An Ideal Solid Solution Model for C–S–H

A model for an ideal solid solution, developed by Nourtier‐Mazauric et al. [Oil & Gas Sci. Tech. Rev. IFP, 60 [2] (2005) 401], is applied to calcium–silicate–hydrate (C–S–H). Fitting the model to solubility data reported in the literature for C–S–H yields reasonable values for the compositions of the end‐members of the solid solution and for their equilibrium constants. This model will be useful in models of hydration kinetics of tricalcium silicate because it is easier to implement than other solid solution models, it clearly identifies the driving force for growth of the most favorable C–S–H composition, and it still allows the model to accurately capture variations in C–S–H composition as the aqueous solution changes significantly at early hydration times.     

Characterization of C–S–H and C–A–S–H phases by electron microscopy imaging,diffraction, and energy dispersive X‐ray spectroscopy

Improving concrete sustainability by increasing durability requires a detailed knowledge about microstructural properties. Due to the nanoscale nature of hydrate phases that determine concrete properties, microstructural characterization remains a challenge. Analytical electron microscopy offers promising techniques to characterize cement hydrates. In this study, electron microscopy imaging, diffraction, and energy dispersive X‐ray spectroscopic information are combined in order to compare the structural properties of calcium silicate hydrate (C–S–H) and calcium aluminum silicate hydrate (C–A–S–H) phases. Results are shown for 28 days hydrated C–(A)–S–H of portland cement and cement containing ground granulated blast‐furnace slag (GGFBS). Electron diffraction patterns of single fibrous C–S–H and foil‐like C–A–S–H phases reveal a nanocrystalline structure. Also, it is shown by electron diffraction pattern that the crystal structures of C–S–H and C–A–S–H phases are similar. It is confirmed that the crystal structure of 14 Å tobermorite serves as good base for the structure of C–S–H. The electron diffraction patterns of fibrous C–S–H show streaks which indicate stacking faults, proofing that polymerization of silicate chains in C–S–H is limited. Here, we demonstrate for the first time that the dreierketten silicate chains contained in the C–S–H structure are oriented in parallel to the long axis of C–S–H fibers. This finding should be implemented in modeling of crystal growth of C–S–H.     

Effect of the densification of C–S–H on hydration kinetics of tricalcium silicate

Effect of water to cement (w/c) ratio and temperature profiles on the densification of C–S–H (calcium silicate hydrate gel) and hydration kinetics of triclinic tricalcium silicate (C₃S) is studied beyond the first day of hydration. Calorimetry and quantitative X‐ray diffraction/Rietveld analysis show that degree of hydration is unaffected by w/c up to 7 days and marginally thereafter. Coupling the degree of hydration with the portlandite content measured from thermal analysis indicate that C/S ratio of C–S–H decreases with increasing w/c. There is a clear increase in the portlandite content with increasing w/c, even though the degree of hydration is unchanged, due to the variations in C/S ratio of C–S–H. On the other hand, when C₃S is initially cured at a lower temperature (20°C) and then at a higher temperature (40°C), there is a significant increase in the reactivity even until 28 days and vice versa. These experimental results were explained using the densified volumetric growth hypothesis, which assumes that hydration kinetics are dependent on the internal surface area of C–S–H.     

Formation of Ferroelectric Phases in Sb–S–I Glasses

We have investigated devitrification of glasses within infrared transmitting xSbSI–(100 ? x)Sb₂S₃ pseudo‐binary series, which forms SbSI and Sb₂S₃ ferroelectric crystal phases. Differential scanning calorimetry (DSC) and X‐ray powder diffraction results show unusual behavior for the formation of the SbSI phase, which occurs by two parallel processes: one‐dimensional crystallization at low temperature which starts from the sample surface, and three‐dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The ratio of the intensities of the high‐temperature exothermal peak to the low‐temperature peak in DSC scans increases as the particle size and heating rate are increased. In contrast to the SbSI phase, the temperature of crystallization for the Sb₂S₃ phase does not depend on the particle size. Models are proposed for the origin of the various crystallization mechanisms.     

C–(N)–S–H and N–A–S–H gels: Compositions and solubility data at 25°C and 50°C

Calcium silicate hydrates containing sodium [C–(N)–S–H], and sodium aluminosilicate hydrates [N–A–S–H] are the dominant reaction products that are formed following reaction between a solid aluminosilicate precursor (eg, slags, fly ash, metakaolin) and an alkaline activation agent (eg NaOH) in the presence of water. To gain insights into the thermochemical properties of such compounds, C–(N)–S–H and N–A–S–H gels were synthesized with compositions: 0.8≤Ca/Si≤1.2 for the former, and 0.25≤Al/Si≤0.50 (atomic units) for the latter. The gels were characterized using thermogravimetric analysis (TGA), scanning electron microscopy with energy‐dispersive X‐ray microanalysis (SEM‐EDS), and X‐ray diffraction (XRD). The solubility products (K_S0) of the gels were established at 25°C and 50°C. Self‐consistent solubility data of this nature are key inputs required for calculation of mass and volume balances in alkali‐activated binders (AABs), and to determine the impacts of the precursor chemistry on the hydrated phase distributions; in which, C–(N)–S–H and N–A–S–H compounds dominate the hydrated phase assemblages.     

