Table of contents

Lower emissions of CO and NOx as well as a higher power density were observed in combustion processes performed in porous media like ceramic foams. Only a few materials are applicable for porous burners. Open-celled ceramic foams made of silicon carbide are of particular interest because of their outstanding properties. Two different SiC materials have been investigated, silicon-infiltrated silicon carbide (SiSiC) and pressureless sintered silicon carbide (SSiC). The oxidation behaviour of both has been characterized by furnace oxidation and burner tests up to 500 h operating time. Up to a temperature of 1200 °C SiSiC exhibited a good oxidation resistance in combustion gases by forming a protective layer of silica. High inner porosity up to 30% in the ceramic struts was found in the SSiC material. Caused by inner oxidation processes the pure material SSiC allows only short time applications with a temperature limit of 1550 °C in combustion gases. An increase of the lifetime of the SSiC foams was obtained by development of a new SSiC with an inner porosity of less than 12%. The result was a considerable reduction of the inner oxidation processes in the SSiC struts.

Porous ceramics incorporates pores to improve several properties including thermal insulation maintaining inherenet ceramic properties such as corrosion resistance and large mechanical strength. Conventional porous ceramics is usually fabricated through an insufficient sintering. Since the sintering accompanies the exclusion of pores, it must be terminated at the early stage to maintain the high porosity, leading to degraded strength and durability. Contrary to this, we have innovated superplastically foaming method to make ceramic foams only in the solid state. In this method, the previously inserted foam agent evaporates after the full densification of matrix at around the sintering temperature. Closed pores expand utilizing the superplastic deformation driven by the evolved gas pressure. The typical features of this superplastically foaming method are listed as follows, 1. The pores are introduced after sintering the solid polycrystal. 2. Only closed pores are introduced, improving the insulation of gas and sound in addition to heat. 3. The pore walls are fully densified expecting a large mechanical strength. 4. Compared with the melt foaming method, this method is practical because the fabrication temperature is far below the melting point and it does not need molds. 5. The size and the location pores can be controlled by the amount and position of the foam agent.

Recent titanium oxide nanotube arrays have attracted attention for their applications. Titanium oxide nanotubes were prepared under potentiostat conditions (10 – 60 V) for various times (1 min – 3 hr). SEM observations revealed that the pore sizes of the nanotubes have a tendency to increase with an increase in the applied potential in the NH₄F-glycerol-H₂O electrolyte. Some corrosive pores were observed on the surface of titanium substrate at 40 V for 1 minute at 40°C. The pores covered the surface of the titanium substrate after 10 minutes, and some small pores were observed in the inner part of the pores, which should correspond to the combining of some small adjacent pores into a large one. The combining of the tubes were observed after 2 h and 3 h anodization times, and the nanotube arrays seem to be formed upward from the SEM side-views. The photocatalytic activity of the titanium oxide nanotubes was evaluated according to the JIS standard (JIS R 1703–2). The R factor of the titanium oxide nanotube arrays formed at 40 V and 40°C for a 3h the anodization time was 9.71 n mol/l·min, which was twice that of the titanium oxide thin film obtained by the rf-sputtering method.

Studies on evaporation-induced vertical convective self-assembly as well as horizontal self-assembly are presented including inversion of the opals and deposition of heterostruc-tures. Opaline coatings were deposited on microscope slides from monodisperse particles of polystyrene and silicon dioxide with the particle sizes in the range from 400 to 1100 nm. Well defined photonic stopgaps were observed for both direct and inverted structures. We show that the horizontal deposition method facilitates self-assembly of large silica particles, so that the limitation of the conventional vertical convective self-assembly can be overcome. Successful stacking of the self-assembled polystyrene templates with unequal particle size is demonstrated.

Organic-inorganic conversion process of a novel precursor composed of polycarbosilane and palladium(II) acetate was investigated in order to develop a SiC-based gas separation membrane. It was found that the precursor was converted to inorganic material forming Si-C-Si, Si-O-Si and Si-O-C network and evolving hydrogen, methane, ethane, carbon monoxide and carbon dioxide gases in a temperature range of 350-1000K. Furthermore, it was found that the volume shrinkage of precursor during pyrolysis process was 50%, which is 14% lower than that of PCS, because of efficient crosslinking of PCS and network formation.

