Delores Spanioe, age 12, of Portland, Ore., for her question:
What is Hafnium?
Scandium, yttrium and titanium, zirconium, hafnium and vanadium are the names of six, steely gray metallic elements. None of them was known to the alchemists of the midd1e ages, and hafnium, the last of them, was discovered only 40 years ago.
One of the most exciting events of the age of science is sorting the chemical elements and placing them on the periodic table. This neat chart is formed from interlocking rows and columns of squares. Each square is a slot for the basic information on one of the chemical elements from which the universe is made. It carries the symbol of the element: c for carbon, 0 for oxygen. It carries the atomic number of the element: 6 for carbon, 8 for oxygen. It carries also the atomic weight of the element, which as a rule is not a whole number.
The up to date periodic tab1e charts 103 elements, all the elements that science so far has discovered. The splendid system was designed long ago, and newly discovered elements were added through the years. There are squares for elements that will, we hope, be discovered in the future. At present, the atomic numbers run from 1, for hydrogen, to element number 103. But for a long time there was no known element to fill slot 72.
The chemists, however, know that the unknown element would have 72 protons in a nucleus orbited by 72 electrons. By nature it would resemb1e the known elements yttrium and titanium, scandium, vanadium and zirconium. It would belong in this family of steely gray, flaky metals. In 1923 the elusive element was found at last, by accident. Two scientists were examining zirconium minerals by x ray, and atoms of number 72 were found mixed with atoms of zirconium, which has an atomic number of 40.
The latin name for Copenhagen, where the discovery was made, was Hafnia. The newly found eiment 72 was named hafnium. Less than 1000th part of 1% of the earth's crust is made of this rare element, and it is very difficult to distinguish it from zirconium. It is a valuable metal of the atomic age because it has a thirsty appetite for neutrons, those speeding particles that keep the chain reaction going in a nuclear reactor. Rods of hafnium are used to quench the fury of an atomic pile and prevent it from seething out of control.
Hafnium is both rare and expensive to come by, and its chores in the modern world must be limited. Aside from nuclear control rods it has been used in radio and tubes, in incandescent lights and x ray tubes. If it were more plentiful it could be used to make sturdy alloys with many metals, including copper and nickel, silver and chromium.