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In present study, nanosized iron oxides particles are synthetised by easy one step precipitation from Mohric salt (NH4)2Fe(SO4)2·6H2O reacting with sodium hydroxide solution in temperature up to 60 °C. When changing the time of reaction, the iron oxide particles of different shape are prepared and when drying wet extracted particles at elevated temperature of 60 °C the change of 2D shaped morphology is observed. Depending on the time of reaction different ratios of FeOOH and Fe3O4 are obtained in this study. DTA – TGA, XRD, FTIR and SEM are used for the characterisation of particles in this study. [ABSTRACT FROM AUTHOR]

The present study is focused on the synthesis and investigation of the physicochemical and biological properties of silver nanoparticles stabilized with a series of cationic gemini surfactants having a polymethylene spacer of variable length. UV-VIS spectroscopy, dynamic light scattering, scanning electron microscopy and zeta potential measurements were applied to provide physicochemical characterization of the silver nanoparticles. The mean size values of the nanoparticles were found to be in the 50 to 115 nm range. From the nanoparticle size distributions and scanning electron microscopy images it results that a population of small nanoparticles with the size of several nanometers was confirmed if the nanoparticles were stabilized with gemini molecules with either a short methylene spacer (two or four -CH2- groups) or a long spacer (12 -CH2- groups). The average zeta potential value for silver nanoparticles stabilized with gemini molecules is roughly independent of gemini surfactant spacer length and is approx. +58 mV. An interaction model between silver nanoparticles and gemini molecules which reflects the gained experimental data, is suggested. Microbicidal activity determinations revealed that the silver nanoparticles stabilized with gemini surfactants are more efficient against Gram-negative bacteria and yeasts, which has a direct relation to the interaction mechanism of nanoparticles with the bacterial cell membrane and its structural composition. [ABSTRACT FROM AUTHOR]

The formation of metastable strontium-yttrium(III) (hexakis) germanium(IV) lacunar apatite ( P 6 3 /m , a=11.426 Å, c=8.224 Å and Z=2) was observed during the thermal treatment of SrCO 3 , Y 2 O 3 , and GeO 2 powder precursors using the ceramic method in an oxygen atmosphere. The utilization of an oxygen atmosphere restricts the extensive reduction of GeO 2 and enables us to explain a new potential mechanism for the stabilization of lead-free lacunar apatites. This mechanism involves the use of electrons localized in a neighborhood of oxygen vacancies. Charged vacancies serve as active sites for the ionosorption of oxygen molecules and their subsequent transformation into lattice oxygen anions, which fill the vacancies at the X-site. The estimation of system thermodynamics shows that apatite undergoes a transformation to a more stable state at δ≥0.1, i.e., at the value that corresponds to the composition of prepared apatite. As the temperature and time of the thermal treatment increases, the process of incongruent melting leads to the formation of oxygen-rich yttrium-germanium apatite (YGAp, Y 9.333+ε [GeO 4 ] 6 O 2+3/2ε ) and strontium-yttrium-germanium glass. The YGAp phase is also formed during the annealing of lacunar apatite in an oxygen atmosphere. [ABSTRACT FROM AUTHOR]

The kinetics and mechanism of delamination including the destruction of kaolinite layered structure of kaolinite from termite nest were investigated by non-isothermal high-temperature X-ray diffraction analysis. The process is controlled by the rate of the 2nd order chemical equation described by the kinetic function F2 : (g( α )=(1−y)−1 −1). The apparent activation energy was assessed to be 417±9kJ·mol−1. The delamination is considered as the first step of the thermal transformation of kaolinite into metakaolinite but the temperature at which the maximum rate of dehydroxylation was reached is lower than the temperature for the maximum rate of delamination if a heating rate of ≤5°C·min−1 was applied and higher for heating rates ≥15°C·min−1. The superposition of both processes within the heating rates of 5 to 15°C·min−1 led to a significant decrease of activation energy. This behavior provides an option to modify the degree of metakaolinite delamination during the thermal treatment. [ABSTRACT FROM AUTHOR]

