检索结果-南通市图书馆

crystallization kinetics OF HOMOGENEOUS AND HETEROGENEOUS LLDPE

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2002年第4期20卷 339-345页

作者： Hong-xiang Teng Wen-hong Tang Yi Shi Xi-gao Jin State Key Laboratory of Polymer Physics and Chemistry Center for Molecular Science, Institute of Chemistry Chinese Academy of Sciences Beijing 100080 China Department of Chemistry Jilin University Changchun 130023, China Chinese Acad Sci Ctr Mol Sci Inst Chem State Key Lab Polymer Phys & Chem Beijing 100080 Peoples R China Jilin Univ Dept Chem Changchun 130023 Peoples R China

Based on thermal analysis, the isothermal and nonisothemal crystallization kinetics of Ziegler-Natta catalyzed linear low density polyethylene (Z-N LLDPE) and metallocene catalyzed LLDPE (m-LLDPE) were studied. Treating the results with the Avrami equation and the Ozawa equation, the crystallization constant Igk and the Avrami exponent n were obtained. Some other crystallization parameters were also discussed. According to the different characteristics of the chain structures of Z-N LLDPE and metallocene LLDPE, their crystallization behaviors were analyzed. It is indicated that the homogeneity and heterogeneity of the two polymers act in different way during the crystallization process of polymers, including the nucleation and the growth of crystals under various conditions.

关键词： crystallization kinetics homogeneity heterogeneity LLDPE

crystallization kinetics of Misch Metal Based Bulk Metallic Glasses

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2007年第2期25卷 189-193页

作者：武晓峰孟力凯赵威索忠源司颐邱克强 Faculty of Materials and Chemical Engineering Liaoning Institute of Technology School of Materials Science and Engineering Shenyang University of Technology

The crystallization kinetics of Mm55Al25Cu10Ni5Co5 bulk metallic glass （BMG） was investigated by means of differential scanning calorimetry （DSC） in the mode of continuous heating or isothermal annealing. It was found that the apparent activation energy Eg, Ex and Ep of the BMG calculated by Kissinger＇s method were 189.58, 170.68 and 170.41 kJ·mol^-1, respectively, which was bigger than those of La55Al25Cu10Ni5Co5 BMG indicating that thermal stability of the former was higher than that of the latter. The local activation energy obtained using Ozawa equation decreased as crystallization proceeded except for the initial stage. The Avrami exponents were calculated to be in the range of 3.26 - 5.23 for different crystallization stages and isothermal temperatures. This implied that crystallization of Mm55Al25Cu10Ni5Co2 BMG was governed by diffusion-controlled three-dimensional growth with either reduced or increased nucleation rate, depending on isothermal temperature. Inconsistency of thermal stability with glass-forming ability for Mm（La）-Al-Cu-Ni-Co BMGs was discussed.

关键词： bulk metallic glasses misch metal thermal analysis crystallization kinetics rare earths

crystallization kinetics and the Fine Morphological Evolution of Poly(ethylene oxide)/Ionic Liquid Mixtures

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2017年第11期35卷 1402-1414页

作者： Wen-ze Li 牛艳华 Chen-ting Zhou Huan Luo Guang-xian Li College of Polymer Science and Engineering State Key Laboratory of Polymer Materials Engineering of ChinaSichuan University

Abstract The overall crystallization kinetics and spherulite morphologies of miscible poly（ethylene oxide）（PEO）/1-butyl-3- methylimidazolium hexafluorophosphate （[BMIM][PF6]） mixtures were studied by differential scanning calorimetry （DSC）, polarized optical microscopy （POM） and rheological measurements. The finer crystal structures were further detected by wide angle X-ray diffraction （WAXD） and small angle X-ray scattering （SAXS）. crystallization of PEO is largely suppressed by [BMIM][PF6] addition especially at higher ionic liquid （IL） concentrations above 20 wt%. Both the overall crystallization rate and the spherulite growth decrease with the increase of IL content and crystallization temperature; however, the crystallization mechanism keeps unchanged as evidenced by the similar Avrami exponent n and WAXD results. The addition of [BMIM][PF6] could induce more nuclei to some extent, but the induction time of crystallization is evidently prolonged, and a linear to non-linear transition of the spherulite growth （R ∝ t to R ∝t^1/2） can be observed. At higher IL concentration, the spherulite texture changes apparently from particular serrated to branch surface due to the diffusion-controlled growth and the dilution effect, which also as a main factor contributes to the increasing trend of the long period of crystals.

