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The abruptly increased dielectric loss in graphene oxide (GO) induced by high-temperature sintering has prevented GO from being used as an absorbent in ceramic-matrix microwave absorbing composites (MACs). Here, we show the first example that the pristine structure of GO can be largely preserved in ceramic composite by using cold sintering technology. Compared with the composites densified by ordinary spark plasma sintering, cold sintered samples possess lower complex permittivity and superior impedance matching. Therefore, the cold sintered ZnO composite with 0.50 wt% GO loading shows the minimum reflection loss of -47.5 dB at thickness of 3.2 mm, and the effective absorption bandwidth of 4.4 GHz at thickness of 1.7 mm. Moreover, both flexural strength and hardness of the cold sintered composite are improved considerably compared to the monolithic cold sintered ZnO. These findings imply that cold sintering enables the thermally unstable materials to be applied in highly effective MACs with robust mechanical performance.

Reactive spark plasma sintering has been utilised as a high-throughput processing route for the synthesis of two simulant zirconolite wasteform materials, targeting Ca0.80Ce0.20ZrTi1.60M0.40O7 (M = Fe3+ and Al3+). Materials were processed under 15 MPa uniaxial pressure, with heating/cooling rates of 100 °C/min to 1320 °C, maintained under vacuum. Despite moderate yield (> 80 wt%) of zirconolite-2M, a considerable Ce-rich perovskite phase was formed in both formulations, attributed to complete reduction of the Ce inventory to Ce3+, as determined by Ce L3-edge XANES analysis. The composition charge balanced with Al3+ was favoured on the basis of lower accompanying perovskite fraction. Graphical abstract

Na2O–Bi2O3–MoO3 ternary microwave dielectric ceramics with high-performance properties have good potential in the application of LTCC/ULTCC technology.

The sinterability, microstructure, and mechanical properties of pure TiB2- and CrB2-doped ZrB2 prepared by spark plasma sintering were investigated. The solid solutions were synthesized by the complete borothermal reduction to form (Zr0.95Ti0.05)B2 and (Zr0.95Cr0.05)B2. The results showed that the solid solution of (Zr0.95Ti0.05)B2 yielded the smaller particle size than that of (Zr0.95Cr0.05)B2. The sinterability was also improved with the use of the solid solutions, as evidenced by an increase of relative density but at the cost of coarsened microstructure. Overall, (Zr0.95Cr0.05)B2 possessed significantly higher relative density and Vickers hardness than ZrB2 and (Zr0.95Ti0.05)B2.

This work elaborates and evaluates approaches to the construction of 2D speciation maps, in an effort to maximize sensitivity to the U oxidation state at the U L 3-edge, applied to a suite of synthetic Chernobyl lava specimens., Uranium speciation and redox behaviour is of critical importance in the nuclear fuel cycle. X-ray absorption near-edge spectroscopy (XANES) is commonly used to probe the oxidation state and speciation of uranium, and other elements, at the macroscopic and microscopic scale, within nuclear materials. Two-dimensional (2D) speciation maps, derived from microfocus X-ray fluorescence and XANES data, provide essential information on the spatial variation and gradients of the oxidation state of redox active elements such as uranium. In the present work, we elaborate and evaluate approaches to the construction of 2D speciation maps, in an effort to maximize sensitivity to the U oxidation state at the U L 3-edge, applied to a suite of synthetic Chernobyl lava specimens. Our analysis shows that calibration of speciation maps can be improved by determination of the normalized X-ray absorption at excitation energies selected to maximize oxidation state contrast. The maps are calibrated to the normalized absorption of U L 3 XANES spectra of relevant reference compounds, modelled using a combination of arctangent and pseudo-Voigt functions (to represent the photoelectric absorption and multiple-scattering contributions). We validate this approach by microfocus X-ray diffraction and XANES analysis of points of interest, which afford average U oxidation states in excellent agreement with those estimated from the chemical state maps. This simple and easy-to-implement approach is general and transferrable, and will assist in the future analysis of real lava-like fuel-containing materials to understand their environmental degradation, which is a source of radioactive dust production within the Chernobyl shelter.

