KDP晶体中散射颗粒形成机理的研究

本文在不同掺杂条件下,采用传统降温法生长了KDP晶体,利用超显微和透射电镜对KDP晶体中的散射颗粒进行了观察,在此基础上对其进行了分类.实验结果表明,不同种类散射颗粒的形成源于溶液中杂质与晶体化学键作用力的不同,造成这一结果的根本原因与KDP晶体的结构特性密切相关.     

泥浆中磨粒对Al2O3增强Y-TZP复合陶瓷材料耐磨性的影响

在不同磨粒的5;NaOH泥浆中,采用销-盘式摩擦磨损试验机考察了磨粒对氧化铝增强四方氧化锆多晶陶瓷材料(ADZ)耐磨性的影响进行了研究.结果表明:尖锐SiO2磨粒对ADZ复合陶瓷材料磨损的影响要比球形SiO2磨粒严重得多,磨料硬度是影响陶瓷材料磨损率的重要因素,磨损率随磨粒硬度的提高而增大.在不同形状的SiO2磨粒的泥浆中,ADZ陶瓷材料的主要磨损机理为塑性变形和微犁削.在高硬度Al2O3磨料的泥浆中,ADZ陶瓷材料磨损表面以断裂机制占主导地位.     

Growth and defect studies of CdTe particles

The paper reports the epitaxial growth of cadmium telluride (CdTe) particles by thermal deposition on cleaved planes of (001)NaCl and (001)KBr. Using high resolution transmission electron microscopy and electron diffraction it was shown that CdTe particles could have different orientation and phase (cubic or hexagonal) depending on the substrate temperature. Their most common defects are twins and stacking faults.     

Investigation on growth defects in Pb(Zn1/3Nb2/3)O3‐PbTiO3 crystals

Relaxor ferroelectric crystal (1‐x)Pb(Zn_1/3Nb_2/3)O₃‐xPbTiO₃ (PZNT) with x=0.07 (PZNT93/7) has been grown by the vertical Bridgman method from the high temperature solution of PZNT‐PbO system. The growth defects, such as nucleation core, inclusions, boundaries and particles, were investigated by optical microscope and scanning electron microscope. Sub‐structures were found in the flux inclusions and the lack of ZnO component in PZNT crystals was attributed to the existence of ZnO particles in the inclusions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Single-cell Trapping Using Microwell Arrays Fabricated from Self-assembled Particle Monolayers

This paper proposes a self-assembly fabrication method of microwells and investigates the effect of surface treatment for the cell trapping. The target cell is unicellular cyanobacterium Synechocystis sp. strain PCC 6803, which has been widely investigated as a model organism for photosynthesis. The self-assembly monolayer of polystyrene particles (3.0 μm diameter) etched by reactive-ion etching was used as a template of polydimethylsiloxane molds. The well diameter in the mold could be controlled by the etching time. The cell-trapping efficiency was discussed with the viewpoint of hydrophilically treatment and poly-L-lysine treatment on the well arrays.     

PEG对纳米BaMgAl10O17:Eu2+蓝色荧光粉颗粒形貌及其发光性能的影响

以聚乙二醇(PEG)为改性剂,采用溶液燃烧法成功制备了准球形的PDP用BaMgAl10O17:Eu2+(BAM)蓝色荧光粉.通过X射线粉末衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)以及荧光光谱对获得的试样进行了表征.结晶表明,获得的BAM荧光粉颗粒为准球形、颗粒尺寸为20～40nm.当PEG的分子量(MW)为10000且质量百分比浓度为5.0;时,能获得最佳形貌和最高发光强度的BAM蓝色荧光粉.     

Micronization of the officinal component baicalin by SEDS‐PA process

Application of micronizing technologies in processing Chinese herbal medicines is very important to improve the forms of prepared Chinese herbal medicines and promote their therapeutic efficacy. Baicalin, a major active component of the typical Chinese herb medicine Scullateria baicallensis Georgi, was micronized using the Solution Enhanced Dispersion by Supercritical fluids though Prefilming Atomization (SEDS‐PA) process with the aim of evaluating the efficiency of applying supercritical fluid precipitation technologies in Chinese herb medicine. This study has shown that acicula or rod‐like baicalin crystals with Particle Size (PS) of about 20×100 μm were successfully micronized by the SEDS‐PA process to long rod‐like, twisted fiber‐like or fibrous net‐like microparticles with PS of 0.1‐2.2 μm in width within the range of experiments performed. It was found that a substantial reduction of baicalin microparticles' sizes could lead to a marked increase of adhesions among them and subsequent microparticles agglomeration. With the increase of supercritical CO₂ flow rate and the decrease of solution concentration and solution flow rate, smaller and much more agglomerated microparticles were obtained. Increasing pressure led to formation of smaller microparticles. A larger tendency of particles agglomeration was produced at a higher temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and morphology control of surface functionalized nanoscale yttrium aluminum garnet particles via supercritical hydrothermal method

Organic-functionalized nanoscale yttrium aluminum garnet (YAG) particles were synthesized via a simple rapid supercritical hydrothermal method in the presence of oleylamine and oleic acid as organic surface modifiers. The presence of the organic molecules resulted in the various morphologies of the produced YAG particles, including cubic, spherical and chainlike structures. Because of their hydrophobic surface character, as-synthesized particles were dispersible in organic solvents.     