关键词： PEO [BMIM][PF6] crystallization kinetics Spherulite morphologies

crystallization kinetics of (Ni_(0.75)Fe_(0.25)_(78-x)Nb_xSi_(10)B_(12)(x=0,5)amorphous alloys

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2006年第4期25卷 342-348页

作者： CHEN Xueding WEI Hengdou WANG Xiaojun State Key Laboratory of Advanced New Non-ferrous Materials l.anzhou University of Technology l.anzhou 730050 China

Amorphous ribbons of （Ni0.75Fe0.25）78-xNbxSi10B12 （x = 0, 5） were prepared by a single roller melt-spinning technique in air atmosphere. The crystallization kinetics of the alloys were investigated by means of continuous heating, and the activation energies of the alloys were calculated using Kissinger plot method and Ozawa plot method on the basis of differential thermal analysis data. The crystallization products were analyzed by X-ray diffraction. After the （Ni0.75Fe0.25）78Si10B12 amorphous alloy was annealed at the temperatures 715 and 745 K, a single phase of γ-（Fe, Ni） solid solution with grain sizes of about 10.3 and 18.5 nm, respectively, precipitates in the amorphous matrix. The crystallized phases are γ-（Fe, Ni） solid solution, Fe2Si, Ni2Si, and Fe3B after annealing at 765 K. The （Ni0.75Fe0.25）73NbsSi10 B12 amorphous alloy was annealed at 720, 750, and 800 K; and the crystallization phases, γ（Fe, Ni） solid solution, （Fe, Ni）23B6. Ni31Si12 and Nb2NiB0.16 form simultaneously.

关键词： amorphous materials thermal analysis crystallization kinetics activation energy

crystallization kinetics and magnetization behavior of RE_(3.5)Fe_(66.5)Co_(10)B_(20)(RE=Pr, Nd) nanocomposite ribbons

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2014年第6期33卷 681-685页

作者： Qiong Wu Peng-Yue Zhang Min-Xiang Pan Dong-Yun Li Hong-Liang Ge Magnetism Key Laboratory of Zhejiang Province College of Materials Science and Engineering China Jiliang University

The influence of hard magnetic phase on the crystallization kinetics and magnetization behavior in nanocomposite RE3.5Fe66.5Co10B20（RE = Pr, Nd） ribbons prepared by melt-spinning was studied. Differential scanning calorimeter（DSC） measurement of the as-cast meltspun amorphous ribbons during the crystallization process shows that precipitation energy of Pr2Fe14 B phase is higher than that for Nd2Fe14 B phase, confirmed by X-ray diffraction（XRD） patterns. It can be explained by the different radii of Pr and Nd atoms. Scanning electron microscopy（SEM）images indicate that the average grain size in Pr3.5Fe66.5Co10B20 ribbon is smaller than that in Nd3.5Fe66.5Co10B20,resulting in an enhancement of exchange coupling between hard and soft phases. It is responsible for the better hard magnetic properties in Pr3.5Fe66.5Co10B20. In addition, the process of magnetization reversal of nanocomposite RE3.5Fe66.5Co10B20（RE = Pr, Nd） ribbons was discussed in detail by the recoil loops.

关键词： Nanocomposite rare-earth magnets crystallization kinetics Magnetization behavior

crystallization kinetics of Lithium Aluminum Germanium Phosphate Glass by DSC Technique

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2012年第1期27卷 63-66页

作者： HE Kun WANG Yanhang ZU Chengkui LIU Yonghua ZHAO Huifeng HAN Bin CHENG Jiang Quartz and Special Glasses Institute China Building Materials AcademyBeijing 100024China

Abstract： The crystallization kinetics of Li20-A12O3-GeO2-P205 （LAGP） glass fabricated via the conventional melt-quenching method was studied by differential scanning calorimetry （DSC） under non- isothermal condition at different heating rates. The activation energy of glass transition Eg is 634.4 kJ/mol, indicating that LAGP glass is easy to crystallize at an elevated temperature. The activation energy of crystallization Eo and Avrami index n obtained from Matusita＇s model are 442.01 kJ/mol and 1.7, respectively. The value of n reveals that bulk crystallization predominates slightly over surface crystallization during crystallization process. LAGP glass-ceramics after different heat treatments have the same crystalline phases determined as major phase LiGe2（PO4）3, with A1PO4 and GeO2 as their impurity phases.

