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Nanocrystalline oxides have been studied for their excellent mechanical and optical properties as well as their great chemical stabilities. These properties make them ideal materials for applications such as armored windows, laser gain media, and catalyst supports. Despite their desirable properties, we have a limited understanding of their mechanical behavior at small grain sizes. This makes it difficult to predict and tailor their properties for commercial applications. Furthermore, this class of materials is inherently metastable due to the sizeable energy contributions from their large interfacial areas. This high energy makes them susceptible to coarsening and grain growth which would diminish the properties that make them desirable. This work will focus on addressing these two issues by studying nanocrystalline zinc aluminate (ZnAl2O4) as a model material. This material was chosen due to its relatively high thermal conductivity which makes it a more attractive material, particularly for laser gain media and catalyst supports, than other oxides.The first goal of this work will address the interfacial stabilities of zinc aluminate nanoparticles and fully dense samples. Solid-solid (surface) and solid-vapor (grain boundary) interfacial energies were tailored using dopant segregation as predicted by molecular dynamics simulations: atomistic simulations on a nanoparticle and two grain boundary structures were used to assess the segregation behavior of four dopants [Sc3+ (74.5 pm), In3+ (80.0 pm), Y3+ (90.0 pm), and Nd3+ (98.3 pm)]. The candidate dopants were chosen to induce segregation by maximizing the elastic strain in the lattice (i.e., large ionic radii). All four dopants were estimated to have favorable segregation energies to surfaces and grain boundaries with Y3+ consistently having the lowest energies at interfaces. Accordingly, undoped and doped (0.5 mol% Y2O3) were prepared to experimentally compare their interfacial energies and coarsening behaviors. Surface energies were estimated by water adsorption microcalorimetry which revealed that surface stabilities were effectively improved in doped nanopowders, as predicted in simulations. This behavior was correlated with coarsening inhibition and lower estimated diffusion coefficients, indicating Y3+ improves zinc aluminate stability against coarsening via kinetics and thermodynamics. Similarly, differential scanning calorimetry was used to measure grain boundary energies as a function of grain size for fully dense samples from both compositions. Grain boundary energies were lower for doped samples at each grain size studied which not only predicts limited grain growth for dense samples, but also elevated hardness and toughness.The mechanical performance (i.e., hardness and toughness) of Y-doped and undoped samples were compared to identify the effects of improved grain boundary stabilty. Hardness and toughness values were statistically similar for both compositions, indicating the dopant had negligible effects on zinc aluminate mechanical properties using a concentration of 0.5 mol%. The only exception was at larger grain sizes (above 25 nm) where Y-doped samples had significantly higher hardness. This was presumed to be a result of higher concentrations of Y3+ in these samples due to lower grain boundary area, hence limiting grain boundary mediated deformation or improving dislocation pinning from dopants segregated to dislocation cores. A more pronounced effect on mechanical properties was found when comparing stoichiometric zinc aluminate (Al:Zn = 2.01:1) to Al-rich zinc aluminate (Al:Zn = 2.87:1). Stoichiometric zinc aluminate exhibited elevated hardness with decreasing grain size until grain sizes of ~20 nm, while Al-rich samples underwent further hardening to grain sizes near 12 nm. Distinct cracking patterns were observed in both samples, suggesting the excess Al postponed the softening by stabilizing high-energy grain boundaries. The results from this work show that interfacial stability can be enhanced significantly by doping zinc aluminate with Y3+. This can be used to effectively tune zinc aluminate coarsening behavior at the nanoscale. The present work also showed that excess Al can be used to tune the grain size hardening behavior of nanocrystalline zinc aluminate; however, it remains unclear whether a similar effect can be induced by doping with Y3+ due to the low concentrations used here. These conclusions will prove beneficial as we employ nanocrystalline ceramics for the next generation of armored windows and catalysts.

