Network Changes in Nitrile Rubber at Elevated Temperatures

1973 ◽  
Vol 46 (2) ◽  
pp. 483-503 ◽  
Author(s):  
T. C. P. Lee ◽  
S. H. Morrell
Keyword(s):  
Heat Resistance ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
Essential Feature ◽  
Nitrile Rubber ◽  
Polymer Backbone ◽  
Thermal Changes ◽  
Effective Antioxidant ◽  
Cleavage Reactions ◽  
Crosslinking Reactions

Abstract The network analysis of the aged sulfur vulcanizates of nitrile rubber serves to re-emphasize the complexity of the structural changes which can occur at elevated temperatures. Three factors control the rate and degree of crosslinking in these systems. First there is the crosslink structure. An essential feature for heat resistance in sulfur compounds is that they should contain, as near as possible, 100 per cent monosulfide crosslinks. Systems which contain polysulfide crosslinks, and probably to a lesser extent disulfide crosslinks, are prone to purely thermal crosslink shortening or cleavage reactions. The physical effect of these thermal changes would be superimposed on the effects brought about by thermooxidative changes. Despite their thermal stability monosulfide crosslinks can oxidize and cleave, a process which will result in stress relaxation if the sample is held in tension or compression. Hence for truly inert systems one will have to turn to non-sulfur cure in conjunction with a suitable stabilizer. Because the results indicate that scission associated with chemistry at the monosulfide crosslink is reversible, this cleavage does not contribute to the change in modulus or hardening during aging. This brings in the second controlling factor. The degree and rate of hardening depends on the nature of the products of vulcanization, and also possibly on those species intermediate between crosslink and accelerator, the pendent accelerator groups. In acting as an antioxidant ZDMC is apparently oxidized to a new source of sulfur. The more heat resistant cadmate system contains no such products and also a minimum of pendent accelerator groups. This leads to the third factor—the added antioxidant. For its heat resistance the cadmate system relies on an antioxidant. It is this which stops crosslinking reactions through autooxidation of the polymer backbone. The efficiency with which the antioxidant (dioctyldiphenylamine) works suggests that there is a synergistic effect in operation, which in some way involves cadmium. Thus the best heat resistance will be obtained where the compound yields monosulfide crosslinks, an uncomplicated network structure, unreactive vulcanization products, and contains a highly effective antioxidant system. Many facets of the aging of nitrile rubber are still open to explanation. Not the least of these is why crosslinks formed during the aging of the TMTD/S vulcanizate, which, by reason of their reactivity to methyl iodide, are thought to be sulfidic, are not themselves oxidized in a manner similar to the original monosulfide crosslinks. Model compound studies would answer this and other questions.

Advances in Nitrile Rubber Technology

1978 ◽  
Vol 51 (3) ◽  
pp. 389-405 ◽  
Author(s):  
J. R. Dunn ◽  
D. C. Coulthard ◽  
H. A. Pfisterer
Keyword(s):  
Heat Resistance ◽  
New Product ◽  
Polymer Structure ◽  
Nitrile Rubber ◽  
Product Form ◽  
Polymer Backbone ◽  
End Groups ◽  
Speed Up ◽  
Made In ◽  
Ozone Resistance

Abstract Considerable advances have been made in NBR technology and still more are possible. The heat resistance of NBR has been raised so that it will with-stand 150°C in air for short periods, instead of 120°C. There is potential in the polymer backbone for still greater stability. It has been demonstrated that the ozone resistance of NBR can be improved by blending with EPDM, but the optimum blend has not yet been developed. The use of PVC to improve the ozone resistance of NBR is now much better understood. Crosslinked NBR has been developed as a non-migratory plasticizer which improves embossing characteristics of PVC and PVC-ABS blends. This, in turn, led to the production of NBR powders which may be used to speed up compounding on conventional equipment and permit rubber to be compounded in equipment generally used for fabricating plastics. Powder black masterbatches of NBR are now being evaluated in industry. Another new product form is liquid NBR, generally with reactive end groups. This is already established as an impact modifier for resins and may be a route to castable reinforced elastomers. Polymer structure modifications such as alternating 50:50 copolymers are interesting but do not appear to have found a market. Carboxylated NBR uses are growing in the wake of improvements in scorch resistance. Reprocessible vulcanizates based on amine-modified NBR have been announced, but a true thermoplastic NBR is still awaited.

