Search Results (20)

The stability of thermal barrier coating (TBC) materials during service is a prerequisite for the normal operation of aircraft engines. The high-temperature corrosion of CaO–MgO–Al₂O₃–SiO₂ (CMAS) is an important factor that affects the stability of TBCs on turbine blades and causes premature engine failure. For traditional 6-8 YSZ, at temperatures of more than 1200 °C, the thermal insulation performance is significantly reduced, which makes it necessary to find new, alternative materials. La₂Zr₂O₇ has good thermal physical properties; the addition of Ce⁴⁺ improves its mechanical properties, while adding Gd₂O₃ affects its corrosion resistance. Herein, high-temperature corrosion studies of (La_1−xGd_x)₂(Zr_0.7Ce_0.3)₂O₇ (L-GZC) (x = 0, 0.3, 0.5, 0.7) ceramic TBC were conducted using CMAS glass at 1250 °C. The results indicate that CMAS rapidly dissolves L-GZC and separates the (La, Gd)₈Ca₂(SiO₄)₆O₂ apatite phase, ZrO₂, and other crystalline phases. These products form a crystalline layer at the contact boundary, which can inhibit further CMAS reactions. Among the coatings examined, the L-GZC ceramic (x = 0.7) exhibits better corrosion resistance, and the penetration depth is <200 μm after high-temperature corrosion at 1250 °C for 5, 10, and 20 h. The failure mechanism and potential risk of CMAS were also analyzed and discussed. The L-GZC ceramic material has good thermal corrosion resistance and is expected to replace the traditional YSZ to better meet the high-temperature working requirements of gas turbines and aircraft engines. Full article

The passively Q-switched mode-locked (QML) operation of a Tm:CaGdAlO₄ (Tm:CALGO) bulk laser pumped by a wavelength-tunable Ti:sapphire oscillator using molybdenum disulfide (MoS₂) as a saturable absorber was demonstrated. By using an output coupler with 3% transmittance, Q-switched mode-locked operation can be achieved with 3.56 W absorbed pump power. At a pump power of 6.77 W, laser pulses with the maximum average power of 1.44 W were obtained, corresponding to a slope efficiency of 21.3%. The laser delivered pulses centered at 1927 nm with a repetition frequency of 131.6 MHz. The experimental results confirm the promising application of the MoS₂ in high-power Q-switched mode-locked solid-state lasers at 2 µm. Full article

The late Permian Emeishan large igneous province (ELIP) in SW China is a melting product of the Emeishan mantle plume. Recently, it has been debated whether peridotite or pyroxenite is the dominant lithology of the mantle source in the ELIP. To address this, systematic analyses of bulk-rock and coexisting spinel and olivine compositions were conducted on picrites from Lijiang–Yongsheng, Dali–Binchuan, Yumen, Muli, and Ertan. The ELIP picrites exhibit positive TiO₂–CaO and negative MgO–CaO correlations, as well as low FC3MS values (−0.24–0.1), supporting a peridotite-dominated mantle source. This lithology of the mantle source is also supported by the high 100 × Mn–Fe (1.43–1.73) and Mn–Zn (13.6–18.4) values but low 10,000 × Zn–Fe (8.0–12.7) ratios of the olivine phenocrysts. The estimated mantle potential temperature for Lijiang, Yongsheng, Yumen–Ertan, Muli, and Dali–Binchuan picrites decreased away from Lijiang and Yongsheng, suggesting that the Lijiang and Yongsheng areas were the center of the ELIP. The Lijiang–Yongsheng primary magma shows similar SiO₂ content but lower Al₂O₃ contents (average of 8.24 wt.%) and higher MgO contents (average of 21.42 wt.%) than those of Dali–Binchuan primary magma (Al₂O₃: 9.86 wt.%; MgO: 19.02 wt.%). Also considering the high Gd–Yb (average of 3.05) and La–Yb (average of 14.61) ratios and mantle potential temperature (average of 1599 °C), we proposed that Lijiang–Yongsheng lavas are produced via the melting of a garnet–peridotitic mantle. In contrast, the Dali–Binchuan lavas with low Gd–Yb (average of 1.91) and La–Yb (average of 5.88) ratios can be explained by their formation in the garnet–spinel transition zone of a peridotitic mantle. The Yumen–Ertan primary magma displays similar mantle potential temperature (average of 1600 °C), Al₂O₃ and FeO content, and Gd–Yb ratios to those of Lijiang–Yongsheng lavas, indicating that YumenvErtan primary magma may be attributed to the partial melting of garnet with minor peridotite. Therefore, heterogeneous plume-head mantle sources lead to the evaluation of melting conditions of the late Permian ELIP picrites. Full article

