The paper presents and analyzes the results of experimental tests performed on two non-alloy low carbon steels (1.1141 and 1.0122) in cases of their exposure to impact fracture energy and uniaxial ...high cyclic mechanical stress-controlled fatigue. The experimental results provide insight into the changes in the Charpy impact fracture energy of the V-notched test specimen that occur as a result of temperature changes. The experimental results also provide insight into the mechanical response of the tested materials to mechanical uniaxial high-cycle fatigue at room temperature in an air atmosphere and at different applied stress ratios. Material fatigue tests refer to symmetric (R = -1), asymmetric (R = -0.5) and pulsating tensile (R = 0) cycles. The test results are shown in the S-N diagrams and refer to the highest applied stresses in relation to the number of failures at a given stress ratio. Using the modified staircase method, the fatigue limit (endurance limit) was calculated for both tested materials at each prescribed stress ratio. For both tested steel alloys, and at prescribed stress ratios, the fatigue limit levels (σ_f) are shown as follows: for steel C15E+C (1.1141)→σf250.8R=-1; 345.4R=-0.5; 527R=0(MPa); and for steel S235JRC+C (1.0122)→σf202R=-1; 310R=-0.5; 462R=0(MPa). All uniaxial fatigue tests were performed on unnotched, smooth, highly-polished specimens. The microhardness of both materials was also tested.
Na0.25K0.25Bi0.5TiO3 (NKBT) perovskite particles are synthesized by solid-state method and used as a filler for polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) co-polymer. X-ray diffraction ...analysis of NKBT powders shows that the particles have a rhombohedral perovskite crystal structure (R3c symmetry). Raman spectroscopy reveals that the co-polymer crystallizes predominantly into the mixture of polar β- and γ-crystals, while there is also a contribution of the non-polar α-crystal phase. The introduction of the NKBT into the PVDF-HFP results with an increase in effective dielectric permittivity and this effect depends on the inorganic content in the composite. The most interesting result of the present study is that the introduction of NKBT particles induces the appearance of an additional transition peak in the dielectric spectra of the co-polymer matrix. At the fixed frequency of ~2 kHz, the observed process appears at ~10 °C (about 45° above the glass transition temperature) and its magnitude strongly depends on the amount of the NKBT in the composite. Dielectric spectroscopy measurements of the composites are carried out in the wide range of frequencies (from 0.1 Hz to 1 MHz) and temperatures (from −100 to 100 °C). They reveal that the novel process can be clearly distinguished in the frequency range between 160 Hz and ~50 kHz.
•Na0.25K0.25Bi0.5TiO3 (NKBT) perovskite particles are synthesized by solid state method.•PVDF-HFP/NKBT composite films were prepared by solution mixing.•NKBT particles induce an increase in effective dielectric permittivity of the films.•An additional transition peak was observed in the dielectric spectra of the composite film.•The magnitude of the novel transition depends on the NKBT content.
The surface modification of nanocrystalline TiO2 particles (45 Å) with salicylate-type ligands consisting of an extended aromatic ring system, specifically 3-hydroxy-2-naphthoic acid, ...3,5-dihydroxy-2-naphthoic acid and 3,7-dihydroxy-2-naphthoic acid, was found to alter the optical properties of nanoparticles in a similar way to salicylic acid. The formation of the inner-sphere charge-transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites and a reduction in the band gap upon the increase in the electron delocalization when including an additional ring. The investigated ligands have the optimal geometry for binding to surface Ti atoms, resulting in ring coordination complexes of a salicylate-type (binuclear bidentate binding-bridging) thus restoring the six-coordinated octahedral geometry of surface Ti atoms. From both absorption measurements in methanol/water = 90/10 solutions and steady-state quenching measurements of modifier fluorescence upon binding to TiO2 in aqueous solutions, stability constants in the order of 10(3) M(-1) have been determined at pH 2 and pH 3. Fluorescence lifetime measurements, in the presence and absence of colloidal TiO2 nanoparticles, indicated that the fluorescence quenching process is primarily static quenching, thus proving the formation of a nonfluorescent CT complex. The binding structures were investigated by using FTIR spectroscopy. Quantum chemical calculations on model systems using density functional theory (DFT) were performed to obtain the vibrational frequencies of charge transfer complexes, and the calculated values were then compared with the experimental data.
We synthesized Eu3+-doped CsY2F7 and RbY2F7 nanoparticles (orthorhombic crystal structure, Pnna space group, No. 52) by the microwave-assisted solvothermal technique and investigated the influence of ...reaction temperature and fluoride ion concentration on the particles’ phase and crystal structure. Fluoride ions were added in excess of the stoichiometric amount to achieve the orthorhombic phase for CsY2F7 and to convert the cubic RbY3F10 to the orthorhombic RbY2F7. Mild synthesis conditions yielded nanoparticles with crystallites ranging in size from 19 to 37 nm and a combination of spherical, rod-like, and hexagonal shapes. Nanoparticles emit a strong orange and red light when excited into the Eu3+5L6 level, which is centered around 390 nm. The strongest emission peak is around 612 nm, which comes from the 5D0→7F2 electronic transitions. Emission intensity dependence on Eu3+ concentration revealed that nanoparticles can be heavily doped with Eu3+, up to 25 % with respect to Y3+. Emission decay measurements provided values of excited state lifetimes of 6.2 ms for the Cs(Y0.75Eu0.25)2F7 and 6.0 ms for the Rb(Y0.75Eu0.25)2F7.
