DOCSLIB.ORG

On the Formation of Aluminum Tungstate and Its Presence in Tungsten Oxide on Gamma-Alumina Catalysts

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
On the Formation of Aluminum Tungstate and Its Presence in Tungsten Oxide on Gamma-Alumina Catalysts On the formation of aluminum tungstate and its presence in tungsten oxide on gamma-alumina catalysts Citation for published version (APA): Thomas, R., Kerkhof, F. P. J. M., Moulijn, J. A., Medema, J., & Beer, de, V. H. J. (1980). On the formation of aluminum tungstate and its presence in tungsten oxide on gamma-alumina catalysts. Journal of Catalysis, 61(2), 559-561. https://doi.org/10.1016/0021-9517%2880%2990409-1, https://doi.org/10.1016/0021-9517(80)90409-1 DOI: 10.1016/0021-9517%2880%2990409-1 10.1016/0021-9517(80)90409-1 Document status and date: Published: 01/01/1980 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 27. Sep. 2021 JOURNAL OF CATALYSIS 61, 559-561 (1980) On the Formation of Aluminum Tungstate and Its Presence in Tungsten Oxide on Y-Alumina Catalysts Tungsten oxide (1-5) and molybdenum W-atoms/nm2) contain no aluminum tung- oxide (1, 2, 5-17) on y-alumina and sul- state. This is in contrast to y-alumina- fided catalysts derived from these sys- supported molybdenum oxide in which tems have been studied by several authors aluminum molybdate has been found in because of their interest, as catalysts catalysts with a coverage of 4.5-7 Mo- in reactions such as metathesis and atoms/nm2 (16). hydrodesulfurization. Measurements on physical mixtures of The purpose of this note is to determine aluminum tungstate and y-alumina showed whether bulk aluminum tungstate is present that the detection limit of aluminum tung- as a major compound in tungsten oxide state in these mixtures is less than 1 wt%. on y-alumina catalysts of pract,ical interest. Consequently one must conclude that alu- Some authors have proposed its formation minum tungstate is not a major compound (1-S), while others present data suggesting in tungsten oxide on y-alumina catalysts. the absence of this compound (4, 5). The This conclusion was recently confirmed by same controversy exists for molybdenum temperature-programmed reduction mea- oxide on y-alumina. Since Raman spec- surements (18), which showed that, the troscopy has proven to be a valuable tool amount of aluminum tungstatc must be in studies on the structure of supported considerably less than 1 wt%. catalysts (1, 4-6, 15-17)) it is applied here The main arguments supporting the con- as the main technique. clusion that tungsten oxide on -y-alumina In Fig. 1 the Raman spectra of alumi- catalysts contain aluminum tungst ite are num tungstate and catalysts prepared by based on results obtained from Raman and wet and dry impregnation of y-alumina luminescence spectroscopy and from ac- (Ketjen 000-1.5E) with ammonium mcta- tivity measurements (1-S). In our opinion, tungstatc (Koch-Light, 99.9y0), calcined however, the purity of the refcrcncc com- at 823”K, arc shown. Experimental details pound used in thesr studic>s was question- on thr Raman spectra are reported else- able. Aluminum tungstat,e was prepared where (4). The spectrum of aluminum at S23”K (16 hr) from a coprecipitate of tungstate is characterized by a sharp band ammonium metatungstate and aluminum at 1046 cm-l. The spectra of the catalysts nitrate, while other literature data indicate show a broad band at about 970 cm-‘, that a higher temperature is to be preferred which has been attributed to a polymeric, (19, 20). We have checked the synthesis octahedrally coordinated, tungsten com- of aluminum tungstate by calcining a co- pound (4). The bands at 71j and 805 cm-’ precipitate of aluminum nitrate and am- are Raman bands of WO,. In these cata- monium metatungst.ate (Baker Chemicals) lysts no aluminum tungstate is present at three temperatures, 823, 1173, and in detectable amounts. Even the catalysts 1373°K. The Raman spectra are shown in with a rather high tungsten content (4-S Fig. 2. From comparison with the spec- 559 0021-9517/80/020559-03$02.00/O Copyright 0 1980 by Academic Press, Inc.. All rights of reproduction in any form reserved. 