Solid Loading Content Research Articles

Microstructural evolution, enhanced mechanical properties, and complex shapes design in high solid content alumina ceramics through additive manufacturing

Manufacturing industrially profitable high solid-loading ceramic materials with finely designed complex shapes is an exciting yet challenging in sustainable additive manufacturing. Here, we propose a resin strategy to achieve a high solid-loading content of 62 vol% alumina slurry for 3D printing high-quality complex shapes using digital light processing (DLP) technology. Remarkably, both high solid-loading content and tuned sintering temperature emerge as key factors in ensuring optimal print quality and mechanical performance. With this strategy, the ceramic slurry containing 62 vol% exhibits lower shear rate and improved layer adhesion. The burnout treatment was designed based on the DSC-TGA results, followed by sintering in an air atmosphere. Comprehensive physical measurements were achieved, alongside precise structural characterization at multilength scales in situ. In depth exploration of post-sintering analysis revealed no changes in phase composition or chemical bonding. The optimum overall performance of sintered specimen exhibited shrinkage of 8.3 %, 8.8 %, and 11.5 % in the X, Y, and Z directions, with a bulk density of 3.76 g/cm3. Mechanical testing demonstrated superior flexural strength of 247.23 MPa, nanoindentation hardness of 30.9 GPa, and modulus of 428.35 GPa. This high-precision printing strategy may significantly contribute to understanding the structure-property relationship of DLP-3D printed Al2O3 ceramic and opening avenue for the applications of high-strength parts in demanding environments.

Advancements in DLP 3D printing: High strength alumina toughened zirconia ceramics for biomedical applications

Digital Light Processing (DLP) enables intricate ceramic part production from photosensitive ceramic slurry. While ZrO2 and Al2O3 are commonly studied, their composites are underexplored despite diverse applications. This study investigates fabricating high-strength, fully dense alumina-toughened zirconia (ATZ) parts using a low-cost desktop DLP printer designed for polymer printing. Various ATZ-based ceramic slurries (30, 35, 42.5 vol%) with different binders and dispersants were prepared and evaluated for curing and rheological properties. Promising formulations underwent debinding and sintering, resulting in homogenous microstructures with a well-distributed blend of the two phases. For the doped samples, SEM analysis revealed a good distribution of dopants and elongated dopant grains infused at higher temperatures. The 35 vol% ATZ exhibited exceptional average flexural strength of 1321 MPa, surpassing previous DLP-fabricated composites. This suggests no need for increased solid loading content. The findings demonstrate the potential of DLP in producing high-performance ceramic parts with tailored properties.

The effect of different GNP/BNNP foam structures in the infiltration of epoxy resin: A fundamental study

AbstractHierarchical 3D architecture of nanoplatelets, also known as foams, has arisen as a promising alternative to overcome agglomeration and promote mechanical reinforcement and electrical and thermal conductivity of polymer composites. Freeze‐drying is a cost‐effective method to manufacture foams with different structures and tailored thermal and electrical properties. This study used freeze‐drying to produce graphene (GNP), boron‐nitride (BNNP), and hybrid foams of different ratios. The interaction between these structures and high‐temperature epoxy grade was investigated via contact angle analysis. The foams were also infiltrated with epoxy to achieve a fully dense nanocomposite. The contact angle monitoring reveals solid loading content, composition, and structure as the main factors affecting wettability. Despite the slight variation in porosity among the foams, all the samples achieved a densification above 96%, suggesting that the epoxy viscosity of 2.34 Pa∙s combined with optimized infiltration parameters can successfully produce dense nanocomposites. The contact angle analysis is a suitable method to compare the infiltration quality of freeze‐dried foams and can be applied to evaluate the production feasibility of other polymer/foam nanocomposites. Furthermore, preliminary thermal data shows a clear temperature increase for the epoxy/foam structures, with GNP and 50:50 GNP:BNNP being the most thermally conductive compositions. This study serves as a starting point for freeze‐dried foams/polymer nanocomposite investigation and may broaden the possibilities for manufacturing and future application of these structures.Highlights The freeze‐dried foams were successfully fabricated and infiltrated with high‐temperature epoxy, obtaining densifications above 96%. The main factors affecting infiltration are foam morphology, porosity, and chemical affinity between polymer and foam platelets. Thermal conductivity has significantly improved by adding GNP and BNNP foam network to epoxy matrix.

