Adrian Volceanov

Development of ZrO2/ ZTA / TiC Composites

TiC was added to a matrix consisting of either (CaO+MgO) stabilised zirconia (PSZ) or Zirconia Toughened Alumina (ZTA), in order to produce composites by uniaxial pressing and sintering in vacuum at 1400 o C. The purpose of the present paper is to establish a correlation between the physical – mechanical and structural properties of composites with different matrices as a function of the amount of secondary phase by varying the TiC content between 5 25 weight %. Comparative microstructure investigations were made by TEM on sample surfaces. The results highlighted the best mechanical properties and homogeneous microstructure for the ZTA composites. The X-ray diffraction analysis was in accordance with the determined properties of the studied compositions. Introduction Stabilised Zirconia pollycrystalls as a tetragonal polymorph have an outstanding bending strength (~ 1000 MPa) and fracture toughness (~10 MPa.m 1/2 ). These materials have a limited hardness (< 1200 kg/mm 2 ). On the other hand, pure TiC has an excellent hardness (> 2800 kg/mm 2 ) but a limited bending strength and fracture toughness. TiC appears to be one of the hardest pure carbides known. For these reasons the main objective of this work was to improve the hardness of (CaO+MgO) stabilised zirconia (PSZ) and Zirconia Toughened Alumina (ZTA), respectively by adding TiC as secondary phase. Experimental Procedure a.) Stabilised Zirconia matrix composites TiC powder was dispersed in a matrix consisting of (3%CaO+1%MgO) stabilised zirconia (PSZ) in amounts varying between 5-25 weight % [1]. b) Zirconia Toughened Alumina (ZTA) matrix composites A mixture of Al2O3 and stabilised ZrO2 mixture was prepared [2] at a ratio of 85:15 by weight. The calcined alumina powder (at 1550 o C, for 4 hours) was added to the doped (3%CaO + 1%MgO)-zirconia mixed and homogenised in an attritor with isopropanol for 2 hours, using alumina balls. The obtained Alumina -Zirconia (ZTA) matrix, TiC powder was dispersed in different amounts (5 25%). The raw materials characteristics are summarised in Table 1. The batches were pressed as cylinders (φ =h =20 mm) and sintered at 1400 o C in vacuum ( at 10 -4 torr) in a Baltzer type kiln, during 2 hours at maximum temperature. The particles size distribution of the powders was determined by using a laser grain size tester (dm) and the Fischer method (d50) [1,2] (Table 1). The compressive strength at room temperature was measured on a Netsch testing machine. The microindentation technique, with a Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2283-2286 doi:10.4028/www.scientific.net/KEM.264-268.2283

High Thermal Shock Resistant Aluminium Titanate Type Ceramics

Microstructure control is a critical issue facing manufacturers of advanced ceramics. Secondary phases, introduced to improve sintering, have become increasingly important in controlling the average grain size and grain-size distribution of the major phase. The effect of ZrO2 addition (1, 5, 10 % by weight) on tialite type, binary TiO2-Al2O3 compositions were investigated at 1550 o C. The influence of CeO2, MgO and Nd2O3 on the thermal shock resistance, mechanical strengths, open porosity, bulk density, and microstructure have been studied. Dilatometric analysis, Fourier Transform – Infrared analysis (FTIR), X-Ray Diffraction (XRD) analyses and Scanning Electron Microscopy (SEM) used to study both phase transformation and sintering processes. The addition of ZrO2 improves the thermal shock resistance of tialite compositions (> 40 reversals of heating at 900 o C followed by rapid cooling in water). Introduction Pure ceramic materials based on ZrO2 or TiO2 show a proper corrosion resistance against slag or slag/metal corrosive environment but are affected from thermal shock conditions [1]. Aluminium Titanate (tialite) represents a high useful refractory ceramic due to the low thermal expansion coefficient (0.1-1x10 -6 o C -1 ), low thermal conductivity (0.9-1.5 W/m o C) and excellent thermal shock resistance. These characteristics make it an attractive material for specialised applications. A limiting factor is the decomposition of tialite in the temperature range 700-1300 o C [2] with formation of Al2O3 and TiO2 (rutile). As a result of decomposition, the tialite (Al2TiO5) no longer exhibits a low coefficient of thermal expansion [3]. The thermal decomposition of Al2TiO5 can be controlled by adding different additives (oxideMgO, SiO2, Fe2O3, fluoride, glass, etc.) [4]. The melting point of tialite is above 1800 o C and the bulk coefficient of thermal expansion is very low and consequently developing an excellent thermal shock resistance [5]. On the other hand, the highly anisotropic materials like Al2TiO5, showing grain boundary microcracking in polycrystalline bodies have extremely low strength [6]. The strength can be improved by alloying with a material of high strength while the matrix maintains the low thermal expansion [7,8]. The aim of this work was to improve the mechanical characteristics of aluminium titanate ceramics, synthesised from equimolar amount of Al2O3 (corundum) and of TiO2 (anatase), by alloying with 5% and 10% (by weight) stabilised zirconia. The influence of some oxides, such as MgO, CeO2 and Nd2O3 on the tialite-zirconia composite thermal stability at the heating-cooling condition has been investigated also. Experimental Procedure

Influence of forming conditions on characteristics of alumina–PSZ composites

Abstract The purpose of the work reported in the present paper was to establish the correlation between the physical, mechanical, and microstructural properties of alumina matrix composites reinforced with (CeO2, Nd2 O3, Y2O3 )–PSZ (partially stabilised zirconia) depending on the processing and thermal treatment conditions. The composites obtained from fine powder mixtures were formed by hydraulic pressing, ceramic injection moulding, and hot pressing under various temperature and pressure conditions. The samples were fired at 1550–1770°C in an oxidising atmosphere and in vacuum depending on the forming conditions. Comparative microstructure investigations were made by TEM on sample surfaces. The XRD results were in accordance with the determined properties of the investigated compositions. The results highlighted that the best physical and mechanical properties and homogenous microstructure for the ZTA composites were obtained by firing in vacuum.

Glazes Using E-Glass Fibers Waste

The main purpose of the paper is to present results of experiments concerning E-glass fibers waste with a content of 7% B2O3 for obtaining glazes for tableware ceramics, as well as to study the consequences upon fabrication technology. The results are encouraging and make possible the use of E-glass fibers waste for preparation of vitreous glazes.

Basicity or Ionicity – A New Approach for Understanding Glass Properties

Basicity of glass is still a challenge in spite of various attempts to measure or calculate it. The values assigned for basicity of glasses, either calculated or experimentally determined, are not always in full agreement with actual facts, and discrepancies among the theoretical ones are not unusual. For instance, SiO2 is described by a single basicity value even if the polymorphs of SiO2 are quite different. Only few attempts were made to face this challenge. Present paper deals with a novel approach on theoretical ionicity / basicity based on electronic energy levels or band structure of solids. Another major adjustment takes into account the possibility of decomposing ionicity of complex chemical bondings into a sum of binary bondings. Considering the distribution of the interbonding angles specific for vitreous systems, it is possible to estimate both a local ionicity (basicity) of bondings and a global (mean) basicity of glass. The variation of basicity (ionicity) with temperature is also presented, this finding being able to open a new view on thermal history of glass considered through chemical character of bondings.