Sintering Step Research Articles

Dry aerosol jet printing of conductive silver lines on a heated silicon substrate

A new method for dry aerosol jet printing conductive lines on a heated substrate is presented. The method is based on the use of a spark discharge generator as a source of dry nanoparticles and a heating plate for their sintering. This method allows creating conductive silver lines on a heated silicon substrate up to 300 °C without an additional sintering step. It was found that for effective sintering lines of silver nanoparticles the temperature of the heated substrate should be about more than 200-250 °C. Average thickness of the sintered silver lines was equal to ∼20 µm. Printed lines showed electrical resistivity equal to 35 μΩ·cm, which is 23 times greater than the resistivity of bulk silver.

Non-isothermal sinter-crystallisation of satin glazes: A kinetic model

Many materials of a glass-ceramic nature are obtained by glass particle sinter-crystallisation, whose process kinetics have been studied very little. The present study analyses the physico-chemical transformations that develop during the firing of a complex commercial satin glaze (containing more than five phases), with high frit content, particularly focusing on sinter-crystallisation kinetics. Glaze sintering and phase evolution were studied by hot stage microscopy (HSM) and X-ray diffraction (XRD). The glaze melting and crystallisation ranges and the kinetic parameters of the crystallisation process were determined by differential thermal analysis (DTA). Glaze sinter-crystallisation behaviour and the development of the crystal mass fractions, residual glass compositions, and effective viscosity, ηeff, during heating are discussed, based on Rietveld analysis of the XRD data. A new kinetic model was developed that describes the non-isothermal sinter-crystallisation of materials exhibiting three-stage sintering. A two-step kinetic model is involved: sintering with concurrent surface crystallisation (corresponding to sintering stages I and II) and sintering with simultaneous partial melting of crystalline phases (sintering stage III). The experimental data obtained by hot stage microscopy (HSM) at different heating rates were compared with those estimated by the model. The results obtained by the two methods exhibited very good agreement. The crystallisation kinetic parameters (activation energy, Ecr, and Avrami index, n, obtained by DTA, were consistent with the viscous flow activation energy, Q2, corresponding to the first sintering step (sintering stages I and II). The model was used to calculate the values of the effective sintering viscosity, ηs, of the glaze melt. These values were compared with the experimental effective viscosity, ηeff, data obtained by hot stage microscopy (HSM). Both sets of results exhibited good agreement. Effective sintering viscosity, ηs, which is readily measurable, helps better understand the role played by the different glaze constituents and by the firing conditions in sintering, enabling more rational design of these materials.

Correction to: Conventional and two step sintering of PZT-PCN ceramics

The original version of this article unfortunately contained a mistake. The presentation of Eq. 1,2, and 3 was incorrect. The correct versions are given below.

Conventional and two step sintering of PZT-PCN ceramics

In this study, PZT-PCN ceramic was made via sol–gel seeding method and effects of conventional sintering (CS) as well as two-step sintering (TSS) were investigated on microstructure, phase formation, density, dielectric and piezoelectric properties. First, high quality powder was achieved by seeding method in which the mixture of Co3O4 and Nb2O5 powder was added to the prepared PZT sol to form PZT-PCN gel. After drying and calcination, pyrochlore free PZT-PCN powder was synthesized. Second, CS and TSS were applied to achieve dense ceramic. The optimum temperature used for 2 h of conventional sintering was obtained at 1150 °C; finally, undesired ZrO2 phase formed in CS procedure was removed successfully with TSS procedure and dielectric and piezoelectric properties were improved compared to the CS procedure. The best electrical properties obtained for the sample sintered by TSS in the initial temperature of T1 = 1200 °C and secondary temperature of T2 = 1000 °C for 12 h.

