Hydration of high alumina cement–silica fume composite with addition of Portland cement or sodium polyphosphate under hydrothermal treatment

Various hydrothermal curing regimes were used to investigate the hydration and physical characteristics of two kinds of inorganic binder composites: high alumina cement–silica fume–Portland cement and high alumina cement–silica fume–sodium polyphosphate. Simultaneous thermal analysis (DTA and TG) was used to identify temperature ranges of thermal decomposition of cured samples and to characterize the nature of hydrate products. Two kinds of products are formed. The first ones consist of C₃AH₆, AH₃, calcium carbonate (C–C) as a product of carbonation, and C₃AH_1.5 resulted from the partial decomposition of C₃AH₆ under higher hydrothermal pressure. The second ones are the products formed by acid–base reaction between monocalcium aluminate and sodium polyphosphate to form NaCaPO₄·xH₂O and Al₂O₃·xH₂O that could convert to chemically bonded ceramic binders like hydroxyapatite (Ca₅(PO₄)₃OH) and gibbsite (Al(OH)₃). These two hydroceramic products formed under these conditions act also as binder and could be useful as cement binders for the protection of petroleum, gas, or geothermal wells. Mercury intrusion porosimeter was used for the estimation of the pore structure parameters of the composites. It turned up that longer curing time coupled with higher hydrothermal pressure has improved the pore structure of the first composite, while that of the second has remained unchanged.     

Effect of hydrothermal curing on early hydration of G-Oil well cement

G-Oil well cement has been cured under standard and hydrothermal conditions with different steam pressures and temperatures. Compressive strength, pore structure parameters, microstructure, and hydrated products were evaluated after 7 days curing by using SEM, MIP, and simultaneous TGA/DSC. Obtained results showed that 7 days aged sample cured under standard conditions has the highest compressive strength with compact pore structure and hydrated products similar to those found after hydration of Ordinary Portland cement. With increasing temperature and pressure from standard conditions (25 °C, 10125 Pa) to hydrothermal ones (150 °C and 0.3 MPa, 200 °C and 1.2 MPa), compressive strength has drastically decreased from 77.5 ± 2.0 to 20.5 ± 1.0 MPa due to the transformation of original hydrated products (C–S–H) to crystallized α-C₂SH and C₆S₂H₃. The crystallization has led, under hydrothermal curing, to the increase of permeability and pore structure depletion. The final compressive strength after curing for 7 days at 150 °C (51.8 ± 2.0 MPa) and 200 °C (20.5 ± 1.0 MPa), which significantly exceeds the recommended values of 3.45 MPa according to API to hold many casings of oil wells is questionable for application in geothermal ones.     

Influence of hydrothermal curing regimes on the hydration of fiber-reinforced cement composites

Simultaneous thermal analysis (DTA and TG) was applied to two fiber-reinforced cement composites cured in autoclave at 0.3, 1.2, and 2.0 MPa for 24, 72, and 168 h. Mercury intrusion porosimeter (MIP) and scanning electronic microscope (SEM) were used to complete the investigations. Thermal analysis was used to identify temperature ranges of thermal decomposition of cured samples and to characterize the nature of hydrate products. Also, fractured surface and surface microstructure were investigated by means of SEM. Based on the results of thermal analysis, three processes occurred during hydrothermal curing. The first one consists of primary hydration reaction leading to the formation of C–S–H, C₃AH₆, and AH₃. The second one is the process characterized by partial decomposition or interaction of primary products to form secondary products (C₂ASH₈, C₃AH_1.5). The last one is the carbonation of some hydrate products. Hydrothermal pressure can enhance the compressive strength, but can also cause its depletion over time. The MIP study has revealed an existence of bimodal pore size distribution that the characteristic depends on the hydrothermal curing conditions.     

Performance of G-Oil Well cement exposed to elevated hydrothermal curing conditions

G-Oil Well cement was modified by blending it with blast furnace slag and silica fume at various ratios. The hydration was carried out under the hydrothermal conditions (200 °C and 1.2 MPa) up to 7 days. TG and DTG were performed on cured pastes to identify the hydrated products, their quantity and their stability under given hydrothermal curing conditions. The microstructure of samples was observed by a scanning electron microscope. The mechanical compressive strength was determined and the pore structure was analyzed using mercury intrusion porosimeter. It was found out that the compressive strength values of blend G-Oil Well cements markedly increased with increasing blast furnace/silica ratio. The pore structure was consolidated, as demonstrated by the displacement of pore size distribution to the region of micro and nano pores.     

