The Heat-treatment Effect

Some recent results have revealed that the optimal activity for N4-chelate catalysts is normally obtained at a heat-treatment temperature range of 500-700 °C [30-32], However, it has also been discovered that a higher pyrolysis temperature ( 800 °C) is necessary in order to achieve stable performance in a PEM fuel cell enviromnent. A deleterious effect on electrode performance was observed at temperatures higher than 1100 °C [33], Even for some carbon-supported Fe- and Co-phthalocyanines, stability can also be considerably improved. For example, an almost 50 times greater enhancement in electrocatalytic activity was achieved at an electrode potential of 700 mV (vs. NHE) when carbon-supported Co-phthalocyanine was heat-treated in an environment of N2 or Ar at 700-800 °C [34]. Furthermore, in experiments with carbon-supported Ru-phthalocyanine, heat treatment at 650 °C could increase the catalytic activity by 20 times at 800 mV (vs. NHE). Unfortunately, there was no insignificant improvement in catalyst stability. Not all heat-treated carbon-supported metal phthalocyanines gave positive results. For example, the activities and stabilities of Zn- and Mn-phthalocyanines were not affected by heat treatment [34]. The duration of heat treatment for these complexes is usually around 0.3 5 hrs. 

Heat treatment can facilitate bonding of the metal ions to the surface nitrogen of a graphite particle surface. The graphite particle surface serves as the catalyst support. It is believed that the inner core structure of the N4 macrocycle remains after pyrolysis and then acts as a catalytic center towards the ORR. The better electrochemical stability of the centers has been assumed to be the result of electronic integration into a stable carbon particle [39]. 

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Study of the temperature dependence of the salt and water permeabilities through heat treated PVA membranes indicates that the heat treatment effect is expressed mainly in changes in permeability activation energies. The activation parameters for water and salt permeability of PVA membranes following various treatments are presented in Table IV. It is evident that the salt permeability activation energy is increasing about 2-3 times as... 

The combined effects of a divalent Ca counterion and thermal treatment can be seen from studies of PMMA-based ionomers [16]. In thin films of Ca-salts of this ionomer cast from methylene chloride, and having an ion content of only 0.8 mol%, the only observed deformation was a series of long, localized crazes, similar to those seen in the PMMA homopolymer. When the ionomer samples were subject to an additional heat treatment (8 h at 100°C), the induced crazes were shorter in length and shear deformation zones were present. This behavior implies that the heat treatment enhanced the formation of ionic aggregates and increased the entanglement strand density. The deformation pattern attained is rather similar to that of Na salts having an ion content of about 6 mol% hence, substitution of divalent Ca for monovalent Na permits comparable deformation modes, including some shear, to be obtained at much lower ion contents. 

Tests in a Clj + Oj mixture at 427°C have shown that the worst elements for promoting susceptibility are Al, Sn, Cu, V, Cr, Mn, Fe and Ni, while the least harmful are Zr, Ta and Mo. a-phase alloys are generally more susceptible than )3-phase alloys. Heat treatment has not been examined extensively, but some heat treatments render some a-alloys more susceptible or change the mode of fracture. The general effect will depend upon the alloy and the heat-treatment cycle. Subsequent cold work can sometimes considerably lower susceptibility. Failure times decrease as either the testing temperature or initial stress value is raised. 

General Aspects and Heat Treatment Effects. After him formation, for most of the hlms aimed at electronic applications (other than amorphous oxides, such as Si02), the hlms are subjected to a heat treatment process for removal of residual organic species (entrapped solvent as well as the organic constituents associated with the precursor species), densihcation (elimination of residual porosity and structural free volume in the him), and crystallization. 

Similar results were obtained in a study of the combined effect of ultrasound (20 kHz) and heat treatment on the survival of two strains of Bacillus subtilis in distilled water, glycerol and milk [17]. When spores, suspended in water or milk, were subjected to ultrasonic waves before heat treatment little or no decrease of the heat resistance was observed. However when heat and ultrasound were applied simultaneously the heat treatment times in milk were reduced by 74% for B. subtilis var, niger-40 and by 63 % for B. subtilis var, ATCC 6051 and similar results were obtained in glycerol. Thermosonication in water was more marked reducing the heat resistance of the spores by up to 99.9 % in the 70 - 95 °C range. The effect of thermosonication was slightly diminished to 75 % as the temperature reached the boiling point of water. 

In a second part of this study, the effect of heat treatment under nitrogen of the reduced palladium catalysts A, B and C with an egg-shell type metal distribution on the metal leaching was investigated. The reduced catalysts were tested for metal leaching after they underwent a heat treatment at temperatures of 100 to 400 °C. The metal leaching of the investigated catalysts decreased after the heat treatment of... 

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