Conventional Sintering Method Research Articles

Effects of borosilicate glass on pollucite crystallization and Cs+ immobilization in geopolymer materials

Since Fukushima nuclear power plant accident there have been many publications on immobilization of radioactive 137Cs in the crystalline structure of pollucite (CsAlSi2O6). In this article, we report a novel method where Cs-polluted soil (metakaolin) and a specially formulated borosilicate glass power are sintered together to form a pollucite-based glass crystalline materials. Fine pollucite crystals are uniformly distributed in the matrix of glass phase. This is equivalent to pollucite being encapsulated by the borosilicate glass and theoretically this should enhance the chemical durability. Extensive characterizations of this material with differential scanning calorimetry (DSC), r-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and electronic differential system (EDS) reveal optimum glass content and that the formation temperatures of pollucite in the glass matrix was as low as 900 ℃, which is significantly lower than those used in forming Cs-pollucite by conventional sintering methods. Test showed that the Cs+ leaching rate of sample with 20 wt% glass content was only 4.19×10–4 g·m–2·d–1, lower than the sample without glass addition almost by an order of magnitude. This study not only presents an improved technique for 137Cs immobilization but may also provide a methodology for immobilization of other potential radioactive species.

Electrophysical features of the hard ferroelectric material PKP-35

In this work, electrophysical features of the hard ferroelectric material PKP-35 are studied in a wide temperature range. Research object is a solid solution of lead zirconate-titanate (PZT) modified with some additives prepared by the conventional solid-state sintering method. The temperature dependences of the dielectric permittivity and dielectric losses in weak fields at frequencies of 1, 10, and 1000 Hz are obtained. The dielectric hysteresis loops at different temperatures are studied, the material features are revealed, the scope of application is determined.

An Overview of High-Entropy Alloys Prepared by Mechanical Alloying Followed by the Characterization of Their Microstructure and Various Properties

Some modern alloys, such as high-entropy alloys (HEAs), are emerging with greater acceleration due to their wide range of properties and applications. HEAs can be prepared from many metallurgical operations, but mechanical alloying is considered to be one of the most simple, economical, popular, and suitable methods due to its increased solid solubility, nano-crystalline structure, greater homogeneity, and room-temperature processing. Mechanical alloying followed by the consolidation of HEAs is crucial in determining the various surface and mechanical properties. Generally, spark plasma sintering (SPS) methods are employed to consolidate HEAs due to their significant advantages over other conventional sintering methods. This is one of the best sintering methods to achieve greater improvements in their properties. This review discusses the mechanical alloying of various HEAs followed by consolidation using SPS, and also discusses their various mechanical properties. Additionally, we present a brief idea about research publications in HEA, and the top 10 countries that have published research articles on HEAs. From 2010 to 18 April 2022, more than 7700 Scopus-indexed research articles on all the fields of HEA and 130 research articles on HEA prepared by mechanical alloying alone have been published.

Investigation of Electrical Transitions in the First Steps of Spark Plasma Sintering: Effects of Pre-Oxidation and Mechanical Loading within Copper Granular Media.

Spark Plasma Sintering (SPS) has become a conventional and promising sintering method for powder consolidation. This study aims to well understand the mechanisms of densification encountered during SPS treatments, especially in the early stages of sintering. The direct current (DC) electrical behavior of copper granular medium is characterized. Their properties are correlated with their microstructural evolutions through post-mortem scanning electron microscope (SEM) observations to allow a thorough understanding of the involved Branly effect that is suspected to occur in SPS. The electrical response is studied by modifying the initial thickness of the oxide layer on particles surfaces and applying various mechanical loads on the granular medium. Without load and at low current, the measured quasi-reversible behavior is connected to the formation of spots at the microcontacts between the particles. By increasing the current, the Branly transition from an insulating to a conductive state suddenly occurs. The insulating oxide layer is destroyed, and micro-bridges are created. The application of a mechanical pressure strongly modifies the DC Branly effect. Increasing low stress leads to a strong decrease in the breakdown field. For high-applied pressure, successive drops in the electric field are detected during the electrical transition. These successive drops are induced by microcracking of the insulating oxide layer.