Although the strengthening and toughening effects on ceramic composites are expected to be maximized by alignment of multi-walled carbon nanotubes (MWCNTs) in matrices, this concept has been rarely realized in practice due to the lack of convenient processing strategy. Here, the alignment of MWCNTs in alumina composite can be readily obtained by using α-Al2O3 nanoplates as raw powder. With the assistance of vacuum filtration and pressure in sintering, the highly aligned MWCNTs in alumina matrix are formed in in-plane direction. Accordingly, the strength and toughness in 1.5 wt% MWCNTs/alumina composite are improved by 58 % and 66 % with respect to monolithic alumina, respectively. Transmission electron microscopy observation reveals that the MWCNTs under great compressive residual stress are mainly embedded inside the grains, leading to much stronger grain boundaries. Meanwhile, the toughening effect is mainly attributed to the highly energy dissipating bridging and pullout, owing to the very effective load transfer.

Background Tumor-associated macrophages (TAMs) are the most abundant stromal cells in the tumor microenvironment. Turning the TAMs against their host tumor cells is an intriguing therapeutic strategy particularly attractive for patients with immunologically “cold” tumors. This concept was mechanistically demonstrated on in vitro human and murine lung cancer cells and their corresponding TAM models through combinatorial use of nanodiamond-doxorubicin conjugates (Nano-DOX) and a PD-L1 blocking agent BMS-1. Nano-DOX are an agent previously proved to be able to stimulate tumor cells’ immunogenicity and thereby reactivate the TAMs into the anti-tumor M1 phenotype. Results Nano-DOX were first shown to stimulate the tumor cells and the TAMs to release the cytokine HMGB1 which, regardless of its source, acted through the RAGE/NF-κB pathway to induce PD-L1 in the tumor cells and PD-L1/PD-1 in the TAMs. Interestingly, Nano-DOX also induced NF-κB-dependent RAGE expression in the tumor cells and thus reinforced HMGB1’s action thereon. Then, BMS-1 was shown to enhance Nano-DOX-stimulated M1-type activation of TAMs both by blocking Nano-DOX-induced PD-L1 in the TAMs and by blocking tumor cell PD-L1 ligation with TAM PD-1. The TAMs with enhanced M1-type repolarization both killed the tumor cells and suppressed their growth. BMS-1 could also potentiate Nano-DOX’s action to suppress tumor cell growth via blocking of Nano-DOX-induced PD-L1 therein. Finally, Nano-DOX and BMS-1 achieved synergistic therapeutic efficacy against in vivo tumor grafts in a TAM-dependent manner. Conclusions PD-L1/PD-1 upregulation mediated by autocrine and paracrine activation of the HMGB1/RAGE/NF-κB signaling is a key response of lung cancer cells and their TAMs to stress, which can be induced by Nano-DOX. Blockade of Nano-DOX-induced PD-L1, both in the cancer cells and the TAMs, achieves enhanced activation of TAM-mediated anti-tumor response. Graphic abstract

In this paper, (1-x)LiWVO6-xK2MoO4 (LWVO-KMO, x = 60, 65, 70, 75, 80, 90 wt%) composite ceramics with >92% relative density were prepared by cold sintering at 160 °C under a uniaxial pressure of 300 MPa for 1 h. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy demonstrate that LWVO and KMO coexist without other impurities. (1-x)LWVO-xKMO composite ceramics exhibit relative permittivity (er) ranging from 6.8 to 8.5, microwave quality factor (Q × f) ranging from 2050 to 7182 GHz, and temperature coefficient of resonant frequency (τf) ranging from −49 to +25 ppm/°C. Based on cold sintered 30 wt%LWVO-70 wt%KMO composite ceramic with er ~7.8, Q × f ~4514 GHz, and near zero τf ~1.3 ppm/°C, a prototype microstrip patch antenna was designed and manufactured. Through testing, it shows excellent antenna performance with a center frequency of 6.58 GHz, a bandwidth of 170 MHz (−10 dB) and a total efficiency of up to 89.5%.

The solid state synthesis of the phase “Ce3NbO7+δ”, from stoichiometric quantities of CeO2 and Nb2O5, was investigated under air atmosphere, as previously described by Zhang et al. (Journal of Rare Earths, 2007, 25, 730–733). A combination of powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and laboratory Ce L3 X-ray absorption spectroscopy, demonstrates the product of the reaction to be a mixture of CeO2 and CeNbO4. These data, and reexamination of the published X-ray diffraction data of “Ce3NbO7+δ”, are consistent with this phase in fact being CeO2. No evidence for the formation of a phase of composition “Ce3NbO7+δ” is found, by solid state synthesis under air atmosphere.

