A novel method for preparation of dense silicon-based ceramics

The dense ceramic part was prepared firstly using silazane with filler. The composition, structure and ceramic yield of silazane were characterized by elemental analysis, nuclear magnetic resonance (NMR), IR and thermogravimetric analysis (TGA). The ceramic yield was 63 wt% upon pyrolysis at 1000 °C under N₂ atmosphere. The fabrication of ceramic part involved cross-linking of the silazane with metallic fillers (Ti particles) followed by a polymer-to-ceramic transformation step. Near net shape manufacturing of polymer derived ceramics could be achieved. The strength of ceramic parts could achieve 450 ± 15 MPa and scanning electron microscopy (SEM) observation showed that there was very low porosity on the fracture surface of pyrolysed body.     

Effect of sintering temperature on the microstructure and transparency of Nd,Y:CaF2 ceramics

1 at% Nd, 3 at% Y doped CaF₂ transparent ceramics were obtained by hot pressing at the sintering temperature varing from 500 to 800 °C under vacuum environment with co-precipitated CaF₂ nanopowders. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed that the obtained nanoparticles were single fluorite phase with grain size around 26 nm. Scanning electron microscopy (SEM) observations of the Nd, Y: CaF₂ ceramics indicated that the mean grain size of the ceramic sintered at 800 °C was about 748 nm. The influence of the temperature on the grain size, microstructure and optical transmittance was investigated. For the ceramic sintered at 800 °C, the transmittance was 85.49% at the wavelength of 1200 nm. The room temperature emission spectra of Nd: CaF₂ and Nd, Y: CaF₂ ceramics were measured and discussed.     

Characterization of transparent glaze for single-crystalline anorthite porcelain

The objective of this work was to design a transparent glaze for matching single-crystalline anorthite porcelain. Excessive amounts of quartz were used in glaze to improve surface hardness. Technological properties including hardness and thermal shock resistance were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were also carried out to analyze the microstructure. The phases found in glaze were aluminosilicate glass, quartz and cristobalite crystals. The Vickers hardness of the transparent glaze was about 2.48 GPa, which was much higher than that of commercial soft glaze and was close to hard porcelain glaze due to forming dispersed crystal particles (quartz and cristobalite) in the glass matrix. Moreover, the thermal expansion coefficient of the glaze was slightly lower than that of porcelain body which was easy to produce compressive stress in glaze surface to increase the strength of porcelain. And no cracks were observed on glaze surface after heat exchange three times from 220 °C to 25 °C, presenting excellent thermal shock resistance.     

Porous cordierite-based ceramics processed by starch consolidation casting – Microstructure and high-temperature mechanical behavior

Porous cordierite-based ceramics with different microstructural features and mechanical behavior were formed by starch consolidation casting (SCC) using native potato and corn starches and sintered at 1275, 1300 and 1330 °C. The composition and microstructure of the ceramic materials were investigated via quantitative phase analysis using X-ray diffraction (with Rietveld refinement), the Archimedes method, mercury porosimetry, scanning electron microscopy and optical microscopy with stereology-based image analysis. The mechanical behavior of samples was evaluated by diametral compression tests at room temperature, 1000 and 1100 °C. The type of starch used and the sintering temperatures were the main factors determining the characteristics of the developed porous microstructures. Materials prepared with corn starch achieved the lowest porosity and the lowest values of mean chord length, mean pore distance and pore throat size. Because of these features, these materials thus presented, in general, higher values of apparent Young's modulus, elastic limit and mechanical strength than those prepared with potato starch. Despite the presence of a silicate glassy phase, both porous materials, mainly those prepared with corn starch, still enhanced the basic mechanical properties at high temperature, in particular, the mechanical strength and the apparent Young's modulus due to the special combination of the porous microstructure features.     

Post-treated incinerator bottom ash as alternative raw material for ceramic manufacturing

New ceramics based on 60 wt% of alternative raw material derived from post-treated municipal solid waste incinerator bottom ashes and 40 wt% of refractory clay were studied. The chemical analysis of the compositions was evaluated by ICP. The thermal and densification behavior of the ceramic batches were evaluated by DTA-TG and dilatometry techniques, respectively. After that, the degree of sintering at different temperatures and soaking times was evaluated in detail, measuring open and closed porosities, linear shrinkage and water absorption. The crystallinity at different temperatures (during heating and after cooling) and microstructure of the obtained samples were evaluated by high-temperature X-ray diffraction (HTXRD) and scanning electron microscopy (SEM), respectively. For these new ceramics, the experimental results highlighted sintering range between 1190–1240 °C. In addition, the specimens demonstrated low water absorption and high crystallinity (with anorthite as main crystalline phase), leading to mechanical characteristics comparable to those of commercial ceramic products (bending strength > 40 MPa).     

