Aging of GR-S Vulcanizates. III. Some Effects of Oxygen and Temperature on Aging

1950 ◽  
Vol 23 (2) ◽  
pp. 390-396 ◽  
Author(s):  
J. R. Scott
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Oxygen Concentration ◽  
High Temperatures ◽  
Natural Aging ◽  
Strain Curve ◽  
Chain Scission ◽  
Bomb Test ◽  
Chain Scission Reaction ◽  
Loss Of Strength

Abstract Experiments at high temperatures (135° to 153° C) show that the fall in tensile strength and elongation and the increase in modulus of GR-S vulcanizates are accelerated by the presence of oxygen. At 70° C an increase of oxygen concentration from 0.2 atm. (air) to 20 atm. likewise promotes both loss of tensile strength and stiffening (increase of modulus), unless the rubber is under-vulcanized, when the increase of oxygen concentration often results in less stiffening. The increase of oxygen concentration also causes the aged rubber to retain more set after stretching. At 80° C, increasing the oxygen concentration from 0.2 to 20 atm. does not promote stiffening even in well vulcanized rubbers, and may even lead to less stiffening. These results indicate the following general conclusions: (1) oxidation, in addition to promoting loss of strength, is one of the causes of the stiffening of GR-S during aging, presumably due to oxygen-bridging between the molecules; (2) oxidation can also cause softening, presumably by chain scission, which further results in a change in the shape of the stress-strain curve and an increased set after deformation; (3) at high temperatures (80° C or above) increase of oxygen concentration, as in the bomb test, favors the softening reaction relative to the stiffening reaction, but at 70° C (and presumably below) this effect is not evident; (4) undervulcanized GR-S is especially susceptible to the softening (chain scission) reaction; (5) the fact that the softening reaction is favored by increase of oxygen concentration at a high temperature casts doubt on the value of a high-temperature oxygen bomb test for simulating the natural aging of GR-S (see Part IV for an analogous conclusion on other accelerated tests). The above conclusions agree with and extend those of Shelton and Winn. Prolonged (60-day) air-aging tests at 100° C confirm a previous suggestion that the tensile strength of GR-S vulcanizates reaches a constant value or even increases eventually; however, they become progressively stiffer and less extensible. Thus, under hot service conditions GR-S is more likely to fail through inability to stretch than through loss of strength.

Comparison Analysis on the Mechanical Properties of HSC and NSC after the Action of High Temperatures

2014 ◽  
Vol 1014 ◽  
pp. 49-52
Author(s):  
Xiao Ping Su
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
High Temperatures ◽  
High Strength Concrete ◽  
Elasticity Modulus ◽  
Strain Curve ◽  
Peak Stress ◽  
High Strength ◽  
Peak Strain ◽  
Strength Concrete

With the wide application of high strength concrete in the building construction,the risk making concrete subject to high temperatures during a fire is increasing. Comparison tests on the mechanical properties of high strength concrete (HSC) and normal strength concrete (NSC) after the action of high temperature were made in this article, which were compared from the following aspects: the peak stress, the peak strain, elasticity modulus, and stress-strain curve after high temperature. Results show that the laws of the mechanical properties of HSC and NSC changing with the temperature are the same. With the increase of heating temperature, the peak stress and elasticity modulus decreases, while the peak strain grows rapidly. HSC shows greater brittleness and worse fire-resistant performance than NSC, and destroys suddenly. The research and evaluation on the fire-resistant performance of HSC should be strengthened during the structural design and construction on the HSC buildings.

