苯酚在水热条件下对棉的碳化影响研究

探讨300℃,反应时间10 h,浓度20~30 g/L下,棉在苯酚作用下的碳化形态。结果表明,棉纤维在不加催化剂下可实现碳化,但是形貌比较差;加入苯酚后依然不能形成球,而且形貌有所下降;葡萄糖加入苯酚后,也没有形成球,对产量的影响也在误差范围内。所以,苯酚对棉和葡萄糖的碳化几乎没影响。     

苯酚在水热条件下对棉的碳化影响研究

探讨300℃,反应时间10 h,浓度20³0 g/L下,棉在苯酚作用下的碳化形态。结果表明,棉纤维在不加催化剂下可实现碳化,但是形貌比较差;加入苯酚后依然不能形成球,而且形貌有所下降;葡萄糖加入苯酚后,也没有形成球,对产量的影响也在误差范围内。所以,苯酚对棉和葡萄糖的碳化几乎没影响。     

Determination of the elastic constants of portlandite by Brillouin spectroscopy

The single crystal elastic constants C_ij and the shear and adiabatic bulk modulus of a natural portlandite (Ca(OH)₂) crystal were determined by Brillouin spectroscopy at ambient conditions. The elastic constants, expressed in GPa, are: C₁₁ = 102.0(± 2.0), C₁₂ = 32.1(± 1.0), C₁₃ = 8.4(± 0.4), C₁₄ = 4.5(± 0.2), C₃₃ = 33.6(± 0.7), C₄₄ = 12.0(± 0.3), C₆₆ = (C₁₁-C₁₂)/2 = 35.0(± 1.1), where the numbers in parentheses are 1σ standard deviations. The Reuss bounds of the adiabatic bulk and shear moduli are K_0S = 26.0(± 0.3) GPa and G₀ = 17.5(± 0.4) GPa, respectively, while the Voigt bounds of these moduli are K_0S = 37.3(± 0.4) GPa and G₀ = 24.4(± 0.3) GPa. The Reuss and Voigt bounds for the aggregate Young's modulus are 42.8(± 1.0) GPa and 60.0(± 0.8) GPa respectively, while the aggregate Poisson's ratio is equal to 0.23(± 0.01). Portlandite exhibits both large compressional elastic anisotropy with C₁₁/C₃₃ = 3.03(± 0.09) equivalent to that of the isostructural hydroxide brucite (Mg(OH)₂), and large shear anisotropy with C₆₆/C₄₄ = 2.92(± 0.12) which is 11% larger than brucite. The comparison between the bulk modulus of portlandite and that of lime (CaO) confirms a systematic linear relationship between the bulk moduli of brucite-type simple hydroxides and the corresponding NaCl-type oxides.     

New insights into the mechanisms of carbon dioxide mineralization by portlandite

Portlandite (Ca(OH)₂; also known as calcium hydroxide or hydrated lime), an archetypal alkaline solid, interacts with carbon dioxide (CO₂) via a classic acid–base “carbonation” reaction to produce a salt (calcium carbonate: CaCO₃) that functions as a low-carbon cementation agent, and water. Herein, we revisit the effects of reaction temperature, relative humidity (RH), and CO₂ concentration on the carbonation of portlandite in the form of finely divided particulates and compacted monoliths. Special focus is paid to uncover the influences of the moisture state (i.e., the presence of adsorbed and/or liquid water), moisture content and the surface area-to-volume ratio (s_a/v, mm⁻¹) of reactants on the extent of carbonation. In general, increasing RH more significantly impacts the rate and thermodynamics of carbonation reactions, leading to high(er) conversion regardless of prior exposure history. This mitigated the effects (if any) of allegedly denser, less porous carbonate surface layers formed at lower RH. In monolithic compacts, microstructural (i.e., mass-transfer) constraints particularly hindered the progress of carbonation due to pore blocking by liquid water in compacts with limited surface area to volume ratios. These mechanistic insights into portlandite's carbonation inform processing routes for the production of cementation agents that seek to utilize CO₂ borne in dilute (≤30 mol%) post-combustion flue gas streams.     