Heat resistance of coatings metal deposited by nickel-manganese-molybdenum fl ux-cored wire

2020 ◽  
pp. 511-515
Author(s):  
E.N. Eremin ◽  
A.S. Losev ◽  
I.A. Ponomarev ◽  
S.A. Borodikhin
Keyword(s):  
Heat Resistance ◽  
Elevated Temperatures ◽  
Mass Gain ◽  
Cored Wire ◽  
Protective Properties ◽  
Average Mass ◽  
Magnetite Fe3o4 ◽  
Hematite Fe2o3 ◽  
Nickel Manganese

The heat-resistance of coating from deposited steel 15N8G6M3FTB at temperature of 900 °С is studied. It is established that this dependence occurs in the first hours. The average mass gain of the metal scale of such coating at 900 °С is 0.0128 kg/(m2 •h). It is shown that the basis of metal scale of the composition 15N8G6M3FTB is hematite Fe2O3 and magnetite Fe3O4, as well as MnO, which have protective properties. The number of other phase compounds with high protective properties is negligible. The coating from steel 15N8G6M3FTB can be used for applying to the surface of parts operating at elevated temperatures.

X-ray diffraction investigations of structural changes in Co/Cu multilayers at elevated temperatures

2002 ◽  
Vol 411 (2) ◽  
pp. 234-239 ◽  
Author(s):  
M Hecker ◽  
W Pitschke ◽  
D Tietjen ◽  
C.M Schneider
Keyword(s):  
Structural Changes ◽  
Elevated Temperatures ◽  
X Ray Diffraction ◽  
X Ray

scholarly journals A Bis-Monophospholyl Dysprosium Cation Showing Magnetic Hysteresis at 48 Kelvin

2019 ◽  
Author(s):  
Peter Evans ◽  
Daniel Reta ◽  
George F. S. Whitehead ◽  
Nicholas Chilton ◽  
David Mills
Keyword(s):  
Data Storage ◽  
Single Molecule ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
Spin Dynamics ◽  
Magnetic Hysteresis ◽  
Relaxation Times ◽  
Magnetic Memory ◽  
Relaxation Processes ◽  
Potential Applications

Single-molecule magnets (SMMs) have potential applications in high-density data storage, but magnetic relaxation times at elevated temperatures must be increased to make them practically useful. <i>Bis</i>-cyclopentadienyl lanthanide sandwich complexes have emerged as the leading candidates for SMMs that show magnetic memory at liquid nitrogen temperatures, but the relaxation mechanisms mediated by aromatic C<sub>5</sub> rings have not been fully established. Here we synthesise a <i>bis</i>-monophospholyl dysprosium SMM [Dy(Dtp)<sub>2</sub>][Al{OC(CF<sub>3</sub>)<sub>3</sub>}<sub>4</sub>] (<b>1</b>, Dtp = {P(C<sup>t</sup>BuCMe)<sub>2</sub>}) by the treatment of <i>in situ</i>-prepared “[Dy(Dtp)<sub>2</sub>(C<sub>3</sub>H<sub>5</sub>)]” with [HNEt<sub>3</sub>][Al{OC(CF<sub>3</sub>)<sub>3</sub>}<sub>4</sub>]. SQUID magnetometry reveals that <b>1</b> has an effective barrier to magnetisation reversal of 1,760 K (1,223 cm<sup>–1</sup>) and magnetic hysteresis up to 48 K. <i>Ab initio</i> calculation of the spin dynamics reveal that transitions out of the ground state are slower in <b>1</b> than in the first reported dysprosocenium SMM, [Dy(Cp<sup>ttt</sup>)<sub>2</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (Cp<sup>ttt</sup> = C<sub>5</sub>H<sub>2</sub><sup>t</sup>Bu<sub>3</sub>-1,2,4), however relaxation is faster in <b>1</b> overall due to the compression of electronic energies and to vibrational modes being brought on-resonance by the chemical and structural changes introduced by the <i>bis</i>-Dtp framework. With the preparation and analysis of <b>1</b> we are thus able to further refine our understanding of relaxation processes operating in <i>bis</i>-C<sub>5</sub>/C<sub>4</sub>P sandwich lanthanide SMMs, which is the necessary first step towards rationally achieving higher magnetic blocking temperatures in these systems in future.

