A novel Nd3+-doped MgO-Al2O3-SiO2-based transparent glass-ceramics: Toward excellent fluorescence properties

Generally, glass-ceramics have superior properties compared to their parent glasses. Here, we prepared a novel Nd³⁺-doped MgO-Al₂O₃-SiO₂-based transparent glass-ceramics with excellent fluorescence properties. The effects of Nd₂O₃ content on the structure and properties of glass-ceramics were studied, aiming to provide a key guidance for preparing this transparent glass-ceramics. The results revealed that the glass stability increased originally and then decreased with increasing Nd₂O₃ content, so did the variation of wavenumbers in infrared spectra. And these glass-ceramics are mainly composed of cordierite with residual glassy phase. The three phenomenological intensity parameters (Ω_2,4,6) and radiative properties were estimated by Judd-Ofelt theory, and the values of Ω₂ first decreased and then increased with increasing Nd₂O₃ content. Three main emission peaks ascribed to the transitions from ⁴F_3/2 to ⁴I_9/2, ⁴I_11/2, ⁴I_13/2 at 898, 1057, 1330  nm were observed, respectively. The branching ratios for ⁴F_3/2→⁴I_11/2 transition increased as the Nd₂O₃ content raised, and the fluorescence lifetimes of the ⁴F_3/2 level were found to increase first and then decrease with Nd₂O₃ content (from 181 to 726 μs). The excellent fluorescence properties indicate that this novel glass-ceramics can be used as a potential solid-state optical functional material for 1.06 μm laser emission.     

Degradation-controlling mechanisms in natural organic acid solutions of CaO–Al2O3–SiO2–B2O3 glass-ceramics by partially substituting Ca2+ with Ba2+ and Sr2+

The degradation of environmentally friendly CaO–Al₂O₃–SiO₂–B₂O₃ (CASB) glass-ceramics, which consist of anorthite and glass phase, was investigated in three natural organic acid solutions. The results indicated that citric acid had the most significant effect on the degradation of CASB glass-ceramics. While the chemical stability of anorthite is relatively poor, the glass phase also contributed significantly to the effective degradation of CASB glass-ceramics. Subsequently, Ba²⁺ or Sr²⁺ was used for full or partial substitution of Ca²⁺ in CASB glass-ceramics, and the degradation-controlling mechanism of the substituted CASB glass-ceramics was further researched. The full substitution of Ca²⁺ in CASB glass-ceramics by the two cations resulted in the occurrence of borate [BO₄] units in the glass phases, and the interlinkage of [BO₄] with broken silicate [SiO₄] network structures caused a complementary network effect. Consequently, the degradation of CASB glass-ceramics by organic acids was reduced due to the improvements in the chemical stability of the modified glass-ceramics. Additionally, degradation control can also be achieved based on a mixed-alkali effect, originating from the partial substitution of Ca²⁺ in CASB glass-ceramics by Ba²⁺ or Sr²⁺. The degradable glass-ceramics have the potential to be applied in low-temperature co-fired ceramic technology because of their good physical properties, which include a dielectric constant of 3–5, a dielectric loss as low as 10⁻³, a coefficient of thermal expansion of 3–9 × 10⁻⁶/°C, and an average bending strength of about 47 MPa. Noticeably, the development of the degradable glass-ceramics is helpful to the low-cost and pollution-free recycling of valuable metal electrodes, which is significant for the sustainable development of electronic packaging technologies.     

