C ND © 2002 by CRC Press LLC N IO SE Materials, Parts, and Finishes O OF • • ENC A Y OPED L C I T I ED C ND N IO SE Materials, Parts, and Finishes O OF • • ENC A Y OPED L C I T I ED Mel Schwar tz CRC PR E S S Boca Raton London New York Washington, D.C TX66613_frame_FM* Page Friday, March 22, 2002 8:29 AM Library of Congress Cataloging-in-Publication Data Schwartz, Mel M Encyclopedia of materials, parts, and finishes / by Mel Schwartz.—2nd ed p cm ISBN 1-56676-661-3 Smart materials—Encyclopedia I Title TA418.9.S62 S39 2002 620.1'18—dc21 2002019220 This book contains information obtained from authentic and highly regarded sources Reprinted material is quoted with permission, and sources are indicated A wide variety of references are listed Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating new works, or for resale Specific permission must be obtained in writing from CRC Press LLC for such copying Direct all inquiries to CRC Press LLC, 2000 N.W Corporate Blvd., Boca Raton, Florida 33431 Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe Visit the CRC Press Web site at www.crcpress.com © 2002 by CRC Press LLC No claim to original U.S Government works International Standard Book Number 1-56676-661-3 Library of Congress Card Number 2002019220 Printed in the United States of America Printed on acid-free paper TX66613_frame_FM* Page Wednesday, March 13, 2002 11:08 AM Preface This encyclopedia represents an update of existing materials and presents new materials that have been invented or changed, either by new processes or by an innovative technique The encyclopedia covers basic materials such as rubber and wood This two-volumes-in-one includes two decades of the process of materials; the process/fabrication selection has been hindered by new and unusual demands from all quarters No change in this trend is expected in the foreseeable future This trend has been visible in several industries — aerospace, automotive, electronic, space, computers, chemical, and oil — and in many other commercial endeavors Metals (wrought, cast, forged, powder), plastics (thermoplastics/thermosets), composites, structural ceramics, and coatings are continually finding new applications in the above industries The trend toward combining high strength and light weight is evident in fiber/particle/whiskerreinforced composites This encyclopedia/handbook covers not only these matrix composites (metallic, plastic, ceramic, and intermetallic), but also other materials of the future — nano and functionally graded structures, fullarenes, plastics (PEEK, PES, etc.), smart piezoelectric materials, shape memory alloys, and ceramics Higher processing temperatures as well as more resistant and effective high-temperature materials have attracted the attention of engineers, scientists, and materials workers in many industries Engines now operate more efficiently at temperatures higher than those attainable with the materials of the past For example, interest in 2000°F (1093°C) turbine engines has brought more hightemperature, high-strength ceramics into development and use The use of a vacuum environment has improved many materials not only in their initial production and processing, i.e., steels, but also eventually in their fabrication For example, a vacuum environment in brazing and welding and in hot isostatic pressing removes voids and consolidates material structures New environmental regulations by government agencies (the Environmental Protection Agency, the Occupational Safety and Health Administration, etc.) have sent the technologist back to the drawing board and laboratory to design and develop new and better materials and processes that are not potential health hazards, and many of these new material substitutes are included in this revised edition Finally, political diplomacy, rather than economics and regulation, could well be the most important factor in materials supply in the near future The major supply of many critical raw materials and supplies for the processes needed to sustain the future economies of many nations lies in the hands of a few small nations Consequently, there is no guarantee of a steady supply of these strategic materials, and we must continually innovate and explore new sources of materials development (ocean floor and space) © 2002 by CRC Press LLC TX66613_frame_FM* Page Friday, March 22, 2002 8:30 AM Editor Mel M Schwartz is a consultant to the vast field of materials and processes He is editor of the Journal of Advanced Materials and editor-in-chief of the Smart Materials Encyclopedia Schwartz received his bachelor of arts degree from Temple University, his master’s degree from Drexel University, and is currently working in the doctorate program at the University of Sarasota His professional experience includes a career in metallurgy, manufacturing research, and development and metals processing at the U.S Bureau of Mines, U.S Chemical Corp., Martin-Marietta Corp., Rohr Industries, and Sikorsky Aircraft, from which he retired in 1999 Awards and honors include Inventor of the Year for Martin-Marietta, the Jud Hall Award (Society of Manufacturing Engineers), the first G Lubin Award (Society for the Advancement of Materials and Processing Engineers), and Engineer of the Year in Connecticut (1973) He is an elected Fellow for the Society for the Advancement of Materials and Processing Engineers and American Society for Materials International, and sits on several peer-review committees; as well, he is a member of numerous national and international societies Schwartz has written 14 books and over 100 technical papers and articles and has given company in-house courses and numerous seminars around the world © 2002 by CRC Press LLC TX66613_frame_FM* Page Wednesday, March 13, 2002 11:08 AM Dedication To Carolyn, Anne-Marie, and Perry whose enormous courage, will, and determined spirit are overwhelming Mel Schwartz © 2002 by CRC Press LLC TX66613_frame_A(1) Page Wednesday, March 13, 2002 11:12 AM A ABRASIVE An abrasive is defined as a material of extreme hardness that is used to shape other materials by a grinding or abrading action Abrasive materials may be used as loose grains, as grinding wheels, or as coatings on cloth or paper They may be formed into ceramic cutting tools that are used for machining metal in the same way that ordinary machine tools are used Because of their superior hardness and refractory properties, they have advantages in speed of operation, depth of cut, and smoothness of finish Abrasive products are used for cleaning and machining all types of metal, for grinding and polishing glass, for grinding logs to paper pulp, for cutting metals, glass, and cement, and for manufacturing many miscellaneous products such as brake linings and