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1.
The hydration of tricalcium silicate containing Al2O3 admixture has been investigated using calorimetry, DTA, TG and XRD methods.
Zusammenfassung Mittels kalorimetrischer, DTA-, TG- und XRD-Methoden wurde die Hydratierung von Trikalziumsilikat unter Zusatz von Al2O3 untersucht.

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2.
3.
The hydration of tricalcium silicate, Ca3SiO5, in a small steel ball mill at room temperature was investigated. The stoichiometry of the reaction is represented by 2Ca3SiO5 + 6H2O = Ca3Si2O7·3H2O + 3Ca(OH)2 The initial products of the reaction are calcium hydroxide (both crystalline and amorphous) and a calcium silicate hydrate, designated as “hydrate III.” The latter shows marked similarities to the calcium silicate hydrate, tobermorite, produced by other methods of hydration of Ca3SiO5. The similarities include CaO/SiO2 ratio, specific surface area, water content, heat of solution, heat of hydration, and surface energy (enthalpy).Hydrate III differs from tobermorite in that it is unstable; it slowly converts to another calcium silicate hydrate, afwillite. The chemical formula of afwillite is Ca3Si2O7·3H2O, the same as that of hydrate III and tobermorite, but afwillite has a different crystal structure, and it is a well-crystallized substance. Hydrate III appears to be a form of tobermorite with a structure so disordered that it exhibits only a single X-ray diffraction line, that corresponding to the strongest line of tobermorite.The kinetics of the hydration reaction and of the conversion of hydrate III to afwillite were examined. A possible mechanism for the former was proposed.  相似文献   

4.
In this research, the influences of nano-limestone (NC) on tricalcium silicate (C3S) hydration, including early hydration rate, setting time, Ca(OH)2 content, quantification of C–S–H, micrographs of hydration products and compressive strength, were investigated by different methods. Calorimetry results show that the first and second exothermic peak of C3S with 1 mass% NC is ~29 and ~5% higher than that of control sample and the second peak appears 32 min in advance. Besides, the total hydration heat of C3S with 1 mass% NC increases by 10.08% compared to control sample at 72 h. The initial and final setting time of C3S with 1 mass% NC shortens by 23 and 17 min, respectively. In addition, thermal analysis results show that adding NC leads to higher Ca(OH)2 and C–S–H content at all ages (1, 3 and 28 days). All of the above results imply that the hydration progress of C3S is accelerated by NC. Correspondingly, the compressive strength of C3S with 1 mass% NC increases by 9.88% at 28 days. Besides, EDS results reveal that the Ca/Si ratio of C–S–H gel decreases after NC modification. However, excessive content NC (4 mass%) reduces the acceleration effect of NC on C3S hydration and finally leads to relative low content of Ca(OH)2 and C–S–H compared with C3S sample containing 1 mass% NC.  相似文献   

5.
The calcium hydroxide content in the tricalcium silicate pastes hydrating with the amorphous silica and solid calcium hydroxide addition were determined using the TG method. The effect of the accelerated Ca(OH)2 growth at the lower silica contents was proved. The significant hydration rate increase at higher silica contents was also confirmed.
Zusammenfassung Unter Anwendung von TG wurde der Calciumhydroxidgehalt bei der Hydratation von Tricalciumsilikat mit Zusätzen von amorphem Siliziumdioxid und festem Calciumhydroxid ermittelt. Der Einfluß des beschleunigten Ca(OH)2 Wachstumes bei niedrigeren Siliziumdioxidgehalten wurde erwiesen. Eine eindeutige Erhöhung der Hydratationsgeschwindigkeit bei höheren Siliziumdioxidgehalten wurde ebenfalls bestätigt.
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6.
The hydration kinetics of C3S pastes can be easily evaluated by DTA using the most intense and reversible transition of C3S. Some modifications are proposed to Ramachandran's method concerning the measurement of this effect, the weight of the sample used for each experiment and the heating rate. The results of the hydration degree versus times of C3S agree reasonably with those reported by Ramachandran, while still better agreement is observed with those of Locher who used X-ray quantitative analysis.
Zusammenfassung Die Hydratisierungskinetik von C3S Pasten kann mittels DTA leicht bewertet werden, falls der intensivste und am meisten reversible Übergang von C3S genutzt wird. Einige Änderungen zur Methode von Ramachandran bezüglich der Messung dieses Effekts, des Gewichts der bei den einzelnen Messungen eingesetzten Proben und der Aufheizgeschwindigkeit werden vorgeschlagen. Die Ergebnisse des Hydratisierungsgrades von C3S in Abhängigkeit von der Zeit sind in guter Übereinstimmung mit denen von Ramachandran, während eine noch bessere Übereinstimmung mit den Werten von Locher beobachtet werden kann, welcher sich jedoch der quantitativen Röntgenanalyse bediente.

