Poppema, Tonnis Johannes

English

In these investigations, the validity was tested of the so-called additive law of NEUMANN-REGNAULT-Kopp, concerning the additivity of the specific heat in intermetallic compounds. SCHIMPFF and later on SCHUBEL had already proved this law for a long series of intermetallic compounds, below 0° C. as well as above this temperature. They conclude that the additive law is not really valid, but that it applies approximately. Many of the deviations observed remain within the limits of the experimental errors. A dependence of these deviations on the temperature could not be generally established. Zie: Summar

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   University of GroningenOver de additiviteit der atoomwarmte in binaire metaalverbindingenPoppema, Tonnis JohannesIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1935Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Poppema, T. J. (1935). Over de additiviteit der atoomwarmte in binaire metaalverbindingen. De Waal.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 13-02-2023SUMMARY. In these investigations, the validity was tested of the so-called additive law of NEUMANN-REGNAULT-Kopp, concerning the additi-vity of the specific heat in intermetallic compounds. SCHIMPFF and later on SCHUBEL had already proved this law for a long series of intermetallic compounds, below 0° C. as well as above this temperature. They conclude that the additive law is not really valid, but that it applies approximately. Many of the deviations observed remain within the limits of the experimental errors. A dependence of these deviations on the temperature could not be generally established. TAMMANN and ROHMANN then tried to ascertain a connection between the deviations observed and other properties of the com-pounds, such as the contraction and the crystal structures as compared with those of the free components. All these attempts, however, led to no general results. Several authors have already shown the deficiency of the supposed law in the case of solid-solutions and simple alloys, although it is not impossible, that some of the greater deviations might be caused by the presence of real compounds in such mixtures. For it will be seen from the results discussed in this thesis, as also from BOTTEMA'S previously published data, that the values of the specific heats in the case of true "compounds" are not ev.en approximately in accordance with the additive law. BOTTEMA studied the compounds: PtSn, AuSn and AuSb2 • In two cases: those of PtSn and AuSn, he found that the molecular heats were smaller than the values calculated from the additive rule. The deviations amounted to 5-8 % and 2-5 % respectively. The com-pound AuSb2 showed deviations in the opposite directon. Even within a small range of temperatures to a cIaer dependence of the deviations on the temperature was stated. In the case of the mixed-crystals of Au and Ag, it may be remarked that the deviations at the 56 lower temperatures were very small and only more rapidly increasing above 6000 C. As still the exact values of the specific heats of the elements of which some compounds are here examined, proved to be raiher uncertain, it was necessary to redetermine the values mentioned. The questions as to the occurrence of true allotropic changes in zinc could up till noW: not yet been completely settled. In the exac; determination of specific heats of this metal in the interval of 100-3600 c.. (at the higher temperatures in vacuo) the presence of a dl~c~ntInUlty at about 1700 C. could be confirmed. An irregularity, origInally observed at 3400 c., proved to disappear after thermal stabilisation of the metal at 3600 C. The X-rays-analysis made by SIMON and VOHSEN, however, does not indicate that true allotropic changes here really occur. Perhaps the discontinuity observed is connected with some recrystallization-phenomena. The maesurements of the specific heats of magnesium at lower temperatures were made with an unprotected lump of the metal, and from 3500 C. upwards with a piece of the metal enclosed in a platinum-vacuum-crucible. The values, obtained with the unprotec-ted lump at temperatures from 3500 C. upwards are all about 0,3-0,7 % higher than those measured in vacuo· the deviations e:,idently being caused by a superficial oxydation 'of the metal in air. Previous investigations have shown that such an oxydation is of much more influence as corresponds to the very small correction for the amount of oxyde formed in the process. . A redetermination of the specific heats of antimony in vacuo and In aIr dId not corroborate the existence of a transformation-temperature at about 413 0 C., as indicated by BOTTEMA. It seems, however, that the values obtained with an unprotected block of antimony, measured in air, are not identical with those obtained with granules of antimony, when determined in vacuo. The latter values are 2-1 % smaller than the first ones. Both series of values are, therefore, used in the comparison of the molecular heats of the compounds with the sum of the atomic heats of the composing elements. The following intermetallic compounds have been investigated: MgZn 2 , PdSb, PdSb2, PdsSb, PtSb2 , PdCu and PdCus. The 57 differences between the observed molecular heats and the values, calculated form the additive law (C'p-~), are all negative in the case of the compounds MgZn2, PdSb, PdsSb and PfSb2 , - these deviations being respectively 1-7 %, 1-4 %, 3-6 %, 7-19 %. They are a function of the temperature; all augmenting with increasing temperatures. The differences are very small in the case of the compound PdSb2 and their algebraic sign is oscillating. It is possible that the compound has been transformed into a solid-solution during the repeated heatings. It may be remarked that beyond any doubt, the preparation having the constitution: PdCu, consisted of mixed-crystals, as by means of X-rays it was established that no true compound was present. The deviations from the additive law were very small, with an uncertain (oscillating) algebraic sign; they become somewhat greater above 7000 C. As it was an established fact, that in mixtures containing 49,8 at. procents of Pd, the compound still appears, but not so in such containing 49,95 at. procents of Pd, the result of our measurements proves to be in perfect agreement with the fact mentioned, because the prepara-tion used contained more than 50 at. procents of Pd. The deviations for PdCus, on the other hand, were positive. Although, the X-rays-spectrogram proved the absence of a true compound (no hyperstructure-Iines being found), the procentual values of the deviations are rather high (1-5 %) for mixed crystals. Possible the compound has, to some extent, been formed during the tempering of the mixed-crystals below 6000 C. The higher values of (C'p-~) at 8000 C. and 9000 C. are not exceptional for mixed crystals. Nevertheless, the final conclusion from this investigation is, that the molecular heats of true compounds are not in agreement with the additive law, but generally deviate from the values thus calculated by amounts which increase with augmenting temperatures. 

Over de additiviteit der atoomwarmte in binaire metaalverbindingen

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Over de additiviteit der atoomwarmte in binaire metaalverbindingen

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