Mastication of Rubber a Study of Some of the Oxidation Rocesses Involved

1939 ◽  
Vol 12 (2) ◽  
pp. 163-175 ◽  
Author(s):  
W. F. Busse ◽  
E. N. Cunningham
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Thermal Oxidation ◽  
Oxygen Concentration ◽  
High Temperatures ◽  
Nitroso Compounds ◽  
Temperature Reaction ◽  
Vulcanized Rubber ◽  
High Temperature Reaction ◽  
Internal Mixer

Abstract The rate of breakdown of smoked sheet, pale crepe, and sprayed-latex rubber in a laboratory internal mixer is a minimum at temperatures around 240° F., and the rate may be increased as much as four- or five-fold by either raising or lowering the temperature 80° F. The high-temperature reaction (above 240° F.) probably is similar to the thermal oxidation which occurs when rubber is heated in air, since the rates of both reactions are increased by increasing the oxygen concentration, and they are reduced by adding antioxidants. The low-temperature reaction (below 240° F.) may involve a mechanical acti-vation of the rubber, as in milling. The rate of this reaction first increases and then remains constant or decreases slightly as the oxygen concentration in the temperature during mastication is increased from about 0.5% to 20% to 100%. Some nitroso compounds are powerful stiffeners of rubber, and they change the softness-retentivity relation, making it more like that of reclaim or semi-vulcanized rubber. The effect of most commonly used “softeners” on the plasticity of rubber is small compared with the effect of changing the mastication temperature ±40° F. Exceptions to this are certain vulcanization accelerators (at high temperatures), hydrazine compounds and thiophenols, which appear to be true mastication acelerators or oxidation catalysts.

scholarly journals Effect of Transition Metal Elements on High-Temperature Properties of Al–Si–Cu–Mg Alloys

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 357
Author(s):  
Chao Gao ◽  
Lingkun Zhang ◽  
Bingrong Zhang
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Transition Metal ◽  
Yield Strength ◽  
High Temperatures ◽  
Test Temperature ◽  
Intermetallic Phases ◽  
Mg Alloys ◽  
Metal Elements ◽  
Transition Metal Elements

In the present work, we studied the effects of transition metal elements on microstructure evolution and high-temperature mechanical properties via the preparation of new modified alloys with micro-additions of Cr, Ti, V, Zr, Mo, and Mn to address the poor high-temperature performance of Al–Si–Cu–Mg alloys for automotive engines. The results show that the addition of transition metal elements formed a variety of new intermetallic phases that were stable at high temperatures, such as (AlSi)3(TiVZr), (AlSi)3Ti, (AlSi)3(CrVTi), Al74Si6Mn4Cr2Fe, Al85Si5Mn2Mo2CrFe, Al0.78Fe4.8Mn0.27Mo4.15Si2, (AlSi)2(CrVTi)Mo, and Al13(MoCrVTi)4Si4, and these phases evidently improved the ultimate high-temperature tensile strength and yield strength. The ultimate tensile strength and yield strength of the modified alloy increased by 17.49% and 31.65% when the test temperature increased to 240 °C, respectively, and by 71.28% and 74.73% when the test temperature increased to 300 °C, respectively. The fundamental reason for this change is that the intermetallic phase hinders the expansion of cracks, which can exist stably at high temperatures. When a crack extends to the intermetallic phases, it will break along with the intermetallic phases or propagate along the morphological edge of the intermetallic phases.

scholarly journals Reuse of ceramic sanitary waste as an aggregate in concrete resistant to high temperature

2013 ◽  
Vol 12 (3) ◽  
pp. 153-160 ◽  
Author(s):  
Anna Halicka ◽  
Paweł Ogrodnik ◽  
Bartosz Zegardło
Keyword(s):  
Tensile Strength ◽  
Compressive Strength ◽  
High Temperature ◽  
High Temperatures ◽  
Sanitary Ware ◽  
Alumina Cement ◽  
High Compressive Strength ◽  
Sanitary Ceramic ◽  
Ceramic Sanitary Ware

In this paper the studies on reuse of ceramic sanitary ware wastes as aggregate in the concrete resistant to high temperatures are presented. Concrete specimens containing alumina cement and crushed sanitary ceramic wastes as an aggregate were heated in 1000oC. It was found that after heating, these specimens preserved their shape and cohesion, and showed no cracks and defects. In contrast, specimens of concrete with alumina cement and traditional aggregate (granite and gravel) after heating were cracked and damaged. Despite some decrease in strength after heating, specimens with sanitary ceramic wastes continued to display high compressive strength and tensile strength. 

