纳米SiO_2混杂纤维混凝土力学特性试验研究

采用高速研磨搅拌加水掺法,制备出含不同质量分数的纳米SiO2混杂纤维(NSPF)混凝土,通过力学试验测得立方体抗压强度、劈裂抗拉强度、变形性能及冲击韧性。通过与钢纤维/聚丙烯二元混杂纤维(SPF)混凝土进行比较,NSPF混凝土的立方体抗压强度、劈裂抗拉强度、疲劳次数、弹性模量、初裂抗冲击次数和破坏抗冲击次数分别提高10.4%、24.1%、90.0%、3.3%、49.8%和46.1%,泊松比无明显变化。综合分析表明,纳米SiO2在SPF混凝土中的合理掺量处于1.0%~2.0%之间。     

黄蒿纤维增强混凝土的受力性能试验研究

混凝土是一种典型的压强拉弱的建筑材料,利用抗拉能力突出的纤维补强混凝土的抗拉缺陷是一条常规思路,这其中韧性较强的植物纤维,如黄蒿纤维,是一种既经济又环保的材料。通过在混凝土中分层均匀地添加黄蒿纤维制得混凝土立方体试块,一方面通过对部分试块进行劈裂试验以探究黄蒿纤维对增强混凝土劈裂抗拉强度的效果;另一方面通过对部分试块进行标准立方体抗压试验以探讨黄蒿纤维对混凝土立方体抗压强度的影响。结果表明,黄蒿纤维的掺入可以有效地提高混凝土的立方体抗压强度,显著地提高混凝土的劈裂抗拉强度。此外,还基于复合材料力学理论对黄蒿纤维增强混凝土进行受力分析,推导出黄蒿纤维增强混凝土的抗拉强度与黄蒿纤维掺入率等参数之间的关系,并利用试验数据拟合了黄蒿纤维增强混凝土劈裂抗拉强度和立方体抗压强度关于纤维掺入率的经验公式,由此得出黄蒿纤维的最优掺入率,最后还讨论了黄蒿纤维的掺入对混凝土立方体抗压强度和劈裂抗拉强度产生影响的原因。     

玄武岩-碳纤维/矿渣混凝土力学性能正交试验

应用正交试验法开展了16组玄武岩-碳纤维(BF-CF)/矿渣混凝土和1组C40级基准混凝土的塌落度、立方体抗压强度和劈裂抗拉强度试验,研究了BF、CF和矿渣三种因素对BF-CF/矿渣混凝土力学性能的影响。结果表明:BF-CF/矿渣混凝土立方体抗压强度和劈裂抗拉强度均高于C40基准混凝土,立方体抗压强度最大提高了21.0%,劈裂抗拉强度最大提高了35.3%。BF和CF的掺入均会减小混凝土的塌落度,BF对于塌落度的减小更加明显,BF对塌落度的最大降幅为67.1%;矿渣代砂率是影响BF-CF/矿渣混凝土立方体抗压强度的显著因素,随着矿渣代砂率的增大,立方体抗压强度先增大后减小,矿渣对立方体抗压强度的最大提高幅度为7.6%;BF是影响BF-CF/矿渣混凝土劈裂抗拉强度的显著因素,劈裂抗拉强度随BF体积率的增加而增大,BF对劈裂抗拉强度的最大增幅为12.0%,CF对劈裂抗拉强度的提升不明显。对正交试验的结果进行回归分析得出BF-CF/矿渣混凝土立方体抗压强度和劈裂抗拉强度预测模型,模型精度较高。      

