Physico-chemical and mechanical properties of geopolymer/zircon composites

The effect of zircon (ZrSiO4) on the physico-chemical and mechanical properties of geopolymer/zircon composites was examined in this study. Four geopolymer/zircon composites containing 10, 20, 30 and 40 wt.% zircon were prepared from metakaolin with alkali activators. Characterization of the obtained geopolymers was performed by X-ray diffraction (XRD), Scanning electron microscope (SEM-EDS), Fourier transform infrared spectroscopy (FTIR) and Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). XRD results did not confirmed the formation of interconnected phases between added zircon, starting aluminum silicates and alkali activators. Compressive strength of prepared geopolymer was examined. The maximum obtained compressive strength of 70.15 MPa was measured in sample containing the smallest fraction of zircon, i.e., 10 wt.%. Addition of larger amount of zircon (20 wt.%) hinders the progress of geopolymerization reaction and consequently decreases compressive strength

The influence of thermodynamic parameters on alkaline activators of geopolymers and the structure of geopolymers

Thermodynamic parameters (densities, viscosities, speed of sound, and refractive index) of four series of alkaline activators were determined over the temperature range from 15 to 60 degrees C for the process of geopolymerization. Mixtures of Na2SiO3 and NaOH of different molar concentrations ( from 2M to 8M with step 2) were used as an alkaline activator. The sample with the highest NaOH concentration also shows the highest values of all thermodynamic parameters. Metakaolin, obtained by calcination of kaolin at 750 degrees C, was used as the starting material. The samples were characterized by X-ray diffraction (XRD), FTIR and Raman spectroscopy, Scanning Electron Microscopy (SEM), and Energy-Dispersive X-Ray (EDX) Spectroscopy. Results of FTIR analysis correlated with results of Raman Spectroscopy. Due to the polymerization process, the changes in the phonon spectrum were confirmed. The different concentrations of activators do not notably change the Si/Al ratio

Study of Nanosized Hydroxyapatite Material Annealing at Different Retention Times

The aim of the study was to investigate the influence of low heating temperatures with two different retention times to optimize the process for obtaining nanosized hydroxyapatite material that can possibly be used in the fields of biology and pharmacy. Nanosized hydroxyapatite was successfully obtained by wet chemical precipitation. The annealing of the material performed at 300 oC with two different retention times i.e. 3 and 6 hours in air atmosphere. Low annealing temperature with extended retention time was selected in terms to reduce energy consumption. FTIR spectroscopy was used to confirm characteristic vibrational bands of hydroxyapatite samples, and presence of carbonate bands of hydroxyapatite annealed for 3h and 6h. X-Ray powder diffraction analysis were used to examine phase composition, determine the size of unit cells and crystallite sizes, and SEMEDS methods were used to obtain particle size and arrangement also grain growth morphology and confirmed the presence of calcium, phosphorous oxygen and carbonate peaks. The results show that different retention time has influence on particle growth as well as unit cell parameters and crystallite sizes changes of hydroxyapatite material

Structural, Mechanical and Chemical Properties of Low Content Carbon Geopolymer

In recent years geopolymers have shown increased interest as binders with low CO2 emission compared to Portland cement. The main goal of this research is focused on connecting green and sustainable characteristics with the mechanical and chemical properties of fly ash-based geopolymer. The samples of different ratios of fly ash (FA) and metakaolin (MK) were prepared. X-ray powder diffraction (XRD) showed that in the geopolymer synthesis reaction a new amorphous phase was formed. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) confirmed characteristic bands of the Si-O and O-Si-O groups at 1045 cm−1. Compressive strength analysis revealed that the optimal ratio of FA and MK is 50:50 and exhibits the highest value. X-ray photoelectron spectroscopy (XPS) analysis revealed the total reduction of carbon content in the alkali-activated geopolymer with the optimal stoichiometry of 50:50. This indicates the possibility of obtaining a geopolymer material with an almost complete absence of carbon, which implies further application as a material with a very high environmental potential and of zero carbon emissions

Composition of red mud and/or metakaolin-based modified geopolymers

There is potential use of red mud for synthesis of inorganic polymeric materials through a geopolymerization process as an alternative in the sectors of construction and building materials. By introducing of inorganic and organic modificators of microstructure (calcium hydroxide, bifunctional epoxy resins, or various types of alkoxylanes) during the geopolymer synthesis the enhanced values of ductility and strength can be obtained. Research was performed on alumosilicate material (red mud and metakaolin) and alkali activator raw mixture with defined quantity of modificator. The best sinthesys conditions were identified. Post-synthesis curing also play important role in obtaining of good-performing geopolymers. Characteristics of geopolymers were defined by measuring of compressive strength, N2-physisorption, as well as by SEM analysis, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In addition the lower value of zeta potential was identified as the assisting factor for the specific structure domains formation (within the certain range of pH) accompanied by the high compressive strength

Effect of Alkaline Activator Properties on Structure of Metakaolin-Based Geopolymer Samples

