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To date, the application of additive manufacturing techniques in fabricating SiAlON ceramics with intricate geometries has been limited. This investigation demonstrates the synthesis of SiAlON ceramics by integrating silicon nitride (Si 3 N 4) powders with variable proportions of aluminum nitride (AlN) utilizing the vat photopolymerization (VPP) approach. The effects of AlN content on the properties of SiAlON ceramic slurries, green bodies, and sintered parts were systematically investigated. Notably, the slurry's viscosity decreases progressively with an increase in AlN, aligning with VPP printing prerequisites. Additionally, the curing depth of the slurry enhanced proportionally with AlN augmentation, elevating from 21 μm to 44 μm at an energy exposure of 800 mJ/cm2, with the pivotal addition being 15 vol% AlN, where optimal properties were achieved. The zeniths of flexural strength, bulk density, relative density, and thermal conductivity were recorded at 385.66 ± 22.63 MPa, 3.34 ± 0.09 g/cm3, 96.22 ± 2.55 %, and 37.4 ± 0.31 W m−1 K−1, respectively. The fabrication of SiAlON ceramics with complex configurations was successfully realized, heralding a novel methodology for future SiAlON ceramic production. [ABSTRACT FROM AUTHOR]

Sintering process is an important factor affecting the properties of porous Si 3 N 4 ceramics. However, there are few studies on the properties of porous Si 3 N 4 ceramics fabricated by combining digital light processing (DLP) technology and spark plasma sintering (SPS) technology. In this study, a method to prepare porous Si 3 N 4 ceramics by combining DLP with SPS technology was proposed, and ceramic samples were successfully prepared. The effect of sintering temperature and holding time of SPS technology on the microstructure and properties of porous Si 3 N 4 ceramics prepared by DLP technology was discussed. With the increase of sintering temperature from 1600 °C to 1700 °C, the conversion content of α-Si 3 N 4 phase to β-Si 3 N 4 phase increased from 19.19% to 76.72%. The fracture mode of porous Si 3 N 4 ceramics gradually transformed from intergranular to transgranular. The porosity of Si 3 N 4 ceramics gradually decreased from 40.34 ± 4.9% to 30.54 ± 2.7% with opposite trend in bulk density. And the flexural strength increased from 109.1 ± 7.6 MPa to 249.5 ± 4.0 MPa. When the sintering temperature was 1700 °C, the content of β-Si 3 N 4 increased first and then remained essentially constant with the increase of holding time from 5 min to 15 min. The porosity increased from 30.54 ± 2.7% to 35.15 ± 2.5%, while the variation in bulk density were opposite. And the flexural strength severely decreased from 249.5 ± 4.0 MPa to 126.1 ± 7.2 MPa. This research provides valuable insights into the DLP-forming ceramic materials sintered by SPS technology. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 -based ceramics with different pore morphologies were prepared choosing Si 3 N 4 and Al 2 O 3 poly-hollow microspheres (PHMs) as pore-forming agents. The phase compositions, morphologies and mechanical properties of the samples were investigated. The SEM results show that the intact Si 3 N 4 and Al 2 O 3 PHMs distribute uniformly in the green body. However, after the sintering process, the basal body of the samples with Si 3 N 4 PHMs is fibrous and Si 3 N 4 PHMs still exist, while the basal body of the samples with Al 2 O 3 PHMs is dense and Al 2 O 3 PHMs disappear. In addition, the samples with Si 3 N 4 and Al 2 O 3 PHMs have different mechanical properties due to their different microstructures. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, novel porous Si3N4 ceramics were prepared by aqueous gelcasting using Si3N4 poly-hollow microspheres as pore-forming agent. The effect of Si3N4 poly-hollow microsphere content on the phase composition, microstructure, shrinkage, porosity and mechanical properties of the prepared porous Si3N4 ceramics were investigated. It is found that there is only β-Si3N4 phase in all the prepared porous Si3N4 ceramics. Meanwhile, the SEM results show that the pores in the porous Si3N4 ceramics distribute uniformly, the added Si3N4 poly-hollow microspheres and the basal body contact closely. With the increase of Si3N4 poly-hollow microsphere content, the shrinkage of the porous Si3N4 ceramics decreases gradually, and the porosity of the porous Si3N4 ceramics decreases firstly and then increases. Furthermore, the flexural strength and fracture toughness of the porous Si3N4 ceramics decrease with the increase of the Si3N4 poly-hollow microsphere content. [Copyright &y& Elsevier]

