This article presents the results of the compositional, structural and morphological study of geopolymers synthesized from metakaolin and an alkali activator. The study involved the investigation of ...the structural and chemical properties of the geopolymer, in addition to thermally treated geopolymers up to 600 and 900°C. The precursor of the geopolymer, and the geopolymer samples before and after the thermal treatment, were investigated by Fourier transformation infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and SEM analysis. The corrected average value of the ratio of silicon and aluminum in the geopolymer samples (SiGP:Al) is about 1.46, which suggests that the obtained geopolymer samples represent a mixture of roughly equal amounts of sialate and sialate-siloxo units. Annealing the geopolymer samples at 600°C decreases the amount of Si-ONa bonds and induces the cross-linking of polymer changes. At the same time, other sodium containing alumino-silicate phases are created. The thermal treatment at 900°C leads to a considerable reduction of oxygen and particularly sodium, followed by significant morphological changes i.e. formation of a complex porous structure. Additionally, a new semicrystaline phase appears. Both XRD and XPS results imply that this new phase may be nepheline and it is plausible that this phase begins to nucleate at temperatures below 900°C.
Geopolymers (GP) were successfully synthesized from metabentonite (MB), metadiatomite (MD) and metakaolinite (MK). Characterization of their phase structure and microstructure was performed by XRD, ...FTIR, SEM/EDX methods. A SEM micrograph of GPMD shows a homogeneous surface with some longitudinal cavities in the gel, and it is significantly different from the micrographs of the other two geopolymer samples, GPMB and GPMK. A considerable amount of unreacted particles, as well as the presence of pores in the geopolymer matrix of GPMK and GPMD, indicate an incomplete reaction in the system. Aluminosilicate inorganic polymers, geopolymers, are quasi solid electrolytes which possess a high electrical conductivity at room temperature in relation to materials of similar chemical composition. The highest conductivity was found for the sample obtained from GPMK, amounting to 2.14 × 10–2 Ω–1cm–1at 700 ºC. The corresponding activation energies of conductivity for this sample amounted to 0.33 eV in the temperature range of 500–700 ºC. The geopolymer synthesized from metakaolin has good ionic conductivity values, which recommends it for use as an alternative material for an SOFC (Solid Oxide Fuel Cell).
The present work was focused on doping of 1% and 5% both of Nd2O3 and Sm2O3 in geopolymer gels. One of the main goals was to determine the influence of the behavior of Nd and Sm as dopants and ...structural nanoparticles changes of the final geopolymer formed. It is shown that the disorder formed by alkali activation of metakaolin can accommodate the rare earth cations Nd3+ and Sm3+ into their aluminosilicate framework structure. The main geopolymerization product identified in gels is Al-rich (Na)-AS-H gel comprising Al and Si in tetrahedral coordination. Na+ ions were balancing the negative charge resulting from Al3+ in tetrahedral coordination. The changes in the structures of the final product (geopolymer/Nd2O3; Sm2O3), has been characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis with energy dispersive spectrometry (EDS). Nucleation at the seed surfaces leads to the formation of phase-separated gels from rare earth phase early in the reaction process. It is confirmed that Nd and Sm have been shown to form unstable hydroxides Nd(OH)3 and Sm(OH)3 that are in equilibrium with the corresponding oxides.
The aim of the presented research was to investigate the application possibility of wood ash and metakaolin to obtain alkali-activated materials as relatively new materials in the building industry. ...Thus, in order to assess the adequate use of these waste materials, structural and radiological characteristics should be considered. Until now, the focus has been on ash from thermal power plants produced by burning coal, but a large part of households in our country have individual fireplaces in which wood is used as the basic raw material; thus, it is very interesting to measure the activity concentration of radionuclide in wood ash as well as the possibility of reusing that ash for other purposes. All materials were studied, in terms of physical and chemical characteristics, by methods such as X-ray diffraction (XRD), Fourier transform infra-red (FTIR) spectroscopy, and scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS). XRD measurements of wood ash samples showed that it consists of calcite and larnite. FTIR spectroscopy revealed a polymeric Si–O–Al framework in alkali-activated materials and Si–O bonding bands corresponding to silicon dioxide. Determination of radionuclide content was performed by means of gamma-ray spectrometry. Results showed that the alkaline activation process led to the decrease in the activity concentration of radionuclides detected in the measured samples. External radiation hazard index (Hex) for wood ash was reduced by more than 50% after alkali activation. The results of activity concentration measurements in alkali-activated materials indicate potential for their safe application in building construction.
