Porous Ceramic Composites Research Articles

Fabrication and Characterization of Porous Zirconia/Alumina Composites

Porous ZrO2-Al2O3 ceramic composites containing 0, 30 and 50 wt% Al2O3 were prepared by solid state sintering in the temperature range of 1375˚-1650°C and effect of temperature and alumina percentage on compressive strength and microstructure of monoclinic zirconia was investigated by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). XRD results on composite samples showed monoclinic ZrO2 and Al2O3 phases. SEM images showed uniform distribution of porosity in microstructure. Compressive strength of monoclinic zirconia improved from 33MPa to 134 MPa with adding of 50%wt alumina in sintering temperature of 1650°C.

Ultrafine silver(II) oxide particles decorated porous ceramic composites for water treatment

Ultrafine silver(II) oxide particles-decorated porous ceramic composites have been prepared directly by chemical oxidation, with diatomite-based porous ceramics as the carrier. The prepared composites were characterized by mercury intrusion method, XRD, XPS, FT-IR, SEM, AAS and shake-flask method. The results show that silver(II) oxide decorated diatomite-based porous ceramic composites possess crystal structure and are composed of tetragonal cristobalite, monoclinic silver(II) oxide and cubic silver(I) oxide. The silver(II) oxide weight percentage content of the composites prepared is 8.5% and the average pore diameter, median pore diameter, apparent density and porosity of the composites are 3.862 μm, 0.354 μm, 1.794 g mL −1, and 57.985%, respectively. The composite can release silver in water solution, with a release rate of 7.420 × 10 −3 mg L −1 h −1. The composites show the strong bactericidal activity. When the contact time with Staphylococcus aureus and Escherichia coli exceeds 20 min, the bactericidal rates reach up to 99.9%.

Effects of Mullite Content on the Properties and Microstructure of Porous Anorthite/Mullite Composite Ceramics

Porous anorthite/mullite composite ceramics with different mullite contents were fabricated by foam-gelcasting method,using CaCO3,SiO2,α-Al2O3 as raw materials.Effects of mullite content on bulk density,po-rosity,compressive strength,thermal conductivity and microstructure of the porous composite ceramics were re-searched.Mullite content has great effect on the apparent porosity of the porous anorthite/mullite composite ceramics.As a result of the appearance of liquid phase in the sintering,the sample shrunk,which is the main reason for the po-rosity decrease.Compressive strength and thermal conductivity increase with the mullite content under the condition of the similar porosity.Dense pore wall and rod-like mullite grain are benefit for compressive strength of porous anorthite/mullite composite ceramics.The apparent porosity of the prepared porous anorthite/mullite composite ce-ramics is in the range of 60.8%?75.2%,the compressive strength is between 12.94 MPa and 36.95 MPa,and the ther-mal conductivity is in the range of 0.30?1.33 W/(m?K).

Synthesis of (α- and β-)Si 3N 4/Si 2N 2O into silicon particulate porous preforms by hybrid system CVI and direct nitridation

An investigation on the microstructure and mechanical properties of Si/Si 3N 4/Si 2N 2O porous ceramic composites, synthesized in a multi-step approach via hybrid precursor system chemical vapor infiltration (HYSYCVI) and direct nitridation (DN) has been conducted. Particulate silicon porous preforms were infiltrated in subsequent stages S1-1, S1-2 (both at 1300 °C for 70 min in high purity nitrogen (HPN) using Na 2SiF 6 as solid precursor) and S2 (1350 °C for 120 min in ultra high purity nitrogen (UHPN)). Chemical reactions that account for the formation of Si 2N 2O and Si 3N 4 are proposed. Results show that the microstructure of the composites was influenced by atmosphere type and processing stage, affecting kind, morphology and size (including nanometric size) of nitrides formed. Porous composites (43% porosity) with modulus of rupture (MOR) ≈ 43 ± 3.5 MPa (evaluated in four-point bending tests) and elastic modulus ( E) ≈ 29 GPa (determined by the pulse-echo ultrasonic method) are routinely obtained.

Fabrication of porous ceramic composites with improved compressive strength from coal fly ash

A freeze–gel casting method has been proposed to fabricate porous mullite–alumina composite with controlled ‘designer’ pore structure and improved compressive strength. In this work, a tertiary butyl alcohol–coal fly ash slurry system with appropriate addition of Al2O3 was used. Unidirectional aligned macropore channels were developed by controlling the solidification direction of the tertiary butyl alcohol solvent. Simultaneously, microsized pores formed in the walls of the pore channels; consequently, the inner section of the walls of the pore channels exhibited a more porous structure than the outer walls. The compressive strength of the sintered porous composite increased as the porosity decreased, i.e. the low porosity gave a high compressive strength. After sintering at 1500°C with 40 wt-% solid loading, the mullite–alumina composite with a porosity of 61·2% exhibited a compressive strength of ∼64·3 MPa.

