碳硫硅钙石形成机制的定量分析

设计了两种人工合成碳硫硅钙石的实验方法以研究水泥基材料中碳硫硅钙石的侵蚀机理。用X射线衍射、Raman光谱对水泥基材料不同龄期的反应产物进行定性分析,并采用Rietveld方法进行定量表征。结果表明：碳硫硅钙石在不能生成钙矾石的环境下仍可形成,说明其可以直接反应生成;在有钙矾石生成的环境下,碳硫硅钙石也可生成,表明碳硫硅钙石形成机理存在Woodfordite转变机理。钙钒石的存在提高了碳硫硅钙石的产率。相比较而言,Woodfordite转变机理比直接生成机理更容易发生,且两种机理可以同时并存。     

碳硫硅钙石和钙矾石的稳定性

采用化学方法合成出纯的碳硫硅钙石和钙矾石,对比研究了二者的稳定性。结果显示:钙矾石比碳硫硅钙石更易受到碳酸钠破坏;碳硫硅钙石与氯化钡几乎不发生反应,钙矾石则较易被氯化钡破坏;在碳化条件下,钙矾石较易分解,碳硫硅钙石则几乎没变化。碳硫硅钙石在碳酸钠或氯化钡溶液中的稳定性、热分解稳定性和碳化稳定性均明显高于钙矾石,可能是由于碳硫硅钙石结构中离子键和氢键强度高于钙矾石。     

碳硫硅钙石鉴别方法研究

碳硫硅钙石和钙矾石的晶体结构和形态极为相似,对其准确鉴别难度较大.本文采用化学方法合成出纯的钙矾石和碳硫硅钙石,并用XRD、EDS能谱、IR光谱和Raman光谱等微观测试手段对它们的结构进行表征,以探求碳硫硅钙石鉴定方法.研究结果表明,碳硫硅钙石和钙矾石的XRD图谱极为相似;碳硫硅钙石EDS能谱显示其主要含有S、Si和Ca等元素,而钙矾石则主要为S、Al和Ca等元素;碳硫硅钙石的IR光谱和Raman光谱分别在500cm-1处和658 cm-1处有特征吸收峰.研究发现,拉曼光谱是鉴别碳硫硅钙石存在的最有效方法.     

以山砂为骨料的电解锰渣蒸压砖工况使用强度失效问题研究

对以山砂为骨料的锰渣蒸压砖在贵州地区自然条件下使用1年后性能的变化进行了分析,利用XRD、XRF和SEM-EDS等方法分析了其强度变化机理.结果显示,失效锰渣蒸压砖出现二水石膏、少量碳硫硅钙石和钙矾石物相,原始锰渣蒸压砖存在的钙铝硅酸盐消失.锰渣蒸压砖性能失效是二水石膏相、钙矾石、碳硫硅钙石综合作用的结果,锰渣高含量的硫酸盐和山砂中大量的碳酸盐是这些物相形成的主要诱因.     

SO42-/C3A对单矿C3S水泥浆体中碳硫硅钙石形成的影响

碳硫硅钙石型硫酸盐侵蚀是一种以碳硫硅钙石为生成产物的硫酸盐侵蚀,碳硫硅钙石的形成过程与水泥基材料中铝源及外界环境中硫酸盐密切相关。以铝酸三钙(C₃A)为铝源,Na₂SO₄溶液为侵蚀介质,采用单矿硅酸三钙(C₃S)制备水泥浆体,通过XRD、FTIR、SEM/EDS等测试技术表征不同SO^2-₄与C₃A摩尔比(S/Al比)对单矿C₃S水泥浆体中碳硫硅钙石形成的影响,旨在揭示碳硫硅钙石形成机理并探讨抑制其形成的方法。结果表明:当S/Al比为3时,侵蚀14个月后在侵蚀产物中依然没有检测到碳硫硅钙石;当S/Al比为6和9时,侵蚀3个月即可检测到碳硫硅钙石,这表明外部硫酸根离子浓度越高越有利于碳硫硅钙石的形成。     

0～20℃养护下硅酸盐水泥水化时钙矾石的生成及转变

采用X射线衍射仪及核磁共振仪研究了0、5、10、20℃硅酸盐水泥水化产物钙矾石的生成及转变。结果表明：硅酸盐水泥水化1d至180d,4种养护温度下钙矾石生成量皆先增大后减小,但该规律随养护温度不同而不同：在10℃和20℃养护时,钙钒石生成量在水化3 d时达到最大,0℃和5℃养护时,水化28d时才达到最大;而从水化龄期来看,钙矾石生成量在水化1d时20℃养护时最高（10.2%）,水化3d时10℃养护时最高（12.1%）,3～180 d时0℃时最高;此外,低温养护显著延迟了钙矾石向单硫型水化硫铝酸钙转变。     

