Effects of surface oxide species and contents on SiC slurry viscosity

The disadvantageous effects of colloidal SiO2 layer and micro-content of metal oxide adsorbed on SiC powder surface on SiC slurry stable dispersion were studied, and the novel method to avoid this disadvantage was proposed. By acidwashing, on the one hand, because the maximum Zeta potential of SiC powder increases to 72.49 mV with the decreasing content of metal oxide adsorbed on the SiC powder surface, the repulsion force between SiC powders that dispersed in slurry is enhanced, thus the SiC powder can be fully dispersed in slurry. On the other hand, after HF acidwashing, with the OH^- group adsorbed on SiC powder surface destroyed and replaced by the Fion, the hydrogen bond adsorbed on the OHgroup is also destroyed. Therefore, the surface property of the SiC powder is changed from hydrophilic to hydrophobic; H2O that adsorbed on SiC powder surface is released and can flow freely, and it actually increases the content of the effective flow phase in the slurry. These changes of SiC powder surface property can be proved by XPS and FTIR analysis. Finally, the viscosity of SiC slurry is decreased greatly, and when the viscosity of the slurry is lower than 1 Pa·s, the solid volume fraction of SiC powder in the slurry is maximized to 61.5 vol.%.

Effects of slurry viscosity and particle additive size on filter cake formation in highly permeable sand

Filter cake is critical to maintaining the stability of the excavation face of an underwater shield tunnel in a high-permeability stratum.In a high-permeability formation,generating an effective filter cake on the excavation face is difficult with a pure bentonite slurry,which penetrates the ground and may not achieve the required suspension pressure.Determining how to efficiently and quickly form a thin and low-permeability filter cake on the tunnel working face has become a key engineering problem in the construction of slurry shield tunnels in high-permeability strata.In this study,the relationship between slurry viscosity and the slurry pressure gradient of pure bentonite was established by performing slurry permeability experiments.The influence of slurry viscosity on the formation of the filter cake in a high-permeability formation was studied under different pressure gradients.In addition,the effect of additive particle size on the slurry filter cake formation was analyzed by introducing additives with different particle sizes to pure bentonite slurries with different viscosities.The test results indicate that(1)for the pure bentonite slurry,the critical initial pressure gradient can be used as a rough indicator of the formation of the filter cake,and the relationship between the critical maximum pore diameter and the average pore diameter of the for-mation can be compared to establish and analyze the formation law of the slurry filter cake;(2)adding particles to the slurry can enhance the effect of the pure bentonite slurry;and(3)adding coarse-grained materials can effectively improve the film-forming effect.The slurry is more compact when the particle size is close to the average pore size of the formation.

Artificial neural network approach for rheological characteristics of coal-water slurry using microwave pre-treatment

Detailed experimental investigations were carried out for microwave pre-treatment of high ash Indian coal at high power level(900 W) in microwave oven. The microwave exposure times were fixed at60 s and 120 s. A rheology characteristic for microwave pre-treatment of coal-water slurry(CWS) was performed in an online Bohlin viscometer. The non-Newtonian character of the slurry follows the rheological model of Ostwald de Waele. The values of n and k vary from 0.31 to 0.64 and 0.19 to 0.81 Pa·sn,respectively. This paper presents an artificial neural network(ANN) model to predict the effects of operational parameters on apparent viscosity of CWS. A 4-2-1 topology with Levenberg-Marquardt training algorithm(trainlm) was selected as the controlled ANN. Mean squared error(MSE) of 0.002 and coefficient of multiple determinations(R^2) of 0.99 were obtained for the outperforming model. The promising values of correlation coefficient further confirm the robustness and satisfactory performance of the proposed ANN model.

Effect of pattern coating thickness on characteristics of lost foam Al-Si-Cu alloy casting

An experimental study on lost foam casting of an Al-Si-Cu alloy was conducted. The main objective was to study the effect of pattern coating thickness on casting imperfection and porosity percentage as well as eutectic silicon spacing of the alloy. The results showed that increasing slurry viscosity and flask dipping time influenced the casting integrity and microstructural characteristics. It was found that thinner pattern coating produced improved mould filling, refined microstructure and higher quality castings containing less porosity.

Experimental study on slurry-induced fracturing during shield tunneling

Facial support in slurry shield tunneling is provided by slurry pressure to balance the external earth and water pressure.Hydraulic fracturing may occur and cause a significant decrease in the support pressure if the slurry pressure exceeds the threshold of the soil or rock material,resulting in a serious face collapse accident.Preventing the occurrence of hydraulic fracturing in a slurry shield requires investigating the effects of related influencing factors on the hydraulic fracturing pressure and fracture pattern.In this study,a hydraulic fracturing apparatus was developed to test the slurry-induced fracturing of cohesive soil.The effects of different sample parameters and loading conditions,including types of holes,unconfined compressive strength,slurry viscosity,and axial and circumferential loads,on the fracturing pressure and fracture dip were examined.The results indicate that the fracture dip is mainly affected by the deviator stress.The fracturing pressure increases linearly with the increase in the circumferential pressure,but it is almost independent of the axial pressure.The unconfined compressive strength of soil can reflect its ability to resist fracturing failure.The fracturing pressure increases with an increase in the unconfined compressive strength as well as the slurry viscosity.Based on the test results,an empirical approach was proposed to estimate the fracturing pressure of the soil.