AE can be used in characterization of oxide ceramic and ceramic matrix fiber composites. In oxide systems the AE activity was influenced by chemical composition, sintering temperature and structure development. AE activity increased from kaolin to pottery mixture as a result of the developing a stronger structure with incorporation of a second phase in the matrix, while decreased in kaolin-fly ash composites due to weakening of the structure and formation of cracks. Kaolin ceramics showed a clear Kaiser effect, while pottery mixture, kaolin-fly ash and brick clay composites were more or less acoustically active during the second loading. Short fiber ceramic matrix composites indicated that fiber composites present higher AE activity since, matrix sub-critical events, fracture of the fibers, fiber-debonding or fiber pull-out from the matrix may produce a comparatively large amount of AE events. Increase of sintering temperature produced composites with higher AE activity for similar reasons to that of powder ceramics. Increase of the volume fraction of fibers increased the AE activity. In the examined fiber ceramic systems Kaiser effect was observed in all cases irrespective of the kind of the fibers, a fact that indicates that the sub-critical activity during loading is not a reversible process. AE examination is a valuable tool giving useful information about the strength, structure and the sintering techniques used during manufacturing of ceramic systems.

Microwave processing holds great potential for improving current composite manufacturing techniques, substantially reducing cure cycle times, energy requirements and operational costs. In this paper, microwave heating was incorporated into the resin transfer moulding technique. Through the use of microwave heating, a 50% cure cycle time reduction was achieved. The mechanical and physical properties of the produced carbon fibre/epoxy composites were compared to those manufactured by conventional resin transfer moulding. Mechanical testing showed similar values of flexural moduli and flexural strength for the two types of composites after normalisation of the corresponding data to a common fibre volume fraction. A 9% increase of the interlaminar shear strength (ILSS) was observed for the microwave cured composites. This enhancement in ILSS is attributed to a lowering of resin viscosity in the initial stage of the curing process, which was also confirmed via scanning electron microscopy by means of improved fibre wetting and less fibre pull-out. Furthermore, both types of composites yielded minimal void content (<2%). Dynamic mechanical thermal analysis revealed comparable glass transition temperatures for composites produced by both methods. A 15°C shift in the position of the β-transition peak was observed between thermally and microwave cured composites, suggesting an alteration in the cross-linking path followed.

In order to manufacture products of acceptable quality within predetermined specification limits, an evaluation of the manufacturing process through the use of capability indices is necessary. Capability indices are used in order to evaluate a process and to monitor the product characteristics and the results of quality improvement cycles. The three point bending strength of kaolin ceramic specimens produced by two different production processes (slip casting and hydroplastic extrusion) were investigated. It was found that under statistical control and normal distribution of strength values, the process capability indices Cp, Cpk, regardless of any disadvantages and the fact that they have limitations, can be combined with other techniques in the field of statistical process control and become valuable tools in process evaluation of ceramic products.

Although structural kaolin based ceramics are attractive and useful materials, having good mechanical characteristics, low density, good corrosion and high temperature resistance, their use is restricted by their brittle behaviour. In order to improve their properties and mainly strength, toughness and high temperature performance, fibre composite ceramics have been developed. In the present work a series of kaolin-short random dispersed Grafil carbon fibre composites were produced and sintered in an inert atmosphere of Argon at 1000oC and 1300oC and characterised using various techniques. XRD analysis of the kaolin matrix at 1000oC showed that the crystalline phases were decomposed without the formation of mullite a fact which also reconfirmed by SEM examination. However at 1300oC mullite formation was well evidenced. XRD analysis of the fibres in “as received” showed that they have graphite structure which was also retained, as SEM examination revealed, after sintering. Examination of the Grafil fibres showed that they were quite uniform in length and diameter and retained their integrity after sintering at the examined temperatures. Examination the fractured composite surfaces showed only a weak bond between fibres and matrix and at the pull out areas the fibres were replicated in the matrix.

Tin dioxide is a wide band semiconductor, with interesting chemical physical and mechanical properties, used in a variety of industrial, domestic, medical and agricultural applications, including gas detectors, transparent conductors, solar cells, anti-static films, nanoelectronic devices etc. The variety of nanosized SnO2 production methods in the form of powders or layers (e.g. solid state, sol-gel, sputtering, laser ablation, template, solution precipitation, precursor oxidation, CVD, PVD, etc) are discussed.

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A series of ceramic materials such as kaolin, a pottery mixture and a 5% kaolin and 10% fly ash composite, were studied by acoustic emission (AE) during three-point bending after slip casting and sintering at various temperatures. Their acoustic behaviour has connected to structure development. AE activity was increased from kaolin to pottery mixture as a result of the developing a stronger structure with incorporation of a second phase in the matrix, while decreased in fly ash composites due to weakening of the structure and formation of cracks. In kaolin ceramics, there was a clear Kaiser effect, while pottery mixture and the kaolin–fly ash composites were acoustically active during the second loading and Felicity ratios were calculated.

