Sintering Of Oxide Research Articles

Effect of atmospheric conditions on the onset electric field of ZnO and Y2O3 ceramics flash sintering at room temperature

Flash sintering of zinc oxide (ZnO) ceramics can be induced at room temperature (25 °C) by electrical breakdown at high electric field strength. However, a strong discharge may degrade the sample. This study investigated the effects of atmospheric pressure and composition on the onset electric field for the flash sintering of ZnO. The experimental results show that flash sintering of ZnO under a low electric field at room temperature can be achieved by adjusting the atmospheric conditions. Compared with the onset electric field strength under normal atmospheric conditions, the value for flash sintering of ZnO at 20 kPa in a mixture of 20% air +80% argon (Ar) can be reduced by 82% to approximately 700 V/cm. This method also applies to yttrium oxide (Y2O3) for a low electric field in flash sintering at room temperature, and is the first report on flash sintering of Y2O3 at room temperature.

Regeneration of an aged hydrodesulfurization catalyst: Conventional thermal vs non-thermal plasma technology

This study compares the regeneration efficiency of an aged industrial hydrodesulfurization catalyst (CoMoP/Al2O3) by conventional and alternative routes: thermal oxidation versus non-thermal plasma technology (NTP). Spent, partially, and fully regenerated catalysts have been characterized by XRD, XPS, and toluene hydrogenation to measure hydrogenating activity. Complete regeneration of the HDS catalyst via NTP requires the heating of the dielectric barrier discharge plasma reactor. Total removal of coke is obtained from 250 °C by applying only 8.6 W/gcatalyst, against 400 °C by conventional thermal treatment. The hydrogenation activity of the regenerated catalyst by NTP assisted by temperature is higher than that obtained by traditional thermal regeneration practiced industrially. Plasma treatment mitigates the oxide sintering but leads to the formation of cobalt oxide species preventing Co of fully playing its role as MoS2 slabs promoter. HDS catalyst regeneration using non-thermal plasma assisted by low temperature appears as a promising alternative to thermal combustion.

Fabrication of Conductive and Gas-Sensing Microstructures Using Focused Deposition of Copper Nanoparticles Synthesized by Spark Discharge

Solvent-free aerosol jet printing has been investigated for fabricating metallic and semiconductor (gas-sensitive) microstructures based on copper nanoparticles on alumina, borosilicate glass, and silicon substrates. The synthesis of nanoparticles was carried out using a spark discharge directly in the printing process without the stage of preparing nano-ink. Printed lines with a width of 100–150 µm and a height of 5–7 µm were formed from submicron agglomerates consisting of primary nanoparticles 10.8 ± 4.9 nm in size with an amorphous oxide shell. The electrical resistivity, surface morphology, and shrinkage of printed lines were investigated depending on the reduction sintering temperature. Sintering of copper oxides of nanoparticles began at a temperature of 450 °C in a hydrogen atmosphere with shrinkage at the level of 45–60%. Moreover, aerosol heat treatment was used to obtain highly conductive lines by increasing the packing density of deposited nanoparticles, providing in-situ transformation of submicron agglomerates into spherical nanoparticles with a size of 20–50 nm. Copper lines of spherical nanoparticles demonstrated excellent resistivity at 5 μΩ·cm, about three times higher than that of bulk copper. In turn, semiconductor microstructures based on unsintered agglomerates of oxidized copper have a fairly high sensitivity to NH3 and CO. Values of response of the sensor based on non-sintered oxidized copper nanoparticles to ammonia and carbon monoxide concentration of 40 ppm were about 20% and 80%, respectively.

