Ceramics, Volume 4, Issue 3 (September 2021) – 13 articles

Electroactive polymers (EAPs) are an advanced family of polymers that change their shape through electric stimulation and have been a point of interest since their inception. This unique functionality has helped EAPs to contribute to versatile fields, such as electrical, biomedical, and robotics, to name a few. Ionic EAPs have a significant advantage over electronic EAPs. For example, Ionic EAPs require a lower voltage to activate than electronic EAPs. On the other hand, electronic EAPs could generate a relatively larger actuation force. Therefore, efforts have been focused on improving both kinds to achieve superior properties. In this review, the synthesis routes of different EAP-based actuators and their properties are discussed. Moreover, their mechanical interactions have been investigated from a tribological perspective as all these EAPs undergo surface interactions. Such interactions could reduce their useful life and need significant research attention for enhancing their life. Recent advancements and numerous applications of EAPs in various sectors are also discussed in this review. Full article

Lanthanum molybdenum oxide (La₂Mo₂O₉, LAMOX)-based ion conductors have been used as potential electrolytes for solid oxide fuel cells. The parent compound La₂Mo₂O₉ undergoes a structural phase transition from monoclinic (P2₁) to cubic (P2₁3) at 580 °C, with an enhancement in oxide ion conductivity. The cubic phase is of interest because it is beneficial for oxide ion conduction. In search of alternative candidates with a similar structure that might have a stable cubic phase at lower temperatures, we have studied the variations of the crystal structure and ionic conductivity for 25, 50, 62.5 and 75 mol% W substitutions at the Mo site using high-temperature X-ray diffraction, dilatometry, and impedance spectroscopy. Highly dense ceramic samples have been synthesized by solid-state reaction in a two-step sintering process. Low-angle X-ray diffraction and Rietveld refinement confirm the stabilization of the cubic phase for all compounds in the entire temperature range considered. The substitutions of W at the Mo site produce a decrement in the lattice parameter. The thermal expansion coefficients in the high-temperature range of the W-substituted ceramics, as determined by dilatometry, are much higher than that of the unmodified sample. The impedance spectra have been modeled using a modified genetic algorithm within 300–600 °C. A distribution function of the relaxation times is obtained, and the contributions of ohmic drop, grains and grain boundaries to the conductivity have been identified. Overall, our investigation provides information about cationic substitution and insights into the understanding of oxide ion conductivity in LAMOX-based compounds for developing solid oxide fuel cells. Full article

The present work shows the path towards the industrial production of ceramic tiles containing a high amount of recycling materials in the substitution of natural raw materials. Starting from the applied research at laboratory scale, which is able to demonstrate the work feasibility, other important milestones consist of pilot scale production until the proper industrial production. Finally, when all these steps are positively achieved, the practice is consolidated and it is possible to reach the concrete sustainability benefits (social, environmental and economic). The results of an industry driven project that aimed to produce porcelain stoneware tiles containing 85% of recycled materials were selected to show this path. This innovative ceramic product—containing soda-lime scrap glass from urban-separated collection (post-consumer waste) and unfired scrap tiles from industrial ceramic process (pre-consumer waste)—was sintered about 200 °C lower than a traditional porcelain stoneware tile. It maintains high technical performances belonging to class BIa of the International Standard of ceramic tile classification (EN ISO 14411). Moreover, this product fulfils the standard requirements for dry-pressed ceramic tiles with low water absorption (≤0.5%), and it obtained the certification UNI Keymark. The LCA study was also performed and the results showed a significantly lower environmental impact of this innovative product compared to a traditional porcelain stoneware tile. Full article

Tailoring electrical and mechanical properties in the fluorite oxides family is of great interest for technological applications. Other than doping and substitution, entropy-driven stabilization is an emerging technique for new solid solutions formation and enhancing or exploring new functionalities. However, there is a high number of possible combinations for higher-order diagram investigations, and the current state of the art shows limited possibilities in predicting phase formation and related properties. In this paper, we expand the compositional space of fluorite oxides in ZrO₂-HfO₂-CeO₂-Nb₂O₅-RE₂O₃ systems. X-ray diffractometry and scanning electron microscopy measurements showed the formation of cubic fluorite-type structures when processing compositions at 1600 °C. Full article

