Effects of sintering temperature on properties of Na0·5K0·5NbO3-LiSbO3-BiFeO3 lead free ceramics

Abstract

Abstract

Lead free 0·95K_0·5Na_0·5NbO₃-0·05LiSbO₃ (KNN-LS) ceramics doped with 0·4?mol.-% BiFeO₃ (BF) have been prepared by the conventional mixed oxide method with sintering temperature at 1065-1135°C in this paper. The samples are characterised by X-ray diffraction analysis and scanning electron microscopy. The dielectric and piezoelectric properties are also investigated. The results present that initially the increase in the sintering temperature is very effective in improving the density and electric properties. However, the properties of the samples would be deteriorated as they are sintered over the optimum temperature. The KNN-LS (doped with 0·4%BF) ceramics shows excellent properties with sintering temperature at 1100°C.     

Diametral strength testing of hydroxyapatites doped with yttrium and fluoride

Abstract

Abstract

This study aimed to investigate the diametral strength testing of hydroxyapatite (HA) doped with Y and fluoride with different compositions. Hydroxyapatites were synthesised by precipitation method and sintered at 900, 1100 and 1300°C for 1?h. High amounts of doping caused a decrease in relative densities of HAs. Higher sintering temperatures helped in increasing the relative densities. No second phases were observed by X-ray diffraction spectra of 2·5?mol.-%Y and 2·5?mol.-%F doped HA after the sintering at all temperatures. Trace amounts of β-tricalcium phosphate was found in 7·5?mol.-%Y and 2·5?mol.-%F doped HA sintered at 1100 and 1300°C. Diametral strength of doped HAs mostly enhanced with the addition of Y³⁺ and F^?. 2·5YFHA sintered at 1300°C had the highest diametral strength of 11·6?MPa with a relative density of 94·3% of theoretical density.     

Effect of preparation method on sinterability and properties of nanocrystalline MgAl2O4 and ZrO2-MgAl2O4 materials

Abstract

Nanocrystalline MgAl₂O₄ and ZrO₂-MgAl₂O₄ powders were synthesised by combustion and conventional solid state reaction routes. The synthesised powders were processed, dry pressed, and sintered for 3 h at temperatures ranging from 1550 to 1625°C. The sintered pellets were then characterised in terms of phase (XRD), microstructure (SEM), relative density, apparent porosity, water absorption, hardness, three point bend strength, and fracture toughness. The XRD studies revealed that ZrO₂ was present in tetragonal form in the case of combustion synthesised powders (CSP), whereas in powders obtained by solid state reaction (SSP) it was present in the monoclinic form. This study also revealed that the addition of ZrO₂ improved the mechanical properties of sintered MgAl₂O₄ samples: 20 wt-%ZrO₂-MgAl₂O₄ composites prepared from CSPs and conventional SSPs and sintered at 1625°C for 3 h had fracture toughness of 5·96 and 4·33 MPa m^1/2 and three point bend strength of 269 and 98 MPa respectively. Higher sintered density, the presence of tetragonal zirconia as a major phase, and the finer microstructure are probably responsible for the superior mechanical properties exhibited by sintered CSP materials as compared with the sintered SSPs.     

Preparation and characterisation of self-flowing refractory material containing 971U type microsilica

Abstract

A newer composition of self-flowing low cement brown fused alumina castable containing 971U type microsilica was developed. Optimum flow characteristics were achieved using water addition of 4·6?wt-%. This batch was sintered at different firing temperatures up to 1500°C. To understand the effect of both firing temperatures and corresponding phases, the present castable was characterised in terms of X-ray diffraction, scanning electron microscopy, bulk density (BD), apparent porosity (AP), water absorption (WA), cold crushing strength (CCS) and self-leveling flowability. The results revealed that gradual increase in firing temperature from 1100 through 1500°C caused low AP and WA, and high CCS properties due to the densification of the castable.     