The paper presents chemical and structural analysis of geopolymer materials which are obtained by alkali-activated calcined clay (metakaolin) originated from Serbia under strictly defined conditions. ...Characterization of the metakaolin and geopolymers molecular structure has been done using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The paper presents the possibility of obtaining geopolymer structure and differences in chemical and structural characterization of these materials taking into account the concentration of NaOH as a variable parameter. The results of MALDI analysis of metakaolin and synthesized geopolymer structures using various matrix system: 2,4,6 trihydroxyacetophenone (THAP), α-cyano-4-hydroxycinnamic, 2,6 dihydroxyacetophenone and laser desorption/ionization, have shown that THAP matrix is the most appropriate for analysing these aluminosilicate materials.
The main goal of the presented research was the preliminary investigation of
possibility of red mud - Hungarian dump sites Almasfuzito (sample A) and Ajka
(sample B) - application as a pigment or as ...a raw material for use in the
construction materials industry. Also, the aim of this work was the
characterization of red mud as industrial waste generated by the Bayer
process in the aluminum industry - which may cause environmental problems if
appropriate treatment is not carried out. The main mineral phases of both red
mud are hematite (Fe2O3), calcite (CaCO3), gibbsite (Al(OH)3) and they
consists of particles of median particle size 2.1 mm (sample A) and 2.5 mm
(sample B) and have a characteristic red color, which was the reason for its
testing for use in the industry of building materials as a pigment for
standard concrete mixtures. The radionuclides content in the samples was
determined by gamma spectrometry, and the radiological hazards originating
from 238U, 232Th, 40K in the samples, were assessed through the radium
equivalent activity, and the external radiation hazard index. The absorbed
dose rate and the annual effective dose were calculated in accordance with
the UNSCEAR 2010 report and the results are presented in this paper.
In the present work, remediation of lead-containing solution using raw and modified kaolinite has been presented. The micro and nanostructure of samples has been characterized by X-ray diffraction ...(XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Laser diffraction and scattering (LDS), was analyzed by particle size analyzer based on laser diffraction and particle size distribution (PSD) was done. The degree of metal adsorption was evaluated analyzing the Pb(II) contaminated samples by inductively coupled plasma atomic emission spectrometry (micro- and nanostructure on immobilization efficiency correlCP AES). The results show the impact of immobilization efficiency and ation between micro- and nanostructure. The thermodynamic data (ΔH°, ΔS°, ΔG°) are calculated from the temperature-dependent sorption isotherms. The results suggest sorption process of Pb(II) on kaolinite as spontaneous and endothermic.
A significant amount of red mud generated as a by-product of the Bayer
process in the aluminum industry may cause environmental problems if
appropriate treatment is not carried out. The presented ...research dealt with
the possibility of application of red mud as a pigment or as raw material
for use in the construction material industry. In relation to the aim of
this work, the physicochemical characterization was performed and the
natural radioactivity of red mud as an industrial waste and a geopolymer
sample based on it was determined. The presented research is a
contribution to the potential solution for environmental protection through
the synthesis of possible construction material based on red mud.
The radiological hazard orginating from 226Ra, 232Th, and 40K in the
samples was assesed throught the absorbed dose rate and the annual effective
dose rate, calculated in accordance with the UNSCEAR 2010 report.
Physicochemical characterization of all samples was conducted using X-ray
diffraction and diffuse reflectance infrared Fourier transform spectroscopy.
The potential re-use of red mud in the building and construction industry has
been the subject of research of many scientists. The presented research is a
contribution to the potential solution of ...this environmental issue through
the synthesis of potential construction materials based on red mud. A
promising way of recycling these secondary raw materials is the synthesis of
alkali-activated binders or alkali activated materials. Alkali-activated
materials or inorganic binders based on red mud are a new class of materials
obtained by activation of inorganic precursors mainly constituted by
silica, alumina and low content of calcium oxide. Since red mud contains
radioactive elements like 226Ra and 232Th, this may be a problem for its
further utilization. The content of naturally occurring radionuclides in
manufactured material products with potential application in the building
and construction industry is important from the standpoint of radiation
protection. Gamma radiation of the primordial radionuclides, 40K and members
of the uranium and thorium series, increases the external gamma dose rate.
However, more and more precedence is being given to limiting the
radiological dose originating from building materials on the population
these days. The aim of this research was to investigate the possible
influence of alkali activation-polymerization processes on the natural
radioactivity of alkali activated materials synthesized by red mud (BOKSIT
a. d. Milici, Zvornik, Bosnia and Herzegovina) and their structural
properties. This research confirmed that during the polymerization process
the natural radioactivity was reduced, and that the process of alkali
activation of raw materials has an influence on natural radioactivity of
synthesized materials.
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