The effect of Ba content on the stress sensitivity of the antiferroelectric to ferroelectric phase transition in (Pb0.94−xLa0.04Bax)(Zr0.60Sn0.40)0.84Ti0.16O3 ceramics is investigated through ...monitoring electric field‐induced polarization and longitudinal strain under compressive prestresses. It is found that incorporation of Ba significantly suppresses the stress sensitivity of the phase transition, as manifested by slight decreases under prestresses up to 100 MPa in the maximum polarization (Pm) and longitudinal strain (xm). The energy storage density is even increased under the mechanical confinement in compositions x = 0.02 and 0.04. X‐ray diffraction, transmission electron microscopy, and dielectric measurements indicate that the suppressed stress sensitivity is associated with the disruption of micrometersized antiferroelectric domains into nanodomains and the transition from antiferroelectric to relaxor behavior.
Abstract
This paper introduces a fast, low‐temperature, pressureless process to chemically bind ceramic parts with the help of infrared (IR) irradiation and phosphate binder condensation. Ceramic ...components are synthesized from slurries of ceramic powders and Al(H
2
PO
4
)
3
binder that are irradiated with short‐waved IR light capable of heating the system to 350°C. This irradiation is found to be sufficient to drive phosphate condensation, binding the ceramic powders together within a matter of seconds. The IR‐irradiated components show an increase in density and Vickers hardness. Layer‐by‐layer spraying and irradiation is demonstrated as a route to additive manufacturing using various ceramic chemistries. While further optimization is needed to control desired microstructure, this process of using chemically bonded ceramic binders with IR heating for additive manufacturing shows the potential to find applications in various ceramic systems, including refractories, bone implants, electronics, and thermal barrier coatings.
The influence of B-site deficiency on the stability of electrically induced long-range ferroelectric order of the stoichiometric Bi.sub.0.5+xNa.sub.0.5-xTi.sub.1-0.5xwhite square.sub.0.5xO.sub.3 ...(BNT-xV.sub.Ti) ("white square" denotes vacancies) ceramics is studied. The depolarization and ferroelectric to relaxor transition are identified as separate and discrete processes in BNT-based materials. For BNT-0.02V.sub.Ti, the resonance and anti-resonance peaks on dielectric permittivity-frequency curves indicate dominating ferroelectric phase at room temperature. The depolarization temperature, determined by thermally stimulated depolarization current, is ~ 65 °C. However, the ferroelectric to relaxor transition temperature is absent, as no distinct frequency-independent anomalies for the dielectric permittivity exist. This depolarization process can be ascribed to nanoscale ferroelectric domain at room temperature for BNT-0.02V.sub.Ti, which is induced by chemical disorder and strong random field as V.sub.Ti generated. Hence, the results imply that the B-site deficiency in BNT is a very effective route to tailor the stability of electrically induced long-range ferroelectric order.
The novel applications of MoSi
and SiC as matrix and reinforcing materials in the creation of high-performance composites were investigated in this work. In particular, Spark Erosion Machining's ...geometric tolerances were studied in order to shed light on the technique's potential for precision manufacture in the realm of MoSi
-SiC composites. Our research focused on evaluating critical parameters and their impact on machining performance, including material removal rate, surface roughness, wear rate and drilled hole accuracy. In-depth research revealed the critical input factors that had the greatest impact on the machining procedure. Notably, parameters such as current (32%), sparking on time (23%), sparking gap voltage (12%), dielectric pressure (12%), and sparking off time (17%) emerged as the most influential factors, as determined by ANOVA analysis. These findings provide valuable insights into optimizing the Sparking EDM approach for MoSi
-SiC composite materials. This study further demonstrated the improvement in composite desirability ratings across multiple performance criteria, highlighting the effectiveness of Sparking EDM in enhancing machining outcomes (e.g., from 0.8523 to 0.9527). Correlations between the EDM's output responses were found to be quite high when geometric tolerances and the coefficient of determination (R2) were used (0.7858, 0.9625, 0.8427, 0.8678, 0.8474, 0.8368, 0.8344, 0.8671). Consider that, for the sake of a more complete understanding of the procedure's approach, the emphasis is on the methodology rather than the multifaceted metal removal mechanisms involved. This research doesn't dive further into the physical concerns of Spark Erosion Machining, but it does provide insights into the practical application of this technique in the precision manufacturing of MoSi2-SiC composite materials. For real-world medical applications such implanted devices, dental implants, surgical instruments, biological sensors and diagnostics, this study provides a valuable and encouraging approach. A validation experiment verifies the results, proving the feasibility of improved spark erosion in high-precision production. The results of this research show that EDM methods can be fine-tuned to produce ceramic composites with much greater MRR, superior surface finishes and a marked decrease in subsurface cracking and microstructural modifications. This is essential for protecting the integrity of materials used in life-saving medical equipment.
Lead-free ceramics (1 - x)Bi.sub.0.5Na.sub.0.5TiO.sub.3-xSr.sub.0.85Bi.sub.0.1TiO.sub.3 (BNT-xSBT, x = 0.4, 0.5, 0.6 and 0.7) were prepared by a solid-state reaction process. Coexistence of ...ferroelectric relaxation at low temperature and Maxwell-Wagner dielectric relaxation at high temperature was revealed for the first time in this system. Meanwhile, hysteresis-free P-E loops combined with a very high piezoelectric strain coefficient (d.sub.33) of 1658 pC/N concurrently with large electrostrictive coefficient Q = 0.287 m.sup.4C.sup.-2 were achieved. The ferroelectric relaxor behavior and large electrostrictive strain might be linked to easy reorientation and reversal of ergodic PNRs and the combined effect of Bi off-center position and lone pair electrons.
