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The effect of microwave treatment on the electric conductivity and structure of a polymer‐derived SiCN ceramic is studied. It is found that the conductivity of the microwave‐treated sample is about 40 times higher than that of the conventional heat‐treated one at the same temperature and dwell time conventionally. The X‐ray diffraction patterns show that both samples are amorphous without obvious crystallization. Raman analysis reveals that the microwave‐treated sample exhibited a narrower full width at half maximum and upper‐shift of G peak. X‐ray photoelectron spectroscopy spectra show that there is a significant sp3‐to‐sp2 transition of free carbon in the microwave‐treated sample. These results suggest that the microwave‐treatment can induce a distinct structure evolution of the free carbon, which contributes to the remarkable enhancement of the conductivity of the sample.

When a water droplet strikes a superhydrophobic surface, there may be several to a few tens of rebounds before it comes to rest. Although this intriguing multiphase flow phenomenon has received a great deal of attention from interfacial scientists and engineers, the underlying dynamics have not yet been completely resolved. In this paper, we report on an experimental investigation into the bouncing behavior of water droplets impinging on macroscopically flat superhydrophobic surfaces. We show that the restitution coefficient, which quantifies the energy consumed during impact and rebound, exhibits a nonmonotonic dependence on the Weber number. It is the droplet–surface friction that restricts the rebound height of the impinging droplet, so its restitution coefficient increases with the Weber number when the impact velocity is below a critical value. Above this value, the viscous friction within a thin liquid layer close to the superhydrophobic surface becomes dominant, and thus, the restitution coefficient decreases sharply. On the basis of energy analyses, semiempirical formulas are proposed to describe the restitution coefficient, and these can be employed to predict the number of successive rebounds of impinging droplets on superhydrophobic surfaces.

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In this paper, a large-scale diffuse interface model is used to describe the evolution of a gypsum cavity formation induced by dissolution. The method is based upon the assumption of a pseudo-component dissolving with a thermodynamic equilibrium boundary condition. A methodology is proposed based on numerical computations with fixed boundaries in order to choose suitable parameters for the diffuse interface model, and hence predict the correct dissolution fluxes and surface recession velocity. Additional simulations were performed to check which type of momentum balance equation should be used. The numerical results did not show a strong impact of this choice for the typical initial boundary value problems under consideration. Calculations with a variable density and Boussinesq approximation were also performed to evaluate the potential for natural convection. The results showed that the impact of density driven flows was negligible in the cases under investigation. The potential of the methodology is illustrated on two large-scale configurations: one corresponding to a gypsum lens located strictly within a porous rock formation and the other to an isolated pillar in a flooded gypsum room and pillar quarry. boundary condition for the small-scale dissolution problem) for limestone, calcite, gypsum, or salt follow a similar form expressed aswhere k s is the surface reaction rate coefficient, c s is the mass concentration of the dissolved species at the surface, and c eq the corresponding equilibrium concentration or solubility. It is worth noticing that the reaction order, n, can lead to a highly nonlinear reaction rate. For instance, it ranges from 1 to 4.5 approximately in the case of gypsum dissolution, depending on c s , as obtained by Jeschke et al. [21]. Also, if the surface Damköhler number is very large, for instance a very large k s , this boundary condition tends to the classical equilibrium condition c s D c eq at the solid surface. This latter condition is often used for salt dissolution, for instance. Dissolution models will be based on the coupling of the transport equations and the interface recession. From a numerical viewpoint, some models have been developed to simulate the early stage of conduit evolution, that is, the dissolution enlargement of preexisting fractures in rock matrix, mainly for hydrology analyses. Early studies used 1D pipe models to analyze the single conduit development in limestone [24][25][26]. A main conclusion of these studies was that the positive feedback of mutual enhancement of conduit enlargement and flow rate governed the early stage of karst genesis. 2D pipe network models representing interconnected conduits were developed in [27][28][29] for more complex limestone structures, and flow types were extended from laminar to turbulent. It was reported in these works that both flow patterns and hydraulic boundary conditions have significant impact on cave patterns, with laminar flow favoring the development of single passages, while turbulent flow triggering the developme...