Preparation of highly oriented β-SiC bulks by halide laser chemical vapor deposition

Highly oriented β-SiC bulks with high hardness were fabricated by halide laser chemical vapor deposition (HLCVD) using SiCl₄, CH₄ and H₂ as precursors. The effects of total pressure (P_tot) and deposition temperature (T_dep) on the preferred orientation, microstructure, deposition rate (R_dep) and micro-hardness were investigated. The 〈110〉-oriented β-SiC bulks were obtained at low P_tot (2–4 kPa), non-oriented β-SiC bulks were obtained at mediate P_tot (6 kPa), and 〈111〉-oriented β-SiC bulks were obtained at high P_tot (10–40 kPa), exhibiting faceted, cauliflower-like and six-fold pyramid-like microstructure, respectively. The maximum R_dep of 〈111〉- and 〈110〉-oriented β-SiC bulks were 3600 and 1300 μm/h at, respectively. The activation energy obtained by the plot of lgR_dep-T_dep⁻¹ is 170 to 280 kJ mol⁻¹, showing an exponential relation with P_Si. The Vickers micro-hardness of β-SiC bulks increased with increasing P_tot and showed the highest value of 35 GPa at P_tot = 40 kPa with a complete 〈111〉 orientation.     

Application of Box–Behnken design and response surface methodology for modeling of some Turkish coals

The aim of our research was to apply Box–Behnken experimental design and response surface methodology for modeling of some Turkish coals. As a base for this study, standard Bond grindability tests were initially done and Bond work indexes (W_i) values were calculated for three Turkish coals. The Box–Behnken experimental design was used to provide data for modeling and the variables of model were Bond work index, grinding time and ball diameter of mill. Coal grinding tests were performed changing these three variables for three size fractions of coals (−3350 + 1700 μm, −1700 + 710 μm and −710 μm).Using these sets of experimental data obtained by mathematical software package (MATLAB 7.1), mathematical models were then developed to show the effect of each parameter and their interactions on product 80% passing size (d₈₀). Predicted values of d₈₀ obtained using model equations were in good agreement with the experimental values of d₈₀ (R² value of 0.96 for −3350 + 1700 μm, R² value of 0.98 for −1700 + 710 μm and R² value of 0.94 for −710 μm). This study proved that Box–Behnken design and response surface methodology could efficiently be applied for modeling of grinding of some Turkish coals.     

Assessment of the initial and aged dentin bond strength of universal adhesives

This study evaluated the effect of mechanical loading on microtensile bond strengths (μTBS) of universal adhesives to dentin and quantified adhesive dentin penetration using micro-Raman spectroscopy. Human molars had occlusal dentin exposed and were allocated into eight groups: All-Bond Universal and Scotchbond Universal using etch-and-rinse and self-etch approaches, Adper Prompt L-Pop, Adper Single Bond Plus, Clearfil SE Bond, and Optibond FL. Following bonding procedures and build-ups, specimens were either stored in water at 37 °C for 24 h or mechanically loaded (50,000 cycles, 50 N) prior to μTBS test. Additional teeth were prepared for micro-Raman analysis of adhesive penetration and FE-SEM. Data were analyzed by two-way ANOVA and Tukey׳s post hoc test (P<0.05). Mechanical loading had no deleterious effect on μTBS with the exception of Adper Prompt L-Pop. Incomplete infiltration of the demineralized dentin was noticed for adhesives using the etch-and-rinse approach and for Scotchbond Universal in the self-etch approach.     