Alloy-type anodes are promising next-generation electrodes for Li-ion batteries because of their high specific capacity, but the severe volume expansion causes fast capacity decay. Here, two methods were explored to improve alloy-type anodes. First, a thermodynamically driven grain boundary engineering was proposed as a potential strategy. SnSb with Bi addition fabricated through ball milling and annealing was selected as a model system. The Bi-doped SnSb demonstrated improved cycling performance with < 1% porosity. Transmission electron microscopy shows grain boundaries Bi segregation, and thermodynamic modeling further indicates the stabilization of a nanoscale liquid-like interfacial phase. In situ X-ray microscopy shows the crack suppression effect for the Bi-doped sample, suggesting a potential grain boundary sliding as a stress relief mechanism. Second, cryogenic milling was demonstrated as a novel method to engineer alloy-type anodes. This process can suppress cold welding, exfoliate bulk graphite into multilayer graphene, and evenly disperse them between the grains to form nanostructured electrodes. Based on the cross-section electron microscopy and X-ray microscopy, the dispersed graphene between the nanosized grains can effectively alleviate the volume expansion upon lithiation. Compared to the traditional ball milling methods under room temperature, the cryomilled SnSb-C composite anode showed improved cycling stability and rate capability. For ceramic processing methods, electric field assisted sintering process can have a lower sintering temperature and faster sintering time compared to conventional sintering. For the second part of the thesis, nonthermal electric field effects on ZnO polycrystalline specimen was investigated. In undoped ZnO, electric field can induce defect polarization and subsequently alter the grain boundary structure. We also demonstrated the possibility of creating and controlling graded microstructure via electric fields. In Bi2O3-doped ZnO, electric field can drive the migration of Bi-rich secondary liquid phase. In summary, the first part of the dissertation introduces grain boundary engineering and cryogenic milling as two novel approaches to improve alloy-type battery electrodes. The second part of the dissertation investigated electric field effects on ceramic microstructure evolution. The feasibility of tailoring ceramic microstructure with electric field was demonstrated.

Aiming to elucidate the hydrogen absorption/desorption cycling properties of Mg-based alloys with in-situ formed Mg2Ni and LaHx (x = 2, 3) nanocrystallines, the hydrogen storage cycle stability, hydriding/dehydriding cycling kinetics and thermodynamic stability of the experimental alloys have been investigated in detail. The results show that the Mg–Ni–La alloys exhibit improved hydrogen storage cycling properties and can remain storage hydrogen above 5.5 wt% after 200 cycles. With the increase of cycling numbers, the dehydrogenation rates of the experimental samples increase firstly and then gradually decrease, and eventually maintain relative stable state. Microstructure observation reveals that powders sintering and hydrogen decrepitation both exist during hydrogen absorption/desorption cycles due to repeated volume expansion and contraction. Meanwhile, the in-situ formed LaHx (x = 2, 3) and Mg2Ni nanocrystallines stabilize the microstructures of the particles and hinder the powders sintering. After 200 cycles, the average particle size of the experimental samples decreases and the specific surface area apparently increases, which leads to the decomposition temperatures of MgH2 and Mg2NiH4 slightly shift to lower temperatures. Moreover, Mg2Ni and LaHx (x = 2, 3) have been proven to be stable catalysts during long-term cycling, which can still uniformly distribute within the powders after 200 cycles.

Current wood-plastic materials available for selective laser sintering (SLS) are limited and often suffer from low-quality and mechanical strength. In this study, a new composite of peanut husk pow...

In this technical world, the properties and internal structure of materials renders a vital part in building up of the components for various specific purposes and improvise their efficiencies in a better way. The combination of copper with other metals is always an interesting one. In this, brass of grade BS90 is an alloy of zinc added with copper and it is lustrous in nature. The amount of zinc that is mixed with copper can be varied to develop different categories of brass with different melting temperatures that develops distinct electrical and mechanical potency. In the process of better understanding of the powder metallurgy technique and analyzing and improvising the properties of brass, this research is carried out. Primarily, this process is carried out based on the powder metallurgy technique. The prime intention of this investigation is to develop and process the specimens under predetermined conditions of powder metallurgy and then their mechanical hardness and the microstructure are to be characterized. The secondary objective is to analyze these characteristic values and compare them relatively to the specified conditions.

