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CERAMICS (NON-OXIDE (ALUMINIUM NITRIDE(AlN) ImageForArticle_4463(2)…

- - - - aluminum
      - nitrogen
    - - High thermal conductivity* (70-180 Wm-1K-1)
      - High electrical resistivity
      - Resistance to corrosion and erosion
      - Excellent thermal shock resistance
      - Chemically stable up to 980°C in H2 and CO2 atmospheres, and in air up to 1380°C
      - Uniform microstructure
      - Thermal expansion coefficient close to that of Silicon
    - - opto-electronic
      - dielectric layers in optical storage media
      - electronic substrates, chip carriers where high thermal conductivity is essential
      - military applications
    - - DIRECT NITRIDATION
        
        precursor (aluminium powder)
        
        synthesis
        (self-sustaining instantaneous reaction of Al in N2 atmosphere)
        
        fragile and porous reacted lumps
        
        crushing,milling and classification
        
        AlN powder
        
        ADVANTAGES
        
        energy efficiency
        
        environmental friendly
        
        DISADVANTAGES
        
        requires milling
        
        introduced impurities
      - CARBOTHERMAL REDUCTION AND NITRIDATION
        
        precursor (alumina+carbon black)
        
        Heat treated to 1,400°C–1,800°C in N2 atmosphere in a high temperature furnace
        
        AlN powder + unreacted carbon
        
        Calcination to burn off excessive carbon
        
        May require milling
        
        AlN powder
        
        ADVANTAGES
        
        higher quality of final particle size and
        purity levels of CRN powders
        
        less milling required
        
        DISADVANTAGES
        
        energy intensive
        
        carbon footprint and environmental impact
- - - - High thermal insulation (1.5 W/mK)
      - Low Young’s modulus (17 to 20 GPa)
      - Very low thermal expansion (<1x10-6K-1 between 20 and 600°C)
      - Good chemical resistance
      - Excellent thermal shock resistance
        (0 – 1,000°C)
      - Poor wettability with molten metals
    - - automotive industry
        
        insulating liner for exhaust manifolds where there is a need to minimise heat loss in advance of a turbocharger
      - foundary industry
        
        Crucibles
        
        Launders
        
        Pouring spouts
        
        Ladles
        
        Riser tubes
    - - aluminium
      - titanium
    - - combustion synthesis
        
        using the corresponding metal precursors-urea mixtures, at low temperature and short reaction times