Papers by Keyword: Ceramic Foam

Abstract: Silica (SiO₂) foams have been widely applied in numerous fields, mainly filters and catalysts supports, due to their characteristics of high permeability, high porosity and specific surface area. In this study, foams of SiO₂ from rice husk ash (RHA) was fabricated via polymeric sponge replication method. Polymeric foam initially was used as template and dipped into SiO₂ slurry followed by drying and sintering to yield the replica of the original polymeric foam. Different solid loadings of SiO₂ as-derived from RHA (20 to 35 wt. %) slurry and sintering temperature of 1150 °C were applied. Phase identification and chemical composition of the green and sintered foams were conducted using X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF). Morphological observations were performed using Scanning Electron Microscopy (SEM). Density and porosity of the SiO₂ foams were characterized using Archimedes method. Compressive strengths of the foams were determined as per ASTM C773-88 (1999). XRD analyses confirmed that the SiO₂ as derived from the RHA were of tridymite and cristobalite phases with as high as 93% purity, as confirmed by XRF analyses. The density of SiO₂ foams fabricated was in the range of 0.614 to 0.989 g/cm³, whereas the porosity values was in the range of 70% to 82%%. Compressive strengths were found to increase from 0.05 to 0.30 MPa respectively, proportionate with the increased SiO₂ solid loading. Excellent properties of the SiO₂ foams definitely signifies that the polymeric replication method is indeed a promising technique for SiO₂ as derived from RHA foam fabrication.

Abstract: In this study, ceramic foams were produced using starch consolidation casting method. This research focused on the preparation of alumina-based ceramic foam by using corn starch as a pore-forming agent. Preparation of alumina based ceramic foam is studied to observe the effect of the addition of corn starch on its physical, mechanical and morphological properties. The composition of the suspension used included 64–58 wt.% alumina, 55 wt.% deionised water and other materials, such as silica and polyethylene glycol (PEG), were used as additive and dispersing agent respectively. Corn starch was added at 4, 6, 8 and 10 wt.%. The samples were preheated for gelation and coagulation processes, then dried and sintered at 1250 °C for 2 h. The ceramic foam gave a linear shrinkage from 1.07% to 3.39%. The obtained flexural strength was between 0.594 and 1.996 MPa. The average total porosity ranged from 54.05% to 70.70%. This study found that the suitable amount of corn starch in alumina foam is 4 wt.% because the resulting porosity values and flexural strength are appropriate for ceramic foams.

Abstract: The contribution deals with modelling and prediction of failure of mechanically loaded open cell ceramic foam structures by using 3D volume FE models constructed from CT scans of real foam specimens. The condition for crack initiation in particular struts comes from the coupled stress-energy criterion which combines two fracture-mechanics parameters of the investigated material – tensile strength and its fracture toughness. By combining of both stress and energy condition one obtains information about the crack initiation length which is later used (together with the tensile strength) for determination of the strut failure in the complex 3D FE model of the ceramic foam structure. The crack onset is considered in the critical location at the moment when the (tensile) principal stress under the strut surface (in a depth corresponding to the crack initiation length) exceeded the tensile strength of the strut. Such approach enables us to define failure also on relatively coarse meshes of the FE models where potential stress concentrations are not described precisely and therefore it is not possible to decide about the failure just based upon the value of tensile stress on the strut surface.

Abstract: Porous ceramic is a type of material that has highly open and partially interconnected pores. It has a wide range of applications which include catalyst support, electrical conductivity, refractory insulation of furnaces, filtration, adsorption, and separation. There are many conventional methods for producing silica foam including direct forming, steam heating, freeze casting and the polymeric sponge method which is also known as the replication method. In this study, SiO₂-NiO foam was fabricated using 25wt. %, 30wt % and 35wt.% of SiO₂ and 5wt.% of NiO under different sintering temperatures (850 °C and 1050 °C) via replication method. The morphologies of SiO₂-NiO foams were observed using Scanning Electron Microscopy (SEM) while the identification of the different phases of foam was analysed using X-Ray Diffraction (XRD). The XRD analysis indicated that there were only SiO₂ and NiO present and no additional phases were detected after sintering. The effects of sintering temperature (850 °C, 1050 °C) and SiO₂ solid loading on properties such as apparent porosity, bulk density and shrinkage were investigated. It was found that when the solid loading of SiO₂ and sintering temperature increased, the density of SiO₂-NiO foams increased in the range of 0.6373 g/cm³ to 0.8165 g/cm³. On the other hand, the porosity percentage obtained increased from 78.51 % to 81.63 %. The density and porosity analyses showed that the density of foam increases when the porosity of SiO₂-NiO foam decreases. However, the shrinkage after sintering ranged between 3.5081cm to 6.9975 cm at 850C ̊ and 7.3618 cm to 8.3704 cm at 1050 °C respectively. Thus, this proves that SiO₂-NiO foam can be successfully fabricated through the replication method.

