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Magnesia porous insulation materials were prepared via foam-gelcasting using industrial grade mid-range magnesia powder as the main raw materials, a copolymer of isobutylene and maleic anhydride (Isobam-104) as the dispersing and gelling agent, sodium carboxymethyl cellulose (CMC) as the foam stabilizing agent, and cetyltrimethylammonium bromide (CTAB) as the foaming agent. The effects of processing parameters such as amount of Isobam-104 (0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, and 0.3 wt%) and firing temperature (1300 ℃, 1350 ℃, and 1400 ℃) on magnesia porous insulation materials were investigated. In addition, the universal testing machine (WDW-100E) and the scanning electron microscope (SEM) were employed to characterize the firing samples. The results indicated that the compressive strength of the prepared samples increased with the increase in firing temperature, and the porosity decreased gradually. When the firing temperature was 1350 °C, the internal pores of the samples were uniformly distributed, the average pore size was in the range of 26.2 μm to 35.6 μm, and the compressive strength was in the range of 7.8 MPa to 11.5 MPa when porosity varied from 65.2% to 60.4%. The thermal conductivity of the prepared magnesia porous insulation materials was in the range of 0.481 W/(m·K) to 0.842 W/(m·K). [ABSTRACT FROM AUTHOR]

In the present work, porous ceramics with open pores were fabricated using the gel casting method, which utilizes carrageenan as a cross-linking agent. Beyond the foaming agents or templates techniques, this approach employed large-sized Al2O3 particles (~ 45 μm) as the underlying framework material, enabling the direct formation of minute open pores within the green bodies and sintered samples. In order to finely adjust the pore structure and bolster flexural strength, micropowders of α-Al2O3 and Kaolin were incorporated as filling materials, alongside the introduction of rare-earth oxides as sintering additives. The study diligently examined the impact of varying the content of sintering additives as well as the sintering temperatures on the characteristics of the porous ceramics. As a result, remarkable achievements were obtained, culminating in the production of Al2O3-based porous ceramics measuring 8 mm in thickness, exhibiting flexural strength exceeding 160 MPa, porosity surpassing 30%, and exceptional gas permeability of over 30 L/min/cm2 under a pressure drop of 100 kPa. [ABSTRACT FROM AUTHOR]

PVC/FeCr2O4/x wt% tetrapropylammonium iodide (TPAI, x = 0, 2.5, 5, 10, 20) polymers were prepared using casting and sol gel methods. Rietveld refinement was used to determine the structural and microstructural properties of FeCr2O4 nanofiller. XRD, FTIR, and SEM techniques were applied to explore the effect of fillers on the structural features of PVC polymer. The effect of FeCr2O4 and/or TPAI on the linear/nonlinear optical properties of PVC was explored. Absorbance was obviously enhanced, and transmittance reduced in the range 200–450 nm upon doping with TPAM. The refractive index and reflectance were increased by loading FeCr2O4. The direct (4.25 eV) and indirect (4.1 eV) bandgap values of the pure PVC were reduced to 4.21 and 3.95 eV upon loading with FeCr2O4; both reduced further, but irregularly, as the amount of TPAI increased attaining lowest values 3.11 and 2.62 eV for TPAI content 2.5 wt%. The optical conductivity and the dielectric constant were greatly enhanced by TPAI doping, while the nonlinear optical parameters were improved by FeCr2O4 loading. Under different excitation wavelengths, the fluorescence intensity was quenched upon loading FeCr2O4, then reduced a little by adding TPAI; the corresponding CIE chromaticity diagrams were obtained. [ABSTRACT FROM AUTHOR]

