Editorial Feature

Pyroceram – The Innovative Glass-Ceramic Material

Pyroceram was produced in the 1950s by Corning Glass during their extensive research on photosensitive glass. S. Donald Stookey discovered this material accidentally when an overheated piece of glass turned out to be too tough to break when dropped. This novel material has been classified by NASA as a glass-ceramic and is produced by controlled crystallization. Pyroceram 9606 was certified as a reference standard after being used informally for over 30 years in high temperature applications that demand working at temperatures of about 1000°C (1832°F).

History of Pyroceram

Way back in 1952, Corning Glass chemist Don Stookey was working on his routine experiment, when he placed a photosensitive glass sample in a furnace of 600°C (1112°F). A controller in the furnace malfunctioned and the temperature accidentally soared to 900°C (1652°F). When Stookey opened the furnace door, he was surprised to see that the lithium silicate had been converted into a plate, milky white in color. While trying to remove it, he accidentally dropped the sample only to find that it resisted breakage and bounced instead of shattering like a normal piece of glass.

That marked the invention of the first ever synthetic glass-ceramic, later named by Corning as Pyroceram. This innovative material was not only harder compared to high-carbon steel and lighter than aluminum, but also was much more stronger than ordinary soda-lime glass. Eventually, Pyroceram was used in a wide variety of applications from microwave ovens to chemistry labs and missile nose cones. In the 1959, Corning came up with its now well-known serving dish line called Corningware that used Pyroceram.

Riding on the success of Pyroceram, Corning initiated comprehensive R&D efforts to find more ways of making stronger glass materials. The company’s scientists later discovered another material called Chemcor by dousing glass containing aluminum oxide in a hot potassium salt bath. The addition of aluminum oxide was believed to make the glass extremely durable and at the same time highly flexible. However, due to its high cost, Chemcor could not be successfully marketed.

Material Properties of Pyroceram

Pyroceram is a transparent ceramic glass that is an excellent transmitter of visible light and creates a warm atmosphere with a light amber colored tint. The chemical and physical properties of Pyroceram have been tested in accordance to NF, DIN, EN or ISO specifications.

Pyroceram is made from a magnesium aluminosilicate glass with titania as nucleating agent, and the key crystalline phase has been identified as cordierite (2MgO-2Al2O3-5SiO2). The material is machined and etched to smoothen surfaces.

Pyorceram has under gone extensive testing such as the following:

  • Constant stress-rate testing as per ASTM standards
  • Tensile testing according to ASTM test methods at three test conditions: room temperature/ distilled water, 93°C (200°F)/distilled water, and 274°C (525°F)/ambient air
  • Compression testing at room temperature in distilled water with ‘fortified,’ specimens as per Test Method SACMA SRM-1
  • Shear testing at room-temperature in distilled water as per ASTM Test Method D 5379
  • Fracture toughness testing using two methods: single edge precracked beam (SEPB) as per ASTM Test Method C 1421 and single edge V-notched beam method.
  • Elastic modulus testing using impulse excitation (ASTM C 1259) and strain gauging.

The following table shows the various properties of Pryoceram®lll along with its dimensions.

Thermal Properties

Continuous use 700°C (1292°F)
Limited time, peak use 800°C (1472°F)
Thermal gradient resistance ΔT max. = 700K
Mean specific heat (20° to 100°C) 0.8 (J/g. K)
Thermal shock resistance ΔT max. = 700K
Thermal expansion coefficient [20 to 700°C (68 to 1292°F)] 0± 3.0 x 10-7 K-1

Chemical Properties

Alkali resistance (ISO 695) Class 1
Water resistance (ISO 719)
Acid resistance (DIN 12 116)

Optical Properties

Photo elastic coefficient 3.11 (Brewster)
ABBE number approx. 55.4
UV transmission at 3mm thickness <1% (wavelength < 355 µm)
Refractive index approx. 1.55

Electrical Properties

Dissipation factor (at 102 Hz) 40 x 10-3
Dielectric constant (at 102 Hz) 8.1
Electrical resistivity, where ρ is in Ω.cm log10 ρ 6.8 at 250° C (482°F)

Mechanical Properties

Poisson ratio (µ) 0.25
Minimal bending strength >110 MPa
Torsion modulus (G=) 37.8 GPa
Specific mass 2.55
Knoop hardness (load 1 N) 705
Young's modulus (E=) 94.3 GPa

Dimensions

Maximum sheet size 2005x1100mm
Glass thickness Available in 3, 4, or 5mm
Cut sizes Customizable

Applications of Pyroceram

The innovative glass ceramic material, Pyroceram, is used in the following applications:

  • Glassware products
  • Microwave ovens
  • In hot plates and stirrers in chemistry and biology labs
  • As nosecones in anti-aircraft missiles

References

G.P. Thomas

Written by

G.P. Thomas

Gary graduated from the University of Manchester with a first-class honours degree in Geochemistry and a Masters in Earth Sciences. After working in the Australian mining industry, Gary decided to hang up his geology boots and turn his hand to writing. When he isn't developing topical and informative content, Gary can usually be found playing his beloved guitar, or watching Aston Villa FC snatch defeat from the jaws of victory.

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Comments

  1. April Hunter April Hunter United States says:

    My Corningware 6 cup, blue cornflower (c. 1960's) coffee pot is stained and I would like to find out of using baking soda & vinegar is safe to remove the staining.
    With glass, this would be okay, with ceramic...maybe not.  Is it glass...or ceramic?

    • James Criswell James Criswell United States says:

      bar keepers friend removes most stains from corningware

    • Andrew Woody Andrew Woody United States says:

      I use muriatic acid to clean my corningware pyroceram so you should be good ;-) The pyroceram itself is very durable. Be careful on the metal and plastic parts though. Muriatic acid would certainly destroy them.

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