Calcite,vaterite and aragonite forming on cement hydration from liquid and gaseous phase

Cement hydration products were studied as influenced by the hydration conditions (hydration time in liquid phase; relative humidity, RH, in gaseous phase). The formation of calcium hydroxide (portlandite, P) and its transformation to calcium carbonates is mainly discussed here. More hydration products, including P, were formed in liquid phase (paste) than in water vapor (powder), due to the higher availability of water molecules. Full hydration was observed only in the paste hydrated for 6 month, otherwise the P content, estimated from its water escape, DM(400-800°C), increased after storage in water vapor of the prehydrated paste. All the three polymorphs of CaCO₃ (calcite, vaterite and aragonite) were found on prolonged contact with air of the hydrated powder (XRD, HRTEM). Their content was dependent on sequence of RH conditions on hydration: higher after water retention, WR, on lowering RH=1.0→0.95→0.5, than after water sorption, WS, on increasing RH in the inverse order. It increased also on wetting and drying, both of hydrated powder and paste. Ca was found to accumulate on the micro-surfaces of WR samples (SEM, TEM), whereas more Al was observed on WS samples and the crystallinity of hydration products was here higher (ED). Dissolution-diffusion-recrystallization was possible: small Al-ions concentrated at one end and the bigger Ca ions - at the other end of some needles (TEM). At 400-500°C the P in cement transforms in air into CaCO₃, which decomposes at 600-700°C. Thus the sensitivity to carbonation was estimated from ΔM(600-800°C). This value was similar in pastes hydrated for 1 month and in powder (WR). It was lower in powder WS and much lower in the paste (6 months). It increased pronouncedly when the prehydrated paste was stored in water vapor in WS. The nanocrystals of portlandite, vaterite and aragonite, embedded in the amorphous matrix, were observed by HRTEM in the hydrated powder. They may contribute to the cement strength. This revised version was published online in July 2006 with corrections to the Cover Date.     

Specific surface of two hydrated cements differing in strength

Specific surface, S, of CSH-gel particles of disordered layered structure, was studied by water sorption/retention in two cement pastes differing in strength, i.e. C-33 (weaker) and C-43 (stronger), w/c=0.4. Hydration time in liquid phase was t _h=1 and 6 months, followed by hydration in water vapour either on increasing stepwise the relative humidity, RH=0.5→0.95→1.0 (WS) or on its lowering in an inverse order (WR). Specific surface was estimated from evaporable (sorbed) water content, EV (110°C), assuming a bi- and three-molecular sorbed water layer at RH=0.5 or 0.95, respectively (WS). On WR it was three- and three- to four-molecular (50 to 75%), respectively, causing a hysteresis of sorption isotherm. At RH=0.5 the S increased with cement strength from 146 m² g^-1 (C-33, 1 m) to 166 m² g^-1 (C-43, 1 m) and with hydration time to 163 (C-33, 6 m) and to 204 m² g^-1 (C-43, 6 m). At RH=1.0 (and 0.95), higher S-value were measured but these differences were smaller: S amounted to 190-200 m² g^-1 in C-33 (1 and 6 m) and 198-210 m² g-1 in C-43 (1 and 6 m). Thus no collapse occurred on air drying of paste C-43 (6 m). This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal mass changes of portland cement and SLAG cements after water sorption

A simple water sorption/retention (WS/WR) test, followed by stepwise static heating, was applied to the study of cement quality and the reactivity of its grain surface. The physically bound water and hence the specific surface both in the unhydrated and in the hydrated state were estimated as a function of the hydration time. Rehydration after heating at 220°C and contact with air was different inWS from that inWR samples, which indicates a difference in microstructure. XRD proved the formation of portlandite during the sorption test and eventual heating at 200°C, and its transformation into carbonates on contact with air, especially on heating at 400°C. The contents of these compounds were estimated from the mass difference between 400 and 800°C, which was compatible with the mass change between 220 and 400°C and this indicates surface reactivity. The test may serve for the routine study of cement. Dedicated to Professor Lisa Heller-Kallai on the occasion of her 65^th birthday     

