The heat dissipation requirements of the new generation of semiconductors are placing higher demands on the overall performance of aluminum nitride (AlN) ceramics. This has led to an increasing emphasis on AlN ceramics that combine thermal conductivity and strength. AlN ceramics are often strengthened by hot-press sintering, but their thermal conductivity is typically modest. In this study, pre-sintering and annealing processes are introduced to optimize the thermal conductivity of hot-pressed AlN ceramics to avoid the detrimental effects of oxygen impurities in the AlN lattice. The effect of the oxide layer on the surface of commercial AlN particles is investigated, including density, phase composition, microstructure, and fracture behavior. The effect of annealing on the improvement of thermal conductivity and flexural strength is also verified. Electron paramagnetic resonance (EPR) analysis is performed to examine the concentration of intercrystalline defects under various conditions. Finally, AlN ceramics with a thermal conductivity of 204 W m−1 K−1 and a flexural strength of 376 MPa are obtained.

Understanding the effect of glass network structure on the solubility properties of bioactive glasses is fundamental for designing new compositions with tailored biological functions and applications. This paper bridged the composition-structure-property relationship utilizing experimental measurements and molecular dynamics simulations. The Sr atom reorganized the network structures through a partial transformation of tetrahedral to trigonal boron units and the change of the ratio of bridged oxygen/non-bridged oxygen, which modified the glass structures at longer lengths scales, such as through changing the ring size distribution. Our results demonstrated that the evolution of solubility properties can be linked to the atomic structure change in short- and medium-range ordering. The structure-property relationship can be used to design and tune bioactive glass composition with specific properties.

The synthesis of the nanosized multifunctional thin film provides new solutions for many technological issues and consider a great step for miniaturized technology. Toward these goals, AgSbTe2 semi-nanocrystalline thin films of different thicknesses were synthesized by the thermal evaporation technique. The structural features were investigated by X-ray diffraction, and selected area electron diffraction (SAED) yielding a semi-nanocrystalline thin film of grain size ranging from 9.98 to 21.38 nm. The energy-dispersive X-ray spectroscopy (EDAX) verified the high purity and stoichiometry of the deposited films. For optoelectronic application, many optical parameters, including band gap (Eg), Urbach energy (Eu), Refractive index (n), dispersion energy (Ed), electronic polarizability (αe), and interband transition strength (JCV) were extensively discussed. The optical band gap reduced from 1.41 to 1.04 eV upon increasing the thickness from 150 to 550 nm. The temperature dependence of the electrical resistivity (ρ) of nanosized thin film was measured and the activation energy was estimated and it was found that the resistivity increased up to 450 K asserting the semiconductor behavior of the films. As for diode application, The Ag/2D-MoS2/p-AgSbTe2 (550 nm)/n-Si/Al heterostructure diode was constructed by thermal evaporation and all the diode parameters alongside conduction mechanism were studied in detail. AgSbTe2-based diode showed a low rectification ratio; however, the ideality factor (n) and zero bias barrier height (Φb) had optimal values of about 1.40 and 0.75 at room temperature, respectively.

The crack of ceramic weld is a worldwide problem for brittle material, high energy laser beam is expected to solve this problem. In this paper, the crack of fiber laser welding of Al2O3 ceramics was studied. The weld crack rate was used to characterize the crack condition of weld, and the influences of laser power, welding speed and defocusing distance on crack characteristics were carried out. The results showed that Al2O3 ceramics weld has obvious crack tendency, and the cracks mainly appeared on the weld center line. When the crack appeared on the weld center line, there was crack-free on the base metal. When the defocusing distance increased from +3 mm to +20 mm, the number of cracks gradually decreased. When the defocusing distance was greater than +17 mm, cracks-free appeared on the weld and base metal. Abaqus software was used to simulate the relationship between crack and stress based on thermal elastoplastic theory. The high crack areas, few crack areas and free crack areas were divided according to the maximum principal stress value. No matter what welding conditions, as long as the maximum principal stress was less than 1576 MPa, there was crack-free on the weld and base metal.

