For the promising erosion and oxidation resistance of carbide cermet coating, Cr39Ni7C cermet coatings were deposited by Diamond Jet spray process using a commercial Sulzer Metco 5241 powder in this study. The microstructure, phase composition and high temperature oxidation behavior of the deposited coatings were investigated. The speed and temperature of in-flight particles were measured by DPV-2000. The results revealed that the speed of in-flight particles decreased from 229 m/s to 150 m/s with the increasing of spraying distance from 100 mm to 300 mm, whereas the average temperature of in-flight particles increased from 1926 to 2245 K. The decarburization of Cr 3 C 2 increased with the increasing of fuel gas flow from 30 FMR to 40 FMR for higher heat enthalpy of flame. Due to the formation of Cr 2 O 3 on/in the coatings at high temperature, the sprayed coatings had good oxidation resistance at 1073 K in air atmosphere. For the lower porosity of the coating deposited under the spraying distance of 150 mm, its oxidation resistance was better than that sprayed under the spraying distance of 200 mm.

Hydroxyapatite (HAp Ca 10 (PO 4 ) 6 (OH) 2 ) is very known to be a biomaterial and an absorbent for chromatography. In this study, HAp was agglomerated with anatase TiO 2 to manufacture thermal spray powders to improve the absorption activity of TiO 2 and then improve its photocatalytic activity. The microstructures and compositions of plasma sprayed TiO 2 , TiO 2 -10%HAp, TiO 2 -30%HAp and HAp coatings were investigated. Due to the low thermal conductivity of HAp compound, not all HAp particles fully melted even under the arc current of 800 A. Low temperature stable β-Ca 3 (PO 4 ) 2 was detected in the sprayed HAp coatings. The addition of HAp inhibited the phase transformation of anatase TiO 2 to rutile. Under the arc current of 600 A, the anatase content in the TiO 2 , TiO 2 -10%HAp and TiO 2 -30%HAp coatings was 10.6%, 20% and 42%, respectively. Although slightly decomposition of HAp to α-Ca 3 (PO 4 ) 2 was found in the TiO 2 -30%HAp coatings, it did not decompose to CaO and P 2 O 5 according to the XRD and EDAX analysis. With the increasing of the spraying distance from 70 mm to 110 mm, the anatase content in the TiO 2 -30%HAp coatings decreased from 34% to 17% under arc current of 700 A. The addition of the secondary gas of helium has no significant influence on the melting state of the TiO 2 -HAp feedstock powders.

The compositions and photocatalytic activity of plasma sprayed TiO 2 , TiO 2 -30%FeTiO 3 , TiO 2 -50%FeTiO 3 and FeTiO 3 coatings were investigated. The influence of FeTiO 3 compound on the photocatalytic activity of TiO 2 coating was clarified. The TiO 2 -30%FeTiO 3 coating sprayed under the arc current of 400 A had good photocatalytic activity because the coating did not contain the unfavorable Fe 2 TiO 5 phase. The relative deposition speed of TiO 2 -30%FeTiO 3 powder under the arc current of 400 A was approximate to 4 µm/pass. Although pure FeTiO 3 compound nearly did not show photocatalytic performance, the existence of FeTiO 3 could improve the photocatalytic activity of anatase TiO 2 if FeTiO 3 contacts coherently with it, which was explained using two-steps electron transfer model.