Effect of Cement on Properties of Inverted Emulsions and Polymers from Vinyl Monomers with Acid Anhydride-Adducted Polypropylene Glycol

Abstract

Adduct polymer (PPGMA) prepared from polypropylene glycol and maleic anhydride was found to give stable inverted emulsions when mixtures of cement, water, and vinyl monomers were vigorously stirred in the presence of PPGMA. In this case, the carboxyl groups of PPGMA were neutralized with metal ions generated from the cement into neutralized PPGMA which acts as an effective W/O type emulsifier. The inverted emulsions containing cement gave a new type of polymer-cement composites by polymerization of the vinyl monomers and also by hardening of the cement. Water-free composites were easily obtained by removing evaporative water. The effect of cement on the physical properties of the water-free composites was remarkable. Further, the use of mixed fillers of cement and Al(OH)₃ was found to improve the flame-retardant properties of the composites; however, increasing the Al(OH)₃ content in the fillers resulted in a decrease in the physical properties. Generally, the composites have improved resistance to acid media in which the usual foamed hydrated cement is eroded.     

Differential thermal studies of polymethyl methacrylate-impregnated cement pastes

Differential thermal curves have been obtained for two polymethyl methacrylate-impregnated cement pastes prepared at a water/cement ratio of 0.37 and 0.70. Complex thermal effects, including a substantial decrease in the endothermal peak for Ca(OH)₂ decomposition, were observed in samples heated in air. These effects originate in the portland cement paste, in the polymer, and from interactions between the polymer and the hydrated cement during heating. Less complex effects resulted when DTA was carried out in N₂. There was no evidence of a reaction between the hydrated cement and PMMA during impregnation.     

Synthesis,characterization and TG-DTA study of diethyl 5-(4-hydroxyethoxyphenylazo)isophthalate

In this work, the hydration rate and products of blended zeolite cements were studied for periods up to 360 days. Thermoanalytical methods (TG/DTG and DTA) were applied in order to evaluate the hydration rate of blended cements, while. X-ray diffraction and FTIR spectroscopy were used in order to identify the hydrated products. As it is concluded the incorporation of zeolite in cement contributes to the consumption of Ca(OH)₂ formed during the cement hydration and the formation of cement-like hydrated products. The pozzolanic reaction of the zeolite is rather slow during the first days of hydration but it is accelerated after the 28 days.     

Composite materials based on zeolite 4A for adsorption heat pumps

Some additives and binders were chosen for the preparation of 4A-zeolite-based composites with high equivalent thermal conductivity for heat pumps application. Additives (SiC, Si₃N₄, graphite) and binders (PTFE, Al(OH)₃) were tested for their effectiveness in terms of equivalent thermal conductivity and maximum water adsorption capacity of the composites. The influence of the equivalent thermal conductivity of the composite adsorbents on the specific power of the heat pump was also calculated. Results show a significant improvement in the equivalent thermal conductivity of the composite samples which are prepared using aluminum hydroxide as binder, over that of zeolite pellet beds. Such composite materials could be used to build adsorption heat pumps with higher specific power and, consequently, with lower investment cost.     

Calorimetric and thermal analysis studies on the influence of waste aluminosilicate catalyst on the hydration of fly ash–cement paste

Binders containing large amounts of cement substitutes have been a subject of interest for many years because of the possibility to reduce the amount of cement in concrete, and in consequence decrease negative influence of cement production on natural environment. In this work, studies related to hydration of binders where 80 % of cement was substituted by blended pozzolana were carried out. The aim of this work was to investigate activation of fly ash–cement system by addition of spent aluminosilicate catalyst, using calorimetry and thermal analysis as main methods of investigations. It was demonstrated that spent fine-grained fluidised catalytic cracking catalyst acts acceleratingly on early hydration of binder. It seems to be beneficial to use up to 10 mass% of this spent catalyst. Higher amounts may cause changes in the mechanism of early hydration. Because Ca(OH)₂ in such systems is quickly consumed due to pozzolanic reaction it seems beneficial to modify composition of binders by introducing additional amounts of Ca(OH)₂ or cement.     

Calcium-based hydrated minerals: Promising halogen-free flame retardant and fire resistant additives for polyethylene and ethylene vinyl acetate copolymers

In this study, we evaluated the potential flame retardant effect of calcium-based hydrated minerals, such as hydrated lime, partially and completely hydrated dolomitic limes in polyethylene (MDPE) and ethylene vinyl acetate copolymers (EVA) and compared to that obtained with magnesium di-hydroxide (MDH). The most significant flame retardant effects, observed using the mass loss calorimeter test, indicated that Ca-based MDPE composites showed similar peak Heat Release Rate (pHRR) level to that obtained with MDH composite while the pHRR was lower for Ca-based fillers in EVA compositions. X-ray Diffraction (XRD) data, combined with thermal analysis results, indicated that the calcium di-hydroxide plays a role in the formation of an intumescent cohesive residue during the combustion. Indeed, Ca(OH)₂ reacts with CO₂ formed during the thermal degradation of the polymer to generate CaCO₃ (calcium carbonate) that contributes to the enhancement of the mechanical resistance of the residue.     

