Pore Structure of Calcium Silicate Hydrate in Hydrated Tricalcium Silicate

Adsorption of N₂ and water vapor was studied in completely hydrated tricalcium silicate and in fully hydrated tricalcium silicate from which Ca(OH)₂ had been extracted. Compared with results obtained using N₂, water vapor adsorption led to increased values for small-pore volume, peak shifts to smaller sizes, and decreased values for large-pore volume. Marked hysteresis was observed in the case of water vapor adsorption; the resorption branch apparently represents the true pore structure. Extraction of Ca(OH)₂ from the paste increased the calculated volume of small pores strikingly, suggesting that adsorption is hindered by Ca(OH)₂; this tendency is more obvious in water vapor adsorption. The adsorption measurements indicate the existence of two kinds of pores, i.e. a wider intergel-particle pore and a smaller pore existing within the gel particle. The latter pore was further classified into intercrystallite and intracrystallite pores.     

Hydration of Tricalcium Silicate

The kinetics of paste, bottle, and ball-mill hydration of 3CaO SiO₂ and the effects of additions of electrolytes and alcohols were studied. Paste and bottle hydrations proceed through periods of induction, acceleration, and decay. If 3CaO SiO₂ is hydrated in an excess of H₂O, as in bottle hydration, the reaction rate is lower than that for paste hydration. The ball-mill hydration rate is much the highest and is controlled by the removal of the hydrate layer coating the 3CaO SiO₂ particles. Electrolytes always accelerate and alcohols retard the reaction rate. Experimental results are discussed with reference to modern theories of the 3CaO SiO₂ hydration mechanism.     

Hydration of Tricalcium Germanate–Tricalcium Silicate Solid Solutions

The hydration characteristics of solid solutions of composition 3CaO· x GeO₂·(1 − x )SiO₂ were investigated at 25°C by isothermal calorimetry. The compositions hydrated were for x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0. Full hydration was achieved for compositions in which x < 0.2. Both the rate of hydration and the total heat evolved for complete hydration vary with composition. Hydrate compositions were determined, and these also show a compositional dependence. The hydration product for tricalcium germanate has a Ca/Ge ratio near 1.5. Although the hydration products of the solid solution are far more fibrous, their morphologies are reminiscent of that of calcium silicate hydrate.     

Early Hydration of Tricalcium Silicate

The hydration of tricalcium silicate (C₃S) in the preacceleration stages was studied. The C₃S particles carry a positive charge during the early stages of hydration. Following a rapid hydrolysis of C₃S, calcium ions adsorbed on the Si-rich surface of C₃S particles, greatly reducing their further dissolution, thus initiating the induction period. The [Ca²⁺] and [OH^-] continue to increase at lower rates and, because Ca(OH)₂ crystal growth is inhibited by silicate ions, become supersaturated with respect to Ca(OH)₂. When the supersaturation reaches a value of ∼1.5 to 2.0 times the saturation concentration, nuclei are formed, and rapid growth of Ca(OH)₂ and C-S-H is initiated. These products act as sinks for the ions in solution, thus enhancing the further dissolution of C₃S.     

Thermal Study of the Effect of Additives on the Hydration of Tricalcium Silicate

The rate of paste hydration of 3C_aO·SiO₂ (C₃S) and the effects of additions of CaCl₂, CdI₂, and CrCl₃, were studied by differential thermal analysis and thermogravimetry. X-ray analyses were used to identify the synthesized C₃S. The salts CaCl₂, CdI₂, and CrCl₃, accelerated the hydration of C₃S. The degree of hydration was estimated by the amount of Ca(OH)₂, formed, as determined by TG.     

硅酸三钙骨水泥浆体的可注射性能研究

本文优化了骨水泥浆体的注射性能研究方法,综合研究硅酸三钙(Ca3SiO5,C3S)骨水泥浆体的液固比(L/P)、凝结时间、固化体力学强度等与可注射性的关系.结果表明高L/P易导致静置后C3S骨水泥浆体注射比的突降,固化体孔隙率增加,强度下降,不利于临床操作和应用;低L/P下,采用较小注射器可以提高C3S骨水泥浆体的注射比,也可避免静置后C3S骨水泥浆体注射比的突降.采用较小的注射器和较小L/P,可以在兼顾骨水泥浆体固化性能和力学性能的基础上,实现C3S骨水泥浆体具有较大的注射比.     

Kinetics of the Hydration of Tricalcium Silicate

The hydration of tricalcium silicate was followed at a water/C₃S ratio of 0.7 between 5° and 50°C by determining free lime and combined water. Free lime was estimated by the o -cresol method, whereas combined water was calculated from the amount of free water remaining in the paste as determined by extraction with methyl ethyl ketone. The ratio of free lime to combined water was constant throughout the hydration; this ratio indicated that CSH(II) may be represented as 1.68CaO · SiO₂· 2.58H₂O. When maximum supersaturation of the solution with Ca^2+] is attained, the induction period terminates and the reaction proceeds rapidly, probably as the result of propagative surface nucleation-growth of CSH(II). Kinetic equations were derived for these reactions. When the surface of C₃S is entirely covered by CSH(II), the reaction becomes slow and is controlled by diffusion of water. Constants involved in the kinetic equations are evaluated and discussed.     

