Investigation of surface-modified anhydrous borax utilisation in raw glazes

This study aims to determine the feasibility of preparing ceramic glaze using a surface-modified borate, which contributes boron to the composition without the need of a fritting process. In this context, surface modification of anhydrous borax powders (ABP) with magnesium stearate (MgSt) via dry powder coating is investigated. The surface modification of ABP with MgSt is optimised by employing modifier dosage of 0.5, 1, and 2?wt% and coating periods of 30, 60, and 120?min. The resulting powders are comparatively characterised via wettability, solubility, and dispersibility tests. The structural changes in surface-treated ABP are investigated using X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT-IR) analyses. The results indicate that ABP surface could be switched from hydrophilic (17°) to hydrophobic (115°), its water solubility decreased from 40% to 10%, and a coating yield of approximately 74% was achieved with MgSt dosage of 1?wt% at a processing period of 2?h. Furthermore, FT-IR and XPS results indicated that MgSt is mainly coated over the surface of ABP via physical adsorption rather than chemical bonding. The glaze containing surface-treated ABP that was fired at 1050?°C, demonstrated complete melting and surface coverage without defects. Thus, effective dry coating as a single-step approach could be applied to obtain surface-modified ABP, which offers controlled solubility in glaze suspensions with improved dispersibility and excellent glaze coverage of the surfaces.     

The impact of wollastonite and dolomite on chemical durability of matte fast-fired raw glazes

Controlled share of wollastonite and dolomite in the recipe was decisive for achieving raw glazes with a matte surface in a fast-firing process. The surface characteristics were studied for 25 experimental glazes containing 9–39 wt% wollastonite and 0–16 wt% dolomite. The glaze suspensions were applied on raw tiles and fired to 1215 °C in an industrial kiln. The chemical durability of the tiles was measured according to the standard ISO 10545-13. Further, the impact of exposure time on surface degradation was measured for 0.1 and 3 vol% HCl-solutions. The changes in the phase composition were studied with SEM/EDXA and XRD. The surface consisted of wollastonite and diopside, some residual quartz and corundum as well as amorphous phases. Wollastonite crystals severely decreased the durability while diopside crystals provided a durable matte surface. The results give guidelines for manufacturing matte and chemically durable fast-fired raw glazes.     

The influence of the grain size distribution of raw materials on the selected surface properties of sanitary glazes

Glazes in significant way influence on most of the final properties of ceramic ware, mainly on surface parameters as colour, glossy or roughness. Usually, these properties has been changed by chemical composition and firing parameters. The results of presented works show, there is a possibility of improvement of surface proprieties by the selective milling and selection of the grain size of group of raw materials. It was shown, that in case of the sanitary glazes, an adequate selection of the grain size of quartz, feldspars, zirconium silicate and rest of raw materials, leads to improvement of whiteness and glossy as well as decreasing of roughness of surface.     

Ablation behaviour of ultra-high temperature ceramic matrix composites: Role of MeSi2 addition

A new class of ZrB₂ composites reinforced with 40 vol% C short fibers and containing 5 vol% SiC in combination with 5 vol% MoSi₂, HfSi₂ or WSi₂ successfully withstood extreme conditions in a oxyacetylene torch. Different responses to the torch testing were recorded depending on which secondary phase was present; this was primarily a result of the final density which ranged between 83 and 94% of the theoretical value. The temperatures achieved on the surfaces of the samples tested also varied as a function of the residual porosity and ranged from 2080 to 2240 °C. HfSi₂ additions offered the best performance and exceeded that of the baseline material that contained only SiC. It is believed that this was due to its ability to promote the elimination of porosity during densification and to the refractory nature of its oxide, HfO₂. In contrast, MoSi₂ and WSi₂ formed highly volatile oxides on the surface, which did not offer better protection than the ZrO₂-SiO₂ scale that developed in the baseline.     

