Chemical
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SYLVANIA GENERAL TELEPHONE & ELECTRONICS
Fantastically soluble W. We've got a chemical called am monium metatungstate which has too long been overshadowed by its less costly brother, ammonium paratungstate. At room temperature, meta is about 70 times as soluble as para: 8.8 pounds of meta dissolve in a gal lon of water compared to .12 pounds of para. You can stuff so much am monium metatungstate into water that the solution gets viscous. Formula: (NH4)(iH2W12O40-xH2O Fortunately, the structure of the metatungstate ion doesn't depend on the number of water molecules in the complex, χ could be as high as 8, but we keep our powder dry by keeping χ down between 3 and 4. If we took out more water, compounds that don't dissolve might form. (We've mentioned the eccentric habits of transition metal complexes in the past.)
range it gets rid of all its attached water. Then it starts to blow off am monia plus combined water and dries out above 500C to tungstic oxide, W 0 3 . This process represents a great way to get catalytic tungsten into your substrates. (And a very poor way to derive ammonia. What to do with it? Well, you could start a factory to produce the world's most expensive fertilizer. ) Ammonium metatungstate is ter rific on impurities : it has practically none. It will give you alkali-free so lutions containing up to 50% by weight of W 0 3 . You end up with a pristine catalyst that's good for all kinds of reactions such as hydrogénation, hydroxylation, polymerization, oxidation. Meta costs 20-25% more than para. Even though we sell tons and tons of para, we suggest that it might be worth the extra dough to use meta and save the time and trouble of fooling around with a far less soluble source of tungsten. Samples on request to the qualified. (You qualify if you're not just adding to your chem kit. ) If you tell us about your potential use, we may give you something even more valuable than the sample. Like good advice.
Phosphor for a faster X-ray.
TEMPERATURE (°C)
If you'll look at the thermogravimetric analysis of meta, you can follow the exciting career of this heavy, white, granular powder as it gets hot. Notice it keeps steaming from about 100C on till in the 300C
You may be surprised to know that photographic film is not very sensitive to X-rays. So the film is placed in contact with a phosphor which glows when X-rays hit it. The film really takes a picture of the light given off by the phosphor. When used this way, the phosphor and what it's spread on are called an image intensifying screen. The first X-ray photographers around the turn of the century were
lucky enough to immediately hit upon a screen that would do the job well. The phosphor was natural scheelite, calcium tungstate ( C a W 0 4 ) , and it's still being used. But now we've found something even better : barium phosphate activated by a suitable dose of europium— Ba3(P04)2:Eu. Behold the graph. You can see how the barium phosphate gives the film a bigger kick of light. It hits the film right where it's most sensitive, at the 415nm peak in the deep blue-violet. This phosphor boosts the speed of diagnostic X-ray film 100%. It's now possible to take X-ray pictures of moving parts of the body such as the heart without blurring the image. And there's much less exposure of patients to radiation. Next time you need an X-ray, think of us Sylvanians toiling away at our phosphors and rare earths to give you this very healthy development. Better still—think of us next time you need a phosphor.
-X-RAY FILM RESPONSE
CALCIUM , TUNGSTATE EMISSION
BARIUM PHOSPHATE EMISSION
AVELENGTH(NM)
The barium phosphor lights up where the X-ray film is most sensitive. Calcium tungstate*s output isn't used efficiently, because the sensitivity of the film drops off at the longer wavelengths.
We're always glad to talk to you about tungsten, molybdenum and phosphor chemistry. Sylvania Precision Materials, Chemical and Metallurgical Division, Towanda, Pa. 18848 2
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