房建工程施工技术探讨

房建工程的建设质量是现代社会比较关注的问题,房建工程的质量水平直接关系到其运行安全。施工技术是房建工程的建设基础,有利于提升房建工程的质量。本文对房建工程进行了研究,分析了主要的施工技术。     

浅析高层房建工程给排水施工技术

本文就当前高层房建工程排水施工技术进行了探讨,通过对排水技术的重点以及相应的排水施工技术的分析,为加强房建工程质量,改善居民居住环境以及生活质量提供了一些技术参考。     

强鼓式燃气热水器燃烧器进风部分结构优化

采用计算流体力学(CFD)方法对某型号强鼓式燃气热水器燃烧器内空气速度场进行数值模拟,分析存在的问题,对燃烧器的进风(空气)部分的结构进行优化。对优化前后的强鼓式燃气热水器的热效率及烟气中一氧化碳体积分数进行了实测。优化后,热效率平均提高1.06%,烟气中一氧化碳体积分数平均下降30%。     

多水源供水管网余氯与节点水龄关系研究

为系统地研究多水源供水管网中余氯随节点水龄的变化规律,运用Microsoft Visual C++编程对某大城市局部供水管网进行供水区域划分,并结合MFC开发系统将每个供水区域以界面形式显示出来。运用EPANET 2计算管网节点水龄值和余氯值,并用实测余氯值进行参数率定。以每一个供水水源为起点、其供水区域内的管网末梢为终点,将每个节点余氯值和水龄值进行曲线拟合分析,得到拟合方程,这为进一步应用节点水龄评价管网水质提供了理论依据,也为水质安全保障及供水系统的调度管理提供了技术支撑。     

盾构隧道已开裂管片的受力变形特性

结合广州地铁某已运营的盾构区间隧道现状,通过采用三维Goodman单元来模拟管片已存在的裂缝,对盾构区间隧道已开裂管片的裂缝深度变化对管片结构造成的影响进行了分析,同时也对侧向土压力、地基弹簧系数以及地下水位等几种重要因素对管片受力变形特性的影响进行了评估。研究表明,随着裂缝深度的增加,管片砼的拉应力、压应力虽然达到最大值,但变化幅度并不大。但当裂缝接近径向贯通的时候,钢筋的拉应力值会大大增加,有可能超过允许值。同时,在盾构管片存在既有裂缝的情况下,盾构管片的最大拉应力值、水平和竖向收敛值、竖向沉降值均随侧向土压力系数、地基弹簧系数的减少而增大,同时随地下水位埋深的增大而增大。根据研究结果,对该区间隧道盾构隧道的裂缝等病害采取了针对性修复措施,目前无新的裂缝出现,总体处于稳定及安全的状态。     

Effect of Zr4+ Content on the Grain Growth,Dielectric Relaxation Behavior,and Ferroelectric Properties of Ba0.4Sr0.6Ti1−x Zr x O3 Nano-Ceramics Prepared by Different Methods Assisted by Fast Microwave Sintering

The effect of Zr⁴⁺ content on the grain growth, dielectric relaxation, and piezoelectric properties of Ba_0.4Sr_0.6Ti_1?x Zr _x O₃ (BSTZ; x = 0, 0.02, 0.04, 0.06) ceramics prepared by solid-state (SS) and sol–gel modified hydrothermal (SH) methods assisted by fast microwave sintering was investigated in this study. A combination of x-ray diffraction (XRD), scanning electron microscopy (SEM), impedance analysis, and ferroelectric analysis was used. All the ceramics had pure perovskite structures at room temperature, as seen from XRD patterns, indicating that Zr⁴⁺ was incorporated into Ba_0.4Sr_0.6TiO₃ lattices to form a solid solution. In the SEM micrographs, SH samples had higher densities and smaller and more homogeneous grain size than SS samples, which was in agreement with density measurements. Nano-ceramics were obtained by this method. When the temperature dependence of dielectric constant and dielectric loss was studied, SH samples had higher permittivity, better thermally activated relaxation, and lower dielectric loss at high temperature. Ferroelectric characteristics can still be detected in Ba_0.4Sr_0.6Ti_1?x Zr _x O₃ ceramics and residual polarization (P _r) decreased with increasing Zr⁴⁺ content.     