Ceramic cores are the key intermediate components of hollow blades for aero-engine. Conventional processes, such as hot-press molding and gel film casting, face difficulties in fabricating complex-structured ceramic cores due to the complexity of moulds and long process cycles. Stereolithography 3D printing provides a new idea for the fabrication of complex-structured ceramic cores. The effect of sintering temperature on open porosity, bulk density, weight loss rate, shrinkage rate, flexural strength and microstructure of the Al2O3-based ceramic core doped with 10vol.% polysilazane (PSZ) was studied. The sintering mechanism of PSZ-reinforced ceramic cores was analyzed. Results show that the optimum sintering temperature of PSZ-reinforced ceramic cores is 1,450 °C. At this temperature, the open porosity of the ceramic core is 36.60%, bulk density is 2.33 g·cm-3, weight loss rate is 22.11%, shrinkage rate along the X, Y, Z directions is 5.72%, 5.01%, 9.61%, respectively; the flexural strength is 28.794 MPa at 25 °C and 13.649 MPa at 1,500 °C. Properties of 3D printing PSZ-reinforced ceramic cores can meet the casting requirement of superalloy hollow blades, which is expected to promote the industrial application of 3D printing complex structure ceramic cores. [ABSTRACT FROM AUTHOR]

Gel casting is one of the new and promising methods for producing ceramics. Current research on the production of ceramic materials by gel casting covers a wide range of materials, including dense as well as porous ceramic materials. The advantages of this method, such as ease of processing, use of the process equipment of conventional methods, heightened productivity, and possibility of obtaining products having large shapes and complex geometries, are creating a surge in new R&D. This article reviews publications devoted to research conducted during recent decades on the production of both dense ceramics for the manufacture of structural elements and porous ceramics for the manufacture of thermal insulation, porous filters, and membranes by the gel casting method. [ABSTRACT FROM AUTHOR]

Polymer networks incorporated with iron and zinc oxide nanoparticles have superparamagnetic and electrical characteristics where it can be employed in a variety of significant applications. To achieve optimal distribution and connection of nanoparticles in various polymeric matrices, it is required to investigate their dispersion performance with varied contents and the impact on their physical characteristics. A controlled sol-gel method is used combined with gel casting to synthesize organic-inorganic nanocomposites of (ZnO)x(1 − x)Fe2O3 loaded within a polystyrene-polyethylene glycol matrix. The structural and morphological assembly of the hydrogen bonds between the inorganic and organic parts is verified using X-ray diffraction (XRD) and scanning/transmission electron microscope (SEM/TEM) for the synthesized nanocomposites. The existence of the Fe aggregates, Zn/Fe pairs, and organic molecules was also confirmed by FTIR spectra. Optical and magnetic properties were evaluated. The band gap, refractive index, optical dielectric constant, and optical electronegativity were extracted. [ABSTRACT FROM AUTHOR]

The use of ceramic–metal laminated composites is an efficient way to improve the toughness of brittle ceramics. Uniform multilayered Al2O3–Ni laminated composites were prepared through a combined method of gel casting and hot pressing, which is less cumbersome than the traditional sequential lamination method. The wettability, diffusion and chemical reaction between Al2O3 and Ni were controlled through surface oxidation treatment of the Ni sheets. The results show that when the surface-oxidized Ni sheets were used, the microstructure of the Al2O3–Ni interface changed with the hot-pressing temperature. As the hot-pressing temperature was increased from 1150 to 1300 °C, a straight and clean interface formed, the interface became interlocked and, finally, a stable layer of NiAl2O4 formed at the interface. The interlocked microstructure was especially beneficial for interfacial bonding, and the plastic deformation of the Ni layers was restrained, thereby leading to slip steps rather than dimple formation on the fracture surfaces of the Ni layers. In addition, the toughening effects of plastic deformation and crack deflection in the Al2O3–Ni laminated composites were significant, which resulted in ductile fracture rather than brittle fracture. As a result, the Al2O3–Ni laminated composite that was prepared using the oxidized Ni sheets and the combined method of gel casting and hot pressing achieved a higher work of fracture than laminated composites that were prepared via other methods. [ABSTRACT FROM AUTHOR]

