Properties of Sr- and Sb-doped PZT–Portland cement composites

Lead zirconate titanate (PZT) ceramic-cement-based composites have increasingly been recognized as an attractive new composite material for use as a sensor in structural applications. In this work, PZT was doped with Sr and Sb (PSZT) to give it greater dielectric constant (ε _r) and higher piezoelectric coefficient (d ₃₃) values than normal PZT and is the first time that it is mixed with normal Portland cement to produce a 0–3 connectivity PSZT–Portland cement composite using PSZT contents of 50% and 70% by volume. Scanning electron micrographs show PSZT ceramic particles closely surrounded by the hydrated cement matrix where a dense microstructure can be observed in the interfacial zone. Both the ε _r and d ₃₃ values were found to increase with PSZT content and the values are amongst the highest so far for these types of composites, where the ε _r and d ₃₃ values reached 590 and 48 pC/N, respectively.     

Use of micro‐Raman spectroscopy to study reaction kinetics in blended white cement pastes containing metakaolin

Curing temperature is known to play an important role in the formation, development, and stability of the hydrated phases appearing during pozzolanic reactions (chemical reaction between puzzolanic addition, metakaolin (MK), and calcium hydroxide from cement hydration). A typical example of this important reaction is to be found in metakaolin‐bearing cement pastes, characterized by hexagonal phases whose thermodynamic stability declines with rising temperature. These phases cannot be exhaustively researched with traditional techniques (such as X‐ray diffraction) due to their poor crystallinity. Consequently, micro‐Raman spectroscopy was used in the present study to explore the behavior of white cement paste blends containing 0, 10, and 25% MK at two curing temperatures (20 and 60 °C). This led to the identification, for the first time using Raman spectroscopy, of phases C₂ASH₈¹ (stratlingite) and C₃ASH₆, which appear in the MK–white cement reaction. The C S H gel formed was characterized by Q¹ dimers and a C/S ratio of 1.3–1.5. Raising the curing temperature favored the formation of C₄AH₁₃. Copyright © 2009 John Wiley & Sons, Ltd.     

Optical and Structural Properties of Ammonia-Free Amorphous Silicon Nitride Thin Films for Photovoltaic Applications

Hydrogenated amorphous silicon nitride (a-SiN_x:H) thin films have been deposited through the green chemistry route using silane (SiH₄) and nitrogen (N₂) as process gases with SiH₄ flow being variable and N₂ flow being constant without the use of pollutant and corrosive ammonia (NH₃) by the plasma-enhanced chemical vapor deposition technique at 13.56 MHz. Fourier transform infrared spectroscopy analysis shows various possible vibrational modes of Si-H, Si-N, and N-H bonds present in the film. Raman spectroscopy is performed on these samples to calculate volume fractions corresponding to amorphous phases present in the a-SiN_x:H films. The refractive index (η) values are calculated using Swanepoel's method, which are in the range of 2.89 to 3.17. The thickness of the deposited films has been evaluated using transmission spectra. Absorption coefficient and band gap (E _g) values are obtained from optical absorption studies. An increase in the E _g and a decrease in the η value have been observed for the samples grown with decreasing SiH₄ flow.     

Theoretical study of hyperfine coupling constants and electron spin g factors for X2Σ+ diatomics from Groups 1 and 2

The ESR parameters of the cations Be⁺ ₂, Mg⁺ ₂, Ca⁺ ₂, BeMg⁺, BeCa⁺, MgCa⁺ and the mixed radicals ZBe, ZMg, ZCa (Z = Li, Na, K), all having a X ²Σ⁺ _u(1σ² _g1σ_u)/X ²Σ⁺(1σ²2σ) ground state, have been studied theoretically. The A _iso and A _dip constants have been calculated with UHF, CISD, MP2, B3LYP, PW91PW91 wavefunctions, and 6–311+G(2df) basis sets. The electron spin g factors (magnetic moment μ_s) have been evaluated from correlated (MRDCI) wavefunctions, using a Hamiltonian based on Breit-Pauli theory with perturbation expansions up to second order, and 6–311 + G(2d) basis sets. As expected for s-rich radicals, the hyperfine spectra are governed by the A _iso terms. Both Δg∥ and Δg⊥ values are negative, but Δg∥ lies close to zero. For Δg⊥, the coupling with 1 ²Π_(u) dominates the sum-over-states expansions. Although the singly occupied MOs (SOMO) are mostly of s character, the |Δg⊥| are relatively large, up to 5200 ppm for cationic, and up to 7850 ppm for neutral radicals. These large values are caused by low excitation energies and high magnetic transition moments, the latter due to the fact that the σ?(s-s) SOMO has the same nodal properties as a pσ orbital. Of the radicals considered here, an ESR spectrum is available only for Mg⁺ ₂. Our theoretical A _iso of ?287 MHz reproduces well the matrix result (-291 MHz). Calculated values of ?10 ppm for Δg∥ and of ?1280 ppm for Δg⊥ give an average 〈Δg〉 = ?860 ppm that lies within the experimental range of ?600(±300) ppm in Ne, and of ?1300(±500) ppm in Ar matrices.     

