Thermal Decomposition of Manganous and Ferrous Carbonates

Abstract

strengths were determined on 276 brick. Exposure of 271 brick to natural weather for 5 years resulted in 214 brick passing (unaffected or slight spalls not exceeding 1 sq. in.) and 52 failing (larger spalls through partial to complete disintegration),The following conclusions appear to be justified from the analysis of the data:(1) Of the 14 samples of deaired shale and fire-clay brick considered in this paper, 12 samples did not significantly differ in their relations among water absorptions by 5-hour boiling, saturation coefficients, and compressive strengths from nondeaired shale and fire-clay brick in the Same range of maturity. The data on two samples were anomalous in that very low absorptions were associated in whole or in part with high saturation coefficients. (3) Of 148 brick habing absorptions by 5-hour boiling not exceeding S.O%, 2 failed. The proportion of failures increased with increasing absorptions. Of 57 brick with absorptions exceeding l2.0%, 35 failed.With the exception of the two samples teferred to in the statement above, high saturation coefficients were, in (2) (4) general, associated with poor weathering resistance and low saturation coefficients with good weathering resistance.(5) In general, the higher the associated compressive strength, the better was the resistance to weathering. The minimum compressive strength indicating satisfactory resistance to weathering varied, however, from sample to sample.For some brick, intermediate weathering durability (between "no effect" and complete disintegration) appeared to be associated with excessive lamination or nonhomogeneous structure.The durability gradings given in A.S.T.M. Specification C G2 for building brick and C 216 for facing brick, when used with a modified waiver clause (acceptance into the top (SW) grade for brick not exceeding 8.0% in absorption by 5-hour boiling irrespective of saturation coefficients), reasonably predicted the durability of the deaired brick considered in this investigation.For samples of deaired brick reported in this paper, no significant differences in properties or behavior were observed in comparison with those described earlier for nondeaired brick made from similar raw materials and by the stiff-mud method of manufacture.The mechanism of decomposition of manganous sad ferrous carbonates has been explored by high-temperature X-ray diffraction in controlled atmospheres, by differential thermal analysis, and by thermogravimetric analysis. The heat effects of the series of reactions which occur are calculated from thermochemical data. The heat effects observed in merentid thermal analysis agree reasonably well with the calculated heats of the proposed reactions. The manner in which the techniques used in obtaining differential thermal andpis patterns may af€ect the results is discussed.

Thermodynamic Assessment of the Fe-Mn-O System

“…[20,30,31,[40][41][42][43][44][45][46] b-Mn 3 O 4 melts according to b-Mn 3 O 4 fi liquid + gas. The measured temperatures ranging from 1835 to 1863 K. [32,33,36,42,47] The eutectic between liquid b-Mn 3 O 4 and halite [33,35,36,42] and the reaction Mn 2 O 3 fi b-Mn 3 O 4 + gas [25,34,36,39,[48][49][50][51][52] have also been measured numerous times.…”

Assessment of the Mn-O system

“…9, 10, 11, and 12, respectively. The measured temperatures of the decomposition of Mn 2 O 3 range from 1150 K [29] to 1243 K [82] in air and from 1241 K [29] to 1363 K [69] in 1 atm O 2 . The other determinations [5,48,70,71] lie in between.…”

“…The scatter of the measured decomposition temperature of MnO 2 is very large. In air the measured temperatures range from 697 K [75] to 943 K [5] in 1 atm O 2 from 742 K [75] to 1238 K, [69] with the other measurements [82,83] lying in between. The measurements of Klingsberg and Roy [73] are not considered as they are clearly wrong.…”

Determinación de carbono orgánico en materias primas cerámicas en presencia de siderita, FeCO₃

“…La presencia de siderita puede generar una importante interferencia en la determinación de carbono orgánico ya que la temperatura de descomposición de ésta difiere muy poco de la temperatura a la cual debe ser sometido un material para analizar el contenido total de carbono orgánico (6)(7)(8)(9)(10)(11); no ocurre lo mismo con la calcita y la dolomita, que presentan temperaturas de descomposición superiores. Es la necesidad de analizar carbono orgánico en muy bajas concentraciones en presencia de carbono inorgánico en concentraciones superiores lo que genera la dificultad de hallar métodos lo suficientemente precisos y exactos.…”