A sample of zirconolite with nominal composition Ca0.80Ce0.20ZrTi1.60Cr0.40O7was processed via Hot Isostatic Pressing (HIP), with a dwell temperature and pressure of 1320 °C/100 MPa maintained for 4 h. The produced wasteform was characterised by powder XRD, SEM–EDS, Ce L3and Cr K-edge XANES. A significant portion of the Ce inventory did not fully partition within the zirconolite phase, instead remaining as CeO2within the microstructure. Inspection of the stainless steel–ceramic interface detailed the presence of an interaction region dominated by a Cr-rich oxide layer. No significant Cr or Fe migration was observed, although a greater concentration of perovskite was observed at the periphery, relative to the bulk ceramic matrix. The X-ray absorption features of Cr remained analogous with Cr3+accommodation within TiO6octahedra in the zirconolite matrix. The absorption edge of Ce was comprised of contributions from zirconolite-2M and unincorporated CeO2, with an average oxidation state of Ce3.9+. As zirconolite-2M accounted for > 92 wt% of the overall phase assemblage, it is clear that the dominant oxidation state of Ce in this phase was Ce4+.Graphic abstract

A series of zirconolite ceramics with composition CaZr1‐xThxTi2O7 (Δx = 0.10) were reactively sintered at 1350 ˚C for 20 h, in air (0 ≤ x ≤ 0.60) and 5% H2/N2 (0 ≤ x ≤ 0.40). A sample with composition corresponding to x = 0.20 was also produced by hot isostatic pressing (HIP) at 1300 ˚C and 100 MPa for 4 h. Th4+ immobilisation was most readily achieved under oxidising conditions, with Th4+ preferentially incorporated within a pyrochlore‐structured phase in the range 0.10 ≤ x ≤ 0.50, yet formation of the zirconolite‐4M polytype was not observed. We report the novel synthesis of single phase pyrochlore with nominal composition CaZr0.40Th0.60Ti2O7 when targeting x = 0.60. Th4+ incorporation under reducing conditions produced a secondary Th‐bearing perovskite, comprising 24.2 ± 0.6 wt. % of the phase assemblage when targeting x = 0.40, alongside 8.8 ± 0.3 wt. % undigested ThO2. Under reducing conditions, powder XRD data were consistent with zirconolite adopting the 3T polytype structure. The sample produced by HIP presented a non‐equilibrium phase assemblage, yielding a major phase of zirconolite‐2M alongside accessory Th4+ bearing phases ThTi2O6, ThO2 and perovskite. These data highlight the efficacy of Th4+ as a Pu4+ surrogate, with implications for the formation of Zr‐stabilised Th‐pyrochlore phases as matrices for waste with elevated Th4+ content.

Zirconolite (CaZrTi2O7) has been identified as a candidate ceramic wasteform for the immobilisation and disposal of Pu inventories, for which there is no foreseen future use. Here, we provide an ov...

Low-temperature soft chemical synthesis routes to transition-metal nitrides are of interest as an alternative to conventional high-temperature ammonolysis reactions involving large volumes of chemotoxic NH3 gas. One such method is the reaction between metal oxides and NaNH2 at ca. 200 °C to yield the counterpart nitrides; however, there remains uncertainty regarding the reaction mechanism and product phase assemblage (in particular, noncrystalline components). Here, we extend the chemical tool box and mechanistic understanding of such reactions, demonstrating the nitridation of Fe3O4 by reaction with NaNH2 at 170–190 °C, via a pseudomorphic reaction. The more reduced Fe3O4 precursor enabled nitride formation at lower temperatures than the previously reported equivalent reaction with Fe2O3. The product phase assemblage, characterized by X-ray diffraction, thermogravimetric analysis, and 57Fe Mossbauer spectroscopy, comprised 49–59 mol % e-Fe2+xN, accompanied by 29–39 mol % FeO1–xNx and 8–14 mol % γ″-FeN. The oxynitride phase was apparently noncrystalline in the recovered product but could be crystallized by heating at 180 °C. Although synthesis of transition-metal nitrides is achieved by reaction of the counterpart oxide with NaNH2, it is evident from this investigation that the product phase assemblage may be complex, which could prove a limitation if the objective is to produce a single-phase product with well-defined electrical, magnetic, or other physical properties for applications. However, the significant yield of the FeO1–xNx oxynitride phase identified in this study opens the possibility for the synthesis of metastable oxynitride phases in high yield, by reaction of a metal oxide substrate with NaNH2, with either careful control of H2O concentration in the system or postsynthetic hydrolysis and crystallization.

