Effects of milling time and calcination condition on phase formation and particle size of lead zirconate nanopowders prepared by vibro-milling

Effect of calcination conditions on phase formation and particle size of lead zirconate (PbZrO₃) powders synthesized by a solid-state reaction with different vibro-milling times was investigated. A combination of the milling time and calcination conditions was found to have a pronounced effect on both the phase formation and particle size of the calcined PbZrO₃ powders. The calcination temperature for the formation of single-phase perovskite lead zirconate was lower when longer milling times were applied. The optimal combination of the milling time and calcination condition for the production of the smallest nanosized (∼28 nm) high purity PbZrO₃ powders is 35 h and 750 °C for 4 h with heating/cooling rates of 30 °C/min, respectively.     

Influence of calcination conditions on phase formation and particle size of indium niobate powders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO₄, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO₄ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. Single-phase InNbO₄ powders have been obtained successfully for calcination condition of 900 °C for 4 h or 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.     

Effect of calcination condition on phase formation and particle size of lead titanate powders synthesized by the solid-state reaction

A perovskite-like phase of lead titanate, PbTiO₃, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. Phase formation of the calcined powders has been investigated as a function of calcination temperature, soaking time and heating/cooling rates by DTA and X-ray diffraction (XRD) techniques. Moreover, morphology and particle size evolution have been determined via SEM technique, respectively. It has been found that single-phase PbTiO₃ powders were successfully obtained for calcination conditions of 550 °C for 4 h or 600 °C for 1 h with heating/cooling rates of 20 °C/min. Higher temperatures clearly favoured particle growth and the formation of large and hard agglomerates.     

Effects of calcination conditions on phase formation and particle size of indium niobate nanopowders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO₄, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO₄ phase in the calcined powders has been investigated as a function of calcination conditions by TG–DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that single-phase InNbO₄ powders have been obtained successfully at the calcination condition of 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.     

Phase and morphology evolution of magnesium niobate powders synthesized by solid-state reaction

Magnesium niobate (MgNb₂O₆; MN) powders have been prepared and characterized by TG-DTA, XRD, SEM and EDX techniques. The effect of calcination temperature, dwell time and heating/cooling rates on phase formation, morphology and chemical composition of the powders are examined. The calcination temperature and dwell time have been found to have a pronounced effect on the phase formation of the calcined magnesium niobate powders. It has been found that the minor phases of unreacted MgO and Nb₂O₅ phases tend to form together with the columbite-type MgNb₂O₆ phase, depending on calcination conditions. It is seen that optimisation of calcination conditions can lead to a single-phase MgNb₂O₆ in an orthorhombic phase. Higher calcination times and heating/cooling rates clearly favoured particle growth and the formation of large and hard agglomerates.     

Improvement in synthesis of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> powders by Ge<Superscript>4+</Superscript> acceptor doping

In this paper, the effects of doping with GeO₂ on the synthesis temperature, phase structure and morphology of (K_0.5Na_0.5)NbO₃ (KNN) ceramic powders were studied using XRD and SEM. The results show that KNN powders with good crystallinity and compositional homogeneity can be obtained after calcination at up to 900°C for 2 h. Introducing 0.5 mol.% GeO₂ into the starting mixture improved the synthesis of the KNN powders and allowed the calcination temperature to be decreased to 800°C, which can be ascribed to the formation of the liquid phase during the synthesis.     

Phase formation and microstructure of Nd<Superscript>+3</Superscript> doped Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> prepared by sol–gel method

The aim of this study was to investigate the effects of the rare earth element neodymium on the phase formation and microstructural development of relaxor ferroelectric lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN) system. Perovskite phase PMN powders were prepared using the sol–gel method and the effect of neodymium doping was investigated at different doping levels ranging from 0.1 mol% to 30 mol%. The precursors employed in the sol–gel process were lead (II) acetate, magnesium ethoxide, and niobium (V) ethoxide. All the experiments were performed at room temperature while the calcination temperatures ranged between 800 °C and 1,100 °C. Results showed that it was possible to obtain the pure perovskite phase at 950 °C using the sol–gel method. Nd⁺³ addition influenced the phase formation and microstructure of the multicomponent system. Pyrochlore was detected along with the perovskite phase above 10 mol% Nd. Results also demonstrated that grain size of the synthesized powders depended on the Nd⁺³ concentration.     

