铜陵地区新桥矿田银金矿化特征及成因探讨

在新桥矿田内银金矿体与硫铁矿体的时空关系研究基础上认为,矿田内的银金矿化是早期硫铁矿化基础上的叠加矿化所致,二者受不同的构造控制,矿化特征明显不同。叠加的银金矿化与包村、朝山、狮子山矿田中的金（银）矿化类似,金矿物均与铋矿物具密切的时空及成因联系,矿石中Au、Ag与Bi呈正相关。该认识对区内独立和伴生金银矿成因研究及找矿工作均具有一定的指导意义。     

广东信宜合水-钱排银金多金属找矿远景及矿床分类

以信宜合水-钱排银金多金属矿区的区域成矿地质背景、区域地球物理特征及区域地球化学特征为入手点,对各类金矿床(点)的地质特征进行研究,并对其成因进行了分类,探讨各类矿床成矿规律,提出了下一步找矿工作的建议.     

Eutectic nucleation and growth in hypoeutectic Al-Si alloys at different strontium levels

The effects of different levels of strontium on nucleation and growth of the eutectic in a commercial hypoeutectic Al-Si foundry alloy have been investigated by optical microscopy and electron backscattering diffraction (EBSD) mapping by scanning electron microscopy (SEM). The microstructural evolution of each specimen during solidification was studied by a quenching technique at different temperatures and Sr contents. By comparing the orientation of the aluminum in the eutectic to that of the surrounding primary aluminum dendrites by EBSD, the eutectic formation mechanism could be determined. The results of these studies show that the eutectic nucleation mode, and subsequent growth mode, is strongly dependent on Sr level. Three distinctly different eutectic growth modes were found, in isolation or sometimes together, but different for each Sr content. At very low Sr contents, the eutectic nucleated and grew from the primary phase. Increasing the Sr level to between 70 and 110 ppm resulted in nucleation of independent eutectic grains with no relation to the primary dendrites. At a Sr level of 500 ppm, the eutectic again nucleated on and grew from the primary phase while a well-modified eutectic structure was still present. A slight dependency of eutectic growth radially from the mold wall opposite the thermal gradient was observed in all specimens in the early stages of eutectic solidification.     

Microstructure,phase composition and wear resistance of low valence electron concentration AlxCoCrFeNiSi high-entropy alloys prepared by vacuum arc melting

The low valence electron concentration(VEC)AlxCoCrFeNiSi(x = 0.5,1.0,1.5 and 2.0)high-entropy alloys(HEAs)were designed by the fundamental properties of the con...     

Environmental fatigue crack propagation of aluminum alloys at low stress intensity levels

Environmental fatigue crack propagation in 2024-T3, 7075-T6, and 7178-T6 has been studied at low levels of cyclic amplitude of stress intensity, ΔK. Both wedge force loading and remote loading techniques were employed to achieve the desired ΔK levels, and preliminary experiments were designed to test their compatibility. Testing was carried out in humid air, distilled water, and 3.5 pct sodium chloride solution, and the observed crack growth rates compared with those in desiccated air. Later studies were also conducted in an inert reference environment with a total water content of less than 2 ppm. When the data are plotted as log ΔK vs log d2a /dN, alloy 2024-T3 exhibits a marked slope transition, alloy 7075-T6 a slight slope transition, and alloy 7178-T6 a rectilinear behavior throughout the whole range of ΔK studied. The basic shape of these curves is discussed in terms of state-of-stress conditions at the crack tip, frequency effects, environmental effects, strain rate sensitivity, and metallurgical structure. An attempt is also made to correlate the rate of fatigue crack propagation in a particular environment and at a particular ΔK level with the fracture topography.     

The influence of interfacial energies and gravitational levels on the directionally solidified structures in hypermonotectic alloys

Several Cu-Pb-Al alloys were directionally solidified under one-g conditions and alternating high-g/low-g conditions in order to determine the influence of interfacial energies and gravitational levels on the resulting microstructures. The low-g conditions were obtained through use of NASA's KC-135 aircraft. In the Cu-Pb-Al system, changes in the Al content are known to result in variations in the interfacial energy relationships between the phases. Theory predicts that this should lead to a transition from an irregular to a regular, aligned microstructure in monotectic composition alloys. Four different hypermonotectic alloy compositions were used in this study in order to vary systematically the interfacial energies between the phases. Preliminary results indicate microstructural variations between control and flight samples and samples processed at different rates under both one-g and high-g/low-g conditions. In addition, directional solidification of low Al content alloys resulted in samples with coarse, irregular microstructures, as compared to finer, more aligned microstructures in alloys with high Al contents. This was seen in samples processed under both one-g and high-g/low-g conditions. The resulting structures have been related to interfacial energies, growth rates, and gravitational levels. This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research” presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25–29, 1988, under the auspices of the ASM/MSD Thermodynamic Data Committee and the Material Processing Committee.     

The role of valence in attempted thought suppression

Thought control was investigated in participants (N = 72) who were shown either a violent, humorous or neutral film and then administered either suppression or nonsuppression instructions. Following the presentation of a three minute segment from one film, participants monitored their thoughts for two 3-minute periods. In Period 1, participants were administered suppression or nonsuppression instructions relating to thoughts of the film. In Period 2, participants were instructed to think about anything. During both periods participants were instructed to press a response button if they had a trauma-related thought. Participants who viewed the violent film gave higher ratings of distress and lower pleasantness ratings than those who viewed the humorous and neutral films. Participants who were given suppression instructions demonstrated a delayed increase in trauma-related thoughts in the period subsequent to suppression across the valence conditions.     

锰锌铁氧体中锰平均价态的分析

根据锰锌铁氧体含铁量高的特点,通过绘制按比例添加硫酸铁的高锰酸钾标准溶液的工作曲线,采用分光光度法测定锰锌铁氧体中的总锰含量。然后采用高锰酸钾标准溶液反滴草酸钠的方法测定其中高价锰含量,从而得到还原电子数,结合总锰含量得出其锰的平均价态。对测定总锰含量的条件,如pH值、草酸钠和过硫酸铵的用量等进行了详细的研究。     

Splitting Failures in Trapezoidal Steel Roof Cladding

High wind events such as hurricanes and storms often cause severe damage to crest-fixed thin steel roof claddings. Past research on wind damage has shown that low cycle fatigue cracking of steel roof sheeting around the fastener holes has been the reason for the premature pull-through failures of roof claddings under fluctuating wind forces. Such a situation will be at its worst if the roof sheeting is already split at the fastener holes. An inspection of trapezoidal steel roofs has shown that roofing has been split in the transverse direction due to overtightening of screw fasteners accidental or caused by poor workmanship. Once split, even slightly, the roofing can survive only a few cycles of wind uplift loading. Therefore an investigation using laboratory experiments and finite element analyses was carried out to study the splitting behavior of two commonly used high tensile steel trapezoidal roof claddings. The analytical and experimental results agree reasonably well and present a good understanding of the splitting behavior of trapezoidal roof claddings. This paper presents the details of this investigation and the results.