Thermal decomposition of solid sodium bicarbonate

Abstract

The thermal decomposition of solid sodium bicarbonate has been studied in the temperature range 360-500 K over a range of partial pressures of carbon dioxide. The effect of water vapour has also been studied. Above 440 K the reaction follows contracting-cube kinetics with an activation energy of 32 kJ mol-l and a frequency factor of lo1 s-l. In this temperature range the presence of water or carbon dioxide has little effect on the kinetics. Below 390 K the reaction follows first-order kinetics. In nitrogen, the activation energy is ca. 64 kJ m o P , the frequency factor is lo5 s-l and water vapour has little effect. High partial pressures of carbon dioxide increase the activation energy to ca. 130 kJ mol-l and the frequency factor to 1013e5 s-l.The results of microscopic examination generally confirm the kinetics but show that at low temperatures in nitrogen and carbon dioxide the processes are different in detail.A number of publications have dealt with the thermal decomposition of solid sodium bicarbonate, under various experimental conditions. These include the use of and c l o ~e d ~? ~ sample containers as well as variation in the composition of the atmosphere round the Both isothermal5? 9 9 lo and temperature-programmed heatingll, l2 regimes have been used, and several fluidised-bed studies have been

Significance of the kinetics of thermal decomposition of NaHCO3 evaluated by thermal analysis

“…This is not necessarily contradictory to the present result because the F 1 law was not markedly inferior and the exponent m in the A m function was extended to nonintegral values between unit and four to find the better linearity [10]. Although it is difficult to rationalize such a nonintegral exponent of m, the A m law with m = 1-1.6 apparently is followed when the true reaction is phase-boundary controlled but there is some distribution of (x among particles in the sample bed [2]. The R n laws with n = 2.3-3.0 were obeyed in the present reaction (Tables 1 and 2) and the R 3 law was followed depending on the experimental condition [14].…”

“…This reaction proceeds in a single step to yield NazCO3, which is well known as one of the main stages in the Solvay process. 2NaHCO 3 -* Na2CO 3 + H2O + CO 2 There are some discrepancies among experimental results reported earlier as well as their interpretation for the kinetics of the decomposition of NaHCO 3 [1][2][3][4]. This implies that the kinetics of the reaction is greatly influenced, as is usually the case with solid-state reactions, by the sample and measuring conditions.…”

Interconnected porous poly(ɛ-caprolactone) tissue engineering scaffolds fabricated by microcellular injection molding

“…Recall that the pores in the parts produced by microcellular injection molding were usually closed pores that were isolated from each other. However, the chemical foaming agent SB decomposed, 30,31 and the released CO 2 and H 2 O (vapor) further increased the porosity by providing more foaming agent. 32 Therefore, some large and connected pores were produced.…”

Thermal degradation behaviour of sodium fire extinguishant powder

“…Table 4 compares the present results with those reported in the literature. Ball et al [3] have reported that, when the thermal decomposition of solid NaHCO 3 (40 mg)is studied by isothermal TG at temperatures varying between 360 and 500 K in nitrogen flowing at 5 cm 3 rain-1, the reaction follows two distinct mechanisms, depending on the temperature region of the test. They obtained average values of 102 kJ mol-1 and 1.43 x 1011 s-1 for the activation energy and frequency factor respectively.…”