加速碳化对水化硅酸钙显微结构的影响

废弃水泥石等固体废弃物碳酸化不仅能够永久固碳,还可实现固体废弃物的再利用,减少对环境的污染。水化硅酸钙(C-S-H)是最主要的可碳化成分之一。合成了钙硅(C/S)比为1.50的C-S-H,研究了加速碳化对其显微结构的影响。用Rietveld全谱拟合的方法和热重-质谱联用的方法对碳化产物进行定量分析,用扫描电镜、N2吸附和29Si固体核磁共振对碳化前后的显微结构进行表征。结果表明:在99.9%CO2,0.2 MPa压力下加速碳化2 h之后,生成了3种不同晶型的碳酸钙和硅胶,碳酸钙从300℃开始分解,文石和球霰石具有较低的分解温度,结晶良好的方解石分解温度较高;多孔结构硅胶具有更高的吸附能力,但C-S-H碳化后的平均孔径从10.33 nm减小到6.69 nm,比表面积由85.6 m2/g减小到67.7 m2/g,这是由于大量的结构致密的碳酸钙晶体堆积造成的;C-S-H双层硅氧链之间的Ca–O层逐渐脱去与CO2反应,硅氧四面体被质子化或与邻近的硅氧四面体链接,形成了聚合度更高的Q3和Q4结构。     

钙硅比对水化硅酸钙加速碳化的影响

废弃水泥石、钢渣等碳酸化固定CO2不仅可以缓解温室效应还可以实现废弃物的再利用,同时制备出性能优良的建材制品。为了研究废弃水泥石矿物组成的碳酸化机理,探讨了钙硅比对水化硅酸钙加速碳化的影响。结果表明:随着钙硅比增加,水化硅酸钙(C-S-H)碳化率逐渐降低,高钙硅比的C-S-H具有相对粗大的孔结构使得早期的碳化速率增加;碳化产物中文石、球霰石、方解石在不同钙硅比时所占比例不同,钙硅比≤0.67时文石占较大比例,钙硅比≥1.00时方解石为主要碳化产物,钙硅比=0.83时球霰石含量最大;加速碳化条件下形成的碳酸钙分解温度分成两部分,在400~620℃范围内文石和球霰石都分解,方解石在650~800℃范围内分解。     

Carbonation of Magnesium Silicate Minerals: An Experimental Study

CO₂ sequestration by magnesium silicate mineral is the only known process that can permanently store CO₂ using a natural feedstock that exists in sufficient quantities to be used practically. Transporting large amounts of mineral over long distances is uneconomical. For Canada to benefit from such a process, identification of suitable Canadian magnesium silicate mineral deposits is crucial. Only carbonation under pressure in NaCl and NaCl/NaHCO₃ solutions results in high Mg conversions (40–80%). Among the minerals examined in this study, the serpentines reacted most easily, and peridotite was the most difficult to carbonate. Increasing carbonation pressure to very high levels reduced the degree of carbonation as hydrolysis reactions became competitive with the carbonation process.     

碱矿渣水泥石碳化产物研究

碱矿渣水泥水化产物不同于硅酸盐水泥,会产生不同的碳化行为.以水玻璃与NaOH为碱组分制备碱矿渣水泥石,采用X-射线衍射(XRD)、红外光谱(FF-IR)与综合热分析(TG-DSC)研究了碱矿渣水泥石的碳化产物.结果表明:碱矿渣水泥石碳化生成的CaCO3的存在形式主要为方解石,球霰石和文石含量较少,随碳化龄期延长,文石与球霰石含量增加;以模数1.0～1.5的水玻璃为碱组分的碱矿渣水泥石碳化后,出现钠的碳酸盐结晶相;碱矿渣水泥石碳化脱钙后生成富硅的C-S-H凝胶,C-S-H凝胶的聚合度增加.     

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.     

Ionic Conductivity in Calcium Silicate Glasses

Glasses in the system CaO–SiO₂ were prepared with the composition varying from 40 to 55 mole % CaO. The Na₂O impurity content ranged from 0.01 to 1.30 mole %. The electrical resistivity was insensitive to the Na₂O content but decreased with increasing CaO concentration. The activation energy for conduction ranged from 33.54 to 31.23 kcal/mole as the CaO concentration increased. The conduction mechanism was considered in terms of three arbitrary parameters: (1) equivalent oxygen packing density, (2) ionic radius, and (3) ion-oxygen attraction.     

