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1.
采用有机碱吡啶(pyridine)代替常见的强碱(如氢氧化钾或氢氧化钠等)调节反应混合物的pH值,探究水热温度对配位聚合物结构的影响。分别以2,5-二甲基对苯二甲酸和间苯二甲酸(以下简称H2dmbdc和H2ip)为配体和硝酸锌通过水热合成配位聚合物[Zn3(dmbdc)3(py)2]n,1和[Zn4(H2O)(ip)4(py)6]n,2。研究发现,在较大的合成温度范围内(120℃~210℃),得到的配位聚合物结构也都不会随水热合成温度的改变而改变。由此表明当有吡啶参与反应时,配位聚合物的结构对水热温度具有一定的不敏感性。  相似文献   

2.
采用分步法制备了聚丙烯酸/N-异丙基丙烯酰胺互穿网络水凝胶,研究了互穿网络水凝胶的溶胀性能。结果表明,当水溶液的pH增大时,水凝胶的溶胀率显著增加。在一定的温度范围内,水凝胶的溶胀率随温度升高而减小。聚丙烯酸/N-异丙基丙烯酰胺互穿网络水凝胶表现出显著的温度及pH敏感双重特性。  相似文献   

3.
刘超 《应用化工》2012,41(2):297-299,313
采用乳液聚合法,以甲基丙烯酸甲酯(MMA)和甲基丙烯酸二甲氨基乙酯(DM)为单体,制备了可直接用于药物包衣的胃溶型丙烯酸树脂乳液。结果表明,当温度为65℃,单体摩尔比为1∶1,引发剂和乳化剂用量分别为0.6%和0.3%,采用单体连续滴加法时,可制得稳定的乳液,聚合物分子量为14.9万。在180℃以下,产品的失重率基本不随温度而变,而在180℃以上,失重率随温度升高而增加。聚合物膜在缓冲溶液中的失重率随pH的增加而减小,当pH为1.0和2.0时,膜几乎全部溶解,pH为3.0时,膜的失重率为65.0%,在pH为4.0时,失重率迅速降低到32.8%,到pH为7.0时,膜已基本不溶。  相似文献   

4.
温度、压力及pH值对水泥固化的影响   总被引:1,自引:0,他引:1  
依据水泥浆固化条件与水泥石的显微结构、化学组成和力学性能的关系原理,进行了养护温度、养护压力和配浆水pH值对水泥浆固化过程的影响的研究。结果表明,在低于110℃养护温度范围内,水泥石抗压强度随温度的升高而升高,高于110℃时则随温度的升高而降低。在2MPa~8MPa养护压力范围内,水泥石的抗压强度随养护压力的升高而升高;在相同的条件下,采用酸性配浆水配制的水泥浆养护得到的水泥石的抗压强度最高。通过初步分析发现温度对水泥浆固化过程的影响最大,配浆水的pH值次之,养护压力的影响最小。  相似文献   

5.
在含偶氮苯的三硫酯链转移剂(CTA-AZO)存在下,将甲基丙烯酸二甲氨基乙酯(DMAEMA)通过可逆加成断裂链转移(RAFT)聚合,制备了pH、温度和光三重敏感的含偶氮苯端基的聚甲基丙烯酸二甲氨基乙酯聚合物(PDMAEMA-AZO)。采用紫外光谱(UV)、红外光谱(FTIR)、核磁共振氢谱(1HNMR)和凝胶渗透色谱(GPC)对PDMAEMA-AZO的结构进行了表征,并考察了聚合物的光敏性、温敏性和pH敏感性。GPC结果表明,PDMAEMA-AZO的相对分子质量可控,且相对分子质量分布(PDI)小于1.78。PDMAEMA-AZO在不同溶剂中(氯仿、乙醇和水)的光敏性实验结果显示,该聚合物在氯仿、乙醇和水中均能够快速进行可逆光致顺反异构反应,在紫外与可见光的交替照射下,快速达到光稳态。PDMAEMA-AZO的温敏性实验表明,与聚甲基丙烯酸二甲氨基乙酯(PDMAEMA)相比,PDMAEMA-AZO的低临界溶解温度(LCST)更低。随着聚合物浓度的增加,其LCST降低,且相变窗口变窄。当pH超过9.44时,该聚合物的LCST保持不变,pH由9.44下降到7.34时,LCST升高,pH<7.34时不再具有温敏性,说明该类聚合物是一种pH控制的具备LCST的温敏性聚合物。在紫外与可见光交替照射下,PDMAEMA-AZO 的LCST 表现为可逆的升高和降低,表明聚合物PDMAEMA-AZO具备光控温敏性。  相似文献   

