Browsing by Author "Ger, Ming-Der"

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A Holey Graphene Additive for Boosting Performance of Electric Double-Layer Supercapacitors
(2020-04-01)
Huang, Jun-Bin
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Patra, Jagabandhu
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Lin, Ming-Hsien
;
Ger, Ming-Der
;
Liu, Yih-Ming
We demonstrate a facile and effective method, which is low-cost and easy to scale up, to fabricate holey graphene nanosheets (HGNSs) via ultrafast heating during synthesis. Various heating temperatures are used to modify the material properties of HGNSs. First, we use HGNSs as the electrode active materials for electric double-layer capacitors (EDLCs). A synthesis temperature of 900 degrees C seems to be optimal, i.e., the conductivity and adhesion of HGNSs reach a compromise. The gravimetric capacitance of this HGNS sample (namely HGNS-900) is 56 Fg(-1). However, the volumetric capacitance is low, which hinders its practical application. Secondly, we incorporate activated carbon (AC) into HGNS-900 to make a composite EDLC material. The effect of the AC:HGNS-900 ratio on the capacitance, high-rate performance, and cycling stability are systematically investigated. With a proper amount of HGNS-900, both the electrode gravimetric and volumetric capacitances at high rate charging/discharging are clearly higher than those of plain AC electrodes. The AC/HGNS-900 composite is a promising electrode material for nonaqueous EDLC applications.
Characteristic V-Mn conversion coating in reinforcing corrosion resistance of electroless Ni-P coated LZ91 Mg alloy
(2020-07-25)
Jian, Shun-Yi
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Chang, Jun-Kai
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Lin, Kung-Feng
;
Chen, Ting-Yu
;
Yuan, Jui-Hung
A V-Mn conversion coating was studied and furthermore employed to improve the corrosion resistance of electroless Ni-P coated LZ91 Mg alloy. A thin, continuous and compact V-Mn conversion coating was formed on LZ91 after the immersion of 60 s in the conversion coating solution. The results of electrochemical impedance spectroscopy (EIS) and salt spray test (SST) showed the enhanced corrosion resistance of LZ91. The impedance in EIS increased from 573 Omega.cm(2) to 11,319 Omega.cm(2), and moreover the deteriorated area ratio of the V-Mn conversion coated LZ91 decreased to < 5% after 120 h of SST exposures. Further study of a V-Mn conversion coating/electroless Ni-P composite coated LZ91 was used to investigate the improvement of the corrosion resistance in the electroless Ni-P coated LZ91. The composite coated LZ91 demonstrated better corrosion resistance of mere electroless Ni-P coated LZ91. Furthermore, the corrosion resistance of the composite coated LZ91 was greatly enhanced. The impedance of the composite coated LZ91 was 500 Omega.cm(2), larger than that of the electroless Ni-P coating of 5 Omega.cm(2). The composite coated LZ91 showed better corrosion resistance in the SST exposures in comparison to mere electroless Ni-P coated LZ91. The composite coating indicated that the positive characteristics of a V-Mn conversion coating usefully enhanced the corrosion resistance electroless Ni-P coated LZ91. Moreover, based on the above results, a mechanism for the conversion coating and corrosion resistance was proposed.
Comparison of field emission performances and durability of three nanocarbon materials
(2020-07-01)
Youh, Meng-Jey
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Lin, Chun-Shuan
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Pu, Nen-Wen
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Liu, Yih-Ming
;
Youh, Ru-Yi
The performances and operation lifetime of field emission (FE) cathodes made by spray-coating three different nanocarbon materials-carbon nanotubes (CNTs), graphene (GE), and carbon nanocoils (CNCs)-were compared. Though CNTs had the benefits of the lowest turn-on field, CNCs exhibited the most stable cycle-to-cycle repeatability and a significantly longer life than CNTs and GE under a continuous high-current-density operation. The microscopic morphology and Raman spectra of these nanocarbon emitters before and after the 50-h life tests were examined in order to understand the damage mechanism and the cause of their distinct performance decay behaviors. The results indicated that CNCs, whose diameters are significantly larger than those of CNTs and the thickness of GE, can withstand the thermal effects of high current density with the least degree of damage in the morphology and microstructure. According to our performance and life tests, CNTs are most suitable for low-voltage small-current FE applications because of their highest field enhancement factor and lowest turn-on field, while CNCs are a more favorable candidate for high-voltage long-term applications such as FE x-ray tubes.