Spherulitic Morphology of Isotactic Polypropylene and its Melting Behavior

Abstract

The crystallization and lamellar morphology of isotactic polypropylene (ipp) have been investigated by thermal analysis and electron microscopy. When ipp samples are crystallized above 132°C, no β-phase was detected and the samples consisted of pure α-spherulites and those showing double melting endotherms, the occurrence of double-peak shapes was attributed to the melting and reorganizing of the radial dominant lamellae, while melting of tangential cross-hatched lamellae belongs to the broad tail endotherm which leads the lower melting endotherm peak.     

Effects of YSZ powder properties on its corrosion behaviour for solid oxide membrane (SOM) electrolysis process

The solid oxide membrane (SOM) process is an environmentally friendly and innovative technology that can produce valuable metals directly from their oxides. In the SOM process, a yttria-stabilized zirconia (YSZ) tube is normally immersed the molten salt containing dissolved metal oxides and oxygen anions that move to the SOM tube where they are reduced without any emission. However, the YSZ phase transition and yttrium dissolution by the reaction with the flux reduce the SOM stability and lifetime. Here, we investigated the effect of powder characteristics on YSZ stability in the SOM electrolysis environment. Thus, powder with good formability such as high flowability and tap/untap density showed a 2% decrease in electrical conductivity, but a 17% decrease in low formability powders. The cause of the degradation is the penetration of salt ions into the lattice and the elution of yttrium ions, which results in a phase transition.     

Evolving antiferroelectric stability and phase transition behavior in NaNbO3-BaZrO3-CaZrO3 lead-free ceramics

The stability of antiferroelectricity in NaNbO₃ ceramics was found to evolve with co-doping x mol% CaZrO₃ and 6 mol% BaZrO₃, from a dominant ferroelectric (FE) orthorhombic Q phase (x = 0) to a gradually stabilized antiferroelectric (AFE) orthorhombic P phase owing to different ionic radii of Ba and Ca ions. Although a complete AFE P phase appears at x = 0.5, the field induced AFE-FE phase transformation is irreversible at first, and then becomes partially reversible at x = 1 and finally completely reversible at x = 3. The above-mentioned change process proves to be associated with the enhancing stability of antiferroelectricity with x, as evidenced by means of dielectric, polarization and strain properties as well as in/ex-situ synchrotron x-ray diffraction and Raman spectra. A composition-field phase diagram for the NN-based lead-free AFE ceramic was constructed on basis of the phase structural change, which would provide a clear understanding of how ion doping influences its antiferroelectricity.     

Poling and depoling influence on the micro-stress states and phase coexistence in KNN-based piezoelectric ceramics

In this work a microstructural qualitative and quantitative study of spatial stress distributions in modified KNN ceramics (K_0.44Na_0.52Li_0.04)_1-xCo_x/2 (Nb_0.86Ta_0.10Sb_0.04)O₃, according to the polarization state is shown. X-ray diffraction reflects a perovskite crystalline structure with coexistence of Tetragonal and Orthorhombic phases (T/O). Confocal Raman microscopy shows that these crystalline phases are distributed in randomly micrometric regions through the ceramic volume. Tetragonal regions show higher piezoelectric coefficient and exhibit a higher micro-stress that hardens the ferroelectric response. By the contrary, the occurrence of orthorhombic micro-regions softened the ferroelectric behavior and reduced their piezoelectric coefficients. The ferroelectric response of ceramics is studied, where poling is also shown as a factor that affects the spatial micro-stress distributions. Finally, a model that relates the results obtained by Raman characterization with the ferroelectric properties and stress states is proposed.     

Copper and silver nanocrystals in lustre lead glazes: Development and optical properties

