Dehydration of a layered double hydroxide – C2AH8
TL;DR: In this article, a structural model of a grafting process of the interlayer [Al(OH)4]− tetrahedron onto hydroxylated octahedrons of aluminum-oxide polyhedrons has been proposed in order to explain observed loss of one water molecule, shrinkage of interlayer spacing and qualitative changes of FT-IR spectra.
Abstract: Thermal dehydration of dicalcium aluminate hydrate, C2AH8, has been investigated by simultaneous differential thermal and thermo gravimetric analysis (DTA/TGA), powder X-ray diffraction (XRD), temperature-dependent infrared spectroscopy (FT-IR), and BET method of surface area measurement. The temperature-dependent infrared measurements were studied by two-dimensional infrared (2D-IR) correlation spectroscopy. The structure of aluminum-oxide polyhedron, characterized by 27Al solid state NMR spectrum method and FT-IR, shows tetrahedron and octahedron as the main forms of aluminum-oxide polyhedrons in C2AH8 sample. From the results obtained a variety of structural transformations observed are explained as a consequence of the removal of loosely held interlayer water molecules at lower temperatures, followed by grafting process of the interlayer [Al(OH)4]− anion. Structural model of a grafting process of the interlayer [Al(OH)4]− tetrahedron onto hydroxylated octahedrons of [Ca2Al(OH)6]+ layers has been proposed in order to explain observed loss of one water molecule, shrinkage of interlayer spacing and qualitative changes of FT-IR spectra. At higher temperatures the dehydroxylation of the lattice and decomposition of the interlayer species occurs, yielding amorphous material that crystallizes into C3A and C12A7 at 885 °C. Those findings provide improvement in the interpretation of thermo-analytical results of calcium aluminate cements (CAC) hydration products, and better understanding of CAC conversion process.
Citations
More filters
TL;DR: In this article, the system of different Ca/Si and Al/Si molar ratios were investigated and it was shown that incorporation of Al increases main basal spacing, amount of bounded water and decreases crystallinity of C-(A)-S-H (calcium (aluminium) silicate hydrate).
Abstract: Systems of different Ca/Si and Al/Si molar ratios were investigated. Incorporation of Al increases main basal spacing, amount of bounded water and decreases crystallinity of C-(A)-S-H (calcium (aluminium) silicate hydrate). Transmission electron microscope observations showed that aluminium results in formation of more compacted, foil-like microstructure. FTIR revealed the presence of rings within the structure of C-(A)-S-H. Low Ca/Si ratio promotes Al incorporation into C-(A)-S-H, while in case of high Ca/Si ratio aluminium is also incorporated into AFm. The results show, that Ca/Si ratio is of key significance deciding on Al incorporation into C-(A)-S-H in hydrating SCMs bearing blended systems.
194 citations
TL;DR: In this paper, the phase assemblage evolution of BSA cement pastes with time is established based on Rietveld quantitative phase analysis of synchrotron and X-ray powder diffraction data coupled with chemical constraints.
Abstract: Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO{sub 2} into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C{sub 2}S (50-60%), C{sub 4}A{sub 3}$$ (20-30%), CA (10%) and C{sub 12}A{sub 7} (10%). Using thermogravimetry, differential thermal analysis, high temperature microscopy, and X-ray powder diffraction with Rietveld quantitative phase analysis, we found that burning for 15 min at 1350 deg. C was the optimal procedure, in these experimental conditions, for obtaining the highest amount of C{sub 4}A{sub 3}$$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt.% of C{sub 4}A{sub 3}$$, had 19.6, 27.1 and 27.7 wt.%, C{sub 4}A{sub 3}$$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the beta-C{sub 2}S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C{sub 4}A{sub 3}$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution.
128 citations
TL;DR: In this paper, the effect of temperature on the formation of the structure and phase composition of the Gorkal 70 grade calcium aluminate cement (CAC) during its hydration at the temperature of +5 °C, +20 °C and +40 °C was investigated.
Abstract: The effect of temperature on the formation of the structure and phase composition of the Gorkal 70 grade calcium aluminate cement (CAC) during its hydration (W/C=1) at the temperature of +5 °C, +20 °C and +40 °C is investigated. The scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray microanalysis were used in investigations. It has been found that after 3 days of hydration were formed such crystalline hydration products: at 5 °C only CAH10 is formed in the CAC stone, at the temperature of 20 °C - CAH10 and C2AH8, at the temperature of 40 °C - the hydrates C3AH6 and AH3. In the cement stone heated at 800 °C, the hydrates are decomposing, and the minerals CA, CA2 and C12A7 are being formed, though the contours of the hydrate crystals’ forms (prisms, plates, irregular cubes) actually remain unchanged, when the process of heating is over. Considerable changes in cement stone microstructure observed, after a heating at a temperature of 100 °C - there had been significant increase in the quantity of fine particles and pores. The results of XRD analysis showed that, at this temperature the reactions in solid state materials proceed and as a result the amounts of mineral C12A7 are decreasing, while those of minerals CA and CA2 are increasing.
