Dialkyldithiophosphate Acids (HDDPs) as Effective Lubricants of Sol–Gel Titania Coatings in Technical Dry Friction Conditions

The goal of this study was the investigation of the effectiveness of dialkyldithiophosphate acids (HDDPs) films in improving the tribological properties of thin, sol– gel derived titania coatings. Amorphous, anatase, and rutile titania coatings were obtained using sol–gel dip–coating deposition after treatment at 100, 500, and 1,000 C, respectively. Titania coatings were then modified from the liquid phase by HDDPs acids having dodecyl-(C12), tetradecyl-(C14), and hexadecyl-(C16) alkyl chains deposited by dip–coating (DC) and Langmuir–Blodgett (LB) methods. The influence of the deposition procedure, the length of the HDDPs alkyl chain and the type of titania substrate on the surface morphology and tribological properties were studied. It was found, using wetting contact angle measurements, that these modifications of titania coatings decrease the surface free energy and increase its hydrophobicity. The surface topography imaged by Atomic force microscopy (AFM), exhibit island-like or agglomerate features for the DC deposition method, while smooth topographies were observed for LB depositions. Tribological tests were conducted by means of a microtribometer operating in the normal load range 30–100 mN. An enhancement of tribological properties was observed upon modification, as compared to unmodified titania

Structural analysis and corrosion studies on an ISO 5832-9 biomedical alloy with TiO2 sol–gel layers

The aim of this study was to demonstrate the relationship between the structural and corrosion properties of an ISO 5832-9 biomedical alloy modified with titanium dioxide (TiO2) layers. These layers were obtained via the sol–gel method by acid-catalyzed hydrolysis of titanium isopropoxide in isopropanol solution. To obtain TiO2 layers with different structural properties, the coated samples were annealed at temperatures of 200, 300, 400, 450, 500, 600 and 800 C for 2 h. For all the prepared samples, accelerated corrosion measurements were performed in Tyrode’s physiological solution using electrochemical methods. The most important corrosion parameters were determined: corrosion potential, polarization resistance, corrosion rate, breakdown and repassivation potentials. Corrosion damage was analyzed using scanning electron microscopy. Structural analysis was carried out for selected TiO2 coatings annealed at 200, 400, 600 and 800 C. In addition, the morphology, chemical composition, crystallinity, thickness and density of the deposited TiO2 layers were determined using suitable electron and X-ray measurement methods. It was shown that the structure and character of interactions between substrate and deposited TiO2 layers depended on annealing temperature. All the obtained TiO2 coatings exhibit anticorrosion properties, but these properties are related to the crystalline structure and character of substrate–layer interaction. From the point of view of corrosion, the best TiO2 sol–gel coatings for stainless steel intended for biomedical applications seem to be those obtained at 400 C.This study was supported by Grant No. N N507 501339 of the National Science Centre. The authors wish to express their thanks to J. Borowski (MEDGAL, Poland) for the Rex 734 alloy

Właściwości tarciowe i zużyciowe powłok tlenku glinu wytwarzanych metodą zol-żel

In this study, alumina coatings were prepared by the sol-gel method using the dip-coating technique. All samples were prepared on silicon wafers Si (100) with the use of aluminium sec-butoxide as a precursor. The surface topographies of alumina coatings were imaged by an atomic force microscope (AFM). Tribological properties were characterised using a microtribometer and an optical microscope. The results show a strong dependence of antiwear and antifrictional properties of alumina coatings on the annealing temperatures. The best performance was exhibited by coatings heated to 1000°C due to the formation of hard alfa-Al2O3.Badane powłoki tlenku glinu zostały otrzymane w oparciu o metodę zol-żel z wykorzystaniem techniki zanurzeniowej (dip-coating). Na powierzchnie płytek krzemowych nanoszono roztwory prekursora, którym był sec-butoksyglin. Analizę topografii powierzchni wytworzonych powłok tlenku glinu przeprowadzono z wykorzystaniem Mikroskopu Sił Atomowych (AFM). Właściwości tribologiczne zostały scharakteryzowane z użyciem mikrotribometru (T-23) i mikroskopu optycznego. Uzyskane wyniki wskazały istnienie zależności między właściwościami przeciwtarciowymi i przeciwzużyciowymi powłok tlenku glinu a temperaturą wygrzewania próbek. Najlepsze właściwości wykazały powłoki wygrzewane w 1000°C, co spowodowane jest obecnością fazy alfa-Al2O3