Addition Of Chromium Research Articles

Improving the ceria-mediated water and carbon dioxide splitting through the addition of chromium

The solar thermochemical water and carbon dioxide splitting, mediated by ceria, has a great potential to produce “green” syngas. Chromium was added to ceria to improve the syngas production. Three preparation methods were applied, resulting in different morphologies allowing to investigate the role of chromium. The samples were characterized by X‐ray diffraction, Raman and X-ray spectroscopy, and electron microscopy. Materials made by polymerized-complex-method and dry-impregnation consisted of two crystal phases: ceria and chromia. In contrast, materials made by flame-spray pyrolysis exhibited a homogeneous Cr-doped ceria phase, and chromia was found only at a chromium-content higher than 25mol%. The chromium-doped ceria released additional oxygen during the formation of CeCrO3 perovskite, which did not enhance hydrogen or carbon monoxide production. All chromia-containing samples exhibited improved oxygen exchange capacity, possibly due to a redox cycle of chromia itself, and significantly improved the activity of water and carbon dioxide splitting. Hydrogen production increased from 3.2 to 6.7mL/g and the time to reach redox equilibrium was shorten from 41 to 3min. The best hydrogen and carbon dioxide production rates were up to 20 and 500 times higher than pure ceria, respectively. The presence of chromium is therefore crucial as a catalyst, promoter, and oxygen storage enhancer. This work emphasises the importance of a catalysed re‐oxidation reaction and demonstrates that a metal oxide, becoming active in situ, can catalyse water and carbon dioxide splitting.

Effect of intensive cooling of alloy AM60 with chromium and vanadium additions on cast microstructure and mechanical properties

AbstractThe work presents the results of the investigations of the effect of intensive cooling of alloy AM60 with additions of chromium and vanadium on the microstructure and mechanical properties of the obtained casts. The experimental casts were made in ceramic moulds preliminarily heated to 180°C, into which alloy AM60 with the additions was poured. Within the implementation of the research, a comparison was made of the microstructure and mechanical properties of the casts obtained in ceramic moulds cooled at ambient temperature and the ones intensively cooled in a cooling liquid. The kinetics and dynamics the thermal effects recorded by the TDA method were compared. Metallographic tests were performed with the use of an optical microscope and the strength properties of the obtained casts were examined: UTS(Rm), elongation (A%), and HB hardness.

Effects of Nickel and Chromium Additions on Microstructure of P/M 316L Stainless Steels

The present study aims to investigate the effects of Ni and Cr additions on microstructure of P/M 316L stainless steels. The optimum content of both elements to maximize the oxidation resistance of the stainless steel with minimum σ phase formation and microstructural development in various sintering times are also examined. The 316L samples were produced by homogeneously mixing Ni and Cr powders in various contents, followed by cold compaction at high pressure for 30 s. The solutioning process was performed at 1300°C for 45 s under hydrogen atmosphere. The sintering temperature was at 800°C and the sintering times were selected at 200, 400 and 600 hrs, in order to simulate working conditions. The development of microstructure was examined through optical microscope. It is found that the addition of Ni and Cr resulted in the formation of different porosity contents. The porosity increases when the content of the powders increases.

A review of chromium(VI) use in chlorate electrolysis: Functions, challenges and suggested alternatives

Sodium chlorate is industrially produced by electrolysis of an aqueous salt solution, in which chromium(VI) constitutes an important excipient component. It is added to a concentration of a few grams Na2Cr2O7/liter to the electrolyte and has several functions in the process, the most important being to increase the Faradaic efficiency for hydrogen evolution in the undivided electrochemical cells. A thin film of Cr(OH)3×nH2O formed by reductive deposition on the cathodes decreases the rate of unwanted side reactions, while still enabling hydrogen evolution to occur. In addition chromium(VI) buffers the electrolyte at the optimum pH for operation and promotes the desired homogeneous reactions in the electrolyte bulk. Chromium species also affect the rates of hydrogen and oxygen evolution at the electrodes and are said to protect the steel cathodes from corrosion.Although chromium(VI) stays in a closed loop during chlorate production, chromate is a highly toxic compound and new REACH legislation therefore intends to phase out its use in Europe from 2017. A production without chromium(VI), with no other process modifications is not possible, and today there are no commercially available alternatives to its addition. Thus, there is an urgent need for European chlorate producers to find solutions to this problem. It is expected that chromium-free production will be a requirement also in other parts of the world, following the European example.As the chromium(VI) addition affects the chlorate process in many ways its replacement might require a combination of solutions targeting each function separately. The aim of this paper is to explain the role and importance of chromium(VI) in the chlorate manufacturing process. Previous achievements in its replacement are summarized and critically evaluated to expose the current state of the field, and to highlight the most promising avenues to be followed. An attempt is also made to reveal connections with other research fields (e.g. photochemical water splitting, corrosion science) facing similar problems. Allied effort of these different communities is expected to open up research avenues to the mutual benefit of these fields.

