prvi kongres hrvatskih znanstvenika iz domovine i inozemstva - HATZ

PRVI KONGRES HRVATSKIH ZNANSTVENIKA IZ DOMOVINE I INOZEMSTVAZagreb - Vukovar, 15. - 19. studenog 2004.P - 35SYNTHESIS OF ZrTiO4 BY BALL-MILLING AND SINTERING OFEQUIMOLAR MIXTURE OF TiO 2 AND ZrO 2 ,Gajović, A., Furić, K., Musić, S., Tomašić, N.Faculty of Science, University of Zagreb, CroatiaHigh-energy ball-milling induces the solid state reaction in equimolar mixture of TiO2 andZrO2. Synthesis of ZrTiO4 was monitored during and after sintering to find out theconditions for the preparation of ZrTiO4 with improved properties.The milling of anequimolar mixture of TiO2 and ZrO2 was performed in air using a Fritsch planetary ballmill “Pulverisette 6” with vial and balls made of zirconia (94% ZrO2). The rotation speedwas 500 rpm. Two different powder-to-ball weight ratios (R) were used; R1=1:50 andR2=1:10. The milling time varied from 1 min to 10 hours. The effect of milling on theformation and microstructure of ZrTiO4 was investigated by transmission electronmicroscopy (TEM), selected area electron diffraction (SAED), Raman spectroscopy (RS)and X-ray powder diffraction (XRD). The sintering processes were monitored in situ athigh temperature (300 to 1100 C) by RS. The final products of sintering wereadditionally investigated by scanning electron microscopy (SEM) to determine their grainsizes. The ball-milling induced the structural changes in the starting materials, as well asthe solid state reaction. In samples milled for longer time the presence of ZrTiO4 wasevidenced by RS and XRD. With prolonged milling the materials were partiallyamorphised and the sizes of the particles decreased to nanovalues (Fig. 1) andconsequently the Raman bands and XRD lines broadened. The rate of solid statereaction, amorphisation and contamination, due to wearing of milling media, depended onthe powder-to-ball weight ratio. The process was faster using R1=1:50, but thecontamination was greater. The milling of oxides did not complete the solid-state reaction,so additional sintering was necessary. Raman spectroscopy performed in situ at hightemperature showed that the mixture milled for 10 h with R2=1:10 was partiallyamorphous at the beginning and stayed amorphous during the heating (Fig. 2a). Thespectrum recorded upon the cooling contained only bands of orthorhombic ZrTiO4, so wecould conclude that heating at 1100 C completed the solid state reaction between TiO2and ZrO2. The solid state reaction was completed faster and at temperatures much lowerthan expected from the reference literature (1500 – 1600 C). On the other hand, duringsintering of the 1 h milled mixture with R1=1:50 the Raman spectrum recorded in situ at900 C showed the shape and relative band intensity that corresponded to the spectrumof ZrTiO4 at this temperature (Fig. 2b). Sintering at higher temperature amorphisedmaterial and after cooling to room temperature the bands of impurities dominated thespectrum. In the mixture milled for 20 min with R2=1:10 containing micron sized particles,amorphisation was not observed below than 1000 C (Fig. 2c) and Raman bands ofZrTiO4 were not observed upon cooling.The sintered oxides were investigated by SEM(Fig. 3). The sintering to 1100 C in argon proceeded through the first stage that isformation of a continues phase of pore. The small grain sizes (1 m) were evident inlong milled mixtures. Samples sintered from micron-sized powders had grains of severalm (Fig. 3c). The high-energy ball milling initiated solid state reaction in equimolarmixture of TiO2 and ZrO2. The oxides achieved by ball-milling underwent amorphisationduring sintering due to lowering of the diffusion temperature. It accelerated the solid state38