The effect of zinc cyanide on the flotation of gold from pyritic ore

In gold processing plants, the process water contains a considerable amount of weak acid dissociable (WAD) cyanide species. The cyanide-containing water recycled to flotation circuits has a deleterious effect on mineral flotation. Zinc cyanide can be a major constituent of the process water due to the cyanide leaching of zinc minerals and the zinc cementation applied to precipitate gold and silver. In the present study, the effect of zinc cyanide on the flotation of gold from a pyritic ore was evaluated and the competitive adsorption between zinc cyanide species and the collector, potassium amyl xanthate (PAX) or Aerophine promoter (3418A), on gold was studied by surface enhanced Raman spectroscopy (SERS). It was found that free cyanide did not depress the flotation of liberated gold, but zinc cyanide with a CN/Zn ratio of 2 did. The depression of gold flotation by zinc cyanide was due to the preferential adsorption of Zn(CN)₂ on gold surface over either 3418A or amyl xanthate in the solution, rendering gold surface hydrophilic.     

Achieving the best glass former in a binary Gd–Co alloy system

In this work, the best glass former in a binary Gd–Co alloy system has been designed by thermodynamic parameter γ^⁎, which has been proved to be valid in the prediction of glass forming ability (GFA) of other binary alloys. A metastable phase has been observed in some Gd–Co melt-spun ribbons and its composition has been ascertained. By analyzing the effect of the metastable phase on the GFA of the Gd–Co binary alloys, we predict the Gd₅₀Co₅₀ alloy as the best glass former in the binary alloy system. The prediction has been confirmed by the experimental results, proving the validity of the parameter γ^⁎ in the Gd–Co binary alloys.     

Effects of heat treatment on the mechanical properties at elevated temperatures of plain-woven SiC/SiC composites

The effects of heat treatment on the mechanical properties of plain-woven SiC/SiC composites at 927 °C and 1200 °C in argon were evaluated through tensile tests at room temperature and at elevated temperature on the as-received and heat-treated plain-woven SiC/SiC composites, respectively. Heat treatment can improve the mechanical properties of composites at room temperature due to the release of thermal residual stress. Although heat treatment can damage the fiber, the effect of this damage on the mechanical properties of composites is generally less than the effect of thermal residual stress. Heat treatment will graphitize the pyrolytic carbon interface and reduce its shear strength. Testing temperature will affect the expansion or contraction of the components in the composites, thereby changing the stress state of the components. This study can provide guidance for the optimization of processing of ceramic matrix composites and the structural design in high-temperature environments.     

型砂级配对树脂砂抗拉强度的影响

采用呋喃树脂为型砂粘结剂,研究了型砂的不同级配对砂型抗拉强度的影响.研究结果表明:当采用单筛砂时,抗拉强度值较低.当采用40/70的三筛砂、40#的配比在10％～20％时,σ1为0.50～0.82 MPa,σ2～σ２４为1.05～1.90 MPa；采用50/100的三筛砂、100#的配比小于10％时,σ1为0.35～0.58 MPa,σ2～σ24为0.62～1.42 MPa.当采用40/100的四筛砂、40#的配比为5％～10％且100#的配比为5％～15％时,σ1为0.32～0.46 MPa,σ2～σ24为0.50～1.35 MPa;当采用50/140的四筛砂、140#的配比为5％～10％时,σ1为0.20～0.35 MPa,σ2～σ24为0.35～1.05 MPa.只要适当提高级砂的粒度,抗拉强度将会提高.     