CeO2/Pt Catalyst Nanoparticle Containing Carbide-Derived Carbon Composites by a New In situ Functionalization Strategy

A new class of CeO2/Pt nanostructures containing highly porous carbide-derived carbon composites was obtained for the first time using a polymer precursor strategy and subsequent ceramization. The catalytic transition metal compounds were incorporated into polymeric polycarbosilane structures using an inverse microemulsion method in precisely tunable nanoscale particle sizes. Porous ceramic and carbon composites were obtained by pyrolysis and subsequent chlorination processes. The adsorption properties of nonoxidic ceramic intermediates can be adjusted by the pyrolysis temperatures from mainly microporous to meso- and macroporous materials, respectively. These pore structures remain during the chlorination process confirmed by comparative nitrogen physisorption and small-angle X-ray scattering investigations. The specific surface areas significantly increase up to 1774 m2/g after selective silicon removal. In comparison to unsupported CeO2/Pt nanoparticle structures, the particle sizes and dispersion of the active metal compounds of composite structures remain during pyrolysis and chlorination process studied by electron microscopy methods. Ceramic and carbonaceous composites show catalytic activity and stability in selective methane oxidation. In contrast to the SiC composites, the CDC materials promote the formation of carbon monoxide and hydrogen in reforming reactions at higher temperatures, a conversion pathway important for the generation of synthetic fuels.

Thermal conductivity of porous SiC composite ceramics derived from paper precursor

Biomorphic porous SiC composite ceramics were produced by chemical vapor infiltration and reaction (CVI-R) technique using paper precursor as template. The thermal conductivity of four samples with different composition and microstructure was investigated: (a) C-template, (b) C-SiC, (c) C-SiC–Si 3N 4 and (d) SiC coated with a thin layer of TiO 2. The SiC–Si 3N 4 composite ceramic showed enhanced oxidation resistance compared to single phase SiC. However, a key property for the application of these materials at high temperatures is their thermal conductivity. The later was determined experimentally at defined temperatures in the range 293–373 K with a laser flash apparatus. It was found that the thermal conductivity of the porous ceramic composites increases in the following order: C-template < C-SiC < C-SiC–Si 3N 4 < SiC–TiO 2. The results were interpreted in regard to the porosity and the microstructure of the ceramics.

Silver nanoparticle-decorated porous ceramic composite for water treatment

Silver nanoparticle-decorated porous ceramic composites have been prepared by overnight exposure to a sliver nanoparticle colloid solution of a porous ceramic modified by an aminosilane coupling agent, 3-aminopropyltriethoxysilane (APTES). The connection between the nanoparticle and the ceramic relies on the coordination bonds between the –NH 2 group at the top of the APTES molecule and the silver atoms on the surface of the nanoparticles. The other end of the aminosilane coupling agent attaches to silicon atoms in the ceramic through a Si–O–Si bond. There is no obvious loss of nanoparticles after immersion in an ultrasonic bath for 15 min, or after keeping the treated ceramic for several weeks in an atmospheric environment. On-line tests were conducted with a mimetic water filter. At a flow rate of 0.01 L/min, the output count of Escherichia coli was zero when the input water had a bacterial load of ∼10 5 colony-forming units (CFU) per millilitre. Combined with low cost and effectiveness in prohibiting the growth of E. coli, such materials should have wide application to drinking water treatment.

In situ porous alumina/aluminum titanate ceramic composite prepared by spark plasma sintering from nanostructured powders

In situ porous alumina/aluminum titanate ceramic composite was fabricated by spark plasma sintering of nanostructured alumina/titania composite powders. The phase composition and microstructure of the nanostructured composite powders and the fabricated porous bulk ceramic composite were investigated by X-ray diffraction and scanning electron microscopy, respectively. The results indicate that a large number of pores were distributed homogeneously in the porous alumina/aluminum titanate ceramic composite, which possessed excellent mechanical properties.

Mechanisms in the generation of grinding wheel topography by dressing

For the process of dressing vitrified bonded grinding wheels with diamond tools it has been unknown how the wheel topography is generated. Moreover, the influence of the kinematical dressing parameters on the wheel wear behavior has not been quantified. In the course of this article the grinding wheel was dealt with as a porous ceramic composite. In FEM simulations common dressing forces and usual dressing tool geometries were applied. The results were verified by dressing tests and grinding wheel scratch tests which show the wheel wear mechanisms. The common practice of decreasing the grinding wheel surface roughness by a finishing dressing stroke has to be reconsidered, because previous dressing strokes with higher depths of cut can weaken the grinding wheel structure and lead to an unsteady phase with high grinding wheel wear after dressing.