Effects of chromium additions on the three-body abrasive wear behavior of Fe-3.0 wt% B alloy

The effects of chromium additions on three-body abrasive wear behavior of Fe-3.0wt% B alloy have been systematically investigated using a moving wedge type of apparatus and two types of abrasives (SiC and SiO2 grains). Features of both the worn surface and subsurface have been discussed with regard to the respective wear rates. As chromium increased, the wear rate of Fe-3.0wt% B alloy first decreases to a minimum and then increases slightly for both abrasives. That behavior exactly reflects an opposite trend to the fracture toughness of the boride. The wear rate against SiC is evidently higher than that against SiO2. Mixed layers comprised of boride fragments and fatigued metallic matrix can be observed on the worn surfaces of the sample without Cr. Furthermore, the surface roughness resulting from wear first decreases and then increases using SiC; however, no obvious change takes place in the case of wear by SiO2. In the worn subsurface, serious fracture of the boride phase appears in 0wt% Cr sample while nearly no such cracks can be found in the 2wt% Cr sample. It is concluded that during three-body abrasive wear process involving both impact and indentation, the fracture toughness of the boride phases, apart from the bulk material hardness, plays a key role in the wear behavior of Fe-3.0wt% B alloy.

Structural and optical properties of lithium tetraborate glasses containing chromium and neodymium oxide

Lithium tetraborate glass samples containing Chromium and Neodymium were prepared. The density, molar volume, Oxygen packing density and N4 indicate the glass samples containing 0.25 and 0.75mol% Nd2O3 have the opening glass structure. From the absorption spectra of glass samples the Judd-Ofelt theory has been applied to the measured oscillator strengths and determines the three phenomenological intensity parameters Ω2, Ω4 and Ω6 for glass. Chromium and Neodymium addition a gradual conversion of chromium ions from Cr6+ ion to Cr3+ ion acts as modifiers breaking up local symmetry and introduces coordinated bond defects in these glasses, which effect on the environment around the Nd3+ ions. The large Ω2 value suggests a lower symmetric coordination around the Nd3+ and they attract Nd3+ cations to form various BONd bonds. The deviation parameters δrms, was determined. The hypersensitive transition, found to be 4f9/2→4G5/2+2G7/2.

Thermal stability, adsorption and rheological behaviors of sulfonated polyacrylamide/chromium triacetate/laponite nanocomposite weak gels

The objective of the present study is to improve the behavior of sulfonated polyacrylamide (SPA) by adding Laponite and/or chromium(III) with a focus on enhanced oil recovery applications. The resultant systems are weak nanocomposite hydrogels which are subjected to rheological, thermal stability and adsorption tests. The interactions between ingredients of the hydrogel are investigated by Fourier transform infrared (FTIR) spectroscopy. In addition, dispersion of Laponite nanoparticles in hydrogel is confirmed by transmission electron microscopy (TEM). The thermal stability is determined by measuring the loss of viscosity after an aging cycle. The adsorption tests are performed on calcite and evaluated using thermo gravimetric analysis. FTIR spectra confirmed the interaction of Laponite and Cr3+ with SPA. TEM micrograph showed an approximately uniform dispersion of Laponite in the crosslinked SPA/Cr3+/Laponite system. The viscoelastic behaviors of the systems improved with the addition of either Laponite or chromium(III). The sulfonated polyacrylamide/chromium(III)/Laponite system slightly loses its viscosifying power when subjected to harsh conditions of themo-chemical aging process. The adsorption behavior of the systems improved with Laponite concentration while the presence of chromium(III) weakened the adsorption. Therefore the introduced polymeric systems of the present study may be a potential option for enhanced oil recovery applications in hostile conditions.

