共查询到20条相似文献,搜索用时 715 毫秒
1.
The preparation of X-zeolite powder was investigatedin hydrothermal system, the crystal growth process of X-zeolite in hydrothermal condition was characterized by means of X-ray diffraction, scanning electron microscope and infrared ray. The results show that X-zeolite powder with uniform granularity and intact crystal shape can be obtained in hydrothermal system of acid-treated stellerite-NaOH-NaAl(OH)4-H2O; the crystallite size is in the range of 2 - 3μm. The best reaction time of hydrothermal preparation is 6 h. The formation phases of X-zeolite crystal are as follows: dissolution of feedstocks → formation of [SiO4]4- and [AlO4]5- tetrahedron, many-membered ring,β cage → formation of crystal nucleus and nano-particle → aggregation growth of nano-particle → coalescence growth of crystallite. The crystal habits of X-zeolite are intimately related with crystallization orientation ofβ cage in crystal and with its coupling stability on every crystal face family. 相似文献
2.
Growth units and the crystallization habit of BaTiO 3 nanocrystals have been investigated. It has been proposed that the growth units of BaTiO 3 were surface hydroxylated Ti(OH) 62− octahedra. The relationship between crystal morphology and the variation of the current intensity in the solution has been
obtained through the measurement of the OH − in the solution and the hydrothermal experiment with superimposed direct electric field. Based on the computation of the
stability energy of the growth units, the relationship between the crystallized morphology of crystallites and the most favorable
growth units under different conditions has been derived. It has been found that there is structure similarity between anatase
(TiO 2) and BaTiO 3 from the crystal chemistry viewpoint, so they are soluble in each other, which can serve as a reasonable explanation for
the abnormal phenomenon of the retention of cubic substable phase at room temperature.
Project supported by the National Natural Science Foundation of China. 相似文献
3.
Calcium phosphate film was prepared by electrochemical deposition technology. Subsequently, the alkaline treatment process
of calcium phosphate film in 0.1 mol/L NaOH solution was monitored on real time by the piezoelectric quartz crystal impedance
(PQCI) technique. The variations of morphology and composition for the alkaline treatment products were characterized by scanning
electron microscopy (SEM), Fourier transform infrared (FT-IR) and X-ray diffraction (XRD), respectively. The dynamic variations
of calcium phosphate can be characterized by the change of equivalent circuit parameters. The results show that the forming
process of hydroxyapatite (HA) is composed of three stages: (1) acidic calcium phosphate dissolution; (2) phase transformation;
and (3) HA formation. Furthermore, the correlative kinetic equations and parameters are obtained by fitting the static capacitance
( C
s)—time curves.
Foundation item: Project(2005CB623901) supported by the Major State Basic Research and Development Program of China 相似文献
4.
Determination of dissolution rate of alumina is one of the classical problems in aluminum electrolysis. A novel method which
can measure the dissolution rate of alumina was presented. Effect of factors on dissolution rate of alumina was studied intuitively
and roundly using transparent quartz electrobath and image analysis techniques. Images about dissolution process of alumina
were taken at an interval of fixed time from transparent quartz electrobath of double rooms. Gabor wavelet transforms were
used for extracting and describing the texture features of each image. After subsampling several times, the dissolution rate
of alumina was computed using these texture features in local neighborhood of samples. Regression equation of the dissolution
rate of alumina was obtained using these dissolution rates. Experiments show that the regression equation of the dissolution
rate of alumina is y=−0.000 5 x
3+0.024 0 x
2−0.287 3 x+ 1.276 7 for Na 3AlF 6-AlF 3-Al 2O 3-CaF 2-LiF-MgF 2 system at 920 °C. 相似文献
5.
Experiments of simultaneous removal of SO 2 and NO from simulated flue gas, using NaClO 2 solution as the absorbent, were carried out in a self-designed bubble reactor, and high simultaneous removal efficiencies
of SO 2 and NO were obtained under the optimal experimental conditions. The mechanism of simultaneous removal based on NaClO 2 acid solutions was proposed by analyzing the removal products. Possibility and limitation of the desulfurization and denitrification
using NaClO 2 acid solutions were calculated by thermodynamic methods. Experimental results of reaction kinetics for simultaneous desulfurization
and denitrification indicated that the oxidation-absorption processes of SO 2 and NO were divided into two zones, namely the fast and slow reaction zones. In the slow reaction zones both were zero order
reactions, and in the fast reaction zones, the reaction order, rate constant and activation energy of SO 2 reaction with absorbent were 1.4, 1.22 (mol·L −1) −0.4·s −1 and 66.25 kJ·mol −1, respectively, and 2, 3.15×10 3 (mol·L −1) −1·s −1, and 42.50 kJ·mol −1 for NO reaction, respectively.
