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Metallic fuels hold numerous advantages over conventional uranium dioxide fuels and are a key component of several liquid metal-cooled advanced reactor concepts including sodium fast reactors. These fuels undergo rapid swelling during early burnup; consequently, they spend most of their reactor lifetime in a porous state. The presence of this porosity alters many of the mechanical properties of the fuel including creep impacting fuel deformation during axial swelling. This work investigates the creep behavior of the porous fuel using a spark plasma sintering technique. Creep tests were performed for the first time on porous α-phase uranium and uranium with 10 wt. % zirconium (U-10Zr) samples. The samples of α-phase uranium and U-10Zr were fabricated from depleted uranium by spark plasma sintering and subjected to uniaxial compressive creep testing. Calculated stress exponents were found to be 2.6 ± 1.6 and 5.7 ± 1.4 for α-U and U-10Zr, respectively, and calculated activation energies were found to be 61.6 ± 1.1 kJ / mol for α-U. The creep data were also used to evaluate existing porosity inclusive in creep models. [ABSTRACT FROM AUTHOR]

Purpose: To compare the adaptation of single metal-ceramic crowns (MCCs) fabricated with three different methods: lost-wax metal casting (LMC), milling of hard cobalt-chromium (HCC) blanks, and milling of soft presintered cobalt-chromium (SCC) blanks. Materials and Methods: In this double-blind parallel randomized clinical trial, 60 single MCCs were fabricated using three different methods. Adaptation of the copings was evaluated radiographically, visually, and microscopically. Data were compared among the three groups using the Kruskal-Wallis test, followed by the Dunn post hoc test, one-way ANOVA, and paired t test (a = .05). Results: Radiographic data showed that the frequency of crowns with no marginal discrepancy was significantly higher in the SCC group than the LMC group. Evaluation of marginal adaptation with an explorer revealed that crowns with excellent marginal adaptation had lower frequency in the LMC group than the HCC and SCC groups. In the silicone replica technique, the recorded data revealed no significant difference. Application of porcelain veneering did not affect the adaptation of the copings. Conclusions: The SCC and HCC groups showed better clinical outcomes compared to the LMC group. However, all MCCs fabricated with the LMC method, milling of HCC blanks, and milling of SCC blanks had acceptable clinical adaptation. [ABSTRACT FROM AUTHOR]

Binders used in binder jetting often pose health and environmental risks during processing and post processing operations. The print-heads which are used to deposit binder selectively on the feedstock are prone to clogging, despite the trend of print-heads being highly customised to suit different kinds of binders. These factors often hide the advantages of binder jetting as an additive manufacturing process, especially its scalability and its faster printing rates in comparison to powder bed fusion methods. The work presented here takes a step back and focuses on the development of an aqueous, polyvinyl alcohol (PVA)-based liquid binder that is easy to manufacture and store, safe to handle, and can be reliably jetted to print parts. The feedstock considered was Inconel 718, a nickel-based super alloy which can be effectively processed by binder jetting without niobium segregation. PVA was added to the Inconel 718 powder in dry, granular form to manufacture a modified feedstock. The study also investigated the role of molecular weight of the PVA used, sintering environments and post-processing methods like hot isostatic pressing (HIP) on process responses like part densification, tensile strength, and hardness. Three different types of PVA were chosen which had molecular weights 10,000 g/mol (low molecular weight or LMW), 26,000 g/mol (medium molecular weight or MMW), and 84,000 g/mol (high molecular weight or HMW). The compatibility of the liquid, aqueous PVA-based binders with virgin Inconel 718 was examined by measuring the contact angle. The liquid, aqueous binder having MMW PVA reported better wetting with the Inconel 718 powder with a wetting angle of 26.6 which was lower than the wetting angle of 42.4°, seen in case of a commercial resin-based binder. The green strength reported by the MMW PVA liquid binder was 220 kPa which was higher than the other two PVA-based liquid binders. Green parts, upon successful printing, were sintered at 1260 °C. It was observed that a part printed using MMW PVA had a densification of 96.16% when sintered in 99.98% by volume argon gas, which increased to 98.96% after undergoing HIP. The same part reported a densification of 88.69% when sintered in a 95% by volume N2 and 5% by volume H2 gaseous environment, which was later attributed to the uptake of nitrogen by the chromium present in Inconel 718, which prevented necking between particles. Tensile specimens printed using MMW PVA, sintered in a 99.98% argon environment, showed the highest ultimate tensile strength of 220 MPa, which increased to 1010 MPa after the HIP process, which can be compared to commercially available Inconel 718. [ABSTRACT FROM AUTHOR]

The recycling of solid waste is widely regarded as the one of the most crucial issues of sustainability. This is particularly evident in the industrial sector, where the production of slags is huge and their handling presents a significant challenge. In this study, solid wastes from the industrial sector, namely ferrochrome slag (Fs) and fluorite tailings (Ft), were employed for the preparation of glass-ceramics by the sintering method. Three glasses were prepared by using the melt-quenching method, with a weight ratio of 60∼70 % Fs and 40∼30 % Ft (designated S30, S35, and S40, where the higher number indicates a greater Fs content). The sintering and crystallization behaviors of these glasses were characterized by hot-stage microscopy (HSM) and differential thermal analysis (DTA). It was observed that S40 glass exhibited a weak sintering capacity in comparison to that of S30 and S35 glass, which can be attributed to the robust crystallization propensity of S40 glass. The coarser glass frits were subjected to sintering experiments at varying temperatures, which demonstrates that the predominant crystalline phase is augite and that Cr 2 O 3 remains present in all sintered samples. Besides, a transition of the Cr 2 O 3 crystal into uvarovite was observed in S40 glass sintered at 1050 °C. The sintering time controlling experiment demonstrated that both wollastonite and the Ca-rich flow formed during sintering are vital for the formation of uvarovite. The formation of uvarovite can enhance the hardness of GCs. All GCs samples sintered at 1050 °C and 1120 °C exhibit comparable mechanical performance. [ABSTRACT FROM AUTHOR]

High Q·f value and temperature-stable MgF 2 -doped MgTi 1-x (Mn 1/3 Sb 2/3) x O 3 ceramics have been successfully prepared by the solid-state reaction method. Microwave dielectric properties and sintering performance of MgF 2 -doped MgTi 1-x (Mn 1/3 Sb 2/3) x O 3 ceramics were systematically investigated by the classic theory and the P-V-L theory. The results show that MgF 2 doping and complex cation (Mn 1/3 Sb 2/3)4+ substitution not only further reduces the sintering temperature of MgTiO 3 ceramics from 1400 °C to 1250 °C, but also effectively improves the quality factor from 110210 GHz to 228713 GHz and adjust the τf value from −53.55 ppm/°C to −20.42 ppm/°C. The ionicity, the bond valence and octahedral distortion confirmed that Ti/(Mn 1/3 Sb 2/3)-O bonds exert a greater influence on microwave dielectric properties than Mg-O bonds in MgTiO 3 ceramics, which provides a guide to further improve the microwave dielectric performances. The optimal microwave dielectric properties: ε r = 18.8 ± 0.28, Q·f = 228713 ± 2500 GHz (at 6.08 GHz), τ f = (−20.42 ± 1.1) ppm/°C were achieved for 3 wt% MgF 2 doped MgTi 0.99 (Mn 1/3 Sb 2/3) 0.01 O 3 ceramics sintered at 1250 °C. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics can generate electrical signals to promote bone defect repair, but they suffer from low bioreactivity. In this study, K 0.48 Na 0.52 NbO 3 & akermanite composite ceramic (KNN & AK) was prepared using digital light processing (DLP). The influence of sintering temperature and AK content was investigated. With the increase of sintering temperature, the piezoelectric coefficient d 33 of the composite ceramics first increased and then decreased, reaching a maximum of 7.80 pC/N at 1070 °C. The doping of AK would lead to a significant decrease in the piezoelectric property, and the AK content should not exceed 10 wt% to achieve the piezoelectric coefficient of human bone. After immersion in Tris-HCl solution for 28 days, the weight loss rate of the composite ceramics doped with 15 wt% AK could reach 8.36 %. The combination of KNN and AK promotes the application of piezoelectric bone scaffolds in the field of bone repair. [ABSTRACT FROM AUTHOR]

