Green light-emitting Lu3Al5O12:Ce phosphor powders prepared by spray pyrolysis

Green light-emitting Lu_2.985Al₅O₁₂:Ce_0.015 (LuAG:Ce) phosphor powders are prepared by spray pyrolysis. The only crystallized phase in the precursor powders and post-treated powders at temperatures below 800 °C is Lu₂O₃ and the other components are amorphous. Phase pure cubic garnet LuAG:Ce phosphor powders are obtained by post-treatment at 1000 °C. Phosphor powders post-treated at temperatures below 1400 °C retain the spherical shape of the precursor powders. The mean crystallite sizes of phosphor powders post-treated at 1200, 1400, and 1500 °C are 30, 46, and 54 nm, respectively. The excitation spectra contain two bands: a weak band with the maximum peak at 345 nm and a strong broad band in the spectral range from 400 to 490 nm with the maximum peak at 455 nm. The LuAG:Ce phosphor powders have broad emission spectra between 480 and 600 nm, with the maximum peak intensity located at 507 nm. The photoluminescence intensity of the phosphor powders post-treated at 1400 °C is 84.2% of that of the powders post-treated at 1500 °C.     

Dilatometry of attrition milled nanocrystalline titanium powders

The sintering behavior of nanosized titanium powders was investigated by dilatometry. The nanosized Ti powders (40 nm) were produced by the attrition milling of micron sized Ti powders (12 μm) in Ar atmosphere. Sintering was carried out in Ar atmosphere in the temperature range of 450–1250 °C for nanosized Ti and 650–1250 °C for micron sized Ti by heating at 10 °C/min, up to the sintering temperature followed by isothermal holding for 1 h. The nanosized Ti powders exhibited a lower sintering onset temperature, larger shrinkage, larger shrinkage rate, and lower activation energy for sintering as compared to the micron sized Ti powders. The sintered micron sized Ti specimens exhibited both intraagglomerate and interagglomerate porosity while the nanosized Ti specimens exhibited well densified agglomerates (almost no interagglomerate porosity) and large intraagglomerate porosity. In nanosized Ti grain growth was found to take place beyond 700 °C and reached a maximum of 66 nm in samples sintered at 1100 °C.     

Synthesis of the giant dielectric constant oxide CaCu3Ti4O12 via ethylenediaminetetraacetic acid precursor

CaCu₃Ti₄O₁₂ powders were prepared via EDTA route and single-phase CaCu₃Ti₄O₁₂ was obtained at 800 °C for 2 h. DTA/TG and XRD were used to characterize the precursor and derived oxide powders. The dielectric properties of CaCu₃Ti₄O₁₂ ceramics were presented. Increasing sintering temperature leads to the increase in dielectric constant. CaCu₃Ti₄O₁₂ ceramics sintered at 1090 °C for 3 h exhibited giant dielectric constant of up to 2.1 × 10⁵ at room temperature and 100 Hz, which is significantly higher than those obtained from other chemical methods.     

Nanoparticles of the giant dielectric material,calcium copper titanate from a sol–gel technique

The precursor of CaCu₃Ti₄O₁₂ (CCTO) nano particles have been successfully synthesized by sol–gel method at 90 °C. The dried precursor powder was milled and then calcined at 450 °C, 550 °C, 650 °C, 800 °C, 850 °C and 950 °C for 3 h. The phase formation of CCTO was analyzed by step by step using FTIR and XRD. Particle size and shape were evaluated by AFM. The XRD results of the powder calcined at 800 °C indicated the formation of CCTO phase. AFM studies showed that average particle size of the CCTO powder range 90–120 nm. The absorption bands corresponding to vibrations of CaO, CuO and TiOTi were observed at 606, 525 and 463 cm^? 1 using FTIR. The samples sintered at 1040 °C showed the densities as high as 96% of theoretical density. The grain sizes of sintered pellets were determined by FE-SEM. The dielectric properties of prepared samples were studied by LCR meter.     

