Structural Studies of the Vulcanization of Rubber under Stretch

1940 ◽  
Vol 13 (2) ◽  
pp. 243-248
Author(s):  
E. A. Hauser ◽  
I. N. Smith
Keyword(s):  
Point Of View ◽  
Chemical Bonds ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Satisfactory Explanation ◽  
Specific Chemical ◽  
X Ray ◽  
Vulcanized Rubber ◽  
Modern Methods ◽  
Definite Proof

Abstract Just one hundred years have passed since the changes were discovered which rubber undergoes when mixed with sulfur and heated. Although “vulcanization”, as this reaction and the changes subsequent thereto have been termed, must be considered the most important development in the rubber industry, we are still far from being in a position to offer a fully satisfactory explanation for this phenomenon. Nevertheless we have been able to improve our concept of these changes by the application of such modern methods of research as x-ray diffraction, and recent attempts to shed more light on the phenomenon from a strictly chemical point of view also have been successful. The outstanding results of the latter work are the definite proof that the changes in physical properties, which become noticeable during vulcanization, show no correlation with the amount of combined sulfur or with the total loss in unsaturation. The experiments offered no direct experimental evidence as to the existence of specific chemical bonds or linkages in vulcanized rubber. However, it could be definitely ascertained that chemical reactions involving the double bonds of the hydrocarbon and its combination with the vulcanizing agent, in one way or another, are necessary to produce a vulcanized structure responsible for the observed changes in properties.

The structure of bacterial flagella: the packing of the polypeptide chains within a flagellum

1961 ◽  
Vol 260 (1303) ◽  
pp. 558-573 ◽  
Keyword(s):  
Point Of View ◽  
X Ray Diffraction ◽  
Detailed Structure ◽  
Satisfactory Explanation ◽  
X Ray ◽  
Bacterial Flagella ◽  
Diffraction Patterns ◽  
Polypeptide Chains ◽  
Ray Patterns ◽  
Single Flagellum

The X-ray diffraction patterns from specimens of bacterial flagella taken by Astbury, Weibull and others consist essentially of three sets of reflexions, two sets on the meridian and one set on the equator. The equatorial set gives information on the packing arrange-merit of the polypeptide chains within a single flagellum. This paper is concerned with the interpretation in terms of a physical model of the equatorial diffraction from flagella from Proteus vulgaris for which the published diffraction data are most detailed. The polypeptide chains are all assumed to be in the α -helical form though the meridional diffraction gives some indication that a smaller ‘cross- β ’ component may also be present. The separation (121 Å) between the flagella in the X-ray specimens is inferred from the spacings of the equatorial reflexions and two alternative models (model I and model II) for the detailed structure of a flagellum are inferred from the intensity data. The structures proposed are similar in outline but differ in detail and postulate that a flagellum is composed of a number of identical interwoven filaments which themselves comprise a limited number of α -helices in a centred hexagonal or pseudo-hexagonal array. In model I the flagella are assumed to be in contact in the X-ray specimens and the structure comprises three filaments of diameter 56 Å each containing 19 single α -helices. In model II the flagella are not in contact and each of the seven filaments of diameter 33 Å contains seven α -helices; the diameter of the flagellum on this model is about 100 Å. The equatorial X-ray patterns from the two models are calculated in detail including effects due to the packing of the flagella within an X-ray specimen, for comparison with the observed diffraction. Both calculated patterns give a satisfactory explanation of the spacings of the observed reflexions and show reasonable agreement with the experimental intensities. The relative merits of the two models are discussed from the diffraction point of view and in conjunction with available data from electron microscopy. The diffraction pattern from model II is in better agreement with the experimental results than the pattern from model I but the latter agreement may be improved if the hexagonal packing of the α -helices within a filament is slightly modified; a cylindrical lattice is considered from this point of view. It is concluded that, at the present time, there is insufficient evidence to differentiate between the two models of a flagellum presented.

Ribosome Structural Organization

1974 ◽  
Vol 32 ◽  
pp. 332-333
Author(s):  
James A. Lake
Keyword(s):  
Ribosomal Proteins ◽  
Structural Organization ◽  
Three Dimensional ◽  
Small Subunit ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Specific Antibodies ◽  
X Ray ◽  
E Coli ◽  
Complete Sequences

The understanding of ribosome structure has advanced considerably in the last several years. Biochemists have characterized the constituent proteins and rRNA's of ribosomes. Complete sequences have been determined for some ribosomal proteins and specific antibodies have been prepared against all E. coli small subunit proteins. In addition, a number of naturally occuring systems of three dimensional ribosome crystals which are suitable for structural studies have been observed in eukaryotes. Although the crystals are, in general, too small for X-ray diffraction, their size is ideal for electron microscopy.