Microstructured ZrO2 coating of iron oxide for enhanced CO2 conversion

This work provides a way to design oxygen carriers for chemical looping. Starting from Prussian blue microcubes, Zr-promoted Fe-based materials are developed for the conversion of CO2 into CO. Thermally induced oxidative decomposition of ZrO2-coated Prussian blue under the protection of the firstly formed ZrO2 shell leads to the formation of hollow structured materials.Detailed activity tests and in-situ characterization are used to investigate the relationship between material structure, stability and CO yield from CO2 conversion. Throughout one hundred H2-CO2 redox cycles, 10 %Fe2O3/ZrO2 exhibits a 27 times higher CO space-time yield (86mmol∙s-1∙kgFe2O3-1) than unpromoted, yet hollow structured Fe2O3. This superior performance derives from the dual role that ZrO2 plays: protecting the structure, thereby improving the iron oxide sintering resistance, and facilitating the reduction of iron oxide during redox cycles. The hollow structure and the interaction between Fe2O3 and ZrO2 are the main reasons for the enhanced redox activity.

Preparation of a porous bulk copper ferrite spinel with high performance in the electrolysis of water

Copper ferrite spinels (CFOs) show potential application for use in the field of water electrolysis. However, CFOs are prepared using traditional fabrication methods and as a result always exist in powder form, making them difficult to utilise in applications. In this work, a porous bulk CFO material was fabricated via the milling and sintering of metal oxides, which can be used directly as an electrode. This CFO shows excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities. The results show that preparing the CFO under an argon (Ar) atmosphere, at high temperature and with a milling pretreatment improves the density of oxygen vacancies (OVs) in the material, thereby enhancing its ability to electrolyse water. The CFO shows high OER and HER performance when sintered at 1000°C under an Ar atmosphere and milled. In 6 M KOH solution at 10 mA cm−2, the OER and HER overpotentials of CFO are as low as 290 and 241 mV, with OER and HER Tafel slopes of 75.5 and 114 mV dec−1. The synthesis route developed in this study is versatile, with the CFO electrode produced exhibiting high performance in water electrolysis.

The effects of Sn substitution on the phase, microstructure, and dielectric properties of 0.94(Bi0.5Na0.5)TiO3–0.06Ba(Zr0.1Ti0.9)O3 ceramic system

0.94(Bi0.5Na0.5)TiO3–0.06Ba(Zr0.1Ti0.9-xSnx)O3 (x = 0, 0.08, 0.1) (BNT-BZST) ceramics were synthesized via conventional mix oxide sintering route. X-ray diffraction, scanning electron microscopy, inductance (L), capacitance (C), and resistance (R) (LCR) measurement meter, d33 meter, and ferroelectric testes system were used for determining the phase, microstructure, ferroelectric and piezoelectric properties of the samples. Dense microstructure with a decrease in the average grain size with an increase in Sn content was observed. Improvement in the ferroelectric and piezoelectric properties such as dielectric constant (εr), dielectric loss (tanδ), polarization (P), and piezoelectric coefficient (d33) was observed for 08 wt% of Sn substituted sample. A maximum values of saturated polarization (Pmax) ~ 55 µC/cm2, a remnant polarization (Pr) ~35 µC/cm2, d33~130 pC/N and εr ~3895 (1 MHz) at Tm~264 °C were obtained for x=0.08.

Design of an instrumented microwave multimode cavity for sintering of nuclear ceramics

This paper describes the development of an innovative instrumented and automated 2.45GHz multimode microwave cavity for sintering of uranium oxide based nuclear fuels (UO2, (U,Pu)O2, (U,Am)O2 …). The cavity and the sintering cell were designed using Finite Element simulation and the expertise acquired over years on microwave heating. This original setup allows for hybrid and homogeneous heating of nuclear fuels. Reliable in situ monitoring of the samples' shrinkage and temperature is performed with an optical dilatometer and infrared pyrometers calibrated with a specific protocol. A dedicated software including a Proportional-Integral-Derivative (PID) controller was developed to precisely control the sintering cycles like under conventional heating. The setup is also designed for operating in a glovebox under reducing sintering atmosphere.A stable and homogeneous heating with controlled sintering cycles is reached to successfully sinter UO2 crack free pellets to high density. This is a key point of innovation compared to previous studies in the literature on microwave sintering of nuclear ceramics. The pellets' final densities are equivalent to those obtained under conventional sintering, but with a significant decrease in the total duration of the sintering cycle.