Supported by the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2007AA061803) 相似文献
6.
Existence of [B 3-O 6] 3− hexagonal ring growth unit in melt solution of β-BaB 2O 4 crystal was proved by the results of high temperature Raman measurements. A morphology evolution process of β-BaB 2O 4 crystal was observed by a high temperature in-situ observation device. The crystal morphology varied with the supersaturation of growth melt solution. The mechanism of β-BaB 2O 4 crystal morphology evolution was analyzed through the growth unit model.
Supported by the National Natural Science Foundation of China (Grant No. 60808026) and the Nanjing University of Aeronautics
and Astronautics Scientific Research Fund (Grant No. S0764-081) 相似文献
7.
1 INTRODUCTIONSn-doped In2O3(ITO) is one kind of n-typesemiconductor material[1].It has excellent electro-optical properties , such as electrical conductivityand high transparency under visible light[2],andiswidely used in electronic , transparent electrode ,solar cells and electro-irradiance , especially inscreen display[3 ,4].Recently nearly half of the met-al indium has been used to prepare ITO materialsin the developed countries[5], such as Japan, A-merica ,France and so on.So the… 相似文献
8.
The growth model of a spherical crystal in the undercooled melt including the surface energy, interfacial kinetics and convective
flow is established. The effect of the convective flow induced by a small far field flow on the evolution and morphological
stability of the interface of the spherical crystal is studied. The interface shape of the spherical crystal, which is affected
by the far field flow, and the dispersion relation of the growth rate of amplitude of the perturbed interface are derived.
It is shown that the convection induced by the far field flow makes the interface of the growing spherical crystal further
grow in the upstream direction of the far field flow and inhibit growth in the downstream direction; the interface of the
decaying spherical crystal further decays in the upstream direction and inhibits decay in the downstream direction. The theoretical
result suggests that both the growth of the sphere in the upstream direction and the decay of the sphere in the downstream
direction make the spherical crystal tend to evolve into an oval; the morphological stability of the interface depends on
a certain radius R
c
such that the spherical crystal is unstable when its radius is greater than R
c
and stable when its radius is less than R
c
. The surface energy and interfacial kinetics have strong stabilizing effects on the growth of the spherical crystal. In the
meantime interfacial kinetics is a table factor of the interface when the interface of the sphere is growing; it is an unstable
factor of the interface when the interface is decaying.
Supported by the National Basic Research Program of China (Grant No. 2006CB605205), the National Natural Science Foundation
of China (Grant Nos. 10672019 and 10572062), and the Science and Technology Foundation of Shanghai (Grant No. 055207081) 相似文献
9.
Electrostatic levitation technique and molecular dynamics simulation were performed to investigate the thermophysical properties, liquid structure and crystal growth dependence on undercooling of Ti85Ni10Al5 alloy. The liquid Ti85Ni10Al5 alloy was substantially undercooled up to 335 K (0.18TL). As undercooling increased, the potential energy of the liquid alloy decreased and the alloy entered into a high metastable state. At this state, the atoms tended to bond with each other and the clusters were inclined to convert into high-coordinated clusters, as confirmed by the fraction of the high-coordinated clusters variation. The enlarged clusters and enhanced local structure stability contributed to the increase of the thermophysical parameters and crystal growth velocity, and eventually dendrite refinement. The density, the specific heat and the surface tension of liquid alloy exhibited a linear relation with temperature and the shear viscosity of liquid alloy showed exponential variation which showed good agreement with the calculation results by molecular dynamics simulation. The growth velocity first increased slowly and then dramatically once the undercooling exceeded the threshold. The achieved maximum crystal growth velocity was 12.4 ms−1 and it was up to 326 times of the value at 94 K undercooling. 相似文献
10.
In this paper, 1 μm n-GaN was grown by using varied and fixed ammonia flow (NH 3) on SiN
x
mask layer on Si(111) substrate using metal organic chemical vapor deposition (MOCVD). In-situ optical reflectivity traces of GaN growth show that the three- to two-dimensional process has been prolonged by using varied
ammonia flow on SiN
x
mask layer method compared with that grown by fixing ammonia flow. Structural and optical properties were characterized by
high-resolution X-ray diffraction and photoluminescence, and compared with the sample grown by fixing ammonia flow, GaN grown
using the varied ammonia flow on SiN x mask layer showed better structure and optical quality. It was assumed that the low NH 3 flow in the initial growth stage considerably increased the GaN island density on the nano-porous SiN
x
layer by enhancing vertical growth. Lateral growth was significantly favored by high NH 3 flow in the subsequent step. As a result, the improved crystal and optical quality was achieved utilizing NH 3 flow modulation for GaN buffer growth on Si(111) substrate. 相似文献
11.