Fabrication of surface-treated BN/ETDS composites for enhanced thermal and mechanical properties

The ceramic/polymer composites based on epoxy-terminated dimethylsiloxane (ETDS) and boron nitride (BN) were prepared for use as thermal interface materials (TIMs). 250 µm-sized BN was used as a filler to achieve high-thermal-conductivity composites. To improve the interfacial adhesion between the BN particles and the ETDS matrix, the surface of BN particles were modified with silica via the sol–gel method with tetraethyl orthosilicate (TEOS). The interfacial adhesion properties of the composites were determined by the surface free energy of the particles using a contact angle test. The surface-modified BN/ETDS composites exhibited thermal conductivities ranging from 0.2 W/m K to 3.1 W/m K, exceeding those of raw BN/ETDS composites at the same weight fractions. Agari׳s model was used to analyze the measured thermal conductivity as a function of the SiO₂-BN concentration. Moreover, the storage modulus of the BN/ETDS composites was found to increase with surface modification of the BN particles.     

Periodic inspection of gauge cutter wear on EPB TBMs using cone penetration testing

Cutterhead maintenance is usually required when the gauge cutters (over-cutters) wear down to the shield diameter. In soft ground pressurized shielded TBMs, inspection of gauge cutters usually involves complete stoppage of the operation. This can be a dangerous, costly, and time consuming process. In this study, a novel approach has been developed to monitor gauge cutter wear by considering the relationship between the overcut length and the length of the gauge cutters. By using the proposed testing system, frequent monitoring of gauge cutter length is possible at appropriate intervals during ring builds or maintenance without the need to enter the harsh environment of the excavation chamber. This monitoring system was used within an EPB TBM during the excavation of the University Link Light Rail Tunnel (U230) in Seattle, WA.     

杭州国际会议中心主楼与裙房的结构体系及相互影响

介绍了杭州国际会议中心的概况及结构特殊性,通过对其结构自振特性、层间地震剪力、楼层层间位移角、楼层的刚重比、主要构件的强度等方面的分析,对主楼和裙房的结构体系和相互影响进行研究,得到其内在的联系,以指导设计。     

Comfort design and optimization of direct expansion multi-connected radiant air conditioning based on 3D flow field simulation

The air conditioning method based on radiation heat exchange has the characteristics of small vertical temperature gradient, high thermal comfort and energy saving, and has become a hot spot of attention. The Fluent numerical simulation, the experiment in this paper studies the direct expansion multi-line radiant air conditioner under the artificially simulated climate environment in winter heating, summer cooling and dehumidification. The temperature difference of the radiation + fresh air mode at the same time indoors under heating conditions is less than 2.5 °C, and the time to reach the indoor set temperature of 24 °C is about 2–3 h. Under cooling conditions, the temperature difference of the radiation + fresh air mode at the same time in the room is about 0.5–2 °C, and the time to reach the indoor set temperature of 26 °C is about 1–3 h. In the fresh air mode, the indoor temperature difference and response time at the same time are slightly larger than the radiation + fresh air mode. The freezing and dehumidification effect of fresh air is obvious, the moisture content of dehumidifying fresh air is between 6.3 and 10.5 g/kg, and the dehumidification efficiency can reach 50%. Under the same artificial simulated climate environment, the consumption of the three modes is not much different. When the outdoor temperature in heating conditions is higher than 9 °C, the fresh air mode can get better, and the radiation + fresh air mode can achieve better comfort when running indoors under various conditions.     

The impact of hydrogen addition to natural gas on flame stability

Injecting hydrogen into existing natural gas networks is a promising step to mitigate global warming. However there is little evidence showing that how much degree of hydrogen admixture can be accepted. Experiments on populations of gas appliances are not available at present, thus a unified estimation method is required. First, a single-port burner was experimentally evaluated using methane-hydrogen mixtures (hydrogen percentage: 0–50%vol, unburned mixture temperature:373–573K, equivalence ratio:0.8–2). Mathematical formulae of the critical boundary velocity gradient, which quantitatively depict the relationships between flashback, lifting and hydrogen percentage, temperature were provided. A multi-ports burner was subsequently assessed, and the results of the two burners showed good agreement. An analysis method for changes in the flame stability region and gas source replacement decision was proposed based on curves of the flashback and lifting limits. This work provides an important basis for introducing hydrogen into gas networks and the design and adjustment of gas appliances.