Evaluation of Ni-Based Flexible Resistance Temperature Detectors Fabricated by Laser Digital Pattering.

Temperature sensors are ubiquitous in every field of engineering application since temperature control is vital in operating, testing and monitoring various equipment systems. Herein, we introduce a facile and rapid laser digital patterning (LDP) process to fabricate low-cost, Ni-based flexible resistance temperature detectors (RTDs). Ni-based RTDs are directly generated on a thin flexible polyimide substrate (thickness: 50 µm) by laser-induced reductive sintering of a solution-processed nonstoichiometric nickel oxide (NiOx) nanoparticle thin film under ambient conditions. The shape of RTDs can be easily adjusted by controlling computer-aided design (CAD) data without using the physical patterning mask while the sensitivity (temperature coefficient of resistance (α) ~ 3.52 × 10−3 °C−1) of the sensors can be maintained regardless of shape and size of the sensor electrodes. The flexible Ni-based RTDs can operate over a wide temperature range up to 200 °C with excellent repeatability. Additionally, the Ni-based RTDs respond quickly to the temperature change and can operate in corrosive environments including water and seawater. Moreover, the Ni-based RTDs show a superior mechanical and electrical stability with a negligible resistance change up to a radius of curvature of 1.75 mm. Finally, a tape-pull test demonstrates the robust adhesion of Ni-based RTDs on the substrate.

Improvement of electrical properties of ITO thin films by melt-free ultra-short laser crystallization

We describe a novel solid state crystallisation method for optimising a thin film transparent conductive oxide when deposited on flexible polymer substrates. The method is based on ultra-short non-thermal laser sintering of indium tin oxide (ITO) thin films. In this study, we used commercial ITO thin films deposited on a flexible polyethylene terephthalate substrate with a relatively low melting temperature compared with ITO on glass. We demonstrate the use of laser scanning with high pulse overlapping at fluences seven times less than the threshold required for melting/damage of ITO. The results confirm greater than four times enhancement in the mobility of charge carriers of ITO thin films after laser scanning and sheet resistance can be reduced up to 25%. There is no reduction in optical transparency observed in laser treated samples. Surface morphology and x-ray diffraction analyses confirm the improvement in crystallite sizes by laser sintering, resulting in a greater than 37% increase in grain size due to enhanced crystallization. Comparison of experimental and simulation based on a delayed two temperature model confirms that ITO thin film crystallization occurred at about one-third of the melting temperature of ITO.

Millisecond photonic sintering of iron oxide doped alumina ceramic coatings

The sintering of alumina (Al2O3) traditionally occurs at high temperatures (up to ca. 1700 °C) and in significantly long times (up to several hours), which are required for the consolidation of the material by diffusion processes. Here we investigate the photonic sintering of alumina particles using millisecond flash lamp irradiation with extreme heating rates up to 108 K/min. The limitation of the low visible light absorption of alumina is resolved by adding colored α-Fe2O3 nanoparticles, which initiated the grain growth during sintering. After the millisecond-long light pulses from a xenon flash lamp, a bimodal mixture of α-Al2O3 precursor particles was sintered and iron segregation at the grain boundaries was observed. The proposed photonic sintering approach based on doping with colored centers may be extended to other refractory ceramics with low absorption in the visible light range once appropriate high-absorbing dopants are identified.