Effect of excess Pb on formation of perovskite-type 0.67Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-0.33PbTiO<Subscript>3</Subscript> powders synthesized through a sol–gel process

Perovskite-type 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMNT) powders were fabricated by using a sol–gel process. Excess Pb(CH₃COO)₂·3H₂O (0, 2, 5, 10 or 15 mol%) was added to starting materials to compensate PbO loss from volatilization during heat treatment. X-ray diffraction (XRD) was employed to investigate the effect of excess Pb on the perovksite phase formation of the PMNT powders. It was found that the optimal level of the excess Pb content is 5 mol%. When the raw materials contained 5 mol% excess Pb, the PMNT powders of purest perovskite form was obtained at the calcination temperature of 850 °C. In the PMNT powders, most part of the intermediate phase was Pb-rich pyrochlore Pb₂Nb₂O₇ which was transformed into perovskite phase after calcination at 650 °C, while the residual pyrochlore phase was Pb-deficient Pb₃Nb₄O₁₃ which required calcination at a higher temperature (650–850 °C) to transform into perovskite phase. Compared with the conventional solid-state reaction methods and the solution-based methods reported previously, the present sol–gel route is better at synthesizing PMNT powders of perovskite phase at a low temperature.     

Phase change in calcination process for BaTi2O5 and proposal of a new temperature profile

The mixture of BaCO₃ and rutile-type TiO₂ powders mixed with wet ball-milling was calcined in air and the phase change in calcination process was investigated in detail. The slow heating in the temperature range from 800 to 850 °C was effective to change BaTiO₃ to BaTi₂O₅ in the following heating process. The influence of two factors in calcination for the synthesis of BaTi₂O₅, which are temperature profile with slow heating and packing state of the mixture, was investigated. The slow heating in two temperature ranges, 800–850 °C and 1100–1160 °C, was effective for the synthesis of BaTi₂O₅. The production amount of BaTi₂O₅ was increased by using powder compacts rather than powder form. By calcining powder compacts at 1160 °C for 2 h, the powder of BaTi₂O₅ having an α_s value of 0.93, which is semi-quantitatively corresponding to BaTi₂O₅ production ratio, was obtained.     

Phase formation and dielectric properties of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> by slow injection sol–gel technique

A simple sol–gel process incorporating slow precursor injection technique was employed to synthesize homogeneous Ba_0.5Sr_0.5TiO₃ nano powders. The Ba_0.5Sr_0.5TiO₃ samples were subjected to calcination temperatures from 600 to 1,100 °C and sintering temperatures from 1,250 to 1,350 °C for the study of phase formation, crystallite size, particle distribution, and dielectric properties. Single phase Ba_0.5Sr_0.5TiO₃ with a cubic perovskite structure was successfully synthesized after calcination at 800 °C. The average size of the nano particles is 42 nm with a narrow size distribution, and a standard deviation of 10%. The highest values recorded within the investigated range for dielectric constant, and dielectric loss measured at 1 kHz are 1,164 and 0.063, respectively, for Ba_0.5Sr_0.5TiO₃ pellets calcined at 800 °C and sintered at 1,350 °C. Leakage current density measured at 5 V for the Ba_0.5Sr_0.5TiO₃ pellet was found to be 49.4 pA/cm².     

The phase conversion of precursor powders for powder melting process YBa2Cu3O7−x superconductors

The effects of heating rate and holding time on the formation of YBa₂Cu₃O_7−x phase in precursor powders for YBa₂Cu₃O_7−x superconducting bulks prepared by powder melting process have been investigated. The phase conversion of the precursor powders is studied by X-ray diffraction and found to be different for different heating rates during heating. The YBa₂Cu₃O_7−x phase is formed during heating to peritectic temperature at 100 and 400 °C/h, but not at 6,000 °C/h. The longer the holding time, the more the amount of YBa₂Cu₃O_7−x phase between 880 °C and about 950 °C. The results are useful for understanding the mechanism of powder melting process and controlling the process conditions.     