钢纤维和碳纤维的混合效应对高性能混凝土力学性能的影响

通过在混凝土基体中加入一种纤维和混合纤维,制备了高性能混凝土试件和混合纤维高性能混凝土试件。通过劈裂抗拉强度试验和落锤冲击试验,研究了单掺钢纤维、单掺碳纤维和混合纤维对高性能混凝土试件劈裂抗拉强度和抗冲击性能的影响,分析了混合效应对试件力学性能的增强作用。劈裂抗拉强度试验结果表明,只掺入碳纤维,且碳纤维掺入量为1%时,试样劈裂抗拉强度的提升系数最多增加了50%;只掺入钢纤维时,钢纤维的掺入量越多,试样劈裂抗拉强度的提升系数越小,而且减小了基体高性能混凝土的劈裂抗拉强度;当钢纤维掺量为4.0%、碳纤维掺量为0.5%时,试样的混合效应系数最大为1.35,此时产生正混合效应,提升了高性能混凝土试样的劈裂抗拉强度。抗冲击性能试验结果表明,单掺碳纤维减弱了高性能混凝土试件的抗压强度,单掺钢纤维虽然可以加强试件的抗压强度但试件的延性比提升率不高,而混合纤维比单一纤维有优势,更能够增强高性能混凝土试件的抗冲击性能。因此,钢纤维与碳纤维的混合效应提升了试件的劈裂抗拉强度与抗冲击性能,明显提升了高性能混凝土的力学性能。     

聚丙烯-钢纤维/混凝土柱大偏心受压承载力计算

对270个聚丙烯纤维掺量(体积分数)分别为0vol%、0.1vol%、0.2vol%、0.3vol%、0.4vol%、0.5vol%、钢纤维掺量(体积分数)分别为0vol%、0.5vol%、1vol%、1.5vol%、2vol%的聚丙烯-钢纤维/混凝土试块进行立方体抗压试验、轴心抗压试验和劈裂抗拉试验,基于复合材料力学理论,考虑纤维的取向系数、长度有效系数和界面黏结系数,对其建立强度预测模型并进行机制分析,同时选取掺量分别为0vol%、0.1vol%、0.3vol%的聚丙烯纤维、掺量分别为0vol%、1.5vol%的钢纤维制作6根聚丙烯-钢纤维/混凝土柱,对其进行大偏心受压试验,在强度预测模型的基础上进行承载力计算,提出聚丙烯-钢纤维/混凝土承载力计算方法。结果表明:钢纤维对聚丙烯-钢纤维/混凝土立方体抗压强度、轴心抗压强度和劈裂抗拉强度均有提高;聚丙烯纤维可提高聚丙烯-钢纤维/混凝土的劈裂抗拉强度,但不能提高聚丙烯-钢纤维/混凝土的抗压强度;聚丙烯-钢混杂纤维加入混凝土柱可有效提高其极限承载力。      

纤维加筋固化黄土浸水强度试验研究

为探究水泥、石灰以及多种纤维复合固化黄土的水稳定性能,进行了浸水无侧限抗压强度试验和浸水无侧限劈裂抗拉强度试验。试验结果表明:加砂对复合固化黄土的水稳定性能不利;水泥固化效果优于其他固化剂;纤维可以提高浸水水泥固化土的浸水抗压强度和浸水劈裂抗拉强度,其中0.15%和0.30%纤维掺量的水泥固化黄土浸水抗压强度较高,但继续提高纤维掺量会导致抗压强度降低;纤维长度越长则复合固化黄土浸水抗压强度和劈裂抗拉强度越高,两种及两种以上的纤维混杂掺入会导致固化黄土浸水抗压强度和劈裂抗拉强度降低;水泥可以大幅提升固化土浸水劈裂抗拉强度,19mm聚丙烯纤维加筋固化土浸水劈裂抗拉强度较高,提高纤维掺量可以提高浸水劈裂抗拉强度,两种及两种以上的纤维混杂不能提高浸水劈裂抗拉强度。     

