The influence of hafnium removal on the microstructure and properties of 8YSZ ceramics

The effects of hafnium removal on the sinterability, phase composition, and microstructural, mechanical, and electrical properties of 8YSZ (8 mol% yttrium stabilized zirconia) were investigated using SEM, XRD, Raman spectroscopy, EBSD, three-point bending, Vickers indentation, and impedance spectroscopy. The 8YSZ and 8YSZ₀ (8 mol% yttrium-stabilized hafnium-free zirconia) ceramics were prepared via dry pressing and atmospheric sintering, respectively. The overall mechanical properties of the 8YSZ₀ ceramic were poor. However, at a sintering temperature of 1450°C, the relative density of 8YSZ and 8YSZ₀ ceramics was almost identical. 8YSZ₀ had a slightly smaller grain size and activation energy, and its electrical properties were slightly better than those of the 8YSZ ceramics. The presence of tetragonal secondary phases in the cubic structure of 8YSZ ceramics inhibited crack propagation and led to an increase in the mechanical properties and a decrease in the ion conductivity. In terms of the crystal structure, the increase in the cubic phase lattice parameters and tetragonal phase c/a values of the 8YSZ₀ ceramics was attributed to the larger Zr⁴⁺radius, reduced local lattice distortion, and increased matrix oxygen vacancy concentration and cubic phase content. The EBSD analysis results indicated that there was no significant difference in grain orientation between the two types of ceramics, but the content of 8YSZ ceramics in large angle grain boundaries was slightly higher, especially in special grain boundaries Σ3 and Σ9. Therefore, this material can be used as a solid-state electrolyte candidate.     

Properties of polyphenylene sulphide/glass fibre composites with negative thermal expansion ceramic fillers

The high coefficient of thermal expansion (CTE) of polymeric composites can cause large deformation under temperature changes, affecting coupling with devices made of other materials in radio frequency (RF) communication systems and limiting their application in RF systems. In order to obtain polyphenylene sulphide (PPS)-based composites with low CTE, a series of PPS-based composites containing different loadings of ceramic powders (including Zr₂WP₂O₁₂, BN, AlN, Al₂O₃) were fabricated by melt extrusion method using PPS with 40 wt% glass fibre (GF) as matrix material. The experimental results showed that the PPS composites with Zr₂WP₂O₁₂ (ZWP) as a filler had a lower CTE compared to the samples with other fillers at the same filler loading. The CTE of PPS/GF/ZWP steadily decreased with increasing ZWP addition. At 20 vol% ZWP loading, a 67% (about 18 ppm/°C) reduction of CTE compared to the PPS/GF was achieved. The addition of ZWP powder to PPS/GF also led to an improvement in the dielectric loss of the composite. When the ZWP content is 20 vol%, the dielectric loss of the composites is about 0.0035, which is 24.4% lower than PPS/GF. Hence, the PPS/GF/ZWP composites have great potential for applications in RF communication systems.     

Effect of ultra accurate control of electrolyte temperature on the performance of micro arc oxidation ceramic coatings

The technique of micro arc oxidation (MAO) uses arc discharge and high-voltage breakdown to produce a ceramic layer on valve metal surfaces. However, the common method of MAO requires immersing the workpiece in an electrolyte solution, which can result in elevated temperatures due to the arc discharge, thus negatively affecting the coating's quality and performance. This article investigates the influence of electrolyte temperature on the performance of MAO ceramic coatings, with the assistance of a robotic arm enabling valve metal reaction without immersion in the electrolyte, and precise control of electrolyte temperature through a MAO temperature monitoring system. Various techniques, such as scanning electron microscopy (SEM), hardness testing, electrochemical corrosion experiments, and friction-wear experiments, were utilized to characterize the performance of the prepared coating. The results indicate a nonlinear correlation between the temperature of the electrolyte and the thickness and hardness of the ceramic coating. The corrosion and wear resistance of the MAO ceramic coatings initially improve with increasing electrolyte temperature but eventually deteriorate. At an electrolyte temperature of 40 °C, the MAO ceramic coating exhibits the optimal corrosion and wear resistance. The variation in electrolyte temperature affects the reactivity of the electrolyte ions, leading to changes in the morphology and properties of the resulting MAO ceramic coating. These findings offer valuable insights into the interaction mechanism between electrolyte temperature and the properties of the resulting MAO ceramic coating. This is of great significance in optimizing the MAO process for specific applications and improving the overall performance of ceramic coatings.     