nonslip floor tile ABRASIVE MATERIALS These may be classified in two groups, the natural and the synthetic (manufactured) The latter are by far the more extensively used, but in some specific applications natural materials still dominate The important natural abrasives are diamond (the hardest known material), corundum (a relatively pure, natural aluminum oxide, Al2O3), and emery (a less-pure Al2O3 with considerable amounts of iron) Other natural abrasives are garnet, an aluminosilicate mineral; feldspar, used in household cleansers; calcined clay; lime; chalk; and silica, SiO2, in its many forms — sandstone, sand (for grinding plate glass), flint, and diatomite The synthetic abrasive materials are silicon carbide SiC, aluminum oxide Al2O3, titanium carbide TiC, and boron carbide B4C The © 2002 by CRC Press LLC synthesis of diamond puts this material in the category of manufactured abrasives There are other carbides, as well as nitrides and cermets, which can be classified as abrasives but their use is special and limited Various grades of each type of synthetic abrasive are distinguishable by properties such as color, toughness, and friability These differences are caused by variation in purity of materials and methods of processing The sized abrasive may be used as loose grains, as coatings on paper or cloth to make sandpaper and emery cloth, or as grains for bonding into wheels ABRASIVE WHEELS A variety of bonds is used in making abrasive wheels: vitrified or ceramic, essentially a glass or glass-plus crystals; sodium silicate; rubber; resinoid; shellac; and oxychloride Each type of bond has its advantages The more rigid ceramic bond is better for precision-grinding operations, and the tougher, resilient bonds, such as resinoid or rubber, are better for snagging and cutting operations Ceramic-bonded wheels are made by mixing the graded abrasive and binder, pressing to general size and shape, firing, and truing or finishing by grinding to exact dimensions Grinding wheels are specified by abrasive type, grain size (grit), grade or hardness, and bond type The term hardness as applied to a wheel refers to its behavior in use and not to the hardness of the abrasive material itself Literally thousands of types of wheels are made with different combinations of characteristics, not to mention the multitude of sizes and shapes available; therefore, selecting the best grinding wheel for a given job is not simple A TX66613_frame_A(1) Page Wednesday, March 13, 2002 11:12 AM A ABS PLASTICS ABS plastics are a family of opaque thermoplastic resins formed by copolymerizing acrylonitrile, butadiene, and styrene (ABS) monomers ABS plastics are primarily notable for especially high impact strengths coupled with high rigidity or modulus Consisting of particles of a rubberlike toughener suspended in a continuous phase of styreneacrylonitrile (SAN) copolymer, ABS resins are hard, rigid, and tough, even at low temperatures Various grades of these amorphous, medium-priced thermoplastics are available offering different levels of impact strength, heat resistance, flame retardance, and platability Most natural ABS resins are translucent to opaque, but they are also produced in transparent grades, and they can be pigmented to almost any color Grades are available for injection molding, extrusion, blow molding, foam molding, and thermoforming Molding and extrusion grades provide surface finishes ranging from satin to high gloss Some ABS grades are designed specifically for electroplating Their molecular structure is such that the plating process is rapid, easily controlled, and economical Compounding of some ABS grades with other resins produces special properties For example, ABS is alloyed with polycarbonate to provide a better balance of heat resistance and impact properties at an intermediate cost Deflection temperature is improved by the polycarbonate, molding ease by the ABS Other ABS resins are used to modify rigid polyvinyl chloride (PVC) for use in pipe, sheeting, and molded parts Reinforced grades containing glass fibers, to 40%, are also available Related to ABS is SAN, a copolymer of styrene and acrylonitrile (no butadiene) that is hard, rigid, transparent, and characterized by excellent chemical resistance, dimensional stability, and ease of processing SAN resins are usually processed by injection molding, but extrusion, injection-blow molding, and compression molding are also used They can also be thermoformed, provided that no post-mold trimming is necessary The triangle in Figure A.1 illustrates the properties and characteristics that each constituent acrylonitrile, butadiene, and styrene © 2002 by CRC Press LLC Acrylonitrile Chemical resistance Heat stability Tensile strength Aging resistance ABS Toughness Impact strength Low temperature properties Butadiene Gloss Processibility Rigidity Styrene FIGURE A.1 Properties and characteristics of acrylonitrile, butadiene, and styrene contributes to the final product Polymerization of these materials produces the ABS terpolymer, a two-phase system consisting of a continuous matrix of styrene-acrylonitrile copolymer and a dispersed phase of butadiene rubber particles Properties are varied principally by adjusting the proportions in which the materials are combined and by altering the molecular weight of the SAN PROPERTIES The unique combinations of excellent impact strength with high mechanical strength and rigidity plus good long-term, load-carrying ability or creep resistance are characteristic of the ABS plastics family In addition, all types of ABS plastics exhibit outstanding dimensional stability, good chemical and heat resistance, surface hardness, and light weight (low specific gravity), Table A.1 These materials yield plastically at high stresses, so ultimate elongation is seldom significant in design; a part usually can be bent beyond its elastic limit without breaking, although it does stress-whiten Although not generally considered flexible, ABS parts have enough spring to accommodate snap-fit assembly requirements The individual commercially available ABS polymers span a wide range of mechanical properties Most suppliers differentiate types on the ASTM or UL Test Standard ABS Grades Property D792 D792 Specific gravity Specific volume (in.3/lb) D638 D638 D638 D790 D790 D256 Tensile strength (psi) Elongation (%) Tensile modulus (105 psi) Flexural strength (psi) Flexural modulus (105 psi) Impact strength, Izod (ft-lb/in of notch) Hardness, Rockwell R D785 D696 D648 UL94 Coefficient of thermal expansion (10–5) in./in.