Thermogravimetry in Self-Generated Atmospheres

The reaction between equimolar silica and barium carbonate powders in oxygen, air or carbon dioxide was studied by means of TG and DTA. The particle size of the silica showed appreciable effects on the reactivity of the silica, on the activation energy of the reaction, and on the formation of an intermediate silicate, Ba2SiO4. The formation of Ba2SiO4 is depressed by a decrease in the silica particle size or by an increase in the partial pressure of carbon dioxide in the ambient atmosphere.

Section: Dtamentioning

confidence: 96%

Study of reaction of finely-divided silica with barium carbonate by TG and DTA

Kato

Suyama

1975

“…This confinement may be by inadvertent design -as in a deep crucible, well or capillary -or by intentional design -as in the self-generated atmosphere sample holder [3,4].…”

Section: Principles Leading To Designmentioning

confidence: 99%

Furnace assembly for reactions in controlled ligand atmospheres

Garn

Kenessy

1981

Self Cite

By impressing a known pressure on a liquid in a properly-designed furnace, a sample can be decomposed or reacted in an atmosphere of that material. If the liquid is a decomposition product of the sample, the variation of decomposition temperature with pressure can be studied for thermodynamic reversibility (van't Hoff plot). Reactions between solid and vapor can be carried out. The system is particularly useful for study of complexes, it can he used with many solvents. Its present use is for differential thermal analysis but it can be used readily for preparative work or corrosion studies.Need for temperature data cn decomposition of complexes at temperatures near the boiling point of the ligand led to the design and construction of a furnace assembly which provides an internally-generated atmosphere at a controlled pressure. The assembly afford direct visual observation of the ligand level to avoid inadvertent dissolving of the sample during the establishment of the steady state operation.This work was initiated because of three classes of problems with which this principal author had been concerned. Certain hydrates, for example, copper(ll) sulfate pentahydrate and barium chloride dihydrate have transitions of the solid1 ~ solid., + water type not far below the boiling point of water at one atmosphere and other decomposition steps not far above. These first transition temperatures have a structural dependence which can be illustrated by the shift of temperature upon substitution of heavy water for ordinary water [1]. For barium chloride, the product is a lower hydrate whose stoichicmetry is in dispute. Some authors assume the monohydrate. The evidence from this laboratory indicated a slightly higher state of hydration, ca. 1.08 H20 [2].Another kind of problem is that of the transition metal Werner complexes, some of which contain water either in the inner complex ion or ~s a salt hydrate. There have been many studies of their thermal decomposition but very few of these have used experimental conditions which provided even the most basic test for reversibility. Generally, air or nitrogen or a vacuum constituted the vapor environment; as a result, the mode of decomposition is highly dependent upon the geometry of the sample.Still other work at this laboratory concerns the so-called "sandwich" complexes, wherein a metal atom, particularly chromium, is coordinated with ~n aromatic 9*

“…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-position), d'abord en thermogravimdtrie (TG) (Garnet Kessler, [1 ]) et ensuite en analyse thermique diffdrentielle (ATD) (Garn,[2]). …”

Section: ) Expdrimentation Sous Pression Constanteunclassified

L'analyse thermique a vitesse de decomposition constante

Rouquérol

1970

113

(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*