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.
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