Influence of carbonation and carbonation methods on leaching of metals from mortars

Mortars with varying water-to-cement (w/c) ratio were spiked with heavy metals. After hardening, some samples were carbonated in a CO₂ chamber, others were carbonated using supercritical CO₂ (SCC). Porosity and carbonation depth of treated and untreated samples were compared. Leaching was tested using the diffusion (NEN 7345) and extraction test (based on DIN 38414-S4). The results show that carbonation decreases the porosity of the samples. The decrease is more important with increasing w/c ratio. Carbonation runs deeper into the monolith with increasing w/c ratio. In the supercritical method, not all samples were carbonated to the same extent. The diffusion test shows that carbonation decreases leaching of Na, K, Ca, Ba, Cu, and Pb and increases leaching of Mg. Ni leaching depends on the pH induced by carbonation. Influence of pH and formation of metal carbonates is evaluated with the extraction test and enhances understanding of metal leaching in the diffusion test.     

Formation of ASR gel and the roles of C-S-H and portlandite

Experimental investigations of the reactions between silica, alkali hydroxide solution, and calcium hydroxide show that alkali-silicate-hydrate gel (A-S-H) comparable to that formed by the alkali-silica reaction (ASR) in concrete does not form when portlandite or the Ca-rich, Si-poor C-S-H of ordinary portland cement (OPC) paste is available to react with the silica. Under these conditions, we observe either the formation of additional C-S-H by reaction of Ca(OH)₂ with the dissolving silica or the progressive polymerization of C-S-H. The A-S-H dominated by Q³ polymerization forms only after portlandite has been consumed and the C-S-H polymerized. These conclusions are consistent with previously published results and indicate that the ASR gel of concrete forms only in chemical environments in which the pore solution is much lower in Ca and higher in Si than bulk pore solution of OPC paste. These results highlight the similarity between ASR and the pozzolanic reaction and are supported by data for mortar bar specimens.     

纳米CaCO3孔径调控及其对碳酸化反应性能的影响

研究了纳米CaCO₃颗粒间孔径调控对CaO与CO₂碳酸化反应性能的影响。通过有机模板法制备得到一系列比表面积相近、孔径分布不同的纳米CaCO₃,并考察其再生和碳酸化反应性能差异。结果表明：增大平均孔径能促进纳米CaCO₃的热分解反应,并降低分解温度约15℃。将平均孔径由15 nm增大至113 nm可显著提高碳酸化反应速率和转化率。研究认为平均孔径和比表面积对碳酸化反应转化率的影响存在交互作用;比表面积小的纳米CaCO₃,表现出碳酸化反应转化率受扩散控制影响较大,而比表面积较大的表现为碳酸化反应转化率以表面反应影响控制为主的规律。     

水泥的碳酸化工艺研究

通过设计正交实验,测定碳酸化水泥复合胶凝材料与纯水泥的水化产物及观察硬化浆体的微观形貌,研究了水泥的碳酸化工艺条件。结果表明：碳酸化水泥复合胶凝材料3d、28d的抗压强度普遍高于纯水泥,且强度等级由42．5提高至52．5;水量、碳酸化温度对碳酸化复合胶凝材料3d抗压强度有显著影响,且水量的影响作用较大;水泥的碳酸化最佳工艺条件为水量：0．2％、CO2压力：0．2MPa、碳酸化温度：25℃、碳酸化时间：30min;复合胶凝材料3d水化产物中有CaCO3微晶析出,28d水化产物中有较多的碳铝酸钙生成。     

