Average Grain Size Of Samples Research Articles

Role of Fe supplantation in tailoring structural, electrical conductivity, and magnetic properties in La2Ni1-xFexMnO6 double perovskites

Double perovskite system La2Ni1-xFexMnO6 (x = 0, 0.2, 0.5, 0.8 & 1.0) were developed using sol-gel method. Rietveld refinement revealed monoclinic structure (ordered) along with occurrence of rhombohedral and orthorhombic structures suggesting antisite cationic disorder. Crystallite size and average grain size of samples varied between 454 and 1058 Å and 0.774–1.429 μm respectively. XPS revealed the dual oxidation states of Ni, Fe, and Mn ions. La2NiMnO6 attained the highest DC conductivity among all compositions. The increase in DC conductivity with temperature suggested the semiconducting behavior of the samples, that explained by Thermal Activation (TA) and Variable Range Hopping (VRH) conduction mechanisms. Obtained activation energy(Edc) showed increasing trend with temperature. M-H loops exhibit a ferromagnetic nature accompanied by antiferromagnetic interactions as suggested by exchange bias and partially saturated loops. La2NiMnO6 attained the highest saturation magnetization (29.81emu/g) and decreased with Fe supplantation. The possible mechanism of tuning conductivity and magnetic properties of La2Ni1-xFexMnO6 has been discussed in detail.

Simultaneously enhancing mechanical and tribological performance in undercooled Co-18.5 at. % B alloys

The wear behavior and its mechanism greatly depend on the microstructure of alloys. Herein, the Co-18.5 at. % B eutectic alloys with three different morphologies and phase constitutions were obtained by undercooling solidification under different magnetic field intensity (0T, 10T, 20T), and the relative mechanical properties and tribological performance were investigated systematically. Results show that the grain size of Co–B alloy decreases first and then increases with the increase of magnetic field strength, the average grain size of samples under 0 T and 20 T was about 3–5 μm, while the grain size of sample with 10 T refined to 20–40 nm. The sample treated under 10 T exhibits the lowest wear rate (1.53 × 10−5 mm3N−1m−1) and highest micro-hardness (868.27 HV). The fine grain strengthening effect is the main reason for the increase in strength and hardness of Co–B alloy. The fine crystalline nano-heterostructures (20–40 nm) and the precipitation enhancement of secondary precipitated Co nanoparticles also has a beneficial effect on mechanical properties. The oxide friction layer consisting mainly of layered H3BO3 lubricant, detected on the worn surface of Co–B alloy (10T) has anti-wear properties. By contrast, Co–B alloys with coarse Co3B grains (0T) and inhomogeneous FCC-Co/Co2B lamellar structure (20T) present higher wear rates and lower hardness. This work can provide guidance for the initial control of mechanical properties from the design of the microstructure.

The influence of nitrogen and oxygen on the high nucleation density diamond growth

High nucleation density diamond films were grown on silicon substrates with a high-density nano-diamond suspension crystal seed. By keeping other parameters constant and varying the amounts of oxygen and nitrogen added, diamond films were grown using MPCVD equipment. The composition, structure, and properties of the diamond films were characterized using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The results show that the average grain size of samples grown with added oxygen and nitrogen as assisting gases significantly decreased, exhibiting improved crystallinity and fewer defects. However, there was a certain increase in the relative content of graphite, along with the presence of trans-polyacetylene. Furthermore, as the ratio of oxygen to nitrogen increased, the samples exhibited better crystallinity, fewer defects, and overall higher growth quality. The relative content of graphite initially increased, then decreased, and increased again.

Structural and Scintillation Properties of Ce3+:Gd3Al3Ga2O12 Translucent Ceramics Prepared by One-Step Sintering.