Objective: This study aimed to investigate and compare the effect of various surface treatments on the micromorphology and the roughness of four CAD/CAM lithium silicate-based glass-ceramics (LSGC). Method: Eighty specimens of four LDGC materials (IPS e. max^® CAD (Ivoclar-Vivadent, Liechtenstein, Schaan), Vita Suprinity^® (Vita Zahnfabrik, Bad Säckingen, Germany), Celtra Duo^® (Dentsply, Hanau-Wolfgang, Germany) and n!ce (Straumann, Basel, Switzerland)) were used for this study. All specimens were highly polished with 400, 600, 1200 grit silicon carbide paper and then polished with 3 µm and 1 µm polycrystalline diamond suspension liquid with grinding devices. Each group of ceramic was assigned to one of the following three surface treatments (1) sand-blasting (SB) with 50 µm Al₂O₃ at 70 psi for 10s, (2) hydrofluoric acid etching (HF) with 5% hydrofluoric acid, according to the manufacturer instructions, (3) and a combination of sand-blasting and hydrofluoric acid (SB + HF). All specimens were cleaned with ethanol for 2 min and placed in an ultrasonic unit with distilled water for 15 min. The microstructure was analyzed by scanning electron microscopy (SEM). The surface roughness and topography were evaluated with atomic force microscopy in tapping mode (AFM). Statistical analysis was done using two-way ANOVA and Tukey tests (α = 5%). Results: All surface treatments had a significant effect on LDGC surface roughness compared to the untreated surface (p < 0.05). The sand-blasting treatment had a significantly higher mean surface roughness value for Vita Suprinity and Celtra Duo compared to other surface treatments (p < 0.05). However, there was no significant difference for surface roughness between sand-blasting and sand-blasting + etching for e.max CAD and n!ce. The hydrofluoric acid produced less surface roughness compared to other surface treatments but was able to change the surface structure. (5) Conclusions: The sand-blasting + etching treatment could be a sufficient method to produce surface roughness for all LSGC types. Full article

In this paper, we examined the dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics fabricated by various routes and discussed the most important conditions affecting their dielectric behavior. We prepared feedstock powder using a molten salt route and compared it with a commercial powder. Both powders were sintered using SPS. For some samples, annealing was applied after sintering. Other samples were obtained by high-pressure forming and conventional sintering, using both powders. Phase composition, porosity and microhardness were evaluated in comparison with the literature. The results showed that a sintering temperature just below or equal to 1000 °C should be set for the SPS process. However, the best dielectric characteristics were obtained in samples prepared by high-pressure forming and conventional sintering, which showed a relative permittivity of 22,000 and a loss tangent of 0.13 at 1 MHz. Full article

Numerical calculations were carried out to simulate, under conditions of close spark plasma sintering (SPS), the temperature distribution during the passage of current in dense cylindrical samples of two materials: aluminum oxide and copper located in graphite forms and clamped between cylindrical graphite punches. The investigated materials differ greatly in their electrical conductivity and other physicochemical properties. Calculations were carried out for various geometric parameters of the samples, as well as graphite molds and punches at varying heating rates from the passing current. Full article

Composite electrolytes containing lithium ion conducting polymer matrix and ceramic filler are promising solid-state electrolytes for all solid-state lithium ion batteries due to their wide electrochemical stability window, high lithium ion conductivity and low electrode/electrolyte interfacial resistance. In this study, we report on the polymer infiltration of porous thin films of aluminum-doped cubic garnet fabricated via a combination of nebulized spray pyrolysis and spin coating with subsequent post annealing at 1173 K. This method offers a simple and easy route for the fabrication of a three-dimensional porous garnet network with a thickness in the range of 50 to 100 µm, which could be used as the ceramic backbone providing a continuous pathway for lithium ion transport in composite electrolytes. The porous microstructure of the fabricated thin films is confirmed via scanning electron microscopy. Ionic conductivity of the pristine films is determined via electrochemical impedance spectroscopy. We show that annealing times have a significant impact on the ionic conductivity of the films. The subsequent polymer infiltration of the porous garnet films shows a maximum ionic conductivity of 5.3 × 10⁻⁷ S cm⁻¹ at 298 K, which is six orders of magnitude higher than the pristine porous garnet film. Full article