Effect of carbonation on the hydro-mechanical properties of Portland cements

We evaluate experimentally the effect of carbonation on the hydro-mechanical properties of Portland cement. Samples were carbonated at 90 °C and 28 MPa under wet supercritical CO₂. Two types of carbonation features were achieved, either the samples were homogeneously carbonated or they displayed sharp carbonation fronts. Using a tri-axial apparatus, the static elastic moduli and the mechanical strength were measured at in-situ pressure conditions (28 MPa) and showed a degradation of the mechanical properties of the samples where a carbonation front prevailed. Water and gas permeabilities were measured and showed that the samples with a carbonation front exhibit a stress sensitive permeability. P and S elastic wave velocities were measured to evaluate dynamic (ultrasonic range, 1 MHz) elastic moduli. The use of an effective medium theory approach enabled us to characterize the density and distribution of cracks within the samples. This approach outlines that the samples which developed a carbonation front were damaged.     

Parametric study and effect of calcination and carbonation conditions on the CO2 capture performance of lithium orthosilicate sorbent

The world is currently facing the challenges of global warming and climate change. Numerous efforts have been taken to mitigate CO_2 emission, among which is the use of solid sorbents for CO_2 capture. In this work, Li_4SiO_4 was synthesised via a sol–gel method using lithium nitrate(LiNO_3) and tetraethylorthosilicate(Si C8 H20 O4) as precursors. A parametric study of Li:Si molar ratio(1-5), calcination temperature(600–800 °C) and calcination time(1–8 h) were conducted during sorbent synthesis. Calcination temperature(700–800 °C) and carbonation temperature(500–700 °C) during CO_2 sorption activity were also varied to confirm the optimum operating temperature. Sorbent with the highest CO_2 sorption capacity was finally introduced to several cyclic tests to study the durability of the sorbent through 10 cycles of CO_2 sorption–desorption test. The results showed that the calcination temperature of 800 °C and carbonation temperature of 700 °C were the best operating temperatures, with CO_2 sorption capacity of 7.95 mmol CO_2?(g sorbent)-1(93% of the theoretical yield). Throughout the ten cyclic processes, CO_2 sorption capacity of the sorbent had dropped approximately 16.2% from the first to the tenth cycle, which was a reasonable decline. Thus, it was concluded that Li_4SiO_4 is a potential CO_2 solid sorbent for high temperature CO_2 capture activity.     

Magnitude of electrogyration effect in crystals

Electrogyration Miller's delta Δ_g is checked for more than 50 crystals. The corelation between Δ_g and other quantites is discussed, similar relation for quadratic electrogyration is introduced.     

Stability of ancient masonry towers: Moisture diffusion, carbonation and size effect

Moisture diffusion and carbonation influence the behavior of multiple-leaf ancient masonry walls, producing during centuries a redistribution of stresses from the core of lime mortar concrete to the external cladding of stiff masonry. This is likely one of the causes of long-time damage of some ancient masonry towers. With these motivations, coupled processes of moisture diffusion, carbon dioxide diffusion and carbonation reaction are analyzed numerically. Due to the absence of models and data for lime mortar, one of the simplest models proposed for Portland cement concrete is adapted for this purpose. The results reveal the time scales of the processes involved and their dependence on wall thickness (size). It is found that the temporal scale is set mainly by diffusion of moisture trough the massive concrete wall and is only slightly modified by carbonation. Moisture evolution in time is needed for stress analysis that is relegated to a subsequent paper.     

Cementation by the carbonation of hydrated lime

In this study, the factors which control carbonate cementation have been examined and several hypothesis developed to explain their interaction. These factors include the pressure, concentration, temperature and velocity of the carbonating gas as well as the thickness, temperature, gas permeability, moisture and Ca(OH)₂ contents of the compact. Of these factors, the greatest limitation for the more popular application of the cement is related to the diffusion of the carbonating gas into thicker or less permeable products. A possible reaction mechanism for the cementing process has been outlined and the matrix examined by electron optics, X-ray diffraction, thermal analysis and mercury intrusion porosimetry. These methods have shown that, in general, the matrix is composed of mostly amorphous or very poor crystalline forms of calcium carbonate. The only phases detected by X-ray diffraction methods were a small percentage of unreacted portlandite Ca(OH)₂, and calcite. Less than half of the calcium carbonate formed was present as crystalline calcite.     