Abstract: Non-aqueous gelcasting and dry pressing were used to prepare 45wt% Ba0.6Sr0.4TiO3–55wt% MgO (BSTM) ceramics. The effects of different forming methods on the microstructures and dielectric properties of the BSTM ceramics were investigated. The densities of the BSTM ceramics prepared by non-aqueous gelcasting are lower but more uniform than that of the BSTM ceramics prepared by dry pressing. The XRD analysis illustrates that phase compositions are completely the same no matter what forming method is adopted. The SEM results show that the BSTM green samples and sintered ceramics prepared by non-aqueous gelcasting are more uniform than that prepared by dry pressing. Furthermore, it is found that the BSTM ceramics prepared by non-aqueous gelcasting have higher and more uniform dielectric constant, tunability and loss tangent (measured at 10kHz and 20°C). Meanwhile, the BSTM ceramics prepared by non-aqueous gelcasting have higher dielectric constant and lower Q × f value (namely more loss) when they are measured at microwave frequencies. [Copyright &y& Elsevier]

Abstract: A novel forming method-aqueous gelcasting was used to prepare 90wt.% (0.75ZnAl2O4–0.25TiO2)–10wt.% MgTiO3 (ZTM) microwave dielectric ceramics and GPS antenna. The effects of aqueous gelcasting and dry pressing on the phase compositions, microstructures and microwave dielectric properties of ZTM ceramics were investigated. The samples’ cracking problem happening in the process of drying and binder removal was successfully overcome. The phase compositions are completely the same no matter what forming method is adopted, but the ZTM ceramics prepared by aqueous gelcasting are denser than that prepared by dry pressing. Fewer pores and more uniform microstructures are observed in the ZTM ceramics prepared by aqueous gelcasting. Therefore, much better microwave dielectric properties are obtained in the ZTM ceramics prepared by aqueous gelcasting. Finally, a GPS antenna was successfully fabricated by aqueous gelcasting using the ZTM material, which meets the requirements of GPS application. [Copyright &y& Elsevier]

Abstract: The effects of aqueous gelcasting and dry pressing on the sinterability and microwave dielectric properties of 90wt.% (0.75ZnAl2O4–0.25TiO2)–10wt.% MgTiO3(ZTM) ceramics have been investigated. It is found that aqueous gelcasting could effectively decrease the sintering temperature of ZTM ceramics by 100°C and acquire more excellent microwave dielectric properties of ZTM ceramics compared with conventional dry pressing. X-ray diffraction (XRD), environment scanning electron microscope (ESEM) and energy-dispersive X-ray spectroscopy (EDX) were used to analyze the phase compositions and microstructures of ZTM ceramics. The results illustrate that the phase compositions are completely uniform no matter what sintering temperature and forming method are adopted. However, the densities, ɛ r and Q × f values are greatly affected by different forming methods, whereas there are few effects on the τ f values. It is observed that ZTM ceramics prepared by aqueous gelcasting exhibit greater densities, more excellent and stable microwave dielectric properties compared with that prepared by dry pressing at the relative low sintering temperatures. However, when the sintering temperature becomes higher, the opposite phenomenon would gradually appear. [ABSTRACT FROM AUTHOR]

