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The present paper reports on the sintering behaviour of several ceramics prepared using a previously selected mixture of incinerated paper mill sludge and glass cullet in the ratio 60/40 which was blended with 10, 20, 30 and 40 wt.% of three different natural materials. The three natural products were: a red quartzitic clay, a yellow quartzitic clay and a kaolin. All mixtures were blended by attrition milling and dried; powders were sieved, pressed into specimens and fired for 1 h at temperatures ranging from 1040 to 1140 °C. The resulting materials were characterized by water absorption, shrinkage, crystallographic composition, microstructure and physico-mechanical properties. It was observed that materials containing kaolin display the best overall behaviour independently of the quantity of kaolin introduced. Conversely the optimal sintering temperature, and consequently the best properties of the materials prepared using red or yellow clay were measured on products fired at temperatures above 1080 °C; materials and temperatures are affected by the amount of clay added.

We examined the production of macroporous monolithic ceramic from mortars prepared using aluminate cements, one or two different types of alumina powders, superfluidificant, water and polyurethane fibres. Some relevant parameters for the preparation process of the mortar are: (i) the weight ratio between cement powder and water, (ii) the weight ratio between superfluidificant and cement powder and (iii) that between superfluidificant and water. Thirty-six percent is the upper limit for the volumetric content of the fibres that can be introduced into the mortar without leading to a material that breaks up by handling after the successive thermal cycle. We also optimized the thermal cycle that may be used in order to avoid the spontaneous break-up of the material during the sintering treatment. Materials containing fine and coarse particles of alumina powders exhibit extended ruptures probably dependent on the thermal stresses that grow on cooling after the sintering process, whereas in materials containing only fine alumina powders the presence of ruptures is more limited so that the fired materials have a sufficient strength and can be handled without a particular care. The ageing time at the maximum temperature plays an important role on the microstructure of the sintered material since it has been seen that after 2 h at 1250 °C the residual porosity seems to be completely closed and the large grain size shows the presence of structures which can be due to the presence of aluminates.

In this paper, a study of the tool wear mechanism in turning aluminium alloy reinforced with alumina using molybdenum-toughened alumina tools is presented. Alumina tools with three different amounts (15, 20 and 25 vol.%) of molybdenum were prepared and tested. The wear type was identified and its evolution with cutting time was measured. The results show that the main mechanism of tool wear is abrasion and not heat. The best overall performance was achieved, as far as flank wear is concerned, using the tool with 20 vol.% of molybdenum added. This has been explained using some of the composites intrinsic properties. SEM examination revealed that molybdenum particles are easily torn from the matrix by flowing chips. Under these conditions the molybdenum particles are not able to carry out their toughening action and they are responsible for the flank wear. Some ideas have been proposed as to engineer the alumina/molybdenum interface in order to increase their adhesion and the composite toughness.

Zirconia-toughened alumina cutting tools have been examined after machining an AISI 1040 steel. The Raman spectrum of zirconia and the fluorescence spectrum from alumina have been used to determine the extent of the tetragonal-to-monoclinic (t-m) transformation and the residual stresses in and around the worn-out crater, respectively. Although about 15% vol. m-zirconia is present even in a brand new cutting tool, it was shown that the crater region undergoes the t-m transformation up to 40% vol. In both cases, the transformed zone is concentrated near the surface. The residual stresses in alumina are slightly compressive in the new cutting tool and away from the crater region, but they become tensile inside the crater, where the t-m transformation of zirconia has occurred to a larger extent. A stochastic model has been used to predict the stresses and it has been found to reproduce very well the experimental data. Some evidence of the formation of a spinel reaction product in the crater region has been found, likely (Mg,Fe)AlO 4 .