Effect of water vapor on the thermal decomposition process of zinc hydroxide chloride and crystal growth of zinc oxide

Thermal decomposition process of zinc hydroxide chloride (ZHC), Zn₅(OH)₈Cl₂·H₂O, prepared by a hydrothermal slow-cooling method has been investigated by simultaneous X-ray diffractometry and differential scanning calorimetry (XRD-DSC) and thermogravimetric-differential thermal analysis (TG-DTA) in a humidity-controlled atmosphere. ZHC was decomposed to ZnO through β-Zn(OH)Cl as the intermediate phase, leaving amorphous hydrated ZnCl₂. In humid N₂ with P_H2O=4.5 and 10 kPa, the hydrolysis of residual ZnCl₂ was accelerated and the theoretical amount of ZnO was obtained at lower temperatures than in dry N₂, whereas significant weight loss was caused by vaporization of residual ZnCl₂ in dry N₂. ZnO formed by calcinations in a stagnant air atmosphere had the same morphology of the original ZHC crystals and consisted of the c-axis oriented column-like particle arrays. On the other hand, preferred orientation of ZnO was inhibited in the case of calcinations in 100% water vapor. A detailed thermal decomposition process of ZHC and the effect of water vapor on the crystal growth of ZnO are discussed.     

The use of thermal analysis in the approximate determination of the cement content in concrete

Thermal analysis was first used to investigate the pattern of dissociation of hydrated ordinary Portland cement. Portlandite (Ca(OH)₂) decomposes at about 500°C. This was confirmed by kinetic calculations. Thermal analysis was then performed to establish the effect of varying the cement content on the percent mass loss associated with the decomposition of Ca(OH)₂ in cement mortar cured for 28 days. An increasing relation was obtained. Standard concrete cubes were then prepared with cement contents ranging from 200 to 450 kg m^-3. The loss in mass on heating, up to 750°C, of concrete samples cured for 28 days was then related to the cement content in concrete. The relation obtained was tested for concrete cubes of known cement content and found to be in better agreement than the results obtained by conventional chemical analysis. This method can be used for an approximate determination of the cement content in concrete. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrothermal synthesis and structural characterization of a novel cadmium-organic framework

A three-dimensional diamondoid cadmium-organic framework, formulated as [Cd(NDC)(H₂O)] (I) (where NDC²⁻=2,6-naphtalenedicarboxylate), has been hydrothermally synthesized and structurally characterized using single-crystal X-ray diffraction. The hydrothermal synthesis of I has been optimized by modifying the composition of the reactive mixture and the temperature programme, so that a highly crystalline and pure homogeneous phase could be obtained. A novel layered structure, formulated as [Cd₂(NDC)(OH)₂], was isolated when the molar ratio of triethylamine exceeds ca. 0.7. Both products have been characterized using powder X-ray diffraction, IR and Raman spectroscopies, and elemental and thermal analyses.     

Characterizations and preparation of Mg(OH)<Subscript>2</Subscript> nanocrystals through ultrasonic–hydrothermal route

Magnesium hydroxide [Mg(OH)₂] nanocrystals with excellent dispersity and good crystallinity were efficiently synthesized through the ultrasonic and hydrothermal synergetic effect. The morphology, structure, and thermochemistry of Mg(OH)₂ nanocrystals were researched by TEM, XRD, FT-IR, and DTA, respectively. The mechanism of ultrasonic–hydrothermal synergistic effect was discussed. In addition, Mg(OH)₂ nanocrystals were added into polypropylene (PP) to form composite materials, and the mechanical properties of Mg(OH)₂–PP composites were investigated. Compared with the other two Mg(OH)₂ PP composites, the Mg(OH)₂–PP composite had the best mechanical property when the Mg(OH)₂ was synthesized by ultrasonic–hydrothermal route.     

