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K. J. Murata

Publications and source records attributed to K. J. Murata.

28 records · Page 2Linked to original sources
USGS1954

Spectrochemical determination of thorium in monazite by the powder-d.c. arc technique

Thorium in monazite is determined by a d.c. carbon-arc technique using zirconium as the internal standard. The analytical curve for Th II 2870.413 Å/Zr II 2844-579 Å is established by means of synthetic standards containing graduated amounts of thoria and 0.500 per cent zirconia in pegmatite base (60 parts quartz, 40 parts microchne, and 1 part ferric oxide). Monazite samples are diluted 14-fold with pegmatite base that contains 0.538 per cent ZrO 2 , so that the zirconia content of the resulting mixture is also 0.500 per cent. In addition, both the standards and the diluted monazites are mixed with one-half their weight of powdered graphite. Approximately 25 mg of the prepared samples are arced to completion at 15.5 to 17.5 amperes. With the 14-fold dilution employed, the accurate range of the method is 3 to 20 per cent thoria in the original monazite. The coefficient of variation for a single determination is 4 per cent at the 7 per cent thoria level. Tests with synthetic unknowns and chemically analyzed monazites show a maximum error of ±10 per cent of the thoria content. If niobium is substituted for zirconium as the internal standard, there is a loss of precision. Platinum as the internal standard gives results of good precision but introduces a marked sensitivity to matrix effects.

Spectrochimica Acta↗
USGS1954

A chemical-spectrochemical method for the determination of rare earth elements and thorium in cerium minerals

In a combined chemical-spectrochemical procedure for quantitatively determining rare earth elements in cerium minerals, cerium is determined volumetrically, a total rare earths plus thoria precipitate is separated chemically, the ceria content of the precipitate is raised to 80·0 percent by adding pure ceria, and the resulting mixture is analyzed for lanthanum, praseodymium, neodymium, samarium, gadolinium, yttrium, and thorium spectrochemically by means of the d.c. carbon arc. Spectral lines of singly ionized cerium are used as internal standard lines in the spectrochemical determination which is patterned after Fassel's procedure [1]. Results of testing the method with synthetic mixtures of rare earths and with samples of chemically analyzed cerium minerals show that the coefficient of variation for a quadruplicate determination of any element does not exceed 5·0 (excepting yttrium at concentrations less than 1 percent) and that the method is free of serious systematic error.

Spectrochimica Acta↗
USGS1953

Systematic variation of rare earths in monazite

Ten monazites from widely scattered localities have been analyzed for La, Ce, Pr, Nd, Sm, Gd, Y and Th by means of a combined chemical and emission spectrographic method. The analytical results, calculated to atomic percent of total rare earths (thorium excluded), show a considerable variation in the proportions of every element except praseodymium, which is relatively constant. The general variation trends of the elements may be calculated by assuming that the monazites represent different stages in a fractional precipitation process, and by assuming that there is a gradational increase in the precipitability of rare earth elements with decreasing ionic radius. Fractional precipitation brings about an increase in lanthanum and cerium, little change in praseodymium, and a decrease in neodymium, samarium, gadolinium, and yttrium. Deviations from the calculated lines of variation consist of a simultaneous, abnormal increase or decrease in the proportions of cerium, praseodymium, and neodymium with antipathetic decrease or increase in the proportions of the other elements. These deviations are ascribed to abnormally high or low temperatures that affect the precipitability of the central trio of elements (Ce, Pr, Nd) relatively more than that of the other elements. The following semiquantitative rules have been found useful in describing the composition of rare earths from monazite: 1. The sum of lanthanum and neodymium is very nearly a constant at 42 ± 2 atomic percent. 2. Praseodymium is very nearly constant at 5 ± 1 atomic percent. 3. The sum of Ce, Sm, Gd, and Y is very nearly a constant at 53 ± 3 atomic percent. No correlation could be established between the content of Th and that of any of the rare earth elements.

Geochimica et Cosmochimica Acta↗
USGS1952

Minor elements in Arkansas bauxite

A study of the minor elements in Arkansas bauxite has revealed some striking relationships between their concentration in the parent nepheline syenite rocks as compared with their concentration in the bauxite . The ratios of concentration, in general, follow a pattern predicted by Gold-schmidt (3),2 based upon the ionic radius and ionic charge of each element present. In the Arkansas deposits, Mg, Ca, Ba, La, and Sr were depleted during the change from nepheline syenite to bauxite . The average concentration of Pb remained the same in the samples tested. Y, Mn, Be, V, Sc, Ti, and Zr were concentrated, but not as much as Al; while Mo, Nb (Cb), Ga, Cu, and Cr were concentrated more than Al.' Niobium (columbium) apparently is found in sufficient quantities to warrant search for methods to extract it commercially as a by-product of alumina plants.

Arkansas↗
USGS1947

The sensitized luminescence of manganese-activated calcite

Synthetic manganese-activated calcites are shown to be practically inert to ultraviolet excitation in the range 2000-3500A, while they are luminescent under cathode-ray excitation. The incorporation of small amounts of an auxiliary impurity along with the manganese produces the strong response to ultraviolet radiation hitherto ascribed to CaCO3:Mn itself. Three such impurities have been studied: lead, thallium, and cerium. The first two induce excitation in the neighborhood of the mercury resonance line, while the cerium introduces a response principally to longer wave ultraviolet. The strong response to 2537A excitation shown by some natural calcites is likewise found to be due to the presence of lead along with the manganese, rather than to the manganese alone. The data do not warrant ascribing the longer wave-length ultraviolet-excited luminescence of all natural calcites to the action of an auxiliary impurity. The essential identity of the cathode-ray excited luminescence spectra of CaCO 3:Mn, CaCO3: (Pb+Mn), CaCO3:(Tl+Mn), and CaCO3:(Ce+Mn) with the 2537A-excited spectra of the latter three is evidence that the luminescent center in all cases is the manganese ion or the MnO6 group. It is shown that a "cascade" mechanism for the action of the auxiliary impurities, lead, thallium, and cerium, is incorrect; and that the phenomenon must be considered as a case of sensitized luminescence. Owing to the nature of cathode-ray excitation, the manganese activator can be excited by this agent even in the absence of a second impurity. For optical excitation, however, an absorption band for the ultraviolet must be established by building into the CaCO3:Mn a second impurity or "sensitizer.".

Journal of Applied Physics↗