Making Small Iron Spheres by Melting Iron Powder*
R. STOVER AND J. W. TRISCHKA
Department of Physics, Syracuse University, Syracuse 10, New York
(Received March 27, 1962)
IN order to make a small number (~20) of Fe spheres approximately 0.003 in. in diameter we tried a method recommended in The Chemical Formulary for AI, Ag, and Cu. [1] According to this method 40-100 mesh metal powder is to be mixed with 325 mesh CaO and the whole heated above the melting point of the metal in a H2 atmosphere. The molten metal forms into spherical drops which are prevented from fusing together by the CaO matrix. We followed this procedure by placing a mixture of 100 mesh Fe powder and powdered CaO in a hole bored in a graphite rod. An induction furnace, through which H2 gas flowed, was used to obtain the required temperature. Unfortunately the spheres so obtained were very imperfect, being flattened or otherwise distorted, because of the caking of the CaO. Evidently small amounts of moisture in CaO cause it to cake at high temperatures. We know of no simple way to remove the moisture. To avoid the problem of getting very dry CaO we tried instead powdered Al2O3 (ignited powder) and found this gave satisfactory results. Not all, but most spheres were free from surface imperfections, which we could detect with a microscope if they were 0.2% of the diameter. Microscope measurement of sphere diameters showed no variations within the accuracy of our measurements, about one percent. The above method is, of course, useful only if a small number of spheres of a certain approximate size are needed. Although the spheres which we made had diameters mostly in the range from 0.0025 to 0.0045 in., we readily found enough of them which were approximately 0.003 in. in diameter.
* This work was supported in part by the Office of Scientific Research. 1 H. Bennett, Editor, The Chemical Formulary (Chemical Publishing Company, Inc., New York, 1948), Vol. VIII, p. 252.