A study of the kogation/etching behavior of thermal ink-jet thin-film heater devices passivated by a plasma-deposited amorphous hydrogenated silicon carbide (α-SiC:H) layer shows that some of the chemicals found in inks suffer thermal decomposition during device operation and deposit the decomposition products onto the heaters (kogation), others are responsible for etching of the heater passivation layer, and some are responsible for both kogation and etching. Those chemicals responsible for kogation include amines, both aliphatic and aromatic (i.e., aniline), and their alkylated homologues. Etching is primarily due to either high pH (HO−) or radicals (i.e., HO•). Kogation is theorized to arise from several thermally activated sources. Chemicals at concentrations of 0.1% or lower can be the major source of the kogation or etching. © 1991, American Chemical Society. All rights reserved.