Facile preparation of BN coatings on graphite substrates and their binding strength

To decrease the curing temperature and achieve excellent binding strength of BN coatings on graphite substrates, a proper Al(H₂PO₄)₃ binder has been carefully designed where MgAl₂O₄ and poly vinyl alcohol (PVA) were used as the curing agent and the dispersant, respectively. XRD, SEM, TEM and DSC showed that the desired binding phase AlPO₄ had been successfully obtained, where MgAl₂O₄ and PVA worked synergistically to lower the curing temperature down to 70–100 °C and promote the formation of AlPO₄. Such optimized binder might have formed hydrogen bond with –NH₂ and –OH groups on the BN flakes. It might also form hydrogen bond with-OH and –COOH groups on graphite substrates to ensure an optimal binding strength of 5.5 N (∼22 MPa) as suggested by the scratch tests. This work affords a better understanding on the curing chemistry of Al(H₂PO₄)₃ and the binding mechanism between BN flakes, AlPO₄ binding phases and graphite substrates.