In this paper, the sintering behavior and microstructural evolution of as-prepared monodispersed β-Ga 2 O 3 micro-ellipsoid particles (E-G), β-Ga 2 O 3 micro-rods particles (R-G) and as-received commercial β-Ga 2 O 3 particles (C-G) were investigated. The XRD analysis showed that the main peak (−202) of E-G and R-G ceramics sintered at elevated temperature, ascribed to the lowest surface energy of the (−202) crystal surface. The in-situ high temperature optical dilatometer analysis revealed that, compared with C-G, the monodispersed E-G and R-G had higher sintering activity with a more uniform particle size and a smaller aspect ratio and the densification temperature of as-prepared β-Ga 2 O 3 was reduced by over 100 °C. The highest density of E-G, R-G and C-G ceramics were 5.96 g/cm 3 sintered at 1400 °C, 5.98 g/cm 3 sintered at 1450 °C and 5.89 g/cm 3 sintered at 1550 °C, respectively. Differential densification and subsequent separation of the pores from the boundaries led to the lower density of C-G ceramics. Due to a higher sintering activity, E-G and R-G ceramics had larger grains than those of C-G ceramics sintered at the same temperature. Furthermore, the sintering temperature had an important effect on the microstructure and weight losses of sintered Ga 2 O 3 ceramics. Finally, the high-density target obtained using Ga 2 O 3 particles with uniform size as the raw materials exhibited promising industrial applications for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Uniformly sized and monodispersed β-Ga 2 O 3 crystalline micro-rods and ellipsoids have been successfully synthesized through a facile direct precipitation technique, respectively, using Ga(NO 3 ) 3 and NH 4 OH solution as starting materials. The as-prepared particles were characterized by XRD, FESEM equipped with EDS, TEM equipped with SAED, TG-DSC and Laser diffraction particle size analyzer, respectively. The results showed that the obtained β-Ga 2 O 3 particles with a narrow particle size distribution were assembled with single crystalline β-Ga 2 O 3 nano-sheets with the thickness of 100 nm. Furthermore, the reaction parameters including aging temperature, the molar concentration of Ga 3+ and pH value had an essential effect on the morphology and size of the particles. Ostwald ripening and oriented attachment growth mechanism of the uniformly hierarchical β-Ga 2 O 3 crystals were proposed. Finally, the target fabricated by using the as-prepared β-Ga 2 O 3 particles as the raw materials exhibited a density as high as 6.01 g/cm 3 , showing potential applications in the high-quality thin film formed by magnetron sputtering for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is raised as one kind of additive manufacturing (AM) which is based on the discrete-stacking concept. This technique can fabricate advanced composites with desirable properties directly from 3D CAD data. In this research, 316L stainless steel (316L SS) and different fractions of calcium silicate (CaSiO 3 ) composites (weight fractions of calcium silicate are 0%, 5%,10% and 15%, respectively) were prepared by SLM technique with a purpose to develop biomedical metallic materials. The relative density, tensile, microhardness and elastic modulus of the composites were tested, their microstructures and fracture morphologies were observed using optical microscope (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the addition of CaSiO 3 particles influenced the microstructure and mechanical properties of specimens significantly. The CaSiO 3 precipitates from the overlap of adjacent tracks and became the origin of the defects. The tensile strength of specimens range 320–722 MPa. The microhardness and elastic modulus are around 250 HV and 215 GPa respectively. These composites were ductile materials and the fracture mode of the composites was mixed mode of ductile and brittle fracture. The 316L SS/CaSiO 3 composites can be a potential biomedical metallic materials in the medical field. [ABSTRACT FROM AUTHOR]

Perovskite Ba 0.67 Sr 0.33 TiO 3 (BST) ceramics with improved dielectric performance were fabricated by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method using 0.5 mol% MgO as the coagulation agent. The influence of sintering temperature on micromorphology, crystal structure, and dielectric performance of BST ceramic components was systematically evaluated. The densification rate of BST samples could reach the maximum at a heating temperature around 1305 °C and end up approximately at 1380 °C. As increasing the sintering temperature from 1400 to 1550 °C, the relative density of BST ceramics decreases from 98.82 ± 0.16% to 96.72 ± 0.06%, and the mean grain size drops gradually from 9.96 to 4.68 μm. The increased sintering temperature promotes the lattice expansion due to Ti4+ replacement at B site by Mg2+, as well as the generation of oxygen vacancies. In addition, as increasing sintering temperature, the dielectric permittivity (ε r) of BST ceramic components decreases first and then slightly increases, while the dielectric loss (tanδ) of ceramics shows the opposite trend. The results indicate that the initial tanδ increase is mainly attributed to the lattice expansion of BST ceramics, and the subsequent loss reduction results from the easily localized conduction electrons on Mg2+ sites reducing the carrier concentration. The samples sintered at 1550 °C show the lowest dielectric loss (tanδ≈0.013), which is significantly reduced by an order of magnitude compared with that of dry-pressed samples (tanδ≈0.262). [ABSTRACT FROM AUTHOR]