Infrared spectroscopic study of the YPO4-YCrO4 system

1985 ◽  
Vol 50 (10) ◽  
pp. 2139-2145
Author(s):  
Alexander Muck ◽  
Eva Šantavá ◽  
Bohumil Hájek
Keyword(s):  
Spectroscopic Study ◽  
Infrared Spectra ◽  
Point Of View ◽  
Mixed Crystals ◽  
Crystal Symmetry ◽  
Infrared Spectroscopic Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Infrared Spectroscopic ◽  
Diffraction Patterns

The infrared spectra and powder X-ray diffraction patterns of polycrystalline YPO4-YCrO4 samples are studied from the point of view of their crystal symmetry. Mixed crystals of the D4h19 symmetry are formed over the region of 0-30 mol.% YPO4 in YCrO4. The Td → D2d → D2 or C2v(GS eff) correlation is appropriate for both PO43- and CrO43- anions.

scholarly journals ZnOTe Compounds Grown by DC-Magnetron Co-Sputtering

Coatings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 570
Author(s):  
Olga Sánchez ◽  
Manuel Hernández-Vélez
Keyword(s):  
Molar Fraction ◽  
Variable Parameter ◽  
Point Of View ◽  
X Ray Diffraction ◽  
X Ray ◽  
Sample Series ◽  
Solid Phases ◽  
The One ◽  
High Bulk ◽  
Substrate Sample

ZnOTe compounds were grown by DC magnetron cosputtering from pure Tellurium (Te) and Zinc (Zn) cathodes in O2/Ar atmosphere. The applied power on the Zn target was constant equal to 100 W, while the one applied on the Te target took two values, i.e., 5 W and 10 W. Thus, two sample series were obtained in which the variable parameter was the distance from the Te targets to the substrate. Sample compositions were determined by Rutherford Backscattering Spectroscopy (RBS) experiments. Structural analysis was done using X-Ray diffraction (XRD) spectrometry and the growth of the hexagonal w-ZnO phase was identified in the XRD spectra. RBS results showed high bulk homogeneity of the samples forming ZnOTe alloys, with variable Te molar fraction (MF) ranging from 0.48–0.6% and from 1.9–3.1% for the sample series obtained at 5 W and 10 W, respectively. The results reflect great differences between the two sample series, particularly from the structural and optical point of view. These experiments point to the possibility of Te doping ZnO with the permanence of intrinsic defects, as well as the possibility of the formation of other Te solid phases when its content increases. The results and appreciable variations in the band gap transitions were detected from Photoluminescence (PL) measurements.

Structural Studies on the Effects of ZrO[sub 2] Coating on LiCoO[sub 2] during Cycling Using In Situ X-Ray Diffraction Technique

2006 ◽  
Vol 153 (11) ◽  
pp. A2152 ◽  
Author(s):  
Kyung Yoon Chung ◽  
Won-Sub Yoon ◽  
James McBreen ◽  
Xiao-Qing Yang ◽  
Si Hyoung Oh ◽  
...  
Keyword(s):  
Structural Studies ◽  
X Ray Diffraction ◽  
X Ray

Structural studies by x-ray diffraction of model phospholipid-insulin membranes

Biochemistry ◽  
1972 ◽  
Vol 11 (6) ◽  
pp. 945-949 ◽  
Author(s):  
R. P. Rand ◽  
S. SenGupta
Keyword(s):  
Structural Studies ◽  
X Ray Diffraction ◽  
X Ray

scholarly journals Crystallographic and optical study of LiNb1 − xTaxO3

2017 ◽  
Vol 73 (3) ◽  
pp. 498-506 ◽  
Author(s):  
S. Huband ◽  
D. S. Keeble ◽  
N. Zhang ◽  
A. M. Glazer ◽  
A. Bartasyte ◽  
...  
Keyword(s):  
Phase Transition ◽  
Lithium Niobate ◽  
Lithium Tantalate ◽  
Flux Growth ◽  
Structural Studies ◽  
Optical Study ◽  
X Ray Diffraction ◽  
Growth Technique ◽  
X Ray ◽  
Li Content

Powders of lithium niobate-tantalate across the full compositional range have been made and crystals grown using a lithium vanadate flux growth technique. The Li-content of a lithium tantalate crystal has been determined using the zero-birefringence temperature and Curie measurements, confirming the Li content is between that of congruent and stoichiometric crystals. X-ray diffraction measurements show the Nb/Ta displacement and octahedral tilt both decrease as the Ta content is increased. This also results in a decrease in the lattice parameters from lithium niobate to lithium tantalate. Birefringence measurements on the crystals as a function of temperature have been used to determine the point that the crystals become zero-birefringent, and by comparison with the structural studies have confirmed that it is not related to a phase transition and the structures remain polar through the zero-birefringence points.

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