Porous Cordierite Research Articles

Preparation of Porous Cordierite with Thermally Stable Pore Structure

A cordierite ceramic with a thermally stable pore structure was prepared by a simple modification of a sol-gel reaction of alkoxide precursors, synthesized from Mg metal or Mg acetate, Al(i-OPr)3, and partially prehydrolyzed Si(OEt)4. For aging and drying, wet cordierite gel was treated with water vapor at 150°C to strengthen the gel network through enhanced hydrolysis and condensation reactions. The cordierite xerogels showed BET surface areas between 220–410 m2/g, depending on the catalyst and treatment conditions used. In particular, water vapor treated xerogel displayed comparatively thermally stable pore characteristics, which exhibited only a 4–17% decrease in BET surface area up to 700°C, while samples prepared using the conventional sol-gel method showed a 55–91% reduction. Both the DTA and XRD patterns showed that crystallization began at 900°C leading to the μ-Cordierite phase and the subsequent phase transition to α-cordierite at temperatures between 1050 to 1250°C.

Assessment of Damage Tolerance and Reliability for Ceramics

The risk of fracture does exist even in the carefully designed ceramic components under excess stress unexpected in design procedure such as high stresses caused by restraining the deformation at the contact region of the component. To assess the safety and the reliability of ceramics components under such circumstances, it is indispensable to take the damage tolerance of the material into consideration. Ceramics is thought to be perfectly brittle and have no damage tolerance. But, though very little, it has the damage tolerance. The important problems open to us now are to estimate the extent of the damage tolerance of ceramics quantitatively and to clear the relation between the damage tolerance of the material and the reliability of the component. In this paper, we demonstrate the existence of the damage tolerance in the ceramics by tests using specimens of a porous cordierite. The nonlinear stress-strain curve of the brittle material is thought to be a reflection of the damage tolerance of the material and it is shown that the nonlinear stress-strain curve obtained can be simulated by the distributed micro cracks model developed here. The relation between the damage tolerance and the reliability is also discussed through several simulation works. These simulations show that when the damage tolerance of the material is getting larger, the reliability of the component becomes higher. This conclusion is supported by the fracture test results using notched specimens of a porous cordierite where the notch sensitivity is shown to be very small in this material. This means that this material has the high reliability under the stress concentration.

Preparation and properties of ZSM-5 zeolite membrane obtained by low-temperature chemical vapor deposition

A zeolite membrane was obtained by in situ crystallization of silicalite-1 from a layer of silica species prepared by the novel method of low-temperature chemical vapor deposition (LTCVD) on a porous cordierite support. The XRD and SEM analyses showed a three-layer membrane: a 3–5 μm-thick compact layer, a 45 μm-thick zeolite-in-pore layer and the support. The pure gas permeation data indicate that the synthesized zeolite layer is dense and pinhole-free. In water-alcohol mixture pervaporation, the membrane exhibited a behavior of hydrophilic materials, with a high selectivity to water and a fair flux. This behavior can be explained by the presence of Al in the framework due to Al migration from the support. The membrane flux and selectivity decreased fairly slowly with time in the transient regime of water—ethanol pervaporation with the dry membrane, suggesting slow sorption equilibria of water and ethanol with the dry zeolite.

Thermal diffusivity of porous cordierite ceramic burners

The applicability of the laser flash method for measuring the thermal diffusivity of highly porous cordierite materials is investigated. Due to the surface roughness of the samples, some indetermination in the sample thickness measurement is produced, which induces errors in the thermal diffusivity calculation. This problem was partially overcome by attaching two thin Cu layers to both surfaces of the samples. The thermal diffusivity and conductivity values of two porous cordierite materials (40 and 50 vol % of porosity) are reported using this procedure and results are discussed comparing with data for three-layer models.

