Lubricant pyrolysis during sintering of powder metallurgy compacts

The chemistry surrounding the pyrolysis of N,N′-ethylenebisstearimide (EBS) compacted with iron powder is described for the first time. Heat treatment is carried out in a 5 vol pct hydrogen atmosphere (balance nitrogen) over the 100 °C to 850 °C range. The exhaust from the furnace is monitored by Fourier transform infrared and dispersive ultraviolet absorption spectroscopy; condensable materials are analyzed by gas chromatography/mass spectrometry (GC/MS). A wide range of analytes emitted from the preceding process were characterized. The aliphatic CH stretch in the 3000 to 2700 cm−1 range and the asymmetric CO stretch in gaseous CO2 at 2350 cm−1 are excellent indicators of the extent of delubrication. A bimodal CO emission phase is observed in the temperature window between delubrication and sintering. Three major large molecule reaction products, along with five minor compounds, are identified by GC/MS. A preliminary reaction mechanism is inferred based on product analysis and known organic chemistry. It appears that hydrolysis of EBS competes with γ-H abstraction yielding an N-vinyl amide and stearamide, which undergoes further reaction. Hydrolysis affords stearic acid, which decarboxylates to heptadecane, and 2-heptadecyl-4,5-dihydroimidazole via ring closure of the corresponding amino-amide.