In this study, porous mullite ceramics were prepared by gel-casting using fused mullite particles as the raw materials, ρ-Al2O3 and polysilicon waste as the binders, and starch as the pore forming agent. In addition, the effects of pore forming agent content on the apparent porosity, compressive strength, pore size distribution, thermal analysis, and pressure drop of porous mullite ceramics were studied. The results show that the as-prepared porous mullite ceramics have high apparent porosity, compressive strength, and gas permeability. Mullite phase formed in situ by adding polysilicon waste and ρ-Al2O3, which bonded the fused mullite particles and improved the performance of porous mullite ceramics. With increasing soluble starch content, the apparent porosity of the samples increased from 49.50 to 62.67%, and the compressive strength decreased from 4.98 MPa to 1.35 MPa. Furthermore, uniform pore size distribution and high gas permeability fully meet the requirements for the application of high-temperature flue gas filtration. [ABSTRACT FROM AUTHOR]

The gelcasting method was used to form gastight Ba0.95Ca0.05Ce0.9Y0.1O3 samples proposed for use as proton-conducting electrolytes in solid oxide fuel cells. Methylcellulose was used as an environmentally friendly shaping agent for Ba0.95Ca0.05Ce0.9Y0.1O3 powder in an ethanol solution. Samples of Ba0.95Ca0.05Ce0.9Y0.1O3 were also prepared from the same powder via traditional isostatic pressing, as a reference for cast samples, and sintered in the same conditions. Comparative studies of the physicochemical properties of Ba0.95Ca0.05Ce0.9Y0.1O3 electrolytes, formed by means of these two methods and then sintered at 1550 °C for 2.5 h, were presented and discussed. Using the X-ray diffraction method, only the pure orthorhombic phase of BaCe0.9Y0.1O3 was detected in the Ba0.95Ca0.05Ce0.9Y0.1O3 powder, as well as in the Ba0.95Ca0.05Ce0.9Y0.1O3 sintered pellets formed via both gelcasting (A) and isostatic pressing (B). Thermal effects occurring during heating of methylcellulose, as well as ceramic Ba0.95Ca0.05Ce0.9Y0.1O3 powder, dried cast samples obtained from the prepared slurry, and sintered Ba0.95Ca0.05Ce0.9Y0.1O3 samples, were examined by differential scanning calorimetry, differential thermal analysis, thermogravimetric analysis, and evolved gas analysis of volatile products using a quadrupole mass spectrometer. The measurements were performed within the temperature range of 20–1200 °C in air. Based on dilatometric tests, it was found that the Ba0.95Ca0.05Ce0.9Y0.1O3 cast samples exhibited slightly higher degree of sinterability than the 5CBCY samples obtained by isostatic pressing. In comparison with pressed pellets, higher values of total electrical conductivity in air or in a gas mixture of 5% H2 in Ar were also attained for Ba0.95Ca0.05Ce0.9Y0.1O3 cast samples. The Ba0.95Ca0.05Ce0.9Y0.1O3 samples were used to construct oxygen–hydrogen electrolytes for solid oxide fuel cells. The results of the electrochemical performance of solid oxide fuel cells with Ba0.95Ca0.05Ce0.9Y0.1O3 electrolytes were comparable to the data in the literature on BaCe0.9Y0.1O3 electrolytes. An electrochemical study of a Ba0.5Sr0.5Co0.8Fe0.2O3−δ|Ba0.95Ca0.05Ce0.9Y0.1O3 interface was also performed. Ba0.5Sr0.5Co0.8Fe0.2O3−δ appears to be a suitable cathode material for a Ba0.95Ca0.05Ce0.9Y0.1O3 electrolyte. [ABSTRACT FROM AUTHOR]

This work concerns the study of ceramic-metal composite materials processed by gel casting method. Due to limited possibilities of fabrication complex-shape elements obtained by classical methods of powder metallurgy (such as isostatic or uniaxial pressing) the colloidal processes are recently willingly applied in manufacturing of ceramic matrix composites. In the present work Al2O3–10 vol.% Mo composites were formed by aqueous gel casting process and sintered in argon atmosphere. Selected physical properties and phase composition have been described. The microstructure of the green and sintered samples was examined with a scanning electron microscope. Molybdenum particles were homogeneously distributed in the ceramic matrix. Moreover, Mo2C was formed during sintering process that had a positive contribution to enhancing the hardness of the composite. The composite after sintering was characterized by a density higher than 95% of theoretical density and high hardness. The performed studies have confirmed the possibility of application of gel casting method to produce Al2O3–Mo composite system. [ABSTRACT FROM AUTHOR]

