ايجاد و بهبود پوشش هاي مقاوم به خوردگي Cr3C7 و CrN بر روي صفحات دوقطبي پيل سوختي با غشاء پليمري

چكيده انگليسي :

Formation and Improvement of Corrosion Resistant CrN and Cr3C7 Coatings on PEM Bipolar Plates Hadi Haghighat Ghahfarokhi Email address haghighat iut ac ir@gmail com Date of Submission 2012 3 13 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Language FarsiDegree M ScSupervisors Ahmad Saatchi asaatchi@cc iut ac ir Sayyed Mahmood Monirvaghefi vagh mah@cc iut ac irAbstractThe global climate changes produced by greenhouse gases emissions such as CO2 NOx and SOx pose aprogressively higher demand for r pl in to y s ossil u l b s n r y pro u tion by l ss pollutanttechnologies Among the alternative energies available proton exchange membrane PEM fuel cells have beenconsidered to power transportation vehicles such as automobiles and buses due to their high power density relatively quick start up low operating temperatures and low greenhouse gas emissions Fuel cells are expectedto play a major role in the economy of this century and future It is predicted that the future aga is hydrogen age One important component in a PEMFC stack is the bipolar plate This multi functional component provides theelectrical connectivity from cell to cell Its functions also include distributing reactant gases and removing heatand produced water Therefore the bipolar plate material must be chemically stable highly electrical andthermal conductive have low contact resistance with the backing carbon paper or carbon cloth goodmechanical strength low gas permeability and inexpensive massive production The earlier traditional optionwas the use of non porous graphite plates due to their intrinsic high electrical conductivity and chemical stabilityin the PEM fuel cell aggressive environment Although the performance of graphite plates are suitable related tothese properties they are brittle and lack mechanical resistance Another drawback is the need for machining theflow field channels which raises the manufacturing cost making it prohibitive for mass production Consideringespecially transportation applications metal bipolar plates are more resistant to mechanical shocks and vibrationsthat could lead to cracking and leaking of reactant gases Metallic bipolar plates are coated with protectivecoating layers to avoid corrosion Coatings should be conductive and adhere to the base metal without exposingthe substrate to corrosive media Stainless steels Ni based alloys Ti based alloys and aluminium based alloyshave been investigated widely and considered candidates for PEMFC bipolar plate materials Coating onstainless steels surfaces has been used for the improvement of corrosion resistance and contact resistance Coatings are normally divided into two types carbon based and metal based The former includes graphite conductive polymers and diamond like carbon The latter includes noble metals metal nitrides and metalcarbides such as titanium chromium and zirconium nitrides and carbides In this work two coats CrN and Cr3C7 were created on 316L stainless steel by chromium electroplating plasmanitriding and chromium electroplating solid carburizing respectively Then the coats were subjected tosandblasting and heat treating in 400 500 and 800 C All the corrosion tests were done in sulfuric acid solution with pH 2 0 and added 5 ppm HF in 70 5 C with air purging The results of potentiostatic corrosion test inPEM simulated cathodic condition constant potential 600 mV SCE indicated that sandblast heat treatmentsignificantly decrease the corrosion current density The lower corrosion current densities for CrN and Cr 3C7obtained in 500 C 40 minutes and 500 C 25 minutes respectively Good behavior of coats is related to lowdissolution rate of passive films Potentiodynamic polarization corrosion test and electrochemical impedancesp tros opy EI t st oul n t pr i t th o ts orrosion b h vior in pot ntiost ti t st Th b h vior o llcoats were passive in potentiodynamic polarization test that indicates formation of a passive layer in oxidizingmedia

حقيقت قهفرخي، هادي

ايجاد و بهبود پوشش هاي مقاوم به خوردگي Cr3C7 و CrN بر روي صفحات دوقطبي پيل سوختي با غشاء پليمري

خوردگي , ماسه پاشي , نيتراسيون پلاسمايي , كربوره كردن جامد