The influence of MgO on the crystallization behaviour and properties of SrO-rich phosphosilicate glasses

A series of glass was produced to investigate the effect of MgO/SrO replacement on the crystallization characteristics and properties of phosphosilicate glasses containing high SrO content. The glass samples were synthesized by conventional melting technique based on 5CaO-(40-X)SrO-X MgO– 43SiO₂–7P₂O₅–5CaF₂ (where; X = 10, 20, 30 and 40 mol%). The influence of MgO/SrO replacement on phase assemblages, microcrystalline structures, thermal expansion, and mechanical properties was examined as a function of basic chemical compositions and crystallization parameters. Predominant strontium meta-silicates together with strontium fluoroapatite phases are crystallized from the base glass free of magnesium. The substitution of strontium by magnesium up to 50% led to formation strontium akermanite phase Sr₂MgSi₂O₇ at the expense of SrSiO₃ phase. Whereas the increase of the MgO/SrO of more than 50%, which led to the crystallization of the clino-enstatite MgSiO₃ as a predominant phase. The results show that the α-values of the glass-ceramics are ranged in 94–125 × 10⁻⁶ K⁻¹ over the temperature range (25–500 °C). On the other hand, MgO/SrO replacements led to enhancing the microhardness of the resultant crystalline materials from 4713 Mpa to 6744 Mpa. As a result of the designed glass compositions, promising crystalline phases were obtained as well as good thermal and mechanical properties for the resultant glass-ceramics. Therefore, the designed glass-ceramics can be strongly used as biomaterials especially for bone reconstruction applications.     

Enhancing glass anode performance for lithium-ion batteries via crystallization

We investigate the thermal and electrochemical properties of xFe₂O₃-(100-x) P₂O₅ glass (x = 20, 30, 40, and 50 mol%) and 50Fe₂O₃-50P₂O₅ (50FeP) glass-ceramics as anodes for lithium-ion batteries (LiBs). The results show that both the glass transition temperature and the energy bandgap monotonically decrease with the increasing Fe₂O₃ while a critical Fe₂O₃ content of 30 mol% is found to give glass the highest thermal stability, the largest capacity at 1 Ag^-1, and the lowest charge-transfer resistance before cycling. Moreover, Fe₃(P₂O₇)₂ crystals formed during heat treatment in 50FeP glass effectively enhances the electrochemical properties. The optimum heat treatment condition for 50FeP glass is found at 1033 K for 4 h, that is, 1033 K-4 h sample enables a reversible capacity of 237 mA h g⁻¹ at the end of 1000 cycles at 1 Ag^-1, which is more than 1.5 times higher than that of the 50FeP glass-based anode. These findings suggest that the Fe₂O₃-P₂O₅ glass-ceramics hold significant potential for the effective development of new types of glass anodes for future advanced LiBs.     

Structural,optical, and spectroscopic properties of Er3+-doped TeO2–ZnO–ZnF2 glass-ceramics

Transparent fluorotellurite glass-ceramics have been obtained by heat treatment of precursor Er-doped TeO₂–ZnO–ZnF₂ glasses. ErF₃ nanocrystals nucleated in the glass-ceramics have a typical size of 45 ± 10 nm. Based on the Judd-Ofelt theory, the main radiative parameters for the ⁴I_13/2 → ⁴I_15/2 transition have been obtained. The split of the absorption and emission bands and the reduction of the Ω₂ parameter, as compared to the glass, confirm the presence of Er³⁺ ions in a crystalline environment in glass-ceramic samples. The analysis of the ⁴I_13/2 decays suggests that a fraction of Er³⁺ ions remains in a glass environment while the rest forms nanocrystals. For the glass-ceramics, intense red and green upconversion emissions were observed with an enhancement of the ⁴F_9/2 → ⁴I_15/2 red one compared to the glass sample. The temporal evolution of the red emission together with the excitation upconversion spectra suggests that energy transfer processes are responsible for the enhancement of the red emission.     

Synthesis of pyrochlore-borosilicate glass-ceramics for immobilization of high-level nuclear waste

In this work, borosilicate based glass-ceramics with pyrochlore as crystalline phase for immobilization of high-level nuclear wastes (HLWs) were successfully synthesized by a one-step heat-treatment method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS) demonstrate that the obtained glass-ceramics show a regularly and uniformly distributed single pyrochlore (Ca,Na)(Nb,Ti)₂Nd_0.67O₆F crystalline phase. Moreover, the glass-ceramics prepared show LR_Na, LR_B, LR_Al, LR_Si, LR_Nd, LR_Ti and LR_Nb of about 6.8 × 10⁻³, 3.7 × 10⁻⁴, 1.5 × 10⁻², 2.2 × 10⁻³, 3.0 × 10⁻⁵, 5.1 × 10⁻⁵ and 5.5 × 10⁻⁶ g m⁻² d⁻¹ respectively after 28 leaching days, which are comparable to stable glass-ceramics for HLW immobilization. The results of this study are expected to provide an experimental reference for the engineering synthesis of glass-ceramics for the immobilization of certain HLWs.     

