Aluminum
Aluminum is inert in the body. In spite of this, injuries to the pulmonary system and fibrosis have been found in animals exposed to prolonged inhalation of heavy concentrations of aluminum dust. In contrast to copper and a number of other metals, aluminum does not accelerate the loss of vitamins in cooking. The aluminum intake due to cooking in aluminum utensils is insignificant. The fact that the aluminum compounds have been used for years in the therapy of peptic ulcers and gastric hyperacidity without any apparent ill effects shows that the oral toxicity of aluminum is practically negligible.
Gallium
When gallium first became available in the metallic form, it seemed to have properties not found in any other material. It is relatively inert, nontoxic, and with a melting point only slightly above room temperature and a boiling point of 2403 ºC. It was considered as a liquid sealant in high-vacuum systems, as a heat-transfer medium in high-temperature engines, such as nuclear reactors, and as a component of dental alloys.
It is somewhat paradoxical that the rather substantial uses of gallium that eventually evolved were based not on the unique physical properties of the metal but on the specific chemistry of some of its compounds. The first significant use of gallium was in the spectroscopic analysis of uranium oxide done in operations of the Atomic Energy Commission.
The application of gallium that has received the most attention is the production of semiconducting compounds. For many years, this technology was dominated by the elemental semiconductors, silicon and germanium. But in 1952, German workers reported the achievement of semiconduction in compounds between elements in group III and group V. Of these, the most important are the compounds of gallium with antimony, arsenic or phosporus. Nowadays gallium arsenide (Ga-As) is undoubtedly the most used. This compound is used in the production of several electronic parts such as diodes and transistors, made for voltage rectification, signal amplification, etc. Other gallium arsenide applications are the semiconductor "lasing" and microwave generation and also in several sensors to measure temperature, light or magnetic field.