不同系列减水剂对碳硫硅钙石形成的影响

研究了不同系列减水剂(萘系、脂肪族和聚羧酸系)对硫酸盐侵蚀下碳硫硅钙石形成的影响及机理。将样品浸泡在5℃,质量分数5%的MgSO4溶液中,观察侵蚀后样品的外观、强度及膨胀率,并对腐蚀产物进行X射线衍射分析、扫描电子显微镜分析、能谱分析、红外光谱分析及激光Raman光谱分析。结果表明,碳硫硅酸钙型硫酸盐侵蚀程度与外加剂品种有关,聚羧酸减水剂不能防止TSA破坏,但聚羧酸减水剂较其它两种减水剂抗硫酸盐侵蚀效果好。     

碳硫硅钙石型硫酸盐侵蚀

介绍了碳硫硅钙石型硫酸盐侵蚀(TSA)的形成机理、形成条件、侵蚀模型、影响因素、预防和处理措施。形成机理包括溶液反应机理和硅钙矾石转变机理;侵蚀模型可分为化学模型和物理模型;形成条件包括硫酸盐、硅酸盐、碳酸盐、水和低温;影响因素主要有水泥种类、C3A和Al2O3含量、矿物掺合料、pH值、侵蚀介质、水胶比等。     

水泥混凝土中碳硫硅钙石的生成机制和防治技术研究进展

重点阐述了国内外在水泥混凝土中碳硫硅钙石的生成机制和防治技术方面的研究现状和未来发展趋势,主要包括碳硫硅钙石的生成机理、生成途径、影响因素和碳硫硅钙石型硫酸盐侵蚀的预防措施等。     

动态水热法合成硬硅钙石的研究

通过对不同形貌硬硅钙石浆体表现粘度的研究,发现硬硅钙石颗粒形貌对其表观粘度有着较大的影响,同时该浆体呈现假塑型。应用ＸＲＤ和ＳＥＭ对动态水热法合成硬硅钙石过程中不同反应阶段料浆的物相组成和形貌进行分析。对不同阶段的浆体在２０℃的表观粘度测试发现,由于反应过程中,颗粒形貌的变化,引起表观粘度变化,以上研究有助于制定合理的硬硅钙石合成工艺过程。     

纳米硬硅钙石的制备及应用研究进展

综述了硬硅钙石材料制备的研究现状,重点对纳米硬硅钙石的制备方法、合成过程中的影响因素及应用进展进行了分析:合成纳米硬硅钙石的方法主要有水热法、微乳液法、微波辅助法、化学沉淀法;适量的Mg、Na离子及化学外加剂CaCl2、Sr(NO3)2、ZrOCl2·8H2O、C2S等有助于纳米硬硅钙石的生成;Al离子会阻碍产物硬硅钙石的生成.最后对纳米硬硅钙石制备及应用中存在的问题和今后的研究提出了建议.     

石英微粉表面结构对硬硅钙石中空二次粒子形貌的影响

利用TEM、SED和EDS方法,检测石英微粉表面非晶态层的厚度,估算出非晶态二氧化硅所占的体积和质量百分含量,并着重研究石英微粉表面非结晶层对水热反应合成硬硅钙石中空二次粒子球形貌的影响．通过XRD和XEM方法鉴别反应料浆的晶相组成和形貌．结果表明：石英微粉表面存在少量非晶态二氧化硅时,未影响硬硅钙石中空二次粒子球的合成;而非晶态二氧化硅的含量较高时,会阻碍硬硅钙石中空二次粒子球的合成,最终形成硬硅钙石晶体和托贝莫来石晶体的堆积体．     

低温环境下赤泥地聚合物抗硫酸盐侵蚀机理研究

通过将内掺不同质量分数硫酸镁和硫酸钠的赤泥地聚合物和普通硅酸盐水泥试件在(5±1)℃的条件下长期浸泡,定期观测试件外观变化,并对长期浸泡后的试件取样进行XRD衍射和FT-IR光谱分析,研究了内掺不同种类和不同质量分数硫酸盐对赤泥地聚合物的侵蚀破坏过程与作用机理,并与同等条件下普通硅酸盐水泥抗硫酸盐侵蚀性能及机理进行了对比。结果表明:当试件内掺硫酸镁和硫酸钠时,赤泥地聚合物发生了石膏型硫酸盐膨胀破坏,而普通硅酸盐水泥则分别发生了TSA型硫酸盐侵蚀破坏和石膏型硫酸盐膨胀破坏。赤泥地聚合物内部孔隙液pH值高,水化产物中C-S-H凝胶钙硅比低和水化生成的铝硅酸盐类物质化学性质稳定是其在长期低温硫酸盐侵蚀环境下未发生TSA型硫酸盐侵蚀破坏的主要原因。     

废弃大麻杆衍生的硫掺杂碳材料的制备及电化学储钠性能

采用不同煅烧温度(600℃、700℃和800℃)将废弃大麻杆在充满氮气的管式炉中进行回收碳化处理后得到3个硫掺杂的生物质多孔碳材料(C-600、C-700和C-800),并研究了碳化温度对其结构、元素组成及电化学储钠性能的影响.结果 表明:3个样品均为硫掺杂的多空碳材料,其中C-600由于具有满意的无序程度和结构缺陷而...     