Thermo-magnetic properties of Fe2O3-doped lithium zinc silicate glass-ceramics for magnetic applications

The crystallization behaviour and thermo-magnetic characteristics of glass-ceramic based on the 15Li₂O–20ZnO–10CaO–55SiO₂ system doped with varied Fe₂O₃ additions (0.0125, 0.025, and 0.05 mol) are described in this work. In some cases, Al₂O₃ was also added to the iron-containing sample. Glasses were successfully prepared by melt-quenching technique and converted into glass-ceramics by controlled heat-treatment, using DTA, SEM, XRD, and VSM techniques. The density, thermal expansion coefficients (TCE), and magnetic characteristics of the glass-ceramic were examined. XRD results confirmed characteristic peaks for various phases like quartz, Li₂ZnSiO₄, wollastonite, Li₂Si₂O₅, ZnFe₂O₄, and β-spodumene. By doping Fe₂O₃ and Al₂O₃ with lowering annealing temperature, the particle size was reduce, resulting in glass-ceramics with a more uniform and dense microstructure. The density of glass-ceramics rises from 2.74 g/cm³ to 3.45 g/cm³, whereas the TCE values in average 14–78 × 10⁻⁷/°C with temperature range of 25–500 °C. The doped glass-ceramics have superior magnetic properties with saturation magnetization (0.143–0.548 emu/g), the coercivity force (65.116–86.359 G), and remanence magnetization (0.074–0.436 emu/g). Under an alternating magnetic field, the presence of the Zn-ferrite phase in the glass-ceramics improves their magnetic properties and increases their heat-generating capability. Certain features of the doped glass-ceramics control the extensive variety of possibilities for their usage in various magnetic applications particularly for cancer hyperthermia treatment.     

Contribution of some transition metal oxides to crystallization and electro-thermal properties of glass-ceramics

Lithium di-silicate (LS₂) glass-ceramics modified with copper oxide using the formula: 34.83Li₂O–xCuO–(65.17-x)SiO₂ (where; x = 1, 2, 4 and 6 mol%) were prepared by melt-quenching followed by controlling heat-treatment. 6 mol% of MnO or Fe₂O₃ transition metal oxides was added instead of SiO₂ in the high CuO-content composition. The effect of the transition cations on phase formation, microstructure, density, thermal expansion, and electrical conductivity was investigated as a function of the controlled crystallization. Results show that up to 4 mol%, Cu⁺² was hosted in stable Li₂Si₂O₅ structure. This enhanced the crystal formation, including Li₂Si₂O₅ and its solid solution (ss), Li₂SiO₃, Li₂Cu₅(Si₂O₇)₂, CuMn₆SiO₁₂, LiFeSi₂O₆ (ss), and the orthosilicate Li₂FeSiO₄ (ss). The prepared materials had different density values ranged from 2.35 to 2.79 g/cm³ for glass and varied from 2.43 to 3.15 g/cm³ for glass–ceramics, whereas the α-values of glass-ceramics ranged in the 95–165 × 10⁻⁷/°C. The progress of electrical properties in glass-ceramics, as a function of composition, was studied. It was markedly improved by adding different transition cations especially, Fe⁺³. The study reveals that the incorporation of transition metal ions in LS₂ composition has a positive effect on the physical-chemical properties of the prepared glass-ceramics. Therefore, it constitutes to prepare future glass-ceramic applications as hermetic seals of metals as well solid electrolyte materials.     