Hot corrosion behavior of multialkaline-earth aluminosilicate for environmental barrier coatings

Multialkaline-earth aluminosilicate Ba_1/3Sr_1/3Ca_1/3Al₂Si₂O₈ (BSCAS) were synthesized to serve as new environment barrier coatings. Their hot corrosion behavior in an Na₂SO₄ environment was studied in the temperature range of 900–1100 °C over a period of 100 h. The phase and cross-sectional morphology evolutions of the corroded samples were characterized via X-ray diffraction and scanning electron microscopy. Combined with the thermodynamic analysis of the possible reactions occurring during hot corrosion, the competitive out-diffusion of the alkaline-earth elements to react with Na₂SO₄ is believed to have a considerable influence on the hot corrosion behavior of BSCAS. The sluggish diffusion and the dense Ca₂Al₂SiO₇ layer, which originate from the competitive reactions of the multialkaline earth elements, lead to an improvement in the hot corrosion resistance of BSCAS. A model is proposed to describe the hot corrosion process.     

Effect of Sn concentration on the corrosion resistance of Pb-Sn alloys in H2SO4 solution

The effect of Sn concentration on the corrosion resistance of Pb-Sn alloy in H₂SO₄ electrolyte was investigated by potentiodynamic polarization. A new approach to calculate the exchange current density, i_corr, was proposed and proved to be in accordance with the experimental results. This study shows that with the increase of alloying Sn, the corrosion rate of the alloy increased and then decreased, with its minimum appearing at 2.60 wt.% Sn. It was also found that the cathodic reaction does not have to be a single-step process, i.e., there are multiple sub-steps involved and complex cations, including H₄³⁺ and H₂⁺, existing in the systems.     

A review on tailored blanks—Production,applications and evaluation

Tailored Blanks is the collective for semi-finished sheet products which are characterised by a local variation of the sheet thickness, sheet material, coating or material properties. With these adaptions the tailored blanks are optimised for a subsequent forming process or the final application. In principle four different approaches can be distinguished to realise tailored blanks: joining materials with different grade, thickness or coating by a welding process (tailor welded blanks), locally reinforcing the blank by adding a second blank (Patchwork blanks), creating a continuous variation of the sheet thickness via a rolling process (tailor rolled blanks) and adapting the material properties by a local heat treatment (tailor heat treated blanks). The major advantage of products made from tailored blanks in comparison to conventional products is a weight reduction. This paper covers the state of the art in scientific research concerning tailored blanks. The review presents the potentials of the technology and chances for further scientific investigations.     

Inverse problem-coupled heat transfer model for steel continuous casting

An integrated approach was proposed for determining the heat transfer coefficient, which combined inverse heat transfer calculation model with temperature measurement and pin-shooting experiment. Based on the roller-layout and spray nozzle distribution, the IHTP (inverse heat transfer problem) model was developed to calculate the secondary cooling heat transfer by means of non-linear estimate method. The method transformed the inverse problem of parameter identification into solution of optimization problem using evolutionary algorithm. With the help of temperature measurement and pin-shooting experiment, the whole procedure of the model solution for identification and application in continuous casting process was given. Simulation and experiment results in plant trial confirmed the efficiency of the method used.     