NbC-Ni cermets have emerged as promising alternatives to the conventional WC-Co due to their superior hot hardness and fracture toughness. However, the recent increase in Ni and Co prices necessitates substituting these binders with economical alternatives for cermet formulations. The Fe-Ni binary alloy shows promise as a binder due to its superior mechanical properties, low cost, and reduced toxicity compared to Co and Ni. This study demonstrated the potential of Fe-Ni as a promising binder material for NbC cermets, offering a balance between cost-effectiveness and properties suitable for various high-performance applications. The NbC-Fe-Ni cermets were fabricated via vacuum Liquid Phase Sintering (LPS) at 1440 °C for 1h and compared to NbC-Ni cermets. Microstructural analysis (SEM + EDX) revealed a continuous decrease in D90 values up to NbC-35Ni-65Fe (65 wt% Fe), indicating that Fe-Ni effectively suppressed grain growth; additionally, it increased the contiguity of NbC grains. Vickers hardness tests revealed that the hardness of the cermets increased with higher Fe content in the binder, reaching a peak value of 1487 ± 15 HV 30 for NbC-35Ni-65Fe, marking a remarkable 34 % improvement over NbC-Ni. However, fracture toughness decreased marginally due to the increased contiguity of NbC grains, which reduced crack inhibition. Nanoindentation hardness tests of the binder phase revealed that partial substitution of Ni with Fe enhanced binder hardness, contributing to the overall improvement in NbC-Fe-Ni cermets' hardness values. A 3-point bend test demonstrated a maximum strength of 649 ± 16 MPa for NbC-35Ni-65Fe cermet, indicating a 19 % improvement over NbC-Ni cermet. These findings highlight Fe-Ni's potential as a cost-effective binder for NbC cermets, suitable for high-performance applications. [ABSTRACT FROM AUTHOR]

Structural damage and shrinkage cracking were exhibited during the pyrolysis of ceramic aerogels prepared by the polymer-derived ceramics (PDCs) route. Herein, the shrinkage of the ceramic precursor during the pyrolysis was offset by utilizing curled molecular chains to store strain in advance. Microspheres composed of curled molecular chains were prepared using polysilazane (PSZ) as a precursor. The microspheres were linked into a three-dimensional skeleton and further fabricated into precursor ceramic microspheres aerogel (PSZ/MCMSA) with shrinkage resistance. The morphology, thermal insulation, and shrinkage resistance properties of the material were tested. The results indicated that PSZ/MCMSA exhibited outstanding thermal insulation and shrinkage resistance properties. The shrinkage of the precursor ceramic microspheres (PSZ/MCMS) was offset by the strain stored through the curled PSZ molecular chains in the PSZ/MCMS. In addition, the microsphere skeleton structural supporting and gas escape channels were formed during the sintering, and the shrinkage resistance of the precursor ceramic aerogel was further enhanced. [ABSTRACT FROM AUTHOR]

Thanks to their exceptional thermal and electrical properties, borosilicate glasses are widely used in chip packaging and electronic pastes. Nonetheless, borosilicate glass powders suffer from the phenomenon of foaming and expansion during sintering process, which greatly affects the sintering densities of the powders and poses limitations to their applications. Herein, we explored the foaming mechanism of borosilicate glasses by ball milling. The foaming of borosilicate glass is due to the adsorption of CO 2 from the atmosphere by the glass powder during ball milling. The CO 2 forms carbonates on the surface of the glass powder and is released during the sintering process, leading to foaming. Additionally, as the specific surface area of the glass powder increases, its corrosion resistance decreases while its foaming strength increases. The foaming strength of the four glass powders, listed in ascending order, is: SrO-B 2 O 3 -SiO 2, ZnO-B 2 O 3 -SiO 2 , BaO-B 2 O 3 -SiO 2 and CaO-B 2 O 3 -SiO 2. Meanwhile, it was found that the foaming strength could be weakened better by ball milling organic modification method. These findings contribute to a deeper understanding of the glass foaming phenomenon. Furthermore, they offer practical strategies to reduce the foaming and optimize the performance of borosilicate glass-based materials in applications of chip packaging and electronic pastes. [ABSTRACT FROM AUTHOR]

Chevrel phase (CP) compounds are a highly multifunctional class of materials but are underused due to the high energy processing required for their synthesis. Self-propagation high-temperature synthesis (SHS) is a low energy and quick alternative for synthesizing this material system. In this investigation, copper-based CPs were synthesized via SHS using either elemental or binary precursor powders. The elemental precursors produced non-stoichiometric Cu 2.76 Mo 6 S 8 , and consisted mainly of grown MoS 2 platelets. The binary precursor, on the other hand, produced stoichiometric Cu 2 Mo 6 S 8. The influences of mixing and precursor concentration are discussed as well as the reaction mechanisms operating for the elemental system and the binary system, separately. The investigation into this synthesis process aims to provide a better understanding of the Chevrel SHS mechanism to accurately control the product. [ABSTRACT FROM AUTHOR]

Magnetic nanocomposite was prepared using the wet chemical precipitation approach with varying amounts of cobaltous oxide (CoO). The concentrations of CoO were 0.5, 3.5, 6.5, and 9.5 g per 100 % wollastonite composition. Samples were sintered separately at 1000 and 1200 °C. X-ray diffraction analysis (XRD) of the sintered parent sample revealed the formation of wollastonite CaSiO 3 and larnite Ca 2 SiO 4 , as well as a minor silicon oxide SiO 2 phase. In CoO-doped samples, Co-åkermanite Ca 2 CoSi 2 O 7 and other phases were formed. The XRD and scanning electron microscope SEM confirm the samples' submicron and nanocrystalline microstructure. The Fourier transform infrared spectroscopy (FTIR) and Raman spectra (RS) of investigated samples sintered at 1000 and 1200 °C revealed their bond structure. Both analyses confirmed that incorporating CoO into CaSiO 3 significantly improved its vibrational modes, reflecting structural modifications. By increasing the cobalt oxide content from 3.5 to 9.5 wt%, the samples attain the ideal paramagnetic state, as demonstrated by the magnetic hysteresis (M − H) curve, which is linearly reversible. Formation of the Ca 2 CoSi 2 O 7 significantly alters the magnetic characteristics of the samples, whether through increasing the cobalt oxide concentration up to 9.5 wt% or modifying the sintering temperature. This enables the prepared nonocomposites to be suitable for novel magnetic applications. [ABSTRACT FROM AUTHOR]

