Assessment of a carbon steel quenching effect on residual magnetization using relations between magnetic parameters

The residual magnetization M _R dependences of carbon steels on the quenching temperature T _q are described using relations between the M _R and the saturation magnetization of the steels, the relaxation magnetization, and coercive force. Many of the reference data on the maximum magnetic permeability ?? _m of carbon steels are shown to be unreliable. Data calculated from the dependence M _R make it possible to estimate ?? _m of carbon steels quenched from various temperatures T _q. It is shown that ?? _m possesses the highest sensitivity to changes in T _q of carbon steels.     

Specific features of reactions of Am(V) with reductants in weakly acidic solutions

In EDTA solutions with pH ??5 at 25°C, Am(V) in a concentration of 5 × 10^?4?3 × 10^?3 M slowly transforms into Am(III). The Am(V) reduction and Am(III) accumulation follow the zero-order rate law. In the range 60?C80°C, the reaction is faster. In some cases, an induction period is observed, disappearing in acetate buffer solutions. In the range pH 3?C7, the rate somewhat increases with pH. In an acetate buffer solution, an increase in [EDTA] accelerates the process. The activation energy is 47 kJ mol^?1. Zero reaction order with respect to [Am(V)] is observed in solutions of ascorbic and tartaric acids, of Li₂SO₃ (pH > 3), and of hydrazine. The process starts with the reaction of Am(V) with the reductant. The Am(III) ion formed in the reaction is in the excited state, *Am(III). On collision of *Am(III) with Am(V), the excitation is transferred to Am(V), and it reacts with the reductant: *Am(V) + reductant ?? Am(IV) + R₁ and then Am(IV) + reductant ?? *Am(III) + R₁, Am(V) + R₁ ?? Am(IV) + R₂. A branched chain reaction arises. The decay of radicals in side reactions keeps the system in the steady state; therefore, zero reaction order is observed.     

Effect of pH on the formation-dissolution processes of anodic films on bismuth

Interrupted polarization measurements indicate that among Na₂SO₄, buffer (pH 7) and NaOH, the most passivating anodic film is formed on bismuth in the buffer solution. Under opencircuit conditions, film growth occurs on the metal surface in buffer solutions of pH 1.81 to 11.25. The rate of growth increases with decrease in pH. The passive metal undergoes dissolution in buffer solutions according to a zero-order mechanism; the most effective pH values for film dissolution lie between 8 and 10. The results indicate the simultaneous importance of the anion type and pH of the electrolyte in determining anodic film stability.     

Microwave Response of Perfect YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript> Thin Films Deposited on CeO<Subscript>2</Subscript>-Buffered Saphire: A Probe for Pairing Symmetry

Microwave surface impedance, Z _s(T), of epitaxial YBCO thin films deposited on CeO₂-buffered sapphire substrates, was measured at several discrete frequencies within the range 5–134 GHz by use of coplanar resonator and end-plate cavity resonator techniques. The main features of obtained experimental results are as follows: (i) surface resistance R _s(T) at low temperatures obeys the exponential law: R _s(T) = R _res+R ₀⋅exp [−δ/T] with a small gap δ value (δ≈ 0.7 T _c); (ii) the most perfect quasi-single-crystalline films reveal a distinct two-peak structure of R _s(T) dependence, which is not observable in films with a less ordered crystal structure. These features are believed to reveal some intrinsic electron properties of such films, namely: (i) mixed (d+is) type symmetry of electron pairing, and (ii) dominant role of extended c-oriented defects (e.g., edge dislocation arrays or twin planes) in quasiparticles scattering for the most perfect films, which demonstrate the two-peak anomalous R _s(T) behavior.     

