Atomistic insight into the hydration and proton conducting mechanisms of the cobalt doped Ruddlesden-Popper structure Sr3Fe2O7-δ

Sr₃Fe₂O_7-δ (SFO) with two-layer Ruddlesden-Popper (R–P) structure has recently been proved to be a promising material for the single phase cathode in proton conducting solid oxide fuel cells (P–SOFCs). To investigate the hydration reactions and proton conducting mechanisms of SFO and cobalt doped SFO (SFCO), both bulk and surface properties were calculated. We conclude that R–P structures have advantages in P–SOFCs. The unique Sr–O–M layer can facilitate the hydration process. Although in Sr–O–F and Sr–O–N layers, it is difficult for the formation and migration of oxygen vacancies, protons are most stable. Furthermore, cobalt doping can not only improve the electronic conductivity but also enhance surface properties of SFCO. The easily exposed Co–Fe–O surface can also facilitate the hydration reactions on the surface. Our work could give an informative insight into the relationships among the doped elements, the R–P structures, the hydration process and the proton conducting properties.     

分散剂FDN对G级油井水泥作用机理探讨

采用液相电导法和酸度法研究了分散剂FDN对G级油井水泥水化速度的影响。发现FDN促进水泥的早期水化,但吸附-络合作用及磺酸根离子对Ca(OH)_2核晶过程的“毒化”作用使后期水化速度减慢。本研究证实ζ电位升高是FDN广生分散作用的主要因素。当FDN的吸附达饱和时,ζ电位达最大值,水泥浆的分散程度最大。     

Intermolecular interactions and formation of the hydration sphere in phosphonic acid model systems as an approach to the description of vinyl phosphonic acid based polymers

Molecular model systems based on propyl phosphonic acid (ppa) were studied by means of density functional theory calculations in order to describe the acid-acid interaction and the formation of the hydration sphere. The formation of ppa dimers is reported and the energetic difference between two dimer structures is presented. The hydration sphere of ppa was represented by model systems ppa(H₂O)_n, for which the system with n=4 formed the first hydration sphere (h¹), while n=7 can be considered a good approximation to the complete inner hydration sphere around the phosphonic acid group. The study of the ppa-H⁺ (H₂O)_n model systems showed an interesting structural behavior comparatively to the ppa(H₂O)_n systems. The protonated acids exhibited equivalent phosphorous-oxygen bonds and a general molecular structure is proposed to represent these protonated species.     

The hydration phase and pore structure formation in the blends of sulfoaluminate-belite cement with Portland cement

Sulfoaluminate-belite (SAB) cements are an attractive class of low-energy cements from the viewpoint of saving energy and releasing less CO₂ into the atmosphere during their production. Their hydraulic activity, however, does not match that of the ordinary Portland cement (PC) and needs improvement before they can be used on their own. However, SAB cements when blended with PC have the potential to be used effectively in traditional applications as shown by this study. Mortars made with blends of SAB cements and PC, and a cement-to-sand ratio of 1:3 by weight and a water-to-cement ratio of 0.5, indicate a superior protection against corrosion of steel to those made with blends of PC and blast-furnace slag (BFSPC). The prepared mortars were stored at 20 °C for 90 days under either a 60% relative humidity (RH)-dry air, or 100% RH-wet air conditions. With further improvement in the SAB cement quality through better understanding of their characteristics, a genuine competition between SAB/PC and BFSPC can be expected in practice.     

溶剂萃取中的盐析效应与软硬酸碱原理

软硬酸碱(HSAB)原理是六十年代美国化学家Pearson首先提出的。这一原理的提出,本是经验总结,然而许多研究者根据酸碱的一些基本性质,如电负性、电离势、电子亲合势、离子势等,提出了几种酸碱软硬度的定量标度,使之具有理论意义,从而定量或半定量地说明碱酸的反应性及其他性质。     

磷石膏的微量组分及其对水泥凝结、水化和硬化的影响

借助差热分析、热失重、X射线衍射和扫描电镜等测试手段,分析了磷石膏的微量组分,研究了磷石膏对硅酸盐水泥物理性能及水化过程和水化产物的影响,进而探讨了磷石膏对水泥单矿物的水化作用机理。     

Limestone filler cement in low w/c concrete: A rational use of energy

The effect of limestone filler (up to 20%) on the degree of hydration, the volume of hydration products, and the optimal replacement of limestone filler in cement pastes at different w/cm ratios (0.25-0.50) were investigated by using a quadratic statistical model. The results show an increase in the degree of hydration in very low w/cm ratio paste when the limestone filler content is increased. However, the largest volume of hydration products occurs for high w/cm ratio pastes, for which the available space also increases with the limestone filler content. Finally, for a given cement, the optimum limestone filler content for different w/cm ratios can be obtained by using the gel-space ratio concept.In addition, concrete mixtures (w/cm=0.30 and 0.34) were made to determine the compressive strength. The results have shown that concretes containing limestone filler cements present a small reduction of strength at 28 days improving the hydration of clinker particles in the system. The strength of concrete depends on the gel-space ratio, which takes into account all of the effects produced by limestone filler addition: the increase of the degree of hydration, the dilution, and the increase of the effective w/c ratio.     

Alkali release characteristics of blended cements

This paper presents results of an experimental program conducted to investigate the capacity of hydration products of different cementing materials to retain “bound” alkalis when the alkalinity of the surrounding solution drops. The study covered paste samples containing high-alkali Portland cement and various levels of silica fume and/or fly ash. The results showed that the ability of the hydration products of cement-fly ash systems to bind alkalis is a function of the CaO content of the fly ash, the binding increasing as the calcium content decreases. High-alkali fly ashes (Na₂O_e > 5.0% and CaO in the range of 15% to 20%) showed considerable amounts of alkali contributed to the test solutions. Silica fume does not have a high capacity to retain alkalis in its hydration products; however, ternary blends containing silica fume and fly ash have excellent capacity to bind and retain alkalis.     

The role of calcium ions and lignosulphonate plasticiser in the hydration of cement

Experiments involving equilibrium dialysis, conductivity, X-ray diffraction analysis (XRD), differential thermal analysis (DTA) and isothermal titration calorimetry (ITC) have been carried out to investigate the role of calcium ions and polymeric plasticisers in cement/admixture hydration. Results from a study of lignosulphonic acid, sodium salt, acetate as a plasticiser shows that a plasticiser has dual role; one mainly as a kinetic inhibitor (poison) in cement hydration mechanism and the other as a dispersant. Evidence of a weak Ca²⁺ binding to lignosulphonate sulphonic moieties was found at low ionic strengths of 0.1 M using ITC. No evidence of formal Ca²⁺ binding to lignosulphonate sulphonic acid moieties was found using equilibrium dialysis at higher ionic strength of 1 M (ionic strengths of 0.4 M are typically found in Portland cement pore solution), as is often suggested in cement/admixture literature.     

Study of alinite cement hydration by impedance spectroscopy

Two types of alinite cements, Mg-alinite and Zn-alinite, were synthesized using the reagent grade chemicals. Their hydration behavior was compared with ordinary Portland cement (OPC) using impedance spectroscopy (IS) and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy. The bulk resistance in the IS spectra and the intensity ratio of the hydrous (Q₁ and Q₂) to anhydrous (Q₀) phases in the NMR spectra were estimated as the extent of hydration. The results obtained from both techniques were consistent each other. Mg-alinite had a comparable hydration rate to OPC and Zn-alinite exhibited faster hydration kinetics than Mg-alinite.