TiO 2 based coatings are promising photocatalyst as they are chemically stable and nontoxic. To develop more effective photocatalyst with cost effective plasma spraying technique, TiO 2 and TiO 2 -Fe 3 O 4 coatings were prepared using agglomerated anatase TiO 2 and composite TiO 2 -Fe 3 O 4 powders, respectively. The photocatalytic activity and photoelectrochemical characteristics of sprayed coatings were examined. The photo-response of the sprayed TiO 2 electrode was comparable to that of single crystal TiO 2 , but the breakdown voltage approximated to 0.5V (vs. SCE). The short-circuit current of TiO 2 was 1.05mA/cm 2 , which was 15 times comparing with that of TiO 2 -Fe 3 O 4 electrode under 30mW/cm 2 xenon light illumination. N-type TiO 2 semiconductor particle reacted with Fe 3 O 4 or Fe 2 O 3 particle and concurrently produced p-type FeTiO3 in plasma spraying processes. FeTiO3 compound obviously improved the photocatalytic activity of the TiO 2 coating for the formation of p-n junction between p-type FeTiO3 and n-type TiO 2 , which may spatially separate the photo-generated electrons and holes. As a result, plasma-sprayed TiO 2 -Fe 3 O 4 coatings are promising candidates for the applications to photocatalyst.

The photoelectrochemical characteristics of plasma sprayed porous TiO 2 , TiO 2 -5%ZnO and TiO 2 -10%ZnO electrodes in 0.1N NaOH solution were studied through a three-electrode cell system. The microstructure, morphology and composition of the electrodes were analyzed using electron probe surface roughness analyzer (ERA-8800FE), scanning electron microscope (SEM) and X-ray diffraction. The results showed that the sprayed electrodes had a porous microstructure, which was affected by the plasma spraying parameters and composition of the powders. TiO 2 -ZnO electrodes consisted of anatase TiO 2 , rutile TiO 2 and Zn 2 Ti 3 O 8 phase. The photoresponse characteristics of the plasma sprayed electrodes were comparable to that of single crystal TiO 2 , but the breakdown voltage was approximate to 0.5V (vs. SCE). The short-circuit photocurrent density increased with a decrease of donor concentration, which was calculated according to Garner-Bulter model. For the lowest donor concentration of a TiO 2 -5%ZnO electrode prepared under the arc current of 600A, the short-circuit photocurrent density was approximately 0.4mA/cm 2 higher than that of the TiO 2 electrodes under 30mW/cm 2 xenon light irradiation. The photocurrent density increased linearly with light intensity.

Owing to the much concern with global environmental problem, photocatalytic TiO 2 coatings were obtained using plasma spraying technique. The influences of the content of Fe 3 O 4 additive to the TiO 2 powder on the phase composition, microstructure and photo-absorption of plasma sprayed TiO 2 coatings were systematically studied. The photocatalytic efficiency of the sprayed coatings is evaluated through the photo mineralization of acetaldehyde. The UV-VIS-NIR absorption spectra of the deposited coatings were obtained by using Shimadzu UV-3100PC scanning spectrophotometer. The results showed that the TiO 2 -Fe 3 O 4 coatings consist of anatase TiO 2 , rutile TiO 2 and FeTiO 3 ilmenite, and Fe 2 TiO 5 pseudobrookite phase appears when the content of Fe 3 O 4 additive is equal to or over 10%. The content of anatase TiO 2 in the sprayed coatings decreases from 14.8% to 5.9% with the increasing of Fe 3 O 4 content to 32.6%. It was found that TiO 2 coatings can decompose acetaldehyde under the illumination of ultraviolet rays, and the degrading efficiency is improved with an increase in the content of FeTiO 3 in the coatings. However, the presence of large amount of Fe 2 TiO 5 compound will substantially lower the photocatalytic efficiency of the sprayed TiO 2 -Fe 3 O 4 coatings for the unfavorable photo-excited electron-hole transfer process.

Titanium dioxide has promising photocatalytic properties that can be used in the treatment and purification of air and water. The aim of this study is to determine how process parameters and oxides added to generate anastasis affect the microstructure and surface properties of plasma sprayed TiO 2 . The photocatalytic effect of the layers and the influence of microstructure are investigated with the help of acetaldehyde degradation. The results show that the layers produced consist of anatase (3-15%) and rutile components. It has been proven that TiO 2 is capable of decomposing acetaldehyde under UV radiation in proportion to the amount of anatase present. Paper includes a German-language abstract.