The Formation and Structural and Phase Transformations of Aluminum Hydroxy Species in Hydrothermal Synthesis under Conditions of Homogeneous Precipitation from Sulfate Solution

By X-ray powder diffraction analysis, Raman spectroscopy, scanning and transmission electron microscopy, and low-temperature nitrogen adsorption method, it was studied how the temperature of hydrothermal synthesis affects the phase composition of precursor species and the structure and morphology of alumina obtained under conditions of low-temperature hydrothermal synthesis at 90–130°C in the system 0.5Al₂(SO₄)₃ · 18H₂O∥0.2C₁₆H₃₃(CH₃)₃NBr∥5i-PrOH∥85H₂O∥2CO(NH₂)₂. It was found that, at T_HTS = 90–110°C, alumina microspheres with globular structure form from X-ray amorphous hydrated alumina with an admixture of NH₄Al₃(SO₄)₂(OH)₆. It was shown that needle-like alumina particles with slitlike pores form from NH₄Al(OH)₂CO₃ obtained at T_HTS = 110–120°C. At T_HTS = 130°C, under conditions of the formation of γ-AlOOH, alumina spherulites constituted by needle-like particles with block–layer structure form. It was determined that the temperature range of the formation of metastable crystalline modifications of alumina is controlled by the phase composition of hydrothermal synthesis products.     

Synthesis, characterization and thermochemistry of K2B5O8(OH)·2H2O

A pure hydrated potassium borate K₂B₅O₈(OH)·2H₂O has been synthesized under mild hydrothermal conditions and characterized by single-crystal X-ray diffraction, XRD, FT-IR, Raman spectra and DTA-TG. The crystal structure consists of two K-O polyhedra and [B₅O₈(OH)]²⁻ polyborate anion. The enthalpy of formation was determined to be −4772.6 ± 4.0 kJ mol⁻¹ by solution calorimetry.     

Synthesis and study of sodium triuranate Na<Subscript>2</Subscript>(UO<Subscript>2</Subscript>)<Subscript>3</Subscript>O<Subscript>3</Subscript>(OH)<Subscript>2</Subscript>

Sodium triuranate Na₂(UO₂)₃O₃(OH)₂ was synthesized by the reaction between aqueous uranyl acetate solution and aqueous sodium nitrate solution under hydrothermal conditions at 200°C. The composition and structure of the synthesized compound were determined, and its dehydration and thermal decomposition were studied, by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis.     

Thermal analysis of nickel oxide films

Nickel oxide films were prepared by chemical deposition on glass substrates using nickel sulphate and potassium persulphate in ammonia solution. Coatings dried in air and at 85°C were characterized by thermal analysis (TG and DTG), FT-IR spectroscopy and X-ray diffraction. The films could be formulated as hydrated forms of 4Ni(OH)₂·NiOOH and Ni₃O₂(OH)₄ respectively. The coatings lost water and oxygen on heating to give NiO.     

Comparative investigation of reactivity of different kinds of fly ash in alkaline media

Comparison of the influence of temperature and different alkali activators on the reactivity of two types of fly ash (conventional, fluidized) was presented. The main emphasis was put on fluidized fly ash as potential component of binding mixtures containing low amount of cement. Conventional fly ash was used as a reference. It was found that for these materials the key differences affecting products of activation are: availability of calcium and sulfate ions as well as structure of fly ash grains influencing dissolution of aluminate and silicate species. Fluidized fly ash, contrary to conventional fly ash, undergoes reaction in 0.1 M solutions of hydroxides forming mainly ettringite. In the case of 4 M hydroxides, both fly ashes undergo hydration processes. Conventional fly ash formed mainly amorphous aluminosilicate gel, while fluidized fly ash may create zeolitic products especially in the case of elevated temperature of early hydration. Sulfate and alkali ions can be incorporated into aluminosilicate structure of new formed products; however, this process depends strictly on the type of used hydroxide and its concentration. The presence of Ca(OH)₂, carbonates and alkali sulfates was also registered in the case of hydrated fluidized fly ash.

     

Synthesis and properties of calcium hydroxyapatite/carbon fiber composites

Composites comprising micrometer-sized carbon fibers (CFs) and biocompatible nanocrystalline calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HA, NCHA), containing 1.0, 2.0, and 5.0 wt % CFs, have been synthesized in the course of precipitation from aqueous solutions in the Ca(OH)₂–H₃PO₄–CF–H₂O system. Some physicochemical characteristics of the precursor CFs and synthesis products have been determined using chemical, X-ray diffraction, and thermal analyses, IR spectroscopy, and scanning and transmission electron microscopy. An analysis of composition–synthesis conditions–structure–particle size–property correlations indicates that the presence of CFs in HA/CF composites strongly decreases the sizes and modifies the habit of NCHA. A rise of CF content in the HA/CF composite is accompanied by a decrease in particle size and a rise in solubility of NCHA.