DOCSLIB.ORG

Jan. 9, 1968 B. MATCHEN 3,362,787 PREPARATION of MOLYBDENUM SILICEDES Filed Feb

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Jan. 9, 1968 B. MATCHEN 3,362,787 PREPARATION of MOLYBDENUM SILICEDES Filed Feb Jan. 9, 1968 B. MATCHEN 3,362,787 PREPARATION OF MOLYBDENUM SILICEDES Filed Feb. 4, 1964 - Bem MarcHENINVENTOR. AT7ORMAY 3,362,787 United States Patent Office Fatented Jan. 9, 968 Sid 3,362,787 tion resistance up to about 1300° C. and it has been re PREPARATION OF MOLY3DENUM, SCDES ported that addition of 10% molybdenum disilicide to Ben Matchen, Niagara Falls, Ontario, Canada, assignor the boride dramatically increases the temperature of effec to Norton Company, Worcester, Mass, a corporation tive oxidation resistance to 1950° C. This property of of Miassachusetts titanium diboride, having good resistance up to about Filed Feb. 4, 1964, Ser. No. 342,357 1400° C., may be similarly improved. 5 Claims. (C. 23-204) Cermets have been produced with molybdenum disili cide as the base material, together with various refractory oxides, to improve thermal shock and oxidation resistance ABSTRACT OF THE DISCLOSURE O and to impart more refractoriness to bodies produced MosSi and MoSi are prepared by heating molybdic therefrom. Suggested applications include kiln furniture, oxide with silicon in the presence of carbon and silicon saggers, sand-blast nozzles, exhaust tube linings, etc. Alu carbide; silica is preferably also present; MoSi may be mina is the most common oxide used because its thermal prepared from MosSi by heating with silicon in the pres expansion coefficient (8.8x10-6/ C.) closely matches ence of carbon; furnace temperatures of 1700 to 1950 that of the disilicide (8.4x10-6/ C.). Other oxides or C. are employed with times of 3 to 8 hours, preferably in mixtures of oxides may be used. The silicide may also be a continuous kiln. Hot pressing of product yields pieces used as a binder for carbide and, as mentioned above, having 94.4% theoretical density, good oxidation resist boride bodies, and has been found to bind with metallic ance. Mixtures of molybdenum silicide with alumina or materials such as nickel, cobalt, iron and stainless steel. 20 Addition of these metals increases thermal shock resist magnesia were hot pressed to give strong products. alCg. Molybdenum disilicide is ideal for use in chemical proc This invention relates to the preparation of molyb essing equipment because of its resistance to most inor denum silicides from molybdenum oxide employing sili ganic acids including aqua regia, aqueous alkali solutions, con carbide as a source for at least some of the silica. 25 and liquid metals such as sodium, zinc, bismuth, and In particular, the objects of this invention are econom gallium. ically to produce compounds of molybdenum and silicon It has recently been suggested to use the disilicide as having Si to Mo ratios of from 1.6 to 2 or higher and one portion of a thermocouple with boron carbide or from 0.55 to 5.65, corresponding to the theoretical com chromium silicide as the other portion. The potential pounds MoSia and MoSi, respectively. 30 application of the thermocouples is associated with pro The drawing shows a flow sheet illustrating the proc duction of molten ferrous and non-ferrous metals. esses described and claimed for producing molybdenum Metallic molybdenum has relatively poor oxidation re silicides. sistance and the disilicide can be used to form a protec Very few of the less common silicides have reached tive covering thereon. Such coatings having a thickness of commercial prominence. However, one of these which 35 less than 0.125 mm. and provide protection for over 1000 appears headed in this direction is molybdenum disilicide hours in air at 1700° C. Thermal shock resistance of the which has been found to be very stable in the ordinary coating is excellent and a film of silicon dioxide on the atmosphere at high temperatures in the range of 2000 silicide heals the cracks which may appear. It has been C. and to exhibit high heat conductivity, resistance to proposed that the molybdenum disilicide coating on me 40 tallic molybdenum consists of a thin intermediate molyb oxidation, and heat shock resistance. For example, the denum-rich layer and a dense silicide layer. Molybdenum heat conductivity of molybdenum disilicide is about 0.075 disilicide, flame-sprayed on molybdenum provides oxida cal./sec./cm.2/ C. (20° to 200° C.), and it has a re tion protection for 60 seconds in a Mach 2 airstream at sistivity of approximately 20 microhms-cms. It has been 3800° F. The disilicide may also be used as a protective found that molybdenum disilicide is useful in electrical coating for graphite linings in uncooled rocket motors. resistance elements and has been used as an impregnant The melting point of molybdenum disilicide has vari in a silicon carbide element to render such resistance bars ously been reported as 1850° C. and as 2030-50° C. serviceable at much higher temperatures than has been It is crystallized in