Effect of MgO addition and sintering parameters on mullite formation through reaction sintering kaolin and alumina

Abstract

In the present work, the influence of MgO addition and sintering parameters on the formation and densification of mullite was investigated. The morphology of powders and the microstructure of the sintered samples were characterised by means of a scanning electron microscope. X-ray diffraction was used to characterise phases formed in sintered samples. The density of sintered samples was measured using a densimeter and quantified according to the Archimedes principle. MgO was added at 1, 2, 3, 4, 5 and 6 wt-% to kaolin and alumina and the powders were ball milled for 5 h then uniaxially compacted at 75 MPa and finally sintered at 1500, 1550, 1600 and 1650°C for 2, 4, 6 and 8 h. It was found that addition of MgO not only affected mullite formation but also promoted grain growth. For samples containing 0, 1 and 2 wt-%MgO only mullite was formed. While, in addition to mullite, Al₂O₃ was present in sample containing 3 wt-%MgO. At higher MgO content (4, 5 and 6 wt-%), three phases, i.e. mullite, Al₂O₃ and spinel, were formed. Addition of 1 wt-%MgO increased the density of all samples for all sintering times and higher densities corresponded to higher sintering temperatures. At higher MgO content, higher temperatures led to lower densities and lower temperatures led to higher densities for almost all sintering times.     

Effect of alloying time on fabrication of Ti3Si(Al)C2 by spark plasma sintering

Abstract

3Ti–Si–2C–0·2Al mixture powders were used to fabricate high purity Ti₃SiC₂ ceramic through mechanical alloying (MA) and spark plasma sintering (SPS). The effect of ball milling time on the fabrication of Ti₃SiC₂ by SPS was also investigated. The results showed that the mixed powders were obviously refined after the MA of 5 h. After milling of 10 h, the mixed powders containing TiC, Ti₃SiC₂ were synthesised by a mechanically induced self-propagating reaction. After further milling to 20 h, the yield powders were refined. Ball milling time had a remarkable effect on SPS fabrication of Ti₃SiC₂. A shorter milling time of 5 h only helped to increase the Ti₃SiC₂ content in the sintered bulk. The samples subjected to the MA treatment of 20 h had a fine and dense organisation. Ball milling of 10 h was most beneficial for fabricating dense and high purity Ti₃SiC₂. Ti₃SiC₂ bulk with a purity of 96 wt-% was obtained by MA for 10 h and subsequent SPS at 850°C. When sintered at 1100°C, Ti₃SiC₂ bulk with a purity of 99·3 wt-% and a relative density of 98·9% was obtained.     

Effect of fuel type on morphology and reactivity of combustion synthesised MgAl2O4 powders

Abstract

Two types of stoichiometric MgAl₂O₄ spinel powders were prepared by combustion synthesis routes, using sucrose (SCS) or urea (UCS) as fuel. For comparative purposes a stoichiometric MgAl₂O₄ powder was also prepared by solid state reaction synthesis (SS powder). Pressed compacts of the three powder types were sintered at various temperatures ranging from 1575 to 1625°C for 2 h. After grinding, SCS and SS powders had very narrow particle size distributions, with average particle sizes of 3·17 and 4·13 μm respectively, whereas UCS powder showed a wide particle size distribution with an average particle size of 37·76 μm. Their corresponding surface areas were found to be 65·8, 8·67, and 8·06 m² g^-1. The SCS MgAl₂O₄ powder sintered at 1625°C for 2 h had a bulk density of 3·44 g cm^-3 (96% of theoretical), an apparent porosity of 1·76%, and water absorption of 0·519%. The superior properties of SCS powders compared with other spinel powders are attributed to the higher surface area induced by the larger size of the sucrose molecule and the greater amount of gas evolved during sucrose combustion.     

Microwave sintered sol–gel derived BaTiO3 and Ba0.95La0.05TiO3 ceramic samples for capacitor applications

Sol–gel derived BaTiO₃ and Ba_0.95La_0.05TiO₃ powders were calcined at 700 °C for 40 min and sintered at 1100 °C for 1 h in a microwave furnace to obtain single-phase perovskite ceramic samples. About 98% of the theoretical density was obtained in the sintered BT ceramic samples. Room temperature (RT) dielectric constant (ε_r) and dielectric loss (tan δ) at 1 kHz frequency of the BLT ceramic samples were found to be ~2220 and 0.005, respectively. High value of ε_r, low value of tan δ and negligible temperature coefficient of capacitance from RT to 60 °C suggested the suitability of BLT ceramic samples for multi-layer capacitor applications.     