Abstract: This work deals with a computational analysis and quantification of the influence of processing (primarily crack-like) defects of various amount on the (tensile) strength of open cell ceramic foam structures. This information is essential e.g. for application of these materials in the mechanically loaded application, where a design with certain reliability to operating conditions is required. The analysed ceramic foam structures are composed of both regular and irregular cells and crack-like defects (pre-cracked struts) are simulated inside them. The foam structure is modelled using a 3D FE beam element based model created by utilization of the Voronoi tessellation technique. The tensile strength upon presence of various amount of pre-cracked struts is analysed based upon an iterative FE simulation on whose base the critical failure force leading to specimen fracture is determined. The performed parametric study relates the tensile strength of the foam structure to the amount of initial defects. With increasing amount of these defects, the foam strength decreases by approximately 30% with every 10% of broken struts. This information can be directly used for a fast estimation of the foam tensile strength if the fraction of broken struts to the intact ones is known (e.g. from a microscopic analysis).

Abstract: The work investigates an influence of the macroscopic stress concentrator inside the ceramic open cell foam structure on the fracture-mechanics response of the foam upon the tensile test. As the concentrator, the central crack/rectangular notch was taken into account. The influence of the crack/notch length and width on the stress concentration ahead the concentrator tip was assessed using the simplified FE beam element based model with irregular cells simulating the real ceramic foam structure. Average principal stresses calculated on set of struts ahead the crack/notch tip were compared with average stresses in the intact structure. It was found that the ratio of these stresses increases linearly with the crack length. The stress concentration ratio is slightly lower in case of thick rectangular notch than in case of a thin crack. Furthermore, the failure load leading to complete fracture of the studied specimens, subjected to the tensile loading, were calculated using the same model. It is shown that the difference factor between the critical fracture force in case of structure without concentrator and with concentrator is very close to the concentration factor calculated from the average stresses on particular struts in the region in front of the concentrator tip.

Abstract: To better understand response or fracture conditions of the ceramic foam materials to the mechanical loading, a finite element (FE) analysis of these structures has to be employed. The cellular structure of foams can be modelled either using a detailed realistic FE model based on the computer tomography scans or by using of simplified, beam element based, models. Nevertheless a main drawback of the realistic foam modelling consists in its high demandingness on computational resources. Therefore, simplified models are welcome substitutions (at least for analysis of the global mechanical foam response). The regular foam structure, based e.g. on Kelvin cells, is simple from the modelling point of view, but it doesn´t exactly capture the fully random character of the real foam structures and corresponding response to the external load. Definition of the random beam foam structure (respecting the real cell shapes and their distribution within volume), can thus improve this deficiency. The main aim of this work is thus to compare these different modelling approaches and quantify the influence of the foam irregularity on the response of ceramic foams to external (tensile) loading for various model sizes.

Abstract: Ceramic foams, a porous material with a gyroid structures, are becoming highly demanded for various applications such as heat insulation, bone implantation and filtration, because of their unique properties such as high specific surface area, high porosity and low heat transfer rate. In this study, the development of ceramic foam utilised white clay with a combination of precipitated calcium carbonate (PCC). The ceramic foam was successfully developed using this combination after the sample was sintered at 1250 °C for 2 hours holding time. The various compositions of PCC (10.0, 12.5, 15.0, 17.5, 20.0, 22.5 and 25.0 wt.%) affected the chemical composition and compressive strength of the ceramic foam. The chemical composition of ceramic foam was analysed by using X -ray fluorescence (XRF) and the result indicated that the PCC was successfully transformed into calcium oxide (CaO) after the sintering process. The mineralogical composition of the ceramic foam was evaluated using X-ray diffraction (XRD) and has shown the presence of mullite (3Al₂O₃.2SiO₂), gehlenite (Ca₂Al₂SiO₇) and anorthite (2CaAl₂Si₂O₈) after the sintering process. The scanning electron microscope (SEM) analysis showed that the presence of porosity on the strut of the ceramic foam. Meanwhile, the compressive strength of the ceramic foam increased from 0.03 to 1.31 MPa, which is directly proportional to the increased amount of PCC.

Abstract: Ceramic foam are a class of high porosity materials that are used for various applications. In this study, foam ceramic porcelain powder was produced by using polymeric sponge replication method at different solid content ranging from 30 to 50 wt. %. Properties of ceramic foam was characterized for porosity and density. Ceramic foam then grafted with methyltriethoxysilane (MTMS) at different concentration ranging from 0 to 9.0% v/v to determine hydrophobic effect and oil absorption capacity. From the results, it was found that the density of ceramic foam increased while porosity was decreased with increasing solid contents. It is clearly seen that, MTMS grafting contribute to hydrophobic effect of ceramic foam which enable repelling of water. The amount of oil absorbed by ceramic was found increased by increasing concentration of MTMS for all solid contents. As conclusion, MTMS give significant effects on hyrdophobic ceramic foam and produce good absorption capacity. The lower solid content produced better oil absorption compared to higher solid content due to presence of higher porosity.

Abstract: High alumina foam ceramics products with low density, high specific surface area, low thermal conductivity, corrosion resistance and other excellent physical and chemical properties are suitable for chemical, metallurgy and other related fields ^[1-4]. Alumina foam ceramics that compression strength increased by 200%, was prepared by Rizwan Ahmad through impregnation process using foamed rubber ^[5]. However foamed rubber was expensive and could be decomposed creating poisonous gases at high temperature. Zhou l z ^[6] prepared mullite porous ceramics with high strength by gel-casting method. Gel-casting is an effective method for preparation of ceramics products with large size and complicated shape. Fiber reinforced dense ceramics composite materials with excellent performance have been studied widely ^[7-10], it is also an important issue to adequately investigate the reinforcement of porous ceramics with fiber.