Synthesis and Structural Probing of Eu3+ Doped BaYF5 Nano-Crystals in Transparent Oxyfluoride Glass-Ceramics

Transparent oxyfluoride glass-ceramics containing Eu: BaYF₅ nano-crystals in the newly developed SiO₂–K₂CO₃–BaF₂–YF₃–Sb₂O₃ glass system are synthesized by melt quenching method followed by optimized ceramization process. The X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy confirmed the precipitation of tetragonal BaYF₅ nano-crystals in glass matrix. The coexistence of Eu²⁺ and Eu³⁺ ions in both glass and glass-ceramics are ascertained from their emission and excitation spectra. The in situ formation of divalent europium (Eu²⁺) along with Eu³⁺ during high temperature synthesis under ambient atmosphere is explained through optical basicity model. The Eu³⁺ emission from upper excitation states (⁵D₃₋₁) and reduced asymmetry ratio (R = I_ED/I_MD) in glass-ceramics have established the dopant ion incorporation into fluoride nano-crystalline environment. The observed luminescence properties of Eu:BaYF₅ are compared with that of Eu:BaYF₅ nanocrystals containing transparent glass-ceramics and their marked differences are discussed.     

Chromium in lead metasilicate glass: Solubility,valence, and local environment via multiple spectroscopy

In this article the doping of chromium in a lead metasilicate glass is explored using Raman, UV–Vis, and Cr K-edge XANES spectroscopy. Our results indicate that the Cr ions are predominantly present as CrO₄^2? complexes, with a minor amounts of Cr(III). The solubility of Cr is limited to ～1 mol % Cr₂O₃. This boundary was inferred from the intensity changes to the CrO₄^2? stretching vibrations and confirmed by the inability to produce a homogeneous glass containing 2 mol % Cr₂O₃. The establishment of the solubility limit of Cr in lead glasses is important to design more effective glass compositions depending on the desired application. Finally, this low solubility indicates that Cr₂O₃ could be used as a potential nucleating agent for lead-silica based glass-ceramics.     

Persistent luminescence of Eu/Dy-doped Sr2MgSi2O7 glass-ceramics processed by aerodynamic levitation

Glass beads of the Sr₂MgSi₂O₇ stoichiometric composition and a non-stoichiometric composition with higher SiO₂/SrO ratio doped with Eu₂O₃/Dy₂O₃ were prepared through aerodynamic levitation coupled to CO₂ laser heating. The glass beads were subsequently treated at 1100 ºC to produce glass-ceramics with Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ as the main crystalline phase. The doped glasses exhibit red emissions; after crystallisation, the corresponding glass-ceramics emit blue light under UV excitation. The starting glass composition considerably affects the crystallisation process, resulting in Sr₂MgSi₂O₇ glass-ceramics with very different microstructures which, in turn, have a significant influence on the luminescence properties. The photoluminescence emission spectra of the glass-ceramics under UV light show a broadband emission (λ = 400–500 nm) with a main peak assigned to the typical Eu²⁺ transition under excitation at 365 nm. Both the intensity of the emission and the persistence time significatively increase on decreasing temperature. Glass-ceramics from the non-stoichimetric glass composition co-doped with 1Eu₂O₃/0.5Dy₂O₃ (mol%.) provided the longest persistence times.     

Effect of ZnO on the crystallization behavior and properties of SiO2–CaO–Al2O3–Fe2O3 glass-ceramics prepared from simulated secondary slag after reduction of copper slag

