Custom Engineered Ceramic Parts

Choosing the Composition or Design

Engineered ceramics are made from a number of materials including oxides, carbides, nitride, and composites. Ceramics are characterized by their ability to withstand high temperatures, good electrical resistance, dielectric strength, high hardness and abrasion resistance, and chemical stability. Many factors are involved in choosing the correct material for the application. The following is a brief description of material available. By clicking on the name, additional information can be obtained. These materials can be formed using several different methods, fired to high densities, and then can be precision machined, polished, and metalized, to exacting specifications.

Choosing the Composition

Oxide ceramics are the most versatile of the ceramic materials when considering cost and ease of forming and machining. They can be pressed, extruded or cast and "green machined" to near net size before firing. Aluminum Oxide is a versatile material with a number of compositions to choose from that have different physical properties that can be matched to the application. We can also select from Zirconium Oxide compositions that are known for their toughness and fracture resistance. Other oxide materials include Magnesium Oxide, Silica, quartz, and Thoria parts can be selected for their unique properties. Sapphire, single crystal alumina, is a material often chosen for its high hardness, transparency, thermal and electrical properties.

We also offer newer silicon nitride, sialons, silicon and boron carbides, titanium borides, magnesium and thorium oxides, and mixed oxides such as mullite ans spinel. The compositions have characteristics such as high toughness, excellent wear properties, and thermal shock resistance. For details of compositions and physical properties of materials, please contact us directly.

For special applications requiring properties such as windows used in high temperature or corrosive atmospheres, Sapphire can be the material of choice.

Choosing the Right Design

The design of the ceramic part is also very important in the successful use of ceramics. Ceramics are by their nature more are ridged and brittle than metals and they are also much stronger in compression than in tension. This means that the ceramic part must not only be designed to meet the physical requirements of the application, but also must be matched to the characteristics of the material as well.

In addition, the manufacturing methods available to form and finish the ceramic part must be considered. For example, a part that is designed too thin for the material's strength will have high breakage when manufactured. Too large of a part may also be difficult to manufacture.

Over designing the part or using unnecessarily tight specification will significantly increase the cost. Careful identification of the tolerances and property required are important considerations.

Each of the ceramics we recommend have their own unique properties and, of course, cost factors for both the material, the initial forming and any final precision machining or finishing of the part. To ensure success, careful consideration and balancing of all factors must be made at the initial stages of design.

Marketech's ceramic engineers provide design and product selection assistance to make ceramics work for your application.

Finishing Options

Once formed, engineered ceramics can be machined, polished, threaded, and metalized. Some materials lend themselves to these processes more than others, and other compositions are specifically designed for a machining or finishing process. For more information, click here for a description of machining, metalizing, brazing, and finishing of engineered ceramics.

Below are listed some of the proprietary and standard engineered ceramic compositions we offer.

Properties of Alumina Ceramics

Because of its high temperatures, chemical electrical and mechanical properties, relatively low cost, and ease of manufacture, alumina is the work horse of engineered ceramics. It is compounded with silica and other trace elements and is available in several common grade ranging from 92% to 99.7% Al2O3. Alumina can be formed by casting, extrusion, or pressing. For large size or smaller quantities, alumina is issotically pressed into chalk like blocks that can be "green machined" to a near net shape, fired and then "finished" machined to high tolerances. Special grades of alumina are often metalized and then brazed to metal parts.

