Strain induced phase transformations in lead monoxide

Abstract

The strain induced phase transformations produced in lead monoxide powders by ball milling at temperatures ranging from -196 to 200~'C have been studied by X-ray diffraction methods. It has been found that either of the two polymorphs, litharge and massicot, was partially converted to the other at all the temperatures investigated, and that, whichever polymorph was the starting material, the end product, after a sufficiently long time, was a mixture of the two polymorphs, both highly strained. The percentage of each phase present was found to be dependent on the temperature of deformation. The results have been interpreted by consideration of the production of the rnicrostrain energy required to overcome the energy barrier to the transformation, and of the shear generated in the mill on the pressuretemperature phase diagram. It is considered that shear stresses can affect the nature of the pressuretemperature phase diagram, in a manner theoretically postulated by Kumazawa. The commercial importance of the results has been briefly outlined.

Some recent developments in mechanical activation and mechanosynthesis

“…The fraction of each phase depends on the microstrain energy ground elemental powders or simply by grinding an already formed compound, attractive materials can also be obtained required to overcome the energy barrier for transformation, and on how shear stresses applied during milling modify the from chemical reactions which take place between ground reactants at temperatures and at rates at which they would pressure-temperature phase diagram. 42 The influence of the type of applied stress, and thus of the milling mode, is further normally not occur.4,9-11 Some reactions, for instance the mechanochemical reduction of SmCl 3 :11 shown by the experiments described below. SmCl 3 +3Na A Sm+3NaCl 3.2 Some recent literature results which would never occur at elevated temperatures due to Recent investigations have dealt with phase transitions induced unfavourable thermodynamical conditions, are even rendered by ball-milling in all kinds of oxides43-45 ( Table 1-3).…”

Hallmarks of mechanochemistry: from nanoparticles to technology

“…The formation of a non-equilibrium phase by milling of oxidic compounds has been also reported in the literature. PbO [118][119][120][121][122][123] and CaCO 3 [123][124][125][126][127][128][129][130][131][132] were taken in the past as reference materials by many authors to study the factors that influence phase transformation by milling. The transformations of lithargemassicot and massicotlitharge were reported for milling of PbO and the transformation aragonitecalcite and calcitearagonite were observed during the milling of calcium carbonate.…”

JCPDS — International Centre for Diffraction Data Sample Preparation Methods in X-Ray Powder Diffraction

“…Burns & Bredig 2 Schrader and Hoffman 3 Dandurand 4 Gregg 5 Northwood and Lewis 6 , Lewis et al 7 Senna & Kuno 8 Dachille & Roy 9 Takahashi 10 Panis 11 Gregg 5 Vegard & Hauge 12…”