THERMAL-BEHAVIOR AND TEXTURE OF MESOPOROUS ZIRCONIA OBTAINED FROM ANIONIC SURFACTANTS

Thermogravimetric and differential thermal analyses of mesoporous zirc onias obtained from anionic surfactants by a scaffolding mechanism rev eal interesting differences between the samples prepared from long-cha in sulfates or sulfonates, which lose their hydration water in two ste ps, and those obtained from long-chain phosphates for which dehydratio n occurs in one step. From the temperature of the tetragonal to monocl inic transition the molar volume of ZrO2 undergoing this transformatio n can be calculated. From the density and from the mesoporous volume ( N-2 adsorption), the thickness of the wall separating the elemental vo lumes of the mesoporous structure can be calculated as well as the pse udo-length of the pores. The calculated surface area of the mesopore f its nicely with the measured T-plot surface area for the sample calcin ed at 500 degrees C. For the sample dried at 140 degrees C, the agreem ent is not as good, probably because of a more disordered organization . The alkyl chain is tilted by about 57 +/- 10 degrees with respect to the normal to the wall. Upon calcination the thickness of the wall in creases to a point where crystallization in monoclinic zirconia occurs . At this point the mesoporous character is lost.