Recycling of refractory metals

Karin Ratschbacher

Research output: ThesisDoctoral Thesis

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Abstract

Recycled materials and scrap represent, especially in the case of critical raw materials, a valuable resource to secure supply and provide the processing companies with a higher degree of independence from fluctuations in prices and delivery bottlenecks. The target of this thesis is the replacement of the current practice of selling and down-cycling valuable refractory metal scrap by laying the groundwork for an on-site recycling process which enables the company to leave assets within company property. To get insights into the conversion-behavior of various refractory-metal alloys under an oxidizing atmosphere over time, kinetic experiments were conducted on a Mo-Ta- as well as aW-Re alloy, which lead to deduction of the corresponding velocity laws. Pilot experiments enabled the investigation on how well and under which conditions the alloys Mo-Ta,W-Re, Mo-Cu, Mo-W, Mo-Nb and Mo-Ti can be separated into their components through oxidation and sublimation of one of the alloying element’s oxide. Very pure products resulted from Mo-Ta, W-Re and Mo-Nb alloys, which were converted in a tube furnace. Furthermore a vacuum technology based approach for the separation of a Mo-Cu alloy into its components is introduced. A statistical design of experiment lead to empirical equations which estimate the influence of the most important process parameters for the conversion of the Mo-Ta alloy, which are temperature, grain size and oxygen content of the process atmosphere on the conversion time and the purity of the product. This offers the opportunity to optimize process parameters in order to achieve minimal conversion time with the highest possible degree of conversion feasible under set conditions. This data was used to determine the process parameters for the transformation of the Mo-Ta chips in a laboratory size rotary kiln, investigating the influence of the movement on the conversion behavior. Process parameters were further adjusted for converting Mo-Ta, W-Re and Mo-Ti chips as well as agglomerated Mo-W abrasive slurry in the kiln. The experiments conducted on an industrial size rotary kiln represent the last scale up. Stable conditions and high purity products as well as an output, which could make this process economically rewarding were achieved.
Translated title of the contributionRecycling von Refraktärmetallen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Antrekowitsch, Helmut, Assessor A (internal)
  • Lehner, Markus, Assessor B (internal)
Publication statusPublished - 2015

Bibliographical note

embargoed until 23-09-2020

Keywords

  • Recycling
  • refractory metals
  • kinetics
  • molybdenum
  • tantalum
  • tungsten
  • rhenium

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