Experimental Investigation on Grinding Temperature of Titanium Alloy

2014 ◽  
Vol 1027 ◽  
pp. 127-130 ◽  
Author(s):  
Bing Jun Hao ◽  
Zhi Gang Dong ◽  
Ren Ke Kang ◽  
Huan Wang ◽  
Ke Cao
Keyword(s):  
Titanium Alloy ◽  
Structural Changes ◽  
Thermal Damage ◽  
Elevated Temperatures ◽  
Chemical Properties ◽  
Grinding Temperature ◽  
Physical And Chemical Properties ◽  
Machine Material ◽  
Physical And Chemical ◽  
And Chemical Properties

Titanium alloy has been widely used in aeronautics and astronautics industry owing to its unique combinations of properties. The unique physical and chemical properties of titanium alloy make it a typical difficult-to-machine material. The elevated temperatures at the machining zones may cause thermal damage, residual stress and micro-structural changes in the surface layer of titanium alloy during grinding. In this study, grinding experiments were performed on the titanium alloy, and the grinding temperature was experimentally tested with the grindable thermocouples. The effects of the grinding parameters on the grinding temperature were analyzed. The grinding temperature rises with the increase of grinding speed and grinding depth.

Genomic and phenotypic analysis of heat and sanitizer resistance in Escherichia coli from beef in relation to the locus of heat resistance

2021 ◽  
Author(s):  
Xianqin Yang ◽  
Frances Tran ◽  
Peipei Zhang ◽  
Hui Wang
Keyword(s):  
Escherichia Coli ◽  
Heat Resistance ◽  
Phylogenetic Relationships ◽  
Core Genome ◽  
Elevated Temperatures ◽  
Resistant Bacteria ◽  
Phenotypic Analysis ◽  
Decimal Reduction Time ◽  
E Coli ◽  
Clade 1

The locus of heat resistance (LHR) can confer heat resistance to Escherichia coli to various extents. This study investigated the phylogenetic relationships, and genomic and phenotypic characteristics of E. coli with or without LHR recovered from beef by direct plating or from enrichment broth at 42°C. LHR-positive E. coli isolates (n=24) were whole genome-sequenced by short- and long-reads. LHR-negative isolates (n=18) from equivalent sources as LHR-positive isolates were short-read sequenced. All isolates were assessed for decimal reduction time at 60°C ( D 60°C ) and susceptibility to E-SAN and Perox-E. Selected isolates were evaluated for growth at 42°C. The LHR-positive and negative isolates were well separated on the core genome tree, with 22/24 of the positive isolates clustering into three clades. Isolates within clade 1 and 2, despite their different D 60°C values, were clonal, as determined by subtyping (MLST, core genome MLST, and serotyping). Isolates within each clade are of one serotype. The LHR-negative isolates were genetically diverse. The LHR-positive isolates had a larger (p<0.001) median genome size by 0.3 Mbp (5.0 vs 4.7 Mbp), and overrepresentation of genes in plasmid maintenance, stress response and cryptic prophages, but underrepresentation of genes involved in epithelial attachment and virulence. All LHR-positive isolates harbored a chromosomal copy of LHR, and all clade 2 isolates had an additional partial copy of LHR on conjugative plasmids. The growth rates at 42°C were 0.71±0.02 and 0.65±0.02 logOD h −1 for LHR-positive and negative isolates. No meaningful difference in sanitizer susceptibility was noted between LHR-positive and negative isolates. Importance Resistant bacteria are serious food safety and public health concerns. Heat resistance conferred by the LHR varies largely among different strains. The findings in this study show that genomic background and composition of LHR, in addition to the presence of LHR, play an important role in the degree of heat resistance in E. coli , and that strains with certain genetic background are more likely to acquire and maintain the LHR. Also, caution should be exercised when recovering E. coli at elevated temperatures as the presence of LHR may confer growth advantages to some strains. Interestingly, the LHR harboring strains seem to have evolved further from their primary animal host to adapt to their secondary habitat, as reflected by fewer genes in virulence and epithelial attachment. The phylogenetic relationships among the isolates point towards multiple mechanisms for acquiring LHR, likely prior to their deposition on meat.

scholarly journals Synergistic Effects of Multiple Environmental Factors on Degradation of Hydrogenated Nitrile Rubber Seals