Fundamental analysis of recombinant human epidermal growth factor in solution with biophysical methods

Correlation of thermodynamic and secondary structural stability of proteins at various buffer pHs was investigated using differential scanning calorimetry (DSC), dynamic light scattering (DLS) and attenuated total reflection Fourier-transform infrared spectroscopy (ATR FT-IR). Recombinant human epithelial growth factor (rhEGF) was selected as a model protein at various pHs and in different buffers, including phosphate, histidine, citrate, HEPES and Tris. Particle size and zeta potential of rhEGF at each selected pH of buffer were observed by DLS. Four factors were used to characterize the biophysical stability of rhEGF in solution: temperature at maximum heat flux (T_m), intermolecular β-sheet contents, zeta size and zeta potential. It was possible to predict the apparent isoelectric point (pI) of rhEGF as 4.43 by plotting pH against zeta potential. When the pH of the rhEGF solution increased or decreased from pI, the absolute zeta potential increased indicating a reduced possibility of protein aggregation, since T_m increased and β-sheet contents decreased. The contents of induced intermolecular β-sheet in Tris and HEPES buffers were the lowest. Thermodynamic stability of rhEGF markedly increased when pH is higher than 6.2 in histidine buffer where T_m of first transition was all above 70?°C. Moreover, rhEGF in Tris buffer was more thermodynamically stable than in HEPES with higher zeta potential. Tris buffer at pH 7.2 was concluded to be the most favorable.     

Pair and Quasiparticle States of YBa2Cu3O7−x Films Deduced from the Surface Impedance and a Comparison with Nb3Sn

Surface impedance data at 19 and 87 GHz of high-quality epitaxial YBCO films on different substrates are compared with data for Nb₃Sn films on sapphire in terms of pair and quasiparticle (qp) transport. Surface resistance R _s and penetration depth λ of YBCO are strongly affected by temperature dependent qp scattering, which is depressed in films with enhanced lattice strain. All films showed a comparable residual resistance R _res(19 GHz)～90 μΩ constituting a qp reservoir which is likely to be caused by the electronic configuration and by impurities. Subtracting R _res from R _s (T) revealed activated behavior with a reduced energy gap Δ₀/k _B T _c～0.9 for a film on sapphire, but power-law behavior for the other films. The penetration depth did not reveal power-law dependences at T≤0.5 ·T _c, but was consistent with a reduced energy gap of 0.45 for a film on MgO. The increase of λ(T) at T≥0.5 · T _c was related to qp scattering, which also caused an extremal conductivity σ₁(T). A shoulder in λ(T) at T=(0.6–0.7) · T _c confirmed evidence for the existence of two superconducting bands. The magnetic-field induced recovery of λ(B) of various YBCO films hinted for an important role of magnetic scattering. The results are in contradiction to a d-wave symmetry of the order parameter, at least for the chain band.     

T-Stress solutions for a semi-elliptical axial surface crack in a cylinder subjected to mode-I non-uniform stress distributions

This paper presents the T-stress solutions (T₁₁ and T₃₃) for semi-elliptical axial surface cracks in a cylinder subjected to mode-I non-uniform stress on the crack surface. Two cylindrical geometries with inner radius (R_i) to wall thickness (t) ratios R_i/t = 5 and 10 were considered. The T-stresses were applied along the crack front for normalized crack depth values a/t of 0.2, 0.4 and 0.5 and aspect ratios a/c of 0.2, 0.4, 0.6 and 1.0. Three stress distribution; uniform, linear and parabolic were applied to the crack face. In addition to these solutions, concrete formulation of the superposition principle is given for the T₃₃-stress, which is known as an elastic parameter that describes the out-of-plane crack tip constraint effect. Then, the validity of the formulation was shown through application of our T-stress solutions to the problem of an axial semi-elliptical surface crack in a cylinder subjected to internal pressure, and checking that the principle of superposition holds for the problem.     