Composition 960 975 980 995
Al2O3 (%) 96 97.5 98 99.7
Tensile strength (Kpsi) 30 30 30 32
Flexural strength (Kpsi) 55 55 55 60
Porosity (%) 0 0 0 0
Coef. thermal exp. (cm/cm x 10-E6 °C)</td> <td align=center>7.5</td> <td align=center>7.6</td> <td align=center>7.7</td> <td align=center>7.8</td> <tr> <td>Max working temp (°C )</td> <td align=center>1600</td> <td align=center>1650</td> <td align=center>1650</td> <td align=center>1700</td> <tr> <td>Dielectric strength (D.C Volts/Mil. @ 0.100" thick)</td> <td align=center>230</td> <td align=center>230</td> <td align=center>240</td> <td align=center>250</td> <tr> <td>Volume resistivity (Ohm-cm (x10E12)) </td> <td align=center>2.0</td> <td align=center>3.1</td> <td align=center>3.2</td> <td align=center>3.5</td> <tr> <td>Dielectric constant (1 kHz - 1 gHz)</td> <td align=center>9.0</td> <td align=center>9.4</td> <td align=center>9.6</td> <td align=center>9.7</td> <tr> </table> </center> <P> <HR> <P> <font size="+2"> <b><a name=bm3>Properties of Zirconia Ceramics</a></b> </font> <p> Zirconium Oxide is widely used and has superior high temperature properties. When combined with compounds of yttria, strength and fracture toughness can be significantly increased. This makes some grades of zirconia superior to most materials for abrasion and wear resistance, brittleness, and thermal shock resistance. Zirconia ceramics are available in single or multi-holed tubes manufactured by casting or extrusion. Large or complex shapes are isostactically pressed, or injection molded. Parts can be machined before and after firing to meet exacting shape requirements. Zirconia is electrical conductive above 900 °C. <p> <center> <table border=1> <th width=100% colspan=4><font size=4><b>Zirconium Oxide Ceramics (zirconia)</b></font></th> <tr> <td><b>Composition</b></td> <td align=center><b>MgO Stab.</b></td> <td align=center><b>Y<font size=1>2</font>O<font size=1>3</font> Stab.</b></td> <td align=center><b>Y<font size=1>2</font>O<font size=1>3</font> Tetragonal</b></td> <tr> <td><b>Properties</b></td> <td><br></td> <td><br></td> <td><br></td> <tr> <td>Density</td> <td align=center>5.75 g/cm³</td> <td align=center>6.60 g/cm³</td> <td align=center>6.10 g/cm³</td> <tr> <td>Modulus of Rupture ( 3 pt @ 25 C° )</td> <td align=center>620 MPa</td> <td align=center>207 MPa</td> <td align=center>1300 MPa (4 pt)</td> <tr> <td>Compressive strength</td> <td align=center>1750 MPa</td> <td align=center>---</td> <td align=center>3900 MPa</td> <tr> <td>Hardness @ 25 °C</td> <td align=center>1200 kg/mm²</td> <td align=center>---</td> <td align=center>1300 kg/mm²</td> <tr> <td>Young's modulus</td> <td align=center>200 GPa</td> <td align=center>160 GPa</td> <td align=center>205 GPa</td> <tr> <td>Coefficient of thermal expansion, 20 - 1000 °C</td> <td align=center>10.1 x 10<dont size=1>-6</font>/K°</td> <td align=center>10.5 x 10<dont size=1>-6</font>/K°</td> <td align=center>10.9 x 10<dont size=1>-6</font>/K°</td> <tr> <td>Thermal conductivity @ 25 °C</td> <td align=center>2.2 W/m°K</td> <td align=center>2.2 W/m°K</td> <td align=center>2.3 W/m°K</td> <tr> <td>Thermal shock resistance</td> <td align=center>~ 350 ^T °C</td> <td align=center>~ 150 ^T °C</td> <td align=center>---</td> <tr> <td>Maximum temperature</td> <td align=center>500 °C</td> <td align=center>2400 °C</td> <td align=center>---</td> <tr> <td>Fracture toughness</td> <td align=center>---</td> <td align=center>---</td> <td align=center>8.0 MPa</td> </tr> </table> </center> <P> <b>Applications</b> <P> Advanced oxide ceramics such as zirconia are available in several families of compositions, and within families, numerous compounds and purity levels are available. Working closely with you, we can select the most appropriate matewrial to meet the needs of your specific application. The data listed above is typical of our more standard grades of material. Modified grades may be recommended for your application. <P> <HR> <P> <font size="+2"> <b><a name=bm5>Properties of Sapphires</a></b> </font> <p> Sapphire is grown by two methods: either in boule form, up to 10" in diameter, or it can be drawn from a melt in a wide variety profiles such as tubes, rods or sheets. Boule grown or Czochralski material is clear, free of seeds or bubbles striates and can be machined into a wide range of shapes for windows, substrates, and other engineered parts. Sapphire that is pulled from a melt through a profile offers suitable for many applications at an economical price and