Bioactive Ceramics - New Processing Technologies for Immobilization of Microorganisms for Filtration and Bioreactor Applications

The metabolism of biocomponents and microorganisms is widely used for the production of medical products as well as for biotechnological processes. The productivity of the related reactions can be improved by the immobilization of the living species in granules or in a gel matrix. Since these structures can suffer during operation due to their weakness a new type of porous ceramic composites was developed where the biological phase is immobilized in a rigid inorganic matrix of high permeability for fluids. During the so-called freeze gelation process (FGP) both, a highly efficient immobilization of the biocomponents and an ideal permeability is achieved. A high versatility is then offered due to the particular advantages of the freezing step necessary for the sol-gel transition and the preservation of embedded microorganisms. While the freezing conditions are decisive for the resulting porosity of the biocer, they are also crucial for the survival rate of the embedded biocomponents. The porosity can be adjusted over a wide range by controlling the composition and the freezing conditions. By the directional ice crystal growth large pore channels can be achieved inside the biocers. Thus, the embedded biocomponents are easily accessible by external reagents and biochemical reactions can proceed with a high rate. Furthermore, cell division is conceivable inside the biocers by safe immobilization at the same time. These biocers allow a wide field of applications depending on the class of immobilized biospecies. Biocatalysis with enzymes can also be applied as bioaccumulation and absorption/desorption of metal ions for separation processes of contaminated water or highly selective filters for metallic complexes in solution.

Electrically conductive carbon-coated ceramic fiber media

Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of either propane or infiltrated phenolic resin in a nitrogen atmosphere at 800-900°C. The amount of carbon coating was varied to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire one, respectively. Up to 30 wt% pyrolytic carbon, the electrical conductivity σ showed linearly increasing tendency and was fitted by the effective conductivity according to the parallel rule of a mixture σ =ΣV i ·σ i with an effective conductivity of pyrolytic carbon σ c and volume fraction of coated carbon V c . The electrical conductivity of coated carbons prepared from propane at 900°C and phenolic resin at 800°C was of the order of 10° and 10 -1 S cm -1 , respectively.

Porous ceramic fiber glass matrix composites for solid oxide fuel cell seals

Porous ceramic fiber glass matrix composites with porosities of 19–24% were prepared with mixtures of a glass and short alumino-silicate ceramic fibers for the sealing of solid oxide fuel cells. The sealing performance was evaluated by measuring leak rates at the seal operation temperature of 650 °C and by investigating adherence at seal–metal interfaces after the seal test. Composite seals prepared with 55 vol% glass in the mixture showed a leak rate of ∼105 sccm/cm and did not adhere to the metal tube. Leak rate could be reduced to ∼0.003 sccm/cm when using composite seals prepared with 65 vol% glass. The maximum size of the pores present at the seal interface was estimated from the standard leak rate by assuming a single leak hole.

Thermal and Electrical Conductivities of Porous Carbon-Coated Ceramic Fiber Composites

Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of infiltrated phenolic resin in a nitrogen atmosphere at 800. The amount of carbon coating was varied to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire one, respectively. Up to 30 wt% pyrolytic carbon, the electrical conductivity σ shows linearly increasing tendency and is fitted by the effective conductivity according to the parallel rule of a mixture σeff = ΣΧi ·σi with an effective conductivity of pyrolytic carbon σc= 0.42 S/cm. The thermal conductivity of the coated composites is in the range 0.05-0.08 W/mK and increases with carbon content.

The effect of BN addition on thermal shock behavior of fiber reinforced porous ceramic composite

Fiber reinforced ceramic composite (mullite fiber/α-Al 2O 3 powder) was produced by the organic flocculating method. Air-quenching was employed to determine the drop in bending strength of the composite after thermal shock, and the critical temperature of the composites with different fiber contents. The thermal shock behavior was found to improve significantly by the addition of 3% hexagonal boron nitride (H-BN). The critical temperature reached up to 1000 °C, compared to 500 °C without presence of BN. The mechanism was investigated through a relative experiment and XRD study.

Electrical and Thermal Properties of Carbon-Coated Porous Ceramic Fiber Composites

Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of propane in a nitrogen atmosphere at 900°C. The amount of carbon coating was varied through adjusting deposition time to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire method, respectively. Up to 7 wt% pyrolytic carbon, the electrical conductivity σ is linearly increased to 0.02 S/cm and well fitted by the effective conductivity according to the parallel rule of a mixture σ eff = Σ Χ i ·σ i with a conductivity of pyrolytic carbon σ c= 20 S/cm .The thermal conductivity of the uncoated and coated composites is in the range 0.065-0.075 W/mK and little affected by carbon coating presumably owing to the small amount of coated carbon in this work.