Microwave Surface Impedance and Complex Conductivity of High-T c Single Crystals: Current State and Unsolved Problems

Common and distinctive features of the temperature dependences of microwave surface impedance Z(T)=R(T)+iX(T) and conductivity σ(T) in the ab-plane and along the c-axis of high-T _c single crystals (HTSC) are discussed. The main attention is focused on an evolution of these dependences in YBaCuO crystal with the oxygen deficiency. Comparison of YBaCuO with other HTSC crystals reveals a number of peculiarities, namely, the linear dependence R_ab(T) ∞ T up to T _c/2 in HTSC single crystals with tetragonal lattice and up to T _c/3 in YBaCuO where R _ab (T) shows also a broad peak at T∼ T_c/2; breakdown of normal skin effect in some HTSC crystals; dramatic effect of pseudogap on the superfluid density in the heavily underdoped YBCO; several orders of magnitude higher residual surface resistance in HTSC when compared to conventional superconductors; etc. Possible explanations are discussed in the context of the specific features of HTSC structure and in the framework of recent models of quasiparticles’ c-transport and pseudogap state in HTSC.     

On the anomalous CMN-He3 3 thermal boundary resistance

It is proposed that the mechanism of the anomalously high thermal transfer rates observed between CAIN and liquid He³ is simply the electromagnetic dipole coupling between electrons and He³ nuclei. A crude theory based on this assumption explains the observed linear dependence of the Kapitza resistanceR _K onT, the order of magnitude of the coefficient, and the absence to date of the effect in dilute He³-He⁴ solutions. We predict that (1)R _K (T) should go through a minimum at about 1 mdeg, (2)R _K should be decreased by applying a magnetic field, (3) a similar linearT dependence (though with much larger coefficient) should be seen in dilute solutions below 5 mdeg, and (4) a similar, though probably less striking effect, should be observed for ferromagnetic metals in contact with He 3 at sufficiently low temperatures.Supported by Nordita.An up-to-date account of the experimental and theoretical situation regarding this effect can be found in Ref. 1:     

Buffer layers for high-T c thin films on sapphire

Buffer layers of various oxides including CeO₂ and yttrium-stabilized zirconia (YSZ) have been deposited onR-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa₂Cu₃O_7?δ (YBCO) thin films. An ion beam channeling minimum yield of ～3% was obtained in the CeO₂ layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO₂ was found to be the best one for YBCO thin films onR-plane sapphire. HighT _c andJ _c were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were ～4 mω at 77 K and 25 GHz.     

Degradation study on ternary zinc magnesium phosphate glasses

Glasses with composition (ZnO)₃₀(MgO) _x (P₂O₅)_70−x (x = 5, 8, 10, 13, 15, 18, and 20 mol.%) have been successfully prepared by the melt-quenching technique. Degradation study has been carried out by means of measuring their chemical durability against buffer solutions with initial pH values of 4.01, 7.00, and 10.01 at an ambient temperature for up to 30 days. The dissolution rate (D _R) was obtained by calculating the measured weight loss of the glasses per unit surface area per unit immersion time. The results show that the glasses have better corrosion resistance in basic solution. It was also found that the weight loss is related to the MgO concentration with lower P₂O₅ concentration exhibiting greater corrosion resistance irrespective of acidic, neutral, or basic solutions as immersion liquid. All the sample surfaces and edges were corroded and the solutions experienced a decrease in pH values during the duration of the corrosion test.     

EIS study of passivation of austenitic and duplex stainless steels reinforcements in simulated pore solutions

Stainless steel reinforcements have proved to be one of the most effective methods to guarantee the passivity of reinforced concrete structures exposed to highly chloride-contaminated atmospheres. In the present work, the corrosion behaviour of two traditional austenitic stainless steels (AISI 304 and 316L types), and one duplex type (2205) are compared with that of a low-nickel, much more economic, austenitic type (204Cu). Ribbed and ground bars of these four materials are studied in non-carbonated and carbonated, saturated Ca(OH)₂ solutions with different chloride contents, using electrochemical techniques. The low-frequency time constant represents the charge transfer resistance (R_t) in parallel with the double layer capacitance. The R_t value of the passive reinforcements seems to be related with the quality of the passive layer. R_t values increase with the immersion time in the testing solutions and decrease with the chloride content. Moreover, R_t tends to increase when the ribs of the bars are removed.     

