基于准弹性中子散射谱分析水化硅酸钙(C-S-H)中受限水的动态

研究水化硅酸钙(C-S-H)中受限水动态的一种重要手段是准弹性中子散射(quasi-elastic neutron scattering, QENS)实验. C-S-H样品的QENS谱数据可通过跳跃扩散和转动扩散模型进行分析拟合, 进而导出C-S-H样品微纳孔中水动态的相关物理参数: 不动水指数C、转动扩散系数D_r、均方位移< u² >、自扩散系数D_t及平均停留时间τ₀. 本文对水与水泥质量比为30%的C-S-H样品, 测量温度为230-280 K的QENS谱进行了分析, 得到的拟合参数可定量描述C-S-H样品内不同尺度的微纳孔中受限水随温度变化的动态过程. 转动扩散系数D_r随散射矢量Q的变化可知, Q值较大时, 水分子的转动对QENS谱影响较大. 均方位移 < u² > 随Q值的不同而变化, 其拟合值可区分C-S-H样品中的不动水、强受限水和受限水. 在Q较小时, D_t 和τ₀ 的拟合值随温度而变化, 并分别在230和240 K突然增大, 由此揭示温度为230-240 K 时, C-S-H 样品中受限水分子的动态特性发生了转变.     

水泥老化过程中水动态的准弹性中子散射(QENS)谱分析

准弹性中子散射(quasi-elastic neutron scattering, QENS)实验是研究水泥老化过程中水动态的一种新颖的实验方法.本文利用老化时间分别为7, 14和30 d水泥样品的QENS谱实验数据, 通过应用四个高斯项的和的能量分辨函数R(Q, E)代替一个高斯项的能量分辨函数来改进经验扩散模型(empirical diffusion model, EDM), 再进行非线性最小二乘拟合.由此导出水泥样品中水动态的相关物理参数: 不动水数密度A, 自由水指数FWI=B₁/(A+B₁+B₂), 洛伦兹函数的半高宽Γ, 移动水跳跃之间的平均停留时间τ ₀及自扩散系数D_t, 而且可得出更为精准的QENS谱拟合曲线.拟合得到的物理参数可定量描述水泥老化过程中水动态过程, 从而为QENS实验在水泥老化过程中水动态研究的应用提供一种合理实用的谱分析方法.     

铝硅玻璃中Fe~(3+)、Cr~(3+)的EPR研究

本文用EPR技术研究了含Fe~(3+)和Cr~(3+)离子的铝硅破璃的结构性质,从理论上分析了实验结果.并且用含有Fe~(3+)离子的多晶样品——莫来石的玻璃样品进行了实验比较,最终认为铝硅玻璃和莫来石中的Fe~(3+)离子附近的局部环境类似.     

基于直接胶体晶体刻蚀技术的高度有序纳米硅阵列的尺寸及形貌控制

以自组装单层胶体小球阵列为掩模，采用直接胶体晶体刻蚀技术在硅表面制备二维有序尺寸可控的纳米结构.在样品制备过程中，首先通过自组装法在硅表面制备了直径200nm的单层聚苯乙烯(PS)胶体小球的二维有序阵列；然后对样品直接进行反应离子刻蚀(RIE)，以氧气为气源，利用氧等离子体对聚苯乙烯小球和对硅的选择性刻蚀作用，通过改变刻蚀时间，制备出不同尺寸的PS胶体小球的有序单层阵列；接着以此二维PS胶体单层膜为掩模，以四氟化碳为气源对样品进行刻蚀；最后去除胶体球后得到二维有序的硅柱阵列.SEM和AFM的测量结果表明：改变氧等离子体对胶体球的刻蚀时间和四氟化碳对硅的刻蚀时间，可以控制硅柱的尺寸以及形貌，而硅柱阵列的周期取决于原始胶体球的直径. 关键词： 胶体晶体刻蚀 纳米硅柱阵列     