Fe/Si 3N 4 composite powder was synthesized by the heterogeneous precipitation-thermal reduction process, and then pressed into flakes
under a pressure of 10 MPa. Flakes were sintered by pressureless and hot-pressing at 1 600 °C under 0.1 MPa N 2. The chemical composition, phases and microstructure of composite powder and sintered flakes were investigated by energy
dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy
(TEM). The results show that the structure of composite powders is Si 3N 4 coated by nano Fe. The crystal phases of sintered flakes by pressureless are Fe(Si) compound, SiC and Si 3N 4. The crystal phases of the sintered samples by hot-pressing are Fe, Fe(Si) compound and Si 3N 4. It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different.
Foundation item: Project(50804016) supported by the National Natural Science Foundation of China 相似文献
12.
In this paper, 1 μm n-GaN was grown by using varied and fixed ammonia flow (NH3) on SiN
x
mask layer on Si(111) substrate using metal organic chemical vapor deposition (MOCVD). In-situ optical reflectivity traces of GaN growth show that the three- to two-dimensional process has been prolonged by using varied ammonia flow on SiN
x
mask layer method compared with that grown by fixing ammonia flow. Structural and optical properties were characterized by high-resolution X-ray diffraction and photoluminescence, and compared with the sample grown by fixing ammonia flow, GaN grown using the varied ammonia flow on SiNx mask layer showed better structure and optical quality. It was assumed that the low NH3 flow in the initial growth stage considerably increased the GaN island density on the nano-porous SiN
x
layer by enhancing vertical growth. Lateral growth was significantly favored by high NH3 flow in the subsequent step. As a result, the improved crystal and optical quality was achieved utilizing NH3 flow modulation for GaN buffer growth on Si(111) substrate. 相似文献
13.
1 INTRODRCTIONWithregardtothestudyofcrystalgrowthunits,researchersmainlyconcentrateonthedissolutionofsolute ,theformationofgrowthunitsandthetransportationofthecrystalgrowthunittotheinterface ,aswellasthecongruencyofthegrowthunitsontheinter facesofthecry… 相似文献
14.
Highly ordered Bi 4Si 3O 12 micro-crystals were prepared at normal atmosphere. Phase identification of the prepared crystals was accomplished by X-ray
diffractometer (XRD). Domain structure and defects were characterized by environmental scanning electron microscopy (ESEM).
XRD shows that the obtained micro-crystals are of eulytite structure with chemical formulation of Bi 4Si 3O 12. A highly ordered growth pattern is confirmed due to the faster growth of the {124} faces than that of the {204} faces by
ESEM. The growing process of the domain structure is of pollen parent and filial generation pattern. The filial generations
of Bi 4Si 3O 12 crystals are generated from the pollen parent. Cracks generate from the defect areas and propagate along the {124} faces
due to their lower binding energy under a proper temperature gradient, contributing to the total transcrystalline fracture.
It is confirmed that the generation and development of the voids in the crystal grains can be developed when unmatched dimensions
of the two opposite faces are formed. And the development of the voids is dependent on the dimensions and orientations of
the two opposite faces.
Supported by the Innovation Research Team Funds of Shaanxi University of Science & Technology (Grant No. SUST-A04) 相似文献
15.
ZrO2 ceramic was made from evenly dispersed ( Y, Ce )-ZrO2 powder with different composi-tions, which was prepared by the chemical coprecipitation, and stabilized by compound additions through appropri-ate techniques. And its mechanical property that is related to the phase content and its microstntcatre was studied by X-ray diffraction(XRD),scan electron microscope(SEM). The results show that Y2O3 has stronger inhibition to the growth of ZrO2 crystal than CeO2 has. TheFEfore, within an appropriate composition range of Y2O3 and CeO2, the higher the content of Y2O3, the lower the content of CeO2, the smaller ZrO2 crystal. Combining this feature and the stabilization technique with complex additions instead of simple addition, ZrO2 ceramic with high density and excellent mechanical properties can be made under normal conditions. It is concluded that the improvement of mecMnical properties originates from the toughening of microcrack, phase transformation and the effect of grain e-vulsions. 相似文献
16.