is available in much longer lengths. <p> <b>Boule Grown Sapphire</b> Each sapphire component is custom manufactured to exacting standards. Parts as large as 8 " diameter and as small as a few mm cross section can be made using boule grown materials. This material is available in a number of crystalographic orientations. <p> <b>Profile Grown Sapphire</b> Profile grown materials can be made with simple cross sections. Rods are available from 0.3 to 5 mm diameter and up to 1800 mm long. Tubes are available from 2.0 to 25 mm OD with wall thickness from 0.5 to 1.5 mm and lengths from 300 to 1800 mm. Ribbons are available 100 mm wide and from 0.4 to 2.0 mm thick with lengths to 700 mm. <p> <center> <table border=1> <th width=100% colspan=2> <font size=4><b>Saphire - Al<font size=2>2</font>O<font size=2>3</font></font></b></th> <tr> <td>Formula</td> <td align=center><em>a</em>-Al<font size=1>2</font>O<font size=1>3</font></td> <tr> <td><b>Crystallographic properties</b></td> <td><br></td> <tr> <td>Crystal Structure</td> <td align=center>trigonal</td> <tr> <td>Lattice Parameter</td> <td align=center>a = 4,758 Å<br> c = 12,991 Å</td> <tr> <td><b>Physical properties</td> <td><br></td> <tr> <td>Density</td> <td align=center>3.98 g/cm³</td> <tr> <td>Hardness</td> <td align=center>9 Mohs</td> <tr> <td>Melting point</td> <td align=center>2030 C°</td> <tr> <td>Thermal expansion coefficient (verticle c):</td> <td align=center>3.24 - 5.66 x 10<font size=1>-6</font> / C°</td> <tr> <td>Thermal conductivity</td> <td align=center>25.2 W / m C° (parallel c)<br> 23.1 W / m C° (vertical c)</td> <tr> <td>Specific heat capacity</td> <td align=center>761 J / kg C°</td> <tr> <td><b>Optical properties</td> <td><br></td> <tr> <td>Transmission range (thickness to 10mm)</td> <td align=center>0.7 <em>u</em>m - 5 <em>u</em>m</td> <tr> <td>Absorption coefficient</td> <td align=center>0.20 / cm at 0.2 <em>u</em>m<br> 0.02 / cm at 0.4 <em>u</em>m<br> 0.46 / cm at 5.0 <em>u</em>m</td> <tr> </table> </center> <P> <HR> <P> <font size="+2"> <b><a name=bm6>Finishing: Machining, Polishing, Metalizing, and Brazing</a></b> </font> <P> Probably the most important aspect of the machining, metallizing and brazing of engineered ceramics is the design of the part to match the application. Consulting with a Marketech engineer early in the design state will help to ensure that the part can be made in the most economical method</b>. <p> <font size=4><b>Machining of Ceramics</b></font> <p> Fired ceramics can be readily machined using a number of diamond grinding techniques. This includes flat and diameter surface grinding and lapping, drilling, cutting, threading, and milling. We can provide ground surfaces with tolerances as tight as 0.0001" (0.0025 mm). The cost of machining to tight tolerances can easily exceed the cost of the starting material. Marketech engineers can work with you to determine the most economical design for your requirements. <p> <font size=4><b>Metalizing of Ceramics</b></font> <p> Ceramics parts have the capability to be metalized in custom designs to meet exacting tolerances for applications such as electronic parts, electrical feed throughs, windows, insulators, standoffs, just to name a few. These parts are commonly used in detector assemblies, microwave and hybrid packages, insulated I/O windows, electron guns, and custom instrumentation. The metallization is done at high temperatures so will be stable under most conditions of brazing and soldering. Once a base coat is applied, the metalized coating is then plated to meet customers needs. <p> <b>Typical Ceramic Materials</b> <p> Typical materials include alumina (92 - 99.6%), Sapphire and Aluminum Nitride. Other materials such as beryllium oxide, boron nitride, and silicon nitride are available. <p> <b>Typical Plated Coatings</b> (both electroless and electrolytic plating) include gold, silver, nickel, copper on tungsten, and moly-manganese. <p> <font size=4><b>Brazing of Ceramics</b></font> <p> Once ceramics are metalized, Marketech can braze to a variety of metal parts. Careful consideration to geometry, matching of thermal expansion and metal type must be made. Typical metals include KOVAR, 42% Nickel-Iron, copper, stainless steel, Inconel, beryllium, titanium, and nickel. Consult a Marketech engineer for details or design recommendations. <p> <hr width=30% align=center noshade> <CENTER> <A HREF="index.htm">RETURN TO MAIN PAGE</A>]</CENTER> <hr width=30% align=center noshade> </BODY> </HTML>