Microwave dielectric properties of (Bi1 − xRx)NbO4 ceramics (R = Ce,Nd,Dy,Er)

(Bi_1 − xR_x)NbO₄ (R = Ce,Nd,Dy,Er; x = 0.03 mol) ceramics with 0.1 wt.% CuO + V₂O₅ as a sintering aid were prepared by conventional solid state reaction process. The microwave dielectric properties of (Bi_1 − xR_x)NbO₄ ceramics were investigated as a functional of R ions. The microwave dielectric properties such as dielectric constant, Q value and temperature coefficient of resonant frequency (TCF) are found to correlate with the R ions. When R = Ce, the dielectric constant, Q value and TCF are 44.7, 5000 and −4.9 ppm/°C, respectively at about 5 GHz. The relation of microwave dielectric properties and the ionic radii, polarizability and bond valence of R (R = Ce, Nd, Dy, Er) was discussed. The Q value decreased with decreasing the bond valence and the size of R ions. The dielectric constant decreased with decreasing polarizability.     

Improvements on the thermal shock behaviour of MgO–spinel composite refractories by incorporation of zircon–3 mol% Y2O3

The effects of incorporations of zircon–3 mol% Y₂O₃ (Y) into MgO–spinel (M–S) compositions to improve mechanical properties and thermal shock behaviour were investigated. Mechanical properties were measured, R ? R_st parameters were calculated, and thermal shock tests were performed. Microstructural features were examined using SEM and XRD. By adding zircon + Y to M–S: (i) up to ～2 and ～3-fold improvements were achieved in mechanical properties and R ? R_st parameters, (ii) there were improvements up to ～2-fold in strength data measured after performing thermal shock tests at 1000 °C. Parameters improving mechanical properties and thermal shock behaviour of M–S–(zircon + Y) materials are given as follows: (i) interlinking and arresting or deviation of microcracks when reaching the ZrO₂–Y₂O₃ grains or pores, increases in (ii) K_Ic, (iii) critical defect size and (iv) bulk density, (v) formation of forsterite phase, (vi) coexistence of intergranular and transgranular fractures, and (vii) reduction in MgO grain size, leading to longer service life.     

CO2 laser peeling of Al2O3 ceramic and an application for the polishing of laser cut surfaces

A laser controlled fracture peeling technique is demonstrated to smooth the Al₂O₃ ceramic surface without thermal damages. It was found that a chip can be separated and curled from the ceramic surface during a focused CO₂ continuous wave (CW) laser dual-scanning. The thickness of the curled chip is ～50 μm and the formed subsurface roughness (R_a ≈ 2 μm) is close to the surface machined by mechanical breaking (R_a = 1.84 μm). The chip formation is attributed to the controlled fracture by the residual tensile stress in the recast layer, whereas the chip curling only occurs when the melting depth is shallower than the position of lateral cracks. The peeling technique can be applied to polish the cut surface of laser fusion cutting in ceramics. The polished cut surface (R_a = 2.18 μm) is free from recast, crack and heat effects. The microstructure is similar to the base material. The material removal rate during polishing is up to 0.125 mm³/s.     

Ball milling assisted hydrothermal synthesis of ZrO2 nanopowders

The formation of ZrO₂ nanopowders under various hydrothermal conditions such as temperature, time, autoclave rotation speed, heating rate and particularly assistance of ball milling during reaction was investigated. Full ZrO₂ formation (with monoclinic phase) from zirconium solution was completed at shorter times with increasing temperature such as after 4 h at 150 °C, 2 h at 175 °C and less than 2 h at 200 °C. Crystallite size increased from 2.9 to 4 nm with increasing reaction temperature from 125 °C to 200 °C, respectively. Ball milling assisted hydrothermal runs were performed to understand the effect of mechanical force on phase formation, crystallinity and particle size distribution. Monoclinic ZrO₂ was formed in both milled and non-milled runs when zirconium solution was used. Mean particle size for the 2 M solution was measured to be 94 nm for the milled and 117 nm for the non-milled powders. However, when amorphous aqueous zirconia gels (precipitated at pH 5.8) were used, tetragonal phase was also formed in addition to monoclinic phase. Mean particle size was measured to be 0.7 μm (d₉₀≅1.3 μm) for the milled and 7.9 μm (d₉₀≅13 μm) for the non-milled powders. Ball milling during hydrothermal reactions of both zirconium solution and aqueous zirconium gel resulted in smaller crystallite size and mean particle size and, at the same time, effectively controlled particle size distribution (or agglomeration) of nanopowders.     

