The variation of thermoelastic properties under conditions of variation of isotopic composition of diamond

The parameters of interatomic interaction in diamonds of ¹²C and ¹³C isotopes are determined. The parameters are determined by two methods, namely, from the elastic modulus (potential no. 1) and from the sublimation energy at T = 0 K (potential no. 2). Based on these parameters, the Debye model is used to calculate the isobaric temperature dependences of the thermoelastic properties for isotopically different diamonds, namely, the coefficient of thermal expansion (CTE), the density, the elastic modulus B _T , and the specific heat capacity. It is demonstrated that the best agreement with the experimentally obtained dependences of the foregoing parameters is obtained when potential no. 1 is used in calculations. The values of CTE, density, and heat capacity increase in the case of transition from ¹²C diamond to ¹³C diamond. It is demonstrated that the inequality B _T (¹²C) < B _T (¹³C) is valid at T = 0 K, which is associated with the reduction of interatomic spacing in the case of transition from ¹²C diamond to ¹³C diamond. However, as the temperature increases, the volumetric isotopic effect in diamond decreases. It is found that the B _T (T) dependences for ¹²C and ¹³C diamonds intersect at a temperature below the Debye temperature. Therefore, at high temperatures, the elastic modulus for light-isotope diamond comes to exceed that for heavy-isotope diamond, B _T (¹²C) > B _T (¹³C). Experimental results are given which confirm this effect. The variation of the properties of isotopically different diamonds with increasing pressure is discussed.     

Unified model of nucleation and growth of fatigue cracks. Part 1. Use of force parameters of fracture mechanics of materials in the stage of crack nucleation

According to the phenomenological model of nucleation of a fatigue macrocrack, the process is considered as a two-parameter process. The process is described by the local stress or strain range and a certain linear parameter of the material. We propose the corresponding parameters, namely, the local stress range Δσ _y ^* and the characteristic sized ^* of the prefracture zone. The formation of this zone is caused by the anomaly of the yield strength of the material in subsurface layers, the microstructure, the loading amplitude, the cyclic strain hardening, and the environment. The quantityd ^* is a constant of the material, which is independent of the geometry of notch and specimen. the boundary of the prefracture zone is considered as a macrobarrier that determines the growth of microstructurally short and physically small cracks. The moment when a physically small crack oversteps the boundary of the prefracture zone is defined by the quantitative criterion (a ₀=d ^*) of the initial sizea ₀ of a macrocrack in the material. The proposed dependences of (Δσ _y ^* ,N _i ),N _i ) and (d ^*,N _i ) can be regarded as a basis for the determination of characteristics of resistance of the material to the nucleation of a fatigue macrocrack. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 1, pp. 7–21, January–February, 1998.     

Determination of the half-life of the spontaneous fission of240PU

Two metallic²⁴⁰Pu sources were certified as reference standards of spontaneous-fission activity and neutron flux. The certification results were used to determine the ratio T_&#x03B1;T_s&f of the alpha-decay and spontaneousfission half-lives of²⁴⁰Pu. The ratio was found to be (5.68&#x002B;-0.11)&#x00B7;10^&#x2212;8, which corresponds to T_s&f =(1.16&#x002B;0.02)&#x00B7;1011 yr for an assumed value T_&#x03B1;=6563&#x002B;7yr.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 57&#x2013;58, February, 1995.     

Coprecipitation of microamounts of radionuclides on chitosans of various molecular weights in solutions

