二氧化钛负载磷钨钼酸催化合成环己酮乙二醇缩酮

首次采用回流法制备了二氧化钛负载磷钨钼杂多酸催化剂H3PW6Mo6O40/TiO2,该催化剂的适宜制备条件为：原料质量比m（TiO2）∶m（H3PW6Mo6O40）=1∶2.0,水用量30mL,回流反应时间2.0h,活化温度150℃。以H3PW6Mo6O40/TiO2为催化剂,对以环己酮与乙二醇为原料合成环己酮乙二醇缩酮的反应条件进行了研究,较系统地研究了酮醇物质的量比、催化剂用量、反应时间对收率的影响。实验结果表明,在n（环己酮）∶n（乙二醇）=1.0∶1.5、催化剂用量占反应物料总质量的0.8%、反应时间1.0h的条件下,环己酮乙二醇缩酮的收率为86.3%。     

H_3PW_(12)O_(40)/TiO_2-SiO_2催化合成环己酮1,2-丙二醇缩酮

采用H3PW12O40/TiO2-SiO2为催化剂,以1,2-丙二醇、环己酮为原料合成环己酮1,2-丙二醇缩酮。探讨H3PW12O40/TiO2-SiO2对该反应的催化活性。实验表明:H3PW12O40/TiO2-SiO2是合成环己酮1,2-丙二醇缩酮的良好催化剂;在n(环己酮)∶n(1,2-丙二醇)=1∶1.6,反应时间为60min,环己烷用量为6mL,催化剂的用量占反应物料总质量的0.8%的适宜条件下,其收率可达81.9%。     

H3PW12O40/SiO2催化合成环己酮乙二醇缩酮

采用溶胶-凝胶法制备了二氧化硅负载磷钨酸H3PW12O40/SiO2催化剂,并通过FTIR、XRD对其进行了表征。以环己酮和乙二醇为原料,合成了环己酮乙二醇缩酮,探讨了H3PW12O40/SiO2对缩酮反应的催化活性,考察了酮醇摩尔比、催化剂用量、带水剂用量、反应时间对产物收率的影响。结果表明,在n(环己酮)∶n(乙二醇)=1∶1.3,催化剂用量占反应物料总质量的1.2%,带水剂环己烷用量3 mL,反应时间45 min的最佳条件下,环己酮乙二醇缩酮收率可达89.7%。     

磷钨酸催化合成丁酮乙二醇缩酮

以磷钨酸H3 PW12 O40 为催化剂 ,通过丁酮和乙二醇反应合成丁酮乙二醇缩酮。探讨了H3 PW12 O40 对缩酮反应的催化活性 ,较系统地研究了酮醇物质的量比、催化剂用量、反应时间等因素对产品收率的影响。实验表明 :H3 PW12 O40 是合成丁酮乙二醇缩酮的良好催化剂 ,在n(酮 )∶n(醇 ) =1∶1.75 ,催化剂用量为反应物料总质量的 1.2 5 % ,环己烷为带水剂 ,反应时间 2 .0h ,反应温度 72～ 96℃的优化条件下 ,丁酮乙二醇缩酮的收率可达 5 9.5 %。     

H_3PW_6Mo_6O_(40)/TiO_2-MoO_3催化合成环己酮乙二醇缩酮

探讨以H3PW6Mo6O40/TiO2-MoO3为催化剂,以环己酮、乙二醇为原料催化合成环己酮乙二醇缩酮反应的催化活性,较系统地研究了酮醇物质量比,催化剂用量,带水剂用量及反应时间等因素对产物收率的影响。实验表明:固定环己酮的用量为0.2 mol时,在n(环己酮)∶n(乙二醇)=1.0∶1.4,催化剂用量为反应物料总质量的1.0%,带水剂环己烷为6 mL,反应时间为60 min的优化条件下,环己酮乙二醇缩酮的收率可达78.9%。     