We report new class of natural nacre-like alumina toughened by zirconia fabricated by the simple two-step approach of unidirectional freeze-casting and spark plasma sintering. The biomimetic alumina-zirconia with a relative density of more than 98 % was achieved by consolidating at temperature of 1300–1425 °C with 50 MPa pressure. The resultant microstructure consists of two levels of structural hierarchy, i.e. level-1: bulk lamellar brick phase (alumina platelets) and level-2: mortar phase (yttria stabilized tetragonal zirconia polycrystals). The increase in volume fraction of zirconia (in tetragonal form) from 0 to 15 vol% was effective in progressively reducing the size of alumina platelets from 12 to 9 μm, and significantly improved the flexural strength of the composite by 60 % (from 172 to 270 MPa). By optimizing the hierarchical architecture from micro to macroscopic level, the structural performance of our synthetic nacre, where strength and toughness of 270 MPa and 13.5 MPa √ m respectively are superior to that of natural nacre and many other engineering materials (illustrated in the form of Ashby map). The exceptional damage resistance is rationalized by both intrinsic (stress induced tetragonal to monoclinic phase transformation of zirconia) and extrinsic (crack deflection, crack branching and bridging, multiple cracking, platelets interlocking) toughening mechanisms. For 15 vol% ZrO 2 composition, the contribution of intrinsic and extrinsic toughness was quantitatively evaluated as 0.9 ± 0.03 and 4.3 ± 0.07 MPa√m respectively (with experimentally measured toughness at crack initiation as 5.2 ± 0.2 MPa√m). [ABSTRACT FROM AUTHOR]

Ceramics or refractories prepared in the Al 2 O 3 -rich corner of the Al 2 O 3 -MgO-CaO system show excellent high-temperature mechanical properties and chemical stability because of the presence of spinel (MgAl 2 O 4) and calcium hexaluminate (CaAl 12 O 19). However, the densification of these two crystals usually requires high firing temperatures due to their poor sinterability. To address this issue, La 2 O 3 -doped MgAl 2 O 4 -CaAl 4 O 7 -CaAl 12 O 19 refractory composites were designed, and the influence of the doping level on the densification, microstructure, and mechanical properties of the composite was investigated. It was found that the doped La3+ was predominantly dissolved in the CA 6 grains by replacing Ca2+, forming uniform solid solutions regardless of doping concentration. This reaction significantly accelerates ion diffusion and CA 2 grain growth. Besides, it reduces the aspect ratio of CA 6 crystals, weakening the negative effect of the elongated grains on mass transfer and sintering. As a result, the relative density increases from 79.5 % to 95.1 % after sintering at 1600 °C with doping only 0.5 wt% La 2 O 3 into the composite, producing a uniform and dense microstructure with regular angular grains. The above effects result in a significant improvement in flexural strength and fracture toughness (increasing by 61 % and 57 %, respectively). Moreover, the La 2 O 3 -doped refractory composite achieves a decline of the high-temperature creep rate by one order of magnitude at 1600 °C. [ABSTRACT FROM AUTHOR]

The co-sintering behavior of a ceramic-metal bilayer is carefully investigated. This bilayer is composed of a gold film deposited by screen-printing on a silica-based low-temperature cofired ceramic (LTCC) layer. First, behaviors of both materials in free sintering are finely characterized. LTCC exhibits a viscous flow sintering mechanism, whereas the densification mechanism of gold is controlled by grain boundary diffusion (with an identified apparent activation energy of 101 ± 15 kJ mol−1). Free sintering of gold is also marked by a two-step densification process due to its large bimodal particle size distribution. A methodology is proposed to estimate gold viscosity at high temperatures directly from raw experimental data in free sintering, without performing dedicated mechanical characterizations. Based on the constitutive laws identified for LTCC and gold materials, analytical and numerical models of the bilayer co-sintering process are built. During co-sintering, stresses generated by densification kinetic mismatch between gold and LTCC are progressively relaxed by camber phenomenon. Calculated evolutions of camber in co-sintering are compared to curvature monitoring by ombroscopy. Finite element simulation in 3D fits well with the experimental data, whereas the analytical solution strongly underestimates camber rates. This shows that the simplified numerical approach suggested here leads to a robust numerical model, faithfully describing thermomechanical interactions occurring in co-sintering within the ceramic-metal bilayer. [ABSTRACT FROM AUTHOR]

Secondary aluminum dross (SAD), a hazardous solid waste derived from the metal aluminum (Al) smelting process, contains 65−90 % aluminide and over 30 different impurity elements, thus being an alternative material for alumina ceramic production to replace traditional sources such as bauxite or industrial alumina powder. The presence of inherent impurities would seriously deteriorate the mechanical properties of ceramics prepared from SAD. This study proposed an innovative process involving grinding-alkali leaching-CO 2 -assisted in-situ precipitation of nano-alumina to effectively eliminate the influence of impurities on the ceramic mechanical properties. Grinding greatly reduced the median particle size from 67.4 to 3.17 μm, improving the particle structure and specific surface area. The active aluminum components were transferred from the interior of SAD particles to the surface to form nano-alumina by alkaline leaching and in-situ precipitation. The nano-alumina layer could completely coat the ground SAD particles. As a result, these impurities in SAD would not form the connected liquid phase but instead form isolated liquid phase points inside the particles during the high-temperature firing process. The sintering mechanism of ceramics changes from liquid phase sintering to solid phase sintering. The fracture mechanism of ceramics changes from intergranular fracture to transcrystalline fracture, and the mechanical properties of ceramics are greatly improved. Alumina ceramics sintered at 1500 °C showed the density, porosity, hardness and flexural strength of 3.42 g/cm3, 3.7 %, 1457 Hv, and 235 MPa, respectively. This process eliminates the negative effects of 21.54 % impurities in SAD and produces alumina ceramics that meet the 90 Al 2 O 3 ceramic standard. [Display omitted] • A process to prepare ceramics from SAD using in-situ nano-alumina precipitation. • Effect of impurities on mechanical properties of ceramics was eliminated. • The nano-alumina coating changes liquid phase sintering to solid phase sintering. • Alumina ceramic prepared from SAD met the 90 Al 2 O 3 ceramic standard. [ABSTRACT FROM AUTHOR]

The synthesis of forsterite can be challenging because the initial oxides react slowly and undesirable compounds like enstatite (MgSiO 3) can form instead of forsterite (Mg 2 SiO 4). Although several methods have been developed to overcome these challenges, the synthesis of forsterite using the solid-state reaction of nanopowders has not been investigated. This study aims to explore the possibility of producing forsterite by reacting MgO and SiO 2 nano-powder. The initial oxides were wet ball milled, dried, and reaction sintered. Spectroscopy and microscopy methods were used to analyze the formed phases and study the formation kinetics. The density, coefficient of thermal expansion (CTE), and hardness of sintered samples were measured using a densimeter, a dilatometer, and a hardness tester, respectively. The results demonstrated that it is possible to synthesize forsterite by solid state reaction of pure MgO and SiO 2 nano-powders. The reaction between the two compounds begins at a temperature as low as 860 °C and leads to the formation of forsterite by a two-step formation mechanism. The first reaction involves the reaction of MgO and SiO 2 to form enstatite, and the second one produces forsterite as a result of enstatite reacting further with MgO. The activation energy values ranged from 1028.89 to 1105.655 kJ/mol for the formation of forsterite, and from 456.316 to 488.08 kJ/mol for the formation of enstatite. Monolithic forsterite was completely formed at a low temperature of 1200 °C for a relatively short duration of 2 h. The sample sintered at 1400 °C for 2 h, had a density of 2.96 g/cm3, a Vickers hardness of 7.64 GPa, and a coefficient of thermal expansion of 10.24 × 10−6/K measured in the temperature range of 200–1300 °C. [ABSTRACT FROM AUTHOR]

