International audienceThe interactions between zirconia (ZrO2) powder and three Algerian hydrated kaolinitic clays were studied at high temperatures. The analysis by X-ray diffraction of the prepared products allowed to follow the different phase developments during heat treatment and to identify the parameters controlling the zirconia conversion into zircon (ZrSiO4). It was found that ZrSiO4 formation, occurring at temperatures above 1150°C, is enhanced by the presence, in the clays, of fusing impurities such as K, Fe, Ca, and Mn, and by a decrease in zirconia particle size. A reactional mechanism, involving zirconia, a flux, and cristobalite is proposed. Moreover, the effect of zirconia additions on sintering was studied. It was also found that the increase in the porosity ratio of the final products for zirconia levels above 20 wt% was governed by a decrease in the flux amount, due to its lower clay content. Finally, it was shown that ceramics obtained by sintering at 1400°C for 2 h of a mixture of 38 wt% of fine zirconia powder and 62 wt% of the more reactive clay were mainly constituted of zircon and mullite

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Thin films of undoped zinc oxide (ZnO) and doped ZnO with copper were deposited on ceramic pellets made from abundant local clay materials with an addition of zirconia (ZrO 2 ).The thin layers were prepared by a thermal method using an autoclave. The resulting structural and morphological properties of the products were studied in order to determine the effectiveness of their photocatalytic activities. X-ray diffraction, Scanning Electron Microscopy, energy-dispersive X-ray spectroscopy and UV-visible spectrophotometry were used in this goal. An application test was carried out to quantify the photocatalytic degradation of a toxic organic dye -Orange II (OII) by these samples under UV light. In similar conditions, the layers deposited on the ceramics with addition of zirconia have shown better performances than those without zirconia. This result can be related to the porosity created when the zirconium oxide reacted with SiO 2 of the clay. The open porosity observed on this type of substrate allows a larger surface for the photocatalysis. The degradation rate of OII reached 90.5 % during a period of 7 hours with Cu doped ZnO thin layers deposited on porous substrates modified with addition of ZrO 2 .

Different percentages of CuO and ZnO were added into a local kaolin ceramic-based powder (DD3) with and without ZrO2. The modified powders were first characterized, then, a test for the photocatalytic degradation of dyes with orange II (OII) was carried out. The DD3 powders that were obtained with the addition of ZrO2, ZnO, and CuO, were prepared by two different methods and have shown a large and very fast photocatalytic activity. Discoloration ratios of about 93.6% and 100% were reached after 15 min and 45 min, for CuO and ZnO respectively. Finally, an alternative photocatalysis mechanism, based purely on chemical reaction processes, is proposed. The photocatalysis results with modified powders are compared with the results obtained with thin films, made with the same materials.

To purify water at low cost for our daily life, the effect of ceramic-based (mullite–cristobalite) and (mullite–zircon) powders doped with different amounts of magnesium oxide (MgO) (10 and 20 wt%) was studied. These compounds are made of a local raw material DD3 with addition of zirconia (ZrO2) to create an open porosity. The powders were prepared by the traditional mixing method with the help of an automated crushing. The effect of MgO doping on structural, morphological and photocatalytic properties of the material was studied by various analytical techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, infrared, and UV–visible spectrometry. The results of XRD proved that there was a deformation in the crystal structure of the two types of ceramics after addition, which resulted in a shift of the spectra to the right, while SEM proved the presence of pores with a larger size as the proportion of MgO increases. The chemical composition of the basic components of the ceramic compounds as well as the additive was confirmed with EDS and IR spectra. The final results show that ceramics with added zirconia (DD3Z) and doped with 10% of MgO have a better photocatalytic efficiency than ceramics without zirconia. This important effect could be related to the higher rate of porosity, which provides a more active surface. The 10% MgO content showed a high photoactivity of 77.33% in only 15 min. The maximum hydrolysis rate obtained with Orange II was 92.95% after a period of 45 min with DD3Z/MgO powders.