G. Berchiesi

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.

Ultrasonic investigation in the eutectic mixture acetamide + sodium thiocyanate

The attenuation of ultrasonic longitudinal waves in the eutectic mixture CH3CONH2+ NaCNS has been measured in the temperature range 255.2–303.2 K and frequency range 5–105 MHz, and the velocities of propagation at 298.4 K for 5 and 15 MHz have been obtained. A distinct structural relaxation process was found in the measured area. Comparing these results with previously reported shear results (G. Berchiesi, G. Vitali, P. Passamonti and R. Plowiec, J. Chem. Soc., Faraday Trans. 2, 1983, 79, 1257), the variation of the loss modulus, M″, as a function of frequency was determined. Agreement was found with theoretical expectations; however, the influence of the eutectic relaxation process, which takes place in the same area, is evident. Additional shear measurements performed at 10 MHz showed this influence to be stronger than at the higher frequencies reported previously.

Supercooling phenomena in binary mixtures of trifluoroacetic acid sodium salt and amides

Abstract Liquid—solid equilibrium temperatures are measured in binary mixtures of trifluoroacetic acid sodium salt and amides (acetamide, propionamide, n -butyramide, stearamide). In some ranges of concentration, all these systems (with the exception of C 17 H 35 CONH 2 + CF 3 COONa) exhibit supercooling phenomena and the liquid becomes very viscous and does not crystallize.

Binary mixtures: CH3CH2CONH2+(Na, K)/(CNS, ClO4)

Abstract The enthalpy of fusion of propionamide is measured by the DSC method, and liquid—solid equilibrium temperatures are measured for the binary systems CH 3 CH 2 CONH 2 +(Na, K)/(CNS, ClO 4 ). The cryoscopic thermodynamic constant is compared with the experimental value. It was found that supercooling phenomena in these systems are very limited.

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.

Electrolytic solutions in succinimide: Cryoscopic behaviour

Abstract The liquid—solid equilibria in the binary systems succinimide + (Na, K)/(CNS, ClO 4 ) are reported. The presence of intermediate compounds is shown. In some concentration ranges these systems (with the exception of KClO 4 ) present supercooling phenomena if the mixtures are cooled without agitation.

Thermodynamic properties of organic compounds. Note III

Calorimetric and cryometric methods are employed to measure the enthalpies of fusion and prefusion of some organic acids.RésuméOn a déterminé les enthalpies de fusion et de préfusion de quelques acides organiques par calorimétrie et cryométrie.ZusammenfassungDie Enthalpien des Schmelzens und des Vorschmelzens einiger organischer Säuren wurden durch Anwendung kalorimetrischer und kryometrischer Methoden bestimmt.РезюмеБыли измерены, исполь зуя калориметрическ ие и криометрические мет оды, энталпии предплавле ния и плавления некот орых органических кислот.