Alkali-activated metakaolins: Mineral chemistry and quantitative mineral composition

The reaction products resulting from the alkali-activation of metakaolin are impacted by the composition of the initial kaolin, and amount of alkali-activated kaolinite and water. The present study focused on analyzing these parameters on the metakaolins calcined at 800 degrees C from three kaolins, and the metakaolins' alkali activation for 2, 3 and 28 days. The first objective was to evaluate the mineral chemistry and quantitative mineral phase composition from the bulk chemical analysis using the chemical quantitative mineral analysis (CQMA) procedure and conduct a comparison of the chemistry of the metakaolins after alkali activation for 28 days according to the elements Al, Si, Na and K, using the leaching test in distilled water. The second task was to search for possible relationships between the quantitative number of phases in alkali-activated metakaolins and compressive strength. The main methods used for the characterization of material were X-ray fluorescence, X-ray diffraction, thermal TG/DTA and infrared spectroscopy. Metakaolins alkali activated for 28 days contained crystalline quartz, muscovite, orthoclase, and unreacted metakaolinite contained zeolite A (Z-A), hydrosodalite (HS) and thermonatrite (TN) in the amorphous/weakly crystalline phase. The compressive strengths (CS) from 6.42 +/- 0.33 to 9.97 +/- 0.50 MPa are related positively to H2O+ and H2O bound in HS and TN.Web of Science1211art. no. 134

Near-infrared spectroscopic analysis of acid-treated organo-clays

The potential use of near-infrared (NIR) spectroscopy as a characterization tool for organo- clays would be a great asset but little work has been done in this regard because the application ofNIR to clay mineral studies is a relatively new phenomenon. The purpose of this study was to use NIR spectroscopy to investigate the effect of alkylammonium cations on the acid dissolution of a high-charge montmorillonite (SAz-1). Detailed analysis ofthe spectra of Li-, TMA- (tetramethylammonium), and HDTMA- (hexadecyltrimethylammonium) saturated SAz-1 montmorillonite in the NIR region was achieved by comparing the first overtone (2v) and combination (v+δ) bands of XH groups (X = O, C) with the fundamental stretching (v) and bending (δ) vibrations observed in the mid-infrared (MIR) region. Comprehensive analysis ofthe vibrational modes of CH -N, CH-C, and CH-C groups of TMA and HDTMA cations detected in the MIR and NIR regions was also performed. Both MIR and NIR spectra demonstrated that exchange of Li by TMA only slightly improved the resistance of SAz-1 layers to dissolution in 6 M HCl at 80°C, while exchange by the larger HDTMA cations almost completely protected the montmorillonite layers from acid attack. Use of NIR spectra in reaching these conclusions was crucial. Only in the NIR region could the creation of SiOH groups be monitored, which is an important indicator of the acidification of the montmorillonite surface. The OH-overtone region in the spectra of Li- SAz-1 and TMA-SAz-1 revealed that the SiOH band near 7315 cm increases in intensity with enhanced acid treatment. In contrast, no SiOH groups were identified in the NIR spectra of HDTMA-SAz-1 treated in HCl, indicating that HDTMA completely covers the inner and outer surfaces of the montmorillonite and hinders access of protons to the Si O bonds created upon acid treatment

Synthesis and structure determination of tetrakis(4-iodoanilinum) b-octamolybdate dihydrate

Tetrakis(4-iodoanilinum) b -octamolybdate dihydrate ( I ) was synthesized and its structure was solved using powder diffraction methods and the atoms positions optimized by the solid state DFT calculations. The structure is triclinic (P-1) with cell parameters: a = 9.7099(4) Å, b = 9.8169(3) Å, c = 14.9842(6) Å, a = 97.349(3) ° , b = 102.989(3) ° , c = 113.335(3) ° , V = 1239.79 Å 3 . The anion type was determined based on Patterson map analysis and the presence and location of water molecules were determined based on the locations of solvent accessible voids in the structure and confirmed with molecular dynamics cal- culations and high temperature IR spectroscopy. Structure of ( I ) consists of molybdenum–oxygen clusters, protonated amine and water molecules. Each cluster consists of eight distorted Mo A O 6 octahedra sharing corners and edges forming b -[Mo 8 O 26 ] 4 anions. Protonated 4-iodoanilinum cations form, apart from electrostatic attraction, moderately strong N A H O hydrogen bonds binding these molecules to the oxygen atoms in Mo 8 O 26 clusters. In addition, one of the amine molecules form a weak O A H I bond with the water molecule, which is loosely bound with a weak O A H O hydrogen bond to molybdenum–oxygen cluster

