Ductile iron pipes (DIP) have been used worldwide since 1960s for water transmission and distribution mains. By 1979, ductile iron pipe largely replaced cast iron as the predominant material in water industry. Zn and Zn/Al 85/15 coatings applied by thermal spray technique are used for the protection of the ductile iron pipe against corrosion in heterogeneous soil conditions. In this study, heat treated and non-heat treated ductile iron pipe samples were coated with Zn and Zn/Al 85/15 in optimum spray parameters by twin wire electric arc (TWEA) spraying technique. The coatings were investigated by optical microscopy, scanning electron microscopy (SEM), and analyzed by energy dispersive spectrometer (EDS). Both Zn and Zn/Al 85/15 coatings showed fairly good lamellar structure with acceptable amount of internal porosities and oxides. Annealing oxides available on pipe surface helped the bonding of coatings. The protection performance of the coatings was compared with accelerated corrosion (salt spray) test according to the ASTM B 117 and corrosion products were analyzed by SEM and EDS technique. Salt spray test results showed that Zn/Al 85/15 coatings have better corrosion resistance than Zn coatings and annealing oxide on ductile iron pipe acts as a good corrosion resistant protective layer.

Twin wire arc sprayed Zn, Al and Zn/Al 85/15 coatings were investigated for comparison of their corrosion resistance, electrochemical behavior. The Zn, Al and Zn/Al 85/15 coatings possess prominent electrochemical passivation behavior. Oxide formation mainly onto the coating surfaces were identified with energy-dispersive X-ray analysis and were believed to be responsible for the passivation phenomena observed in the electrochemical polarization. Zn and Al are more negative in electrochemical potential than iron. Zn coatings act as a sacrificial anode and providing cathodic protection. Aluminum shows passive corrosion protection according to stable oxide layer occurs on coating surface. Zn/Al 85/15 coating show two corrosion protection mechanisms together. In this study, steel samples were coated with Zn, Al and Zn/Al 85/15 in optimum conditions by wire arc spraying technique. These coatings were investigated behaviors of polarization and corrosion resistance with electrochemical test.

Zn and Zn/Al coatings were manufactured by using twin wire arc spray (TWEA) system under various gas pressure and current. Microstructure, hardness, surface roughness and adhesion strength of the coatings were investigated by using standard characterization methods. Test results show that increasing atomizing gas pressure increased mechanical properties and surface quality. The process current had an important role on microstructural, mechanical properties and surface quality.

The objective of the present work is to produce Mg-PSZ (magnesia partially stabilized zirconia) powders that were used to coat oxygen sensor tubes by plasma spraying. It is well known fact that zirconia based oxide thin films are the most widely used material as ionic conductors of oxygen. In this study, MgO stabilized ZrO 2 powders were produced by the sintering and crushing method. Starting powders were a high grade ZrO 2 , and a natural hydromagnesite (Mg-HC) as MgO source. ZrO 2 , and MgO were mixed in the compositions of ZrO 2 - 9mol % MgO. The mixtures were ball milled by using ZrO 2 balls. The fine powders were stabilized via thermal treatment in air at 1540°C for 24 hours. The powders were calibrated to the correct particle size distribution for plasma spraying. All powder samples were characterised by a well-defined techniques with an exhibited an average particle size of 10 µm. The powders consisted of monoclinic, tetragonal and cubic phases. They were sprayed by plasma spray to produce high temperature Mg-PSZ coatings on oxygen sensor tubes. It is worthwhile to point out that high temperatures were generated in the plasma spray jet, and the rapid quenching of the molten Mg-PSZ droplets deposited on the cold substrate subsequently occurred. After this process, thermal treatments were carried out to improve the film density and microstructural stability.