-°F Deflection temperatureb (°F) At 264 psi At 66 psi Flammability rating High Impact Superhigh Impact Special-Purpose ABS Grades Medium Impact High Heat Flame Retardant Clear Expandable Plating SAN Grades 1.19–1.22 — 1.05 26 0.55–0.85 — 1.05–1.07 26 1.07–1.08 26 5,500–10,000 5–25 3.2–3.7 9,000–12,250 3.0–3.4 4.0–13.0 5,800–6,300 25–75 3.0–3.3 10,500 3.4–3.9 2.5–4.0 3,000–4,000 — 1.0–2.5 3,000–8,000 1.4–2.8 — 5,500–6,600 — 3–3.8 8,700–11,500 3.0–3.8 5.0–7.0 9,000–12,000 1–4 4.5–5.6 14,000–17,000 5.5 0.35–0.50 90–117 100–105 60–70a 103–109 M85 3.7–4.6 4.6 4.9 4.7–5.3 3.0 180–220 198–238 V-0 to V-1c 168 180–185 HB 160 185 HB–V-0 189 214 HB 210 — HB 400+ 20–60 400 120–130 — — — — — — 1.01–1.05 27 1.02–1.05 27 1.04–1.06 28 Physical 1.04–1.06 28 6,000 5–20 3.3 10,500 3.4 6.5 5,000–6,300 5–70 2.0–3.4 6,000–11,500 2.0–3.5 7.0–8.0 6,000–7,500 5–25 3.6–3.8 11,500 3.6–4.0 4.0–5.5 Mechanical 6,000–7,500 3–20 3.0–4.0 10,000–13,000 3.1–4.0 2.3–6.0 103 69–105 107 5.3 5.6 4.6 Thermal 3.9–5.1 188 203 HB 192 208 HB 184 201 HB 220–240 230–245 HB 111 Electrical D149 D495 a b c Dielectric strength (V/mil) Short time, 1/8-in thk Arc resistance (s) 400 89 350–500 50–85 350–500 50–85 Density has a marked effect Unannealed 0.060-in.-thick samples ASTM = American Society for Testing and Materials; UL = Underwriters’ Laboratories Source: Mach Design Basics Eng Design, June, p 674, 1993 With permission © 2002 by CRC Press LLC 350–500 50–85 TX66613_frame_A(1) Page Wednesday, March 13, 2002 11:12 AM TABLE A.1 Properties of ABS and SAN TX66613_frame_A(1) Page Wednesday, March 13, 2002 11:12 AM A basis of impact strength and fabrication method (extrusion or molding) Some compounds feature one particularly exceptional property, such as high heat deflection temperature, abrasion resistance, or dimensional stability Impact properties of ABS are exceptionally good at room temperature and, with special grades, at temperatures as low as –40°C Because of its plastic yield at high strain rates, impact failure of ABS is ductile rather than brittle Also, the skin effect, which in other thermoplastics accounts for a lower impact resistance in thick sections than in thin ones, is not pronounced in ABS materials A long-term tensile design stress of 6.8 to 10.3 MPa (at 22.8°C) is recommended for most grades General-purpose ABS grades are adequate for some outdoor applications, but prolonged exposure to sunlight causes color change and reduces surface gloss, impact strength, and ductility Less affected are tensile strength, flexural strength, hardness, and elastic modulus Pigmenting the resins black, laminating with opaque acrylic sheet, and applying certain coating systems provide weathering resistance For maximum color and gloss retention, a compatible coating of opaque, weather-resistant polyurethane can be used on molded parts For weatherable sheet applications, ABS resins can be coextruded with a compatible weather-resistant polymer on the outside surface ABS resins are stable in warm environments and can be decorated with durable coatings that require baking at temperatures to 71°C for 30–60 Heat-resistant grades can be used for short periods at temperatures to 110°C in light load applications Low moisture absorption contributes to the dimensional stability of molded ABS parts Molded ABS parts are almost completely unaffected by water, salts, most inorganic acids, food acids, and alkalies, but much depends on time, temperature, and especially stress level Food and Drug Administration (FDA) acceptance depends to some extent on the pigmentation system used The resins are soluble in esters and ketones, and they soften or swell in some chlorinated hydrocarbons, aromatics, and aldehydes Properties of SAN resins are controlled primarily through acrylonitrile content and by © 2002 by CRC Press LLC adjusting the molecular weight of the copolymer Increasing both improves physical properties, at a slight penalty in processing ease Properties of the resins can also be enhanced by controlling orientation during molding Tensile and impact strength, barrier properties, and solvent resistance are improved by this control Special grades of SAN are available with improved ultraviolet (UV) stability, vapor-barrier characteristics, and weatherability The barrier resins — designed for the blown-bottle market — are also tougher and have greater solvent resistance than the standard grades FABRICATION AND FORMS ABS plastics are readily formed by the various methods of fabricating thermoplastic materials extrusion, injection molding, blow molding, calendering, and vacuum forming Molded products may be machined, riveted, punched, sheared, cemented, laminated, embossed, or painted Although the ABS plastics process easily and exhibit excellent moldability, they are generally more difficult flowing than the modified styrenes and higher processing temperatures are used The surface appearance of molded articles is excellent and buffing may not be necessary Moldings The need for impact resistance and high mechanical properties in injection-molded parts has created a large use for ABS materials Advances in resin technology coupled with improved machinery and molding techniques have opened the door to ABS resins Large complex shapes can be readily molded in ABS today Pipe The ABS plastics as a whole are popular for extrusion and they offer a great deal for this type of forming The outstanding contribution is their ability to be formed easily and to hold dimension and shape In addition, very good extrusion rates are obtainable Because ABS materials are processed at stock temperatures of 400 to 500°F, it is generally necessary to preheat and dry the material prior to extrusion TX66613_frame_Z(24) Page 889 Wednesday, March 13, 2002 12:05 PM Z ZINC AND ALLOYS A bluish-white crystalline metal, zinc (symbol Zn) has a specific gravity of 7.13, melts at 420°C and boils at 906°C The commercially pure metal has a tensile strength, cast, of about 62 MPa with elongation of 1%, and the rolled metal has a strength of 165 MPa with elongation of 35% But small amounts of alloying elements harden and strengthen the metal, and it is seldom used alone Zinc is seldom used alone except as a coating In addition to its metal and alloy forms, zinc also extends the life of other materials such as steel (by hot dipping or electrogalvanizing), rubber and plastics (as an aging inhibitor), and wood (in paints) Zinc is also used to make brass, bronze, and nickel silver; die-casting alloys in plate, strip, and coil; foundry alloys; superplastic zinc; and activators and stabilizers for plastics Additionally, zinc is used for electric batteries; for die castings; and in alloyed sheets for flashings, gutters, and stamped and formed parts The metal is harder than tin, and an electrodeposited plate has a Vickers hardness of about 45 Zinc is also used for many chemicals PRODUCTION The metallurgy of zinc is dominated by the fact that its oxide is not reduced by