What Makes Zirconium Oxide Unique?

USE-TEMPERATURES

ZYP ZIRCONIUM OXIDE products have the highest use-temperatures
of our paintable refractory/ceramic coatings, allowing utility of >2000 C
[3632 F].   The ZIRCONIUM OXIDE coatings can be used in most atmospheres (see individual product datasheets for specifics), but vacuum/reducing in contact with carbon/graphite can limit use or possibly cause reaction/carbon-contamination around 1350-1400 C.

THERMAL PROPERTIES

ZYP ZIRCONIUM OXIDE paints have the lowest thermal conductivity of any refractory/ceramic … resulting from zirconium oxide being the lowest thermal-conductivity oxide – 0.005-0.006 cal/cm-sec-K (2.09-2.51 Watts/m-K) for ‘dense’ zirconia from room temperature to 1400 C.  Thermal expansion is moderately-high … typically 8 to 10.5 x 10^-6/C (25-1000 C)
depending on ‘stabilization’ (described at Chemical Resistance). 

ELECTRICAL PROPERTIES

ZIRCONIUM OXIDE has electrical resistivity of 10⁷ to 10⁸ ohm-cm at room temperature, dropping to around 10²-10³ ohm-cm at 1000 C – thus has moderate high-temperature electrical conductivity.  Zirconium Oxide absorbs microwaves and readily heats when exposed to microwave energy.

CHEMICAL RESISTANCE

ZYP ZIRCONIUM OXIDE paints are very chemically resistant -- offered as
                        * Partially-Stabilized – which has 4 wt.% Calcium Oxide (Calcia)  incorporated into the crystal structure to move it mostly towards the “cubic” phase in preference to the “monoclinic” phase.  This Calcia also helps out the thermodynamic stability of the oxide somewhat, making the Partially-Stabilized Zirconia better for some situations … melting steel, precious metals, etc.  The Partially-Stabilized Zirconia is utilized in coatings with the designation “ZO” as well as the Z-Aerosol. 
                        * Unstabilized – which is “natural” zirconium oxide that does not contain any added ‘stabilizer’ for making the crystal-structure ‘cubic’, which gives more-linear thermal expansion.  It is the “monoclinic” phase.  For most industrial applications, the Unstabilized version is fine.  The thermal expansion and variations of the expansion of the oxide in a PAINT does not lead to spallation/flaking etc.  Zircwash is a typical paint that uses “Unstabilized” zirconia.

NOTE:  All ZYP ZIRCONIUM OXIDE (ZIRCONIA) products are NOT ZIRCON (which is Zirconium Silicate).  This confuses some people, since the names are so similar.   The ZIRCON/Zirconium-Silicate compound is not as chemically stable as ZIRCONIUM OXIDE/Zirconia: the ZIRCON can lead to significant silicon contamination in melting operations.  ZIRCONIUM OXIDE has high stability with molten metals, only being surpassed by YTTRIUM OXIDE due to its thermodynamic stability.

OTHER PROPERTIES OF INTEREST

ZYP ZIRCONIUM OXIDE paints are often used when melting alloys that have reactive-metal constituents such as titanium, hafnium, etc. See our Compatibility Guide for more information. Also, the stabilized zirconia paints are excellent for melting platinum and its alloys. Additionally, they are all right to use with copper alloys [although ‘wetting’].