In the present work, hydrothermal treatment combined with ball-milling technique (HTBT) was attempted to recover SiC powder from bulk sintered DPF. Various parameters including the material and size of the milling-ball, the type of the solvent medium, the rotation speed, the ratio of solvent/DPF, the treatment temperature and time were optimized. The pulverization rate, impurity content and the particle size of the recovered SiC powder were investigated to assess the effect of HTBT. Dilute HF solution was selected as the main solvent and SiC milling-ball was the most suitable for pulverization of the sintered DPF. The rotation speed played a significant role for the pulverization rate and more than 90% of bulk sintered DPF was recovered as SiC powder using SiC balls (5 mm in diameter) in the mixed aqueous solutions of HF (0.05 mol/dm³) and H₂O₂ (0.25 mol/dm³) with rotation speed ≥ 275 rpm and solvent/DPF = 1.5 at 200°C after 20 h HTBT . Generally the average grain size of the recovered SiC powder was less than 1.5 μm and decreased with the extended treatment time and the increased rotation speed. The result of purity analysis showed that the recovered SiC powder totally met the demand of the raw SiC powder for DPF production under the optimized conditions.

We propose surfactant-free core-shell poly(lactic acid) (PLA) / calcium phosphate (CaP) hybrid particles as drug delivery carriers. These particles were prepared by biomineralization process using ultrasonic irradiation, and their drug release profiles were investigated. Drug release rate was earlier when particles were prepared by PLA with a low molecular weight, and/or by Ca(CH₃COO)₂ and (NH₄)₂HPO₄. Also, these were shown good protein adsorption. This work indicates that these particles have sustained-release ability without initial burst and can do targeting capability by biomolecule conjugation.

Porous alumina ceramic were produced by slip casting of aqueous alumina slurry with added small amount of metallic aluminium powder. Pores form in result of chemical reaction of aluminum with water by hydrogen gas evolution reaction and solidification of suspension. Porosity of such materials sintered at a temperature of 1600 – 1750°C varies from 60 to 90%. Pore size distribution and mechanical strength of these materials depend largely on the grain size of used raw materials. The major part of pores in the materials produced without additive of silica are larger than 10 ±m, but with 5 – 10 wt.% additive of silica in the raw mix pore size decreases considerably. The sintering shrinkage decreases to 2.5%. Coefficient of thermal expansion equally decreases from 8.9-10⁻⁶ K⁻¹ to 7.1 10⁻⁶ K⁻¹ and classification temperature increases to 1600°C, while deformation at high temperature decreases considerably.

Activated charcoal has been widely used as an odor absorbent in household and water purification industry. Filtration equipment for drinking water generally consists of four parts, which are microporous membrane (porous alumina ceramic or diatomite, or porous polymer), odor absorbent (activated carbon), hard water treatment (ion exchange resin), and UV irradiation. Ceramic filter aid is usually prepared by slip casting of alumina or diatomite. The membrane offers high flux, high porosity and maximum pore size does not exceed 0.3 μm. This study investigated the fabrication of hybrid activated charcoal tube for water filtration and odor absorption by slip casting. The suitable rice husk charcoal and water ratio was 48 to 52 wt% by weight with 1.5wt% (by dry basis) of CMC binder. The green rice husk charcoal bodies were dried and fired between 700–900 °C in reduction atmosphere. The resulting prepared slip in high speed porcelain pot for 60 min and sintered at 700 °C for 1 h showed the highest specific surface area as 174.95 m²/g. The characterizations of microstructure and pore size distribution as a function of particle size were investigated.

The microstructural feature, oxygen storage capacity and hydrogen reduction reaction of alumina-supported ceria were examined to determine the activation energy of hydrogen consumption. The scanning and transmission electron microscopy under high magnification indicate the small agglomeration and the surface coverage of CeO₂ on alumina. The activation energy E was 80–140 kJ/mol for reduction peaks at around 420 °C and 550 °C in the first reduction run. However, in the second run, E for the second peak changed depending on the CeO2 content. The results suggest the surface modification of CeO2 surface with alumina via heat treatment in both reducing and oxidizing atmosphere.

By controlling the cooling rates and the composition of slurries, the gradient porous hydroxyapatite ceramics are fabricated by the freeze casting method. According to the different cooling rate, the pores of HAP ceramics fabricated by gradient freeze casting are divided into three parts: one is lamellar pores, another is column pore and the last one is fine round pores. The laminated freeze casting is in favour of obtaining the gradient porous ceramics composed of different materials and the ceramics have unclear interfaces.

In this study organically modified nanoclay were prepared by exchanging of the cetyltrimethylammonium (CTAB), with inorganic/metal ions/cations in montmorillonite structure. To investigate the influence of the amount of modifier on basal spacing and subsequent removal efficiency of hydrocarbon, different amount of modifier was used. The modified and unmodified nanoclays characterized by XRD, CHN and FTIR techniques. The X-ray diffraction results showed that the interlayer spacing of CTAB-modified clays increased from 12 to 22Å. The effectiveness of the sorbent materials for sorption of a range of products was investigated using crude oil, kerosene, gasoline and toluene. The process parameters such as sorbent dosage and contact time were reported. The results showed that the adsorption capacity was in the range of 2 to 8 gram per gram of adsorbent. Results also showed that adsorption capacity of the organoclay was clearly higher than of the unmodified clay. These results were confirmed by CHN analysis.