Gel Casting Research Articles

Toughening effect and mechanisms of AlN whiskers on a low‐temperature sintered AlNw/AlN ceramics

AbstractConventional aluminum nitride (AlN) ceramics exhibited insufficient mechanical properties expected from their potential applications in the presence of dynamic loads and intensive stresses caused by thermal shock. In this study, the mechanical properties of AlN ceramics were enhanced by toughening them using AlN whiskers (AlNw) via gel casting followed by low‐temperature sintering at 1650°C. The addition of AlNw simultaneously increased the bending strength, toughness and thermal conductivity of the AlN ceramics. The maximum values of the bending strength, toughness, and thermal conductivity of 9.0 wt% AlNw/AlN were 303.92 MPa, 3.92 MPa·m1/2 and 186.53 W·m−1·K−1, respectively, which were higher than those of the AlN ceramics by 39.93%, 61.31% and, 15.61%, respectively. The AlNw in AlNw/AlN ceramics tightly bonded with the ceramic matrix, leading to two characteristic toughening mechanisms in the ceramics: crack pinning and deflection at irregular grain boundaries caused by doped whiskers, as well as bridging and stress relaxation caused by whiskers incorporated with the grains. Moreover, the one‐dimensional morphology of AlNw can provide a channel for quick photon transport, thereby enhancing the thermal conductivity of AlNw/AlN.

Mechanical and dielectric properties of porous Si3N4 ceramics prepared by modified water‐based gel casting

Mechanical and dielectric properties of porous Si₃N₄ ceramics prepared by modified water‐based gel casting

Effect of bioceramic inclusions on gel-cast aliphatic polymer membranes for bone tissue engineering applications: An in vitro study.

Polylactic acid (PLA) has been extensively used in tissue engineering. However, poor mechanical properties and low cell affinity have limited its pertinence in load bearing bone tissue regeneration (BTR) devices. Augmenting PLA with β-Tricalcium Phosphate (β-TCP), a calcium phosphate-based ceramic, could potentially improve its mechanical properties and enhance its osteogenic potential. Gels of PLA and β-TCP were prepared of different % w/w ratios through polymer dissolution in acetone, after which polymer-ceramic membranes were synthesized using the gel casting workflow and subjected to characterization. Gel-cast polymer-ceramic constructs were associated with significantly higher osteogenic capacity and calcium deposition in differentiated osteoblasts compared to pure polymer counterparts. Immunocytochemistry revealed cell spreading over the gel-cast membrane surfaces, characterized by trapezoidal morphology, distinct rounded nuclei, and well-aligned actin filaments. However, groups with higher ceramic loading expressed significantly higher levels of osteogenic markers relative to pure PLA membranes. Rule of mixtures and finite element models indicated an increase in theoretical mechanical strength with an increase in β-TCP concentration. This study potentiates the use of PLA/β-TCP composites in load bearing BTR applications and the ability to be used as customized patient-specific shape memory membranes in guided bone regeneration.

In situ shaping of intricated 3D bacterial cellulose constructs using sacrificial agarose and diverted oxygen inflow

Bacterial cellulose (BC) is gathering increased attention due to its remarkable physico-chemical features. The high biocompatibility, hydrophilicity, and mechanical and thermal stability endorse BC as a suitable candidate for biomedical applications. Nonetheless, exploiting BC for tissue regeneration demands three-dimensional, intricately shaped implants, a highly ambitious endeavor. This challenge is addressed here by growing BC within a sacrificial viscoelastic medium consisting of an agarose gel cast inside polydimethylsiloxane (PDMS) molds imprinted with the features of the desired implant. BC produced with and without agarose has been compared through SEM, TGA, FTIR, and XRD, probing the mild impact of the agarose on the BC properties. As a first proof of concept, a PDMS mold shaped as a doll's ear was used to produce a BC perfect replica, even for the smallest features. The second trial comprised a doll face imprinted on a PDMS mold. In that case, the BC production included consecutive deactivation and activation of the aerial oxygen stream. The resulting BC face clone fitted perfectly and conformally with the template doll face, while its rheological properties were comparable to those of collagen. This streamlining concept conveys to the biosynthesized nanocelluloses broader opportunities for more advanced prosthetics and soft tissue engineering uses.

