Porous Ceramic Bodies Research Articles

Development of Ceramic Filters for Household Water Treatment in Nigeria

Ceramic water filtration is the process that makes use of a porous ceramic (fired clay) medium to filter microbes or other contaminants from water. Ceramic water filtration has been greatly improved upon such that it takes care of most microbial contamination in water. However, the ceramic filter is not known to treat chemical contaminants in water. Therefore this project was aimed at developing a ceramic filter that could treat certain chemical contamination in water at the household level. Porous ceramic bodies were formulated and constituted from various materials such as kaolin, laterite, bonechar and charcoal. Bone char was added as a defluoridation agent while the charcoal doubled as the porecreating combustible material and as an Activated Carbon media in the ceramic body for the adsorption of metals from water. The formulated ceramic bodies were shaped into filters (pot) using the slip casting technique and fired bisque (850?C - 900?C). The developed filter samples were subjected to physical properties tests, while analysis on the microbial and physio-chemical parameters of the filter-treated water samples were compared vis-a-vis the raw water samples. The results indicate that the developed filters were effective in the treatment of chemical contaminants detected in the raw water samples; with significant reductions in fluoride, lead, and sulphate levels amongst others. The resulting filter samples also showed viability in physical handling strength and flow rate; while the availability of the raw materials and the processing technique used, makes a good economic case for the production of the developed filters.

Solvent effect on observation of nanostructural hydrated porous ceramic green bodies using hydrophilic ionic liquid

A convenient characterization method of a nanostructural hydrated porous ceramic body using a hydrophilic ionic liquid is established.

Porous alumina infiltrated with melt and its dynamic analysis during pressureless infiltration

Porous alumina ceramic bodies prepared by freeze casting were pressureless infiltrated with molten metal. The dynamic process during pressureless infiltration was analyzed through numerical calculations. The results indicated the ceramic bodies to present well interconnected pore channels that can be easily infiltrated under the capillary driving force. The numerical calculation indicated that the dynamic behavior during pressureless infiltration is strongly affected by the size of pore channels and the wetting angle, but it is relatively unaffected by the surface tension of melt, the coefficient of viscosity and the gravity exerted on the melt.

Porous Ceramic Bodies Using Banana Stem Waste as a Pore-Forming Agent

The use of banana stem waste (BW) was evaluated as a pore-forming agent to manufacture a porous clay ceramic body. Raw clay was characterized by XRD, XRF and TGA. After the clay was mixed with banana stem waste, in various proportions, the mixtures were pressed before being fired at different temperatures i.e 1100°C, 1125 and 1150°C, for 3 h with a heating rate of 5°C/min. Pore formation and microstructure in the fired samples were characterized using FE-SEM, whilst bulk densities, porosities and water absorption were determined using the Archimedes method. The mechanical strength was also investigated in order to optimize the fabrication process itself. The results obtained showed shrinkages between 13.08-16.10%, density values ranging between 1.37-1.51g/cm3, whilst porosity was determined to be between 18.5 to 18.78 % and water absorption 9.77-10.06 %, respectively. The tensile strength was in the range of 9.03 to 9.80MPa. These results proved that banana stem waste (BW) is potentially capable to produce porous ceramic materials.

Dynamic, In Situ Generated Interfaces Between Carbon‐Bonded Alumina Filters and Steel During Spark Plasma Sintering/Field‐Assisted Sintering

The aim of this study was to analyze possible reactions taking place during filtration of steel melts. The heterogeneous reactions and interface creation during short‐time contact of liquid steel and newly developed carbon bonded alumina ceramic filter (Al2O3‐C) were examined. The samples were produced using spark plasma sintering (SPS) to assure the absence of liquid convection. The production of the samples included very high heating rates of up to 1000 K min−1, short holding times just above liquidus temperature and a rapid cooling. The focus of the research was put on the inorganic inclusions (endogenous as well as exogenous), agglomerates, and phase formation. Exogenous inclusions (Al2O3) were added to the steel grade 42CrMo4 by a ball milling process. The results indicate the formation of MnS inclusions due to the high sulfur content in the used steel. The formation took place at the interfaces between steel and ceramic and at the grain boundaries within the steel. Penetration of the porous ceramic body by the steel was identified. Exogenous Al2O3 inclusions were found to agglomerate, adhere at the steel/Al2O3‐C interfaces and tended to float on top of the melt.