Radioactive analysis and radiological hazards in different types of Egyptian cement

Studies of the natural γ-emitting radionuclides in different types of cements manufactured by different companies in Egypt (e.g. Iron (HI), Karnak (HK), and Super fine (HSu) products from Helwan Ltd.) have been done to determine their natural levels of radioactivity using a high-purity germanium detector (HPGe). Knowledge of radioactivity present in cement materials enables one to assess any possible radiological risks to human health. The results show that the highest mean values of ²²⁶Ra and ²³²Th activity are 234.01±20.12 and 46.56±4.65 Bq kg^?1, respectively, measured in cement sample ‘Iron’ from Helwan company (HI). The corresponding value of ⁴⁰K is 333.53±26.68 Bq kg^?1 measured in cement sample ‘Karnak’ from Helwan company (HK). For ¹³⁷Cs, this value is 3.27±0.31 Bq kg^?1 measured in cement sample (HI). The average concentrations of measured radionuclides in the different cement samples are 72.21±6.39, 24.98±2.24, 134.49±10.45, and 0.58±0.08 Bq kg^?1 for ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs, respectively. The measured activity concentrations for these radionuclides were compared with the reported data of other countries. Radium equivalent (Ra_eq) activities and different hazard indices were calculated to assess the radiation hazard. Iron HI cement sample shows a higher Ra_eq activity of 311.91±31.10 Bq kg^?1. Calculations of absorbed doses in nGy h^?1 show that the Iron (HI), Karnak (HK), and Super fine (HSu) products from Helwan company have higher activities than the permissible level (80 nGy h^?1). On the basis of the external hazard index (H _ex), Ra_eq activities, and annual effective dose rates for organs (H _organ), the natural radioactivity of cement samples is not greater than the recommended values in the established standards and hence safe for use in building constructions and therefore for inhabitants.     

Calorimetric study of Te15(Se100− x Bi x )85 glassy alloys using differential thermal analysis

A calorimetric study of Te₁₅(Se_{100? x} Bi _x )₈₅ glassy alloys (x = 0, 1, 2, 3 and 4 at. %) is reported. Differential thermal analysis (DTA) was performed at heating rates of 10, 15, 20 and 25 K/min. The spectra were used to determine the glass transition temperature, T_g , the crystallisation temperature, T_c and the melting temperature, T_m . All these parameters shift to higher values with increasing heating rate, β. The glass transition temperature and the melting temperature increase, and the crystallisation temperature decreases, with increase in the Bi content, x. The activation energy of the glass transition, E_g , was evaluated using the Moynihan and Kissinger methods. The activation energy of crystallisation, E_c , was calculated using modified Kissinger and Matusita approaches. The thermal stability of these glasses has been studied and found to decrease with increase in Bi content. The results obtained are explained on the basis of a chemically ordered network model and an average coordination number.     

Negative muon capture in3He

We compute the partial capture rate of negative muons in³He by following the analysis of Peterson to include the relativistic corrections and the exchange effects, for various values of theg _p /g _A ratio. We also calculate the total capture rate. The ground state of³He is assumed to be spherical. The radial dependence of the ground state wave function is taken to be (a) one parameter Irving function, (b) a modified three-parameter Irving function and (c) a function having ‘soft-core’, whose parameters have been fixed in a variational calculation of the binding energy of the triton using a non-local momentum-dependent potential involvingp ² terms. The calculated values of the capture rates are compared with the experimental data to find a value for theg _p /g _A ratio.     