Mechanical and optical properties of porous black Al2O3: Experimental, DFT, and wave optics investigation

Porous black Al2O3 was fabricated by gel casting and pressureless sintering (PS). MnO2 and Fe2O3 incorporated in Al2O3 led to the formation of MnAl2O4 and FeAl2O4 at ≥1200 °C, enhancing its opacity. The influence of various MnO2 content and sintering temperature on the mechanical and optical properties of porous black Al2O3 was investigated. The results showed that as MnO2 content and sintering temperature increased, porosity decreased, bulk density increased, compressive strength increased, and opacity increased. Using density functional theory (DFT), the intrinsic properties of MnAl2O4 and FeAl2O4 were investigated, including band structure (BS), electron distribution, partial density of states (PDOS), and optical properties such as refractivity, absorption, dielectric constant, conductivity, and dissipation factor across various wavelengths. These DFT calculations were incorporated into the wave optics model to assess the response and impedance matching of porous black Al2O3 to transverse electric (TE) and transverse magnetic (TM) waves with various MnAl2O4 content.

Effect of applied stress on microstructural evolution during the sintering of nanocrystalline tetragonal zirconia below 1000 °C

Microstructural evolution during the sintering of tetragonal ZrO2 nanoparticles was investigated using stress-free sintering and sinter forging. The green body prepared via gel casting had a densely packed structure with a narrow pore size distribution. Special attention was paid to the evolution of pore structures in the initial and intermediate stages of sintering. Pore coarsening, which is considered an important issue in the nanoceramics densification, was not remarkable in sinter forging. The accelerated densification rate, coupled with the retention of finer pore size than that in stress-free sintering throughout densification, lowered the sintering temperature requirement. This temperature reduction effectively inhibited grain growth, allowing samples prepared via pressure-assisted sintering to maintain a nanometric structure.

Design and preparation of sandwich structured Si3N4 ceramics for broadband microwave transmission

To develop high-temperature structural materials with broadband microwave transmission ability used for high-speed aircraft radome, a sandwich-structured silicon nitride (Si3N4) ceramic consisting of porous core and dense shell is designed based on CST simulation, which helps to obtain the optimized structural and dielectric properties. After that, its near-net-shape preparation strategy is presented by a controllable combined process including gel-casting (GC), polymer infiltration and pyrolysis (PIP), and chemical vapor deposition (CVD). The mechanical and electromagnetic performances were studied. The results show that the optimally-structured sandwich Si3N4 processes a flexural strength of 216.5 MPa and a microwave transmissivity of 80 % in 2–13.4 GHz, which are obviously higher than that of traditional Si3N4 ceramics. Besides, this sandwich-structured Si3N4 ceramics also shows excellent dielectric and mechanical stabilities after a high-temperature oxidization at 1600 °C for 2 h in air atmosphere. Our prepared Si3N4 ceramics achieves excellent mechanical strength, high microwave transmissivity, and good high temperature stability, indicating a great application potential as high-speed aircraft radome materials.

Sustained release of human placental extract from chitosan patch incorporated with GO/Zn(Cu)O nanocomposite for enhanced healing of diabetic wounds

Chronic wounds are caused due to microbial infections at wound site. Especially, diabetic wounds are a major challenge worldwide. Infection is the major concern in diabetic wound healing. In severe cases, it leads to amputation and death. Human placental extract (HPE) acts as therapeutic agent which possesses anti-inflammatory and angiogenesis property. In this work, HPE was incorporated along with GO/Zn(Cu)O nanocomposite in the wound dressing chitosan patch. It has antibacterial activity and enhances the cell proliferation. The HPE and nanocomposite incorporated polymeric patches are fabricated using gel casting technique. The patch was tested for its antibacterial activity against E. coli, P. aeruginosa, S. typhi, S. flexneri, S. aureus and E. faecium. The PVA/Cs/GO/Zn(Cu)O/HPE patch has swelling percentage of 70 ± 3.5% on 7th day. The water vapour transmission rate (WVTR) for PVA/Cs/GO/Zn(Cu)O/HPE patch is 2249 ± 2.94 g/m2 day−1. The PVA/Cs/GO/Zn(Cu)O/HPE patch shows a porosity of 77 ± 3.8%. In scratch assay the rate of wound closure for PVA/Cs/GO/Zn(Cu)O/HPE patch is 99.4 ± 4.9%. The sustained release of HPE was observed to be 78% at day 14. So far up to our knowledge, sustained release of HPE was not established for diabetic treatment. The biocompatibility and hemocompatability analysis were performed using NIH 3T3 fibroblast cells. In in vivo study the patch shows healing efficiency of 98%. The patch does not cause any toxic effects.