Traditional roadway lighting is intended to provide safe guidance for drivers and pedestrians, but the large-scale application of roadway lighting has resulted in significant energy consumption and light pollution. However, road markings prepared by luminous coating are a kind of multi-functional road marking that can meet the needs of highway lighting at night and save energy. Here, CaAl₂O₄:Eu²⁺,Nd³⁺,Gd³⁺ blue long-afterglow phosphor is obtained by the high-temperature solid-state method, and the blue luminescent coating is synthesized by the blending method. The phase composition, microscopic morphology, luminescence properties and water resistance of the phosphor and luminescent coatings are characterized. The best components and processes of the luminescent coating are explored to meet the application of an expressway. Considering the afterglow’s performance, the optimal calcination temperature of the phosphor is determined to be 1300 °C. The afterglow of the phosphor can be over 8 h after 2 h of daylight excitation. The addition of 1.25% SiO₂ to the luminescent coating improves the uniformity of the components, and the incorporation of 3.5% CaCO₃ improves the denseness of the coating. When the coating thickness is 0.8mm, the luminescent coating can achieve the best luminous effect. After 120 h of immersion in water, the afterglow intensity of the luminescent coating reduced to 70% of the original, which has excellent water resistance. The blue luminescent coating with the addition of appropriate amounts of CaCO₃ and SiO₂ improves the dispersion as well as the densification of the components in the coating to achieve the best luminescent effect. In the Shenyang area, different weather conditions (cloudy, sunny, rainy) have no significant effect on the afterglow performance of the luminescent coatings, all of which can achieve over 5 h of afterglow and are suitable for expressways. Full article

What is reported here is an advanced anti-counterfeiting ink whose luminous effect changes over time and at different excitation wavelengths. Unlike traditional anti-counterfeit fluorescent materials, the phosphors used here exhibit multicolor emissions under multiple excitation modes. In this work, the most important building blocks are three classic phosphors with primary colors, red (Ca₂YNbO₆:0.4Eu³⁺), green (SrAl₂O₄:0.01Eu²⁺, 0.02Dy³⁺) and blue (CaAl₂O₄:0.012Eu²⁺, 0.06Nd³⁺, 0.036Gd³⁺), which were synthesized using the high-temperature solid-state method. The phosphors formed homogeneous solid solutions and were uniformly distributed throughout the mixture. A homogeneous transparent luminescent ink was obtained by blending the multi-mode phosphors with transparent screen-printing ink, resulting in multi-mode luminescence by simply varying the proportions of the red (R), green (G) and blue (B) phosphors. Thanks to this simple process, an advanced anti-counterfeiting ink with low production costs was achieved. Anti-counterfeiting logos of a “Giraffe” and “Steam Train” were printed using the transparent fluorescent ink onto black cardstock, exhibiting the characteristic of dynamic luminescence dependent on the duration and excitation wavelength. The anti-counterfeiting effect of the patterns suggests that the fluorescent ink is worth developing and is reliable in its application. Full article

