单模聚焦微波辐射催化合成邻苯二甲酸二异辛酯

利用Discover微波精确有机合成系统,以一水合硫酸氢钠为催化剂合成邻苯二甲酸二异辛酯。考察了催化剂用量、微波辐射的功率和时间、反应物料配比对苯酐的转化率的影响。当n(异辛醇)：n(邻苯二甲酸酐)=0．065：0．025,催化剂0.3g,微波辐射功率120W,辐射时间8min时,转化率达98．6％。     

微波辐射固体酸催化合成邻苯二甲酸二丁酯的研究

以硅胶担载对甲苯黄酸（PTSA）作催化剂，采用微波技术，邻苯二甲酸酐和正丁醇直接酯化合成邻苯二甲酸二丁酯。最佳反应条件为：苯酐和正丁醇的摩尔比为0．02∶0．05，PTSA担载质量分数为16．2％的催化剂用量1．2g，微波功率560W，微波辐射时间280s，产率可达98％。催化剂易分离，且可重复使用。     

邻苯二甲酸二正丁酯实验室制备工艺的改进

以邻苯二甲酸酐和正丁醇为原料，硫酸氢钠为催化剂合成邻苯二甲酸二正丁酯，考察了影响收率的因素，确定最佳工艺条件为：n(邻苯二甲酸酐)：n(正丁醇)：1：2．5，反应时间2h，硫酸氢钠用量占邻苯二甲酸酐质量的3．4％，最终产率达95％以上。     

微波辐射固体酸催化合成邻苯二甲酸二丁酯的研究

以硅胶担载对甲苯黄酸 (PTSA)作催化剂 ,采用微波技术 ,邻苯二甲酸酐和正丁醇直接酯化合成邻苯二甲酸二丁酯。最佳反应条件为 :苯酐和正丁醇的摩尔比为 0 .0 2∶ 0 .0 5 ,PTSA担载质量分数为 16 .2 %的催化剂用量 1.2 g,微波功率 5 6 0 W,微波辐射时间 2 80 s,产率可达 98%。催化剂易分离 ,且可重复使用     

微波加热常压快速合成醋酸正丁酯的研究

冰醋酸和正丁醇为原料，对甲苯磺酸催化，利用微波技术，在常压下快速合成醋酸正丁酯，最佳反应条件为:n(正丁醇）：n(冰醋酸）＝2．0：1．0（mol/mol)，对甲苯磺酸用量0．25g，微波功率462W，辐射时间8min，产率达98％以上。     

微波辐射硫酸氢钠催化合成邻苯二甲酸二丁酯

采用微波合成技术,在水合硫酸氢钠存在下由邻苯二甲酸酐和正丁醇合成了邻苯二甲酸二丁酯。最佳反应条件为:邻苯二甲酸酐、正丁醇与硫酸氢钠的摩尔比为1∶4∶0 22,微波功率为650W,功率百分比为30%,微波辐射时间为35min,此条件下产率为98 0%。     

微波辐射稀土固体超强酸SO^2-4／TiO2／La^3＋催化合成苯甲醛乙二醇缩醛

苯甲醛和乙二醇以稀土固体超强酸SO^2-4／TiO2／La^3 为催化剂，经微波辐射直接催化合成苯甲醛乙二醇缩醛。结果表明，当微波输出功率为210W，辐射时间3min，n(苯甲醛)：n(乙二醇)：1：2，催化剂用量0．7g(苯甲醛为0．10m01)时，苯甲醛乙二醇缩醛的收率为88．3％。     

微波辐射四丁基溴化铵催化合成肉桂酸苄酯

研究了以肉桂酸钠和氯化苄为原料，四丁基溴化铵作催化剂，采用微波辐射技术，在常压下直接合成肉桂酸苄酯，以及催化剂用量、微波辐射功率和辐射时间对酯产率的影响。最适宜的反应条件为：当n(肉桂酸钠)／n(氯化苄)为1：1．2时，四丁基溴化铵的用量1．0g，微波功率300W，辐射25min，产率达83％以上。     

丙酸丁酯的合成研究

研究了利用微波辐射技术,在对甲苯磺酸的催化下以正丙酸和正丁醇为原料合成丙酸丁酯的反应,探讨了原料配比、反应时间、催化剂用量、带水剂用量、微波功率等参数对酯化率的影响。结果表明:此法工艺简单,催化剂用量少,催化活性高,反应时间较短,正丙酸转化率高。通过实验确定了最佳工艺条件为:n(正丁醇)∶n(正丙酸)=1.8∶1.0,对甲苯磺酸用量0.3g,带水剂环己烷的用量5mL,微波功率595W,微波辐射时间10min,酯化率达99%以上。     

微波辐射催化合成硬脂酸乙酯

采用微波辐射技术，以硬脂酸和无水乙醇为原料，浓硫酸为催化剂制备了硬脂酸乙酯，通过正交设计实验优化了微波工艺条件。结果表明，微波辐射技术对硬脂酸乙酯的催化合成具有非常好的效果，优化的最佳工艺条件为，微波功率130W，辐射时间45min，酸醇摩尔比1．0：1．8，催化剂质量分数0．60％。在此条件下反应转化率达87．32％。     

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.