Annealing effect on the microstructure and photoluminescence of ZnO thin films

Zinc oxide thin films have been obtained by pulsed laser ablation of a ZnO target in O₂ ambient at a pressure of 0.13 Pa using a pulsed Nd:YAG laser. ZnO thin films deposited on Si (1 1 1) substrates were treated at annealing temperatures from 400 °C up to 800 °C after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, resistivity and IR absorption spectra. The results show that the obtained thin films possess good single crystalline with hexagonal structure at annealing temperature 600 °C. Two emission peaks have been observed in photoluminescence spectra. As the post-annealing temperature increase, the UV emission peaks at 368 nm is improved and the intensity of blue emission at 462 nm decreases, which corresponds to the increasing of the optical quality of ZnO film and the decreasing of Zn interstitial defect, respectively. The best optical quality for ZnO thin films emerge at post-annealing temperature 600 °C in our experiment. The measurement of resistivity also proves the decrease of defects of ZnO films. The IR absorption spectra of sample show the typical Zn–O bond bending vibration absorption at wavenumber 418 cm⁻¹.     

Sintering of grey cast iron powder recycled via jet milling

Porous grey cast iron powder metallurgy parts were made from grey cast iron powder manufactured via target jet milling of machining scraps. The powders were used in the as-milled state without any further physical or heat treatment.Sintering was conducted at 1025, 1100 and 1175 °C in an argon atmosphere and the effect of sintering temperature on microstructure, sintered density and apparent hardness of the grey cast iron specimens pressed to 5.8 g/cm³ was investigated.Although diffusion processes were partially activated at 1025 °C, it was determined that a temperature of 1175 °C proved to be the ideal temperature for solid state sintering of grey cast iron parts. The hardness value and sintered density for the specimens sintered at 1175 °C were found to be 96 BHN and 6.1 g/cm³ (around 15% porosity) respectively, all of which lends itself to promising properties for making self-lubricating bearings and parts with sliding properties.     

Martensitic transformation behaviors of rapidly solidified Ti–Ni–Mo powders

For the fabrication of bulk near-net-shape shape memory alloys and porous metallic biomaterials, consolidation of Ti–Ni–Mo alloy powders is more useful than that of elemental powders of Ti, Ni and Mo. Ti₅₀Ni_49.9Mo_0.1 shape memory alloy powders were prepared by gas atomization, and transformation temperatures and microstructures of those powders were investigated as a function of powder size. XRD analysis showed that the B2–R–B19 martensitic transformation occurred in powders smaller than 150 μm. According to DSC analysis of the as-atomized powders, the B2–R transformation temperature (T_R) of the 25–50 μm powders was 18.4 °C. The T_R decreased with increasing powder size, however, the difference in T_R between 25–50 μm powders and 100–150 μm powders is only 1 °C. Evaluation of powder microstructures was based on SEM examination of the surface and the polished and etched powder cross sections and the typical images of the rapidly solidified powders showed cellular morphology. Porous cylindrical foams of 10 mm diameter and 1.5 mm length were fabricated by spark plasma sintering (SPS) at 800 °C and 5 MPa. Finally these porous TiNi alloy samples are heat-treated for 1 h at 850 °C, and then quenched in ice water. The bulk samples have 23% porosity and 4.6 g/cm³ density and their T_R is 17.8 °C.     

Synthesis and characterization of nanocrystalline barium strontium titanate powders prepared by citrate precursor method

Nanocrystalline and well dispersed barium strontium titanate (BST) powders were prepared by a novel and simple citrate precursor method. This method involved direct crystallization of a white precursor from a stable solution in the citric acid (CA)–ethylene glycol (EG)–tetrabutyl titanate–M²⁺ (M = Ba, Sr) system under a specific pH value range. Subsequent heat treatment of the precursor at 850 °C led to a pure phase BST powder. TG/DTA was used to examine the decomposition behaviour of the precursor. The crystalline phase and morphology of the BST powders were investigated by XRD and TEM. It was found that the BST powders synthesized by citrate precursor process were more homogeneous and uniform than that obtained by the citrate gel method.     