Five kinds of 2D chiral ceramics of 3 mol% yttria-stabilized tetragonal ZrO2 (3Y-TZP) material with an extensive relative density range was fabricated by an additive manufacturing technique based on the digital light processing (DLP) system. The in-plane compressive behaviours of the chiral structures were investigated with a uniaxial compression test. The effects of geometric parameters, including the ligament length-radius ratio and the wall thickness-radius ratio, were studied carefully through experiments. Furthermore, the relationships between Poisson's ratios and relative densities of the five chiral structures were obtained by finite element analysis. The results illustrated that increasing the relative density, like decreasing L/r or increasing t/r, is an excellent way to increase the mechanical properties of chiral ceramics, while decreasing L/r is a better way to increase the energy absorption capacity for chiral ceramics from an engineering perspective. Anti-tetrachiral ceramics own the best energy absorption capacity due to their strong deformation abilities brought by the deformation mode. The Poisson's ratio of 2D chiral structures also varies with the relative density.

Absorbers at microwave frequencies with multiple frequency-band response are particularly important for use in military for stealth technology. Specially, ferrite based absorbing materials are significant for electromagnetic shielding and signal attenuation. The enhancement of reflection loss of ferrites along with carbonaceous materials are even more beneficial. Recently double-layer absorbers have extensively studied to meet the requirements of advanced absorbing materials in multiple frequency-band response. It still remains a challenge how to determine the type and thickness to couple the impedance-matching-layer to the absorption-layers for a double-layer absorber. We applied hydrothermal method to prepare Fe3O4 nanoparticle and combine them with either graphene oxide (GO) or reduced graphene oxide (rGO) to prepare a composite of specific quality to obtain Fe3O4@GO and Fe3O4@rGO nanocomposite. We studied microwave attenuation capabilities of single and double-layer absorbers containing these two materials. We have demonstrated that with a thin impedance matching layer as a first layer and an absorbing layer behind this layer for the double-layered absorber has much higher reflection loss (RL) than a single-layer. The Fe3O4@rGO composite as a single-layer absorber shows the best microwave absorption performance with RL close to −30 dB in all three microwave bands (X, Ku and K bands). The use of a double-layer structure as Fe3O4@GO as impedance matching layer and Fe3O4@rGO as absorbing layer exhibits the best absorption of −50 dB. This is much larger than the single-layered absorbers at all three frequency-bands. Such a performance is superior to many reported ferrite-based carbonaceous composites. Therefore, a double-layer absorber is best suited to coat the whole body of the aircraft or missiles to evade satellite detection, a preparation towards new-generation weapons for future warfare. Before performing the absorption studies we have characterized the ferrites, GO and rGO materials with various microstructural and magnetic characterizations.

High-temperature heat treatment was performed on Submerged-Entry Nozzle (SEN) refractory materials, coupled with in-situ gas analysis, to identify the emitted gas species. Various SEN refractories, including “oxide-based” ones containing SiO2(s) and C(s), exhibited a carbothermic reaction: SiO2(s) + 3C(s) = SiC(s) + 2CO(g). The emission of CO(g) was confirmed for the first time using a quadrupole mass spectrometer, while the emission of SiO(g) was not observed. An ”oxide-less” refractory composed of AlON–AlN–BN emitted only N2(g). Considering the reactivity of CO(g) in the reoxidation of molten steel passing through the SEN, it is crucial to minimize CO(g) emissions during continuous casting. The extent of CO(g) emission was discussed with respect to the compositions of the refractories. This study elucidates the gas emission mechanism of SEN refractories, which is the main cause of initial clog deposit growth. The effectiveness of the oxide-less refractory in suppressing CO(g) emission was demonstrated.

The low efficiency of upconversion luminescence hinders the pratical applications in many optical fields. During the past years, much attention have focused on the fluorides, reports of lanthanum vanadate (LaVO4) in oxides are scarce. Herein, a series of LaVO4:Yb3+/Er3+ crystals codoping with Ba2+ ions are synthesized through one-pot facile hydrothermal route. Many instruments, such as XRD, ICP, TEM equipped with EDS, luminescence spectroscopy are applied to characterize the products. By optimizing the impurity doping content to 15 mol%, the upconversion luminescence intensities of the green and red emissions are enhanced by 23 and 25 times, respectively. A formation mechanism for morphology evolution is proposed. The enhancement of upconversion performance are systematacially investigated upon the grain size, crystal structure symmetry and doping concentration. Moreover, additional operations are carried out by DFT calculations to confirm the experimental result. This work will guide to enhance upconversion performance based on lanthanum vanadate nanocrystals through impurity doping, which may realize the prospective applications in many fields.

