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During recent yea rs a co nsid erable nurnber of t heo retical a nd exp erimental stud ies have been published o n t he kin etics and mechanism of t he t hermal d eco mposition of poly mers. The tr eatment of depo. lymerization as a free-rad ical chain reaction involv ing t he four basic steps of initiation, p ropagat…
Abstract Melt viscosities of styrene homopolymers and copolymers with 1.5 to 23 mole‐% methacrylic acid were measured with a parallel plate plastometer. Apparent viscosities were found to drop off sharply with increasing rate of shear in the range 10 −4 to 10 −1 sec. −1 . An increasing concentration of carboxyl groups…
Abstract Silicon nitride has been prepared by heating pure silicon in purified nitrogen at 1450°. X ‐ray studies showed the presence of two nitrides, and a method was therefore devised to separate them. Although these nitrides differ in their crystal structure, they have the same compositions, corresponding to Si3N4.…
The crystal structure of the low-temperature form of sodium triphosphate, Na~P3010, Phase II, has been determined by Fourier methods. The unit cell is monoelinic with [a] -----16.00, [b] ----5-24, [c] --~ II.25 A, fl --93 . The space group is C2/c and the unit cell contains 4 units of NasP3010. The triphosphate ions h…
The twist due to a screw dislocation parallel to the axis of an isotropic cylinder of arbitrary cross section can be found from the solution of the ordinary torsion problem for the same cylinder. Some particular cases are worked out. The results are also valid for certain kinds of anisotropy.
The refractive index n and the absorption coefficient k of evaporated CeO2 films were measured in the wavelength region from 0.22 μ to 1.0 μ. Films produced by direct evaporation of CeO2 were found to be extremely durable and nonabsorbing in the visible and can be used as beam splitters and as high-index films in mult…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT1,3,5-Triaryl-2-pyrazolines for Use as Scintillation SolutesRICHARD H. WILEY, C. H. JARBOE, F. N. HAYES, E. HANSBURY, J. T. NIELSEN, P. X. CALLAHAN, and M. C. SELLARSCite this: J. Org. Chem. 1958, 23, 5, 732–738Publication Date (Print):May 1, 1958Publication History Publishe…
Transmission electron micrographs of aged aluminium 4%-copper foils have shown unusual contrast near precipitated particles. This is interpreted in terms of Bragg diffraction from regions distorted by elastic coherency strains between the precipitate and the matrix.
A body armor panel consisting of twelve identical layers of 2 X 2 basket weave nylon fabric was investigated after impact by a fragment simulator .22-caliber steel missile in the range of 330-420 m. sec. (1100-1400 ft. sec.) striking velocities. The kinetic energy of the projectile was either slightly higher or lower…
The antiferromagnetic structure of Mn${\mathrm{Br}}_{2}$ (${T}_{N}=2.16\ifmmode^\circ\else\textdegree\fi{}$K) has been determined by single-crystal neutron diffraction measurements at temperatures down to 1.35\ifmmode^\circ\else\textdegree\fi{}K and with magnetic fields (0-13 kilo-oersteds) applied to the sample. The…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Electrical Conductivity of Solutions of Alkali Metals in their Molten Halides1H. R. Bronstein and M. A. BredigCite this: J. Am. Chem. Soc. 1958, 80, 9, 2077–2081Publication Date (Print):May 1, 1958Publication History Published online1 May 2002Published inissue 1 May 1958…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermal Expansion of Some Transition Metal CarbidesReed O. Elliott and Charles P. KempterCite this: J. Phys. Chem. 1958, 62, 5, 630–631Publication Date (Print):May 1, 1958Publication History Published online1 May 2002Published inissue 1 May 1958https://pubs.acs.org/doi/10.10…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA NEW CRYSTALLINE MODIFICATION OF BORONL. V. McCarty, J. S. Kasper, F. H. Horn, B. F. Decker, and A. E. NewkirkCite this: J. Am. Chem. Soc. 1958, 80, 10, 2592Publication Date (Print):May 1, 1958Publication History Published online1 May 2002Published inissue 1 May 1958https:/…
The mechanisms for bulk viscosity are different between associated and nonassociated liquids. Here, a new mechanism for bulk viscosity is proposed from the standpoint of the hole theory of liquids and the rate process theory. This mechanism can explain the temperature and pressure dependencies of acoustic absorption f…
The KBr technique to obtain spectra of cotton cellulose has been applied satisfactorily to an investigation of physical and crystalline modifications and to changes resulting from oxidation. Several experiments to illustrate applications are described. The potential applications to investigations suggested in the lite…
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In this paper, the main characteristics of the swelling, solution, and delustring of secondary cellulose acetate are elucidated. It is shown that the formation of cavities is general in acetate–solvent–nonsolvent and acetate–partial solvent systems. Studies on four other polymers are also reported. The mechanism of ca…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Lower Oxidation States of Gallium. II. The Ga2Br4-GaBr SystemJohn D. Corbett and Alex HershaftCite this: J. Am. Chem. Soc. 1958, 80, 7, 1530–1532Publication Date (Print):April 1, 1958Publication History Published online1 May 2002Published inissue 1 April 1958https://pubs…
Examination of mixtures of extremely pure silica and alumina shows that the greatest reactivity is not encountered with stoichiometric ratios to form mullite with the formula 3Al 2 O 3 . 2SiO 2 but rather with the formula 2A1 2 O 3 ‐SiO 2 , and that reactivity also depends on the crystalline modification of alumina. A…
Abstract Tensile tests have been carried out on polytetrafluoroethylene, polycaprolactam, polyvinyl chloride and polytrifluoromonochloroethylene at four temperature levels ranging from +20° to −196°C. The tensile strength of polytetrafluoroethylene increased from 1·44 × 10 3 lb./sq. in. at room temperature to 13·8 × 1…