Ceramic powder casting technique using ovalbumin, i.e., egg protein, as natural amino-based binder. The study has shown successful gelcasting of high-performance 3D thermal conductivity aluminum nitride (AlN) for application in the 3D integrated circuits (3D-IC). The green body has a good flexural strength of 3 MPa, which is sufficiently be trimmed with computerized numerical controlled (CNC) machining prior to the pyrolysis manufacturing processes, i.e., sintering technologies. Different particle sizes of AlN powder was being investigated and the results indicated bimodal particle size ratio of 1.5 to 2 attributed the most favorable combination in this study. Doped of rare earth element, yttrium oxide (Y2O3) nano particle size, has shown an improvement in overall thermal conductivity of 3D sintered objects. SEM images also well demonstrated higher thermal conductivity value are linked with a compact structure of higher density of 3D ceramic objects. [ABSTRACT FROM AUTHOR]

Several types of alloplastic (artificial) grafts, known as scaffolds, have been developed for the treatment of bone defects caused by trauma and/or infection. Among the materials used to manufacture scaffolds, 45S5 Bioglass is a bioceramic that arouses significant interest due to ease preparation and excellent bioactive response. Among the various processing methods cited in the literature for the production of bioactive glass scaffolds, gelcasting is a method that produces macroporous structures, with interconnected and spherical pores and high mechanical strength. However, in the literature there are few reports about bioactive glass scaffolds produced by gelcasting method. In this work, 45S5-BG scaffolds were produced by gelcasting of foams varying the amount of foaming agent in order to optimize the desirable characteristics of the scaffold. The scaffolds show porosity between 70 and 86% and compressive strength of 1.22 ± 0.7 and 0.78 ± 0.4 MPa. In the biological studies, all 45S5-BG scaffolds showed cytocompatibility towards human osteoblastic cells and bioactive properties using SBF assay. [ABSTRACT FROM AUTHOR]

A method of coating aluminum powder with Nylon-12 via a dissolution-precipitation process to prevent hydrolysis reaction in gel casting was introduced in this study. Aluminum powder additive was adopted to facilitate the synthesis of mullite via Al-SiO reaction which could help to improve the high-temperature strength of AlO-based ceramic molds. However, the aluminum powder would have hydrolysis reaction and affect the rheological properties of the slurry. While adding the aluminum powder that was treated by corroding oxidation film and coated with Nylon-12, the slurry could finish the gel casting process. The coated aluminum almost had no impact on the rheology property of the slurry, as the viscosities of the slurries with different diameters of coated aluminum additive were all under 1 Pa s. The microstructures and phase compositions of the sintered ceramic samples were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Effects of coated aluminum powder additive on the high-temperature strength of AlO-based ceramic containing nano-SiO and MgO were investigated. The bending strength of the ceramic mold at 1500 °C peaked at 20.88 MPa with 1 μm coated aluminum powder additive. Finally, a porous AlO-based ceramic mold was fabricated with adoption of this method and successfully applied to cast a turbine blade, indicating that the high-temperature strength of the ceramic mold could meet the casting requirements. [ABSTRACT FROM AUTHOR]

The paper presents the analysis of thermal stability and decomposition of AlO and (Ba,Sr)TiO green bodies as well as commercially available organic additives which are used in shaping of ceramics by colloidal processing. The first analyzed ceramic material was AlO green body obtained by gelcasting. The second examined material was elastic ceramic-polymer composite based on ferroelectric powder BaSrTiO with NiO obtained by tape casting method. This flexible and durable material is characterized by high value of dielectric constant and finds the application in devices operating at very high frequencies up to sub-THz. Most organic additives are indispensable just in forming step but must be then eliminated in order to obtain pure ceramic phase, additionally some of them have to be stable in a wide temperature range. The analyzed organic substances were as follows: 2-carboxyethyl acrylate, SYNTRAN 8250, DURAMAX D-3005, DURAMAX B-1000. The DTA/TG measurements coupled with mass spectrometry allowed to gain new knowledge concerning degradation of selected organic additives, thermal stability of ceramic-polymer composite and type of gases released from samples during thermal treatment. [ABSTRACT FROM AUTHOR]