A novel wet polymeric precipitation synthesis method for monophasic β-TCP

β-Tricalcium phosphate (β-Ca₃(PO₄)₂, β-TCP) powders were synthesized using wet polymeric precipitation method for the first time to our best knowledge. The results of X-ray diffraction analysis showed the formation of almost single a Ca-deficient hydroxyapatite (CDHA) phase of a poor crystallinity already at room temperature. With continuously increasing the calcination temperature up to 800 °C the crystalline β-TCP was obtained as the main phase. It was demonstrated that infrared spectroscopy is very effective method to characterize the formation of β-Ca₃(PO₄)₂. The SEM results showed that β-Ca₃(PO₄)₂ solids were homogeneous having a small particle size distribution. The β-TCP powders consisted of spherical particles varying in size from 100 to 300 nm. Fabricated β-TCP specimens were placed to the bones of the rats and maintained for 1–2 months. The histological properties of these samples will be also investigated.     

A low temperature route to prepare LaMnO3

A combination of digestion and further low temperature calcination to crystallize the product is employed to prepare LaMnO₃(LM) ceramics. Freshly co-precipitated lanthanum and manganese hydroxides gel is allowed to react at 100 °C under refluxing and stirring conditions for 6–12 h. The X-ray amorphous product so formed is heated at 300 °C to form crystalline LM powders. This is the lowest temperature so far reported for the formation of LaMnO₃. Transmission electron microscope (TEM) investigations revealed that the average particle size is 50 nm for the calcined powders.     

Low-temperature synthesis of Sr<Subscript>0.3</Subscript>Ba<Subscript>0.7</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> ultrafine powder and its characteristics

Ultrafine strontium barium niobate (Sr_0.3Ba_0.7Nb₂O₆, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO₃)₂, Ba (NO₃)₂, NbF₅, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature (1 kHz) was found to be 930 and below 0.025.     

Synthesis of BaZrO3 by a solid-state reaction technique using nitrate precursors

High phase purity barium metazirconate powders have been synthesized from a modified solid-state reaction. Reactive powders consisting of submicron particles and narrow particle size distribution were obtained by heating a 1:1 molar mixture of barium nitrate and zirconyl nitrate at 800°C up to 8 h. Simultaneous thermal analysis (TG-DTA) assisted in elucidating the probable reaction pathways leading to the formation of the target compound in the BaO-ZrO₂ system. Systematic structural and microstructural characterization on the green powders and the compacts sintered up to 1700°C were carried out. A two-stage sintering schedule consisting of a 6 h soak at 1600°C followed by slow heating up to 1700°C with no dwell, led to highly dense microstructural features.     

A systematic study on solid-state synthesis of monticellite (CaMgSiO4) based ceramic powders obtained from boron derivative waste

Solid-state synthesis of monticellite based ceramic powders from boron derivative waste in an eco-friendly route and the investigation of phase transformation mechanisms were studied. The heat-treatment of boron derivative waste, mainly composed of dolomite, calcite and quartz, was systematically carried out at 650?°C and 800?°C for various dwell times between 1?min and 4?h. The heat-treatment temperatures were selected considering TG-DTA curves of waste and ΔG – T diagrams obtained using FactSage Thermochemical Software. XRF, XRD, FTIR, TG-DTA and SEM analysis, particle size measurement and crystallite size determination carried out extensively. The obtained results showed that monticellite based ceramic powder synthesized at 800?°C for 4?h was composed of monticellite, akermanite, diopside, calcium magnesium borate and zeolite. The calcination of dolomite was completed both at 650?°C for 1?h and up to 800?°C, and calcite was decomposed at 800?°C for 30?min. Both diopside and monticellite were firstly detected at 650?°C for 30?min and at 800?°C for 1?min. Also, akermanite was presented at 800?°C for 1?min. The presented method offers the lowest temperature (800?°C) in literature for synthesis of monticellite and akermanite which reduces the energy consumption during heat-treatment.     

