三氧化二铝对环氧树脂固化动力学及 热降解动力学的影响

采用热分析法研究了高含量Al₂O₃填料对环氧树脂（E51）/二氨基二苯甲烷（DDM）体系的固化表观活化能、热降解动力学和性能的影响.非等温差式扫描量热法（DSC）固化动力学研究表明,加入Al₂O₃体系的反应活化能由51.49 kJ/mol降低至48.12 kJ/mol;用n级非等温动力学法分析获得了固化反应的动力学参数.利用热重分析研究了环氧固化物体系的热降解动力学,用FWO方法计算固化物降解活化能结果表明,Al₂O₃粉体对E51/DDM体系初始分解活化能影响不大,当降解率达到30%时,Al₂O₃粉体对E51/DDM体系分解有明显的抑制作用.热重红外联用测试结果表明,甲烷、羰基化合物、胺和双酚A是E51/DDM热分解过程中的主要产物,Al₂O₃粉体能提高E51/DDM体系的热稳定性.动态热机械研究表明,Al₂O₃的加入增大了环氧树脂固化产物的储能模量.DSC测试结果表明,Al₂O₃加入后,体系的玻璃化转变温度由114.16℃提高到121.51℃.     

Test and simulation on moisture flow in earlyage concrete under drying

In this paper, moisture flow in two concrete with and without internal curing using presoaked lightweight aggregate (PSLWA) under surface drying is experimentally investigated by measuring the weight of the concrete samples. Mathematical modeling on moisture flow, especially moisture transfer coefficient between concrete and surrounding air, normally called surface factor is performed. The results show that moisture flow through the drying surface of concrete can be characterized by a constant moisture loss stage (I) followed by a gradually reducing moisture loss stage (II). For the given environmental condition, the length of stage I increases with a decrease in water-to-cement ratio. Internal curing with PSLWA will prolong the length of Stage I. Surface factor is a function of location along air flow direction, air flow speed, and temperature of air and concrete surface, while it is independent of mix proportions of concrete. Higher air flow rate, higher temperature of air and/or concrete will result in a larger surface factor. Element size along air flow direction significantly influences the value of surface factor. Smaller element size along the air flow direction will result in a larger surface factor. The comparison on surface factor between experimental determination and theoretical calculation is performed and a good agreement between them is obtained.     

硫酸盐侵蚀对不同养护制度UHPC水化产物微结构的影响

采用29Si和27Al MAS NMR、XRD、SEM等测试技术研究了硫酸盐侵蚀对不同养护制度的超高性能混凝土(UHPC)水化产物微结构的影响.结果表明:标准养护和80 ℃高温蒸汽养护条件下,UHPC水化产物主要为C-S-H、Ca(OH)2、AFt、AFm和TAH;210 ℃、2 MPa蒸压养护8 h后,水化产物主要为tobermorite、Ca(OH)2和TAH.硫酸盐侵蚀对不同养护制度的UHPC抗压强度和水化产物微结构的影响微弱,但可促进210 ℃蒸压养护的UHPC胶凝浆体中TAH向AFm和AFt的转化.同时硫酸盐侵蚀180 d时,C-S-H凝胶MCL和Al[4]/Si略有降低,但降低幅度较小,UHPC具有良好的抗硫酸盐侵蚀能力.     

硅钙基固废原料配比及蒸养条件对硅酸钙板力学性能的影响

研究协同利用硅钙渣、粉煤灰、水泥和脱硫石膏制备硅酸钙板时,原料配比、蒸养条件对硅酸钙板力学性能、水化产物的影响,并利用XRD、IR和SEM表征了原料的协同水化历程和水化产物的微观结构和表面形貌.试验结果表明:最佳原料配比为硅钙渣60%、粉煤灰24%、水泥10%和脱硫石膏6%;最佳蒸压养护条件为蒸养温度180℃,恒温蒸养时间8 h,硅酸钙板抗折强度满足国家标准强度的D1.3的Ⅱ级要求;随着蒸养温度升高,原料水化依次生成C-S-H凝胶、托贝莫来石和针状硬硅钙石,大量托贝莫来石和硬硅钙石的生成使得硅酸钙板的强度得以提升.     

重金属离子对蒸养混凝土力学性能影响及其浸出特性研究

蒸养混凝土具有早期强度高、模具周转速度快和生产效率高等显著优势,成为混凝土预制构件主要制备工艺.通过抗压强度、离子浸出试验、X射线衍射等测试方法,研究了锌、铬、铜对蒸养混凝土的力学性能、水化产物结构及其浸出特性,并探讨了粉煤灰对蒸养混凝土固化重金属离子效果的影响规律.结果表明:①Zn、Cr和Cu离子能够在不同程度上降低蒸养混凝土的抗压强度,当掺量为1.0％时,抗压强度分别降低了50.63％、13.23％和99.27％;Zn、Cr和Cu离子不能明显改变水化产物的微观形貌,但是会抑制氢氧化钙(CH)和钙矾石的生成和结晶.②当掺量低于1.0％时,蒸养混凝土对Zn和Cr离子具有很好地固化作用,浸出浓度均小于0.21 mg/L,但是Cu离子的浸出浓度高达0.92 mg/L以上.掺加20％粉煤灰的蒸养混凝土抗压强度会降低5～8 MPa,并不能提高其对重金属离子的固化性能.     

