ustrial
pplications
MOLYBDENUM CHEMISTRY The symposium on industrial applications of molybdenum chemistry was a presentation of the Division of Industrial and Engineering Chemistry a t the 127th Meeting, American Chemical Society, Cincinnati, Ohio. CATALYSTS
ORGANIC PIGMENTS
...... W. G. Huckle and E. Lalor . . . . . . . . . 1501 Donald Price . . . . . . . . . . . . . . . J. Z. Briggs . . . . . . . . . . . . . . . . . . . . . . . . . . . 1513 Benjamin
H. Danziger
...........
1495
INORGANIC PIGMENTS
W. W. Williams and J. W. Conley
1507
METAL COATINGS
151 1
ALLOYS F O R THE CHEMICAL PROCESS INDUSTRIES
"Molybdenum in Agriculture," by E. R. Purvis, is published in the August 1955 issue of Agriculfurol and Food Chemistry
Downward view into large striking tank just after pigment has been precipitated [the colors used here and on page 1493 are shades of molybdenum orange)
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 8
T H I S i s the first symposium involving the chemistry o f molybdenum. Molybdenum has belonged almost exclusively to the metallurgists. It still does in spite of a chemical history extending back nearly t w o centuries to Scheele’s discovery in 1778. Berzelius devoted a great d e a l o f his effort a n d talent t o investigating the chemistry o f molybdenum, a n d his “Lehrbuch der Chemie,” published in 1826, contains a substantial section devoted to researches on the subject, both o f his own a n d o f others. Even several decades before that, Lavoisier h a d suggested new names for the great number of known molybdenum compounds to fit them into his newly systematized chemical nomenclature. But metallurgical uses still consume most o f the world’s output of molybdenum. The best estimates place the present consumption o f molybdenum in ferrous alloys a t about 90% o f the total. A small, but important, output o f metallic molybdenum and high molybdenum alloys used principally in electrical applications accounts for another 5%. That leaves no more than 5% to cover all chemical uses. Even 5% represents a n increase in the amount of molybdenum going into chemical uses following the end o f stimulation of steel production in W o r l d W a r II. Element 42 thus suffers from comparison with COURTESY CLIMAX MOLYBDENUM CO.= the extraordinary value o f the metal in metallurgy. But the element possesses exciting posFlotation units separate molybdenum disulfide from ground rock sibilities through its remarkable chemical reactivity a n d its highly variable chemical character. Perhaps the-reason that these are not better known a n d dextrous, bisexual, a n d polygamous.” Linus Pauling in his more generally utilized i s the chaotic state o f the chemical “General Chemistry’’ (1 948) devoted only eighteen words literature o f molybdenum. The comprehensive treatisesto the chemistry o f molybdenum: “The chemistry o f molybGmelin, Abegg, Mellor, Friend-report everything pubdenum i s complicated. It forms compounds with oxidation lished about the chemistry o f the element, true and false, numbers o f +6, +5, 4-4, f3, a n d +2.” probable a n d fantastic. Pokorny published a brief monoIt is still difficult to present a satisfying picture o f the g r a p h on the chemistry o f molybdenum in 1927, but a t that whole chemistry o f molybdenum. It is our hope that this time the development o f molybdenum pigments h a d not yet very inadequacy will spur chemists everywhere to seek solubecome important. The late beloved Edgar Fahs Smith was tions to the many problems that remain to b e solved. fond o f describing molybdenum to his classes as “ambiARTHUR LINZ, Chairman
the element possesses exciting possibilities
B
AFFLIKG chemical puzzles characterize molybdenum, because it has several highly variable properties and because much of the research t o determine its characteristics was done in the early days of chemistry. Scheele, Lavoisier, and Berzelius, all names t o conjure with even while these men lived, conducted early studies of molybdenum compounds and published much about them. STow we realize more than ever before that it was impossible for the buret-and-balance methods used by these eminent chemists and by others for more than a century after them t o resolve the chemical problems of molybdenum. It is not surprising that the literature of molybdenum chemistry should be filled with uncertainties and that many of the important problems of molybdenum behavior should remain unsolved; it was practically impossible even t o define the problems exactly by the means available t o the older chemists. Modern chemists readily discern complexities in molybdenum chemistry and contradictions in the record that were not apparent August 1955
t o the original investigators. Even today many of these anomalies and uncertainties remain unsolved, and furthermore some cannot even be stated clearly as problems that can be Bolved! The variable valence of molybdenum is its basic complexity. This is particularly confusing because t h e observed valences are different for compounds with different elements and because there are gaps in each series. For instance, compounds are known in which the valence or oxidation state of the molybdenum atoms assumes each of the values in the series, + 2 , +3, +4, +5, and +6, and in which the atoms have coordination numbers of 4, 6, and 8, hut in no series of related compounds are all these values represented. I n addition to these normal states, molybdenum assumes a nonvalent, zero state in the hexacarbonyl, Mo(C0)G. Disproportionation commonly occurs t o transform compounds of molybdenum of a single valence t o mixtures containing several valence states; coordination numberschange readily under slightly modified conditions. Molybdate ions in solution readily aggregate
INDUSTRIAL AND ENGINEERING CHEMISTRY
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