多孔SiO2凝胶玻璃中孔的控制与表征

较全面地讨论了用溶胶－凝胶法制备多孔ＳｉＯ２的研究中，关于孔的工艺控制及表征技术的发展状况，阐述了多孔ＳｉＯ２中纳米级孔在纳米材料科学。精细复合技术及其它相关领域中的重要意义。     

Al2O3和P2O5共同掺杂的SiO2玻璃的溶胶-凝胶法制备及其光学性质研究

以磷酸三乙酯、硝酸铝和正硅酸乙酯为原料，采用溶胶－凝胶法成功地制备了掺杂有Ａｌ２Ｏ３和Ｐ２Ｏ５的ＳｉＯ２玻璃。通过热分析和表面分析研究了凝胶向玻璃的转化过程，解释了热处理过程中的碳化现象，确定了热处理的适宜温度和时间。研究了掺杂有Ａｌ２Ｏ３和Ｐ２Ｏ５的ＳｉＯ２玻璃的光学性质。     

HF催化快速制备SiO2气凝胶

ＳｉＯ２气凝胶晃一种新型轻质纳米多孔泡沫材料,本文以正硅酸乙酯（ＴＥＯＳ）为原料,以乙醇为溶剂,以ＨＦ为催化溶胶－凝胶法快速制备出了ＳｉＯ２气凝胶。ＨＦ的加入大大加速了溶胶－凝胶反应速度,使凝胶时间减少至几分钟甚至更短;同时使凝胶温度降低至室温。ＢＥＴ及ＴＥＭ测试结果表明所制备的ＳｉＯ２气凝胶具有大比表面积（６７３．８ｍ＾２ｇ＾－１）、纳米多孔结构（骨架颗粒为几纳米,孔洞尺寸为５～３０ｎｍ）。     

溶胶—凝胶法制备SiO2气凝胶及其特性研究

本文以ＴＥＯＳ为原料，采用溶胶－凝胶法和超临界干燥工艺制备了轻质纳米多孔材料ＳｉＯ２气凝胶。研究了溶剂用量ｐＨ值对溶胶的凝胶化过程和最后制成的气凝胶的特性的影响。并用ＢＥＴ、ＸＲＤ、ＳＥＭ等实验手段研究了这些气凝胶的结构和一些基本物理现象。     

溶胶－凝胶法制备SiO_2气凝胶及其特性研究

本文以ＴＥＯＳ为原料，采用溶胶－凝胶法和超临界干燥工艺制备了轻质纳米多孔材料ＳｉＯ２气凝胶．研究了溶剂用量及ｐＨ值对溶胶的凝胶化过程和最后制成的气凝胶的特性的影响．并用ＢＥＴ、ＸＲＤ、ＳＥＭ等实验手段研究了这些气凝胶的结构和一些基本物理现象．     

纳米ZrO2/(1-n)SiO2-nAl2O3介孔复合作的制备与光致发光

采用溶胶－凝胶法和超临界干燥技术制备了（１－ｎ）ＳｉＯ２－ｎＡｌ２Ｏ３（ｎ＝０、０．０１、０．１）混合气凝胶体系，并以此作为载体，成功地将纳米ＺｒＯ２粒子组装到（１－ｎ）ＳｉＯ２－ｎＡｌ２Ｏ３介孔体系中，而形成纳米ＺｒＯ２／（１－ｎ）ＳｉＯ２－ｎＡｌ２Ｏ３介孔复合材料。光致发光光谱研究表明，室温下以３１６ｎｍ（３．９２ｅＶ）波长激发时，纳米ＺｒＯ２粒子５４０ｎｍ（２．３０ｅＶ）荧光峰，在介孔复合体     

溶胶—凝胶法制备的SiO2膜的结构与性质

本文用ＴＥＯＳ和硅溶胶作原料，用溶胶－凝胶法制备了无支撑体和有支撑体的ＳｉＯ２膜。用ＴＥＯＳ制得的无支撑体ＳｉＯ２膜，无１．７ｎｍ以上的微孔，由硅溶胶制得的无支撑体ＳｉＯ２膜平均孔径为７．５ｎｍ，且孔径分布集中，这种差异主要来自于由不同原料制备的溶胶，其聚合物分子具有不同的形态和生长模式。用ＴＥＯＳ作原料，在无过滤层的α－Ａｌ２Ｏ３多孔支撑体上制得了无大孔缺陷、厚约１５μｍ的ＳｉＯ２膜，膜对ＢＳＡ     