Tuning piezoproperties of BiFeO3 ceramic by cobalt and titanium dual doping

Bismuth ferrite is a potentially interesting lead-free piezoelectric material for use in high-temperature applications due to its high Curie temperature. However, the high coercive field and high leakage currents of pure BiFeO3 (BFO) prevent reaching its theoretical performance level. The classic approach to tailoring piezoceramic properties to their desired use conditions is the use of doping. In this work, we produce bulk BFO piezoceramic by the conventional sintering method with single element doping with cobalt (0.125–3 at. %) or titanium (1–5 at. %) and dual doping (Co and Ti added simultaneously). Cobalt doping reduces the required field for poling and also increases the leakage currents. Titanium doping reduces the leakage currents but destroys the piezoelectric properties as the coercive field strength cannot be reached. However, when both elements are used simultaneously at their appropriate levels (0.25 at. % each), a piezoelectric ceramic material is obtained, requiring a low field for full poling (9 kV/mm) and showing excellent room temperature performance such as a d33 = 40 pC/N, a dielectric constant in the region of 100 and dielectric losses less than 1%.

High transparency and good electric properties in low symmetry BNT-based ceramics

The multifunctional development of dielectric materials are necessary for the intellectualization and high performance of electronic components. Lead-free relaxor ferroelectric (1-x)Bi0.5Na0.5TiO3-xBi1.05(Mg1/3Nb2/3)O3 ((1-x)BNT-xBMN, x = 0, 0.03, 0.06, 0.08, 0.15) ceramics with high transparency and good dielectric properties were synthesized by a conventional sintering method. The effect of BMN doping on optical properties, phase transition, microstructure, electrical and mechanical properties of BNT ceramic were systematically investigated. It is worth mentioning that 0.97BNT-0.03BMN ceramic achieved high transmittance (T = 74%, 0.3 mm) and good dielectric properties (εm = 2213, tan δ ∼ 0.015) on the basis of low symmetry. This improved transmittance in BNT is closely related to the presence of submicron grain size and the enhanced relaxation behavior causing by BMN doping. This work realized the synergy of electric and optical properties in BNT ferroelectrics, which reveals that BNT materials have great potential in multi-functionalization.

Abrupt high grain growth in hydroxyapatite during flash sintering

ABSTRACT The electric flash generated by an electric field aided the sintering of hydroxyapatite (HA) in relatively less time and at lower furnace temperatures than the conventional sintering method. The current work has reported a comparative study to explain thermodynamically the effects of the increasing DC electric field strength at 1000°C and 1100°C sintering furnace temperatures during flash sintering in terms of the grain growth and densification of the HA in air. The abrupt change in current density and conductivity of HA during the flash peak correlates the high grain growth and rapid densification with increasing electric field strength. The increased electric field strength reduced the power dissipation from the HA. The abrupt high-rise grain growth phenomenon during flash sintering might consist of the thermal effect and enhancement in ionic conductivity due to the application of an electric field.

Improved ferroelectric, piezoelectric, and dielectric properties in pure KNN translucent ceramics by optimizing the normal sintering method

In this study, it is reported that various properties can be selectively derived in a pure (K0.5Na0.5)NbO3, KNN ceramics through optimizing the sintering temperature by the conventional sintering method. High piezoelectric, ferroelectric, and dielectric properties such as d33 = 127 pC/N, Pr = 31 μC/cm2, and εr = 767 are obtained at the sintering temperature of 1100 °C. On the contrary, the specimen sintered at 1130 °C does not show high piezoelectric and ferroelectric properties, but it is translucent with a transmittance of 22% and 57% at the wavelength of 800 and 1600 nm respectively and shows a very high dielectric constant εr of 881. The origin of the high piezoelectric constant owes to large remanent polarization and dielectric constant, and dense microstructure with uniform distribution of large grains with the conjunction of relatively large crystal anisotropy. On the other hand, dense microstructure with almost no porosity, highly compacted grain boundaries, uniform distribution of grains, and relatively low crystalline anisotropy are responsible for the translucency and large dielectric constant of the ceramic specimens. This study demonstrates that the lead-free KNN ceramic has the potential to show multiple noteworthy properties such as piezoelectric, ferroelectric, dielectric, and transparent properties. This work provides a pure KNN ceramic simultaneously with high piezoelectric and transparent characteristics prepared only by using the conventional sintering method at a moderate sintering temperature for the first time in the literature.

