X射线荧光光谱法测定彩涂板涂层中铅、镉和总铬

自行制备了12块校准样品,其涂层厚度和涂层中铅、镉和铬含量均按梯度分布。涂层的厚度采用GB/T 13448-2019标准所推荐的DJH法测定和定值。分析这系列样品时,测定涂层中铅、镉和总铬时用IEC 62321-5的微波法溶解后,按电感耦合等离子体原子发射光谱法定值。应用上述校正样品试验,并提出了直接测定彩涂板涂层中铅、镉和总铬含量的X射线荧光光谱法(XFS)彩涂板的基板为冷轧板,在其外表面有镀锌层。在这2种材料中都可能含有与有机涂层中待测定的含量近似的相同元素,将对测定造成干扰。此外,有机涂层中的基体元素钛及硅也对测定造成干扰。利用XRF仪器自带的薄层分析软件和基本参数法软件对上述干扰分别予以校正,使铅、镉、铬校准曲线的线性相关系数达到0.9。所提出方法测定铅、镉、铬的检出限(3s)依次为5×10^-4%,3×10^-4%,5×10^-4%。随机取3个校正样品,按所提出方法测定其中铅、镉与总铬的含量,并用IEC 62321-5标准方法进行校对分析。结果表明:两种方法的结果相互一致,所得测定值的相对标准偏差(n=6)为8.5%(铅),9.2%(镉)和11%(铬),均分别小于IEC标准方法测定值的相对标准偏差(n=6)为29%,14%,17%。本方法达到快速、准确的要求,适合用于RoHS规定对彩涂层的检量检测。

Determination of Lead,Cadmium and Total Chromium in Coating of Prepainted Steel Sheet and Strip by X-Ray Fluorescence Spectrometry

Twelve calibration samples,with their coating thickness and amounts of lead,cadmium and total chromium in the coating distributed in definite gradient,were self-prepared.Thickness of the coatings were determined by the DJH method given in GB standard of GB/T 13448-2019,and the values of contents of lead,cadmium and total chromium in the coatings were determined by ICP-AES with sample pretreated by ultrasonication,as described in IEC 62321-5.A method of X-ray fluorescence spectrometry(XRF)for direct determination of lead,cadmium and total chromium in coating of prepainted steel sheets and strip was proposed by using this set of calibration samples.Base material of the prepainted steel sheets and strip was cold-rolled steel with a thin layer of Zn-plating,both of which might contain the same elements having contents at close concentration lavels to those in the coating or more strictly the organic layer which was the object of analysis,and thus serious interference would be encounted.Furthermore,the matrix elements,titanium and silicon,in the organic coating were also a source of interference.However,all these interferences were overcome by using the film analysis software and the software of fundamental parameter method which were attached to the XRF intrument.As shown by the testing results,values of correlation coefficients obtained for lead,cadmium and chromium attained to 0.9,and detection limits(3s)found for the 3elements were 5×10^-4%for lead and chromium,and 3×10^-4%for cadmium.Three calibration samples were taken at random and analyzed by the present method,giving results of the 3elements in consistency with the values determined by the standard method given in IED 62321-5,and values of RSDs(n=6)found by this method were 8.5%for lead,9.2%for cadmium and 11%chromium,which were found smaller than the RSDs(n=6)found by the same standard method mentioned above,29%for lead,14%for cadmium and 17%for chromium.The present method showed its merits of rapidity and accuracy,and was suitable to be used for quality examination of the coating of prepainted steel sheet and strip as required by RoHS.