Three ceramic insert materials, zirconia-toughened alumina (Al 2 O 3 –7vol%ZrO 2 ), mixed-based alumina (Al 2 O 3 –TiN–TiC–ZrO 2 ) and alumina reinforced with SiC whiskers (Al 2 O 3 –SiC w ), were used to cut AISI 1040 steel at 3.9 m s −1 . In addition, a traditional grade P10 insert (WC–TiC–Co) was tested. The lifetimes, according to KT/KM and VB B criteria, were determined using a profilometer and by image processing. The worn zones were observed with scanning electron microscopy techniques. Adhesion and plastic deformation were dominant wear mechanisms in zirconia-toughened alumina, mixed-based alumina and sintered carbide P10, both in the craters and in the cutting edges. As well as adhesion in alumina reinforced with SiC whiskers, a chipping wear mechanism was observed.

Cordierite porous ceramics are attractive materials for diesel particulate traps, but are sensitive to the thermal shocks provoked by the ignition of accumulated soot. The present paper reports an investigation on a commercial porous cordierite to be used as a substrate for catalysts in exhaust pipes. Samples have been subjected to thermal shock tests to study the response of these ceramics to the repetitive thermal shock that occurs within automotive systems during the regeneration processes. In particular, the effect of thermal treatment on microstructure and mechanical properties has been examined and explained.MST/1992

An attractive method for the fabrication of Al 2 O 3 -ZrO 2 laminar composites is described in this paper. The process consists in the centrifugation of colloidal suspensions containing alumina and zirconia particles. With this procedure, it is possible to grow thin layers with different composition and smooth interfaces. The effects of the slurry compositions, as well as aging times and centrifuging conditions on the morphology of the laminae are discussed.

The authors propose a multiple approach for the evaluation of cutting temperatures in ceramic tools. The first approach was the experimental evaluation of equitemperature lines, obtained in three-dimensional cutting by employing constant melting point powders scattered on planes parallel to rake face. In the second approach, a numerical finite element analysis was performed. At this step the determination of the percentage of total heat produced in the operation that flows into the tool was considered and, consequently, the temperature distribution within the whole volume of the insert. Finally, the examination of the crater zone with SEM microscopy confirmed the temperature levels as previous estimated.

The present paper reports on the results of some experiments on the progress of a previous research and describes the production, in single fast firing, of tiles containing 30 wt% of a natural red clay and a mixture of 42 wt% of paper mill sludge and 28 wt% of glass cullet which were coated with a commercial “matt white” glaze. Fired materials were characterized as a function of the top temperature (1090 or 1140 °C) reached during the fast sintering process made in an industrial roller kiln. It is observed that tiles fired at 1090 °C display the best overall performances since the matt glaze well covers the substrate concurring to maintain in line with the official standard for production the mechanical and physical properties of the tiles.

An attractive method for the fabrication of Al 2 O 3 -ZrO 2 laminar composites is described in this paper. The process consists in the centrifugation of colloidal suspensions containing alumina and zirconia particles. With this procedure, it is possible to grow thin layers with different composition and smooth interfaces. The effects of the slurry compositions, as well as aging times and centrifuging conditions on the morphology of the laminae are discussed.

The sintering behaviour of several ceramics prepared using a previously selected mixture of incinerated paper mill sludge and glass cullet which was blended with 10, 20, 30 and 40 wt% of some natural clayey materials has been studied. Three natural commercial product were used: a red clay, a yellow clay and a kaolin. Mixtures were blended by wet attrition milling, dried, sieved, pressed into specimens and then fired for 1 h at temperatures ranging from 1040 to 1140 °C. The resulting materials were characterized by water absorption, shrinkage and crystallographic composition. It was observed that materials containing kaolin display the best overall behaviour independently of the quantity of kaolin introduced. Conversely the optimal sintering temperature, and consequently the best properties of materials prepared using red or yellow clay was found above 1080 °C and depends of their specific composition being affected by the amount of clay added.