Cerium-doped gadolinium aluminum gallium garnet (Ce3+:Gd3Al3Ga2O12, Ce3+:GAGG) ceramic is a promising scintillation material. In this study, Ce3+:Gd3Al3Ga2O12 scintillation ceramics were prepared by the one-step sintering of commercially available Gd2O3, Al2O3, Ga2O3, and CeO2 powders in a flowing oxygen atmosphere at 1600 °C by solid-phase reaction sintering. For all the Ce3+:Gd3Al3Ga2O12 ceramic samples doped with different amounts of Ce3+ doping, dense ceramics were obtained. The structure, photoluminescence, and scintillation properties of the Ce3+:Gd3Al3Ga2O12 ceramics have been investigated. The average grain size of samples sintered at 1600 °C is about 2 μm. The X-ray excitation luminescence peak is around 560 nm, which is consistent with that of Ce3+:Gd3Al3Ga2O12 single crystals, matching well with the computed tomography X-ray detector's response sensitivity. The light yield is higher compared to the standard reference sample-lutetium yttrium orthosilicate single crystal.

Influence of TiC content on microstructure and mechanical properties of (Ta, Ti)C ceramics

(Ta, Ti)C ceramics with different TiC contents have been fabricated by hot pressing using as-synthesized carbide powders via carbothermal reaction. The effect of TiC content on densification, microstructure and mechanical properties was investigated. All samples with adding TiC exhibit high relative density of >98%, and even the relative density can reach 99.6% when TiC content is 33 mol%. Besides enhancing sinterability, the average grain sizes of samples significantly become large in the range of 19.9–39.4 μm. (Ta0.83Ti0.17)C ceramic possesses an optimized combination of mechanical properties with a Vickers' hardness, flexural strength, Young's modulus and fracture toughness of 17.5 GPa, 306 MPa, 544 GPa and 3.7 MPa·m1/2, respectively.

Improving physical and mechanical properties of foil for anodes of high-voltage electrolytic capacitors by introducing an intermediate annealing

The results of studies of influence of intermediate and final annealing on the level of physical and mechanical properties of foil for anodes of highvoltage capacitors made of high-purity aluminum (99.99%) are presented. A comparative analytical analysis of efficiency of introduction of the intermediate annealing stage in the thermo-deformation processing mode in comparison with its absence in the scheme was performed. The starting material for the research is a strip with a thickness of 0.45 mm, obtained from hot-rolled strip with a thickness of 8 mm by cold rolling (deformation degree is 0.9437). The chemical composition of the strip corresponds to the A99 aluminum grade according to GOST 11069–2019. Content of basic impurities in the initial strip by the actual chemical composition,%: 0,0018 Si; 0.0012 Fe; 0.0020 Cu. A set of studies of physical and mechanical properties, which allowed to determine the dependence of the maximum value of specific capacity of high-voltage anode foil on the average grain size and crystallographic orientation (in this case - the maximum value of cubic texture, with allowable values of foil ultimate strength). It is shown that with an increase in the intensity of the cubic texture from 90 to 95%, the specific capacitance increases from 29 to 32 μF/dm2. This is achieved through the use of intermediate annealing at 380 оC and further final annealing at 550 оC. The hereditary character of the average grain size of samples with a thickness of 0.45 mm during intermediate annealing and the grain size of the foil with a thickness of 0.100 mm after the final annealing is shown.

Influence of Cu substitution and Bi2O3 doping on magnetic properties of low-temperature-fired NiCuZn ferrites

Two groups of low-temperature-fired Ni0.6-xZn0.4CuxFe1.98O4 (x = 0.1–0.325 in intervals of 0.025) under two different doping modes, namely, low, i.e., group A with 0.25 wt% Bi2O3 and high, i.e., group B with 1 wt% Bi2O3, were prepared by solid-state reaction method. Their crystal phase composition, microstructure, and soft magnetic properties were studied and compared. The series of ferrite samples of both groups presented single spinel ferrite phase. However, average grain sizes of samples in group A were significantly smaller than those in group B. Microstructures of samples changed significantly with the increase in Cu content. Furthermore, relative density, permeability, saturation flux density (Bs), and quality factor, first increased and then decreased with increasing Cu content, in both groups. Snoek constants in the two groups increased monotonously. However, densified samples in group A had higher Snoek constants than samples in group B, which indicated that they were more suitable for high-frequency applications. In general, overall performance of samples in group A was better than that of samples in group B, but properties of the former were more sensitive to Cu content. Therefore, to achieve better overall performance, it was best to choose samples with proper Cu substitution (x = 0.275) in group A. For improved robustness of ferrite composition and process, it was more appropriate to choose samples with proper Cu substitution ((x = 0.25) in group B.