Résumé La cinétique de l'hydratation des pâtes de C3S peut être facilement déterminée par ATD, en utilisant la transition de C3S la plus intense, qui est réversible.On propose des modifications à la méthode de Ramachandran, concernant la mesure du phénomène, le poids des échantillons utilisés pour chaque expérience et le choix de la vitesse de chauffage. Les résultats donnant le degré d'hydratation de C3S en fonction du temps sont en bonne concordance avec ceux publiés par Ramachandran tandis qu'une concordance encore meilleure est observée avec les résultats de Locher obtenus par analyse quantitative aux rayons X.

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Financial support by Consiglio Nazionale delle Ricerche (Italy).  相似文献   

7.
Portland cement is a mixture of solid phases which all react with water. Tricalcium silicate (Ca3SiO5) is its main component and is often used in model systems to study cement hydration. It is generally recognized that setting and hardening of cement are due to the formation, by a dissolution-precipitation process, of a calcium silicate hydrate (C-S-H) on anhydrous grains during Ca3SiO5 hydration. The purpose of this paper is to study the effect of Ca3SiO5 particle size on the nucleation-growth process of C-S-H. An experimental study of the rate of hydration by using different grain sizes under controlled conditions has been performed. The experimental data have been compared with results obtained by numerical simulation based on a particles-aggregation model. The thickness of the C-S-H layer when the reaction becomes limited by diffusion has been then estimated.  相似文献   

8.
Marton A  Kocsis E  Inczédy J 《Talanta》1983,30(9):709-712
The adsorption of water vapour on anion-exchangers of various degrees of cross-linking ( x 2, x 4, x 8, x 10) and in different ionic forms (Cl(-), Br(-), I(-)) was studied by the isopiestic technique. The calculated integral free-energy changes were independent of the degree of cross-linking of the resins. With increase in the number of adsorbed water molecules the free-energy functions approached limiting values which were characteristic for the counter-ions. The free-energy change was combined with the enthalpy of water sorption (obtained from direct calorimetric measurements) to obtain the entropy change due to the water uptake. Both the enthalpy and the entropy functions indicated the existence of several processes during the adsorption of water, among which the most relevant are hydration, swelling of the matrix, and dilution of the internal electrolyte of the ion-exchanger.  相似文献   