The necessity for efficient heat dissipation compels AlN packaging materials towards a thinner profile. In response to the ensuing concerns regarding the reliability of strength, the effects of the grain edge phases and grain size on flexural strength are investigated in this study. Different preparation processes, including (hot-pressed sintering, pressureless sintering, and annealing) are employed to prepare AlN ceramics with different grain edge phases and grain sizes. After classifying the morphology of the grain edge phases and fitting the Hall-Petch relationship, it is found that the grain edge phases had a more significant influence on the flexural strength. Depending on the morphology, the negative effects can be divided into three degrees. While the finer grain size proves advantageous for the flexural strength. Consequently, in the non-additive system, the flexural strength of AlN ceramic is 422 MPa, with an average grain size of 8.47 μm. For the additive-doped system, the maximum flexural strength can reach 532 MPa, which can be attributed to the limited average grain size resulting from the hot-pressed sintering process, approximately 1.32 μm. These results could potentially be employed in the microstructural design of high-strength AlN ceramics. [ABSTRACT FROM AUTHOR]

The rapid preparation of high-performance microwave dielectric ceramics has always been a technical challenge in the field of electronic ceramics. In this investigation, we rapidly fabricate MgTiO 3 –CaTiO 3 microwave ceramics with homogenous microstructure and high quality factor Q by microwave-assisted sintering, highlighting the efficiency gains and sintering time reductions. As the sintering time increases from 15 min to 45 min, the bulk density and relative density of MT-CT ceramic rapidly increase. The relative density of samples sintered for 30 min exceeds 97 %, which is difficult to achieve through conventional sintering methods. Combined with Rietveld refinement and Raman spectra, it is confirmed that the cell volume of MT-CT ceramics shrinks with the extension of sintering time, resulting in the weaken of Ti–O bond strength. More refined grain size distribution and uniform microstructure obtained by microwave-assisted sintering are likely to be pivotal factors in enhancing the microwave dielectric properties of MT-CT ceramics. MT-CT ceramics sintered at 1300 °C for only 45 min by microwave-assisted sintering exhibit excellent dielectric properties: Q×f = 87, 300 GHz, ε r = 20.42, and τ f = 2.11 ppm/°C, thereby demonstrating the potential of achieving rapid densification of microwave ceramics through microwave-assisted sintering. [ABSTRACT FROM AUTHOR]

Aiming to further improve the properties of novel MgAl 2 O 4 -Si 3 N 4 ceramic used as solar thermal absorbing material in concentrating solar power, effects of Sm 2 O 3 and TiO 2 on performance of the composites were investigated especially the mechanisms of different additives on microstructure and high temperature stability. The results show that both additives can accelerate sintering, reduce sintering temperature, improve the density and high temperature stability via liquid phase sintering mechanism. Besides, TiO 2 can form displacement solid solution with Al 2 O 3 to promote the sintering process. Sm 2 O 3 is more conducive to improving the bending strength due to its function of increasing the length diameter ratio of β-Si 3 N 4. TiO 2 is more favorable for improving solar absorption owing to the distinctive absorption spectrum and large number of cation vacancy caused by substitution of Al3+ by Ti4+. MgAl 2 O 4 -Si 3 N 4 composites with Sm 2 O 3 and TiO 2 additives have better performance than MgAl 2 O 4 -Si 3 N 4 , Si 3 N 4 and SiC ceramics prepared via the same procedure, which makes it a certain choice for solar thermal absorbing material. [ABSTRACT FROM AUTHOR]

Densification behavior, grain growth kinetics, mechanical and thermal properties of pressurelessly sintered zirconium diboride–silicon carbide (ZrB2–SiC) fabricated by extrusion of high solids loading pastes have been studied. The effects of sintering temperature (1600–2300°C), heating rate during constant heating rate sintering (10–50°C/min), and time during isothermal sintering (3–24 h) on density and grain size were examined. The apparent activation energy for densification was determined to be 940 ± 90 kJ/mol, suggesting lattice diffusion as the dominant sintering mechanism. Grain growth of both ZrB2 and SiC followed a normal grain growth power law with grain growth exponent n = 2 indicating diffusion‐controlled coarsening. The activation energies for grain growth were 267 ± 10 kJ/mol for ZrB2 and 264 ± 15 kJ/mol for SiC. Sintered microstructures were homogeneous with relative densities of 95%–99% depending on heat treatment schedules. Flexural strength (270 ± 40 MPa) was lower than hot‐pressed materials of equivalent composition by a factor of two or more due to the presence of pores originating from paste inhomogeneities. Young's modulus (482 ± 20 GPa) and Vicker's microhardness (22 ± 5 MPa HV0.2), as well as thermal diffusivity and thermal conductivity up to 1800°C were found to be comparable to hot‐pressed materials. [ABSTRACT FROM AUTHOR]

Binder jetting (BJ) additive manufacturing of zirconia (ZrO 2) ceramics presently encounters the challenges of achieving high relative density, dimensional precision, and superior mechanical properties of the prepared ceramics. This study extensively investigates the impacts of BJ processing parameters—namely, binder saturation, layer thickness, roller speed, and printing layout—on the dimensional accuracy, density, and mechanical strength of the resulting green parts. The identification of optimal BJ processing parameters is pivotal in the fabrication of ZrO 2 ceramic green bodies with superior dimensional precision and mechanical strength. The study shows that while solid-phase sintering alone can result in a relative density of 50.99%–54.27 % for BJ-processed ZrO 2 ceramics, glass infiltration after sintering substantially elevates the relative density and flexural strength. Specifically, infiltration at an optimal temperature of 800 °C increases the relative density of the sintered ceramic to 94.49 % and flexural strength to 76.48 ± 3.25 MPa, which represent a significant improvement of 40.22 % in density and a 35-fold increase in strength of the sintered ZrO 2 ceramics, respectively. These findings underscore the potential of BJ printing and subsequent glass infiltration as a synergistic approach to achieve high-performance ZrO 2 ceramics through additive manufacturing. [ABSTRACT FROM AUTHOR]

The present research focuses on the electrical properties of lead-free piezoceramics (0.985- x)(K 0.485 Na 0.485 Li 0.03)(Nb 0.96 Sb 0.04)O 3 -0.015(Bi 0.5 Na 0.5)ZrO 3 - x SnO 2 (KNNLS-BNZ- x SnO 2 , x = 0.003, 0.006, 0.009, 0.012, and 0.015). This study examines the influence of varying SnO 2 doping levels on the microstructure and piezoelectric properties of the ceramics. All the ceramics prepared demonstrate pure perovskite structure without any secondary phases. The Rietveld refinement analysis of XRD data reveals the existence of multiphase evolution around room temperature. The tetragonality (c/a) and cell volume of the ceramics tend to rise with an increase in Sn4+ content, potentially leading to improved ferroelectric characteristics. The optimum values obtained were Curie temperature (T c) = 395 oC, remnant polarization (P r) = 21.07 μC/cm2, piezoelectric coefficient (d 33)=357 pC/N, piezoelectric voltage constant (g 33) = 24 × 10−3 Vm/N, and figure of merit (FOM off) = 10.34 pm2/N, corresponding to the ceramic doped with x = 0.012 SnO 2. The findings indicate that an optimal amount of Sn4+ in the host composition KNNLS-BNZ improves piezoelectric properties by constructing an R-O-T phase boundary near room temperature. This study suggests that the ceramic with x = 0.012 SnO 2 exhibits a favorably high T c coupled with an exceptional energy harvesting capability, making it a suitable candidate for energy harvesting applications. [ABSTRACT FROM AUTHOR]

