High-and Room-temperature Electrolytic Coloration And Production Mechanism Of Defect Centers Of Sulfate Crystals

Electrolytic coloration of barite crystals at high temperature and gypsum andpotassium alum crystals at room temperature are realized for the first time using ahomemade electrolysis apparatus. Many defect centers are produced in coloredcrystals. The absorption spectra of the colored crystals are measured and analyzedsystematically, and the species of the defect centers in the crystals are confirmed. Thesame production and transformation mechanisms of the defect centers in the sulfatecrystals are presented. By using measured current time curves, the production andtransformation mechanisms of the defect centers are explained further.After the electrolytic coloration using a pointed cathode at high temperature ofthe barite crystals, SO4, SO3, O and Ba+defect centers are produced in the coloredcrystals. The most effective condition for the electrolytic coloration is temperature at550oC, voltage1100V and electrolysis time5h. By improving the experimentaltechnique, the temperatures of the electrolytic coloration of the gypsum and potassiumalum crystals are gone down to room temperatures (2025oC) from the previous nearroom temperatures (70130oC). After the electrolytic coloration using a pointedcathode at room temperature of the gypsum crystals, SO3, SO2, O3and O defectcenters are produced in the colored crystals. The most effective condition for theelectrolytic coloration is voltage1100V and electrolysis time35h. The most effectivecondition for the electrolytic coloration using a pointed anode at room temperature ofthe gypsum crystals is voltage1100V and electrolysis time37h. After the electrolyticcoloration using a pointed cathode at room temperature of the potassium alum crystals,SO3and SO2defect centers are produced in the colored crystals. The most effectivecondition for the electrolytic coloration is voltage1100V and electrolysis time37h.The most effective condition for electrolytic coloration using a pointed anode at roomtemperature of the potassium alum crystals is voltage1100V and electrolysis time24h.In the process of the electrolytic coloration of the barite, gypsum and potassiumalum crystals, the oxygen-related chemical radicals can be produced. According to traditional electrolysis mechanism, the crystals cannot be colored electrolytically, inparticular at room temperature. In this work, the electrolytic coloration of the baritecrystals at high temperatures, gypsum and potassium alum crystals at roomtemperatures mainly benefits from the appropriate electrolysis conditions as well asthe unique structure of the used electrolysis apparatus. During the electrolyticcoloration, some SO42–radicals in the crystals can be decomposed into SO4–, SO3–,SO2–, O2–, O3–or O–defect centers. By the diffusion of the defect centers, the otherregions of the crystals are colored. After the electrolytic coloration of the differentcrystals under the different electrolysis conditions, the species of the defect centersproduced in the different crystals are different. The Ba+defect centers can beproduced in the barite crystals except for the above defect centers. Small chargedradicals can move toward the corresponding electrodes with reversed polarities andexchange electrons with the electrodes, which induces the current.