In this study, the potential use of waste diatomaceous earth from the production of diatomaceous earth for filtration purposes, as an alternative raw material for foam glass production, was explored. The chemical and mineralogical composition and the high temperature behavior of waste diatomite were studied to assess its suitability for foam glass production. Glass-ceramic foams were prepared using NaOH solution as a foaming agent, via a hydrate mechanism. The influence of different pretreatments and firing temperatures on the foam's structure, bulk density and compressive strength was investigated. High temperature behavior was studied using TG/DTA analysis and high temperature microscopy. Phase composition was studied using X-ray diffraction analysis. Glass-ceramic foam samples of a high porosity comparable to conventional foam glass products were fabricated. The pretreatment temperature, foaming temperature and sintering holding time were found to have a significant influence on foam properties. With increased pretreatment temperature, pyrogenic carbon from the thermal decomposition of organic matter contained in the raw material acted as an additional foaming agent and remained partially unoxidized in prepared foams. The bulk densities of prepared samples ranged from 150 kg/m3 to 510 kg/m3 and their compressive strengths were between 140 and 1270 kPa. [ABSTRACT FROM AUTHOR]

Phosphorus-containing heterocyclic cationic surfactants alkyldimethylphenylphospholium bromides with the alkyl chain length 14 to 18 carbon atoms were used for the stabilization of silver nanodispersions. Zeta potential of silver nanodispersions ranges from +35 to +70 mV, which indicates the formation of stable silver nanoparticles (AgNPs). Long-chain heptadecyl and octadecyl homologs of the surfactants series provided the most intensive stabilizing effect to AgNPs, resulting in high positive zeta potential values and smaller diameter of AgNPs in the range 50–60 nm. A comparison with non-heterocyclic alkyltrimethylphosphonium surfactants of the same alkyl chain length showed better stability and more positive zeta potential values for silver nanodispersions stabilized with heterocyclic phospholium surfactants. Investigations of biological activity of phospholium-capped AgNPs are represented by the studies of antimicrobial activity and cytotoxicity. While cytotoxicity results revealed an increased level of HepG2 cell growth inhibition as compared with the cytotoxicity level of silver-free surfactant solutions, no enhanced antimicrobial action of phospholium-capped AgNPs against microbial pathogens was observed. The comparison of cytotoxicity of AgNPs stabilized with various non-heterocyclic ammonium and phosphonium surfactants shows that AgNPs capped with heterocyclic alkyldimethylphenylphospholium and non-heterocyclic triphenyl-substituted phosphonium surfactants have the highest cytotoxicity among silver nanodispersions stabilized by the series of ammonium and phosphonium surfactants. [ABSTRACT FROM AUTHOR]

Increasing utilization of secondary raw materials and alternative fuels results in increasing contents of metals in cements. Zinc is one of these elements. It comes to cement with secondary raw materials such as slag or fly ash or by the utilization of used tires as an alternative fuel. Zinc ions significantly prolong the hydration process in cement. This work deals with the influence of zinc ions in the form of very poorly soluble ZnO salt and easily soluble ZnCl2 and Zn(NO3)2 on the hydration of cement blended with fly ash. Zinc was dosed in the range of 0.05%, 0.1%, 0.5% and 1% of cement weight. The effect of zinc on hydration was monitored by isothermal and isoperibolic calorimetry. A 15% addition of fly ash to cement mainly causes further retardation of hydration reactions due to the reactions of fly ash particles with Ca2+ ions from cement. The strongest effect on the hydration retardation from all investigated compounds showed in ZnO as it dissolves very slowly. On the contrary, for the dosage of 1% of zinc in the form of ZnCl2 significant acceleration of hydration occurred. In this work, a synergistic effect on the prolongation of hydration with a combination of cement, zinc and fly ash was demonstrated. The lengths of induction periods were assessed from detected calorimetric curves and from these lengths the curves were gained by fitting with the exponential function. Final products were next analyzed using X-ray diffraction. [ABSTRACT FROM AUTHOR]

This work deals with the influence of zinc on cement hydration. The amount of zinc in cement has increased over recent years. This is mainly due to the utilization of solid waste and tires, which are widely used as a fuel in a rotary kiln. Zinc can also be introduced to cement through such secondary raw materials as slag, due to increased recycling of galvanized materials. The aim of this work was to determine the effect of zinc on the hydration of Portland cement, blended with ground blast furnace slag (GBFS). This effect was studied by isothermal and isoperibolic calorimetry. Both calorimetry methods are suitable for measurements during the first days of hydration. Isoperibolic calorimetry monitors the hydration process in real-life conditions, while isothermal calorimetry does so at a defined chosen temperature. Zinc was added to the cement in the form of two soluble salts, namely Zn(NO3)2, ZnCl2, and a poorly soluble compound, ZnO. The concentration of added zinc was chosen to be 0.05, 0.1, 0.5, and 1mass percent. The amount of GBFS replacement was 15% of cement dosage. The newly formed hydration products were identified by X-ray diffraction method (XRD). [ABSTRACT FROM AUTHOR]

