New ways for purifying lead iodide appropriate as spectrometric grade material

In order to overcome some unsolved problems of lead iodide purification such as lack of stoichiometry, decomposition, and polytype admixture, several purification methods were compared. Lead iodide from different suppliers and synthesized from lead nitrate and potassium iodide was purified by zone refining, by zone refining followed by sublimation, by repeated sublimation and by repeated evaporation under different conditions. Purification methods were evaluated by studying parameters of the purified material like decomposition, stoichiometry, purity, and polytype composition, and also taking into account purification yield and rate. Stoichiometry was measured by wet procedures, purity by inductively coupled plasma (ICP) and, polytypes by powder X-ray diffraction. Sublimation and evaporation give the best stoichiometry (PbI/sub 1.90/), especially when compared with zone refining (PbI/sub 1.40/). Purification by 100 zone refining passes gives similar impurity concentration to purification by three evaporations. Furthermore, evaporation exhibits maximum yield and rate (16%/day). Therefore, the work performed indicates that evaporation in Ar atmosphere is the quickest and most efficient purification method for producing spectrometric grade lead iodide, avoiding material decomposition and achieving high purity, maintaining the best stoichiometry.