Strong and super tough: Layered ceramic‐polymer composites with bio‐inspired morphology

Bio‐inspired layered ceramic‐polymer composites with high strength and toughness were prepared from sintered aluminum oxide ceramic sheets and cationically curing epoxy resins toughened with poly(ε‐caprolactone) (PCL). The architecture of the composite is inspired by nacre but is arranged on a larger scale. Ceramic sheets with a nominal thickness of 250 μm were assembled into composite plates by adhesive layers with a nominal thickness of 20 μm. Before the manufacturing of the composites, the stress‐strain properties of the polymer component were tailored by the variation in the PCL content between 0 and 39 wt%. For composites with 4 and 15 ceramic layers, the bending strengths achieved 327 MPa and 376 MPa, which are higher than that of pure ceramic sheets. Moreover, composites with 15 ceramic layers show a 16 times higher toughness compared to that of the pure ceramic sheets. The results indicate that the toughness of the layered composites increases significantly with the number of layers. Inspired by the geometrical ratio of the natural sheet composite nacre, we have achieved a similar strength but a 2 times higher toughness than nacre by only adding up to 6 vol% of the polymer.     

Ultrafast Nanoscale Polymer Coating on Porous 3D Structures Using Microwave Irradiation

Thin polymer coatings are very popular, but the coatings on uneven surfaces or porous 3D structures are difficult to obtain with traditional methods. The pores are easily clogged due to nonuniform polymer curing processes caused by inevitable macroscale temperature gradients from their hotter outer to colder inner sides. Here an ultrafast and simple fabrication method is developed to obtain nanoscale coating layers on the inner and outer surfaces of a porous 3D sponge‐like carbon nanotube (CNT). Microwave irradiation rapidly and selectively heats the CNT immersed in a mixture solution of an uncured polymer and a diluent solvent, solidifying the polymer only adjacent to the CNT with five repeated 3 s microwave irradiation. The coating layers can be controlled by adjusting the concentration of the uncured polymer in the solution and controlling the CNT temperature via microwave power and irradiation time. The nanoscale coating strongly ties the junction between CNTs without filling the pores with the polymer, resulting in excellent resilience to compressive stress with large strains (≈180 kPa at 60%), which is maintained throughout repeated 8000 cycles of 0–60% strain. The unfilled pores allow for maintaining the low thermal conductivity, ≈26 mW m^?1 K^?1, and the electrical resistance is varied with strain. This facile selective polymer curing methodology can be utilized in processing various materials with uneven surfaces or pores.     

Resorcinol in high solid phenol−formaldehyde resins for foams production

The acid curing agent content and foaming temperature could be reduced by improving the resol reactivity. In this study, highly active and solid phenol?resorcinol?formaldehyde copolymer resins (PRFRs) with different resorcinol/phenol (R /P ) molar ratios and formaldehyde/(phenol + resorcinol) [F /(P + R )] molar ratios were synthesized through the copolymerization of resorcinol, formaldehyde, and phenol. Phenol?resorcinol?formaldehyde foams (PRFFs) were prepared with synthetic PRFRs. The results showed that PRFR‐2 exhibited higher reactivity, faster curing speed, and better thermal stability. In addition, the foam produced with the PRFR‐2 had improved mechanical and flame retardation properties and a compressive strength of 0.18 MPa, a flexural strength of 0.25 MPa, and a limited oxygen index (LOI) greater than 37%. The increased reactivity of the PRFRs correlated with the changing mechanical properties of PRFFs because of the effects of resorcinol and the molar ratio of formaldehyde to phenol and resorcinol. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44881.     

An adaptive neuro-fuzzy approach to bulk tobacco flue-curing control process

Bulk tobacco flue-curing process significantly affects the quality and fragrance of cured tobacco leaves. The control of bulk tobacco flue-curing process is therefore quite important for tobacco industry. In this work, a neuro-fuzzy-based method for controlling bulk tobacco flue-curing process was proposed. In particular, an adaptive network-based fuzzy inference system (ANFIS) was developed to predict the set point changing time. To illustrate the applicability and capability of the ANFIS model, the proposed approach was tested with a bulk tobacco flue-curing barn database, which included totally 574 data sets obtained in the four curing cycles. The results demonstrated that the proposed approach could be applied successfully and provide high accuracy and reliability for bulk curing barns. Furthermore, to analyze how input factors affect the bulk tobacco flue-curing control process, the selection of input linguistic factors was also discussed. The factors of color and curing phase were found to have the most substantial influence on curing control process. A comparative study among the proposed neuro-fuzzy approach and other related methods was also performed. Both the statistical measures and visual assessment illustrated that the proposed ANFIS method outperformed the other methods in this study, which further showed the effectiveness and reliability of the neuro-fuzzy approach to bulk tobacco flue-curing control process.     

基于FBG的不同工艺下环氧树脂固化监测研究

不同工艺下复合材料固化时的温度变化、固化速率及产生的应变会对复合材料的成型质量产生巨大影响。针对在不同工艺条件下对树脂基复合材料固化过程的监测要求,采用将光纤布喇格光栅埋入环氧树脂内部的方法,对环氧树脂在恒温40℃和室温24℃两种不同工艺下的固化过程进行实时在线监测,固化时间均持续18h。结果表明,环氧树脂在恒温40℃工艺条件下固化时的温度变化、固化速率及产生的应变都比在室温24℃工艺条件下大。