carbon below the boiling point of the metal A large fraction of the world’s zinc is still produced from relatively small horizontal retorts with one furnace (or bank) containing hundreds of such units Other large, continuously operated vertical retorts have operated, with top charging of briquets of zinc oxide and bituminous coal, and metal tapping from an outside condenser © 2002 by CRC Press LLC Another continuous method involves electrothermic reduction, using a novel condenser in which the retort vapors are sucked through molten zinc Neither horizontal or vertical retorts, electrothermic units, nor blast furnaces normally produce zinc of the extreme high purity required by much of the total market for zinc Since 1935, a redistillation process has been used as the thermal means of meeting this demand The principles of fractional distillation are utilized and zinc of 99.99+% purity is made There is also an electrolytic method of producing metallic zinc Because the selective flotation process made additional quantities of zinc concentrates available in localities where electric power is cheap, the production of electrolytic zinc was increased In the electrolytic process, the zinc content of the roasted ore is leached out with dilute sulfuric acid The zinc-bearing solution is filtered and purified and the zinc content recovered from the solution by electrolysis, using lead alloy anodes and sheet aluminum cathodes Current passing through the electrolytic cell, from anode to cathode, deposits the metallic zinc on the cathodes from which it is stripped at regular intervals, melted and cast into slabs Zinc so produced is 99.9+ or 99.99+% pure depending on need and the process control exercised COMPOUNDS AND ZINC FORMS Zinc is always divalent in its compounds, except for some of those with other metals, which are classed as zinc alloys Most of the more important zinc compounds are inorganic, since they are much more widely used than the organic zinc compounds Z TX66613_frame_Z(24) Page 890 Wednesday, March 13, 2002 12:05 PM Z The old name spelter, often applied to slab zinc, came from the name spailter used by Dutch traders for the zinc brought from China Sterling spelter was 99.5% pure Special high-grade zinc is distilled, with a purity of 99.99%, containing no more than 0.006% lead and 0.004 cadmium High-grade zinc, used in alloys for die casting, is 99.9% pure, with 0.07 max lead Brass special zinc is 99.10% pure, with 0.6 max lead and 0.5 max cadmium Prime western zinc, used for galvanizing, contains 1.60 max lead and 0.08 max iron Zinc crystals produced for electronic uses are 99.999% pure, metal On exposure to the air, zinc becomes coated with a film of carbonate and is then very corrosion-resistant Zinc foil comes in thicknesses from 0.003 to 0.015 cm It is produced by electrodeposition on an aluminum drum cathode and stripping off on a collecting reel But most of the zinc sheet contains a small amount of alloying elements to increase the physical properties Slight amounts of copper and titanium reduce grain size in sheet zinc In cast zinc the hexagonal columnar grain extends from the mold face to the surface or to other grains growing from another mold face, and even very slight additions of iron can control this grain growth Aluminum is also much used in alloying zinc In zinc used for galvanizing, a small addition of aluminum prevents formation of brittle alloy layer, increases ductility of the coating, and gives a smoother surface Small additions of tin give bright spangled coatings Zinc has 12 isotopes, but the natural material consists of stable isotopes, of which nearly half is zinc-64 The stable isotope zinc–67, occurring to the extent of about 4% in natural zinc, is sensitive to tiny variations in transmitted energy, giving off electromagnetic radiations that permit high accuracy in measuring instruments It measures gamma-ray vibrations with great sensitivity, and is used in the nuclear clock Zinc powder, or zinc dust, is a fine gray powder of 97% minimum purity usually in 325-mesh particle size It is used in pyrotechnics, in paints, as a reducing agent and catalyst, in rubbers as a secondary dispersing agent and to increase flexing, and to produce Sherardized steel © 2002 by CRC Press LLC In paints, zinc powder is easily wetted by oils It keeps the zinc oxide in suspension, and also hardens the film Mossy zinc, used to obtain color effects on face brick, is a spangly zinc powder made by pouring the molten metal into water Feathered zinc is a fine grade of mossy zinc Photoengraving zinc for printing plates is made from pure zinc with only a small amount of iron to reduce grain size and is alloyed with not more than 0.2% each of cadmium, manganese, and magnesium Cathodic zinc, used in the form of small bars or plates fastened to the hulls of ships or to underground pipelines to reduce electrolytic corrosion, is zinc of 99.99% purity with iron less than 0.0014% to prevent polarization APPLICATIONS For many years, the greatest use of zinc has been to protect iron and steel against atmospheric corrosion Because of the relatively high electropotential of zinc, it is anodic to iron If zinc and iron or steel are electrically connected and are jointly exposed in most corrosive media, the steel will be protected while the zinc will be attacked preferentially and sacrificially This, along with the fact that zinc corrodes far less rapidly than iron in most environments, forms the basis for one of the great fields of use of zinc — in galvanizing (by hot dipping or electrolytically), metallizing, sherardizing, in zinc pigmented paint systems, and as anodes in systems for cathodic protection The six techniques are described below Hot Dip Galvanizing Zinc alloys readily with iron Therefore, steel articles, suitably cleaned, will be wet by molten zinc and will acquire uniform coatings of zinc the thickness of which will vary with time, temperature, and rate of withdrawal Such coats are continuous and reasonably ductile Ductility is improved considerably by the restriction of immersion time and by the addition of small amounts of aluminum to the galvanizing bath Millions of tons of steel products are protected by zinc annually The time before first rusting of the iron or steel base is proportional to the thickness of zinc coat which in turn is TX66613_frame_Z(24) Page 891 Wednesday, March 13, 2002 12:05 PM subject to control — depending on product and processing — within a range from thin wiped coats on some products to as much as 0.20 mm on certain low-alloy steels allowed to acquire a full natural coat The usefulness of zinc as a coating material comes from its dual ability to protect, first as a long-lasting sheath, and then sacrificially when the sheath finally