a tetragonal system having lattice possible heretofore. Such a bar is disclosed in the co constants of a=3,200 A., c=7.86 A., c/a=2.457. The pending application of John Fredriksson, Ser. No. 43,877 50 density from X-ray data is 6.24 grams per cubic centi for Electrical Bars, filed July 19, 1960, now Patent No. meter and its tensile strength, like that of graphite, in 3,171,871. creases with increasing temperature. The resistance to oxidation at temperatures up to The silicide of molybdenum having the formula MosSi3 1650-1750° C. makes molybdenum disilicide promising has been considered one of the lesser important of the for electrical heating elements as noted above and as silicides. However, it has been found that this silicide of structural shapes in specific locations of combustion molybdenum may be combined as a major constituent chambers, gas turbines, kilns, high temperature dies, in with various oxides or mixtures of oxides from the sec duction-brazing fixtures, etc. The mechanism of the oxi ond and third groups of the periodic table including alu dation resistance is not precisely known, except that it is mina, calcium aluminate, magnesium aluminate and relatively poor below 1000-1200° C., then becomes 60 magnesia. These compositions exhibit desirable electrical speculated as due to formation of a silica skin stable up resistivity and strength properties for use in high tempera to its melting point of about 1700 C. Another theory ture (1500 to 1700° C.) heating elements. MoSi is also claims that protection is provided by a very adherent useful as a major constituent of elements in electrical glassy layer 0.003 to 0.1 mm. thick consisting of a com appliances. Because of the high quantity of contained plex molybdenum-silicon oxide. It is recommended (with 65 molybdenum (85.1% compared with 63.1% for molyb in this theory) that molybdenum disilicide speciments be denum disilicide) this silicide finds application as an preheated above 1400° C. to insure formation of the additive in metallurgical processes. It is also used as an protective glass layer and thus protect the material against oxidation-resistant protective coating for molybdenum oxidation at lower temperatures. and may be foamed to provide lightweight, easily-shaped, Molybdenum disilicide greatly improves the oxidation 70 oxidation resistant refractory linings for certain types of resistance of borides. Zirconium diboride has good oxida furnaces and kilns. Additionally, it has been found that this silicide of molybdenum is suitable and may be effec 3,362,787 3. 4. tively utilized as a raw material in one process for the pass through (T) a certain screen size and be retained production of molybdenum disilicide. (on) on a screen of finer mesh (U.S. Sieve Series). MosSi is crystallized in a hexagonal system having TABLE 1. lattice constants of a=7.271 A., c=4.992 A. and c/a=0.687. It is not a true binary compound, but a ter Mo03 Mix SiC Coke nary compound which is stabilized by around 1% by (MoO3-SiO2-C) T54 T24 weight of or by carbon, nitrogen, oxygen or boron. The Percent Percent Percent amounts of these materials can vary considerably without T24 on 44------------------------ i6.5 ---------- 48,3 T44 on 72------------------------ 2.0 37. 26.2 affecting the basic structure of the silicide, although such T72 on iOX--- 9.4 23.5 7.6 variations will cause corresponding variations in the size O TOX on 18X- 7. 2.8 15.9 of the lattice parameters. T18X on 25S 9.3 5.2 0.3 The silicides of molybdenum, and particularly the di T25S----------- 35.7 13.4 1.7 silicide, have heretofore been prepared by melting ele 00, () 100.0 00, 0 mental molybdenum with elemental silica. However, at the temperature required for the fusion of these elements, 5 As noted above, molybdenum oxide mix contains small a reaction may occur between the material and the con amounts of silicon oxide and carbon. It is commercially tainer such that the products are contaminated and the available and has an average product analysis of approxi desirable properties thereof are impaired. Moreover, the mately 77.4% molybdenum oxide (MoC), 10% silicon elemental products of substantial purity which are re oxide (SiO2) and 12% coke. In the process of this in quired, are unduly high in price. 20 vention the reaction mixture contains from about 65 to 75 In attempting to overcome these difficulties, the prior parts of MoC), from about 15 to 25 parts silicon carbide art has suggested reacting molybdenum oxide with silicon and from about 7 to 20 parts carbon (in the form of in a furnace heated by an oxy-hydrogen blow pipe. It coke), each by weight of the total reaction mixture. When has also been proposed to use fluxes such as lime and employing the above specified MoC)3-SiO2-coke mix magnesia or cryolite, the resulting product being leached (available in briquetted form), I have found that the foll with nitric acid and dilute hydrofluoric acid to obtain lowing proportions within the above range are preferred: the crystals of molybdenum disiiicide.
