RELATIONS BETWEEN CRYSTALLOGRAPHIC CHARACTERISTICS AND CRYSTAL STRUCTURE AND THE PROPERTIES FOR AMMONIUM BICARBONATE

The crystal of ammonium bicarbonate belongs to orthorhombic system with symmetry 3L2 3PC. They exist in three forms: prismatic, slaty or particle shape. The crystals appear colorless to white or light grey, transparent to semitransparent. The cleavage parallel to (110) is perfect. Hardness H=1.55. Density D= 1.573 g/cm3. They are biaxial negative crystals, with Ng=c= 1.5540, Nm = b = 1.5355, Np =α=1.4220; 2V=40°56′. γ=v is weak. On the curves of DTA, there is a big and wide endothermic peak (between 50-150℃ ). The curves of TGA showed a continuous weight-loss. On the infrared absorption spectra, there are two strong peaks (3330-3030, 1430-1380), corresponding to the stretching and bending of the ions NH4+. And there are two less strong peaks (2850, 2550), corresponding to the stretching and bending of the anions HCO3-. The unit cell dimensions are α = 7.220(1)?, b=10.672(l)?,c = 8.719(2)?, v = 671.927(3)?3. There are eight moloculs in the unit cell and the space group is Pccn. Dx =1.5215. In the structure, the HCO3- anion groups are connected by hydrogen bonds to form chains parallel to c axes. The NH4+ ione groups constitute tetrahedrons connected by four chains of the HCO3- anions. In the crystal, there are two form of hydrogen bonds, namely O-H…O and N-H…O.The framework exists as huge and complicated network of hydrogen bonds. It is obvious that the physical and chemical properties of the crystal are influenced greatly.