Effect of Fluorine and Magnesium on the Polymorphism of Tricalcium Silicate: A New Fluorine-Containing Tricalcium Silicate Superlattice

There is evidence both by XRPD and by TEM electron diffraction of the presence of a new tricalcium silicate phase containing fluorine with triclinic cell parameters a = 2.32(7), b = 0.71(3), c = 1.28(3) nm, α= 106.5(3), β= 90(1), γ= 118(1)°. It is a superlattice of the rhombohedral C₃S, whose structure is probably deformed by the fluorine/oxygen substitution plus some calcium vacancies, the deformation being nevertheless smaller than that found in the triclinic polymorph of pure C₃S. Magnesium proves to have an effect additional to that observed for fluorine probably because it fixes the fluorine to the silicate lattice.     

Structure and Reactivity of Chromium-Doped Tricalcium Silicate

The correlation between the structure and reactivity of Cr-doped tricalcium silicate was studied by ir spectrophotometry and X-ray diffractometry. A very sensitive method of detection of defects (thermostimulated exoelectron emission) allowed differentiation of three types of electron traps; the activation energy for the third trap was 0.8 eV. These crystal defects seem to be associated with sites of high Cr concentration (disordered structure) which may also be responsible for the increased reactivity of the doped phases. The reactivity of the system tricalcium silicate-H₂O ( w/c =0.6) was studied by an electrical conductometric method. Curves of conductivity vs time for tricalcium silicate with varied Cr concentrations indicated significant differences in hydration kinetics.     

Composition and Morphology of Hydrated Tricalcium Silicate

Hardened C₃S paste cured for 1 year at 20°C was examined to confirm the composition and the morphology of hydrated tricalcium silicate. A new technique was used in which the samples for scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were etched in 1% HNO₃-alcohol or in glycerol-alcohol (4:6 by volume). After the surface was etched in 1% HNO₃-alcohol, SEM clearly showed the difference in texture in the outer and inner C-S-H products. The existence of a zonal texture within the inner C-S-H products was shown, in addition to the unreacted core; particles 0.1 to 0.2 μm in diameter were observed. After free CH extraction with glycerol-alcohol, two new types of C-S-H grains could be identified. One type has a smooth surface, which seems to be produced from C₃S grains trapped within the growing CH crystals in the early stage of hydration, the C/S mol ratio for these being >3. The other type is covered with many acicular outer C-S-H gel hydration products and has a C/S mol ratio >3.     

Superstructure in a Triclinic Phase of Tricalcium Silicate

A triclinic phase of tricalcium silicate (TI) was investigated using transmission electron microscopy (TEM). Electron diffraction patterns were analyzed by introducing a subcell with the cell parameters of a = 7.081 Å, b = 7.043 Å, c = 25.230 Å, α= 89.97°, β= 90.37°, and γ= 119.44°. It was proven that the coordinates of all the reflections can be expressed to be ha *+ kb *+ lc *± m /6( a *+ 2 b *+ 2 c *), where m = 0, 1, 2, and 3. The result indicates that the structure modulation in TI is a one-dimensional type with a structural modulation normal to (122). The modulated structure could be observed in a high-resolution TEM image as wavy contrast streaking parallel to the plane with an interval of six times the (122) spacing.     

Polymorphism of Tricalcium Silicate and Its Solid Solutions

In tricalcium silicate and its solid solutions six modifications were established: one rhombohedral ( R ), two monoclinic ( M _I, M _II), and three triclinic ( T _I, T _II, T _III). All these forms are rhombohedral or pseudorhombohedral and extremely similar; the variations in the X-ray diagrams and the transformation enthalpies are minute. Only three of the five transitions were observed by both X rays and DTA: T _I- T _II (600°), T _III– M _I (980°), and M _I– M _II (990°); one was established by DTA ( T _II– T _III, 920°) and one by X rays only ( M _II– R , 1050°C). This scheme of polymorphism is compared critically with results of other authors, and the nature of the various displacive transformations is discussed. X-ray and DTA investigations of solid solutions of Ca₃SiO₅ with Al₂O₃ and ZnO established the phase relations as functions of temperature and composition. With Al₂O₃, two modifications ( T _I and T _II) were stabilized; and with ZnO, five polymorphs ( T _I T _II, M_I, M _II, and R ). With both pure C₃S and the solid solutions, the results are consistent and have a close bearing on the constitution of alites in portland cement clinker.     