磷钨杂多酸掺杂聚苯胺催化合成环己酮乙二醇缩酮

采用浸渍法制备的磷钨杂多酸掺杂聚苯胺H3PW12O40/PAn作催化剂,通过环己酮和乙二醇为原料合成环己酮乙二醇缩酮,探讨了磷钨酸掺杂聚苯胺催化剂对缩酮反应的催化活性,系统地研究了原料量比,催化剂用量,反应时间诸因素对产品收率的影响。实验表明,在n环己酮∶n乙二醇=1∶1.5(物质的量比),催化剂用量为反应物料总质量的0.25%,环己烷为带水剂,反应时间1.0 h的优化条件下,环己酮乙二醇缩酮的收率可达80.4%。     

TiSiW_(12)O_(40)/TiO_2催化合成环己酮1,2-丙二醇缩酮

以固载杂多酸盐TiSiW1 2 O4 0 /TiO2 为多相催化剂 ,通过环己酮和 1 ,2 丙二醇反应合成了环己酮 1 ,2 丙二醇缩酮 ,探讨TiSiW1 2 O4 0 /TiO2 对缩酮反应的催化活性 ,较系统地研究了酮醇量比 ,催化剂用量 ,反应时间诸因素对产品收率的影响。实验表明 :TiSiW1 2 O4 0 /TiO2 是合成环己酮 1 ,2 丙二醇缩酮的良好催化剂 ,在n(酮 )∶n(醇 ) =1 0∶1 5 ,催化剂用量为反应物料总质量的 0 6 % ,环己烷为带水剂 ,反应时间 40min的优化条件下 ,环己酮 1 ,2 丙二醇缩酮的收率可达 92 2 %。     

磷钨钼杂多酸催化合成环己酮乙二醇缩酮

以H3PW6Mo6O40为催化剂，对以环己酮与乙二醇为原料合成环己酮乙二醇缩酮的反应条件进行了研究，较系统地研究了酮醇物质的量比、催化剂用量、反应时间对收率的影响。实验结果表明，在n（环己酮）：n（乙二醇）=1．0：1．5，催化剂用量占反应物料总质量的0．8％，反应时间0．75h，带水剂环己烷8mL的条件下，环己酮乙二醇缩酮的收率为84.9％。     

稀土改性固体超强酸催化剂SO42-/TiO2-La2O3催化合成环己酮乙二醇缩酮

制备了稀土改性固体超强酸催化剂SO42-/TiO2-La2O3,并利用该催化剂催化合成了环己酮乙二醇缩酮,探讨了SO42-/TiO2-La2O3对缩酮反应的催化活性,较系统地研究了酮醇物质的摩尔比,催化剂用量,反应时间诸因素对产品收率的影响。实验表明:SO42-/TiO2-La2O3是合成环己酮乙二醇缩酮的良好催化剂,在n(酮)∶n(醇)=1∶1.5,催化剂用量为反应物料总质量的0.5%,环己烷为带水剂,反应时间1.5h的优化条件下,环己酮乙二醇缩酮的收率可达84.3%。     

SO4^2-／TiO2-MoO3-La2O3催化合成环己酮乙二醇缩酮

以固体超强酸SO4^2-/TiO2-MoO3-La2O3为多相催化剂,通过环己酮和乙二醇反应合成了环己酮乙二醇缩酮。探讨SO4^2-/TiO2-MoO3-La2O3对缩酮反应的催化活性,较系统地研究了酮醇量比、催化剂用量、反应时间等因素对产品收率的影响。实验表明,SO4^2-/TiO2-MoO3-La2O3是合成环己酮乙二醇缩酮的良好催化剂。在n（酮）∶n（醇）=1∶1.4、催化剂用量为反应物料总质量的0.6%、环己烷为带水剂、反应时间1.0h的优化条件下,环己酮乙二醇缩酮的收率可达87.3%.     

Interactions between shrinkage reducing admixtures (SRA) and cement paste's pore solution

