G. Vitali

Supercooling phenomena in binary mixtures of acetamide and inorganic salts

Abstract Liquid—solid equilibrium temperatures are measured in binary mixtures of acetamide and inorganic salts [NaClO 4 , LiCNS, LiNO 3 , CH 3 COOLi, Ca(NO 3 ) 2 , (CH 3 ) 4 NCl, (C 2 H 5 ) 4 NBr]. In some ranges of concentration all these systems (with the exception of CH 3 COOLi, R 4 NX) exhibit supercooling phenomena and crystallization occurs only through vigorous agitation and in the presence of crystalline nuclei, or does not occur at all, according to the type of salt. A probable explanation is presented on the basis of the trend of Δ T /ν mK vs. m .

Viscoelastic relaxation in the acetamide + sodium thiocyanate binary system

The shear impedance, density and viscosity of the eutectic mixture NaCNS + CH3CONH2 have been measured in the temperature range 253–313 K and at the frequencies 31 and 87 MHz. The real parts of the complex impedance and of the rigidity modulus have been obtained. The relaxation region is shifted in comparison with that of the Maxwell model and is interpreted using the modified B.E.L. model. Irregularities in the real part of the mechanical impedance (around 283 K) and in the Arrhenius plot of the viscosity (around 293 K) may be attributed to changes in the liquid structure.

Electrolyte-acetamide molten mixtures

Abstract Sodium trifluoroacetate—acetamide molten mixtures have been investigated with several techniques in order to understand the structure of these systems. The presence of polymeric structures has been confirmed.

Cryoscopic and dynamic study of the molten system fluoroacetamide-sodium trifluoroacetate

The behavior of the molten system acetamide-electrolyte, including the peculiarity of the structure and the consequent relevant properties, such as the megavalue of the dielectric constant, was reported earlier. The probable structure is a micellar system composed of salt micelles dispersed in an amorphous solvent. The present paper reports measurements in a related system: fluoroacetamide-sodium trifluoroacetate. The phase diagram, the ultrasonic absorption of both longitudinal and shear waves, and the longitudinal relaxation time of the nuclear magnetic momentum were measured at different temperatures. The most importnat result was thatT1 (NMR relaxation time) on the19F nucleus shows that the amide and salt participate in different environments. The amide environment is less rigid; this proves that the system must be considered microheterogeneous. Moreover, the present system exhibited: 1) a less extended concentration area where supercooling phenomena occur; 2) a much broader curve of the real part of the mechanical impedance versus frequency; 3) a higher bulk viscosity in comparison with the CH3CONH2−CF3COONa supercapacitive system.ZusammenfassungBereits früher wurde über das Verhalten des geschmolzenen Systemes Acetamid-Elektrolyt, einschließlich der besonderen Konfiguration der Struktur und der darausfolgenden relevanten Eigenschaften, wie z.B. der besonders hohe Wert der Dielektrizitätskonstante, berichtet. Die wahrscheinliche Struktur ist ein Mizellensystem, bestehend aus Salzmizellen, die in einem amorphen Lösungsmittel dispergiert sind. Vorliegend werden Messungen an einem verwandten System beschrieben: Fluoracetamid-Natriumtrifluoracetat. Bei verschiedenen Temperaturen wurde das Phasendiagramm, die Ultraschallabsorption sowohl für Longitudinalals auch für Schubwellen und die longitudinale Relaxationszeit des Kernmagnetmomentes gemessen. Das wichtigste Ergebnis war, daß dieT1 (NMR Relaxationszeit) an den19F-Kernen zeigt, daß Amid und Salz in verschiedener Umgebung vorkommen. Die Amid-Umgebung ist weniger starr; dies zeigt, daß das System als mikroheterogen betrachtet werden muß. Weiterhin ergab das fragliche System: 1) einen weniger ausgedehnten Konzentrationsbereich, in dem Unterkühlungserscheinungen vorkommen; 2) eine breitere Kurve des reellen Teiles der mechanischen Impedanz in Abhängigkeit von der Frequenz; 3) eine größere Viskosität als das superkapazitive System CH3CONH2−CF3COONa.

Ultrasonic investigation in aqueous solutions of sucrose

Abstract Ultrasonic velocity and absorption of longitudinal waves and mechanical impedance have been measured in aqueous solutions of sucrose at different concentrations and temperatures and also in the ternary mixture of NaClO4 in 5.13 m sucrose solution. Longitudinal and shear moduli as well as isoentropic compressibility may be explained on the base of aggregation phenomena that seem to be cooperative in type. Introduction of ions in sucrose solutions shifts the relaxation frequency towards low frequencies and increases the retardation processes.

Viscoelastic and ultrasonic relaxation in molten mixture of acetamide and calcium nitrate

Ultrasonic and viscoelastic relaxation spectra were determined for a mixture of acetamide and calcium nitrate [X (acetamide)= 0.7644]. Retardation phenomena are present in the viscoelastic relaxation spectrum and they seem to be affected by the type of container used; the ultrasonic spectrum is due to a chemical equilibrium. There was no evident structural phenomenon.

Supercooling phenomena in the binary systems: Acetamide-electrolytes

This paper presents a final discussion on studies of solutions of electrolytes in molten acetamide. These studies deal with cryoscopic and ultrasonic (by shear waves) techniques and reveal the complexity of the behaviour of these systems due to strong ion-solvent interactions.ZusammenfassungDie über Lösungen von Elektrolyten in geschmolzenem Acetamid ausgeführten Untersuchungen werden diskutiert. Diese Untersuchungen erstrecken sich auf kryoskopische und Ultraschall-Methoden und vermitteln ein Bild von der durch starke Ionen-Lösungsmittel-Wechselwirkungen bedingten Komplexität des Verhaltens dieser Systeme.РезюмеПредставлено обсужд ение исследований растворов электроли тов в расплавленном ацетамиде. Исследова ния проводились крио екопическим и ультразвуковым мет одом, показавшие сложное п оведение этих систем из-за сильных взаимодейст вий типа ион-раствори тель.

Free energy of interchange between COO and CH3 or CH2 groups

Abstract The liquid—solid equilibrium temperatures in the binary systems between n -octacosane and methyl or ethyl octadecanoate are determined in order to obtain the interchange parameters between CH 3 or CH 2 and COO groups by means of the statistics of group interaction.

Cryoscopy, viscosity, and electrical conductivity measurements of the strontium nitrate-acetamide molten system

Abstract Liquid-solid equilibrium temperatures of the strontium nitrate-acetamide molten binary system were measured in the range of concentrations allowed by the thermal stability of the amide. The measurements show a mole-fraction range where a limited supercooling phenomenon appears. The measurements of viscosity and electrical conductivity were performed for the mole fraction X 1 = 0.8745 mixture, up to the temperature allowed by the supercooling phenomenon.

A statistical analysis of the liquid-solid equilibrium temperatures in binary dotriacontane + ester systems

The liquid-solid equilibrium temperature in the binary systems between n-dotriacontane and methyl or ethyl octadecanoate and methyl nonadecanoate are determined in order to obtain the interchange parameters between CH3 or CH2 and COO groups, by means of the statistics of group interaction.