Triple-layered, thick glassy grain boundaries in porous cordierite ceramics

Mechanical tests and microstructural investigations were performed on porous cordierite ceramics. Four-point bending tests were carried out both in air and in water. It was shown that the mechanical strength was strongly influenced by the experimental conditions. Triple-layered, thick amorphous grain boundaries were observed by high-resolution transmission electron microscopy. The composition of each layer as measured by energy dispersive X-ray spectroscopy was shown to be different. It is concluded that applying an external stress causes water-induced stress corrosion cracking preferentially occurring at the amorphous grain boundaries and at the triple grain junctions. This may have caused the dramatic decrease in the mechanical strength in water compared with that in air.

Preparation of Porous Cordierite Using Gelcasting Method and its Feasibility as a Filter

Various-shaped porous cordierites with different pore sizes and with constant porosity of 80% were prepared by conventional mechanical foaming method combined with gelcasting using water-soluble polymers. Foamed slurries and pore structure of the products were characterized by image analysis and SEM. Apparent bubble size was dependent on the type of surfactant and not on surfactant concentration. Mean pore diameters of anionic and cationic surfactants were 100 and 200 μm, respectively. Feasibility of porous cordierites of foam type structure as filters for dust-collection was investigated. Membrane layers of 150 μm were uniformly built up on the external surfaces of candle-shaped supports to prepare trial filters. Gas permeability was above 200 × 10−13 m2 and was dominantly determined by that of membrane layer. In the dust collection test, removal efficiency for particulates finer than 10 μm was above 99.99%.

Preparation of ZSM-5 thin film on cordierite honeycomb by solid state in situ crystallization

Thin films of ZSM-5 zeolite were prepared on porous cordierite honeycombs by a solid state in situ crystallization method and were characterized by XRD, FTIR, SEM and nitrogen gas adsorption. The zeolite films were formed by coating the zeolite precursor sol on the cordierite honeycomb substrate and gelling it in the surface pores of the substrate. This gel was then converted into ZSM-5 by heating the coated substrate in an autoclave without adding solution. The amount of coating was increased by forming an interfacial layer of microporous silica on the cordierite substrate by acid leaching. The maximum specific surface area of the honeycomb coated with zeolite film was 249 m 2/g. Recoating the substrate with zeolite film was effective not only in increasing the amount of zeolite film and its surface area but also in reducing the macropores in the honeycomb surface. The zeolite film was found to retain its porous properties up to the calcining temperature of 900°C. The zeolite film is considered to be formed by a vapor transport mechanism initiated by the water included in the gel.

Processing of porous cordierite bodies by starch consolidation

Porous cordierite ceramics, formed from a mixture of ball clay, talc, alumina, and silica sand, were developed by a new direct consolidation method based on the properties of starch in water. The gelling capability of starch granules in warm water allows the transformation of a stable suspension into a rigid and stiff body that can be machined in the green state. Starch consolidation can be performed in nonporous molds, enabling materials with controlled porosity to be obtained by varying the starch content in the slip composition. The simplicity of the process as well as the low price of starches makes this new consolidation technique very promising from an industrial point of view. The results showed good agreement with the expected porosities of the cordierite sintered bodies, thus enabling the design of porous textures and tailoring of the material to applications.

Thermal shock resistance of cordieritic filter for diesel engines

Cordierite porous ceramics are attractive materials for diesel particulate traps, but are sensitive to the thermal shocks provoked by the ignition of accumulated soot. The present paper reports an investigation on a commercial porous cordierite to be used as a substrate for catalysts in exhaust pipes. Samples have been subjected to thermal shock tests to study the response of these ceramics to the repetitive thermal shock that occurs within automotive systems during the regeneration processes. In particular, the effect of thermal treatment on microstructure and mechanical properties has been examined and explained.MST/1992

Preparation and Water Permeation Property of Bimodal Porous Cordierite Ceramics

Porous cordierite ceramics were prepared from the flyash exhaust of a power plant. Addition of the coal powder to the cordierite green bodies was effective for increasing the open pore volume. The size and the shape of pores were approximately the same as those of the original coal powder particles, and pore size could be controlled in the range from 50 to 1000μm by controlling the particle size of the coal powder. While, the intrinsic pore size of cordierite ceramics without coal additives was about 10μm. Thus, the porous ceramics showed bimodal pore size distributions. The observed correlation between the content of coal particle and the open pore volume percent well agreed with the calculation based on the density of the dried body and the coal. Pure water flux through the disc sample without coal powder addition was 2.08×10-5m3/m2⋅s, but it increased 40 times when the volume percent of the large pores in the body became 45%. The increase in the pure water flux was well explained by a model in which pure water passes preferentially through the larger pores.