107 citations
TL;DR: A survey of 2D correlation spectroscopy can be found in this paper, where the authors surveyed the publication activities in the field of two-dimensional correlation spectrograms with the emphasis on papers published during the last two years.
Abstract: The publication activities in the field of 2D correlation spectroscopy are surveyed with the emphasis on papers published during the last two years. Pertinent review articles and conference proceedings are discussed first, followed by the examination of noteworthy developments in the theory and applications of 2D correlation spectroscopy. Specific topics of interest include Pareto scaling, analysis of randomly sampled spectra, 2D analysis of data obtained under multiple perturbations, evolution of 2D spectra along additional variables, comparison and quantitative analysis of multiple 2D spectra, orthogonal sample design to eliminate interfering cross peaks, quadrature orthogonal signal correction and other data transformation techniques, data pretreatment methods, moving window analysis, extension of kernel and global phase angle analysis, covariance and correlation coefficient mapping, variant forms of sample–sample correlation, and different display methods. Various static and dynamic perturbation methods used in 2D correlation spectroscopy, e.g., temperature, composition, chemical reactions, H/D exchange, physical phenomena like sorption, diffusion and phase transitions, optical and biological processes, are reviewed. Analytical probes used in 2D correlation spectroscopy include IR, Raman, NIR, NMR, X-ray, mass spectrometry, chromatography, and others. Application areas of 2D correlation spectroscopy are diverse, encompassing synthetic and natural polymers, liquid crystals, proteins and peptides, biomaterials, pharmaceuticals, food and agricultural products, solutions, colloids, surfaces, and the like.
106 citations
TL;DR: In this article, thermal diffusivity and thermal conductivity during calcium aluminate cements (CAC) hydration was investigated by a transient method with a numerical approach and a transient hot wire method, respectively.
Abstract: As the hydration of calcium aluminate cements (CAC) is highly temperature dependent, yielding morphologically and structurally different hydration products that continuously alter material properties, a good knowledge of thermal properties at early stages of hydration is essential. Thermal diffusivity and thermal conductivity during CAC hydration was investigated by a transient method with a numerical approach and a transient hot wire method, respectively. For hydration at 15 °C (formation of mainly CAH 10 ), thermal diffusivity shows a linear decrease as a function of hydration degree, while for hydration at 30 °C there is a linear increase of thermal diffusivity. Converted materials exhibited the highest values of thermal diffusivities. The results on sealed converted material indicated that thermal conductivity increased with an increase in temperature (20–80 °C), while thermal diffusivities marginally decreased with temperature. The Hashin–Shtrikman boundary conditions and a simple law of mixtures were successfully applied for estimating thermal conductivity and heat capacity, respectively, of fresh cement pastes.
105 citations
References
More filters
Book•
01 Jan 1970
TL;DR: The chemistry of cement and concrete as discussed by the authors, The chemistry of concrete and its properties, and the relationship between concrete and cement, is a classic example of such an approach. But it is not suitable for outdoor use.
Abstract: The chemistry of cement and concrete , The chemistry of cement and concrete , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
2,424 citations
TL;DR: In this paper, a two-dimensional correlation method for various types of spectroscopy, including IR and Raman spectrograms, is proposed, where an external perturbation is applied to a system while being monitored by an electromagnetic probe with the application of a correlation analysis to spectral intensity fluctuations induced by the perturbations.
Abstract: A two-dimensional (2D) correlation method generally applicable to various types of spectroscopy, including IR and Raman spectroscopy, is introduced In the proposed 2D correlation scheme, an external perturbation is applied to a system while being monitored by an electromagnetic probe With the application of a correlation analysis to spectral intensity fluctuations induced by the perturbation, new types of spectra defined by two independent spectral variable axes are obtained Such two-dimensional correlation spectra emphasize spectral features not readily observable in conventional one-dimensional spectra While a similar 2D correlation formalism has already been developed in the past for analysis of simple sinusoidally varying IR signals, the newly proposed formalism is designed to handle signals fluctuating as an arbitrary function of time, or any other physical variable This development makes the 2D correlation approach a universal spectroscopic tool, generally applicable to a very wide range of applications The basic property of 2D correlation spectra obtained by the new method is described first, and several spectral data sets are analyzed by the proposed scheme to demonstrate the utility of generalized 2D correlation spectra Potential applications of this 2D correlation approach are then explored
1,566 citations
Book•
01 Jan 2001
TL;DR: In this article, the authors present an overview of the current body of LDH knowledge from a wide array of views, including synthesis and physicochemical characterisation, and applications of layered double hydroxides.
Abstract: Layered double hydroxides are one of the variety of names given to a family of layered materials first discovered in Sweden in 1842. These materials are interesting because their layer cations can be changed among a wide selection, and the interlayer anion can also be (nearly) freely chosen. Like cationic clays, they can be pillared and can exchange interlayer species -- thus increasing applications and making new routes to derivatives. The principle areas of application include catalyst support, anion scavengers, polymer stabilisers, and antacids. In the last several years, reviews and studies of LDHs have dealt with these uses. This book aims to update the current body of LDH knowledge from a wide array of views. The first section addresses the synthesis and physiochemical characterisation of these materials, and section two focuses on the applications of LDHs.
1,066 citations