Role of different types of water in bentonite clay on hydrate formation and decomposition

The equilibrium and kinetic of hydrate in sediments can be affected by the presence of external components like bentonite with a relatively large surface area.To investigate the hydrate formation and decomposition behaviors in bentonite clay,the experiments of methane hydrate formation and decomposition using the multi-step decomposition method in bentonite with different water contents of 20%,40%and 60%(mass)were carried out.The contents of bound,capillary and gravity water in bentonite clay and their roles during hydrate formation and decomposition were analyzed.In bentonite with water content of 20%(mass),the hydrate formation rate keeps fast during the whole formation process,and the final gas consumption under different initial formation pressures is similar.In bentonite with the water contents of 40%and 60%(mass),the hydrate formation rate declines significantly at the later stage of the hydrate formation.The final gas consumption of bentonite with the water contents of 40%and 60%(mass)is significantly higher than that with the water content of 20%(mass).During the decomposition process,the stable pressure increases with the decrease of the water content.Hydrate mainly forms in free water in bentonite clay.In bentonite clay with the water contents of 20%and 40%(mass),the hydrate forms in capillary water.In bentonite clay with the water content of 60%(mass),the hydrate forms both in capillary water and gravity water.The bound water of dry bentonite clay is about 3.93%(mass)and the content of capillary water ranges from 42.37%to 48.21%(mass)of the dry bentonite clay.

Improving the Thermal Conductivity and Mechanical Properties of Twocomponent Room Temperature Vulcanized Silicone Rubber by Filling with Hydrophobically Modified SiO_2-Graphene Nanohybrids

The SiO_2 nanoparticles were coated on the surface of graphene oxide(GO) by sol-gel method to get the SiO_2-G compound.The SiO_2-G was restored and oleophylically modified to prepare hydrophobic modified SiO_2-G(HM-SiO_2-G) which was subsequently added to silicone rubber matrix to prepare two-component room temperature vulcanized(RTV-2) thermal conductive silicone rubber. The morphology, chemical structure and dispersity of the modified graphene were characterized with SEM, FTIR, Raman, and XPS methods.In addition, the heat-resistance behavior, mechanical properties, thermal conductivity, and electrical conductivity of the RTV-2 silicone rubber were also studied systematically. The results showed that the SiO_2 nanoparticles were coated on graphene oxide successfully, and HM-SiO_2-G was uniformly dispersed in RTV-2 silicone rubber. The addition of HM-SiO_2-G could effectively improve the thermal stability, mechanical properties and thermal conductivity of RTV-2 silicone rubber and had no great influence on the electrical insulation performance.

A Multiple-Relaxation-Time Lattice Boltzmann Model for Natural Convection in a Hydrodynamically and Thermally Anisotropic Porous Medium under Local Thermal Non-Equilibrium Conditions

To investigate the natural convective process in a hydrodynamically and thermally anisotropic porous medium at the representative elementary volume(REV)scale,the present work presented a multiplerelaxation-time lattice Boltzmann method(MRT-LBM)based on the assumption of local thermal non-equilibrium conditions(LTNE).Three sets of distribution function were used to solve the coupled momentum and heat transfer equations.One set was used to compute the flow field based on the generalized non-Darcy model;the other two sets were used to solve the temperature fields of fluid and solid under the LTNE.To describe the anisotropy of flow field of the porous media,a permeability tensor and a Forchheimer coefficient tensor were introduced into the model.Additionally,a heat conductivity tensor and a special relaxation matrix with some off-diagonal elements were selected for the thermal anisotropy.Furthermore,by selecting an appropriate equilibrium moments and discrete source terms accounting for the local thermal non-equilibrium effect,as well as choosing an off-diagonal relaxation matrix with some specific elements,the presented model can recover the exact governing equations for natural convection under LTNE with anisotropic permeability and thermal conductivity with no deviation terms through the Chapman-Enskog procedure.Finally,the proposed model was adopted to simulate several benchmark problems.Good agreements with results in the available literatures can be achieved,which indicate the wide practicability and the good accuracy of the present model.

An improved Hummers method to synthesize graphene oxide using much less concentrated sulfuric acid

The production of graphene oxide with less acid is beneficial to reduce the costs and lower the impact on the environment,but it is still a great challenge.In this work,a relatively simple,safe method for synthesizing graphene oxide with much less acid(decrease∼40%)is proposed.With assistance of the heat absorbed from environment and reaction system,the temperature of reaction system of low acid can be well controlled.More interestingly,the graphite can be completely oxidized into graphite oxide by using much less acid,with lowering the production of high-concentration aqueous waste acid(>1 mol/L,decrease∼40%).A series of characterizations show that the prepared graphene oxide has similar yield and functional groups compared with that of using the conventional method.This work provides a safe and environmentally friendly choice for the large-scale production of graphene oxide and its derivative materials.