Effect of Pretreatment Process on the Adhesion and Corrosion Resistance of Nickel-Boron Coatings Deposited on 8620H Alloy Steel
(2020-01-01)
Cheng, An-Yu
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Sheu, Hung-Hua
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Liu, Yih-Ming
;
Hou, Kung-Hsu
;
Hsieh, Pei-Yi
In this work, Ni-B coatings were electrodeposited on the 8620H steel substrates, the substrates were carried out with different pretreatment including without pretreatment, after sandblasting by glass sand and after sandblasting by emery powders. The results of scratch test indicated that the best adhesion strength of Ni-B coatings occurred at the 8620H steel substrates carried out with sandblasting by emery powders, the Ni-B coatings still did not be damaged when the load increase to 50 N. The values of Ni-B coatings deposited on different pretreatment condition such as without pretreatment, after sandblasting by glass sand and after sandblasting by emery powders are approximately at 9.46x 10(-6), 8.62x 10(-6) and 2.31 x 10(-6) A/dm(2), respectively. All the samples carried out with a wear process at a load of 20 N, the icorr values of Ni-B coatings deposited on different conditions 1.96x 10(-5), 1.54x 10(-5) and 6.72x 10(-6) A/dm(2), respectively. The results show that the Ni-B coatings deposited on the 8620H steel substrates carried out with sandblasting by emery powders has the best adhesion strength and corrosion resistance due to the Ni-B coatings did not be damaged during wear process.
Effect of Saccharose Concentration and Temperature on the Internal Stress and Corrosion Resistance of Electroplated Chromium Coatings Prepared from Chromium (III) Bath
(2020-04-01)
Sheu, Hung-Hua
;
Chen, Yuan-Rong
;
Ger, Ming-Der
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交大名義發表
;
National Chiao Tung University
The trivalent chromium carbon coatings are electroplated from different electroplating temperature (10, 0 and -5 degrees C) and different concentration (0.01, 0.02 and 0.03 M) of saccharose (C12H22O11). The saccharose play a role of stress inhibitor in the bath during electroplating process. The results of internal stress analysis show that the internal stress of the trivalent chromium carbon coating decreases with the increase of concentration of saccharose at individual electroplating temperatures, this shows that saccharose has the effect on suppressing the accumulation of stress within the coating. Moreover, the electroplating temperature also affect the internal stress of trivalent chromium carbon coatings i.e. the lower electroplating temperature (-5 degrees C) will reduce the accumulation of stress within the coating during electroplating. The smallest internal stress of trivalent chromium carbon coatings is 13.4 MPa, electroplated at -5 degrees C with a concentration of saccharose at 0.02 M. The best i(corr) is approximately at 1.32x 10(-6) A/dm(2), this coatings is also electroplated at -5 degrees C and the concentration of saccharose at 0.02 M. The results indicated that both electroplating temperature and concentration of saccharose can reduce the internal stress within trivalent chromium carbon coatings and decrease the through-deposit cracking within coatings, thereby improving the corrosion resistance of coatings.
Hydrous ruthenium oxide-tantalum pentoxide thin film electrodes prepared by thermal decomposition for electrochemical capacitors
(2020-07-01)
Xie, Jian-De
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Hsu, Kai-Hsiang
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Patra, Jagabandhu
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Su, Ching-Yuan
;
Lee, Sheng-Wei
In this work, we have fabricated high-performance thin-film electrodes for electrochemical capacitors (ECs) via thermal decomposition syntheses of RuO2-Ta2O5 coating layers on Ti substrates. The influences of decomposition temperature as well as the Ru/Ta molar ratio on material and electrochemical properties of the EC electrodes are systematically investigated. The thermal decomposition of 300 degrees C preserves a large fraction of hydrous RuO2 center dot xH(2)O within the hybrid oxide and consequently improves the electrode capacitance. The amorphous Ta2O5 incorporation can manipulate the RuO2 crystallinity and thus its specific capacitance. An optimal Ru/Ta molar ratio of 7:3 is determined for the RuO2-Ta2O5 electrode, which can deliver an energy density of 4.8 Wh kg(-1) at a power density of 8720 W kg(-1) (or 8.3 Wh L-1 at 15,000 W L-1). In addition, an excellent durability of 97.6% capacitance retention after 3000 charge-discharge cycles is found for this electrode. The proposed RuO2-Ta2O5 thin-film electrode has paved the way for next-generation ECs with superior capacitances, energy/power densities, and cyclability.
The study of corrosion behavior of manganese-based conversion coating on LZ91 magnesium alloy: Effect of addition of pyrophosphate and cerium
(2020-07-01)
Jian, Shun-Yi
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Tzeng, Yu-Chih
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Ger, Ming-Der
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Chang, Ko-Lun
;
Shi, Gia-Nan
A previous study by the authors reported that a Mn-Ce based conversion coating protects the surface of LZ91 magnesium alloy from corrosion. However, the acidic permanganate solution decomposes after several days of storage and this significantly affects the properties of the coating. To address this problem, this study presents a method to stabilize the acidic permanganate bath by adding pyrophosphate into the bath. The results show that all conversion coatings are amorphous and comprise two layers: a porous layer that contacts the substrate and a compact overlay. Coatings that are produced using a bath with Ce are more resistant to corrosion than those that are produced in a bath without Ce ions. Coatings that are stored in the Mn-Ce bath for 2 weeks are significantly less resistant to corrosion than coatings that are produced using an as-prepared Mn\\Ce bath. The salt spray test results of coatings that are produced using the as-prepared bath and stored for 2 weeks are found similar because the bath is rendered more stable by the addition of pyrophosphate. (C) 2020 The Authors. Published by Elsevier Ltd.