Load more

Recommended publications
  • Processing, Microstructure, and Mechanical Properties of Zirconium Diboride-Molybdenum Disilicide Ceramics and Dual Composite Architectures
    Scholars' Mine Doctoral Dissertations Student Theses and Dissertations Spring 2017 Processing, microstructure, and mechanical properties of zirconium diboride-molybdenum disilicide ceramics and dual composite architectures Ryan Joseph Grohsmeyer Follow this and additional works at: https://scholarsmine.mst.edu/doctoral_dissertations Part of the Energy Systems Commons, and the Materials Science and Engineering Commons Department: Materials Science and Engineering Recommended Citation Grohsmeyer, Ryan Joseph, "Processing, microstructure, and mechanical properties of zirconium diboride- molybdenum disilicide ceramics and dual composite architectures" (2017). Doctoral Dissertations. 2561. https://scholarsmine.mst.edu/doctoral_dissertations/2561 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. PROCESSING, MICROSTRUCTURE, AND MECHANICAL PROPERTIES OF ZIRCONIUM DIBORIDE-MOLYBDENUM DISILICIDE CERAMICS AND DUAL COMPOSITE ARCHITECTURES by RYAN JOSEPH GROHSMEYER A DISSERTATION Presented to the Faculty of the Graduate School of the MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY in MATERIALS SCIENCE AND ENGINEERING 2017 Submitted to: Gregory Hilmas, Advisor William Fahrenholtz Jeffrey Smith David Van Aken Lokeswarappa Dharani iii PUBLICATION DISSERTATION OPTION This dissertation consists of the following five articles that will be submitted for publication as follows and have been formatted in the style of the journal Ceramics International. The manuscripts entitled, “ZrB2-MoSi2 Ceramics with Varying MoSi2 Content: Part 1. Processing and Microstructure with Varying ZrB2 Particle Size:” (Paper I, Pages 50–80), and the manuscript entitled “ZrB2-MoSi2 Ceramics with Varying MoSi2 Content: Part 2.
    [Show full text]
  • Research Memorandum
    RM E52B06 NACA RESEARCH MEMORANDUM SOME FACTORS AFFECTING FABRICATION AND HIGH-TEMPERATURE STRENGTH OF MOLYBDENUM DISILICIDE By W. A. Maxwell Lewis Flight Propulsion Labora tory Cleveland, Ohio NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WASHINGTON April 17 , 1952 1U NACA RM E58B06 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS RESEARCH MEMORANDUM SOME FACTORS AFFECTING FABRICATION AND HIGH-TEMPERATURE STRENGTH OF MOLYBDENUM DISILICIDE By W. A. Maxwell SUMMARY In an investigation of the properties of molybdenum disilicide, a fine-grain material having a moderately high oxygen content has been produced by cold-pressing and sintering, and a large-grain material having a lower oxygen content and a density of 99 percent of the theo­ retical density has been produced by hot-pressing. In a series of experiments with the fine-grain material in which the only variable was the amount of carbon added, marked increases in modulus-of-rupture strength were found at carbon contents between 0.15 and 0.3 percent. Improvements in the long-time deformation properties, as shown by the flexure-creep test, and decreased high-temperature plasticity accompanied the carbon additions. The Knoop hardness was 1160. The beneficial effects of carbon additions on strength are attri­ buted to partial deoxidation of the material, particularly the reduction of molybdenum oxides, and the formation of silicon carbide and other carbides. Exceptionally high short-time strengths, in comparison with other high-temperature materials, were obtained with sintered molybdenum disilicide containing from 1.0 to 1.4 percent oxygen. The effects of such oxygen contents on sintering and binding may be beneficial. The large-grain, hot-pressed molybdenum disilicide having a low oxygen content possessed superior high-temperature deformation resist­ ance, slightly inferior short-time strength, and decreased high­ temperature plasticity as compared with the fine-grain molybdenum disili­ cide to which carbon was added.