Monolithic catalysts have attracted attention as a substitute for particulate catalyst beds in gas-liquid-solid three-phase reactions. In this work, carbon gel monoliths with a microhoneycomb structure (carbon gel microhoneycombs, CMHs) were synthesized, and Pt particles with an average particle diameter of 3.0 nm were supported on them in a highly dispersed state through the incipient wetness method. In addition, it was confirmed that the supported Pt shows a high resistance to sintering. Hydrogenation of p-nitrophenol was carried out in order to evaluate the catalytic activity of Pt/CMHs in three-phase reactions. As a result, Pt/CMHs showed a high catalytic activity even at ambient temperature and normal pressure. Furthermore, the hydrogenation reaction significantly proceeded even when hydrogen was provided at the minimum flow rate required to complete the reaction. Since Pt/CMHs showed higher reaction activity than the same catalyst in the form of particles, it was concluded that the efficiency of three-phase reactions can be significantly improved by using monolithic catalysts with a microhoneycomb structure.

Atomically dispersed precious metal catalysts maximize atom efficiency and exhibit unique reactivity. However, they are susceptible to sintering. Catalytic reactions occurring in reducing environments tend to result in atomically dispersed metals sintering at lower temperatures than in oxidative or inert atmospheres due to the formation of mobile metal-H or metal-CO complexes. Here, we develop a new approach to mitigate sintering of oxide supported atomically dispersed metals in a reducing atmosphere using organophosphonate self-assembled monolayers (SAMs). We demonstrate this for the case of atomically dispersed Rh on Al2O3 and TiO2 using a combination of CO probe molecule FTIR, temperature programmed desorption, and alkene hydrogenation rate measurements. Evidence suggests that SAM functionalization of the oxide provides physical diffusion barriers for the metal and weakens the interactions between the reducing gas and metal, thereby discouraging the adsorbate-promoted diffusion of metal atoms on oxide supports. Our results show that support functionalization by organic species can provide improved resistance to sintering of atomically dispersed metals with maintained catalytic reactivity.

Development of methane dry reforming catalyst is very important for economical production of syngas from CH4 and CO2 and reduction of greenhouse gases. Ni-based hydrotalcite derived spinel catalysts were synthesized for dry reforming of methane (DRM). Properties of the catalyst such as reducibility, basicity, morphology, texture and crystal structure, had a great impact on catalyst’s activity and stability. Superior catalytic activity and stability during DRM process was achieved with the formation of hydrotalcite derived spinel (NiAl2O4) structures, eruption of carbon nanofibers (CNFs) from carbon layer, and formation of Ni0 active sites on the tips of these CNFs. The Ni particles from reduction of NiO and NiAl2O4 evolved on top of the CNFs and provided a strong metal–support interactions resulting in high resistance against sintering and coking at 850 °C during the long-term DRM process (200 h).

MgAl2O4 spinel mesh with micro-features of 410 and 250 μm unit cell length and rib thickness, respectively, was three-dimensional (3D) printed and sintered followed by Hot Isostatic Pressing (HIPin...

La2Sn2O7/SnO2 powder was synthesized by chemical co-precipitation method, and Ag-La2Sn2O7/SnO2 composites were prepared by hot-pressing sintering. The electrical resistivity, density, Brinell hardness and flexural strength of Ag-La2Sn2O7/SnO2 composites were measured. Moreover, the effect of La2Sn2O7 content on the arc erosion behavior of Ag-La2Sn2O7/SnO2 composites at 7 kV voltage was studied. With the increase of La2Sn2O7 content, the arc duration and arc energy decrease, and the breakdown strength increases. The surface morphology of Ag-La2Sn2O7/SnO2 composites after arc erosion was investigated using scanning electron microscopy and three-dimensional laser confocal scanning microscopy. With the increase of La2Sn2O7 content, the smaller the erosion damage, the better the anti-arc erosion performance. However, too much La2Sn2O7 results in the decrease of Ag-La2Sn2O7/SnO2 properties and severe arc erosion. X-ray photoelectron spectroscopy was used to determine the composition of the erosion region. The effect of La2Sn2O7 on wettability between Ag and SnO2 was investigated, and the erosion mechanism of Ag-La2Sn2O7/SnO2 composites was discussed systematically. This study can provide a reference for the application of Ag matrix electrical contact materials in high-voltage electrical appliances.