聚甲基丙烯酸甲酯掺杂Ce3+的飞秒激光三维信息存储

用飞秒激光(200 fs,1 kHz,800 nm)脉冲在掺杂稀土离子Ce3 的聚甲基丙烯酸甲酯(PMMA)膜中进行了光存储实验研究,包括对样品的吸收光谱、激光照射前后的电子旋转共振(Electron spin resonance,ESR)光谱的测量和讨论。结果表明掺杂稀土离子Ce3 的聚甲基丙烯酸甲酯膜具有较低的写入阈值,有利于高速、并行的三维光存储。实验结果采用传统光学显微镜并行读出。给出了四层存储结果(点间距和层间距分别是4μm和16μm),并讨论了脉冲能量的大小对空腔尺寸的影响,进行高密度存储时,在保证读出信号灰度值足够大的情况下,应选择尽量小的激光脉冲写入能量。实验结果表明这种材料可以应用于三维光信息存储。     

含纳米硅和纳米锗的氧化硅薄膜光致发光的比较研究

分别以硅-二氧化硅和锗-二氧化硅复合靶作为溅射靶,采用磁控溅射技术在p型硅衬底上淀积了含纳米硅的氧化硅薄膜和含纳米锗的氧化硅薄膜.各样品分别在氮气氛中经过300至1100℃不同温度的退火处理.使用高分辨透射电子显微镜可以观察到经900和1100℃退火的含纳米硅的氧化硅薄膜中的纳米硅粒,和经900和1100℃退火的含纳米锗的氧化硅薄膜中的纳米锗粒.经过不同温度退火处理的含纳米硅的氧化硅和含纳米锗的氧化硅薄膜的光致发光谱均具有相似的峰型,且它们的发光峰位均位于580nm(2.1eV)附近.可以认为含纳米硅的氧化硅和含纳米锗的氧化硅薄膜的光发射主要来自于SiO₂层中发光中心上的复合发光,对实验结果进行了合理的解释     

左手材料中通过改变层间距实现谐振频率的移动

为了研究周期性结构的左手材料中层间距和频率的关系,分别制作了层间距分别为3.08 mm,2.93 mm,2.73 mm 和 2.33 mm的棱镜形样品。用网络分析仪HP8720ES测量了电磁波通过样品折射后的强度和频率的关系图。同时还模拟了层间距为3.23 mm,3.13 mm,3.03 mm,2.93 mm 和2.73 mm的样品,得到了相应的频率和电磁波强度的关系曲线。实验和模拟结果一致,即：随着层间距的减小,谐振频率从高频向低频移动。     

左手材料中通过改变层间距实现谐振频率的移动(英文)

为了研究周期性结构的左手材料中层间距和频率的关系,分别制作了层间距分别为3.08mm,2.93mm,2.73mm和2.33mm的棱镜形样品。用网络分析仪HP8720ES测量了电磁波通过样品折射后的强度和频率的关系图。同时还模拟了层间距为3.23mm,3.13mm,3.03mm,2.93mm和2.73mm的样品,得到了相应的频率和电磁波强度的关系曲线。实验和模拟结果一致,即:随着层间距的减小,谐振频率从高频向低频移动。     

掺杂量对超高压烧结多晶体金刚石耐热性的影响

过去的实验表明,掺杂物的类型对高压烧结多晶体金刚石的耐热性有显著的影响。但同种类型掺杂物含量的影响规律还不清楚,因此我们进行了钛、硅掺杂量对高压烧结多晶体金刚石耐热性影响的研究. 一、实验技术与方法 实验用的设备、压力、温度和样品装配等与文献[1]中一样. 本实验中钛、硅掺杂量分别以金刚石原料为100时的重量计算,钛的重量为0,5,9,15和硅的重量为0,3,9,15以及它们的组合. 二、实验结果和样品分析 实验结果列入表1中. 从表1中数据可见:(1)除了个别情况外(例如钛0硅15),都可以找到较佳的烧结工艺,使样品具有较高的磨耗比,但成团…     

