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Author: search.filters.author.Kuo, CT

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Now showing 1 - 10 of 73
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    Microstructures and electrical properties of V2O5-based multicomponent ZnO varistors prepared by microwave sintering process
    (1997-03-01)
    Chen, CS
    ;
    Kuo, CT
    ;
    Wu, TB
    ;
    Lin, IN
    ;
    材料科學與工程學系
    The V2O5-based ZnO varistor materials were successfully densified using microwave sintering process. The materials can reach a high density as 94.6% T.D. (theoretical density) when sintered at 800 degrees C (10 min) but the grain growth was initiated only when sintered at a higher temperature than 1000 degrees C (10 min). The varistor characteristics, including breakdown voltage (V-bk), nonlinear coefficient (alpha) and leakage current density (J(L)), degraded markedly for the samples sintered at too high temperature (i.e., T greater than or equal to 1000 degrees C) and for too long period (i.e., t greater than or equal to 10 min) that was ascribed to the occurrence of abnormal grain growth. Contrarily, the intrinsic characteristics, including potential barrier height (phi(b)) and donor density (N-d), varied only moderately with these sintering conditions. The V2O5-based ZnO materials sintered at 1000 degrees C (5 min) possessed good varistor characteristics as V-bk = 248 V/mm, alpha = 31 and J(L) = 4.6 x 10(-5) A/cm(2). The corresponding intrinsic parameters are phi(b) = 0.63 eV and N-d = 2.37 x 10(24) m(-3).
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    Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: I, effect of V2O5 doping
    (1998-11-01)
    Kuo, CT
    ;
    Chen, CS
    ;
    Lin, IN
    ;
    材料科學與工程學系
    ;
    Department of Materials Science and Engineering
    The modification of the densification behavior and the grain-growth characteristics of the microwave-sintered ZnO materials, caused by the incorporation of V2O5 additives, have been systematically studied. Generally, the addition of V2O5 markedly enhances the densification rate, such that a density as high as 97.9% of the theoretical density and a grain size as large as 10 mu m can be attained for a sintering temperature as low as 800 degrees C and a soaking time as short as 10 min. Increasing the sintering temperature or soaking time does not significantly change the sintered density of the ZnO-V2O5 materials but it does monotonously increase their grain size. Varying the proportion of V2O5 in the range of 0.2-1.0 mol% does not pronouncedly modify such behavior. The leakage current density (J(L)) of these high-density and uniform-granular-structure samples is still large, which is amended by the incorporation of 0.3 mol% of Mn3O4 in the ZnO materials, in addition to 0.5 mol% of the V2O5 additives. Samples that are obtained using such a method possess good nonohmic characteristics (alpha = 23.5) and a low leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)).
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    Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: II, effect of Mn3O4 doping
    (1998-11-01)
    Kuo, CT
    ;
    Chen, CS
    ;
    Lin, IN
    ;
    材料科學與工程學系
    ;
    Department of Materials Science and Engineering
    The microstructure and nonlinear current-voltage characteristics of Mn3O4-doped ZnO-V2O5 ceramics, microwave-sintered at 800 degrees-1200 degrees C for 10 min, have been investigated. A high density (96% of the theoretical density) has been achieved. The incorporation of Mn3O4 additives does not significantly alter the densification behavior of the ZnO-V2O5 materials, but rather pronouncedly increases the non-linear coefficient (alpha = 23.5) and markedly suppresses their leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)). On the other hand, the intrinsic properties of the materials, including the Schottky barrier height (Phi(b)) and the donor density (N-d), are only moderately modified; that is, Phi(b) = 1.16 eV and N-d = 5.4 x 10(17)/cm(3). X-ray diffractometry analyses and energy-dispersive X-ray microanalyses (via scanning electron microscopy) indicate that the V2O5 species facilitate the densification and the development of microstructure via the formation of a liquid phase (Zn-3(VO4)(2)) along the grain boundaries, whereas the Mn3O4 species markedly enhance the nonohmic behavior of the ZnO-V2O5 materials by forming the surface states along the grain boundaries.
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    Improvement on the degradation of microwave sintered ZnO varistors by postannealing
    (1998-06-01)
    Chen, CS
    ;
    Kuo, CT
    ;
    Lin, IN
    ;
    材料科學與工程學系
    ;
    Department of Materials Science and Engineering
    The microwave sintering process not only densified the ZnO materials in a higher rate, but also resulted in significantly better varistor characteristics. Large nonlinear coefficient and low leakage current density were attained by cooling the samples under a rate of 80 degrees C/min after sintering, followed by 600 degrees C postannealing for 60 min under oxygen atmosphere. Inappropriate annealing deteriorated the varistor characteristics that can either be attributed to the insufficient reoxidation along grain boundaries when annealed in N-2 (or air) or loss of Zn species in these regions when annealed at 750 degrees C (900 degrees C). By contrast, the degradation behavior of these materials can be improved by the annealing process regardless of the annealing atmosphere or temperature.
