2 research outputs found
Korszerű kerámiák újszerű szerkezettel = Advanced Ceramics with Novel Structure
A kutatás távlati cĂ©lja az volt, hogy olyan kerámikus alapĂş kompozitok kifejlesztĂ©sĂ©nek magalapozásához járuljunk hozzá, amelyek tulajdonságai felĂĽlmĂşlják mĂ©g a jelenleg ismert korszerű kerámiákat is, kĂ©pesek megfelelni komplex igĂ©nybevĂ©teleknek. A vizsgált kompozitok valamelyik karbon mĂłdosulatot tartalmazták szilĂcium nitrid mátrixban, gáznyomásĂş szintererelĂ©st, izosztatikus melegsajtolást Ă©s plazma szinterelĂ©st alkalmaztunk. ElektronmikroszkĂłpos Ă©s röntgendiffrakciĂłs szerkezetvizsgálatokat vĂ©geztĂĽnk, mĂ©rtĂĽk a mechanikai sajátságokat, a fajlagos villamos vezetĹ‘kĂ©pessĂ©get, egyes termikus jellemzĹ‘ket. Az eredmĂ©nyek fĹ‘bb vonásait magyarázza az a feltevĂ©s, hogy karbon nanocsĹ‘, vagy korom, vagy grafit adalĂ©k Ă©s a kerámia rĂ©szecskĂ©k közötti vonzás gyenge, ebbĹ‘l következik, hogy a rugalmassági modulust a sűrűsĂ©g meghatározza, a villamos vezetĹ‘kĂ©pessĂ©g pedig attĂłl fĂĽgg, hogy a kerámia-kerámia kötĂ©sek kiĂ©pĂĽlĂ©se közben hol van ĂĽres hely a nanocsövek rĂ©szĂ©re. Viszont fellĂ©p vonzás a fĂłliásĂtott grafit nanolemezei Ă©s a kerámia rĂ©szecskĂ©k között, ennek hatására a kopás csökken, a vezetĹ‘kĂ©pessĂ©g koncentráciĂłfĂĽggĂ©se gyengĂĽl | The aim of the project was to contribute to the basic knowledge necessary to the development of ceramic composites withstanding to complex hits. The examined composites contained silicon nitride as matrix and one of the modifications of carbon as additive. The finishing step of processing was gas pressure sintering (GPS), hot isostatic pressing (HIP) or spark plasma sintering (SPS). The structure was studied by electron microscopy and X-ray diffraction, mechanical properties, specific electrical conductivity and some thermal characteristics were determined. The main features of the behavior of studied composites can be explained by supposing that the interaction between the ceramic particles and carbon nanotubes, or carbon black, or graphite is weak. In this case the modulus of elasticity is depends only on the density, and the electrical conductivity is controlled by the shape of the space between the ceramic particles. On the other hand, attractive force occurred between the ceramic particles and exfoliated graphite sheets, consequently the wear of this composites is weaker, its conductivity is smaller than that of materials containing the other carbonaceous modifications
Changes of Temperature and Precipitation Extremes following Homogenization
Climate indices to detect changes have been defined in several international projects on climate change. Climate index calculations require at least daily resolution of time series without inhomogeneities, such as transfer of stations, changes in observation practice. In many cases the characteristics of the estimated linear trends, calculated from the original and from the homogenized time series are significantly different. The ECA&D (European Climate Assessment & Dataset) indices and some other special temperature and precipitation indices of own development were applied to the Climate Database of the Hungarian Meteorological Service. Long term daily maximum, minimum and daily mean temperature data series and daily precipitation sums were examined. The climate index calculation processes were tested on original observations and on homogenized daily data for temperature; in the case of precipitation a complementation process was performed to fill in the gaps of missing data. Experiences of comparing the climate index calculation results, based on original and complemented-homogenized data, are reported in this paper. We present the preliminary result of climate index calculations also on gridded (interpolated) daily data