    [Show full text]
  • The Disilicides of Tungsten, Molybdenum, Tantalum, Titanium, Cobalt, and Nickel, and Platinum Monosilicide: a Survey of Their Thermodynamic Properties
    The Disilicides of Tungsten, Molybdenum, Tantalum, Titanium, Cobalt, and Nickel, and Platinum Monosilicide: A Survey of Their Thermodynamic Properties Cite as: Journal of Physical and Chemical Reference Data 22, 1459 (1993); https:// doi.org/10.1063/1.555922 Submitted: 21 December 1992 . Published Online: 15 October 2009 M. S. Chandrasekharaiah, J. L. Margrave, and P. A. G. O’Hare ARTICLES YOU MAY BE INTERESTED IN Thermodynamic considerations in refractory metal-silicon-oxygen systems Journal of Applied Physics 56, 147 (1984); https://doi.org/10.1063/1.333738 Thermal and Electrical Conductivity of Graphite and Carbon at Low Temperatures Journal of Applied Physics 15, 452 (1944); https://doi.org/10.1063/1.1707454 Formation of thin films of NiSi: Metastable structure, diffusion mechanisms in intermetallic compounds Journal of Applied Physics 55, 4208 (1984); https://doi.org/10.1063/1.333021 Journal of Physical and Chemical Reference Data 22, 1459 (1993); https://doi.org/10.1063/1.555922 22, 1459 © 1993 American Institute of Physics for the National Institute of Standards and Technology. The Disilicides of Tungsten, Molybdenum, Tantalum, Titanium, Cobalt, and Nickel, and Platinum Monosilicide: A Survey of Their Thermodynamic Properties M. s. Chandrasekharaiah and J. L. Margrave HARC, Materials Science Research Center, 4802 Research Forest Drive, The Woodlands, TX 77381 and P. A. G. O'Hare Chemical Kinetics and Thennodynamics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-0001 Received December 21, 1992; revised manuscript received February 19, 1993 A critical evaluation is presented of the thermodynamic properties of six disiIi­ cides and one monosilicide that are important in the manutacture ot very large scale integrated circuits.
    [Show full text]
  • Research Memorandum
    RESEARCH MEMORANDUM PROPERTIES OF CERTAIN INTER&UXTALLICS AS RELATtiD . TO ELEVATED-TEMPERATURE APPLICATIONS I - MOLYBDENUM DISILKXDE Ld By W. A. MaxweJ.l. Lewis l&&t Propulsion Laboratory Cleveland, Ohio .: _i. I_ -.ClASSIFICATfON CANC NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WASHINGTON October 6,1949 NACA RM E9GOl NA!KCONALADVISORYCOMKETEEFORAXRONAUTICS I -MOL~DISILIC~ By W. A. Maxwell A method for the preparation and purification of the inter- metallic, molybdenum disilicide, was developed and the following properties were determined for the sintered material: Tanperature Room 2000°F 2400°F Modulus of rupture, lb/sq in. 50,700 35,700 20,700 Total elongation calculated f4 fletietests, percent . 0.09 0.72 3.2 Plastic elongation calculated from flexure tests, percent . none 0.39 1.4 DeIlBity: Theoretioal (X-ray data), grams/cm1 . 6.24 Potiered,gramsbl........, . 6.2 Sintered,msj%l... ..5.66 Rockwell hardness (superpioial) . , . C-57 Crystal structure tetragonal body-centered Oxidation resistax.d,'s~a;le'&Z ;n'aL 200ooF' 2400°F (gnmgaFnlBqcm)fhr. -0.000ooo4 0.000005 Chemical mpertles of molybdenum disilicide were found to be: highly inert, unattadsed by boilin@; hydroohloric acid, sulfuric acid, or aqueous sodium hydroxide; elightly attacked by nitrio acid; dis- solved by molten sodium h-de. The sintered material is silvery white in co&, possesses high eleutria oonductivity, and is resistant to thermal shock. Molybdenum disilicide melts at 3500° &IL@ F with decomposition. 2 NACA FM lBGO1 Plastic deformation of the intermetallic at temperatures well below the melting point was observed although only brittle behavior wasapparentatroomtemperature. From the Investigation c&Tpropertiee of molybdenum dieilioide, it appear0 that: 1.