Sliding wear of CaZrO3-MgO composites against ZrO2 and steel

The wear behaviour of a fine grained and dense CaZrO₃-MgO composite is presented. Un-lubricated Pin-on-disc tests at room temperature have been performed using 10 N as normal force and 0.10–0.15 ms^-1 as sliding rate and ZrO₂ and steel counterparts. The coefficient of friction versus the sliding distance and the specific wear, together with a complete microstructural analysis of the worn surfaces by field emission scanning electron microscopy is reported. The composite presents a wear resistance similar to other ceramics under ceramic/ceramic sliding contact and improved wear resistance in contact with steel.Initial wear is dominated by abrasion independently of the chemical nature of the counterpart. The second stage wear depends on the characteristics of the third body formed. Zirconia leads to a brittle particulate third body with little protective capability. Steel forms a strongly bonded and plastic cermet third body that protects the material limiting the level of further wear.     

Preparation and characterization of glazes from combinations of different industrial wastes

The work reported here involves the preparation and characterization of ceramic glazes made from combinations of different industrial wastes. The wastes were float glass, granite and lime shale (a raw material waste from the oil shale industry in São Mateus do Sul, state of Paraná, Brazil), which were used to replace natural raw materials in a proportion of up to 50% in weight. The compositions were formulated using the Seger method and prepared by conventional ceramic processing. The stabilized suspensions were applied in commercial wall tile and porcelain stoneware tile, which were sintered at temperatures of 1080 °C and 1150 °C, respectively, using two different heating cycle. Three compositions were developed, two of which yielded opaque glazes and one a transparent glaze. Linear thermal expansion coefficients (α) of 80.10^?7 °C^?1 to 100.10^?7 °C^?1, and glaze softening temperatures of 600–700 °C were characterized by dilatometric analysis. The glaze compositions showed chemical resistance against acid and alkaline attack after 96 h, showing a mass loss of less than 0.1% in weight. The surface hardness of the glazes determined by the Mohs scale, Vickers microhardness and abrasion resistance (PEI indices) were between 6–7, 3–3.7 GPa and 3–4, respectively. These properties are compatible with those of commercial glazes for wall tiles and porcelain stoneware ceramics.     

High wear resistance white ceramic glaze containing needle like zircon single crystals by the addition of sepiolite n-ZrO2

Sepiolite with homogeneous zirconia nanoparticles distribution has been added to a transparent ceramic glaze to study opacification, mechanical and wear resistance properties. It has been observed that monodispersed zircon single crystals with needle-like shape have been formed in the ceramic glaze. These in situ zircon single crystals give white color and increase opacification (L = 94 vs L = 90), mechanical properties (hardness and toughness) and wear resistance by a factor of 4 compared to the commercial crystalline glaze containing a similar fraction of micrometer commercial zircon.     

Metallurgy dusts as a pigment for glazes and engobes

This study is focused on using the dust from metallurgy as a pigment. The agglomerating dust is formed during metallurgical processes. This waste product is interesting for recycling process. The main mineralogical phase of dust is hematite α-Fe₂O₃. Both synthetic and natural iron oxides are commonly used as pigments in ceramic industry. In this experiment the metallurgy dusts were used as a pigment for preparation of glazes and engobes. Agglomerating dusts were used both precalcined thermally at 700 °C and 900 °C and in an original state. The prepared glazes were composed of a transparent glaze base with 10 wt% agglomerating dusts as pigment. The glazes calcined at 1060 °C were finally yellow colored and glazes calcined at 900 °C were brown colored. Engobes contained a ceramic clay base with 1, 5, 10 and 50 wt% of dust as pigment. Engobes calcined at 900 °C were red and grey colored. The pigments were characterized by X-ray diffraction (XRD), chemical (XRFS) analysis, granulometry (PSD), thermogravimetric (TG) and differential thermal (DTA) analysis, scanning electron microscopy (SEM) and CIELab values.     

