Papers by Keyword: Si/Al Ratio

Abstract: Geopolymers are prospective cement substitutes because their production generates smaller amounts of carbon dioxide and they have sufficient mechanical strength. Geopolymers have attracted increasing interest from construction industries because of their recyclability and eco-friendliness. The compressive strength of geopolymers is known to be associated with their Si/Al ratio. Fused slag from gasification processes using low-grade coal (FSLC) and spent catalyst slag (SCS) were used as raw materials for making geopolymers; the Si/Al ratio was controlled by mixing different ratios of FSLC and SCS. The compressive strength of a geopolymer with a Si/Al ratio of 1.04 had the highest strength (125.6 MPa). Scanning electron microscopy (SEM) analysis was also in good agreement with the compressive strength measurements of compressive strength. There were many small crystallites in the geopolymer matrix. Using transmission electron microscopy (TEM), these crystallites were found to be single crystals, which have a perfect crystal structure. It is speculated that the formation of small crystallites 10-30 nm in size, as well as large single crystals with diameters greater than 80 nm, in the matrix of a geopolymer during the geopolymerization process might increase its compressive strength.

Abstract: ZSM-5/MCM-41 composite zeolites were synthesized by a two-step hydrothermal crystallization procedure using binary templates of cetyltrimethylammonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH). The effects of aluminum content on zeolite particle morphology and structure were studied. Powder X-ray diffraction (XRD) results showed that the composite zeolites are of both MCM-41 structure and zeolitic MFI structure. SEM results showed that the morphology of composite zeolites is significantly influenced by the aluminum content.

Abstract: This paper presents the application of Design of Experiments (DOE) to an alkaline treatment in mordenite zeolite, in order to identify the optimum settings of the variables (temperature and concentration of NaOH) that promote greater desilication. Samples of commercial mordenite with Si / Al ratio = 9 have been treated with aqueuos NaOH solution of various concentration (0,1;0,5;1,0) and temperature (30,50,70°C). Statistical analysis was carried out based on a 2² factorial design with center point replicates. Seven experiments were executed and the data of Si/Al ratio obtained. The resulting samples were characterized by x-ray difraction (XRD) and energy dispersive x-ray (EDX), to identify the structures and crystalline phases, and to determine the percentages of silicon and aluminum, respectively. In all samples, a decrease in the Si / Al ratio was observed, keeping the crystalline structure. The treatment was most effective, especially, at high temperature and NaOH concentration (experiment 4). DOE was shown to be a powerful techinique for the study of the variables, allowing determining which variables and value ranges have more influence on response, enabling optimization.

Abstract: Six mixtures with different ratios (0%, 50% and 100%) were designed to investigate the compressive strength, elastic modulus and Poissons ratio of geopolymeric recycled concrete (GRC). The mechanical properties and failure mechanism of recycled concrete (RAC) and GRC were tested and discussed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). The results show that, GRC concretes are stronger than RAC concretes due to different reaction products and better microstructure in interfacial transition zones (ITZs). The EDX results show that the higher compressive strength with higher Si/Al ratio.