Ultrahigh Permittivity, Ultralow Loss and Stability in (In0.5Ta0.5)0.1Ti0.9O2 Ceramics With Temperature Range From -100 to 235 °C

Dielectric materials with excellent dielectric properties are being promoted in requirements of microelectronic devices. In this study, (In0.5Ta0.5)0.1Ti0.9O2 ceramics were achieved by a solid-state reaction with reducing atmosphere of N2. Also, dense microstructure, ultrahigh permittivity (εr = 1.18 × 105) and ultralow dielectric loss (tanδ = 0.0072) were demonstrated at1 kHz. Interestingly enough, the temperature coefficient of permittivity which satisfies X9D (-100 °C - 235 °C, Δεr/ε25°C < ± 3.3 %) maintained stability at 1 kHz, and the dielectric mechanism could be connected to the electron-pinned defect dipoles (EPDD), which has favourable potential applications in electronic devices.

Self-Grinding Silage Knife Strengthened with Ni–WC Alloy Prepared by Laser Cladding

The working environment of agricultural cutting tools is poor, and the operational quality and efficiency are reduced after they become blunt. This study aimed to develop a high wear-resistant agriculture knife with a long life. A Ni–WC alloy, wear-resistant layer was prepared using laser cladding technology on one side of the cutting edge of a 65 Mn silage knife. A self-grinding edge was formed when the cladded knife was used, which improved the cutting quality and service life of the knife. The microstructure, phase, composition, and hardness distribution of the cladding layer were detected and analyzed. The impact toughness and wear resistance of the laser-cladded samples were analyzed, and the cladded knife was tested in the field. The results show that a cladded layer with a dense microstructure formed metallurgical bonds with the substrate. The microhardness was uniform across the cladded layer, and the average hardness of the micro Vickers was approximately 1000 HV(0.2), which was approximately three times the hardness of the substrate. The impact toughness and wear resistance of the coated knife were obviously higher than those of uncoated knives. The field tests showed that compared with a conventional 65 Mn knife, the self-grinding knife with laser cladding could maintain its sharp cutting shape after operation for 76 h, which greatly extended the service life of the knife. This study improved the service life of an agricultural cutting tool, which enhanced the cutting performance and efficiency at the same time.

Microstructure evolution and phase transformation of ZrB2-45MoSi2-10Al coating at high temperature

The ZrB2-45MoSi2-10Al coating was prepared by a Robotic complex for detonation spraying of coatings equipped with a multi-chamber detonation accelerator on surface of carbon/carbon composites without adhesion sublayer. The coating has a lamella-type structure typical for gas-thermal coatings, well connected with C/C composite substrate without sublayer, and composed of m-ZrO2, t-ZrO2, t-MoSi2, some h-ZrB2, and c-Al phases. Heat treatment of the samples at 1500 °C for 1, 3 and 6 h was carried out in air. The effect of heat treatment on the microstructure and phase composition of the ZrB2-45MoSi2-10Al coating was investigated by X-ray diffraction and scanning electron microscopy. The c-ZrO2 and h-(α-Al2O3) were formed after oxidation at 1500 °C for 6 h. The uniform distribution of ZrO2 ceramic particles and the formation of a-Al2O3 enhanced the thermal stability of the coating. The coating after heat treatment (1, 3 and 6 h) exhibited structure without cracks and low porosity. The dense microstructure of the coating contributed to its good oxidation-resistant property at high temperature.

How Efficient are LC3 and GGBFS-Contained Mortar Mixtures Submerged into Na2SO4 Solution against External Sulfate Attack at an early Age?

Ordinary Portland cement (OPC) is one of the most widely used construction materials in civil engineering infrastructure construction but it is susceptible to sulfate attack. One of the ways to improve the sulfate resistance of an OPC mortar/concrete is to replace a certain amount of OPC with different pozzolanic materials such as ground granulated blast furnace slag (GGBFS) and metakaolin. The use of pozzolanic materials to mortar/concrete not only enhances durability but also reduces carbon dioxide (CO2) emission due to the less usage of OPC at the initial construction state. As considering these aspects, limestone calcined clay cement (LC3) has been developed in recent decades. However, the influence of LC3 on sulfate attack resistance has not been fully evaluated. Therefore, this study investigated the efficiency of LC3 mortar mixtures against sulfate attack at an early age (approximately 4.5 months) after two different curing periods, namely 1-day and 3-day curing, since the strength of the LC3 mixture is lower than OPC mixtures. To evaluate the synergistic effect of a combination of LC3 and GGBFS on the sulfate resistance, the LC3 and OPC mixtures containing 25% GGBFS were also assessed in terms of density, porosity, compressive strength, volumetric expansion, and weight changes. The experiment results show that the expansion of the LC3 mixture regardless of the addition of GGBFS and an initial curing strength made a plateau after a rapid increase up to 7 days, while the expansion of the OPC mixture kept increasing throughout the period. Furthermore, the addition of GGBFS to OPC or LC3 mixture provides the synergistic effect on reducing the expansion due to sulfate attack. Therefore, if LC3 mixture has high initial strength (min. 15 MPa) and dense microstructure to minimize the penetration of sulfate ion into the mixture, it is expected that LC3 mixture is more efficient than OPC mixture against the sulfate attack.

