What are you feeding them? What do they look like before they die? Finally, what type of substrate do you have? Is it possible it is too harsh for their barbels?
Even very unsuitable gravel is unlikely to cause death in such a short space of time. I would imagine the fish would die from infection due to barbel wear and not simply because the barbels are damaged, which would take longer than the short space of time in which these fish were in the tank.