钼掺杂铜硅钙石的制备及其抗菌性能和细胞相容性研究

含铜生物材料在高浓度铜离子释放时对细菌有优异的抑制作用,但同时具有细胞毒性;而在低浓度铜离子释放时虽然具有良好的细胞相容性,但其抗菌性能低.因此,开发一种含铜生物材料,使其能够在高浓度铜离子释放情况下同时具有优异抗菌性能和良好细胞相容性,具有重要意义.本研究利用钼和铜之间的拮抗作用原理,采用溶胶-凝胶法制备了钼掺杂铜硅...     

锂硫二次电池硫/碳正极复合材料的研究进展

锂硫电池因其具有高能量密度、较好的安全性、绿色环保和低成本等特点,成为未来动力电池最具吸引力的体系之一。但是,因其放电产物多硫化物易溶于有机电解液以致锂硫电池循环性能差,制约了锂硫电池的快速发展。碳材料利用其高的比表面积和多孔结构吸附电极反应的中间产物多硫化锂,起到固硫的作用,提高电池的循环性能。综述了锂硫电池硫/碳正极复合材料的研究现状;分析了影响锂硫电池循环性能的主要因素;简述了锂硫电池硫/碳正极复合材料今后研究的方向。     

Investigations on the influence of cement type on thaumasite formation

A high sulfate resistance is required if cements are to be used in sulfate bearing waters and soils especially under conditions favouring thaumasite formation. A long period program of laboratory investigations was carried out on CEN cements to assess thaumasite and ettringite formation. The experimental concept involved mixing ground cement pastes with stoichiometrical components of gypsum, calcite and water. The specimens were stored at 6 °C whereby chemical worst case conditions for thaumasite formation were simulated. At time intervals XRD analysis was conducted. Apart from pure cements mixtures containing additives, pure C₃S pastes with and without Al₂O₃ addition were investigated. The results confirm that thaumasite formation can be accelerated by Al₂O₃ bearing components in cements. However, thaumasite formation is also possible without active participation of Al³⁺. The assessment of sulfate resistance of cements only from the chemical point of view apparently gives results which are contrary to the field experience.     

硅酸钠浓度对镁合金阳极化的影响

采用电压-时间曲线、全浸腐蚀实验、极化曲线法、X射线衍射法(XRD)、扫描电镜(SEM)、能量色散谱仪(EDS)和X射线光电子能谱法(XPS)等方法研究了AZ91D镁合金在含不同浓度硅酸钠的阳极化溶液中的阳极氧化行为和膜层的成分、结构.结果表明:在本文给定工艺中,AZ91D镁合金的阳极化过程可分为三个阶段:电火花出现之前的致密层生成阶段,少量小电火花出现的多孔层生成阶段,出现较大电火花的多孔膜层稳定生长阶段.阳极氧化过程中,随着阳极氧化溶液Na2SiO3浓度的升高,出现电火花的时间缩短,出现电火花时的电压值降低;阳极化膜的颗粒度变大甚至膜层出现裂纹,膜层厚度基本不变.阳极化膜层中主要含有Mg2 、O2-、Si4 和B3 ,主要相结构为MgO、MgSiO3和Mg3B2O6.硅酸钠浓度对阳极化膜的耐蚀性影响较大,当硅酸钠浓度为120g/L时,膜层耐蚀性能最好.     

Effects of humidity and temperature on the fatigue behaviour of an extruded AZ61 magnesium alloy

Load‐controlled fatigue tests were performed at 20 and 50 °C using two relative humidity levels of 55 and 80% to characterize the influence of humidity and temperature on the fatigue behaviour of an extruded AZ61 magnesium alloy. Fatigue tests were also conducted at 150 °C. No significant variation in fatigue properties was noticed with respect to temperature over the range from 20 to 50 °C for both the humidity levels. Fatigue limits in the range 140–150 MPa were observed for relative humidity of 55%. Fatigue strength decreased significantly with increase in temperature to 150 °C. Further, a significant reduction in fatigue strength with a fatigue limit of ～110 MPa was observed with increase in relative humidity to 80% at 20 and 50 °C. The crack initiation and propagation remained transgranular under all test conditions. The fatigue fracture at low stress amplitudes and high relative humidity of 80% results from the formation of corrosion pits at the surface and their growth to a critical size for fatigue‐crack initiation and propagation. The observed reduction in fatigue strength at high humidity is ascribed to the effects associated with fatigue–environment interaction.     

