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71.
72.
表面能与晶体生长/溶解动力学研究的新动向 总被引:3,自引:0,他引:3
界面现象使物质在结晶过程中出现了临界现象.但最近的研究指出在物质溶解过程中,在表面能量的控制下也存在着临界现象以及尺寸效应.实验发现,当晶体自身小到一 定的程度时(通常在纳米尺度上并和临界蚀坑的大小相近),在溶解过程中其速度会自发降 低,反应被抑制乃至停止.尽管在热力学上表面能的因素可以赋予小颗粒晶体较大的溶解度 ,但表面能却也能通过对临界条件的控制而使这些微粒在动力学上不被溶解.这个发现不仅 解决了纳米颗粒在水溶液中稳定性的问题,而且还从动力学的角度解释了生物矿物选择纳米 尺度作为其基本构成单元的原因.由于表面能和晶体生长/溶解的动力学有着密切的关系, 我们可以通过对表面能的调节来修改它们的动力学速度和晶体的形貌.反过来,也可以用动力学的方法来测定表面能及表面吸附/脱附常数等.相对于常规的界面研究手段,通过生 长和溶解动力学途径所得的数据有着很好的可靠性及重复性.我们认为,晶体生长和溶解的 动力学和表面能的研究相结合,不仅为界面研究提供了新的思路和方法,而且也会推动晶体生长和材料科学的发展. 相似文献
73.
大肠杆菌有限生长的微量热及非线性动力学研究 总被引:2,自引:0,他引:2
The finite growth of Escherichia coli was studied by using a LKB 2277 BioActivity Mollitor. We found that the finite growth is a nonliear dynamic process. The nonlinear dynamic behaviour in the finite growth process and the nonlinear dynamic models describing the process were discovered and established. The curve of logistic map corresponding to the finite growth thermogram of Escherichia coli was obtained and the nonlinear dynamic parameters were calculated by means of a computer. Moreover, we also discussed the nonlinear dynamic characters of Escherichia colt in its finite growth process. 相似文献
74.
Svilen Bobev Paul H. Tobash Joe D. Thompson John L. Sarrao 《Journal of solid state chemistry》2005,178(6):2091-2103
A number of rare-earth alumo-silicides (R-Al-Si) have been synthesized from the corresponding elements by high-temperature reactions, carried out in excess of aluminum to serve as a flux. Under these experimental conditions, large single crystals of all R-Al-Si ternary phases were readily produced. The crystal structures these ternaries adopt were studied by means of powder and single-crystal X-ray diffraction and were classified as follows: (1) the early rare-earths (R=La, Ce, Pr, Nd, Sm, Gd) yield RAlxSi2−x, x∼1, non-stoichiometric ternary derivatives of the body-centered α-ThSi2-type; (2) the late rare-earths (R=Tb, Dy, Ho, Er, Tm) form stoichiometric R2Al3Si2 compounds that crystallize in the C-centered monoclinic Y2Al3Si2-type; (3) the divalent Eu and Yb produce EuAl2Si2 and YbAl2Si2 with the trigonal CaAl2Si2-type, whereas the last lanthanide element, Lu, forms LuAlSi with C-centered orthorhombic YAlGe-type. These structural trends are reviewed, and the evolution of the basic physical properties such as magnetism, heat capacity and electrical resistivity when moving across the series is described in detail. 相似文献
75.
LIN Zhou-Bin HU Zu-Shu ZHANG Li-Zhen WANG Guo-Fu 《结构化学》2002,21(6):637-639
<正>The crystal of Nd0.06Y0.94Sr6Sc(BO3)6 with the dimensions up to 35 mm × 28 mm × 13 mm was grown by a top-seeded solution growth method from Li6B4O9 flux. The grown crystal was characterized by X-ray powder diffraction. The optical absorption of the crystal shows that it has a strong absorption band at 8070 A, and the absorption coefficient is 2.17cm-1 with a FWHM of 41 A, which can match with the wavelength of the diode-laser (LD) and is suitable for the LD pumping. Based on the Judd-Ofelt theory, the three parameters of line oscillator strength Ω(λ) (λ = 2, 4 and 6) of the Nd3+ion in the crystal were calculated as follows: Ω2= 1.194 × 10-20, Ω4= 4.186 × 10-20 and Ω6 = 3.351 × 10-20cm2, which are relatively larger. The results indicate that the crystal Nd0.06Y0.94Sr6Sc(BO3)6 may be a kind of high-efficient laser material for diode-pumped. 相似文献
76.
