Time and Stress Effects in the Behavior of Rubber at Low Temperature

1950 ◽  
Vol 23 (1) ◽  
pp. 54-66 ◽  
Author(s):  
J. R. Beatty ◽  
J. M. Davies
Keyword(s):  
Shear Stress ◽  
Low Temperature ◽  
Natural Rubber ◽  
Applied Stress ◽  
Dynamic Modulus ◽  
Rate Of Change ◽  
Rate Process ◽  
X Ray ◽  
Stress Effects ◽  
Rubberlike Materials

Abstract The stiffening of rubberlike materials at low temperature involves several different phenomena, sometimes with their effects superimposed. One of these is crystallization. This is a rate process which is generally very fast at high stresses and very slow at zero stress. In these experiments at temperatures near −25° C and under a shear stress of about 148 lb. per sq. in. the dynamic modulus of the rubber increased at a rate convenient to study. Correlation with x-ray data showed that crystallization was very likely responsible for the increase in stiffness. The rate of change of stiffness increased rapidly with increase in applied stress, and there was no optimum rate at −25° C, as has been found for unstressed rubber. The degree of vulcanization influenced the rate of change, tighter cures giving smaller changes. Neoprene-FR, GR-S, and polybutadiene, which ordinarily show little evidence of crystallization, showed very definite, but small increases in stiffness. Mixing GR-S with natural rubber seems to limit the crystallization of the natural rubber rather effectively, but apparently Neoprene-FR does not mix intimately enough with natural rubber to affect the crystallization of the latter appreciably.

Detection of the Molecular Orientation in Nonvulcanized and Vulcanized Natural Rubber Compounds by the Low-Temperature X-Ray Method

1989 ◽  
Vol 62 (2) ◽  
pp. 179-194 ◽  
Author(s):  
Y. Udagawa ◽  
M. Ito
Keyword(s):  
Low Temperature ◽  
Carbon Black ◽  
Natural Rubber ◽  
Molecular Orientation ◽  
Ray Method ◽  
Processing Methods ◽  
X Ray ◽  
Rubber Compounds

Abstract The low-temperature x-ray method can detect the orientation of NR molecules in both vulcanizate samples and nonvulcanizate samples of NR compounds. The presence of carbon black is important for causing the orientation. NR molecules orient in the direction of stretch-relaxation in the case of uniaxially fatigued vulcanizates or in the direction of shear in the case of nonvulcanizates prepared by various processing methods. The orientation of NR molecules in nonvulcanizates usually disappears when vulcanized, but a fairly large extent of molecular orientation remains, even after vulcanization, if there exist crosslinks in the oriented nonvulcanizate and the sample is prevented from shrinkage.

Yield Stress in Frozen Rubbers

1954 ◽  
Vol 27 (1) ◽  
pp. 104-119
Author(s):  
J. M. Buist ◽  
R. L. Stafford
Keyword(s):  
Low Temperature ◽  
Natural Rubber ◽  
Yield Stress ◽  
Shear Deformation ◽  
Applied Stress ◽  
Room Temperature ◽  
Large Temperature ◽  
Shear Stresses ◽  
Tension Tests ◽  
Deformation Properties