The feasibility of preparing low-cost glass-ceramics from Zn-containing dust and secondary molten slag generated during the carbothermal reduction of copper slag was investigated. Analytical-grade agents, such as ZnO, Fe₂O₃, SiO₂, CaO, and Al₂O₃, were used to simulate the dust and secondary slag. The effect of ZnO content on the crystallization behavior, structure, and mechanical properties of the glass-ceramics was investigated through X-ray diffraction analysis, scanning electron microscopy-energy dispersive spectrometry, differential scanning calorimetry, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results showed that with increased ZnO content from 0 to 6 wt%, the crystallization activation energy of base glass increased from 386.05 to 425.89 kJ/mol. Meanwhile, the average value of the crystal growth index increased from 1.91 to 4.10, and the highest crystallization rate of the glass-ceramics increased from about 1.44 to 23.11 mm³/min. The increased ZnO in glass-ceramics promoted the precipitation of gehlenite, but inhibit the crystallization of anorthite. When the ZnO content was 6 wt%, the comprehensive properties of the glass-ceramics were better; the flexural strength, microhardness, volume density, water absorption rate, and open porosity were 58.67 MPa, 738.35 HV, 2.92 g/cm³, 0.44% and 1.27%, respectively.     

Preparation and characterization of alkali-free glass substrates with enhanced properties for TFT–LCDs applications

To obtain an alkali-free glass substrate with enhanced properties for thin-film transistor–liquid crystal displays (TFT–LCDs) applications, we chose a base glass composed of 3B₂O₃-15Al₂O₃-58SiO₂-22MgO-0.5SrO-1.5MgF₂ (mol%) for nucleation–crystallization. The results show that when the nucleation–crystallization processes of the base glass are 810 °C/6 h + 880 °C/6–9 h, the prepared GC/6–GC/9 glass-ceramics exhibit enhanced properties because of the precipitation of nano-sized cordierite. The transmittances in the visible range of the GC/6–GC/9 glass-ceramics exceed 85%, the densities are 2.564–2.567 g/cm³, thermal expansion coefficients are 2.934–3.059 × 10^-6/°C (25–300 °C), compressive strengths are 417–589 MPa, bending strengths are 141–259 MPa, Vickers hardnesses are 6.8–7.8 GPa, and strain points are approximately 735 °C. Considering these properties, the prepared GC/6–GC/9 glass-ceramics have good potential as candidate materials for alkali-free glass substrates. Additionally, these results demonstrate that it is feasible to improve the properties of alkali-free glass substrates by nucleation–crystallization.     

Lithium concentration effect on crystallization kinetics and spectral properties of Cr-doped Li2O–K2O–Al2O3–B2O3 glass-ceramics

Alkali-aluminaborate glass-ceramics doped with Cr ions are synthesized by volume crystallization. According to non-isothermal DSC method three parallel processes occur in material: 2D Avrami-Yerofeev nucleation, 2D and 3D crystallization. During the heat treatment, the LiAl₇B₄O₁₇ crystalline phase is formed. With Li₂O content rising crystallinity of the material increases from 27 to 69% and the crystalline field strength Dq/B of Cr³⁺ increases from 2.25 to 3.55. The photoluminescence spectra possess intense bands at 685, 700, and 715 nm for glass with 6.8 mol.% Li₂O and higher and its decay kinetics is described by the sum of two exponentials. The maximum luminescence QY obtained is 50% at 16.1 mol.% Li₂O. The highest conversion efficiency of the 532 nm LED luminescence obtained by glass-ceramics with chromium is 10%. Thus, Cr-doped alkali-alumina-borate glass-ceramics are a promising material for use in the design of radiation sources for the red and NIR spectral regions.     

Greatly enhanced energy storage density of alkali-free glass-ceramics after dual optimizations by thickness and crystallization temperature

Glass-ceramics show a great application potential in sustainable development, environmental protection, high temperature, high voltage resistance, and so on. Given the breakdown strength has a great contribution to the energy storage density, alkali-free niobate-based glass-ceramics have emerged as a prominent energy storage material. In this study, the 13.64BaCO₃-13.64SrCO₃-32.72Nb₂O₅-40SiO₂ alkali-free glass-ceramics were optimized in thickness and crystallization temperature. The thinning of thickness improves the breakdown strength. At the same time, the dielectric constant gets a maximum value by adjusting the crystallization temperature. Therefore, an ultra-high theoretical energy storage density of 27.47 J·cm⁻³ is obtained. In addition, the finite element software simulates the electric field distribution and electric potential evolution during the development of electric branches, which illustrates the role of glass phase in hindering the development of electric branches and partaking the high electric field. Finally, the effective energy storage density obtained by using P-E loops is 1.49 J·cm⁻³ under 850 kV/cm.     

