Experimental Study On The Solution Stability And Crowth Of KDP Winth L-Alanine As Additive

As one of the excellent electro-optical and non-linear optical materials, thepotassium dihydrogen thophosphate (KH2PO4, KDP) crystal has been widely used inseveral applications, such as electro-optics modulation, laser frequency conversion, raycelerity switch and so on. KDP has been known to be the first choice to ICF due to theirexclusive physical properties, which include transparency in a wide region of the opticalspectrum, resistance to damage by laser radiation, and relatively high nonlinearefficiency, in combination with reproducible growth to large size and easy finishing.With the development of ICF technology, more high-quality and large-sized KDPcrystals are needed urgently. Recently, the investigations on KDP crystal focus onimproving its growth rate and the quality of crystal. It is well known that the opticalproperties of KDP crystals with L-alanine are better than the pure KDP crystals.However, the effect of L-alanine in the growth of KDP crystals is still a brainteaser forus. In this paper, the experiments of the stability of KDP solutions and crystal growthwere carried out, meanwhile the influence of L-alanine on the stability of KDP solutionsand the growth of KDP crystal was analyzed. On this basis, the large scale KDP crystalswere grown in the experiments.①The solubility curves, the width of metastable and induction period of pure andL-alanine added KDP solutions were measured experimently. It is found that thesolubility of KDP decreases and the metastable zone width and the induction periodincrease with the increase of the additive concentration.②According to the classical nucleation theory, the effect of additives onnucleation characteristic was analyzed. The results indicate that the mode of nucleationis the homogeneous nucleation when S≥1.3, while heterogeneous plays a dominatingrole in the nucleation when S≤1.25. The thermodynamic and kinetic parameters ofnucleation such as solid-liquid interracial tensions, critical nucleation radius andthermodynamic barrie, were also calculated according to the classical nucleation theory.③The growth rate of KDP crystal with L-alanine has also been investigated atdifferent supersaturation at35℃, and the growth mechanism of the (100) face of KDPcrystal was analyzed using the crystallization kinetics. The results show that the growthrate decreases with the increase of additive concentration. In addition, throughinvestigating on the growing surface morphology by in situ AFM, the growth of the (100) face of KDP crystal with L-alanine is dominated by the two-dimensionalnucleation mechanism when the supersaturation is higher than0.04.④The KDP crystals were grown with L-alanie and EDTA by the solution coolingmethod. It is found that the growth rate of prismatic section with EDTA is higher thandoped L-alanine, which indicates that doped with EDTA can effectively inhabit theadsorption of Fe3+, Al3+, Cr3+in the prismatic section of KDP crystal. The KDP crystalwith L-alanine is long and thin, that maybe caused by low growth rate of the prismaticsection and high growth rate of the pyramidal section. The experiments show that thegrowth rates of KDP crystals were affected by the radius of rotation and the scale ofseed crystal. The growth rate increases with the increase of the radius of rotation and thescale of seed crystal...