Optimized consolidation process at a near-room temperature of nano-hydroxyapatite and sodium silicate glass composites for bone healing applications

ABSTRACT Hydroxyapatite nanoparticles (nHap) with chemical and structural characteristics similar to the bone mineral are widely used for orthopaedic applications. However, conventional sintering methods applied to consolidate nHap alter significantly their properties. Recently, a near-room temperature process was developed to consolidate nHap using a sodium silicate solution (SS) as a mineral binder to produce highly reactive composites. In this work, a central composite design is employed to determine the best parameters to elaborate nHap/SSG with optimized mechanical properties. The studied factors were the molar ratio of SS (n), liquid-to-solid ratio (Ls) and drying temperature (T°C). A maximum compressive strength of 24.01 MPa was achieved when composites were formulated using SS with a ratio of 1, Ls of 0.4 cm3/g and drying temperatures below 50 °C. In vitro biocompatibility of bone cells (MG-63) revealed that the optimized composite enhanced cellular proliferation and differentiation which make them a promising candidate for bone regeneration.

Comparison of electrical properties of ZnO-Bi2O3-based ceramics prepared by conventional and spark plasma sintering (SPS) methods

Comparison of electrical properties of ZnO-Bi2O3-based ceramics prepared by conventional and spark plasma sintering (SPS) methods

Reducing atmosphere to manufacture graphene alumina composite

The so-called advanced ceramics or engineering ceramics attract various industrial sectors on account of characteristics such as high hardness, biocompatibility, thermal stability, chemical inertia, and corrosion resistance. However, its use ends up being limited by its fragility. The use of carbon allotropes (graphene, nanotubes, and fullerenes) as reinforcement material in ceramics has been widely studied; however, the performance of these allotropes is restricted to specific mixing and sintering conditions. The present work produced a composite material with an Al2O3 (alumina) matrix from commercially available techniques such as conventional sintering and achieved mechanical properties as good as those of composites produced by modern laboratory techniques such as Spark Plasma Sintering. Alumina powders were mixed with multi-layered graphene (MLG) on a ball mill, followed by uniaxial and isostatic pressing and sintered in a reducing atmosphere. The pure alumina ceramic was compared to the alumina-MLG composite, and a 75% increase in microhardness and 40% increase in fracture toughness for the composition with 0.75 wt% of multi-layered graphene was measured. Results showed that alumina-MLG composite can be produced through the conventional mixture and sintering methods, maintaining its properties on par with more modern techniques.

Green Synthesis of Nanoparticles Using Bio-Inspired Systems and Electrically Conductive Pattern Fabrication through Laser-Direct Writing.

Systems existing in nature have evolved to operate efficiently over a long period of time, enabling efficient material transformation and processing. These natural systems provide hints for the synthesis of metal nanoparticles through efficient electron generation and transport towards metal ions for the reduction process. In this study, based on the efficient electron transfer mechanism between tryptophan (Trp) in the living body, the possibility of advanced silver patterning on flexible substrates has been presented through laser-direct writing. Irradiation of a low-power laser on the precursor induces the reduction of silver ions to nanoparticles. The sintering of these generated nanoparticles induces a silver conductive pattern by a photothermal/chemical reaction. The method of this study has strength as it supports the possibility of conductive pattern fabrication on various substrates (e.g., glass and PDMS) using a silver-based organic ink with low laser power compared to the conventional nanoparticle-based sintering method. It also suggests its suitability to various applications in terms of sophisticated pattern fabrication with minimized substrate denaturation.