is perforated Zinc-Pigmented Paints Evidence has accumulated to demonstrate that paints heavily pigmented with zinc dust perform similarly to zinc coats otherwise applied Electrical contact must exist between the steel and the zinc-dust particles; consequently, special vehicles must be used and the steel surface must be clean Zinc Anodes Electrogalvanizing Zinc may be electrolytically deposited on essentially all iron and steel products Wire and strip are commonly so treated as are many fabricated parts Electrodeposited coats are ductile and uniform but normally are thinner and therefore find application in less rigorous service Metallizing Zinc wire or powder is melted and sprayed on suitably grit-blasted steel surfaces — a growing use Its virtues are flexibility in application and substantial thicknesses that may be applied The method is particularly useful for renewal of heavy coatings on areas exposed to particularly critical corrosive conditions and the coating of parts too large for hot dipping Although metallized coats may be somewhat porous, the sacrificial nature of zinc nevertheless makes them protective Suitable pore sealants may be used as a part of a metallizing system Sherardizing Zinc powder is packed loosely around clean parts to be sherardized in an airtight container When sealed, heated to temperature near but below the zinc melting point, then slowly rotated, the zinc alloys with the steel forming a thin, abrasion-resistant, and uniform protective coating (0.4 to 1.8 g/cm2) Sherardizing is used commonly to coat small items such as nuts, bolts, and screws; an exception is tubular electrical conduit Sherardized coats receive varnish, paints, and lacquers particularly well © 2002 by CRC Press LLC High-purity zinc, normally alloyed with small additions of aluminum, with or without cadmium, is cast or rolled into anodes that, when electrically bonded to bare or painted steel, will protect large areas from the corrosive attack of such environments as seawater The advantages of zinc in this application include self-regulation (no more current is generated than is required), a minimum generation of hydrogen, and long life This is a growing application for the protection of ship hulls, cargo tanks in ballast, piers, pilings, etc General Comment Reference has been made to the importance of coating thickness — the heavier the coat, the longer the time before first rusting All evidence at hand indicates that the amount of zinc in a coat is the controlling factor and the method of application is of secondary importance Uniformity of coat and adhesion must be good No data are known to demonstrate that common zinc impurities normally present in amounts to or slightly above specification limits have any significantly deleterious or beneficial influence on the ability of zinc to protect iron or steel against atmospheric corrosion Although any grade of zinc may be used for galvanizing, Prime Western is the one most commonly employed Die casting is a market for zinc that may soon become its largest market These alloys melt readily, are highly fluid, and not attack steel dies or equipment When used under good temperature control and with good die design practices, casting surfaces are excellent and easily finished Physical properties are good and dimensional stability excellent Z TX66613_frame_Z(24) Page 892 Wednesday, March 13, 2002 12:05 PM Z Alloy control within the specified limits ensures long life Low aluminum results in decreased casting and mechanical properties and adversely affects the performance of plated coatings High aluminum can lead to brittleness (an alloy eutectic forms at 5% aluminum) High copper content decreases dimensional stability Iron as commonly encountered is not critical Lead, tin, and cadmium, if present above specification limits, can lead to intercrystalline corrosion with objectionable growth and serious cracking or brittleness as a result Magnesium minimizes the deleterious influence of lead, tin, or cadmium but at or near specification maximum decreases ductility and castability and can lead to objectionable hot shortness Other impurities such as chromium and nickel, which may be encountered, are not critical Zinc die castings are used by the automotive, truck, and bus industry for functional, decorative–functional, or decorative purposes A majority is plated with copper–nickel–chromium in a variety of plating systems especially adapted to withstand severe service conditions Other major outlets for zinc die casting include household appliances, business machines, machine tools, air-brake systems, and communication equipment Even such nonstructural materials as cardboard can be zinc-coated by low-temperature flame spraying Other important uses of zinc are in brass and zinc die-casting alloys, in zinc sheet and strip, in electrical dry cells, in making certain zinc compounds, and as a reducing agent in chemical preparations A so-called tumble-plating process coats small metal parts by applying zinc powder to them with an adhesive, then tumbling them with glass beads to roll out the powder into a continuous coat of zinc Rechargeable nickel-zinc batteries offer higher energy densities than conventional dry cells Foamed zinc metal has been suggested for use in lightweight structures such as aircraft and spacecraft Some other uses of zinc are in dry cells, roofing, lithographic plates, fuses, organ pipes, and wire coatings Zinc is believed to be needed for normal growth and development of all living species, including humans; actually, life without zinc would be impossible Zinc is a common element that is present in virtually every type of © 2002 by CRC Press LLC human food, and zinc deficiency is therefore not considered to be a common problem in humans Zinc is a trace element that is present in biological fluids at a concentration below ppm (parts per million), and only a small amount (normally 2205°C) Zircon has excellent thermal properties and its thermal conductivity is 14.5 Btu/ft2/hr/°F/in and coefficient of thermal expansion is 1.4 × 10–6 The extremely high thermal conductivity and chilling action of zircon makes it very useful in controlling directional solidification and shrinkage in heavy metal sections USES Zircon sand is used as refractory bedding material for heat-treating metal parts It is used as a Z TX66613_frame_Z(24) Page 898 Wednesday, March 13, 2002 12:05 PM sealing medium for prevention of atmospheric leaks around doors and parts of heat-treating furnaces Also, it is a high-qualiIty, uniform sandblasting medium for metal preparation prior to plating, enameling, or buffing The heavy, rounded grains give consistent peening without stray digs or gouges to mar the finish The tough, resilient grains resist breakdown