Development and mechanical characterization of novel ceramic foams fabricated by gel-casting

Porous ceramic materials are of considerable interest for a variety of chemical and industrial applications in extremely harsh conditions, particularly at very high temperatures for long time periods. A combined gel-casting-fugitive phase process employing agar as a natural gelling agent and polyethylene spheres as pore formers was exploited to produce porous ceramic bodies. Alumina and alumina–zirconia powders were used to prepare samples having a porosity of about 65–70–75 vol%. The composite powder was produced by a surface modification route, i.e. by coating a well-dispersed alpha-alumina powder with a zirconium chloride aqueous solution. On thermal treatment, ultra-fine tetragonal zirconia grains were formed on the surface of the alumina particles. SEM observations and image analysis were used to characterize the microstructure of porous samples and uniaxial compressive tests were carried out to measure their mechanical behavior.

Orthogonal Preparation and Microscopic Analysis of Porous Ceramic Foamed by Aerogen

Porous ceramics foamed by aerogens with pores of specific characteristics in shape and size can be widely applied in many fields such as biological engineering, enzyme engineering, environmental engineering, etc. However, the Preparation is prone to structure defects such as inequality of pore size and distribution, crack, contraction deformation, etc. Four-level orthogonal tests based on three improving factors such as water content and carboxymethyl cellulose (CMC) and stirring time (ST) were carried out to improve the method of preparing porous ceramic body foamed by aerogens at ordinary temperature. It is concluded that water content is the key improving factor followed by stirring time and CMC content, and the optimized formula could be A3B3C1 or A3B4C2. Microscopic analysis indicates that there are about 107 pores within 100μm2 with diameter below 10μm and about 117 pores within 10000μm2 with diameter range from 20μm to 100μm in the sample.

Microporous glass ceramics from combination of silicate, borate and phosphate wastes

Borate mineral wastes and phosphate ash resulting from the incineration of meat and bone meal represent two particularly abundant inorganic wastes. This paper is dedicated to the combination of such wastes, together with kaolin clay, focused on the development of highly porous ceramic bodies. Borate waste has a multiple effect, providing liquid phase at the sintering temperature (1050°C), gas release (from the decomposition of its calcite fraction) and a CaO source, which reacts with residues from clay and promotes the formation of anorthite crystals as a newly formed phase. Control of the heating rate, i.e. adoption of fast heating (20°C min−1) and, above all, introduction of recycled soda–lime–silica glass as secondary additive, allowed obtaining lightweight microporous bodies (density below 0·45 g cm−3) with uniform pore structure that could be useful for thermal and acoustic insulations.

Application of hydrophilic ionic liquid treatment to the morphological observations of hydrated porous ceramic green bodies

In this study, a simple and convenient method for observing the surface morphology of hydrated porous ceramic green bodies is proposed. The porous hyrdoxyapatite (HAp) green body was prepared by a gelcasting process and was dried in a humid chamber from 90 to 50% relative humidity at 25°C before subsequent treatment with a hydrophilic ionic liquid (IL). The surface morphology of the IL-treated porous HAp green body was observed using FE-SEM. The results showed that the pore morphology and microstructure of the HAp green body was readily observable without evidence of charging. The as-prepared sample showed pores approximately 300–600μm in diameter, which gradually contracted to approximately 200–400μm upon drying in the humid chamber. Following sintering at 1000°C, the pores had further contracted to approximately 100–300μm. The IL binds with the surrounding water to prevent the sample from drying in vacuum and acts as a conductive media, allowing the HAp ceramics to be observed in the electron microscope. In comparison to the micro-focused X-ray CT analysis, the fine pore structure (less than 100μm) could only be observed using FE-SEM when the porous body had also been subjected to the IL treatment.

Development of porous ceramic bodies from kaolin deposits for industrial applications

The possibility of fabricating porous ceramic bodies from kaolin using maize, rice, saw-dust, charcoal, millet and Styrofoam as pore formers have been explored in this work after chemical analysis of two kaolin deposits located at Assin Fosu and Saltpond both in the Central Region of Ghana.Batch formulations of the Kaolin samples were formed into greenbodies and fired to 1400°C at a controlled rate. Samples with charcoal, millet, sawdust, maize and rice pore formers showed severe surface cracks and low thermal shock after firing. A control batch process using Styrofoam exhibited uniform surface characteristics with pores, high strength, thermal stability and no surface cracks thereby confirming the viability of the process modules. Apparent porosity as high as 38% has been calculated.

