Is voluntary slavery Islamic?

As you know, in Islam sexual relations are allowed between spouses and possessions of the right hand, with the latter being gained from war. Is it halal for a women to voluntarily submit as a slave to a man? In this hypothetical situation a proper contract would be put in place, no coercion would take place, the potential slave would be of sound mind and treated with respect. I haven't found anything in my research to indicate that this isn't Islamic. Thoughts?