Organic gels in the preparation of silico-aluminate powders. II. Cordierite

The elaboration of cordierite powders from aqueous or alcoholic solutions, gelled by organic polymers, has been studied. The aqueous solution, made from Al and Mg nitrates or citrates and Si alkoxide, tetraethylorthosilicate (TEOS) or 3-(triethoxysilyl)propylamine (TESPA), is gelled by polyacrylamide and the aqueous gel is calcined at 750°C. The behaviour of the powder depends strongly on the precursor solution. A powder produced from citrates and TESPA expands upon sintering to a porous cordierite, while that elaborated from nitrates and TEOS densifies completely before crystallizing into μ- and then α-cordierite. In the same way, an ethanolic solution of nitrates and TEOS, gelled by poly(2-hydroxyethyl methacrylate) (pHEMA) produces a very homogeneous powder that densifies completely; α-cordierite is obtained at a particularly low temperature (1000°C). Die Herstellung von Cordieritpulvern aus wässrigen oder alkoholischen Lösungen, die durch Zugabe organischer Polymere gelierten, wurde untersucht. Wässrige Lösungen, die aus Al- und Mg-Nitraten oder -Zitraten und Si-Alkoxid, TEOS oder 3-(Triethoxysilyl)propylamin (TESPA) hergestellt wurden, wurden mit Polyacrylamid geliert. Dieses wässrige Gel wurde bei 750°C kalziniert. Das Verhalten der Pulver hängt in großem Maße von der verwendeten Ausgangslösung ab. Pulver, die aus Zitraten und TESPA gewonnen wurden, dehnten sich beim Sintern aus und bildeten porösen Cordierit. Jene aus Nitrat und TEOS verdichten völlig, ehe sie zu μ-und anschließend zu α-Cordierit kristallisierten. In analoger Weise ergab eine Lösung aus Nitraten und TEOS in Äthanol, die mit Poly(2-hydroxyäthyl methacrylat) (pHEMA) geliert wurde, ein sehr homogenes Pulver das völlig verdichtete. Bereits bei sehr niedrigen Temperaturen (1000°C) bildete sich α-Cordierit. L'élaboration de poudres de cordiérite par voie de solutions aqueuses ou alcooliques, gélifiées par des polymères organiques, a été étudiée. Les solutions aqueuses sont réalisées à partir de nitrates ou citrates d'Al et Mg et d'un alcoxyde de Si, TEOS ou triéthoxysilyl-3-propylamine (TESPA), puis gélifiées par le polyacrylamide. Les gels aqueux sont ensuite calcinés à 750°C. Le comportement de la poudre dépend fortement de la nature de la solution précurseur. Alors qu'une poudre obtenue à partir de citrates et TESPA gonfle pour former une cordiérite alvéolaire, très peu dense, celle élaborée à partir de nitrates et TEOS densifie complètement avant de cristalliser en cordiérites μ puis α. De la même manière, une solution éthanolique de nitrates et TEOS, gélifiée par le polyméthacrylate d'hydroxy-2-éthyle (pHEMA), produit une poudre très homogène qui densifie complètement, et la cordiérite α est obtenue à plus basse température (dès 1000°C).

Thermophysical properties of highly porous cordierite and ultraporcelain

Thermophysical properties of highly porous cordierite and ultraporcelain

Some properties of porous cordierite ceramics

Some properties of porous cordierite ceramics