Shrinkage reducing admixtures (SRA) have been developed to combat shrinkage cracking in concrete elements. While SRA has been shown to have significant benefits in reducing the magnitude of drying and autogenous shrinkage, it has been reported that SRA may cause a negative side effect as it reduces the rate of cement hydration and strength development in concrete. To examine the influence of SRA on cement hydration, this study explores the interactions between SRA and cement paste's pore solution. It is described that SRA is mainly composed of amphiphilic (i.e., surfactant) molecules that when added to an aqueous solution, accumulate at the solution-air interface and can significantly reduce the interfacial tension. However, these surfactants can also self-aggregate in the bulk solution (i.e., micellation) and this may limit the surface tension reduction capacity of SRA. In synthetic pore solutions, SRA is observed to form an oil-water-surfactant emulsion that may or may not be stable. Specifically, at concentrations above a critical threshold, the mixture of SRA and pore fluid is unstable and can separate into two distinct phases (an SRA-rich phase and an SRA-dilute phase). Further, chemical analysis of extracted pore solutions shows that addition of SRA to the mixing water depresses the dissolution of alkalis in the pore fluid. This results in a pore fluid with lower alkalinity which causes a reduction in the rate of cement hydration. This may explain why concrete containing SRA shows a delayed setting and a slower strength development.     

Influence of bleed water reabsorption on cement paste autogenous deformation

The effects of bleed water reabsorption and subsequent early age expansion on observed autogenous deformation are investigated in this research. Bleeding was induced by varying superplasticizer and shrinkage-reducing admixture dosages and by increasing the water-to-cement ratio. This research revealed that significant early age expansion occurs with increasing chemical admixture dosages and higher water-to-cement ratios, as expected, due to increasing bleeding of those samples. When samples were rotated, negligible early age expansion was observed. Thus, bleed water reabsorption is shown to be the primary mechanism causing initial expansion in sealed autogenous deformation samples. Thermal dilation and ettringite growth appear to have a minimal influence on the observed expansion. Rotating the samples during setting eliminates the potential for bleed water reabsorption and is recommended for all autogenous deformation testing.     

Chemical model for cement-based materials: Thermodynamic data assessment for phases other than C-S-H

In the context of waste confinement, concrete may be used both as a confinement and as a building material. Concerning radwaste, the heat released during radioactive decay will modify the equilibrium constants of the minerals forming the concrete. The present work aims to elucidate the temperature dependency of the thermodynamic functions related to minerals from the concrete or associated with some of its degradation products. A large set of experimental data has been collected, for the chemical systems SO₃-Al₂O₃-CaO-CO₂-Cl-H₂O and SiO₂-Al₂O₃-CaO-H₂O, including iron and magnesium bearing phases. Most of the data collected concern experiments in aqueous media but results from calorimetric studies were also included, when available. Based on selected thermodynamic properties for each phase, predominance diagrams were drawn for the chemical elements listed above. Phase relations reported into predominance diagram appear rather consistent with most of the literature results. The case of katoite has been especially discussed, because it shows inconsistencies with respect to a hydrogarnet-grossular solid solution and with respect to phase relations reported into already published works. Finally, we underline the chemical compatibility of Portland cement pastes with carbonate aggregates, compared to silicates, for long-term storage applications.     

An investigation of microstructure evolution in cement paste through setting using ultrasonic and rheological measurements

The response of hydrating cement paste through setting are monitored using rheological measurements and ultrasonic reflection measurements. Increases in the elastic modulus and yield stress of cement paste with time are obtained from the rheological measurements. Ultrasonic measurements are performed using horizontally polarized shear waves (SH) reflected off of the hydrating cement paste. Changes in the ultrasonic signal through setting are related with changes in the porosity and stiffness of an equivalent water-filled poroelastic material, which provides identical acoustic impedance. The measured changes in the shear modulus obtained from ultrasonic measurement are shown to correlate well with increase in elastic modulus obtained from rheological measurements. The increase in the shear modulus of the porous material obtained from the ultrasonic measurements is shown to correspond well with the observed increase in the yield stress of the cement paste. By combining the information from rheological and ultrasonic measurements, it is found that even in the fluid stage there is sufficient structural integrity in the arrangement of cement grains to support low-amplitude shear stress and the evolution of a continuously connected network of cement particles within the paste is coincident with a rapid increase in the shear modulus of the porous skeleton.     

Nonlinear ultrasonic evaluation of load effects on discontinuities in concrete

The presence of discontinuity surfaces in concrete structures, i.e. two or more layers in contact, may be an existing situation with evident relapses on damage formation and progression. Differences occur depending on the type of discontinuity, which could be a thin weaker layer or a pre-existing crack. The behavior of pre-existing interfaces is here studied by means of the Scaling Subtraction Method, a Nonlinear Ultrasonic Non-Destructive Technique, that revealed to be effective in describing the mechanical evolution of concrete samples with discontinuity surfaces under the effects of compressive loads.     

