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SILICONES CERIUM SUPERSILICONES
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1 ! Those remarkable polymers we g ι know as silicones and use as £ | hydraulic fluids, lubricants, seal5 I ants, elastomers and water repel,E î lent resins, owe their thermal Î2I I stability to their backbones — THE LOOK OF TOMORROW through LANTHANIDE CHEMISTRY ' g l s i l o x a n e chains (-O-Si-O-Si-O-) ^ optical lenses, and as a constit It 1 more resistant to scission than ua uent in tinted glass filters for j | I carbon chains (-C-C-C-). a selective light absorption. L·--. g I However, there's an Achilles - 5 CIRCLE 40 ON READER SERVICE CARD «f | heel to be considered — degrada• | ! tion of organic substituents on I SWAPPING TRANSITION jg | the siloxane backbone. Such degS METALS FOR LANTHANIDES α î radation means, for example, cross linking(hardenΕ in polymerization catalysis ;!§ϊ ?} unwanted ing or thickening) or the evolu100 5 New developmental catalysts for ; g | tion of volatiles which raise flash " r S~"~ S olefin polymerization —in which g | points (less fire resistance). Z i 0 4 / "~ Pr TILE y ^ Ê neodymium salts replace transi- g I That's where the protective GLAZE / =j tion metal compounds such as \ · | one-electron redox virture of the \^ OTHER g TiCl:{ within Ziegler-Natta type ;a S lanthanide, cerium, can help. It / / / YELLOWS α systems — have produced stereo- jg Jean mop up reactive free radiL g regular elastomers with ex- j S | cals by temporarily changing its g tremely high cis-contents (above ÎE î spots —from Ce(lV) to Cedll) and ' " "™ " .™ 3 98% in certain polybutadienes). ! 2 | b a c k . 400
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S ! The secret lies in both: (1) the Ce 3 + +R H I Ce 4+ + R COLOR ME YELLOW "^ large coordination spheres around vrïth 2 lanthanideatomslikeneodymium, with vrawadvwiu™ praseodymium with praseodymium Ε J with low steric restrictions on bond Ask your interior designer. Yel The trick is to incorporate the orientations (i.e. larger template low is a favored color for glazed cerium into the silicone. There \ surfaces on which reactions can tile in kitchen and bath. And are several methods. Some in take place), and (2) the relathe preferred ceramic pigment volve the treatment of silica fill the preferred ceramic pigment 3 tive strengths of Ln-C and Ln-H — not only for pure yellow ers; some use metallo-organic — for pure yellow g ι — 1 but not for only blending to produce additions like the octoates; some but for greens blending to produce browns, and oranges — is a | i — Nd(0R)3/A5alkyls + nC4H6 |—ι use a partial pre-oxidation step a Pr-doped zirconium silicate. and posit the formation of a CH CH -Ce-O-Si- bond. Why praseodymium? CH CH But the result is the same — a No other glaze yellow is as good thing made better. l±L bright and clean, without grayCIRCLE 42 ON READER SERVICE CARD ness. Note its reflectance curve, 2 j bonds, comparable to those for j g compared to other ceramic yel § ! the early transition metals. 13 THE LANTHANIDE MINERAL lows. Further, none so well with a ^ IE is bastnasite, 12% of the ore we stands the high processing tem Ξ Γ Italian, Chinese, American and f Dmine at Mtn. Pass, California peratures needed to convert the g à German workers have published | g (supplying over half of free world need). It contains all nine glazing slip into a glassy coat. a ί studies of such lanthanide-based J g of the principal lanthanides, in The Pr ion is trapped at around Ê | catalysts, filed patents, or actu- j g proportions much as in the 5% in the zircon lattice. In that α I ally announced pilot plants for j g exploding pie chart at the left. Forty million tons of ore are lattice it exists, not as Pr(lll), S I cost-saving butadiene rubber | 2 in the deposit — ample for S Γ production. S S the typical trivalent lanthanide, decades to come. L-± | Ε but as Pr(IV) — usually deemed • | Want the references? highly reactive, but here held a l CIRCLE 41 ON READER SERVICE CARD I 2 and tamed within a host crystal. As the oxide Pr 6 On — in which Pr(IH) and Pr(IV) are both pres M O U N T A I N PASS, CALIFORNIA ent — praseodymium has other É | MOLYCORP, INC., 709 Westchester Avenue uses, e.g. as the vacuum-depos α | White Plains, New York 10604 ited antireflective coating on • I Tel. 914/997-8880 · TWX 710/568-0305 2
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