Enhancing sintering resistance of atomically dispersed catalysts in reducing environments with organic monolayers

Atomically dispersed precious metal catalysts maximize atom efficiency and exhibit unique reactivity. However, they are susceptible to sintering. Catalytic reactions occurring in reducing environments tend to result in atomically dispersed metals sintering at lower temperatures than in oxidative or inert atmospheres due to the formation of mobile metal-H or metal-CO complexes. Here, we develop a new approach to mitigate sintering of oxide supported atomically dispersed metals in a reducing atmosphere using organophosphonate self-assembled monolayers (SAMs). We demonstrate this for the case of atomically dispersed Rh on Al2O3 and TiO2 using a combination of CO probe molecule FTIR, temperature programmed desorption, and alkene hydrogenation rate measurements. Evidence suggests that SAM functionalization of the oxide provides physical diffusion barriers for the metal and weakens the interactions between the reducing gas and metal, thereby discouraging the adsorbate-promoted diffusion of metal atoms on oxide supports. Our results show that support functionalization by organic species can provide improved resistance to sintering of atomically dispersed metals with maintained catalytic reactivity.

The Formation of Mn-Ce Oxide Catalysts for CO Oxidation by Oxalate Route: The Role of Annealing Conditions

A series of Mn-Ce oxide catalysts with Mn:Ce = 1 was synthesized by oxalate route under different annealing conditions. The physicochemical properties were characterized by means of XRD, HRTEM, N2 adsorption, TPR, XPS and DD technique. All the catalysts were investigated in the CO oxidation reaction. The annealing conditions exhibited a great impact on the structural properties, which resulted in different catalytic performance. The activity of the samples calcined in air exceeds the activity of the samples prepared in argon at a similar temperature. In the inert at 300–400 °C, the oxalate precursor does not completely decompose to oxide; at 500–600 °C, MnO and ceria are formed. For the Mn-Ce oxide catalyst obtained in air, the combination of XRD, DD and TPR showed that the catalyst consists of a MnxCe1-xO2-δ (x ~ 0.2) solid solution, amorphous and crystalline manganese oxides (Mn3O4, Mn2O3, Mn5O8). XPS analysis indicates that the catalyst surface contains Mn cations in the form of Mn2+, Mn3+ and Mn4+. An increase in the calcination temperature results in the oxide sintering. During the variation of the calcination time at 300 °C, the composition of the MnxCe1-xO2-δ solid solution does not change, while transformations occur in Mn oxides. The most active Mn-Ce catalyst was obtained by annealing at 300 °C for 10 h in air and consists of a MnxCe1-xO2-δ solid solution and Mn5O8.

Cold Sintering of Calcium Carbonate for Construction Material Applications.

An alternative to traditional binder-based construction materials using “cold sintering”, a hydrothermal mechanism that involves subjecting the sample to simultaneous pressure and comparatively low temperatures, was explored. Ground and precipitate calcium carbonates (GCC and PCC) were used as the primary starting materials. Ordinary portland cement (OPC) and zinc oxide were studied for comparison. Compressive strength tests showed promising results from the OPC mortars with the cement mostly replaced by GCC. Scanning electron microscopy showed sintering of calcium carbonate and zinc oxide with the selection of suitable solutions. Porosity of sintered samples measured by nitrogen adsorption–desorption improved considerably. These data support the feasibility of cold sintering as an alternative method for production of conventional precast construction materials.

Investigating the Effect of Temperature on Sulfur Deportment in Nickel Laterite Calcination

The majority of the ferronickel production from nickel laterite ores is through the Rotary kiln- electric furnace (RK-EF) process. Calcination and partial reduction of the laterite ore is typically carried out in a rotary fuel fired furnace. Sulfur is one of the most deleterious impurities in nickel alloys and degrades the mechanical properties of the product. Considering the insubstantial concentration of sulfur in laterites, it is assumed that sulfur partially originates from added fuel and reductant in the calcination stage. Investigating the effects of the temperature in the calcination stage on the sulfur distribution can provide valuable information on controlling the level of sulfur in the calcine. In this study, the atmosphere resulted from coal combustion is simulated by purging a gas mixture of N2, CO, CO2, and SO2 to the electrical horizontal tube furnace. The effect of temperature (600, 700, 800, and 900 ⁰C) on the sulfur deportment was studied. Inductively coupled plasma optical emission spectrometry (ICP-OES), and X-ray diffraction tests were used to measure the sulfur content and identify the phase composition of the products. The dominant compound of the calcine that contains sulfur is identified as pyrrhotite. Raising temperature from 600 to 700 ⁰C, increases %S in the calcine from 0.29 to 0.34%; however, promoting the temperature above 700 ⁰C diminishes the sulfur deportation percentage because of decreasing the surface area of solids by recrystallization of magnesia silicate compounds and sintering of oxides.

