Change search
ReferencesLink to record
Permanent link

Direct link
Processing and Sintering of Yttrium-Doped Tungsten Oxide Nano-powders
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
Show others and affiliations
(English)In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896XArticle in journal (Other academic) Submitted
Abstract [en]

Innovative chemical methods are capable of fabricating nanoscale tungsten oxide compoundsd oped with various rare-earth elements with high purity and homogeneity, which can be processed under hydrogen into nanostructured oxide-dispersed tungsten composite powders having several potential applications. However, hydrogen reduction of doped-tungsten oxide compounds is rather complex, affecting the morphology and composition of the final powder. In this study we have investigated the reduction of tungstic acid in the presence of Y and weprovide the experimental evidence that Y2O3 can be separated from Y-doped tungstic acid via hydrogen reduction to produce Y2O3-W powders. The processed powders were further consolidated by spark plasma sintering at different temperatures and holding times at 75 MPa pressure and characterized. The optimized SPS conditions suggest sintering at 1400 °C for 3 min holding time to achieve higher density composites with an optimum finer grain size (3 μm) and a hardness value up to 420 HV. Major grain growth takes place at temperatures above 1300 °C during sintering. From the density values obtained, it is recommend to apply higher pressure before 900 °C to obtain maximum density. Oxides inclusions present in the matrix were identified as Y2O3•3WO3 and Y2O3•WO3 during high resolution microscopici nvestigations.

Keyword [en]
nanostructured W, ODS-tungsten, Nano W-Y2O3, tungsten oxide reduction, Tungstic acid
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-101166OAI: diva2:546632

QS 2012

Available from: 2012-08-24 Created: 2012-08-24 Last updated: 2012-08-27Bibliographically approved
In thesis
1. Development of Nanostructured Tungsten Based Composites for Energy Applications
Open this publication in new window or tab >>Development of Nanostructured Tungsten Based Composites for Energy Applications
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tungsten (W) based materials can be used in fusion reactors due to several advantages. Different fabrication routes can be applied to develop tungsten materials with intended microstructure and properties for specific application including nanostructured grades. Therein, innovative chemical routes are unique in their approach owing numerous benefits. This thesis summarizes the development of W-based composites dispersed-strengthened by rare earth (RE) oxides and their evaluation for potential application as plasma facing armour material to be used in fusion reactor. Final material development was carried out in two steps; a) fabrication of nanostructured metallic tungsten powder dispersed with RE-oxides and b) powder sintering into bulk oxide-dispersed strengthened (ODS) composite by spark plasma process. With the help of advanced characterization tools applied at intermediate and final stages of the material development, powder fabrication and sintering conditions were optimized. The aim was to achieve a final material with a homogenous fine microstructure and improved properties, which can withstand under extreme conditions of high temperature plasma.

Two groups of starting materials, synthesized via novel chemical methods, having different compositions were investigated. In the first group, APT-based powders doped with La or Y elements in similar ways, had identical particles’ morphology (up to 70 μm). The powders were processed into nanostructured composite powders under different reducing conditions and were characterized to investigate the effects on powder morphology and composition. The properties of sintered tungsten materials were improved with dispersion of La2O3 and Y2O3 in the respective order. The oxide dispersion was less homogeneous due to the fact that La or Y was not doped into APT particles. The second group, Ydoped tungstic acid-based powders synthesized through entirely different chemistry, contained nanocrystalline particles and highly uniform morphology. Hydrogen reduction of doped-tungstic acid compounds is complex, affecting the morphology and composition of the final powder. Hence, processing conditions are presented here which enable the separation of Y2O3 phase from Y-doped tungstic acid.

Nevertheless, the oxide dispersion reduces the sinterability of tungsten powders, the fabricated nanostructured W-Y2O3 powders were sinterable into ultrafine ODS composites at temperatures as low as 1100 °C with highly homogeneous nano-oxide dispersion at W grain boundaries as well as inside the grain. The SPS parameters were investigated to achieve higher density with optimum finer microstructure and higher hardness. The elastic and fracture properties of the developed ODS-W have been investigated by micro-mechanical testing to estimate the materials’ mechanical response with respect to varying density and grain size. In contrast from some literature results, coarse grained ODS-W material demonstrated better properties. The developed ODS material with 1.2 Y2O3 dispersion were finally subjected to high heat flux tests in the electron beam facility “JUDITH-1”. The samples were loaded under ELM-like thermal-shocks at varying base temperatures up to an absorbed power density of 1.13 GW/m2, for armour material evaluation. Post mortem characterizations and comparison with other reference W grades, suggest lowering the oxide contents below 0.3 wt. % Y2O3.

As an overview of the study conducted, it can be concluded that innovative chemical routes can be potential replacement to produce tungsten based materials of various composition and microstructure, for fusion reactor applications. The methods being cheap and reproducible, are also easy to handle for large production at industrial scale.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 48 p.
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:13
Tungsten, Nano-tungsten, ODS tungsten, W-La2O3, W-Y2O3, SPS, Plasma-facing materials, Armour material, fusion material
National Category
Metallurgy and Metallic Materials
urn:nbn:se:kth:diva-101319 (URN)
Public defence
2012-09-04, Sal/Hall C2, KTH-Electrum, Isafjordsgatan 26, Kista, 10:00 (English)

QC 20120827

Available from: 2012-08-27 Created: 2012-08-27 Last updated: 2012-11-19Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Yar, Mazher AhmedWahlberg, SverkerAbuelnaga, Mohammad OmarMuhammed, Mamoun
By organisation
Functional Materials, FNM
In the same journal
Journal of nanoparticle research
Electrical Engineering, Electronic Engineering, Information Engineering

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 217 hits
ReferencesLink to record
Permanent link

Direct link