Herein, a facile triple pulse electrodeposition was used to fabricate porous films such as tungsten trioxide (WO3) and nickel oxide (NiO) on indium tin oxide (ITO) substrates. These porous films outperformed corresponding compact films formed by continuous electrodeposition in terms of long-term stability. The maximum transmittance modulation of P-WO3 and P–NiO films were 57.0% and 52.1%, respectively, and changed insignificantly after 10,000 cycles, whereas C-WO3 and C–NiO films were degraded after 2500 and 1000 cycles, respectively. Not only does the porous morphology increases the electrochemical active surface area, but it also provides an efficient pathway for ion diffusion and charge transfer, resulting in fast kinetics, low resistance, high electro-activity, and excellent ion reversibility. This work will hopefully inspire more researchers to improve electrodeposition film fabrication and promote electrochromic device industrialization.

The rapid reactivity of hydrofluoric acid (HF) and irregular Si-O network has been successfully applied in the chemical processing of glass/glass-ceramics surface. It is found that the low glass and diopside (D-G) interface binding energy will promote the reaction of HF and the residual glass phase at the interface, resulting in the formation of defects and the fall of grain. Raman spectroscopy has found that residual stress will be generated on the surface of the sample during corrosion, which will improve the performance of glass-ceramics, and the Vickers hardness increases from 761.5HV to 834.8HV. The corrosion process can be divided into three stages, including reaction of glass phase with hydrofluoric acid, formation of sediment on the surface of glass-ceramics and a corrosive layer. The whole process is closely related to insoluble crystal phase, which provides a theoretical basis for the study of hydrofluoric acid processing glass/glass-ceramics.

LaMgAl11O19 (LMA) with magnetoplumbite structure has been identified as a potential candidate for the next generation of thermal barrier coatings (TBCs). However, the as-sprayed LMA coating presents a large amount of amorphous phase originating from the rapid quenching from the molten droplets, which may compromise the reliability of coating during high-temperature service. A logical approach to improve LMA TBC life, therefore, is to enhance its crystallinity. In the present study, three LMA powders with different particle size distributions (fine, medium and coarse feedstocks) were utilized to deposit TBCs to investigate whether the thermal durability of LMA can be improved by increasing particle size. It was based on a hypothesis that large particle size can decrease the melting degree of in-flight particles and thus result in high crystallinity of as-sprayed LMA coating, making less recrystallization stress to enhance the thermal shock resistance of LMA coating. Results show that prolonged thermal cycling durability can indeed be achieved by increasing particle size. However, excessive particle size could lead to higher porosity derived from unmelted particles, which function as the weak regions for the coating system, thereby damaging the structural integrity and adhesive strength between the topcoat and bond coat. This could cause microcrack linking when the accumulated thermal stress exceeds its fracture toughness under consecutive heating-cooling cycles despite its higher crystallinity. Concerning the coating fabricated by medium powder, it achieves the optimal balance of crystallinity and structure integrity, resulting in the longest thermal cycling lifetime. The results provide guidance for the development and design of high thermal durability LMA TBCs. When optimizing the recrystallization stress within the coating, attention should be paid to improving its bonding strength simultaneously.

Plasma electrolytic oxidation (PEO) was performed on 6061 aluminum alloy in organosilicon electrolyte using a stepwise constant potential control method for 23 min. The resulting coating was a sponge-like structured amorphous silica ceramic with a thickness of about 130 μm. Its exceptional wear resistance was attributed to the high hardness of the silica ceramic and the low elastic modulus of the sponge-like structure. The corrosion resistance was enhanced by a dense layer of approximately 2 μm between the coating and the substrate. Impressively, the indentation depth of the PEO coating during nano-indentation tests was only 50–60% of that of 6061 aluminium alloy under varying loads, while the recovery depth of the PEO coating after unloading was 2.5–3.1 times greater than that of 6061 aluminium alloy. Due to its special composition and structure, the PEO coating caused serious wear to the high hardness Si3N4 friction balls during the friction and wear test. In the electrochemical tests, the coating reduced the corrosion current density from 1.056 × 10−5A·cm−2 to 1.239 × 10−7A·cm−2, while extending the passivation region from 0.322 V to 1.032 V.

