Bi12SiO20晶体下降法生长及Pt包裹缺陷研究

采用改进的坩埚下降法成功生长了硅酸铋Bi12SiO20(BSO)单晶,探讨了工艺参数对晶体生长的影响.用电子探针方法研究了硅酸铋晶体中的铂金包裹体及其相关缺陷.铂金包裹物的尺寸一般在30μm～5mm之间.包裹物经常导致晶体开裂,使成品率大为降低.铂坩埚中的杂质是导致坩埚受侵蚀的主要原因,通过延长铂坩埚熔炼时间和适当降低晶体生长炉温,可明显减少铂包裹体及其相关缺陷.通过优化生长工艺,获得了尺寸为50mm×35mm×35mm的优质BSO单晶.     

A Study of Ca-Mg Silicate Crystalline Glazes--An Analysis on Forms of Crystals

In the study on Ca-Mg silicate crystalline glazes, we found some disequilibrated crystallization phenomena,such as non-crystallographic small angle forking and spheroidal growth, parasitism and wedging-form of crystals, dendritic growth, secondary nucleation, etc. Those phenomena possibly resulted from two factors:(1) partial temperature gradient, which is caused by heat asymmetry in the electrical resistance furnace,when crystals crystalize from silicate melt ; (2) constitutional supercooling near the surface of crystals. The disparity of disequilibrated crystallization phenomena in different main crystalline phases causes various morphological features of the crystal aggregates. At the same time, disequilibrated crystallization causes great stress retained in the crystals, which results in cracks in glazes when the temperature drops. According to the results, the authors analyzed those phenomena and displayed correlative figures and data.     

A Study of Ca-Mg Silicate Crystalline Glazes ——An Analysis on Forms of Crystals

In the study on Ca-Mg silicate crystalline glazes, we found some disequilibrated crystallization phenomena,such as non-crystallographic small angle forking and spheroidal growth, parasitism and wedging-form of crystals, dendritic growth, secondary nucleation, etc. Those phenomena possibly resulted from two factors:(1) partial temperature gradient, which is caused by heat asymmetry in the electrical resistance furnace,when crystals crystalize from silicate melt; (2) constitutional supercooling near the surface of crystals. The disparity of disequilibrated crystallization phenomena in different main crystalline phases causes various morphological features of the crystal aggregates. At the same time, disequilibrated crystallization causes great stress retained in the crystals, which results in cracks in glazes when the temperature drops. According to the results, the authors analyzed those phenomena and displayed correlative figures and data.     

高氯酸镁吸收重量法测定铁矿石中结晶水的含量

建立了铁矿石中结晶水含量的测定方法.利用铁矿石中结晶水高温分解的特性,采用高纯氩气为载气,试样在1 000℃管式炉中加热,结晶水随载气逸出,由装有无水高氯酸镁的吸收管吸收后称量,计算出铁矿石中结晶水的含量.测定结果的相对标准偏差(RSD)小于3％(n=6),加标回收率在95％～ 104％之间.     

Growth, Band Structure and Optical Properties of LiSrBO3 Crystal

The bulk crystal of LiSrBO3 (8.39 g) with a size of 21mm×20mm×15mm was grown by high temperature solution growth method. The relationship between growth habit and crystal structure was discussed. The transmission spectrum shows an UV absorption edge at about 300 nm. The melting temperature of this crystal was determined to be 942 ℃ by DTA-TG measurement. The band structure of the LiSrBO3 crystal was studied by means of the first principle method. An indirect band gap was found to be about 4.0 eV,and a low dielectric constant was estimated to be about 1.9 in terms of theoretical results.     

Temporal Variations in Gas Temperature in an Atomization Stage of Cadmium and Tellurium Evaluated by Using the Two-line Method in Graphite Furnace Atomic Absorption Spectrometry

In order to discuss the atomization process of an analyte element occurring in a graphite furnace for atomic absorption spectrometry, we measured variations in the characteristic temperature with the progress of an atomization stage, by using a two-line method under the assumption of a Boltzmann distribution. For this purpose, iron was chosen as the analyte element. Also, the atomic absorption of two iron atomic lines, Fe I 372.0 nm and Fe I 373.7 nm, was simultaneously monitored as a probe for the temperature determination. This method enables variations in the gas temperature to be directly traced, yielding a temperature distribution closely related to the diffusion behavior of the probe element in the furnace. This temperature variation was very different from the furnace wall temperatures, which were monitored in conventional temperature control for atomic absorption spectrometry. Correlations between the gas temperature and the charring/atomizing temperatures in the heating program of the furnace were investigated. The atomization of cadmium and tellurium was also investigated by a comparison between the gas temperature with the wall temperature of the furnace. The atomic absorption of cadmium or tellurium appeared to be apart from the absorption of iron while the gas temperature was still low. Therefore, the analyte atoms could be atomized through direct contact with the wall of the graphite furnace, which has a much higher temperature compared to the gas atmosphere during atomization. Their atomization would be caused by conductive heating from the furnace wall rather than by radiant heating in the furnace.     

