The role of chemical activation on the combustion and phase formation laws in the Ni–Al-promoter system

In this work we first time investigate the reaction mechanism and possibility of synthesizing NiAl intermetallic compound under the activated combustion mode. A halogen containing organic polymer, namely, polytetrafluoroethylene – PTFE is used as promoter. It is shown that the single-phase target product is obtained when amount of the promoter is 0.1%. Differential thermal (DTA), thermogravimetric (TG) and XRD analyses testify that reaction proceeds stepwise. It is shown that in first stage decomposition products of PTFE remove the oxide film from Al particles; then follows reaction between Ni and pure Al. This reaction undergoes two different modes. First the solid-state reaction takes place, then Al melts and reaction continues between solid Ni and molten Al. It is established that the increase in the promoter amount higher than 1% shifts kinetic activation mode to thermal-kinetic mode. The latter leads to misbalance of green mixture and formation of undesired by-products. The optimal conditions of chemically activated synthesis for NiAl intermetallic are established.

► It is shown that the reaction between Ni and Al undergoes non-stable combustion mode.
► The non-stable mode caused by oxide layer existing on Al particles’ surface.
► Using 0.1% polytetrafluoroethylene (PTFE) allows to perform stable combustion.
► Firstly PTFE removes the oxide film from Al particles; then follows Ni–Al reaction.
► Initially solid state reaction occurs then follows Ni–molten Al reaction.