Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Fabrication of Nanostructured W-Y2O3 Materials by Chemical Methods
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
2012 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 25, 12622-12628 p.Article in journal (Refereed) Published
Abstract [en]

A novel method for the fabrication of highly uniform oxide dispersion-strengthened (ODS) materials made by chemical processing is presented. The powders are fabricated by a two-step route starting with a chemical synthesis at room temperature, producing nanocrystalline yttrium doped tungsten trioxide hydrate precursor powders. Thermogravimetric analysis with evolved gas analysis revealed the presence of ammonium nitrate in the precursors. The second step is the reduction of the precursor in a hydrogen atmosphere at 600 and 800 degrees C. The reduced powders, containing W-1.2%Y2O3, showed two types of tungsten particles, cube-shaped with a size less than 250 nm and finer particles (<50 nm) of both spherical and cubic shape. The powder was consolidated by spark plasma sintering at 1100 degrees C, producing a bulk material with a relative density of 88%. Characterization of the sintered materials by high resolution scanning electron microscopy revealed a uniform microstructure with tungsten grains of less than 300 nm and nanosized oxide particles uniformly dispersed at the tungsten grain boundaries, as well as inside the tungsten grains. Experimental determination of the elastic properties was conducted by nanoindentation tests and fracture toughness was studied by radial indentation cracking.

Place, publisher, year, edition, pages
2012. Vol. 22, no 25, 12622-12628 p.
Keyword [en]
doped ammonium paratungstate, tungsten blue oxide, mechanical-properties, technical reduction, youngs modulus, co powder, composites, decomposition, indentation, precursor
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-43229DOI: 10.1039/c2jm30652bISI: 000304884000030Scopus ID: 2-s2.0-84862231536OAI: oai:DiVA.org:kth-43229DiVA: diva2:447820
Funder
EU, FP7, Seventh Framework ProgrammeSwedish Research Council
Note
Updated from manuscript to article in journal. QC 20120702Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Nanostructured Tungsten Materials by Chemical Methods
Open this publication in new window or tab >>Nanostructured Tungsten Materials by Chemical Methods
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Tungsten based-materials are used in many different technical fields, particularly in applications requiring good temperature and/or erosion resistance. Nanostructuring of tungsten alloys and composites has the potential to dramatically improve the materials’ properties, enhancing the performance in present applications or enabling totally new possibilities. Nanostructured WC-Co composites have been the focus of researchers and industries for over two decades. New methods for powder fabrication and powder consolidation have been developed. However, the fabrication of true nanograined WC-Co materials is still a challenge. Nanostructured tungsten composites for applications as plasma facing materials in fusion reactors have in recent years attracted a growing interest. This Thesis summarizes work on the development of chemical methods for the fabrication of two different types of nanostructured tungsten based materials; WC-Co materials mainly aimed at cutting tools applications and W-ODS composites with rare earth oxide particles, intended as plasma facing materials in future fusion reactors. The approach has been to prepare powders in two steps: a) synthesis of uniform powder precursors containing ions of tungsten and the doping elements by co-precipitation from aqueous solutions, and b) further processing of the precursors into W or WC based nano-composite powders.

Highly homogenous W and Co containing powder precursors for WC-Co composites were prepared via two different routes. Keggin-based precursors ((NH4)8[H2Co2W11O40]) with agglomerates of sizes up to 50 μm, were made from sodium tungstate or ammonium metatungstate and cobalt acetate. The powder composition corresponded to 5.2 % Co in the final WC-Co composites. In a second approach, paratungstate-based precursors (Cox(NH4)10-2x[H2W12O42]) were prepared from ammonium paratungstate (APT) and cobalt hydroxide with different compositions corresponding to 3.7 to 9.7 % Co in WC-Co. These particles had a plate-like morphology with sides of 5-20 μm and a thickness of less than 1 μm. Both precursors were processed and sintered into highly uniform microstructures with fine scale (<1μm). The processing of paratungstate-based precursors was also further investigated. Nanostructured WC-Co powders with grains size of less than 50 nm by decreasing processing temperatures and by applying gas phase carburization.

W-ODS materials were fabricated starting from ammonium paratungstate and rare earth elements (Y or La). Paratungstate-based precursors were prepared with different homogeneity and particle sizes. The degree of the chemical uniformity varied with the particle size from ca 1 to 30 μm. Tungsten trioxide hydrate-based precursors made from APT and yttrium nitrate under acidic conditions had dramatically higher homogeneity and smaller particle size. The crystallite size was decreased to a few nanometers. These precursors were further processed to composite nanopowder and sintered to a nanostructured W-1.2%Y2O3 composite with 88% relative density.