Loess deposits are widely distributed across the globe and provide detailed records of climatic changes since the Quaternary period. Their geochemical element characteristics are important indicators of paleoenvironmental evolution and provenance. Therefore, four typical loess sections from four different islands of the Miaodao Islands were selected for systematically geochemical analysis of major and trace elements. The geochemical data of major and trace elements are very similar, indicating that the loess of all islands on the Miaodao have a common provenance. The geochemical test results show that t SiO₂, Al₂O₃, Fe₂O₃ and CaO are the major chemical components of loess, with an average total content of 85–90%. The average Eu/Eu*, ΣLREE/ΣHREE, La_N/Yb_N, Gd_N/Yb_N values of the Miaodao Islands loess range from 0.65 to 0.69, 7.84 to 8.31, 8.02 to 9.99, 1.40 to 1.76. These data are similar to and different from those of the Chinese Loess Plateau, indicating the diversity of Miaodao Islands Loess provenance. The CIA (Chemical Index of Alteration) (50–65) and Na/K results suggest that the loess here had experienced incipient chemical weathering. The A-CN-K (Al₂O₃-CaO* + Na₂O-K₂O) diagram indicates that the weathering trend of the loess sections is consistent with that of continental weathering. The local loess data points are close and parallel to the A-CN line, suggesting that the loess dust material on the Miaodao Islands originated from the extensive upper continental crust, and was highly mixed in the process of wind transport and deposition. The relationships of Log[(CaO + Na₂O)/K₂O] versus Log(SiO₂/Al₂O₃), Na₂O/Al₂O₃ versus K₂O/Al₂O₃, LaN/YbN versus Eu/Eu*, Sc-Th-La and Zr-Sc-Th plots of major and trace elements reveal that the loess sources for the Miaodao Islands are similar to those of the Loess Plateau, which were derived from alluvial fan deposits flanking the Qilian Shan in China, the Gobi Altay and Hangayn Mountains in Mongolia. However, the loess of the Miaodao Islands is coarser in average grain size and contains abundant marine fossils, with gravel layers, indicating it is allochthous and near-source, which suggests it mainly originated from the adjacent exposed sea floor sediments of the Bohai Sea during glacial periods. Finally, we conclude that the loess of the Miaodao Islands is the result of a gradual accumulation process, in which the relative amount of distant-source material decreased and the near-source material increased in response to changes in sea level and paleoclimate. Our findings support that the loess of the Miaodao Islands was formed by mixing material from distant and proximal sources. Full article

The current policy of managing high-level waste (HLW) derived in the closed nuclear fuel cycle consists in their vitrification into B-Si or Al-P vitreous forms. These compounds have rather limited capacity with respect to the HLW (5–20 wt%), and their properties change over time due to devitrification of the glasses. Cardinal improvement in the management of HLW can be achieved by their separation onto groups of elements with similar properties, followed by their immobilization in robust waste forms (matrices) and emplacement in deep disposal facilities. One of the possible fractions contains trivalent rare-earth elements (REEs) and minor actinides (MAs = Am and Cm). REEs are the fission products of actinides, which are mainly represented by stable isotopes of elements from La to Gd as well as Y. This group also contains small amounts of short-lived radionuclides with half-lives (T_1/2) from 284 days (¹⁴⁴Ce) to 90 years (¹⁵¹Sm), including ¹⁴⁷Pm (T_1/2 = 2.6 years), ¹⁵⁴Eu (T_1/2 = 8.8 years), and ¹⁵⁵Eu (T_1/2 = 5 years). However, the main long-term environmental hazard of the REE–MA fraction is associated with Am and Cm, with half-lives from 18 years (²⁴⁴Cm) to 8500 years (²⁴⁵Cm), and their daughter products: ²³⁷Np (T_1/2 = 2.14 × 10⁶ years), ²³⁹Pu (T_1/2 = 2.41 × 10⁴ years), ²⁴⁰Pu (T_1/2 = 6537 years), and ²⁴²Pu (T_1/2 = 3.76 × 10⁵ years), which should be immobilized into a durable waste form that prevents their release into the environment. Due to the heat generated by decaying radionuclides, the temperature of matrices with an REE–MA fraction will be increased by hundreds of centigrade above ambient. This process can be utilized by selecting a vitreous waste form that will crystallize to form durable crystalline phases with long-lived radionuclides. We estimated the thermal effects in a potential REE–MA glass composite material based on the size of the block, the content of waste, the time of storage before immobilization and after disposal, and showed that it is possible to select the waste loading, size of blocks, and storage time so that the temperature of the matrix during the first decades will reach 500–700 °C, which corresponds to the optimal range of glass crystallization. As a result, a glass–ceramic composite will be produced that contains monazite ((REE,MA)PO₄) in phosphate glasses; britholite (Ca_x(REE,MA)_10-x(SiO₄)₆O₂) or zirconolite ((Ca,REE,MA)(Zr,REE,MA)(Ti,Al,Fe)₂O₇), in silicate systems. This possibility is confirmed by experimental data on the crystallization of glasses with REEs and actinides (Pu, Am). The prospect for the disposal of glasses with the REE–MA fraction in deep boreholes is briefly considered. Full article

