... Science Frontiers ONLINE No. 71: Sep-Oct 1990 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Novel Forms Of Matter Clusters . What is the difference between "vanilla" and "chocolate" niobium? To begin with, these two forms of niobium are neither single atoms nor crystalline arrays of atoms. Both "flavors" of niobium consist of 19 niobium atoms (Nb19+ ), but the atoms are clustered differently, as illustrated. The different clusters react quite differently chemically. The "chocolate" niobium, on the right, is a capped icosahedron and reacts readily with hydrogen. The "vanilla" double pyramid (left) has flatter surfaces and does not readily combine with hydrogen. Cluster research is embryonic, with new surprises popping up almost every day. Once a cluster size exceeds a few hundred atoms, its properties begin to resemble those of the bulk material. However, "cluster-assembled materials" have been made by attaching clusterto-cluster in a sort of patchwork quilt. Such materials have unique properties that are quite different from those of the normal crystalline and amorphous materials. (Pool, Robert; "Clusters: Strange Morsels of Matter," Science, 248:1186, 1990.) Comment. One would expect that the effects of clustering would be important in biology, too. We obviously have a lot to learn about this new realm between single atoms/molecules and bulk materials. Quasicrystals . Quasicrystals, once considered physically impossible, have been found easy to grow -- once one' ...
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... Science Frontiers ONLINE No. 15: Spring 1981 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Those Darn Quarks There's no escaping it, those fractionally charged niobium balls just can't be swept under the rug. In fact, more recent experiments have served only to accentuate the anomaly. Researchers at Stanford University have been magnetically suspending superconducting niobium spheres in a modern version of Millikan's oil-drop experiment. With the niobium spheres thus suspended, their net electrical charges can be measured. The trouble is that several of the spheres have fractional electrical charges -- + 1/3 or -1 /3 electronic charges. For decades the charge on the electron was supposed to be the basic, indivisible natural unit of electrical charge. In 1964, however, theorists began muddying the waters with talk of new fundamental constituents of matter called quarks, which could possess 1/3 or 2/3 electron charges. No one really expected that quarks, if they existed at all, would be floating around free. But the niobium balls tell us that not only are quarks free but that we could have detected them with relatively simple experiments decades ago if we had not been so blinded by the idea of integral electronic charges. (Robinson, Arthur L.; "Evidence for Free Quarks Won't Go Away," Science, 211:1028, 1981.) From Science Frontiers #15, Spring 1981 . 1981-2000 William R. Corliss ...
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