Effect of porosity and density on the mechanical and microstructural properties of sintered 316L stainless steel implant materials

In this study, the microstructure and mechanical properties of sintered AISI 316L stainless steel implant materials produced by powder metallurgy (P/M) method were investigated as a function of porosity amount. AISI 316L stainless steel powders were cold-pressed with 800 MPa pressure and sintered at 1200 °C, 1250 °C and 1300 °C for 30 min in a nitrogen atmosphere. The mechanical properties of the 316L implant samples were determined by tensile, fatigue and microhardness tests. Metallographic studies such as pore formation, and fractured surface analyses were performed by Scanning Electron Microscopy (SEM) and Light Optical Microscopy (LOM). The results of this study indicate that, irregular pore formation tendencies increase with an increase in porosity (%). Furthermore, an increase in porosity was shown to decrease the mechanical properties of sintered AISI 316L stainless steel. Sintering temperature is important parameter in decreasing the porosity of P/M materials.     

Sol–gel derived Cr(III) and Cu(II)/γ-Al2O3 doped solids: Effect of the dopant precursor nature on the structural,textural and morphological properties

Powders of xerogel γ-Al₂O₃ doped with various concentrations of Cr³⁺ and Cu²⁺ (M/M + Al molar fraction = 0.75–10%) were prepared via a sol–gel method. Cr³⁺ and Cu²⁺ precursors (acetylacetonate, nitrate or chloride) were added to 0.12 M 2-propanol solution of aluminum tri-sec-butoxide (ASB) and hydrolysis was performed using a H₂O/ASB molar ratio of 4.7. The effect of the dopant precursor on structural, textural and morphological properties was studied. Employing acac precursors resulted in unique properties after calcination at 500 °C including high surface areas, as high as 455 m²/g, homogeneous mesopores, 3–12 nm, and amorphous powders (5–10 nm particles in diameter). On the other hand, the acac precursor enhanced the resistance to sintering mainly at higher metal loads (10%) and elevated temperature (800 °C). Nevertheless, the solids issued from nitrate and chloride precursors exhibited lower surface areas at high metal loads, and lower resistance to sintering.     

Modified sol–gel preparation of LiNbO3 target for PLD

When preparing LiNbO₃ thin layer by PLD, the maximal density of polycrystalline target is important. In this work, we prepared the precursor powders by sol–gel method and used them at PLD target synthesis. The gels were synthesized by Pechini polyesterification, using citric acid and ethylene glycol as an organic matrix constituents, and then decomposed using various temperatures (800, 600 and 400 °C) and atmospheres (air, nitrogen and oxygen in sequence). Out of several combinations tested, the decomposition at 800 °C in nitrogen followed by the oxidation at 400 °C in oxygen was found to be the best way to achieve the minimal particle size of powder precursor resulting in denser targets. The prepared targets were characterized by XRD and SEM.The optimized process was subsequently used for preparation of LiNbO₃ target. Thin layers prepared by PLD from this target resulted smoother than the layers prepared from commercial monocrystalline target.     

Synthesis,processing and characterization of calcia-stabilized zirconia solid electrolytes for oxygen sensing applications

Precursor powders of calcia-stabilized zirconia (CSZ) solid electrolytes have been synthesized by a sol–gel method. The phase evolution of the precursor powders after thermal treatments at different temperatures were analysized by X-ray diffraction technique. Disc-shaped sensor elements were fabricated via uniaxial pressing of the calcined powders and subsequently sintered at 1650 °C. Scanning electron microscopy (SEM) was used to analyze the microstructure of the sintered pellets. Platinum electrodes were applied to the sintered elements to produce potentiometric/electrochemical gas sensors. The electrical response of the gas sensors to oxygen and the complex impedance of the sensors in air were measured at various temperatures. Impedance analyses indicate that the sensor cell with 15 mol% CaO has much lower resistance (the sum of bulk and grain-boundary resistance) than the sensor cell with 22 mol% CaO. This is also reflected by the EMF responses of both sensor cells to various oxygen concentrations in the testing gas. The EMF deviation from the theoretical value of the CSZ sensor cell with 22 mol% CaO was larger than that of the CSZ sensor cell with 15 mol% CaO. The corrrelations between material compositions, microstructures of the sintered pellets and the electrical properties of the sensors are discussed.     