Influence of two different fly ashes on the hydration of portland cements

Fly ashes from the combustion of coal thermal power stations are commonly incorporated into portland cements and/or concretes and mortars. The chemical and morphological composition of fly ashes, together with their particle size, make them suitable as pozzolanic(non-calcic) or pozzolanic/hydraulic(highly calcic) additions to manufacture such building materials. This work focuses on the incorporation of two different fly ashes (non-calcic but of very different Fe₂O₃(%) contents, fineness and morphology) to two ordinary portland cements (of very different mineralogical composition as well), to determine the effects those have and the interactions they produce in the hydration reactions of portland cement. The main techniques employed for this study have been: conduction calorimetry and Frattini test; secondary techniques applied have also been: determination of setting times and analysis by X-ray diffraction and SEM. Analysis of the results obtained permitted to find different effects of fly ash addition on the hydration reactions of portland cements. Thus, dilution and stimulation effects augment with the increased fly ash percentage. Delay and acceleration of the reactions depend mainly on the type of portland cement and are accentuated with increased fly ash contents. Their behaviour as concerns heat dissipation mainly, depends on the type of fly ash used and is more pronounced with increased cement replacement. On the other hand, the pozzolanic activity of these fly ashes has been revealed at 7 and 28 days, but not at 2 days. Finally, pozzolanic cements can be manufactured using different portland cements and/or types of fly ashes, in the appropriate proportions and compatible qualities, depending on the effect(s) one wish to enhance at a specific age, which is according to previous general conclusions drew out of sulphate attack and chloride attack researches. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simultaneous IR/TG study of calcium carbonate in two aged cement pastes

Two aged cement pastes (7 years) were studied for H₂O and CO₂ evolution, the combined amounts of which were measured by TG and identified by thermo-IR analysis. This indicated the presence of three forms of carbonates, which decomposed at different temperatures. The displacement with time of the evaporation of sorbed water to higher temperatures (500–700°C, TG, MS) shows the possibility of its incorporation into carbonate hydrates and/or hydroxy hydrates, postulated previously. The decomposition of all the hydration products needed a thermal energy increasing with ageing (increased temperature measured by TG). The carbonation process proceeded for 7 years in the weaker paste, whereas it terminated before 5 years in the stronger one. The CSH water content did not change with ageing, whereas that of portlandite was lowered, which though did not account for the increase in carbonate content (TG). Possibly some Ca²⁺ from the CSH gel was involved in this process. In the stronger paste the growth with time of organic matter was found (IR, TG/DTG).     

A Study on the Hydration of Portland Limestone Cement by Means of TG

Subject of this paper is to investigate the hydration process of Portland limestone cement containing 10-35% limestone. Cements, produced by co-grinding of clinker, limestone and gypsum, were hydrated for periods 6 h to 28 d and were studied by means of TG and XRD. The Ca(OH)₂ content of the cements containing limestone is higher than in pure cements, specifically for 10% limestone content and ages more than 1 day. These results are in accordance with the strength development of the studied cements. In earlier ages the Ca(OH)₂ content is slightly lower in the limestone cements and independent of the limestone content. After 1 day curing, the increase of limestone addition causes a relative increase of the non evaporable water. The XRD patterns indicated the presence of carboaluminates in the hydrated limestone cements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of hydration andpH on the thermal stability of proteinase K

The effect of hydration andpH on the thermal stability of proteinase K was studied in the temperature range 310–450 K by differential scanning calorimetry. The dependences of the denaturation temperatureT _d, the specific enthalpy of denaturation H _d and the maximum of excess apparent specific heat capacityC _ex ^max upon the degree of hydrationh and thepH of the buffers used are presented. The relation betweenT _d andh is of the Flory-Garrett's type. By means of Ooi's model, the two components of the denaturation enthalpy arising from hydration and conformational change, respectively, were estimated. The fact that the specific denaturation enthalpy of proteinase K is very low may be attributed to its very low enthalpy of conformational change per heavy atom.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThis major project was supported by the National Natural Science Foundation of China.     