9.
A new experimental approach based on the combination of calorimetric and FTIR spectroscopic measurements was proposed to study simultaneously the sorption of water and organic solvent, and corresponding changes in the structure of protein films in the water activity range from 0 to 1.0. Enthalpy changes (ΔHtot) on the interaction of water with the dried human serum albumin (HSA) in the presence and absence of acetonitrile (AN) have been measured using a Setaram BT-2.15 calorimeter at 298 K. Spectroscopic data on water and organic solvent vapor sorption by the HSA films and the corresponding changes in the protein secondary structure were determined by means of a Bruker Vector-22 FTIR spectrometer. By using a water activity-based comparison we characterised the effect of acetonitrile on the hydration and structure of the HSA films. Acetonitrile (AN) sorption isotherm resembles a smooth curve. HSA film binds about 250 mol AN/mol protein at the lowest water activities. As the water activity increases from 0 to 0.8, the sorption of AN gradually decreases from 250 to 150 mol AN/mol HSA. At aw > 0.8, the sorption of AN sharply decreases to zero. Acetonitrile decreases markedly the water content at a given aw. This behavior suggests that the suppression in the uptake of water is due to a competition for water-binding sites on the HSA films by acetonitrile. Changes in the secondary structure of HSA were determined from infrared spectra by analyzing the structure of amide I band. Acetonitrile increases the intensity of the 1654 cm−1 band that was assigned to the α-helix structure. Changes in the intensity of the 1654 cm−1 band agree well with the decrease in water uptake in the presence of AN. An explanation of the acetonitrile effect on the hydration and structure of the HSA films was provided on the basis of hypothesis on water-assisted disruption of polar contacts in the initially dried protein.  相似文献   

10.
Although amino trimethylene phosphoric acid (ATMP) has been widely used as a retarder for Portland cement, its effect on cement hydration is poorly understood at the atomic level. In this study, we combine static calculation and ab initio molecular dynamics (AIMD) simulation to reveal the mechanism of the effect of ATMP on the initial stage of C3S hydration from multiple perspectives, quantitatively analyze the structural reconstruction and charge migration at the ATMP/C3S interface in the aqueous environment. By adsorbing on the surface of C3S, ATMP occupies the adsorption site of water molecules. Compared with the pure C3S surface, the addition of ATMP delays the hydroxylation of the C3S surface and inhibits the formation of Ca-Ow bonds. This work gives new insights into understanding the hydration of C3S with ATMP and offers new approach of designing new cement retarder at the molecular level.  相似文献   

11.
The effect of the temperature on the co-extraction of water molecules with Na+ from water to nitrobenzene (NB) in the presence of dipicrylaminate ion has been studied. The number (n) of water molecules co-extracted with a Na+ ion, as measured by the Karl Fischer method, increased from 3.1 to 5.2 with increasing temperature (6-65 degrees C). This observation is in apparent contradiction to the expectation from simple thermodynamics because hydration is generally an entropically unfavorable process. Additional 1H NMR experiments for the selective hydration of Na+ in deuterated NB have confirmed that the association constants of water with Na+ indeed decrease with increasing temperature. On the other hand, however, it has been shown that water solubility into NB substantially increases with temperature. We conclude that the latter effect overwhelms the former unfavorable entropy effect, which results in a net increase of the n-value, as observed.  相似文献   

12.
《Liquid crystals》2000,27(1):137-143
Differential scanning calorimetry was used to investigate the confinement effects on the phase transition behaviour of a discotic liquid crystal. The liquid crystal studied is the hexa-n-octanoate of rufigallol (RHO); Millipore membranes of various pore sizes were the confining materials. The polymorphism of RHO is affected by confinement. The transition from an enantiotropic columnar phase (D1) to a monotropic columnar phase (D2) is supressed in membranes with pore sizes 500 A. The transformation from D1 to the crystalline phase is also perturbed, particularly in the membrane having an average pore size of 250 A. In the first case the crystal formed displays a double-melting endotherm, with a distinct structure melting at lower temperatures; in the other, the induction period of isothermal crystallization becomes longer and the global rate of crystallization is slowed. However, confinement shows no effect on the overall crystallization mechanism; a similar Avrami constant of n ~ 3 was obtained for both confined and bulk RHO. An analysis of the results is presented.  相似文献   