Elongation and spheroidization of phase-separated particles in glass

When certain phase-separated glasses are elongated by redrawing near their softening point, the spherical second-phase particles are found to elongate as well. The elongation process is discussed, and the conditions under which high particle elongations are possible are estimated. Annealing the glass tends to spheroidize cylindrical-shaped particles by an ‘ovulation’ process. The spacing of the resulting spheroidal particles is compared with theoretical predictions.     

Physical boundaries within aggregates – differences between amorphous,para‐crystalline,and crystalline Structures

The structural properties of finely divided inorganic materials such as metal and metalloid oxides, silicates or carbonates of both synthetic and natural origin are compared by means of electron microscopy and tomography. The structure of the outer surfaces of various compact or compacted agglomerates may suggest some striking similarities between various amorphous silica on the one hand and crystalline titania and alumina on the other however the details of the interior fine structure are completely different. Inside of the crystalline aggregates of, for example, alumina and titania distinct grain boundaries between the inter‐grown primary crystallites exist. Also physical boundaries between different solid phases and crystalline/amorphous transitions in core/shell structures can occur. No physical grain or phase boundaries were found inside of synthetic amorphous silica or para‐crystalline carbon black thus, the aggregate is the constituent particle. Synthetic amorphous silica from different production technologies (fumed/pyrogenic, precipitated, aerogel, gel) may exhibit different macro‐morphology but distinct similarities of the amorphous silica networks. Computational studies on silica and titania underline the stability of constituent particles and aggregates as observed by means of TEM after dispersing the original materials by ultra‐sonication.     

Synthesis,morphology and structure of the dense (Y1‐xEux)2O3 spherical shape particles

The method to decrease of the porosity (densification) of crystalline spherical particles of the solid substitution solution, obtained by the method of precipitation from aqueous solution followed by low temperature crystallization of the amorphous intermediate product was proposed. The comparative analysis of morphology and structure of the particles before and after densification have been carried. It has been established that porosity of (Y_1‐xEu_x)₂O₃ particles has decreased 5 times compared to their initial state. It has been shown that densification process of the (Y_1‐xEu_x)₂O₃ spherical particles changes their morphology and structure: the size of the crystals doubles, the number and area of crystalline boundaries decrease, the intercrystalline spaces, which forming pores, are almost absent.     

单分散SiO2微球的制备及疏水改性研究

采用改进的凝胶-溶胶法制备了200~800 nm的单分散SiO2微球,并通过真空冷冻干燥法得到不易团聚的单分散SiO2粉体,采用乙醇超临界方法对制备的SiO2微球进行疏水改性.通过扫描电镜和氮吸附-脱附分析仪对SiO2微球的表面形貌、粒径以及孔径分布进行表征;用傅里叶红外变换测试和测量接触角对疏水改性的SiO2微球进行分析.结果表明SiO2微球粒径随二次加入TEOS体积增加呈先增大后减小.经过乙醇超临界处理,SiO2微球表面成功接枝上了疏水烷基,微球尺寸越小,疏水性越好,其接触角高达149°,单次SiO2微球处理量对结果无明显影响.采用本方法可以单次处理12 g以上的SiO2微球,接触角均在140°左右,可充分满足实验室使用需求.经过真空冷冻技术和乙醇超临界技术得到疏水单分散SiO2微球粉体,具有不易团聚及单分散性良好的优点,能够作为胶体晶体原料和三维有序材料(3-DOM)模板剂进行广泛应用.     

Synthesis,characterization and optical properties of ZnO nanoparticles with controlled size and morphology

Zinc oxide monodispersed nanoparticles were synthesized using a modified polyol process without any requirement to use a catalyst or calcination step at high temperature. The morphology and the size of the resulting oxide particles were adjusted by using several synthesis parameters (temperature, alkaline ratio, hydrolysis ratio, etc.). The increasing of the alkaline ratio results in a great change of the elaborated particles morphology that evolved from irregular and anisotropic forms (conical, nanorod-like and elliptical) to spherical one. A growth mechanism of these particles was proposed on the basis of zincite crystal structure and the morphology evolution as a function of the synthesis parameters. The photoluminescence spectra show UV-excitonic and visible emission bands. The strongest intensity of the visible emission was observed in nanorod-like particles, which implies an increased fraction of oxygen vacancies in this sample. The rod-like particles with 1 μm length show the dominant UV-emission, which evidences their improved stoichiometry.     