内掺硫酸镁加速水泥基材料TSA破坏

为满足实验室研究水泥基材料的碳硫硅钙石型硫酸盐侵蚀(thaumasite form of sulfate attack,TSA)破坏的需要,研究了一种快速生成碳硫硅钙石的途径。将内掺10%硫酸镁的水泥-石灰石粉净浆样品浸泡在(5±2)℃水中,进行硫酸盐侵蚀加速试验,观察侵蚀后样品外观,并用X射线衍射、红外光谱分析腐蚀产物。结果表明:浸泡6个月后,样品失去强度,变为一种白色、柔软且无黏结力的烂泥状物质,腐蚀产物以碳硫硅钙石、石膏为主,并含有少量钙矾石,具有典型的TSA破坏特征。与硫酸盐溶液外部侵蚀相比,内掺法显著加速水泥基材料TSA破坏。X射线衍射结合红外光谱分析可以有效鉴定碳硫硅钙石存在。     

温度对铝酸盐水泥基三元体系早期水化的影响

采用X射线衍射仪、环境扫描电子显微镜(背散射电子成像)、压汞仪分析了养护温度对铝酸盐水泥-硅酸盐水泥-无水石膏三元体系水化早期的水化相组成、抛光断面微观结构和孔结构等微结构演变的影响。结果表明:无论0℃还是40℃养护,三元体系的主要水化产物始终为水化硫铝酸钙类物相;但养护温度越高,所生成的钙矾石越易向单硫型水化硫铝酸钙转变,且转变得越早,所得硬化浆体的最可几孔径越大。此外,40℃养护3 d后的浆体中还生成了水化钙铝黄长石和三水铝石。     

矿粉对水泥基材料抗碳硫硅钙石侵蚀破坏的定量分析

研究了矿粉对水泥基材料抗碳硫硅钙石侵蚀性的影响,将制得试件在温度5℃、质量浓度10%MgSO4溶液中养护,对不同龄期试件进行力学性能测试,并对侵蚀产物进行X射线衍射、拉曼光谱定性分析及Rietveld方法定量分析。结果表明：未掺矿粉试件受侵蚀后腐蚀产物中碳硫硅钙石占12.68%,而掺20%和40%矿粉试件中碳硫硅钙石分别只占2.79%和2.19%。矿粉的掺入可以使水泥基材料的抗碳硫硅钙石侵蚀破坏性能提高,但不能完全抑制碳硫硅钙石侵蚀破坏的发生。     

电脉冲对加速水泥基材料碳硫硅钙石型硫酸盐侵蚀的影响

通过测试电场环境中不同电脉冲参数条件下水泥净浆试件碳硫硅钙石型硫酸盐侵蚀(TSA)后的外观及抗压强度变化,结合扫描电子显微镜、红外光谱、X射线衍射分析侵蚀产物组成,探讨了不同电脉冲参数对加速TSA的影响。结果表明:4组不同参数电脉冲(20 V-20 s、30 V-20 s、30 V-40 s及40 V-20 s)均明显加速了水泥基材料TSA反应,加快了碳硫硅钙石生成;电脉冲作用下加速了侵蚀试件的劣化,使其强度下降。脉冲周期20 s时,脉冲电压越高试件强度下降幅度越大,40 V-20 s电脉冲组试件90 d强度降低67%;脉冲电压为30 V时,脉冲周期20 s试验组90 d强度降低48%,较脉冲周期40 s组试件降低幅度更大。电脉冲作用120 d的侵蚀产物中出现大量碳硫硅钙石,脉冲周期为20 s时,脉冲电压由20 V升高到40 V,侵蚀产物中碳硫硅钙石的含量随之增长,高脉冲电压40 V组试件侵蚀程度最严重;脉冲电压不变,较短脉冲周期20 s时,TSA反应程度更高。     

Thaumasite-ettringite solid solutions in degraded mortars

The thaumasite form of sulfate attack (TSA) has been observed in mortar prisms made from Portland-limestone cements after laboratory storage in 1.8% magnesium sulfate solution at 5 °C for 5 years. The prisms all showed evident signs of degradation, which increased with increasing limestone content. X-ray powder diffraction indicated that a solid solution was formed in all the prisms, which was based on the crystal structure of thaumasite, but extended towards the chemical composition of ettringite. The prism made from the cement with the highest level (35%) of limestone replacement gave the greatest amount of the thaumasite solid solution and had a composition close to the thaumasite end member, whereas those cements with lower (15%, 5% and 0%) levels of replacement gave reduced amounts of the solid solution and had greater lattice parameters. The solid solutions that have been observed are compared with those reported by Barnett et al. for synthetic thaumasite samples grown from sucrose solution.     