560 NOTES trum of tungsten oxide it is clear that the formation of aluminum tungstate is not yet completed at 823 and 1173°K. In the spectrum of the sample calcined at 823°K there is a small band due to aluminum tungstate, together with two broad bands (807 and 719 cm-l) of tungsten trioxide. In addition there is a broad band at 980 cm-‘, which is also present in the spectra of our catalysts. The sample cal- cined at 1173°K contains more aluminum tungstate, but still a considerable amount of tungsten trioxide. The system is now better defined, as can be seen from the sharpness of t,he bands of tungsten trioxide and from the disappearance of the poly- meric compound. This can also be con- cluded from the X-ray diffraction (XRD) d patterns. By XRD no crystalline tungsten J& trioxide is observed, implying that it is cm-l 1200 800 400 FIG. 2. Raman spectra of (a) tungsten trioxide and (b, c, d) coprecipitates of aluminum nitrate and ammonium metatungstate calcined at (b) 823”K, (c) 1173”K, and (d) 1373°K. amorphous, microcrystalline, or present in nondetectable amounts. All samples show the diffraction patterns of aluminum tung- state; the increasing sharpness of the pat- terns indicates a. drastic increase in crystal- linity when the calcination temperature is increased from 873 to 1123°K. Further increase of the temperature does not in- fluence the crystallinity significantly. From the XRD pattern alone it, might be con- cluded that the transition of aluminum nitrate and ammonium metatungstate into aluminum tungstate is already complete at low temperature. The Raman spectra show that this is not the case. Also the fact that catalytic activity for metathesis was observed for a coprecipitate of aluminum nitrate and ammonium metatungstate cal- cined at 823°K (S) is not a firm basis for the statement that aluminum tungstate is a cm4 1200 800 400 reasonable precursor for the active site in FIG. 1. Raman spectra of (a) aluminum tungstate metathesis, because, as shown here, the and (b-e) WOa/y-A1203 catalysts; (b) 25 wt% calcined coprecipitate used as a cata- WOt, wet (4 W-atom/rim*); (c) 29 wt% WOZ, dry (5 W-atom/nnP); (d) 8 wt% WO,, wet (1 W-atom/ lyst, contained more than one tungsten rime; (e) 7 wt% WO,, dry (0.9 W-atom/nma). compound. NOTES 561 The conclusion that aluminum tungst,ate 7. Ashley, J. H., and Mitchell, P. C. H., J. Chem. is not a major compound does not com- Sot. A (1969), 2730. Richardson, J. T., Ind. Eng. Chem. Fund. 3, ” pletely rule out the possibility that it is 154 (1964). the catalytically active phase. Especially 9, De Beer, V. H. J., Van der Aalst, M. J. M., in metathesis it has been proven that t,he Machiels, C. J., and Schuit, G. C. A., J. number of active sites is low (21, 22). Calal. 43, 78 (1976). Therefore, a priori, it is always possible 10. Lipsch, J. M. J. G., and Schuit, G. C. A., J. Catal. 15, 163, 174, 179 (1969). that the precursor of the active site is a II. Krylov, 0. V., and Margolis, L. Ya., K&t. compound present in amounts below the Katal. 11, 358 (1970). detection limit. 1.2. Asmolov, G. N., and Krylov, 0. V., Kinet. This not,e can be summarized by the Katal. 11, 847 (1970). following conclusions : IS. Sonnemans, J., and Mars, P., J. Catal. 31, 209 (1973). (1) The formation of significant amounts 14. Giordano, N., Padovan, N., Vaghi, A., Bart, of aluminum tungstate in tungsten oxide J. C. J., and Castellan, A., J. Catal. 38, 1 (1975). 15 on -y-alumina catalysts of practical interest Brown, F. R., Makovsky, L. E., and Rhee, is improbable. K. H., J. Catal. 50, 162 (1977). (2) The evidence reported in the litera- 16. Medema, J., Van Stam, C., De Beer, V. H.