    [Show full text]
  • Mosi2 and Other Silicides As High Temperature Structural Materials
    MoSi2 AND OTHER SILICIDES AS HIGH TEMPERATURE STRUCTURAL MATERIALS DILIP M. SHAH Pratt & Whitney 400 Main St. E. Hartford, CT. 06108 Abstract There has been a revival of interest in MoSi;? and other refractory silicides, hitherto used for heating elements and coatings, as high temperature structural materials. With their high melting point and excellent high temperature oxidation resistance, silicides as a class of intermetallics, have potential for developing temperature capability beyond nickel base superalloys. Though metal like in their physical properties, silicides are in general brittle at room temperature. This drawback is being addressed through a variety of in-situ and artificial composite approaches. This paper attempts to provide a perspective on these approaches with a review of current activities. To provide a background, the development strategies for high temperature structural materials are discussed, followed by an overview on formation of silicides. The relevant mechanical and physical properties and environmental resistance of silicides are compared using superalloys as the benchmark, to help assess the risks versus benefits. Finally, the paper concludes with a brief summary of primarily fiber reinforced MoSi2 composites and ductile phase reinforced in-situ composites based on other silicides. The unavailability of suitable fibers and interface coating for conventional composites and containerless solidification for in-situ composites are identified as the principal problems. Superalloys 1992 Edited by S.D. Antolovich, R.W. Stusrud, R.A. MacKay, D.L. Anton, T. Khan, R.D. Kissinger, D.L. Klarstmm The Minerals, Metals & Materials Society, 1992 409 Introduction Since as early as 1956, molybdenum disilicide (MoSi2) based material has been commercially available as Super Kanthal [l], along with nickel-chromium based heating elements.
    [Show full text]
  • Research Memorandum
    RM E52A04 NACA RESEARCH MEMORANDU M OXIDATION-RESISTANCE MECHANISM AND OTHER PROPERTIES OF MOLYBDENUM DISILICIDE By W. A. Maxwell Lewis Flight Propulsion Laboratory Cleveland, Ohio NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WASHINGTON March 14, 1952 lW NACA RM E52A04 NATIONAL ADVISORY COMMITTEE FOR AERONAUTIeS RESEARCH MEMORANDUM OXIDATION-RESISTANCE MECHANISM AND OTHER PROPERTIES OF MOLYBDENUM DISILICIDE By W. A. Maxwell SUMMARY An experimental investigation was conducted to determine the oxidation-resistance mechanism, the melting characteristics, the electric resistiVity, and the modulus of elasticity of molybdenum disilicide. Molybdenum disilicide MoSi2 bodies are protected from oxidation at high temperatures by the formation of a protective siliceous coating in which ~cristobalite has been identified as the sole or principa~ constituent. In powdered form, MoSi2 is not inherently resistant to oxidation and burns in air at comparatively low temperatures. Molybdenum disilicide decomposed at the melting point with the loss of appreciable silicon. This phenomenon has so far prevented casting of satisfactory ingots. Decomposition below the melting point was indicated. The electric resistivity of MoSi2 at room temperature varies from 23 to 27 microhm-centimeters depending on the method of fabrication. The conductivity was found to be metallic in nature and to decrease with increasing temperatures to 20000 F. The room-temperature modulus of elasticity as determined by a dynamic method was 59 Xl06 pounds per square inch. Poor damping character­ istics are indicated for the material at room temperature. INTRODUCTION The outstanding oxidation resistance of molybdenum disilicide MoSi2 at high temperatures, as previously reported (references 1 and 2) and as summarized in table I, places it among the most resistant of materials in the temperature range from 20000 to 28500 F.
    [Show full text]
  • Oxidation Behavior of Molybdenum Silicides and Their Composites K
    ET/CP- 776 / 7 Oxidation Behavior of Molybdenum Silicides and Their Composites K. Natesan Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439, USA and S. C. Deevi Research and Development Center, Philip Morris USA, Richmond, VA 23234 February 2000 The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory ("Argonne") under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others act- ing on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, dis- tribute copies to the public, and perform pub- F.\ s* licly and display publicly, by or on behalf of ^HtP Cr the Government. <f{^ C A % V\ - Invited paper presented at the International Symposium on Intermetallics for the Third Millennium, ASM Materials Solutions, Cincinnati, November 1-4, 1999. *Work supported by the U.S. Department of Energy, Office of Fossil Energy, Advanced Research and Special Technologies Materials Program and Office of Energy Research, Basic Energy Sciences, Division of Materials, under Contract W-31-109-Eng-38. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.