The kinetic process of the excited state population of Nd³⁺ ion in Nd: CaY_0.9Gd_0.1AlO₄ (Nd: CYGA) crystal were studied in detail to estimate the optimal doping concentration, which maximize ~1 μm fluorescence emission from the ⁴F_3/2 state to the ⁴I_9/2 state of Nd³⁺. The analysis was accomplished by revealing the dependence of the excited state population on the doping concentration in a relatively convenient way in theory. After comparing the theoretical prediction results with the experimental findings and approximating the results obtained using the aforementioned method, the optimal relative doping concentration of Nd: CYGA was determined to be 2.1 at.%, which closely matched the 2.0 at.% obtained through experimental comparison. This verifies the effectiveness and accuracy of the proposed method. In particular, it is worth mentioning that in this method only one doping concentration of the crystal is required to obtain the optimal concentration, which may be used to guide the concentration optimization process for improving efficiency and saving resources. Full article

We investigate in-band pumping of a Tm,Ho,Lu:CaGdAlO₄ laser using a Raman-shifted Er-fiber laser (1678 nm), in the continuous-wave (CW) and mode-locked (ML) regimes. A maximum output power of 524 mW is obtained in the CW regime with a 5% output coupler at an absorbed pump power of 2.04 W, corresponding to a slope efficiency of 27.9%. A maximum CW wavelength tuning range of 160 nm at the zero level, from 1984 to 2144 nm, is obtained with a 0.2% output coupler. In the ML regime, pumping with 5.5 W (unpolarized), the average output power (0.2% output coupler) reaches 148 mW at a repetition rate of ~96 MHz. The output spectrum is centered at 2071.5 nm with a FWHM of 21.5 nm (σ-polarization). The pulse duration amounts to 218 fs (time-bandwidth product equal to 0.327). Full article

With the development of industry, the operating temperature of aero engines and gas turbines continues to increase; developing thermal barrier coatings (TBCs) with superior resistance to CaO-MgO-Al₂O₃-SiO₂ (CMAS) corrosion has become a prominent research focus. In this study, atmospheric plasma spraying (APS) was used to prepare yttria-stabilized zirconia (YSZ), nanostructured yttria-stabilized zirconia (n-YSZ), and Gd-Yb-Y-stabilized zirconia (GYYSZ) coatings. The effects of CMAS exposure on the microstructure, chemical composition, phase transition, and microhardness of the coatings were investigated. Comparative analysis revealed that both phase transition and exfoliation occurred in corroded YSZ and n-YSZ coatings, with n-YSZ exhibiting more pronounced changes. In contrast, GYYSZ coatings remained stable without phase transition and exhibited a smaller increase in microhardness (270 HV0.3). Consequently, doping Gd/Yb/Y elements into ZrO₂ can improve the performance of TBCs. Full article

Gadolinium aluminate perovskite (GdAlO₃) was studied at high pressures of up to 23 GPa in a diamond anvil cell (DAC) using monochromatic synchrotron X-ray powder diffraction. Evidence of a pressure-induced phase transformation from orthorhombic (Pbnm) to rhombohedral (R$\overline{3}$c) structure was observed at 21 GPa and further proved by DFT calculations. Before phase transition, the volumetric ratio of polyhedron A and B (i.e., V_A/V_B for ABX₃ general notation) in the Pbnm phase continuously increased towards the ideal value of five at the transition, indicating a pressure-induced decrease in the structural distortion as opposed to the trend in many other orthorhombic perovskites (e.g., CaSnO₃, CaGeO₃, MgSiO₃ and NaMgF₃). Pressure–volume data of the Pbnm phase were fitted to the third-order Birch–Murnaghan equation of state yielding a bulk modulus (K_o) of 216 ± 7 GPa with a pressure derivative of the bulk modulus ($K_o^{\prime }$) of 5.8 GPa (fixed). This work confirms the pressure-induced phase transformation from orthorhombic to a higher symmetry structure previously predicted in GdAlO₃ perovskite. Full article

