Year 2011, Volume 31

Abstract

Alumina as a basic raw material for abrasives, cements, ceramics, chemicals, metals, refractories, etc. has no parallel. With its fairly extensive occurrence in nature coupled with its numerous useful physical, mechanical, thermal and electrical properties, it has turned out to be the most extensively studied and widely used ceramic raw material that refuses to diminish its value even in the age of composites and nano-structured materials. This article is an endeavour to capture in a concise manner the story of this wonder material spanning over three centuries.

Abstract

The introduction of metallic powders in traditional porcelain stoneware bodies, makes the well known ceramic system a new complex composite material which thermal behaviour during fast firing processes and final mechanical properties, should be taken under control. Innovative porcelain stoneware tiles with a surface layer containing stainless steel particles, are currently produced by the Double Charge Technology and considering this layer as a composite material, it appear evident the importance of mechanical investigations such as Young modulus, fracture toughness and flexural strength. In particular, the study of the sintering behaviour has been pointed out in order to clarify the role of the metal-ceramic interface and to investigate, with a contactless technology, effects of the oxidizing atmosphere of ceramic roller kilns on metal particles. The use of the Vertical Dilatometer MISURA® ODHT (Figure 1) enables a careful simulation of industrial firing cycles and represents therefore the ideal equipment for advanced experimental high temperature analysis.

Abstract

The susceptibility to staining of polished porcelain tile has been investigated by various authors for over a decade. However, the literature offers little information about the characteristics the finished product should present in terms of final porosity in order to prevent staining. This paper discusses the results of a comparative analysis of the final porosity of two types of commercial unglazed polished products showing dissimilar staining behaviors. The approach to this theme differs from that of other works reported in the literature in that it clearly identifies the main types of pores responsible for staining under the conditions evaluated here.

Abstract

The investigations on the usage of alternative raw materials have been always popular for porcelain tile production. Manufacturers have been interested in this subject for both increasing product quality and decreasing production costs. In the study, the possibility to use granite, as fluxing agent, in a body recipe used for porcelain tile, was determined. Our standard composition (STD GR) was comprised of 30 wt % Na-Feldspar + 40 wt % plastic clay + 30 wt % pegmatite. We have formed three different body recipes, namely “GR 1, GR 2 and GR 3” replacing by different amounts of Na-Feldspar (7.5, 15 and 22.5 wt%) by the complementary amounts of granite (22.5, 15 and 7.5 wt % respectively). The results showed that 15 wt. % as a substitute of albite completely in the standard formulation was satisfactory to carry out further experiments. In the second part, both “STD GR” and “GR 2” formulations were further fired at different peak temperatures under laboratory conditions in order to establish their physicomechanical ranges and optimum firing temperatures. X-Ray diffraction (XRD) was used in order to analyze the phases formed after firing. In addition, SEM was also employed in order to observe the microstructural characteristics of the selected fired bodies. Obtained results revealed that the possible use of granite material as an effective fluxing agent in porcelain tile bodies.

Abstract

The mechano-chemical and microstructural evolution using magnesiumaluminium spinel in a MgO-CaZrO₃ sintered refractory matrix acting as ceramic bonding was investigated. The microstructural study reveals MgAl₂O₄ spinel phase at contact points between MgO and CaZrO₃ particles. In addition, the cold crushing strength of the MgO-CaZrO₃ matrix increases with the addition of 2.5-3.5 wt% MgAl₂O₄ spinel, this being attributed to the strong bond formed between MgO and CaZrO₃ due to the MgAl₂O₄ spinel phase aid. Finally, this refractory matrix exhibits a good thermal stability and excellent chemical resistance against cement raw meal.

Abstract

The main target of this work is to prepare refractory magnesia- and aluminabased ceramics within the MgO-Al₂O₃-ZrO₂-SiO₂ system. These include periclase (MgO) and its composites with MgAl₂O₄-spinel and forsterite (MgSiO₄)-zirconia (ZrO₂) as well as corundum (α-Al₂O₃) and its composite with mullite (Al₆Si₂O1₃)- zirconia (ZrO₂). These were processed from recycled pure and fine magnesium and aluminium hydroxide precipitates as well as raw zircon, ilmenite and rutile raw materials. Up to 5.0% lmenite and rutile as well as Mg(OH)₂ , Al(OH)₃ or MgO were used as doping materials to accelerate sintering rate of the periclase and corundum products. Also 5-20% of calcined alumina and raw zircon were mixed with the magnesium as well as aluminium hydroxides to prepare varieties of periclase-spinel, periclase-forsterite-zirconia as well as corundum-mullitezirconia composites, respectively. The corresponding batches were prepared, semi-dry pressed and fired at two-stages up to 1600 °C. The densification rate was followed by determining linear shrinkage, bulk density and apparent porosity. Phase composition as well as microstructure and microchemistry were investigated by XRD as well as EPMA techniques, respectively. The refractory quality was assessed by determining load-bearing capacity and volume stability up to1600 °C. The results indicate that doping magnesia with 1% rutile accelerates its rate of solid-state sintering by lattice diffusion with a maximum relative density (RD) of 97%. The dense bodies have developed periclase network with a high degree of direct bonding and encloses some fine euhedral spinel [MgO(Al,Fe,Ti)₂O₄] solid-solutions. Similarly, RD of the alumina is improved up to a maximum of only 93%, after doping with 1.0 % MgO. The dense bodies are mainly composed of rounded corundum (α-Al₂O₃) network enclosing some pores. This indicates that such doping material and/or firing temperature (1600 °C) are insufficient for sintering of the corundum bodies. Meanwhile, dense periclasespinel and periclase-forsterite-zirconia as well as corundum-mullite-zirconia composite bodies could be prepared. All of the processed periclase- and alumina- based bodies show high refractory quality, except those of the corundum as indicated from the high temperature corresponding to maximum expansion (To = ≥ 1500 °C) and beginning of subsidence under load (Ta ≥ 1500 °C) and rate of creep at 1500 °C (<0.02 mm/hr) as well as limited permanent linear change (PLC) on re-firing at 1600 °C (<1.0%).