Inhibitive characteristics of cetylpyridinium chloride and potassium chromate addition on type A513 mild steel in acid/chloride media

AbstractLinear polarization resistance and open circuit potential methods were used to assess the inhibitive and adsorption behaviour of Potassium chromate (K2CrO4) and Cetylpyridinium chloride (CPC) on mild steel (MS) in HCl/NaCl solution. Results obtained show that K2CrO4 and CPC inhibit MS significantly against massive degradation. However, under open circuit potential method, inhibition efficiency of K2CrO4 decreased at higher concentration. The synergistic effect of both inhibitors is positive on the protection of mild steel against corrosion. An inhibitive efficiency of over 60% was recorded for the combined admixture. Morphological study showed that the exposed steel with the presence of K2CrO4 and CPC possess some corrosion product with lesser pitting effect compare to unprotected steel with severe surface deterioration and uniform corrosion degradation. The corrosion inhibition performance of K2CrO4 and CPC on mild steel surface was found to follow Langmuir adsorption isotherm model.

Electrochemical Impedance Study of an Al6063-12%SiC-Cr Composite Immersed in 3 wt. % Sodium Chloride

Aluminium Matrix Composites (AMCs) have received considerable attention among researchers and emerging as a prominent choice material for building and construction purposes. The preference of AMCs as replacement for conventional aluminium alloys is chiefly due to its excellent strength-to-weight ratio. However, the problem of accelerated corrosion attributed to the reinforcement particles used in the production of AMCs is well documented in the literature and serves as potential limitations for its applications. In this work, an attempt was made to study the influence of chromium (Cr) additions on the corrosion behaviour of Al6063-SiC-Cr composites. The novel Al6063-12%SiC-Cr composites were prepared with 0, 3 and 6 wt. % Cr by using a double stir casting technique. Electrochemical Impedance Spectroscopy (EIS) was used to study the corrosion behaviour of the as cast composites surfaces when immersed in 3 wt. % Sodium Chloride buffered to a pH of 8 ± 0.3 using 0.1 M Sodium Hydroxide (NaOH) solution for 72 hours. From the Nyquist plots and equivalent circuit fitting results, the charge transfer resistance values were observed to change from 10 to 3.7 KΩ, 30 to 9.5 KΩ, 19 to 2.8 KΩ for 0, 3 and 6 wt. % Cr content respectively after 72 hours of exposure. The increase in charge transfer resistance (Rct) values obtained with increasing Cr content was a clear indication of improved resistance to corrosion.

Effect of Chromium and Nickel Additions on the Transformation Characteristic and Ferrite Grain Size Refinement of Low Carbon Structural Steels Containing 0.13% C

The effect of small addition of chromium and nickel alone or in combination on the transformation characteristic and ferrite grain size of low carbon (0.13%C) structural steels have been studied by cooling suitable steels at four different cooling rates ranging from 120°C/min to 3.6° C/min from temperatures giving a constant austenite grain size of 37 μm. Radio Frequency generator with control system was used for the heat treatment of the steel samples. Optical microscopy of the heat treated samples was carried out. Ferrite grain size was determined from the fictitious ferrite grain size measured by mean linear intercept method and the volume fraction of pearlite obtained by optical microscopy and point counting. It was found that although the heat treatment of the steels was started from a common austenite grain size, their subsequent ferrite grain size after cooling at the same cooling rate were not the same. Both chromium and nickel enhance the formation of Widmanstatten structure. But chromium is more effective than nickel in the formation of Widmanstatten structure. It was also found that the undissolved particles of chromium carbide (Cr2C) present during austenitizing have no role in determining the ferrite grain size. The precipitating particles of chromium carbide (Cr2C) are excellent ferrite grain size refiners. Nickel refines the ferrite grain size. In presence of nickel, Cr2C precipitates are less effective than Cr2C precipitates in absence of nickel in the refinement of ferrite grain size.

Effects of Chromium and Nickel Additions on the Austenite Grain Coarsening of Low Carbon Structural Steels Containing 0.13% C

The austenite grain coarsening behavior of low carbon (0.13% C) structural steels containing chromium and nickel singly or in combination were studied by heating the steels at successive high temperature in the austenite zone in the temperature range of 900-1100°C with an interval of 50°C. The carburizing technique has been adopted to reveal the prior austenite grain boundaries and mean linear intercept method was used to measure the austenite grain size.It was found that on heating the undissolved particles of chromium carbide, Cr2C refine the austenite grain size at temperature below 1000°C, but the effect decreases with increasing temperature. Nickel does not produce any austenite grain refinement. In the presence of nickel particles of chromium carbide are less effective than chromium carbide particles in the absence of nickel in the refinement of austenite grain size.