Zirconolite is a candidate ceramic wasteform under consideration for the immobilisation of the UK civil PuO₂ inventory. In the present work, a baseline dual-substituted zirconolite with the target composition (Ca_0.783Gd_0.017Ce_0.2)(Zr_0.883Gd_0.017Ce_0.1)(Ti_1.6Al_0.4)O₇ was fabricated by hot isostatic pressing (HIPing). In order to optimise the microstructure properties and improve the obtained yield of the zirconolite phase, a range of planetary ball milling parameters were investigated prior to consolidation by HIP. This included milling the batched oxide precursors at 400 rpm for up to 120 min, the pre-milling of CeO₂ (PuO₂ surrogate) to reduce the particle size and using a CeO₂ source with finer particle size (<5 µm). The HIPed zirconolite product consisted of both zirconolite-2M and zirconolite-3T polytypes in varying proportions; however, an additional perovskite phase was obtained in varying quantities as a secondary phase. Ce L₃-edge X-ray absorption spectroscopy was utilised to determine the Ce oxidation state. In this study, the ideal milling parameter for the fabrication of zirconolite waste forms was defined as 60 min at 400 rpm. Full article

Geochemical baselines are crucial to explore mineral resources and monitor environmental changes. This study presents the first Laos geochemical baseline values of 69 elements. The National-scale Geochemical Mapping Project of Lao People’s Democratic Republic conducted comprehensive stream sediment sampling across Laos, yielding 2079 samples collected at 1 sample/100 km², and 69 elements were analyzed. Based on the results of LGB value, R-mode factor analysis, and scatter plot analysis, this paper analyzes the relationship between the 69 elements and the geological background, mineralization, hypergene processes and human activities in the study area. The median values of element contents related to the average crustal values were: As, B, Br, Cs, Hf, Li, N, Pb, Sb, Zr, and SiO₂, >1.3 times; Ba, Be, Cl, Co, Cr, Cu, F, Ga, Mn, Mo, Ni, S, Sc, Sr, Ti, Tl, V, Zn, Eu, Al₂O₃, Tot.Fe₂O_3, MgO, CaO, and Na₂O, <0.7 times; and Ag, Au, Bi, Cd, Ge, Hg, I, In, Nb, P, Rb, Se, Sn, Ta, Th, U, W, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and K₂O, 0.7–1.3 times. R-mode factor analysis based on principal component analysis and varimax rotation showed that they fall into 12 factors related to bedrock, (rare earth, ferrum-group, and major Al₂O₃ and K₂O elements; mineralization–Au, Sb, and As) and farming activities–N, Br, S, and C). This study provides basic geochemical data for many fields, including basic geology, mineral exploration, environmental protection and agricultural production in Laos. Full article

Yb:CaGdAlO₄, or Yb:CALGO, a new laser crystal, has been attracting increasing attention recently in a myriad of laser technologies. This crystal features salient thermal, spectroscopic and mechanical properties, which enable highly efficient and safe generation of continuous-wave radiations and ultrafast pulses with ever short durations. More specifically, its remarkable thermal-optic property and its high conversion efficiency allow high-power operation. Its high nonlinear coefficient facilitates study of optimized mode locking lasers. Besides, its ultrabroad and flat-top emission band benefits the generation of complex structured light with outstanding tunability. In this paper, we review the recent advances in the study of Yb:CALGO, covering its physical properties as well as its growing applications in various fields and prospect for future development. Full article

A stable, passively Q-switched Yb:CaGdAlO₄ laser based on Mo:BiVO₄ saturable absorber was demonstrated. Close observations of the structure and morphology of the nanoparticles by using transmission electron microscope, Raman spectrum and linear absorption were measured. The nonlinear transmission of Mo:BiVO₄ was characterized by a 30 ps laser with a central wavelength of 1064 nm and a repetition rate of 10 Hz. The experimental maximum output power of the pulsed laser was 510 mW with a repetition rate of 87 kHz and pulse width of 3.18 μs, corresponding to a peak power of 1.84 W and a single pulse energy of 5.8 μJ. The experimental results indicate that Mo:BiVO₄-SA is a great candidate for passively Q-switched lasers in the near infrared region. Full article