Effect of metastable phase on the crystallization and mechanical properties of MgO-Al2O3-SiO2 glass-ceramics without nucleating agents

Glass-ceramics without nucleating agents usually undergo surface crystallization, which deteriorates the overall performance of the products. In this paper, we evaluated the effects of the metastable MgAl₂Si₃O₁₀ crystalline phase on the crystallization behavior of a MgO–Al₂O₃–SiO₂ (MAS) glass without nucleating agents and mechanical properties of the glass-ceramics obtained. The results demonstrated that the precipitation of metastable MgAl₂Si₃O₁₀ crystallites promotes the crystallization mechanism transformed from surface crystallization into volume crystallization with two-dimensional crystal growth. Furthermore, the grain size of MgAl₂Si₃O₁₀ near the surface of the prepared glass-ceramics was larger than that of MgAl₂Si₃O₁₀ inside, which helps to generate compressive stress and improves its mechanical properties. The glass-ceramics containing metastable MgAl₂Si₃O₁₀ phase exhibited an enhanced hardness in the range of 7.6 GPa–9.5 GPa for indentation loads ranging from 2.94 N to 98 N, and indentation size effect behavior was observed in Vickers hardness tests of both MAS glass and glass-ceramics. The load-independent hardness values for MAS glass and glass-ceramics were reliably evaluated by the modified proportional specimen resistance (MPSR) model of 7.1 GPa and 7.6 GPa, respectively, with a high correlation coefficient of more than 0.9999. This work reveals the unexploited potential of the metastable phase in improving the crystallization ability and mechanical properties of glass-ceramics.     

The influence of iodide on glass transition temperature of high-pressure nuclear waste glasses

The glass transition temperature (T_g) is a key parameter to investigate for application in nuclear waste immobilization in borosilicate glasses. T_g for several glasses containing iodine (I) has been measured in order to determine the I effect on T_g. Two series of glass composition (ISG and NH) containing up to 2.5 mol% I and synthesized under high pressure (0.5 to 1.5 GPa) have been investigated using differential scanning calorimetry (DSC). The I local environment in glasses has been determined using X-ray photoelectron spectroscopy and revealed that I is dissolved under its iodide form (I⁻). Results show that T_g is decreased with the I addition in the glass in agreement with previous results. We also observed that this T_g decrease is a strong function of glass composition. For NH, 2.5 mol% I induces a decrease of 24°C in T_g, whereas for ISG, 1.2 mol% decreases the T_g by 64°C. We interpret this difference as the result of the I dissolution mechanism and its effect on the polymerization of the boron network. The I dissolution in ISG is accompanied by a depolymerization of the boron network, whereas it is the opposite in NH. Although ISG corresponds to a standardized glass, for the particular case of I immobilization it appears less adequate than NH considering that the decrease in T_g for NH is small in comparison to ISG.     

Facile obtainment of luminescent glass-ceramics by direct firing of a preceramic polymer and oxide fillers

Rare-earth (RE) doped glass-ceramics represent very interesting luminescent materials. The thermal annealing of the glass precursor causes the controlled precipitation of several crystalline phases, in which RE may be variously distributed, also with different oxidation states, e.g. Eu²⁺ and Eu³⁺. The present investigation demonstrates the feasibility of preparation of RE-doped alumino-boro-silicate glass-ceramics by direct firing in air (at 1000–1200 °C) of a preceramic polymer, filled with nano- and micro-sized particles, as an alternative to glass melting and annealing. In particular BaCO₃ or SrCO₃ micro-particles, mixed with nano-sized γ-Al₂O₃, were found to react with amorphous silica, available from the oxidative decomposition of a commercial silicone, yielding a strontium or a barium alumino-silicate phase. Boric acid micro-particles contributed both to the development of a liquid phase upon firing (promoting ionic interdiffusion) and to the formation of a La-borate phase, by interaction with La₂O₃ micro-particles. The blue and red luminescence of the obtained glass-ceramics is attributed to the incorporation of Eu²⁺ and Eu³⁺ ions, from nano-sized Eu₂O₃ filler, in alumino-silicate and borate phases, respectively.     