关键词： phosphate glass crystallization kinetics thermal stability XRD analysis

crystallization kinetics and Magnetic Properties of Fe_(73.5)Si_(13.5)B_9Cu_1Nb_1V_2 Nanocrystalline Powder Cores

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2013年第5期28卷 876-881页

作者：汪汝武刘静 WANG Zhen GAN Zhanghua XIANG Zhidong LI Yunbao College of Materials Science and Metallurgical Engineering Wuhan University of Science and Technology Hubei Province Key Laboratory of Systems Science in Metallurgical Process State Key Laboratory for Advanced Metals and Materials

Amorphous ribbons of the alloy Fe73.5 Si13.5B9Cu1Nb1V2 were prepared by the standard single copper wheel melt spinning technique in the air atmosphere. The crystallization kinetics of amorphous ribbons was analyzed by non-isothermal differential scanning calorimetry （DSC） measurements. The crystallization activation energies of amorphous ribbons calculated by using Kissinger model were 364 and 337 kJ/mol for the first and the second crystallization, respectively. The Avrami exponent n was calculated from the Johnson- Mehl-Avrami （ MA） equation. The value of the Avrami exponent showed that the crystallization mechanism in the non-isothermal primary crystallization of amorphous ribbons was all shapes growing from small dimensions controlled by diffusion at decreasing nuclectcn rate. The variation of soft magnetic properties of nanocrystalline Fe73.5 Si13.5B9Cu1Nb1V2 alloy powder cores s a tunction of milling times has been investigated. It is found that the effective permeability of the cores shows high frequency stability and decreases with the increase of milling times. The quality factor increases with increasing frequency in lower frequency range, and reaches a maximum at the frequency of 80 kHz then decreases gradually with increasing frequency.

关键词： finemet crystallization kinetics powder core

Effect of Y_2O_3 on the crystallization kinetics of TiO_2 nucleated LAS glass for the production of nanocrystalline transparent glass ceramics

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 2013年第5期20卷 450-455页

作者： Mohammad Sadegh Shakeri Materials and Energy Research Center (MERC) P.O. Box 31779-83634KarajIran

crystallization kinetics of metastable B-quartz solid solution as a desirable phase for the production of trans- parent lithium aluminosilicate （LAS） glass ceramics was investigated in the presence of Y203. Accordingly, differential thermal analysis scans were performed thoroughly to study the mechanism of crystallization kinetics. The aim of this investigation is to discover the complicated mechanism of crystallization process in the presence of co-additives and ac- cordingly find a way for increasing the transparency of glass ceramics. It is shown that the bulk （3D） growth is intensively increased by the enhancement of Y203. Then again, reducing nucleation and increasing growth mechanisms were recog- nized for the LAS system in the presence of Y2O3. Results of the investigation illustrate that when co-additives are added to glasses, it is necessary to nucleate the optical component separately before the growth process.

关键词： glass ceramics lithium aluminosilicate yttria crystallization kinetics nanocrystals transparency

Role of Ag microalloying on glass forming ability and crystallization kinetics of ZrCoAgAlNi amorphous alloy

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2021年第1期30卷 471-476页

作者： A Surendar K Geetha C Rajan M Alaazim Department of Pharmacology Saveetha Dental College and HospitalSaveetha Institute of Medical and Technical SciencesChennaiIndia CSE Excel Engineering CollegePallakapalayamKomarapalayam637303India IT K S Rangasamy College of Technology TiruchengodeNamakkalTamil Nadu 637215India Faculty of Engineering Universitas Muhammadiyah Surakarta(UMS)Indonesia

Bulk metallic glasses(BMGs) with new chemical compositions(ZrCoAgAlNi) were fabricated and the effects of Ag minor addition on the glass forming ability(GFA) and crystallization kinetics were studied. The x-ray diffraction(XRD) test was applied to identify the amorphousness of BMGs or possible crystalline phases. Using differential scanning calorimeter(DSC), the thermal stability and crystallization kinetics under a non-isothermal condition at the different heating rates were studied. Considering the heating rate dependency of glass transition and crystallization kinetics, the activation energy was evaluated and measured for the mentioned processes. It was revealed that the rise in Ag content led to the decrease in activation energy for glass transition, while the activation energy for crystallization increased. The thermal stability and GFA were also studied and it was found that the Ag addition strongly affected the inherent features of BMGs. With the increase in Ag content, the atomic mobility and structural rearrangement changed in the material and consequently, the GFA and thermal stability were significantly improved.

关键词： bulk metallic glass materials design crystallization kinetics glass forming ability