Mechanical behaviour of a low-clay translucent whiteware

A novel low-clay translucent whiteware body, using mostly non-plastic prefired materials and only a small amount of clay, was fabricated by slip casting and the effect of slip's solid content and sintering temperature on the mechanical behaviour was investigated. The degree of densification in the sintered specimens was determined by measuring the bulk density. The mechanical behaviour was determined by measuring the flexural strength and fracture toughness. Young's modulus and hardness were also measured. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were carried out to analyse the microstructure.The flexural strength and fracture toughness increase with both increasing the slip's solid content and the sintering temperature up to a certain level, but further increase in solid content and sintering temperature had an adverse effect on the properties. The maximum flexural strength (∼135 MPa) and fracture toughness (∼1.85 MPa m^1/2) values were attained with specimens produced from a slip having 45 vol.% solid content at a sintering temperature of 1350 °C. It was found that the amount and distribution of closed pores, their size and possible link with each other control the flexural strength and fracture toughness of the low-clay translucent whiteware.     

Development of anorthite based white porcelain stoneware tile compositions

The scope of the present study is to develop alternative white porcelain stoneware tile compositions without using zircon (ZrSiO₄) which have shown better whiteness values than standard white porcelain stoneware tile composition containing zircon. These new compositions are designed to develop anorthite crystals in the microstructure. Technological properties of compositions such as water absorption (%), firing shrinkage (%) and colour (L^⁎, a^⁎, b^⁎) were measured and compared with standard white porcelain stoneware tile. Scanning electron microscopy (SEM), X-ray diffraction (XRD) analyses were also carried out. One of the new anorthite-based compositions was manufactured as white porcelain stoneware tile substitute of standard white porcelain stoneware containing zircon.     

Development of anorthite based white porcelain glaze without ZrSiO4 content

The aim of this study was to develop new compositions of white glazes without the addition of ZrSiO₄designed for sanitary products obtained in a 12-h firing cycles at a maximum temperature of 1230 °C.Alternative glazes with a good opacity and a high degree of whiteness were obtained, composed primarily of raw materials available on the domestic market in Poland. The opaque effect was achieved due to crystallisation of anorthite, which was identified as a major crystalline phase in the system. The glazes were characterised by a high whiteness value L*, greater than 90 in the CIELAB colour space, and a gloss, measured with a 60° light incident angle on the glaze surface, above 50%.The microstructure and structure of the glazes were measured with the use of a Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD). The colour and gloss of glazes were measured with the use of a spectrophotometer and a gloss metre at a 60° angle of incidence. The topography of glazes surfaces, as well as the roughness level (Ra), were measured with the use of a confocal microscope.     

Preparation of anorthite ceramics using SPS

A mixture of kaolin (92 wt.% of kaolinite) and laboratory-grade CaCO₃ was used for anorthite preparation using the spark plasma sintering (SPS) technique. The powder was heated up to the maximum temperature (850 °C–1100 °C with a step of 50 °C, heating rate 50 °C/min) using the SPS device. The as-prepared samples were compared with a reference sample produced by dry pressing and conventional firing. Rietveld refinement performed on the X-ray diffraction data revealed that before anorthite formation, gehlenite and Ca-feldspar appeared, which gradually transformed into anorthite with increasing temperature. The sample prepared by SPS at 1100 °C contained 90 wt.% of anorthite, while the anorthite content in the reference sample reached only 47 wt.%. The porosity of the samples prepared by SPS reached significantly lower values compared to that of the reference sample. Therefore, SPS can be considered as a promising technique in the preparation of anorthite ceramics at lower temperatures.     

Fabrication and properties of cordierite / anorthite composites

The designed cordierite/anorthite batch compositions were studied to gain the favorable properties of both materials where, cordierite has low thermal expansion coffecient and high strength than anorthite.Low cost starting materials such as sugar beat filter cake and talc carbonate were used in the present study. Examination of the effect of cordierite addition (in the range of 10-25mass-%) on the physical, mechanical, electrical and thermal expansion coefficient properties as well as the phase composition and microstructure for the fabricated cordierite/anorthite composites were carried out. The results reveal that the increase in the cordierite content up to 20 mass-%, improves the sinterability and electrical properties. In addition, it increases the bending strength, hardness and decreases the thermal expansion coffecient. However, further increase in the cordierite content up to 25 mass% has negative influence on the physical, electrical and mechanical properties of the cordierite/anorthite composites.     