Soft X‐ray Ptychographic Imaging and Morphological Quantification of Calcium Silicate Hydrates (C–S–H)

Morphological details of calcium silicate hydrate (C–S–H) stemming from the hydration process of Portland cement (PC) phases are crucial for understanding the PC‐based systems but are still only partially known. Here we introduce the first soft X‐ray ptychographic imaging of tricalcium silicate (C₃S) hydration products. The results are compared using both scanning transmission X‐ray and electron transmission microscopy data. The evidence shows that ptychography is a powerful method to visualize the details of outer and inner product C–S–H of fully hydrated C₃S, which have fibrillar and an interglobular structure with average void sizes of 20 nm, respectively. The high‐resolution ptychrography image enables us to perform morphological quantification of C–S–H, and, for the first time, to possibly distinguish the contributions of inner and outer product C–S–H to the small angle scattering of cement paste. The results indicate that the outer product C–S–H is mainly responsible for the q^?3 regime, whereas the inner product C–S–H transitions to a q^?2 regime. Various hypotheses are discussed to explain these regimes.     

In‐Situ XRD Measurement and Quantitative Analysis of Hydrating Cement: Implications for Sulfate Incorporation in C–S–H

The study of hydration kinetics by in‐situ X‐ray powder diffraction can provide fundamental details on the time evolution of the phase assemblage in hydrating cement pastes. The main limit of the technique is the lack of quantitative information about the amount of C–S–H and unbound water, which cannot be measured directly by conventional quantitative phase analysis procedures based on X‐ray diffraction, due to their X‐ray amorphous nature. Here, a mass balance algorithm, which can be used to determine the amount of both C–S–H and capillary water, is presented and compared with methods based on standards. This method can also provide information about the stoichiometry of C–S–H formed by the reaction of C₃S, hydrated in the presence of gypsum, suggesting the incorporation of 0.3 mol of sulfate per mole of C–S–H precipitated. In addition, the results show a significant increase in the rate of C₃S hydration, when gypsum is added to the system.     

Morphology of Zirconia Synthesized Hydrothermally from Zirconium Oxychloride

Monoclinic zirconia has been synthesized hydrothermally from zirconium oxychloride in the range 20–100 MPa, 250–650°C, for run duration from 20 to 100 h and in the presence of NaOH, Na₂CO₃, Na₂SO₄, NH₄F, HNO₃, and H₂SO₄ additives. Isometric, platelike, and elongated crystal morphologies were obtained depending on the additive. Both spherulitic and isolated textures were encountered with H₂SO₄. Growth of isometric crystals follows a general dissolution–precipitation mechanism. For H₂SO₄, two growth steps were identified: an early spherulitic step followed by an isolated crystals step resulting from Ostwald ripening of preexisting spherulites. The formation of spherulites is consistent with the specific properties of the sulfuric hydrothermal medium.     

利用半干法烟气脱硫渣制备新型胶凝材料的试验研究

以广州恒运和齐鲁石化燃煤电厂半干法烟气脱硫渣为研究对象,针对其成分复杂和高硫高钙的特点,通过机械和化学活化的方式,制备出一类新型绿色胶凝材料——高硫型灰渣胶凝材料。研究表明：亚硫酸钙对高硫型胶凝材料的水化活性有促进作用,脱硫渣氧化后,材料的早期强度提高;继续提高脱硫渣的掺量则会出现强度倒缩现象。     

Aluminum Incorporation in the C–S–H Phase of White Portland Cement–Metakaolin Blends Studied by 27Al and 29Si MAS NMR Spectroscopy

The composition and structure of the calcium‐silicate‐hydrate (C–S–H) phases formed by hydration of white portland cement–metakaolin (MK) blends have been investigated using ²⁷Al and ²⁹Si MAS NMR. This includes blends with 0, 5, 10, 15, 20, 25, 30 wt% MK, following their hydration from 1 d to 1 yr. ²⁹Si MAS NMR reveals that the average Al/Si ratio for the C–S–H phases, formed by hydration of the portland cement–MK blends, increases almost linearly with the MK content but is invariant with the hydration time for a given MK content. Correspondingly, the average aluminosilicate chain lengths of the C–S–H increase with increasing MK content, reflecting the formation of a C–S–H with a lower Ca/Si ratio. The increase in Al/Si ratio with increasing MK content is supported by ²⁷Al MAS NMR which also allows detection of strätlingite and fivefold coordinated aluminum, assigned to AlO₅ sites in the interlayer of the C–S–H structure. Strätlingite is observed after prolonged hydration for MK substitution levels above 10 wt% MK. This is at a somewhat lower replacement level than expected from thermodynamic considerations which predict the formation of strätlingite for MK contents above 15 wt% after prolonged hydration for the actual portland cement–MK blends. The increase in fivefold coordinated Al with increasing MK content suggests that these sites may contribute to the charge balance of the charge deficit associated with the incorporation of Al³⁺ ions in the silicate chains of the C–S–H structure.     