Sintering deformation is a great hindrance to the development of ceramic components with complex shapes. In this work, single-face coating method has been used to prepare the special shaped Al 2 O 3 components by taking advantage of the difference in shrinkage between substrate and coating. By adjusting the content of SiO 2 in the coating material which consisted of SiO 2 and Al 2 O 3 powder, the sintering deformation of Al 2 O 3 ceramics coated with the above material would be controlled during the sintering process. The sintering behavior of Al 2 O 3 green body with and without single-face coating were studied through visual in-situ tests combined with photographing technology. By comparing the images of specimens under different sintering temperatures (defined this method as the image relative method), the warped deformation and the shrinkage behavior of the above specimens were discussed. Moreover, the relationship between curvature radius and shrinkage rate was deduced. Results indicate that, due to the discrepancy in shrinkage of substrate and coating, the deformation of samples occurred in the heating process. And the shrinkage, the elasticity modulus and the ratio of the sectional coating area to substrate area play a major role in determining the shape of ceramics. The way to fabricate the shape controlled ceramic components by the gradient shrinkage is a novel and effective method, which can be used for the plate and shell products with complex shapes. [ABSTRACT FROM AUTHOR]

Calcium hexaaluminate (CaAl 12 O 19 , CA 6) has great potential for application in high-temperature industries. However, owing to its intrinsic hexagonal lamellar crystal structure, it is difficult to obtain calcium hexaaluminate materials with high densification. In this study, using a two-stage sintering method and TiO 2 sintering aid, the densification of calcium hexaaluminate materials (relative density >95 %) was achieved. The evolution behaviors of the phase composition and microstructure and the intrinsic sintering kinetics were investigated in detail. The results showed that the addition of TiO 2 promoted the formation of CA 6 grains with a more homogeneous morphology and an increased-density equiaxial morphology. The elevation of the sintering temperature the sintering temperature also facilitated the densification of CA 6 , as the growth rate of the CA 6 grains along the C-axis raised significantly with the sintering temperature. When 1 wt% of TiO 2 was added and the sintering temperature was 1750 °C, a CA 6 material with a bulk density of 3.61 g/cm3 (relative density over 95 %) could be fabricated. [ABSTRACT FROM AUTHOR]

In this study, the feasibility of preparing quinary equimolar high-entropy oxides within the Co–Cu–Fe–Mg–Mn–Ni–O system was explored using the reactive flash sintering (RFS) technique. Various compositions were tested using this technique under atmosphere pressure, leading to the formation of two primary phases: rock-salt and spinel. Conversely, a new high-entropy oxide was produced as a single-phase material with the composition (Co 0.2 ,Cu 0.2 ,Mg 0.2 ,Mn 0.2 ,Ni 0.2)O when RFS experiments were conducted in nitrogen atmosphere. The reducing conditions achieved in nitrogen enabled the incorporation of cations with oxidation states different from +2 into the rock-salt lattice, emphasizing the critical role of the processing atmosphere, whether inert or oxidizing, in the formation of high-entropy oxides. The electrical characterization of this material was obtained via impedance spectroscopy, exhibiting a homogeneous response attributed to electronic conduction with a temperature dependence characteristic of disordered systems. [ABSTRACT FROM AUTHOR]

Production techniques used in processing alloy and composite materials have the propensity of improving their properties or deteriorating them. Therefore, appropriate choice of processing routes is a prerequisite for the development of top-notch high entropy alloys (HEAs). The types and forms of phase(s) developed in HEAs are also influenced by the processing technique. Incidentally, their properties are influenced by the phases present. So, the aim of this study was to investigate the characteristics of phases present in HEAs, and how they affect their properties and applications. More so, to investigate the processing techniques used in the development of HEAs and their influence on their properties and applications. The resource materials were sourced from Scopus database and google scholar website of articles published in the last ten years, laying more emphasis on the most recently published works. In the study, it was discovered that formation of the phases was dependent on: was dependent on: the type of the production process, present elements and the employed processing parameters. Hence, it was concluded that optimization of processing parameters and careful selection of elements are the key factors to develop HEAs of reputable properties. [ABSTRACT FROM AUTHOR]

Perovskite-type proton conductors exist in two structural forms, ABO3 and A 2 B ′ B ″ O 6 . In this study, novel A-site double-perovskite proton conductors ( A ′ A ″ B 2 O 6 ) were proposed. Na1+xLa1-xZr2O6-δ (x = 0, 0.1, 0.2) perovskites were prepared by a solid-state reaction at 1200 °C. However, raising the sintering temperature to 1300 °C resulted in the Na to volatilize, converting the Na1.1La0.9Zr2O6-δ into La0.9Zr2O6-δ. The conductivities of these materials in a humid atmosphere were tested using electrochemical impedance spectroscopy, and their carrier transport numbers were measured using the defect equilibria model and concentration cell method. Na1.1La0.9Zr2O6-δ and Na1.2La0.8Zr2O6-δ are predominantly proton conductors, with Na1.1La0.9Zr2O6-δ exhibiting the highest proton transport number of 0.52 at 800 °C. In contrast, NaLaZr2O6 is predominantly an electronic conductor, while La0.9Zr2O6-δ functions as an oxide ion conductor. Due to their high protonic transport numbers, these Na1+xLa1-xZr2O6-δ A-site double-perovskite oxides present a promising avenue for the development of proton conductors. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the possibility of using mechanical spectroscopy to determine the strength of tool coatings from their lifespan. Mechanical spectroscopy with the determination of the index tan δ (internal friction) was used as the research method. Samples were coated with lamellae composed of WC-6wt% Co cemented carbides. The specimens measured 1.0 mm, 3.0 mm, and 40.0 mm, created using a conventional industrial liquid phase sintering procedure. The original powder consisted of cobalt with traces of chromium and vanadium, and submicron WC grains. The tools tested included carbide cutting tools, and the workpieces were steel alloys. Comparative results showed that coated tools had significantly improved tool life and durability. The relationship between the coating and tool life was evident, providing a practical approach for predictive and non-destructive analyses of coatings on tool durability for composite and finely structured materials. [ABSTRACT FROM AUTHOR]

The aim of this work is to fabricate a low‐cost ceramic microfiltration (MF) membrane made from a new geomaterial named peridotite. The membrane was prepared by uniaxial pressing and followed by sintering. The effect of sintering temperature, in the range of 1100–1225°C, on the permeability, porosity, mechanical strength, and pore size was investigated. The optimized MF membrane sintered at 1200°C exhibits 1198.9 L h−1 m−2 bar−1 of permeability, 36.41% of porosity, 12.9 MPa of mechanical strength, and 1.56 µm of pore size. The prepared membrane was used for the MF treatment of dairy wastewater. It was found that the membrane is able to remove 88.56% and 69.54% of turbidity and chemical oxygen demand, respectively. Furthermore, the cost of the peridotite membrane was estimated to be $10.3 m−2. [ABSTRACT FROM AUTHOR]

This study evaluates Algerian kaolin (Djebel Debbagh (DD1) and Tamazart (KT2)) as potential substitutes for commercial kaolin (Lab) in the production of mullite‐based ceramics. Three compositions were prepared by incorporating the appropriate percentage of alumina to each calcined kaolin to achieve stoichiometric mullite precursors. The phase evolution of individual kaolin powders, as well as their mixtures with alumina, depends strongly on the calcination temperature and kaolin impurities. The differential scanning calorimetry combined with thermogravimetric analysis (TGA) showed lower secondary mullite formation temperature for the KT2‐based mixture. However, X‐ray diffraction revealed a complete mullitization in DD1 mixture. The K2O hindered cristobalite formation and reduced secondary mullite formation rate. Microstructure analysis showed lath‐shaped primary mullite and equi‐axed secondary mullite particles. After sintering at 1600°C, The KT2‐based sample (M3) exhibited higher density (3.013 g/cm3) and hardness (9.9 GPa), whereas the DD2‐based sample (M2) showed moderate densification (2.91 g/cm3) and higher flexural strength (159.42 MPa). Impurities (mainly Fe2O3, and K2O) promoted liquid phase sintering, resulting in greater densification in M3, whereas M2 showed more homogeneous microstructure, refined grains, and lower glassy phase content, contributing to enhanced strength. [ABSTRACT FROM AUTHOR]