Porous mullite materials with high porosity of 71.8-88.2% were prepared by foaming of coal gangue/Al2O3/starch composite slurry and subsequent pore structure stabilization using starch consolidation and sintering. Coal gangue was recycled to prepare porous mullite foams. Starch was used as gellant, replacing commonly used poisonous chemical and expensive animal protein additives in foaming. Sintered mullite foams exhibited tri-modal pore structure, including large-sized pores (50-300 μm) replicating gas bubbles, moderate-sized pores (~10 μm) embedded in pore walls, and small-sized pores (<5 μm) appearing among mullite crystals. The compressive strength of mullite foams was between 0.21 and 8.7 MPa with low thermal conductivity between 0.1056 and 0.3848 W/m K, indicating that porous mullite foams are candidate materials for applications in thermal insulation. [ABSTRACT FROM AUTHOR]

A new water-soluble calcia-based ceramic core of using epoxy resin binder was developed for investment casting by aqueous gel casting. The influences of dispersant addition and solid loading on the rheological property of the slurries were investigated. The low-shrinkage and high-strength ceramic body was obtained by adjusting binder addition and solid loading. The water-soluble behavior of the calcia-based ceramic core and its solution mechanism were studied. The results show that the 48 vol% slurry composing of 6 wt% dispersant content, 16 wt% binder content, and 20 wt% hardener content can prepare a stable and fluidic slurry, and the bending strength of the dried green body is 29.5 ± 1.4 MPa, the linear shrinkage is 3.62 %, and the green relative density is 58.5 % with a homogeneous microstructure. After sintering at 1300 °C, the ceramic core exhibits a uniform microstructure with a bending strength of 25 ± 1.2 MPa, a sintered shrinkage of 11.31 %, a relative density of 92.3 %, and an apparent porosity of 30.5 %. The solubility rate of the ceramic core is 2.83 kg/min m, and the dissolution of the ceramic core in water is exothermal. The water-soluble calcia-based ceramic core fabricated by aqueous gel casting using epoxy resin could overcome the poor leachability of the common ceramic core and enhanced the production efficiency. [ABSTRACT FROM AUTHOR]

The main objective of producing ceramic-metal composites is to improve the fracture toughness of the brittle ceramic matrix. Classical methods of powder metallurgy (such as isostatic or uniaxial pressing) are not capable of fabricating complex-shape elements. For this reason, colloidal processes have been applied recently in manufacturing of ceramic matrix composites. In the present work, AlO-3 vol.% Ni composites were prepared by aqueous gelcasting process and sintering in reducing atmosphere. The commercially available monomers 2-hydroxyethyl acrylate and N,N′-methylenebisacrylamide as cross-linking agents were used. The activator was N,N,N′,N′,-tetramethylenediamine (TEMED) and ammonium persulfate was added as an initiator of the polymerization process. Composite slurries were obtained from alumina powders (grain size 0.21 μm) and 3% (in respect to the total solid volume) of two nickel powders of different grain size (~10 and ~0.4 μm). The paper describes the rheological properties of the obtained composite slurries. The properties of green and sintered elements have also been presented. It was found that the presence of nickel particles had a significant influence on the slurry polymerization process. The green and sintered relative density was in every case higher than 57 and 97%, respectively. [ABSTRACT FROM AUTHOR]

By gel casting with polymethylmethacrylate microbeads (PMMA) as pore-forming agent, porous boron nitride/silicon nitride (BN/SiN) composite ceramics were successfully prepared. The obtained ceramic shows bimodal hierarchical structures that composed of spherical-shaped micro pores depending on PMMA content and irregular sub-micro pores formed by the stacking of ceramic particles. Porosity of the porous BN/SiN ceramics can be well controlled from 53.0 to 60.6 % by the PMMA content from 10 to 40 wt%, as well as the mechanical and dielectric properties. Effect of PMMA content on phase composition and the relationship between microstructure and the basic properties of the porous BN/SiN ceramics was discussed in detail. Microstructure analysis reveals that the sub-micro pores acted as channels between micro pores. BN particles have a relatively denser distribution on the wall of spherical-shaped micro pores with a window between micro and sub-micro pores, and resulting in a half-closed micro pore structure, which is meaningful for material design with concentration of BN particles on the wall of pore structure. [ABSTRACT FROM AUTHOR]

