Hedvall

It is appropriate today for those interested in shock-compression science to recognize the situation posed by the eminent Swedish solid state chemist, J. Arvid Hedvall, who called attention to the situation of the hypnotic power of mental habitudes [66H01]. 

H01 J.A. Hedvall, Solid State Chemistry Whence, Where and Whither, (Elsevier, New York, 1966). 

Early discussions, by Tammann and by Hedvall, considered the possible existence of a common characteristic (approximate) temperature for a solid at which chemical interactions with other reactants became detectable. For example [111], such a characteristic temperature for CaO, measured in various reactions with CuS04, Co3(P04)2, MgC03, and MnSi03, was found to be 788—838 K. Similarly, the onset of reaction of BaO with the sulphates of Mg, Ca, Sr, Co, Cu, and Zn occurred between 601 and 645 K. In the latter example, it has been shown that the fusion of Ba(OH)2 (an impurity not easily excluded from BaO) could contribute to the initiation of reaction. Eutectic formation during the reactions of BaCl2 with alkali metal sulphates... 

As a phase transition occurs, there is a change of some type in the lattice. The units (molecules, atoms, or ions) become more mobile. If the solid is reacting in some way and the temperature is at or very near that at which the solid undergoes a phase transition, there may be a rapid increase in the rate of the reaction with a slight increase in temperature because lattice reorganization enhances the ability of the solid to react. A similar situation can occur in cases in which two solids are reacting if the temperature is at or near the temperature corresponding to a phase transition in one of the solids. This phenomenon is sometimes referred to as the Hedvall effect. 

The magnetocatalytic effect, found by Hedvall and co-workers (70), may be similarly explained. In this case the energy of activation for the... 

Rose, loo. cit. see also Hedvall and Zwoigbergk, Zeitsch. anorg. Chem., 1919,108,119. 

Current Problems of Heterogeneous Catalysis J. Arvid Hedvall Adsorption Phenomena J. H. De Boer... 

Boehmite Based. Catalysts. Hedvall (24) has discussed the formation of cobalt aluminate from CoO and AI2O3. He has shown that a relatively fast solid state reaction takes place when the alumina undergoes a phase change, viz. y-Al203 ->rt-A Og. This phenomenon is known as the Hedvall effect. 

Some bulk cobalt aluminate formation is expected to take place for the boehmite based catalyst, owing to a Hedvall effect (24).The spectrum of adsorbed pyridine on CoMo-124 B shows indeed a weaker 1612 cm l band, comparable with the intensity of this band for the MoCo-123 catalyst. This indicates that about 25 % of the cobalt ions has disappeared in the bulk of the alumina. (Figure lid). 

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