The superlattice La-Y-Ni-based hydrogen storage alloys have high discharge capacity and are easy to prepare. However, there is still a gap in commercial applications because of the severe corrosion of the alloy in electrolyte and poor high-rate dischargeability (HRD). Therefore, (LaSmY)(NiMnAl)3.5 alloy was prepared by magnetic levitation induction melting, and then the alloy was coated with different contents (0.1 wt%–1.0 wt%) of nano-carbons by low-temperature sintering with sucrose as the carbon source in this work. The results show that the cyclic stability and HRD of the alloy first increase and then decrease with the increase of carbon contents. The kinetic results show that the electrocatalytic activity and conductivity of the alloy electrodes can be enhanced by carbon coating. The electrochemical properties of the alloy are the best when the carbon coating content is 0.3 wt%. Compared with the uncoated alloy, the maximum discharge capacity (Cmax) improves from 354.5 to 359.0 mAh/g, the capacity retention rate after 300 cycles (S300) enhances from 73.15% to 80.01%, and the HRD1200 of the alloy enhances from 74.39% to 74.39%.

This study investigates the synthesized NiO- and CuO-based carriers supported by Al2O3, CeO2, ZrO2 and their combinations in chemical looping combustion (CLC). The oxygen carriers were tested in a thermogravimetric analyzer (TGA), where the results showed that the oxygen capacity increased using mixed support oxides in both NiO-based and CuO-based samples. The reducibility of CeO2 played a role in the increase of oxygen capacity and in the case of NiO-based samples, the reduction of NiAl2O4 phase as promoted by the formation of CeAlO3 played a role, as well. For NiO-based samples, a significant increase of carbon deposition occurred for mixed support oxides (Al2O3-ZrO2, Al2O3-CeO2 and Al2O3-ZrO2-CeO2) at 750 °C in comparison with the use of one support while the differences were negligible at 950 °C. To examine the structure and properties of the oxygen carriers, they were characterized by XRD, SEM/EDX and XPS. Comparison of fresh and used samples revealed sintering of active-sites particles on the surface of supports as evident of EDX mapping images and the decrease in active-site to support ratio in the XPS analysis. NiO/Al2O3-ZrO2-CeO2 was found to be a potential oxygen carrier for further CLC studies and scaleup.

To evaluate the effect of sintering speed and polishing or glazing on the failure load (FL) of monolithic zirconia fixed partial dentures (FPDs).A total of 40 three-unit FPDs extending from the mandibular first premolar to the first molar were evaluated. The prepared typodont teeth were scanned, and the prostheses were designed. Afterwards, the prostheses were milled from monolithic zirconia blanks. The samples were divided into classic and speed sintering groups (n = 20 each). Half of the samples in each group (n = 10) were polished with an electric handpiece according to the manufacturer's instructions, and the other half (n = 10) were glazed. All of the samples were thermocycled for 3,500 cycles between 5ºC and 55ºC in water baths. The FL was calculated in Newtons with the three-point bending test.The mean ± SD FL values were as follows: classic sintering/polished group = 2,026.5 ± 172.8 N; classic sintering/glazed group = 1,917.58 ± 174.45 N; speed sintering/polished group = 1,787.58 ± 145.81 N; and speed sintering/glazed group = 1,719.6 ± 143.9 N. There was a significant difference in the mean FL between the two sintering methods (P.001), with the classic sintering group exhibiting the highest FL.Classic sintering of the monolithic zirconia FPDs led to the maximum amount of FL and strength.

In this article, it is intended to evaluate the performances of previously synthesized different nanometric compounds as SOFC components under real conditions. For this purpose, anodic supports SOFCs have been manufactured in different configurations. The compounds NiO-(Y2O3)0.08(ZrO2)0.92 (NiO–YSZ), (Y2O3)0.08(ZrO2)0.92 (YSZ), Sm0.2Ce0.8O1.9 (SDC), La0.6Sr0.4FeO3 (LSF) and LaNi0.6Fe0.4O3 (LNF) were used as anode support, electrolyte, barrier, cathode and contact layer, respectively. To obtain the cells, the anode supports were produced by uniaxial pressing and the remaining layers were added using the airbrush technique, assembling them by different sintering processes. The cells developed have been electrochemically tested in a temperature range between 750 and 865 °C. Additionally, degradation tests have been carried out under constant current. Moreover, to characterize the microstructure of the cells, a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDX) analyzer has been used. The results obtained show that the incorporation of cathode and contact layers increases the power densities and decreases the total resistances of the cells with respect to the cell without cathode, especially with the addition of the LNF contact layer. Despite the improvement obtained, more tests have to be carried out in order to optimize the performance of SOFC devices in degradation tests.