In this work, high-purity alumina ceramics were prepared by using two-step reverse polarity flash sintering (PR-FS). The effects of the time distribution between the first flash and the second flash on microstructure and hardness were studied. The results show that compared to the conventional DC flash sintered alumina, the RP–FS–ed samples exhibited more uniform-microstructure, finer grains, higher relative density, and higher hardness. The underlying mechanism for such more homogeneous microstructure was related to uniform distribution of point defects under effect of reverse polarity. Two-step reverse polarity flash sintering method offers a great potential in obtaining highly densified alumina ceramics with homogeneous microstructure. [ABSTRACT FROM AUTHOR]

In this study, a neutron and γ-ray absorbing (Gd 2 O 3 +W)/Al composite was fabricated by vacuum sintering. Firstly, through Monte Carlo Neutron and Photo Transport Code (MCNP) calculations, the content of Gd 2 O 3 and W in the composite was determined to be 10 wt% and 25 wt%, respectively. Then, the influence of sintering temperature and sintering time on the microstructure, density, compression properties and electrochemical corrosion behavior of the (Gd 2 O 3 +W)/Al composites were investigated. The results indicate that sintering temperatures below 600 °C and sintering times shorter than 2 h led to insufficient density of the composite. Conversely, sintering temperatures above 600 °C and sintering times longer than 2 h caused W to agglomerate, resulting in a decrease in the density of the composite and a deterioration of its electrochemical performance. Therefore, the optimal sintering temperature and sintering time for the (Gd 2 O 3 +W)/Al composites were determined to be 600 °C and 2 h, respectively. Finally, the immersion corrosion performance in H 3 BO 3 solution of the composite fabricated by the optimal process parameters was studied in detail. It was found that pitting was the main corrosion form of the (Gd 2 O 3 +W)/Al composite, and an oxidation film mainly composed of Al 2 O 3 was formed on the surface. [ABSTRACT FROM AUTHOR]

Spark plasma sintering (SPS) is a promising method for producing titanium components from powder but a limitation is that high sintering temperatures (>900 °C) are normally required to eliminate porosity. Herein, the SPS of commercially pure titanium powder is reported using both cyclic and constant uniaxial pressure and compare densification, microstructure, and mechanical behavior. The following parameters are varied: sintering temperature, TS, 400 to 900 °C; cyclic and constant pressures, 100 to 500 MPa; with and without an isothermal dwell of 60 min at TS. The mechanical behavior is determined by bend and tensile testing. It is demonstrated that the application of cyclic pressure (cyclic‐SPS) gives superior densification over the range of parameters investigated compared with a constant pressure. Bend testing reveals improved ductility after cyclic‐SPS compared with a constant pressure. The dwell at TS further improves mechanical properties, giving excellent tensile ductility and strength. Consequently, at the ultralow temperature of 500 °C, nearly fully dense, ductile, titanium is achieved. It is shown that cyclic pressure enhances the degree of powder compaction at room temperature, and mechanisms are proposed to rationalize the effect of cyclic‐SPS on enhancing the rates of densification and sintering as the temperature increases during processing. [ABSTRACT FROM AUTHOR]

The article presents the results of the study of radiotransparent celsian ceramics, in which part of the components were introduced using eutectic glass of the pseudoternary BaO– AI2O3-SiO2 system. The bonding of the components of the experimental glass into the celsian phase was realized according to the principle of reactive structure formation by adding the missing components (crystalline fillers). In this case, the obtained dense sintered water-resistant ceramic, the only crystalline phase in the composition of which is the monoclinic form of celsian, which forms a microhomogeneous structural matrix of the material. Celsian is represented by distinct prismatic crystals of tetragonal and hexagonal shape. The size of celsian crystals increases from 3–5 µm to 7–10 µm with increasing the content of eutectic glass. The developed celsian ceramic has a set of enhanced physical and thermal properties: zero water absorption and open porosity, mechanical compressive strength (up to 157 MPa), refractory index is 1540–15800C. Celsian ceramic is characterized by a coefficient of linear thermal expansion of 3410–7 0C–1, which provides a sufficiently high thermal shock resistance of 700 0C. In terms of the level of relative dielectric permittivity (5.5) and dielectric losses (0.0005) at a frequency of 1010 Hz, the developed ceramic meets the requirements for ultra-high-frequency radiotransparent materials for aviation and rocket technology, which operate under conditions of high-speed high-temperature heating. [ABSTRACT FROM AUTHOR]

This study investigated the impact and non-impact of tuned energy density (ED) on sinterability and other physicochemical characteristics of a sintered 3D-printed material tableting structure. The selected SLS 3D printer enables the alteration of direct ED values, which aids in analyzing the impact and non-impact of the overall process parameters, including hatch spacing (HS), laser scanning speed (LSS), layer thickness (LT), and laser power (LP). The progressively enhanced ED from 200 J/cm3 to 350 J/cm3 and 500 J/cm3 was impacted by the increased weight, hardness, and amorphization of the rifampicin (RIF) in the sintered 3D-printed material tableting structure. In the case of the surface morphology of sintered 3D-printed material tableting structure, inter-particle spaces were reduced, which increased neck formation and ultimately, increased consolidation. An increase in the ED decreased the average surface roughness of the sintered 3D-printed material tableting structure. The in vitro release of RIF diminished over 12 h as the ED progressively increased from 200 J/cm3 to 350 J/cm3 and 500 J/cm3. In addition, tuning the progressively enhanced ED had no impact on the printing yield, average thickness of the sintered layers, or thermal analysis of the 3D printed material tablet structures. The ultimate finding of this study is that it is necessary to optimize the ED and other sintering parameters according to the desired features of the sintered 3D printed material tableting structure. In addition, the utilization of SLS and incorporation of the co-processed polymer Eudragit L 100–55 in the printing process resulted in the release of RIF above physiological pH-5.5. This strategy effectively reduces the degradation of RIF under acidic conditions. Subsequently, the sintered 3D printed material tableting structures can be subjected to an in vivo pharmacokinetic study to confirm the obtained results. [ABSTRACT FROM AUTHOR]

In binder-jetting of superalloys, challenges remain as the highly porous green bodies struggle to sinter to full density. Particle rearrangement during supersolidus sintering helped remove printing defects and promote densification, but the segregated elements are often detrimental. Here, a new two-step sintering process was applied to alloy 625. Results indicated that during the first step the material efficiently densified at supersolidus temperatures. Then, segregated elements diffused back into the bulk, resulting in a homogeneous microstructure. [ABSTRACT FROM AUTHOR]

