Alberto Schiraldi

Formation of high conductivity glasses in the system AgIAg2OB2O3

Glass phases showing high ionic conductivity at room temperature were prepared through a rapid quenching of the molten mixtures of the system AgIAg2OB2O3 (a fixed Ag2O/B2O3 = 1 molar ratio was always considered): the obtained specimens were homogeneous and transparent cylindrical blocks. Disk shaped cells prepared with such specimens did not show any grain-grain effect as supported by the comparison between four electrodes dc and ac conductivity determinations. A less than 10−9(ohm cm)−1 electronic conductivity was found. According to X-rays diffraction and DTA investigations, XAgI > 0.8 samples contained crystallized AgI, whereas 0.1 < XAgI < 0.8 samples could be considered actual vitreous homogeneous phases. AgI contents lower than 10 mole% were not considered due to the observed presence of segregated metallic silver. Room temperature density and conductivity data showed a regular behaviour vs XAgI in the vitreous phases range, whereas an evident discontinuity was observed about XAgI = 0.8. Linear fits in the Arrhenius plots of the bulk conductivity were obtained in the 120 K−Tg (glass transition temperature) range: the corresponding activation energies, as well as the high room temperature conductivities, allowed to closely compare these vetrous phases with the so called “superionic” conductors.

AgIAg oxysalt high conductivity glasses: a tentative approach to their structure

Abstract As a result of electronic microscopy observations the amorphous nature of the high conductivity AgI Ag oxysalt electrolytes seems due to a random orientation of structurally ordered microdomains having less than 1 micron size. A tentative approach to the structure of these domains is suggested in order to account for (i) the fast silver ion migration, which would occur along “smooth” passageway tracked by iodide ions, (ii) the critical composition, vis 80 mole% AgI, corresponding to the conductivity maximum found for most of these materials at room temperature, (iii) the low activation energy of the conductivity Arrhenius plots, (iv) the presence of some immobile Ag + which closely surround the oxyanions.

AgI — Ag oxysalt electrolytes for solid state cells

Among the family of solid electrolytes obtained from AgI and Ag oxysalts, new materials exhibiting high electric conductivity have been identified. The investigation is extended to the study of their behaviour at temperatures higher than 25° C.The product with the composition of 80 mol % AgI in the system AgI- Ag2Cr2O7 performs well at 25° C; the product with the composition of 75 mol % AgI in the system AgI-Ag2TeO4 is the most promising at 60° C.Solid state electrolytic cells containing such materials have been discharged against various external loads.

A new ionic conductor from AgI and Ag2O.B2O3

Abstract A room temperature conductivity maximum was recognized in the system AgI:Ag 2 O.B 2 O 3 at 78.8 mole% AgI, the mobile species being silver ions. X-rays diffraction and DTA showed the glass-like nature of this material which maintains its good electrochemical performances in the temperature range 25–230°. The discharge behaviour of solid state galvanic cells containing this material is close to that obtained from 4AgI:Ag 2 WO 4 .

Complex admittance of AgI—Ag oxysalt high conducting solids

Abstract Complex admittance determination allowed it to be established that the high ionic conductivity of the 4 AgIAg 2 XO 4 (X  W, Mo, Cr) solids does not depend on the granular arrangement of the investigated salt powders: it was indeed found that the overall conductance of the cells increased with decreasing grain-size probably because both intergranular contacts and grain-boundary conduction play some role in the ionic migration; however this dependence, though evident, was not so large as expected for a dominant intergranular or grain boundary migration process.

Kinetics of polymerization of epoxy adhesives and composites

Abstract The polymerization kinetics of epoxy materials are examined with particular emphasis in assessing (i) the proper use of non-isothermal DTA or DSC data, (ii) the correlation between glass transition temperature and cure degree, (iii) the effect of the filling agent on the phenomenological kinetics of the cure process.