scholarly journals Prediction of the Tensile Strength of Normal and Steel Fiber Reinforced Concrete Exposed to High Temperatures

2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Mehrdad Abdi Moghadam ◽  
Ramezan Ali Izadifard
Keyword(s):  
Tensile Strength ◽  
Reinforced Concrete ◽  
High Temperature ◽  
High Temperatures ◽  
Steel Fiber ◽  
Fiber Reinforced Concrete ◽  
Steel Fibers ◽  
Steel Fiber Reinforced Concrete ◽  
High Temperature Exposure ◽  
Temperature Exposure

AbstractThe tensile strength of concrete has a great impact on the performance of concrete structures, especially for members exposed to high temperatures. The inclusion of steel fibers in concrete is one of the measures to retrieve the loss of tensile strength. The previous equations for the prediction of the tensile strength, are valid for conventional concrete and can predict the tensile strength after high-temperature exposure. Therefore, they are unsatisfactory for forecasting the tensile strength of plain and steel fiber reinforced concrete under high-temperature exposure. To establish a model that can effectively simulate the tensile strength of plain concrete, specimens with compressive strengths of 20–80 MPa are tested. Then by performing tensile strength tests on the specimens containing various content of steel fiber, an equation for prediction of the tensile strength at the ambient temperature is proposed. Meanwhile, the tensile strength tests are conducted at temperatures of 100–800 °C to develop a model for high-temperature exposure. The results indicate that an increase of compressive strength from 20 to 84 improves the tensile strength by 169.4%, and the incorporation of 0.25 and 0.5% of steel fibers can improve the tensile strength of normal concrete by 58.48 and 80.29% on average at the tested temperatures, respectively. Moreover, the proposed model is able to predict the tensile strength of normal and steel fiber reinforced concrete exposed to high temperatures accurately. This equation would help a wider application of the steel fibers in the construction industry with the risk of a fire accident.

scholarly journals Uniaxial Tensile Behavior, Flexural Properties, Empirical Calculation and Microstructure of Multi-Scale Fiber Reinforced Cement-Based Material at Elevated Temperature

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1827
Author(s):  
Li Li ◽  
Mehran Khan ◽  
Chengying Bai ◽  
Ke Shi
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Tensile Properties ◽  
High Temperatures ◽  
Cement Matrix ◽  
Uniaxial Tensile ◽  
Flexural Properties ◽  
Fiber Reinforced ◽  
Multi Scale ◽  
Reinforced Cement

Fire is one of the most unfavorable conditions that cement-based composites can face during their service lives. The uniaxial tensile and flexural tensile properties of the steel-polyvinyl alcohol fiber-calcium carbonate whisker (CW) multi-scale fiber reinforced cement matrix composites (MSFRCs) under high temperatures are studied, including strength, deformation capacity, energy dissipation capacity, and its ability to be assessed through the empirical calculation method. The study showed that with the increase of the treatment temperature, the MSFRC residual bending strength, bending toughness, and tensile strength decreased overall, but the decline was slow at 600 °C. The peak flexural deflection and peak tensile strain of MSFRC first reduced and then increased with the increase of the temperature. As the temperature increased, the nominal stiffness of MSFRC bending and straight gradually reduced, and the rate of decline was faster than that of its strength. However, the uniaxial tensile properties were more sensitive to the temperature and degraded more rapidly. A quantitative relationship was established between MSFRC residual bending, tensile strength, and temperature. A comparison with existing research results shows that MSFRC has achieved an ideal effect of high temperature resistance. The multi-scale hybrid fiber system significantly alleviates the deterioration of cement-based composite’s mechanical properties under high temperatures. With the help of an optical microscope and scanning electron microscope (SEM), the high temperature influence mechanism on the uniaxial tensile and flexural properties of MSFRC was revealed.