Comparison between microwave and conventional calcination techniques in regard to reactivity and morphology of co-precipitated BaTiO3 powder,and the electrical and energy storage properties of the sintered samples

Barium titanate (BaTiO₃) nanopowders were synthesized by an aqueous co-precipitation method followed by calcination. Either 2.45 GHz microwaves or conventional heating was used in order to investigate the impact of these techniques on the synthesis time, microstructure, and electrical properties of the materials. The heating temperatures ranged from 620 °C to 810 °C. X-ray diffraction (XRD) revealed pure BaTiO₃ formation by microwave heating in a noticeably shorter time (five minutes) compared to conventional heating (3 h). Field emission scanning electron microscopy (FESEM) results confirmed that the microwave process led to nanocube formation, whereas in the conventional procedure, the particles tended to form spherical shapes. To evaluate the electrical properties, the samples heated at 620 °C were conventionally sintered at 1280 °C, 1330 °C, and 1380 °C. Higher dielectric, piezoelectric, and ferroelectric properties and more energy-saving efficiency (ε_r=1012, tan δ=0.035 d₃₃=85 pC/N, p_r=6.2 µC/cm² and η=48% respectively) were achieved in the microwave-heated BaTiO₃ sintered at 1380 °C compared to the conventionally heated BaTiO₃ (ε_r=824, tan δ=0.030 d₃₃=75 pC/N, p_r=5 µC/cm² and η=27%) demonstrating that microwave calcination substantially affects the final electrical properties.     

Phase equilibria of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl): Measurements and modeling

We report experimental measurements of the phase behavior of (CO₂ + H₂O + NaCl) and (CO₂ + H₂O + KCl) at temperatures from 323.15 K to 423.15 K, pressure up to 18.0 MPa, and molalities of 2.5 and 4.0 mol kg⁻¹. The present study was made using an analytical apparatus and is the first in which coexisting vapor- and liquid-phase composition data are provided. The new measurements are compared with the available literature data for the solubility of CO₂ in brines, many of which were measured with the synthetic method. Some literature data show large deviations from our results.The asymmetric (γ–φ) approach is used to model the phase behavior of the two systems, with the Peng–Robinson equation of state to describe the vapor phase, and the electrolyte NRTL solution model to describe the liquid phase. The model describes the mixtures in a way that preserves from our previous work on (CO₂ + H₂O) the values of the Henry's law constant and the partial molar volume of CO₂ at infinite dilution Hou et al. [22]. The activity coefficients of CO₂ in the aqueous phase are provided. Additionally, the correlation of Duan et al. [14] for the solubility of CO₂ in brines is tested against our liquid-phase data.     

Effect of CH4/SiCl4 ratio on the composition and microstructure of 〈110〉-oriented β-SiC bulks by halide CVD

Halide chemical vapor deposition process was carried out for fast fabricating oriented stoichiometric β-SiC through controlling flow rate of precursors (SiCl₄ and CH₄). The effects of molar ratio of C and Si precursors (R_C/Si) on composition, preferred orientation, microstructure and deposition rate (R_dep) were investigated. The deposits transformed from silicon-rich to stoichiometric β-SiC to carbon-rich with increasing R_C/Si. 〈110〉-oriented stoichiometric β-SiC with lower density of defects were obtained at R_C/Si in the range of 0.86–1.00, where the maximum R_dep was 883 μm/h at R_C/Si = 1.00, leading to a thickness of 1.7 mm in 2 h deposition. Formation of ridge-like morphology has been discussed based on a twin plane propagation model.     