13.
Differential scanning calorimetry was used to investigate the confinement effects on the phase transition behaviour of a discotic liquid crystal. The liquid crystal studied is the hexa-n-octanoate of rufigallol (RHO); Millipore membranes of various pore sizes were the confining materials. The polymorphism of RHO is affected by confinement. The transition from an enantiotropic columnar phase (D1) to a monotropic columnar phase (D2) is supressed in membranes with pore sizes 500 A. The transformation from D1 to the crystalline phase is also perturbed, particularly in the membrane having an average pore size of 250 A. In the first case the crystal formed displays a double-melting endotherm, with a distinct structure melting at lower temperatures; in the other, the induction period of isothermal crystallization becomes longer and the global rate of crystallization is slowed. However, confinement shows no effect on the overall crystallization mechanism; a similar Avrami constant of n ~ 3 was obtained for both confined and bulk RHO. An analysis of the results is presented.  相似文献   

14.
N,N-Dimethylformamidine and novel N,N-diisopropylformamidine protecting groups were used to carry out a one-pot conversion of aminobenzoic acids into the corresponding amides. General conditions for an in situ transformation of aminobenzoic acids and their heterocyclic analogues into the corresponding formamidine-protected acid chlorides were developed. These chlorides were used in reactions with amines, including poorly reactive anilines. The protected amides were then smoothly deprotected by heating with ethylenediamine derivatives, resulting in a general procedure for the one-pot transformation of aminobenzoic acids into their amides. Our one-pot procedure was successfully applied to the preparation of several compounds of pharmaceutical interest.  相似文献   

15.
Molecular dynamics simulations are performed to study the effects of pressure on the hydrophobic interactions between neopentane molecules immersed in water. Simulations are carried out for five different pressure values ranging from 1 atm to 8000 atm. From potential of mean force calculations, we find that with enhancement of pressure, there is decrease in the well depth of contact minimum (CM) and the relative stability of solvent separated minimum over CM increases. Lower clustering of neopentane at high pressure is also observed in association constant and cluster-structure analysis. Selected site-site radial distribution functions suggest efficient packing of water molecules around neopentane molecules at elevated pressure. The orientational profile calculations of water molecules show that the orientation of water molecules in the vicinity of solute molecule is anisotropic and this distribution becomes flatter as we move away from the solute. Increasing pressure slightly changes the water distribution. Our hydrogen bond properties and dynamics calculations reveal pressure-induced formation of more and more number of water molecules with five and four hydrogen bond at the expense of breaking of two and three hydrogen bonded water molecules. We also find lowering of water-water continuous hydrogen bond lifetime on application of pressure. Implication of these results for relative dispersion of hydrophobic molecules at high pressure are discussed.  相似文献   

16.
The enthalpies of formation in the condensed and gas states, Delta f H m degrees (cd) and Delta f H m degrees (g), of 2- and 3-thiopheneacetic acids were derived from their respective enthalpies of combustion in oxygen, measured by a rotating bomb calorimeter, and the variation of vapor pressure with temperature determined by the Knudsen effusion technique. Theoretical calculations at the G3 level were performed, and a study on molecular and electronic structure of the compounds has been carried out. Calculated Delta f H m degrees (g) values using atomization and isodesmic reactions are compared with the experimental data. Experimental and theoretical results show that the 3-thiopheneacetic acid is thermodynamically more stable than the 2-isomer.  相似文献   

17.
The precipitation of calcium phosphate was studied using a heat flow twin calorimeter (C80, Setaram, France). The process was carried out using two identical membrane vessels. In the lower parts of both vessels 2 mL of a supersaturated solution (solution A) containing Ca(H2PO4)·2H2O (0.054 M) and CaCl2·H2O (0.125 M) with a molar ratio Ca/P = 1.67 were added. Then 0.05 mL of an ammonium solution (25% w/w) (solution B) and 0.05 mL of distilled water were transferred in the upper parts of sample and reference vessels, respectively. After temperature had been maintained at 303, 313, 323 and 333 K the membranes of both sample and reference vessels were broken simultaneously. The precipitation process also repeated with the same conditions for periods of 15, 60 and 120 min in a bath. The first two calorimetric curves (303, 313 K) show a single exothermic step during the process as a sharp peak in the initial stage. On the contrary at the experimental temperature of 323 K except of the sharp peak in the initial stage, a steadily exothermic tendency appears after 100 min time. In higher temperature (333 K) the sharp peak appears in the initial stage followed by a broad exothermic step between 75 and 320 min time. The XRD analyses show that the solids in the initial experimental stages are mainly consisted of dicalcium phosphate dihydrate (DCPD) for the lower temperature and a biphasic or triphasic system consisted of hydroxyapatite (HA), dicalcium phosphate anhydrous (DCPA) and octacalcium phosphate (OCP) for the rest temperatures. The XRD analyses show also that during the solution aging the initial products are transformed into the more stable thermal forms of HA and octacalcium phosphate (OCP).  相似文献   

