Structural study of geopolymers obtained from alkali-activated natural pozzolan feldspars

Fesaghandis

Int J Applied Ceramic Tech

et al. 2018

K-Feldspar was used as a raw material for in situ synthesis of leucite particles by solid-state reaction method. Prior to synthesis of leucite, K-Feldspar was treated by oxalic acid (C 2 H 2 O 4 ) to eliminate Fe content. The parameters affecting the structure and amount of Fe in K-Feldspar was investigated to reach an optimal leaching condition. Next, kasilite removal was studied by introducing CaF 2 to the composition of dental porcelain. To synthesis leucite, the prepared materials were heated up to 1450°C for 3 hours until fusion phenomena occurred, then cooled down to 865°C to permit the leucite crystals nucleate and grow. To find out the chemical composition of powder, XRF, EDX, and Atomic absorption spectroscopy were used. Fourier Transform Infrared Spectroscopy and X-Ray Diffractometer and Scanning Electron Microscopy were employed to study the structure of mineral. Spectrophotometry was chosen to analyze whiteness index of powder after acid treatment. Differential Thermal Analysis was employed to determine the crystallization temperature. Results indicated a dramatic decrease in Fe content (0.018%wt) by employing C 2 H 2 O 4 as a leachant at 50°C. In addition, whiteness index of 91% was achieved through this procedure for raw feldspar. Finally, 1% wt of CaF 2 prevented formation of kalsilite.

Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 98%

See 1 more Smart Citation

In situ synthesis of leucite‐based feldspathic dental porcelain with minor kalsilite and Fe₂O₃ impurities

Fesaghandis

Int J Applied Ceramic Tech

et al. 2018

“…The changes that have been characterized correspond to the second and third stages of the geopolymerization process [15]. Geopolimerization mechanism involves dissolving and hydrolysing aluminum and silicon in alkaline solution, transport and orientation of dissolved species accompanied by polycondensation and the creation of three-dimensional aluminosilicate networks [16].The changes in XRDP and FTIR spectrum indicate that there are fine changes of the aluminosilicates structure as the geopolymer synthesis progresses.…”

Section: Resultsmentioning

confidence: 99%

The effect of the concentration of alkaline activator and aging time on the structure of metakaolin based geopolymer

et al. 2020

This paper outlines the production of an inorganic polymer/geopolymer using a metakaolin by an environmental friendly, energy saving, clean technology to conserve natural environment and resources. The influence of alkali activation, i.e. different concentration of NaOH as a component of alkali activator mixture on the process of geopolymerization of metakaolin is investigated. Also, process of aging time of geopolymer is followed by several analytical methods. The structure of metakaolin and metakaolin based geopolymers and their physicochemical properties were studied using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and after 28days scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was applied for the surface characterization of the samples. A shift of the Si-O or Si-O-X (X=Al, Si, Na...) bands as the molarity of activator increasing during geopolymerization process was observed by FTIR. Mass spectra of geopolymers were characterized by MALDI TOF mass spectrometer. Structural reorganization of geopolymer samples occurs during the curing/aging in accordance with a geopolymerization mechanism.

Rev. IBRACON Estrut. Mater.

“…Besides metakaolin and fly ash, other types of precursors that have low amounts of calcium have reaction mechanisms typical of geopolymers. For example, other types of burnt clay can be cited as illite-smectites [43] or feldspars [44], [45]. There are also other precursors such as volcanic ash, natural pozzolans, and metallurgical slags with low amounts of calcium [46]- [49].…”

Section: Main Low-calcium Precursorsmentioning

confidence: 99%

Reaction mechanisms of alkali-activated materials

Marvila

Azevedo

Vieira

2021

The Alkali-Activated Materials (AAM) are defined as materials obtained through the reaction between precursors and activators, and are separated into two classes depending on the products formed in the reaction, those rich in calcium, as the blast furnace slag, whose Ca/(Si+Al) ratio is higher than 1; and poor in calcium, which is the geopolymers subclass. In this review article, some bibliographical aspects were discussed regarding the discovery of these materials, through research conducted by Victor Glukhovsky and through the characterization of historical monuments by Davidovits, which began in the 50s and 60s and persist to the present day. The main products obtained in the alkaline activation reaction were also addressed, using the definition of polysialates and zeolites, in the case of geopolymers, and the tobermorite structure, in the case of materials rich in calcium. The main steps of the alkali-activated reaction, such as dissolution, condensation, polycondensation, crystallization, and hardening, were discussed. Some techniques for characterizing the AA reaction products were also examined, such as X-ray diffraction (XRD), nuclear magnetic resonance spectrometry (NMR), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Finally, the main factors that interfere in the kinetics of AA reactions were explored, in which the type of cure and the activating solution used in the alkali-activated materials production stands out.