Fenton sludge containing (20–40% iron content) is produced by Fenton oxidation technology during the treatment of refractory organic pollutants, which is a hazardous industrial waste. Moreover, the landfill and incineration of Fenton sludge result in the waste of iron resources. In this context, Fenton sludge obtained from the advanced treatment of papermaking wastewater was mixed with coal slime and coal fly ash to prepare water treatment fillers via a high-temperature sintering. Specifically, the effects of raw material ratio, sintering temperature and sintering time on the filler properties were analyzed, including compressive strength, bulk density and water absorption of capacity, and the optimum process conditions were determined. It was confirmed that under the optimal process conditions of Fenton sludge: coal fly ash: coal slime = 5:3:2, sintering temperature 950 ℃, sintering time 40 min, preheating temperature 400 ℃ and preheating time 30 min. The analysis was carried out on the physical properties, the leaching concentration of heavy metals, micromorphology, phase composition and element content of the fillers. Under the conditions of pH 3, m(CODCr):m(H2O2) 1:1.5, catalyst dosage 15 g L−1, reaction time 100 min, CODCr reduced to 48.65 mg L−1. [ABSTRACT FROM AUTHOR]

Fabricating a thermo‐electro‐magnetic material that exhibits simultaneously excellent magnetocaloric (MC) and thermoelectric (TE) performance is challenging since the interfacial reaction causes severe deterioration of MC and TE performance. In this work, a construction of multi‐scale interfaces in LaFe10.4Co0.8Si1.8/Bi0.5Sb1.5Te3 (LFS/BST) composites is realized by adopting a low‐temperature high‐pressure sintering strategy. It is revealed in the atomic‐scale that the interfacial reaction between LFS and BST leads to the formation of (Fe,Co)(Sb,Te)2 micro‐grains and LaTe2 nano‐grains, and the latter form low‐mismatch phase boundaries with LFS matrix. Benefiting from the multi‐scale interfacial phases, excellent MC performance of LFS is preserved alongside a minor impact on TE properties, e.g., a peak zT of 1.04 and a small decrease of 3.0% in relative cooling power are achieved in the 2%LFS/BST composite. Compared with other thermo‐electro‐magnetic materials, a good trade‐off between MC and TE performance is realized in LFS/BST composites with simultaneously high MC and TE performance. The 20%LFS/BST composite exhibits a room‐temperature zT of 0.46 with large maximum magnetic entropy change and relative cooling power of 0.81 J kg−1 K−1 and 44.83 J kg−1, respectively. This work provides an effective material design for developing the all‐solid‐state MC/TE hybrid refrigeration technique. [ABSTRACT FROM AUTHOR]

Various approaches have been developed to address the challenges of difficult densification in traditional BaZrO 3 -based and BaCeO 3 -based protonic ceramic fuel cells (PCFCs) electrolytes. The addition of sintering additives, the most widely used approach, has been found to potentially compromise electrical performance while improving sinterability in traditional sintering. Recently, SrSn 0.8 Sc 0.2 O 3- δ (SSS) has emerged as a promising proton-conductor material; however, there is still space for improvement in its electrical and sintering properties. In this study, a systematic investigation was conducted into the effect of sintering additives (NiO, ZnO, CuO) on the electrical performance of the new proton conductor SSS. Notably, SSS-1wt%NiO was found to decrease the sintering temperature from 1600 °C to 1400 °C (reaching 92 % relative density) and increase protonic conductivity from 2.61 × 10−3 S cm−1 to 3.06 × 10−3 S cm−1 at 600 °C, without any increase in electronic conductivity. This demonstrates a synergistic beneficial effect on both sinterability and electrical properties. Furthermore, the Ni-SSS|SSS-1wt%NiO|SSS-BCFZY single cell achieved the highest peak power density (528.5 mW cm−2 at 800 °C), surpassing all the other SSS-based single cells. Therefore, the addition of NiO to the SSS electrolyte demonstrates the significant sintering and electrical properties of SSS, proving evidence for the potential commercial application of SSS electrolytes for PCFCs. [ABSTRACT FROM AUTHOR]

High-conducting and long-term stable proton-conducting electrolytes are of utmost importance. This study investigates the synthesis and characterization of BaCe 0.7 Zr 0.1 Cu x Y 0.2-x O 3-δ (BCZCu x Y; x = 0, 0.005, 0.01, 0.02, 0.05, and 0.1) electrolytes tailored for proton-conducting solid oxide fuel cells (SOFCs). Through Cu2+ doping at the B-site of BaCe 0.7 Zr 0.1 Y 0.2 O 3-δ (BCZY), a successful reduction of the sintering temperature to 1200 °C was achieved. BCZCu 0.02 Y exhibited a high relative density of approx. 98.1% at this temperature, but beyond 2 mol% Cu doping, the appearance of a BaCuO 2 secondary phase adversely impacted conductivity. The electronic properties of BCZY and BCZCu x Y are elucidated via partial density of states (PDOS) analysis, revealing optimized crystal structures and band gap reductions (from approx. 1.9 eV–1.1 eV) upon Cu doping. Notably, BCZCu 0.02 Y demonstrated a commendable conductivity, with values of 3.5 × 10−2 S. cm−1 in air and 4.8 × 10−2 S. cm−1 in a moist atmosphere at 750 °C. Remarkably, excellent electrochemical stability was observed in a moist hydrogen atmosphere for up to 450 h at 600 °C. Single cells incorporating BCZCu 0.02 Y electrolytes exhibited peak power densities of 380 mW/cm2 at 750 °C. The incorporation of 2 mol% Cu2+ in the BCZY lattice holds promise for achieving low-temperature sintering and high-performance proton-conducting SOFCs. [ABSTRACT FROM AUTHOR]

In order to achieve low-temperature densification of SiC ceramic, β-SiC nanopowder was doped with Li 2 O together with Y 2 O 3 –Al 2 O 3 –MgO as sintering aids, and then spark plasma sintered at temperatures ranging from 1450 °C to 1600 °C for 30 min under 30 MPa pressure in argon. The densities, microstructures and mechanical properties of SiC ceramics were systematically investigated, in comparison to the counterparts sintered with Y 2 O 3 –Al 2 O 3 –MgO additives. Since Li 2 O has a low melting point, Li 2 O addition effectively decreased the formation temperature of liquid secondary phase, enabling SiC ceramics to obtain higher density and lower porosity after low-temperature sintering (T ≤ 1550 °C). Besides, Li 2 O addition was found to decrease the viscosity of liquid phase and enhance grain growth of SiC through dissolution-reprecipitation process. When sintered at 1550 °C, Li 2 O addition led to a remarkable increase of density from 3.03 g/cm3 to 3.21 g/cm3 for SiC ceramic. Meanwhile, the SiC ceramic with Li 2 O addition exhibited a high Vickers hardness of 22.75 ± 0.35 GPa and a good fracture toughness of 3.83 ± 0.27 MPa m1/2. The research results are expected to benefit the low-cost fabrication of SiC ceramics based on pressure-assisted sintering and alleviate the thermal damage of SiC fiber in hot-pressed SiC f /SiC composites. [ABSTRACT FROM AUTHOR]

In this study, the microstructural and mechanical properties of sintered NbCN-Ni cermets with various WC contents were investigated. The density and grain size of the NbCN-Ni cermets increased with an increase in the sintering temperature from 1420 to 1510 °C, whereas after WC addition, the average grain size of NbCN decreased significantly. The added WC was initially dissolved in the binder phase and then dissolved in NbCN crystals and formed a white W-rich (Nb,W)CN shell phase and gray Nb-rich (Nb,W)CN core phase structure for WC contents up to 10 wt%. Meanwhile, the formation of the shell-core structure enabled the morphology of NbCN grains to gradually change from polygonal to spherical, which can be attributed to the high solubility of WC in the Ni binder. The hardness and transverse rupture strength (TRS) of the cermets first increased and then decreased with increasing sintering temperature and WC content. At a WC content of 10 wt% and sintering temperatures of 1480 and 1450 °C, the HV 10 and TRS of the cermets reached maximum values of 1405 kg/mm2 and 1280 MPa, respectively. The friction coefficient of the NbCN-Ni cermets decreased from 0.7 to 0.55–0.6 after WC addition. Hence, the cermets exhibited excellent wear resistance because the introduction of WC decreased their friction coefficient and increased their hardness. [ABSTRACT FROM AUTHOR]