Eu2+掺杂KCaCl3晶体的生长及发光性能

通过坩埚下降法生长出不同物质的量分数Eu²⁺掺杂的KCa_1-xEu_xCl₃(x=0.005、0.01、0.02、0.03、0.05)单晶,并对晶体进行了X射线粉末衍射、热重、透过率、光致发光光谱、衰减时间、X射线激发发射光谱等测定。通过相图及结构分析,判断出该晶体为一致熔融化合物,并得出其为正交结构,晶胞参数为a=0.75604 nm,b=1.04823 nm,c=0.72657 nm,空间群为Pnma(62)。在紫外光的激发下,晶体在434 nm左右有一个宽的发射峰,对应于Eu²⁺的4f⁶5d¹→4f⁷跃迁;光致衰减时间1.473μs,晶体在X射线激发下的发光强度随Eu²⁺离子浓度增加而增强。     

Synthesis of nanocrystals via microreaction with temperature gradient: towards separation of nucleation and growth

By utilizing the symmetrical temperature distribution in a tube furnace chamber, a capillary microreactor was designed with the microchannel passing two well-controlled, stable temperatures in steep temperature gradients. The two-temperature microreator, first developed and implemented by this research team, provides an opportunity to separate the nucleation and growth of semiconductor nanocrystals, leading to better control of nucleation and growth kinetics. For the synthesis of CdSe nanocrystals as a model system, we demonstrated the improved size uniformity achieved by the two-temperature approach, confirming the success of the use of high temperature to burst nucleation and low temperature to promote growth.     

Interaction of Antifreeze Proteins with Hydrocarbon Hydrates

Recombinant antifreeze proteins (AFPs), representing a range of activities with respect to ice growth inhibition, were investigated for their abilities to control the crystal formation and growth of hydrocarbon hydrates. Three different AFPs were compared with two synthetic commercial inhibitors, poly‐N‐vinylpyrrolidone (PVP) and HIW85281, by using multiple approaches, which included gas uptake, differential scanning calorimetry (DSC) temperature ramping, and DSC isothermal observations. A new method to assess the induction period before heterogeneous nucleation and subsequent hydrate crystal growth was developed and involved the dispersal of water in the pore space of silica gel beads. Although hydrate nucleation is a complex phenomenon, we have shown that it can now be carefully quantified. The presence of AFPs delayed crystallization events and showed hydrate growth inhibition that was superior to that of one of the benchmark commercial inhibitors, PVP. Nucleation and growth inhibition were shown to be independent processes, which indicates a difference in the mechanisms required for these two inhibitory actions. In addition, there was no apparent correlation between the assayed activities of the three AFPs toward hexagonal ice and the cubic structure II (sII) hydrate, which suggests that there are distinctive differences in the protein interactions with the two crystal surfaces.     

有机溶剂热生长技术合成碱金属硒化物Cs2PdSe16及其热稳定性的研究

以PdCl₂,Cs₂Se及Se为原料在乙二胺溶液中用有机溶剂热生长技术(SolvothermalTechnique)制备碱金属硒化物Cs₂PdSe₁₆,用单晶X射线衍射技术对其进行晶体结构分析.Cs₂PdSe₁₆属四方晶系,空间群为P4b₂,晶胞参数为:a=1.2601(2)nm,b=1.2601(2)nm,c=0.7044(1)nm,V=1.1185(3)nm₃,Z=2,R=0.0514,wR=0.0991.该晶体由相互交错的[CsPd(Se₄)₂]^-层和[CsSe₈]⁺层组成.热分析结果表明,其分解温度为334℃.     

Phase diagram of the system KF-K<Subscript>2</Subscript>TaF<Subscript>7</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

As an asymmetric organic molecular crystal, p-N,N-dimethylaminobenzaldehyde (DAB) exhibits peculiar optical property. It was first grown by solution technique adopting slow evaporation method at room temperature using CCl₄ as growth medium. The solubility of DAB increases with temperature. Good quality transparent crystals of p-N,N-dimethylaminobenzaldehyde were carefully collected and subjected various characterization studies such as UV, FTIR, ¹H and ¹³CNMR spectral studies and thermal (TG-DTG) studies to determine the purity and application oriented properties of the grown crystals.     

