Hot Surface Igniters. PRESENTED BY:. Joe Barker. Brent Blume. Sam Alauddin. This is an example of the series of igniters developed by the Norton Corporation which incorporates an alumina base with a recrystallized silicon carbide heating element. Ceramic Materials in the Igniter SiC
This is an example of the series of igniters developed by the Norton Corporation which incorporates an alumina base with a recrystallized silicon carbide heating element.
Silicon Carbide (SiC) is a common non-oxide ceramic heating element material.
The ceramic crystal is not cubic (zinc blende) but hexagonal (Hemi-hedral class).
SiC is known as a wide bandgap semiconductor
Existing in many different polytypes. The difference between polytypes is the stacking order between succeeding double layers of carbon and silicon atoms. This affects all electronic &optical properties of the crystal.
All polytypes are extremely hard (brittle), very inert, and possess high thermal conductivity.
Norton CRYSTAR Black Silicon Carbide
Silicon carbide has exceptional thermal and electrical properties making it advantageous to use at varying voltage settings and high temperatures.
Thermal Conductivity (W/m oC)
(x 10-6/oC) (RT to 1000oC)
Electrical Resistivity(ohm cm) @ RT
@ 1000 oC
Why is SiC preferred over other materials?
Modern industrial fabrication of SiC is done via Epitaxial CVD.
CVD, also known as Chemical Vapor Deposition, consists of growing pure crystals from a substrate.
In the case of SiC, a graphite substrate is generally used.
In order to obtain the crystals, raw SiC (from silica sand and coke) is sublimated in a graphite chamber in a high temperature environment ( 1600 – 1800 C).
The resulting gaseous phase, then cools and deposits on the substrate, leaving highly pure crystals.
From this point, the SiC is now ready to be processed for engineering applications
From here powder is obtained and sized in order to hot press. Hot pressing allows the ceramic to be sintered and densified simultaneously.
The igniter must be pressed into the near final shape due to material hardness. Finally the piece is machined for assembly.
Electrical wire leads are soldered to the ends, then it is partially encased in Alumina for insulation.
It is essential that process variables (temperature, pressure, cooling rate) be controlled to maintain purity, low porosity, etc…….this leads to desired thermal and electrical properties.
The cost of a single heating element from the Norton Corporation for a Model 201n is roughly 60$ - 80$. The estimated production cost is in the range of 30$ - 40$ per piece.
The cost could be lowered if a different processing technique other than hot pressing was chosen, but the quality of the part would drastically decrease.