Preparation of Mn3O4 nanocrystallites by low-temperature solvothermal treatment of γ-MnOOH nanowires
The preparation of trimanganese tetroxide (Mn3O4) nanocrystallites from γ-MnOOH nanowires under mild conditions has been achieved by two steps: first, γ-MnOOH nanowires with a mean diameter of about 12 nm and lengths of up to several micrometers were directly prepared via hydrothermal reaction between KMnO4 and toluene in water at 180°C for 24 h; then, pure Mn3O4 nanocrystallites could be obtained by solvothermal treatment of the γ-MnOOH nanowires in ethylenediamine (EDA) and ethylene glycol (EG) at 150°C for 24 h. It was found that the Mn3O4 product obtained in EDA comprised well-defined nanocrystallites with the size in the range of 15-35 nm, while the one obtained in EG consisted of aggregated nanoparticles with the size of less than 18 nm.The possible formation mechanism of nanocrystalline Mn3O4 in EDA and EG and reasons for the different effects of various solvents on the products were also proposed. 相似文献
77.
T.?L.?Shanker Rao K.?N.?Lad A.?PratapEmail author 《Journal of Thermal Analysis and Calorimetry》2004,78(3):769-774
The crystallization kinetics of amorphous Cu50Ti50 has been studied using differential scanning calorimetry (DSC) under non-isothermal conditions. The curves at different linear heating rates (2, 4, 8 and 16 K min–1) show sharp crystallization peaks. The crystallization peak shifts to higher temperatures with increasing heating rate. The Kissingers method of analysis of the shift in the transformation peak is applied to evaluate the activation energy (E
c). The KJMA formalism, which is basically developed for isothermal experiments, is also used to obtain E
c and the Avrami parameter (n).The DSC data have been analysed in terms of kinetic parameters, viz. activation energy (E
c), Avrami exponent (n) and frequency factor K
0 using three different theoretical models. It is observed that the activation energy values derived from KJMA approach and modified Kissinger equation agree fairly well with each other. The activation energy values obtained from normal Kissinger method, and Gao and Wang expression underestimate the activation energy.The financial support provided by All India Council for Technical Education (AICTE), New Delhi (Govt. of India) is gratefully acknowledged. 相似文献
78.
Ge JP Wang J Zhang HX Wang X Peng Q Li YD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(6):1889-1894
Three-dimensional, orthogonal lead sulfide (PbS) nanowire arrays and networks have been prepared by using a simple, atmospheric pressure chemical vapor deposition (APCVD) method. These uniform nanowires (average diameter 30 nm) grow epitaxially from the surface of the initial PbS crystal seeds and form orthogonal arrays and networks in space. The growth mechanism has been explored, and the process was classified as homogeneous, epitaxial growth in the 200 directions. Furthermore, Raman spectra of PbS nanowires are reported here, and their characteristic Raman peak (190 cm(-1), no shoulder) could be used as a unique probe for the study of PbS nanomaterials. 相似文献
79.
Crystal Structure of Hexamine Cyclotriphosphazene, P3N3(NH2)6 In the presence of KNH2 hexamine cyclotriphosphazene semi ammoniate (molar ratio 12:1) in NH3 gives crystals of solvent free P3N3(NH2)6 within 5 d at 130°C and p(NH3) = 110 bar. The structure was solved by X-rax methods: P3N3(NH2)6: P21/c, Z = 4, a = 10.889(6) Å, b = 5.9531(6) Å, c = 13.744(8) Å, β = 97.83(3)°, Z(Fo) = 1 721 with (Fo)2 ≥ 3σ(Fo)2, Z(var.) = 157, R/Rw = 0,036/0,041 The structure contains columns of molecules P3N3(NH2)6 all in the same orientation. The six-membered rings within one molecule have boat conformation. The columns are stacked together in a way that one is surrounded by four others shifted by half a lattice constant in direction [010]. Strong hydrogen bridge-bonds N? H…?N connect molecules within the columns and between them. 相似文献
80.
Phase diagram of durene–resorcinol system, determined by the thaw-melt method, shows the formation of a monotectic (0.109
mole fraction of durene) and an eutectic (0.964 mole fraction of durene) with a large liquid miscibility gap in the region
from 0.109 to 0.964 mole fraction of durene. The eutectic, monotectic and consolute temperatures are 78.4, 107.8 and 165.0°C,
respectively. The growth behaviour studied by measuring the linear velocity of crystallization (v) in a capillary at different undercoolings (ΔT) suggests that the data obey the Hillig–Turnbull equation,v=u(ΔT)n, where u and n are constants depending on the nature of materials involved. From the values of enthalpy of fusion of the pure components,
the eutectic and the monotectic determined by the DSC method using Mettler DSC-4000 system, entropy of fusion, enthalpy of
mixing, Jackson’sroughness parameter, size of the critical nucleus interfacial energy and excess thermodynamic functions were
calculated. The microstructures of the eutectic, and the monotectic, determined by the Leitz Laborlux D optical microscope
show their characteristic features.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献