Influence of electric field strength on structure, microstructure, and electrical properties of flash sintered 8% mol Yttria-stabilized zirconia as a solid oxide fuel cell electrolyte

To study the effect of electric field on the characteristics of flash sintered materials, 8% mol. Yttria-stabilized zirconia (8YSZ) was isothermally flash sintered under various electric field strengths as a solid oxide fuel cell (SOFC) electrolyte. Structural, microstructural, and electrical characteristics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Electrochemical impedance spectroscopy (EIS), respectively. Results show that the electric field did not affect the relative density of flash sintered 8YSZ. Electric fields stronger than 300 V cm−1, however, transformed the cubic structure to tetragonal. Microstructural studies show that the average grain size of samples is independent of the applied electric field strength. Electrochemical impedance spectroscopy showed changes in the grain boundary characteristics upon using the electric field for flash sintering. Oxygen vacancy concentration in the grain boundary of flash sintered samples was more than ten times higher than conventionally sintered ones, which improved the conductivity in flash sintered samples.

Additive manufacturing of stellite 6 superalloy by direct laser metal deposition – Part 2: Effects of scanning pattern and laser power reduction in differrent layers

In this study, the purpose is to investigate two strategies for direct laser metal deposition method (DLMD) additive manufacturing of stellite 6 Cobalt-based superalloy experimentally. The first one was the effect of scanning pattern, and the second one was the influence of laser power reduction in different layers in additive manufacturing (AM). For the experiments a coaxial nozzle head coupled with a 1 kW continuous fiber laser was used. This research aim was to examine the effect of these two strategies on characteristics of the additive manufactured components. The macro section of the geometrical dimensions, including height and width, profiles of microhardness, grain size, and microstructure of the 3D printed wall samples were investigated. The height stability of samples was also examined. The results indicated that scanning pattern has an important role in all the additive manufactured components features. Results show that when the unidirectional scanning pattern was used, the more stability will be obtained. The average grain size of samples which were produced by unidirectional scanning pattern and bidirectional scanning pattern was 2.25 μm and 2.83 μm, respectively. The trend of changes in the grain size of the samples shows that the beginning and the end of the LAMed wall are larger than the sample’s center, and the trend of the microhardness variation is in reverse regime of the grain size. Also, it was shown that with decreasing the laser power from the substrate upwards, the width of samples has reduced.

A Promising Proton Conducting Electrolyte BaZr1-xHoxO3-\u03b4 (0.05 \u2264 x \u2264 0.20) Ceramics for Intermediate Temperature Solid Oxide Fuel Cells

In this study, the Ho-substituted BaZrO3 electrolyte ceramics (BaZr1-xHoxO3-δ, 0.05 ≤ x ≤ 0.20) were synthesized through a low-cost flash pyrolysis process followed by conventional sintering. The effects of Ho-substitution in BaZrO3 studied in terms of the structural phase relationship, microstructure and electrical conductivity to substantiate augmented total electrical conductivity for intermediate temperature solid oxide fuel cells (IT-SOFCs). The Rietveld refined X-ray diffraction (XRD) patterns revealed that pure phase with Pmbar{3}m space group symmetry of cubic crystal system as originated in all samples sintered at 1600 °C for 8 h. The Raman spectroscopic investigations also approved that Ho incorporation in BaZrO3 ceramics. Field Emission Scanning Microscopic (FESEM) study informed a mixture of fine and coarse grains in the fracture surface of Ho-substituted BaZrO3 sintered samples. The relative density and average grain size of samples were observed to decrease as per the addition of Ho-substitution in BaZrO3 ceramics. The electrical conductivity study was accomplished by Electrical Impedance Spectroscopy (EIS) under 3% humidified O2 atmosphere from 300 to 800 °C. Furthermore, the total electrical conductivity of BaZr0.8Ho0.2O3-δ ceramic was found to be 5.8 × 10−3S-cm−1 at 600 °C under 3% humidified atmosphere, which may be a promising electrolyte for IT-SOFCs.