溶胶—凝胶法在玻璃表面涂膜

利用溶胶－凝胶法以浸涂方式在玻璃基体上制备了ＳｉＯ２薄膜，研究了某些工艺参数，尤其是加水量Ｒ（水与正硅酸乙酯的摩尔比）对薄膜形成过程及薄膜质量的影响，用ＳＥＭ观察了不同薄膜的微观结构，并结合ＳｉＯ２的溶胶－凝胶过程中聚合物的结构及涂膜特性进行了讨论。     

凝胶—SiO_2玻璃的转化与特性研究

本文研究了在不同ｐＨ条件下由ＴＥＯＳ－ＥｔＯＨ组成的水解溶液体系制备的凝胶的性质以及不同密度的干凝胶在玻璃转化过程中的特性。发现在５００℃以下干凝胶的微孔结构基本无变化。８００℃左右干凝胶发生碎裂。１０００℃左右低密度的干凝胶能转化为ＳｉＯ２玻璃。合成ＳｉＯ２玻璃与熔融ＳｉＯ２玻璃性质相似     

TiO2-SiO2复合半导体气凝胶制备及光催化活性研究

ＴｉＯ２－ＳｉＯ２复合半导体气交是一种新型纳米光催化氧化剂。本文以正硅酸乙酯、钛酸丁酯为原料,用溶胶－凝胶法经超临界干燥制备出了ＴｉＯ２－ＳｉＯ２复合半导体气凝胶。研究了ＴｉＯ２：ＳｉＯ２不同配比对溶胶－凝胶过程的影响;用ＢＥＴ、ＸＲＤ、ＳＥＭ、ＴＥＭ等测试方法对其结构进行了表征;以苯酚为探针考察了ＴｉＯ２－ＳｉＯ２复合半导体气凝胶的光催化氧化活性,并与普通锐钛矿型钛白粉光催化剂进行了对比结果表明     

Improvement in colloidal sol-gel SiO2 glass by attrition of aggregates in sols

The two-step colloidal sol-gel process for forming SiO₂ glasses has been improved by the use of attrition in ball mills consisting of borosilicate glass jars with fused SiO₂ cylinders as milling media. The average size of aggregates was reduced from more than 40 μm to less than 3 μm by milling up to 64 h depending on the hardness of the dried gel. Data on pore size distribution in the twice dispersed and dried gels show that 24 to 30 vol% of the pores are due to interaggregate spaces (pores whose sizes are larger than those represented by the average 16 nm pores between primary SiO₂ particles). These large pores cause a bimodal size distribution with the secondary peak at 3 to 4 μm with no milling and the position of the secondary peak decreases with milling until it is no longer resolved from the primary peak. The average size of the interaggregate pores is more than an order of magnitude smaller than the average size of the aggregates due to the efficiency of packing the aggregates of a broad size distribution. Milling is shown to markedly improve the transparency of the SiO₂ glass after sintering.     

Templated pores in hydrogels for improved size selectivity in gel permeation chromatography

The pore structures of cross-linked polyacrylamide gels can be altered by polymerizing in the presence of high concentrations of unreactive, micellar surfactant cosolutes which act as "templates". Removal of surfactant after polymerization is expected to leave pores with the approximate shape and dimensions of the surfactant micelles. A simple model was developed to simulate gel permeation chromatography (GPC) separations of globular proteins on templated gels. The model assumes that the partition coefficient for sieving of a protein is equal to the fraction of gel volume accessible to a sphere with a radius equal to the protein Stokes radius. The total gel volume is considered to include a fraction that is a conventional, random gel matrix and a remaining fraction contributed by templated pores. The pore size distribution of the conventional gel was estimated using the Ogston equation, which approximates the matrix as a random collection of long, thin, rigid fibers. Templated pores were assumed to have a Gaussian distribution of radii centered about some mean determined by the micelle radius. In comparison to conventional media, gels with templated pores are predicted to exhibit more sharply defined exclusion limits and improved resolution over a narrow size range centered on the mean templated pore size. Selectivity and resolution are expected to increase as the volume fraction of templated pores is increased and as the dispersion of templated pore radius is decreased. Small changes in template radius lead to large changes in the molecular weight range of optimal separation of globular proteins. It should be possible to create a series of GPC media that collectively offer high resolution over the molecular weight range of most globular proteins of interest.     