Statistical Theory of Stable and Meta stable Transition for Crystallization and Fusion of Homopolymers ⅣStatistical Dynamics of Polymeric Crystallization by Molecular Segregation-Division of Crystal Grow-rate Regimes and Their Temperature and Grown Mechan

First a short review on the crystal growth theories and the experimental data was presented. Then a set of quantitative expressions for the size growth-rate of crystals produced by four different micro-growth mechanisms (folding, extending and two types of combination for folding and extending) was derived by a general evaluating method. A set of quantitative expressions for the correlations between the crystal size growth-rate and the product of crystalline temperature and super-cooling temperature at four different micro-growth mechanisms was obtained. Three growth-rate regimes were divided, the variations of the morphology for the crystals in the three types of regimes with the crystalline and super-cooling temperatures were discussed. They showed that these theoretical correlations between the morphology of crystals and the crystalline and super-cooling temperatures are in agreement with the later important observation on the lateral shape of crystals.     

Influence of chain structure on crystal polymorphism of poly(lactic acid). Part 1: effect of optical purity of the monomer

The influence of chain structure on crystal polymorphism of poly(lactic acid) (PLA) with high l-lactic acid content (97.8–100 %) is detailed in this contribution. Upon usual processing conditions of PLA, only α and α′ crystals grow, which makes these two polymorphs of major interest for research. The two crystal modifications have similar chain packing, which complicates their quantitative analysis by diffraction methods. The two crystal modifications are instead easily identified by analysis of the crystallization kinetics, which varies not only with temperature, but also with crystal polymorphism. The dependence of the rate of ordering on temperature shows two distinct maxima around 105–110 and 120–125 °C, which are related to growth of α′ and α crystals, respectively. Addition of d-lactic acid co-units leads to a decrease of the overall crystallization rate of PLA, as well as of the rate of spherulite growth (G) of both the crystal modifications. The relative crystallization rates of α and α′ forms are highly affected by stereoregularity, especially in the PLA grades that have a high crystallization rate. A high d-lactic acid content results not only in an overall slower crystal growth, but also in a varied temperature range where each of the two crystal modifications prevail, with a shift to lower temperatures of both the maxima of the G vs. temperature plots, indicating that inclusion of d-lactic acid units in the PLA chain affects crystallization rate of both α and α′ crystal modifications.     

Statistical Theory of Stable and Meta-stable Transition for Crystallization and Fusion of Homopolymers Ⅵ. Statistical Dynamics of Polymeric Crystallization by Molecular Segregation-Dependence of Crystal Growth Rate on the Grown Mechanism and Concentratio

First a short review on the dependence of crystal growth rate on the growth mechanism and concentration is present. Based on the structural model of micronucleus and crystal constituent chains, and the feature of statistical dynamics for polymeric crystallization by molecular segregation, a general method for characterizing number the growth rate and micro crystal constituent chains and the size growth rate for crystals was proposed. According to this method, a set of quantitative expressions for correlating the growth rate in number and size with the four types of growth (folding, extending and combination of folding and extending), the crystalline temperature and the crystalline concentration was derived. Then combined the concentration index is combined with the fraction of conformation for segments, a new correlation of the concentration index to the temperature of crystallization and the flexibility of polymeric chain is theoretically obtained. The dependences of the index on the different types of growth are also studied. Finally the relationships between the growth rate for crystals and the concentration of solution were verified by the experimental validating the predictions made by the theory.     

Synthesis and Characterization of ZnO Nanowires

Zinc oxide is a wide bandgap (3.37 eV) semiconductor with a hexagonal wurtzite crystal structure. ZnO prepared in nanowire form may be used as a nanosized ultraviolet light-emitting source. In this study, ZnO nanowires were prepared by vapor-phase transport of Zn vapor onto gold-coated silicon substrates in a tube furnace heated to 900 ?C. Gold serves as a catalyst to capture Zn vapor during nanowire growth. Size control of ZnO nanowires has been achieved by varying the gold film thickness…     

New concept of solute distribution around a diffusive crystal-solution interface of a binary Lennard-Jones mixture from the viewpoint of molecular dynamics