Effects of Cr and V additions on the microstructure and properties of high-vanadium wear-resistant alloy steel

The effects of chromium and vanadium additions on the microstructure, hardness and wear resistance of high-vanadium alloy steel (containing 5–10 wt-% V and 2–10 wt-% Cr) were studied by means of optical microscopy, scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Vickers hardness and Rockwell-hardness tester & M-200 ring block wear tester. Researching results showed that the solidification structure of high-vanadium wear-resistant alloy steel was mainly consisted α-Fe (martensite), vanadium carbide (VC), M3C and M7C3. Vanadium is mainly distributed over VC, and certain amount of vanadium exists in the matrix and M7C3 type eutectic carbide. Chromium is mainly distributed over the M7C3, and the matrix also contains a small quantity of chromium. It is found that the content of VC increases with the increase of vanadium content when carbon and chromium contents are constant. The change of micro- and macro-hardness was not obvious with the increase of vanadium content. The content of M7C3 type eutectic carbides increases gradually with the increase of chromium content when carbon and vanadium contents are constant. The micro- and macro-hardness increases with the increase of chromium content. The increase of vanadium content brings to the increase of wear resistance of alloy steel when carbon and chromium contents are constant. The change of chromium content had no obvious effect on wear resistance of high-vanadium alloy steel when carbon and vanadium contents. The increase of vanadium content brings to the increase of wear resistance of alloy steel when carbon and chromium contents are constant. The wear resistance of as-cast high-vanadium alloy steel is the best when the content of vanadium and chromium is 10 wt-% and 5 wt-% respectively.

Red and green emission from chromium metal or oxide on co-doped lithium tetraborate glass

Effect the addition of chromium metal or oxide on the structural and optical properties (absorption and emission) of the lithium tetraborate glass samples was studied. Samples of composition 99Li2B4O7-1 (Cr metal, Cr2O3 and CrO3) mol% were prepared by the melt quenching technique. The amorphous nature is determined using the XRD and DTA techniques. FTIR spectroscopy measured for glass samples. The addition of chromium splitting the broad bands of borate groups and the band around 420 nm indicates that the chromium ions enter the glass structure as a network former. The density indicates that the glass become more compact with the increase the number of oxygen. The optical properties measured and the absorption band indicates that the chromium has three absorption band at 446 and 620 nm were assigned to 4A2g (F) → 4T2g (F) and 4A2g (F) → 4T1g (F) that indicate the presence Cr3+ and the band at 688 nm was assigned to 4A2g (F) → 2Eg (G) that indicate the presence of Cr+6. The emission spectra measured in the excited wavelength λ = 274 nm and λ = 370 nm. A relative strong green and red emission can be observed in the Cr co-doped samples.

Ladle-treated high manganese steel reinforced by Cr7C3 phase

This research programme was designed to study the effect of chromium addition on the characteristic properties of Hadfield steel that has been produced by using the ladle treatment process. Chromium-containing ladle-treated Hadfield steel and chromium-free ladle-treated Hadfield steel have been produced, comparing with the Hadfield steel that has been produced by the conventional process. It has been found that chromium addition has a significant effect on the characteristic properties of the ladle-treated Hadfield steel. For instance, wear abrasion resistance was enhanced approximately five times much higher than conventional Hadfield steel. Moreover, an industrial trial indicates that chromium-containing ladle-treated Hadfield steel has significant benefits from the perspective of performance, and production cost as well.

