亲水基团对有机和炭气凝胶孔结构的影响

热固型酚醛树脂、三聚氰胺、间甲酚和甲醛水溶液在碳酸钠催化下,通过溶液-溶胶-凝胶过程合成有机水凝胶,有机水凝胶经溶剂置换、超临界干燥和裂解形成了有机气凝胶和炭气凝胶.在固定酚醛树脂浓度、间甲酚/酚醛树脂、甲醛/三聚氰胺、碳酸钠/酚醛树脂比值,改变三聚氰胺/酚醛树脂比值的条件下,研究了亲水基团对有机气凝胶和炭气凝胶孔结构的影响.结果表明:亲水性的三聚氰胺可增加分子间作用力,有利于凝胶的稳定;但增加三聚氰胺会加大有机气凝胶裂解过程中的质量损失,不利于凝胶的稳定.二种因素协同作用决定着炭气凝胶的孔结构、孔容和比表面.     

苯酚-间甲酚-糠醛基炭气凝胶的制备及微结构控制

以苯酚、间甲酚和糠醛为原料,在正丙醇溶剂中以盐酸为催化剂经溶胶-凝胶过程合成了醇凝胶,直接超临界正丙醇干燥得到有机气凝胶,在氮气保护下裂解制备出富含中孔的炭气凝胶.用IR、N2吸附、SEM、TEM等表征气凝胶的结构特征,考察了问甲酚苯酚摩尔比对凝胶结构的影响.结果发现:提高间甲酚的含量能够增强聚合物的交联密度,减小聚合物与溶剂的相溶性,缩短相分离时间,有利于得到较小的纳米颗粒和孔径的炭气凝胶.所制得的炭气凝胶平均中孔孔径随间甲酚含量的增加从47 nm逐渐减小至13 nm,BET比表面积和中孔孔容在m-C/P=0.33时达到最大值.     

氧化前处理对炭气凝胶孔结构的影响

在110℃～170℃范围内对糠醛-酚醛基有机气凝胶进行氧化处理1h～7h,考察了氧化对有机气凝胶热裂解产生的炭气凝胶孔结构的影响.结果表明:氧化可避免有机气凝胶纳米骨架在裂解过程中的塑性阶段发生,有机气凝胶的适度氧化有利于纳米结构的稳定化;由于空气在大、中、微孑L中扩散的差别,氧化前处理对炭气凝胶的大、中、微孔有不同的影响,尤其对接近中孔的大孔影响最大.在所考察的氧化温度和时间内,130℃/7h时或150℃/3h时的适度氧化条件下,可显著提高中孔孔容、中孔比表面和BET比表面.     

小角X射线散射研究制备炭气凝胶过程中凝胶的微结构演化

酚醛树脂和羟甲基化蜜胺在碱性水溶液中在80℃水浴中反应5d经溶胶－凝胶过程形成了水凝胶。水凝胶经丙酮置换产生酮凝胶，而后经超临界二氧化碳干燥生成有机气凝胶。有机气凝胶在氮气氛中800℃下裂解3h形成了炭气凝胶。采用小角X－射线散射技术和散射理论对上述四种凝胶的微结构进行了分析。结果发现：水凝胶粒子是单分散的，被水溶胀并在0．15nm处有强的散射峰，表明具有纳米尺度的空间周期结构，这种结构是通过不稳态纳米尺度相变－旋节微相分离产生的。由丙酮置换产生的酮凝胶也是单分解的，被丙酮稍微溶胀并在0．15nm具有肩峰，表明水凝胶在溶剂置换过程中发生轻微团聚产生的大粒子在较小角处发生强烈的散射致使强峰演化成肩峰。有机气凝胶和炭气凝胶都是多分散的，在小角处没有散射峰，表明在超临界干燥过程中粒子的团聚继续发生惜驳分散性并掩盖了纳米尺度的空间周期结构致使散射峰消失。有机气凝胶中存在的扩散界面层在其裂解过程中消失，这可能是由于在裂解过程中扩散界面层向粒子迁移以降低界面能所致。从小角X－射线散射数据用Shull-Roess法得到的有机气凝胶和炭气凝胶的回转半径分布比较可知，在裂解过程中，粒子的团聚长大、质量损失和致密化共同作用的结果使得炭气凝胶的回转半径分布比较可知，在裂解过程中，粒子的团聚长大、质量损失和致密化共同作用的结果使得炭气凝胶的回转半径分布比有机气凝胶稍宽，最可几回转半径稍微减少。     