Coprecipitation of ²³³U, ²³⁹Pu, ²⁴¹Am, ¹⁵²Eu, ⁹⁰Sr, ⁹⁰Y, and ⁶⁰Co on chitosans of various molecular weights (MW) was studied. Low-molecular-weight chitosan (LMWC) with MW of 5 kDa (5 × 10³ g mol⁻¹) proved to be a more effective coprecipitant than high-molecular-weight chitosan (HMWC) with MW of 700 kDa (7 × 10⁵ g mol⁻¹). With HMWC, the degree of coprecipitation (α) was 80% for ¹⁵²Eu and ⁹⁰Y, 99% for ²³³U and ²⁴¹Am, and 85% for ²³⁹Pu. For ⁶⁰Co, α monotonically increased with an increase in the chitosan concentration in solution and reached 40% at [HMWC] = 5 g l⁻¹. For ⁹⁰Sr, α did not exceed 3% in the entire examined range of chitosan concentrations. With LMWC, the α values for An, ¹⁵²Eu, and ⁹⁰Y differed insignificantly (92–99%). For ⁶⁰Co and ⁹⁰Sr, α increased to 40% in the range of chitosan concentrations from 0 to 1 g l⁻¹. The presence of inorganic salts in solution considerably decreases α of UO₂²⁺ with chitosans but does not noticeably affect the behavior of Am, Pu, and Eu. The effect of salts on the efficiency of ²³³UO^2/2+ coprecipitation on HMWC decreases in the order Na₂SO₄ > NaCl > Na₂CO₃ > NaNO₃ > Na₃PO₄. Based on the results obtained, a procedure suitable for expedition conditions was developed for preconcentration of Pu from seawater on chitosan, with simultaneous separation of Pu from U, for radioecological monitoring of natural waters. The specific activity of Pu in samples of near-bottom seawater of gulfs of the Novaya Zemlya archipelago was (150–170) ± 20 mBq m⁻³. The results are well consistent with the published data.     

Comparative Assessment of Ambient Air Quality of Major Cities of Pakistan

The deterioration of ambient air quality is one of the emerging environmental problems in developing countries of South Asia. Unplanned urbanization, population growth, degradation of vegetation cover and industrial and vehicular emissions, particularly in urban areas, have resulted in substantial rise in the level of air pollutants and emission sources. This study focused on monitoring of different cities as per traffic volume and flow. Air quality monitoring was conducted on hourly basis to determine the major parameters; i.e. PM₁₀, NO_x, SO₂, CO by using fixed station for 8 h from 1:30 pm to 9:30 pm. All the measuring values were then compared with the National Environment Quality Standards (NEQS) and Air Quality Index (AQI). Results revealed that the concentration of PM₁₀ at the selected areas of these cities ranged from 156 to 390 μg/m³, CO ranged from 1.18 to 6.01 mg/m³, and NO_x ranged from 32.65 to 129.47 μg/m³. It was evident that all these concentration had been higher than the permissible limits of NEQS, whereas only SO₂ was found within the permissible limits (15.60–110.52 μg/m³⁾. Air Quality Index (AQI) of all the designated points of cities was also assessed, and most of the vehicular and commercial areas had shown unhealthy and severe conditions ranging from 191 to 320, respectively.

     

Investigation of the thermodynamic criterion of crack resistance of steels

The article shows the validity of the previously proposed criterion K_Ic = K_Ic ^* + _0.2iK_Ic/_0.2 (K_Ic is reduced crack resistance, _0.2i is internal component of yield strength _0.2) for a wide range of body-centered cubic metals such as iron—carbon alloys (cast iron; low-, medium-, and high-strength carbon and alloy steels). It examines the relationship between this criterion and energy and force concepts of the fracture micromechanism. Existence of a common temperature dependence of the effective yield strength component in ferrite—pearlite carbon and alloy steels in the annealed, normalized, and heat-treated states is established. It is shown that the fraction of effective stress In the total yield strength, i.e., _0.2 ^*/_0.2 controls crack resistance K_Ic over a wide range of temperatures and deformation rates. For impact strength KCV, linear dependences of KCV — KCV/_0.2 and KCV-KCV/HB are observed In the zone of transition temperatures and cold brittleness threshold. A correlation equation connecting KCV and K_Ic over the indicated range is obtained. An applied software package has been worked out for computer-aided prediction of crack resistance and impact strength.Translated from Problemy Prochnosti, No. 8, pp. 14–22, August, 1993.     