Understanding the Filler Effect on the Nucleation and Growth of C‐S‐H

The “filler effect”, due to the physical presence of mineral additions in cement, is mainly known to accelerate the hydration of the clinker component. Previously, this was attributed to the surface of the filler providing nucleation sites for C‐S‐H as there is a clear dependence on the surface provided by the filler particles. Our results reveal that the increase in nucleation is quite low compared to the area provided. Based on the isothermal calorimetry experiments and SEM images, we demonstrate that the most important parameter is the interparticle distance. We propose that this is mainly the result of the shearing conditions rather than extra surface available for C‐S‐H as formerly assumed. Quantitatively slag and fly ash behave very similarly to quartz. Limestone, on the other hand, seems also to stimulate C‐S‐H nucleation giving it a higher efficiency in accelerating clinker hydration.     

Reactions between carbon and a reduced C–O–H fluid under diamond-stable HP–HT condition

Reactions between graphitic carbon and a reduced C–O–H fluid were investigated using a mixture of stearic acid C₁₈H₃₆O₂ and oxalic acid dihydrate C₂H₆O₆, as the fluid source at high pressure and temperature (HP–HT) of 7.7 GPa and 1500°C in a platinum sealed capsule. A reduced C–O–H fluid mainly composed of methane and water, was formed by the thermal decomposition of the fluid source before reaching the HP–HT condition. An exchange reaction between carbon and methane occurred and starting carbon was re-crystallized to flaky graphite crystals, but no diamond was formed for the duration up to 24 h. In the experiment for 48 h, octahedral diamond crystals of a few to a few tens of micrometers in size were observed along with the recrystallized graphite. These results show that reduced C–O–H fluid acts as a diamond forming catalyst, although a long incubation time is necessary for diamond formation.     

Wollastonite from Hydrothermally Synthesized Calcium Hydrometasilicate Obtained from Various Modifications of Silica

A hydrothermally CaO–SiO₂–H₂O system was investigated at 150°–200°C, 2.5 h (CaO:SiO₂=0.95) using various modifications of SiO₂ in the presence of a mineralizer. Synthetic (stabilized) γ-tridymite is the most reactive among SiO₂ modifications. In the reaction mixture, the optimal concentration of the mineralizer (KOH) is 2% (versus the solid phase). The binding degree of CaO with SiO₂ practically is 100% at 150°C. It is impossible to synthesize CSH free of C₂SH on the basis of β-cristobalite and β-quartz under the investigation conditions without the use of mineralizer. The calorimetric effects as well as heat of de-hydration of hydrosilicates were determined during their transformation into wollastonite. The entropy change at the peaks has been calculated.     

Diamond and graphite crystallization from C–O–H fluids under high pressure and high temperature conditions

Crystallization of diamond was studied in the CO₂–C, CO₂–H₂O–C, H₂O–C, and CH₄–H₂–C systems at 5.7 GPa and 1200–1420°C. Thermodynamic calculations show generation of CO₂, CO₂–H₂O, H₂O and CH₄–H₂ fluids in experiments with graphite and silver oxalate (Ag₂C₂O₄), oxalic acid dihydrate (H₂C₂O₄·2H₂O), water (H₂O), and anthracene (C₁₄H₁₀), respectively. Diamond nucleation and growth has been found in the CO₂–C, CO₂–H₂O–C, and H₂O–C systems at 1300–1420°C. At a temperature as low as 1200°C for 136 h there was spontaneous crystallization of diamond in the CO₂–H₂O–C system. For the CH₄–H₂–C system, at 1300–1420°C no diamond synthesis has been established, only insignificant growth on seeds was observed. Diamond octahedra form from the C–O–H fluids at all temperature ranges under investigation. Diamond formation from the fluids at 5.7 GPa and 1200–1420°C was accompanied with the active recrystallization of metastable graphite.     