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    The use of a biomolecular target for crystalline carbon nitride film deposition by Ar ion-beam sputtering without any other source of nitrogen
    (1998-06-29)
    Chen, LC
    ;
    Lu, TR
    ;
    Kuo, CT
    ;
    Bhusari, DM
    ;
    Wu, JJ
    Carbon nitride films have been synthesized by argon ion-beam sputtering from a biomolecular compound target, 8-aza-6-aminopurine (C4N6H4) The compound has a six-membered ring structure similar to that existing in the hypothetical beta-C3N4. Except fur the target material, no other source of nitrogen was used during sputtering deposition. It was found that crystalline carbon nitride with high N/C atomic composition ratios of 0.43-0.56 can be formed even at room temperature. The infrared spectra of the film exhibit two peaks at 1383 and 1643 cm(-1), corresponding to C-N and C=N stretching modes, respectively. No detectable peak at 2200 cm(-1) (C=N stretching mode) is observed. Both x-ray diffraction and transmission electron microscopy show a very strong broad peak at 3.2 Angstrom, comparable to the d spacing of the (110) orientation in the beta-C3N4 structure. However, it is suggested that the film contains a nanocrystalline phase with a crystal structure yet to be determined. (C) 1998 American Institute of Physics.
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    High adhesion and quality diamond films on steel substrate
    (1998-06-01)
    Lin, CR
    ;
    Kuo, CT
    ;
    材料科學與工程學系
    ;
    Department of Materials Science and Engineering
    A process to deposit a diamond coating on steel substrates has been successfully developed. It includes the electroplating of nickel by using an electrolyte dispersed with micro-diamonds, and then a diamond deposition through a microwave plasma chemical vapor deposition system. The diamond films were characterized by Raman and CL spectroscopy, XRD, SEM and SEM line scanning. The results show a high diamond crystal quality, low residual stress (about 0.67 GPa) and high nucleation density. The adhesion of the films was evaluated by a cutting test and an interface examination. The results show that the retentivity of the diamond grits in the films after the cutting test is much better than that in the commercial electroformed diamond tools. The advantages of the process are: (1) the formation of nickel-carbon-hydrogen alloys to enhance diamond nucleation and growth, (2) the micro-diamonds acting as the seeds for diamond nucleation and growth, and forming effective mechanical interlocking with the nickel interlayer, and (3) the formation of good diffusion bonding of the nickel interlayer with the steel substrate. (C) 1998 Elsevier Science S.A.
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    Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: II, effect of Mn3O4 doping
    (1998-11-01)
    Kuo, CT
    ;
    Chen, CS
    ;
    Lin, IN
    ;
    材料科學與工程學系
    ;
    Department of Materials Science and Engineering
    The microstructure and nonlinear current-voltage characteristics of Mn3O4-doped ZnO-V2O5 ceramics, microwave-sintered at 800 degrees-1200 degrees C for 10 min, have been investigated. A high density (96% of the theoretical density) has been achieved. The incorporation of Mn3O4 additives does not significantly alter the densification behavior of the ZnO-V2O5 materials, but rather pronouncedly increases the non-linear coefficient (alpha = 23.5) and markedly suppresses their leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)). On the other hand, the intrinsic properties of the materials, including the Schottky barrier height (Phi(b)) and the donor density (N-d), are only moderately modified; that is, Phi(b) = 1.16 eV and N-d = 5.4 x 10(17)/cm(3). X-ray diffractometry analyses and energy-dispersive X-ray microanalyses (via scanning electron microscopy) indicate that the V2O5 species facilitate the densification and the development of microstructure via the formation of a liquid phase (Zn-3(VO4)(2)) along the grain boundaries, whereas the Mn3O4 species markedly enhance the nonohmic behavior of the ZnO-V2O5 materials by forming the surface states along the grain boundaries.
  • Thumbnail Image
    Item type:Item,
    Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: I, effect of V2O5 doping
    (1998-11-01)
    Kuo, CT
    ;
    Chen, CS
    ;
    Lin, IN
    ;
    材料科學與工程學系
    ;
    Department of Materials Science and Engineering
    The modification of the densification behavior and the grain-growth characteristics of the microwave-sintered ZnO materials, caused by the incorporation of V2O5 additives, have been systematically studied. Generally, the addition of V2O5 markedly enhances the densification rate, such that a density as high as 97.9% of the theoretical density and a grain size as large as 10 mu m can be attained for a sintering temperature as low as 800 degrees C and a soaking time as short as 10 min. Increasing the sintering temperature or soaking time does not significantly change the sintered density of the ZnO-V2O5 materials but it does monotonously increase their grain size. Varying the proportion of V2O5 in the range of 0.2-1.0 mol% does not pronouncedly modify such behavior. The leakage current density (J(L)) of these high-density and uniform-granular-structure samples is still large, which is amended by the incorporation of 0.3 mol% of Mn3O4 in the ZnO materials, in addition to 0.5 mol% of the V2O5 additives. Samples that are obtained using such a method possess good nonohmic characteristics (alpha = 23.5) and a low leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)).
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    Improvement of mechanical properties of electroplated diamond tools by microwave plasma CVD diamond process
    (1998-11-10)
    Lin, CR
    ;
    Kuo, CT
    ;
    材料科學與工程學系
    ;
    Department of Materials Science and Engineering
    The growth and surface modification of irregular diamond grains of electroplated diamond tools have been developed successfully. Results show that the adherence, cutting ability, and wear resistance of diamond grains are improved by this process. In this study, the crystallization and quality of diamond grains were determined by SEM (SE and BSE), Raman spectroscopy, and XRD determination. Tests using a block-on-ring tribotester were also carried out to examine the adherence, cutting ability, and wearing resistance of the electroplated diamond tools, The adherence of diamond grains was also observed on a SEM microphotograph of the cross-section view of specimens. SEM line scanning was performed to determine whether the alloy elements are effectual in promoting the diffusion bonding strength among diamonds, the interlayer and substrate. (C) 1998 Elsevier Science S.A. All rights reserved.