Electrolytic Coloration And Spectral Properties Of Natural Calcite Crystals

Natural calcite crystals are successfully colored electrolytically at the first time. Several kinds of color centers are produced in colored crystals. Absorption spectra of the colored calcite crystals are measured and analyzed systematically. Mechanism of production and transformation of color centers is given. By means of measured current - time curve.The process and mechanism of color centers are explained further.F (Ca⁺),V (CO₃^-),Pb²⁺,Mn²⁺ impurity and unknown color centers are produced electrolytically in colored calcite crystals by using a pointed cathode. Different kinds and intensities of color centers are produced under different conditions. The most effective condition, at temperature 480 oC, voltage 1200 V and electrolysis time 270 min, of the electrolytic coloration of the natural calcite crystal is gained by contrasting to the absorption spectra of the electrolytically colored calcite crystals at different voltage, temperature and time. Mechanism of electrolytic coloration of natural calcite crystals is given. This mechanism is different from the previous mechanisms of the other crystals. This research result not only expands the range of electrolytically colored crystals, but also enriches the previous mechanisms of the electrolytic colorations.Data of current and time are recorded in the process of electrolysis, with which current - time curve is plotted. After analyzing the curve, it is known that that the electrolytic coloration of the natural calcite crystal undergoes two processes. The first one is the formation of the secondary alkaline earth cathode and the second one marks the beginning of the massive coloration and maintains the coloration. The former corresponds to the first zone of the current-time curve and the latter to the other zones. The first-zone current mainly consists of the motions of Mn²⁺, Pb²⁺impurity ions, Ca²⁺, CO₃^2- constituent ions, Ca⁺, CO₃^-ions and the electron exchanges between the CO₃^2- radicals and graphite anode matrix. The second-zone current mainly consists of the electron transport, motion of Mn²⁺, Pb²⁺ impurity ions, Ca²⁺, CO₃^2- constituent ions, Ca⁺, CO₃^- ions and electron exchanges between the CO₃^2- radicals and graphite anode matrix. The electron transport is dominant in the second-zone current. This is because the electrolysis results in the electron excess in the crystals. By analysis of the curve of current - time, the mechanism of the electrolytic colorations of the natural calcite crystals is further explained and verified.F (Ca⁺), V (CO₃^-) color centers and Pb²⁺, Mn²⁺ impurity color centers and unknown color centers are produced electrolytically in colored calcite crystals by using a pointed anode. The change regulation of the curve of the current - time and coloration mechanism by using a pointed anode are similar with those by using a pointed cathode and. The main difference between the electrolytic colorations by using the pointed anode and the pointed cathode is that herein there is only one pointed anode and does not a graphite anode matrix. This research of the electrolytic coloration of the natural calcite crystals by using a pointed anode is favorable to understanding further the mechanism of the electrolytic colorations of the natural calcite crystals. The most effective condition, at temperature 505 oC, voltage 3000 V and electrolysis time 160 min, of the electrolytic coloration of the natural calcite crystal is gained by contrasting to the absorption spectra of the electrolytically colored calcite crystals at different voltage, temperature and time.The most effective condition, at temperature 480 oC, voltage 1200 V and electrolysis time 270 min, of the electrolytic coloration of the natural calcite crystal is gained by contrasting to the absorption spectra of the electrolytically colored calcite crystals at different voltage, temperature and time by using a pointed cathode and by using the pointed anode .