Characterization of synthesizedA-zeolite

Confirmations of the successful synthesis of a particular zeolite demand investigation of the crystals by XRD, SEM, MAS-NMR and chemical analysis. In this work, we have used the DTA exothermic lattice breakdown of theA-zeolite, which gives typical peaks at around 900–1200°C for characterization. The effects ofpH, concentration, time of crystallization and temperature were studied and it was quickly and easily possible to distinguishA-zeolite formation from others originating from the synthesis matrix under different conditions by using DTA/TG analyses. The parameters were optimized for the synthesis of the zeolite and DTA measurements yielded enough information to identify theA-zeolite; this was confirmed by XRD and SEM.     

不同条件对硫酸钙结晶影响的实验研究

近年来由于微波化学的快速发展使人们认识到微波作为一种手段对化学反应的过程有着深刻的影响,在材料领域更是得到了日益广泛的应用,因此把微波应用于结晶过程也成为人们关注的热点。早在1966年磁场就被应用于晶体的生长。近年来,已有很多文献报道电场、磁场对晶体生长的影响。     

Degree of hydration in cement paste and C<Subscript>3</Subscript>A-sodium carbonate-water systems

This research provides a fundamental understanding of the early stage hydration of Portland cement paste, tricalcium aluminate (C₃A) paste at water to cement ratio of 0.5 and C₃A suspension at water to cement ratio of 5.0 modified by 2 or 4 mass% of sodium carbonate. A high conversion of unreacted clinker minerals to gel-like hydration products in the cement-Na₂CO₃ pastes takes place rapidly between 1^st to 24^th h. Contrary the Ca(OH)₂ formation within the same time interval is retarded in the excess of CO₃²⁻ ions due to intensive rise and growth of CaCO₃ crystals in hydrated cement. Later, the conversion of clinker minerals to the hydrate phase is reduced and higher contents of calcite and vaterite relative to that of Ca(OH)₂ in comparison with those found in the Portland cement paste are observed. As a consequence a decrease in strength and an increase in porosity between hardened Portland cement paste without sodium carbonate and those modified by Na₂CO₃ are observed. C₃A hydrates very quickly with sodium carbonate between 1^st and 24^th h forming hydration products rich in bound water and characterized also by complex salts of (x)C₃A·(y)CO₂·(zH₂O type, whereas C₃A-H₂O system offers C₃AH₆ as the main hydration product. Higher content of the formed calcium aluminate hydrates in C₃A-Na₂CO₃-H₂O system also contributes to early strength increase of Portland cement paste.     

Thermodynamic study of poly(N-vinyl caprolactam) hydration at temperatures close to lower critical solution temperature

The lower critical solution temperature of aqueous solutions of poly(N-vinyl caprolactam) falls in the 305–307 K range and depends on the molecular weight of the polymer. The thermodynamic functions of mixing at 298 K have been calculated from measurements of vapor pressures and heats of dissolution and dilution. Partial Gibbs energy, partial enthalpy, and partial entropy of mixing were negative over the entire range of composition. Increasing temperature resulted in a decrease in the exothermal character of mixing. Excessive heat capacity values, calculated from the dependencies of enthalpy of mixing on temperature, were positive over the entire composition range. Heat capacity of dilute solutions was measured at 298 K and partial heat capacity of poly(N-vinyl caprolactam) at infinite dilution was shown to be positive. The data obtained point out the hydrophilic and hydrophobic hydration of poly(N-vinyl caprolactam) in aqueous solutions. Hydrophobic hydration dominates at temperatures close to binodal curve. As a result, the mutual mixing of the polymer with water is decreased and phase separation takes place.     