High luminous efficiency and excellent thermal performance in rod-shaped YAG:Ce phosphor ceramics for laser lighting.

High power and high brightness laser lighting puts forward new requirements for phosphor converters such as high luminous efficiency, high thermal conductivity and high saturation threshold due to the severe thermal effect. The structure design of phosphor converters is proposed as what we believe to be a novel strategy for less heat production and more heat conduction. In this work, the rod-shaped YAG:Ce phosphor ceramics (PCs) and disc-shaped YAG:Ce PCs as control group were fabricated by the gel casting and vacuum sintering, to comparatively study the luminescence performance for LD lighting, on the premise that the total number of transverse Ce3+ ions and the volume of samples from two comparison groups were same. All rod YAG:Ce PCs with low Ce3+ concentration exhibited the high luminous efficiency and better thermal stability than YAG:Ce discs with high Ce3+ concentration. Under the laser power density of 47.8 W/mm2, the luminous saturation was never observed in all rod-shaped YAG:Ce PCs. The high luminous efficacy of 245∼274 lm/W, CRI of 56.3∼59.5 and CCT of 4509∼4478 K were achieved. More importantly, due to the extremely low Ce3+ doping concentration (0.01 at%), rod-shaped ceramics based LDs devices showed the excellent thermal performance and their surface temperatures were even below 30.5 °C surprisingly under the laser power density of 20.3 W·mm-2 (2 W). These results indicate that the rod shape of phosphor converter is a promising structure engineering for high power laser lighting.

Effect of gamma radiation on the optical and color properties of Makrolon/Pocan/ZnS-NiO nanocomposite films

Makrolon/Pocan is a polymer blend of amorphous polycarbonate (PC) and semicrystalline polybutylene terephthalate (PBT). We fabricate a nanocomposite (NC) of PC/PBT polymer blend, Zinc sulfide (ZnS) and Nickel oxide (NiO) nanoparticles by the sol–gel and ex-situ casting processes. We trust that this study is novel in the area of the impact of γ radiation on this NC. The Rietveld modification of XRD records indicates that both the prepared ZnS and NiO have a nano-nature of an average particle size of 4 and 18 nm, respectively. Samples of the PC-PBT/ZnS-NiO NC films are irradiated with several γ doses (10 − 100 kGy). We investigate the resulting outcome of the γ irradiation on the linear and non linear optical behavior of the NC films, using ultraviolet spectroscopy (UVs) and the International Commission on Illumination (CIE) color changes technique. Upon increasing the γ dose up to 100 kGy, the maximum dose used, both direct and indirect bandgaps decreased. The Urbach energy exhibits a reverse trend. We attribute this to the dominance of chain crosslinks that damaged the ordered configuration and thus increased the amorphous phase. This suggests that the γ radiation can facilitate the spreading of the nanoparticles within the composite matrix suggesting an extra compacted structure of the NC samples. Also, we detect the nature of microelectronic transitions, using the optical dielectric loss (ε”), and found that the PC-PBT/ZnS-NiO NC films had direct allowed transitions. Moreover, we study the γ-induced modifications in the optical conductivity, dielectric parameters and nonlinear optical parameters. Further, the color changes between the pristine and irradiated films were estimated. The pristine NC film exhibited significant color differences upon γ irradiation. The induced improvements in the optical characters suggest that the γ is a suitable mean that permits the use of PC-PBT /ZnS-NiO NC in the optoelectronic devices.

