Till today several kinds of ceramics and ceramic matrix composites are developed for extreme environmental conditions. Most of these ceramics have microstructures with relatively "big" crystals, having high rigidness and strong inclination to nick, pitting and rigid fractures, so they are not usable for collision with metallic or other bodies under high speeds like 800 m/sec or more. On the basis of several years experiments in development and testing of ceramic materials and corundum matrix composites the authors successfully developed new alumina-matrix composite materials reinforced with Si 2 ON 2 , SiAlON, AlN and Si 3 N 4 . These new alumina based ceramic matrix composites were tested under collisions with different metallic bodies having high densities and speeds higher than 800 m/sec. During the collisions the kinetic energy of flying metallic objects distributing to fracture energies, heatings and recrystallizations both of ceramic and metallic bodies. In the centres of collisions, where oxygen was absent, the authors have found new, high density "diamond-like Si 3 N 4 " materials with cubic crystals, where nitrogen atoms distributed in the centres of the cubes. These new crystal structures of Si 3 N 4 in the alumina matrix have extreme dynamic strength and hardness, like diamond. Having surplus of oxygene in the centres of collisions this new "diamond-like Si 3 N 4 " was not observed, when a very strong oxydation of metallic bodies was taken place. Using the energy conception of collision, the authors mathematically described the energy engorgements of destruction of ceramic materials and heating of participating bodies as well as energy engorgement used for the phase transformations of ceramic and metallic particles during their collision.

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Összefüggések tégla és cserépipari termékek anyagszerkezeti és száradási tulajdonságai között (A XXIII. Téglás Napokon elhangzott előadás alapján.) Napjainkban, amikor az energiaköltségek eldönthetik egy-egy vállalat, vagy iparág versenyképes-ségét, különösen fontos, hogy megértsük a tégla és cserépipari termékek szárításakor lejátszódó termodinamikai folyamatokat és anyagszerkezeti változásokat. Munkájukban a szerzők rámu-tatnak a formázott nyers téglák és kerámia tetőcserepek anyag-és pórusszerkezetének a szárí-tási folyamatban betöltött szerepére, különös tekintettel a 100°C-nál magasabb hőmérsékleten történő szárítás lehetőségeire és korlátaira. Az elvégzett vizsgálatok, elemzések rámutattak, hogy a formázott nyerstégla és kerámia tetőcserép tele van néhány mikrométer, vagy ennél is kisebb méretű pórusokkal és kapillárisokkal, amelyekből a vízcsepp eltávolításához -felületi feszültségé-nek leküzdéséhez -több MPa nagyságú belső nyomás létrehozása szükséges. Ekkora belső "gőz-nyomás" előállítása csak a jelenleg elterjedtnél lényegesen magasabb szárítási hőmérsékleten lehetséges! A szárítási hőmérséklet növelésével -a szárítási művelet gyorsításával -minden esetben csökkent a formázott nyerstégla és kerámia tetőcserép száradási zsugorodása; jelentősen lecsökkentve így a zsugorodás által gerjesztett húzófeszültség nagyságát.

this work investigates the behavior of porous alumina ceramics (within the porosity range of 18% to 70%) when subjected to deformation by compression and shear. the analysis of straindeformation curves showed that there was a transition from a typically brittle state for relatively dense ceramics (≤20% porosity), to a pseudo-plastic one with a high rate of porosity (above 50%). the values of the modulus of elasticity, shear modulus and Poisson's ratio decrease with an increase in volume in the pore space of Al 2 o 3 ceramics, which correlates with the appearance of multiple cracking during the deformation of ceramics with a high level of porosity.

A novel approach to obtain ceramic matrix composites with extreme high mechanical wear and thermal shock resistance abilities is presented. The developed corundum matrix composites were reinforced with nanoparticles, submicron fibres and whiskers of Si2ON2, SiAlON, AlN and Si3N4. These kinds of materials have several Young’s modulus simultaneously. These new alumina based ceramic matrix composites were obliged to collisions with different metallic bodies having high densities and impact speeds larger than 900 m/s at the moment of the hits. During the experiments in the places of collisions where oxygen was absent new high density „diamond-like” c-Si3N4 cubic crystals have developed with spinel structures, where nitrogen atoms were distributed in the centres of the cubes. These new spinel crystals of c-Si3N4 in the alumina matrix have extreme high dynamic strength, hardness and wear resistance, like diamond. They were fully resistance to oxygen and thermal shock at the tested temperature of 1200 oC.

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