The Influence Of Additives On The Crystal Growth Of Pentaerythritol(PET)

Pentaerythritol(C(CH2OH)4, PET) crystal is an important X-ray analyzing crystal used in analytical science field such as X-ray fluorescence spectrometer, laser plasma X-ray spectrometer instrument because of its high diffraction coefficient, low spectral background and good thermal stability. The spectral range of detection of PET crystal is 0.55~0.8 nm, and it can mainly be used for detection of elements from Al13 to Zr40.Firstly, the crystallization experiments of PET were down respectively in aqueous solution at the presence of weak acids(boric acid, oxalic acid, citric acid) and ethanol as additives selected preliminary. The results showed that the adding of boric acid(1~2%) and ethanol with low concentration can improve PET crystallization property effectively: the grains are perfect and transparent. So boric acid and ethanol have been selected as additives for PET crystal growth. Then the solubilities and metastable zones of PET in solution containing the two kinds of additives respectively were measured carefully. The results showed that the PET solutions adding boric acid and ethanol have greater solubilities, solubility temperature coefficients, and broader metastable zones. The PET crystals were grown separately by slow-cooling method at the adding of boric acid and ethanol, the growth solutions were more stable and the macroscopic integrity of the crystals obtained was better significantly than the condition without additives.Then the crystal integrity and optical homogeneity of the face(001) were analyzed by measurement and observation of rocking curve and optical axis interferogram, the results showed the PET grain got by natural cooling method from the solution with boric acid(0.8mol/L) adding is suitable to process seed, because the grain's(001) plane diffraction peak full width at half maximum is narrowest and the structure integrity is best. The diffraction peak full widths at half maximum of the(001) of the PET crystals grown from the solution of ethanol's(1.5~2.0%(v)) adding are narrow and show small difference, this indicates that the integrity of the plane structure is nice. There is no obvious difference in optical axis interferograms of PET crystals grown at various conditions, most of they are regular. Expect add the 1% and 1.25% ethanol's, it have some deformation can be seen.