Indirect selective laser sintering (SLS) was combined with reactive melt infiltration (RMI) to fabricate RB-SiC, and the effects of preform impregnation with different carbon source on the carbonized sample and final RB-SiC were investigated. Results show that the impregnation treatment led to increased bulk density and mechanical strength of samples at all stages. The pore size dwindled and the porosity decreased significantly for the carbonized sample, and the content of Si reduced for the final RB-SiC. The impregnation with PF resin containing 30 % nano carbon black (PFnanoC) seems more promising for the comprehensive properties improvement, the final RB-SiC had a relatively fewer amount of residual pore and carbon and showed superior mechanical properties compared with those of sample impregnated with only PF resin. Kinetics analysis indicates a slower pore-clogging rate under the PFnanoC impregnation condition, which avoided or hindered a too-early infiltration cease during the RMI process. [ABSTRACT FROM AUTHOR]

Ba 0.67 Sr 0.33 TiO 3 (BST) ceramics with highly improved dielectric performance were fabricated by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method. The influence of solid loading on densification behavior, micromorphology, and dielectric performance of the samples was investigated. With the increase of solid loading from 40 to 50 vol%, the maximum densification rate of BST ceramics increased from 0.090 to 0.122 s−1, and the densification temperature decreased from 1424 to 1343 °C, which indicated that high solid loading could promote the densification behavior of samples during sintering. BST ceramics fabricated by the DCC-HVCI method showed uniform grain size and microstructure, which was beneficial for the dielectric properties of BST ceramics. Samples obtained from 45 vol% suspensions possessed the lowest dielectric permittivity (ε r ≈ 2801), and the dielectric loss (tanδ≈0.0262) was about 1/10 of that of dry-pressed samples (tanδ≈0.301), which could be attributed to the composition homogenization. [ABSTRACT FROM AUTHOR]

Selective laser sintering was combined with reactive melt infiltration to fabricate SiSiC part, and the effects of carbon fiber (C f) on the properties of the SLS green body, the carbonized and final SiSiC sample were investigated. Results show that the addition of an appropriate amount of C f (1.59 wt%~2.97 wt%) can increase the bulk density and geometric precision of the sample at all stages, and improve the mechanical properties of green and carbonized samples. The main phases composed of the SiSiC composite were free Si, a-SiC, β-SiC, plus a very small amount of Al–Si alloy. With 1.59 wt% C f addition, a relatively comprehensive favorable macro-properties of both the green sample and carbonized sample was achieved, and the homogeneous microstructure of the latter favored the decreased free Si content and increased β-SiC content of the final composite. The evolution mechanism of C f added to the raw material is inferred to be the mutual diffusion of [C] and [Si] that occurred at the C f /Si melt boundary leading to the formation of the siliconized C f with relatively large diameter size (24.3 μm) and high aspect ratio (>30). Amorphous C, which derived from the pyrolysis of epoxy resin E12, undergone a dissolution-precipitation mechanism with the formation of fine-grain β-SiC. [ABSTRACT FROM AUTHOR]

In this study, different posttreatment methods, including silica‐sol infiltration (SI), vacuum silica‐sol infiltration (vSI), debinding (DB), and pressure‐less sintering (PS), were combined with selective laser sintering (SLS) to fabricate Al2O3‐SiO2 ceramics. The macro‐morphology and microstructure of sample fabricated under different laser processing parameters and posttreatment process were investigated. Results show that the geometric dimension accuracy and surface quality of the final samples can be effectively improved with appropriate SLS parameters and posttreatment. The optimal SLS processing parameters are determined to be 0.15 mm, 10 W, 0.1 mm, and 1500 mm/s for the hatch spacing, laser power, layer thickness, and scanning speed, respectively. The SLS/DB/vIN/FS samples have the smallest linear shrinkage ratio (<1%), the least warpage degree (<3%), and the best surface quality (surface altitude difference <170 μm). Mullite, quartz, corundum, and cristobalite composed the phases of the sample, of which cristobalite came largely from the infiltrated silica‐sol. Since a higher amount of silica‐sol infiltrated into the sample under SLS/DB/vIN/FS process, more cristobalite phase formed in the pore of the sample during sintering, which avoided excessive microstructure shrinkage during sintering and ensured the high geometric accuracy and surface quality of the final sample. [ABSTRACT FROM AUTHOR]