The Effects of Iron, Silicon, Chromium, and Aluminum Additions on the Physical and Mechanical Properties of Recycled 3D Printing Filaments

AbstractWith the increasing use of 3D printers especially the fused filament fabrication type in the industries and general public, there is indeed a need to consider the after‐use treatment for the products. The use of recycled filaments as the feedstock for 3D printers is a feasible alternative, but its application is limited to rather poor product quality. This study, thus, evaluates the effects of adding iron (Fe), silicon (Si), chromium (Cr), and aluminum (Al) nano‐crystalline powders into the recycled polypropylene/high‐density polyethylene plastics feedstock for filament extrusion. Physical and mechanical analysis tests revealed that the addition of 1% Fe–Si–Cr or Fe–Si–Al resulted in better thermal stability, and up to 37% and 17% improvement, respectively, in yield strength and Young modulus compared with the original recycled filaments, possibly due to the enhancement of interfacial adhesion between the nano‐metal powders and the polymer, leading to reduced crack formation.

Effect of Cr Addition on Mechanical Properties and Wear Rate of Cast Al-Cu Alloy

Objectives: This paper investigates the effect of Cr addition on hardness, tensile properties and wear behaviour of Al-4.5Cu alloy A206. Methodology: The base alloy was melted and stirred well, fine Cr powder added in required amount, in oil fired pit furnace and poured into a permanent cast iron mold. The cast specimens were solution heat treated at 540⁰C for 4 hrs and were aged at 170⁰C for 17 hrs and 20 hrs. The as-cast and aged specimens were subjected to microstructure and EDAX evaluation followed by hardness, tensile and wear testing. Findings: The microstructure analysis and EDAX analysis reported an irregularly distributed polyhedral structures that appear blocky due to the phase formation of Al-Cr-Mn-Fe-Si. The hardness, ultimate tensile strength and yield strength were found to increase, reach a peak value and then decrease upon further chromium addition in aged condition. The wear rate decreased with increasing hardness and coefficient of friction remained constant with time. Application/Improvements: Evaluate the effect of Cr in Al alloys on the mechanical strength and wear properties.

On the Microstructure and Wear Behavior of Fe–xCr–4Mn–3C Hardfacing Alloys

The present paper describes an investigation aimed at evaluating the microstructural and dry sliding adhesive wear characteristics of Fe–xCr–4Mn–3C hardfacing alloys applied through shielded metal arc welding. The effect of chromium addition on the microstructure of hardfacings was carried out by using optical microscope, field emission scanning electron microscope and X-ray mapping. Dry sliding wear tests were performed on a pin-on-disc wear tribometer. From the experimental results, it was observed that the primary carbides were refined and increased with the increase of chromium content. The morphology of carbides revealed that the primary carbides were rod shaped. The increased chromium content was also found to be beneficial to enhance hardness and wear resistance of hardfacings. The correlation between hardness and wear resistance exhibited the reliability of hardness as an indicator of the wear performance of hardfacings.

Effect of Re-Oxidation Rate of Additive Cation on Corrosion Rate of Stainless Steel in Boiling Nitric Acid Solution.

Fuel reprocessing plant is important for atomic energy cycle which is aimed to re-use uranium (U) and plutonium (Pu) from the spent nuclear fuels after barning-out in light water reactor. PUREX process, in which boiling nitric acid is used for dissolving fuel elements, is adopted in Japan. Many structural materials are used stainless steels protected by passive layers of the surface. At the beginning of developing the plant, many troubles of intergranular corrosion of stainless steels were experienced. According to the investigations of these problems, very low carbon type austenitic stainless steels were utilized for the materials.However, these stainless steels were corroded in some cases. For example, addition of hexavalent chromium (Cr (VI)) is heavily accelerated corrosion rate of these stainless steels in boiling nitric acid solutions. The corrosion potential of stainless steel in Cr (VI) added solution is much higher than that in pure nitric acid solution.The authors introduced that heptavalent vanadium (V (V)) was also accelerated corrosion rate of these stainless steels but the tendency of acceleration process was different from the case of containing Cr (VI). We analyzed the valence stats of Cr and V during corrosion test and showed that Cr (VI) reduced to Cr (III) with corrosion of stainless steel propagating. On the other hand, amount of V (V) was not changed during the corrosion test. It was concluded that V (IV) was easily re-oxidized in boiling nitric acid solution. Namely, V (V) is reduced to V (IV) on stainless steel surface by cathodic reaction of corrosion and then V (IV) is re-oxidized immediately to V (V) in the balk nitric acid solution.These data were obtained using non-radioactive solutions in the ordinary laboratory. The present work is aimed to compare the data of re-oxidation rate of actinides which are included in the actual solutions used in a reprocessing plant. We implemented a specially designed electrochemical test cell used for analyzing the valence states of actinide cations, i.e. neptunium (Np) and Pu, in a boiling nitric acid solution. The cell was set into glovebox in a hot laboratory which could be handled nuclear fuel materials. The cell was designed for minimizing the solution. The amounts of solution used are about 15 cm3 and sample size of working electrode is about 4 mm2. Electrochemical measurements and spectrum analyses were conducted with this apparatus. Analyzed cations were Cr (VI), V (V), Pu (VI) and Np (VI). Polarization curves showed that corrosion potentials of stainless steels changed to higher direction by addition of these cations and also corrosion current densities increased. The higher order of those is Cr (VI), Np (VI), V (V) and Pu (VI). Re-oxidation rates were obtained by the changes of absorption spectra with time using lower valence state ions added solutions, i.e. Cr (III), V (IV), Pu (IV) and Np (V). These species are re-oxidized to Cr (VI), V (V), Pu (VI) and Np (VI), respectively. Re-oxidation rates of them were very much different among them. Very fast re-oxidation rates were obtained by the V (IV) and Np (V) added solutions. A very low re-oxidation rate was obtained by the Cr (III) added solution. The Pu (IV) added solution was in the middle of them. The corrosion of stainless steel is controlled by corrosion potential of cation added solution at the initial stage and controlled by re-oxidation rate of cation as time passed. The element Np which indicates high corrosion potential and has fast re-oxidation rate influences too much the corrosion of stainless steel in boiling nitic acid solution among these elements in consideration.