钙长石结合莫来石轻质耐火砖的研究

研究了以蓝晶石作主要原料,以白水泥作结合剂生产钙长石结合莫来石轻质耐火砖的可行性。实验表明：蓝晶石从１２００℃开始莫来石化,到１３００℃基本完成,并与白水泥发生反应生成钙长石。钙长石结合莫来石轻质耐火砖体积密度为０．５ｇ·ｃｍ－３时的耐压强度超过３．５ＭＰａ,最高使用温度超过１４００℃,而３５０℃时的热导率只有０．１５Ｗ·（ｍ·Ｋ）－１。     

Formation of translucent nanostructured zirconia ceramics

In this work the mechanisms that affect the optical transparency of nanostructured translucent ZrO₂ ceramics are studied. The translucent ceramic samples were obtained from a low agglomeration nanosized powder at low pressure and low temperature sintering. Even low pressures cause structural changes and defect creation in the nanocrystals. Annealing was used to study the grain formation, structure and impact of defects. Significant changes in translucency were observed with increase in pore size. In order to further understand the defect creation, the obtained ceramics were doped with Er³⁺ ions and studied optically. Photoluminescence studies revealed a change in the ratio of green to red parts of the spectrum as well as luminescence quenching when samples were pressed into pellets. Additionally, grain and pore size dependence on annealing temperatures was studied using X-ray diffraction, scanning electron microscopy and transmission electron microscopy.     

Optical and photostimulated luminescence properties of Eu:BaFBr translucent ceramics synthesized by SPS

Eu:BaFBr translucent ceramics were synthesized by the spark plasma sintering method, and then the crystal structure, optical and photostimulated luminescence (PSL) properties were investigated. The synthesized 0.05–0.5% Eu:BaFBr are translucent, and the optical transmittance is 30–50%. The photoluminescence and PSL spectra consist of an emission band peaking around 390 nm due to the presence of Eu²⁺ ion. The photoluminescence quantum yield and the sensitivity of PSL to X-rays are the highest when the doping concentration is 0.5%, and they are higher than those of the commercial Eu:BaFBr imaging plate (IP). In addition, the spatial resolution of an X-ray image obtained by using the 0.5% Eu:BaFBr translucent ceramic as an imaging plate is higher than the one obtained by using the commercial IP.     

Pressure filtration assisted gel casting in translucent alumina ceramics fabrication

High density and homogeneous green body is important for fabricating transparent ceramics. Inspired by the improved samples’ homogeneity in slip casting, we introduced low pressure filtration to gel casting to further increase the relative density and homogeneity of the green body and to shorten the drying time. The effect of pressure filtration on drying characteristics, bulk density and porosity of the pre-sintered bodies, and the microstructure and optical transmittance of the resultant ceramics were intensively investigated. The results showed that pressure filtration can reduce the drying time by 27.3%, improve the density of the pre-sintered bodies and reduce the residual pores of the sintered ceramics. The in-line transmittance of the translucent alumina prepared by the pressure filtration assisted gel casting was 32.7% at 600?nm with a thickness of 1?mm, which is about 6% higher than that without pressure filtration. In principle, this process can be applied to fabricate any other high-performance ceramic.     

Microstructure and mechanical properties of diopside and anorthite glazes with high abrasion resistance

The paper presents the results of research on the influence of the chemical composition of frits on the microstructure and mechanical properties of ceramic glazes. Glaze sets are designed based on frits of different chemical composition and increasing B₂O₃ content. Thermal DSC analysis showed a high tendency to crystallize the designed glazes, and in the obtained glazes the main crystalline phases were diopside or anorthite, which was also confirmed by XRD analysis and SEM microscopic observations. In glazes not containing B₂O₃ and at a SiO₂/Al₂O₃ molar ratio in the 5.3–5.6 range, mainly diopside crystallized, while a decrease in the SiO₂/Al₂O₃ molar ratio to a value below 4.9 and an increase in B₂O₃ content contributed to an increase in the anorthite crystal phase content. The obtained glazes were characterized by a surface roughness of Ra in the range of 0.2–1.1 μm and a high abrasion resistance measured with a mass loss of less than 50 mg after 6000 abrasion cycles in accordance with the EN ISO 10545-7 standard. Such high abrasion resistance was achieved thanks to the high hardness of the glazes in the range of 6.4–8.0 GPa, which was confirmed by the Vickers hardness measurement.     