Improving Preparation of Porous Ceramic Foamed by Microbe

Preparation of porous ceramic body foamed by microbe is prone to structure defects such as inequality of pore size and distribution, crack, contraction deformation, etc. Four-level orthogonal tests based on three improving factors such as water content(WC) and carboxymethyl cellulose (CMC) and stirring time(ST) were carried out to improve the method of preparing porous ceramic body foamed by microbe at ordinary tempreature. It is concluded that water content is the key improving facor followed by stirring time and CMC content, and the optimized formula could be A3B3C1 or A3B4C2.

Investigation on the Freeze Casting Porous Al<sub>2</sub>O<sub>3</sub> Ceramic Bodies Infiltrated with Nb-Ti-Al-Cr Alloy by Pressureless Infiltration

This paper adopted freeze casting method to prepare porous Al2O3 ceramic bodies with different volume percentage and interconnected pore channels as the preform. The porous Al2O3 ceramic bodies were pressureless infiltrated with Nb-35Ti-20Al-10Cr alloy (atom percentage, at%) by using electromagnetic induction furnace. The results indicated that there is a well wettability between Nb-35Ti-20Al-10Cr melt and porous Al2O3 ceramic body. And it would be possible to infiltrate Nb-35Ti-20Al-10Cr melt into porous Al2O3 ceramic body through pressureless infiltration. The microstructure observation for the Nb-35Ti-20Al-10Cr/Al2O3 composites demonstrated that it was still retained the layer structure characteristics of the preform. The Nb-35Ti-20Al-10Cr melt was filled into the interconnected pore channels existed in the porous Al2O3 ceramic bodies and the Nb, Ti, Al, Cr alloy elements diffused into the reinforced Al2O3 particles during pressureless infiltration.

Modeling the Influence of Carbon Spheres on the Porosity of SOFC Anode Materials

The influence of fabrication pressure and other ceramic processing variables, including volumetric loading fraction and the particle size ratio of pore-forming agents, on the porosity of fabricated ceramic anodes, was investigated using an integrated experimental approach with mathematical modeling to differentiate the impacts of each parameter. Despite historic observation of the properties of ceramic bodies, to date, there is a lack of available models to accurately interpret the ceramic properties as a function of the processing variables. Herein, we focus on the open porosity of the solid oxide fuel cell anode prepared from NiO/YSZ (nickel oxide/yttria stabilized zirconia) as the ceramic powder and using CMS (carbon microspheres) as a pore-forming agent. A range of pore-former volumetric blend ratios (4.4%–44.6%) and different particle size ratios between NiO/YSZ and CMS (11.27, 4.29, and 0.26) were used, whereas the influence of the applied uni-axial fabrication pressure on the open porosity of sintered anode was studied in a range of atmospheric pressure up to 40 MPa. A good agreement was observed between the proposed model and the experimental data, implying that the approach could be used to determine the significant processing parameters to fabricate ceramics with desired porosity. The model could also be used to interpret the physical basis of pore formation when using a pore-forming agent in a fabricated porous ceramic body.

Properties and microstructure of porous ceramic bodies containing fly ash

Effect of two kinds of fly ash collected from the thermal power plants on the green properties and sintering behavior of clay ceramic tile bodies was investigated. Flow time, unit weight, color difference, water absorption, flexural strength, and linear shrinkage of the ceramic samples with four different fly ash percentages of replacement with feldspath varying between 0% and 20% by weight were determined. Furthermore, thermal characterization and morphology of phases of selected ceramic compositions were studied. This work proves the possibility of using fly ashes with appropriate physicochemical properties in manufacturing porous clay ceramic tiles with satisfactory features suitable for construction industry. Comparison of the properties of the resulting tile bodies with varying proportions of different fly ashes indicated that tiles with acceptable properties can be obtained by introducing up to 10% of fly ash by weight into the clay ceramic mixes.

Sintered silicon nitride/nano-silicon carbide materials based on preceramic polymers and ceramic powder

Abstract A flexible method is presented, which enables the fabrication of porous as well as dense Si 3 N 4 /nano-SiC components by using Si 3 N 4 powder and a preceramic polymer (polycarbosilazane) as alternative ceramic forming binder. The SiCN polymer benefits consolidation as well as shaping of the green body and partially fills the interstices between the Si 3 N 4 particles. Cross-linking of the precursor at 300 °C increases the mechanical stability of the green bodies and facilitates near net shape machining. At first, pyrolysis leads to porous ceramic bodies. Finally, subsequent gas pressure sintering results in dense Si 3 N 4 /nano-SiC ceramics. Due to the high ceramic yield of the polycarbosilazane binder, the shrinkage during sintering is significantly reduced from 20 to 15 lin.%. Investigations of the sintered ceramics reveal, that the microstructure of the Si 3 N 4 ceramic contains approx. 6 vol.% nano-scaled SiC segregations, which are located both at the grain boundaries and as inclusions in the Si 3 N 4 grains.