Cold sintering and electrical characterization of lead zirconate titanate piezoelectric ceramics

This paper describes a cold sintering process for Pb(Zr,Ti)O3 ceramics and the associated processing-property relations. Pb(Zr,Ti)O3 has a very small, incongruent solubility that is a challenge during cold sintering. To circumvent this, a Pb(NO3)2 solution was used as the transient liquid phase. A bimodal lead zirconate titanate powder was densified to a relative density of 89% by cold sintering at 300 °C and 500 MPa. After the cold sintering step, the permittivity was 200, and the dielectric loss was 2.0%. A second heat-treatment involving a 3 h anneal at 900 °C increased the relative density to 99%; the resulting relative dielectric permittivity was 1300 at room temperature and 100 kHz. The samples showed well-defined ferroelectric hysteresis loops, having a remanent polarization of 28 μC/cm2. On poling, the piezoelectric coefficient d33 was ∼200 pC/N. With a 700 °C 3 h post-annealing, samples show a lower room temperature relative permittivity (950 at 100 kHz), but a 24 h hold time at 700 °C produces ceramics where there is an improved relative dielectric constant (1050 at 100 kHz).

Production and Characterization of Magnesium‐Doped Copper Chromite Fibers

In this study, Mg‐doped CuCr1−xMgxO2 (x = 0, 0.01, 0.03, 0.05) fibers are synthesized via electrospinning process followed by a two‐step heat treatment in air and Ar atmospheres. The produced samples are all crystalline with a fiber diameter ranging from 120 to 140 nm. The effect of Mg2+ substitution for Cr3+ on the structural, morphological, and optical properties of CuCrO2 fibers is investigated systematically. Structural characterizations indicate that the solubility limit of Mg2+ is around 3 at.% and beyond this concentration the formation of MgO phase is observed. This also leads to the formation of Cu cations with (+2) oxidation state. In addition, the incorporation of Mg into the CuCrO2 lattice hinders the formation of perfect hexagonal‐shaped isolated grains and contribute to the preservation of fiber morphology after the final sintering step. Further, the optical transmittance in the visible range decreases with increasing Mg‐doping ratio. The corresponding optical band gaps are determined to be 3.53, 3.47, 3.30, and 3.22 eV, respectively, for x = 0, 0.01, 0.03, 0.05.

Physico-chemical characterization of shaped mesoporous silica prepared by pseudomorphic transformation as catalyst support in methane steam reforming

In this work, pseudomorphic transformation is introduced as an effective method to prepare mesoporous silica in the shape of millimeter sized disc from a biosilica precursor. The samples were prepared by two approaches. In the former method, pre-shaped silica discs were autoclaved in a basic solution containing cethyltrimethyl ammonium bromide (CTAB) and trimethyl benzene (TMB) to perform pseudomorphic transformation (S1) and in the latter case, silica powders were initially transformed by a pseudomorphic reaction following by shaping them before the removal of CTAB and TMB in calcination and sintering step (S2). The textural properties of the obtained mesoporous silica discs present that S2 sample results in larger pore size and also higher pore volume. The prepared samples have been utilized for preparation of Ni impregnated-silica catalysts in steam reforming of methane. Ni/S2 sample has been shown superior catalytic activity in comparison with other samples (methane conversion of 75% and hydrogen yields more than 40% at 550 °C). The measured physicochemical properties of the samples have been implemented to describe the catalytic results and possible coking mechanism on different samples.

A new approach for fabrication of titanium-titanium boride periodic composite via additive manufacturing and pressure-less sintering

Abstract This study proposes a new additive manufacturing (AM) based methodology to fabricate periodic metal matrix composite architectures, with a focus on titanium (Ti)-titanium boride whisker (TiBw) composites. The manufacturing method includes binder jetting AM of the titanium matrix reinforced periodically by the extrusion of a custom-developed highly loaded resin, containing titanium di-boride (TiB2) particles. A low-temperature pressure-less sintering method was then applied to increase the mechanical strength of green samples produced from the additive manufacturing step. The sintering process also fosters the chemical reaction between the matrix and ceramic, resulting in the growth of titanium boride whisker (TiBw). The ceramic volume fraction and sintering protocol were studied as two main input variables in the design and fabrication steps. Investigating the influence of input parameters on the volume fraction and morphology (whisker formation) of TiB determined that the physical properties of the specimens, such as stiffness, were affected. The data analysis suggested a higher possibility for the formation and growth of TiBw as the temperature elevated in the sintering step (1400 °C). The ranges of 1.6 ± 0.2 GPa–3.7 ± 0.4 GPa and 83.9 ± 18.7 MPa–165 ± 13.2 MPa for the Young's modulus and Yield stress of the specimens were obtained, respectively. The stiffness of the samples was enhanced significantly by increasing the temperature and volume fraction. In particular, those samples sintered up to 1400 °C displayed 6.4%–15.2% improvement in the stiffness, although only a small fraction of the ceramic material was incorporated into the design: 2% and 4%, respectively. The similar trend of the improvement in density of the porous matrix was observed (i.e., 4.5%–19%). The range of mechanical and structural properties of the periodic composite developed in this study demonstrated the relevance of applying this method to the fabrication of biomedical and other lightweight titanium composite structures.