and loss ZIRCONIA (ZIRCONIUM OXIDE) Zirconium oxide, ZrO2, is a white crystalline powder with a specific gravity of 5.7, hardness 6.5, and refractive index 2.2 When pure, its melting point is about 2760°C, and it is one of the most refractory of the ceramics It is produced by reacting zircon sand and dolomite at 1371°C and leaching out the silicates The material is used as fused or sintered ceramics and for crucibles and furnace bricks From 4.5 to 6% of CaO or other oxide is added to convert the unstable monoclinic crystal to the stable cubic form with a lowered melting point Zirconia is produced from the zirconium ores known as zircon and baddeleyite The latter is a natural zirconium oxide It is also called zirkite and Brazilite Zircon is zirconium silicate, ZrO2 · SiO2, and comes chiefly from beach sands The sands are also called zirkelite and zirconite, or merely zircon sand The white zircon sand has a zirconia content of 62%, and contains less than 1% iron USES Z Fused zirconia, used as a refractory ceramic, has a melting point of 2549°C and a usable temperature to 2454°C The Zinnorite fused zirconia is a powder that contains less than 0.8% silica and has a melting point of 2704°C A sintered zirconia can have a density of 5.4, a tensile strength of 82 MPa, compressive strength of 1378 MPa, and Knoop hardness of 1100 Zircoa B is stabilized cubic zirconia used for making ceramics Zircoa A is the pure monoclinic zirconia used as a pigment, as a catalyst, in glass, and as an opacifier in ceramic coatings As an opacifier, zirconium compounds are used in glazes and porcelain enamels Zirconium dioxide is an important constituent of © 2002 by CRC Press LLC ceramic colors and an important component of lead–zirconate–titanate electronic ceramics Pure zirconia also is used as an additive to enhance the properties of other oxide refractories It is particularly advantageous when added to high-fired magnesia bodies and alumina bodies It promotes sinterability and, with alumina, contributes to abrasive characteristics Zirconia brick for lining electric furnaces has no more than 94% zirconia, with up to 5% calcium oxide as a stabilizer, and some silica It melts at about 2371°C, but softens at about 1982°C The IBC 4200 brick is zirconia with calcium and hafnium oxides for stabilizing It withstands temperatures to 2316°C in oxidizing atmospheres and to 1849°C in reducing atmospheres Zirconia foam is marketed in bricks and shapes for thermal insulation With a porosity of 75% it has a flexural strength above MPa and a compressive strength above 0.7 MPa For use in crucibles, zirconia is insoluble in most metals except the alkali metals and titanium It is resistant to most oxides, but with silica it forms ZrSiO4, and with titania it forms ZrTiO4 Because structural disintegration of zirconia refractories comes from crystal alteration, the phase changes are important considerations The monoclinic material, with a specific gravity of 5.7, is stable to 1010°C and then inverts to the tetragonal crystal with a specific gravity of 6.1 and volume change of 7% It reverts when the temperature again drops below 1010°C The cubic material, with a specific gravity of 5.55, is stable at all temperatures to the melting point, which is not above 2649°C because of the contained stabilizers A lime-stabilized zirconia refractory with a tensile strength of 138 MPa has a tensile strength of 68 MPa at 1299°C Stabilized zirconia has a very low coefficient of expansion, and white-hot parts can be plunged into cold water without breaking The thermal conductivity is only about one third that of magnesia It is also resistant to acids and alkalies, and is a good electrical insulator To prepare useful formed products from zirconium oxide, stabilizing agents such as lime, yttrium, or magnesia must be added to the zirconia, preferably during fusion, to convert the zirconia to the cubic form Most commercial stabilized zirconia powders or products contain calcium oxide as the stabilizing agent TX66613_frame_Z(24) Page 899 Wednesday, March 13, 2002 12:05 PM The stabilized cubic form of zirconia undergoes no inversion during heating and cooling Stabilized zirconia refractories are used where extremely high temperatures are required Above 1649°C, in contact with carbon, zirconia is converted to zirconium carbide Zirconia is of much interest as a construction material for nuclear energy applications because of its refractoriness, corrosion resistance, and low nuclear cross section However, zirconia normally contains about 2% hafnia, which has a high nuclear cross section The hafnia must be removed before the zirconia can be used in nuclear applications FORMS Zirconia is available in several distinct types The most widely used form is stabilized in cubic crystal form by a small lime addition This variety is essential to the fabrication of shapes because the so-called unstabilized, monoclinic zirconia undergoes a crystalline inversion on heating, which is accompanied by a disruptive volume change Zirconia is not wetted by many metals and is therefore an excellent crucible material when slag is absent It has been used very successfully for melting alloy steels and the noble metals Zirconia refractories are rapidly finding application as setter plates for ferrite and titanate manufacture, and as matrix elements and wind tunnel liners for the aerospace industry OTHER TYPES Toughening mechanisms, by which a crack in a ceramic can be arrested, complement processing techniques that seek to eliminate crack-initiating imperfections Transformation toughening relies on a change in crystal structure (from tetragonal to monoclinic) that zirconia or zirconium dioxide (ZrO2) grains undergo when they are subjected to stresses at a crack tip Because the monoclinic grains have a slightly larger volume, they can “squeeze” a crack shut as they expand in the course of transformation Because of the transformation toughening abilities of ZrO2, which impart higher fracture toughness, research interest in engine applications has been high In order for ZrO2 to be used © 2002 by CRC Press LLC in high-temperature, structural applications, it must be stabilized or partially stabilized to prevent a monoclinic–tetragonal phase change Stabilization involves the addition of calcia, magnesia, or yttria followed by some form of heat treatment PSZ ceramic, the toughest known ceramic, has been investigated for diesel-engine applications PSZ is a transformation toughened material consisting of a cubic zirconia matrix with 20 to 50 vol% free tetragonal zirconia added in the matrix The material is converted into the stabilized cubic crystal structure using oxide stabilizers (magnesia, calcia, yttria) The conversion is accomplished by sintering the