有机/无机杂化制备低密度高中孔率炭气凝胶

通过溶胶-凝胶途径,将间苯二酚-甲醛预聚物和二氧化硅溶胶混合,在碱性溶液中制备出有机/无机杂化水凝胶.水凝胶经溶剂置换、超临界干燥、裂解和氢氟酸刻蚀制备得到炭气凝胶.采用氮气吸附法研究了水凝胶向炭气凝胶转化的结构演变规律.固定间苯二酚/甲醛摩尔比为0.5,二氧化硅溶胶浓度为15g/100mL,考察了二氧化硅胶体颗粒的尺寸及间苯二酚和甲醛浓度对炭气凝胶孔隙结构的影响.结果表明:无机二氧化硅溶胶骨架有效减少了有机物在超临界干燥和裂解过程中的体积收缩.中孔率随间苯二酚和甲醛浓度的升高而增加,孔隙率随二氧化硅溶胶粒子的增大而减小.当间苯二酚和甲醛质量分数之和的达到20%时,7nm二氧化硅溶胶体系的密度低达0.22g/cm3,中孔率达到96%,12nm二氧化硅溶胶体系的密度低达0.26g/cm3,中孔率达到98%.     

酚醛树脂气凝胶的溶胶-凝胶法制备及合成机理

以商业酚醛树脂为原料,介绍了一种工艺简单、制备周期短、成本低的低温溶胶-凝胶聚合和常压干燥工艺制备酚醛树脂气凝胶的方法。使用3种酚醛树脂(低黏度钡酚醛、普通热塑性酚醛和硼酚醛)在醇溶剂中制备了3种系列的凝胶。采用扫描电子显微镜、比表面积及孔隙率分析仪和红外光谱分析了所制备气凝胶的骨架结构和孔结构及合成机理。所制备的多孔纳米酚醛树脂气凝胶密度低至0.17～0.23 g/cm³、压缩强度为0.68～0.80 MPa,热导率为0.039～0.046 W/(m·K)。研究表明,酚醛树脂与醇溶剂之间有较强的选择匹配性,轻质多孔的钡酚醛树脂气凝胶只能在乙醇中合成,热塑性酚醛树脂在正丙醇溶剂中得到的气凝胶结构更均匀,而硼酚醛树脂由于固化温度过高,难以通过该方法获得气凝胶材料。这种低成本、简捷的气凝胶制备工艺对实现酚醛树脂气凝胶的大尺寸制备和产业化发展具有重要意义。     

超临界石油醚干燥和超临界二氧化碳干燥在制备有机和炭气凝胶中的比较研究

热固性酚醛树脂—羟甲基三聚氰胺经历聚合反应、溶胶—凝胶、超临界干燥和裂解过程生成了有机和炭气凝胶。比较了超临界石油醚干燥(240℃、6．0MPa下1h)和超临界二氧化碳干燥(60℃、10．0MPa下7d)在制备有机和炭气凝胶过程中的作用。结果发现：超临界石油醚干燥时间比超临界二氧化碳的显著短，虽然前者制备的有机气凝胶的BET比表面和中孔孔容比后者小，但前者制备的有机气凝胶在热裂解过程中的热稳定性比后者好，因此，超临界石油醚干燥制备的炭气凝胶的BET比表面和中孔孔容均比超临界二氧化碳的大。超临界石油醚干燥可以替代超临界二氧化碳干燥来制备炭气凝胶。     

间苯二酚-糠醛气凝胶的制备与表征

以氢氧化钠为催化剂和乙醇为溶剂合成间苯二酚-糠醛凝胶,经乙醇超临界干燥后得到有机气凝胶.间苯二酚与催化剂的摩尔比、间苯二酚与糠醛的摩尔比以及反应物总浓度等制备条件是影响有机气凝胶密度的主要因素.TEM和N2吸附法表明,有机气凝胶具有典型的三维纳米网络结构,网络颗粒约为10nm,平均孔径为7.8nm,其BET表面积和中孔体积分别为589 m2/g和1.106 cm3/g.     

