminate and silicate species; followed by (b) a slow condensation stage solely involving silicate species.     

彩钢岩棉夹芯屋面板、墙面板节点性能研究

为了掌握彩钢岩棉夹芯屋面板、墙面板与檩条的螺钉连接节点抗拉破坏机理,采用理论分析、试验验证及有限元模拟相结合的方法研究了不同钢板厚度及芯材厚度时节点破坏情况.分析结果表明:屋面板节点连接破坏是由于钢板局部屈曲引起的,墙面板则是钢板被冲剪破坏造成的,同时,结合对有限元模拟结果的回归,提出了节点承载力设计公式,可为以后节点设计提供参考.增加岩棉刚度及其与侧向钢板的粘结,或增加钢板厚度对提高屋面板节点极限承载力起着重要作用.     

Effect of ultrasonic vibration on the dechromisation corrosion of a CuCr alloy in HCl solution

The effect of ultrasonic vibration on the dechromisation corrosion of a CuCr alloy in HC1 solution was studied and the corrosion mechanisms were analyzed. It is found that ultlasonic vibration reduces the dechromisation incubation time, accelerates the dechromisafion corrosion rate, decreases the temperature and concentration of HC1 solution, and when the dechromisation occurs it seriously weakens the microstmcture of dechromisation layer. It is concluded that ultrasonic vibration can accelerate destruction of the passivation film on the Cr surface and increase the activities of Cl^- and Cr.     

Accelerating the kernel-method-based feature extraction procedure from the viewpoint of numerical approximation

The kernel method suffers from the following problem: the computational efficiency of the feature extraction procedure is inversely proportional to the size of the training sample set. In this paper, from a novel viewpoint, we propose a very simple and mathematically tractable method to produce the computationally efficient kernel-method-based feature extraction procedure. We first address the issue that how to make the feature extraction result of the reformulated kernel method well approximate that of the naïve kernel method. We identify these training samples that statistically contribute much to the feature extraction results and exploit them to reformulate the kernel method to produce the computationally efficient kernel-method-based feature extraction procedure. Indeed, the proposed method has the following basic idea: when one training sample has little effect on the feature extraction result and statistically has the high correlation with regard to all the training samples, the feature extraction term associated with this training sample can be removed from the feature extraction procedure. The proposed method has the following advantages: First, it proposes, for the first time, to improve the kernel method through formal and reasonable evaluation on the feature extraction term. Second, the proposed method improves the kernel method at a low extra cost and thus has a much more computationally efficient training phase than most of the previous improvements to the kernel method. The experimental comparison shows that the proposed method performs well in classification problems. This paper also intuitively shows the geometrical relation between the identified training samples and other training samples.     

基于AMR传感器的车辆检测算法

深入研究了各向异性磁阻(AMR)传感器的数据采集原理和特征波形向量提取方法,提出了一种基于AMR传感器的车辆检测算法:自适应状态机的车辆检测算法。该算法可以自适应地更新阈值和基线,利用状态机,达到对车辆的准确和高效的检测。可以用于检测道路交通车流量,也可以应用在大型停车场的车辆诱导系统。     

基于有限元模型的超声切割刀优化设计

超声切割刀在材料加工领域中有广泛的应用前景,可用于切割各种复合材料等硬脆材料。该文利用ANSYS有限元分析软件建立超声切割刀的有限元模型,对其进行模态分析和谐响应分析。仿真结果显示,超声切割刀在40kHz频率附近存在轴向纵振模态,其振动节点位于安装环和压电陶瓷中心线上,符合设计要求。基于有限元模型研制超声波切割刀,通过阻抗分析仪与激光多谱勒测振仪对换能器的固有频率与响应进行测试,获得的超声切割刀阻抗曲线平滑,谐振频率为40.261kHz,设计误差为0.83%,最大振幅达到14.52μm,结果与有限元计算相互吻合。     

Distribution of contact pressure over the surface of ceramic floor tiles during the polishing process

Assisted with computational simulation this work quantitatively determined the distribution of contact pressure over the surface of porcelain stoneware tiles during the industrial polishing process. In modern polishing lines there are basically three movements responsible for the scratching velocity and the position of the abrasives. Combining the kinematic equations obtained by these movements with a pre-existing model the contact pressure between abrasive tool and tile surface could be determined as function of time. The spatial distribution of average, standard deviation and maximum values of contact pressure were then obtained and mapped over the entire surface. The simulation results showed that the contact pressure tends to be 50% higher near to the center, in regions worked by the innermost abrasives. Additionally, periodical variations of up to 10% were found to occur due to the partial retreat of the abrasive tool.     

碳纳米管增强铜－石墨复合材料电刷的制备与性能研究

采用粉末冶金法制备了碳纳米管增强铜-石墨复合材料电刷,研究了碳纳米管对铜-石墨电刷静态和动态性能的影响。结果表明：碳纳米管的加入增加了铜-石墨电刷的破碎力和硬度,对电刷的电阻率影响不大。碳纳米管的加入使铜-石墨电刷的摩擦系数减小,并减少了电刷的磨损率,提高了电刷的使用寿命。