Effects of carbonation on the pore structure of non-hydraulic lime mortars

The pore structures of carbonated non-hydraulic lime mortars made with a range of different aggregates and concentrations of lime have been determined using mercury intrusion porosimetry (MIP). MIP data have been correlated with scanning electron microscopy images and other porosity data. During carbonation there is an increase in pore volume in the ∼ 0.1 μm pore diameter range across all mortar types which is attributed to the transformation of portlandite to calcite. Also there is a monotonic increase in the volumes of pores with diameters below 0.03 μm. A model is proposed for the changes in pore structure caused by carbonation. This attributes the increase in the volume of sub 0.03 μm pores to the attachment of calcite crystals to the surface of aggregate particles, and in some cases to the surface of portlandite crystals. This phenomenon may explain the continuing presence of portlandite in mortars that, apparently, have fully carbonated.     

Analysis of carbonation behavior in concrete using neural network algorithm and carbonation modeling

Carbonation on concrete structures in underground sites or metropolitan cities is one of the major causes of steel corrosion in RC (Reinforced Concrete) structures. For quantitative evaluation of carbonation, physico-chemo modeling for reaction with dissolved CO₂ and hydrates is necessary. Amount of hydrates and CO₂ diffusion coefficient play an important role in evaluation of carbonation behavior, however, it is difficult to obtain a various CO₂ diffusion coefficient from experiments due to limited time and cost.In this paper, a numerical technique for carbonation behavior using neural network algorithm and carbonation modeling is developed. To obtain the comparable data set of CO₂ diffusion coefficient, experimental results which were performed previously are analyzed. Mix design components such as cement content, water to cement ratio, and volume of aggregate including exposure condition of relative humidity are selected as neurons. Training of learning for neural network is carried out using back propagation algorithm. The diffusion coefficient of CO₂ from neural network are in good agreement with experimental data considering various conditions such as water to cement ratios (w/c: 0.42, 0.50, and 0.58) and relative humidities (R.H.: 10%, 45%, 75%, and 90%). Furthermore, mercury intrusion porosimetry (MIP) test is also performed to evaluate the change in porosity under carbonation. Finally, the numerical technique which is based on behavior in early-aged concrete such as hydration and pore structure is developed considering CO₂ diffusion coefficient from neural network and changing effect on porosity under carbonation.     

Understanding the effect of surface flaws on the strength distribution of brittle single crystals

The dependence of strength on the surface quality of brittle single crystals is highly relevant in microelectronic applications, where a certain roughening of the crystal surface is required to guarantee or enhance the functional properties of the final component. In this work, the effect of surface conditioning on the strength distribution of single crystals is assessed on LiTaO₃ and LiNbO₃ samples with distinct surfaces (i.e., polished, grinded, and scratched). Artificial surface cracks (scratches) were introduced using a Berkovich nanoindenter tip oriented under various angles with respect to the most critical {012} cleavage plane. Biaxial tensile tests were performed using the ball‐on‐three‐balls test, supported by fractographic analyses to interpret the strength results. A direct correlation between sub‐surface damage and strength was observed, associated with the hardness and elastic constants of the material, being strongly dependent on the crystal orientation with respect to the loading axis. Furthermore, we provide an explanation for the usually low Weibull modulus in single crystals and discuss the validity of the biaxial tests on scratched specimens for fracture toughness evaluation.     