特性环境对水泥砂浆硫酸盐侵蚀类型的影响

研究了硫酸盐种类(Na2SO4,MgSO4)及温度(5 ℃,20 ℃)等影响因素对水泥砂浆硫酸盐侵蚀类型的影响,以明确碳硫硅酸钙型硫酸盐侵蚀的特性环境条件.试验结果表明:掺加石灰石粉的水泥砂浆试件置于5% MgSO4溶液、5 ℃及20 ℃温度环境下浸泡450 d后,均能生成碳硫硅酸钙.而一般水泥砂浆试件置于5% Na2SO4溶液、5 ℃及20 ℃温度环境浸泡侵蚀后,未生成碳硫硅酸钙.证明水泥混凝土在＞15 ℃的硫酸盐侵蚀环境下亦可生成碳硫硅酸钙,而Mg2 的存在对碳硫硅酸钙的形成过程具有加速催化作用.     

Effect of cement C3A content, temperature and storage medium on thaumasite formation in carbonated mortars

The purpose of this study is to determine the effect of cement C₃A content, temperature and composition of the immersion medium (water, gypsum and magnesium sulphate solution) on the rate of thaumasite formation in cement mortars. It also aims to ascertain how the C₃A content influences the composition of the salt formed.The mortar prisms for this study were made with two different cements, one with low and the other with high Al₂O₃ content, with or without gypsum and/or calcium carbonate. After hydration, curing and carbonation, the prisms were partially immersed in distilled water and stored at temperatures ranging from 0 to 5 °C for up to 5 years. Some of the prisms were immersed in a 2% (w/w) gypsum solution or in 1.4% (w/w) magnesium sulphate solution at ambient temperature. Samples were taken at different ages and mineralogical and micro-structurally characterised.Some of the specimens tested were observed to expand, in a process concurring with the formation of thaumasite or a solid solution of thaumasite and ettringite, at both ambient and cooler temperatures. A correlation was found between cement C₃A content and the composition of the deterioration product involved in the expansive process: thaumasite forms in mortars made with low C₃A cement, whereas mixed crystals or solid solutions of thaumasite and ettringite form in mortars made with high C₃A content cement.     

基于三苯胺的D-A-π-A-D型化合物的合成及光物理性能

以甲氧基三苯胺为电子供体,苯并噻二唑为电子受体,咔唑为共轭π桥,通过三步Suzuki偶联反应合成了D-A-π-A-D型荧光化合物4,4′-[(7,7′-9 H-咔唑-2,7-)-二(苯并噻二唑-7,4-)]-二(N,N-二(4-甲氧基苯基))苯胺(DTB-CZ),并用1HNMR、¹³CNMR、MALDI-TOF等手段对其结构进行表征。研究了它的光谱性能、电化学性能、轨道能级和热性能,并与D-π-D型化合物2TPA-CZ1的性能进行了比较。初步探索了DTB-CZ作为空穴传输材料在PSC中的应用。研究结果表明,DTB-CZ在甲苯溶液中的最大吸收波长为479 nm,最大发射波长为608 nm,在薄膜状态下最大吸收波长为495 nm,HOMO/LUMO能级为-4.91/-2.82 eV,带隙值为2.09 eV,热分解温度(T_5d)为449.6℃,玻璃化转变温度(T_g)为143.1℃。相比2TPA-CZ1,在甲苯溶液中吸收和发射波长分别红移了104、182 nm,在薄膜状态下吸收波长红移109 nm;带隙值降低0.84 eV;T 5d和T g分别提高了9.6、24.7℃。结果表明,苯并噻二唑的引入,使化合物的共轭程度增大,带隙值降低,使得吸收和发射波长红移,使其具有更好的热稳定性和形态稳定性。     

Prevention of thaumasite formation in concrete exposed to sulphate attack

Thermodynamic calculations were performed to investigate at which sulphate ion concentration hardened concrete can be damaged by the formation of thaumasite. It is indicated that thaumasite can be formed from C-S-H phases and portlandite at very low sulphate concentrations in an aggressive solution. Higher sulphate ion concentrations are required in the absence of portlandite. Still higher sulphate ion concentrations are needed if C-S-H phases with a low calcium/silicon ratio are consumed. Therefore, it is suggested that the formation of thaumasite at low and moderate sulphate concentrations in the attacking solution can be avoided by lowering the calcium/silicon ratio in the C-S-H phases. This can be achieved by the addition of pozzolanic and latently hydraulic admixtures. During the reaction of these materials, portlandite is consumed and the calcium/silicon ratio of the C-S-H phases is lowered. The aforementioned concept was confirmed by studies published in the literature and also by experimental investigations reported in this paper.     