Lo studio della collezione di vasi in maiolica, prodotti soprattutto in Sicilia tra il XVII e XVIII secolo, dell'avvocato Giacomo Spadaro (1912-2019), raffinato collezionista, donata al Museo ...Diocesano di Palermo nel 2014, grazie all'interessamento del nuovo direttore Mons. Filippo Sarullo, è l'argomento del contributo.
Dental Ceramics for Restoration and Metal Veneering Zhang, Yu; Kelly, J. Robert
Dental clinics of North America/The Dental clinics of North America,
October 2017, 2017-10-00, 20171001, Letnik:
61, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A survey of the development of dental ceramics is presented to provide a better understanding of the rationale behind the development and clinical indications of each class of ceramic material. ...Knowledge of the composition, microstructure, and properties of a material is critical for selecting the right material for specific applications. The key to successful ceramic restorations rests on material selection, manufacturing technique, and restoration design, including the balancing of several factors such as residual stresses, tooth contact conditions, tooth size and shape, elastic modulus of the adhesives and tooth structure, and surface state.
Nonstoichiometry lead-free 0.94Na.sub.xBi.sub.yTiO.sub.3-0.06Ba.sub.zTiO.sub.3 (N.sub.xB.sub.yT-0.06B.sub.zT) (from x = y = 0.5, z = 1.00 to x = 0.5, y = 0.534, z = 1.02) ceramic compositions were ...prepared by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. The depolarization temperature (T.sub.d) can be lowered by modifying x, y and z. The pyroelectric coefficient (p) of nonstoichiometry N.sub.xB.sub.yT-0.06B.sub.zT compositions is greatly increased, compared with stoichiometry NBT-0.06BT composition, from 3.15 x 10.sup.-4 C m.sup.-2 °C.sup.-1 at room temperature (RT) and 23.9 x 10.sup.-4 C m.sup.-2 °C.sup.-1 at T.sub.d, and reaches maxima of 6.99 x 10.sup.-4 C m.sup.-2 °C.sup.-1 at RT and 75.3 x 10.sup.-4 C m.sup.-2 °C.sup.-1 at T.sub.d for x = y = 0.52 and z = 1. The figures of merits, F.sub.i, F.sub.v, and F.sub.D, also have been improved from 1.12 x 10.sup.-10 m v.sup.-1 and 0.021 m.sup.2 C.sup.-1 to 2.50 x 10.sup.-10 m v.sup.-1, 0.047 m.sup.2 C.sup.-1 and 16.63 x 10.sup.-6 Pa.sup.-1/2, respectively, for N.sub.0.52B.sub.0.52T-0.06BT composition at RT. Furthermore, N.sub.0.52B.sub.0.52T-0.06BT composition shows a huge enhancement in F.sub.i, F.sub.v and F.sub.D to 26.9 x 10.sup.-10 m v.sup.-1, 0.39 x 10.sup.-10 m.sup.2 C.sup.-1 and 138.7 x 10.sup.-6 Pa.sup.-1/2, respectively, at T.sub.d. The same composition also presents F.sub.C values which are ~2.58 and ~2.86 (x10.sup.-9 C cm.sup.-2 °C.sup.-1) at RT at 100 and 1000 (Hz). N.sub.0.5B.sub.0.534T-0.06BT and N.sub.0.5B.sub.0.534T-0.06B.sub.1.02T compositions show a large p values at a wide temperature range. The enhanced pyroelectric properties make nonstoichiometry N.sub.0.52B.sub.0.52T-0.06BT composition a promising candidate for pyroelectric and other applications at wide temperatures range.
The development of novel high-temperature structural and multifunctional thermal protection materials for harsh environment applications, such as high-temperature oxidation, severe thermal shock, ...ablation by combustion gas flow etc., is one of the urgent needs of the modern aerospace industry. Ceramic matrix composites such as Cf/(C, SiC, Si3N4), SiCf/ZrB2, SiCp/(Si3N4, HfB2) have received much attention in recent years. Coincidently, metastable silicoboron carbonitride (Si-B-C-N) ceramics and corresponding matrix composites stand out from all recent materials offering great potential at high temperatures due to their high microstructural stability and excellent high-temperature properties including resistance to oxidation, thermal shock and ablation. Using inorganic powders (such as Si, C, B, BN, etc.) instead of organic precursor as raw materials, the inorganic processing route based on mechanical alloying (MA), one of the non-equilibrium processing technique, coupled with sequential sintering, although apparently very ‘hard’ compared to the ‘soft’ polymer precursor method, is actually a simple and effective way to prepare monoliths with the uniform microstructures and superior properties. It has been used to obtain dense Si-B-C-N monoliths and structural parts stable at high temperatures providing new experimental data and therefrom a more detailed understanding of the intrinsic properties of metastable Si-B-C-N materials, benefitting progress towards engineering applications. This review summarizes the state-of-the-art research in Si-B-C-N ceramics and their matrix composites obtained by the inorganic processing route in the last decade compared with those of precursor-derived counterparts, including material design and preparation, microstructural features and evolutionary process, mechanical and thermophysical properties, resistance to oxidation, thermal shock and ablation, and the mechanisms of oxidation, ablation and crystallization of amorphous Si-B-C-N ceramics. Future trends for Si-B-C-N relevant materials are also pointed out.
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