Recently, the existence of a relation between the rupture of 1,4-b-glycosidic bonds in the cellulose during thermal-ageing of paper/oil systems and the detection of methanol in the oil has been reported for the first time in this journal (Jalbert et al. 2007). The present study addresses the rate constants of the reaction for standard wood kraft papers, two immersed in inhibited naphthenic oil under air (paper/oil weight-volume ratio of 1:18) and one in non-inhibited paraffinic oil under nitrogen (paper/oil weight-volume ratio of 1:30). The isotherms in the range of 60-130°C show that the initial rate of methanol production markedly increases with temperature and to a lesser extent with the moisture of the specimens (initially between 0.5 and 2.25% (w/w)), similarly to what is noted for the depolymerization through the Ekenstam's pseudozero order model. The Arrhenius expression of the rate constants reveals linear relationships that confirm the dominance of a given mechanism in both cases. A very good agreement is also noted for the activation energy over the entirely paper/oil systems studied (106.9 ± 4.3 and 103.5 ± 3.7 kJ mol -1 for methanol and scissions, respectively). Furthermore, a comparison of the rate constants k CH 3 OH =k scissions ð Þshows approximately constant values indicating an apparent yield for the methanol of about one-third molecule per every scission for the tests under air (0.27 ± 0.04 for Clupak HD75 and 0.37 ± 0.14 for Munksjö TH70) and even lower for the ones under N 2 (0.12 ± 0.03 for Munksjö E.G.). As expected from a pseudo-zero order model, these values were shown to be consistent with a similar comparison of the amount of CH 3 OH and chain-end groups produced under specific time-temperature ageing conditions (168 h at 120°C). Finally, an additional test carried out with unaged cellulose in contact with a fresh solution of methanol in oil (cellulose/oil weightvolume ratio of 1:18) shows that at equilibrium, over 58% of the species is lost from the solution due to penetration into the fibres. Such results reveal the importance of the species partitioning in establishing the true correspondence between the molecules of CH 3 OH produced and the scissions.

In order to go further in demonstrating that methanol can be used as a universal cellulose degradation indicator in power transformers, the ageing study of standard wood kraft specimens in oil in the range of 60-130°C (Gilbert et al. in Cellulose 16:327-338, 2009) has been extended to thermally-upgraded (TU) papers. The kinetic model that best tracks the ageing patterns was shown to be a function that can accelerate or decelerate the pseudozero kinetics by the adjustment of a free parameter. The results showed a non-negligible contribution of 1,4-b-glycosidic bond breaking in the crystalline regions suggesting that the degradation at this level is not necessary occurring through a quantum mode mechanism. The results also showed a significant error in the determination of the rate constants when obtained from isotherms of varying degree of depolymerization. In the case of TU papers, provided that there is a sufficient amount of stabilizers in the fibrous structure, not only could the self-catalyzing nature of the cellulose ageing process as well as the effect of an external supply of catalysts be lost but the chain-breaking could decrease to nearly zero for an undetermined period well before reaching the levelling-off degree of polymerization. The initial rate constants (k 1o ) for the depolymerization and methanol formation of these papers were found to be very near those of standard cellulose (giving about the same activation energy), which indicates that they are obtained from the ageing patterns well before the retardant action has fully taken place. The life extension of TU papers is achieved by a reduction with time of the frequency at which the bonds are ruptured. Moreover, the production of methanol and chain-end groups showed about the same value for the frequency factor, which introduces the possibility that the rate of production of CH 3 OH from chopped chains is much higher than the rate of depolymerization, so that the latter becomes the rate determining step of the overall reaction. On the other hand, the apparent yield of CH 3 OH molecules per scission is seen to increase substantially with the amount of stabilizers (from *0.4 to 0.8 and to 1.4 for a paper containing 0 to 1.15 and to 3.9% (w/w) N 2 ) and to a lesser extent, with the moisture in the specimens. However, these variations could either be attributed to a modification of the CH 3 OH paper/oil partitioning by the stabilizers and moisture in fibrous structure. Finally, pre-aged systems (130°C for 168 h) conditioned at 20°C for variable lengths of time provided further evidence that O 2 is not necessarily involved in CH 3 OH production.

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Abstract. SOFCs are expected to become competitive devices for electrical power generation, but successful application is dependent on decreasing working temperature from 1000 to 800 ~ without detrimental effects on resistance and on electrode processes. This requires a reduction of the stabilised zirconia electrolyte thickness and an optimisation of the electrodes and interfaces.We have studied the preparation of a thin film SOFC device working at intermediate tem-

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