Low driving field-induced large strain in ternary lead-free Na0.5Bi0.5TiO3-SrTiO3-ABO3 piezoceramics

In this letter, three ternary lead-free Na0.5Bi0.5TiO3-SrTiO3-ABO3 piezoceramics (ABO3 = LiNbO3, BaZrO3, and LaFeO3) were studied. The addition of ABO3 into Na0.5Bi0.5TiO3-SrTiO3 ceramic induces a ferroelectric tetragonal-to-ergodic relaxor pseudocubic phase transition, resulting in the significant disruption of ferroelectric order with the shift of the ferroelectric-relaxor transition temperature down to below room temperature. The conventional furnace sintering and microwave sintering methods are conducted in this study to improve the electric field-induced strain properties of BNST-LN piezoceramic. Interestingly, the Na0.5Bi0.5TiO3-SrTiO3-LiNbO3 sample sintered via microwave sintering method shows an ultrahigh normalized strain of 995 pm/V at an ultralow driving field of 2 kV/mm, suggesting a potential candidate for lead-free piezoactuator applications.

Enhanced ferroelectric and piezoelectric properties of BiFeO3–BaTiO3 lead-free ceramics by simultaneous optimization of Bi compensation and sintering conditions

Lead-free piezoelectric ceramics 0.7Bi1+xFeO3-0.3BaTiO3 (B1+xF-BT, 0 ≤ x ≤ 0.04) with excellent piezoelectric performance were synthesized with conventional sintering methods. The impacts of Bi compensation and sintering conditions on the structure and electrical properties of the piezoelectric ceramics were studied. The results showed that the samples (x ≤ 0.02) exhibited pure perovskite structures, and a Bi25FeO40 impurity phase appeared in the samples (x ≥ 0.03). Appropriate compensation with Bi had an important effect on microstructures and electrical properties. Optimal piezoelectric and ferroelectric properties and the highest relative density were achieved with the x = 0.02 sample. In addition, various dwell times (ts) were used during quenching for the sample with x = 0.02. Excellent piezoelectric and ferroelectric properties (d33 = 192 pC/N, Pr = 41.71 μC/cm2, Tc = 493 °C) were achieved with the sample at ts = 3 hQ, which was ascribed to the decreased concentration of oxygen vacancies and enhanced lattice distortion. The present research on simultaneous optimization of Bi compensation and sintering conditions will provide guidelines for designing BF-BT ceramics used in several device applications.

A Comparative Study on the Properties of the Iron Ore Perform Sintered Through Conventional and Microwave Sintering Methods

A Comparative Study on the Properties of the Iron Ore Perform Sintered Through Conventional and Microwave Sintering Methods

Fabrication and Stability Study of W-Coated Diamond/Tungsten Composites by Conventional and Rapid Sintering Methods

Fabrication and Stability Study of W-Coated Diamond/Tungsten Composites by Conventional and Rapid Sintering Methods

Modified microstructure, magnetic and ferroelectric properties in narrow bandgap Bi0.5Na0.5Ti1-xCoxO3 ceramics

The multiferroic (Bi0.5Na0.5)Ti1-xCoxO3 (xBNTCO) ceramics, where x = 0, 0.02, 0.04, 0.06 and 0.08, have been fabricated by using conventional solid-state sintering method. The effects of doped metal concentrations on microstructure, visible-light response, ferromagnetic and ferroelectric orders have been investigated in detail. X-ray diffraction patterns show that all samples are single rhombohedral phase, but also demonstrate the lattice dilatation phenomenon based on the Williamson-hall analysis theory. The band gaps of samples significantly decrease from 3.0 eV to 1.43 eV with increasing Co concentrations up to 0.08, which results from the appearance of Co 3d electronic orbits between the valence band and the conduction band of BNTO. According to ferroelectric hysteresis loop, the improvement of ferroelectric properties can be attributed to the accurately dominating element content in perovskite compounds. When × = 0.04, the sample with maximum remnant polarization Pr (11.47 μC/cm2) is obtained. Besides, the ferromagnetic order is observed at room temperature (RT), which is explained using an F center exchange theory. These results are significant in perovskite oxides for the further research on optical, ferroelectric and magnetic properties and exhibit significant values in solar energy cells and multiferroic applications.

