pH值对ADP晶体(100)面生长的影响

Effect of pH value on the growth of the(100) face of ADP crystal

通过对40℃、不同pH值和过饱和度下ADP晶体(100)面法向生长速度的研究,发现在同一过饱和度下,改变pH值后晶面的生长速度明显加快。实验数据显示,在过饱和度较低时,(100)面的生长以螺旋位错生长机制为主;过饱和度较高时,以二维成核生长机制为主,而且pH值的改变会促使ADP晶体在较低的过饱和度下就从位错生长机制向二维成核生长机制转变。利用实验数据计算出了不同pH值下、二维成核生长机制控制晶体生长时的台阶棱边能。最后,运用原子力显微镜(AFM)非实时观察了不同过饱和度、不同pH值下生长的ADP晶体(100)面的微观形貌,发现与正常pH值相比,在较低的过饱和度下,pH=2.5和5.0的晶面上就出现了二维核。

Through investigating the growth rate of the（100） face of ammonium dihydrogen phosphate（ADP） crystal with different pH values at different supersaturations at 40℃,it is found that the growth rates of the（100） face improved noticeably after changing the pH value in the same supersaturations.The experimental results show that the growth of crystal is controlled by the dislocation mechanism at the lower supersaturations,and at the higher supersaturations,two-dimensional（2D） nucleation mechanism dominates the growth.Moreover,the growth mechanism transition from dislocation to 2 Dnucleation mechanism would occur at the lower supersaturations with the change of pH values.The edge free energy of the（100） face of ADP crystal with different pH values are calculated when the growth is controlled by 2 Dnucleation mechanism.Finally,the topography of the（100） surface of ADP crystal with different pH values at different supersaturations are observed by ex situ AFM.It is found that there are 2 Dnucleations appearing in the crystal surface with pH=2.5 and 5.0 at lower supersaturations compared with the normal pH.