Effect of shifting orthorhombic-tetragonal phase transition on structure and properties of K0.5Na0.5NbO3-based lead free ceramics

KNN-based piezoceramics were prepared by three step sintering method. Phase structure, phase transition temperature and properties were investigated. Low temperature and high temperature XRD pattern results indicated that the temperature of orthorhombic phase change to tetragonal phase was about −20 °C, and the tetragonal phase change to cubic phase was about 300 °C.

Fabrication of anode-supported microtubular solid oxide fuel cells by sequential dip-coating and reduced sintering steps

The expensive and time-consuming fabrication of microtubular solid oxide fuel cells (MT-SOFCs) is one of the main barriers for their commercialization. In this study, a sequential dip-coating coupled with co-firing process was developed to fabricate anode-supported MT-SOFCs using carbon rods as a sacrificial template. Both anode and electrolyte layers underwent co-firing at 1400 °C rather than conventional pre-sintering and co-sintering steps. The whole cell structure was fabricated through sequential dip-coating and drying cycles that are flexible to various tube sizes and fast in turnaround time. The fabricated MT-SOFCs were comprised of Ni–yttria-stabilized zirconia (3YSZ) anode support, scandia-stabilized zirconia (ScSZ) electrolyte, Ni-ScSZ anode functional layer, strontium-doped lanthanum manganite (LSM)–ScSZ cathode functional layer, and LSM cathode current collector layer, respectively. The electrochemical performance of the fuel cell was measured at temperatures between 650 and 800 °C. The MT-SOFC delivered stable performance for more than 50 h operation at 700 °C. The fabricated fuel cell also exhibited excellent thermal cycling stability. The results demonstrated that the sequential dip-coating coupled with co-firing is a simple, flexible and cost-effective fabrication process to produce reliable and robust MT-SOFCs.

An improved internal gelation process without cooling the solution for preparing uranium dioxide ceramic microspheres

An improved internal gelation process for the preparation of UO2 ceramic microspheres with diameter of 790±20µm is described. The UO2 ceramic microspheres are prepared by optimizing feed solution compositions and heating up rate during sintering and calcination steps. The two feed solutions Hexamethylenetetramine (HMTA)-urea and UO22+ were mixed just before the drop formation driven by two liquid chromatographs at room temperature without Cooling the Solution. A urea/UO22+ mole ratio of 1.45 is applied to ensure the stability of the solution. After accurate washing steps to wipe out the impurities, good spherical and little cracked UO2 ceramic microspheres will be obtained at a heating-up rate of 5K/min during sintering and calcination. Different from the traditional methods reported previously, solution which is not cooled is employed during the improved process in this paper.

Synthesis and characterization of titanium doped barium ferrite and effects of doping on electrical and magnetic properties of the compound

ABSTRACTEffects of titanium substitution on electrical and magnetic properties of ceramics of barium ferrites having general formula BaTixFe12-xO19, with values of x as 0.00, 0.005, 0.01, 0.02 and 0.03 have been investigated. The compounds are synthesised using two step sintering solid-state rout and characterized by employing SEM and x-ray diffraction. All the titanium substituted compounds show hexagonal single phase symmetry. Gradual loss of saturation magnetization, significant increase in total polarization, rise in value of dielectric constant and upward trend in resistivity are the main parameters observed with titanium substitution on Fe ions. The Curie temperature shows declining trend with dopant concentration. The material is found to exhibit electrical behaviour at expense of its intrinsic magnetic characteristics paving way for Ti ion substitutions for controlled magnetic and electrical properties of barium ferrite.