Ba0.5Sr0.5TiO3–ZnAl2O4 composite ceramics were prepared by double sintering and conventional sintering. The results show that the double sintering can effectively reduce the ion diffusion between Ba0.5Sr0.5TiO3 and ZnAl2O4 phases. The double sintered samples exhibit higher density and more uniform grain size distribution than the conventional sintered samples. The dielectric permittivity of double sintered samples is lower than that of conventional sintered samples. Impedance spectrum analysis shows that the oxygen vacancy content and grain boundary resistance of the double sintered samples is lower than that of the conventional sintered samples, which indicates that the Q value of the double sintered samples is higher than that of the conventional sintered samples. The optimum dielectric tunability and Q value of double sintered 60wt.%Ba0.5Sr0.5TiO3-40wt.%ZnAl2O4 sample are 23.4% at 30 kV/cm and 276 at 2.257 GHz, respectively. Therefore, double sintering is a strategy that can effectively adjust the dielectric tunability and Q value of BST-ZA composite ceramics.

In this study, we synthesize a porous silica nanoparticles (SiO2) derived from recycled semi-conducting silica sludge via a conventional hydrothermal and microwave-assisted hydrothermal methods for flame-resistant applications. The corresponding thermal properties of as-synthesized SiO2 nanoparticles are investigated. The effects of reaction temperature and urea concentration are investigated in terms of surface morphology and thermal conductivity. The results of thermal conductivity tests indicate that 180 °C reaction temperature for both conventional hydrothermal reaction and microwave-assisted hydrothermal reaction demonstrated the best thermal insulator performance. The thermal conductivities are determined to be 0.0193 W/m·K and 0.0192 W/m·K, respectively. For flame penetration and combustion tests, microwave-assisted one exhibits much better performance, maintaining a temperature of 34 °C after 600 s of combustion under a butane torch at nearly 800 °C. Furthermore, there is no deformation occurred when direct contact with the flame at a high temperature, proving that microwave-assisted hydrothermal reaction-synthesized silica is a potential candidate for thermal barrier applications.

Novel AlCoCrNiMox (x = 0.1 wt%) non-equiatomic high entropy alloy (HEA) powders were synthesized by mechanical alloying. A single solid-solution was formed. X-Ray Diffraction (XRD) analysis of milled powders reveals a BCC phase after 20 h of milling. Field emission scanning electron microscopy (FESEM) with EDAX mapping confirmed the formation of a homogenous mixture. The milled alloy was coated onto a 316 steel substrate using High-velocity Oxy-fuel (HVOF) coating. The slurry erosion resistance exhibited by the coating was tested using Water-jet Erosion tester with 24 m/s to 30 m/s jet velocity at 30°, 45°, 60°, and 90° angular impingement. Spallation due to adhesion with subsequent layered lamellae fracture was observed to occur during erosion.

A non-conventional mechanochemical processing mechanochemical processing technique was used to prepare fine-grain of mixed iron and vanadium oxides with a lead titanate system at boron oxide matrix. The structures of the ball milled samples were analyzed at different milling times and temperatures. After 30h of mechanical milling, the vanadium peaks completely disappeared, and partially supersaturated solid solution was formed. The average crystallite size of the 30h milled sample calculated from XRD patterns decreases rapidly from 3.72 μm to 69.4 nm while the crystallite size of the 50h was 26.3 nm. The DSC curve confirms the mechanochemical reactions. Metastable phases of lead vanadium oxide obtained after heat treatment with average crystallite size 65 nm in a non-crystalline matrix. The conductivity of the heat-treated samples increases with increasing heating temperature. The conductivity of all the prepared samples was found to be consistent with small polaron hopping, Mott’s theory which confirmed by studying the power law behavior of its AC conductivity. The AC conductivity increases with increasing temperature and frequency.