材料比热容测试国内外试验方法比较

比热容是衡量材料热物理性能的重要参数,但是国内尚无可供参考的测试方法标准,目前常采用传统的比较法。分别采用比较法和国外的ASTM E1269-2011和DIN 51007-1994方法对蓝宝石标准试样的比热容进行了测试。结果表明:按照ASTM E1269-2011和DIN 51007-1994方法测试得到的比热容更接近于蓝宝石比热容的标准值,测试相对偏差较低,在1.3%~3.7%;而传统比较法的测试相对偏差在1.7%~4.3%。由此可见,ASTM E1269-2011和DIN51007-1994方法的测试精度更高,更适合用于材料比热容的测试。     

Decoration of reduced graphene oxide with dandelion-like TiO2 and their dielectric properties in poly(arylene ether nitriles) composites

Novel dandelion-like titanium oxide (TiO₂) decorated reduced graphene oxide (rGO@TiO₂) hybrids were obtained by a one-step solvent-thermal reduction of GO and tetrabutyl titanate simultaneously. The hybrids were used as a novel filler for high performance poly(arylene ether nitriles) (PEN) composites. The thermal stability and morphological properties of the PEN composites were, respectively, investigated by the thermo gravimetric analysis and scanning electron microscope, aiming at examining the effect of surface decoration on the dispersion of rGO@TiO₂ in PEN matrix. The results indicated that the rGO@TiO₂ present better dispersion in the PEN matrix. Meanwhile, the derived composite films exhibited high thermal stability with initial decomposition temperatures (T _id ) in the range of 477–487 °C. DSC curves showed that the glass transition temperatures were in the range of 219–227 °C. Moreover, all of the composite films also showed excellent flexibility and mechanical properties. The tensile modulus and strength were increased about 4 and 6 % with 5 wt% rGO@TiO₂ loading, respectively. More importantly, for 30 wt% rGO@TiO₂ reinforced PEN composite film, the dielectric permittivity dramatically increased from 3.8 to 81 at 1 kHz.     

Effects of Kaolinite additions on sintering behavior and dielectric properties of CaCu3Ti4O12 ceramics

Commercial Kaolinite was employed as sintering aid to reduce the sintering temperature of CaCu₃Ti₄O₁₂ (CCTO) ceramics. The effects of Kaolinite content and sintering temperature on the densification, microstructure and dielectric properties of CCTO ceramics have been investigated. The density characterization results show that the addition of Kaolinite significantly enhanced the relative density of CCTO ceramics to about 92 %. X-ray diffraction results show CCTO ceramics with a low amount of Kaolinite exhibited perovskite-like structure, but 1.0 wt% Kaolinite additions resulted in the formation of a secondary phase, CaO–TiO₂–Al₂O₃–SiO₂ glass phase was formed and improved the dielectric constant of ceramics, which was supported by scanning electron microscopy–energy dispersive X-ray results. CCTO ceramic with 1.0 wt% Kaolinite addition possessed well temperature and frequency stability of dielectric constant. It was found that Kaolinite lowered the dielectric loss of the samples.     

Enhanced giant dielectric response in Sr[(Fe0.5Nb0.5)1−xTix]O3 solid solutions

In the present work, the modified dielectric relaxations with extended giant dielectric constant step were observed in Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions. The structure of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions changed from orthorhombic to cubic with increasing x. A dielectric relaxation following Arrhenius law of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions was observed at lower temperature. The dielectric constant of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions decreased firstly and then increased with increasing SrTiO₃ content at 1 kHz, while the dielectric loss was suppressed monotonically. At x = 0.8, the dielectric loss at room temperature and 1 kHz was 0.16 which was much smaller than that for x = 0 (tanδ = 0.37), while the dielectric constant was increased to 6,815, and the temperature stability was also improved. This indicated that the dielectric characteristics of Sr(Fe_0.5Nb_0.5)O₃ ceramics could be significantly improved by forming solid solution with SrTiO₃.