PREPARATION O F FLUORESCENT CALCITE
435
3. A like procedure may be employed with the function h, while ;(. plot of the quotient of log solvent activity by jY2against ionic strength should have similar properties. REFEREKCES (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19)
DEBYE:Physik. Z. 26, 97 (1924). DEBYEAND HOCKEL:Physik. Z. 24, 185 (1923). HALLA N D HARKINS:J. Am. Chem. Soc. 38, 2658 (1916). HARKINSAND ROBERTS:J . ,4m. Chem. SOC.38, 2676 (1916). LEBLANCA N D NOYES:Z. physik. Chem. 6, 385 (1890). LEWISA N D RANDALL: Thermodynamics and the Free Energy of Chemical Substances. McGraw-Hill Book Company, Inc., New York (1923). RANDALL: J . Am. Chem. Soc. 38, 788 (1916). RANDALL: J. Am. Chem. SOC.48, 2512 (1926). RANDALL: J. Chem. Education 8, 1062 (1931). RANDALL: Am. Physics Teacher 7, 292 (1939). RANDALL A N D BRECKENRIDGE: J . Am. Chem. SOC.49, 1435 (1927). RANDALL A N D CANN:J . 4 m . Chem. Soc. 60, 347 (1928). RANDALL A N D FAILEY:Chem. Rev. 4, 271, 285, 291 (1927). RANDALL AND LANGFORD: J. Am. Chem. Soc. 49, 1445 (1927). RANDALL, LIBBY,A N D LONGTIN: J. Phys. Chem. 44, 313 (1940). RANDALL A N D SHAW:J. Am. Chem. SOC. 67, 427 (1935). RANDALL A N D VIETTI: J. Am. Chem. SOC.60, 1526 (1928). RANDALL AND WEST: To be published. RANDALL AND WHITE: J . Am. Chem. Soc. 48, 2514 (1926).
T H E PREPARATION OF FLUORESCENT CALCITE GORTOS R. FONDA
Research Laboratory, General Electric Company, Schenectady, New York Received August 16, 1950
Certain specimens of natural calcite, such as those occurring a t Franklin, New Jersey, show a rose fluorescence when excited by ultraviolet. According to Pringsheim (6), this is to be ascribed to the presence of manganese as activator. Such calcite is unique among natural phosphors, in that it has resulted from a sedimentation rather than from an igneous process. This distinction has stimulated attempts to produce it experimentally. Of several methods tried by the author, the most successful proved to be the precipitation of the carbonate in the presence of a manganese salt. The excitation of its fluorescence was stronger in the f$r ultraviolet in the neighborhood of the resonance line of mercury, 2536 A., than in the near ultraviolet. The conditions for precipitation had to be so chosen that
436
GORTON R. FONDA
calcite crystallized out rather than aragonite, a fluorescent form of which could not be prepared. The inability of a thermal treatment to form true fluorescent calcite was shown by tests in an atmosphere of carbon dioxide. When the fluorescent mineral, which is naturally white, was fired, a non-fluorescent product was obtained a t all temperatures, darkened by decomposition of the manganese carbonate and liberation of manganese oxide. Thermal treatment of synthetic mixtures did nevertheless produce fluorescence when a mixture of calcium oxide or carbonate with less than 0.1 per cent of manganese oxide was fired under such conditions that a calcium oxide was formed which contained a small amount of carbonate. The brightest fluorescence resulted by introducing 0.005 per cent manganese as oxide to the carbonate and by firing at 1000°C. in an atmosphere of carbon dioxide for a period of 30 to 60 min. The resulting phosphor was a calcium oxide which still retained 1.5 to 10.0 molar per cent of calcium carbonate. Its phosphorescence was negligible. Its characteristic rose fluorescence disappeared when the carbonate waa completely decomposed by firing in air. It is, therefore, distinct from the oxide phosphor emitting red fluorescence, which can be prepared by firing at 1000°C. in air a mixture of calcium oxide or carbonate with manganese activator in the presence of a suitable flux. This latter phosphor is probably the fluorescent calcium oxide obtained by Nichols ( 5 ) in his studies on the fluorescence of calcite. The rose fluorescence of the calcium oxide-carbonate phosphor disappeared also when the carbonate content was unduly increased by firing the phosphor in carbon dioxide at a temperature below 800OC. The upper limit of carbonate at which fluorescence could still be just barely perceived corresponded to about 50 molar per cent. I n the absence of manganese, no fluorescence could be observed a t any proportion of carbonate and oxide. The product is, therefore, not to be confused with those phosphors in which the introduction of a foreign salt of the same metal ion serves as activator (2). Furthermore, it is essentially different in composition from the natural mineral. A successful synthesis of the natural fluorescent calcite was carried out by precipitating the carbonate from a mixture of calcium and manganese chlorides with a solution of ammonium carbonate at a temperature not too high. As the manganese content was increased, the fluorescence was found to rise to a peak and then to decrease. The optimum concentration for the solution of chlorides was a t a composition of one atom of manganese to thirty of calcium. The other conditions favorable to a maximum intensity of fluorescence were (1)-the use of dilute solutions containing 1.8 per cent of CaC12.6H%0and 1.5 per cent of (NH&COs.HgO, (2) a 50 per cent e x c w of ammonium carbonate, and (8)precipitation at about
PIiEPAKhTION OF FLUOKESCENT CALCITE:
437.
iO'Y?.,followcd by holding at room temperature for several weeks heforc filtwing or, more efft.ctively, by boiling for 10 min. Under them coiiditions t h c prcripitatc, whellirr wet or dry, had a fluoresconce that was 30 per rrnt of that of natural calcite from Franklin, New .Jersey, and was of the same rosr color. Furthermore, its phosphorescenet: was similar in intensity and duration, I t made no differmce whether the carbonate solution was added to the chloride or vice versa. The products were pnrr white in color. The diffraction pattcwu of some typiral oiies, oht,aincd with MoK, radiation through thr roiirksy of L. 1,. p of this lahoratoly, are shown in fiRiirt1 1. The unrrflect,ed beam, xhicli is not, shown in these patterns, lit% to thr! left, and the angle of reHr.r,tion hcconiw progrcssirdy greater m , on(: pa.ses from
R a . 1. Modified forins of caleiiiiii rnibonate. n, prceipitat,cd aragosite without in;tn&mes~; 11, n n t k r i i i l airigoiritr; c, n s t u m l