Effect of the Zirconia Particle Size on the Compressive Strength of Reticulated Porous Zirconia-Toughened Alumina

Reticulated porous ceramics have attracted researchers owing to the separation and collection properties of porous materials and the combined high thermal resistance and chemical stability of ceramics. Among various kinds of reticulated porous ceramics, we investigated the feasibility of using reticulated porous Zirconia-toughened Alumina as applications such as dielectric barriers, insulators, and filters with acceptable properties. An acceptable range of the compressive strength for reticulated porous ZTA applications is approximately 1 MPa. However, when the pore density of the reticulated porous ZTA specimen prepared using coarse zirconia was 60, maximum compressive strength of 1.63 MPa was obtained. To enhance the compressive strength of reticulated porous ZTA specimens, rheological control of the ZTA slurry is most important by optimizing the viscosity of the ZTA slurry, and the composition (average particle size, solid loading, organic binder, and thickener) of the ZTA slurry was controlled. The optimized processing conditions to enhance the compressive strength of reticulated porous ZTA specimens were determined. Consequently, we enhanced the compressive strength of the reticulated porous ZTA specimens from 0.37 MPa to 3.11 MPa by optimizing the ZTA slurry when the solid loading content, the pore density, the sintering temperature, the amount of PVA, and the amount of thickener were 66 wt.%, 60 PPI, 1600 °C, 2 wt.%, and 0.15 wt.%, respectively.

Ti6Al4V alloy fabricated by gelcasting based on low-oxygen gel system using hydride-dehydride titanium alloy powders

Oxygen and carbon impurity residues and low density are the main issues for Ti gelcasting. To overcome these difficulties, this study develops a low-oxygen isoprene (Ip)/polyvinyl butyral (PVB) gel system to achieve Ti gelcasting using hydride-dihydride (HDH) Ti6Al4V powder. Slurries with 48 vol% solid loading content are employed to achieve moulding followed by cold isostatic pressing. During gelcasting, powder particles are held in place by the cross-linking of Ip monomer with PVB as adhesive to maintain shape. After sintering, nearly fully dense (4.38 g/cm3) Ti6Al4V alloys with low interstitial contamination (O: 0.356 wt%, C: 0.14 wt%) are successfully fabricated. The samples exhibit acceptable mechanical performance, with ultimate tensile strength of 1062 MPa, yield strength of 987 MPa, and elongation of 8.75%. Typical plastic fracture with river patterns is observed, which is distinctly different from that of HEMA based sample.

Multifunctional porous SiC nanowire scaffolds

Porous SiC nanowire (SiCNW) ceramics have great potentials for engineering applications. We herein report the fabrication of 3D SiCNW scaffolds with tuneable microstructures, densities, and therefore properties, by regulating the solid loading content in the reticulated melamine foam (MF) template and finalizing with a modified carbothermal reaction. We first demonstrate the resulting samples exhibiting high strength (modulus up to ∼167.3 kPa), good recoverability (11% residual strain and 72% maximum stress after 100 compressive cycles at a ε = 20%), low thermal conductivity of 32−54 mW m−1 K−1 at room temperature, and good fire retardance performance. We further show that these unique and tuneable SiCNW scaffolds could act as efficient organic solvent/oil absorbent, as excellent support for MOF-derived TiO2-C catalyst to achieve enhanced photocatalytic performance, and as competent electromechanical strain sensors. These multifunctionalities could find niche applications in energy and environment devices.

Preparation of Ti3AlC2 bulk ceramic via aqueous gelcasting followed by Al-rich pressureless sintering

Ti3AlC2 bulk ceramics were prepared via aqueous gelcasting followed by C-rich and Al-rich pressureless sintering. The optimized pH value, zeta potential, dispersant content, and solid loading content were determined to be 10, 72.6 mV, 1.6 wt%, and 52 vol%, respectively. Impurities at ppm level containing in the flowing argon could cause severe decomposition of gelcasted bulk Ti3AlC2, forming whiskers of Al2OC and Al4O4C and floccule of AlN. C-rich pressureless sintering resulted in the delamination of a duplex layer of Ti(CO) and Ti3(AlO)Cx-Ti(O,C). The channels formed after debinding facilitated the outward diffusion of Al and the inward diffusion of O and C, and thereby promoting the decomposition of C-rich sintered Ti3AlC2. The combined effect of the unclosed channels and the porous reaction Ti3(AlO)Cx-Ti(O,C) layer brought a catastrophic reduction in the density and mechanical properties of the C-rich sintered Ti3AlC2 ceramic. While the Al-rich pressureless sintering system isolated C, CO and N2 and supplied a closed Al-rich atmosphere, thereby suppressing the decomposition reactions and promoting the sintering densification and ultimately leading to the superior in mechanical properties. The density, hardness, flexural strength and fracture toughness of the Al-rich sintered ceramic reaches 4.13 g/cm3, 4.36 GPa, 345 MPa, 4.79 MPa m1/2, respectively.