This work describes the non-isothermal kinetics and mechanism of gas-solid (dry) carbonation of lime obtained by thermal decomposition of dolomite. The course of the process was studied by constant cooling rate derivative thermogravimetric analysis in the flow of carbon dioxide. The activation energy of thermal decomposition during heating of dolomite is lower than that for the process of gas-solid carbonation of lime during cooling. From a thermodynamic point of view, this difference in activation energy is equal to the positive isobaric work. In the mechanism of both processes, diffusion is a rate-determining reaction step. However, the different geometry of the growing nuclei causes a difference in their mechanism. [Display omitted] • Dry carbonation of lime shows a higher E a than thermal decomposition of CaCO 3. • The difference in activation energy is equal to the positive isobaric work. • The effective mass of the activated complex is higher for dry carbonation. • Both processes are controlled by the rate of CO 2 diffusion. • The difference in the mechanism lies in the geometry of growing nuclei. [ABSTRACT FROM AUTHOR]

The crystallization of the Al–Si spinel phase (Si3Al4O12) during thermal treatment of the middle ordered kaolinite was investigated by the non-isothermal thermodilatometric analysis (TDA) under load. The disc of compacted kaolinite powder was heated with constant rate of heating (CRH) from 0.25 to 10°C·min−1 up to 1400°C. The parameters of kinetic triplet were evaluated via model-free Kissinger equation and mechanisms fitting method based on the KJMA equation. It was found that the mechanism of the process is sensitive to the heating rate. The formation of Al–Si spinel phase includes the nucleation and subsequent diffusion controlled growth of nuclei that is changed to the process controlled by the rate of nucleation on the interface if heating rate ≥3°C·min−1 is used. This change significantly reduces the value of apparent activation energy of the process from 954kJ·mol−1 to 562kJ·mol−1. The reconstruction based on the assessed values of apparent activation energy, frequency factor and mechanism is in the good agreement with the experimental data. The thermodynamic parameters of spinel phase were evaluated using Eyring laws. [ABSTRACT FROM AUTHOR]

Abstract: The thermal decomposition of kaolinite was studied by differential thermogravimetry (DTG) technique under non-isothermal conditions. Samples of industrially treated (washed) kaolin with high content of the medium ordered kaolinite were calcined using a heating rate from 1 to 40Kmin−1. The apparent activation energy and frequency factor for the dehydroxylation of kaolinite was evaluated by Kissinger method as 195±2kJ×mol−1 and (8.58±0.33)×1014 s−1, respectively. Avrami exponent of the process was estimated using Kissinger empirical kinetic models and Carne equation. [Copyright &y& Elsevier]

Abstract: The thermal decomposition of kaolin with high-content of the medium ordered kaolinite was studied by Effluent Gas Analysis (EGA) under non-isothermal conditions. This technique enables to distinguish two overlaying processes during the thermal decomposition of kaolin: oxidation of organic compounds and dehydroxylation. The kinetic of non-isothermal dehydroxylation of kaolinite is controlled by the rate of the third-order reaction. For the given reaction mechanism, the overall activation energy (E A ) and pre-exponential (frequency) factor (A) values are 242kJmol− 1 and 2.21×108 s− 1, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The crystallization of Al–Si spinel from medium ordered kaolin with high content of kaolinite was investigated using the differential thermal analysis (DTA). The apparent activation energy of the process was evaluated from the dependence of exothermic peak of crystallization on heating rate. Within the applied interval of heating rate (1–40Kmin−1) the temperature of peak maximum increases from initial value of 1220.5K in about 54.2K. The apparent activation energy of the process 856±2kJmol−1was calculated using the Kissinger equation. The growth morphology of Al–Si spinel crystal was evaluated from the Avrami parameter. The average value of morphology parameter determined within the observed interval of heating rate is 3.08±0.03. This value indicates that crystallization mechanism of Al–Si spinel phase proceeds by bulk nucleation of the new phase with constant number of nuclei and that the three-dimensional growth of crystals is controlled by the reaction rate on the phases interface. [ABSTRACT FROM AUTHOR]