doped zirconia at 1700°C Magnesia-stabilized zirconia exhibits serrated plastic flow during compression at room temperature The flow stress is strain rate sensitive Several different grades are available for commercial use, and the properties of the material can be tailored to fit many applications One typical PSZ used for applications requiring maximum thermal shock resistance has a four-point bend strength of 600 MPa; PSZ is used experimentally as heat engine components, such as cylinder liners, piston caps, and valve seats Vanadium impurities from fuel oil can cause zirconia destabilization, and sodium, magnesium, and sulfur impurities can cause yttria to dissociate from yttria-stabilized zirconia Another area of interest for PSZ is in bioceramics, where it has use in surgical implants A new zirconia ceramic being developed, tetragonal zirconia polycrystal (TZP) doped with Y2O3, has the most impressive room-temperature mechanical properties of any zirconia ceramic The commercial applications of TZP zirconia include scissors with TZP blades suitable for industrial use for cutting tough fiber fabrics, e.g., Kevlar, cables, and ceramic scalpels for surgical applications One unique application is fish knives The knife blades are Y-TZP and can be used when the delicate taste of raw fish would be tainted by slicing with knives with metal blades Another zirconia ceramic-developed material is zirconia-toughened alumina (ZTA) ZTA zirconia is a composite polycrystalline ceramic containing ZrO2, as a dispersed phase (typically ~15 vol%) Close control of initial starting Z TX66613_frame_Z(24) Page 900 Wednesday, March 13, 2002 12:05 PM powder sizes and sintering schedules is thus necessary to attain the desired ZrO2 particle dimensions in the finished ceramic Hence, the mechanical properties of the composite ZTA ceramics limit current commercial applications to cutting tools and ceramic scissors PSZ is also finding application in the transformation toughening of metals used in the glass industry as orifices for glass fiber drawing This material is termed zirconia grain-stabilized (ZGS) platinum Clear zircon crystals are valued as gemstones because the high refractive index gives great brilliance Zirconia fiber, used for high-temperature textiles, is produced from zirconia with about 5% lime for stabilization The fiber is polycrystalline, has a melting point of 2593°C, and will withstand continuous temperatures above 1649°C These fibers are as small as to 10 µm and are made into fabrics for filter and fuel cell use Zirconia fabrics are woven, knitted, or felted of short-length fibers and are flexible Ultratemp adhesive, for high-heat applications, is zirconia powder in solution At 593°C, it adheres strongly to metals and will withstand temperatures to 2427°C Zircar is zirconia fiber compressed into sheets to a density of 320 kg/m3 It will withstand temperatures up to 2482°C and has low thermal conductivity It is used for insulation and for high-temperature filtering ZIRCONIUM AND ALLOYS Z A silvery-white metal, zirconium (symbol Zr), has a specific gravity of 6.5 and a melting point of about 1850°C It is more abundant than nickel, but is difficult to reduce to metallic form as it combines easily with oxygen, nitrogen, carbon, and silicon The metal is obtained from zircon sand by reacting with carbon and then converting to the tetrachloride, which is reduced to a sponge metal for the further production of shapes The ordinary sponge zirconium contains about 2.5% hafnium, which is closely related and difficult to separate The commercial metal usually contains hafnium, but reactor-grade zirconium, for use in atomic work, is hafnium-free © 2002 by CRC Press LLC Commercially pure zirconium is not a highstrength metal, with a tensile strength of about 220 MPa, elongation 40%, and Brinell hardness 30, or about the same physical properties as pure iron But it is valued for atomic-construction purposes because of its low neutron-capture cross section, thermal stability, and corrosion resistance It is employed mostly in the form of alloys but may be had in 99.99% pure single-crystal rods, sheets, foil, and wire for superconductors, surgical implants, and vacuum-tube parts The neutron cross section of zirconium is 0.18 barn, compared with 2.4 for iron and 4.5 for nickel The cold-worked metal, with 50% reduction, has a tensile strength of about 545 MPa, with elongation of 18% and hardness of Brinell 95 The unalloyed metal is difficult to roll, and is usually worked at temperatures to 482°C Although nontoxic, the metal is pyrophoric because of its heat-generating reaction with oxygen, necessitating special precautions in handling powder and fine chips resulting from machining operations The metal has a close-packed hexagonal crystal structure, which changes at 862°C to a body-centered cubic structure that is stable to the melting point At 300 to 400°C the metal absorbs hydrogen rapidly, and above 200°C it picks up oxygen At about 400°C it picks up nitrogen, and at 800°C the absorption is rapid, increasing the volume and embrittling the metal The metal is not attacked by nitric (except red fuming nitric), sulfuric, or hydrochloric acids, but is dissolved by hydrofluoric acid Zirconium powder is very reactive, and for making sintered metals it is usually marketed as zirconium hydride, ZrH2, containing about 2% hydrogen, which is driven off when the powder is heated to 300°C For making sintered parts, alloyed powders are also used Zirconium copper (containing 35% zirconium), zirconium nickel (with 35 to 50% zirconium), and zirconium cobalt (with 50% zirconium), are marketed as powders of 200 to 300 mesh PROPERTIES In addition to resisting HCl at all concentrations and at temperatures above the boiling temperature, zirconium and its alloys also have TX66613_frame_Z(24) Page 901 Wednesday, March 13, 2002 12:05 PM excellent resistance in sulfuric acid at temperatures above boiling and concentrations to 70% Corrosion rate in nitric acid is less than mil/year at temperatures above boiling and concentrations to 90% The metals also resist most organics such as acetic acid and acetic anhydride as well as citric, lactic, tartaric, oxalic, tannic, and chlorinated organic acids Relatively few metals besides zirconium can be used in chemical processes requiring alternate contact with strong acids and alkalies However, zirconium has no resistance to hydrofluoric acid and is rapidly attacked, even at very low concentrations USES Small amounts of zirconium are used in many steels It is a powerful deoxidizer, removes the nitrogen, and combines with the sulfur, reducing hot-shortness and giving ductility Zirconium steels with small amounts of residual zirconium have a fine grain, and are shock