Study on self-glazed ceramic tiles based on geopolymer gel casting

The preparation of ceramic materials from alkali-activated geopolymers has formed a new research direction. This study focuses on the preparation of ceramic tiles based on geopolymer alkali activation and by gel casting to investigate the mechanism of natural glaze formation and its microstructure evolution. For this reason, different Si/Al ratios (3.0–4.5) with different sintering temperatures (1080–1170 ℃) were chosen for the experiments to be discussed. The results showed that gel casting is conducive to the natural formation of the glaze and the close combination with the body. The amount and viscosity of the liquid phase on the surface of the sample at high temperatures will affect the forming effect of the glaze. Therefore, higher Si/Al ratio and sintering temperature are more conducive to the development and formation of the glass glaze. The optimum sintering temperature of the sample was 1110 ℃, the Si/Al ratio was 3.5, and the holding time was 2 h. Under these preparation conditions, the linear shrinkage was 18%, the rupture modulus was 48.08 MPa, the water absorption was 0.02%, the bulk density was 2.42 g∙cm−3, and the thickness of the glaze layer was about 190 µm.

Fabrication of silica glass for UV-transmission by gel-casting method

We present the gel casting preparation of sintered silica glass and analyze its structural and optical properties in both atmospheric and 10−4 Pa high-vacuum conditions, with annealed and non-annealed samples, alongside a comparison to synthetic silica glass. The crystallization temperature of SiO2 bodies sintered in high-vacuum is higher than that in atmosphere since high-vacuum sintered body has less β-OH, the suitable temperature range is on the high temperature side compared to in the atmosphere. Fluorescence spectrum, ESR spectra and the transmittance spectrum indicate the existence of NBOHC, POR and E′ center in atmospheric sintered silica glass as well as ODC(I) and E′ center in high-vacuum sintered silica glass. High-vacuum sintering and annealing in hydrogen atmosphere can eliminate oxygen defects, NBOHC, POR, and E’ centers, resulting in the transmittance reached 91.1 % at 265 nm and 87.3 % at 230 nm. These are equivalent to 98.9 % and 94.9 % of the synthetic silica glass, respectively.

Fabrication of in-situ Ti-Cx-N1−x phase enhanced porous Si3N4 absorbing composites by gel casting

In view of the lack of a conformal, load-bearing, lightweight, and high-temperature resistant integrated microwave-absorbing composites for applications under extremely complex conditions, this study successfully applies gel casting craft to porous Si3N4 microwave-absorbing composites. The high-temperature decomposition reaction of Ti3SiC2 powder was utilized to generate uniform Ti-Cx-N1−x grains in situ and to enhance the mechanical and microwave-absorption properties of porous Ti-Cx-N1−x/Si3N4 composites. The bending strength, fracture toughness, density, maximum reflection loss value, absorption bandwidth and matched thickness in P-band of the composite with 30 wt% Ti3SiC2 addition were 164.87 ± 7.56 MPa, 2.61 ± 0.13 MPa·m1/2, 2.077 g/cm3, 32.42 dB, 1.74 GHz and 4.2 mm, respectively. The fracture toughness and bending strength of the composite were increased by 71.71% and 58.13%, respectively, compared with monolithic porous Si3N4. The electromagnetic wave loss mechanisms of the composites are proposed as a combination of conductivity loss, multiple reflections and scattering, interfacial polarization and defect polarization.

Effect of Laser Radiation on the Linear and Nonlinear Optical Characteristics of Polyvinyl Alcohol/Carboxymethyl Cellulose/Nickel Oxide Nanocomposite Films

A nanocomposite (NC) of polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and nickel oxide (NiO) nanoparticles (NP) was prepared using sol–gel and ex-situ casting techniques. The results indicated that the NiO had a single phase with the space group (R-3m). Its average grain size was 18 nm. We used an infrared pulsed laser to irradiate the PVA/CMC/NiO NC samples with energy fluences ranging from 4 to 16 Joule/cm2. The induced changes in the linear and nonlinear optical properties of the NC samples due to the laser irradiation were investigated by means of UV spectroscopy. When the laser fluence increased up to 16 Joule/cm2, the maximum fluence used, both the direct and indirect bandgaps decreased. Additionally, we used the optical dielectric loss (ε″) to detect the type of microelectronic transition for the PVA/CMC/NiO NC samples, which was found to be a direct allowed transition. The laser effects on the absorbance, extinction coefficient, refractive index, dielectric parameters, optical conductivity, and the nonlinear parameters of the NC were studied. The enhancement in the optical properties indicated that the laser radiation is a useful tool that allows the application of the resulting PVA/CMC/NiO NC in optoelectronic devices.