Herein, the structure and dielectric properties of Sm(Nb1−xVx)O4 (SNV-x) (0.0 ≤ x ≤ 0.9) ceramics were studied by crystal structure refinement, Raman, transmission electron microscope (TEM), far-infrared/THz reflectivity spectroscopy and microwave dielectric tests. Three kinds of ultra-low dielectric loss and temperature-stable Sm(Nb1−xVx)O4 (0.2 ≤ x ≤ 0.4) ceramics with permittivities of 18.01–16.89, Q × f values of 97 800–75 200 GHz (@∼8.6 GHz), and TCF of −5.6 (x = 0.2), to +2.3 ppm °C−1 (x = 0.3), then −6.3 (x = 0.4) ppm °C−1 were synthesized in this system. It was found that V5+ substitution can reliably induce the phase transition of monoclinic fergusonite (M-fergusonite, I2/a) to tetragonal zircon phase (T-zircon, I41/amd) (x ≈ 0.3), while effectively reducing the phase transition temperature. TEM shows that there were two different orientation domain structures in the M-fergusonite phase, and the widths of the two domain structures get closer with an increase in B-site substitution. Moreover, the variations in permittivity (er), quality factor (Q × f), and the temperature coefficient of resonance frequency (TCF) were strongly related to the crystal distortion and phase transition. Notably, a rectangular dielectric resonator antenna (RDRA) was fabricated with an Sm(Nb0.8V0.2)O4 (SNV-0.2) specimen. The antenna resonated at 27.04 GHz and had a bandwidth of ∼820 MHz (S11 < −10 dB). This system is a good candidate for 5G and future millimeter-wave applications.

Detailed chemical analysis of the solidified molten fuel still residing in the stricken Chernobyl reactor unit 4 are inferred using multi-modal micro-focus X-ray analysis of a low-radioactivity proxy. A fascinating mixture of molten UO2, nuclear fuel cladding, concrete, stainless steel and other nuclear reactor components, these materials behaved like lava, solidifying to form a complex, highly radioactive glass-ceramic. Using element-specific chemical probes (micro-X-ray fluorescence and X-ray absorption spectroscopy), coupled with micro-diffraction analysis, the crystalline phase assemblage of simulants of these heterogeneous materials was established, which included “chernobylite” and a range of compositions in the (U1−xZrx)O2 solid solution. Novel insight to nuclear accident fuel chemistry was obtained by establishing the oxidation state and local coordination of uranium not only in these crystalline phases, but uniquely in the amorphous fraction of the material, which varied depending on the history of the nuclear lava as it flowed through the reactor. This study demonstrates that micro-focus X-ray analysis of very small fractions of material can yield rich chemical information, which can be applied to nuclear-melt down materials to aid decommissioning and nuclear fuel management at nuclear accident sites.

Textured high-entropy boride ceramics, prototypically (Hf0.2Zr0.2Ta0.2Cr0.2Ti0.2)B2, with nearly single phase were fabricated for the first time by spark plasma sintering (SPS) of the corresponding powder, which was derived from boron/carbothermal reduction. Lotgering orientation factor calculation and the pole figures revealed that the c-axis of high-entropy boride grains aligned parallel to the SPS pressing direction after sintering and grains grew along the a,b-axis to form platelet-like morphology. The remarkably high Vickers’ hardness of ∼29 GPa was observed on both of the side surface and the top surface of textured ceramics. The surface perpendicular to the SPS pressing direction demonstrated an improved fracture toughness owing to the oriented elongated grains.

The joining of liquid-phase sintered SiC (LPS-SiC) ceramics was conducted using spark plasma sintering (SPS), through solid state diffusion bonding, with Ti-metal foil as a joining interlayer. Samples were joined at 1400 °C, under applied pressures of either 10 or 30 MPa, and with different atmospheres (argon, Ar, vs. vacuum). It was demonstrated that the shear strength of the joints increased with an increase in the applied joining pressure. The joining atmosphere also affected on both the microstructure and shear strength of the SiC joints. The composition and microstructure of the interlayer were examined to understand the mechanism. As a result, a SiC-SiC joining with a good mechanical performance could be achieved under an Ar environment, which in turn could provide a cost-effective approach and greatly widen the applications of SiC ceramic components with complex shape.