Highly resistive SiC ceramics sintered with Al2O3-AlN-Y2O3 additions

A polycrystalline SiC ceramic prepared by pressureless sintering of α-SiC powders with 3 vol% Al₂O₃-AlN-Y₂O₃ additives in an argon atmosphere exhibited a high electrical resistivity of ~10¹³ Ω cm at room temperature. X-ray diffraction revealed that the SiC ceramics consisted mainly of 6H- and 4H-SiC polytypes. Scanning electron microscopy and high resolution transmission electron microscopy investigations showed that the SiC specimen contained micron-sized grains surrounded by an amorphous Al-Y-Si-O-C-N film with a thickness of ~4.85 nm. The thick boundary film between the grains contributed to the high resistivity of the SiC ceramic.     

Degradation evaluation of Si3N4 ceramic surface layer in contact with molten Al using microcantilever beam specimens

Although Si₃N₄ ceramics are often utilized as structural components in the Al casting industry due to their excellent properties, they occasionally suffer breakage after long-term use. In this study, the bending strength, fracture toughness, and Young’s modulus in the vicinity of the Si₃N₄ ceramic surfaces after contact with molten Al were evaluated using microcantilever beam specimens, which were fabricated using a focused ion beam technique. Fracture testing of the specimens was carried out by nanoindentation. The bending strength of the ceramic surface before and after contact with molten Al was 5.89 ± 1.33 and 3.03 ± 0.28 GPa, respectively. The fracture toughness of the corroded layer in Si₃N₄ ceramics also decreased compared to that of the polished surface. Using fractography by observation with scanning electron microscopy, it was shown that changes in the grain boundary glassy phase resulted in the degradation of strength and fracture toughness.     

Synthesis of SiC–TiO2 hybrid aerogel via supercritical drying combined PDCs route

The SiC-TiO₂ hybrid aerogels were obtained from polycarbosilane (PCS) and tetrabutyltitanate (TBT) as precursors using supercritical drying and polymer derived ceramics route. The polymer to ceramic conversion and the crystallization behavior were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM), suggesting the preceramic aerogels converted to the SiC-TiO₂ ceramic aerogels through pyrolysis process at different temperatures. At 1200 °C, the ceramic aerogels were homogeneous with well-distributed element components, composed of rutile TiO₂ and the β-SiC crystalline phases. The results show that the SiC-TiO₂ ceramic aerogels with netwoks structure have 23.36 nm average pore size, high surface area (58 m²/g) and pore volume (0.22 cm³/g).     

Low temperature firing of BiSbO4 microwave dielectric ceramic with B2O3–CuO addition

The influence of B₂O₃–CuO addition on the sintering behavior, phase composition, microstructure and microwave dielectric properties of BiSbO₄ ceramic have been investigated. The BiSbO₄ ceramics can be well densified to approach above 95% theoretical density in the sintering temperature range from 840 to 960 °C as the addition amount of B₂O₃–CuO increases from 0.6 to 1.2 wt.%. Sintered ceramic samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microwave permittivity ?_r saturated at 19–20 and Qf values varied between 33,000 and 46,000 GHz while temperature coefficient of resonant frequency shifting between ?70 and ?60 ppm/°C at sintering temperature around 930 °C. Lowering sintering temperature of BiSbO₄ ceramics makes it possible for application in low temperature co-fired ceramic technology.     

High temperature investigation of SiO2-Al2O3-ZnO-Na2O glass for ceramic-glaze: in‐situ/ex-situ synchrotron diffraction and conventional approaches

The temperature dependent behaviour of a complex aluminosilicate glass (SiO₂-Al₂O₃-ZnO-Na₂O system), which is a reference for ceramic glaze technology, has been determined, by combining techniques that cover a scale ranging from atomistic to macroscopic. The system shows a linear thermal expansion up to about 600 °C. The glass transition temperature is at 620 °C, as observed from Differential Scanning Calorimetry. Ex situ synchrotron diffraction experiments found a further transformation consisting of albite crystallization above 810 °C. This reaction is very slow and induces permanent structural modifications in the material at both intermediate and short ranges, as shown by in situ synchrotron diffraction experiments. These observations explain why ceramic glaze technology still faces challenges for large scale manufacturing and show the critical thermal range where interventions should be focussed. Eventually, melting takes place at 1190 °C, from hot stage microscopy.     

Fabrication and optical characterizations of Yb,Er codoped CaF2 transparent ceramic

Nanoparticles of Yb, Er codoped calcium fluoride were obtained by a co-precipitation method. Scanning electron microscope (SEM) and X-ray powder diffraction (XRD) analysis showed that the obtained nanoparticles were single fluorite phase with grains size around 30–50 nm. Yb, Er:CaF₂ transparent ceramics were fabricated by hot pressing (HP) the nanoparticles at a temperature of 800 °C in a vacuum environment. For a 2 mm thickness ceramic sample, the transmittance at 1200 nm reached about 83%. Microstructures were characterized using SEM analysis, and the average grain size was about 700 nm. Grain boundaries of the ceramic sample were clean and no impurities were detected. The absorption, upconversion and infrared emission spectra of transparent ceramic sample under 978 nm excitation were measured and discussed.     