In the early 9th century AD ancient potters of Iraq discovered that after firing some copper oxides and silver salts with clay, iron oxides and some sulphur compounds applied on a ceramic glaze produced a beautiful layer with a wide range of colours, from reddish to yellowish or even greenish, and some with a characteristic metallic copper or purplish shine. Modern studies of these layers showed that they are formed by nanocrystals of copper and silver embedded in a glass matrix. Some attempts have been performed to understand ancient lustre coloration and characteristic gloss but have failed to give a clear correlation between chemical composition and colour, and generally make some assumptions on the shape and the size of the nanoparticles and the lustre nanostructure. The aim of this paper is to establish a basis for understanding lustre nanostructure linked to its optical properties from a sequence of lustre reproductions on traditional lead glazed tiles. These modern lustre decorations have been studied by means of optical microscopy, transmission electron microscopy and electron energy loss spectroscopy, UV–vis spectroscopy, low irradiation angle X-ray diffraction, synchrotron radiation X-ray diffraction and electron microprobe analysis. These results show that changes in the lustre nanostructure affect the glaze colour and shine during the lustre formation process. Lustre nanostructure showed crystal size range as a function of depth, that subsequently disappeared followed by an increase of nanoparticles mean diameter and reduction of the interparticle distances. Consequently, the dipole plasmon coupling between copper nanoparticles appeared, and seems to be responsible for the metallic shine and copper metal like coloration of the copper lustre. However, colour from the glaze surface differs when calculated for diffuse or reflected light. Diffuse coloration appears strongly affected by the copper nanocrystals, while specular coloration is not only affected by copper but also by the presence of an inhomogeneous distribution of silver nanocrystals which gives the lustre a characteristic purplish shine.     

Effects of quenching on phase transformations and ferroelectric properties of 0.35BCZT-0.65KBT ceramics

Solid solutions of 0.35(Ba,Ca)(Zr,Ti)O₃-0.65(K_0.5Bi_0.5)TiO₃ (BCZT-KBT) having various Ca and Zr contents were synthesized by solid state reaction. The sintered ceramics exhibited interesting features comprising core-shell type microstructures and relaxor ferroelectric behaviour. The influence of air-quenching on structure and electrical properties has been systematically investigated. The results indicate that the compositional heterogeneity in the shell regions, for the slow-cooled state, was reduced by air quenching. Improvements are evident in ferroelectric tetragonal phase content, accompanied by increased polarisation values and depolarisation temperatures. Comparing the results obtained for two BCZT compositions, it was demonstrated that the stability of the ferroelectric tetragonal phase in slow-cooled BCZT-KBT samples was improved for the ceramic with lower Ca and Zr concentrations, denoted x = 0.06, comparing with that for higher levels, denoted x = 0.15. Furthermore, the electric field-induced ferroelectric state in the quenched ceramic with x = 0.06 was found to be more stable during heating, yielding an enhanced depolarisation temperature.     

Lattice structure analysis and optimised microwave dielectric properties of LiAl1-x(Zn0.5Si0.5)xO2 solid solutions

Low-permittivity LiAl_1-x(Zn_0.5Si_0.5)_xO₂ microwave dielectric ceramics were prepared by the solid-state reaction method. Single-phase LiAlO₂ solid solutions with a tetragonal structure were achieved at x ≤ 0.12. Partial substitution of [Zn_0.5Si_0.5]³⁺ for Al³⁺ could improve the microstructure and prevent from absorbing moisture of pure LiAlO₂ ceramics, which slightly increases their relative permittivity (ε_r). The quality factor (Q × f) and temperature coefficient of resonant frequency (τ_f) were closely related to the crystallinity and cation disorder of the B-site characterized by the full width at half-maximum of B₁⁽¹⁾ –mode assigned to Li–O–Al stretching. The optimum microwave dielectric properties (ε_r = 6.12, Q × f = 56986 GHz and τ_f = -122 ppm/°C) were obtained in the sample with x = 0.02 sintered at 1300 °C.     

Enhanced energy storage and fast discharge properties of BaTiO3 based ceramics modified by Bi(Mg1/2Zr1/2)O3