A Workflow to Produce a Low-Cost In Vitro Platform for the Electric-Field Pacing of Cellularised 3D Porous Scaffolds.

Endogenous electrically mediated signaling is a key feature of most native tissues, the most notable examples being the nervous and the cardiac systems. Biomedical engineering often aims to harness and drive such activity in vitro, in bioreactors to study cell disease and differentiation, and often in three-dimensional (3D) formats with the help of biomaterials, with most of these approaches adopting scaffold-free self-assembling strategies to create 3D tissues. In essence, this is the casting of gels which self-assemble in response to factors such as temperature or pH and have capacity to harbor cells during this process without imparting toxicity. However, the use of materials that do not self-assemble but can support 3D encapsulation of cells (such as porous scaffolds) warrants consideration given the larger repertoire this would provide in terms of material physicochemical properties and microstructure. In this method and protocol paper, we detail and provide design codes and assembly instructions to cheaply create an electrical pacing bioreactor and a Rig for Stimulation of Sponge-like Scaffolds (R3S). This setup has also been engineered to simultaneously perform live optical imaging of the in vitro models. To showcase a pilot exploration of material physiochemistry (in this aspect material conductivity) and microstructure (isotropy versus anisotropy), we adopt isotropic and anisotropic porous scaffolds composed of collagen or poly(3,4-ethylene dioxythiophene):polystyrenesulfonate (PEDOT:PSS) for their contrasting conductivity properties yet similar in porosity and mechanical integrity. Electric field pacing of mouse C3H10 cells on anisotropic porous scaffolds placed in R3S led to increased metabolic activity and enhanced cell alignment. Furthermore, after 7 days electrical pacing drove C3H10 alignment regardless of material conductivity or anisotropy. This platform and its design, which we have shared, have wide suitability for the study of electrical pacing of cellularized scaffolds in 3D in vitro cultures.

Research on the gel casting process and flexural strength of high-stability alumina ceramics

Gel casting is an advanced wet-forming method for ceramics. In this paper, Isoabm 104 is selected as the dispersant and gelation agent for gel casting. The optimization of gel casting slurry and the preparation of the green and sintered alumina bodies are investigated. TAC reduces the viscosity of the slurry significantly due to electrostatic interaction. Isopropanol alcohol and vacuum tank eliminates the slurry’s air bubbles, thus improving the density of green bodies. A staged drying process is necessary to produce smooth and defect-free green bodies. After optimization of the slurry formulation and gel casting process, alumina ceramics with a Weibull modulus of 11.1 are successfully prepared.

Enhancing the activity of ECG Surface Electrodes with super p carbon black additive

The recent developments in the area of surface electrodes materials for biomedical devices such as ECG, EEG are unforeseeable. The role of novel materials in electrode development is highly required for futuristic applications in health and biomedical industry to fulfill the patients’ demand. The proposed project has emphasized on the uses of conductive materials Super p carbon black (SPCB) in electrodes, for enhancing the activity of surface electrodes to capture the better signal of the patients. A great challenge lies not only in fabrication of such materials but also in physical characterization of such conductive materials. In the recent era carbon based nano-materials like CNTs, Graphene, GO and rGO overruled on Ag/AgCl based on its better conductivity. The research work has focused on the electrode fabrication with a conventional slurry-based gel cast method by using Super p carbon black and polymer Ethylene Co Vinyl Acetate (EVA). Further the study has aimed on the quantitatively use of Super p carbon black conductive materials on the surface of the electrode and fictionalized it by using EVA. The electrode material was characterized by in-situ non- destructive conductivity study using the Electrochemical Impedance Spectroscopic (EIS) method. This Super p carbon black could be used directly on the surface of the electrode as inbuilt in a dry form to avoid the un-comfortableness of the patient and longevity of the electrode in various biomedical devices like ECG, EEG, etc.