离子注入硅的椭圆偏振光谱和光性

为了进一步发展测定离子注入损伤层的椭圆偏光法,我们测量了离子注入硅在4000—7000?波长范围内的椭圆偏振光谱,并由此得到它的色散关系。注入条件为150keV,10¹⁵cm^-2和10¹⁶cm^-2的砷离子注入。由于在硅样品表面处形成无定形层,我们用单层模型,从(ψ,Δ)-λ数据计算出(n,k)-λ关系,并可定出损伤层厚度。在～4800?处,出现折射率n的谱峰,峰值约4.9。本文还比较了离子注入损伤层、溅射无定形硅膜层、蒸发无定形硅膜层和单晶硅的实验结果。 关键词：     

Theoretical and experimental study of structures and properties of cement paste: The nanostructural aspects of C-S-H

Ordinary Portland cement (OPC) paste with water to cement ratio 0.5 has been studied by FTIR spectroscopy and TEM/SAED techniques. The progressive shift in frequencies and change in intensity of characteristic peaks in the FTIR spectra of cement powder indicate polymerization of silicates due to hydration reaction. The appearance of new peaks around 975-985 and 3640-3650 cm⁻¹ in FTIR spectra of cement paste has been attributed to the formation of two principal hydration products (C-S-H) and Ca(OH)₂, respectively. There is a strong resemblance of peak shape at 980 cm⁻¹ of cement paste with that of synthesized 1.1 nm Tobermorite. TEM/SAED techniques reveal the presence of three distinct types of C-S-H nanostructures viz. spherical particles, fibres and bundle of fibres, and nano tubes in cement paste. Theoretical study of two C-S-H clusters by MNDO and Density Functional Techniques shows excellent agreement between computed structural data and reported experimental results of Tobermorite and Jennite. The computed interplanar Ca-Ca distance (11.162 Å) of C-S-H cluster (Ca/Si=1.125) indicates greater structural similarity of this cluster to 11 Å Tobermorite. There is a strong similarity of IR profile of C-S-H cluster (Ca/Si=1.125) with 1.1 nm Tobermorite. Above study indicates that this cluster is probably the most likely basic unit of C-S-H phases formed during the early stage of OPC cement hydration.     

XRD和FTIR的掺硅酸钠富水材料强度演化机制

硅酸盐水泥和铝酸盐水泥是广泛应用的无机注浆材料,混合使用这两种材料可制备凝结时间短及强度高的胶凝材料。然而,在富水条件下（水灰比大于1）,添加适量二水石膏所制备的硅酸盐-铝酸盐水泥基材料水化后期发生强度衰减。为了改善硅酸盐-铝酸盐水泥基富水材料的强度性能,将一定量的硅酸钠掺入硅酸盐水泥-铝酸盐水泥-二水石膏三元体系中。采用RMT-150力学试验系统测试含不同硅酸钠掺入量的硅酸盐-铝酸盐水泥基富水材料的强度,分析其强度演化特性及掺入硅酸钠对其强度的影响;采用扫描电镜（SEM）,X射线衍射（XRD）及傅里叶变换红外光谱（FTIR）对不同硅酸钠掺量的富水材料微观结构进行表征,分析其微观形貌、物相的变化规律,进而揭示该富水材料的强度演化机制。强度试验结果显示,不掺硅酸钠的富水材料早期强度低,并且后期强度发生衰减;而硅酸钠的掺入有助于提高硅酸盐-铝酸盐水泥基富水材料的早期强度,并且在一定程度上减少材料固化后的后期强度衰减量,当硅酸钠掺入量高于3%以上时,可以有效控制该富水材料后期强度的衰减。SEM,XRD及FTIR研究结果表明：不掺硅酸钠的硅酸盐-铝酸盐水泥基富水材料水化14 d时,检测到所属六方晶系的物相CAH₁₀ 及C₂AH₈转变为具有立方晶系结构的C₃AH₆,这种晶型转变是导致该富水材料强度衰减的原因。相比不掺硅酸钠的富水材料,当硅酸钠掺入1%时,富水材料水化3 d生成更多的水化硅酸钙（C-S-H）凝胶,这有利于提高富水材料的早期强度;水化14 d后,XRD结果显示,在d=11.75, 6.24 Å出现C₂ASH₈的衍射峰,而直至28 d才检测到C₃AH₆（d=5.16, 3.18 Å）衍射峰,并且C₃AH₆衍射强度较不掺硅酸钠的材料低,FTIR谱3 643 cm-1处出现的振动带证实了这一发现。这说明掺入1%硅酸钠促使六方晶系（CAH₁₀ 及C₂AH₈）转变为C₂ASH₈,进而抑制了CAH₁₀及C₂AH₈向C₃AH₆的转变。但是,添加1%的硅酸钠却不足以完全抑制富水材料水化后期的晶型转变,因此富水材料水化后期仍会发生强度衰减。当硅酸钠掺入量升至4%时,硅酸盐-铝酸盐水泥基富水材料中的C₂ASH₈生成量显著增大,并且水化28 d后未检测到C₃AH₆,表明富水材料内的晶型转变完全得以抑制,材料水化后期强度衰减得到有效控制。     