Significantly Improved Colossal Dielectric Properties and Maxwell—Wagner Relaxation of TiO2—Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

In this work, the colossal dielectric properties and Maxwell—Wagner relaxation of TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 (x = 0–0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na1/2Y1/2Cu3Ti4O12 is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (Rgb). The colossal permittivities of ε′ ~ 0.7–1.4 × 104 with slightly dependent on frequency in the frequency range of 102–106 Hz are obtained in the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016–0.020 at 1 kHz due to the increased Rgb. The semiconducting grain resistance (Rg) of the Na1/2Y1/2Cu3Ti4+xO12 ceramics increases with increasing x, corresponding to the decrease in Cu+/Cu2+ ratio. The nonlinear electrical properties of the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO2–rich Na1/2Y1/2Cu3Ti4+xO12 ceramics are explained by the Maxwell–Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.

Evaluation of the long-term compressive strength development of the sewage sludge ash/metakaolin-based geopolymer

This paper aimed to evaluate the long-term compressive strength development of the sewage sludge ash/metakaolin (SSA/MK)-based geopolymer. SSA/MK-based geopolymeric mortars and pastes were produced at 25ºC with different SSA contents (0 - 30 wt.%). Compressive strength tests were run within the 3-720 curing days range. A physicochemical characterisation (X-ray diffraction and scanning electron microscopy) was performed in geopolymeric pastes. All the geopolymeric mortars presented a compressive strength gain with curing time. The mortars with all the SSA evaluated contents (10, 20, 30 wt.%) developed a compressive strength over 40 MPa after 720 curing days at 25ºC. The maximum compressive strength of the mortars with SSA was approximately 61 MPa (10 wt.% of SSA), similarly to the reference mortar (100% MK-based geopolymer). The microstructure analyses showed that the SSA/MK-based geopolymer presented a dense microstructure with N-A-S-H gel formation.

Preparation of W-C-Co Composite Micropowder with Spherical Shaped Particles Using Plasma Technologies

The possibility of obtaining composite micropowders of the W-C-Co system with a spherical particle shape having a submicron/nanoscale internal structure was experimentally confirmed. In the course of work carried out, W-C-Co system nanopowders with the average particle size of approximately 50 nm were produced by plasma-chemical synthesis. This method resulted in the uniform distribution of W, Co and C among the nanoparticles of the powder in the nanometer scale range. Dense microgranules with an average size of 40 microns were obtained from the nanopowders by spray drying. The spherical micropowders with an average particle size of 20 microns were received as a result of plasma treatment of 25.36 microns microgranule fraction. The spherical particles obtained in the experiments had a predominantly dense microstructure and had no internal cavities. The influence of plasma treatment process parameters on dispersity, phase, and chemical composition of spherical micropowders and powder particles microstructure has been established.

STRUCTURE, MICROSTRUCTURE, AND PIEZOELECTRIC PROPERTIES OF KNLNS-BNKZ LEAD-FREE CERAMICS UNDER THE EFFECT OF DIFFERENT SINTERING TEMPERATURES

Samples of 0.96(K0.48Na0.48Li0.04)(Nb0.95Sb0.05)O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 piezoelectric ceramic were fabricated with conventional ceramic techniques and sintered at different temperatures. The effect of sintering temperature (TS) on the structure, microstructure, and piezoelectric properties of the ceramics was studied in detail. The experimental results showed that with an increase of the TS temperature, the structure of the ceramics transformed from an orthorhombic-tetragonal mixed phase (O-T) at TS £ 1100 °C into a rhombohedral-tetragonal (R-T) mixed phase with a dense microstructure of uniform grain size at TS = 1110 °C. When TS was further increased (TS ³ 1120 °C), the ceramics showed only a rhombohedral phase (R). The ceramics showed the best electrical properties for TS = 1110 °C at which the rhombohedral and tetragonal (R-T) phases coexist. Specifically, the ceramic density reached its highest value (4.22 g/cm3), the electromechanical coupling coefficients kp and kt were 0.46 and 0.50, respectively, and the piezoelectric coefficient d33 was 245 pC/N.

High energy storage density with ultra-high efficiency and fast charging–discharging capability of sodium bismuth niobate lead-free ceramics

Ceramics-based capacitors with excellent energy storage characteristics, fast charging/discharge rate, and high efficiency have received significant attention. In this work, Na[Formula: see text]Bi[Formula: see text]NbO3(NBN) ceramics were processed through solid-state sintering route. The investigated ceramics were crystallized in a single perovskite phase. Dense microstructure, with small average grain size ([Formula: see text]0.92 [Formula: see text]m) is obtained for the investigated ceramics. A high dielectric constant >1000 accompanied by a low dielectric loss was achieved for these ceramics at ambient temperature. A recoverable energy density [Formula: see text]0.92 J/cm3and ultra-high efficiency of 96.33% at 138 kV/cm were obtained at room temperature. Furthermore, a lower discharging time of 0.14 [Formula: see text]s was also achieved. This material is a suitable candidate for power pulsed applications.