Load more

Recommended publications
  • In Search of the Active Sites for the Selective Catalytic Reduction on Tungsten-Doped Vanadia Monolayer Catalysts Supported By
    In Search of the Active Sites for the Selective Catalytic Reduction on Tungsten-Doped Vanadia Monolayer Catalysts supported by TiO2 Mengru Li,y Sung Sakong,y and Axel Groß∗,y,z yInstitute of Theoretical Chemistry, Ulm University, 89069 Ulm, Germany zHelmholtz Institute Ulm (HIU), Electrochemical Energy Storage, 89069 Ulm, Germany E-mail: [email protected] Abstract Tungsten-doped vanadia-based catalysts supported on anatase TiO2 are used to re- duce hazardous NO emissions through the selective catalytic reduction of ammonia, but their exact atomistic structure is still largely unknown. In this computational study, the atomistic structure of mixed tungsta-vanadia monolayers on TiO2 support under typical operating conditions has been addressed by periodic density functional theory calcu- lations. The chemical environment has been taken into account in a grand-canonical approach. We evaluate the stable catalyst structures as a function of the oxygen chemi- cal potential and vanadium and tungsten concentrations. Thus we determine structural motifs of tungsta-vanadia/TiO2 catalysts that are stable under operating conditions. Furthermore, we identify active sites that promise high catalytic activity for the selec- tive catalytic reduction by ammonia. Our calculations reveal the critical role of the stoichiometry of the tungsta-vanadia layers with respect to their catalytic activity in the selective catalytic reduction. 1 Keywords Vanadium-based catalyst; Density functional theory; Selective Catalytic Reduction; stoi- chiometry; chemical potential Introduction Nitrogen oxide (NOx) emission from various stationary and mobile sources is significantly contributing to air pollution and causing, among others, ozone depletion, smog, acid rain, 1,2 eutrophication, and eventually global warming.
    [Show full text]
  • Titanium-Doped P-Type WO3 Thin Films for Liquefied Petroleum Gas
    nanomaterials Communication Titanium-Doped P-Type WO3 Thin Films for Liquefied Petroleum Gas Detection Yuzhenghan He 1, Xiaoyan Shi 1, Kyle Chen 2 , Xiaohong Yang 1,* and Jun Chen 2,* 1 Key Laboratory of Functional Materials of Chongqing, School of Physics & Information Technology, Chongqing Normal University, Chongqing 400047, China; [email protected] (Y.H.); [email protected] (X.S.) 2 Department of Bioengineering, University of California, Los Angeles, Los Angeles, CA 90095, USA; [email protected] * Correspondence: [email protected] (X.Y.); [email protected] (J.C.) Received: 21 February 2020; Accepted: 8 April 2020; Published: 11 April 2020 Abstract: Gas sensors are an important part of smart homes in the era of the Internet of Things. In this work, we studied Ti-doped P-type WO3 thin films for liquefied petroleum gas (LPG) sensors. Ti-doped tungsten oxide films were deposited on glass substrates by direct current reactive magnetron sputtering from a W-Ti alloy target at room temperature. After annealing at 450 ◦C in N2 ambient for 60 min, p-type Ti-doped WO3 was achieved for the first time. The measurement of the room temperature Hall-effect shows that the film has a resistivity of 5.223 103 Wcm, a hole concentration × of 9.227 1012 cm 3, and mobility of 1.295 102 cm2V 1s 1. X-Ray diffraction (XRD) and X-ray × − × − − photoelectron spectroscopy (XPS) analyses reveal that the substitution of W6+ with Ti4+ resulted in p-type conductance. The scanning electron microscope (SEM) images show that the films consist of densely packed nanoparticles.