Effect of abrasive water jet machining parameters on aramid fibre reinforced plastics composite

This paper presents a study on the effect of abrasive water jet machining (AWJM) process parameters on surface roughness (R _a) and kerf taper ratio (T _R) of aramid fibre reinforced plastics (AFRP) composite. Taguchi’s design of experiment was used as the experimental approach. Through analysis of variance (ANOVA), it was found that the traverse rate was considered to be the most significant factor in both R _a and T _R quality criteria. R _a and T _R were reduced as increasing the hydraulic pressure and reducing the standoff distance and traverse rate. However, there was no clear pattern for abrasive mass flow rate on both R _a and T _R. Therefore, it was confirmed that increasing the kinetic energy of water jet may produce a better quality of cuts. Mathematical models were also developed using multiple linear regression analysis to predict the performance of R _a and T _R in terms of AWJM process parameters. Considerably, the models are useful in predicting R _a and T _R in AWJM of AFRP laminate as shown in present study.     

Coprecipitation of Pu(IV) with Fe(III) and Cr(III) hydroxides from nitrate-acetate solutions under hydrothermal conditions simulating deep disposal of liquid radioactive wastes

Precipitation of Fe(III), Cr(III), Ni(II), and Mn(II) from nitrate-acetate solutions and coprecipitation of Pu(IV) with Fe(III) and Cr(III) were studied. The degree of precipitation of 80–95% is attained for Fe(III) at 95–200°C and pH>0.5–0.6, and for Cr(III), at T=95°C and pH≥4.0 or T=200°C and pH≥1.0. The phase composition of the precipitates formed by thermal hydrolysis of iron nitrate in model solutions was analyzed. Depending on pH and temperature, the solid phase contains various modifications of Fe₂O₃, FeOOH, and amorphous phases. Noticeable coprecipitation of plutonium from nitrate-acetate solutions is observed at pH≥4, and it is incorporated in the precipitate only at formation of FeOOH. No coprecipitation of Pu(IV) with Fe₂O₃ was found. Under the given experimental conditions, plutonium in aqueous solutions occurs in the oxidation state +4 forming monoacetate (or, probably, hydroxo acetate) complexes.     

Cleavage to quasicleavage fracture transition in steels

Abstract

The cleavage behaviour of plain carbon steels containing from 0· 2 to 0·8%C has been investigated. It is observed that each steel displays two characteristic temperatures at which a transition in the mode of fracture occurs. These are the transition temperatures for cleavage T_c and for general yielding T_g. At temperatures below T_c, the steels fail by pure cleavage. This involves the generation of a cleavage crack nucleus in a carbide particle followed by cleavage crack propagation. The cleavage fracture stress σ _f is independent of temperature. Between temperatures T_c and T_g, the steels fail by quasicleavage. This involves the generation of a crack nucleus by a localised fibrous process followed by cleavage crack propagation. The crack nucleation stage is shear stress controlled and therefore the quasicleavage fracture stress σ_q increases with decreasing test temperature. Above temperature T_g, failure occurs at or after general yielding.

MST/1045     

Influence of the chemical composition on transformation behaviour of low carbon microalloyed steels

In order to design thermomechanical schedules for processing low carbon microalloyed steels, the various critical transformation temperatures, i.e. the start and finish of the austenite transformation (A_r3, A_r1) and the non-recrystallization temperature (T_nr), must be determined. Continuous cooling torsion and compression testing are useful ways to measure these values. In this study six low carbon microalloyed steels with different additions (Nb, Cu, Si and Mo) were examined using these techniques. Moreover, the equilibrium phase diagrams for each alloy were calculated using FactSage. The comparison of the thermomechanical testing results with the thermodynamic calculations leads to a better understanding of the effect of the different elements on the transformation behaviour of pipeline steels. Regarding transformation temperatures, Cu in residual contents showed a strong effect on decreasing both A_r3 and A_r1, which indicates a hardenability effect of this element. On the other hand, increasing Nb contents increased T_nr by accelerating Nb(C,N) precipitation. However, when Si was added to a Nb-microalloyed steel, the T_nr decreased.     