    [Show full text]
  • Oxidation Behaviour of Molybdenum Disilicide Coatings at 1500 °C
    published at the ITSC 2004, Osaka, J, May 10th - 12th Oxidation behaviour of molybdenum disilicide coatings at 1500 °C B. Wielage, G. Reisel, A. Wank, G. Fritsche, Chemnitz / D Molybdenum disilicide (MoSi2) is a suitable material for high temperature applications especially because of its excellent high temperature oxidation resistance. For several high temperature applications MoSi2 shows high potential to be used as a protective coating. The oxidation behaviour of HVOF sprayed MoSi2 coatings is studied at 1500 °C. The oxidation tests are carried out in a simultaneous thermogravimetric device and the mass change is measured in dependence on the oxidation time. The microstructure of the coatings before and after oxidation is examined by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXS). The mass of the coating increases according to a parabolic function. During the oxidation test the microstructure changes significantly from a typical thermal spray coating microstructure with lamellae, pores and a phase mixture of MoSi2 and Mo5Si3 to a two phase system with sharply separated grain boundaries. On the surface of the coating a silicon dioxide layer with a thickness of less than 10 µm is formed. 1 Introduction 1.0 MoSi2 0.9 Monolithic molybdenum disilicide (MoSi2) shows an 0.8 excellent resistance against high temperature 0.7 oxidation. Other good properties of this material are 0.6 -3 the relatively low density of 6.25 g·cm , the high 0.5 melting point of 2030 °C and the high toughness 0.4 0.3 above the brittle-ductile transition at approximately Intensity fraction SiO2 800 - 1100 °C.
    [Show full text]
  • Optimization of Molybdenum Electrodes for Glass Melting
    Optimization of Molybdenum Electrodes for Glass Melting by WenDi Liu A Dissertation Submitted to the Faculty of WORCESTER POLYTECHNIC INSTITUTE In partial fulfillment of the requirements of the Degree of Doctor of Philosophy in Materials Science and Engineering April 2015 APPROVED: _______________________________ Dr. Diran Apelian, Advisor Alcoa-Howmet Professor of Engineering _______________________________ Dr. Richard D. Sisson Jr. Director of Manufacturing and Materials Engineering George F. Fuller Professor ABSTRACT The U.S. glass industry is a $28 billion enterprise and millions of tons of glasses are melted each day by different heating techniques, such as conventional oil fired furnaces or via electrical heating. The share of electrical heating is bound to rise steadily because it is cleaner and more energy efficient. Due to this situation molybdenum will play a significant role in electrical glass melting, since it is the most frequently used electrode material to deliver the electricity into the glass melts. Although it has a high melting point, high electrical and thermal conductivity and a low coefficient of expansion, molybdenum electrodes fail because of lack of sustainability during the glass melting process. Melt reaction with electrodes is the fundamental barrier to higher melting temperatures. Glass manufacturers have suggested that the need for better performance of molybdenum electrodes will see a rapid advancement in the use of electric heating system in the U.S. This work first focused on post-mortem analysis on used molybdenum electrodes with and without the current load in order to establish failure mechanisms for molybdenum during glass melting. It was determined that service life of molybdenum electrodes are limited by poor oxidation and corrosion resistance of molybdenum with redox reactions.
    [Show full text]
  • Fermi Surface and Electrical Characteristics of Molybdenum Disilicide S
    Physics of the Solid State, Vol. 45, No. 2, 2003, pp. 201–206. Translated from Fizika Tverdogo Tela, Vol. 45, No. 2, 2003, pp. 193–197. Original Russian Text Copyright © 2003 by KurganskiÏ, Pereslavtseva, Levitskaya. SEMICONDUCTORS AND DIELECTRICS Fermi Surface and Electrical Characteristics of Molybdenum Disilicide S. I. KurganskiÏ, N. S. Pereslavtseva, and E. V. Levitskaya Voronezh State University, Universitetskaya pl. 1, Voronezh, 394006 Russia e-mail: [email protected] Received April 9, 2002 Abstract—Semirelativistic self-consistent calculations of the electronic structure of MoSi2 are performed within the framework of the linearized augmented-plane-wave (APW) method in the local density functional approximation. The results of investigations of the band structure, the Fermi surface, and electrical character- istics (effective cyclotron masses, the conductivity anisotropy constant, the mean free path, and the coefficient γ of the heat capacity component linear in temperature) are reported. The Fermi surface consists of two sheets, namely, an electron sheet and a hole sheet. The extreme sectional areas of the Fermi surface agree well with the experimental data on the de Haas–van Alphen effect. The results of first-principles calculations need no addi- tional correction. © 2003 MAIK “Nauka/Interperiodica”. 1. INTRODUCTION tional approximation, specifically for the band structure [20, 21, 24], densities of states [17, 20–24], and the Molybdenum disilicide possesses high microhard- Fermi surface [22, 24]. However, none of the first-prin- ness [1], resistance to oxidation during heating both in ciples calculations of the Fermi surface [22, 24] agrees air and in an oxygen flow [1], high thermal stability [2], in full measure with the experiment [19].