    [Show full text]
  • Bulk Tungsten-Substituted Vanadium Oxide for Low-Temperature Nox
    ARTICLE https://doi.org/10.1038/s41467-020-20867-w OPEN Bulk tungsten-substituted vanadium oxide for low- temperature NOx removal in the presence of water Yusuke Inomata 1, Hiroe Kubota2, Shinichi Hata3, Eiji Kiyonaga4, Keiichiro Morita4, Kazuhiro Yoshida4, Norihito Sakaguchi 5, Takashi Toyao 2, Ken-ichi Shimizu2,8, Satoshi Ishikawa6, Wataru Ueda6, ✉ Masatake Haruta1 & Toru Murayama 1,7,8 NH3-SCR (selective catalytic reduction) is important process for removal of NOx. However, 1234567890():,; water vapor included in exhaust gases critically inhibits the reaction in a low temperature range. Here, we report bulk W-substituted vanadium oxide catalysts for NH3-SCR at a low temperature (100–150 °C) and in the presence of water (~20 vol%). The 3.5 mol% W- substituted vanadium oxide shows >99% (dry) and ~93% (wet, 5–20 vol% water) NO −1 −1 conversion at 150 °C (250 ppm NO, 250 ppm NH3,4%O2,SV= 40000 mL h gcat ). Lewis acid sites of W-substituted vanadium oxide are converted to Brønsted acid sites under a wet condition while the distribution of Brønsted and Lewis acid sites does not change + without tungsten. NH4 species adsorbed on Brønsted acid sites react with NO accompanied by the reduction of V5+ sites at 150 °C. The high redox ability and reactivity of Brønsted acid sites are observed for bulk W-substituted vanadium oxide at a low temperature in the presence of water, and thus the catalytic cycle is less affected by water vapor. 1 Research Center for Gold Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University Hachioji, Tokyo 192-0397, Japan.
    [Show full text]
  • Tungsten-Based Nanocomposites by Chemical Methods
    Tungsten-Based Nanocomposites by Chemical Methods Sverker Wahlberg Doctoral Thesis in Materials Chemistry Stockholm 2014 KTH Royal Institute of Technology SE-100 44 Stockholm, Sweden TRITA-ICT/MAP AVH Report 2014:20 KTH School of Information and ISSN 1653-7610 Communication Technology ISRN KTH/ICT-MAP/AVH-2014:20-SE SE-164 40, Kista, Sweden ISBN 978-91-7595-368-7 Akademisk avhandling som med tillstånd av KTH i Stockholm framlägges till offentlig granskning för avläggande av teknisk doktorsexamen torsdagen den 11 december kl 10.00 i sal 205, Electrum, KTH, Isafjordsgatan 22, Kista. © Sverker Wahlberg, 2014 Universitetsservice US-AB, Stockholm 2014 2 Abstract 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.
    [Show full text]
  • Microwave Assisted Pure and Mg Doped Tungsten Oxide WO3 Nanoparticles for Superconducting Applications V
    Microwave Assisted Pure and Mg Doped Tungsten Oxide WO3 Nanoparticles for Superconducting Applications V. Hariharan, V. Aroulmoji, K. Prabakaran, V. Karthik To cite this version: V. Hariharan, V. Aroulmoji, K. Prabakaran, V. Karthik. Microwave Assisted Pure and Mg Doped Tungsten Oxide WO3 Nanoparticles for Superconducting Applications. International jour- nal of advanced Science and Engineering, Mahendra Publications, 2020, 7 (2), pp.1776-1781. 10.29294/IJASE.7.2.2020.1776-1781. hal-03093008 HAL Id: hal-03093008 https://hal.archives-ouvertes.fr/hal-03093008 Submitted on 3 Jan 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Int. J. Adv. Sci. Eng. Vol.7 No.2 1776-1781 (2020) 1776 E-ISSN: 2349 5359; P-ISSN: 2454-9967 Microwave Assisted Pure and Mg Doped Tungsten Oxide WO 3 Nanoparticles for Superconducting Applications V. Hariharan 1*, V. Aroulmoji 2, K. Prabakaran 1, V. Karthik 1 1PG & Research Department of Physics, Mahendra Arts and Science College (Autonomous), Kalipatti, Namakkal District, Tamilnadu 637 501, India 2Centre for Research & Development, Mahendra Engineering College, Mahendhirapuri, Mallasamudram 637503, Namakkal District, Tamil Nadu, India ABSTRACT: The aim of the present work focuses the role of “Mg” in WO 3.H 2O nanopowders, doped with Magnesium using a facile microwave irradiation process and the annealing process was carried out at 600°C in air for 6 h in order to remove the impurities and enhance the crystallinity of the end products.