Composite ceramics of stabilizer oxide coated ytterbia-samaria costabilized zirconia (1.5Yb1.5Sm-TZP) and 24–32 vol% of tungsten carbide as an electrically conductive dispersion were manufactured by hot pressing at 1300–1400 °C for 2 h at 60 MPa pressure. The materials were characterized with respect to microstructure, phase composition, mechanical properties and electrical discharge machinability by die sinking. Materials with a nanocomposite microstructure and a strength of up to 1700 MPa were obtained. An attractive toughness of 6–6.5 MPa√m is achieved as 40–50% of the zirconia transformed upon fracture. The materials show fair material removal rates of 1 mm³/min in die sinking. Smooth surfaces indicate a material removal mechanism dominated by melting. Full article

Brushing with bonded abrasives is a flexible finishing process used for the deburring and the rounding of workpiece edges as well as for the reduction of the surface roughness. Although industrially widespread, insufficient knowledge about the contact behavior of the abrasive filaments mainly causes applications to be based on experiential values. Therefore, this article aims to increase the applicability of physical process models by introducing a new prediction method, correlating the contact forces of single abrasive filaments, obtained by means of a multi-body simulation, with the experimentally determined process forces of full brushing tools during the surface finishing of ZrO₂. It was concluded that aggressive process parameters may not necessarily lead to maximum productivity due to increased tool wear, whereas less aggressive process parameters might yield equally high contact forces and thus higher productivity. Full article

Fine biocompatible powders with different phase compositions were obtained from a 0.5 M solution of ammonium sulfate (NH₄)₂SO₄ and calcium lactate Ca(C₃H₅O₃)₂. The powder after synthesis and drying at 40 °C included calcium sulfate dehydrate CaSO₄·2H₂O and calcite CaCO₃. The powder after heat treatment at 350 °C included β-hemihydrate calcium sulfate β-CaSO₄·0.5H₂O, γ-anhydrite calcium sulfate γ-CaSO₄ and calcite CaCO₃. The phase composition of powder heat-treated at 600 °C was presented as β-anhydrate calcium sulfate β-CaSO₄ and calcite CaCO₃. Increasing the temperature up to 800 °C leads to the sintering of a calcium sulfate powder consisting of β-anhydrite calcium sulfate β-CaSO₄ main phase and a tiny amount of calcium oxide CaO. The obtained fine biocompatible powders of calcium sulfate both after synthesis and after heat treatment at temperature not above 600 °C can be recommended as a filler for producing unique composites with inorganic (glass, ceramic, cement) or polymer matrices. Full article

Ceramic tiles and ceramic tile adhesives (CTA) are two impressive materials that have changed construction history. Ceramic tiles could not provide their beauty and durability for buildings when used as a covering both for the inside and exterior finishing without CTA. Nowadays, they are complex multi-component systems. Among the various CTAs, cementitious products are the most commonly used. This article presents an extensive review of the literature, showing how they are perceived in the scientific literature today. In this paper, an attempt is made to review individual adhesives’ ingredients’ effects on their properties, with particular reference to redispersible polymer powders and methylcellulose ethers. The article presents the basics of the CTAs, assessing and verifying the constancy of their performance in force in European Union countries. Furthermore, it gives a critical review of CTA’s normalized measurement methodologies. The study also draws attention to the need to consider measurement uncertainty in decision-making and conformity assessment, supported by an analysis of the results of multi-annual inter-laboratory studies and market surveillance tests. Future research suggestions are also made based on the review, mainly from the adhesive manufacturer’s perspective. Full article

Anisotropic CuCrO₂ thin films were successfully prepared on glass substrate by the electrospinning method followed by annealing at 600 °C. The directionality of the nanowires increased with increases in rotation speed. In addition, the structural formation and optoelectronic behavior of the CuCrO₂ thin films have been studied by X-ray powder diffraction studies, transmission electron microscopy, field emission scanning electron microscopy, and UV-vis spectroscopy. The X-ray diffraction studies revealed a delafossite properties of the CuCrO₂. The electrical conductivity in the parallel and vertical directions of the films produced at 2000–3000 rpm differed by two to three orders of magnitude. The optical transmittance properties of the CuCrO₂ thin films were improved by increasing the rotation speed. Full article