Efficient near Net-Shape Production of High Energy Rare Earth Magnets by Laser Beam Melting

In this publication we report on our progress in investigating the energy efficient production of rare earth permanent magnets by Laser Beam Melting in the powder bed (LBM). This innovative additive manufacturing process offers the potential to produce magnets of complex geometries without an energy intensive oven sintering step. Another advantage that increases the efficiency of this possible new process route is the high degree of material utilization due to a near net shape production of the magnets. Hence only little material is wasted during a post processing machining step. The main challenge in processing rare earth magnet alloys by means of LBM is the brittle mechanical behavior of the material and the change in microstructure due to the complete remelting of the magnet powder. We therefor expanded the parameter study presented in previous work in order to further increase relative density and magnetic properties of the specimens. In this context process stability and reproducibility could also be increased. This was achieved by investigating the impact of different exposure patterns and varying laser spot sizes. Simultaneously to the experiments the energy consumption of the LBM process was measured and compared with conventional rare earth magnet production routes.

Low-Temperature Solid-State Synthesis of High-Purity BiFeO3 Ceramic for Ferroic Thin-Film Deposition.

The synthesis of high-purity BiFeO3 (BFO) ceramic by solid-state reaction is known to be very difficult due to inevitable formation of the secondary phases, mostly mullite-type Bi2Fe4O9 and sillenite-type Bi25FeO39. In particular, it is very difficult to completely remove the Bi-deficient Bi2Fe4O9 phase from sintered ceramic BFO targets. This problem consequently leads to the difficulty of fabricating high-quality BFO thin films using these sintered targets. Herein, we introduce a simple but effective low-temperature processing scheme for removing impurity phases in which optimized processing conditions are obtained by chemically correlating the first calcination step with the subsequent leaching and sintering steps. More specifically, we suitably avoid the formation of the high-temperature-stable Bi2Fe4O9 phase by performing the calcination at significantly low temperatures (between 650 and 675 °C) with Bi-excess starting powders. We have then fabricated epitaxially grown BFO thin films using these phase-pure ceramic targets and consequently achieved high-quality ferroelectricity and switchable photovoltaic responses. On the basis of the present experimental observations, we suggest that a low impurity concentration in the sintered BFO ceramic target, even with a low relative density, is advantageous for high-quality thin-film fabrication.

Synthesis and characterization of rare earth‐doped silica nanoparticles for optimizing vapor phase doping technique

AbstractThe synthesis of rare earth‐doped aluminosilicate soot particles through vapor phase doping technique has been systematically investigated to achieve better control of rare earth homogeneity in silica glass. The experiments were designed to establish the correlation of process conditions with the physicochemical properties of the formed soot particles. Attained results depict that the characteristics of soot particles are much dependent on vapor phase compositions as well as the deposition temperature. Doping of alumina/rare earth oxide into silica matrix lowers the viscosity of the glass material at a level where size of soot particles becomes independent of deposition temperature. But dopant concentration in the formed soot samples moderately depends on the main burner temperature and by altering it appropriately one can eliminate soot layer sintering step. The paper also reports on the optimum conditions which are necessary to produce rare earth‐doped preforms of better homogeneity and thus, assist in achieving greater control over the process technology of vapor phase doping. As per the authors’ knowledge, this investigation presents completely new findings which have not been reported by any other research group earlier.

Manufacturing and testing of a metal supported Ni-YSZ/YSZ/La2NiO4 IT-SOFC synthesized by physical surface deposition processes

The manufacture of the last generation metal supported IT-SOFC complete cell by dry surface deposition processes is really challenging. Atmospheric Plasma Spraying (APS) and Reactive Magnetron Sputtering (RMS) processes are respectively adapted to deposit Ni-YSZ anode and YSZ electrolyte layers. RMS is also used to coat a thin and dense La2NiO4 (LNO) cathode layer. In this work, we have realized a complete cell on metallic support (ITM) produced by PLANSEE SE. The innovative LNO cathode layer was compared with screen-printed LNO layers, with and without RMS bonding layer. Electrochemical and Voltammetry tests were performed on these samples. It reveals lower performances than literature due to the high density of the RMS cathode layer, and too high temperature during sintering step which deteriorate layers manufactured by RMS and metallic substrate. Nevertheless, using LNO bonding layer manufactured by RMS seems to be an interesting way to improve the polarization resistance of the cell.