Development and Characterization of Titanium Dioxide Ceramic Substrates with High Dielectric Permittivities.

Titanium dioxide substrates have been synthesized by means of solid-state reactions with sintering temperatures varying from 1150 °C up to 1350 °C. X-ray diffraction and scanning electron microscopy (SEM) where employed to investigate the crystal structure, grain size and porosity of the resulting samples. The obtained ceramics are tetragonal (rutile phase) with average grain sizes varying from 2.94 µm up to 5.81 µm. The average grain size of samples increases with increasing temperature, while the porosity decreases. The effect of microstructure on the dielectric properties has been also studied. The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectric permittivity and loss tangent) in comparison to those of commercial substrates, indicating that the obtained ceramic substrates could be useful in the miniaturization of telecommunication devices.

Effect of grain size of dental zirconia on shear bond strength of composite resin cement.

The effect of grain size of dental zirconia on the shear bond strength of composite resin cement was newly studied. Disc-shaped dental zirconia with small (sample S) and large (sample L) grains were made by sintering of pre-sintered dental zirconia at 1450°C for 0.5 h and 40 h, respectively. After the sintering, the average grain size of sample S was 1.37 ± 0.15 µm, while that of sample L was 3.74 ± 0.50 µm. The sintered discs were successively polished with different grades of diamond and alumina slurries. The interfacial free energies were 63.5 ± 4.2 dyne/cm for sample S and 52.1 ± 5.5 dyne/cm for sample L. Stainless steel cylinders, previously sandblasted with 50 µm alumina powder, were bonded to the zirconia discs using composite resin cement. Next, samples were kept in an oven for 7 d at 36.5°C. The shear bond strength of sample S was 23.0 ± 4.5 MPa while that of sample L was 17.5 ± 4.6 MPa. After the fracture, the areal % values of composite resin cement remaining on the zirconia surfaces were 89.7 ± 5.9% for sample S and 61.6 ± 5.5% for sample L. The results suggest that grain size reduction has a potential to enhance the degree of bonding between a composite resin cement and a dental zirconia due to the increase of interfacial free energy.

Fine tuning of tensile properties in CrCoNi medium entropy alloy through cold rolling and annealing

In the present study, tensile properties of CrCoNi medium entropy alloy with different microstructures (recovery, partial recrystallization, recrystallization) were investigated by subjecting cold-rolled samples to different annealing conditions. The microstructure of the cold-rolled sample showed the presence of severely deformed grains with several deformation twins. Annealing of the cold-rolled samples at 700 °C and above for 60 min led to fully recrystallized microstructure, while annealing at temperatures lower than 700 °C led to recovery and partially recrystallized microstructures. The annealed samples showed a typical strength-ductility trade-off with an increasing fraction of recrystallized grains and increasing average grain size in samples with partially recrystallized and fully recrystallized microstructure, respectively. Fine tuning of microstructure led to a remarkable combination of strength (~1 GPa) and uniform elongation (28%) in the sample with partially recrystallized microstructure, which consists of ~77% of recrystallized grains with an average recrystallized grain size of ~3 μm.