A number of brick-clay specimens sintered by traditional and fast cycles, was studied by acoustic emission during three-point bending. Acoustic behaviour was connected with structure development. Acoustic emission activity was generally increased with an increase of sintering temperature as a result of the development of a stronger structure. Specimens sintered by the fast sintering programs, remaining for short period of time at 850, 950 and 1050°C maximum temperatures and then furnace cooled to room temperature, were much more acoustically active compared with specimens sintered traditionally at similar temperatures. Examination in repeated loading showed an absence of the Kaiser effect. During the second loading, major acoustic activity was shown from the beginning of the second loading, indicating a low Felicity ratio. The behaviour of brick-clay specimens during acoustic examination under loading could give useful information about the strength, structure and the sintering techniques used during manufacturing of bricks, tiles and similar products.

Thermogravimetry, differential themal analysis, 3-point bending, water absorption and frost resistance were examined on five brick clays collected from central Greece in order to assess their ceramic potential and mechanical properties. Endothermic peaks show that the main reactions during thermal analysis dehydrations, decompositions and volatilizations. Water absorptivity varied between 12.5 and 34.4 % and the Modulus of Rupture varied between 5,46 and 9.12 Mpa, depending on the clay type the solid brick samples were made of Resistance to frost was found to be inversely proportional to water absorptivity, and the weight loss after exposure to frost of the solid brick samples varied between 15 and 40%.

ii series of kaolin based composites, Remblend china clay a pottery mixture, a brick clay composition, and a clay-fly ash composition have been sintered in air at various temperatures and the resulting products characterised with respect to chemical and mineralogical composition, thermal analysis, mechanical properties and microstructures. Sintering of the clay based ceramics changed the microstructure from a point bonded to a dense glass-ceramic microstructure whose composition depended on the original clay composition. Structure flaws existing where glass formation had started but was insufficient to produce a strong network, and sand particles, in well developed glass bonded structures, could act as sites of fracture initiation. Generally, kaolin and pottery mixtures had similar microstructures after sintering at temperatures differing by similar to 200 ti. Brick clay mixtures showed an increase up to 1150 degrees C, but any further temperature increase resulted in melting. Kaolin and pottery specimens sintered at temperatures higher than the optimum showed reduced properties as a result of increased porosity and bloating. Modulus of rupture (MOR), fracture toughness K-1c, and modulus of elasticity E were found to be closely related to the microstructure of the ceramics. Those ceramics where glass formation had started but was insufficient to produce a well developed glass bonded structure, with large flaws present such as sand particles which act as sites of fracture initiation, had medium values of E (similar to 10-20 GN m(-2)), MOR (similar to 15-20 MN m(-2)), and K-1c (0.4-0.7 MN m(-3/2)). Well developed glass bonded microstructures without major paws (e.g. kaolin sintered at 1200 and 1300 degrees C. or pottery mixture sintered at 1100 degrees C) had relatively high E (similar to 30-40 GN m(-2)), MOR (similar to 35-40 MN m(-2)), and K-1c (0.7-0.9 MN m(-3/2)) values. Kaolin compositions sintered at 1400 degrees C reached their maximum properties while pottery mixture specimens attained optimum properties after sintering at 1150 degrees C. (C) 1996 The Institute of Materials.

Brick clays from central Greece were examined by Tg and DTA.

The reaction of NO+H2 on polycrystalline wires and foils is studied from temperatures between 550 and 1800 K, and partial pressures between 10−3 and 1 Torr. N2 and N2O are the main products formed during this reaction. Below about 750 K and above 1500 K, the rates of N2 and N2O formation are about equal. Both rates go through a maximum then a minimum and rise again with increasing temperature above 1500 K and 1200 K respectively. Rate data for the formation of N2 and N2O at low, intermediate and high temperature regimes are fitted with Langmuir-Hinshelwood (LH) bimolecular rate expressions within about ± 30%. Heats of adsorption for NO and H2, obtained from these rate expressions are 25.3 and 12.4 kcal/mol respectively.

The NO+H2 reaction was found to oscillate on Pt. The oscillations were of the relaxation type and non-isothermal. The temperature amplitude of the oscillation was from 120 to 190 K, and the rate varied between about 5×1015 and 5×1017 molec./cm2.

The selectivity of the NO+H2 reaction towards N2 and N2O was found to vary by more than four orders of magnitude as compared with that on polycrystalline wires and foils of Pt, Rh and Ir. NH3 is also produced during this reaction. Ir is the most selective catalyst towards N2 formation, by more than 3 orders of magnitude below 1000 K, as compared to Pt and Rh.

The decomposition of N2H4 has been studied on polycrystalline Ir. It was found that hydrazine decomposition is very fast compared with other previously reported unimolecular reactions [3, 4]. Three products were detected, namely N2, H2 and NH3. NH3 formation rates were equal to those of N2 formation up to about 700–800 K, depending on the pressure, but rapidly decreased above that temperature, while those of N2 formation became flux-limited at high temperatures.