Tungsten wires were used as templates for the deposition of tubes of micro-crystalline diamond or of 'spongy' carbon nanostructures. A hot-filament chemical vapor deposition system fed with highly diluted ethanol in hydrogen and argon was used. Argon was intentionally added to the feed at different concentrations to affect the crystalline growth. As the argon concentration was increased beyond 65 vol.% in the reactor feed, the morphology drastically changed from micro-crystalline diamond to complex carbon nano-structures. While the samples produced at argon concentrations of 65 vol.% or less resulted in a radial columnar structure of micro-crystalline diamond, the samples produced at higher argon concentrations showed radial flaws and 'spongy' structures. Each type of morphology is of potential interest for the use of these tubes as molecular filters or in electron emission devices.