钙磷物质的量比对磷酸钙骨水泥性能的影响

本研究通过在磷酸钙骨水泥(calcium phosphate cement,CPC)固相配方中添加不同量的氯化钙(CaCl2),制备不同钙磷物质的量比的CPC,研究不同钙磷物质的量比对CPC性能的影响。测试CPC的初、终凝时间。将CPC体外模拟浸泡3d和7d,研究模拟生理条件下CPC的性能,分别利用X-射线衍射(XRD)、力学性能实验机、扫描电镜(SEM)等研究CPC相成分、抗压强度和断面微观形貌。通过化学滴定测定浸泡液中氯离子浓度。结果表明:提高钙磷物质的量比不会显著延长CPC凝结时间;模拟浸泡液中的氯离子浓度处于正常生理条件的范围内;随钙磷物质的量比的增加,水化后CPC的抗压强度显著提高,而经过体外模拟浸泡后,钙磷物质的量比为1.67和1.80的CPC的抗压强度明显下降;具有较高钙磷物质的量比的CPC体外模拟浸泡后,形成多孔结构、弱结晶类骨磷灰石的终产物。     

Hydration of the carboxylate group: Anab initio molecular orbital study of acetate-water complexes

The hydration of the carboxylate group in the acetate anion has been investigated by performingab initio molecular orbital calculations on selected conformers of complexes with the form CH₃CO₂ ^– ·nH₂O·mH₂O, wheren andm denote the number of water molecules in the first and second hydration spheres around the carboxylate group, andn + m 7. The results of RHF/6–31G^* optimizations for all the complexes and MP2/6–31+G^** optimizations for several one-water complexes are reported. The primary consequence of hydration on the structure of the acetate anion is a decrease in the length of the C-C bond. Enthalpy and free energy changes calculated at the MP2/6–31+G^** and MP2/6–311+ +G^** levels are reported for the reactions CH₃CO₂ ^– + [H₂O] _P CH₃CO₂ ^– ·nH₂O ·mH₂O where [H₂O] _P is a water cluster containingp water molecules andp=n+m 7. The calculations show that conformers with the lowest enthalpy change on complex formation are often not those with the lowest free energy change, due to a greater entropic loss in complexes with tighter and more favorable enthalpic interactions. Hydrogen bonding of six water molecules directly to the carboxylate group in CH₃CO₂ ^– is found to account for approximately 40% of the enthalpy change and 37% of the free energy change associated with bulk solvation.     

Equilibria and kinetics characterisation of two different structured nutshell-derived activated carbons

Adsorption equilibria and dynamics ofn-butane on two activated carbon samples prepared from the physical activation of nutshell are studied in this paper. The micropore size distribution (MPSD) is considered as the main source of solid heterogeneity. Lennard-Jones' potential theory and Dubinin's theory (TVFM) are used in the equilibria data to derive the MPSD, which is well fitted by a Gamma distribution function. The adsorption energy distribution derived from the MPSD is very asymmetric for both the samples studied, and this energy distribution used in the HMSD/HMSMD kinetics models for the study of adsorption dynamics ofn-butane.     

The Role of Titanium Dioxide on the Hydration of Portland Cement: A Combined NMR and Ultrasonic Study

Titanium dioxide (TiO₂) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO₂ influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO₂ were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO₂ enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T₁ results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T₁ values and large capillary pores with long T₁ values. During early hydration times, TiO₂ is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO₂ appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results.     

Study on spectroscopy of two flavonyl glycosides from Andrographis paniculata

To study the bioactive constituents from Andrographis paniculata, two compounds were isolated and purified by column chromatography on AB-8 macro-porous adsorption resin and polyamide. Their structures were determined by various spectroscopic methods, including UV, FABMS, ¹H-NMR, ¹³C-NMR, DQFCOSY, TOCSY, HMQC, HMBC, and NOESY. The ¹H-NMR and ¹³C-NMR signals of the two compounds were assigned. The structures of the two compounds were elucidated as 5,4′-dihydroxy-7-methoxyflavone-6-yl-β-D-glucopyranoside and 5,4′-dihydroxy-7-methoxyflavone-8-yl-β-Dglucopyranoside, respectively. __________ Translated from Acta Chimica Sinica, 2007, 65(14): 1399–1402 [译自: 化学学报]     

Process optimization and characterization of thin films of SrFeO3-x by the pechini method

Nanostructured coatings have recently attracted increasing interest because of the possibilities of synthesizing materials with unique physical-chemical properties. Highly sophisticated surface related properties, such as optical, magnetic, electronic, catalytic, mechanical, chemical and tribological properties can be obtained by advanced nanostructured coatings, making them attractive for various industrial applications. In this report we describe our efforts at developing methodology for the fabrication of SrFeO_3-x based thin films using a modified Pechini method. Thin films of SrFeO_3-x were fabricated using spin coating and a drop coating method developed in-house on Al₂O₃ and Si- substrates. The films annealed at 600°C for one hour show a perovskite phase. The grain size increases with increase in annealing temperature. The influence of various variables such as metal to chelant ratio, drying control reagents, calcination conditions, substrate type and mode of film formation were studied using XRD, optical microscopy, SEM and AFM.     

