INTRODUCTION TO THE TITRATION TGA TECHNIQUE AND ITS APPLICATION TO THE QUANTIFICATION OF EVOLVED ARGON FROM A TITANIUM BASED ALLOY

摘要

Titration TGA is a method for dosing a gas or a vapor aliquot (i.e. of known amount) on a sample being weighed by the balance of a Thermogravimetric Analyzer. The dosing system, namely the Autoinjector, allows injecting the aliquots into the TGA furnace at a given frequency or at user selected times. The Autoinjector and transfer lines being temperature controlled, injection of vapors of higher boiling point (water, solvents, volatile organic compounds,...) can be achieved. It can be applied to the study of physisorption or chemisorption phenomena and to some extent to all gas-solid reactions (e.g. oxydo-reductions). Moreover, it can be applied to quantitative Evolved Gas Analysis measurements. The method requires the calibration of the Evolved Gas Analyzer by injecting different volumes (for instance from 1μl to 1ml) of a given gas or vapor in the TGA gas flow and determining the gas analyser response for each injection. The obtained Titrated volume vs. Gas analyser response calibration plot allows for the quantification of evolved volumes of the gas or vapor of interest from an unknown substance. After introducing the technique, the presentation will focus on its application to the calibration of a TG-GC/MS system. The primary objective of the study was to detect and quantify the argon desorption from a « TA6V » (Ti based, 6% Argon, 4% V) high temperature alloy sample typically used in the space and aeronautic industry to make turbine blades and different engine structure parts. The quantification is made challenging in TGA only as carbon dioxide evolution occurs simultaneously with the argon desorption. After the application of the appropriate calibration method, which included injections of 1μL, 2.5 uL and 5μL argon doses, the integration of the corresponding GC peaks envelope, and the construction of a Titrated volume vs. Peaks envelope chart, desorbed argon amounts in the 2-3 ppm range have been detected in unknown TA6V samples.