新型纳米甲酚-甲醛气凝胶的制备及表征

首次以混甲酚（J）和甲醛（F）为原料,在NaOH(C)催化作用下制备混甲酚甲酸气凝（JF）,考察了制备条件与气凝胶性能的关系,并用TG,TEM,NMR,FT－IR,N2吸附表征了气凝胶结构,结果表明,JF气凝胶的密度随反应物浓度和催化剂含量的增加而增加,混;甲酚与甲酝酿落空－凝胶过程中形成的交联键是亚甲基醚键和亚甲基键,JF气凝胶是可孔约30nm,网络粒子直径约20nm,是典型的中孔材料,有机气凝热解可以得到炭气凝胶,在300－600度之间,JF气凝胶失重显著。     

酚醛-糠醛基炭气凝胶的合成和表征

用低软化点线性酚醛树脂和糠醛为原料以正丙醇为溶剂在盐酸催化下经溶液-溶胶-凝胶过程合成了醇凝胶，将其在石油醚（30℃-60℃）中，超临界条件250℃，7MPa下干燥1h获得酚醛-糠醛比的增加，炭气凝胶的大孔和中孔孔容分别减小，大孔孔容变化幅度较大，微孔孔容很小。TEM图片表明：炭气凝胶的纳米骨架随酚醛-糠醛比的增加而增大。     

Gender differences in publication productivity in psychology in India

An analysis of gender differences in psychology in India provides quantitative and qualitative assessment of R&D output contributed by psychologists with the indication of the trend of growth, skewness, relatedness, co-authorship pattern of productivity.     

Metrology in Chemistry in Germany

The system for Metrology in Chemistry in Germany is described. At the national standards level, a network of high-level chemistry institutes coordinated by the national metrology institute, PTB, provides the primary references for chemical measurements. A dissemination mechanism employs chemical calibration laboratories accredited within the framework of the German Calibration Service (DKD). They act as “multipliers” between the national standards level and the user level by providing the user with calibration means which are traceable to the SI via national standards. Traceability structures in clinical chemistry, electrochemistry, elemental analysis and gas analysis are described     

Natural radioactivity in drinking water in private wells in Finland

Natural radioactivity in drinking water was determined in population-based random study of 472 private wells. The mean concentrations of (222)Rn, (226)Ra, (234)U, (238)U, (210)Pb and (210)Po in drilled wells were 460, 0.05, 0.35, 0.26, 0.04 and 0.05 Bq l(-1), and in wells dug in the soil were 50, 0.016, 0.02, 0.015, 0.013 and 0.007 Bq l(-1), respectively. Approximately 10% of the drilled wells exceeded a radon concentration of 1000 Bq l(-1) and 18% a uranium concentration of 15 microg l(-1). The mean annual effective dose from natural radionuclides for a drilled well user was 0.4 mSv and 0.05 mSv for a user of a well dug in the soil. The effective dose arising from (222)Rn was 75% of the total of all natural radionuclides for drilled well users. As regards long-lived radionuclides, (210)Po and (210)Pb caused the largest portion of the effective dose. The dose arising from (238)U, (234)U and (226)Ra was only 8% of the total of all natural radionuclides.     

Natural radioactivity in drinking water in private wells in Finland

Radiation Protection Dosimetry     

Radioactivity in building materials in Iraq

Activity concentrations of (226)Ra, (232)Th and (40)K in 45 samples of different building materials used in Iraq were measured using gamma-spectroscopy system based on high-purity germanium detector with an efficiency of 40 %. Radium equivalent activity, air-absorbed dose rate, annual effective dose, external and internal hazard indices and alpha index due to radon inhalation originating from building materials were measured to assess the potential radiological hazard associated with these building materials. The activity concentrations of the natural radionuclides (226)Ra, (232)Th and 40K were found to range from below detection limit (BDL) to 223.7 ± 9, BDL to 93.0 ± 3 and BDL to 343.1 ± 12, respectively. Values of average radium equivalent activity, air-absorbed dose rate, indoor and outdoor annual effective doses, external and internal hazard indices and alpha index ranged from 6.5 to 124.9, 16.2 to 89.5 (nGy h(-1)), 0.08 to 0.44 mSv, 0.02-0.11 mSv, 0.09 to 0.53, 0.13 to 0.69 and 0.03 to 0.62, respectively. These values indicate a low dose. Therefore, the building materials used in the current study are quite safe to be used as building materials.     

Optische in situ Schichtdickenmessung in Bedampfungsanlagen. Optical in situ film thickness monitoring in coating systems

Optical film thickness monitoring is more precise than crystal monitoring. The optical measurement makes use of the fact that the intensity of a monochromatic light beam which is reflected on a film will change periodically with increasing film thickness. The measurement is performed at an exchangeable test glass that is positioned beside the substrates and is therefore coated in the same way as the substrates. The accuracy of cut‐off is achieved by a “fit” of a theoretical curve shape to the measured values. Order filters are used to ensure that, at a certain wavelength, higher deflection orders do not influence the measurement when a monochromator grating is used.