Zirconia thermal analysis

Shock-modified zirconia powder was reacted with lead oxide in controlled differential thermal analysis (DTA) experiments and compared to the unmodified material by Hankey and co-workers [82H01]. This reaction yields... 

Fig. 7.10. The solid state reactivity of shock-modified zirconia with lead oxide as studied with differential thermal analysis (DTA) shows both a reduction in onset temperature and apparent increase in reaction rate. The shock-modified material has a behavior much like the much higher specific surface powder shown in B (after Hankey et al. [82H01]).

Shalliker, R.A. Douglas, G.K. Rintoul, L. Russell, S.C. The analysis of zirconia-silica composites using differential thermal analysis, Fourier transform-Raman spectroscopy and X-ray scattering/scanning electron microscopy. Powder Technol. 1998, 98, 109-112. 

Figure 4. Dihferential thermal analysis of ahimina-zirconia siqiports.

Thermal analysis of co-precipitated ZTA powders. DTA, TGA and DTG curves for the coprecipitated alumina-zirconia precipitated mixture are shown in Figure 2 revealing the loss of... 

The peak 5 at around 470°C, observed in DSC curve, corresponds to an exothermic phenomenon without any loss of weight. It can thus be attributed to the crystallization of the amorphous zirconia. This is confirmed by the X-ray diffraction pattern obtained after the thermogravimetric analysis (Fig. 9). According to del Monte et al. [17] the peaks located at 20 = 28 and 31.5° are characteristic of the monoclinic zirconia whereas those situated at 20 = 30, 34.5 and 50° belong to the tetragonal structure.This study showed that nanostructured porous zirconia has a low thermal stability. In the preparation of the stable and efficient catalysts for the complete oxidation of aromatics, this low thermal stability will be taken into account. 

A synthesis protocol of porous zirconia catalyst support, through a neutral Ci3(EO)6-Zr(OC3H7)4 assembly pathway has been developed. Our studies evidenced the role played by the surfactant. It has also been observed that the increase of hydrothermal treatment time and temperature have a benefical effect on tailoring the pore sizes. The synthesized materials will be used in preparation of Au / ZrOz, Au / VO / ZrOz catalysts, which will be tested in the benzene oxidation reaction. Thermogravimetric analysis shows that the recovered zirconia present a relatively low thermal stability. Then the structure collapses due to the crystallization to more stable tetragonal and monoclinic phase. 

Figure 2. Thermal gravimetric analysis of alumma zirconia supports.

Microstxuctural studies of the sintered pellet depicted highly dense grain morphology. Furthermore, conductivity analysis evidenced an Arrhenius-type thermally activated ionic conduction above 300 °C. However, the electrical conductivity of the system was foimd to increase with the bismuth content up to X = 0.05, and thereafter decreased due to less solubility of Bi " into zirconia matrix. A better conductivity, 0.019 S/cm, was achieved for 5 mol% Bi203 cal-cia-codoped cubic zirconia system at 760 °C. Thus, the cost-effective bismuth codoped calcia-stabilized zirconia might be a possible alternative to YSZ, due to its ionic conductivity comparable to that of the YSZ. 

Aerogels composed of 60% silica and 40% zirconia were calcined in air, at 400°C, 800°C and 1000°C. After thermal treatment, the porous texture of the samples have been analyzed by mercury porosimetry (Fig. 11-15) (Pirard, 1997c). The three samples are irreversibly densified by isostatic pressure in the whole pressure domain, from 0.01 to 200 MPa. The data analysis (Fig. 11-16) has been done using equation (11-7), with a constant k estimated at 48 nm MPa°-, by nitrogen adsorption-desorption isotherm analysis. The volume distributions versus pore size obtained show that the pore volume decreases for all pore sizes during aerogel calcination at increasing temperatures. This is... 

As we will see, the differences in OSC are not solely influenced by thermodynamic factors. Depending on the temperature at which the OSC is measured and also on the nature of the reducing agent (H2,C0), other surface-related processes may have a significant influence on the measured OSC values. Kinetic factors and, in connection with them, the surface structure of the oxides have a relevant role. In general, the interplay between surface and bulk structure determines the observed total OSC values. As with the OSC differences between ceria and ceria-zirconia metal-loaded catalysts, a more in-depth analysis is required in order to fully understand the redox response of thermally aged oxides. 

---