A brief presentation of ceramic coatings

1. What is a coating?
•A layer of a substance applied onto a surface for protection or
decoration; a covering layer.
•Coatings protect a substrate from a variety of environmental
problems such as: corrosion of solder joints, moisture and
mildew, fuels and process solvents, service temperatures, and
dust, dirt and physical damage from handling.

2. CERAMIC COATINGS
There are a wide range of ceramic coatings that can be applied to metal
components in order to enhance their functional properties.
• electrically nonconductive
• abrasion resistance (greater than metals).
• capable of maintaining their integrity under severely elevated temperatures,
sometimes up to 4,500 degrees Fahrenheit.
Type of Ceramic Coatings
Some of the most popular plasma sprayed ceramic coatings include:
•Alumina-Titania based ceramics for wear, corrosion and variable texture
surfacing.
•Chrome-oxide ceramic coatings are extremely durable, ideal for seal surfaces.
•Zirconia based ceramic are un-matched as thermal barrier and heat-shield
coatings.
Aluminia based ceramics are of interest due to their thermal properties.

3. Chemical bonding
• H2Cr2O7 ·XH2O · Cr2
+3O3 in ceramic slurry is applied to the
surface to be coated.
• Fe+0 · Fe+2O in substrate metal
• Heat of 900° F oxidizes metal surface
• Cr and Fe (or other substrate metals) migrate into oxide
layer, forming spinel bond layer about 10 microns thick
• Spinel = Fe+2O·Cr2
+3O3

4. Physical Properties
Physical property Values
Hardness 1000-1850 Vickers
Bond Mechanism Chemical
Bond Strength Over 10,000 PSI
Thickness 0.002 – 0.004 Inches, typical (50 – 70
microns)
Coefficient of friction .22 - .28 Against fibre .10 - .13 Against
metal

5. Advantages of Ceramic over Teflon
• Pyrolysis of PTFE is detectable at 200 °C (392 °F), and it evolves
several fluorocarbon gases and a sublimate. An animal study conducted in
1955 concluded that it is unlikely that these products would be generated
in amounts significant to health at temperatures below 250 °C (482 °F)
• At high temp of around 2700C, the bonds break and
release perflurooctanic acid (PFOA) which is identified as a possible
carcinogen by EPA .
• Ceramic may also be longer-lasting than PTFE, which has a lower threshold
for heat-based decay (pyrolysis).
• Ceramics can resist temperatures upto 14000C as opposed to teflon which
is around 2700C.

6. Durablity and Cost considerations
• Chemically bonded
• Extreme wear resistance
• Resistant to thermal cycling/shock
• Ultra fine grain size
• Surface finish adjustable from 5 - 60 Rms
• Applied to inside diameters and outside diameters
• Low friction
• Absolutely dense, pore free, corrosion barriers
• Delivered via water based slurries that can be applied like paint to complicated
geometries and internal bores
• Low friction; the coated surface is anti-fouling and yarn friendly.
• The given dimensions of the roller fit inside commercially available kilns.

7. Examples of Coated Parts
• Petroleum – wire line, FMT, MWD unit components
(pulsars), mud motors
• Pumps – plungers, cylinder liners
• Plastic Extrusion – screws, barrels
• Textiles – precision gear pumps, fiber guides, godet
rolls
• Glass – fluorescent tubing mandrels