Praseodymium oxides. Complete characterization by determining oxygen content

Abstract

Praseodymium ions are available in many oxidation states, so they are capable to form a huge number of different oxides, which make them an interesting and versatile material in many industries, such as ceramics or optics.Although praseodymium oxides behavior has been studied, the information found in the literature is sometimes contradictory. The different conditions of experimentation have led to opposite results due to rapid praseodymium oxide transformations. Many authors have pointed out the high oxygen mobility upon phase transformations during heating and cooling processes.Four materials based on praseodymium oxide compounds were characterized by physicochemical analysis. Praseodymium concentration was determined by WD-XRF and oxygen content was determined by the elemental analyzer TC-436, while XRD gave crystalline phases information and thermal analysis was carried out to obtain information about phase transformations. The combination of these analytical techniques allowed to have the real and accurate praseodymium concentration of a determined product, as it was found out that, two products that intended to have the same praseodymium concentration, were actually different.PrO2 and Pr2O3 were the major phases identified in these materials by XRD, although Pr(OH)3, and Pr6O11 were also found as minor phases in the original materials. From the results obtained by WD-XRF, XRD and simultaneous thermal analysis; crystalline phases concentration was calculated, but the determination of oxygen content by the elemental analyzer TC-436 was the key to validate the results obtained from WD-XRF, XRD and simultaneous thermal analysis. The oxygen determination method was optimized by increasing a 400% the sample weight introduced into the piece of equipment, which resulted in a precision improvement.In addition, one sample underwent different thermal treatments at the temperatures of 500, 650, 760, 980 and 1040 °C and two different cooling processes (slow cooling and quenching), to study phase transformations at these temperatures by measuring the oxygen content and determine the crystalline phases by XRD. It was found that, when the sample was quenched, different phases were formed at different temperatures, such as Pr9O16 and Pr7O12, while cooling slowly the calcined sample was always giving Pr6O11 because the intermediate phases were not stable enough to be determined.Thus, the aim of this work was to devise an adequately robust test method and use it to expand the present knowledge base concerning the praseodymium oxide physicochemical characterization and its behavior across different heating and cooling processes.