纤维对超高性能混凝土残余强度及高温爆裂性能的影响

采用普通原材料制备56 d龄期抗压强度为140~160 MPa的空白组超高性能混凝土、钢纤维超高性能混凝土及混杂纤维超高性能混凝土,测定其遭受高温作用后的残余抗压强度和劈裂抗拉强度,并对100%含湿量的混凝土试块进行高温爆裂试验。此外,测定大小2种加热速率对超高性能混凝土高温爆裂行为的影响。结果表明:所配制混凝土的残余抗压强度均随着目标温度的升高呈现先增大再降低的趋势,800℃高温后的残余抗压强度约为常温强度的30%。钢纤维与混杂纤维混凝土的残余劈裂抗拉强度亦呈现先升高再降低的趋势,800℃高温后的残余劈裂抗拉强度分别为常温强度的15.1%和35.4%。空白组混凝土的残余劈裂抗拉强度随着目标温度的升高而单调下降,800℃高温后的强度值约为常温强度的20.3%。7.5℃/min加热速率下,100%含湿量的3种混凝土试块均发生了严重高温爆裂,单掺钢纤维可以改善超高性能混凝土的高温爆裂,但不能避免爆裂的发生,而混杂纤维对超高性能混凝土高温爆裂的改善效果并未显著优于钢纤维。2.5℃/min加热速率下,混杂纤维可避免部分超高性能混凝土试块发生爆裂。      

钢纤维及陶粒掺量对轻质混凝土基本力学性能的影响

制备了3种强度等级共13组配合比的钢纤维增强轻质混凝土（Steel Fibre Reinforced Lightweight Aggregate Concrete,SFRLAC）,测量了立方体抗压强度、劈裂抗拉强度和轴心抗压强度,得到了SFRLAC轴心受压应力-应变曲线。试验结果表明,钢纤维能小幅度提高轻质混凝土（Lightweight Concrete,LC）的抗压强度,随陶粒比率（Haydite Ratio,V_h）的增大,抗压强度降低,且强度等级越低,降幅越大。钢纤维能显著提高LC的劈裂抗拉强度,钢纤维对低强度等级LC劈裂抗拉强度的贡献优于对高强度等级LC的贡献。低强度等级SFRLAC （LC30和LC40）的劈裂抗拉强度受V_h的影响较大,而高强度等级SFRLAC （LC50）与之相反。当V_h达到80%时,V_h不再是影响SFRLAC劈裂抗拉强度的主要因素,而钢纤维的增强效应显著。试块的破坏形态表明钢纤维能改善LC的塑性。V_h对抗拉强度的降低效应远大于对抗压强度的降低效应。建立了SFRLAC轴心抗压强度与立方体抗压强度的关系式。SFRLAC应力-应变曲线综合体现了钢纤维的增强效应和陶粒的削减作用,陶粒降低LC的峰值应力和韧性,钢纤维主要提高LC的韧性。     

喷嘴行进速度及高度对3D打印混凝土力学性能影响的试验

为研究喷嘴行进速度、喷嘴高度等打印参数对3D打印混凝土力学性能的影响,制备了相同配合比的浇筑试块和不同打印参数组合下的打印试块,通过混凝土立方体抗压试验、棱柱体轴心抗压试验和立方体劈裂抗拉试验,考察了其受力破坏过程和破坏形态,分析了喷嘴行进速度、喷嘴高度对3D打印混凝土力学性能的影响,得到了3D打印混凝土轴心受压应力-应变曲线,建立了3D打印混凝土各强度之间的关系。结果表明：3D打印混凝土立方体抗压强度、轴心抗压强度、劈裂抗拉强度均随喷嘴行进速度的加快、喷嘴高度的升高而降低,且喷嘴高度对强度的不利影响强于喷嘴行进速度;在较优打印参数组合下,打印试块的抗压强度高于浇筑试块,但因打印试块存在层间粘结弱面,其劈裂断面在其层间界面处,致使断面明显平滑,劈裂抗拉强度低于浇筑试块;通过回归分析,建立了3D打印混凝土各强度与打印参数间的函数关系及轴心抗压强度、劈裂抗拉强度与立方体抗压强度之间的换算关系。     