Considering geopolymers as inorganic polymers, they are actually amorphous network of interlinked silicate and aluminate groups, so they could be prospective ceramic precursors for materials with defined dimensions obtained by casting and firing, but not from powder processing. In this research, the starting material is metakaolin, which was obtained by calcining domes tic kaolinite clay. Initially, four series of alkaline activators of NaOH and sodium silicate have been used. Activators present the mixtures of Na2SiO3 and solutions of NaOH, of different molarities 2M, 4M, 6M and 8M. The prepared geopolymer slurries were cast into the designated near shape at room temperature and after that at 60oC. In fact, the post-synthesis curing process (28 days) has an important role in the obtaining good characteristics of geopolymers. Densities, viscosities and refractive index of alkaline activators were determined over the temperature range 15-60oC of process of geopolymerizations. Based on the obtained results of investigated parameters have been selected to predict the properties of materials. All geopolymer samples were characterized by XRD, FTIR, SEM/EDS analysis and Raman spectroscopy providing complementary and valuable information of the investigated materials. This route of ceramics production has advantages associated with producing an environmental friendly, energy saving, clean new technology of geopolymer materials

Synthesis and characterization of Brushite-metakaolin-based geopolymer materials

In a field of green chemistry, environmental protection and ecological conservation of the environment there are ways to come up with new and more advanced materials using on the one hand natural, recyceled or waste materials and on the other hand syntethic materials obtained by using green chemistry synthesis procedures. The aim of this paper was to synthesize and characterize Brushite-metakaolin-based geopolymer materials and to examine the possibility of using these materials in the fields of construction, cement industry, as well as in environmental protection as potential adsorbents. Initial materials which were used for geopolymer synthesis was Brushite (CaHPO4·2H2O) which was obtained by solutionprecipitation reaction form acetate solutions and Kaolinite clay from Rudovci deposit (Serbia). The obtained mixture powders were dissolved in a strong alcaline solution with addiction of water glass. Produced geopolymers was cast into mods and preserved for 28 days. The starting materials and the synthesized Brushite-metakaolin-based geopolymer material were examined using XRPD, FTIR SEM-EDS methods. The contact angle measurements were made to test hydrophilic and wettable properties of synthesized material

Thermal Induced Phase Transformation of Cs-Exchanged LTA framework zeolite

Cesium aluminosilicate phases are of great interest as possible hosts for 137Cs immobilization in radioactive waste management. Cs+ exchanged forms of two synthetic zeolites (4A and 3A) were prepared by standard procedure, and content of exchanged ions was determined by ion chromatography. Obtained samples were investigated by differential thermal gravimetry TG/(DTG) and SEM/EDS analysis. All samples were annealed in the range of 600–1500 °C. High temperature phase transformations of Cs+ exchanged zeolites (LTA) were investigated. Based on data obtained by XRD analysis of the samples, it was concluded that above 1000 °C Cs-LTA (4A and 3A) frameworks recrystallized in a pollucite phase

De la variabilité des usages en interaction à des descriptions linguistiques réutilisables : l’exemple de wa-llah

Cet article aborde la question posée dans le numéro « langue, discours, culture » à travers l’analyse de corpus d’interactions en arabe. La formule wallah qui est étudiée a été choisie en raison de la fréquence de son usage, et parce qu’elle correspond à un élément linguistique culturellement spécifique : il s’agit d’un serment signifiant littéralement « par Dieu », répertorié par la tradition grammaticale arabe parmi les procédés de « corroboration » (proche d’une modalité de « renforcement »). L’analyse des 90 occurrences de la formule dans les corpus analysés conduit à distinguer deux types d’usages : les emplois de type « corroboratif », et les emplois dans lesquels la formule s’est figée et fonctionne quasiment à la manière d’une particule discursive. Cet exemple illustre surtout la relation complexe entre langue et culture, telle qu’elle se reflète dans les usages.This paper deals with the question of the inter-relationship between language, discourse and culture which is the guiding theme of this volume via an examination of spoken Arabic in interaction. The expression “wa-llah” has been selected for a descriptive analysis for two reasons : because of its high rate of occurence in spoken Arabic and because it is a culturally specific linguistic item. It is in fact an oath, which literally means “by God”, and which is listed in the Arabic grammatical tradition as a “corroboration” device, a way of adding emphasis. The analysis of the 90 occurences of “wa-llah” that were found in the data leads, in fact, to drawing a distinction between two separate kinds of usage : Firstly, one that falls into the traditional category of “corroboration” and, secondly, one where the term appears to have been grammaticalized and to work largely as a discourse particle. The analysis of thisparticular example highlights the intricate nature of the relationship between language and culture that emerges from speakers’ usage

Aluminosilicate matrix of alkali activated mixture of metakaolin/fly ash and wood ash/metakaolin

Presented research related to the structure of a different kind of alumosilicate matrix of alkali activated materials (AAM). Fly ash (FA), wood ash (WA) and metakaolin (MK) were used as a solid precursors of final AAM samples. Synthesis of the AAM was conducted by mixing in a determined ratio solid precursors and an alkali activator (sodium silicate solution, NaOH solutions concentration-4 mol dm-3 and 12 mol dm-3 ). AAM samples were synthesized by a two-component system: MK/FA and WA/MK. The ratio of components MK/FA and WA/MK was 0.9. The AAM samples were cured at determined laboratory conditions (time, temperature, humidity, aging) in covering mold. The X-ray diffraction (XRD), Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and Scanning Electron Microscopy (SEM) were provided to the samples after twenty-eight days of geopolymerization process. The higher background of both MK/FA and WA/MK based AAM samples indicates the achievement of amorphization during the geopolymerization process. In investigated samples, the characteristic stretching asymmetric vibrations C=O, and carbonate vibrations were expected in highly alkaline FA/MK and WA/MK mixture. SEM morphology of all AAM samples noticed an amorphous phase with irregularly distributed, agglomerated particles, and some crystal phases originating from raw materials on the surface alumosilicate matrix.X Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 26-27, 2022; Belgrad