The possibility of reusing ceramic roller waste to produce cordierite and mullite refractories was investigated. Five batches were designed using wastes representing ceramic roller waste, magnesite, and silica sand, shaped and fired at 1300 °C/2 h, and one batch was selected at 1200 °C. The chemical composition and precipitated phases of the used raw materials and the fired batches were analyzed using XRF and XRD techniques, respectively. Densification parameters, morphology, microstructure and electrical properties were also studied to evaluate the effect of the formed phases on the properties of fired materials. Bulk density increases with an increase in mullite and a decrease in cordierite, and it also increases with increasing temperature, whereas porosity and water absorption show a opposite behavior to density (it decreases with an increase in mullite and temperature). The main phases developed after firing at 1300 °C/2 h were cordierite, mullite, corundum, baddeleyite, and spinel. Bending strength increases with increasing mullite percentage and density, and decreasing grain size and porosity. The microstructure develops and becomes finer with increasing mullite percentage and density. The grain size of the crystals was very fine at 1200 °C/2 h and increased at 1300 °C/2 h. Broadband dielectric spectroscopy was employed to study the electrical and dielectric behavior of the investigated samples. The increase in mullite concentration shows a remarkable increase in ε', especially at lower frequencies, as it is three times higher than that of M10. At f > 103 Hz ε', frequency independence is accompanied by an increase in mullite concentrations due to the lag of dynamics fluctuations after the alteration of the electric field. The generation of new free ions leads to the enhancement of conductivity as the mullite concentration increases. [ABSTRACT FROM AUTHOR]

High pressure sintering shows great superiority in promoting the densification of the hard‐to‐densify refractory ceramics, and the underlying mechanisms are thus of great interest. In the present work, the densification process of tantalum carbide (TaC) ceramics affected by pressure was discussed through comparing the microstructural characteristics and sintering kinetics. The TaC ceramics sintered at 30–250 MPa show dense and uniform microstructure without oxide impurities and high‐density dislocations. With the increase of sintering pressure, particle rearrangement becomes prominent at initial stage, whereas grain boundary diffusion rather than lattice diffusion dominants the final stage mechanism. Grain growth is enhanced under high pressure through the plastic deformation process. Our work should facilitate to understand the mass transport mechanisms during the high pressure sintering or deformation process of carbide ceramics. [ABSTRACT FROM AUTHOR]

A coarsening treatment in an HCl containing atmosphere was performed to stabilize the porosity of Al 2 O 3 /ZrO 2 composites up to elevated temperatures. There is minimal shrinkage during the reactive coarsening treatment and the porous microstructure is stable during subsequent heat treatments. The reaction bonding of aluminum oxide (RBAO) process was used to fabricate the samples. Coarsening was investigated as a function of initial density (40–60 % TD) and coarsening temperatures (1250–1400 °C). After the HCl coarsening step, samples were sintered in air to determine the effect of coarsening treatment on pore stability. Up to the temperature of the coarsening treatment no further densification is observed. Above the HCl coarsening temperature densification is significantly retarded. Thus, it is shown that the porosity in RBAO can be stabilized by heat treatment in a 10 vol % HCl containing atmosphere. During the coarsening treatment in HCl at 1300 °C, 1350 °C and 1400 °C little densification was observed (Δ ρ ≤ 2 % TD) in comparison with the densities that result from sintering reaction bonded samples in air at 1350 °C (Δ ρ ∼ 5–8 % TD). Therefore, the HCl coarsening is a promising approach to adjust a desired level of porosity for high temperature applications of porous materials. It is postulated that at a given density, the coarsened materials should exhibit increased strength compared to un-coarsened materials due to increased contact area between the particles. [ABSTRACT FROM AUTHOR]

Transparent alumina ceramics produced by pulsed electric current sintering (PECS) include black dots, which can be observed with the naked eye. These black dots have porous structures caused by the aggregates in the raw powder. In order to investigate the detailed mechanism of black dot formation, transparent alumina ceramics were prepared by sintering α-alumina granules to produce large pseudo-aggregates and introducing them into α-alumina powder for PECS. Macroscopic black dots were formed in the sample. Characteristic Raman peaks of graphite were detected in porous parts of these macroscopic black dots. Analysis of gas phases generated from graphite sheets for PECS suspected to be involved in carbon contamination showed CO and CO 2 generation. In thermodynamic calculations on carbon activity during PECS, gas phase including CO and CO 2 generated from the hot graphite mold/sheet permeates the porous part of the cold sample, and the carbon activity of gases including CO and CO 2 on the porous surface theoretically exceeds unity. Then, CO is adsorbed and decomposed on the porous surface, resulting in carbon contamination. The formation of macroscopic black dots is caused by carbon deposition in agglomerates of the raw powder from CO generated by graphite sheets during PECS. [ABSTRACT FROM AUTHOR]

Spark plasma sintering (SPS) is one of the most promising technologies for producing polycrystalline transparent ceramics. However, it has limitations regarding the complexity of the geometries that can be produced. This study addresses these limitations by combining additive manufacturing techniques with spark plasma sintering. Additionally, a Multiphysics sintering model based on the continuum theory of sintering is employed to predict the outcomes of the SPS process, particularly the microstructure of the densified parts. As a result, the geometrically complex Al 2 O 3 transparent parts manufactured in this study exhibit a uniform microstructure, high density (∼99 %), and a linear transmittance of 16 % at 490 μm. [ABSTRACT FROM AUTHOR]

In so-called Field Assisted Sintering Techniques such as Spark Plasma Sintering (SPS) or Flash Sintering (FS), ceramic powder compacts are densified at high sample temperature in the presence of an electrical field. The formation of a plasma is often discussed without actual evidence for its appearance. In this work, which is the first of two parts, the mechanisms of plasma formation as well as its properties under FS conditions were investigated. Field induced breakdown of various atmospheres was conducted by a DC-field (up to 350 V/cm) at temperatures between 1000 and 1500 °C. Experiments were conducted both with and without a sample mounted between the electrodes. Alumina, boron carbide and silicon carbide in green or sintered form were used as the samples. The electrical and optical properties of the plasma were characterised, and the early stages were visualised by high-speed camera recordings. The results showed that the breakdown is caused by a flashover mechanism and the conductance of the plasma under the present conditions was of the same order as the conductivity of a boron or silicon carbide green body. Plasma formation did not lead to extensive sintering but the plasma was able to infiltrate the green body and cause transfer of matter from the interior to the surface and beyond. Based on the present results, it seems unlikely that a gas plasma is formed under the normal conditions of SPS or FS. [ABSTRACT FROM AUTHOR]

Various types of grain growth behavior have been observed in polycrystals with faceted boundaries. The grain growth behavior observed in many different ceramic as well as metallic systems has been well explained by the mixed mechanism principle of grain growth and microstructural evolution. However, relatively few studies have considered repetitive grain growth in materials. To examine the generality of the microstructural evolution principle, two cases of repetitive grain growth during solid-state sintering are considered, one metallic (Ni) and one ceramic system (BaTiO 3). The observed repetitive grain growth behavior with an increased sintering temperature (in the case of Ni) and sintering time (in the case of BaTiO 3) supports well the generality of the mixed mechanism principle. [ABSTRACT FROM AUTHOR]