Ferrites: magnetic materials as an alternate source of green electrical energy

Ferrites samples Mg1-xLixFe2O4 for x = 0.0, 0.1, 0.2, 0.3, were synthesized by solid-state sintering method. Detailed investigations were made on the structural, morphological, magnetic and electrical proprieties of these samples. A detailed investigation was performed on power generation of these samples and role of Li-doping has been discussed. The X-ray Diffraction (XRD) pattern confirms the spinel phase formation in samples without any impurity. It is observed from Scanning Electron Microscopy that average grain size of samples decreases with lithium doping in MgFe2O4. The saturation magnetization of MgFe2O4 (15.4 emu/g) is found to increase with Lithium percentage and maximum 39.3 emu/g for Mg0.7Li0.3Fe2O4 sample. Ferrites play a crucial role in magnetic recording, microwave magnetic devices and many applications in medical sciences. Recently, it was observed that ferrites can be an alternate source of green energy by inventing hydroelectric cell (HEC). The processes of water adsorption and dissociation on the metal-oxide surface, plays an important role in production of electricity in ferrites. When, water is sprayed on hydroelectric cell the thermodynamic driving force is responsible for the formation of stable metal-oxygen or metal-hydroxyl bonds. The reactivity of ferrite surface towards water is based on the interaction of these ions and the d orbital of the Fe atom. Due to this interaction, water dissociated in H3O+ and OH− ions and migrates toward silver and zinc electrodes respectively. A typical hydroelectric cell of 2 inch diameter produces 17.1 mA of peak current and 949 mV voltage with a maximum output power of 15.85 mW for Li = 0.2 doped MgFe2O4 sample.

Microstructure evolution and mechanical behaviour of severely deformed pure titanium through multi directional forging

Multi directional forging (MDF) is one of the severe plastic deformation methods utilized for production of ultrafine grained materials with improved mechanical properties. The main goal of the current study is to enhance mechanical properties of commercial pure (CP) titanium using grain refinement by MDF method. For this purpose, after one hour annealing at 800 °C, the CP titanium was forged by MDF process up to six passes at room and 220 °C temperatures. The results of microstructure analysis by scanning electron microscope equipped with EBSD showed that average grain size of samples after six MDF passes at room and 220 °C temperatures was about 60 times finer than that of the annealed specimen. The mean grain size of the titanium is reduced from 64 μm to 1 μm after 6 passes at room temperature. Also, the tensile and shear strengths are notably improved by increasing number of MDF passes and reduction of the processing temperature. Yield tensile and shear strengths of six passes MDFed samples at room temperature were about 2.5 times greater than those of the annealed specimen. The correlation between tensile and shear strengths was studied as well. The ratio between yield tensile and shear strengths and also between ultimate tensile and shear strengths was achieved about 1.5 and 2, respectively.

Magnetocaloric properties of double-perovskite Sr1.98Al0.02FeMoO6

In this paper, we concluded a series of studies on the magnetic properties of double-perovskite Sr2FeMoO6 and Sr1.98Al0.02FeMoO6. Samples were prepared by a sol-gel method. Analysis of the X-ray diffraction data showed that both samples were monophasic and belonged to the I4/m space group. By analysing the scanning electron microscope patterns, we found that doping of aluminium reduced the average grain size of samples from 889 nm to 831 nm. The magnetic hysteresis loop of the samples at 5 K indicated that saturation magnetization did not change significantly with doping. Field-cooled magnetization curves showed that Al doping caused the Curie temperature (TC) of the samples to drop from 386 K to 356 K. Arrott plot analysis indicated that the magnetic phase change of both samples was a second-order magnetic phase transition. The maximum magnetic entropy change |SMmax| of the samples in the magnetic field of 2.5 T increased from 0.559 J kg−1 K−1 to 0.589 J kg−1 K−1, and the relative cooling power also increased for the doped sample.

Effects of (Cr0.5Ta0.5)4+ on structure and microwave dielectric properties of Ca0.61Nd0.26TiO3 ceramics