Synthesis of fine Pb(Fe0.5Nb0.5)O3 perovskite powders by coprecipitation method

Lead iron niobate, Pb(Fe_0.5Nb_0.5)O₃ (PFN) is an optimal material for multilayered ceramic capacitors (MLCCs). Fine lead iron niobate powders with average size of 500 nm were prepared from the precipitation precursor. In the experiment, Nb₂O₅ was used as Nb source to substitute Nb alkyloxide or oxalate and successfully converted into aqueous Nb⁵⁺ solution. The results shows that the perovskite PFN was emerged at a temperature as low as 400 °C, and pure perovskite was obtained at the temperature of 800 °C. The formation of perovskite at a low temperature was attributed to the core–shell structure in the precipitates of hydroxide. Besides, the particles of perovskite PFN show the good chemical stoichiometry and small size of 300–500 nm.     

Artificial neural network prediction of aging effects on the wear behavior of IN706 superalloy

In this study, the effect of aging parameters on wear behavior of PM Inconel 706 (IN 706) superalloy was experimentally investigated and an ANN model was developed to predict weight loss after wear tests. IN 706 superalloy powders were cold pressed (700 MPa) and sintered at 1270 °C for 90 min. The sintered components were gradually aged for 16 h at 730 °C and for 12–20 h at 620 °C. The samples of IN706 superalloy were subjected to wear test at a constant sliding speed of 1 m/s under three different loads (30 N, 45 N and 60 N) and for five different sliding distances (400–2000 m). The results clearly showed that δ, γ′ and γ″ phases were observed around grain boundaries of IN 706 superalloy aged for different periods. The highest hardness was measured for the samples aged for 12 h. Weight losses were found to increase as the sliding distance increased. Moreover, the ANN modeling of weight loss values for IN 706 superalloy gave effective results and can be successfully used to predict weight loss values in the parameters that were determined by the obtained high R² value.     

Microwave-assisted synthesis and characterization of Ti1 − xVxO2 (x = 0.0–0.10) nanopowders

Ti_1 ? xV_xO₂ (x = 0.0–0.10) nanopowders were successfully synthesized by a microwave-assisted sol–gel technique and their crystal structure and electronic structure were investigated. The products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and UV–Vis spectroscopy. The results revealed that TiO₂ powders maintained the anatase phase for calcination temperature below 600 °C, but gradually changed to the rutile phase above 800 °C. The formation of the rutile phase was completed at 1000 °C. For Ti_1 ? xV_xO₂ (x = 0.05) powders, the phase transformation appeared at 600 °C. The absorption edge of Ti_1 ? xV_xO₂ (x > 0) powders broadened to the visible region with increasing V concentration and a strong visible light absorption was obtained with 10% V doping. V doping and subsequent coexistence of both anatase and rutile phases in our Ti_1 ? xV_xO₂ nanoparticles are considered to be responsible for the enhanced absorption of visible light up to 800 nm.     

Optical,electrical properties,characterization and synthesis of Ca2Co2O5 by sucrose assisted sol gel combustion method

Sol–gel combustion method has been used as an efficient and simple method to synthesize pure Ca₂Co₂O₅ (CCO-225) ceramic powder using sucrose which play a dual role as the gelling agent and combustion fuel. The advantage of this method is simple low cost and environmental friendly. The synthesized sample is sintered at various temperatures the products were characterized by powder X-ray diffraction (XRD), Thermogravimetric and differential thermal analysis (TGA-DTA), Fourier transformer infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and UV–Visible diffuse reflectance spectroscopy (DRS). X-ray diffraction pattern of sintered sample at 800 °C confirmed the formation of single phase Ca₂Co₂O₅ and also it is proved in thermal analysis. SEM image indicates the obtained samples are diffused platelet like morphology and its grain size will be in the range of 150–300 nm. CCO-225 ceramic material has a wide range of optical and electronic applications due to its wide band gap energy of 3.50 eV. The dielectric constant, dielectric loss and AC conductivity were analyzed at different temperatures and frequencies of the applied field. The AC conductivity studies carried out in the frequency range of 50 Hz to 5 MHz at various temperatures from 30 °C to 400 °C. The result reveals that the space charge polarization leads for conduction mechanism.     