    [Show full text]
  • Nomination Background: Tungsten Trioxide (CASRN: 1314-35-8)
    Tungsten trioxide & suboxides SUMMARY OF DATA FOR CHEMICAL SELECTION Tungsten Trioxide & Suboxides BASIS OF NOMINATION TO THE NTP Tungsten trioxide and its suboxides are brought to the attention of the Chemical Selection Working Group because of recent concerns that these substances may be fibrogenic in certain industrial settings. Previously, most information on tungsten compounds was from the cemented tungsten carbide industry. Although hard metal disease in this industry is well known, most effects have been attributed to cobalt. Tungsten oxides were selected for review for several reasons. In the US, all sources of unrefined tungsten are presently imported for preparation of tungsten powder that is used to produce cemented tungsten carbide. Exposure to various tungsten oxides and suboxides occurs in the metallurgical processes used to produce tungsten powder. Recent studies in Sweden have shown that calcination of tungsten oxide (yellow oxide), ammonium paratungstate, and blue oxide (WO2.90) results in the formation of asbestos-like tungsten oxide whiskers that are thought to be much more toxic than tungsten powder. Respirable tungsten oxide fibers with a diameter <0.3 :m have also been found in dust from the hard metal industry. Tungsten oxide uses in the textiles, ceramics, and plastics industries, contribute further to potential worker exposure. No adequate 2-year carcinogenicity studies of tungsten trioxide or its suboxides were found in the available literature. In vitro reports described the fibrous form of tungsten oxide as an inducer of hydroxyl radicals and a cytotoxic agent to human lung cells. INPUT FROM GOVERNMENT AGENCIES/INDUSTRY CSWG member, Dr. Yin-Tak Woo of the US Environmental Protection Agency (EPA) provided additional information on the toxicity of tungsten and tungsten compounds.
    [Show full text]
  • Toxicological Profile for Tungsten
    TUNGSTEN 73 4. CHEMICAL AND PHYSICAL INFORMATION 4.1 CHEMICAL IDENTITY Tungsten is a naturally occurring element found in the earth=s surface rocks. Tungsten metal typically does not occur as the free element in nature. Of the more than 20 tungsten-bearing minerals, some of the commonly used commercial ones include feberite (iron tungstate), huebnerite (manganese tungstate), wolframite (iron-manganese tungstate), and scheelite (calcium tungstate). Tungsten appears in Group VIB of the periodic table. Natural tungsten is composed of five stable isotopes: 180W (0.12%), 182W (26.5%), 183W (14.3%), 184W (30.6%), and 186W (28.4%). Twenty-eight radioactive isotopes of tungsten are known; most of these isotopes have short half-lives. Tungsten forms a variety of different compounds, such as tungsten trioxide, tungsten carbide, and ammonium paratungstate (Penrice 1997a). Information regarding the chemical identity of elemental tungsten and tungsten compounds is located in Table 4-1. 4.2 PHYSICAL AND CHEMICAL PROPERTIES Tungsten has several common oxidation states (e.g., W[0], W[2+], W[3+], W[4+], W[5+], and W[6+]). However, tungsten alone has not been observed as a cation. Tungsten is stable, and therefore its most common valence state is +6. The naturally occurring isotopes of tungsten are 180 (0.135%), 182 (26.4%), 183 (14.4%), 184 (30.6%), and 186 (28.4%). Artificial radioactive isotopes of tungsten are 173–179, 181, 185, and 187–189 (O’Neil et al. 2001). Elemental tungsten metal is stable in dry air at room temperature. Above 400 °C, tungsten is susceptible to oxidation. Tungsten is resistant to many chemicals and is also a good electrical conductor (Penrice 1997a).
    [Show full text]
  • Safety Data Sheet
    Tungsten-doped Lithium Lanthanum Zirconate Revision Date: Dec 2018 Safety Data Sheet 1. Product and Company Identification Product Name: Tungsten-doped Lithium Lanthanum Zirconate Product Number: EQ-Lib-LLZWO Synonym: LLZWO CAS#: Chemical Formula: Li6.3La3Zr1.65W0.35O12 Identified uses: Scientific research and development Contact Information: MTI Corporation 860 South 19th Street Richmond, CA 94804, USA Tel: 510-525-3070 Fax: 510-525-4705 Email: [email protected] Website: www.mtixtl.com Non-emergency assistance: 1-888-525-3070 Emergency assistance: Company: CHEMTEL (MTI Contract# MIS2559467) Day or Night Tel (Within USA and Canada): 1-800-255-3924 Tel (Outside USA and Canada): 1-813-248-0585 2. Hazards Identification Emergency Overview: GHS Classification in accordance with 29 CFR 1910 (OSHA HCS) Skin corrosion (Category 1B), H314 Eye Irritation (Category 2), H335 For the full text of the H-Statements mentioned in this Section, see Section 16. HMIS Rating Health hazard: 3 Chronic Health Hazard: * Flammability: 0 Physical Hazard: 1 GHS Label elements, including precautionary statements Pictogram Signal Danger Hazard statement(s) H314 Causes severe skin burns and eye damage H335 May cause respiratory irritation Precautionary statement(s) P260 Do not breathe dust/fume/gas/mist/vapors/spray. 1 Tungsten-doped Lithium Lanthanum Zirconate Revision Date: Dec 2018 P303 + P361 + P353 IF ON SKIN: Remove/Take off immediately all contaminated clothing. Rinse skin with water/shower. P305 + P351 + P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. P301 + P330 + P331 IF SWALLOWED: Rinse mouth. Do NOT induce vomiting.
