Formation of methane hazard in longwall coal mines with increasingly higher production capacity

Directional drilling has been established in the coal industry as a viable means of gas drainage, exploration and water management. But the environment in and around coal seams is not always conducive to stable conditions while drilling and borehole stability after the drilling has been completed. This paper identifies the conditions which cause unstable drilling conditions and the various means which are used to attempt to manage or bypass those conditions. Ultimately, equipment does become bogged in these adverse environments and requires recovery by over-coring.     

Preparation and characterization of directional conducting and lower methanol permeable ultrathin membrane based on poly (vinyl alcohol) and imidazolium compounds

To produce directional conducting and lower methanol permeable ultrathin membrane for fuel cell, the imidazolium salt as both cross-linking agent and proton donor has been designed to build a directional proton conducting channel in a poly (vinyl alcohol)-based membrane. The methanol permeability of directional conducting membrane is very low, which is about twice smaller than that of Nafion₁₁₇. In addition, the membranes show a relatively high oxidative durability in H₂O₂ solutions, with only about 10% weight loss after the membrane being immersed in 3% H₂O₂ solution for 120 h. All the properties of prepared directional conducting membrane indicate their promising prospects in proton conducting membrane applications.     

Electrical resistivity distribution of silicon ingot grown by cold crucible continuous melting and directional solidification

A multicrystalline silicon ingot was grown by cold crucible continuous melting and directional solidification. The electrical resistivity, shallow level impurities׳ concentrations and microstructure of the ingot were measured, and their relationships were studied and discussed. The results show that in the vertical direction the electrical resistivity gets its maximum value at the height of 90 mm and then decreases toward both sides. In the horizontal direction, it is distributed uniformly in the inner area and increases slightly in the peripheral area. The electrical resistivity of the silicon ingot is affected by its shallow level impurities׳ concentrations and its microstructure. Among these impurities the effect of Al is less than those of B and P, since Al tends to form complex precipitates with other elements.     

Microstructure evolution of directionally solidified Nb–Si alloy

Abstract

By taking the method of liquid–metal cooled directional solidification, alloys with a nominal composition of Nb–14Si–24Ti–10Cr–2Al–2Hf (at-%) were prepared under different conditions. Alloys were initially directional solidified with different withdrawal rates (R?=?1·2, 6, 18 mm min^?1) at 1750°C and subsequently heat treated at 1450°C for 10 h. These processes aimed to investigate the microstructure of directionally solidified (DS) and heat treated (HT) alloys by XRD, SEM, and EDS. The microstructure of DS alloy was composed of (Nb,Ti)_SS, (Nb,Ti)₅Si₃, and Laves phase Cr₂Nb, and the former two components formed (Nb,Ti)_SS+(Nb,Ti)₅Si₃ eutectics. In addition, (Nb,Ti)₅Si₃ laths only presented in DS1·2 alloy. With the increasing withdrawal rates, the microstructure of alloy altered from hypereutectic into pseudo-eutectic, accompanied with the eutectic morphology transformation from petaloid into coupled. Also, the dimension of constituent phases reduced. However, after heat treatment, the constituent phases did not change. The petaloid morphology of eutectics in DS specimens disappeared and coupled eutectic transferred into network. The block or needle-like Cr₂Nb gathered along the boundary between (Nb,Ti)₅Si₃ and (Nb,Ti)_SS, and the overall alloy composition became homogenisation.     

Directional hydraulic fracturing to control hard-roof rockburst in coal mines

Hard roof is the main factor that induces rock-burst.In view of the present obvious weakness of control measures for hard roof rockburst in domestic collieries,the mechanism and field application of di...     

相场法模拟凝固微观组织演化研究进展

相场法是凝固组织模拟中最有潜力的方法之一,近年来已成为凝固领域研究的热点.本文论述了相场法模拟凝固微观组织的原理,并分别介绍了无流动和流动条件下相场法模拟自由枝晶、定向凝固界面及小平面枝晶在国内外的研究进展,指出了进一步的研究方向.     

苏里格气田定向井井壁稳定性分析研究

通过坐标转换关系,建立了定向井井壁围岩的应力分布函数,分析了定向井井壁周围应力的分布情况.依据库伦-摩尔强度准则和最大拉应力破裂准则,建立定向井井壁坍塌压力和破裂压力计算模型,并据此编制了定向井井壁稳定计算分析软件.利用苏里格气田某井的实际数据资料,计算出了定向井井壁坍塌压力和破裂压力,绘制出坍塌压力和地层破裂压力随井...     

扶正器钻具组合在定向井施工中的应用

本文介绍了单扶钻具组合、双扶钻具组合的特点及用途,分析了影响井眼轨迹控制的因素,并结合现场应用,分析了扶正器钻具组合对定向井施工的影响。实钻结果表明调整单扶正器组合中扶正器的安放位置,可以获得理想的稳斜效果,既能保证井下安全,又能实现定向钻井的目的,是理想的钻具选择。     

民航中波NDB导航信号监测方法探讨

本文主要研究了民航无线电导航信号监测方法,结合日常监测的工作经验,以乌鲁木齐国际机场NDB导航台为例多次测试分析,详细给出了针对NDB系统导航信号进行监测的技术方法。     

复杂环境下八角高楼的爆破拆除

介绍了复杂环境下爆破拆除一栋八角高楼的工程实例.通过增大爆破切口高度及采用单向折叠定向爆破的方式,有效地控制了大楼的倒塌范围;通过采用半秒差分段延时起爆技术、合理控制炸药单耗、开挖减振沟等措施,显著地降低了爆破振动和塌落振动;并阐述了炮孔布置、单孔装药量等爆破参数和安全防护措施,以及爆破振动的监测结果;为此类高楼的爆破...