Ineed to construct a device that minimizes heat transfer so that i can keep an ice cube anew ice cube for a long period of time. idk what to do

You could put an ice cube into a zip-lock bag and then put that into a bucket of ice that has about 15°F and the ice cube shouldn't melt. Hopefully this helps.

You'll need some sort of thermal insulator like plastic or wood and it should have as much pressure in it as you can manage because that will make the melting point lower.
You could use a material like the one used in emergency blankets to insulate a plastic box, you could also put another box in that box to further insulate it.

Hope this helps :)