A novel method to fabricate high-performance Al 2 O 3 Ceramics by indirect Selective Laser Sintering (idSLS) based on particle packing optimization was reported. Al 2 O 3 ceramics with the particle size distribution (PSD) being adjusted based on a particle packing model was prepared with the idSLS method, and the effects of PSD on the macro-performance and microstructure of the idSLSed ceramics part was investigated. Results show that an appropriate PSD of raw material is not only essential to the good SLS formability of powder bed but also contribute to the favorable sintering characteristics of the SLSed green body through an ideal particle packing. The improvement of overall properties including mechanic strength, dimensional accuracy, and surface flatness of the SLSed green body and the final parts were achieved with a fine-tuned PSD exponent. When the raw material has a PSD exponent of 0.5–0.6, the final ceramic parts showed relatively balanced comprehensive properties of bulk density >2.0 g cm−3, linear change <1.4%, fracture strength >3.97 MPa, compressive strength >5.25 MPa and surface altitude difference <148 μm. [ABSTRACT FROM AUTHOR]

Ni-Al2O3-MoS2 composite coatings were prepared on the surface of aluminum alloy substrates by an integrative method of electrophoresis and electrodeposition from the electrolytic solution with different MoS2 concentrations. The surface morphology and compositions of the coatings were studied by scanning electron microscopy equipped with an energy dispersive spectroscope. The microindentation hardness and tribological properties of the coatings were tested using a Vickers hardness tester and friction performance tester in dry sliding condition, respectively. Results showed that the cross-sections of the coatings exhibited smooth morphology and uniform distribution of the compositions. Al2O3 and MoS2 particles were uniformly dispersed in the Ni matrix. The coatings were sufficiently adhered on the aluminum alloy substrates. The addition of MoS2 particles can significantly improve the wear resistance of the coatings. When the MoS2 concentration is 1.0 g/L, the Ni-Al2O3-MoS2 coatings exhibit superior mechanical properties. [ABSTRACT FROM AUTHOR]

A novel way has been reported to fabricate porous silica ceramics, which is based on the in-situ foaming process of densely packed silica poly-hollow microspheres (SPHMs) at elevated temperature and inert atmosphere. The results show that sintering atmosphere and temperature have great effects on the formation and evolution of the porous structure. The original holes inside or between SPHMs could grow up to form uniform pores as the sintering temperature increases under inert atmosphere, and the optimal sintering temperature for well homogeneous microstructure could be 1575 °C. This novel method is facile and efficient, by which porous silica ceramics with the compressive strength ranging from 0.60±0.28 MPa to 29.77±2.28 MPa and the porosity of 39.0–77.2% have been prepared. [ABSTRACT FROM AUTHOR]

Fabrication of microstructures for imparting omniphobicity to a surface generally requires the use of lithographic techniques and specialized equipment. We report instead a simple strategy for the synthesis of microstructured surfaces via metal–organic framework (MOF) self-assembly. Our method allows us to localize epitaxial growth of MOF at the tips of needle crystals to create mushroom-shaped structures, thus conferring re-entrant textures to the MOF-functionalized surfaces. These structures synthesized via wet chemistry were found to have omniphobic properties due to the resulting re-entrant texture. [ABSTRACT FROM AUTHOR]

The initial growth and microstructure feature of Ag films formation were investigated, which were prepared by using the very-high-frequency (VHF) (60 MHz) magnetron sputtering. Because of the moderate energy and very low flux density of ions impinging on the substrate, the evolutions of initial growth for Ag films formation were well controlled by varying the sputtering power. It was found that the initial growth of Ag films followed the island (Volmer—Weber, VW) growth mode, but before the island nucleation, the adsorption of Ag nanoparticles and the formation of Ag clusters dominated the growth. Therefore, the whole initial stages of Ag films formation included the adsorption of nanoparticles, the formation of clusters, the nucleation by the nanoparticles and clusters simultaneously, the islands formation, and the coalescence of islands. [ABSTRACT FROM AUTHOR]