 Beryllium oxide is useful for many applications that require the combined properties of an electrical insulator and an excellent heat conductor , with high strength and hardness , and a very high melting point . Beryllium oxide is frequently used as an insulator base plate in high @-@ power transistors in radio frequency transmitters for telecommunications . Beryllium oxide is also being studied for use in increasing the thermal conductivity of uranium dioxide nuclear fuel pellets . Beryllium compounds were used in fluorescent lighting tubes , but this use was discontinued because of the disease berylliosis which developed in the workers who were making the tubes . 
