Illuminated about 1475–1480, the Salting Hours(London, Victoria and Albert Museum) contains two miniatures whose precise relationship is at first sight problematic. Facing each other at the beginning of the Office of the Dead, one miniature shows a Last Judgment, the other a view of Purgatory. This juxtaposition of subjects appears at first glance to contravene Church doctrine, which taught that at the Final Reckoning, Purgatory would be emptied of its souls and cease to exist. However, the pairing of Purgatory and the Last Judgement in this case most likely modified the latter scene in a way that reminded viewers of the private judgment that each soul must undergo immediately after death. This conflation of the once and future judgments appears in medieval devotional literature, and Last Judgment scenes often allude to the Particular Judgment. Readers of the Salting Hours, therefore, would very likely have contemplated the Last Judgment as a warning of the post mortem judgment, when their fate was decided for all eternity, while its companion, Purgatory, offered them the hope that even sinners might ultimately achieve salvation, a fitting pair of images to open the Office of the Dead.
Conventional calorimetry has always the difficulty of choosing between near to equilibrium working conditions and high thermal
ramp rates. Thus, either the transport phenomena and sample homogeneities are good but the signals become weak due to thermal
losses, or the signals are sharp, but strong gradients across the sample lead to chemical and thermal heterogeneities. The
described pulsed fluidized bed technique, by strongly stirring the sample, allows good sample homogeneities even at high ramp
rates. Moreover, the permanently regenerated cover gas allows as well a good heat transfer towards the thermocouples as a
constant atmosphere composition leading to very precise onset temperatures.
Pure alkali metal preparation is a complex problem: in most available commercial samples, all of them are simultaneously present. Conventional separation techniques are not always effective enough to reach parts per million total impurity levels. However, near the melting point, superficial segregation occurs. A zone melting derived technique coupled with a specifically developed solvent extraction process allows the total impurity content of sodium to be lowered below a few parts per million. The described thermal process, although using chemical reactions, is purely physically steered: it purifies as well potassium containing sodium as sodium containing potassium. 4 alkali metals are considered: Li, Na; K, and Cs.
Solid state purification generally requires efficient diffusion mechanisms in order to allow impurity migration towards the sample surface, from which it can be removed by a suitable mean. Since solid state diffusion just becomes efficient near the melting point, generally high working temperatures are required, resulting in expensive, energy consuming processes. The addition of small amounts of a common liquid solvent of both matrix and impurity results, even at low temperatures, in effective diffusion mechanisms the thermodynamical aspects of which are discussed in this work. Thermal cycling enhances the efficiency of the described process. Its concerns industrial and analytical applications.
Heating a milligram-sized sample of material at a constant heating rate is usually achieved by controlling the temperature
of an electric-resistance furnace with a proportional integral derivative (PID) controller. Here we present a new method for
constant-rate heating that is based on a semi-empirical mathematical expression relating sample temperature, heating rate,
and electric power supplied to the furnace. This method uses PID control only for second-order corrections of the heating
rate. The linearity of the sample temperature vs. time curves obtained by applying this method to a simple furnace setup is the same as the linearity of the curves generated
by modern commercial thermogravimetric analyzers.
A thermal analysis method that separately reproduces the gas and condensed phase processes of flaming combustion in a single
laboratory test is described. Anaerobic pyrolysis of solid plastics at a constant heating rate and complete thermal oxidation
(nonflaming combustion) of the evolved gases provides the rate, amount, and temperatures over which heat is released by a
burning solid. A physical basis for the method, the test procedure, and the relationship of flammability parameters to fire
response and flame resistance of plastics are described.
Authors:S. Helle, S. Neunlist, P. Llopiz, A. Faust, and S. Walter
SPME is a powerful trace analysis technique which involves several thermal processes: fiber cleaning, conditioning, surface
analyte adsorption, and desorption in the analytical device. Fiber conditioning is a main operation, since it results in a
severe modification of the fiber surface, enhancing its adsorptive properties. The influence and orders of magnitude of the
thermal parameters required for desorption are evaluated and discussed. The cooling down due to adsorbate desorption is completely
negligible in comparison with the heat transfer capabilities of the system. Thus, the limiting factor is not heat transfer,
but desorption activation energy.
Authors:A. Hadj Mebarek, C. Cogneville, S. Helle, and S. Walter
The formation of alkali metal alcoxides by an alcohol reacting on the elemental metal itself cannot be completed under stoichiometric
conditions. As a consequence of solvation, the chemical activity of the reacting alcohol is drastically reduced. Thus, the
reaction cannot undergo completion without a large excess of alcohol with respect to the alkali metal. Moreover, solvation
processes can drop the reaction kinetics down to nearly zero. When an excess of alkali metal is reacted with alcohol, the
heat accumulated by solvation can be suddenly released by an addition of pure alcohol. Extremely dangerous thermal runaways
can be started this way.
Authors:A. Hadj Mebarek, S. Walter, G. Killé, and C. Cogneville
Alkali metal alkoxides can be formed by the direct reaction of alkali metals with the corresponding alcohol. Under certain conditions, however, these reactions become dangerous. One of the reasons for the instability build-up in the reaction mixture is related to the electrochemical behaviour of the heterogeneous medium. Another reason is the instability introduced by the simultaneous presence of oxygen and alkali metal atoms in the reagents. Accelerating rate calorimetry is an excellent way to determine safe working conditions for the handling of such compounds. The hazards that are encountered are discussed by means of some examples.