Effect of substrate hardness and surface roughness on the film formation of aerosol-deposited ceramic films

The aerosol deposition (AD) method is a novel ceramic coating technique that allows manufacturing of dense ceramic films at room temperature directly from ceramic powders without any high temperature sintering steps and without expensive (ultra) high vacuum processes. The deposition mechanism can be separated into two stages: the creation of an anchor layering and the subsequent film formation. Step one involves an initial plastic deformation of the substrate surface by the first impacting particles. Especially in the first stage, substrate properties affect the deposition and determine the dominant bonding mechanism. Ductile substrates can be expected to give strong film anchoring, whereas high hardness substrates might require higher particle velocities to form adhering layers. In this study, the influence of the substrate hardness in combination with the surface roughness on the deposition was investigated. Four ceramic substrates (two types of Al2O3, sapphire, and LTCC) with different hardness and surface roughness were coated with Al2O3 in order to study the formation of an anchoring layer and their effect on the deposition rate. As a result, no anchoring layer was found on the hard ceramic substrates.

Rapid and Low-Energy Fabrication of Symmetrical Solid Oxide Cells by Microwave Methods.

Solid oxide fuel cells are highly efficient, low-emission, and fuel-flexible energy conversion devices that can also run in reverse as solid oxide electrolysis cells, converting CO2 and/or H2O to useful fuels and pure O2. Our team has recently developed a highly promising mixed conducting oxide catalyst (La0.3Ca0.7Fe0.7Cr0.3O3−δ) that can be used at both the anode and cathode in either the fuel cell or electrolysis mode in a lower-cost symmetrical cell. However, there is still a need to improve material processing and cell manufacturing methods in this field. Here, we report, for the first time, fabrication of a symmetrical solid oxide cell, based on our very promising catalysts, using rapid, low-cost, low-energy, and green microwave (MW) processing techniques. These cells were fabricated with MW-sintered powders and were then MW-sintered without the use of any MW susceptors inside the electrode layers or any additional presintering steps. The catalyst layers show very stable nanostructures and do not delaminate, and the cells exhibit reaction rates that are similar to those obtained using normal ceramic processing methods. Importantly, the powder preparation and cell sintering steps, carried out using MW methods, require only ca. 1/3 and 1/9 of the time/energy, respectively, versus those required in traditional furnace methods, thus translating to significant cost savings.

High performance planar perovskite solar cells by ZnO electron transport layer engineering

ZnO as electron extraction layer in photovoltaic devices has many advantages, including high mobility and low processing temperature. However, it has been underutilized in perovskite solar cells due to the reported instabilities of perovskite layers deposited on ZnO resulting in poor device performance. Herein, we modify the ZnO layer by incorporating Cs or Li dopants in its bulk and depositing a self-assembled monolayer on its surface. This combined approach of engineering both the bulk and surface properties of ZnO results in significant improvements in the performance of planar MAPbI3 perovskite solar cells with a maximum power conversion efficiency of 18%, accompanied by a reduction in hysteresis and a significant enhancement of the device stability. Our work makes engineered solution-processed ZnO layers a practical alternative to TiO2 as electron extraction layers in perovskite solar cells, while also eliminating the need for high temperature sintering steps from the device fabrication.

Phase Content and Conductivity of Aluminum- and Tantalum-Doped Garnet-Type Lithium Lanthanum Zirconate Solid Electrolyte Materials

Cubic garnet-type Li7La3Zr2O12 (LLZO) was prepared by co-precipitation method. X-ray diffraction results showed that aluminum additions of 0.2 - 0.3 mol% or a tantalum addition with a 0.25 mol% with excess 10% LiOH added in the final sintering step, led to the formation of the cubic LLZO phase. Samples have a low relative density of ~80%, which is the main reason for low ionic conductivity. The total conductivity at 25°C and activation energies of Li6.28La3Zr2Al0.24O12 and Li6.28La3Zr1.75Ta0.25O12 were 2.8×10-6 S/cm (0.39 eV for bulk and 0.33 eV for grain boundary) and 7.0×10-6 S/cm (0.065 eV at low temperature and 0.99 eV at high temperature), respectively.