The Ca0.61Nd0.26Ti1-x(Cr0.5Ta0.5)xO3 (CNT-CTx) ceramics with orthorhombic perovskite structure were prepared using the conventional solid-state method. The X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectra (XPS) were employed to investigate the correlations between crystal structure and microwave dielectric properties of CNT-CTx ceramics. The XRD results showed that all CNT-CTx samples were crystallized into the orthorhombic perovskite structure. The SEM micrographs indicated that the average grain size of samples depended on the sintering temperature. As (Cr0.5Ta0.5)4+ concentration increased, there was a significant decrease in the average grain size of samples. The short range order (SRO) structure and structural distortion of oxygen octahedra proved to exist in CNT-CTx crystals according to the analysis of Raman spectra results. The microwave dielectric properties highly depended on the full width at half maximum (FWHM) of Raman spectra, oxygen octahedra distortion, reduction of Ti4+ to Ti3+ and bond valence. At last, the CNT-CT0.05 ceramic sintered at 1420 °C for 4 h exhibited the good and stable comprehensive microwave dielectric properties: relative permittivity of 96.5, quality factor of 14,360 GHz, and temperature coefficient of resonant frequency of +153.3 ppm/°C.

Preparation and flash sintering of MgTiO3 nanopowders obtained by the polyacrylamide gel method

Using a polyacrylamide gel method, phase pure and well-dispersed MgTiO3 nanopowders were prepared at 800 °C for 2 h. It was found that a high mole ratio of monomers to precursors resulted in low formation temperature of MgTiO3, due to the highly mixing homogeneity and smaller particle sizes of precursors. Sintering behaviors of MgTiO3 nanopowders under DC electric field from 500 to 800 V/cm were investigated. Nearly full dense MgTiO3 ceramics can be prepared in 30 s. An abrupt and simultaneous increase in current density and power dissipation were observed in sintering process, which are characteristics of flash sintering. The power dissipation for the flash sintering was found to be 82 mW/mm3. The densities and average grain sizes of samples increase with the increase of the electrical field strength. It was suggested that Joule heating was the main mechanism of flash sintering of MgTiO3 ceramics. Our work provides a useful route for the fabrication of dense MgTiO3 ceramics at low temperature in short time.

Structure–property relationships of perovskite-structured Ca0.61Nd0.26Ti1-x(Cr0.5Nb0.5)xO3 ceramics

A series of Ca0.61Nd0.26Ti1-x(Cr0.5Nb0.5)xO3 (CNTCNx) (0 ≤ x ≤ 0.1) ceramics were prepared via a solid state reaction method. All CNTCNx samples were crystallized into the orthorhombic perovskite structure. The SEM micrographs indicated that the average grain sizes of samples depended on (Cr0.5Nb0.5)4+ concentration. And as (Cr0.5Nb0.5)4+ concentration increased, the average grain size of samples decreased significantly. The short range order (SRO) structure and structural distortion of oxygen octahedra proved to exist in CNTCNx crystals from Raman spectra analysis results. The microwave dielectric properties highly depended on the B-site bond strength, oxygen octahedra distortion, reduction of Ti4+ to Ti3+ and internal strain η. At last, the CNTCN0.06 ceramic sintered at 1400°C for 4h exhibited good and stable comprehensive microwave dielectric properties of εr = 92.3, Q × f = 13,889GHz, τf = + 152.8ppm/°C.

Microstructure and hardness inhomogeneity of fine-grained AM60 magnesium alloy subjected to cyclic expansion extrusion (CEE)

In the present paper, the effect of cyclic expansion extrusion (CEE) process on the microstructure inhomogeneity and microhardness distribution of AM60 magnesium alloy is investigated. The results demonstrated that after the first pass of CEE at 300°C, ultrafine grains nucleated along initial grain boundaries which caused a bimodal structure. The area fraction of the newly formed grains and Mg17Al12 dissolution was higher in the outer region rather than the central areas which is related to the different contribution of shear and normal strains. By increasing the number of passes to three, the level of inhomogeneity decreased and the average grain size of samples reduced from ∼185μm to ∼6μm. After the second pass of CEE, an excellent combination of ultimate strength (∼367MPa) and elongation to fracture (∼20%) was improved with the initial values of 261MPa and 13.8%, respectively. To show the variations of hardness, Vickers microhardness measurements were performed over the cross-section. After the first pass, heterogeneous microhardness distribution was seen. However, the microhardness inhomogeneity decreased by increasing the number of passes. Harness results were in good agreement with the microstructure results.