This study focused on chromium addition (0 wt%, 3 wt%, 6 wt%, 9 wt% and 12 wt%) on the boride layer formation, microhardness, fracture toughness and elevated temperature friction and wear behaviour of alloys formed by powder metallurgy (P/M). The boride layers obtained on P/M alloys were characterized by examining density, porosity, surface roughness, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray difraction, surface proflometry, microhardness, and fracture toughness. The addition of Cr has a signifcant efect on both boride layer formation and friction-wear behaviour of P/M alloys. Increasing the Cr addition up to 6 wt% has an improving efect on the microhardness, fracture toughness and wear resistance of the P/M alloys, whereas in the case of 9–12 wt% Cr addition causes exfoliation in the boride layer and low fracture toughness, thus reducing wear resistance. Coefcients of friction and wear volume losses at elevated temperatures are higher than room temperature. The best wear resistance at room temperature was obtained in the sample containing 3 wt% Cr with the highest fracture toughness, while the best wear resistance at 250 °C and 500 °C was obtained in the sample containing 6 wt% Cr, where the highest hardness value was obtained.

To upgrade the electric properties of lead-free piezoceramics, (1–x)(Ba0.98Ca0.02Ti0.94Sn0.04Zr0.02)O3-xY2O3 (abbreviated as (1–x)BCTSZ-xY, x = 0 mol%, 0.02 mol%, 0.04 mol%, 0.06 mol%, 0.08 mol% and 0.1 mol%) ceramics were successfully synthesized by traditional solid-state sintering method. The phase structure and microstructure of ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and piezoresponse force microscopyeramics (PFM). The electric properties of ceramics were researched through piezoelectric, dielectric and ferroelectric test instruments. The results show that all samples have pure perovskite structure and favorable electric properties. The optimal electric properties which especially include superior ferroelectric properties are gained when Y2O3 content is 0.06 mol% (d33 = 419 pC/N, kp = 52%, Tc = 89.5 °C, er = 26900, tanδ = 2.86%, Pr = 14.41 μC/cm2, Ec = 1.8 kV/cm). Moreover, the temperature-dependent dielectricity of samples shows apparent relaxor behavior under different frequencies. The Curie–Weiss law further proves that all samples are typical relaxor ferroelectrics, and the relaxor degree of samples decreases with increase of Y2O3 content. In conclusion, Y2O3 plays a significant role in enhancing electric properties of BCTSZ ceramics.

Additive manufacturing (AM) of Ti-6Al-4V enables rapid fabrication of complex parts, including porous lattices which are of interest for aerospace, automotive, or biomedical applications, however currently the fatigue resistance of these materials is a critical limitation. Engineering the alloy microstructure provides a promising method for increasing fatigue strength, but conventional heat treatment procedures are known to produce atypical results for AM and porous samples, and must therefore be optimised for these materials. Using vacuum heat treatment, microstructures comparable to those observed for conventional wrought and heat treated alloys were achieved with porous AM Ti-6Al-4V. Fine lamellar microstructures were produced using sub-transus heat treatment at 920 °C, while coarse lamellar microstructures were produced using super-transus heat treatment at 1050 °C or 1200 °C. Increasing the heat treatment temperature increased the elastic modulus from 2552 ± 22 MPa to a maximum of 2968 ± 45 MPa, due to strut sintering increasing the effective strut thickness, and removal of prior β-grain orientation. Heat treatment eliminated the brittle α’ martensite phase in favour of an α + β mixture, where the phase boundaries and β-phase provide greater resistance to crack propagation. Super-transus heat treatments increased the α-lath size which typically reduces crack propagation resistance, however strut sintering reduced surface crack initiation sites, increasing the fatigue strength by 75% from 4.86 MPa for the as-built material to a maximum of 8.51 MPa after 1200 °C heat treatment. This work demonstrates that vacuum heat treatment is effective at tuning the micro- and macro-structure of porous AM Ti-6Al-4V, thereby improving the crucial fatigue resistance.