Estimation of the accuracy of measurements of the corrosion rate by the method of polarization resistance

The method of polarization resistance is extensively used for the determination of the rate of corrosion. At the same time, the accuracy of measurements of the corrosion rate performed with industrial corrosion meters is often not estimated. By using an indicator, we find the accuracy of the measurements of the corrosion rate for 20 steel placed in 1N H₂SO₄ and 0.01N Na₂SO₄ solutions and for 12Kh18N10T steel placed in 1N and 10N H₂SO₄ solutions.Kiev Polytechnic Institute, Kiev. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 3. pp. 22–27, May–June, 1995.     

Viscosity of Some Binary Mixtures of Arenes

The viscosity of 12 binary mixtures of benzene+toluene, +ethylbenzene, +isopropylbenzene, +tert-butylbenzene; toluene+ethylbenzene, +isopro- pylbenzene, +tert-butylbenzene; ethylbenzene+isopropylbenzene; isopropylbenzene+tert-butylbenzene; o-xylene+m-xylene; m-xylene+p-xylene; and p-xylene+o-xylene has been measured over the entire range of composition. The viscosity deviations and excess Gibbs energy of activation G ^*E of viscous flow based on Eyring's theory have been calculated. The results have been analyzed in terms of the change in the structure of pure component molecules. The viscosity data have been correlated with the equations of Grunberg and Nissan; Hind, McLaughlin, and Ubbelohde; Tamura and Kurata; Katti and Chaudhri; McAllister; and Heric and Brewer. The Prigogine–Flory–Patterson– Bloomfield–Dewan (PFPBD) theory has been applied to analyze the excess viscosity of the present binary mixtures.     

Measurement of the heat of mixing of moderately dense gases

We have measured the heat of mixing of the gaseous mixtures CO₂-H₂, CO₂-He, Ar-He, and N₂-He at constant volume, at pressures from 2 to 25 bar, temperature 295°K, and a 14.3% concentration of the heavy component. We have determined the excess enthalpy of these mixtures, which varies slowly with pressure.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 6, pp. 946–949, June, 1982.     

Investigation of Near-Critical States of Molybdenum by Method of Isentropic Expansion

In this work release isentropes of shocked porous molybdenum were investigated. Samples with an initial porosity m = ρ₀/ρ = 1.4 and 3.1 were studied to achieve near-critical entropy states of metal after shock compression. Compressed samples were expanded into helium with different initial pressures. The brightness temperature of the metal and the helium shock wave velocity were measured with a fast multichannel pyrometer. The helium shock wave velocity was used to determine the final pressure (P_S) of expansion of the metal and the velocity of metal expansion (W_S). Location of peculiarities on the P_S–W_S and P_S–T_P curves of the isentropes gives the location of their entrance into the two-phase region. Estimation of the molybdenum critical temperature and pressure was carried out on the basis of the experimental data. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Study of effects of deep cryotreatment on mechanical properties of 1.2542 tool steel

Normally, increase in strength and wear resistance of tool steels is associated with a reduced ductility. However, deep cryotreatment (DCT) may be used to simultaneously increase tensile strength and hardness and improve ductility of tool steels. In this work, effects of different DCT cycles on mechanical properties of 1.2542 tool steel have been studied. Three sets of specimens were investigated: two sets of untreated specimens, for studying the effect of some hardening parameters on the metal properties, and a third set consisting of cryotreated specimens. Soaking and tempering temperatures were kept constant at −196 °C and 200 °C, respectively. Different cryotreatment cycles were implemented by varying soaking time (24, 36 and 48 h) and tempering duration (60, 120 and 180 min). In order to ensure optimum treatment conditions, time gaps between various treatment steps were kept to minimum. Results show that two cryotreatment cycles consisting of: (i) 36 h soaking at −196 °C and 1 h tempering at 200 °C, and (ii) 48 h soaking at −196 °C and 2 h tempering at 200 °C produce the best effects in the cryotreated 1.2542 tool steel specimens, namely 32–36% increase in tensile strength, 9–12% increase in hardness, and 12–35% improvement in ductility.     

