Twin Microcalorimeter Research Articles

Kalorimetrische neubestimmung der halbwertszeit des 241Am

Commercially available americium oxide of about 98% purity was refined by ion exchange, extraction chromatography and oxalate precipitation. After reduction with lanthanum to americium metal, it was further purified by repeated sublimation at 1100°C and a pressure of less than 1.3 × 10 −4 Pa. The remaining impurity content was determined by spectroscopic analysis to be 0.65%. The amount of 237Np formed by decay of 241Am after the last sublimation was calculated to be 0.55%. Repeated determinations of the heat output in a twin microcalorimeter resulted in 7659.8 μW. From this value and from the 241Am mass of 66.783 mg the specific heat output of 0.1147 W/g, the half-life of 432 yr and the decay constant of 5.084 × 10 −11 sec −1 were calculated.

The Effect of Treatment of Polyphosphate Surface with Amines on the Heats of Immersion in Organic Solvents

Organic cations were substituted for some of alkali cations on the surface of metaphosphates by immersion in aqueous solutions of hydrochlorides of ethylamine, hexamethylenediamine and aniline. The heats of immersion of the surface-treated phosphates in benzene and methanol were measured with a twin microcalorimeter, and the following results were obtained.(1) When the phosphates were treated with ethylamine, little change of their surface properties was observed.(2) The specific surface area of surface-treated phosphate increased with the amount of organic cation substituted.(3) The heat of immersion of the phosphates treated with hexamethylenediamine increased, especially in benzene, with increasing surface concentration of the organic cation.(4) In benzene the heat of immersion of the phosphates treated with aniline decreased with increasing surface concentration of the anilinium cation, while the immersional heat in methanol increased with the concentration. This dependence in methanol can be interpreted in terms of the OH-π interaction between the anilinium cations on the surface of the phosphate and the methanol molecules.

Heats of Immersion of Metaphosphates in Aromatic Hydrocarbons

Heats of immersion of alkali and alkaline earth metaphosphates in some aromatic hydrocarbons were measured with a twin microcalorimeter to investigate the interaction of the interfaces between the phosphates and the hydrocarbons.The heats of immersion in benzene for the phosphates with long chains were lower than those for the phosphates with short chains. The dependence of heat of immersion on chain lengh is attributed to the change in the concentration of the hydroxyl groups, which can interact with π-electron of benzene, with an increase of chain length.The heats of immersion in benzene increased with an increase in polarizing power, z+/r+2 (where z+ is the number of positive charge and r+ the ionic radius), of the cations of the phosphates. This variation is considered to be interpreted in terms of the polarizing effect of the phosphate surface on benzene molecules. The relatively high values, especially of lithium metaphosphate, suggest that the acid-base interaction between the surfaces of the phosphates and benzene may contribute to the heat of immersion.In order to examine the effect of substitution of methyl group, the heats of immersion of lithium and sodium metaphosphates in benzene, toluene and p-xylene were measured. The heat decreased with an increase of the number of the substituent. It is not clear at the present stage that which the predominant factor is, the electron donor strength or the steric factor of the aromatic hydrocarbon.

754. A new twin micro-calorimeter, and the heat of transformation of α- into β-quinol

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