Mixed convection flow in an inclined enclosure under magnetic field with thermal radiation and heat generation

The influence of thermal radiation and heat generation on an unsteady two-dimensional natural convection flow in an inclined enclosure heated from one side and cooled from the adjacent side under the influence of a magnetic field using staggered grid finite-difference technique has been studied. The governing equations have been solved numerically for streamlines, isotherms, local Nusselt numbers and the average Nusselt number for various values of thermal radiation and heat generation parameters by considering three different inclination angles and magnetic field directions, keeping the aspect ratio fixed. The results indicate that the flow pattern and temperature fields are significantly dependent on the above mentioned parameters. It is found that magnetic field suppresses the convection flow and its direction influences the flow pattern which results in the appearance of inner loop and multiple eddies.     

PtFe and Fe3C nanoparticles encapsulated in Fe–N-doped carbon bowl toward the oxygen reduction reaction

The high-temperature calcination strategy facilitates the formation of alloy atoms but inevitably results in the aggregation and deactivation of the metal particles for the oxygen reduction reaction (ORR) electrocatalysts. Herein, we report the successful encapsulation of Platinum–Iron (PtFe) nanoparticles (∼4.7 nm) in the N-doped hollow carbon hemisphere matrix (NCB) containing Fe–N and Fe₃C without employing high-temperature pyrolysis, which effectively facilitates the well-dispersed Pt nanoparticles and the formation of PtFe nanoalloys. The hollow carbon hemisphere structure contributes to the expansion of the specific surface area and exposure of active sites of the catalyst, meanwhile, the modification of the surface of the carbon nano-bowl from a predominantly Fe to a functional electrocatalyst with a primarily PtFe alloy can boost the ORR catalytic activity and stability. It is found that the Pt3Fe/Fe₃C-NCB catalyst exhibits the optimum ORR performance with a mass activity (0.97 A mg⁻¹_Pt), 5.10 times higher than the commercial Pt/C (0.19 A mg⁻¹_Pt). Pt3Fe/Fe₃C-NCB also displays excellent durability in comparison to the commercial Pt/C after 20,000 potential cycles. Combined with the Physical characterization and the electrochemical test results, Fe₃C-NCB plays a strong metal-support role for the encapsulated PtFe nanoparticles structure, thereby preventing nanoparticle migration and corrosion. Experimental characterization and theoretical calculations show that the appropriate PtFe alloy composition and the strain effect induced by Fe–N/Fe₃C active sites are sufficient to accelerate the detachment of oxygenated species from the alloy surface, resulting in a catalyst with excellent ORR performance.     

A hydrogen-based technique for determining the number density of acoustic microreactors (actives bubbles) in sonicated solutions

In sonochemistry, acoustic bubbles are a population of microreactors where hydrogen and oxidants are produced. Optimizing the effectiveness of sonochemical processes and, as a result, designing ultrasonic reactors for diverse uses, including hydrogen generation, requires determining the number density of acoustic microreactors.The number density of micro-bubbles during water sonolysis was determined in this study using a novel semi-empirical method developed (for the first time) using hydrogen sono-production. The technique is based on relying on the overall molar production rate of hydrogen (i.e. resulted from the sonicated solution) to the amount of hydrogen produced per a single collapsing bubble, either from its internal gas phase reaction (pyrolysis) or from both the bubble inside and its liquid shell (via H^•+H^•→H₂). The retrieved number density of bubbles varied between ∼10⁸ to ∼10¹³ L⁻¹ s⁻¹ (depending on empirical conditions), showing an excellent order with that reported in the literature. As the frequency increased, the number of active bubbles increased, regardless of whether the number density is calculated through the amount of hydrogen formed inside the bubble or the total single-bubble yield (gas phase + liquid shell). However, a reduced number density was obtained as it was calculated via the total single-bubble yield, where this decrease goes up with the rise of ultrasound frequency (from 210 to 724 kHz) and the decrease of the liquid temperature. It has been deduced that hydrogen is mainly formed at the bubble's liquid shell (via H^•+H^•→H₂), particularly at higher frequency and cold liquid.