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Soda ash (Na2CO3) roasting of the chromite is commonly used worldwide for the production of chromium compounds. However, chromium conversion yield of the chromite only reached 70–80% in industry owing to slow chromium conversion rate in the late stages of Na2CO3 roasting process, resulting in serious waste of resources. Through XRD, SEM, EDS, TG-DTA and HRTEM analysis, phase transformation and structure evolution of chromite in the late stages of Na2CO3 roasting of chromite were investigated. The results revealed that the chromite transformed from MgCrFe2O4 phase to the MgCr0.4Fe1.6O4 main phase and Mg1.5Na9Si12Al12O48 and NaSiAlO4 minority phases first. The MgCr0.4Fe1.6O4 phase gradually transformed to MgFe1.8Cr0.2O4, MgFe1.9Cr0.1O4 and MgFe2O4 phase. Microstructure, especially of the vacancies, was proved to play the key role in chromium conversion. Vacancies generated by thermal vibration needed greater activated energy, resulting in the low chromium conversion rate of chromite in the late stages of Na2CO3 roasting process.

The pore characteristics and pore size distribution of porous near-equiatomic NiTi shape memory alloy fabricated by self-propagating high-temperature synthesis (SHS) are described in detail. The effects of different heat treatments on the transformation of porous NiTi alloy were investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that heat treatment had strong influences on the transformation temperatures and latent heats of transformation. When the porous alloy was annealed at 648K and 748K for 3.6ks, two steps transformation including R transformation occurred during cooling and heating and the R transformation temperatures are lower than B2↔B19' transformation temperatures. However, no transformation was detected within the experimental temperature range if the porous alloy was solution treated at 1133K for 2.4ks. This novel phenomenon was the results of extensive Ti2Ni intermetallic compound precipitation. The transformation temperatures of porous NiTi alloy after annealing at 1323K for 3.6ks were much lower than those of the untreated alloy.