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Synthesis of nano sized Cu and Cu-W alloy by hydrogen reduction
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The major part of the present work, deals with the reduction kinetics of Cu2O powder and a Cu2O-WO3 powder mixture by hydrogen gas, studied by ThermoGravimetric Analysis (TGA). The reduction experiments were carried out both isothermally and non-isothermally on thin powder beds over different temperature intervals. During the experiments, the reductant gas flow rate was kept just above the starvation rate for the reaction to ensure that chemical reaction was the rate-controlling step. The activation energy for the reactions was evaluated from isothermal as well as non-isothermal reduction experiments.

In the case of the reduction of Cu2O, the impact of the stability of the copper oxide on the activation energy for hydrogen reduction under identical experimental conditions is discussed. A closer investigation of additions of Ni or NiO to Cu2O did not have a perceptible effect on the kinetics of reduction.

In the case of the reduction of the Cu2O-WO3 mixture, the reaction mechanism was found to be affected in the temperature range 923-973 K, which is attributed to the reaction/transformation in the starting oxide mixture. At lower temperatures, Cu2O was found to be preferentially reduced in the early stages, followed by the reduction of the tungsten oxide. At higher temperatures, the reduction kinetics was strongly affected by the formation of a complex oxide from the starting materials. It was found that the Cu2O-WO3 mixture underwent a reaction/transformation which could explain the observed kinetic behavior.

The composition and microstructures of both the starting material and the reaction products were analyzed by X-ray diffraction (XRD) as well as by microprobe analysis. vi Kinetic studies of reduction indicated that, the mechanism changes significantly at 923 K and the product formed had unusual properties. The structural studies performed by XRD indicated that, at 923 K, Cu dissolved in W forming a metastable solid solution, in amorphous/nanocrystalline state. The samples produced at higher as well as lower temperatures, on the other hand, showed the presence two phases, pure W and pure Cu. The SEM results were in conformity with the XRD analysis and confirmed the formation of W/Cu alloy. TEM analysis results confirmed the above observations and showed that the particle sizes was about 20 nm.

The structure of the W/Cu alloy produced in the present work was compared with those for pure copper produced from Cu2O produced by hydrogen reduction under similar conditions. It indicated that the presence of W hinders the coalescence of Cu particles and the alloy retains its nano-grain structure. The present results open up an interesting process route towards the production of intermetallic phases and composite materials under optimized conditions.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , x, 36 p.
Keyword [en]
hydrogen reduction, kinetics, activation energy, copper oxide, copper tungsten composite, alloy powder, manostructure
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-353OAI: oai:DiVA.org:kth-353DiVA: diva2:9345
Presentation
2005-06-02, Sal B2, Brinellvägen 23, Stockholm, 10:00
Supervisors
Note
QC 20101222Available from: 2005-08-01 Created: 2005-08-01 Last updated: 2010-12-22Bibliographically approved
List of papers
1. Kinetics studies of hydrogen reduction of Cu2O
Open this publication in new window or tab >>Kinetics studies of hydrogen reduction of Cu2O
2006 (English)In: Zeitschrift für Metallkunde, ISSN 0044-3093, Vol. 97, no 1, 72-78 p.Article in journal (Refereed) Published
Abstract [en]

In present work, reduction kinetics Of Cu2O by hydrogen gas was studied by thermogravimetric analyses (TGA). The TGA experiments were carried out both isothermally and non-isothermally on shallow powder beds. It was established that additions of Ni or NiO did not have any serious effect on the kinetics of reduction of Cu2O. The composition and microstructures of the reaction products were analyzed after each experiment by X-ray diffraction (XRD) as well as by scanning electron microscopy (SEM). The activation energy for the reaction was evaluated from isothermal as well as non-isothermal reduction experiments and was found to be in good agreement. The impact of the stability of the oxide on the activation energy for hydrogen reduction is also discussed.

Keyword
copper oxide, hydrogen reduction, kinetics, activation energy, cuo, oxides, powder, gas, tungstate
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-15460 (URN)000235609500012 ()2-s2.0-32644471395 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-12-22Bibliographically approved
2. Hydrogen reduction of a Cu2O-WO3 mixture
Open this publication in new window or tab >>Hydrogen reduction of a Cu2O-WO3 mixture
2006 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 2, 265-274 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, the reduction kinetics of Cu2O-WO3 mixtures by hydrogen gas was studied by thermogravimetric analyses (TGA). The reduction experiments were carried out both isothermally and nonisothermally on shallow powder beds in the temperature interval 673 to 1073 K. During the experiments, the reductant gas flow rate was kept just above the starvation rate for the reaction to ensure that chemical reaction was the rate-controlling step. The composition and microstructures of the reaction products were analyzed after each experiment by X-ray diffraction (XRD) as well as by microprobe analyses. In the temperature interval 673 to 923 K, copper oxide was found to be preferentially reduced in the early stages of the experiment followed by the reduction of tungsten oxide. The reaction mechanism was found to be affected by a reaction/transformation in the starting copper-tungsten oxide mixtures in the temperature interval 923 to 973 K. At temperatures higher than 973 K, the reduction of the complex oxide formed was found to have a strong impact on the reaction kinetics. The activation energy was evaluated, from the isothermal as well as nonisothermal reduction experiments, for the two stages of reduction identified. The XRD and scanning electron microscopy (SEM) studies indicated the formation of a metastable solution of copper in tungsten at about 923 K. The advantage of the hydrogen reduction route toward the bulk production of alloy powders in the nanosize is demonstrated.

Keyword
copper tungstate, alloys, powder, kinetics, oxides
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-15600 (URN)10.1007/BF02693156 (DOI)000236750000013 ()2-s2.0-33646563417 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-12-22Bibliographically approved
3. Morphology studies of a W/Cu alloy synthesized by hydrogen reduction
Open this publication in new window or tab >>Morphology studies of a W/Cu alloy synthesized by hydrogen reduction
2006 (English)In: Journal of Materials Research, ISSN 0884-2914, Vol. 21, no 6, 1467-1475 p.Article in journal (Refereed) Published
Abstract [en]

Because of the applications for W/Cu composite materials in high technology, the advantages of synthesizing this alloy by the hydrogen reduction route were investigated, with special attention to the properties of the product that was formed. Kinetic studies of reduction indicated that the mechanism changes significantly at 923 K, and the product had unusual properties. In the present work, morphological studies of the W/Cu alloy with 20 wt% Cu, produced at 923 K, were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. The structural studies performed by XRD indicated that, at 923 K, Cu dissolved in W, forming a metastable solid solution in the nanocrystalline state. The samples produced at higher as well as lower temperatures, on the other hand, showed the presence of two phases, pure W and pure Cu. The SEM results were in agreement with the XRD analysis and confirmed the formation of W/Cu alloy. TEM analysis results confirmed the above observations and showed that the particle sizes were about 20 nm. The structure of the W/Cu alloy produced in the present work was compared with those for pure Cu, produced from Cu2O produced by hydrogen reduction under similar conditions. This indicated that the presence of W hinders the coalescence of Cu particles, and the alloy retains its nano-grain structure. The present results open up an interesting process route toward the production of intermetallic phases and composite materials under optimized conditions.

Keyword
tungsten, powder, mixture
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-15738 (URN)10.1557/jmr.2006.0181 (DOI)000238191300016 ()2-s2.0-33746176088 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-12-22Bibliographically approved

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