Both gases are usefull, it is only important the oxygen content.  Required purity of process gases 99,999% or better (Ar-5.0 or H2-5.0). The low oxygen content of the gas must be due to oxidation of aluminum.

My company has worked closely with AVIC Beijing Institute of Aeronautical Materials establishing their capabililty with alumunizing.  Contact Limin He, PhD at [email protected]

Thanks for your kind answer.

Is Ar or H2 atmosphere also help with the halide gas flowing to produce uniformly product?

If yes, Is there a general flow rate I can use?

Ammonium chloride (NH4Cl) serves to transfer of aluminium through the gas phase. The amount of transferred aluminium (coating thickness per unit time) is depended from this flow of NH4Cl-gas. Argon or hydrogen replace the part of ammonium chloride and reduces the concentration of active chlorine atoms into volume of the furnace.

The greater is the content of inert gas (Ar or H2 ) and less the content of active gas (NH4Cl) into gas mixture, the more uniform and slower the aluminization. To achieve optimum speed process with good quality requires a number of experiments with different ratios of gases in the mixture (empirically optimizing of gas composition).

In my case, I'm using a vapor phase facility which is showed in the schematic.

Donor(preferably FeAl), activator(NH4Cl) and Specimens are put into a box which is surrounded by flowing Ar atmosphere in the chamber. Ar gas is transformed through the inlet pipe on top of the furnace to bottom of the chamber, and will flow upward due to heat. Finally the exhaust gas is pumped out through the outlet.Pressure is controlled in 0.08 atm.

Because all the powders have been set before the aluminzing process, so the control of NH4Cl flow rate is impossible and I can only control the inert gas flow. I will try without the control of NH4Cl, if I fail, I will further change it so I can control both inert gas flow and NH4Cl flow.

Thanks again.

Kind Regards