The paper reports the decomposition of saccharides derivatives in comparison to commercial substances during the process of binder removal from ceramic samples. The saccharides derivatives are polymers synthesized from glucose and fructose with acryloyl group in the sugar molecule. The synthesized compounds played the role of binder in the shaping of ceramic powders by gelcasting method. The method belongs to colloidal processes and allows to produce ceramic elements of complicated geometry. As ceramic powder AlO was used. The thermal analysis have been done on apparatus coupled with mass spectrometer. MS analysis showed what types of gasses are released to the atmosphere during the thermal decomposition of polymers. The obtained results showed important differences in decomposition of polymers obtained from commercial acrylamide, 2-hydroxyethyl acrylate and N, N′-methylenebisacrylamide in comparison to synthesized glucose and fructose derivatives. The measurements allowed to establish the sintering program of the green ceramic samples and evaluate whether harmful NO gases are released to the atmosphere. [ABSTRACT FROM AUTHOR]

Film cooling is an important cooling method to decrease the turbine blade surface temperature, and its average cooling efficiency is mainly dependent on the cooling structures of internal passageways and the shapes of film cooling holes. Compared with standard cylindrical film cooling holes, abnormal film cooling holes have higher average cooling efficiency. But it is difficult to manufacture these holes using traditional machining methods. In this paper, a novel process was developed to fabricate turbine blades with abnormal film cooling holes by combining stereolithography (SL) technology with gelcasting technology. To decrease the drying shrinkage, the freeze-drying technique was applied to treat the wet ceramic casting mold green body surrounded by the SL mold, and the proper sintering process parameters were determined for lowering the sintered shrinkage. Finally, the integral ceramic casting mold was obtained, and a turbine blade with converging–diverging film cooling holes was rapidly cast to verify the feasibility of the proposed process. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide (SCCO2) was used for the preparation of foamed sponges and intermingled fibers of biopolymers with potential applications in tissue engineering and drug delivery. The work was focused on the processing of both biodegradable polylactic acid ( l-PLA) and non-biodegradable polymethylmethacrylate (PMMA) homopolymers. Monolithic porous sponges of amorphous PMMA were prepared using SCCO2 as a porogen agent by simple swelling and foaming. Under similar experimental conditions, l-PLA was crystallized. The study also addresses the impregnation of biopolymers with an active agent dispersed in SCCO2. The drug used for impregnation was triflusal, a platelet antiaggregant inhibitor for thrombogenic cardiovascular diseases. Foaming often leads to a closed pore structure after depressurization which is disadvantageous for 3D scaffolds as it does not fulfill the requirement of interconnectivity necessary for cell migration. To overcome these drawbacks, fibers forming macroporous structures were prepared using a semicontinuous antisolvent (SAS) technique. [ABSTRACT FROM AUTHOR]

The development of texture in barium hexaferrite by templated grain growth was studied as a function of the Fe2O3/BaCO3 ratio, B2O3 additions in the starting materials, and sintering temperature. A magnetic field was used to orient the template particles during the gelcasting process. Excess BaCO3 resulted in abnormal grain growth and maximized texture, while B2O3 additions promoted coarsening, but no abnormal grain growth. [ABSTRACT FROM AUTHOR]

Key issue in the gelcasting method is the way water is released from the ceramic–hydrogel system. It is the first step to the formation of ceramic materials called green body. The purpose of the presented investigations is to establish the range of temperatures in which dehydration of the various hydrogels takes place, and at what temperatures the eight prepared hydrogels are disintegrated. The set of hydrogels polymers was obtained by radical polymerization from ionic and non-ionic monomers. The polymers were solved in water causing formation of clear gels. The dehydration and thermal decomposition of the obtained hydrogel samples was studied using thermal analysis techniques. The amount of water contained in hydrogels was determined as well as the temperature and products of polymer disintegration. Enthalpies of dewatering were also determined. [ABSTRACT FROM AUTHOR]