Strong and Rapid Induction of Osteoblast Differentiation by Cbfa1/Til-1 Overexpression for Bone Regeneration

Core binding factor alpha-1 (Cbfa1), known as an essential transcription factor for osteogenic lineage, has two major N-terminal isoforms: Pebp2alphaA and Til-1. To study the roles of these isoforms in bone regeneration, we applied an adenoviral vector carrying their genes to transduce primary osteoprogenitor cells in vitro and in vivo. Overexpression of the two isoforms induced rapid and marked osteoblast differentiation, with Til-1 being more effective in vitro, by examination of the alkaline phosphatase activity, calcium content, and Alizarin red staining. Til-1 overexpressing cells/porous ceramic composites were transplanted into subcutaneous and bone defect sites in Fischer rats (cultured bone transplantation model) and markedly affected in vivo bone formation and osteoblast markers. The results demonstrated that the reconstitution of bone tissues, such as cortical bone and trabecular bone was accelerated by implantation of Til-1 overexpressing cells/porous ceramic composites. Moreover, the new bone formation by Til-1 overexpression appeared to reflect replacement of new bone within the implant boundaries. To ascertain whether implanted Cbfa1 overexpressing cells could differentiate into osteogenic cells to create bone or whether it stimulated the surrounding recipient tissue to regenerate bone, implanted male donor cells were visualized by fluorescent in situ hybridization analysis. The proportion of implanted cells in the presumptive bone forming region was over 80% and did not change throughout from 3 days to 8 weeks after implantation. These findings suggested that the newly formed bone in the porous area of the scaffold is mostly produced by the implanted donor cells or their derived cells, effectively by Til-1 overexpression.

20604 人工股関節用多孔質セラミック基複合材斜における機械的特性の評価(OS9 バイオエンジニアリング)

20604 人工股関節用多孔質セラミック基複合材斜における機械的特性の評価(OS9 バイオエンジニアリング)

Mullite/Alumina Mixtures for Use as Porous Matrices in Oxide Fiber Composites

Weakly bonded particle mixtures of mullite and alumina are assessed as candidate matrixes for use in porous matrix ceramic composites. Conditions for the deflection of a matrix crack at a fiber‐matrix interface are used to identify the combinations of modulus and toughness of the fibers and the matrix for which damage‐tolerant behavior is expected to occur in the composite. Accordingly, the present study focuses on the modulus and toughness of the particle mixtures, as well as the changes in these properties following aging at elevated temperature comparable to the targeted upper‐use temperature for oxide composites. Models based on bonded particle aggregates are presented, assessed, and calibrated. The experimental and modeling results are combined to predict the critical aging times at which damage tolerance is lost because of sintering at the particle junctions and the associated changes in mechanical properties. For an aging temperature of 1200°C, the critical time exceeds 10 000 h for the mullite‐rich mixtures.

Molecular Chemical Concepts for the Synthesis of Novel Ceramics

There is presently much effort in basic science and applied research to work on-novel ceramics with properties far beyond those of the existing materials. Aim and scope of the research in this field is to develop materials with superior thermomechanical, physical and chemical properties. In particular, the synthesis of carbide- and nitride-based ceramic,devices from molecular compounds such as inorganic polymers has attracted increasing attention for the production of dense and porous ceramic composites, fibers or coatings. Another important novel development is the synthesis of hybrid materials using sol-gel techniques. In our studies hybrid organic-inorganic xerogels; of general formula (NCN)(1.5)Si-(CH2)(n)-Si(NCN)(1.5) and (NCN)(1.5)Si-CH2-C6H4-CH2-Si(NCN)(1.5) were prepared. These polymeric carbodiimide-gels represent a novel approach to the field of non-oxidic hybrid materials. All the products were characterized by nitrogen adsorption (BET), SEM, TEM and FTIR spectroscopy. Moreover, novel ceramic compositions such as binary carbon nitrides can be synthesized by the polymer-to-ceramic transformation route. The sp(3)-hybridised carbon nitrides are expected to exhibit ultra high hardness. We prepared ON precursor compounds based on the tri-s-triazine unit. The molecular, oligomeric and polymeric compounds exhibit not only high thermal stability, but also interesting optical properties such as strong photoluminescence. Preliminary experiments indicate that the precursors are promising candidates for high pressure bulk synthesis of ceramic CNx materials.