Improvement of yield strength of LM24 alloy

In this study, Al₂O₃ particles were employed to improve the microstructure of LM24 and therefore, to increase the yield strength and tensile strength of this kind of alloy. In situ Al₂O₃ particles were obtained by direct reaction between oxygen and Al melt at 750–800 °C. Microstructure examination shows that the size of in situ formed Al₂O₃ particles was about 1–2 μm, and interestingly, with addition of in situ Al₂O₃ particles, the coarse primary Si phase was disappeared completely. More important, the yield strength and the tensile strength of Al₂O₃/LM24 are increased by 52 MPa, 16 MPa than that of LM24 alloy with 0.1% Sb addition. The value of 181 MPa and 315 MPa is for yield strength and tensile strength of Al₂O₃/LM24 respectively. Besides, the yield strength and tensile strength are 180 MPa and 314 MPa respectively for Al₂O₃/LM24 alloy after remelting and casting. This verifies that the improvement of mechanical properties of such kind of material possesses stability and reliability.     

Synthesis of Spinel MnCo2O4 by Thermal Decomposition of Carbonates and Kinetics of Thermal Decomposition of Precursor

The cubic MnCo₂O₄ was prepared by calcining MnCO₃-2CoCO₃?1.5H₂O above 600 ^°C in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometer. The result showed that high-crystallized MnCo₂O₄ with cubic structure [space group Fd-3m(227)] was obtained when the precursor was calcined above 600 ^°C in air for 6 h. Magnetic characterization indicated that cubic MnCo₂O₄ behaved weak magnetic behavior at room temperature. The thermal process of the precursor in air experienced three steps, which are: first, the dehydration of 1.5 water molecules, then the decomposition of MnCO₃-2CoCO₃ into cubic MnO₂ and cubic Co₃O₄, and at last the reaction of MnO₂ with Co₃O₄ into cubic MnCo₂O₄. Based on the KAS equation, the values of the activation energies associated with the thermal process of MnCO₃-2CoCO₃?1.5H₂O were determined.     

Investigation of the Serviceability of Tubing Strings Made of Steel of Strength Group K

The resistance of steel of strength group K to corrosion, hydrogen-corrosion, and stress-corrosion fracture is analyzed for hydrogen-sulfide-containing media of the Lokachi gas field and in the NACE solution. It is shown that the indicated type of steel is not susceptible to hydrogen-induced cracking, its resistance to sulfide fracture σ _ssc ≈ 0.8 σ_{0.2 min}, and the rate of corrosion is much lower than the dangerous threshold value. This enables us to conclude that the tubing and casing strings made of this type of steel can be safely exploited at the Lokachi gas field.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 1, pp. 109–110, January–February, 2005.     

Effect of mechanical properties of material on rate of fatigue crack propagation

Many experimental and analytical equations on a rate of a fatigue crack propagation have been proposed. However, it seems that they can not fully express its complex behavior. There are still many problems remaining to be solved in order to clarify its mechanism. One of them is to clarify the relation between the rate of the crack propagation and the mechanical properties of material. In this paper, the rate of the crack propagation is analysed to clarify this problem. This analysis is based on the observation results of the fatigue crack propagation behavior previously by the authors. The analytical result is compared with the experimental one to make sure that they agree with each other. The conclusion obtained is; the rate of fatigue crack propagation is expressed by using the stress intensity factors as

$\text{dl}\text{dN}\text{= {}\text{c}\text{[Y}{}^2\text{F}{}^{\mathrm{a}}\text{E}{}^{\mathrm{a(1?n)}}\text{]}\text{} (K}{}_{\max }\text{)}{}^2\text{(K}{}_{\mathrm{a}}\text{)}{}^{\mathrm{a(2?n)}}$

. where C is a constant; E, Young's modulus; F, plastic coefficient; Y, yield stress; K_max and K_a, maximum and amplitude of the stress intensity factor, and α and n, exponents of the Manson-Coffin's law and work-hardening.     