Microstructure and properties of Pb(Mg1/3Nb2/3)O3–Portland cement composites

Lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), ceramics particles was mixed with Portland Cement (PC) using a water to cement ratio of 0.50 and PMN content at 40% and 60% by weight to produce 0–3 Pb(Mg_1/3Nb_2/3)O₃–Portland cement (PMN–PC) composites. Microstructure and hydration of the composites were investigated. Calcium silicate hydrate gel can be seen surrounding the PMN particles. Dielectric constant of the composites was found to increase with PMN content. Successful poling of the composites was achieved. Interestingly, SEM micrographs of the PMN40 composite clearly showed calcium silicate hydrate gel (an essential hydration product of Portland cement) surrounding the PMN particles. In PMN60 composite, the gel can also still be seen but of less quantity. This is thought to be due to the increase in the volume ratio of the ceramics where the amount of calcium silicate hydrate gel was reduced in relation to the overall volume.     

A remark on nano-particle stability of cement C-S-H gel

Hydrated pastes of ordinary Portland cement prepared with different water-to-cement ratios were investigated by using the small-angle neutron scattering technique in the region of Q ∈ (0.0045, 0.11) Å^?1. Samples of cement pastes were subjected to non-standard hydration conditions using a mix with D₂O, low RH, and water-to-cement ratios spread over a very wide interval (0.4; 1.4). The investigation was focused on testing the structural stability of nano-metric particles in the cement C-S-H gel. Owing to the high structural stability of these nano-particles, their average diameter might be used as a microscopic parameter characterizing the nano-metric structure of C-S-H gels. The average diameter of the nano-particles of the studied ordinary Portland cement CEMI 42.5 R-SC was found to be close to the value of 4.2 nm and independent of the water-to-cement ratios.     

Increase of the reactivity of densified silica fume by sonication treatment

Five silica fumes from different manufacturers were subjected to ultrasonic treatment in order to decrease particle agglomeration and improve particle dispersion. The effectiveness of the sonication was observed as a reduction in particle size distribution of sonicated silica fume (SSF) compared to non-sonicated silica fume. SSF was added to Portland cement, and then the hydrated paste was analysed by thermogravimetric analyses (TGA/DTG) and scanning electron microscopy (SEM/EDX). The results were compared with those of control pastes made with untreated densified silica fume (DSF), as well as a reference cement paste of ordinary Portland cement (OPC). A maximum grade of de-agglomeration by the sonication was obtained, with a high volume of particles of diameter less than 1 μm. Images obtained by transmission electron microscopy (TEM) of the SSF showed sintered particles that could not be fragmented by the treatment. Micro-structural characterisation results showed an increase in the reactivity of the silica fume after the treatment.     

