| Résumé | It is recognized that humidity affects the properties of metallic powders (e.g., flowability, density, composition). Although standards exist to evaluate the water content in various materials, there is presently no standard method validated or specifically adapted for the evaluation of the water content in metallic powders. This article evaluates the water content in titanium powders using different techniques (gravimetry, Karl Fischer titration, quantification of volatiles with a relative humidity sensor). The effect of measurement conditions, particle size, and types of powder were investigated. The results showed that the adsorption of water is a function of the relative humidity in the environment and the characteristics of the powders. The relative humidity in the laboratory has, however, limited effect if the exposure of the powder to the environment is limited prior to the measurements. Water adsorption/desorption is a function of the surface area of the powder. The measured values were underestimated as the methods used (i.e., heating at temperature lower than 275°C) did not allow recovering all the water from the powders (i.e., chemisorb water is strongly bonded to the surface and cannot be completely desorbed at temperatures lower than 275°C). Although some variability has been observed, the measurement of volatiles with the relative humidity sensor allowed discriminating powders with water contents ranging from 0 to 108 ppm. The amount of water measured using the gravimetric technique was not sensitive enough to precisely monitor the small amount of water adsorb/desorb on the powders investigated in this study. Additional studies are needed to assess the variability and reproducibility of the results and evaluate the techniques on other types of metallic powders. |
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