Field Effect in the Linear and Nonlinear Conductivity of the Layered Quasi-One-Dimensional Semiconductor TiS3

Field-effect transistor structures based on whiskers of layered quasi-one-dimensional semiconductor TiS₃ have been fabricated. The dependences of the conductivity σ on the gate voltage V_g, as well as the current-voltage characteristics of whiskers (“source-drain”) at different V_g values, have been measured in the temperature range of 4.2-300 K. As the temperature decreases, the sensitivity of the conductivity to the gate voltage, α ≡ 1/σdσ/dV_g, increases in the range from 300 to 80 K and decreases sharply below 80 K, where the nonlinear conductivity begins to depend on V_g. The results can be explained by the formation of an electronic crystal at low temperatures.

     

EPR,FTIR, Powder XRD and Optical Absorption Studies of Cu(II) Ion in Triaqua(1,10-Phenanthroline-k<Superscript>2</Superscript><Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′)(Sulfato-kO)Zinc(II)

Electron paramagnetic resonance (EPR), optical, Fourier-transform infrared (FTIR) and powder X-ray diffraction (XRD) studies have been carried out on Cu(II)-doped triaqua(1,10-phenanthroline-k² N,N′)(sulfato-kO)zinc(II) to get information about the position and spin Hamiltonian parameters of the dopant. Angular variation of copper hyperfine structure lines in EPR study shows the presence of a single site with g and A values as: g _xx  = 2.003, g _yy  = 2.001, g _zz  = 2.223; A _xx  = 4.41 mT, A _yy  = 2.39 mT and A _zz  = 12.16 mT. The slightly lower parallel value obtained for the copper nucleus has been explained by considering admixture of the ground state with the excited state. The direction cosines of principle g and A values suggest that the impurity is present interstitially. Admixture coefficients and additional parameters (P, k, α ², α′) have also been evaluated. Optical, FTIR and powder XRD techniques have been used to reconfirm the structure of the host lattice.     

On the calculation of the orientational correlation parameter g 2

The g ₂ factor for a model of liquid carbon disulphide has been calculated by molecular dynamics simulation. The values of g ₂ for the model at three points along the orthobaric curve are: 1·17 ± 0·04 (298 K), 1·27 ± 0·03 (245 K), 1·39 ± 0·06 (193 K). These values are in good agreement with available experimental values. By calculating g ₂ in shells of cubic symmetry it is found that the value of g ₂ is determined by the orientational correlation of a molecule with neighbours within a few (two to three) molecular diameters. Spurious orientational correlations are introduced by the periodic boundary conditions and the calculation of collective correlation functions by averaging over the whole cube is shown to be unreliable. A theoretical calculation of g ₂ using RISM + SSA fails to reproduce the state dependence of the g ₂ values calculated from the simulation. This failure is not due to the small differences between the simulation and RISM g _αβ(r) for r < 4·5 Å but to inaccuracies in the SSA in the intermediate region r ～ 6 Å.     

Density functional theory design D-D-A type small molecule with 1.03 eV narrow band gap: effect of electron donor unit for organic photovoltaic solar cell

Six new low-band-gap copolymers of donor–donor–acceptor (D-D-A) architecture have been designed using density functional theory and time-dependent density functional theory methods in order to use them in organic photovoltaic cell (OPVC). Phenanthro[3,4-d:9,10-d′]bis([1,2,3]thiadiazole)-10,12-dicarbonitrile moiety has been used as an acceptor for all compounds. We insert benzo[1,2-b:4,5-b′]dithiophene and N,N-diphenylbenzo[1,2-b:4,5-b′]dithiophen-2-amine units as donor to complete designing of copolymers. In order to tuning the optical and electronic properties, we have modified the donor unit by substituted with amine, methoxyamine, N-methylenethiophen-2-amine, methoxy, alkoxy moieties. The band gap (E_g), HOMO and LUMO values and plots, open circuit voltage (V_OC) as well as optical properties have been analysed for designed copolymers. The optimised copolymers exhibit low-band-gap lying in the range of 1.03–2.24 eV. DPTD-6 copolymer presents the optimal properties to be used as an active layer due to its low E_g (1.03 eV) and a moderate V_OC (0.56 eV). Thus, OPVC based on this copolymer in bulk-heterojunction composites with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as an acceptor has been modelled. E_g and V_OC values of composite material DPTD-6:PCBM are found as 1.32 and 0.65 eV, respectively. A model band diagram has been established for OPVC, simulating the energy transfer between active layers.     