Influence of cement and aggregate type on thaumasite formation in concrete

In this study the influence of binder type on the formation of thaumasite in mortar prisms made with expanded clay lightweight aggregate (LWA) or quartz sand was examined. For this purpose mortar prisms were made, which after 28 days of curing in deionised water were exposed to a sulphate solution or deionised water. The length and weight change of the prisms was recorded in triplicate as a function of time of exposure to dry–wet cycles at 5 ± 1 °C.The influence of the binder type on the expansion in the sulphate solution can be ordered from strong to weak as follows: (1) CEM I + limestone filler, (2) CEM I, (3) CEM I + fly ash, and (4) CEM III/A. Because the porosity of the LWA was able to accommodate the growing sulphate crystals, the mortar prisms made with LWA were still largely intact after 3 years of exposure. The only exception being the mortar prisms containing limestone filler. The mortar prisms made with quartz sand and exposed to the sulphate solution were all bent, broken or disintegrated after 24 weeks. The prisms exposed to deionised water showed minimal expansion. Key factors controlling the formation of thaumasite are discussed.     

Steam locomotive soot and the formation of thaumasite in shotcrete

After approximately 40 years the sprayed concrete lining in the Koblenz railway tunnel started to break off from its stonework support. The old masonry showed relicts of a soot layer from the ages of steam locomotive services. Locally small amounts of low mineralised water were running through the tunnel lining. Due to the finding of ettringite at the rear surface of the shotcrete together with soot it was assumed that sulfur from the locally present soot layer was the cause for the shotcrete detachment.

Detailed investigations showed the formation of thaumasite at the concrete interface to its support and up to 15 mm inside the concrete. Thaumasite could be detected filling microcracks and veins parallel to the shotcrete surface. The amount of secondary sulfate minerals and the extent of sulfate uptake are orders of magnitude larger to what could be expected if the sulfur of the soot layer would be present as sulfate.

It is assumed that the finding of thaumasite in cracks and veins is caused by long term interaction with a low mineralised groundwater and is leading toward a complete alteration of the concrete into a mushy material.     

Mechanism of thaumasite formation in concrete slabs on grade in Southern California

Thaumasite formation has been observed in residential concrete slabs on grade in Southern California. The concrete examined did not contain any carbonate bearing aggregates or fillers. Microstructural analyses showed a carbonated layer with calcite and gypsum at the bottom of the concrete. Above the carbonation layer, deposits of intermixed gypsum and thaumasite were observed. Further into the concrete towards the upper surface, deposits of thaumasite alone or in combination with ettringite were observed. Most of the thaumasite deposits were observed in air voids. SEM–EDS analysis showed deposits of ettringite, thaumasite and intermediate phases within the same air voids. The formation of thaumasite, ettringite and gypsum was caused by ingress of sulfate and carbonate ions from ground water. The presence of thaumasite, ettringite and intermediate phases in the same air void indicates that ettringite is first formed followed by thaumasite with a series of solid solutions. In this reaction process the pH of the local environment and the balance between sulfate, silicate and carbonate ions are important parameters.     

Effects of thaumasite on bond strength of reinforcement in concrete

The conditions necessary for the formation of thaumasite are well known and much work is in progress to identify concrete mixes resistant to thaumasite form of sulfate attack (TSA). However, there have been no data to indicate how TSA affects the nature and strength of the bond between reinforcement steel and concrete and hence the load capacity of reinforced concrete elements.

During works to repair and strengthen the thaumasite-affected Tredington–Ashchurch Overbridge in Gloucestershire, sections of column were removed and placed in storage. These column sections presented an opportunity to perform pullout tests on full size TSA-affected structural elements and unaffected control specimens from the same structure. In total 63 pullout tests were performed on plain round reinforcement bars embedded in two unaffected and four TSA-affected reinforced concrete elements. The sections were also characterised in terms of estimated in situ cube strength and depth of softened zone.

A statistical analysis of the experimental results indicates that the bond of the plain round reinforcement bars in the unaffected concrete exceeded that of the plain round reinforcement bars in the TSA-affected concrete. TSA reduced the mean experimental bond coefficient by 24% for corner bars and 10% for other bars, representing an average reduction in mean experimental bond coefficient of 15% for all bars.     

添加稀土Gd对Mg-6Al镁合金组织和耐蚀性的影响

Mg-6Al镁合金具有较好的铸造性能和力学性能,目前鲜见单一稀土元素对其腐蚀性能影响的报道。通过合金制备、微观组织分析和耐蚀性测试等方法研究了稀土Gd添加量对Mg-6Al镁合金微观组织和耐蚀性能的影响。OM、SEM、EDS、XRD分析结果表明,稀土Gd的添加改善并细化了Mg-6Al合金的铸态组织,形成杆状或块状的Al2Gd新相;动电位极化、浸泡试验等测试结果表明Gd的添加显著提高了Mg-6Al合金在3.5%NaCl溶液中的耐腐蚀性能,Mg-6Al-2%Gd镁合金的腐蚀速度最小,为0.83 mm/a,且腐蚀后组织较为致密,腐蚀产物和腐蚀坑均变小,Mg-6Al-x Gd合金的腐蚀产物主要为Mg(OH)2。