text: Pack cementation is a widely used CVD technique that consists of immersing the components to be coated in a metal powder mixture and ammonium halide activators and sealing them in a retort. The entire apparatus is placed inside a furnace and heated in a protective atmosphere to a lower than normal temperature that allows diffusion, due to the halide salts chemical reaction that causes a eutectic bond between the two metals. The surface alloy that is formed due to thermal-diffused ion migration has a metallurgical bond to the substrate and an intermetallic layer found in the gamma layer of the surface alloys.
  The traditional pack consists of four components at temperatures below (750 °C): 
  * Substrate or parts
  * Ferrous and non-ferrous powdered alloy: (Ti and/or Al, Si and/or Zn, B and/ or Cr)
  * Halide salt activator: Ammonium halide salts 
  * Relatively inert filler powder (Al2O3, SiO2, or SiC)
  This process includes:
  * Aluminizing
  * Chromizing
  * Siliconizing
  * Sherardizing
  * Boronizing
  * Titaniumizing
  Pack cementation has reemerged when combined with other chemical processes to lower the temperatures of metal combinations and give intermetallic properties to different alloy combinations for surface treatments.