Some New Aspects of Chlorination of Fullerenes

Abstract

The effect of the reagent ratio, reaction time and power of the reagent on the product composition in chlorination of [60]fullerene was studied. Chlorofullerenes C₆₀Cl₆, C₆₀Cl₈, C₆₀Cl₁₀, C₆₀Cl₁₂, C₆₀Cl₁₄, and C₆₀Cl₂₆ were synthesized and characterized by chemical analysis, FTIR, ¹³C NMR, and MALDI TOF mass spectrometry. The experimental data supported the coexistence of several isomers of C₆₀Cl _n (n = 8, 10, 12, 14, 26); the mixtures were not separated so far. Semiempirical calculations (AM1, PM3) were used to analyze the addition patterns and resulted in the most favorable structures of C₆₀Cl_8–26. Chlorination of C₇₀ under various conditions invariably yielded C₇₀Cl₁₀.     

Specific features of the interaction of alloys of the didymium-iron-boron system with hydrogen

We study the interaction of alloys of the Dd-Fe-B system [M-82, M-83, M-84, and M-85 alloys with a mass content of 33–40% didymium, up to 0.5% aluminum, and 1–1.25% boron (the rest is iron)] with hydrogen using volumetric, X-ray phase, and differential thermal analysis. If the initial hydrogen pressure is 1.0 MPa, hydrides with 0.4–0.6 mass % of hydrogen are formed. The saturation of these alloys with hydrogen is accompanied by an increase in the spacing a of an elementary cell by 1.2–1.4% and in c by 0.8–1.1% (the general increase in volume is 3.2–3.9%). If the initial pressure is 0.15–0.2 MPa, the time of complete saturation with hydrogen is 15–20 min for most alloys. At 973–1033 K, the alloys under study in hydrogen disproportionate into DdHx didymium hydride (a = 0.5449 – 0.5458 nm), -iron (a = 0.2864 – 0.2866 nm), and Fe2 B iron boride (a = 0.5112 – 0.5117 nm, c = 0.4228 nm). An increase in the initial hydrogen pressure from 0.1 to 5.0 MPa is accompanied by a decrease in the disproportionation temperature to 930 K.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 2, pp. 105–112, March–April, 2004.     

Magnetic resonance of intercalation compounds of graphite: Questions of ionicity and mobility of inserted species

Graphite will react at room temperature with Lewis acids as PF₅ and BF₃ in the presence of the oxidant C1F to form intercalation compounds containing closed-shell anions. In the case of “C₁₆BF₄”, the chemical shifts of both ¹¹B and ¹⁹F nuclear magnetic resonances point to the existence of BF^?₄, rather than the initial BF₃, within the graphite planes. The existence of second order quadrupolar coupling of the ¹¹B resonance suggests, however, possible hybrid $\text{BF}{}_3\text{BF}{}^{\mathrm{?}}{}_4$ character, as in B₂F^?₇, a known dimeric anion of BF₄ and BF₃. NMR results on ¹⁹F and ³¹P in the two compounds “C₁₄PF₆” and “C₂₈PF₆” support this hypothesis, as “C₂₈PF₆” shows only the presence of PF^?₆, but the more concentrated “C₁₄PF₆” shows composite $\text{PF}{}_5\text{PF}{}^{\mathrm{?}}{}_6$ character. Our claim for intercalated anions in these systems is reinforced both by radical cation-type signals in the ESR and by deshielding effects in the ¹³C NMR. The narrow linewidths of the nuclear magnetic resonance absorptions of the intercalated species are suggestive of “liquid-like” behavior.     

Characterization of Flow Properties of Fine Powders

ABSTRACT

This paper reports on the development of a scries of theoretical and experimental approaches to characterize fine powders. Based on our current research, we propose the following powder rheological approach to characterize fine, very fine, and ultra fine powders. (1) Preparation of homogeneous, reproducible fine powder structures under the aerated powder conditions (U_mf < U < U_mp). (2) Definition of rheological, mechanical parameters, e.g. deformation coefficients (Y) and fracture strength (< σf), under aerated conditions. (3) Experimental measurement methods of Y and Of and their theoretical interpretation at ambient and elevated temperatures.