•Botanical origin of honey can be obtained from PARAFAC analyses of fluorescence EEM.•Method provides detection of fake honey samples with 100% sensitivity and specificity.•Fluorescence of phenolic ...and Maillard reaction compounds shows the largest variance.
Fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) and Partial least squares Discriminant Analysis (PLS DA) were used for characterization and classification of honey. Excitation emission spectra were obtained for 95 honey samples of different botanical origin (acacia, sunflower, linden, meadow, and fake honey) by recording emission from 270 to 640nm with excitation in the range of 240–500nm. The number of fluorophores present in honey, excitation and emission spectra of each fluorophore, and their relative concentration are determined using a six-component PARAFAC model. Emissions from phenolic compounds and Maillard reaction products exhibited the largest difference among classes of honey of different botanical origin. The PLS DA classification model, constructed from PARAFAC model scores, detected fake honey samples with 100% sensitivity and specificity. Honey samples were also classified using PLS DA with errors of 0.5% for linden, 10% for acacia, and about 20% for both sunflower and meadow mix.
An experimental metallographic method for determining strain distribution in a cold formed workpiece is presented in this paper. The method, based on the dependence of recrystallized grain size on ...prior deformation, was applied to a bulk formed element made of low carbon steel. Strain distribution was obtained by the calibration curve which gives the relation between recrystallized grain size and prior deformation. To determine strain values, the average grain size was measured in the longitudinal cross-section of the formed element. To accurately differentiate deformation zones, additional observation of carbides and nonmetallic inclusions morphology was utilized, also. The grain size and strain noticeably differ through the cross-section. It is observed that in the middle part, material flows freely through the die opening without significant deformation. From this zone, strain increases gradually, reaching the highest value at the contact surface of the die slope, while the top part flows radially having intermediate values of strain.
Eu3+, Sm3+ and Tb3+ ions have been incorporated into anatase TiO2 nanocrystals via hydrolytic sol–gel method. Pure anatase phase was confirmed with XRD and TEM measurements. Band gap energies change ...slightly with rare earth incorporation, from 3.32 eV for undoped TiO2 to 3.15 eV, 3.25 eV and 3.29 eV for Tb3+, Sm3+ and Eu3+ doped TiO2. Photoluminescence of Eu3+ and Sm3+ originated from three different sites in TiO2 nanocrystals have been identified with the laser-excited site-selective spectroscopy measurements at 10 K. One site exhibits broad emission peaks, which are ascribed to the distorted lattice site near the surface. Other two sites, associated with the inner lattice, show significantly sharper fluorescence lines as a consequence of an ordered crystalline environment. The emission decays of Eu3+ and Sm3+ have similar values for inner-lattice sites and longer lifetimes for near-surface sites. The luminescence of Tb3+ doped TiO2 nanocrystals was immeasurably weak.
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► Sm3+, Eu3+ and Tb3+ are incorporated into anatase nanocrystals via sol–gel route. ► Sm3+ and Eu3+ luminescence originate from 3 different sites in TiO2 nanocrystals. ► Details on multisite structure for Sm3+ doped TiO2 are presented for the first time.
Herein we present the enhancement of photoluminescence properties of nano-sized LuPO4:Pr3+ phosphor powders synthesized by sol gel process with incorporation of yttrium ions inside of this single ...matrix to obtain (Lu1-xYx)PO4:Pr3+ (x = 10, 20, 30, 40, 50 at. %) powders. Under UV excitation at 270 nm the emission spectra of LuPO4:Pr3+ nanopowder do not present any characteristics emission band attributed to 4f15d1→4f2 transitions of Pr3+ ions, while a large emission band has been observed which due to defects created in LuPO4 cell by doping considering the ionic radius of Pr3+ is larger compared to the ionic radius of Lu3+, this band extinguishes gradually at the time insertion of the Y3+ ions until its total disappearance (for x = 40 at. %).It was found that the emission spectra of (Lu1-xYx)PO4:Pr3+ nanopowders under λex = 230 nm presents only the characteristics emission bands of Pr3+ ions with a remarkable influence of the rate of Y3+ ions on the intensity of this bands. Furthermore, it was observed that the improvement in the luminescence properties of (Lu1-xYx)PO4:Pr3+ nanopowders is very remarkable in visible range.
•Pr3+ doped LuPO4 and (Lu1-xYx)PO4 (x = 10, 20, 30, 40, 50 at. %) nano-sized phosphors were successfully synthesized by sol gel process.•Ionic radius of Pr3+ ion on the structural and photoluminescence properties of LuPO4 and (Lu1-xYx)PO4 nanopowders.•Enhancement of photoluminescence properties of nano-sized LuPO4:Pr3+ phosphor powder with incorporation of yttrium ions inside of LuPO4 matrix.
Parallel factor analysis (PARAFAC) was demonstrated as a tool for the analysis of the time-resolved emission spectra of mixtures of rare-earth phosphors. The time-resolved luminescence spectra of ...mixtures of europium(III)-doped Gd2O3, Gd2Ti2O7, and GdVO4 powders were measured in the 570–650nm emission range with time delays varying between 0 and 10ms. Then, PARAFAC was applied to decompose the time-resolved spectra of the mixtures into the emission spectra and emission decay profiles of the individual phosphors. The second-order advantage of this method was demonstrated by calculating the concentrations of the phosphors in the mixtures after calibrating the PARAFAC model by using samples of known concentrations. This method offered 0.1% detection limit and an average prediction error of 0.034%.
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