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Featured researches published by H. Shih.


Corrosion Science | 1987

Pitting and surface modification of SIC/Al

Florian Mansfeld; S. Lin; K. Kim; H. Shih

Pitting of Al based alloys can be detected by characteristic changes in the low-frequency region of the impedance spectra. Immersion in CeCl3 produces very corrosion resistant. SIC/Al surfaces.


Journal of The Electrochemical Society | 1990

Pitting and Passivation of Al Alloys and Al‐Based Metal Matrix Composites

Florian Mansfeld; S. Lin; S. Kim; H. Shih

Pitting and crevice corrosion of Al alloys and Al-based metal matrix composites can be detected by characteristic changes of the impedance spectra in the low frequency region. A pitting model has been developed which is in agreement with the experimental data. A fitting procedure has been used to analyze a large amount of data which have been obtained for as-received samples and samples which had been passivated in CeCl 3 solutions


Electrochimica Acta | 1992

The CeMo process for the development of a stainless aluminum

Florian Mansfeld; You Wang; H. Shih

Abstract A process for surface modification of Al-based materials is described which involves immersion in boiling Ce(NO 3 ) 3 and CeCl 3 followed by anodic polarization in a deaerated molybdate solution. Each of these steps is carried out for 2 h. Al 6061-T6 treated in this manner did not show any signs of uniform or localized corrosion after immersion for 60 days in 0.5 N NaCl. A sample with a scratch in the modified surface also did not show any corrosion after 25 days in NaCl. Since this surface modification process produces exceptional corrosion resistance, it should be considered as a candidate for the replacement of chromate conversion coatings.


Electrochimica Acta | 1989

Surface modification of Al alloys and Al-based metal matrix composites by chemical passivation

Florian Mansfeld; S. Lin; S. Kim; H. Shih

Chemical passivation by immersion of Aluminum 6061 and Aluminum 6061/Silicon Carbide and Al 6061/graphite metal matrix composites in a Cerous Chloride solution produces very corrosion resistant surfaces. Al 6061 which had been immersed in 1000 ppm Cerous Chloride for one week did not suffer from pitting corrosion during immersion in aerated 0.5 N Sodium Chloride for 90 days. A comparison with the corrosion resistance of Aluminum alloys treated with chromate conversion coatings shows that chemical passivation provides a valuable alternative to this process. The passivation process in CeCl3 and the corrosion process in NaCl have been monitored continuously with electrochemical impedance spectroscopy (EIS) which has been shown to be a very sensitive technique for the evaluation of these reactions. Pitting can be detected by the occurrence of a new time constant at low frequencies and a decrease of the impedance in the capacitive region. A model which describes the impedance for a surface which undergoes pitting and a fitting procedure for the analysis of the experimental EIS-data are presented.


Corrosion Science | 1989

A fitting procedure for impedance data of systems with very low corrosion rates

H. Shih; Florian Mansfeld

Abstract For systems with very low corrosion rates it is often very difficult to determine the polarization resistance from impedance spectra obtained in the frequency range which can be covered in a reasonable time period. This makes it impossible to use methods of analysis such as the integration technique. A new fitting procedure has been developed for such systems and has been successfully used to analyze data for Al alloys and Al-based metal matrix composites exposed to NaCl.


Corrosion Science | 1992

Corrosion protection of aluminum alloys and metal matrix composites by polymer coatings

S. Lin; H. Shih; Florian Mansfeld

Abstract An epoxy coating and a combination of chemical passivation in rare earth metal chlorides with the polymer coating provide excellent corrosion resistance for Al 6061, Al/SiC, Al/graphite and Al-Li 2091-T6. An accelerated corrosion test for polymer coatings based on electrochemical impedance spectroscopy (EIS) and a model for the impedance of polymer coated samples with an artificial defect have been developed to evaluate the quality of coatings and to predict the lifetime of coated metals in a short time.


Corrosion Science | 1992

An electrochemical and surface analytical study of stainless steels and titanium exposed to natural seawater

Florian Mansfeld; Raymond Tsai; H. Shih; Brenda J. Little; Richard Ray; Patricia Wagner

Abstract Samples of three stainless steels and titanium grade 2 were exposed to flowing seawater at Port Hueneme, California under natural and reduced light environments. A total of four sets of samples were exposed for times up to 120 days. Open-circuit potential ( E corr ) and electrochemical impedance data as a function of exposure time were used to monitor the electrochemical behavior of the four materials. Surface examination showed a gradual increase in coverage by the biofilm as a function of exposure time. A small increase of E corr was observed, independent of exposure conditions and similar in magnitude to that observed in an abiotic, synthetic salt solution. Impedance data remained capacitive over the entire test period. Capacitance values were similar in natural and synthetic seawater. Localized corrosion was not observed for any sample. Pitting scans in 3.5% NaCl, performed as a function of pH, showed that the pitting potential of 304 stainless steel (SS) reached a value of about 0 mV at pH = 2.


ASTM special technical publications | 1990

Determination and Elimination of the Uncompensated Resistance in Low Conductivity Media

Florian Mansfeld; Y. C. Chen; H. Shih

The positive feedback and the interrupter technique have been used for the continuous elimination of the uncompensated resistance R u during the recording of potentiodynamic polarization curves. The positive feedback technique was evaluated with a PAR model 173 potentiostat and a Solartron model 1286 potentiostat. The Solartron potentiostat was also used with the interrupter technique. The application of both techniques was initially evaluated with suitable dummy cells followed by the tests with steel and stainless steel in ethanolic hydrochloric acid (HCl) and in hydrazine. It was found that great care has to be used to determine the optimum parameters for the interrupter technique such as potentiostat bandwidth and interrupter frequency. The potential-time trace in the interrupter period needs to be observed on an oscilloscope in order to determine the optimum conditions. The saturated calomel electrode and similar reference electrodes cannot be used with the interrupter technique. Wire electrodes such as the silver/silver chloride (Ag/AgCl) or platinum give satisfactory results. The positive feedback technique is easier to use, however 100% compensation cannot be achieved in the PAR potentiostat. Since in most cases R u will decrease during the recording of a polarization curve, it is difficult to obtain satisfactory results with this technique.


Journal of Environmental Engineering | 1991

Microbial Ecology of Crown Corrosion in Sewers

Robert L. Islander; Joseph S. Devinny; Florian Mansfeld; Adam Postyn; H. Shih


Journal of The Electrochemical Society | 1988

Minimization of High‐Frequency Phase Shifts in Impedance Measurements

Florian Mansfeld; S. Lin; Y. C. Chen; H. Shih

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Florian Mansfeld

University of Southern California

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S. Lin

University of Southern California

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You Wang

University of Southern California

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S. Kim

University of Southern California

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Brenda J. Little

United States Naval Research Laboratory

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H. Xiao

University of Southern California

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Joseph S. Devinny

University of Southern California

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K. Kim

University of Southern California

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Raymond Tsai

University of Southern California

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