Influence of particulate morphology on microstructure and tribological properties of cold sprayed A380/Al_2O_3 composite coatings

In this study, three kinds of A380/Al_2O_3 composite coatings were prepared by cold spray(CS) using spherical, irregular and spherical + irregular shaped Al_2O_3 particulates separately mixed in the original A380 alloy powders. The influence of Al_2O_3 particulates' morphology on the microstructural characteristics(i.e.retention of Al_2O_3 content in coatings, coating/matrix interfacial bonding, pore size distribution and morphology etc.) and wear performance of the coatings was investigated by scanning electron microscopy(SEM), X-ray computed tomography(XCT) and 3-D optical profilometry. Results indicated that the spherical Al_2O_3 shows obvious tamping effect during deposition process. As a result, the interface showed a wavy shape while the matrix and particulates were mechanical interlocked with much improved adhesion. In addition, the porosity of the coating was minimized and the pores exhibited curved spherical structure with reduced dimensions. The irregular Al_2O_3 particles predominantly displayed the embedding effect together with fragmentation of Al_2O_3 particulates. Consequently, poor coating/matrix interfacial bonding, high porosity and the formation of angular-shaped pores were resulted in the coating. Dry sliding wear tests results revealed that the wear resistance of the coating is directly related with the retained content of Al_2O_3 in the coating. The coating containing irregular Al_2O_3 particulates displayed superior wear performance with its wear rate one seventh of that of the pure A380 alloy coating. The coating containing both kinds of Al_2O_3 particulates showed mixed characteristics of above two kinds of Al_2O_3 composite coatings.     

The importance of dehydration in determining ion transport in narrow pores

The transport of hydrated ions through narrow pores is important for a number of processes such as the desalination and filtration of water and the conductance of ions through biological channels. Here, molecular dynamics simulations are used to systematically examine the transport of anionic drinking water contaminants (fluoride, chloride, nitrate, and nitrite) through pores ranging in effective radius from 2.8 to 6.5 Å to elucidate the role of hydration in excluding these species during nanofiltration. Bulk hydration properties (hydrated size and coordination number) are determined for comparison with the situations inside the pores. Free energy profiles for ion transport through the pores show energy barriers depend on pore size, ion type, and membrane surface charge and that the selectivity sequence can change depending on the pore size. Ion coordination numbers along the trajectory showed that partial dehydration of the transported ion is the main contribution to the energy barriers. Ion transport is greatly hindered when the effective pore radius is smaller than the hydrated radius, as the ion has to lose some associated water molecules to enter the pore. Small energy barriers are still observed when pore sizes are larger than the hydrated radius due to re‐orientation of the hydration shell or the loss of more distant water. These results demonstrate the importance of ion dehydration in transport through narrow pores, which increases the current level of mechanistic understanding of membrane‐based desalination and transport in biological channels.     

Assessment of in-situ alkali-silica reaction (ASR) development of glass aggregate concrete prepared with dry-mix and conventional wet-mix methods by X-ray computed micro-tomography

A recent study showed that concrete products prepared with the dry-mix method have better alkali-silica reaction (ASR) resistance than that prepared by the wet-mix method. But the mechanism of ASR in dry-mix glass concrete remains unclear. Meanwhile, the techniques such as Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) cannot reflect the in-situ evolution of the microstructure with the progress of the ASR. In this study, two common casting methods, the wet-mix and dry-mix methods, were adopted to prepare the glass concrete. The non-destructive X-ray computed micro-tomography (X-ray μCT) technique was applied to observe the pore geometries of both the wet-mix and dry-mix glass concrete, to determine their porosities using 3D volumes and to investigate the generation of cracks during ASR development. This study firstly observed the irregular pore geometry of the glass concretes by quantitatively comparing the pore geometries using the sphericity developed by Wadell for both dry-mix and wet-mix glass concrete. The test results of the porosity measured by 3D volume showed that the porosity of the dry-mix glass concrete decreased after the ASR test. However, no obvious change was observed in the porosity of the wet-mix glass concrete. This change may be attributed to the large pores in the dry-mix glass concrete which can accommodate the ASR gel. Through the in-situ observation using 3D X-ray μCT, no new cracks were generated in the dry-mix glass concrete during the progressive development of ASR. On the contrary, new cracks which were filled with ASR gel were densely distributed in the wet-mix glass concrete, which led to failure of the concrete matrix. This is because the expansive ASR gel formed could not be accommodated by the limited pore space in the wet-mix glass concrete, and the swelling pressure of ASR gel induced new cracks in the wet-mix glass concrete.     