Study of a hydraulic DCPA/CaO-based cement for dental applications

A CPC was obtained by mixing calcium hydrogenphosphate (DCPA: CaHPO₄) and calcium oxide with either water or sodium phosphate (NaP) buffers. Physical and mechanical properties such as compressive strength (CS), initial (I) and final (F) setting times, cohesion time (T_C), dough time (T_D), swelling time (T_S), dimensional and thermal behavior, injectability (t_100%), antimicrobial properties, setting reaction kinetics, and powder stability over time were investigated by varying different parameters such as liquid-to-powder (L/P) ratio (0.35 to 0.7 mL g⁻¹), molar calcium-to-phosphate (Ca/P) ratio (1.67 to 3), the pH (4, 7 or 9) and the concentration (0 to 1 M) of the NaP buffer. The best results were obtained with the pH 7 NaP buffer at a concentration of 0.75 M. With this liquid phase, physical and mechanical properties depended on the Ca/P and L/P ratios, varying from 3 to 11 MPa (CS), 6 to 10 min (I), 11 to 15 min (F), 15 to 45 min (T_S), 3 to 12 min (t_100%), 16 min (T_D). This cement expanded during its setting (2.5–7%), and is thus appropriate for tight filling. Finally the cement has antimicrobial activity from Ca/P = 2 and the whole properties were conserved after 8 months storage. Given the mechanical, rheological and antimicrobial properties of this new DCPA/CaO-based cement, its use as root canal sealing or pulp capping material may be considered as similar to calcium hydroxide or ZnO/eugenol-based pastes, without or with a gutta-percha point.     

Current opinion in medium manganese steel

Abstract

Medium Mn steels have been actively investigated due to their excellent balance between material cost and mechanical properties. The steels possess a single α′ martensite phase in hot and cold rolled states and multiphases after intercritical annealing. Many studies have focused on investigating the influences of chemical composition and annealing conditions on the microstructure, particularly the grain size and retained γ (γ_R), and on the tensile properties. The steels exhibit high strength and good ductility due to transformation induced plasticity occurring in γ_R, whose volume fraction is approximately 0·2–0·4. The present review summarises the important results of previous studies about the effects of both intercritical annealing conditions and alloying elements on the microstructure and tensile properties of medium Mn steels.     

Two-Peak Temperature Dependence of Microwave Surface Impedance of Single-Crystalline YBCO Thin Films: Role of Pairing Symmetry and Defect Structure

Temperature dependencies of microwave surface impedance were measured for c-oriented highly perfect YBCO thin films deposited by off-axis dc magnetron sputtering onto CeO₂-buffered r-cut sapphire substrates. A distinct two-peak structure of R _s(T) and X _s(T) dependencies with peaks at 28–30, K and 50, K has been revealed. The peaks become smeared at higher frequencies or in applied dc magnetic field, while the peak positions remain almost unchanged. The two-peak Z _s(T) behavior is believed to be an intrinsic electron property of extremely perfect quasi-single-crystalline YBCO films. A theoretical model is suggested to explain the observed anomalous Z _s(T) behavior. The model is based on the Boltzman kinetic equation for quasiparticles in layered high-T _c superconductors (HTS) cuprates. It takes into account the supposed s + d wave symmetry of electron pairing and strong energy-dependent relaxation time of quasiparticles, determined mainly by their elastic scattering on extended defects parallel to the c-axis.