Lead-free (1-x)BaTiO₃-xBi(Mg_1/2Zr_1/2)O₃ ((1-x)BT-xBMZ) ceramics with perovskite structure were synthesized by solid-state reaction methods. (1-x)BT-xBMZ solid solution transforms from tetragonal (x≤0.04) to pseudocubic (x≥0.08) and exhibits a dispersive dielectric behavior with respect to frequency, showing typical relaxor characteristics with BMZ increasing. The optimal energy storage density of 1.25 J cm^?3 and energy efficiency of >95% are obtained at x = 0.15, with maximum dielectric breakdown strength of 185 kV cm^-1 at 200 μm thickness., The energy storage density and energy efficiency of 0.85BT-0.15BMZ ceramics maintain at about 0.8 J cm^?3 and 89% at 150 kV cm^-1 over temperature range of 25 °C～150 °C, exhibiting good thermal stability. The pulse discharge capability of 0.85BT-0.15BMZ ceramics were measured under different electric fields, showing a short charge-discharge time of 1.3 μs. Therefore (1-x)BT-xBMZ solid solution with high energy density and efficiency, good temperature stability and fast discharge speed, is promising candidate for high power applications.     

Temperature-dependent piezoelectric strain and resonance performance of Fe2O3-modified BiScO3-PbTiO3-Pb(Nb1/3Mn2/3)O3 ceramics

The piezoelectric strain and resonance performance of 0.37BiScO₃-0.6PbTiO₃-0.03Pb(Mn_1/3Nb_2/3)O₃ (BS-PT-PMN-xFe) ceramics with different amounts of Fe content addition were investigated from room temperature to 200 °C. Both the piezoelectric strain and resonance performance are improved by Fe addition in wide temperature range. Piezoelectric strain of BS-PT-PMN-xFe with 1 mol% Fe is 0.23%, which is comparable to that of BiScO₃-PbTiO₃ (BS-PT) ceramics, while the strain hysteresis is only one-third. At 200 °C, the high-field strain coefficient of BS-PT-PMN-Fe with 1 mol% Fe is as large as 700 pm/V. Variation of piezoelectric strain and hysteresis is clearly reducing by Fe addition. The maximum vibration velocity is enhanced up to approximately 1 m/s in 2 mol% Fe-modified BS-PT-PMnN-xFe ceramics, and the vibration velocity is stable from room temperature to 200 °C when the electric voltage magnitude was below 60 V_pp. These results indicate that BS-PT-PMN-xFe ceramics are potential candidates for high-temperature piezoelectric actuator application.     

Gas release during clay firing and evolution of ceramic properties

Gas release, crystalline structure and ceramic properties were analysed during firing of clay raw materials and extruded bricks. Carbon monoxide, carbon dioxide, nitrogen oxides, and methane emissions were measured during the firing cycle. Ammonia and sulphur dioxide were not observed within the detection limits. The evolution of crystalline phases, open porosity, volumetric shrinkage, rupture tension and apparent density were correlated to the amount of gases produced at different temperatures, ranging from 300 to 1200 °C. These results can be applied for optimising the production process.     

Thermodynamic assessment of the group IV,V and VI oxides for the design of oxidation resistant multi-principal component materials

Multi-principal component materials (MPCMs) are currently being investigated for use in high and ultra-high temperature environments. The design of oxidation resistant multi-component materials requires as input the oxidation behavior of each of the components. FactSage free energy minimization software and databases were used to calculate the equilibrium oxide phases and free energies of formation for the oxides of the Group IV, V and VI refractory metals, and their carbides, nitrides and borides. The results are summarized in Ellingham diagrams. Periodic trends were noted; Group IV elements form the most stable oxides with the highest melting temperatures (T_m), Group V elements form oxides with low T_m, and Group VI elements form gaseous oxide species. Oxygen diffusion data from literature for some of these oxides were also reviewed and summarized. The results are utilized to identify strategies for optimizing oxidation resistance of MPCMs for service at temperatures above 1700°C.     

Nanostructured NdF3 glass ceramic: An efficient bandpass color filter for wide-color-gamut white LED

Up-to-date LED-lit LCD technology pursues a wide color gamut to ensure reproduction of all natural colors. Herein, a novel NdF₃ glass ceramic was developed as bandpass color filter for pc-wLEDs. In-depth microstructural and optical analyses reveal the alteration of local environment of Nd³⁺ from the oxide-amorphous matrix to the fluoride-crystalline phase after crystallization. A prototype pc-wLED is constructed by coupling all-inorganic “YAGG:Ce³⁺+CASN:Eu²⁺” phosphor-in-glass plate and NdF₃ glass ceramic plate with blue-emitting chip in a stacked configuration. Thanking to the efficient absorption from hypersensitive Nd³⁺: ⁴I_9/2 → ⁴G_5/2, ²G_7/2 transition, the electroluminescent spectral profile of phosphors can be well separated into two narrowed bands in the green and red regions, and so an improved color gamut of 78.8% is achieved. The present work demonstrates an efficient route for wide-color-gamut white LED in a facile and cost-effective way.     