Scintillation and dosimeter properties of CaF2 translucent ceramic produced by SPS

We have developed CaF₂ translucent ceramics by spark plasma sintering (SPS) and investigated the scintillation and dosimeter properties, in comparison with a CaF₂ single crystal. Under X-ray irradiation, light emission was observed at 270 and 300 nm, due to self-trapped exciton (STE). The scintillation light yield of CaF₂ translucent ceramic was measured to be about 6000 photons/MeV under ¹³⁷Cs irradiation, and this value was smaller than that of the single crystal by a factor of approximately 2. The afterglow level, after X-ray irradiation, of the ceramic sample was lower than that of the single crystal. Thermally stimulated luminescence (TSL) glow peaks were observed at 100 and 150 °C in both ceramic and single crystal samples, however the TSL intensity was much stronger than that of the single crystal sample.     

Effects of boron addition and intensive grinding on synthesis of anorthite ceramics

Anorthite ceramics were synthesized starting from mixtures prepared by using mechanochemical methods with boron oxide addition. The raw materials used in this study were Sivas Kaolin, calcined alumina/Al(OH)₃ and calcite. Statistical experimental design techniques (SED) were used in order to determine and analyze the more important process variables for synthesizing anorthite ceramics. Phase characterizations of synthesized powders were performed by XRD using Cu Kα radiation. Microstructural characterization was performed by SEM. The results of screening experimental design clarified that the temperature was the most important process variable. Second most important process variable was grinding speed of starting mixture which was followed by additive amount and additive type. The effect of both additive use and grinding on anorthite synthesis helped decrease the synthesis temperature down to 900 °C.     

Seed assisted in-situ synthesis of porous anorthite/mullite whisker ceramics by foam-freeze casting

Porous anorthite/mullite whisker ceramics with both high strength and low thermal conductivity have been successfully prepared by combining seed-assisted in situ synthesis and foam-freeze casting techniques. The addition of mullite seed was conducive to a reduction in the sintering shrinkage, pore size, and anorthite grain size. This increased the high aspect ratio of mullite whiskers, which enhanced the strength and diminished the thermal conductivity. Mullite whiskers overlapped to form a stable three-dimensional network structure similar to the bird's nest, which was also beneficial to heighten the mechanical properties of the prepared porous ceramics. Through this method, the prepared materials had a high apparent porosity of 87.7–90.2%, a low bulk density of 0.29–0.36 g/cm³, a high compressive strength of 0.65–3.31 MPa, and low thermal conductivity of 0.067–0.112 W/m·K. The results indicated that the method described here can fabricate porous ceramics with excellent properties for further thermal insulating applications.     

Recycling of lime mud and fly ash for fabrication of anorthite ceramic at low sintering temperature

Lime mud is a kind of waste generated during causticization reaction of an alkali recycling process in paper industry. Lime mud and fly ash were reused as raw materials to fabricate anorthite ceramics through solid state reactions. Both sintering temperature and lime mud content influenced the crystalline phases in the prepared ceramics. Anorthite was the major phase in all samples (samples L36, L40, L50 and L60) and it was prominent in sample L36 (containing 36 wt% lime mud). The results also showed that anorthite ceramic can be synthesized at low sintering temperature (1100 °C). Gehlenite and wollastonite were formed in the samples possessing higher calcium (above 40 wt% lime mud) or at lower sintering temperatures. Bulk density, water absorption and compressive strength were measured. These ceramics were of light weight and had high water absorption. Recycling of lime mud and fly ash as raw materials of anorthite ceramic is a feasible approach to solve the solid wastes.     

Production of anorthite refractory insulating firebrick from mixtures of clay and recycled paper waste with sawdust addition

Production of porous anorthite refractory insulating firebricks from mixtures of two different clays (K244 clay and fireclay), recycled paper processing waste and sawdust addition are investigated. Suitability of alkali-containing-clay, low-alkali fireclay, pore-making paper waste and sawdust in the products was evaluated. Prepared slurry mixtures were shaped, dried and fired. Highly porous anorthite ceramics from the mixtures with up to 30% sawdust addition were successfully produced. Physical properties such as bulk density, apparent porosity, percent linear change were investigated as well as the mechanical strengths and thermal conductivity values of the samples. Thermal conductivities of the samples produced from fireclay and recycled paper waste decreased from 0.25 W/mK (1.12 g/cm³) to 0.13 W/mK (0.64 g/cm³) with decreasing density. Samples were stable at high temperatures up to 1100 °C, and their cold strength was sufficiently high. The porous anorthite ceramics produced in this study can be used for insulation in high temperature applications.     

