Thermomagnetic analysis

This term is generally considered to mean plotting specific magnetizations and temperature for the purpose of identification of components such as may be present in catalytically active solids. In favorable cases it is possible to extend the method to quantitative determination, and to the study of rate processes. A somewhat different application of thermomagnetic analysis, namely, to particle size determination, will be described in the next section. But apart from this last application, the uses of thermomagnetic analysis in catalysis have been reviewed elsewhere ). 

Thermomagnetic analysis is also useful in the detection and estimation of trace ferromagnetic components such as iron or magnetite in concentrations as low as 1 part in 10. Applications to this area must involve consideration of how magnetic properties may be altered by particle size and by the presence of adsorbed gases. 

Still another application of thermomagnetic analysis to nickel catalysts relates to the addition of other components, such as copper, which may be thought to have a favorable influence on catalyst behavior. Nickel has a magnetic moment corresponding to 0.6 unpaired electron per atom in the d-band. Alloys of nickel and copper become progressively less magnetic until, at 60 atom % copper, the magnetic moment becomes zero. It is, therefore, a simple matter to determine to what extent solid solution has taken place if, say, some copper nitrate is added to the nickel solution used in preparation of the catalyst. Similarly, any influence of the copper on particle size distribution is readily observed. 

Magnetization Resulting from Carburization. Thermomagnetic analysis (TMA) identified magnetite as the only ferromagnetic phase in the unreduced catalyst, and iron in the reduced samples. TMA measurements were made after isothermal carburization and after temperature-... 

Figure 1. Mass gain during carburization of catalyst B-6 in H2/CO (3/1) at 1 atm. Asterisk ( ) indicates time at which thermomagnetic analysis was made.

Table VI. Thermomagnetic Analysis of Catalysts B-2 and B-6 after Short-Term Isothermal Carburization...

The more recent applications of mimetic measurements to catalyst structure have come from an understanding of two principles. These principles are (f) that effective dispersion of an active catalyst component may often be revealed by susceptibility measurements, and ( ) that thermomagnetic analysis often reveals the identity of a ferromagnetic catalyst component. 

Thermomagnetic analysis on both carbides had previously been attempted, but the work of Hofer and his associates was the first in which... 

Preliminary tests on these catalyst samples indicated that they were highly active and that they possessed an appreciable specific magnetization. But if the active catalysts were heated in pure nitrogen at 400° for several hours, they progressively lost all their activity and all their ferromagnetism. The active, and progressively deactivated, catalysts were then subjected to thermomagnetic analysis, with the results described below. 

Jos] Dilatometry, thermomagnetic analysis < 1000°C, 74.5 mass% Ni, 5.6 mass% Cu, heat treated samples... 

Kvim] X-ray diffiaction, thermomagnetic analysis (TMA-2 apparatus technique), metallography 1000 50°C, > 3 mass% Fe, > 3 mass% P... 

Kum] Mechanical and electrical properties tests, thermomagnetic analysis (TMA-2 apparatus) Strength, yield point, electrical resistivity... 

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