Hydrothermal Formation of Calcium Silicate Hydrates

The kinetics of solution of quartz and the crystallization of calcium silicate hydrate during hydro-thermal treatment of single crystals of quartz in saturated lime solutions were studied. Microscopic examination of sections of the product layer showed that the calcium silicate hydrate was of fibrous crystal habit and grew radially from nucleating centers in a general direction away from the quartz surface. X-ray diffraction established that the mineral was mainly xonotlite. The crystallization of the mineral did not follow the receding surface of the quartz; the product layer was extended only on the surface in contact with the lime solution. The silicate ions apparently diffused preferentially through the product layer although separate measurements proved that the membrane had no selective action against the diffusion of calcium ions. Plots of the weight of xonotlite versus square root of time gave straight lines indicating that the process was diffusion-controlled at 235° and 335°C.     

超轻型硅酸钙保温材料的研究

用ＸＲＤ，ＳＥＭ，ＢＥＴ等仪器和方法，重点研究了三种不同硅质原料，四种不同的石英粉及三种不同煅烧温度得到和生石灰对硬硅钙石料浆合成过程中晶粒生长的影响，从而确定了选择原料的原则。     

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.     

活性硅酸钙高温相变历程研究

通过TGA/DSC、XRD、FTIR、SEM等测试手段,对高铝粉煤灰提取氧化铝副产物-活性硅酸钙在各温度区间的相变历程进行系统研究.TGA/DSC结果表明活性硅酸钙结构中有5个结晶水,160℃时开始逐渐失去结晶水,600℃前结晶水脱除完毕,672℃时部分Si-O-H键断裂,失去羟基.XRD和FTIR结果表明700℃时活性硅酸钙结构已破坏,衍射峰消失,转变为无定形的非晶态;700～800℃时发生晶型转变,结构开始转变为有序的硅灰石晶体结构;1 100℃时完全转变为低温型2M型硅灰石结构;1300℃时完全转变为高温型假硅灰石结构.活性硅酸钙的高温相变经历了“活性硅酸钙→脱水硅酸钙→脱羟基硅酸钙→2M型硅灰石→假硅灰石”的转变历程.     

Proposed Structure for Calcium Silicate Hydrate Gel

Calcium silicate hydrate gel is a very poorly crystalline material that is the main product of reaction of portland cement with water. Evidence is presented for a disordered layer structure, in which most of the layers are structurally imperfect ones of jennite (Ca₉Si₆O₃₂H₂₂), and others are similarly related to 1.4-nm tobermorite (Ca₅Si₆O₂₆H₁₈), both structures being modified by omission of many of their silicate tetrahedra. The evidence comprises conditions of formation, silicate anion type, Ca/Si ratio, H₂O/Ca ratios and densities for various drying conditions, thermogravimetric curve, X-ray powder and selected-area electron diffraction patterns, and results of analytical electron microfcopy.     

钙镁摩尔比对氢氧化钙碳化性能的影响

为提高矿物周碳效率,采用固体法碳化,在CO2质量分数为99.9％、压力为0.3 MPa、液固比为0.10、碳化时间为2.0h条件下,探讨了不同Ca与Mg摩尔比(Mr)对氢氧化钙和氢氧化镁混合物碳化质量增加率的影响.结果表明:当Mr为5时,碳化质量增加率达到最大值23.75％;加入氢氧化镁,可使碳化产物结构疏松、细化氢氧化钙的碳化产物,碳化程度提高;同条件下,氢氧化镁碳化程度远低于氢氧化钙的.     

Developments in TEM Nanotomography of Calcium Silicate Hydrate

This investigation was designed to explore the possibility of using transmission electron microscope (TEM) tomography on cement‐based systems gain a greater understanding of their nanostructure and pore network. The preliminary results show a clearly a well‐defined pore network at the nanoscale, with pore size approximately 1.7–2.4 nm in diameter and spaced around 5–8 nm apart. A comparison of small angle X‐ray scattering data with 2‐D TEM images analyzed with the Fourier slice theorem documents an excellent structural correlation.     