Investigate the effect of process parameters of magnetic inductively assisted spark plasma sintering (SPS) of iron oxide (Fe3O4) on microstructure behaviour – Part I

Abstract A new magnetically assisted spark plasma sintering as a novel method of adding a continuous intensive magnetic field during the sintering process was briefly introduced as an alternative method of traditional SPS in which the sintering process passed through several processes started with jet milling, aligning, densifying, and then ended up with sintering during the production of a material with excellent magnetic, electrical, and mechanical properties. Furthermore, the use of an external magnetic field parallel with the sintering process leads to a shortening of these processes in addition to driving the molten metal in a certain way for grain refinement and grain re-orientated, resulted in the reduction of porosities and cavities. In this paper (Part I) Iron oxide (Fe3O4) nanopowder has been characterized to study the sintering process's effect on microstructure behavior using FESEM, XRD, XPS, and VSM. Based on the results obtained, Fe3O4 has cubic shaped particles with an average size of 100–200 nm, and the indexed peaks are (1 1 1), (2 2 0), (3 1 1), (2 2 2), (4 0 0), (4 2 2), (5 1 1), and (4 0 0), which confirmed with the standard.

Plasma-Spark Sintering of Oxide–Non-Oxide Components with the Addition of a TiC–ZrC Solid Solution and Various Metal Powder Mixtures

The effects of powder mixtures of W–Mo and Zr–Ti combined with sintered solid solution TiC–ZrC during spark plasma sintering of compositions at a pressing load of 60 MPa in the range 1200 – 1600°C on the phase composition, microstructure, grain sizes of crystalline phases, relative density, linear shrinkage, physical-mechanical properties, and linear correlation of elasticity modulus and fracture toughness of mullite–β-Si3N4–c-BN samples are shown in the present work. Synthesized powders of β-Si3N4 and c-BN are characterized by extensive crystallization of β-Si3N4 and c-BN. Solid solution TiC–ZrC sintered by a spark-plasma method at 1800°C shows roughly equal crystallization of (Zr,Ti)C and (Ti, Zr)C and a nonuniform and incompletely sintered crystalline microstructure. Samples with W–Mo and Zr–Ti mixtures sintered in the range 1200 – 1600°C show extensive mullitization; active crystallization of β-Si3N4, (Ti,Zr)C, solid solutions Mo, Wand W, Mo, and β-Zr,Ti; and lower crystallization of c-BN, (Zr,Ti)C, and β-Ti,Zr. The W–Mo mixture in the range 1400 – 1600°C favors the formation of a more uniformly and densely sintered microstructure of the ceramic phase; roughly round-shaped particles of solid solutions Mo, W and W, Mo in the metallic phase; more reinforced boundary areas of ceramic-metallic and metallic phases; and polydisperse grain compositions of crystalline phases. As a result, the composition with the W–Mo mixture sinters more uniformly and gradually in the range 1200 – 1600°C with the corresponding sample showing greater values of physical-mechanical properties, higher cracking resistance, and a greater linear correlation of the elasticity modulus and fracture toughness.