Controlling the microstructure of ceramic particle stabilized foams: influence of contact angle and particle aggregation

Porous cellular alumina ceramic green bodies have been produced by combining the particle stabilized foam method with gelcasting. The suspension foams were stabilized by particles rendered weakly hydrophobic with short chain sulfonate surfactants. Poly vinyl alcohol (PVA) and 2,5-dimethoxy-2,5-dihydrofuran (DHF) were used as the gelcasting reagents. The microstructure (amount of porosity, average pore size, and morphology) of alumina (Al2O3) ceramic green body foams has been studied as a function of surfactant concentration and chain length. The morphology of gelled ceramic foams changes from closed cell (bubble like morphology) to open cell (granular morphology) as the surfactant concentration is increased beyond a critical level. The density (and porosity) of the gelled alumina green body foams changes as a function of the surfactant concentration in a non-linear manner. Measurement of the suspension viscosity, contact angle and aggregate size are used to explain the changes in density and morphology. The transition from the bubble like structure to the granular structure is due to an increase in the particle aggregate size rather than phase inversion induced by an increase in the contact angle. The same behavior is observed with three different chain length surfactants (ranging from 4 to 10 carbon atoms on the hydrophobic portion of the surfactant) but at a lower surfactant concentration as the chain length increases.

Preparation and characterization of porous fibrous mullite bodies doped with TiO 2

The preparation and characterization of porous mullite ceramic bodies doped with TiO 2 are described. The bodies were prepared from sol–gel by the replication process with cellulosic nonwoven fabric as the template. The microstructure and the dependence of the porosity and the mechanical properties on the TiO 2 content are discussed. Clear differences were found in the microstructure of doped and undoped samples. Rodlike anisotropic mullite grains were grown in titania-doped mullite bodies fired at 1650 °C, while fine almost homogeneously distributed mullite grains were formed in the latter. Strength measurements showed that increasing TiO 2 content increased the bending strength of the bodies.

Effect of bentonite addition on fabrication of reticulated porous SiC ceramics for liquid metal infiltration

SiC with different particles and a clay mineral bentonite (montmorillonite) were mixed in water to prepare ceramic slurry. The slurry was then infiltrated high porous polyurethane sponge. Excess slurry was squeezed out to adjust ceramic rate in the infiltrated body. The pore walls were coated with ceramic mix after the infiltrated body was dried. The polyurethane containing SiC particles and bentonite was fired in a box furnace to burn out the polyurethane from the body at 500 °C for 30 min. The remaining porous ceramic bodies were sintered at elevated temperatures to give strength. SiC particles with bentonite surface coating took polyurethane pore forms after firing the sponge. Bentonite was both used as binder for ceramic slurry at room temperatures and the sintering additives at elevated temperatures. Therefore, increasing bentonite addition gives higher strength to the resulting ceramic performs.

Camphene-based freeze-cast ZrO 2 foam with high compressive strength

Highly porous zirconia ceramic bodies with interconnected pores were fabricated by freeze-casting technique using camphene-based slurries. The pore volume fraction and pore size are controllable by adjusting the initial solid content in the mixed slurries. The pores are replicas of connected dendrites of frozen camphene, which sublimed during room temperature drying. As the solid content was increased from 10 to 20 vol.%, the compressive strength was significantly increased from 19 ± 2 to 58 ± 3 MPa, and the examined porosity was decreased from 81.5 to 66.5%. This technique is considered potentially useful in producing novel porous ceramics, and introduces a new application field of freeze-casting.

Method for making minor dopant additions to porous ceramics

An infiltration technique for doping porous ceramic bodies before sintering is evaluated for calcia additions to yttria stabilised zirconia. The method involves impregnating the porous body with a solution containing the required dopant nitrate, followed by drying and sintering to decompose the nitrate and densify the ceramic body. The resulting dopant distributions show equivalent homogeneity to the popular ball milling approach for dopant contents below 3 mol.-%CaO, while giving a product with a higher relative density.