Protikorozijska zaščita aluminijeve zlitine v kloridnem mediju z inhibitorji na osnovi lantanoidnih soli

diplomsko delo univerzitetnega študijskega programa

Barbara Volarič (Author), Regina Fuchs-Godec (Mentor), Aljana Petek (Co-mentor), Ingrid Milošev (Co-mentor)

Abstract

Inhibicija korozijskih procesov na aluminijevih zlitinah z lantanoidnimi solmi bi lahko bila potencialno nadomestilo škodljivim kancerogenim kromatnim Cr6+ prevlekam, saj so lantanoidne soli neškodljive za okolje, so cenovno ugodne in jih lahko v večjih količinah najdemo v okolju. Aluminijevo zlitino 7075-T6 smo protikorozijsko zaščitili s korozijskimi inhibitorji, lantanoidnimi solmi cerija, lantana in neodima. Raziskovalno delo je bilo razdeljeno na dve področji: a) raziskovanje dodatka korozijskega inhibitorja v korozivni medij 0,1 M NaCl ter b) predhodna priprava konverzijskih prevlek, ki ji sledi meritev v korozivnem mediju. Rezultati elektrokemijskih meritev vzorcev v 0,1 M raztopini NaCl so pokazali bistveno izboljšanje protikorozijskih lastnosti, kar se je odražalo v povečanju polarizacijske upornosti (Rp), zmanjšanju korozijskega toka (jkor) za več velikostnih razredov ter povečanju potenciala preboja (Epr). Izračunana inhibicijska učinkovitost si sledi v naslednjem vrstnem redu: CeCl3, La(NO3)3, LaCl3, Ce(NO3)3 in Nd(NO3)3 (čas stabilizacije potenciala je 1 ura). CeCl3 se je izkazal kot izredno učinkovit, saj je inhibicijska učinkovitost znašala več kot 99 %. Raziskovali smo tudi mešanice različnih soli. Konverzijske prevleke smo pripravili s potopitvijo kovine v raztopino lantanoidnih soli in dodatkom močnega oksidanta - vodikovega peroksida (H2O2) pri različnih temperaturah. Pri tem se lantanoidna sol oksidira ali dehidratizira. Elektrokemijske meritve so potrdile učinkovito korozijsko zaščito, saj je inhibicijska učinkovitost pri temperaturi 60 °C v primeru La(NO3)3 pri triurni potopitvi in Nd(NO3)3 pri 12urni potopitvi znašala 99 %. Protikorozijsko učinkovitost smo dodatno potrdili s testom v slani komori, ki je trajal 24 ur. Površinsko-analizne metode: vrstična elektronska mikroskopija in energijsko-disperzijska spektroskopija rentgenskih žarkov, so potrdile prisotnost lantanoidnih ionov na površini. Prevleka Ce(NO3)3 se tvori po celi površini vzorca, vendar so na prevleki vidne razpoke. Prevleki La(NO3)3 in Nd(NO3)3 pa se vežeta na vključke zlitine in je torej mehanizem zaščite drugačen kot pri Ce(NO3)3. Dobljeni rezultati potrjujejo, da so lantanoidne soli učinkoviti korozijski inhibitorji za aluminijevo zlitino AA7075-T6 in potencialno nadomestilo kromatnim prevlekam.

Keywords

korozija;aluminijeva zlitina 7075-T6;soli lantanoidov;konverzijske prevleke;

Data

Language:	Slovenian
Year of publishing:	2013
Typology:	2.11 - Undergraduate Thesis
Organization:	UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher:	[B. Volarič]
UDC:	669.71:620.193(043.2)
COBISS:	17432854
Views:	1874
Downloads:	258
Average score:	0 (0 votes)
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Other data

Secondary language:	English
Secondary title:	THE CORROSION INHIBITING BEHAVIOUR OF LANTHANIDE SALTS FOR ALUMINUM ALLOYS IN CHLORIDE MEDIUM
Secondary abstract:	Inhibition of corrosion processes on aluminium alloys using lanthanoid salts is considered as a potential replacement of toxic and cancerogenic chromate coatings. Lanthanoid compounds are environment friendly, their price is reasonable price and are available in nature sources. Aluminium alloy AA7075-T6 was protected by corrosion inhibitors of lanthanoid salts of cerium, lanthanum and neodymium. Research work was divided in two areas: a) Addition of corrosion inhibitor directly to corrosive medium, b) Preparation of conversion coating followed by testing in corrosive medium. Electrochemical results in corrosive medium of 0.1 M NaCl showed improved of corrosion characteristics of inhibited alloy, as was reflected in increase in polarization resistance (Rp), decrease in corrosion current density (jcorr) for several orders of magnitude and shift of breakdown potential (Epr) to positive values. Effectiveness of inhibition (UI) increases in the following order: CeCl3, La(NO3)3, LaCl3, Ce(NO3)3 in Nd(NO3)3 (stabilization time 1 h).The UI value of CeCl3 reached 99% indicating exceptional effectiveness. The mixtures of particular salts were also investigated. Conversion coatings were prepared by immersion of alloy in salt solution containing a strong oxidant (H2O2) at various temperatures. Lanthanoid salt is thereby oxidized or dehydrated. Electrochemical measurements confirmed that the UI of 99% was achieved for La(NO3)3 coating prepared for 3h at 60 C, and for Nd(NO3)3 coating for 12 h at 60 C. Corrosion protection was confirmed by salt spray testing for 24h. Surface analytical methods of scanning electron microscopy and energy dispersive X-ray spectroscopy identified the present of lanthanoid element at the surface. The Ce(NO3)3 was formed at the whole surface of the sample, whereas La(NO3)3 and Nd(NO3)3 were formed preferentially at the metallic inclusions. Obtained results confirmed that lanthanoid salts can be effectively used as corrosion inhibitors of aluminium alloy AA7075-T6 and are therefore a potential replacement for chromate coatings.
Secondary keywords:	corrosion;alluminium alloy AA7075-T6;lanthanoids salts;conversion coatings;
URN:	URN:SI:UM:
Type (COBISS):	Undergraduate thesis
Thesis comment:	Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages:	XV, 75 f.
ID:	8726798