The method of using an applied electric field during the sintering process (flash sintering) has the potential to be a cost and energy saving method for the manufacturing of many ceramic products. Since flash sintering is still an emerging field of research, most of the work has been centered on single phase systems. This study will evaluate the viability of applying flash sintering to a multiphase composite system; more specifically ceramic composites consisting of Al2O3 (alumina), 8 mol % yttria-stabilized zirconia (8YSZ), and MgAl2O4 (Spinel). Various flash sintering conditions were studied, as well as in-situ characterization methods. By tailoring the flash sintering parameters, fully dense, fine grained, three-phase composites were formed with improved mechanical properties. Reaction sintering was also found to be possible with flash sintering of multiphase composites, with the formation of high alumina spinel specifically. In addition, 8YSZ was discovered to have a catalytic effect with flash sintering. The results of this study show that flash sintering has promise as a quick and energy efficient method to sinter complex systems as well as form unique phases when applied to ceramic composites.

Solid-state activated sintering of TiO2-CuO system was systematically studied to reveal the effects of grain boundary structures on low temperature densification. Specifically, the eutectic temperature and composition of the TiO2-CuO system were carefully measured to be 1010 ± 10 °C and 83CuO:17TiO2, respectively. Subsequently, a TiO2-CuO phase diagram was computed. Activated (enhanced) sintering of TiO2 with the addition of CuO occurring at >300 °C below the eutectic temperature was observed. High resolution transmission electron microscopy (HRTEM) characterization of water-quenched specimens revealed the formation of nanometer-thick, liquid-like, intergranular films (IGFs), a type of grain boundary (GB) complexion, concurrently with accelerated densification and well below the bulk eutectic temperature. Consequently, activated sintering is explained from the enhanced mass transport in this premelting-like complexion. An interfacial thermodynamic model was used to quantitatively explain and justify the stabilization of liquid-like IGFs below the eutectic temperature and the temperature-dependent IGF thicknesses. A GB λ diagram was computed, for the first time for a ceramic system, to represent the thermodynamic tendency for general grain boundaries to disorder.Activated flash sintering of ZnO through a bulk phase transformation or a GB complexion transition was investigated. Specifically, in undoped and Al2O3-doped ZnO, the flash sintering is activated by natural thermal runways that can be quantitively predicted. In contrast, a bulk eutectic reaction and the associated formation of premelting-like IGFs in Bi2O3-doped ZnO can lead to a nonlinear rise in the specimen conductivity (above the Arrhenius extrapolation) to trigger flash sintering prior to the occurrence of the predicted natural thermal runaway. This work uncovers the roles of the bulk phase and interfacial (phase-like) complexion transformations in initiating flash sintering. Beyond high temperature interfacial liquids, water was used as an example of low temperature, transient, interfacial liquid to activate flash sintering at room temperature. ZnO powder pellets was water-assisted flash sintered (WAFS) to achieve ~ 98% of the theoretical density in 30 s without any external furnace heating. The specimen conductivity can be increased by > 10,000 times via absorbing water vapor to enable the room-temperature flash. The initial electric field must be higher than a critical threshold to lead to densification, suggesting bifurcation in kinetic pathways.Another method called two-step flash sintering (TSFS) was proposed as a new ceramic fabrication method to achieve fast densification with suppressed grain growth. Using ZnO as an examplar, ~ 96.5% of theoretical density was achieved using TSFS with a grain size of ~ 370 nm, representing a > 3 times reduction of the grain size in comparison with conventional flash sintering. TSFS achieved this result in a few minutes, > 200 times faster than that needed for conventional two-step sintering to obtain comparable results.Lastly, the effect of electric field on grain growth and grain boundary structure was studied in the presence of ionic grain boundary liquids at high temperatures. Using Bi2O3-doped ZnO as a model system, this study reveals the electrochemical polarization of ionic defects driven by an external electric field and current. A mixed conducting model was developed to explain the asymmetric grain growth of sandwiched single crystal, abnormal grain growth near the cathode, as well as the pore formations. The ionic blocking, electric conducting single crystal decouples the effect of electric potential and electrochemical potential on grain growth. It is assumed that electric field and current polarized ionic defects and thereafter modified local space charges. Grain boundary complexion transitions were also observed after annealing under electric field and current.

