Thermomagnetic Behavior of Magnetic Susceptibility—Heating Rate and Sample Size Effects

Abstract

Thermomagnetic analysis of magnetic susceptibility k(T) was carried out for a number of natural powder materials from soils, baked clay and anthropogenic dust samples using fast (11 • C/min) and slow (6.5 • C/min) heating rates available in the furnace of Kappabridge KLY2 (Agico). Based on the additional data for mineralogy, grain size and magnetic properties of the studied samples, behavior of k(T) cycles and the observed differences in the curves for fast and slow heating rate are interpreted in terms of mineralogical transformations and Curie temperatures. The effect of different sample size is also explored, using large volume and small volume of powder material. It is found that soil samples show enhanced information on mineralogical transformations and appearance of new strongly magnetic phases when using fast heating rate and large sample size. This approach moves the transformation at higher temperature, but enhances the amplitude of the signal of newly created phase. Large sample size gives prevalence of the local micro-environment, created by evolving gases, released during transformations. The example from archeological brick reveals the effect of different sample sizes on the observed Curie temperatures on heating and cooling curves, when the magnetic carrier is substituted magnetite (Mn0.2Fe2.70O4). Large sample size leads to bigger differences in Tcs on heating and cooling, while small sample size results in similar Tcs for both heating rates.

A Mineral Magnetic Approach to Determine Paleo‐Firing Temperatures in the Neolithic Settlement Site of Mursalevo‐Deveboaz (SW Bulgaria)

“…This thermal instability of the material could be linked to thermodynamic disequilibrium during ancient fire resulting from significantly different heating/cooling regimes in the past and in the laboratory conditions. As demonstrated by Jordanova and Jordanova (2016), reversibility of high-temperature magnetic susceptibility curves depends on the heating rate as well. Moreover, an experimental study simulating archeological fire (Brodard et al, 2015) evidenced that extremely high temperatures (over 900°C) are reached almost instantaneously and persist only for short time during burning.…”

Green and facile approach for enhancing the inherent magnetic properties of carbon nanotubes for water treatment applications

“…Upon cooling, this phase dominates ( Fig 5B ). Based on the cooling curve the Curie temperature is around 580°C, which may indicate the formation of magnetite, or it may be due to the conversion of some Fe in the sample to magnetite during heating [ 44 ]. The lower temperature phase, however, is still present (i.e., the new formation is not at the expense of the original phase).…”

High‐Velocity Friction Experiments Indicate Magnetic Enhancement and Softening of Fault Gouges During Seismic Slip

“…(Partial) thermal decomposition of clay minerals induced by frictional heating is also hinted at by lower clay mineral reflections in the X‐ray diffractograms of the sheared samples, when compared to the starting material GG (Figure ). The increase in magnetic susceptibility and magnetization, as a result of neoformation of ferrimagnetic phase(s) due to thermochemical transformation of iron‐bearing clay minerals, is also widely observed during the thermal treatment of soils and sediments (e.g., Jordanova & Jordanova, , and references therein).…”