Abstract The work reported on the low temperature shear deformation properties of natural rubber and Neoprene-GN gum compounds shows that, under the conditions of storage and applied stress investigated, there is little evidence of a yield effect with Neoprene-GN. It is suggested that the very large temperature-stiffening of this polymer is too great to give the yield effect under the low shear stresses studied. In tension, however, the yield effect is very marked with Neoprene-GN. On the other hand, a definite yield effect is shown as a result of shear deformation measurements on natural rubber stored at −40° C, whereas previous tension tests failed to detect this. It is shown that, under suitable conditions of storage time and at high shearing stresses, a natural rubber unit might fail in service by yielding and giving too much deflection. The more usual type of failure of a shear unit in service arises from loss of flexibility and hence deflection properties; the oil-resisting rubbers are particularly likely to suffer from this defect. The x-ray data on natural rubber and Neoprene-GN gum compounds failed to reveal any evidence of random crystallite formation in the unstretched frozen rubbers. If the yield effect is due to crystallite formation in the unstretched state at low temperatures, then the crystallites are too small to be detected under the conditions of this investigation. In this connection, it is emphasized that a temperature of −40° C is below the temperature for maximum rate of development of crystallization for both rubbers. With both natural rubber and Neoprene-GN, crystallization resulting from stretching occurs more readily and at lower elongations at −40° C than at room temperature. In the case of Neoprene-GN stored at −40° C and then stretched, crystallization does not increase with elongation as it does at room temperature. It is suggested that this is due to the cold-drawn state of Neoprene-GN on stretching after storage at −40° C. These investigations have important practical and theoretical implications. Suggestions have often been made to include a test for crystallization in any characterization of compounds for low-temperature resistance. The results of the present work emphasize that the important factor is the time of storage at low temperature and the effects that this produces on crystallization and yield stress. The presence of crystallization is not so important as its continued development under long period exposure or its reorientation under applied stress.

Rheological Analysis of Raw Elastomers with the Multispeed Mooney Shearing Disk Viscometer

1966 ◽  
Vol 39 (2) ◽  
pp. 436-451 ◽  
Author(s):  
James L. White ◽  
Noboru Tokita
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Shear Rate ◽  
Natural Rubber ◽  
Viscoelastic Behavior ◽  
Rheological Analysis ◽  
Stress Effects ◽  
Linear Viscoelastic Behavior ◽  
Linear Viscoelastic ◽  
Analytical Research

Abstract Mooney's shearing disk viscometer is one of the most important analytical research and process control instruments for elastomers. In this paper a new method is developed for computing the shear stress and shear rate of materials from data obtained on this instrument. In addition, the non-linear viscoelastic behavior of elastomers in the viscometer is analyzed with special emphasis upon normal stress effects. Experimental data for natural rubber, SBR, and polyisobutylene are discussed.

Low temperature x-ray microanalysis of frozen-hydrated tobacco leaves

1984 ◽  
Vol 42 ◽  
pp. 284-285
Author(s):  
S. Edith Taylor ◽  
Patrick Echlin ◽  
May McKoon ◽  
Thomas L. Hayes
Keyword(s):  
Low Temperature ◽  
Lemna Minor ◽  
Root Tips ◽  
Tobacco Leaves ◽  
X Ray ◽  
Whole Cells ◽  
Carbon Coated ◽  
The Right ◽  
Beam Currents ◽  
The University

Low temperature x-ray microanalysis (LTXM) of solid biological materials has been documented for Lemna minor L. root tips. This discussion will be limited to a demonstration of LTXM for measuring relative elemental distributions of P,S,Cl and K species within whole cells of tobacco leaves.Mature Wisconsin-38 tobacco was grown in the greenhouse at the University of California, Berkeley and picked daily from the mid-stalk position (leaf #9). The tissue was excised from the right of the mid rib and rapidly frozen in liquid nitrogen slush. It was then placed into an Amray biochamber and maintained at 103K. Fracture faces of the tissue were prepared and carbon-coated in the biochamber. The prepared sample was transferred from the biochamber to the Amray 1000A SEM equipped with a cold stage to maintain low temperatures at 103K. Analyses were performed using a tungsten source with accelerating voltages of 17.5 to 20 KV and beam currents from 1-2nA.