In summary, APT can be converted to highly homogenous powder precursors of different compositions. The transformations are carried out in aqueous suspensions as a solvent mediated process, in which the starting material dissolves and the precursor precipitates. Powders with fine scale morphologies are obtained, e.g. plate-like particles with thickness less than 1 μm or spherical particles with size of a few nanometers. These precursors were processed further in to nano-sized composite powders and sintered to highly uniform tungsten composites with fine microstructures.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 47 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2011:13
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-42702 (URN)978-91-7501-130-1 (ISBN)
Presentation
2011-11-02, sal 539, Forum, Isafjordsgatan 39, Kista, 10:00 (English)
Opponent
Supervisors
Note
QC 20111013Available from: 2011-10-13 Created: 2011-10-11 Last updated: 2011-10-25Bibliographically approved
2. 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.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:13
Keyword
Tungsten, Nano-tungsten, ODS tungsten, W-La2O3, W-Y2O3, SPS, Plasma-facing materials, Armour material, fusion material
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101319 (URN)
Public defence
2012-09-04, Sal/Hall C2, KTH-Electrum, Isafjordsgatan 26, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20120827

Available from: 2012-08-27 Created: 2012-08-27 Last updated: 2012-11-19Bibliographically approved
3. Tungsten-Based Nanocomposites by Chemical Methods
Open this publication in new window or tab >>Tungsten-Based Nanocomposites by Chemical Methods
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tungsten based-materials find use in many different fields of engineering, particularly in applications where good temperature and/or erosion resistance is important. Nanostructuring of tungsten composites is expected to dramatically improve the materials’ properties and enhancing the performance in present applications but also enabling totally new possibilities. Nanostructured WC-Co materials have been the focus of researchers and engineers for over two decades. New fabrication methods have been developed. But, the fabrication of true nanograined WC-Co composites is still a challenge. Nanostructured tungsten-based materials for applications as plasma facing materials in fusion reactors have attracted a growing interest. This Thesis summarizes work on the development of chemical methods for the fabrication of two different types of nanostructured tungsten-based materials; WC-Co composites mainly for cutting tools applications and W-ODS materials with yttria particles, intended as plasma facing materials in fusion reactors. The approach has been to prepare powders in two steps: a) synthesis of uniform powder precursors containing ions of tungsten and cobalt or yttrium by precipitation from aqueous solutions and b) processing of the precursors into WC- or W-based nano-composite powders.

Highly homogenous W- and Co- containing precursors for WC-Co composites were prepared via two different routes. Keggin-based precursors ((NH4)8[H2Co2W11O40]) were made from sodium tungstate or ammonium metatungstate and cobalt acetate. The powder composition corresponded to 5.2 % Co in the final WC-Co material. In a second approach, paratungstate-based precursors (Cox(NH4)10-2x[H2W12O42]) were prepared from ammonium paratungstate (APT) and cobalt hydroxide with different compositions corresponding to 3.7 to 9.7 % Co in WC-Co. Both precursors were processed and sintered into uniform microstructures with fine scale (<1μm). The processing of paratungstate-based precursors was also further investigated. WC-Co powders with grains size of less than 50 nm were obtained by decreasing processing temperatures and by applying gas phase carburization.

W-ODS materials were fabricated starting from ammonium paratungstate and yttrium salts. Paratungstate-based precursors were prepared with different homogeneities and particle sizes. The degree of the chemical uniformity varied with the particle size from ca 1 to 30 μm. Tungsten trioxide hydrate-based precursors made from APT and yttrium salts under acidic conditions had higher uniformity and smaller particle size. The tungsten oxide crystallite size was decreased to a few nanometers. Yttrium was included either by doping or in a nanocomposite structure as yttrium oxalate. The nanocomposite precursor was found to be more reactive during hydrogen reduction, facilitating its conversion to pure W-Y2O3 nanopowder. The doped precursor were further processed to nanopowders and sintered to highly uniform W-1.2%Y2O3 composites.

In  summary, APT was converted to highly homogenous or uniform powder precursors ofdifferent compositions. The transformations were carried out in aqueous suspensions as a water-mediated  process. These precursors were processed  further in to nano-sized  powders  and sintered to highly uniform tungsten composites with fine microstructures.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. 46 p.
Series
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2014:20
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-156604 (URN)
Public defence
2014-12-11, Sal/hall 205, Electrum, KTH-ICT, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20141201

Available from: 2014-12-01 Created: 2014-12-01 Last updated: 2014-12-04Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Wahlberg, SverkerYar, Mazher AhmedAbuelnaga, Mohammad OmarMuhammed, Mamoun
By organisation
Functional Materials, FNM
In the same journal
Journal of Materials Chemistry
Materials Chemistry

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 160 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf