A method is developed for measuring diffusion constants in transparent mixtures by means of double-exposure holographic interferometry. The diffusion constant is deduced by a simple and direct measurement of the interferograms. The method was checked with sugar solution and water and gives reasonable agreement with other methods.

The Mössbauer effect in 57Fe has been used to study carbide phases appearing during the tempering process of an alloy steel containing 1.33 wt.% Si, 1.13% wt. Mn, and 0.38 Wt.% C. Carbides were chemically extracted from the samples which had been isothermally tempered for 2 h at various temperatures. Carbides obtained from samples tempered at 300° and 400°C were identified as ε and χ phases, respectively. The ε carbide has an isomer shift (I.S.) of 0.18 mm/sec relative to α iron and an effective hyperfine field (Hn) of 162 kOe at 300°K. The χ carbide has an I.S. of 0.28 mm/sec relative to α iron and Hn of 179 kOe at 300°K. Carbides precipitated at and above 500°C were found to have the orthormbic cementite structure, with a composition of (Fe1−xMnx)3C. As the tempering temperature increases from 500° to 700°C the Curie temperature changes from 440° to 270°K, and x increases from 0.02 to 0.10. Curie points and extrapolated values of Hn(0) were found for all the carbides in question. The early stages of tempering in which transition carbides appear are explained as being controlled by the elastic strain. The elastic binding energy between an interstitial carbon atom and a substitutional silicon atom can then be estimated. Other phases which were found in the chemically extracted samples after tempering the alloy at a low temperature, were identified as oxyhydeoxides and iron gel. In a sample tempered at 700°C the carbide was detected in the steel matrix and compared with the same carbide after chemical extraction.

Rbsum6.-La tension superficielle 5 l'interface entre les phases liquides sCpar6es de m6langes 3 ~e -4 ~e a St6 etudise en fonction de la temperature de 0,3 K 2 0,7 K, et de la pression entre la pression de vapeur saturante et vingt atmosphPres. La hauteur du msnisque mesurEe depuis sa base, a Et6 dbterminge par une technique d'interferometrie holographique.

No abstract

No abstract