    [Show full text]
  • Chapter 1 Introduction
    In-situ single step synthesis of MoSi2 nano powder A Thesis Submitted in partial fulfillment of the requirements for the award of degree of MASTER OF SCIENCE by Taranpreet Kaur (Registration No. 301504036) Under the Supervision of Dr. O.P. Pandey (Senior Professor) School of Physics & Materials Science Thapar University, Patiala-147004 July, 2017 ABSTRACT Molybdenum disilicide (MoSi2) has emerged as a promising material for high temperature applications. This transition metal silicide exhibits superior temperature stability, excellent oxidation resistance, low contact resistivity and is highly resistant to electro-migration. The low temperature synthesis of molybdenum disilicide has been investigated in a specially designed autoclave. The powder blend of MoO3-Si-Mg is heated at different temperatures for various interval of time. The impact of initial composition of the formation of MoSi2 is also studied. The prepared samples are characterized through various techniques i.e. X- ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscope (HRTEM). The best results are obtained at 900 ºC for 10 hrs. dwell time. In this case, molybdenum disilicide (MoSi2) phase is obtained along with molybdenum silicide (Mo5Si3). This study provides the complete understanding associated with the formation of MoSi2. iii LIST OF FIGURES CHAPTER 1: INTRODUCTION PAGE Fig.1.1 Three different forms of molybdenum silicide. 3 Fig.1.2 Binary phase diagram of Mo-Si system. 3 Fig.1.3 Crystal structure of molybdenum disilicide (MoSi2). 5 CHAPTER 3: EXPERIMENTAL DETAILS Fig.3.1 Flow chart of MoSi2 synthesis. 22 Fig.3.2 Schematic diagram of synthesis route for MoSi2.
    [Show full text]
  • Research Memorandum
    https://ntrs.nasa.gov/search.jsp?R=19930087009 2020-06-17T13:45:51+00:00Z RM E52B06 NACA RESEARCH MEMORANDUM SOME FACTORS AFFECTING FABRICATION AND HIGH-TEMPERATURE STRENGTH OF MOLYBDENUM DISILICIDE By W. A. Maxwell Lewis Flight Propulsion Labora tory Cleveland, Ohio NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WASHINGTON April 17 , 1952 1U NACA RM E58B06 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS RESEARCH MEMORANDUM SOME FACTORS AFFECTING FABRICATION AND HIGH-TEMPERATURE STRENGTH OF MOLYBDENUM DISILICIDE By W. A. Maxwell SUMMARY In an investigation of the properties of molybdenum disilicide, a fine-grain material having a moderately high oxygen content has been produced by cold-pressing and sintering, and a large-grain material having a lower oxygen content and a density of 99 percent of the theo­ retical density has been produced by hot-pressing. In a series of experiments with the fine-grain material in which the only variable was the amount of carbon added, marked increases in modulus-of-rupture strength were found at carbon contents between 0.15 and 0.3 percent. Improvements in the long-time deformation properties, as shown by the flexure-creep test, and decreased high-temperature plasticity accompanied the carbon additions. The Knoop hardness was 1160. The beneficial effects of carbon additions on strength are attri­ buted to partial deoxidation of the material, particularly the reduction of molybdenum oxides, and the formation of silicon carbide and other carbides. Exceptionally high short-time strengths, in comparison with other high-temperature materials, were obtained with sintered molybdenum disilicide containing from 1.0 to 1.4 percent oxygen. The effects of such oxygen contents on sintering and binding may be beneficial.
    [Show full text]