C–H bond activation in hydrocarbon oxidation on heterogeneous catalysts

The activation of C–H bonds in different hydrocarbons on the surfaces of metal oxide and metal catalysts is considered. On oxides, it appears that the initial activation may occur through either homolytic or heterolytic scission of the C–H bond, but the reaction is surface-catalysed. The activation of methane requires highly basic sites which are susceptible to severe poisoning by carbon dioxide. With metal surfaces, the extent of oxidation of the surface can strongly affect the oxidation activity. For rhodium catalysts, it is shown that the intrinsic activity for methane combustion is high. However, rhodium is strongly deactivated under oxidising conditions when alumina is used as the support: deactivation is not observed when the support is zirconia. Transient effects on the activity of an alumina-supported palladium catalyst are reported and these show that the steady state is not easily established. Water severely inhibits the methane combustion reaction on palladium, and chlorine and sulphur dioxide are strong poisons. In contrast, for the combustion of propane on alumina-supported platinum catalysts, sulphur dioxide is a significant promoter of the reaction.     

利用钢渣、矿渣制备低碳型胶凝材料

以钢渣、矿渣和脱硫石膏为主要原料,添加少量激发剂制备低碳型胶凝材料,试验确定了制备该产品的最佳物料配比:矿渣41.75%,钢渣41.75%,800℃锻烧的脱硫石膏10%,硅酸盐水泥熟料5%,激发剂Ⅱ1.5%.产品达到GB175-2007<通用硅酸盐水泥>42.5复合硅酸盐水泥标准要求.     

The Effect of Alkali Ions on the Incorporation of Aluminum in the Calcium Silicate Hydrate (C–S–H) Phase Resulting from Portland Cement Hydration Studied by 29Si MAS NMR

The incorporation of aluminum in the calcium–silicate–hydrate (C–S–H) phases formed by hydration of three different white Portland cements has been investigated by ²⁹Si MAS NMR. The principal difference between the three cements is their bulk Al₂O₃ contents and quantities of alkali (Na⁺ and K⁺) ions. ²⁹Si MAS NMR allows indirect detection of tetrahedral Al incorporated in the silicate chains of the C–S–H structure by the resonance from Q²(1Al) sites. Analysis of the relative ²⁹Si NMR intensities for this site, following the hydration for the three cements from 0.5 d to 30 weeks, clearly reveals that the alkali ions promote the incorporation of Al in the bridging sites of the dreierketten structure of SiO₄ tetrahedra in the C–S–H phase. The increased incorporation of Al in the C–S–H phase with increasing alkali content in the anhydrous cement is in accord with a proposed substitution mechanism where the charge deficit, obtained by the replacement of Si⁴⁺ by Al³⁺ ions in the bridging sites, is balanced by adsorption/binding of alkali ions in the interlayer region most likely in the near vicinity of the AlO₄ tetrahedra. This result is further supported by similar ²⁹Si MAS NMR experiments performed for the white Portland cements hydrated in 0.30M NaOH and NaAlO₂ solutions.     

Soft X‐ray Spectromicroscopic Investigation of Synthetic C‐S‐H and C3S Hydration Products

Calcium silicate hydrates (C‐S‐H), the primary binding phase in concrete, is the most prominent physiochemical factor controlling the mechanical and chemical properties in the production of concrete. This paper reports the local‐binding structure and morphological details of C‐S‐H as determined by high‐resolution X‐ray spectromicroscopy. Hydrated tricalcium silicate (C₃S) was used to determine the properties and role of the outer products (Op) of C₃S. C‐S‐H with different molar ratios of Ca/Si, were synthesized (Syn‐CSH) to quantitatively evaluate the effect of silicate polymerization on Ca L and Si K edge of C‐S‐H. Near edge X‐ray absorption fine structure (NEXAFS) spectroscopy of Syn‐CSH showed no variation in peak positions and energy separation for CaL_{III, II} edge for the Ca/Si ratios investigated. Compared to Syn‐CSH, C₃S, when hydrated for 17 d, had a similar local structure around Ca. Si K edge NEXAFS analysis on Syn‐CSH showed a tendency for the peak positions of both the Si K edge and the peak induced by multiple scattering to shift to higher energy levels. The results also indicated that the distance between the two peaks increased with a decrease of the Ca/Si ratio in Syn‐CSH. Silicate polymerization influenced the multiple scattering of distant shell atoms more than the binding energy of the core atoms. Op of C₃S had a uniform and higher degree of silicate polymerization compared to the core area. The results imply that Op reduces the hydration process of C₃S into the core area thereby playing a key role on the properties of concrete upon formation.     

Novel Crystal Growth of In Situ WC in Selective Laser‐Melted W–C–Ni Ternary System

The bulk‐form in situ WC‐based cermets were prepared by selective laser melting of W–C–Ni ternary powder system. The in situ formed WC crystals generally had a unique triangular microstructure which was developed via a layer‐by‐layer growth mechanism by the multilayered stacking of (0001) basal planes of WC. An increase in the applied laser energy density, which was realized by increasing laser power or decreasing scan speed, resulted in the coarsening of in situ WC crystals in both side length and thickness, due to the elevated heat accumulation at the tips of the triangular WC crystals.