The mechanism and kinetics of the process of thermal decomposition of low-manganese ferroan dolomite were investigated by non-isothermal derivative thermogravimetric analysis in this work. The study of the effect of the composition of gaseous phase on the mechanism and kinetics of thermal decomposition process includes the kinetics experiments performed in nitrogen, carbon dioxide, air and oxygen. While the process of endothermic decomposition takes place in one-step in a carbon dioxide-free atmosphere or in air, three separate reactions take place in carbon dioxide. The activation energy of these three reactions is also significantly higher than that of the thermal decomposition of ferroan dolomite in nitrogen, oxygen or air. [Display omitted] • The influence of the kiln atmosphere on the thermal decomposition of dolomite was described. • In O 2 , air and N 2 , the E a of thermal decomposition are 182, 232 and 234 kJ mol−1, respectively. • In CO 2 , the decomposition of dolomite is divided into three separate endothermic steps. • These reactions show higher E a than the thermal decomposition of dolomite in air, N 2 , or O 2. • The content of Mn and Fe in the dolomite leads to the formation of Mn-srebrodolskite. [ABSTRACT FROM AUTHOR]

This work is aimed at the comparison of the effects of high-temperature fly ash and fluidized bed combustion ash on the hydration of Portland cement and compressive strength of resulting materials. Two samples of high-temperature fly ash (FA), one sample of fluidized bed combustion ash (FBCA) and one sample of fluidized filter ash (FFA) were selected for this work. The pastes were prepared with the same water-to-binder ratio (0.4). The replacement of cement was 10, 20, 40 and 60 wt.%. The influence of ashes on the hydration of ordinary Portland cement (OPC) was measured by means of isoperibolic calorimeter. The compressive strength was determined after 1, 7 and 28 days of curing. The hydration slows down with increasing amount of fly ash, due to lower reactivity of FA compared to OPC. For fluidized ash, the hydration is accelerated through free lime. When comparing calorimetric curves with mechanical properties, it was found out that for the pastes with the same OPC_replacement, the samples with the highest developed heat also achieved the highest strength after one day of hydration. After 28 days of hydration some samples achieved even higher strength than OPC paste. [ABSTRACT FROM AUTHOR]

The formation of metakaolinite during the thermal treatment of kaolinite consists of three processes which include the destruction of kaolinite sheet structure, the dehydroxylation and the recombination of silica and alumina into the structure of metakaolinite. The sequence of these steps is significantly affected by heating rate. The kinetics, mechanism and the influence of heating rate on the course of these processes were investigated by the methods of thermal analysis (DTG and TDA) and high-temperature X-ray diffraction analysis (HT-XRD) using the Kissinger kinetic equation. The activation energy required for the delamination, dehydroxylation and recombination of silica and alumina tetrahedron into metakaolinite is 538, 195 and 143 kJ mol- 1, respectively. The thermodynamic data of the activated complex, calculated from the Wertera and Zenera law, enable to explain experimentally the observed influence of heating rate on the thermal transformation of kaolinite during heating. [ABSTRACT FROM AUTHOR]

Abstract: The effective method for preparation and stabilization of nanostructured ceramic foam from kaolinite is described in this work. The technique is based on the redistribution of particles from original kaolinite aggregates and on the formation of solid framework of aqueous foams stabilized by surfactants. This process is spontaneous and highly effective as the surface energy of the system decreases and provides the driving force for rearrangement of solid phase in foam. The stability of these structures is time-limited, as water flowing from the bubble walls reduces their thickness. Therefore the structure of foam must be stabilized by the materials absorbing water physically or by formation of hydrates. The following high-temperature treatment provides solid foam prepared by sintering and having certain mechanical strength. The foams of bubble walls thickness within the nanometers scale can be prepared by this method hence the thickness of wall is considerably smaller than the median of particle size of original kaolinite. [Copyright &y& Elsevier]

Abstract: The densification of kaolin with high content of middle ordered kaolinite was investigated by non-isothermal thermodilatometric analysis (TDA) under load. The compacted powder was heated with constant heating rate (CRH) from 0.75 to 10°Cmin−1. The sintering reaction of kaolin upon the temperature interval, where sinter-crystallization of mullite and cristobalite takes place (1090–1250°C), is significantly affected by the heating rate. The dTDA results show that the process is sensitive to heating rate and the formation of both phases can be studied separately if heating rate higher than 4°Cmin−1 is used. The mechanism of involved formation of mullite and cristobalite is changed at heating rates higher than 6°Cmin−1. The values of apparent activation energies of mullite and cristobalite formations were determined by Kissinger equation and by several equations of model-free integral type of p(y)-isoconversional methods. The mechanism and thermodynamics of the process were evaluated through Kissinger and Eyring laws, respectively. [Copyright &y& Elsevier]