Flocculation and sedimentation in suspensions using ultrasonic wave reflection

This work was undertaken to help understand and interpret the ultrasonic wave reflection response of Portland cement paste as it transforms from a fluid-like suspension to a solid in the first hours after mixing. A high impact polystyrene buffer (delay line) was used to measure small changes in the P- and S-wave reflection coefficients. Two materials were studied: a non-hydrating colloidal alumina suspension whose microstructure was manipulated between dispersed and flocculated states by adjusting the pH and a coarse silica suspension that readily sedimented. The S-wave reflection coefficient clearly distinguished between dispersed and flocculated states. Sedimentation of particles in dispersed suspensions was distinguished using the P-wave reflection coefficient. Based on these findings, the observed P- and S-wave responses from hydrating Portland cement paste are interpreted in terms of flocculation and sedimentation processes.     

The influence of hydration time on the Ni uptake by cement

In this study, Ni uptake by hardened cement paste has been investigated with the aim of improving our understanding of the immobilization process of Ni(II) in cement and the influence of the hydration time on the Ni speciation on the microscopic scale. Information on the Ni distribution and speciation of the Ni phases formed in the cement system has been gained by employing synchrotron-based μ-X-ray fluorescence (μ-XRF) and μ-X-ray absorption spectroscopy (μ-XAS). The Ni-doped cement samples were prepared at a water/cement ratio of 0.4 and with a metal loading of 5000 mg/kg using a sulphate-resisting Portland cement. The samples were hydrated for six hours and one year to account for the chemical environment in a fresh and aged cement paste, respectively. The μ-XAS measurements reveal that a mixture of Ni phases is formed at single regions of interests, independent of the hydration time. Data analysis further indicates that Ni(II) is predominantly immobilized in a layered double hydroxide (LDH, Ni-Al LDH) and only to a minor extent precipitates as Ni-hydroxides. A comparison of the results from this micro-spectroscopic investigation with those from an earlier macro-spectroscopic study, indicate that the same Ni phases are formed both on the macro- and micro-scale.     

The1HT 1 study of the influence of clay addition on Portland cement hydration

Effects of addition of three standard clay minerals, Na-montmorillonite, illite and kaolinite, on Portland cement hydration properties were studied. The¹H spin-lattice relaxation of exchangeable water was monitored during hydration time and the data were processed by spin-grouping analysis. The values and evolution dynamics of both resolvedT ₁ components and corresponding magnetization fractions show that each day mineral lowers the fluidity of Portland cement paste and accelerates its hydration in dormant. In advanced stages of hydration, the Na-montmorillonite provides the accelerating influence, while the kaolinite exhibits the retarding effect. The final values of gel pores to capillaries percentage fractions ratio indicate a slightly lower porosity of samples with Namontmorillonite and a higher porosity of pastes with the same percentage of illite or kaolinite, regarding to the pure hardened Portland cement.     

Assessment of strength properties of cemented paste backfill by ultrasonic pulse velocity test

Ultrasonic pulse velocity (UPV) test is one of the most popular non-destructive techniques used in the assessment of the mechanical properties of concrete or rock materials. In this study, the effects of binder type/dosage, water to cement ratio (w/c) and fines content (<20 μm) of the tailings on ultrasonic pulse velocity (UPV) of cemented paste backfill (CPB) samples were investigated and correlated with the corresponding unconfined compressive strength (UCS) data. A total of 96 CPB samples prepared at different mixture properties were subjected to the UPV and UCS tests at 7, 14, 28 and 56-days of curing periods. UPV and UCS of CPB samples of ordinary Portland cement (CEM I 42.5 R) and sulphate resistant cement (SRC 32.5) initially increased rapidly, but, slowed down after 14 days. However, UPV and UCS of CPB samples of the blast furnace slag cement (CEM III/A 42.5 N) steadily increased between 7 and 56 days. Increasing binder dosage or reducing w/c ratio and fines content (<20 μm) increased the UCS and UPV of CPB samples. UPV was found to be particularly sensitive to fines content. UCS data were correlated with the corresponding UPV data. A linear relation appeared to exist between the UCS and UPV of CPB samples. These findings have demonstrated that the UPV test can be reliably used for the estimation of the strength of CPB samples.