白云灰乳碳酸化工艺研究

中国白云石蕴藏量巨大,白云灰乳碳酸化是白云石碳化法制备轻质碳酸镁、氧化镁等镁化合物的关键步骤之一,关系到镁的产率、产品中钙的含量及生产成本。通过单因素实验和正交实验,研究了碳酸化过程镁的溶出率及重镁水中的钙含量与碳酸化反应温度、反应终点pH、白云灰乳质量浓度的关系,从而为提高碳酸化过程镁的溶出率,实现钙镁的有效分离提供可靠的依据。研究表明：影响镁的溶出率及重镁水中钙含量的主要因素为pH。白云灰乳碳酸化最佳工艺条件：白云灰乳质量浓度为9.00 g/L（以氧化镁计）,反应温度为30 ℃,反应终点pH为7.50。在此条件下镁的溶出率为74.49%,重镁水中钙的质量浓度为0.10 g/L。     

白云石的灰乳碳酸化工艺条件初探

本文在模拟碳化塔中用人工模拟窑气成分，对由白云石制灰乳碳化制取重镁水的工艺条件进行了研究，讨论了灰乳中的液固比在不同气体组成下对MgO提取率的影响，确定了MgO提取率最大时液固比为40：1，窑气中CO2的体积分数为30％。并为提高MgO的提取率寻找到合适的添加剂DETA，得出与未加添加剂相比，在相同碳化条件下，相应提取率提高了16．77％。     

Influence of portlandite on Pyrex glass dissolution and the formation of alkali‐silica chemical reaction products

The dissolution behavior of Pyrex glass in a model system consisting of 1‐M NaOH with varying amounts of portlandite, representing the glass dissolution in alkaline environment and alkali‐silica reaction (ASR) in cementitious materials, is studied. The Pyrex glass dissolution and the reaction products were characterized using X‐ray diffraction (XRD), ²⁹Si nuclear magnetic resonance (²⁹Si‐NMR), and scanning electron microscopy with energy dispersive X‐ray (SEM/EDX), and the silica and calcium concentrations in the liquid phase were determined using inductively coupled plasma atomic emission spectroscopy (ICP‐AES). The experimental results show that the dissolution of the Pyrex glass continued until it consumed the portlandite and then reached a constant rate, with a linear relationship with the amount of portlandite. The absence of calcium and reduction of silica concentration in the liquid phase with the increase in portlandite indicate the formation of high‐reaction products with portlandite, confirmed by XRD and ²⁹Si‐NMR. The calcium sodium silicate hydrate (C–N–S–H) and sodium silicate hydrate (N–S–H) are the main ASR products; their composition and proportions strongly depend on the reaction time and the amount of portlandite added. A thermodynamic model, which couples geochemical code (PHREEQC) and the experimental silica dissolution rate, was used to predict ASR products and the remaining portlandite. The simulation results predicted the experimental data fairly well for different portlandite additions. The mechanism for Pyrex glass dissolution in the presence of varying portlandite additions is discussed with regard to experimental data and simulation results.     

Assessment of protective properties of organic coatings by thermal cycling

Researchers’ efforts are focused on understanding how coatings can be tested in order to determine their real capabilities and selected for different purposes. Outdoor exposures are certainly reliable and offer a good representation of the actual service life. However, such tests cannot be considered quick.

On the other hand, a quick test, even if reliable, very often disagrees with the actual degradation mechanisms occurring under natural conditions. In fact, in order to determine an acceleration of the natural weathering, it is necessary to increase the effect of natural parameters affecting the protection properties of a coating.

The usual modern way to operate is to take advantage of ageing tests where temperature plays a big role in the ageing of the material, permitting to gather faster information for coating corrosion resistance evaluation.

Following the recent new experience realised by the Bierwagen group, we carried out different thermal cycling tests consisting in daily series of electrochemical measurements on coated samples, carried out using electrochemical impedance spectroscopy (EIS).

The cumulative effects of such a thermal cycling on the film, based on a large variety of theoretical explanations, should permit the ranking of a variety of materials, by constituents, characteristics and application purposes, in a short time while remaining objective and reliable.

The used ageing procedure and data evaluation allowed to quickly and precisely obtain information concerning both barrier properties and adhesion properties of the studied materials.