Influence of size on the supercooling in the crystallization of small particles in Bismuth island films

There has been measured the crystallization temperature of supercooled Bi particles versus their size in the 3–100 nm range in island films on amorphous carbon substrates. Crystallization temperature is found to decrease with particle size decreasing and the supercooling vanishes for particles of 2–3 nm in diameter. The results obtained are analyzed in the frame of the classic theory of crystallization.     

Dissolution retardation of solid silica during glass-batch melting

During glass-batch melting, solid silica (quartz) usually dissolves last. The measured rate of dissolution, while the temperature was increasing at a constant rate, was compared with the hypothetical diffusion-controlled volume flux from regularly distributed particles through concentration layers of a uniform thickness. The actual rate was up to two orders of magnitude lower than that of the “ideal” case, revealing a progressive inhibition of silica dissolution. As a measure of this retarded dissolution, we introduced a retardation factor defined as a ratio of the actual and “ideal” dissolution rates measured as the volume flux at the melt-particle interface. The severe inhibition of silica dissolution has been attributed to the irregular spatial distribution of silica particles that is associated with the formation of nearly saturated melt on a portion of their surfaces. Irregular shapes and unequal sizes of particles also contribute to their extended lifetime.     

Magnetic properties of ferromagnetic ultrafine particles prepared by vacuum evaporation on running oil substrate

Ultrafine particles of ferromagnetic metals (Fe, Co and Ni) were prepared by the vacuum evaporation onto a running oil substrate. Particles thus obtained were suspended in the oil and their average diameter was about 25 Å. An electron diffraction analysis indicated that the particles were oxidized and the main component was Fe₃O₄, CoO and NiO for Fe, Co and Ni fine particles, respectively. From magnetic measurements in the temperature range between 4.2 and 300 K, the main magnetic behavior of the fine particles can be explained in terms of the superparamagnetism or superantiferromagnetism. Furthermore, it was concluded that the Fe₃O₄ particles may be covered with several atomic layers of α-Fe₂O₃. For CoO and NiO particles, existence of an imperfect oxide structure was required besides the main components in order to explain the magnetic behavior.     

Crystal structure and habit of fine metal particles formed by gas-evaporation technique; bcc metals (V,Fe, Cr,Mo and W)

Fine particles of several kinds of bcc metals were prepared by evaporation in an argon atmosphere. They were collected at various growth zones in the smokes and their structures and habits were studied by electron microscopy. Vanadium and iron particles grown in all zones have the ordinary bcc structure. However, chromium and molybdenum particles grown in the inner part of the smokes have the bcc structure, and those in the outer part have the A-15 type structure. Habits of particles with the bcc structure can be generally described in terms of rhombic dodecahedra truncated by six (100) faces with various degrees of truncation from 0 to 100%. The truncated rhombic dodecahedron is a common habit to the bcc metals, though the degree of truncation is dependent on the metal. For vanadium it varies from zone to zone systematically. Molybdenum particles of rounded cube and {211} icositetrahedron are found to have the A-15 type structure in addition to the well known {211} icositetrahedron and rhombic dodecahedron found in chromium.     

Electron microscopic study on nucleation and growth of silver particles in a thin glass film

Nucleation and crystal growth of silver particles in a thin glass film of Li₂O·2.6SiO₂ glass containing 0.1 wt% of Ag₂O were observed by transmission electron microscopy and studied by an electron diffraction technique. Anomalies of the image contrast which appeared in the heat-treated specimens were explained to be caused by phase separation of the glass. Nucleation of silver particles was found to occur on the surface of the phase-separated silica-rich droplets. As the silver particles grew, their shape changed into that of a regular cube which was covered with a thin diffusion layer of silver ions about 50 Å in thickness. The presence of this thin layer and the cubic shape suggest that the growth of silver particles proceeds by a layer-by-layer growth mechanism.     

Periodical temperature changes and the behaviour of individual crystals

The influence of periodical temperature (or supersaturation) changes on the behaviour of individual crystal particles immersed in their solution is studied.     

Investigation of the kinetics of Ga–Pb melt separation using an acoustic method

Using a phase pulse method for ultrasound velocity measurement, the kinetics of meniscus movement in the course of the hypermonotectic Ga–30 at.%Pb and Ga–40 at.%Pb melts separation was measured. Assuming that the process is limited by sedimentation of Pb-rich particles, their size distribution at various temperatures was determined. The time dependences of the volume fraction of dispersed particles and degree of sedimentation were calculated based on the experimental results. It was shown that coagulation of the particles is sufficient for surface energy reduction in the phase separation process.