煤矸石硅酸盐胶结料的研究

基于煤矸石胶结料的水化产物及由水化产物构成的硅酸盐的内部结构状况与其原材料的化学组成、激发剂用量、制备工艺、养护方法等的密切关系 ,我们针对原料性质和配合比中自燃煤矸石、生石灰、二水石膏三组分的变化与胶结材料的物理力学性能关系 ,进行了较系统的研究。根据实验结果 ,提出了胶结料的合理配比、制备工艺及方法。     

利用珍珠岩尾矿合成多孔硅灰石陶瓷的实验研究

以内蒙宁城珍珠岩尾矿为主要原料,以碳酸钙为平衡原料,在成孔剂和粘结剂的配合下,采用烧结法,在1200℃合成了多孔硅酸钙质陶瓷材料.该材料为全晶质多孔结构,主要物相是呈片状、板状的硅灰石.制品的体积密度为1.17～1.28g/cm3,显气孔率为42.08%～56.02%,吸水率为40.90%～47.70%.     

Interactions between Polymeric Dispersants and Calcium Silicate Hydrates

To better understand the mechanism of interaction between hydrating silicate-based cements and polymeric dispersants of the type used as superplasticizers in modern construction concretes, two different types of polymeric dispersant were added (at concentrations of 1 and 10 g/L) during the synthesis of calcium silicate hydrate (C-S-H) via the pozzolanic reaction in dilute slurries of lime and reactive silica, at Ca/Si ratios in the range of 0.66–1.50. Although both polymers gave degrees of adsorption of >79% in all cases studied, no significant structural modifications of the resulting C-S-H products were observed via X-ray diffraction or ²⁹Si magic angle spinning–nuclear magnetic resonance. These results differ from recent work in which it was shown that similar types of polymer could intercalate into the interlayers of C-S-H that was made using an alternative process. It is suggested that the process by which the C-S-H is formed may have a strong influence on whether C-S-H can intercalate polymers. This observation is relevant to understanding the fate of such polymers in concrete.     

Silicon Substitution for Aluminum in Calcium Silicate Hydrates

²⁷Al MAS and multiquantum (MQ) MASNMR (magic-angle spinning nuclear magnetic resonance) spectroscopy were used to study the substitution of silicon by aluminum in calcium silicate hydrates (C-S-H), which are the main component of hydrated portland cement. Synthetic C-S-H samples were prepared, and their chemical stability was studied. Two-dimensional 3Q-MASNMR spectra revealed the chemical shift and quadrupolar parameters (delta_iso, nu_Q) that labeled aluminum sites in the C-S-H. Tetrahedral aluminum was observed in the bridging and nonbridging sites of the silicate chains.     

穆斯堡尔谱在钙铁硅铁磁体微晶玻璃研究中的应用

应用穆斯堡尔谱来研究钙铁硅铁磁体微晶玻璃中氧化铁的适宜允许含量、熔制条件、热处理气氛和晶化过程。结果表明,穆斯堡尔谱对于准确地研究钙铁硅微晶玻璃形成、热处理过程中铁离子的价态、配位、结构情况具有重要价值,与XRD等其它方法的研究结果相比可以得到更多的信息。     

Thermodynamics of Calcium Silicate Hydrates and Their Solutions

The solution that surrounds hydrating cement particles contains dissolved species which are important in the overall process. A method, based on the Gibbs-Duhem equation for a three-component system, has been developed for computing the composition of one phase from values for its equilibrium solubility in a second phase. The method has been used to compute the CaO:SiO₂ ratio for two types of calcium silicate hydrate (C-S-H) gel, one of which is thought to form from hydrating tricalcium silicate (Ca₃SiO₅), and the other by precipitation from appropriate solutions. The results agree well with measured values reported in the literature. They have also been used to help define the probable composition of the C-S-H layer which forms on tricalcium silicate surfaces during the early stages of hydration when the reaction is slow. A chemical potential phase diagram is constructed from which thermodynamic quantities can be computed directly. The free energies of formation have been estimated for two types of C-S-H formed from CaO, SiO₂, and H₂O, These results provide insight into the structure and composition of C-S-H, which is the most abundant product in portland cement systems.