Observations on the Shape of Chromium Oxide Particles in Hydrogen + Oxygen + Nitrogen Pre-mixed and Diffusion Flames

Abstract

CERTAIN metals, when introduced into pre-mixed, hydrogen + oxygen + nitrogen flames (T ∼ 2,000° K) burning above a Meker type burner, give a whitish, streaky appearance to the flame¹. Such streaks appear, for example, when chromium, vanadium, titanium, cobalt, nickel or iron (to mention but a few) are introduced in the form of fine sprays of dilute salt solutions. These streaks almost certainly originate from chemiluminescent reactions involving H and/or OH radicals on the surfaces of particles of involatile oxides¹, and their visible appearance alone clearly indicates that the particles consist of many molecular units. Light scattering and electron microscopy studies^2,3 have shown similar particles to have sizes in the range 0.005–25µ.