Selective Tests of Grouting Material for Fractured Coal and Rock Masses in a Water-borne HS Environment
Coal mining is vulnerable to multiple kinds of threat from water incursion. Many coal seams contain dissolved H2S, which may be released during mining, seriously endangering the health of workers. Orthogonal testing was used to analyze the physical and mechanical properties of composite slurries in different proportions. The results showed slurry with a water-solid ratio of 0.8:1 to have the optimal combination of properties. A uniform experimental method was used to investigate the impact of the water-cement ratio, concentration of sodium silicate, and volume of cement-sodium silicate (CS) on the setting time and consolidating strength of CS slurry. This paper provides the appropriate application scope of two grouting materials (optimized composite slurry and CS slurry), based on experimental data and the results of a large number of in situ trials. Finally, the optimized composite slurry and cement-sodium silicate slurry were used to carry out grouting of the center auxiliary transport roadway of the 3 coal seam at the Ningtiaota Coal Mine, operated by the Shaanxi Coal Industry Group. It was shown that the type and formula of the slurry could be changed in a timely manner, based on the water outlet and concentration of H2S at the site, achieving successful grouting reinforcement and seepage-proofing.
Experimental characterization and performance evaluation of geothermal grouting materials subjected to heating–cooling cycles
Abstract In recent years, the increasing rise in environmental awareness among energy consumers has led to an increasing use of renewable energies such as the geothermal energy. An important role in the efficient exploitation of the geothermal resource is played by the grouting material placed in the borehole between the pipes and the ground. Actually, the use of proper grouts is essential to provide an effective heat transfer between the ground and the heat carrier fluid in the pipes, and also to comply with the mechanical and environmental demands. However, when it comes to the construction of the GHP installations, the grout is especially required to be easy to work with (workable) and for this reason more water than required is sometimes added. In order to assess the suitability of grouting materials with significant water/solid ratios, the thermal conductivity, mechanical strength and permeability of five different grouts and grout–pipe specimens were measured for their laboratory characterization. In addition, the grouts were subjected to heating and cooling cycles to evaluate their durability with time in terms of the potential degradation of the materials and the loss of quality of the grout–pipe interface. According to the results obtained, the grouts here tested are appropriate for most of the geothermal heat pump installations, especially for those with low to medium ground thermal properties.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.