Surface Characterization and Anti-Biofilm Effectiveness of Hybrid Films of Polyurethane Functionalized with Saponite and Phloxine B

The main objective of this work was to synthesize composites of polyurethane (PU) with organoclays (OC) exhibiting antimicrobial properties. Layered silicate (saponite) was modified with octadecyltrimethylammonium cations (ODTMA) and functionalized with phloxine B (PhB) and used as a filler in the composites. A unique property of composite materials is the increased concentration of modifier particles on the surface of the composite membranes. Materials of different compositions were tested and investigated using physico-chemical methods, such as infrared spectroscopy, X-ray diffraction, contact angle measurements, absorption, and fluorescence spectroscopy in the visible region. The composition of an optimal material was as follows: nODTMA/mSap = 0.8 mmol g−1 and nPhB/mSap = 0.1 mmol g−1. Only about 1.5% of present PhB was released in a cultivation medium for bacteria within 24 h, which proved good stability of the composite. Anti-biofilm properties of the composite membranes were proven in experiments with resistant Staphylococcus aureus. The composites without PhB reduced the biofilm growth 100-fold compared to the control sample (non-modified PU). The composite containing PhB in combination with the photodynamic inactivation (PDI) reduced cell growth by about 10,000-fold, thus proving the significant photosensitizing effect of the membranes. Cell damage was confirmed by scanning electron microscopy. A new method of the synthesis of composite materials presented in this work opens up new possibilities for targeted modification of polymers by focusing on their surfaces. Such composite materials retain the properties of the unmodified polymer inside the matrix and only the surface of the material is changed. Although these unique materials presented in this work are based on PU, the method of surface modification can also be applied to other polymers. Such modified polymers could be useful for various applications in which special surface properties are required, for example, for materials used in medical practice

Effect of Corrosive Media on the Chemical and Mechanical Resistance of IPS e.max® CAD Based Li2Si2O5 Glass-Ceramics

The influence of 4% acetic acid (pH~2.4) and an alkaline solution of NaOH (pH~10) on the corrosion resistance and micromechanical properties of disilicate crystals containing glass-ceramics (LS2-GC’s) is studied. Partially crystallized lithium metasilicate crystal containing glass-ceramics (LS-GC’s) are annealed to fully LS2-GC’s using a one stage and a two-stage heating to induce nucleation. Materials with various chemical and wear resistance are prepared. The content of the crystalline phase in the material annealed in the two-stage process A is 60.0% and increases to 72.2% for the material heated in the one-stage process B. The main elements leached in the acidic medium are lithium and phosphorus, while lithium, silicon, and phosphorus leached into the alkaline environment. Material B exhibits better chemical resistance to the corrosive influence of 4% acetic acid under quasi-dynamic conditions. In the alkaline corrosion medium, silicon is leached from material A faster compared to the material B. After prolonged exposure to acidic or basic environments, both materials show evidence of surface structural changes. A decrease of the sliding wear resistance is observed after corrosion in the acidic environment under dynamic conditions. In both materials, the wear rate increases after corrosion

Structure, thermal properties and crystallization behavior of binary Y2O3–Al2O3 glasses with high alumina content

Five compositions in the system Al2O3–Y2O3 with high level of homogeneity were prepared in the form of glass microspheres by flame synthesis. The amorphous nature of prepared glasses with highly disordered structure was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. In the NMR spectra, typical signals with chemical shifts of 75, 42 and 12 ppm were observed, which were attributed to the presence of AlO4, AlO5 and AlO6 motifs in the glass structure. The ratio of individual motifs in glass samples did not change significantly with the composition. The crystallization of yttrium-aluminium garnet (YAG) phase was observed as a major process in the glasses thermally treated up to 1450 °C, with slow crystallization of θ- and α-Al2O3 phases detected in the temperature interval 980–1450 °C. IR and Raman spectra of the microspheres crystallized at 998, 1300 and 1500 °C for 4 h contained typical bands, that were assigned to the vibrations of AlO4 and AlO6 groups in YAG and Al2O3 structures. The comparison of 27Al and 89Y magic angle spinning (MAS) NMR spectra showed the presence of only YAG and α-Al2O3 phase in the samples crystallized at 1500 °C and the presence of a trace amount of θ-Al2O3 in the sample crystallized at 998 and 1300 °C. The yttrium aluminium perovskite (YAP) and yttrium aluminium monoclinic (YAM) phases, expected in this system, were no detected