The outstanding performances of the Al2O3 cutting tools in terms of potential cutting speed can lead to substantial economies in the machining of metallic materials. Nevertheless, their widespread use is limited by some drawbacks such as the tendency to edge chipping and to the propagation of microcracks, which can lead to premature failures. These shortcomings are due to the intrinsic low toughness of the ceramic material, which is in turn related to its characteristics non-metallic bonds. A well-recognised method of increasing the toughness of brittle materials is the introduction of surface compressive stresses, which can be obtained through a suitable lamination geometry of the tools as consequence of the different coefficients of thermal expansion (CTE) of the constituent layers. The performances of an alumina/zirconia laminated cutting tool used for machining steel have been investigated and compared to those of a non-laminated commercial alumina/zirconia cutting tool. The different wear mechanisms are explained on the basis of the different microstructures and chemical compositions. We have shown that residual compressive stresses, measured by Piezo-Spectroscopy, are effective in avoiding the microchipping on the flank zone but cannot avoid larger fractures caused by the residual porosity.

In this paper we report on the preparation and characterization of porous ceramic substrates in the group of NaZr 2 (PO 4 ) 3 , CaZr 4 (PO 4 ) 6 , SrZr 4 (PO 4 ) 6 and BaZr 4 (PO 4 ) 6 with low thermal expansion coefficients. The starting powders were obtained by a sol–gel process and attrition milling both before and after calcination. The resulting sintered bodies exhibited high porosity also after further thermal treatments at high temperature. On the other hand their thermal expansion coefficient (CTE) is low over the range 25–1000 °C. In particular the blend between NaZr 2 (PO 4 ) 3 and SrZr 4 (PO 4 ) 6 has a CTE close to zero in the whole temperature range. According to these properties the above mentioned materials seem to be potential candidates as ceramic substrates for catalytic applications in combustion reactions since they maintain a high level of micrometric porosity when operating at temperatures exceeding 1000 °C.

Sandwich-structured three-layered ceramic inserts were made with the aim of obtaining ceramic cutting tools with an increased useful life.

A layered Al2O3-ZrO2 ceramic composite has been fabricated using a colloidal processing method. The technique uses sequential centrifuging of slurries containing suspended ceramic powders to form a three-layered structure. The outer layers have a high alumina content while the central layer contains mainly stabilized zirconia. These laminae are subjected to residual stresses due to their different thermal expansion coefficients. These stresses depend on the configuration of the system as well as on the amount of the zirconia in the two layers. If the residual stresses exceed the strength of the inner layer, periodic parallel cracks are produced. Such cracks of course adversely influence the structural performance of the composite and should be avoided. A model for this problem is presented. Vickers indentations were also placed into the tensile layer with the intent to explore the crack propagation in such system. Cracks were split after they reached the compressive layer. The effects of the layer thickness on the depth of the cracks beneath the interface were systematically explored.

Layered ceramics are being developed as a new class of composite materials with enhanced strength, toughness and hardness, due to residual stresses built up during their production. In particular, by this method it is possible to improve the strength as well as the toughness without reducing hardness. This fact has been documented in this work which reports the results obtained on material consisting of two outers layers of alumina alternated by an inner layer of alumina containing different amounts of CeO2-partially stabilized zirconia.

Some test cycles have been carried out in continuous cutting conditions, employing cutting parameters (feed, depth of cut and cutting speed) chosen following experimental planes and suitable test fields. The wear tests have been carried out on AISI 1040 steel with cutting speeds from 5m/sec to 11m/sec. The silicon nitride, sintered carbide, cubic boron nitride and alumina reinforced with SiC whiskers inserts, have shown, at each assigned cutting parameter, poor wear resistance when cutting steel. Alumina and alumina in submicron grain, which has been toughened by ZrO2 phase transformation, and the oxide-based alumina, have been the better wear resistance. The mixed based alumina has shown a wear resistance, a little lower than the previous materials. The low chemical stability seems to be the reason for the poor performances of the silicon nitride and the silicon carbide whiskers reinforced alumina inserts. The high wear rate of the sintered carbide and the cubic boron nitride is essentially due to the pull out of the ceramic particles. From the other hand, the chemical stability, together with their good mechanical properties can explain the appreciable results obtained with the other alumina based materials.

Preparation de composites Al 2 O 3 −ZrO 2 (15% vol.)-trichites de SiC (10% vol.) par une methode de floculation-defloculation. La presence de zircone monoclinique et de trichite entraine une bonne tenacite, mais une faible resistance a la flexion