X-ray fluorescence method for the determination of rare earths, uranium and thorium in allanites

Summary An X-ray fluorescence (XRF) method for the determination of La, Ce, Pr, Nd, Sm, Gd, Th and U in allanites is described. The estimation limits for different impurity elements are La 0.5–10%, Ce 2–20%, Pr 0.1–2.0%, Nd 0.5–10%, Sm 0.1–2%, Gd 0.1–2.0%, Th 0.2–4% and U 0.2–4%. The sample is diluted in the ratio of 19 by boric acid and double layer pellets are prepared. The precision of the method which varies from 0.2–15% has been determined for every element in each standard. Accuracy of the method is assessed by comparison of the values for rare earth, thorium and uranium content with those obtained by optical emission spectroscopic method and the values for uranium and thorium with those obtained by neutron activation analysis.

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Röntgenfluorescenzmethode zur Bestimmung von Seltenen Erden, Uran und Thorium in Allaniten

Zusammenfassung Das beschriebene Verfahren eignet sich zur Bestimmung von La, Ce, Pr, Nd, Sm Gd, Th und U in Allaniten. Die Bestimmungsgrenzen für die einzelnen Elemente betragen: La 0,5–10%; Ce 2–20%; Pr 0,1–2%; Nd 0,5–10%; Sm 0,1–2%; Gd 0,1–2%; Th 0,2–4%; U 0,2–4%. Die Probe wird mit Borsäure im Verhältnis 19 vermischt und zu Doppelschicht-Tabletten gepreßt. Die Reproduzierbarkeit beträgt 0,2–15% und wurde für jedes Element im jeweiligen Standard bestimmt. Die Richtigkeit des Verfahrens wurde durch Vergleich mit Ergebnissen der Emissionsspektralanalyse (SE, U) sowie der Neutronenaktivierungsanalyse (U, Th) beurteilt.

     

Correlation of structure and fragmentation modes of costunolide and its derivatives

Mass spectral studies on costunolide and lactones derived therefrom, have revealed some general fragmentation modes involving the losses of 44, 55, 57, 59, 71, 73 and 83 mass units from the molecular ion. The probable genesis of these ions is established by high resolution, metastable transitions and deuterium labelling studies. Comparison has been made with the mass spectra of some C₆- desoxy esters.     

Alteration in tacticity of polymethyl methacrylate obtained with vocl3-alet3 in the presence of an electron donor

Polymethyl methacrylate has been obtained at 40° with a VOCl₃-AlEt₃ catalyst in the presence of various amounts of basic additives, at a ratio of 1·5 of Al/V. The configuration of the polymers was affected by the presence of additives. An increase in the percentage of syndiotacticity and no alteration of the stereoblock structure were indicated by i.r. and n.m.r. The effects of additives on the formation of syndiotactic structures are discussed on the basis of their electron donating powers.     

Polymerization of styrene with ZrCl4 and ZrCl3 in combination with Al(C2H5)3

The polymerization of styrene with two catalyst systems consisting of Al(C₂H₅)₃ in combination with ZrCl₄ or ZrCl₃ has been studied. The rate of polymerization with catalyst concentration was first-order with ZrCl₄ system and second-order with ZrCl₃ system, but at higher catalyst concentrations in both cases, the rate progressively decreases and finally attains a low value. The rate of polymerization is, however, proportional to the square of the monomer concentration in both the cases. The overall energy of activation was 10.9 kcal./mole and 6.45 kcal./mole in these systems. The polymers obtained with ZrCl₄ were of lower molecular weights as compared to those obtained with ZrCl₃. The polymers in both the cases had amorphous character.     

Electroluminescence in lead titanate single crystals

Electroluminescence in PbTiO₃ single crystals is studied with variation in applied electric field, frequency (20 Hz to 5 kHz) and temperature. The EL onset depends on the rate at which the dipole switches. Extremely sharp upward rising nature of the pulses of micro second duration suggest that there is a self maintained discharge in the dielectric due to secondaryγ _p mechanism. Frequency dependence of EL suggests that both the secondary mechanisms, viz. theγ _p andγ _i are active after the application of a high field and the critical field at which this occurs decreases with increase in the frequency of the applied voltage. Similarly the onset voltage decreases with increase in frequency. The temperature dependence of EL at the applied frequency of 50 Hz shows that the onset voltage is intimately connected with the coercive field of the crystal and it is minimum at the Curie point. The study suggests that EL occurs in the bulk and there is a breakdown in the dielectric due to an avalanche formation.     

Use of 2, 3, 4-trihydroxyacetophenone in the spectrophotometric determination of calcium

A critical examination of the calcium-2,3,4-trihydroxyacetophenone system in an aqueous medium is presented. This system showed a broad absorbance maximum at 540 nm (?₅₄₀ = 3.55 × 10³ liters/mole-cm). The spectrophotometric determination of calcium can be effected at pH 11.2 to 12.0 in the optimum calcium concentration range of 2.5 to 9 ppm if the concentration of 2,3,4-trihydroxyacetophenone corresponds to 4 ml of 8 × 10^?3M reagent in a final volume of 25 ml. Absorbance measurements must be made within the interval of 15 to 60 min. Beer's law is followed at 540 nm for 0.5 to 10 ppm of calcium (1-cm cell). Among the ions commonly occurring with calcium, the following were found to cause an error of +2% at a calcium concentration of 5 ppm: vanadate, chromate, manganese (II), uranyl (10 ppm) and molybdate and zirconate (60 ppm); an appreciable error from strontium, barium, and iron (III) (even at 1 ppm) and an error from magnesium due to partial co-precipitation of calcium with magnesium hydroxide.