Effects of chlorides on the phase transformation of alumina

The discovery that γ -alumina can be prepared at lower calcination temperature from an ammonium aluminum carbonate hydroxide (AACH) precursor templated with rosinyl trimethyl ammonium chloride has led to the assumption that Cl - is capable of lowering the temperature of the phase transformation of AACH to γ -alumina. To verify this hypothesis, several chlorides were introduced into the calcination process of the AACH precursor. The samples were characterized using X-ray diffraction, thermogravimetry and differential scanning calorimetry as well as X-ray photoelectron spectroscopy. The results showed that Cl - has great effects on the crystallinity of γ -alumina obtained by the calcination of AACH. The effects varied with the type, dosage and introduction method of the particular chloride. It was also found that Cl - began to take effect only after the AACH had been decomposed to form amorphous alumina . Therefore, the true function of Cl - is to decrease the temperature of the phase transformation from the amorphous phase to γ -alumina: the phase transformation temperature decreases by as much as 115 K.