Experiment on preparation of porous glass-ceramics by inorganic gel casting from coal-based slag

Porous glass-ceramics have aroused extensive attention due to their thermal insulation and sound insulation properties. An emerging research focus is the utilization of solid waste as raw material for producing porous glass-ceramics. The inorganic gel casting method, involving alkali activation and mechanical stirring, has been proposed to achieve a hierarchical porous structure. In this study, porous glass-ceramics were fabricated using coal-based slag as the raw material through inorganic gel casting and the effects of the key parameters on the properties of porous glass-ceramics were revealed. Five key factors, namely the mass ratio of raw materials (A), gelation time (B), curing time (C), and sintering temperature (D), and heating rate (E), were identified as the design variables. The Taguchi method of L16 orthogonal array was employed to establish the mix proportions based on these design variables. Subsequently, the influences of these design variables on the microstructure of intermediate porous glass embryo, as well as the porosity and compressive strength of porous glass-ceramics, were analyzed. The results revealed the optimal parameter combination for gel generation as follows: a material mass ratio of 61:35:4 wt%, a gel time of 60 min, and a curing time of 36 h. The effects of these factors on pore structure and compressive strength followed the descending ranks of A > E > B > C > D and A > B > D > C > E, respectively. The maximum gel yield was reached at a mass ratio of 61:35:4 wt%, while the optimal pore structure was obtained at a mass ratio of 66:35:4 wt%. The sintering temperature exhibited minimal influence on the pore structure, whereas the sintering heating rate had minimal effect on the compressive strength. At a gelation time of 90 min and a curing time of 36 h, the porosity were exceeded 30%, and the pore size exhibited uniform distribution.

Preparation and properties of lightweight, conformal, and load‐bearing TiC/Si3N4 absorbing composites by gel casting

AbstractIn view of the lack of conformal, load‐bearing, light‐weight, and high temperature‐resistant integrated wave‐absorbing composites suitable for extremely complex conditions, the gel‐casting process was successfully applied to porous Si3N4 wave‐absorbing composites in this work. A universal low‐slurry for gel casting was prepared by using two dispersants acting together (tetramethylammonium hydroxide solution and sodium lauryl sulfate), which ensured the smooth completion of the gel casting process. Combining the thermogravimetric and differential thermal gravity curves of the composite green body, reasonable parameters of the rubber discharge process are given to avoid the problem of the green body swelling and cracking. The porous TiC/Si3N4 composites were successfully prepared by holding them at 1650°C for 3 h. The bending strength, density, minimum reflection loss, absorption bandwidth, and matched thickness in the P‐band of the composites with 30 wt.% TiC addition were 54.08 ± 3.02 MPa, 1.906 g/cm3, ‐37.75 dB, 1.9 GHz, and 4.1 mm, respectively. The electromagnetic wave loss mechanisms of the composites are a combination of conductivity loss, multiple reflections and scattering, interfacial polarization, and defect polarization.

Enhanced thermal conductivity of Si3N4 ceramics through pyrolytic carbon prepared by gel casting using DMAA

To reduce the lattice oxygen content of Si3N4 green bodies, samples were prepared using an N,N-dimethylacrylamide (DMAA) system. The endothermic and exothermic peaks are related to the decomposition of organic matter and the reaction between pyrolytic carbon and impurity oxides in the sintering process. Multi-step heat preservation during the thermal degreasing process reduced the carbon content and defects. The α→β phase transformation and aspect ratio of grains changed from 89.2% to 4.84:1 at 1640 °C to 96.3% and 7.80:1 at 1700 °C, respectively. The relative density, hardness, fracture toughness, and thermal conductivity of the Si3N4 samples reached 98.5%, 1353 HV, 8.51 MPa·m1/2, and 97.1 W·m−1·K−1, respectively. Pyrolytic carbon can react with SiO2, which reduces the content of the glass phase in the green body and affects the dissolution and precipitation process and lattice oxygen content. In the structure of the Si3N4 sample, carbon particles with sizes of 100–500 nm and near-spherical shapes were observed. Intergranular-phase YMgSi2O5N was formed during the sintering process, which was conducive to improving the thermal conductivity. This article uses lower temperature and no pressure conditions to prepare Si3N4 ceramics, which can provide reference for batch and low-cost production.