聚羧酸减水剂在水泥水化过程中的微观表现

采用SEM、IR、XRD、pH值和电导率等分析手段研究了聚羧酸减水剂对水泥水化初期的影响,结果表明,聚羧酸减水剂具有减缓水泥的初期水化作用,水泥水化产物的聚合度随水化时间增加而增大,但晶型不改变。在水泥中添加0．3％聚羧酸减水剂,32．5#水泥3d、7d和28d的抗压强度分别提高了50．9％、40．4％、35％。     

Model verification of limiting concentration by electrodialysis of an electrolyte solution

The concentration of LiCl in brine and brine volume are obtained as functions of current density by the method of limiting concentration by electrodialysis. These relationships are used for model calculations of current efficiency, the diffusion, osmotic, and electroosmotic permeability of an MK-40/MA-40 membrane pair, and also salt hydration numbers. These theoretical values of water transport numbers and LiCl hydration numbers are compared with corresponding experimental and literature data. It is shown that the model adequately describes the phenomena of the mass electrotransport occurring in electrodialyzers with noncirculating concentration compartments, and it can be successfully applied in calculating the technological parameters of the process, finding the transport properties of ion-exchange membranes, and determining salt hydration numbers in aqueous electrolyte solutions.     

砷和砷酸铁水化结构和红外光谱理论研究

水体中砷的去除与其水化作用密切相关,而不同质子化砷和砷酸铁水化特征相关报道甚少,且缺乏不同质子化砷和砷酸铁水化层红外光谱解析。在B3LYP/6-311G(d, p)计算水平上比较不同质子化砷酸根[H_mAsO₄]m-3(m=0～2)和铁-砷酸盐络合物种[FeH_mAsO₄]m+(m=0-2)水化能,利用约化密度梯度函数图形化分析其与水分子相互作用的强度、类型和位置,并解析不同质子化砷酸根和砷酸铁水化层红外光谱特征。结果表明,随着氢质子化,砷酸根[H_mAsO₄]m-3(m=0～2)水化能力减弱,而铁-砷酸盐络合物种[FeH_mAsO₄]m+(m=0～2)水化能力随着氢质子化增强。当水分子中1个氢与[H_mAsO₄]m-3(m=0～2)中1个氧相互作用时倾向形成氢键;而水分子中2个氢同时分别与[H_mAsO₄]m-3(m=0～2)中两个氧相互作用时,相互作用变弱,以范德华力相互作用;水分子通过其氢与砷酸根中氧形成的氢键强于水分子通过其氧与质子化砷酸根中氢形成的氢键。未质子化O_N倾向与2~4个水分子形成氢键,而质子化O_P最多与2个水分子形成氢键且O_P…H_W氢键弱于O_N…H_W氢键。红外光谱中,2 954,3 114,3 179,3 252和3 297 cm-1是AsO3-₄第一水化层中水分子Ow-Hw伸缩振动峰,3 277,3 324和3 376 cm-1是HAsO2-₄第一水化层中水分子的Ow-Hw伸缩振动峰,3 189,3 277,3 306和3 383 cm-1是H₂AsO-₄第一水化层中水分子Ow-Hw伸缩振动峰;[FeH_mAsO₄]m+(m=0～2)第一水化层中水分子Ow-Hw伸缩振动对应区域依次是2 500~3 060,2 660~3 200和2 900~3 360 cm-1。因此,随质子化,[H_mAsO₄]m-3(m=0～2)和[FeH_mAsO₄]m+(m=0～2)第一水化层中水分子的Ow-Hw伸缩振动峰蓝移;相对于[H_mAsO₄]m-3(m=0～2),[FeH_mAsO₄]m+(m=0～2)第一水化层水分子的弯曲振动峰和伸缩振动峰都明显红移。[FeH_mAsO₄]m+(m=0～2)第一水壳层形成Fe-Ow-Hw…Ow-Hw…O_N-As氢键桥,该氢键桥中Ow-Hw具有特殊吸收峰,伸缩振动峰依次位于2 195,2 526和2 673 cm-1,质子化导致明显蓝移但峰强度几乎无变化;而其弯曲振动峰随质子化红移且强度明显降低;独立O_P-H伸缩振动峰不受Fe络合影响,而O_P-H…Ow中O_P-H伸缩振动峰位置因Fe络合而发生明显蓝移。该研究有助于更好地解析不同PH下砷和砷酸铁在水中溶解性,可用于红外光谱监测水溶液中砷和砷酸铁水化特征。     

Insight into hydration inhibition mechanism of amino trimethylene phosphonic acid on tricalcium silicate from first-principles calculations

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.     