Usually the improved coercivity of rare earth (RE) based 2:14:1-type permanent magnets via RE-rich intergranular additives is achieved at the cost of more corrosion channels and deteriorated corrosion resistance, which remains a challenging hurdle in the RE-Fe-B community. Distinctly, here we report the concurrent improvements of corrosion resistance and coercivity in 40 wt.% Ce-substituted Nd-Ce-Fe-B sintered magnets through engineering the intergranular phase using simple (Nd, Pr)Hx additive. The dehydrogenated Nd/Pr changes the RE concentration gradients between 2:14:1 matrix and intergranular phases during sintering and enlarges the fraction of corrosion-resistant REFe2 phase, rather than the conventionally assumed Nd/Pr-rich intergranular phase with high chemical vulnerability. The spontaneous formation of REFe2 intergranular phase after (Nd, Pr)Hx addition generates the uniquely enhanced corrosion resistance against the hot/humid and acidic environments, and counts as one peculiar feature of Nd-Ce-Fe-B magnets at high Ce substitution level, being distinct from previously reported Ce-free/lean RE-Fe-B. Simultaneously, the formation of continuous grain boundaries enhances the coercivity from 8.7 to 12.5 kOe with trace addition of (Nd, Pr)Hx. Above findings may spur progress towards developing a high-performance Nd-Ce-Fe-B permanent magnet.

Sensors are crucial in the understanding of machines working under high temperatures and high-pressure conditions. Current devices utilize polymeric materials as electrical insulators which pose a challenge in the device’s lifespan. Ceramics, on the other hand, is robust and able to withstand high temperature and pressure. For such applications, a co-fired ceramic device which can provide both electrical conductivity and insulation is beneficial and acts as a superior candidate for sensor devices. In this paper, we propose a novel fabrication technique of complex multi-ceramics structures via 3D printing. This fabrication methodology increases both the geometrical complexity and the device’s shape precision. Structural ceramics (alumina) was employed as the electrical insulator whilst providing mechanical rigidity while a functional ceramic (alumina-doped zinc oxide) was employed as the electrically conductive material. The addition of sintering additives, tailoring the printing pastes’ solid loadings and heat treatment profile resolves multi-materials printing challenges such as shrinkage disparity and densification matching. Through high-temperature co-firing of ceramics (HTCC) technology, dense high quality functional multi-ceramics structures are achieved. The proposed fabrication methodology paves the way for multi-ceramics sensors to be utilized in high temperature and pressure systems in the near future.

By intergranular addition of Pr-Cu-Ti alloy powders in the Nd-Fe-B sintered magnets with the normal B component, we propose an approach to the optimization of grain boundary and local Nd-Fe-B composition system. The coercivity is enhanced from 1.42 to 1.86 T, while further addition leads to a reduction in remanence and coercivity. The analyses of phase composition reveal that Ti mainly exists in the form of metallic Ti alloy, and part of Ti combines with B to form the TiB2 phase after the liquid phase sintering process. This process results in a consumption of B in the local Nd-Fe-B composition system and a change of the grain boundary component, which contributes to the formation process of the RE6(Fe,M)14 phase after the annealing process. Therefore, with the modification of grain boundary and composition system, the intergranular addition of Pr-Cu-Ti induces the generation of continuous thin grain boundary phases. It promotes the intergrain exchange decoupling, increasing the coercivity in the annealed magnet. While the excess addition results in the segregation of TiB2, as well as the precipitation of TiB2 into the Nd-Fe-B phase, which leads to structural defects. Thus, the further effort for the addition alloy with Ti to reduce the deterioration of the microstructure will lead to a further improvement in magnetic properties.

In this study, the variation of microstructural properties in porcelain stoneware tiles was determined by changing the holding time at peak temperature during sintering, and effects of these microstructural changes on impact resistance of porcelain stoneware tiles were examined. Only the F4 samples passed the impact resistance test according to CSTB-NF-UPEC test. This sample has 12.3 wt.% quartz, 1.5 wt.% corundum, 5.8 wt.% anorthite, 13.5 wt.% mullite, and 66.9 wt.% glassy phase. When the relationship between mechanical properties and impact resistance was evaluated, it should be emphasized that only F4 sample with a breaking strength higher than 75 MPa passed the impact test. It can be said that there is a critical threshold in terms of impact resistance, especially for samples which have bending strength greater than 75 MPa. When evaluating the microstructural details, this study shows that a single crystalline phase is not effective for impact resistance behavior of the porcelain stoneware tiles and many factors should be evaluated together.