Reactions of benzophenone imine complex [Tp(NH═CPh2)(PPh3)Ru–Cl] with alkyne and dimerization of terminal alkynes in the presence of Et3N

Treatment of benzophenone imine complex [Tp(PPh₃)(NH═CPh₂)Ru–Cl] (1) {Tp═HB(pz)₃, pz = pyrazolyl} with 4-Ethynyltoluene in the presence of H₂O in distilled ethanol afforded the chelate alkenyl ketone complex [Tp(PPh₃)RuCCH₂(p-MeC₆H₄)═CHC(O)(p-MeC₆H₄)] (2). On the other hand, reaction of 1 with HC≡C(O)OR₁ in R₂OH produced the chelate vinyl ether complexes [Tp(PPh₃)Ru–C(OR₂)═CHC(O)OR₁] (3a, R₁ = Me, R₂ = Me; 3b, R₁ = Et, R₂ = Me; 3c, R₁ = Et, R₂ = Et; 3d, R₁ = Me, R₂ = Et), respectively. Preliminary results on the catalytic activity of 1 are also presented. Intriguingly, complex 1 is found to catalyze the dimerization of terminal alkynes HC≡CR (R = p-MeC₆H₄, C(O)OCH₃) in the presence of Et₃N to give eynes. The structures of 3c and 3d have been determined by X-ray diffraction analysis.     

First μ3-oxalato-bridged cis and trans configurations nickel macrocyclic complex: Synthesis,structure and magnetic properties

A novel nickel macrocyclic complex {[Ni₂(cyclam)₂(μ₃-C₂O₄)]}_n · (ClO₄)₂ · H₂O has been synthesized and structural characterized by single-crystal X-ray diffraction. The complex forms a chain-like one-dimensional structure linked through a novel μ₃-oxalato-bridging mode, which has never been reported for nickel. The complex adopts both trans-III configuration with the R, R, S, S arrangement of the four chiral nitrogen centers and cis-V conformation with the R, R, R, R nitrogen configuration. Variable-temperature magnetic susceptibility studies indicate the existence of weak antiferromagnetic (zj = −1.07 cm⁻¹) coupling.     

Open circuit voltage increase by substituted spacer and thieno[3,4-c]pyrrole-4,6-dione for polymer solar cells

We reported on two donor polymers containing thieno[3,4-c]pyrrole-4,6-dione(TPD) derivatives as electron withdrawing units for organic photovoltaics (OPVs). To control molecular weight and solubility of polymers, hexyl side chains are inserted to thiophene spacers. Due to the electron donating characteristic of hexyl side chains, highest occupied molecular orbital (HOMO) energy level of polymer is decreased as 0.18 eV, whereas the open circuit voltage is increased to 1.08 V. When bulk heterojunction devices were fabricated, the best PCE value of 0.360% (V_OC = 0.89 V, J_SC = 1.2 mA/cm², FF = 36.3%) under 100 mW/cm² irradiation.     

Crystal and geometry-optimized structure,Hirshfeld surface analysis and spectroscopic studies of tetrachlorocuprate and nitrate salts of 1-(2-fluorophenyl)piperazine cations, (C10H15FN2)[CuCl4] (I) and (C10H14FN2)[NO3] (II)

Two new organic-inorganic hybrid materials, 1-(2-fluorophenyl)piperazine-1,4-diium tetrachlorocuprate, (C₁₀H₁₅FN₂)[CuCl₄] (I) and 1-(2-fluorophenyl)piperazin-4-ium nitrate, (C₁₀H₁₄FN₂)[NO₃] (II), have been synthesized by an acid/base reaction at room temperature in the presence of 1-(2-fluorophenyl)piperazine as an organic-structure directing agent and their structures were determined by single crystal X-ray diffraction. Compound (I), (C₁₀H₁₅FN₂)[CuCl₄], crystallizes in the monoclinic system and P2₁/c space group with a = 7.5253 (2), b = 20.6070 (7), c = 9.7281 (3) Å, β = 103.6730 (17)°, V = 1465.82 (8) Å³ with Z = 4. Full-matrix least-squares refinement converged at R = 0.037 and wR(F²) = 0.088. Compound (II), (C₁₀H₁₄FN₂)[NO₃], belongs to the monoclinic system, space group P2₁/c with the following parameters: a = 10.8034 (2), b = 7.5775 (1), c = 14.4670 (3) Å, β = 111.761 (2)°, V = 1099.91 (4) ų and Z = 4. The structure was refined to R = 0.044, wR(F²) = 0.136.In the structures of (I) and (II), the anionic and cationic entities are interconnected by means of set of hydrogen bonding contacts forming three-dimensional networks. Intermolecular interactions were investigated by Hirshfeld surfaces and the contacts of the four different chloride atoms were notably compared. The results of the optimized molecular structure are presented and compared with the experimental one. The Molecular Electrostatic Potential (MEP) maps and the HOMO and LUMO energy gap of both compounds were computed. The vibrational absorption bands were identified by infrared spectroscopy. Theory (DFT) calculations of normal mode frequencies are compared with experimental ones.     