The perovskite structure oxide, CaMnO3, has been extensively investigated and applied as a potential microwave absorption material due to its versatile dielectric and spontaneous polarization. However, the low conductivity of pure CaMnO3 material limits its further application. Herein, to increase dielectric loss and achieve better microwave absorption properties, lanthanum (La)-doped CaMnO3 (Ca1-xLaxMnO3) ceramics were fabricated by a high temperature solid state reaction. The results of XRD and XPS show that the La atom was efficiently doped at the Ca site in CaMnO3, which carries excess positive charges and affects the valence state of Mn ions and the concentration of oxygen vacancies. Therefore, the conductivity and imaginary permittivity of Ca1-xLaxMnO3 ceramics increased dramatically with La-doped content. Benefiting from the tunable dielectric and impedance properties, Ca1-xLaxMnO3 ceramics can be utilized in a highly efficient way to absorb microwave radiation with a thin thickness. The sample with x = 0.04 shows the best microwave absorption property, with an RLmin value of -52.63 dB (d = 1.41 mm) and effective absorption bandwidth coves full X band in the thickness range from 1.315 mm to 1.395 mm.

Various defects have a profound impact on the dielectric properties and polarization mechanisms of (Nb,Ga) codoped TiO2 crystals. However, the research conducted in this area remains limited. To address this, we grew (Nb,Ga) codoped TiO2 crystals via the Verneuil method and investigated their dielectric properties under various atmospheric annealing conditions. Annealing in oxygen reduces the number of defects. In this case, the point defects associated with oxygen vacancies is unable to fully form the ideal complex defect clusters which can form effective pegging of free electrons. On the other hand, the defects are mainly in the form of simple defect clusters that causes hopping polarization. Annealing under mixed gas (Ar:H2 = 95%:5%) increases the number of defects and contains more free carriers, which migrate to the interface between the sample and the electrode, leading to interfacial polarization. Both hopping polarization and interfacial polarization are slow polarization, resulting in an increase in dielectric loss and a decrease in frequency stability. Annealing in air or nitrogen atmospheres forms ideal defect dipole clusters, where the electron-pinned defect dipoles (EPDD) are predominantly polarized, resulting in superior dielectric properties. It has been clarified that EPDD as the main polarization form can yield better dielectric properties. By focusing on single crystals as the research subject, we effectively eliminate the influence of grain boundaries, enabling a more accurate assessment of the effects of various crystal defects on dielectric properties. This study holds substantial implications for the advancement of TiO2-based dielectric materials, offering valuable insights into their performance optimization.

In marine environment, thermal barrier coatings (TBCs) face coupling corrosion of calcium magnesium aluminum silicate (CMAS) and molten salt leading to premature failure. In this study, microstructure evolution of TBCs resulting from CMAS + NaVO3 (CN) coupling corrosion is investigated, and a corrosion protection method based on laser glazing is proposed. TBC degradation by the CN coupling corrosion is mainly due to the high penetration ability of the melt. Laser glazed TBCs have improved resistance to the coupling corrosion, however, the vertical cracks in the glazed layer provide paths for melt penetration. TBCs with double laser-glazed layer are designed, with vertical cracks in the glazed layer being bifurcated and staggered, which could largely suppress CN melt infiltration, and also exhibits excellent phase and microstructure stability in the coupling corrosion condition. This type of laser modified TBC is confirmed to be attractive against the coupling corrosion.

In Part 1 of this study, we investigated the macrokinetic parameters and phase formation mechanism in the combustion front of Zr-Nb-B mixtures. In the second part, we produced consolidated samples of solid solutions NbB2-(0.100%)ZrB2 by hot pressing the combustion-derived powders at 1900 °C. By measuring the crystallographic parameters, mechanical and thermophysical properties of the produced bulk samples, we obtained valuable insights into the behavior of the solid solutions. Our results pave the way for the application-specific fine-tuning of the mechanical properties and thermal conductivity of diboride solid solutions in the Zr-Nb-B system for ultra-high temperature applications. Our findings have significant implications for the development of advanced materials with outstanding performance in extreme environments.