Enhanced ferroelectric, piezoelectric and dielectric properties of (1-x)CaBi2Nb2O9-xBaZr0.2Ti0.8O3 high-temperature piezoelectric composite ceramics

Among Aurivillius layer-structured materials, CaBi2Nb2O9 is a best potential candidate for ultrahigh-temperature applications because of its highest Curie temperature of about 940 °C. In this paper, (1-x)CaBi2Nb2O9-xBaZr0.2Ti0.8O3 composite ceramics were prepared by conventional solid-state sintering method. The dielectric results show that the introduction of BaZr0.2Ti0.8O3 not only increases the permittivity of the material, but also reduces its dielectric loss. The optimum electrical properties were obtained in the x = 0.01 sample with piezoelectric coefficient (d33) of 15.1 pC/N and high ferroelectric remnant polarization (Pr) of 9.9 μC/cm2. Furthermore, the composite samples show good thermal depoling performance, the d33 of the x = 0.01 sample is 13.8 pC/N, which is about 91% of the initial value after depoling at 800 °C. Therefore, (1-x)CaBi2Nb2O9-xBaZr0.2Ti0.8O3 is one of the candidates for high temperature piezoelectric materials.

High nonlinearity in 0.1 mol.% In2O3 added ZnO–V2O5 based varistors prepared at different sintering temperatures

High-performance ZnO-V2O5 based varistors doped with 0.1 mol.% In2O3 have been prepared via conventional sintering method at 850–925 °C. Experimental results show that indium doping helps to improve the nonlinear exponent (α), breakdown field (Eb) of the developed varistors. Added In2O3 restricts the grain growth in the ZnO ceramics, which in turn, causes an increase in the breakdown potential of the varistor samples. High nonlinearity (α > 100) has been obtained consistently in the developed varistors at all the sintering temperatures (850–900 °C). Doped In3+ ions appear as a donor at the grain boundaries, leading to an increase in the Schottky barrier height. The comparatively high leakage current density in ZnO–V2O5 based varistors (usually >100 μA cm−2) could be restricted within 62–83 μA cm−2 in these samples. The sample sintered at 875 °C resulted in a dense (98% TD) fine-grained (1.1 ± 0.1 μm) varistor showing optimum electrical properties with Eb value of 14.2 kV cm−1, α value of 153, and JL equals to 62 μA cm−2.

Multifunctional performance and ferroelectric phase characteristic of BCTH-Eu ceramics prepared by low-temperature sintering via LiBO2 doping

Multifunctional performance [(Ba0.85Ca0.15)0.995Eu0.005](Ti0.9Hf0.1)O3 (BCTH-Eu) ceramics were prepared by conventional solid-state low-temperature sintering method via LiBO2 doping, in which the sintering aid LiBO2 was introduced into the calcined perovskite precursor powder through liquid phase coating technique. Phase-pure perovskite structure BCTH-Eu ceramics are obtained by the method, and the sintering temperature is decreased about 150 °C as compared with the conventional method whose sintering temperature is normally above 1450 °C. The ceramics present rather high density, uniform distribution of grains and elementals, and have submicron meter grain size. Due to complex substitution of cations at A-site and B-site of the perovskite structure, the LiBO2-doped BCTH-Eu ceramics exhibit displacive driven normal ferroelectrics accompanied by apparent diffused relaxation characteristic. The 1340 °C sintered LiBO2-doped BCTH-Eu ceramics present maximum piezoelectric constant d33 value of 314 pC/N poled under 20 kV cm−1, and the ceramics sintered between 1320 °C–1330 °C exhibit excellent comprehensive electrical properties and multifunctional performance. Such excellent multifunctional properties obtained in this work can be partially attributed to the coexistence of multi-ferroelectric phases, which is confirmed by dielectric response fitting and Raman Gaussian fitting.