Coexistence of “ $ \alpha$ + 208Pb ” cluster structures and single-particle excitations in 212 84Po128

Excited states in ²¹²Po have been populated by a \alpha transfer using the ²⁰⁸Pb(¹⁸O,¹⁴C) reaction at 85MeV beam energy and studied with the EUROBALL IV g \gamma multi-detector array. The level scheme has been extended up to ∼ 3.2 MeV excitation energy from the triple-g \gamma coincidence data. Spin and parity values of most of the observed states have been assigned from the g \gamma angular distributions and g \gamma -g \gamma angular correlations. Several g \gamma -lines with E _γ < 1 MeV have been found to be shifted by the Doppler effect, allowing for the measurements of the associated lifetimes by the DSAM method. The values, found in the range [0.1-0.6]ps, lead to very enhanced E1 transitions. All the emitting states, which have non-natural parity values, are discussed in terms of a \alpha - ²⁰⁸Pb structure. They are in the same excitation-energy range as the states issued from shell-model configurations.     

Grain growth in ultrafine titanium powders during sintering

Grain growth behaviour of fine (∼3 μm) and attrition milled nanocrystalline (∼32 nm) titanium powers during sintering have been studied. The activation energies of grain growth (Q _g) in fine titanium were found to be 192.9 and 142.4 kJ/mol at lower and higher temperature ranges, respectively. The nanocrystalline titanium showed very low values of Q _g (54.6 kJ/mol) at lower temperatures and it increased to 273.2 kJ/mol at higher temperatures. The constant (n) in nano Ti system was found to have unusually very high values of 6.5–8.2. The grain boundary rotation along with the diffusional processes could be the grain growth mechanism in nanocrystalline and in fine titanium powders.     

Gamma-radiolysis of deaerated cysteine solutions

The electron paramagnetic resonance (EPR) spectra of gamma-irradiated single crystals of phenidone (fenidon C₉H₁₀N₂O) have been studied for different orientations of crystals in a magnetic field. Phenidone single crystals have been irradiated with ⁶⁰Co-γ rays at room temperature. The EPR spectra have been investigated at temperatures between 125 and 450 K. The spectra have been found to be temperature independent. The spin-Hamiltonian parameters have been obtained from the single-crystal EPR analysis. The principal values of the hyperfine coupling tensor of the unpaired electron and the principal values of the g-tensor have been determined.     

The Evolution of Interfacial Strength as a Way to Characterize a Low-Temperature Limit of the Surface Glass Transition of an Amorphous Polymer

The evolution of autoadhesive strength, σ, with healing temperature, T _h, at the symmetric amorphous polystyrene (PS)?PS interfaces of the samples with vitrified bulk has been used to characterize a low-temperature limit of the surface glass transition temperature T _g ^surface(low). The existence of a linear relationship between the square root of σ and T _h has been found for both polydisperse and monodisperse polymers. By the extrapolation of straight lines σ ^1/2 ? T _h to σ ^1/2 = 0, the values of T _g ^surface(low) have been determined and compared with those of a high-temperature limit of T _g ^surface, T _g ^surface(high), measured earlier. The differences between T _g ^surface(low) and T _g ^surface(high) have been found to be insignificant, 10–20°C. Using an average value of the shift of T _g ^surface(low) with healing time, t _h, the quasi-equilibrium value of the surface glass transition temperature of amorphous PS T _∞ ^surface has been estimated to be 10–15°C.     

A study of 223Ra populated by α-decay

The low spin states of ²²³Ra have been populated via α-decay from ²²⁷Th which was itself produced following β⁻ decay of an ²²⁷Ac source. α–γ and α−e _K,L,M angular correlation measurements have been analysed using the correct ground state spins of ²²⁷Th(=1/2⁺) and ²²³Ra(=3/2⁺) for the first time. The analysis has allowed unique J^π values to be assigned to almost all levels below 400 keV excitation in ²²³Ra. Values of (g _K−g _R)/Q ₀ have been deduced for several members of the K= 3/2^± bands (for the first time in an odd N nucleus in this mass region) allowing estimates of g _K and g _R to be extracted. The values of g _K and g _R are not significantly different for the positive and negative parity band members and tend to support other strong evidence that stable octupole deformation exists in ²²³Ra at low excitation energies. Received: 17 November 1997 / Revised version: 8 January 1998     