resistant and fatigue resistant In amounts above 0.15% the zirconium forms zirconium sulfide and improves the cutting quality of the steel A noncrystalline metal that reportedly has twice the strength of steel and titanium, has been developed The material, known as Vitrelloy, is an alloy composed of 61% zirconium, 12% titanium, 12% copper, 11% nickel, and 3% beryllium Its yield strength is 1900 MPa, compared with 800 MPa for titanium alloy, Ti–6% Al–4% V, and 850 MPa for cast stainless steel Fracture toughness is said to be 55 MPam1/2, the same as high-strength steel but half that of titanium Its resistance to permanent deformation is said to be two to three times higher than that of conventional metals The density of Vitrelloy is 6.1 g/cm3 between cast titanium at 4.5 g/cm3 and cast stainless steel at 7.8 g/cm3 The material is particularly recommended for aerospace applications because of its surface hardness of 50 HRC Cast titanium and steel are both tested at 30 HRC The beneficial properties of the alloy are ascribed to its noncrystalline structure Because there are no patterns or grains within the structure, weak areas caused by grain boundaries are eliminated © 2002 by CRC Press LLC An advanced machinable ceramic that may be used to produce thermal shock-resistant components for aerospace, automotive, electrical, heat treating, metallurgical, petrochemical, and plastics applications up to 1550°C has been introduced The new material (AremcoloxTM 502-1550) is based on the zirconium phosphate system (Ba1+xZr4P6-2xSi2xO24) and is especially unique because of its low coefficient of thermal expansion (CTE) of 0.5 × 10–6 in./in.°F This characteristic sets the material apart from standard ceramic materials such as alumina and zirconia which have CTEs of 4.0 x 10-6 and 2.5 × 10–6, respectively A low CTE ensures that as a component is thermally cycled the mechanical stress induced through expansion and contraction does not cause the part to crack This feature enables engineers to adapt the material to high thermal shock applications, such as combustion and heater systems, that were not previously feasible Additional properties and applications of the machinable ceramic include their use as molds, optical stands, microwave housings, engine parts, and applications in which high mechanical strength, hardness, and low porosity are required A low-density version of the material (502-1550 LD) is recommended for use as brazing fixtures, induction heating liners, rocket nozzles, and high-temperature gauges, tooling, and structures The material is easily machined using carbide tooling and no postfiring is required ALLOYS Zirconium alloys generally have only small amounts of alloying elements to add strength and resist hydrogen pickup Zircoloy 2, for reactor structural parts, has 1.5% tin, 0.12% iron, 0.10% chromium, 0.05% nickel, and the balance zirconium Tensile strength is 468 MPa, elongation 37%, and hardness Rockwell B89; at 316°C it retains a strength of 206 MPa Zirconium alloys can be machined by conventional methods, but they have a tendency to gall and work-harden during machining Consequently, tools with higher than normal clearance angles are needed to penetrate previously work-hardened surfaces Results can Z TX66613_frame_Z(24) Page 902 Wednesday, March 13, 2002 12:05 PM Z be satisfactory, however, with cemented carbide or high-speed steel tools Carbide tools usually provide better finishes and higher productivity Mill products are available in four principal grades: 702, 704, 705, and 706 These metals can be formed, bent, and punched on standard shop equipment with a few modifications and special techniques Grades 702 (unalloyed) and 704 (Zr–Sn–Cr–Fe alloy) sheet and strip can be bent on conventional press-brake or roll-forming equipment to a 5t bend radius at room temperature and to 3t at 200°C Grades 705 and 706 (Zr–Cb alloys) can be bent to a 3t and 2.5t radius at room temperature and to about 1.5t at 200°C Small amounts of zirconium in copper give age-hardening and increase the tensile strength Copper alloys containing even small amounts of zirconium are called zirconium bronze They pour more easily than bronzes with titanium, and they have good electric conductivity Zirconium–copper master alloy for adding zirconium to brasses and bronzes is marketed in grades with 12.5 and 35% zirconium A nickel–zirconium master alloy has 40 to 50% nickel, 25 to 30% zirconium, 10% aluminum, and up to 10% silicon and 5% iron Zirconium–ferrosilicon, for alloying with steel, contains to 12% zirconium, 40 to 47% silicon, 40 to 45% iron, and 0.20% max carbon, but other compositions are available for special uses SMZ alloy, for making high-strength cast irons without leaving residual zirconium in the iron, has about 75% silicon, 7% manganese, 7% zirconium, and the balance iron A typical zirconium copper for electrical use is Amzirc It is oxygen-free copper with only 0.15% of zirconium added At 400°C it has a conductivity of 37% IACS, tensile strength of 358 MPa, and elongation of 9% The softening temperature is 580°C Zirconium alloys with high zirconium content have few uses except for atomic applications Zircoloy tubing is used to contain the uranium oxide fuel pellets in reactors because the zirconium does not have grain growth and deterioration from radiation Zirconia ceramics are valued for electrical and high-temperature parts and refractory coatings Zirconium oxide powder, for flame-sprayed coatings, comes in © 2002 by CRC Press LLC either hexagonal or cubic crystal forms Zirconium silicate, ZrSi2, comes as a tetragonal crystal powder Its melting point is about 1649°C and hardness about 1000 Knoop Zirconium Beryllides Intermetallic compounds, ZrBe13 and Zr2Be17, have good strengths at elevated temperatures ZrBe13 is cubic, density 2.72 g/cm3, melting point 1925°C; Zr2Be17 is hexagonal, density 3.08 g/cm3, melting point 1983°C; parts can be formed by all ceramic-forming methods plus flame and plasma-arc spraying Materials are subject to safety requirements for all beryllium compounds These intermetallics, because of their greater densities (BeO = 1.85 g/cm3), contain more beryllium atoms per unit volume than beryllia, a decided advantage for compact, beryllium-moderated nuclear reactors Zirconium Carbide Zirconium carbide, ZrC2, is produced by heating zirconia with carbon at about 2000°C The cubic crystalline powder has a hardness of Knoop 2090, and a melting point of 3540°C The powder is used as an abrasive and for hotpressing into heat-resistant and abrasion-resistant parts Zirconium Diboride Zirconium diboride (ZrB2) has a density of 6.09 g/cm3 and a hexagonal (AlB2) crystal structure with a melting point of 3040°C Zirconium diboride is oxidation resistant at temperatures