L'analyse thermique a vitesse de decomposition constante

Abstract

(Re~u le 2 f6vrier 1970)A general method of thermal analysis is presented, whose aim is to reduce at will pressure and temperature gradients inside the sample submitted to thermolysis. The basic idea is to control the sample temperature so as to keep constant a parameter related to the decomposition rate. Attention is specially called on the case when the controlled parameter is pressure, which allows to monitor at the same time two parameters (pressure and decomposition rate). As an example, one apparatus is described, working in the pressure range between 20 and 10 -3 torr. This method of Constant Rate Thermal Analysis (CRTA) appears to be specially suited for thermal analysis under controlled vacuum, for the preparation of well defined porous samples, and for the study of decomposition mechanisms. A -Exigences pos~es par l'~tude des d~compositions thermiquesLa plupart des auteurs 6tudiant la d6composition thermique des solides conviennent de la n6cessit6 de contr61er au cours d'une thermolyse non seulement la temp6rature de l'6chantillon, mais aussi la composition et la pression de la phase gazeuse qui l'entoure. Ce sont ces exigences qui retiendront notre attention.I1 en r6sulte, comme nous allons le voir plus en d6tail, la n6cessit6 de r6soudre deux types de probl~mes (exp6rimentation sous pression constante d'une part, 61imination des gradients de pression et de temp6rature d'autre part) auxquels la m6thode d'analyse thermique que nous pr6sentons se propose d'apporter une solution. 1) Expdrimentation sous pression constanteUn mode op6ratoire fr6quemment adopt6 consiste h balayer le solide 6tudi6 par un gaz qui entra~ne la vapeur produite par la d6composition. Toutefois la pression partielle de cette vapeur au niveau de l'6chantillon (pression dont d6pend le plus souvent la vitesse de d~composition) est tr6s difficile h estimer. C'est pourquoi, sauf dans les cas rares off le gaz de balayage intervient dans la r6action 6tudi6e (oxyg~ne par exemple), il semble pr6f6rable de l'61iminer compl6tement. La pression totale au voisinage de l'6chantillon est alors effectivement la pression de la vapeur produite. C'est la solution propos6e par Garn dans son dispositif h "self generated atmosphere" (atmosphbre uniquement engendr~e par la d6com-2*

CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments

“…[34]). Analysis (CRTA) [37,38]. In the CRTA pretreatment, the evolution of temperature during preheating is controlled by means of a feedback mechanism based on mass changes during the carbonation/decarbonation reactions, which are forced to occur at prefixed low rates.…”

Evolution of the Porous Structure and Surface Area of Palygorskite Under Vacuum Thermal Treatment

“…The method was described under the name of "reciprocal thermal analysis" by Grillet et aL, 1988and Rouquerol (1970, 1989. In conventional thermal analysis, a physical property of a substance is measured as a function of temperature.…”

“…For clay minerals, this type of procedure usually results in a partial overlap of successive dehydration or outgassing steps. In the present study, this problem was overcome by applying controlled transformation-rate thermal analysis (Rouquerol, 1970(Rouquerol, , 1989. In this process, the rate of dehydration or outgassing is kept constant (or controlled) over the entire temperature range of the experiment by means of an appropriate heating control loop, which results in an a priori unknown temperature program.…”

Controlled Rate Thermal Analysis (CRTA) as New Method to Control the Specific Surface in Hydroxyapatite Thin Coatings

“…The method for the thermal analysis developed by Rouquerol [26,27], known as "control rate thermal analysis" (CRTA), has been tested in formulations for the control of textures in solids [28][29][30]. This method is very useful in cases of complex thermolysis usually lapses through superimposed, parallel or serial reactions.…”