18.
The influence of the linear, positively charged detergent cetyltrimethylammoniumchloride (CTAC1) on the well known phase behaviour of fully hydrated dipalmitoylphosphatidylcholine (DPPC) has been studied along fourteen isopleths of the phase diagram using high sensitivity scanning microcalorimetry. Particular interest was focused towards the effects of very small amounts of detergent down to the region of 1 CTAC1 per 104 DPPC-molecules.Even starting with such low concentrations distinct changes of the thermograms are detectable by high sensitivity DSC. Essentially, the phase diagram is cut into four domains between the two limiting cases of pure phospholipid multilamellar dispersion and isotropic solution of detergent micelles, respectively. At the present stage these four regions in the phase diagram are identified as follows : 1. 0–1 Mol % CTAC1: a modified lamellar phase 2. 1–50 Mol % CTAC1: a two-phase region with this modified lamellar phase coexisting with a newly formed detergent-rich phase. 3. 50–90 Mol % CTAC1: large mixed micelles. 4. > 90 Mol % CTAC1: an isotropic solution of small mixed phospholipid/detergent micelles.  相似文献   

19.
Sulfate-rich belite sulfoaluminate (BSA) cements with varied phase compositions were synthesized in this work. The presence of sulfate in the clinker is in the form of anhydrite in addition to calcium sulfoaluminate. The aim of this paper is to study the effect of mineral composition on cement properties. Experimental results indicate that the improvement of early-age strengths mainly depends on the hydration of ye’elimite. The increase of ferrite content promotes the compressive strength after 7 days of hardening, but has adverse effect on cement strength at early ages. The optimum content of ferrite is between 10 and 20% for BSA cement containing approximately 35% ye’elimite. Different amounts of natural gypsum were added to the synthetic sulfate-rich BSA clinkers and we found that anhydrite formed in BSA clinkers can replace natural gypsum to facilitate the hydration of ye’elimite.  相似文献   

20.
DTA was used to study the formation of calcium aluminoferrite from CaO, Al2O3 and Fe2O3 (proportion=2 x 1–x),x=0-3/4) and the effects of C4A3 C11 A7·CacF2, -C2S and MgO on that process. The fusion of CF and the eutectic of CaO-Fe2O3, CA-C12A7, CA-C3A, C12A7-CA-C3A and CA-C2AxF(1–x) will be favourable for the formation. The presence of -C2S and MgO will decrease its formation temperature by an extra eutectic while C4A3 . and C11A7·CaF2 will not.The early heat evolution during the hydration of C2AxF(1–x) were measured by the conduction calorimeter made by ourselves and the products after 1 day hydration were examined by TG and DTA. The results revealed that the peak of heat evolution rise, the amount of the hydrating product iron hydrate gel decreases, CAH10 and C3(A, F)H6 increase with the increase of the value x. The more MgO (up to 5%) soluted in C6AF2, the higher the hydration heat for this solid solution is, when TiO2 soluted in C6AF2 is 2%, the hydration heat for the system reaches the highest.This project is supported by National Natural Science Fundation of China and by the National Science and Technology Developing Fundation in Building Materials Field.  相似文献   

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