Solidification of glass-ceramics of simulated fission products RE3+, Sr2+, Ba2+ in chlorine-containing waste molten salt

Embedding nuclear waste in glass-ceramic and immobilizing nuclides in ceramic lattice is an effective way for the disposal of high-level radioactive waste. In this paper, a method of solidification of simulated various nuclides was proposed, i.e., RE³⁺(RE = La, Sm, Nd, Dy), Sr²⁺ and Ba²⁺ precipitated from waste molten salt in the form of REPO₄, SrCO₃ and BaCO₃ were solidified in glass-ceramics. To avoid the decomposition of SrCO₃ and BaCO₃ at high temperature, SrCO₃/BaCO₃ containing Cl⁻ salt was further sintered with NH₄H₂PO₄ to form Sr₅(PO₄)₃Cl/Ba₅(PO₄)₃Cl ceramics. It was found that the prepared REPO₄ belonged to monoclinic or tetragonal crystal system, while Sr₅(PO₄)₃Cl and Ba₅(PO₄)₃Cl belonged to hexagonal crystal system. REPO₄, Sr₅(PO₄)₃Cl and Ba₅(PO₄)₃Cl ceramics were co-solidified in iron phosphate glass. BET results showed that the ceramics had a dense structure without any pore inside. XRD, TEM and HRTEM results showed all ceramics had high crystallinity, and nuclides could enter the lattice structure of ceramics through isomorphic replacement, which made the nuclides stable in the crystal structure. The effects of embedding rate on the volume density, Vickers hardness and wettability of glass-ceramics were explored. It was found that the density of the glass-ceramics gradually increased with the increase of ceramic embedding rate, however, the Vickers hardness firstly increased and then decreased. When the embedding rate reached 20 wt%, the Vickers hardness of the glass-ceramics could reach 583.90 GPa. The water contact angles of glass-ceramics with an embedding rate 0–40 wt% were measured to be 70.45°–84.05°, indicating glass-ceramics having a good water leaching resistance. Furthermore, the normalized leaching rate NR_i of La³⁺, Sm³⁺, Nd³⁺, Dy³⁺, Sr²⁺, Ba²⁺, Cl⁻ on the 28th day were estimated to be 7.53 × 10⁻⁷, 5.02 × 10⁻⁷, 5.12 × 10⁻⁷, 4.04 × 10⁻⁷, 1.22 × 10⁻³, 1.59 × 10⁻⁴, 1.07 × 10⁻⁴ g‧m⁻²‧d⁻¹, which indicating that all elements remained good leaching resistance.     

Preparation of Gd2Zr2O7 nanoceramics from two-step thermal treatment and the aqueous durability analysis

Gd₂Zr₂O₇ ceramics demonstrate important prospect in the immobilization of high-level radioactive wastes (HLWs). In this study, Gd₂Zr₂O₇ nanoceramics were fabricated using two-step method, where Gd₂Zr₂O₇ nanopowder was firstly synthesized by solvothermal method and Gd₂Zr₂O₇ nanoceramics were subsequently sintered via self-propagating chemical furnace plus quick pressing (SCF/QP). The characterization results display that the Gd₂Zr₂O₇ nanocrystalline ceramics with average grain size of 78 nm and bulk density of 5.53 g cm⁻³ were successfully prepared. The results of MCC-1 static leaching experiments show that the normalized release rate (LR_i) of Gd is 2.2 × 10⁻² g m⁻²•d⁻¹ on the first day and converges to 1.2 × 10⁻³ g m⁻²•d⁻¹ after 42 days. Zr shows superior chemical stability as the 21 days LR_Zr value is as low as 2.7 × 10⁻⁶ g m⁻²•d⁻¹, which becomes constant as the leaching duration prolongs.