    [Show full text]
  • Chemical Vapor Deposition of Tungsten Oxide Rein U
    APPLIED ORGANOMETALLIC CHEMISTRY, VOL. 12, 155–160 (1998) Chemical Vapor Deposition of Tungsten Oxide Rein U. Kirss* and Lamartine Meda Department of Chemistry, Northeastern University, Boston, MA 02115, USA Crystalline and amorphous thin films of tung- literature contains several reports of electro-opti- sten(VI) oxide can be prepared by chemical cally inactive WO3 films prepared by sputtering, vapor deposition using a variety of volatile evaporation or spray methods,3 although later work precursors below 500 °C. Deposition parameters has yielded electrochromic WO3 films by these 1 for preparation of WO3 films from tungsten methods. No attempt is made here to review the hexacarbonyl [W(CO)6], tungsten hexafluoride literature pertaining to WO3 films prepared by these (WF6), tungsten ethoxides [W(OEt)x, x =5,6] methods. 3 and tetra(allyl)tungsten [W(h -C3H5)4] are sum- The present review focuses on CVD of amor- marized. The electrochromic behavior of these phous and crystalline tungsten oxide films, in- films is comparable with that observed for WO3 cluding thermal CVD, plasma-enhanced CVD films prepared by evaporation, sputtering and (PECVD) and photo-assisted CVD (PACVD). The electrodeposition. # 1998 John Wiley & Sons, principle advantage of chemical vapor deposition Ltd. of electronic materials over other methods is in step Appl. Organometal. Chem. 12, 155–160 (1998) coverage, the absence of radiation damage, throughput and the possibility for selective 4 Keywords: tungsten trioxide; electrochromism; growth. For example, CVD of WO3 occurs at thin films; chemical vapor deposition (CVD) temperatures significantly below those for evapora- ° 5 Received 5 December 1996; accepted 3 March 1997 tion (1300 C).
    [Show full text]
  • Structural and Thermodynamical Properties of Tungsten Oxides from first-Principles Calculations
    Structural and thermodynamical properties of tungsten oxides from first-principles calculations Master’s thesis in Applied Physics CHRISTOPHER LINDERÄLV Department of Physics Chalmers University of Technology Gothenburg, Sweden 2016 Structural and thermodynamical properties of tungsten oxides from first-principles calculations CHRISTOPHER LINDERÄLV Department of Physics Division of Materials and Surface Theory Chalmers University of Technology Gothenburg, Sweden 2016 Structural and thermodynamical properties of tungsten oxides from first-principles calculations CHRISTOPHER LINDERÄLV © CHRISTOPHER LINDERÄLV, 2016. Supervisor: Paul Erhart, Department of Physics Examiner: Paul Erhart, Department of Physics Department of Physics Division of Materials and Surface Theory Chalmers University of Technology SE-412 96 Gothenburg Telephone +46 31 772 1000 Cover: Crystal structure for ground state WO3. Typeset in LATEX Printed by Chalmers reproservice Gothenburg, Sweden 2016 iii Structural and thermodynamical properties of tungsten oxides from first-principles calculations CHRISTOPHER LINDERÄLV Department of Physics Chalmers University of Technology Abstract Tungsten as a material has obtained attention because of its prominent role in fusion reactor design, where it is employed in the divertor region of the first wall. In case of an accident, the tungsten tiles may be exposed to atmospheric conditions and high temperatures which would oxidize the material. Over the years there has been a lot of studies on tungsten oxides, specially WO3, but not from the perspective of tungsten oxidation. The mechanism of oxidation is unclear and a sound understanding of which oxides are formed is still lacking. In this work, first principles calculations have been employed to study the rela- tive phase stabilities from a mechanical and thermodynamical perspective.
