Herstellung von Molybdänpulvern mit besonderen Eigenschaften
Research output: Thesis › Doctoral Thesis
Due to the rapidly growing sector of the molybdenum thin film containing TFT-LCDs and touch panels, the requirements on the efficiency of the sputter deposition process are increasing. Superior material utilization and higher deposition rates lead to the substitution of planar by rotary targets. Spraying processes allow the use of a wide range of material designs and target dimensions and are considered as the most promising production methods for rotary targets. However, the spraying process examined in this work is particularly suitable for processing ductile materials with face-centered cubic or hexagonal dense-packed lattices. The production of dense coatings of brittle body-centered cubic metals like molybdenum with this technique has to be considered as challenging. Based on the knowledge of previous researches, the working hypothesis was proposed, that by using molybdenum powders tailored for this procedure, dense layers can be produced even with these materials. The aim of this work is the identification of particle properties relevant for this spraying process and the development of suitable production technologies. The modification of the powder properties rests on the reduction of molybdenum trioxide (MoO3) to molybdenum. The investigated parameters are temperature (T), reduction gas flow rate (VFR), argon content (Ar) and partial pressure of water vapour (pH2O) in the atmosphere. Additionally, the influence of the size fractions and structure of MoO3 and MoO2 on the molybdenum formation is also taken into account. Results indicate that the reduction temperature and the characteristics of the intermediate phase have a major impact on the final product. Based on the statistical experimental design and evaluation, models for the specific surface area (SSA), porosity and particle size of the intermediate and final powder were determined. These allow an optimization of the reduction process to achieve a molybdenum powder with a desired morphology. The powders of various properties, produced on the basis of this knowledge, are used in the spraying process to examine their suitability to produce pure molybdenum or molybdenum-titanium coatings. By optimizing the powder morphology an increase in deposition efficiency by a factor of four for the production of pure molybdenum layers on titanium substrate and by a factor of ten on molybdenum was achieved.
|Translated title of the contribution||Production of Molybdenum Powder with Special Properties|
|Publication status||Published - 2019|