Study On The Determination Of Trace Ag, Pb, Te And T1 In Nickel-based Alloys By GF-AAS With Microwave Digestion

Due to the excellent properties in high temperature performance, wear-resistance, corrosion resistance, fatigue properties and fracture toughness, nickel-based super alloys have been widely used in aero-engine blades, nuclear power, high temperature energy conversion device components, etc. Due to the high saturation of nickel-based super alloys, and therefore the content of trace elements requires strict control. Inductively Graphite Furnace Atomic Absorption Spectrometry(GF-AAS) which has the advantages of high sensitivity, reproducibility, low interference, sampling less, etc., has become the most successful method of analysis in nickel-base super alloys of trace elements. Microwave digestion,as a new sample digestion technology, is much more efficient than traditional methods and is expected to be more widely used in the future.Determination of nickel-base super alloys by GF-AAS method has been reported in some literatures, but there is seldom systematic. This thesis focuses on research of simultaneous determination of 4 trace elements in nickel-based super alloys by GF-AAS method, including, silver, lead, tellurium and thallium, combined with microwave digestion for sample pre-treatment. By optimizing digestion conditions, selecting matrix modifiers, optimization of the operating parameters and etc., the GF-AAS method for analysis trace elements of nickel-base super alloys has been built. Furthermore, the method was verified by the analysis of trace elements in the synthesized samples and certified reference materials, and the uncertainty of analytical results has also been evaluated. This work provides technical and experimental basis for the establishment of a new standard method for GF-AAS analysis of nickel-based super alloys.Firstly, the background, contents and the purpose of this research work are briefly introduced. Some conceptual background and basic knowledge of GF-AAS methods related to this research are summarized. Theoretical basis and analytical capability are also introduced. Moreover, by focusing on domestic and foreign research progresses of correction methods and applications of GF-AAS, the main problems of GF-AAS method existed in recent time are outlined.Secondly, systematically study on the determination of trace silver, lead, tellurium and thallium in nickel-based alloys by GF-AAS. The following works have been carried out:1. Optimizing digestion conditions. Select different nickel-base super alloys for microwave digestion, to optimize the amount of microwave digestion instrument parameter, acid species s and other factors, eventually come to the best nickel-based super alloys digestion conditions.2. Selecting matrix modifiers. By determined the absorbance of sample adding different matrix modifier and the amount to elect the matrix modifier that most increase the sensitivity of the measuring element.3. Optimization of the operating parameters. Focused on optimizing furnace temperature program, choose a different graphite tube, drying temperature, purification temperature, atomization temperature, atomization time and purification temperature selected instrument operating parameters for each element.Finally, the method of establishment, the precision, accuracy and recovery of the method were verified by the analysis of trace elements in the synthesized samples and certified reference materials. Statistical methods were used to verify the correctness. Also, the uncertainty of analytical results has been evaluated. The results show that the proposed method is accurate and reliable. In case of lacking standards, this method is capable of providing reference method for determination of trace elements in nickel-based super alloys.