混杂纤维增强再生砖骨料混凝土增强机制与抗压性能计算方法

通过钢-聚烯烃混杂纤维增强再生砖骨料混凝土（HF/RBAC）的抗压与弹性模量试验,研究了再生砖骨料（RBA）取代率、混杂纤维掺量、纤维种类对混凝土抗压强度和弹性模量的影响。根据RBA的XRD图谱、X-CT图像、RBA火山灰活性成分与水泥水化产物反应原理及能量平衡原理,分析了HF/RBAC的破坏机制和纤维增强机制。研究表明,当RBA全取代天然骨料（NA）时,HF/RBAC立方体抗压强度、轴心抗压强度和弹性模量分别降低了36.72%、24.95%和43.53%。当钢-聚烯烃混杂纤维体积掺量为1.5%时,HF/RBAC立方体抗压强度、轴心抗压强度和弹性模量分别增加了20.51%、30.33%和35.84%。最后,提出了考虑RBA压碎指标和取代率、纤维种类和掺量等因素影响的HF/RBAC抗压强度和弹性模量的计算方法。     

中高温太阳能选择性吸收涂层的研究进展

近年来太阳能中高温选择性吸收涂层的研制及应用成为人们关注的焦点。对中高温涂层的国内外研究现状做了详细描述,着重介绍了金属陶瓷吸收涂层和半导体金属光干涉涂层,并提出一种新型的具有核壳结构纳米级金属陶瓷复合涂层,理论上其具有很好的光学性能及高温稳定性。     

单体固化特性对光热敏微胶囊显影密度的影响

利用界面聚合技术制备了以不同单体为囊芯的新型感光材料光热敏微胶囊.借助于傅里叶红外光谱及原子力显微技术对不同单体的双键交联固化及固化产物的表面形貌进行了分析,利用热显影打印技术检测了光热敏微胶囊显影密度随曝光时间的变化.实验结果表明,不同单体的双键交联固化速度主要与单体官能度有关,并且单体固化产物的表面形貌与单体的双键...     

Absorbeurs selectifs de l'energie solaire elabores a partir d'acier inoxydable : Influence de la composition chimique et de l'etat metallurgique de l'alliage sur les proprietes optiques

Efficient photothermal converters exhibit high solar absorptance and low thermal emittance. An original method has allowed spectrally selective coatings to be obtained by chemical conversion of stainless steel. These coatings exhibit high selectivity (absorptance higher than 95 % and emittance lower than 20 %) and excellent durability.The dependance of the optical properties of these coatings on the chemical composition and metallurgical state of the substrate is studied. Low emittance appeared to be closely related to the corrosion resistance of the metallic surface in the treatment bath. Owing to this fact, convenient conditions can be found to produce selective coating for each alloy.     

Hochselektive Absorberschichten für thermische Sonnenkollektoren

High‐selective absorber coatings for solar thermal collectors Highly selective absorber coatings are necessary for the effective operation of state‐of‐the‐art solar thermal collectors. The thin film gradient optical coating with its spectrally selective characteristics achieves high solar absorptance combined with low thermal emittance. Such complex multi‐layer systems are produced in modular vacuum coating processes. Industrial air‐to‐air coating lines allow the continuous coating of metal bands in a pass‐through process and provide absorber coatings which meet highest demands for efficiency, durability and esthetics.     

Infrared spectrally selective low emissivity from Ge/ZnS one-dimensional heterostructure photonic crystal

Ge/ZnS one-dimensional heterostructure photonic crystal (1DHPC) was successfully prepared by alternating thin films of Ge and ZnS on the quartz substrate by using the optical coating technology. The microstructure and spectral emissivity of as-prepared 1DHPC were characterized by using scanning electron microscopy (SEM) and fourier transform infrared spectrometer (FTIR), respectively. The test result of spectral emissivity shows that the average emissivities of as-prepared Ge/ZnS 1DHPC in the atmospheric windows of 3–5 μm and 8–14 μm can be as low as 0.046 and 0.190, respectively, but the average emissivity in the non-atmospheric window of 5–8 μm can be as high as 0.579. The results indicate that the as-prepared Ge/ZnS 1DHPC has obviously infrared spectrally selective low emissivity characteristic, basically meets the requirements of our design. The as-prepared 1DHPC with infrared spectrally selective low emissivity is promising for use as a material to unify the infrared stealth and effective cooling of the aircraft.     