A modified two-stage mixed oxide synthetic route to lead zirconate titanate powders

An approach to synthesis lead zirconate titanate [Pb(Zr_1−xTi_x)O₃; PZT] powders with a modified two-stage mixed oxide synthetic route has been developed. To ensure a single-phase perovskite formation, an intermediate phase of zirconium titanate (ZrTiO₄) was employed as starting precursor. The formation of perovskite phase in the calcined PZT powder has been investigated as a function of calcination temperature, soaking time and heating/cooling rates by differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. The morphology evolution was determined by scanning electron microscopy (SEM) technique. It has been found that the unreacted PbO and ZrTiO₄ phases tend to form together with PZT, with the latter appearing in both tetragonal and rhombohedral phases, depending on calcination conditions. It is seen that optimisation of calcination conditions can lead to a 100% yield of PZT in a tetragonal phase.     

Preparation and characterization of BaSnO<Subscript>3</Subscript> powders by hydrothermal synthesis from tin oxide hydrate gel

BaSnO₃ powders have been prepared from the tin oxide hydrate gel and the Ba(OH)₂ solution via hydrothermal synthesis route. The influence of the process parameters on the characteristics of BaSnO₃ has been studied. A powder with the single-phase of BaSnO₃ can be obtained only when the concentration of Ba(OH)₂ solution is no less than 0.2 M and the ratio of Ba:Sn lies between 1.0 and 1.2. At a hydrothermal temperature of 330 °C or higher, uniform BaSnO₃ powders can be directly prepared through hydrothermal reaction. When the hydrothermal temperature is lower than 250 °C, the as-prepared powder consists of BaSn(OH)₆ that transforms through an amorphous phase into BaSnO₃ by calcination at 260 °C. In the hydrothermal temperature range of 130–250 °C, a higher temperature can promote the crystallization of BaSnO₃, increases its specific surface area and decreases the average particle size. The duration of the hydrothermal reaction affects the morphology of the powder particles. The effects of the nonaqueous solvents on the properties of powders have also been investigated.     

Low temperature preparation of nanocrystalline solid solution of strontium barium niobate by chemical process

Sr_xBa_1-xNb₂O₆ (with x = 0.4, 0.5 and 0.6) powders have been prepared by thermolysis of aqueous precursor solutions consisting of triethanolamine (TEA), niobium tartarate and, EDTA complexes of strontium and barium ions. Complete evaporation of the precursor solution by heating at ∼ 200°C, yields in a fluffy, mesoporous carbon rich precursor material, which on calcination at 750°C/2 h has resulted in the pure SBN powders. The crystallite and average particle sizes are found to be around 15 nm and 20 nm, respectively.     

Oxidation Behavior of Zirconium Diboride Nanoparticles

The products of oxidation of ZrB₂ powders with average particle sizes of ~100 and ~30 nm by atmospheric oxygen under isothermal conditions and during heating have been characterized by thermal analysis, X-ray diffraction, scanning electron microscopy, IR frustrated total internal reflection spectroscopy, energy dispersive X-ray analysis, and elemental analysis. The oxidation onset has been observed at 594 and 396°C, respectively. Oxidation at temperatures of ≥800°C leads to the formation of boron oxide and monoclinic ZrO₂, independent of the particle size of ZrB₂. The reaction rate constants for the oxidation of ZrB₂ nanoparticles ~100 and ~30 nm in size have been determined to be 0.03, 0.15, and 0.31 h^–1 at 600, 650, and 700°C and 0.11, 0.35, and 0.81 h^–1 at 500, 600, and 700°C, respectively. The apparent activation energies for the oxidation of the ZrB₂ nanoparticles ~100 and ~30 nm in size are 161 ± 4 and 62 ± 3 kJ/mol, respectively, as evaluated from the temperature dependence of the rate constants at the above temperatures.