多孔PZT95/5铁电陶瓷的机械性能和铁电性能研究

采用添加造孔剂的方法制备多孔锆钛酸铅(PZT95/5)铁电陶瓷, 研究了孔结构包括孔隙率、孔径及孔形状对多孔PZT95/5陶瓷机械性能和电性能的影响及机理, 并揭示多孔PZT95/5陶瓷微观结构、机械性能和铁电性能的内在联系。研究表明: 孔隙率的增加降低了多孔PZT95/5陶瓷的声阻抗, 改善了陶瓷与封装材料的声阻抗匹配. 孔隙率增加, 多孔PZT95/5陶瓷的屈服应力和剩余极化强度降低, 矫顽场强增大。孔结构对多孔PZT95/5陶瓷屈服应力的影响可由应力集中理论解释; 多孔PZT95/5陶瓷剩余极化强度随孔结构的变化可用内应力结合空间电荷理论加以解释。     

Electrolyte-doped ice as a platform for atto- to femtoliter reactor enabling zeptomol detection

Rapid freezing of an aqueous electrolyte in liquid nitrogen provides an effective way to fabricate uniform-sized liquid pores with the radius ranging from 0.15 to 3 μm (<1% rsd), corresponding to atto- to femtoliter volumes. The size of liquid pores depends on the temperature, and the concentration and type of a salt incorporated into an original aqueous solution. When the concentration of a salt is kept lower than 20 mM, liquid pores are discretely distributed in an ice matrix. Unlike usual small spaces accommodating liquid water, the pore size is tunable and continuously variable by changing the above experimental parameters. The liquid pore has been utilized as microreactors, in which the fluorescent complexation between Mg(2+) and 8-hydroxyquinoline-5-sulfonic acid (HQS) is studied. Under the optimum condition, fluorescence from Mg(2+) ions in the zeptomol level confined in a liquid pore is detected.     

颗粒尺寸对SiC_P预制体孔洞三维特征的影响

通过模压成型和高温烧结制备了不同SiC_P颗粒尺寸(20、50、100和150μm)的预制体,采用高分辨率(~1.0μm)三维X射线断层扫描和三维孔隙网络结构模型,研究了SiC_P颗粒尺寸对预制体孔洞三维特征的影响。结果表明:随着SiC_P颗粒尺寸的增大,淀粉的间隙膨胀作用逐渐减弱,而颗粒堆积间隙逐渐增大。当SiC_P颗粒尺寸由20μm增大到100μm时,截面孔洞形貌更加平齐,面孔隙率均值减小,孔洞体积的空间分布均匀性和连通性都变差,孔洞和喉道的平均尺寸增大,而小尺寸孔喉数量减少,平均孔洞配位数减小;当颗粒尺寸继续增大至150μm时,间隙被更多较小尺寸颗粒填充,且颗粒表面残留网状粘结剂,都大大降低了孔洞体积的空间分布均匀性和连通性,使小尺寸孔喉数量增多,平均孔洞配位数增大。     

Pore exclusion chromatography-inductively coupled plasma-mass spectrometry for monitoring elements in bacteria: a study on microbial removal of uranium from aqueous solution

The interstitial spaces between spherical particles in a packed column can act as a sieve that passes microorganisms below a certain size. If the bed is a perfusion-type material (containing a binary distribution of large and small pores), colloidal-size microorganisms are subject only to pore exclusion, while all molecules are subject to size exclusion among the various pores. Thus, microorganisms elute first, followed by macromolecules, and then small molecules. Coupling this separation method to an ICP magnetic sector mass spectrometer provides a sensitive, direct means to study the microbial uptake of heavy metals (i.e., uranium) from their surrounding environments. Multiple metal ions can be monitored in the microorganism and in the surrounding solution. In this way, definitive information can be provided for the remediation of radioactive waste sites. The effect of uranium on microbial growth is also discussed.     

Processing of magnesium foams by weakly corrosive and highly flexible space holder materials

High-quality magnesium foams were fabricated by an infiltration technology using tailor-made salt–flour mixture space holders. The pore structures and mechanical properties of space holder particles as well as the resultant foam production with spherical pores were characterized in the present study. The particles after high-temperature sintering dissolved rapidly in water due to their porous structures, guaranteeing the weak corrosion and high-purity of magnesium foams. The spherical pores foams exhibited usual stress–strain behaviors and nearly isotropic properties. The yield strengths of the foams increased with the decrease of sample porosity, and the relative mechanical properties of foams were mostly dependent on their relative densities, which obeyed a power law relation. Moreover, porous magnesium materials with tunable pore structures could be fabricated owing to the flexible forming features of salt–flour mixture, showing great application prospects in bone implant material field.