Polymers ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 897 ◽  
Author(s):  
Weitao Lou ◽  
Weifang Zhang ◽  
Tingzhu Jin ◽  
Xuerong Liu ◽  
Wei Dai
Keyword(s):  
Environmental Factors ◽  
Elevated Temperatures ◽  
Synergistic Effects ◽  
Degradation Process ◽  
Nitrile Rubber ◽  
Oxidation Products ◽  
Compression Stress ◽  
Hydraulic Systems ◽  
Hydraulic Oil ◽  
Higher Temperature

Degradation tests of hydrogenated nitrile rubber seals, often used as sealing components in hydraulic systems, were conducted under the free and compression state in air and hydraulic oil at three elevated temperatures for several days to investigate the synergistic effects among three factors. The crosslinking and chain scission reactions both occurred simultaneously at higher temperature during the degradation process, and crosslinking predominated for most cases. Additionally, the synergistic effect between compression stress and hydraulic oil further slowed the degradation rate by limiting oxygen access. However, the higher temperature and hydraulic oil both promoted the formation of oxidation products, whereas the compression stress restrained the formation of amide groups. The fracture morphology results show that the defects gradually formed on the fracture surface, especially for the uncompressed specimens. The increase of the compression set aged in air was more than that in hydraulic oil, implying the more serious degradation. Moreover, rubber seals under the synthetic effect of three environmental factors presented the minimum degradation level. The degradation of the compressed and uncompressed specimens exposed to hydraulic oil is more serious than that of specimens exposed to air.

scholarly journals Influence of Plastic Deformation During Extrusion Process on Heat Resistance Alloys Fe40Al

2017 ◽  
Vol 62 (4) ◽  
pp. 2281-2286 ◽  
Author(s):  
D. Pasek ◽  
J. Cebulski
Keyword(s):  
Plastic Deformation ◽  
Heat Resistance ◽  
Structural Changes ◽  
Extrusion Process ◽  
Test Results ◽  
Research Setting ◽  
Alloy Matrix ◽  
X Ray ◽  
Kinetics Of ◽  
Corrosion Research

AbstractThe article presents the results of studies on the effects wrought on the corrosion resistance of the alloy matrix phase inter-metallic FeAl. Researches were carried out on the Fe40Al5Cr0.2TiB alloy and involved the oxidation of the samples after the crystallization after plastic deformation made by extrusion. The tests were performed in an oven in air at 1100°C for 100, 300 and 500 h. Determined to change the mass of the samples after corrosion research setting kinetics of corrosion processes, as well as an analysis of the microstructure of the alloy after the crystallization and after forming. The structure was examined using light microscopy and scanning electron microscopy and X-ray microanalysis with EDS chemical composition of the corrosion products. The test results revealed that plastic deformation during extrusion of intermetallic alloy led to structural changes, the effect of which was to improve the heat resistance at a temperature of 1100°C.

Mechanical and Basic Physical Properties of High-Strength Concrete Exposed to Elevated Temperatures

2018 ◽  
Vol 760 ◽  
pp. 108-113 ◽  
Author(s):  
Lenka Scheinherrová ◽  
Monika Čáchová ◽  
Michaela Petříková ◽  
Lukáš Fiala ◽  
Eva Vejmelková ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Physical Properties ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
Water Environment ◽  
High Strength ◽  
Steel Fibers ◽  
Quartz Powder ◽  
Matrix Density ◽  
Drying Treatment

In this paper, the effect of elevated temperatures on the mechanical and basic properties of two different newly-designed high-strength concretes is studied. The studied materials were prepared from Portland cement, steel fibers, reactive finely milled quartz powder and quartz sand, silica fume, plasticizer, and with a relatively low water/cement ratio of 0.24. The samples were stored in water environment for the first 28 days of hydration to achieve better mechanical properties. Then, after pre-drying at 105 °C to constant mass, the materials were exposed to elevated temperatures of 600 °C and 1000 °C where they were kept for 2 hours. The basic physical properties, such as matrix density, bulk density and open porosity were determined as a function of temperature. Mechanical properties (compressive and flexural strength) were also studied. The measured parameters exhibited a high dependence on temperature and the obtained results pointed to the structural changes of the studied materials. Spalling was not observed because of the pre-drying treatment.

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