Effect of different particle sizes of nano-SiO2 on the properties and microstructure of cement paste

Nano-materials modified cement-based materials have attracted wide attention due to their advantages of improving strength and durability. In this paper, the effect of nano-SiO2 (NS) with particle sizes of 15 and 50 nm on the mechanical properties and microstructure of cement paste was studied. The results showed that 50 nm NS provided a greater compressive strength than that of 15 nm NS, while 15 nm NS afforded a denser microstructure than that of 50 nm NS. A fluctuation in the compressive strength was revealed using a physicochemical reaction equation, and the microstructure was interpreted by a pore structure analysis. In addition, the orientation index of calcium hydroxide (CH) with 15 nm NS could be reduced significantly in the early stages (the early stages refer to the first three days from the maintaining of specimens) compared with when the 50 nm NS was used. The experimental results also showed that NS helped increase the mechanical strength of cement paste, advance the endothermic peak of CH, and refine the size of the CH crystals. The microstructural changes at different stages of cement paste with different particle sizes of NS were investigated by X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry and differential thermal analysis. This study is expected to promote the research and application of nano-materials in the cement industry by clarifying the performance of NS with different particle sizes.

SO2Gas Physicochemical Removal through Pulse Streamer Discharge Technique Assisted by Vapor Additive

SO2removal has drawn extensive attentions for air pollution treatment. In this paper, the pulse streamer discharge technique is investigated. Emission spectra diagnosis experimentally indicates that the SO2molecule has been physically dissociated into SO and O radicals by electron collision and can be remediated through further chemical reactions during and after discharge. In order to quantitatively analyze the removal physical chemistry kinetics, a zero-dimensional physicochemical reaction model is established. Without H2O vapor additive, the SO2removal efficiency is leanly low and only 0.296% has been achieved under pulse discharge duration of 0.5 μs. Through increasing the electrical concentration six times, the removal efficiency has been slightly heightened to 1.796% at pulse duration of 3 μs. Contrarily, vapor additive can effectively improve the removal kinetics, and removal efficiency has been remarkably heightened to 13.0195% at pulse duration of 0.5 μs with H2O/SO2initial concentration ratio of 0.1 : 1. OH radicals decomposed from H2O through electron collision are the essential factor to achieve such improvement, which have effectively adjusted the chemical removal process to the favorite directions. The major productions have been transformed from HSO3and HOSO2to H2SO4when vapor ratio increased above 1.27 : 1.

Microbially mediated attenuation potential of landfill bioreactor systems

The origin and fate of landfill leachate and gas constituents generated during the sequential phases of solid waste transformation and stabilization are emphasized within the perspective of the in situ processes of microbially mediated attenuation. The fundamental biochemical and physicochemical reaction mechanisms are presented in terms of their spatial and temporal dimensions and their significance for transformation of both nonhazardous and hazardous waste constituents. Supporting information from laboratory, pilot-scale and full-scale applications is used as a basis for interpretive analysis and for providing operational guidance and promoting future developments. The diversity, domains, and functional interdependence of the acidogenic, methanogenic, sulfate and nitrate reducing, nitrifying and denitrifying, and methanotrophic consortia are addressed in order to reveal opportunities for landfill process modifications and associated operational optimization. Controlled attenuation, linked with operational and regulatory realities, are used to suggest innovative landfill configurations involving prospective compartmentalization and integrated waste loading, dedicated treatment zones for in situ transformation of waste and leachate constituents with associated gas capture, control and utilization. Monitoring requirements are emphasized to provide guidance and feedback for operational control and environmental compliance. Finally, technology needs for establishing a more unified approach to the development and management of bioreactor landfills are presented.

Theoretical foundation for the discrete dynamics of physicochemical systems: Chaos, self-organization, time and space in complex systems

A new theoretical foundation for the discrete dynamics of physicochemical systems is presented. Based on the analogy between theπ-theorem of the theory of dimensionality, the second law of thermodynamics and the stoichiometry of complex physicochemical reactions, basic dynamic equations and an extreme principle were formulated. The meaning of discrete time and space in the proposed equations is discussed. Some results of numerical calculations are presented to demonstrate the potential of the proposed approach to the mathematical simulation of spatiotemporal physicochemical reaction dynamics.