Thermoplastic processing and debinding behavior of NbC-M2 high speed steel cemented carbide

The aim of this study is to evaluate the thermoplastic processing on a new generation of hard metals based on NbC bonded with high speed steel. The conventional technique in producing cemented carbide parts is dry pressing with paraffin binder and post production. To overcome shape restriction in pressing and post production, thermoplastic shaping processes can be used. For this purpose, a previously known binder system for ceramic feedstocks containing paraffin wax and ethylene vinyl acetate was selected and used for the first time with cemented carbides. The stated organic binders were mixed with NbC-12 wt.% M2 high speed steel powder and feedstocks with solid loading content from 50 to 60 vol.% were obtained. The rheological behavior of the feedstocks as well as the critical solid loading content were assessed using a capillary rheometer. A model fitting approach was used for the first time in hardmetal feedstocks to estimate the critical solid loading. Experimental values were fitted to a model from Chong (1971) which is based on bimodally disperse powder mixtures and a critical powder loading of 70 vol.% could be calculated. However, based on the abrasion problems during mixing at high filler content, feedstock with 57.5 vol.% powder loading had the optimum processability characteristics, and was therefore selected for further shaping processes. Thermo gravimetric analysis on green samples was performed after shaping in order to develop an optimum thermal debinding profile. The thermal debinding program was adjusted with special attention on decomposition onset, maximum mass loss rate and decomposition offset temperatures. Initial trials using decomposition offset temperature as holding steps, resulted in fragmented samples after debinding. The final designed heating profile resulted in a consistent mass loss rate according to thermo gravimetric analysis which limited crack formation during debinding. Debinding under a forming gas (95N2-5H2) atmosphere using optimized heating cycles resulted in sound sintered bodies only when green parts were embedded in a powder bed during debinding.

Effect of the particle size and solids volume fraction on the thermal degradation behaviour of Invar 36 feedstocks

Abstract Degradation kinetics and the thermal stability of Invar 36 powder injection moulding feedstocks (PIM) based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) binders were investigated using simultaneous thermogravimetric analysis (STA) and differential scanning calorimetry (DSC). The initial decomposition temperature (IDT) and the integral procedure decomposition temperature (IPDT) were used to analyse the thermal stability of the binder system as a function of the solid loading content and powder particle size. The degradation kinetics was studied, and the process apparent activation energies were assessed using isoconversional methods. All the methodologies revealed changes in the thermal degradation behaviours of the feedstocks for solid loadings that were previously determined to correspond to optimal solid loadings using other experimental procedures. The studies also contrast previous similar findings with a ceramic powder. Therefore these results strengthen the proposal of thermodynamic degradation studies of feedstocks as an alternative or complementary technique to determine optimal solid loading contents in metal injection moulding (MIM).

Thermal stability and degradation kinetics of feedstocks for powder injection moulding – A new way to determine optimal solid loading?

Degradation kinetics and the thermal stability of zircon powder injection moulding feedstocks (PIM) based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) binders were investigated using simultaneous thermogravimetric analysis (STA). The initial decomposition temperature (IDT) and the integral procedure decomposition temperature (IPDT) were used to analyse the thermal stability of the binder system as a function of the solid loading content. The degradation kinetics was studied, and the degradation activation energy was assessed for varying zircon powder contents using isoconversional methods. All the methodologies revealed changes in the thermal degradation behaviours of the feedstocks for solid loadings that were previously determined to correspond to optimal solid loadings using other experimental procedures. These results may promote the proposal of thermodynamic degradation studies of feedstocks as an alternative or complementary technique to determine optimal solid loading contents in powder injection moulding (PIM). The studies in this paper also examined PIM process operation temperatures for zircon feedstocks.

Fabrication of gradient porous β-SiAlON ceramics via a camphene-based freeze casting process

Gradient porous β-SiAlON ceramics were prepared by unidirectional freezing of camphene-based suspensions on a cold substrate at 0°C and subsequent sintering at 1800°C for 2h. Effects of solid loading content in the suspensions on porosities, pore structures and strengths of the porous ceramics were investigated. The results showed that a gradient microstructure consisting of aligned channels, dendritic and equiaxed pores from the bottom to the top of the sample was created by the freezing process. Both the microstructure observation and the pore size distribution indicated that with the increase of the solid content from 10vol% to 30vol%, the porosity decreased from 71.3% to 36.1% and the pore size decreased from 20μm to 5μm. As a result, the compressive strength increased significantly from 49MPa to 313MPa. The sample fabricated from the slurry with 10vol% solid loading content showed a large strain for failure up to ∼9%.

Effects of solid content on the phase assemblages, mechanical and dielectric properties of porous α-SiAlON ceramics fabricated by freeze casting

Porous Y-α-SiAlON ceramics were prepared by freezing camphene-based suspensions at 0°C and subsequently sintering at 1900°C for 1h. The effects of solid loading content in the suspensions on porosities and formation of α-SiAlON as well as mechanical and dielectric properties of the porous ceramics were investigated. An XRD analysis performed on sintered samples indicated that the α-SiAlON did not fully form in the sample with initial solid loading content of 10vol%, due to the high porosity of 90vol% and interconnected pore of the green body. With the increase of initial solid loading content from 10vol% to 30vol%, the porosity decreased from 62.3% to 23.1% and the average pore size decreased from 19μm to 8μm. As a result, the flexural strength increased significantly from 72.4MPa to 190.2MPa, fracture toughness increased from 1.20MPam1/2 to 3.48MPam1/2, as well as the dielectric constant increased from 3.3 to 6.3. The dielectric loss (tanδ) of obtained material varied between 1.4×10−2 and 2.8×10−2, which did not depend on the porosity of samples.