层间水分子含量对铜铁水滑石超分子作用力的影响

构建铜铁水滑石[Cu₃Fe-LDHs-yH₂O(y=0-2)]周期性计算模型, 采用密度泛函理论(DFT), 选取CASTEP程序模块, 对体系进行几何全优化, 从结构参数、氢键布居、Mulliken电荷布居、逐级水合能等角度研究了层间NO₃^-和H₂O的分布形态及其与水滑石(LDHs)层板的超分子作用, 探究了水分子数目对体系姜-泰勒效应的影响. 结果表明, Cu₃Fe-LDHs-yH₂O主客体间存在着较强的超分子作用力, 主要包括氢键和静电作用, 其中氢键作用在水合过程中起主导作用, 氢键强度的顺序是层板-阴离子(L-A)型＞阴离子-水(A-W)型＞层板-水(L-W)型＞水-水(W-W)型; 随着层间水分子数的增加, 层间距先略微降低后显著升高, Cu₃Fe-LDHs体系的Cu—O八面体被逐渐拉长, 层板Cu²⁺的姜-泰勒畸变程度逐渐增大, 体系的逐级水合能绝对值逐渐降低, 说明Cu₃Fe-LDHs的水合程度不会无限增加, 而是具有一个饱和值. Cu₃Fe-LDHs-1H₂O构型接近理想六方晶胞, 层板金属畸变程度最小, 稳定性最高, 层间距与实验值较吻合, 推测其为实验上合成的Cu₃Fe-LDHs较稳定的构型.     

Calculating pKa values for substituted phenols and hydration energies for other compounds with the first‐order fuzzy‐border continuum solvation model

We have computed pK_a values for 11 substituted phenol compounds using the continuum Fuzzy‐Border (FB) solvation model. Hydration energies for 40 other compounds, including alkanes, alkenes, alkynes, ketones, amines, alcohols, ethers, aromatics, amides, heterocycles, thiols, sulfides, and acids have been calculated. The overall average unsigned error in the calculated acidity constant values was equal to 0.41 pH units and the average error in the solvation energies was 0.076 kcal/mol. We have also reproduced pK_a values of propanoic and butanoic acids within about 0.1 pH units from the experimental values by fitting the solvation parameters for carboxylate ion carbon and oxygen atoms. The FB model combines two distinguishing features. First, it limits the amount of noise which is common in numerical treatment of continuum solvation models by using fixed‐position grid points. Second, it uses either second‐ or first‐order approximation for the solvent polarization, depending on a particular implementation. These approximations are similar to those used for solute and explicit solvent fast polarization treatment which we developed previously. This article describes results of using the first‐order technique. This approximation places the presented methodology between the Generalized Born and Poisson‐Boltzmann continuum solvation models with respect to their accuracy of reproducing the many‐body effects in modeling a continuum solvent. © 2012 Wiley Periodicals, Inc.     

Hydration behavior of C2S and C2AS nanomaterials, synthetized by sol–gel method

Hydration behavior of dicalcium silicate (C₂S) (Cement chemistry nomenclature is used where C=CaO, S=SiO₂, A=Al₂O₃, S=SO₃) and gehlenite (C₂AS), synthesized by sol–gel method was investigated by means of isothermal heat flow calorimeter at different temperatures. These phases were obtained by crystallization processing at different temperatures from their xerogels (nano-crystalline) prepared by the sol–gel method at ambient temperature. The crystallization of C₂S begins below 600°C and it is well crystallized at 900°C. X-ray diffraction patterns reveal that β-C₂S is formed and it remains stable since after slow cooling. The crystallization of C₂AS xerogels starts with the formation of C₂S, then it reacts with alumina to form mineral C₂AS at 1100°C. The effect of hydration temperature upon the hydration reaction of C₂S obtained at 600 and 900°C and C₂AS annealed at 600 and 1100°C was investigated by means of isothermal calorimeter. An increase in the temperature of hydration brought about initial acceleration of all samples, as indicated by the increased magnitude of peak of calorimetric curves. The microstructure of the samples cured at hydrothermal condition after 1 and 7 days has been examined by means of scanning electron microscopy (SEM). Fine crystals of calcium silicate hydrate (C–S–H) were developed in C₂S samples, while C₂AS has been hydrated to form gehlenite hydrate supplemented by C–S–H.     

