Physicochemical properties of nanocrystalline composites based on ZrO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and rare-earth oxides

Powder precursors have been prepared by means of the sol-gel technique and codeposition, and nanoceramics in the ZrO₂-Al₂O₃-rare-earth (RE) oxide system (RE = Ce, Sc, or Y) based on them have been obtained. Physicochemical properties of the resulting ceramic composites have been investigated. The energy model for oxygen-ionic transport processes in a solid solution based on ZrO₂, which relies on computer simulation procedure, has been proposed, and the structural, strength, and electrophysical characteristics of the solid solution have been calculated. The obtained materials are promising as high-melting electrochemical sensors in molten oxides.     

Heat exchange during a slow flow of a liquid between coaxial conical surfaces

The problem of convective heat transfer during a slow liquid flow in conical annular channels is considered. For third-kind thermal boundary conditions, the problem is solved by separation of variables. The temperature distribution is represented as the product of an infinite Whittaker-function series in lateral coordinate and an exponential of longitudinal coordinate. Heat transfer in a variable-width annular conical channel is analyzed by stepwise approximation. Optimization of the distributing sections of extruder dies is shown to be possible.     

Fracture toughness, strength, and other characteristics of yttria-stabilized zirconium ceramics

The mechanical behavior of zirconium ceramics with different porosities (456 and 1330 MPa) is studied with an accent on the fracture toughness (the study of other characteristics in a wide temperature range plays an auxiliary role) The tests are predominantly performed with the use of a Vickers pyramid (theIF andIS methods) and under flexure (theSEVNB andSENB methods) The results of the indentation and subsequent bending of the specimens are used to plot aR-curve that turns out to be plane It is shown that despite the substantial difference in the strength of the studied variants of ceramics their crack resistance differs inconsiderably The values of the critical coefficients of stress intensity determined by various methods for the same ceramics are shown to differ The results obtained are analyzed using the data of a micro-Raman analysis The tests for crack resistance by the method ofSEVNB (bending of a beam with a polishedV-notch) show that the specimens do not undergo a tetragonal-monoclinic phase transformation during the deposition of a stress concentrator Transleted from Ogneupory i Technicheskaya Keramika, No. 8, pp. 7 – 13, August, 2000.     

High-strength ceramics from Zr02

Specimens of powder fabricated by codeposition of zirconium and yttrium nitrates with the using special dry ing techniques and regranulation by the method of hot isostatic pressing have been tested in air allowing for the laws of compaction of granulated powder at a final firing temperature of about 1500°C. The resulting ma terial had the following properties: a density p = 5.91 g/cm (98% of the theoretical value), an ultimate bend ing strength a = 1100 MPa, and a crack resistance K = 19.5 MPa . rn A set of the specimens was sub jected to hot isostatic pressing after natural sintering and exhibited the following properties: p = 6.08 g/cm = 1400 MPa, K = 17.5 MPa · m^1/2.     

High-carbon binders in refractories and corrosion-resistant ceramics technology

The authors review the literature sources and patents of foreign companies in the field of application of high-carbon organic binders for refractories, composites and technical ceramics. The review reveals the advantages of the new generation of binders with improved properties and describes binders meeting contemporary environmental requirements and not containing free phenol and other carcinogenic and toxic components. Translated from Steklo i Keramika, No. 5, pp. 12 – 15, May, 1998.     

Critical conditions for initiation of cylindrical multifront detonation

A quantitative relation between the characteristic scales determining the excitation and propagation of cylindrical and spherical detonation waves is found with the use of a technique for diffraction reinitiation of multifront detonation. The effect of the channel depth on the reinitiation conditions is studied. The ideal character (the smallness of losses) of a cylindrical multifront wave is estimated, and this estimate is found to be in agreement with experimental data. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 114–120, March–April, 1998.