Synthesis of monodisperse nanocrystalline 8 mol-% yttria doped ceria powder by oleate complex route

Abstract

Preparation of monodisperse nanocrystalline yttria doped ceria powder by the oleate complex route has been reported. Y(III) and Ce(III) oleate complexes have been prepared by the reaction between YCl₃, Ce(NO₃)₃ and sodium oleate at the interface of hexane rich and water rich conjugate layers of water-ethanol-hexane ternary liquid system. Cubic yttria doped ceria crystallises when the waxy solid containing Y(III) oleate and Ce(III) oleate complexes was heat treated at 400°C. The powder after planetary ball milling contains monodisperse near spherical particles of 0·2?μm. These particles contain monodisperse nanocrystallites of size <10?nm. The yttria doped ceria powder pellets were sintered to >98% theoretical density at 1450°C. The sintered ceramic showed an ionic conductivity of 0·0623?S?cm^?1 at 800°C and activation energy of 1·0?eV.     

Biphasic calcium phosphate (BCP) macroporous scaffold with different ratios of HA/β-TCP by combination of gel casting and polymer sponge methods

Abstract

Open and interconnected porous scaffolds were prepared with various ratios of hydroxyapatite (HA)/β-tricalcium phosphate by a combination of gel casting and polymer sponge methods to improve the mechanical properties and structure. The scaffolds were prepared using slurries containing 50 vol.-% of ceramic powders and sintered at 1100°C for 2 h. Thermogravimetric analysis result shows that the proper temperature to burn out organic materials and polyurethane foams is 600°C. The compressive strength was between 5·3 and 8·4 MPa. Field emission scanning electron microscope shows an open, relatively uniform and large interconnected porous structure with pore size ranging between 150 and 400 μm. X-ray diffraction and Brunauer–Emmett–Teller methods were employed to determine the microstructural crystallite and surface area respectively. The results show that the compressive strength of scaffolds increased with the increase in HA concentration. The reason can be explained by the increasing pore wall thickness and density in scaffolds.     

Influence of synthesis method and praseodymium doping on stability and sintering of Ca stabilised zirconia

Abstract

The effects of doping with praseodymium and of preparation method on the Ca-FSZ (fully stabilised zirconia) system were studied. Samples were prepared by a ceramic method (CE) and several sol-gel methods, namely colloidal (CG), citrate (CI) , and polymeric (PG). Two samples with the compositions (ZrO₂)_0·7(CaO)_0·2(Pr₂O₃) _0·05 (doped) and (ZrO₂)_0·8(CaO)_0·2 (undoped) were prepared by each method, in order to study the influence of praseodymium doping. DTA-T G analysis was carried out on all samples. Powders fired for 12 h at 500 and 900°C were sieved at 60 μm, uniaxially pressed at 20 MPa, and fired for 2 h at 1500 and 1600°C. The resulting compacts were characterised by XRD, SEM-EDX, Vickers microhardness testing, and density and lattice parameter measurements. The results indicate that the praseodymium enters the CaO-Z rO₂(c) solid solution, improving densification and microhardness. Samples prepared by sol-gel methods showed better densification and higher microhardness than samples prepared by the ceramic method. Citrate samples stood out for their non-porous microstructure and high Vickers microhardness.     

Microstructures and thermal conductivities of reaction sintered SiC ceramics

Abstract

Reaction sintered SiC ceramics were prepared by the silicon melt infiltration method over temperatures of 1450?1550°C. The effects of the carbon and silicon contents of the starting materials as well as the sintering temperature and time on the thermal conductivities and microstructures of the ceramic materials were studied. The thermal conductivities and microstructures of the samples were characterised using thermal conductivity measurements, X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy and mercury injection porosimetry. The results showed that sintering temperature and time as well as the carbon and silicon contents of the green specimens are the main factors affecting the microstructure and porosity of reaction bonded SiC ceramics. Increasing the reaction temperature and time decreased the porosity of the ceramics. This was due to the infiltration of the silicon melt into the ceramic specimens. The thermal conductivity and porosity of the sample sintered at 1550°C for 3 h in an argon atmosphere were 102·5 W m K^?1 and 0·3% respectively.     