Cellular mullite materials processed by direct foaming and protein casting

In this paper, cellular mullite bodies were developed by thermal direct-consolidation of foamed aqueous mullite-bovine serum albumin (BSA) and mullite-BSA-methylcellulose suspensions, burning out (650 °C, 2 h) and sintering (1600 °C, 2 h). Some modifications to the shaping route conventionally used in protein casting were incorporated in the proposed processing to obtain bodies with controlled and homogeneous microstructures. The materials were characterized by porosity measurements, analysis of phases by XRD, and microstructural analysis by SEM and Hg-porosimetry. Characteristic parameters of cell size distributions, percentage of open and closed cells, window size and interstitial pore size distributions, and microstructural features of the mullite matrix were determined. Moreover, basic 2D cell size parameters and global 3D stereological parameters were analysed. The obtained results showed that mullite bodies with hierarchical porosity and different microstructural features were developed from the design and control of processing routes, which use BSA as a foaming and binder/consolidator agent.     

The role of firing temperature, firing time and quartz grain size on phase-formation, thermal dilatation and water absorption in sanitary-ware vitreous bodies

This work reports a study on (i) the evolution of mineral phases versus time and temperature, and (ii) some relationships between phases observed, process parameters, and macroscopic properties (thermal expansion and water absorption), in sanitary-ware vitreous bodies. These properties are relevant to satisfying the technical requirements of sanitary-ware. We have fixed the green body composition, varying some key process parameters, such as firing temperature (T_f), firing time (t_f) and quartz grain size (d₅₀); a grid of 30 T_f-t_f-d₅₀ points has been explored. We have spanned the t_f-T_f space (0-80 min; 1200-1280 °C) using firing temperatures representative of the plateau values of the heating curve in industrial processes. X-ray powder diffraction has been used to determine the phase composition for each T_f-t_f-d₅₀ point. Scanning electron microscopy proved useful in enhancing the micro-structural characterization. Quartz d₅₀ seems to be the process-parameter which most effectively co-relates with the thermal expansion of the glassy matrix.     

Fabrication and properties of C/SiC porous ceramics by grinding-mould pressing-sintering process

High temperature resistant porous ceramics are considered to be prime candidates for applications in the transpiration cooling system of a hypersonic vehicle. This paper describes a new preparation process including grinding-mould pressing-sintering process, which is successfully used to fabricate C/SiC porous ceramics with high compressive strength and excellent permeability. The effects of carbon fiber content on the microstructure, mechanical property, pore size distribution and permeability of this porous ceramic are investigated in detail. The results indicate that this porous ceramic prepared in this study exhibits high compressive strength (～270.82 MPa) and excellent permeability (～3.937 × 10^?8 mm²). The C/SiC porous ceramics fabricated in this study will have potential application in active thermal protection systems.     

Pressure-assisted microwave sintering: A rapid process to sinter submicron sized grained MgAl2O4 transparent ceramics

This work focuses on the development of an original process based on a 2.45 GHz single-mode microwave cavity equipped with a uniaxial press, to sinter transparent spinel MgAl₂O₄ ceramic in air. The samples were conventionally pre-sintered to a density of 90% TD before microwave sintering to the final stage of densification. The influence of thermomechanical cycle on the material properties was investigated. Transmittance, grain size distribution, hardness and fracture toughness of the samples were measured and correlated to the microstructure. This new sintering process has allowed obtaining transparent samples with sub micrometric grain size and high mechanical properties, with relatively short times and low temperature. These first results can be compared to some obtained by SPS or HIP. The technical input of this method is that all the process is here conducted in air atmosphere.