Development of spinel opaque glazes for ceramic tiles

The feasibility of developing fast-firing opaque wall tile glazes obtained from zircon-free frits was studied. The structural and morphological characteristics of the glazes were determined by differential scanning calorimetry, an optical dilatometer, X-ray diffraction and scanning electron microscopy. The studied glaze was characterized by a high whiteness value L* greater than 94, very low values of a* and b* which is about ?0.65 and 0.01, respectively, and a high gloss value above 98%. The opaque effect is due to the presence of spinel crystals with a size range of 0.2–1.0 μm, which is formed by devitrification during fast-firing. The Vickers micro-hardness of the studied glaze is higher than the one of the commercial zircon based glass-ceramic glazes. This type of frit can be an alternative one for fabricating opaque ceramic glazes.     

Roman glazed inkwells from the “Nuovo Mercato di Testaccio” (Rome,Italy): Production technology

This study is focused on Roman lead-glazed inkwells from the archaeological site of the “Nuovo Mercato di Testaccio” (Rome, Italy) dated in the half 2nd century AD. Optical microscopy (OM), X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and electron microprobe analysis (EMPA) have been used. Petrographic analysis of the body indicated the occurrence of only one fabric. The reaction zone at the contact glaze/body is marked by the enucleating of euhedral Pb-bearing alkali feldspar from a felsic melt enriched in Pb as revealed by EMP analysis. The mineralogical assemblages of the body and glaze, the microstructure and the chemical composition suggest that the inkwells were fired in the range 950–1100 °C, under oxidizing conditions.     

Development of gold-bronze metallic glazes in a clay-based system for stoneware bodies

In this study, a triaxial glaze system consisting of red clay, kaoline, quartz, MnO, CuO and CoO is systematically developed to produce gold-bronze raw metallic glazes for stoneware bodies. At first, all of the glazed samples in the developed system were fired in an electrically-heated kiln at 1160 °C. Then, the selected successful gold-bronze metallic glazes were applied onto 3-D forms of stoneware bodies and fired at the same conditions. Microstructural characterizations of the glazes are done with scanning electron microscopy (SEM) and energy dispersive x-ray analyses (EDS). This study revealed that triaxial blending of the ceramic raw materials is a beneficial method for glaze production and gold-bronze surfaces are obtained in glazes G 9, G 26, and G 34. It is observed that chemical composition of the glazes directly influence the color and the amount of CuO is more significative than MnO for achieving gold-bronze effect.     

The influence of particle size distribution on the surface appearance of glazed tiles

Matte glaze was milled in for different times (15–50 min) and the glazes obtained were applied over ceramic bodies which were then fired using an industrial cycle and the final surfaces were analyzed using a glossmeter. The same glazes were also uniaxially pressed, forming cylindrical samples; the specimens were placed on engobe surfaces and fired at 1100 °C in a laboratory oven. The contact angles between the melted specimens and the ceramic surfaces were measured to determine their wettability. The results showed a correlation between the glaze particle size distribution and the surface aspect of the final product.     

Ba0.6Sr0.4TiO3–MgO ceramics from ceramic powders prepared by improved aqueous gelcasting-assisted solid-state method

Based on aqueous gelcasting-assisted solid-state method (AGASSM), improved aqueous gelcasting-assisted solid-state method (IAGASSM) was proposed to prepare the 45 wt% Ba_0.6Sr_0.4TiO₃–55 wt% MgO (BSTM) ceramic powders. It is found that the BSTM ceramic powders prepared by IAGASSM are the most uniform with the smallest particles (D_av = 0.83 μm) than those prepared by solid-state method (SSM) and AGASSM. The phase compositions of the BSTM ceramic powders and ceramics from the prepared ceramic powders are the same whatever ceramic powder preparation method is adopted. Compared with SSM and AGASSM, the BSTM green samples and ceramics from ceramic powders prepared by IAGASSM are the most uniform. Furthermore, it is found that adopting IAGASSM to prepare ceramic powders could not only improve the dielectric properties of the BSTM ceramics considerably, but also decrease their sintering temperature.