CeraMat

Two α-Al2O3/YAG composite powders have been prepared by reverse-strike precipitation, starting from chlorides aqueous solutions, the former containing 50 vol% of the two phases (labelled as AY50) and the latter made of 90 vol% of alumina and 10 vol% of YAG (AY90). The as-prepared powders were characterised by DTA/TG simultaneous analysis as well as by XRD analysis performed after calcination at different temperatures.

Al2O3-YAG (50vol.%) nanocomposite powders were prepared by wet-chemical synthesis and characterized by DTA-TG, XRD and TEM analyses. Amorphous powders were pre-heated at different temperatures (namely 600◦C, 800◦C, 900◦C and 1215◦C) and the influence of this thermal treatment on sintering behavior, final microstructure and density was investigated. The best performing sample was that pre-calcined at 900◦C, which yields dense bodies with a micronic/slightly sub-micronic microstructure after sintering at 1600◦C.

The preparation of pure Y3Al5O12 (YAG) and 50 vol% Al2O3–YAG composite powders by a wet chemical route is presented. The role of the synthesis temperature during reverse-strike precipitation has been investigated, showing its relevant effect on the purity and homogeneity of YAG powder. The composite material was prepared by comparing two different synthesis routes. A composite powder was synthesized via reverse-strike temperature-controlled co-precipitation. In the latter case, a pure-alumina precursor was firstly reverse-strike precipitated and then doped with an yttrium salt solution.

Wet chemical synthesis of precursor oxide ceramics is a method to obtain small particulate powders. Such powders are far more prone to ageing in air than more traditional precursors. Thermogravimetric analysis is used to highlight the species responsible for the ageing of ceramic precursors. Indeed water and carbon dioxide are observed to evolve from aged powders. Ceramics obtained from aged precursors can reach a very low final density with respect to the theoretical value.

The influence of inorganic precursors on phase evolution and powder sinterability of YAG has been investigated. YAG powders were synthesised by reverse-strike precipitation, from yttrium and aluminium chlorides or nitrates aqueous solution. The powders were characterised by thermal analysis and XRD measurements. Pure-YAG was obtained after calcination at high temperature from both precursors, but the chlorides-derived materials yield mixtures of YAG and metastable YAlO3 phases from 800°C to 1100°C.

UV-cured polysiloxane epoxy coatings containing titanium dioxide were prepared by means of a cationic photopolymerization process. A good distribution of the inorganic filler was achieved within the polymeric network with an average size dimension of around 500 nm. UV-vis analysis performed on organic dye (methylene blue) stained coatings showed a high efficiency of the titania photocatalytic activity: a complete degradation of the dye on the coating surface is reached after 60 min of UV irradiation without affecting the matrix photo-degradation.

De-agglomeration of a nanocrystalline transition alumina powder was performed in distilled water at its natural pH under magnetic stirring for 170 h or by ball milling for 3 h. Gibbsite appeared near transition aluminas in the magnetic stirred sample. In addition, a relevant lowering of the α-Al2O3 crystallization temperature was observed in the dispersed materials with respect to the as-received powder. However, the activation energy of the above transformation, determined by the Kissinger method, was in any case about 480–500 kJ/mol and unaffected by the dispersion route.

The composite powders 90 vol.% Al2O3–5 vol.% YAG–5 vol.% ZrO2 were produced by doping commercial alumina powders with zirconium and yttrium chloride aqueous solutions. Both a nanocrystalline transition alumina and a pure α-phase powder were used as starting materials. The obtained materials were characterized by DTA-TG, XRD and dilatometric analyses and compared to the respective biphasic systems developed by the same procedure.

Doping of commercial alumina nanopowders by using aqueous solutions of metal salts was exploited to prepare alumina-based nanocomposites. The same procedure was applied to produce a composite made of immiscible phases, that is an alumina–zirconia material, by doping an α-alumina powder with a zirconium chloride solution, as well as to produce an alumina–YAG (yttrium aluminium garnet) system by doping alumina with a yttrium chloride solution and promoting YAG formation by solid-state reaction at high temperature. For this latter case, the difference in reactivity between two commercial po

Al2O3/YAG composite powders have been synthesised by reverse strike precipitation. The powders were characterised by DTA/TG simultaneous analysis; the phase evolution was studied by XRD analysis, while the crystallite formation and growth were followed by TEM observations. A fully dense, homogenous material was obtained by sintering 900°C pre-treated powders at 1600°C for 3 h. For limiting grain growth, both a doping with 500 ppm MgO followed by a free sintering and a fast sintering procedure involving a high heating rate (50°C/min) were performed.