β-Si3N4 powders prepared by self-propagating high-temperature synthesis (SHS) with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering (SPS). The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homo- geneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200°C lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa?m1/2. 相似文献
17.
Properties of hydroxyapatite (HA, Ca 10(PO 4) 6(OH) 2), including bioactivity, biocompatibility, solubility and adsorption could be tailored over wide ranges by the control of
particle composition, particle size and morphology. In order to satisfy various applications, well-crystallized pure HA nanoparticles
were synthesized at moderate temperatures by hydrothermal synthesis, and HA nanoparticles with different lengths were obtained
by adding organic additives. X-ray diffractometry (XRD) and Fourier transform infrared (FTIR) spectrometry were used to characterize
these nanoparticles, and the morphologies of the HA particles were observed by transmission electron microscopy (TEM). The
results demonstrate that shorter rod-like HA particles can be prepared by adding cetyltrimethylammonium bromide (CTAB), as
the additive of CTAB can block the HA crystal growth along with c-axis. And whisker HA particles are obtained by adding ethylenediamine tetraacetic acid (EDTA), since EDTA may have effect
on the dissolution-reprecipitation process of HA. 相似文献
18.
BiB 3O 6 (BIBO) single crystals with size of 46×23×10 mm 3 and weight of 26.0 g have been successfully grown by top-seeded method. Problems encountered in the growth process of this crystal have been discussed in detail, and the methods of growing high-quality large crystals have been put forward. The relationship between their structure and properties is studied. The space group of monoclinic BiB 3O 6 is C2 and the cell parameters are a=7.1203(7) Å, b=4.9948(7) Å, c=6.5077(7) Å, β=105.586(8)″, and V=222.93(5) Å 3. The density of BIBO is 4.8965 g/cm 3. The Mohs’s scale of hardness is 5.5–6. There is no cleavage face in the crystal. The transmittance of BIBO is about 80 percent in the range from visible coherent light to near-infrared light. The ultraviolet cutoff wavelength is at 276 nm. BiB 3O 6 is a biaxial crystal and has two sets of axes, and the relative orientation of ( X, Y, Z) with regard to ( a, b, c) is: X//b, (Y, c)=47.2°, ( Z, a)=31.6°, determined by X-ray analysis combined with polarized microscopy. Second-harmonic-generation (SHG) experiments were carried out for the first time. In type I phase-matching (PM) directions (11.1°, 90°) and (168.9°, 90°), SHG conversion efficiencies of two directions for 1.064 μm light are up to 67.7% and 58%, respectively. We have also obtained the third-harmonic-generation (THG) of 1.064 μm. The comparative experiments between BIBO and KTP were carried out on conversion efficiency, transmittance and hardness. All the above results indicate that BiB 3O 6 is a kind of excellent nonlinear optical (NLO) crystal. 相似文献
19.
Ba0.6Sr0.4TiO3/Mg1-xZnxO (MZO, x = 0, 0.05, 0.10, 0.15 and 0.20) ceramic composites were prepared by traditional ceramic processing. The crystal structure, fracture surface morphology, and dielectric properties were investigated. The samples with x = 0, 0.05 and 0.10 exhibited favorable sintering behavior, and homogeneous diphase microstructure was obtained. Nevertheless, the microstructure of the samples with x = 0.15 and 0.20 was inhomogeneous and abnormal grain growth could be observed, and the abnormal grain growth induced the degradation of dielectric strength. The sample with x = 0.10 has relatively low dielectric loss (1.26×10-3) and the optimal FOM value (about 174). 相似文献
20.
In the present study, rapidly solidified ribbons of A187 Ni7 Cu3 Nd3 metallic glass was prepared by using melt spinning. Devitrification process of the totally amorphous ribbons was investigated by high temperature X-ray diffraction analysis, combining with differential scanning calorimetry, under continuous and isothermal heating regime. The X-ray diffraction intensity and full width at the half maximum (FWHM) were analyzed to investigate the increase of crystallized amount and growth of α-Al crystal particles. The results show that under continuous heating regime, the metallic glass devitrifies via two main stages: primary crystallization, resulting in two-phase mixture of α-Al plus residual amorphous phase, and secondary crystallization, corresponding to rapid precipitation of some inter-metallic phases in the form of dispersion or eutectic mixture. Under isothermal heating regime, only Al crystal precipitates from the Al-rich amorphous matrix at low temperature, and when heating at 280 ℃ only Al 相似文献
|