Aging of Rubber in the Oxygen Bomb at Room Temperature

1943 ◽  
Vol 16 (4) ◽  
pp. 924-925
Author(s):  
J. R. Scott
Keyword(s):  
Tensile Strength ◽  
Oxygen Concentration ◽  
Room Temperature ◽  
Accelerated Aging ◽  
Natural Aging ◽  
Tensile Tests ◽  
Oxygen Bomb ◽  
Vulcanized Rubber ◽  
Accelerated Aging Test ◽  
Aging Test

Abstract The work described below was carried out as a first step in determining whether an oxygen-bomb test at room temperature could be used as an accelerated aging test for unvulcanized rubber compositions, e.g., as used on surgical and adhesive plasters and for combining shoe fabrics, because a high-temperature test is unsatisfactory in such cases, owing to the melting of the compositions. The only infallible way of assessing the value of an accelerated test for such compositions is by comparison with natural aging, but as this is a very lengthy process and as the deterioration is difficult to measure quantitatively, it was decided to make preliminary tests on the effect of high oxygen concentration at room temperature by using vulcanized rubber. Although the results proved to be negative so far as the original purpose of the work was concerned, it is considered of interest to place them on record in view of the prominence given in some papers on aging to the relationship between oxygen concentration and rate of oxidation and deterioration of rubber. A mix composed of rubber 100, sulfur 3, zinc oxide 5, stearic acid 1, and diphenylguanidine 0.75, was vulcanized for 30 minutes at 153° C. Tensile tests, using standard ring-specimens and the Schopper machine, were made on unaged specimens and on specimens that had been aged (1) in an oxygen bomb at 300 lb. per sq. in. oxygen pressure and at room temperature (about 10° C), (2) in a Geer oven at 70° C. Four rings were used for each test, the tensile strength and breaking elongation figures quoted being the average for the two rings giving the highest tensile strength, and the figures for the elongations at constant loads the average of all four rings.

scholarly journals Dynamic Splitting Experimental Study on Sandstone at Actual High Temperatures under Different Loading Rates

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Qi Ping ◽  
Mingjing Wu ◽  
Pu Yuan ◽  
Haipeng Su ◽  
Huan Zhang
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Strain Rate ◽  
Failure Mode ◽  
High Temperatures ◽  
Radial Strain ◽  
Tensile Tests ◽  
Average Strain ◽  
Striker Velocity ◽  
Average Strain Rate

The tensile failure of rocks is a common failure mode in rock engineering. Many studies have been conducted on the tensile strength and failure mode of rocks after high-temperature treatment under dynamic loading. However, research on the effects of high temperature on the dynamic splitting tensile characteristics of sandstone at actual high temperatures is lacking. To investigate the dynamic tensile characteristics of rocks at actual high temperatures, split Hopkinson pressure bar (SHPB) test apparatus and high-temperature environment box were used to perform dynamic splitting tensile tests under six striker velocities for sandstone specimens at 25°C–800°C. The dynamic splitting tensile strength, radial strain, average strain rate, and failure mode of sandstone under different test conditions were investigated. Test results revealed that the brittleness of sandstone specimens is enhanced at 200°C and 400°C, but slight ductility is observed at 600°C and 800°C. The strain rate effect of dynamic tensile strength is closely related to temperature. When the striker velocity exceeds 2.3 m/s, the dynamic radial strain first decreases and then increases with rising temperature. A quadratic polynomial relationship between the dynamic radial strain and temperature was observed. The temperature effect on the average strain rate is strong at low striker velocity and weak at high striker velocity. In the dynamic splitting tensile tests, high-temperature sandstone specimens are split into two semicylinders along the radial loading direction.