Synthesis of nanoporous silicon carbide via the preceramic polymer route

Nanoporous silicon carbide materials were prepared by the pyrolysis of the preceramic polymer, polycarbosilane (PCS), with and without the addition of an inert filler (nano- and micron-sized silicon carbide powders). Hydrosilylation crosslinking of PCS with divinylbenzene prior to pyrolysis appeared to have little influence on the development of micro- and mesoporosity. Maximum micropore volumes were 0.28 cm³ g^?1 for non-crosslinked PCS and 0.25, 0.33 and 0.32 cm³ g^?1 for PCS crosslinked with 2, 6 and 10 wt.% DVB respectively. Micropore volumes decreased under hydrothermal conditions to 0.03 cm³ g^?1 for non-crosslinked and 0 cm³ g^?1 for crosslinked PCS. Porosity was also lost at temperatures above 700 °C. The addition of nano-sized SiC powders to PCS prior to pyrolysis maintained mesoporosity to temperatures of 1200 °C, however, micron-sized SiC powders did not maintain porosity above 800 °C. The modal pore size in pellets formed by compressing micron-sized powders with the preceramic polymer was 5 μm compared to 30 nm when nano-sized powders were used.     

Combustion characteristics of the heat pellet prepared from the Fe powders obtained by spray pyrolysis

Fe powders for thermal batteries were prepared by reduction of iron oxide powders obtained by spray pyrolysis. The iron oxide powders prepared by spray pyrolysis had fine size, spherical shape and high surface area. The morphologies of the Fe powders were affected by the preparation temperatures of the iron oxide powders. The Fe powders obtained from the iron oxide powders prepared by spray pyrolysis at 900 and 1000 °C had slightly aggregated structure of the primary powders with several microns sizes. The powders had pure Fe phases at reducing temperatures between 600 and 800 °C. The heat pellets with diameter of 18.2 mm were prepared using Fe powders and potassium perchlorate (KClO₄). The porosity of the prepared heat pellet was about 40%. The break strength of the heat pellet was 0.9 kgf. The ignition sensitivity of the heat pellet was 4 W. The maximum burn rate of the heat pellet obtained from the Fe powders were 8.6 cm s^?1.     

Experimental and prediction of sintered Cu–W composite by using artificial neural networks

High-energy mechanical milling was used to mix Cu and W powders. Cylindrical preforms with initial preform density of 85% were prepared using a die and punch assembly. The preforms were sintered in an electric muffle furnace at 750 °C, 800 °C, 850 °C, and subsequently furnace cooled and then the specimens are hot extruded to get 92% preform density. Scanning Electron Microscope and X-ray diffraction observations used to evaluate the characteristics. The pore size reduction during extrusion was studied using Auto CAD 2010. Neural networks are employed to study the tribological behavior of sintered Cu–W composites. The proposed neural network model has used the measured parameters namely the weight percentage of tungsten, sintering temperature, load and sliding distance to predict multiple material characteristics, hardness, specific wear rate, and coefficient of friction. The predicted values from the proposed networks coincide with the experimental values. In addition, a relative study between the regression analysis and the networks revealed that the artificial neural networks can predict the tribological characteristics of sintered Cu and W composites better than regression polynomials within a very few percent error.     

Rapid carbothermal synthesis of nanostructured silicon carbide particles and whiskers from rice husk by microwave heating method

This paper reported a simple and rapid route to large-scale synthesis of nanostructured SiC powders using rice husk as the precursor. Rapid carbothermal reduction reactions were achieved in a 2.45 GHz microwave field in an argon atmosphere. The XRD patterns revealed that complete carbothermal reduction of silica was achieved at 1300 °C for 60 min or at 1500 °C for only 15 min by microwave heating, resulting in β-SiC formation. The FE-SEM images showed that the β-SiC powders were mixtures of particles and whiskers. The β-SiC particles had diameters of 60–130 nm and the β-SiC whiskers, which were several to tens of micrometers in length, had diameters of 110–170 nm. The β-SiC powder synthesized at 1500 °C for 15 min showed the highest BET surface area of 12.2 m²/g. Compared to the conventional heating method, the microwave heating method proved to be an efficient approach for synthesis of SiC in terms of energy and time saving, as well as for fabrication of nanostructured SiC.