Abstract

We have investigated the influence of coating of the abrasive particles with thermosetting or thermo-plastic resin on the cutting performance or lifetime of the abrasives both by a direct test using a AWJ system and by an indirect test using a sand belt. Our results show that the coated abrasives offer a shorter cutting time, a lower surface roughness of the cutting section, and a longer life time than the conventional abrasives. The impact strength of the coated abrasives has been found to be far higher than that of the conventional abrasives although there is little difference in hardness between the two kinds of abrasives. In addition, SiC abrasives have been found to be superior to Al₂O₃ abrasives in cutting performance.

Abstract

The design of bioceramic scaffolds, i.e. artificial structures employed as temporary templates for cell proliferation, is a crucial issue in bone tissue reconstruction and regeneration. An ideal scaffold should be highly porous and bioactive. Additionally, a resistant and permeable surface is required in order to have manageable samples. The production of scaffolds by means of the widely used replication method can lead to samples with weak and brittle surfaces and poor mechanical properties, therefore alternative preparation procedures are necessary. In this work a new protocol to realize bioceramic scaffolds is presented. The obtained samples have an original structure, characterized by an external resistant surface together with a highly porous internal network. The external surface, which behaves as a load-bearing structure for the entire scaffold, guarantees high permeability and manageability. Here the proposed protocol is briefly discussed, together with an overview on the structure of the realized samples. Finally, some preliminary data regarding the scaffolds in-vitro bioactivity are reported.

Abstract

This study evaluates the effects of adding waste bottle glass or boric acid as fluxing agents on the stain resistance of a porcelain stoneware tile body. Different amounts of waste bottle glass, 5, 10 and 15 wt. %, were replaced with the same amounts of sodium feldspar in body formulation. In addition, 0.1, 0.3 and 0.5 wt. % of boric acid were added to the standard body formulation. These new compositions were sintered at 1210 and 1220 °C with a thermal cycle of 45 min. The densification behaviour of the samples was investigated by determining the water absorption, linear shrinkage and bulk density of the fired samples. The results show that the presence of waste bottle glass or boric acid positively influences the sintering behaviour, increases shrinkage, decreases open porosity and improves the stain resistance with respect to standard bodies.

Abstract

Magnesium oxychloride cement (MOC) polishing bricks developed for fine polishing of porcelain stoneware tiles were produced and characterized with respect to MgO/MgCl₂ molar ratio of 6/1, 7/1, and 8/1. X-Ray diffraction analysis revealed that the main crystalline phase formed in the bricks was 5Mg(OH₎₂ .MgCl₂ .8H₂O. Density, abrasion resistance, compressive strength, and chemical durability in water of the MOC bricks were determined to provide information on polishing behavior. Polishing of the tiles was accomplished both in laboratory scale and in online industrial scale. Polishing performance of the bricks was evaluated in terms of average roughness and gloss of the tile surface and of abrasive brick consumption occurred during polishing. The roughness of the tile surface and abrasive brick consumption decreased but the gloss increased when MgO/MgCl₂ ratio in the MOC brick is increased. Scanning electron microscope examinations revealed that the MOC bricks composed of MgO/MgCl₂ ratio of 7/1 had the best qualifications in terms of polishing performance.

Abstract

The aim of this work is to study the possibility to use crockery ware scrap in floor tile engobe formulations. The scrap powder was added to engobe formulation in substitution of china clay and its influence on slip properties like density and fluidity was studied. Fired properties such as whiteness and thermal expansion were determined. The effect of these engobes on the fired properties of matt glazed floor tiles was also evaluated. Incorporation of 5-10wt. % scrap resulted in significant improvement in fluidity. Coefficient of thermal expansion was found to be increased slightly and no detrimental effect was observed in whiteness as well as in maturity of engobes. Fired glazed tiles do not show any defect in appearance and exhibit good glaze to body fit. Thus, this study demonstrates the possibility to reuse waste materials like crockery ware scrap in engobe formulations which have a well defined role in glazed floor tile manufacturing.

Abstract

This study investigates the migration of SO₄^–2 and Ca⁺² ions in a red-clay ceramic, simulating the process of efflorescence. Ceramic bodies were molded (70x27x9 mm³) by vacuum extrusion formulated with different contents of CaSO₄.2H₂O (0%, 4%, 8%, and 16% in weight) and burnt at different temperatures (800 °C, 850 °C, 900 °C, and 950 °C) for 12 h. Ceramic bodies were characterized in terms of water absorption, apparent porosity and pore size distribution. Efflorescence was evaluated according to the ASTMC67/2003 Standard and by testing the solubilization of SO₄^–2 and Ca⁺² ions after 1 h with the ceramic bodies immersed in hot water as well as after 7, 14 and 28 consecutive days immersion in cold water. In the quantification of efflorescence, a new image analysis methodology was developed by using the graphic software Image Tools 3.0. The results allowed in establishing a relationship between the efflorescence of the investigated ions, physical properties (water absorption and apparent porosity), pore size distribution and solubilization.