ABSTRACT
Highly porous sodium geopolymer structures were successfully produced through the chemical direct foaming approach at ambient temperature. The impact of the thermal treatment, as well as the influence of various additions of hydrogen peroxide, as a foaming agent, on the porosity, microstructure and mechanical characteristics of the produced geopolymers was investigated. The evaluation of bioactivity was carried out by assessing the formation of an apatite layer on the samples' surface, using scanning electronic microscopy and inductively coupled plasma spectrometry for the simulated body fluid solution, in which the geopolymer samples were kept up to 28 days. In addition, the biodegradability was estimated through the weight change of the samples and pH-measurements. The results demonstrated that the geopolymer foams, produced using 4.5 vol% H2O2 and heat-treated at 500 °C for 1 h, possessed a high open porosity (71 vol %), excellent compressive strength (3.56 ± 0.27 MPa), and suitable chemical stability. The pH value of SBF solutions, in which these geopolymers were immersed for 28 days, remained close to the physiological one. The in vitro study indicated that the developed geopolymer foams possessed bioactivity, as demonstrated by the formation of apatite particles on their surface after immersion in the simulated body fluid solution for 28 days.
Subject(s)
Biocompatible Materials , Hydrogen Peroxide , Compressive Strength , Polymers , PorosityABSTRACT
This study was conducted to investigate the influence of various reaction conditions, namely the silica modulus SiO2/Na2O, H2O/Na2O molar ratio, and liquid/solid ratio on the geopolymerization reaction of the waste fired clay bricks (Grog). The starting raw material and the generated geopolymer specimens produced by different geopolymerization reaction conditions have been characterized using different techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermal analysis. Furthermore, physico-mechanical characterization has been carried out through the determination of bulk density, porosity, water absorption, and compressive strength for each sample at interval curing times of up to 28 days. The results indicated that the geopolymerization system of the waste fired clay bricks is influenced by the investigated reaction conditions at room temperature. The compressive strength of the geopolymer sample produced at optimum conditions increased significantly by up to 37.5 MPa, in comparison with 4.5 MPa for other conditions. Finally, an optimum recommendation and useful conclusions concerning the recycling and utilization of this waste material through the geopolymerization process are made for compatibility with construction applications.
ABSTRACT
A series of organo-modified nanoclays was synthesized using three different surfactants having different alkyl chain lengths and concentrations [0.5-5.0 cation exchange capacity (CEC)]. These surfactants were Ethanolamine (EA), Cetyltrimethylammoniumbromide (CTAB) and Tetraoctadecylammoniumbromide (TO). The obtained modified nanoclays were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) and compared with unmodified nanoclay. The results of XRD analysis indicated that the basal d-spacing has increased with increasing alkyl chain length and surfactant concentration. From the obtained microstructures of these organo-modified nanoclays, the mechanism of surfactant adsorption was proposed. At relatively low loading of surfactant, most of surfactant entered the spacing by an ion-exchange mechanism and is adsorbed onto the interlayer cation sites. When the concentration of the surfactant exceeds the CEC of clay, the surfactant molecules then adhere to the surface adsorbed surfactant. Some surfactants entered the interlayers, whereas the others were attached to the clay surface. When the concentration of surfactant increased further beyond 2.0 CEC, the surfactants might occupy the inter-particle space within the house-of-cards aggregate structure.