Praseodymium-doped zirconolite ceramics targeting nominal composition Ca1-xPrxZrTi2-5x/3Al5x/3O7 (x ≤ 0.20, Δx = 0.05) were fabricated by a mixed oxide solid state reaction, at 1350 °C in air for 20 h. Praseodymium (Pr) was employed as a surrogate for neptunium (Np), with Al3+ co-accommodated to provide charge balance. High-resolution transmission electron microscopy and electron diffraction analyses confirmed that zirconolite crystallised as the 2M monoclinic polytype throughout the phase evolution, with no evidence of transformation to other polytype structures. Phase assemblage and microstructural data were consistent with zirconolite occupying a high fraction of the phase assemblage (>ca. 93 wt.%), alongside a minor secondary perovskite phase at all levels of targeted Pr incorporation. Despite this, it was demonstrated near theoretical density formed through a solid-state fabrication route, and we therefore propose that, through analogy with the corresponding Pr solid solution, zirconolite may be a suitable candidate for the immobilisation of Np-bearing wastes.

Struvite-K (MgKPO4·6H2O) is a magnesium potassium phosphate mineral with naturally cementitious properties, which is finding increasing usage as an inorganic cement for niche applications including...

The synthesis, structure, and thermal stability of the periodate double perovskites A2NaIO6 (A= Ba, Sr, Ca) were investigated in the context of potential application for the immobilization of radio...

A series of Ca1-xCexZrTi2-2xCr2xO7 zirconolite ceramics (0 ≤ x ≤ 0.35) were reactively sintered in air at 1350 °C for 20 h. Single phase zirconolite-2M was formed for x ≤ 0.15, with Cr2O3 and an undesirable Ce-bearing perovskite phase present above x = 0.20. Electron diffraction analysis confirmed that the zirconolite-2M polytype was maintained over the solid solution. X-ray absorption near edge structure (XANES) data determined that between 10–20% Ce was speciated as Ce3+, and Cr was present uniformly as Cr3+ with near edge features consistent with occupation of octahedral sites within the zirconolite-2M structure. A sample corresponding to x = 0.20 was processed by reactive spark plasma sintering (RSPS), with a rapid processing time of less than 1 h. XANES data confirmed complete reduction to Ce3+ during RSPS, promoting the formation of a Ce-bearing perovskite, comprising 19.3 ± 0.4 wt. % of the phase assemblage.

Starting from ZrO2 and boron (molar ratio: 1:4), four ZrB2 powders were synthesized by borothermal reduction method, three of which were designed to introduce minor modifications by combining solid solution with Ti and/or water-washing. The sinterability, microstructures, mechanical properties and thermal conductivity were investigated. In comparison with the conventional borothermal reduction, the modified methods offered significant improvement in terms of densification of ZrB2 ceramics, particularly the mixture that included water-washing. Owing to the refined particle size and boron residues, ZrB2 ceramics from the modified borothermal reduction which included water-washing demonstrated nearly full densification, Vickers hardness of 14.0 GPa and thermal conductivity of 82.5 W/m K after spark plasma sintering at 2000 °C for 10 min. It was revealed that the properties of ZrB2 ceramics could be enhanced utilizing the proposed minor modification, starting from the same raw materials and adopting the same sintering conditions.

Cold sintered, Li2MoO4‐based ceramics have recently been touted as candidates for electronic packaging and low temperature co‐fired ceramic (LTCC) technology but MoO3 is an expensive and endangered raw material, not suited for large scale commercialisation. Here, we present cold sintered temperature‐stable composites based on LiMgPO4 (LMP) in which the Mo (and Li) concentration has been reduced, thereby significantly decreasing raw material costs. Optimum compositions, 0.5LMP‐0.1CaTiO3‐0.4K2MoO4 (LMP‐CTO‐KMO), achieved 97% density at

Silicon carbide ceramics were pressureless joined by using Ti foil and Si powder, which generated Ti3SiC2 phase as the interlayer. The phase composition, microstructure and the shear strength were investigated. It was revealed that the SiC assembly after joining at 1500oC showed the high shear strength of 76.2 ± 19.5 MPa. The secondary phase of TiC within the interlayer was expected to contribute to densification improvement of Ti3SiC2 phase and thermal stress reduction.

High-entropy boride ceramics of (Zr0.2Ta0.2Ti0.2Nb0.2Hf0.2)B2 and (Zr0.2W0.2Ti0.2Mo0.2Hf0.2)B2 were prepared by combining powder synthesis via borothermal reduction process at 1600 °C and subsequent ceramic densification by spark plasma sintering at 2000 °C in argon. High-entropy diboride powdered products exhibited ultra-fine particle size (