Bulk standards for low-temperature biological x-ray microanalysis

1984 ◽  
Vol 42 ◽  
pp. 282-283
Author(s):  
P. Echlin ◽  
M. McKoon ◽  
E.S. Taylor ◽  
C.E. Thomas ◽  
K.L. Maloney ◽  
...  
Keyword(s):  
Phase Separation ◽  
Low Temperature ◽  
Analytical Method ◽  
Salt Solutions ◽  
Absolute Concentration ◽  
Cooling Process ◽  
X Ray ◽  
The Absolute ◽  
Analytical Procedures ◽  
Electrical Conductors

Although sections of frozen salt solutions have been used as standards for x-ray microanalysis, such solutions are less useful when analysed in the bulk form. They are poor thermal and electrical conductors and severe phase separation occurs during the cooling process. Following a suggestion by Whitecross et al we have made up a series of salt solutions containing a small amount of graphite to improve the sample conductivity. In addition, we have incorporated a polymer to ensure the formation of microcrystalline ice and a consequent homogenity of salt dispersion within the frozen matrix. The mixtures have been used to standardize the analytical procedures applied to frozen hydrated bulk specimens based on the peak/background analytical method and to measure the absolute concentration of elements in developing roots.

Micro X-Ray Diffraction Study of Polycrystalline MgB 2 Wire and Evaluation of Carbon Doping Effect Via Low-Temperature Sintering

2019 ◽  
Author(s):  
Minoru Maeda ◽  
Dipak Patel, Dr. ◽  
Hiroaki Kumakura, Dr. ◽  
Gen Nishijima, Dr. ◽  
Akiyoshi Matsumoto, Dr. ◽  
...  
Keyword(s):  
Low Temperature ◽  
Diffraction Study ◽  
Carbon Doping ◽  
Doping Effect ◽  
Low Temperature Sintering ◽  
X Ray Diffraction ◽  
X Ray

The Application of X-Ray Diffraction at Elevated Temperatures to Study the Mechanism of Formation of Sodium Tripolyphosphate

1961 ◽  
Vol 5 ◽  
pp. 276-284
Author(s):  
E. L. Moore ◽  
J. S. Metcalf
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Amorphous Phase ◽  
Elevated Temperatures ◽  
Sodium Tripolyphosphate ◽  
X Ray Diffraction ◽  
Mechanism Of Formation ◽  
X Ray ◽  
Temperature Form ◽  
High Temperature Form

AbstractHigh-temperature X-ray diffraction techniques were employed to study the condensation reactions which occur when sodium orthophosphates are heated to 380°C. Crystalline Na4P2O7 and an amorphous phase were formed first from an equimolar mixture of Na2HPO4·NaH2PO4 and Na2HPO4 at temperatures above 150°C. Further heating resulted in the formation of Na5P3O10-I (high-temperature form) at the expense of the crystalline Na4P4O7 and amorphous phase. Crystalline Na5P3O10-II (low-temperature form) appears after Na5P3O10-I.Conditions which affect the yield of crystalline Na4P2O7 and amorphous phase as intermediates and their effect on the yield of Na5P3O10 are also presented.

X-ray diffraction and Raman investigations of thickness dependent stress effects on Pb(ZrxTi1−x)O3 thin films

2006 ◽  
Vol 88 (25) ◽  
pp. 252901 ◽  
Author(s):  
Jyrki Lappalainen ◽  
Vilho Lantto ◽  
Johannes Frantti ◽  
Jussi Hiltunen
Keyword(s):  
Thin Films ◽  
X Ray Diffraction ◽  
X Ray ◽  
Stress Effects

scholarly journals Low Temperature Water-Gas Shift: Enhancing Stability through Optimizing Rb Loading on Pt/ZrO2

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 210
Author(s):  
Caleb Daniel Watson ◽  
Michela Martinelli ◽  
Donald Charles Cronauer ◽  
A. Jeremy Kropf ◽  
Gary Jacobs
Keyword(s):  
Low Temperature ◽  
Hydrogen Transfer ◽  
Water Gas Shift ◽  
Significant Shift ◽  
Catalyst Activation ◽  
X Ray ◽  
Temperature Programmed ◽  
Water Gas ◽  
X Ray Absorption ◽  
Temperature Water

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO2 is examined herein. Pt/ZrO2 catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an X-ray absorption near edge spectroscopy (XANES) difference procedure, extended X-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate ν(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C–H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55–0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst.

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