Determination of surface area of carbon-black by simple cyclic-voltammetry measurements in aqueous H2SO4

Determination of the surface area of commercial carbon-black (CB) by cyclic-voltammetry (CV) measurements of the electrochemical double-layer charge (Q) in aqueous sulfuric acid was investigated. Various factors that affect the Q value associated with CB, including: the presence of redox-reversible function-groups, the binders used for the formation of thin-film CB electrodes, the scan rates of the CV measurement, H₂SO₄ electrolyte concentration and the volume of air contained in the pores of the CB samples were examined. Conditions for measuring Q without interference from these factors were investigated and the data derived, without interference, was found to correlate well with the surface area of the CB. The results show that the total Brunauer–Emmett–Teller (BET) surface area shows good correlation (R² = 0.993) with the Q value corresponding to a full charge/discharge of the CB (Q₀), obtained by extrapolation at a zero scan rate; additionally, the CB micropore surface area (diameter < 2 nm) shows good linear correlation with the Q deficiency (Q₀–Q), measured at 5 mV s^?1 (R² = 0.998).     

The effects of the post-annealing time on the growth mechanism of Bi2Sr2Ca1Cu2O8+∂ thin films produced on MgO (100) single crystal substrates by pulsed laser deposition (PLD)

Bi₂Sr₂Ca₁Cu₂O_8+∂ thin films were deposited on MgO (100) substrates by pulsed laser deposition (PLD). The effects of post-annealing time on the phase formation, the structural and superconducting properties of the films have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature dependent resistivity (R–T), atomic force microscopy (AFM), and DC magnetization measurements. The films deposited at 600 °C were post-annealed in an atmosphere of a gas mixture of Ar (93%) and O₂ (7%), at 860 °C for 10, 30, and 60 min. All films have demonstrated a mainly single phase of 2212 with a high crystallinity (FWHM≈0.159°) and c-axis oriented. The critical temperature, T_C, of the films annealed for 10, 30, and 60 min were obtained as 77, 78, and 78 K, respectively. The highest critical current density, J_C, was calculated as 3.34×10⁷ A/cm² for the film annealed at 860 °C for 30 min at 10 K.     

Shielding properties of CuNiZn ferrite in the radio frequency range

Shielding properties of copper-doped NiZn ferrites in the frequency range 1 MHz–1.8 GHz, were explored. Samples of composition Cu_xNi_0.4?xZn_0.6Fe₂O₄ with x=0.0, 0.1, 0.2, 0.3 and 0.4, were prepared by the ceramic method. Powders and pellets were sintered at 1100 °C for 2 h. The effect of compositional variation on structural, dielectric and magnetic properties was investigated in order to relate them with the attenuation behavior. X-ray diffraction measurements confirmed the formation of a spinel structure at the selected sintering temperature. The addition of copper promotes grain growth, increases the samples density and modifies saturation magnetization, permeability and permittivity in the explored frequency range. As the reflection loss absolute values (|R_L|) for all the samples are above 35 dB, they can all be considered as shielding materials. The optimum attenuation was observed for x=0.2, reaching a maximum |R_L| of almost 60 dB at 10 MHz with an attenuation bandwidth of at least 3 MHz.     