Grain growth kinetics and magnetic properties of a V-doped ZnO dilute magnetic oxide

Zn_0.95V_0.05O ceramics, elaborated from milled ZnO and V₂O₅ nanopowders, were sintered at 900, 1000 and 1100 °C for 1, 2, 4, 6, 10 and 14 h. The growth kinetics was studied identifying the grain growth exponent, the activation energy and the pre-exponential factor. The high V₂O₅ concentration allowed a rapid grain growth at 900 °C only at the very first stages (t < 1 h). Meanwhile, at temperatures of 1000 and 1100 °C, the grain growth was extremely fast with a growth exponent of 0.72. The magnetic properties of the samples indicate that ferromagnetism exist in all samples in different magnitudes depending on the sintering conditions. In particular, the maximum magnetization was obtained on the sample sintered at 1100 °C for 14 h, despite the reduction of V concentration. Additionally, secondary paramagnetic phases were detected in the samples sintered at lower temperatures and shorter sintering times.     

Microstructural features and mechanical properties of Al2O3-Al2TiO5 composite processed by gel assisted ceramic extrusion

Abstract

The influence of aluminium titanate particulates as second phase reinforcement for alumina matrix composites has been investigated with respect to sintering characteristics, microstructural development, and associated mechanical properties. Composites were fabricated by gel assisted extrusion, using boehmite gel as binder. The aluminium titanate precursor was synthesised by a sol-gel technique and dispersed intimately in the alumina matrix by a colloidal method. A boehmite sol was used as dispersing medium and the extrudable composite paste with high viscosity and yield stress was obtained by controlled gelation followed by filtration. The extruded composite was dried and sintered at a temperature in the range 1350-1550°C. The sintered bodies were characterised in terms of density, room temperature flexural strength, microhardness, and microstructure. Aluminium titanate contents up to 10 wt-% were found to lower the sintering temperature of alumina, from 1550 to 1400°C. The composite sintered at 1400°C attained 97% of theoretical density and showed room temperature flexural strength of 318 MPa and microhardness of 21 GPa. The addition of aluminium titanate resulted in a high density alumina composite at lower sintering temperature with an average grain size of about 2 μm.     

Composite materials with ZrO2–TiO2 matrix and ZrO2 containing ceramic fibres

Abstract

The aim of the work reported in the present paper was to obtain composites consisting of a ZrO₂–TiO₂ matrix reinforced with ceramic fibres containing 12 wt-% ZrO₂, which are resistant to temperatures higher than1500°C. The resulting ceramic matrix consisted of 95 wt-% ZrO₂, partially stabilised with CaO, and 5 wt-% rutile TiO₂. A ceramic fibre content of 0·82 vol.-% was used and for the matrix, several grades of ZrO₂ partially stabilised with CaO were explored, prepared by dry and wet grinding for various grinding periods. Composites were prepared by uniaxial die pressing at 350 MPa and sintered at two temperatures: 1360°C for 1 h and 1500°C for 3 h. The resulting composites showed the following range of properties: total drying and firing shrinkage 0·4–3·3%; apparent density 3·51–3·96 g cm^-3; porosity 25–34%; water absorption 6–10%; bend strength 12–43 MPa. The optimum ZrO₂ grades were determined based on physical and mechanical properties, and on structural determinations carried out by thermodifferential and thermogravimetric analyses, X-ray diffraction (XRD), and scanning electron microscopy (SEM). SEM evaluation illustrated the increase in average size of crystallites typical of ZrTiO₄ solid solution as a function of temperature, from 2 μm at 1360 up to 14 μm at 1600°C, and of their tendency to sinter.     

Effects of rapid thermal annealing treatment on 0·95(Na0·5Bi0·5)TiO3-0·05BaTiO3 thin films

Abstract

Abstract

A 0·95(Na_0·5Bi_0·5)TiO₃-0·05BaTiO₃+1?wt-%Bi₂O₃ (NBT-BT3) ceramic was used as target to deposit the NBT-BT3 thin films. The excess 1?wt-%Bi₂O₃ was used to compensate the vapourisation of Bi₂O₃ during the depositing processes. The optimal deposition parameters were substrate temperature of 500°C, radio frequency power of 100?W, chamber pressure of 10?mtorr and oxygen concentration of 40%. Rapid thermal annealing treated processes were carried out on NBT-BT3 thin films from 600 to 800°C in ambient or in oxygen atmosphere for 1?min. The surface morphologies and thicknesses of NBT-BT3 thin films were characterised by field emission scanning electron microscopy, and the thickness was ～216?nm. It would be shown that the NBT-BT3 thin films annealed in oxygen atmosphere had the smaller grain size, larger memory window, smaller leakage current density, larger remanent and saturation polarisation and smaller coercive field than the NBT-BT3 thin films annealed in ambient atmosphere.     