Three kinds of texture-reinforced oxide ceramic laminates with strongly bonded interfaces have been fabricated. All three were based on highly textured α-alumina interlayers, but each with a different oxide laminate matrix and a correspondingly different thermal mismatch between the textured interlayers and the matrix. Alginate-based, aqueous gel casting was used to produce a flexible tape for all the compositions studied. The highly textured alumina (TA) interlayers were derived from gel-cast tapes containing aligned alumina seed platelets. It has been found that the strongest texture derived from 9.1 vol% of the seed platelets in the gelled precursor tape. Using the March–Dollase model for texture analysis, the oriented volume fraction in the highly textured interlayers was estimated to vary from 60 to 80%. [ABSTRACT FROM AUTHOR]

In this study, we propose a new process to fabricate electrically semi-conductive alumina by the combination of gelcasting and reduction sintering. The process is similar to the conventional gelcasting method except for varying amounts of methacrylamide monomer dosages at 2.83, 5.50, and 8.04 wt% relative to the mass of the slurry. Correspondingly, the rheological evaluation of aqueous slurry was conducted. The resulting fluidity exhibited that monomer dosage until 8.04 wt% yielded slurry viscosity of 1628 MPA·s at shear rate of 20 s−1, which was feasible for gelcasting without noticeable casting defects. The freshly gelled bodies were demolded, carefully dried, and then sintered at different schedules in nitrogen atmosphere. The reduction-sintered samples were re-sintered in air for comparative evaluation of physical property. The sintered alumina body was characterized by electrical resistance, X-ray diffraction, and scanning electron microscopy. The results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistivity. The obtained lowest value was 3.6 × 106 Ω-cm with 8.04 wt% monomer dosage and sintering at 1550°C with 2 h holding time. The resulting material is classified as semi-conductive, which is potential for electrostatic shielding applications. The effect of physical property and microstructure on electrical conductivity and the corresponding reaction mechanism were discussed in details. [ABSTRACT FROM AUTHOR]

reports on reactive ion etching of organic polymers for application in waveguide trench molds. Importance of organic polymers in the development of optical waveguides; Realization of suitable techniques for patterning and etching; Avoidance of complex lithographic procedure.

Manufacturing of organic–inorganic composites with enhanced properties particularly, Fe2O3–ZnO/high impact polystyrene (HIPS) nanocomposites promising candidates for many requests. The presence of nanoparticles enhances the structural, thermal, and chemical stabilities, mechanical and operational performance of the nanocomposite matrices. Modified HIPS nanocomposites based on Fe2O3 doped by (0.0–0.6) ZnO were synthesized using the sol–gel method and gel casting approach. The structures, spectroscopic, dielectric and mechanical properties of the synthesized polymeric nanocomposites were investigated by XRD, TEM, FT-IR, UV–vis-DRs, terahertz (THz), dielectric and mechanical analysis. From chemical structural results, it can be confirmed the existence of ZnO in Fe2O3 and the internal structure rearrangement of iron oxide before dispersion into the HIPS matrix. The UV–Vis DRs show that the optical band gap decreases significantly with the increase of ZnO content in the nanocomposite. THz spectra in the spectral range of 0.2–2.5 THz showed an increase in the refractive indices and absorption coefficients for the prepared nanocomposites. Besides, the mechanical properties were affected by the addition of ZnO to HIPS-Fe2O3 where the elongation at break %, Young's modulus, and maximum strength varied values relying on the applied ratio of ZnO especially for the ratio of 0.4. Finally, the produced nanocomposites can find widespread applications in optoelectronic, chemical, and biological applications besides their feasibility to apply on a large scale. [ABSTRACT FROM AUTHOR]

Investigates the effects of the plasticizers on the cracking of the green bodies. Detection of the cracks in all green bodies containing glycerine in the suspension; Observation of the inefficacy of glycerine as platicizer; Usefulness of polyethylene glycol as an excellent plasticizer capable of reducing internal stress in the green bodies formed by gelcasting.