Understanding the Photothermal Conversion Efficiency of Gold Nanocrystals

Plasmon‐based photothermal therapy is one of the most intriguing applications of noble metal nanostructures. The photothermal conversion efficiency is an essential parameter in practically realizing this application. The effects of the plasmon resonance wavelength, particle volume, shell coating, and assembly on the photothermal conversion efficiencies of Au nanocrystals are systematically studied by directly measuring the temperature of Au nanocrystal solutions with a thermocouple and analyzed on the basis of energy balance. The temperature of Au nanocrystal solutions reaches the maximum at ～75°C when the plasmon resonance wavelength of Au nanocrystals is equal to the illumination laser wavelength. For Au nanocrystals with similar shapes, the larger the nanocrystal, the smaller the photothermal conversion efficiency becomes. The photothermal conversion can also be controlled by shell coating and assembly through the change in the plasmon resonance energy of Au nanocrystals. Moreover, coating Au nanocrystals with semiconductor materials that have band gap energies smaller than the illumination laser energy can improve the photothermal conversion efficiency owing to the presence of an additional light absorption channel.     

Structured selective coatings

Nickel-impregnated anodized Al₂O₃ films on aluminium substrates were investigated as possible selective coatings for the photothermal conversion of solar energy. A purely chemical dip process for producing these spectrally selective coatings was developed as an alternative to the electrochemical process reported earlier. The process parameters were optimized to give α = 0.92 and ε = 0.19. These coatings are cheap, efficient and durable.X-ray diffraction, scanning electron microscopy and electron spectroscopy for chemical analysis investigations were performed at various stages during the formation of these coatings and their structure was determined from the data obtained. The proposed structure agrees with that reported earlier. Maxwell Garnett theory and the concept of the equivalent homogeneous medium were used to determine the theoretical optical properties of these films as a function of (1) the thickness and porosity of the Al₂O₃ layer and (2) the thickness of nickel deposited in the pores. The optimum values of the theoretical parameters are in good agreement with those determined experimentally.     

镁合金铈化学转化工艺及性能研究

镁合金稀土转化膜技术是一种环保型镁合金表面处理新技术.通过正交实验对压铸镁合金AZ91D铈化学转化处理工艺进行了研究,并对膜层性能进行了测试.结果表明,铈转化处理工艺能够在压铸镁合金AZ91D表面形成均匀、完整的转化膜;膜层主要由Ce2O3、CeO2和MgO以及少量的Al2O3组成;铈转化处理提高了镁合金的耐腐蚀性能.     

Spectrally selective reflector surfaces for heat reduction in concentrator solar cells: modeling and applications of TiO₂:Nb-based thin films

The energy conversion efficiency of a conventional pn junction solar cell decreases as the temperature increases, and this may eventually lead to failures in the photovoltaic system, especially if it uses concentrated solar radiation. In this work, we show that spectrally selective reflector (SSR) surfaces can be important for reducing the heat buildup on passively cooled solar cells. We outline a computational scheme for optimizing DC magnetron-sputtered TiO?:Nb-based SSRs tailored for silicon solar cells and find good agreement of the reflectance with an experimental realization of the optimal SSR. A figure of merit for SSRs has also been derived and applied to the experimental data.     

镁锂合金表面处理技术研究现状及展望

镁锂合金具有优异性能,是部件轻量化的理想材料,但镁锂合金极易腐蚀,其应用受到限制。为提高镁锂合金耐蚀性,国内外对其表面处理进行了研究。综述了国内外镁锂合金表面处理技术的研究现状,介绍了化学转化、阳极氧化、金属镀（涂）层、气相沉积、有机涂层等表面防护技术的研究进展,并展望了镁锂合金表面处理理论与技术的发展趋势。