Epoxy polymers: Glass transition/cure degree correlation

The correlation between the glass transition temperature,Tg, and the cure degree, α, of epoxy polymers has been analysed on the basis of an extension of the Vogel-Tamman-Fulcher equation for the viscosity of polymers and glasses.A physical meaning has been given to the coefficients of the series expansion of the functionTg=Tg(α).This analysis allows one to verify that the experimental (Tg,α) data support the conclusion that, in the case of thermoset polymers, the ideal glass transition temperature,To, appearing in the VTF equation, is larger thanTg.This conclusion may be supported by the thermodynamic interpretation ofT0 as the temperature at which the excess entropy of the systems tends to vanish: in the case of partially cured thermosets;T0 would represent the minimum temperature at which the system becomes able to enhance its cure degree.ZusammenfassungDie Korrelation zwischen der Glasumwandlungs-temperaturTg und dem Aushärtungsgrad α von Epoxidpolymeren wurde analysiert, und zwar basierend auf einer Erweiterung der Vogel-Tamman-Fulcher-Gleichung für die Viskosität von Polymeren und Gläsern. Den bei der Reihenentwicklung der FunktionTg=Tg(α) auftretenden Koeffizienten wurde eine physikalische Bedeutung zugeschrieben. Diese Analyse ermöglicht nachzuweisen, daß die experimentellen Daten (Tg),α die Schlußfolgerung stützen, daß im Falle von hitzehärtbaren Polymeren die in der VTF-Gleichung auftretende sogenannte ideale GlasumwandlungstemperaturT0 höher alsTg ist. Diese Konklusion wird auch durch die thermodynamische Interpretation vonT0 gestützt, nämlich als die Temperatur, bei der die Überschußentropie des Systems gegen Null geht: im Falle von teilweise ausgehärteten hitzehärtbaren Polymeren würdeT0 die minimale Temperatur darstellen, bei der eine Erhöhung des Aushärtungsgrades des Systems einsetzt.РезюмеКорреляция между тем пературой расстекловыванияTg и степенью вулканизац ии (α) эпоксиполимеров ана лизировалась на осно вании расширенного уравне ния вязкости ВогеляТ аммана-Фульчера ВогеляТаммана-Фульч ера для полимеров и стеко л. Дано физическое зна чение коэффициентов широкого ряда функци йqTg=Tg(α). Проведенный ан ализ экспериментальных д анныхTg и α подтвердил заключен ие, что так называемая идеальная температура расстек ловыванияT0, появляющаяся в уравн ении Вогеля-Таммана-Ф ульчера, в случае термореактив ных полимеров выше чемTg. Это заключе ние подтверждается т акже термодинамической и нтерпретациейT0, как температуры, при к оторой избыточная эн тропия систем стремится к ну лю. В случае частично вулканизированных т ермореактивных поли меров,T0 представляет ту мини мальную температуру, при которой системы с тановятся способным и к увеличению степени в улканизации.

Epoxy polymers: temperature-time-transformation diagram by means of DSC investigations

Abstract The aim of this work is to show that isothermal and non-isothermal DSC investigations allow the temperature-time-transformation diagram of a polymer system to be drawn. DSC data can be worked out according to a simple model which supports the interpretation of the gelation process in terms of viscosity. It is seen that the degree of cure attained at the gelation point depends on the temperature of cure and that this crucial process is similar to the formation of a glass phase from a melt.

Thermodynamic properties and thermoelectric power of solid electrolytes

Abstract Thermoelectric power determinations may significantly improve the characterization of the solid electrolytes, if a convenient procedure is followed to work out the experimental results. The peculiar physical properties of a solid electrolyte are generally due to a single fastly moving ionic species; therefore, thermocells assembled with proper electrodes reversible to the mobile ion allow to evaluate its partial molar entropy at various temperatures and, if side informations about the structure of the solid electrolyte are available, to compute other thermodynamic properties.

Fast ionic diffusion in AgI-Ag oxysalt glasses

Abstract Ag + , Cu + and Na + diffusion were determined in AgI-Ag oxysalt high conductivity glasses 4AgI:Ag 2 WO 4 , 3AgI:Ag 2 MoO 4 and 4AgI:Ag 2 O·B 2 O 3 . The first and the third were investigated at various temperatures whereas for the second glass, due to its thermal instability, only room temperature data could be obtained. Similar diffusion coefficient values were found for Ag and Cu throughout the temperature range inverstigated for each kind of glass. Significant differences between D Ag and D Na were interpreted on the ground of the short range structure proposed some years ago for these materials. The room temperature Haven ratios seem suggestive of a cooperative transport mechanism.