Sodium sulfate decomposition in dry atmospheres

Na2SO4 in silicate glass batches is an environmental issue, since it releas es SO2 upon decomposition. Decomposition of Na,S04 in different environment s is studied by mass-loss measurements combined with evolved gas analysis, and thermochemical modeling. The decomposition experiments are undertaken i n dry, pure O-2(S), Ar(g), N-2(g), and air(g) at 95 kPa total pressure. The rmochemical calculations using the code F*A*C*T predict SO2(g), Na(g), Na2S O4(g), NaO(g), and, in some cases. NO(g) as major emission species, The con centrations of these species increase with temperature. Na2SO4 decompositio n initiates at approximate to 1373 K. Isothermal decomposition exhibits lin ear behavior with respect to time in 1473 to 1673 K range. At 1673 K, the d ecomposition rate is 24 . 10(-4) mg/(mm(2) min) in UHP (ultra-high purity) O-2 and 69 10(-4) mg/(mm(2) min) in UHP N-2. Evolved gas analyses identify SO(g)/SO2(g) as the emitted pollutants. In O-2-rich atmospheres, SO(g) is a significant product as well as SO2(g). In inert atmospheres. SO2(g) is the sole decomposition product. At 1673 K in UHP O-2. the concentration is 55 ppm (by volume) for SO(g) and 61 ppm for SO2. At 1673 K in UHP N-2 SO2(g) c oncentration is 651 ppm. The decomposition is described by a surface reacti on mechanism. in which SO2 is generated by surface rearrangement of sulfur- oxygen complexes on the Na2SO4 melt surface. Inert atmospheres increase SO2 emission by facilitating this rearrangement process. O-2-rich atmospheres passivate the melt surface, which favors the emission of lighter molecules such as SO(g).