The role of pH in thaumasite sulfate attack

The thaumasite form of sulfate attack (TSA) has been recognised in recent years as a distinct mechanism by which degradation of buried concrete can occur in the presence of an external source of sulfate ions. There is, however, disagreement about the role of pH. It has been proposed that attack by sulfuric acid, produced by oxidation of pyrite, is sometimes the primary cause of deterioration. Others believe that the acid is rapidly neutralised giving a higher concentration of sulfate ions in the ground, hence increasing the extent of attack. The aim of the laboratory study reported here was to understand the role of sulfuric acid in TSA by examining concrete cubes, made from three types of cement and two types of aggregate, immersed at low temperature in two solutions, one alkaline corresponding to BRE Design Sulfate Class DS-3 and the other acidic. It is concluded that the presence of acid does not promote the formation of thaumasite. Although degradation of the concrete was observed in acid conditions, the mechanism was not TSA as observed in alkaline conditions.     

Effect of ettringite on thaumasite formation

Deterioration of cementitious building materials is often caused by sulphate attack where ettringite and gypsum play the most destructive role at moderate ambient temperatures. In contrast, thaumasite [Ca₃Si(OH)₆·12H₂O](SO₄)(CO₃) is mostly observed at comparatively low temperatures of less then 15 °C. This mineral forms from calcium, sulphate, carbonate and silicon. The latter originates from the decomposition of C-S-H which results in deterioration of the hardened cement paste structure. To investigate the effect of ettringite on thaumasite formation, pastes were mixed using synthetic clinker phases, fly ash and nanosilica. Aqueous suspensions were prepared with the ground-hydrated pastes mixed with calcite and either gypsum or sodium sulphate. Following different storage periods, the solid phase was separated by filtration, dried and analysed by XRD using the Rietveld method as well as ESEM and TEM. The liquid phase was analysed by ICP-OES. The results indicate that thaumasite formation occurs through the heterogeneous nucleation of thaumasite on the surface of ettringite, due to the structural similarities of these minerals. This reaction is followed by further epitaxial growth of thaumasite from its components present in solution.     

A novel process for precipitation of ultra-fine particles using sub-critical CO2

Supercritical CO₂ has been utilized as solvent, cosolvent or antisolvent in several processes for production of ultra-fine solid particles with narrow size distribution. The key to the precipitation of such particles is to produce a very large, rapid and uniform supersaturation in the solution of a solid substance. This can be achieved either by a rapid and large reduction in the temperature of solution or by drastically increasing the CO₂ solubility for imparting the antisolvent effect. Most of these CO₂ processes require high-pressure pumps, specially designed nozzles and accurate control of process parameters. In order to obviate these requirements, a simple technique of precipitation by pressure reduction over the gas-expanded liquids (PPRGEL), such as CO₂-expanded organic solutions has been utilized to impart a large, uniform and rapid reduction of temperature in the solution for instantaneous precipitation of ultra-fine particles. This process utilizes sub-critical CO₂ at relatively low pressures of 40-70 bar and near ambient temperature of 303 K for creating a temperature drop of 30-70 K in the solution within seconds, without using any specially designed nozzle or high-pressure pumps. The present paper validates the process principle for precipitation of Zinc acetate (ZnAc) nanoparticles from its organic solution in a mixed solvent of acetone and dimethyl sulfoxide (DMSO). Nanoparticles are produced with the average size of 20-250 nm (from 100 ml of solution in a high-pressure vessel of 1.09 L working volume), and vary in shapes such as long needles, rods and near spherical depending on pressure (40-70 bar at 303 K), solid concentration (0.01-0.05 g/ml) and addition of stabilizer.     

Thermodynamic Assessment of the System CoO-MnO

The thermodynamic properties of pure CoO and CoO-MnO solutions have been analyzed in terms of thermodynamic models applying various experimental data. Expressions for the Gibbs energy of the individual phases have been obtained and the phase diagram is calculated. It reveals a homogeneous solid solution at temperatures above room temperature but a miscibility gap at very low temperatures.     

掺氮TiO_2的制备与光谱分析

用硫酸钛与氨水反应得到TiO2前体,煅烧后制得掺氮TiO2粉体,研究了不同温度和加热时间下掺氮TiO2的XPS、FTIR和紫外可见光谱,结果表明,掺氮TiO2在400℃下加热1 h,所得粉体是锐钛矿相结构,与未掺杂TiO2相比,吸收边红移22 nm,对400~510 nm的可见光有一定的吸收率。氮的掺杂不仅使TiO2带隙变小,而且有助于氧空位的形成。