静态顶空-气质联用法测定企业环境水中丙烯酸丁酯残留量

建立静态顶空-气相色谱-质谱联用（HS-GC-MS）测定水样中丙烯酸正丁酯残留量的方法.通过优化顶空进样过程中的平衡温度、平衡时间、盐离子浓度等前处理条件,确定连续测定水样中丙烯酸正丁酯含量的测试方法.水样中丙烯酸正丁酯在顶空平衡温度为50℃、盐离子的质量分数为30%、平衡15 min的条件下,经过毛细管色谱柱进行分离,采用气相色谱-质谱联用仪进行分析,以目标化合物的保留时间和选择离子进行定性,通过氘代乙苯作内标法定量.丙烯酸正丁酯在5~250 mg/L的质量浓度范围内相关系数r²为0.999 8,具有良好的线性关系,通过低、中、高（5、25、100 mg/L）不同质量浓度的加标试验,对方法进行质控,回收率在85.7%~94.6%之间,精密度（RSD）为1.81%~2.79%,方法检出限为0.109 mg/L.方法操作简便,灵敏度和准确度高,稳定性好,适用于水样中丙烯酸正丁酯的残留量测定.     

Synthesis and Microstructural Properties of Fe-TiO2 Nanocrystalline Particles Obtained by a Modified Sol-Gel Method

A series of iron/titanium oxide nanocrystalline particles with Fe/Ti molar ratios up to 0.15 were synthesized by a modified sol-gel technique using Ti(IV)-isopropoxide and anhydrous Fe(II)-acetate. The precursors were mixed and subsequently hydrolyzed with water molecules generated in situ by an esterification reaction between acetic acid and ethanol. As-synthesized samples were amorphous for XRD, independently of the relative amount of doped iron. The undoped samples and samples with the molar ratio Fe/Ti = 0.01, treated at up to 500°C, contained anatase as the dominant phase and rutile as the minor phase. The samples with the Fe/Ti molar ratio of 0.15, treated at the same temperature, contained anatase (major phase), rutile (minor phase) and a very small amount of an unidentified phase. The crystallite size of the dominant phase in the samples was estimated from the XRD line broadening using the Scherrer formula. Thermogravimetric analysis showed that weight loss was accelerated and completed at lower temperatures as the relative concentration of iron in the Fe-TiO₂ samples increased. The strong exothermic peak in the DTA curve between 300 and 450°C in the undoped TiO₂ sample shifted to the lower temperatures and became much more asymmetrical with increased iron doping. This DTA peak corresponded to the amorphous-to-anatase-transition and it included several steps such as (i) the thermal degradation of strongly bound organic molecules, (ii) the condensation of unhydrolyzed –OR groups, (iii) the sintering and growth of particles and (iv) the rearrangement of newly formed chemical bonds. The center of the most intense Raman band of the E _g mode at 143.8 cm^–1 in the undoped TiO₂ sample continually shifted to higher wave numbers and the full-width at half maximum increased with iron doping. Transmission electron microscopy revealed decrease of the mean particle size from 16.3 nm in undoped sample to 9.7 nm in the highest iron doped sample. The particle size distribution becomes narrower with iron doping. The narrowest particle size distribution was found in sample with the Fe/Ti molar ratio of 0.05, calcined at 500°C. Scanning electron microscopy of undoped samples calcined at 580°C showed irregular aggregates having a relatively flat surface. On the contrary, the samples doped with 15 mol% of iron and treated at the same temperature exhibited a non-uniform sponge-like surface with distributed micrometer holes.