    [Show full text]
  • Synthesis and Characterization of Tungsten Trioxide Powders Prepared from Tungstic Acids Helena I.S
    CORE Metadata, citation and similar papers at core.ac.uk Provided by Repositório Institucional da Universidade de Aveiro Materials Research Bulletin 39 (2004) 683–693 Synthesis and characterization of tungsten trioxide powders prepared from tungstic acids Helena I.S. Nogueira, Ana M.V. Cavaleiro, Joa˜o Rocha, Tito Trindade, Ju´lio D. Pedrosa de Jesus* Department of Chemistry, CICECO, University of Aveiro, Aveiro 3810-193, Portugal Received 16 June 2003; received in revised form 30 October 2003; accepted 25 November 2003 Abstract WO3 powders were prepared by the thermal decomposition of tungstic acids (WO3ÁnH2O, n ¼ 1/3, 1, 2). The 2À tungstic acids were synthesized from WO4 aqueous solutions under a variety of conditions of pH, temperature and W(VI) concentrations. The thermal decomposition of the tungstic acids into WO3 was analysed by TG and DSC methods. Nano-sized WO3 powders with different morphological characteristics were obtained by thermal treatment of the tungstic acids at 500 8C in air atmosphere. The morphologies of WO3 powders were characterised by scanning electron microscopy and infrared absorption spectroscopy. Patterns of infrared spectra were related with distinct powder morphologies. # 2003 Elsevier Ltd. All rights reserved. Keywords: A. Oxides; B. Chemical synthesis; C. Fourier transform infrared spectroscopy; C. Scanning electron microscopy 1. Introduction Tungsten trioxide (WO3) has been the subject of great interest due to its special electrochromic [1,2], gas sensing [3,4] and catalytic properties [5]. In these applications, the morphological characteristics of the materials like grain size or shape are very important and depend strongly on the preparation method. Therefore, WO3 has been prepared, both in the form of powders and thin films, by a plethora of methods which include chemical vapour deposition [6], sol-gel procedures [7], spray pyrolysis [8], and r.f.
    [Show full text]
  • The Vapor Pressures of Molybdenum Oxides And
    THE VAPOR PRESSURES OF MOLYBDENUM OXIDES AND TUNGSTEN OXIDES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By PAUL EDWARD BLACKBURN, B. A. The Ohio State University 1954 Approved by* 1 ASMQMtfMlgMI The writer wishes to express his appreciation for the helpful guidance and criticism of Professor Herrick L. Johnston, under whose supervision this work was oarried out. He is also most appreciative to Dr, Michael Hoch for their many useful discussions and for his sugges­ tions . The author is very grateful to Mr. Janes Jones and Mr, L. £. Cox of the laboratory shop for their fine work on the apparatus used in this study. THE VAPOh PRESSURES OF MOLYBDENUM OXIDES AND TUNGSTEN OXIDES IflTBQPgCTIQM Although earlier investigations on the vapor pressures of molybdenum trioxide and tungsten tri- oxide have been reported in the literature (1,2) there is some doubt about the accuracy of the data. For this reason, and in order to extend the work to the other oxides, a study of the solid-vapor equili­ brium of the molybdenum-oxygen and tungsten-oxygen systems vas undertaken. The study was carried out by measuring the vapor pressures of the oxides using the Knudsen rate of effusion method. THEORY Sato of fiffmlga Hitfaad The Xnudaen (3) rate of effusion method consists of measuring the rate at which gas molecules escape through an orifice in the wall of a cell in which the gas la in equilibrium with a solid sr liquid. The equation for the pressure of a gas determined by the rate of effusion method is (4 ) p - » ^ * 5 “ , a ) where m is the rate of effusion in grams per square centimeter per second, R is the gas constant, T is the absolute temperature and M is the moleoular weight.
    [Show full text]