Effects of high temperature on the mechanical behavior of calcium silicate hydrate under uniaxial tension and compression

2021 ◽  
pp. 105678952199187
Author(s):  
Yao Zhang ◽  
Qing Chen ◽  
J Woody Ju ◽  
Mathieu Bauchy
Keyword(s):  
Tensile Strength ◽  
Compressive Strength ◽  
High Temperature ◽  
High Temperatures ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Atomic Scale ◽  
Stress Strain ◽  
Residual Compressive Strength ◽  
Residual Properties

When subjected to high temperatures, cement-based materials can dehydrate, which, in turn, affects the mechanical property of the main binding phase (calcium silicate hydrate) at the atomic scale. However, the effects of high temperature on the tensile and compressive behavior of calcium silicate hydrate (C−S−H) grains under uniaxial loading remains poorly understood. In this work, based on reactive molecular simulations, the tensile strength, compressive strength, and stress-strain relations of C−S−H grains with four calcium/silicon (C/S) ratios (1.10, 1.33, 164, and 1.80) both under and after (residual properties) high temperatures are investigated. It is shown that C−S−H grains can shrink due to the water loss induced by high temperature, and a low C/S ratio can lead to a thermo-stable molecular structure. Meanwhile, the residual tensile strength can be enhanced, particularly the tensile strength in the z-direction. Upon the residual compressive strength, in the x and y directions, high temperature can decrease the residual compressive strength for C/S = 1.10 or 1.33 but has no apparent effect for C/S = 1.64 or 1.80. While in the z-direction, the residual compressive strength can be enhanced due to the reduction in the interlayer space. In addition, high temperature can improve the residual tensile ductility but has no obvious effect on the residual compressive stress-strain relations. As for the mechanical properties under high temperature, both the tensile and compressive strengths can be weakened except that the tensile strength in the z-direction can undergo an increasing trend when the temperature is below 800 K due to significant shrinkage in the z-direction. Moreover, high temperature can make stress-strain curves exhibit good plasticity. Discussion indicates that the strength degradation of C−S−H gels or cement paste exposure to high temperatures is likely caused by the increasing porosity and coarsening of the void or defect size.

High Temperature n- and p-type Doped Microcrystalline Silicon Layers Grown by VHF PECVD Layer-by-Layer Deposition

2003 ◽  
Vol 762 ◽  
Author(s):  
A. Gordijn ◽  
J.K. Rath ◽  
R.E.I. Schropp
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
High Temperatures ◽  
Continuous Wave ◽  
Hydrogen Plasma ◽  
Silicon Layer ◽  
Dark Conductivity ◽  
High Deposition Rate ◽  
Layer By Layer ◽  
Microcrystalline Silicon

AbstractDue to the high temperatures used for high deposition rate microcrystalline (μc-Si:H) and polycrystalline silicon, there is a need for compact and temperature-stable doped layers. In this study we report on films grown by the layer-by-layer method (LbL) using VHF PECVD. Growth of an amorphous silicon layer is alternated by a hydrogen plasma treatment. In LbL, the surface reactions are separated time-wise from the nucleation in the bulk. We observed that it is possible to incorporate dopant atoms in the layer, without disturbing the nucleation. Even at high substrate temperatures (up to 400°C) doped layers can be made microcrystalline. At these temperatures, in the continuous wave case, crystallinity is hindered, which is generally attributed to the out-diffusion of hydrogen from the surface and the presence of impurities (dopants).We observe that the parameter window for the treatment time for p-layers is smaller compared to n-layers. Moreover we observe that for high temperatures, the nucleation of p-layers is more adversely affected than for n-layers. Thin, doped layers have been structurally, optically and electrically characterized. The best n-layer made at 400°C, with a thickness of only 31 nm, had an activation energy of 0.056 eV and a dark conductivity of 2.7 S/cm, while the best p-layer made at 350°C, with a thickness of 29 nm, had an activation energy of 0.11 V and a dark conductivity of 0.1 S/cm. The suitability of these high temperature n-layers has been demonstrated in an n-i-p microcrystalline silicon solar cell with an unoptimized μc-Si:H i-layer deposited at 250°C and without buffer. The Voc of the cell is 0.48 V and the fill factor is 70 %.

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