Assessment of the long-term stability of cementitious barriers of radioactive waste repositories by using digital-image-based microstructure generation and reactive transport modelling

Cement-based grout plays a significant role in the design and performance of nuclear waste repositories: used correctly, it can enhance their safety. However, the high water-to-binder ratios, which are required to meet the desired workability and injection ability at early age, lead to high porosity that may affect the durability of this material and undermine its long-term geochemical performance.In this paper, a new methodology is presented in order to help the process of mix design which best meets the compromise between these two conflicting requirements. It involves the combined use of the computer programs CEMHYD3D for the generation of digital-image-based microstructures and CrunchFlow, for the reactive transport calculations affecting the materials so simulated. This approach is exemplified with two grout types, namely, the so-called Standard mix 5/5, used in the upper parts of the structure, and the “low-pH” P308B, to be injected at higher depths.The results of the digital reconstruction of the mineralogical composition of the hardened paste are entirely logical, as the microstructures display high degrees of hydration, large porosities and low or nil contents of aluminium compounds.Diffusion of solutes in the pore solution was considered to be the dominant transport process. A single scenario was studied for both mix designs and their performances were compared. The reactive transport model adequately reproduces the process of decalcification of the C-S-H and the precipitation of calcite, which is corroborated by empirical observations. It was found that the evolution of the deterioration process is sensitive to the chemical composition of groundwater, its effects being more severe when grout is set under continuous exposure to poorly mineralized groundwater. Results obtained appear to indicate that a correct conceptualization of the problem was accomplished and support the assumption that, in absence of more reliable empirical data, it might constitute a useful tool to estimate the durability of cement-based structures.     

Wavelet-based analysis of ultrasonic longitudinal and transverse pulses in cement-based materials

Ultrasonic pulse velocity has been used for decades to detect localized damage and to estimate concrete properties. More recent applications aim at diffuse damage characterization, such as environmental and mechanical damage. In most applications the methodology to calculate pulse speed is a very important issue. This work, applying continuous wavelet transform (CWT) to construct time-frequency signal representations, calculates frequency-dependent velocity of longitudinal and transverse ultrasonic pulses using wavelet scales. The method is applied to a total of 14 specimens of 5 different mixes and frequency-dependent velocities are calculated using four wavelet families. The CWT capability to decompose the inquiring pulse spectrum and analyze phase velocities is discussed with regard to wavelet, pulse type, and mixture. Frequency-dependent velocity of longitudinal pulses at lower frequencies (from 100 kHz up to 250 kHz) was proven to be much more sensitive to mix proportions than transverse pulses.     

La掺杂(Na_(0.5)Bi_(0.5))_(0.82)(K_(0.5)Bi_(0.5))_(0.18)TiO_3系统无铅压电陶瓷的制备工艺探讨

采用传统陶瓷工艺,研究了制备[(Na0.5Bi0.5)0.82(K0.5Bi0.5)0.18]1-xLaxTiO3(x=0.00,0.01,0.03,0.05,0.10)无铅压电陶瓷的工艺条件对陶瓷的物相组成、显微结构和压电性能的影响。利用XRD、SEM等技术分析结果表明,合成温度的提高有利于主晶相的形成,且此系统烧成温度范围较窄,故需控制在合适的烧成温度下才能得到高致密度的陶瓷。同时,研究了极化工艺条件对材料压电性能的影响,结果表明,提高极化电场强度、控制适当的极化温度有利于提高材料的压电性能。     

Effects of adhesive type and polystyrene concentration on the shear strength of bonded polystyrene/high-density polyethylene blends

The lap-shear strengths of adhesively bonded polystyrene (PS), high-density polyethylene (HDPE), and their blends, were studied as a function of adhesive type and blend composition. The performance of virgin and recycled polymer systems was examined. The lap-shear strength depended strongly on the amount of PS in the blend and the type of adhesive, and the acrylic adhesives demonstrated the best performance for all compositions. Bonded strengths of HDPE increased by approximately 50% when HDPE was blended with 34% PS, the co-continuous composition. The results indicate that structural elements made from PS/HDPE immiscible blends may be effectively bonded with adhesives without expensive surface treatments.