Effect of aging process on some properties of conventional and multilayered translucent zirconia for monolithic restorations

The purpose of this study was to evaluate the surface characteristics and optical and mechanical properties of materials through hydrothermal aging using different types of translucent monolithic zirconia.Three conventional materials (LT, KT, and ET) and three multilayered materials (LM, KM, and EM) of translucent monolithic zirconia were investigated. 45 bar-shaped specimens in each group were fabricated for the measurement of surface characteristics and mechanical properties and were randomly divided into 3 subgroups. 10 plate-shaped specimens in each group were fabricated for the measurement of optical properties. All specimens were autoclaved for 0, 5, and 10 h, respectively. The various properties of translucent monolithic zirconia, such as phase distribution, surface roughness, surface texture, elemental analysis, total transmittance (Tt), contrast ratio (CR), three point flexural strength (TFS), nanoindentation hardness (NH), and Young's modulus (YM), were measured through different tests. Statistical analyses were performed with one-way ANOVA, Tukey HSD post hoc test, independent sample t-test, paired sample t-test, and two-way ANOVA (α = 0.05).After aging, the monoclinic phase of all groups increased relative to the tetragonal phase. All groups exhibited an increase in the surface roughness and oxygen levels, but exhibited a decrease in the zirconium and yttrium levels (P < .05). All groups had increased microcracks and grain push-out. Tt increased and CR decreased in the LT, KT, and ET groups. However, Tt decreased and CR increased in the LM, KM, and EM groups (P < .05). The TFS, NH, and YM showed a decreasing tendency, but there were no significant difference in several materials (P > .05).Alterations in the surface characteristics were found on the surfaces of translucent monolithic zirconia after aging. The aging process caused conventional materials to become more translucent, but multilayered materials were more opaque. The various properties of translucent monolithic zirconia were affected by the materials fabricated with different types after aging.     

Novel fabrication of pressure-less sintering of translucent powder injection molded (PIM) alumina blocks

A new method of fabricating translucent alumina brackets using powder injection molding (PIM) is reported. Alumina powder was mixed with MgO, La₂O₃, and Y₂O₃ to control grain size and porosity. The powders were mixed with a binder consisting of a mixture of paraffin wax and polyethylene in a 1:1 ratio to make feedstock for injection molding. The total amount of binder was limited to 14 wt% to minimize shrinkage and cracking after sintering. After injection molding, debinding was performed using the wicking method and samples were sintered in a vacuum at 1700 °C to achieve high density. Ultimately, translucent corundum was fabricated. The sintering additives resulted in a decrease in porosity and an improvement in translucency by promoting grain growth during pressure-less sintering. After sintering, Vickers hardness, bending strength, density, and transmittance of the fabricated parts were measured to show that those values were comparable to those of the commercially available dental brackets. Therefore, the translucent alumina block was successfully fabricated using PIM method to be potentially used as a dental bracket.     

Yb3+ rare earth structural probe and correlation between morphology and spectroscopic properties in La2Mo2O9. Comparative analysis with mixed cubic La2MoWO9 translucent ceramics

We present and discuss the structural and spectroscopic properties of micro-crystalline Yb³⁺-doped La₂Mo₂O₉ molybdates (0–25?mol% of Yb³⁺ ions) synthesized by the high-temperature solid-state reaction in which Yb³⁺ optical rare earth ion play the role of a structural probe. The main objective is to apply these materials to transparent optical ceramics. The XRD and SEM analysis reveal a strong structural dependence of the crystal structure on Yb³⁺ ion concentration. The high-resolution of the ²F_7/2???²F_5/2 0-phonon line of Yb³⁺ ions in absorption and emission spectroscopy at low temperature allows us to evidence three types of polyhedral around Yb³⁺ ions. Clear differences for cubic Yb³⁺-doped both La₂Mo₂O₉ and mixed La₂MoWO₉ are observed as a result of the introduction of tungsten ions leading to greater disorder in the lattice. First translucent cubic ceramics have been successfully fabricated and the comparison turns out in favor of Yb³⁺-doped mixed La₂MoWO₉.