Reaction of Beta-Dicalcium Silicate and Tricalcium Silicate with Carbon Dioxide and Water Vapor

The carbonation-reaction kinetics of beta-dicalcium silicate (2CaO·SiO₂ or β-C₂S) and tricalcium silicate (3CaO. SiO₂ or C₃S) powders were determined as a function of material parameters and reaction conditions and an equation was developed which predicted the degree of reaction. The effect of relative humidity, partial pressure of CO₂, surface area, reaction temperature, and reaction time on the degree of reaction was determined. Carbonation followed a decreasing-volume, diffusion-controlled kinetic model. The activation energies for carbonation of β-C₂S and C₃S were 16.9 and 9.8 kcal/mol, respectively. Aragonite was the principal carbonate formed during the reaction and the rate of carbonate formation was coincident with depletion of the calcium silicates; C-S-H gel formation was minimal.     

高铝粉煤灰中莫来石及硅酸盐玻璃相的热分解过程

研究了高铝粉煤灰-Na2CO3体系中莫来石(3Al2O3·2SiO2)和硅酸盐玻璃相在焙烧过程中可能发生的化学反应,并以热力学计算为指导,研究了物料配比、焙烧温度、焙烧时间对反应的影响.实验结果表明:在Na2CO3与粉煤灰的质量比为1.0、焙烧温度为880℃、恒温1h时,粉煤灰中莫来石(3Al2O3·2SiO2)和硅酸盐玻璃相的分解率可达到98%以上.对粉煤灰中莫来石及硅酸盐玻璃相的热分解过程的动力学研究结果表明,该过程符合CrankGinstling-Braunshtein方程,由实验结果计算,其表观活化能为149.19kJ·mol-1.     

Polymorphism and Hydration of Tricalcium Silicate Doped With ZnO

Up to 4.7% ZnO can be incorporated into the crystalline lattice of C₃S. Five allotropic forms (i.e. T_I, T_II, M_I, M_II, and R) can be stabilized at room temperature, depending on the amount of ZnO. When heated to high temperature, the C₃S-ZnO solid solution decomposes and ZnO escapes from the crystalline lattice. The hydration and strength development of C₃S are altered by ZnO doping.     

Heteroepitaxial Growth of Calcium Silicate Hydrate on Calcium Germanate Hydrate

The hydration of tricalcium silicate at 25°C was accelerated by seeding with 5 wt% tricalcium germanate. Based on heat evolution, seeding resulted in the elimination of the induction period. However, the shape of the hydration peak remained the same. Because tricalcium germanate hydrates first, the microstructure of the calcium silicate hydrate which subsequently forms is influenced by the calcium germanate hydrate morphology. Calcium silicate hydrate formed in the presence of calcium germanate hydrate exhibits the morphology typical of the latter. Acceleration of hydration and morphological variation indicate heteroepitaxial growth.     

High-Temperature Microscopic Investigation of Tricalcium Silicate and Dicalcium Silicate Phases in Portland Cement Clinker

Birefringence was measured as a function of temperature up to 1400°C for (1) alite and various types of belite in portland cement clinker, and (2) alite in fused cement. The characteristic optical changes in alite and belite grains which accompany polymorphic transformations and facilitate, in certain cases, determination of the modification without necessitating the separation of the pure phase are given. The β and α'modifications were differentiated for belite from clinker and also for alite in fused cement. A method is described for measuring birefringence of minerals at high temperatures, as well as the apparatus and the preparation of samples.     

Formation of Calcium Hydroxide from Aqueous Suspensions of Tricalcium Silicate

The release of Ca²⁺ and OH" from tricalcium silicate into the aqueous phase was monitored over the first few hours. The solution becomes supersaturated with respect to pure calcium hydroxide with the maximum activity product being about 3.5 times greater than the solubility product. Evidence is presented in support of "silicate poisoning" of calcium hydroxide nuclei. The addition of soluble salts changes the time at which maximum supersaturation is attained but not its magnitude. The analytical data are compared with the rate of heat released from companion pastes.     

不同SO3掺量下C3S矿物的形成

通过化学分析,应用等温煅烧的方法对不同SO3掺量为(0%,1%,2%,3%,3.5%,5%)的C3S矿物形成过程从动力学角度进行了系统探讨.通过拟合得到了C3S矿物形成的动力学模型,并根据该动力学模型对不同SO3掺量下C3S矿物形成的速率常数进行了计算.结果表明:在1450℃,不同SO3掺量下,C3S矿物形成由三维球形对称扩散动力学模型f(a)=(1-3√(x+y)2控制;随着SO3加入量的增加,C3S矿物形成的速率常数呈非线性变化;从游离CaO的含量和反应速率常数的角度来说,SO3的加入有利于C3S的形成.并且SO3加入量的增加有利于C3S的多相体M1的稳定.