Universal effective coupling constants for the generalized Heisenberg model

The aim of this study is to find universal critical values of the effective dimensionless coupling constant g ₆ and refined universal values g ₄ for Heisenberg ferromagnets with n-component order parameters. These constants appear in the equation of state and determine the nonlinear susceptibilities χ ₄ and χ ₆ in the critical region. Calculations are made of the first three terms of the expansion of g ₆ in powers of g ₄ in the limits of O(n) symmetry three-dimensional λϕ ⁴ theory, the resultant series is resummed by the Padé-Borel method, and then by substituting the fixed point coordinates g ₄ ^* in the resultant expression, numerical values of g ₆ ^* are obtained for different n. These numbers g ₄ ^* for n>3 were determined from a six-loop expansion for the β-function resummed using the Padé-Borel-Leroy technique. An analysis of the accuracy of these g ₆ ^* values showed that they may differ from the true values by no more than 1.6%. These values of g ₆ ^* were compared with those obtained by the 1/n expansion method which allowed the level of accuracy of this method to be assessed. Fiz. Tverd. Tela (St. Petersburg) 40, 1284–1290 (July 1998)     

Microhardness of condensation polymers and copolymers. 1. Coreactive blends of polyethylene terephthalate and polycarbonates

The microhardness of coreactive blends of polyethylene terephthalate (PET) and bisphenol A polycarbonate (PC) was investigated over the whole range of compositions. The occurrence of one single glass transition temperature (T _g) step in the differential scanning calorimetry (DSC) curves indicated that intensive chemical interactions had taken place during melt blending, resulting in formation of copolycondensates with dominating random sequential order. The parallel decrease of microhardness (H) and of T_g with increasing PET content in the blends has been ascribed to the formation of new copolymer molecules enriched in the component characterized by lower H and T _g values. It is emphasized that such noncrystallizable copolymers offer the possibility to evaluate the intrinsic contribution of the repeating units to the H and T _g characteristics of copolymers with various compositions and sequential orders.     

Radiation effect on optical,morphological and magnetic properties of aluminum-substituted M phase barium hexaferrite

The effect of gamma irradiation on the features of aluminum-substituted barium hexagonal ferrite particles BaAl_xFe_12?xO₁₉ with 0?≤?x?≤?3.5 has been studied. Optical absorption measurements have been performed and the results reflected a great dependence of the fundamental absorption edge on the radiation dose. It is found that the calculated optical band gap (E_g) increases due to an increase in the homogeneity with an increase in the Al content. Increasing the radiation dose up to 1?MGy induces a direct transition and consequently decreases the energy gap. This behavior is associated with the generation of excess electronic localized states. Moreover, the characteristic features of the irradiated samples have been studied using a scanning electron microscope. Also, all samples were characterized using the X-ray diffraction technique, and the values of crystal size, microstrain and dislocation density were calculated. On the other hand, the magnetic behavior of the samples was studied using a vibrating sample magnetometer technique after each radiation dose. The saturation magnetization (M_s) and the magneton number (n_B) decrease with an increase in the Al³⁺ substitution and at the same time decrease with the radiation dose 250?kGy to 1?MGy.     

Dielectric, ferroelectric and piezoelectric properties of 0-3 barium titanate–Portland cement composites

In this work, barium titanate (BT) and cement composites of 0-3 connectivity were produced with BT concentrations of 30%, 50% and 70% by volume using the mixing and pressing method. The dielectric constant (ε _r ) and the dielectric loss (tan δ) at room temperature and at various frequencies (0.1–20 kHz) of the ferroelectric BT-Portland cement composites with different BT concentrations were investigated. The results show that the dielectric constant of BT-PC composites was found to increase as BT concentration increases, and that the highest value for ε _r —of 436—was obtained for a BT concentration of 70%. In addition, the dielectric loss tangent decreased with increasing BT concentration. Moreover, several mathematical models were used; the experimental values of the dielectric constants are closest to those calculated from the cube model. The 0-3 cement-based piezoelectric composites show typical ferroelectric hysteresis loops at room temperature. The instantaneous remnant polarization (P _ir ), at an applied external electrical field (E ₀) of 20 kV/cm (90 Hz) of 70% barium titanate composite, was found to have a value ≈3.42 μC/cm². Furthermore, the piezoelectric coefficient (d ₃₃) was also found to increase as BT concentration increases, as expected. The highest value for d ₃₃ was 16 pC/N for 70% BT composite.