Lignite humic acids aggregates studied by high resolution ultrasonic spectroscopy

The thermodynamic stability of lignite humic acids (sodium salt) aggregates was studied by high resolution ultrasonic spectroscopy within the temperature interval from 5 to 90°C. The changes in differential ultrasonic velocity (U12) showed strong differences among humic solutions within the concentration range from 0.005 to 10 g L⁻¹. Measurement revealed several transitions which were attributed to the weakening of humic secondary structure. Concentration around 1 g L⁻¹ seemed to be a limit under which the change of the prevalence and importance of hydration occurred. Above this concentration the difference in U12 decreased following the temperature increase which was explained as a dominance of hydrophilic hydration. In contrast, below this concentration, the temperature dependence of U12 resulted in increasing tendency which was attributed to the prevalence of hydrophobic hydration, i.e. uncovering of apolar groups towards surrounding water. Additional experiments in which the humic sample was modified by hydrochloric acid resulted in a slight structural stabilization which lead to the conclusion that humic micelle-like subaggregates form an open-layer assemblies easily accessible for interaction with an extraneous molecule. That was partly verified by addition of propionic acid which brought about even larger reconformation of humic aggregates and exhibition of polar groups towards hydration water. The reversible changes in humate solutions induced by elevated temperatures provided the evidence about the existence of significant physical interactions among humic molecules resulting in formation of various kinds of aggregates. The nature of aggregates, mainly the stability and conformation, strongly depends on the concentration. Evidently, the changes observed in this work cannot be simply explained as expansions or conformational changes of macromolecular coils.     

Identification of Composite Cement Hydration Products by Means of X-Ray Diffraction

 In this paper the effect of limestone, fly ash, slag and natural pozzolana on the cement hydration products is studied. Four composite cements containing limestone, natural pozzolana from the Milos Island, slag and fly ash have been produced by intergrinding clinker (85%), the above main constituent (15%) and gypsum. The grinding process was designed in order to produce cements of the same 28d compressive strength. The hydrated products, formed after 1–28 days, were studied by means of X-ray diffraction. Unhydrated calcium silicate compounds of clinker and hydration products such as C*H, C*S*H and ettringite are clearly observed. Although there is not significant differentiation among samples hydrated for the same period of time, modifications of calcium aluminate hydrates as well as sulfoaluminate hydrates, are indicated by the XRD patterns. In samples of limestone cement, monocarboaluminate is formed in the first 24 hours and is still present after 28 days.     

Thermodynamics of Solution of Some Alkyl Acetates in Water

Summary.  The temperature dependence of the solubility of methyl acetate (MeOAc), ethyl acetate (EtOAc), 1-propyl acetate (1-PrOAc), 1-butyl acetate (1-BuOAc), 2-methyl-1-propyl acetate (iso-BuOAc), 2-butyl acetate (sec-BuOAc), and 2-methyl-2-propyl acetate (tert-BuOAc) in water in the temperature range from 298.2 to 318.2 K was determined. The experimental solubility data together with some literature values are presented as a function of temperature and given in analytical form. The solubilities of the investigated compounds at 298.2 K were correlated with the number of carbon atoms in the solute molecule. The standard thermodynamic functions for solubility, i.e. Gibbs free energy, enthalpy, heat capacity, and entropy, were calculated. The Gibbs free energy is positive and increases linearly with the number of carbon atoms, whereas the enthalpy and entropy are negative. The standard thermodynamic functions were converted to thermodynamic quantities for hydration. The Gibbs free energies of hydration of alkyl acetates, which are negative, are compared with the Gibbs free energy of hydration of some n-alkanes, 1-alcohols, and 1-alkylamines. The standard thermodynamic functions of hydration were analyzed using a modified version of the theoretical approach developed by Lee and Graziano [1]. Received October 16, 2000. Accepted May 14, 2001