Analysis of wear properties of aluminium based journal bearing alloys with and without lubrication.

Apart from classical bearing materials, Aluminium alloys are used as bearing materials these days because of their superior quality. In this analysis, new Aluminium based bearing materials, with filler metals Si, Ni, and Cr are prepared by metal mould casting in burnout furnace machine, and tribological properties of these alloys with and without lubrication were tested. The experiments for wear with lubrication are conducted on multiple specimen tester and experiments without lubrication is conducted on Pin on disk tribometer. The disc material used was SAE 1050 steel. Wear tests were conducted at a sliding speed of 0.785 m/s and at a normal load of 20 N. Coefficient of friction values, temperature changes and wear of the specimens were plotted on graph according to the above mentioned working conditions. Hardness and weight losses of the specimens were calculated. The obtained results demonstrate how the friction and wear properties of these samples have changed with the % addition of Silicon, Chromium and Nickel to the base metal aluminium.

Features of Brittle Material Powder Compaction During Pressing

The compaction of (i) titanium, vanadium, and molybdenum carbide powders, (ii) mixtures of these powders with the addition of nickel, chromium, and niobium carbide powders, and (iii) coarse titanium and tungsten carbides as well as diamond powders clad with cobalt under compressive loading with a constant rate on the powder in a die at room temperature is studied. Based on the variation of the relative density of the compacts with current pressure, the variation of stresses in the matrix (forming a porous body) with its strain is determined. This enables to reveal the features of compaction, strain hardening, and fracture of brittle powder particles during pressing. It is established that for the molybdenum carbide powder, consisting of powder particles with pronounced irregular shape, the initial elastic deformation of the matrix abruptly transits into the stage of plastic deformation with almost linear strain hardening. At the final stage of the powder compaction, the particles are fractured. At the initial stage of pressing, an increase in the packing density of the powder particles and in their strain hardening occurs for titanium and vanadium carbide powders, whose particle shape is close to the rounded. With the increase in the density of the porous body, it is observed an almost linear strain hardening of the matrix, which changes into decay with decreasing shear stress, when the powder body approaches its non-porous state. As a result of pressing, the size of the coherent X-ray scattering areas decreased to 62 nm and the dislocation density in the titanium carbide particles grew to 8.3 · 1010 cm–2. With an increasing content of plastic metallic particles in the matrix with the particles of brittle materials, it is the metallic particles that predominantly undergo the plastic strain with strain hardening. This causes a sharp increase in the total strain hardening, reducing the density of the porous body during pressing. It is established an effective compacting of coarse titanium and tungsten carbide powders with cobalt-clad particles 200–600 μm in size. In this case the variation of the stress in the matrix with the strain of the matrix has a sharp yield point associated with high elastic limit, significantly exceeding the yield stress, and the time delay in the transition from a purely elastic deformation of the body to its plastic flow.