6.
王祝敏  王国胜  孙怀宇  刘云义 《当代化工》2005,34(2):112-113,116
研究了水溶液中氯苯酚在活性炭纤维上的吸附平衡,实验探讨了反应温度、溶液pH值对活性炭纤维吸附平衡的影响。实验结果表明,平衡吸附量随着温度降低而升高;当pH值<7时,平衡吸附量几乎不随溶液的pH值而变化,而当pH值>7时,氯苯酚在活性炭纤维上的平衡吸附量随着pH值的增加而减小,pH值愈大,平衡吸附量减小的愈快。分别采用Langmuir模型和Freundlich模型描述吸附平衡等温线,在实验范围内Langmuir模型与实验数据吻合较好。  相似文献   

7.
将有机硅RAFT试剂三甲氧基硅基丙基三硫代羰基苄基酯(BTPT)固载于硅球表面,通过可逆加成-断裂链转移自由基聚合表面接枝法制备了pH值、温度双敏感聚合物聚甲基丙烯酸-2-(二甲氨基)乙酯(PDMAEMA)修饰的纳米硅球,通过表面保护法在常温下用氨水对该修饰过的硅球进行刻蚀,制得PDMAEMA修饰的纳米空心介孔硅球(HMS@PDMAEMA)。通过核磁、红外、GPC和透射电子显微镜等方法对其结构和表面形貌进行了表征,并用纳米粒度及zeta电位仪测试了其pH值响应行为,预测HMS@PDMAEMA在癌症药物的控制释放和基因递送等领域具有潜在的应用价值。  相似文献   

8.
谷惠文  肖云  陈超  叶丽娟  肖圣雄 《广州化工》2010,38(12):105-109
采用单因素控制法,分别制备了在不同温度及pH值下的DyCl3.nH2O(s)和LaCl3.nH2O(s);运用滴定分析及差减法,测定了不同条件下所得稀土氯化物的结晶水含量,以温度-结晶水含量及pH值-结晶水含量作图,结果表明稀土氯化物中结晶水的含量随温度的升高先减少后增加,在60℃时出现最小值;结晶水含量随pH的增加呈S型曲线递增。  相似文献   

9.
针对海上某油田油井管柱腐蚀严重现象,采用静态挂片失重法研究了采出水中硫化物含量、pH值、腐蚀温度以及氯离子含量等因素对腐蚀速率的影响,在分析油井管柱腐蚀影响因素的基础上,提出了相应的防治措施,评价了缓蚀剂STB-11对目标油田油井管柱钢片的缓蚀性能。结果表明,腐蚀速率随采出水中硫化物含量、腐蚀温度以及氯离子含量的升高而逐渐加快,腐蚀速率随pH值的增大而逐渐减慢;当采出水中缓蚀剂STB-11加量为30 mg·L~(-1)、腐蚀温度为120℃时,腐蚀速率可以控制在0.071 mm·a~(-1),缓蚀率可以达到85%以上,能够满足行业标准要求。  相似文献   

10.
采用电化学阻抗谱(EIS)及动电位扫描技术研究了温度和pH值对X80管线钢在库尔勒土壤中的腐蚀行为,并利用金相显微镜观察了不同温度及pH值下的腐蚀形貌。结果表明:X80管线钢在库尔勒土壤环境中会形成一层保护性较好的钝化膜,且随着温度的升高,钝化膜稳态电流增大;而膜电阻及扩散电阻则随介质pH值的增强而减小,X80钢的腐蚀速率随之减小。  相似文献   

11.
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.  相似文献   

12.
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.  相似文献   

13.
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。  相似文献   

14.
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。  相似文献   

15.
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.  相似文献   

16.
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.  相似文献   

17.
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.  相似文献   

18.
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.  相似文献   

19.
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.  相似文献   

20.
Hardening of cement mortars modified with small amounts of water-soluble polymers implies both cement hydration and polymer film formation. In this paper, the effect of the presence of water-soluble polymers on the cement hydration reactions is investigated by means of isothermal calorimetry, thermal analysis, FT-IR spectroscopy and SEM investigation. In spite of an initial retardation of the hydration reactions, a higher degree of hydration is found after 90 days for 1% PVAA, MC and HEC modified mortars, due to a better dispersion of the cement particles in the mixing water. MC also affects the morphology of the Ca(OH)2 crystals. Polymer bridges are detected between the layered crystals, gluing the layers together and strengthening the microstructure. Additionally, the internal cohesion of all bulk polymer modified cement pastes is improved. In the presence of the polymers, a more cohesive microstructure with a smaller amount of microcracks is created.  相似文献   

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