Densification,microstructural evolution and dielectric properties of Ba6 − 3x(Sm1 − yNdy)8 + 2xTi18O54 microwave ceramics

Utilizing different rare-earth cations R³⁺ to the Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ compounds is one of effective route to tailor the dielectric constant, quality factor and temperature coefficient of frequency. In this study, densification, microstructural evolution, and microwave dielectric properties of Ba_6 − 3x(Sm_1 − yNd_y)_8 + 2xTi₁₈O₅₄ compound, with x ranging from 0.3 to 0.7; and y from 0 to 1.00, were investigated. The ceramics with x = 0.7 [Ba_3.9(Sm_1 − yNd_y)_9.4Ti₁₈O₅₄] has a higher densification compared with others, due to the formation of vacancy, in the perovskite-like tetragonal cavity of the tungsten bronze-type framework structure. Differential thermal analysis and density results show that the densification of Ba_6 − 3x(Sm_yNd_1 − y)_8 + 2xTi₁₈O₅₄ ceramics during sintering is primarily resulting from the solid state sintering process. The phase homogeneity for the Ba_6 − 3x(Sm_0.5Nd_o.5)_8 + 2xTi₁₈O₅₄ system is at least extended in the range of x between 0.3 and 0.7. Combining different rare-earth cations appears not alter the single phase range in tungsten bronze-type Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ ceramics. The size of the columnar-grain in the microstructure increases with increasing the Nd/Sm ratio as well as the x value. Dielectric constant changes from 91.0 to 84.2 as the x increases from 0.3 to 0.7. Variation of the Nd/Sm ratio allows one to control the τ_f value to the nearly 0 ppm/°C.     

Interplay between exchange interaction and magnetic anisotropy for iron based nanoparticles in aligned carbon nanotube arrays

In this work, we investigate magnetic properties of iron based nanoparticles (NP) intercalated into carbon nanotube (CNT) aligned arrays synthesized by injection chemical vapor deposition. We have analyzed the temperature (T) and the ferrocene concentration (C_F) dependences of the macroscopic magnetic parameters. From these experiments a weaker interaction between magnetic moments of NP was obtained for low C_F values. The random anisotropy model for the experimental data analysis was applied and micromagnetic parameters were evaluated. The law of the approach to magnetic saturation (LAS) was analyzed using the general expression with the correlation function C(r = x/R_a) of magnetic axes, R_a being the magnetic anisotropy correlation length. We obtained that, while for C_F = 0.5% C(r) is a step-like (C(r < 10) = 1, C(r > 10) = 0), for C_F ⩾ 1% C(r) decays rapidly on a short range, (2-3)R_a. Such extended correlations for C_F = 0.5% could be associated with the dominant role of the coherent anisotropy, which is caused by the influence of the alignment of CNT. When the aligned CNTs for C_F = 0.5% are destroyed into powder, the LAS is changed to H^−1/2, which means the dominant role of the exchange mechanism.     

The effect of RO oxides on microstructure and chemical durability of borosilicate glasses opacified by P2O5

The microstructure, devitrification and chemical durability of borosilicate glass specimens opacified by P₂O₅, with the general composition SiO₂ 70, B₂O₃ 12, Al₂O₃ 2, P₂O₅ 2, Na₂O (13 − X), RO X (wt.%) (R = Ca, Mg, Ba, Zn) were investigated after being subjected to various heat treatment conditions, using DTA, XRD and SEM. It was shown that while heat treatments at 1073 K and >1123 K were generally detrimental for the hydrolytic resistance of glasses, due to the enhanced phase separation or formation of excessive amounts of cristobalite, heating at 1123 K for 1 h usually improved the resistance due to the partial crystallization or microstructural changes of specimens. It was also found that a progressive decrease in hydrolytic and alkaline resistance occurred during prolonged heat treatment at 1123 K due to the formation of exessive amounts of cristobalite. It was also revealed that ZnO and MgO had the worst effect on chemical durabilities of specimens containing 7 and 5.5 wt.% Na₂O, respectively.