Nano-diamond lifetimes (left panel) as a function of radius and temperature: 1000, 1500, 1750, 2000, 2100, and 2350 K shown by red, orange, pink, yellow, violet, and blue, respectively. The solid lines correspond to sublimating nano-diamonds and the dashed lines to sublimating nano-diamonds transformed into graphite. The right panel shows a zoomed-in view and also indicates the de-hydrogenation timescales (dashed grey lines) at nano-diamond temperatures T_nd = 1100, 1200, 1300, 1400, and 1500 K. The light blue lines show the re-hydrogenation timescale for a gas density n_H = 10⁶ cm⁻³ at temperatures T_gas = 200, 400, 600, 800, and 1000 K (upper to lower).