Directional crystallization from a binary mixture was performed by pseudo-NpT ensemble molecular dynamics. The initial crystal phase having a face-centered-cubic (fcc) structure grew toward the whole cell according to the temperature gradient in the universal cell. The growing crystal phase was not planar even though the solute molecules grew in two-dimensional coordinates because the solvent molecules disturbed the crystallization of the solute molecules at the diffusive crystal-solution interface. This represented the essential phenomenon of solute distribution during crystallization. Consequently, the growing crystal phase still contained solvent molecules having a liquid structure. The time change of the solute composition in the early phase of crystal growth showed an increase in solute composition as the time step proceeded. The resulting solute composition in this early phase was considered at different temperature gradients in the universal cell and it increased as the temperature of the initial crystal-solution interface increased. A new distribution coefficient model was proposed as a function of the difference between the local solute composition and bulk solute composition in the solution around the crystal-solution interface. The impurity-solvent distribution coefficient could be represented by the new model for faster growth of the lower temperature's initial interface. As regards a better distribution coefficient, there was found to be a very dilute solution phase over the crystal phase. The new variable "distribution rate" instead of the ambiguous variable "growth rate" was considered as a function of temperature gradient in the universal cell.     

Molecular mechanism leading to memory effect of mesomorphic isotactic polypropylene

In this study, memory effect of mesomorphic isotactic polypropylene (iPP) was investigated using polarized optical microscope and small‐angle X‐ray scattering. Differing from classical memory effect, mesomorphic iPP melt had a higher growth rate and a higher memory temperature. The relative growth rate increased with increasing crystallization temperature. Lauritzen–Hoffman plots indicated that the increased growth rate arose from reduced surface nucleation barrier. The highest memory temperature was estimated to be 185 °C, which was close to the equilibrium melting point of iPP crystal. Additionally, Small‐angle X‐ray scattering measurements showed that a liquid crystal layer might exist between lamellar and amorphous layers. Based on above results, a crystallization model was proposed. In the mesomorphic iPP melt, there exist aggregates structurally similar to β phase except α‐phase crystal residuals, which cannot act as nucleation sites or transform to β crystal through surface nucleation. The only way for the aggregate is to transform to α crystal during crystal growth. The aggregate decreases the surface nucleation barrier and promotes the helical growth, leading to higher growth rate. Only when the aggregate relaxes to polymer coils through thickening at a higher temperature, can the memory effect be erased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1573–1580     

The dependence of slow crack growth in a polyethylene copolymer on test temperature and morphology

The slow crack growth resistance was measured in an ethylene-octene copolymer as a function of the morphological changes produced by varying the thermal history. Morphology was varied by annealing the quenched state at temperatures between 86°C and the melting point. The slow crack growth behavior was measured by the lifetime of a notched tensile specimen under a constant load. In general, the lifetime exhibited a maximum at a critical value of the annealing temperature. This critical annealing temperature decreased with a decrease in the temperature at which the lifetime was measured. The former result is understandable in terms of the increase in crystal strength as the annealing temperature is increased and the decrease in the number of tie molecules when more material is melted as the annealing temperature increases. The latter result depends on the relationship between crystal size and the effect of testing temperature. Differential scanning calorimetry data played a key part in analyzing the results. © 1992 John Wiley & Sons, Inc.     

乙烯装置裂解炉管焦炭燃烧特性的研究

齐鲁石化公司乙烯厂是我国最先引进计算机控制下蒸汽 空气在线烧焦技术的乙烯厂 ,在线烧焦使其过程自动化程度大大提高 ,裂解炉没有升降温过程 ,延长了裂解炉管的使用年限[1～ 5] 。但裂解气盘管管径较小 ,易于堵塞 ,烧焦时间稍短 ,管壁上的焦炭就燃烧不完全 ,目前在线烧焦时间还需 70ｈ～ 80ｈ。为了进一步缩短烧焦时间 ,节约能源 ,提高炉子运行周期 ,必须对乙烯装置裂解炉管焦炭的微观结构及燃烧过程进行深入研究 ,以提出进一步加快烧焦速度的办法 ,满足工业生产的需要。本研究采用国内某乙烯厂裂解炉管焦炭为实验原料 ,研究了焦炭的微观…     

Crystal growth kinetics exhibit a fragility-dependent decoupling from viscosity

In this paper we establish the temperature dependence of the kinetic coefficient associated with crystal growth into the supercooled liquid for a wide range of organic and inorganic materials. We show that the kinetic coefficient for crystal growth scales with the shear viscosity eta as eta(-xi) and that the exponent depends systematically on the fragility of the liquid. The greater the fragility (i.e., deviation away from an Arrhenius temperature dependence for eta), the larger the difference 1-xi. We argue that this breakdown in scaling between the crystal growth kinetics and the viscosity is a manifestation of heterogeneous dynamics in supercooled liquids. In addition, we show that the absolute growth rate at intermediate viscosities is correlated with the entropy difference between the liquid and the crystal.