Effect of heat treatment on crystal phase and photocatalytic activity of Tm doped TiO2 nanoparticles

Abstract

Abstract

Tm doped TiO₂ nanoparticles have been synthesised by hydrolysis-precipitation method. The effect of heat treatment on the crystal phase and photocatalytic activity of Tm doped TiO₂ nanoparticles has been studied. The prepared samples were characterised by transmission electron microscopy, X-ray diffraction, Fourier transformed infrared and diffuse reflection spectrum analysis. The results show that Tm³⁺ doping can effectively inhibit the phase transformation from antase to rutile and decrease the crystallite size of nano-TiO₂ particles. There is an optimal Tm doping (1·4?mol.-%) after calcination at 550°C for the photocatalytic activity of methylene blue degradation.     

Preparation and sintering behaviour of nanostructured SrBi2Ta2O9 ceramics

Abstract

Nanostructured SrBi₂Ta₂O₉ powders have been prepared by sol-gel processing and the resulting precursors characterised after calcination by DTA-TG and XRD. The results show that pure powders can be obtained above 600°C with a particle size of 60 nm, as determined by TEM . Pressed pellets sintered in air increased in density with increasing sintering temperature, reaching a maximum of 8·42 g cm ^{- 3} after 2 h at 1250°C. In order to improve densification, Bi₂O₃ contents between 3 and 10 wt-% were added to pure SrBi₂Ta₂O₉. The results show that these additions tend to increase density, but that decomposition by volatilisation of Bi₂O₃ at high temperature is retarded to a degree depending on the Bi₂O₃ content. This behaviour is attributed to the increased density resulting from Bi₂O₃ addition, which reduces volatilisation, and hence decomposition, at higher temperatures.     

Structural and electrical properties of sol-gel prepared Sm modified Pb(Zr0·60Ti0·40)O3 ceramics

Abstract

Polycrystalline samples of Pb_1-zSm_z(Zr_0·60Ti_·4)_1-z/4O₃ (abbreviated as PSZT), with z=0·07, 0·08, and 0·10, have been prepared by a metal-alkoxide sol-gel method. Preliminary X-ray diffraction and transmission electron microscopic analysis of the compounds suggests the formation of nearly single phase compounds in the tetragonal crystal system. SEM analysis of pellet samples sintered at 1300°C for 7 h shows a uniform distribution of nearly spherical grains throughout the sample surfaces. Detailed studies of dielectric constant and tangent loss of PSZT as a function of temperature (from 30 to 400°C) at 1 and 10 kHz frequencies reveal the existence of di ffuse phase transitions in the samples. The transition temperature T_c, broadening of the permittivity peak, remanent polarisation P_r, and coercive field E_c of PSZT change significantly with increasing Sm3 + doping concentration.     

Hydroxyapatite reinforced with Ti–Fe particle: correlation between composition,microstructure and mechanical properties

Abstract

Composites of hydroxyapatite (HA) with 5 wt-% Ti–Fe reinforcing particles were pressureless sintered in vacuum at a temperature range between 950 and 1100°C. It was found that although the decomposition of HA and interaction between HA and Ti occurred, the desirable Ti phase still remained in the composites sintered at all temperatures. The outer Ti shell thickness of the distinctive core–shell Ti–Fe particles was observed to become larger as the sintering temperature increased. It was also found that minor pores appearing near the interface were beneficial to obtain appropriate interfacial bonding between HA matrix and Ti–Fe particles. The composite sintered at 1050°C exhibited superior flexural strength, fracture toughness, and fatigue resistance owing to the remained Ti phase and dense microstructure as well as good interfacial bonding.