Cold sintering of yttria-stabilized cubic bismuth oxide: Conductivity and microstructural evolution of metastable grain boundaries with annealing

Yttrium-doped bismuth oxide (BYO) is densified by the cold sintering process (CSP) at 300 °C. The relative density reached is ∼90% of the theoretical density. The as-sintered BYO ceramic shows a total conductivity of >1 mS/cm at 500 °C. The conductivity slightly increased after the annealing process. The scanning and transmission electron microscopy analysis revealed that a metastable secondary phase formed adjacent to BYO grains in the as-CSP specimens. Once annealed, the secondary phase recrystallized and there is an associated total conductivity improvement.

Synthesis of glass composite material with bismuthate glass powder and zeolite-4A for immobilization of iodine waste

The immobilization of iodine 129 released during the reprocessing of spent nuclear fuels has attracted increasing interest in the field of nuclear waste management. Glass composite materials have been developed to decrease the sintering temperature considering the iodine volatilization. In this study, the effects of the addition (5–25 ​wt%) of a bismuthate oxide glass powder and sintering temperature (500–1100 ​°C) on the iodosodalite formation in waste forms were investigated. Microstructure characterization techniques including X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy were employed to elucidate the I states in the waste form. Phase composition calculations show that the maximum phase mass of iodosodalite was 94%. The sintering temperature was decreased to 600 ​°C, lower than the decomposition temperature of NaI, after the addition of a 15 ​wt% bismuthate glass powder. The leaching rate of iodine shows the considerable chemical durabilities of the sintered sample under alkaline and neutral conditions.

Thermal performance enhancement of an ultra-thin flattened heat pipe with multiple wick structure

Low heat-transport capability has been the biggest problem that has retarded the development of ultra-thin heat pipes (UFHPs). In this study, a high-performance multiple mesh wick structure, fabricated by oxidation treatment and sintering, was proposed for enhancing the thermal performance of UFHPs. The effects of various heat inputs and flattened thicknesses on the thermal performance of the UFHPs with copper mesh wicks were investigated and analysed, and the experimental results compared with those of UFHPs with conventional sintered powder wicks. The experimental results demonstrated that the heat-transport capability of the UFHP with the mesh wick could be effectively enhanced by oxidation, and the oxidized mesh wicks had the same capillary performance as sintered powder wicks. The temperature difference of the UFHP with the oxidized mesh wick was significantly lower than that of the UFHP with the un-oxidized mesh wick and sintered powder wick under identical heat input. Moreover, the performance improvement of the UFHP with the mesh wick was more significant after treatment with chemical oxidation when the flattened thickness was larger, the ultimate heat-transport capabilities of the UFHPs with a flattened thickness of 1.2 mm increased by 6 W and 9 W, respectively, compared with those with a flattened thickness of 1.0 mm.

Pristine detonation nanodiamonds as regenerable adsorbents for metal cations

The usability of pristine (not functionalized by grafting) detonation nanodiamonds as reversible and repeatedly regenerated adsorbents for metal cations was shown by examples of sorption of cadmium, zinc, nickel, and copper from aqueous solutions. Various pristine nanodiamond surface treatments are discussed. The procedure of oxidative sintering with nitric acid at 250 °C provided a surface with an increased number of carboxyl groups with a sorption capacity above 100 μmol/g for all test cations. Sorption isotherms for test metals (copper, nickel, zinc, and cadmium) can be divided into two distinct parts: a lower part for concentrations of up to 10–15 mmol/L belong to the Langmuir L5 type by Giles and absorption free energies are 8–12 kJ/mol according to the Dubinin–Radushkevich model, evidencing a primarily chemisorption mechanism of the studied cations on micropores in ND surface. The parts of curves above 10–15 mmol/L are described with linear equations, free energies of absorption are 4–6 kJ/mol by Dubinin–Radushkevich that are assigned to physisorption in mesopores. A procedure for the surface regeneration, which is based a similar sintering treatment with nitric acid, was developed. It provided sorption parameters not degraded compared to the starting material; and the regeneration process is repeatable at least for 10 cycles.