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Karakterizacija tribokorozijskih procesov na dentalnih zlitinah pri različnih vplivih okolja
Močnik, Petra (Avtor), Bizjak, Milan (Mentor) Več o mentorju... Povezava se odpre v novem oknu, Kosec, Tadeja (Komentor)

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Izvleček
Tribokorozija, ki je sočasni proces korozije in mehanske obrabe, lahko privede do večjih obrab dentalnih materialov med njihovo uporabo. Cilji doktorske naloge so bili pridobiti informacije o vplivih okolja na material, o tribokorozijskih procesih in koncentracijah izločenih kovinskih ionov na dveh dentalnih zlitinah, in sicer na žici zlitine NiTi in žici iz nerjavnega jekla v simulirani slini. Z elektrokemijskimi metodami smo ugotovili korozijske lastnosti, z različnimi fizikalnimi in spektroskopskimi metodami pa smo določili mehanske in mikrostrukturne lastnosti ter sestavo oksidnih plasti. S tribokorozijskimi preiskavami smo ovrednotili skupno stopnjo obrabe in posamezne prispevke k skupni obrabi. Z elektrokemijskimi metodami smo ovrednotili, kako na korozijske lastnosti vpliva slina, nizek pH ter prisotnost fluoridov. Zlitina NiTi ima dobre repasivacijske lastnosti, vendar je pri nizkih pH in ob prisotnosti fluoridov izpostavljena intenzivnemu raztapljanju. Žica iz nerjavnega jekla ima v primerjavi z zlitino NiTi nižjo polarizacijsko upornost in večjo nagnjenost k lokalnim oblikam korozije, kar smo določili iz pozitivne histereze ciklične krivulje. Tribokorozijske procese smo spremljali na preizkuševališču z izmeničnim gibanjem. Med tribokorozijsko obrabo smo uporabili in ovrednotili tri elektrokemijske metode za spremljanje tribokorozijskih procesov: metodo s spremljanjem potenciala, potenciostatsko metodo ter meritev elektrokemijskega šuma. Pridobili smo informacije o skupni stopnji obrabe in določili posamezne prispevke. Žica iz zlitine NiTi se zaradi manjše trdote, mikrostrukture in sestave oksidne plasti obrablja bolj kot nerjavna žica. Delež mehanskega prispevka k skupni stopnji obrabe je večji pri žici NiTi. Z meritvami XPS/AES smo določili sestavo in razlike med osnovno ter novonastalo oksidno plastjo v obrabni razi po tribokorozijskem preizkusu. Prav tako smo spremljali izločanje ionov pri izpostavitvi žic z določevanjem kovin v simulirani slini z ICP-MS med obrabo in statično izpostavitvijo. Koncentracije kovinskih ionov se s časom izpostavitve znižujejo in koncentracija niklja pri statični izpostavitvi ne presega mejne vrednosti, določene z EU-direktivo 0,5 μg/cm2 × (7 d). S tribokorozijskim preizkusom smo simulirali enodnevno obrabo in določili koncentracijo izločenega Ni, ki je bila pri žici NiTi 134-krat presežena vrednost iz EU-direktive in 65-krat pri žici iz nerjavnega jekla.

Jezik:Slovenski jezik
Ključne besede:dentalne zlitine, NiTi, nerjavno jeklo, simulirana slina, tribokorozija, XPS/AES, izločanje ionov
Vrsta gradiva:Doktorsko delo/naloga (mb31)
Organizacija:NTF - Naravoslovnotehniška fakulteta
Leto izida:2018
COBISS.SI-ID:1731935  Povezava se odpre v novem oknu
Število ogledov:403
Število prenosov:610
Metapodatki:XML RDF-CHPDL DC-XML DC-RDF
 
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Sekundarni jezik

Jezik:Angleški jezik
Naslov:Characterization of Tribocorrosion Processes on Dental Alloys in Different Environments
Izvleček:
As a simultaneous process of corrosion and mechanical wear, tribocorrosion can cause accelerated wear of dental materials during their use. The goal of the doctoral thesis was to obtain information about two environmental effects which affect these materials, i.e. tribocorrosion processes and the quantity of metal ions released onto them. The materials involved were two dental alloys, i.e. NiTi alloy wire, and stainless steel wire, both in simulated saliva. Their corrosion properties were determined by electrochemical methods, whereas their mechanical and microstructural properties, as well as the composition of their oxide layers, were determined by means of various physical and spectroscopic methods. Tribocorrosion tests were used to evaluate the total wear rate and the contributions to total wear. The corrosion properties of the wires in saliva, as well as in saliva with low pH values and in the presence of fluorides, were determined by means of electrochemical methods. It was confirmed that, on the one hand, the NiTi alloy has good repassivation properties, although at low pH values and in the presence of fluorides it undergoes accelerated dissolution. On the other hand it was found that the stainless steel wires had a lower polarization resistance compared to that of the NiTi alloy, as well as a greater tendency to local corrosion, which was determined from the positive hysteresis of the cyclic polarization curve. During the tribocorrosion tests, using a reciprocal tribometer, three electrochemical methods for monitoring tribocorrosion processes were used: firstly, a method for the monitoring of potential, secondly a potentiostatic method, and thirdly electrochemical noise measurements. Data about the total wear rate and individual contributions were obtained and evaluated. It was found that the NiTi alloy wire became more quickly worn, compared to the stainless steel wire, due to the alloy's hardness and different microstructural properties / oxide layer. The mechanical contribution to the total wear rate was higher in the case of the NiTi wire. The composition and differences between the base and newly formed oxide layer were determined by means of XPS/AES analysis. The ion release of wires exposed to simulated saliva was observed by ICP-MS analysis. The concentrations of metal ions decreased with exposure time, and the concentration of Ni did not exceed the limit values set by the EU Directive, i.e. 0.5 μg/cm2 × (7d). The concentrations of metal ions which could be transferred into the human body were monitored in the tribocorrosion experiments by means of simulated 1-day wear tests. It was found that in the case of the NiTi wire the concentration of Ni exceeded the value prescribed by the EU directive by a factor of 134, whereas in the case of the stainless steel wire this factor amounted to 65.

Ključne besede:dental alloys, NiTi, stainless steel, simulated saliva, tribocorrosion, XPS/AES, ions release

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