Yttrium Silicate Research Articles

Geopolymers made using organic bases. Part III: Cast magnesium, yttrium, and zinc aluminosilicate and silicate ceramics

AbstractIt was shown in Part II of this series of articles that geopolymers synthesized with organic bases could be used as precursors to mullite and mullite + glass composites. A natural next step is to determine whether it is possible to synthesize materials outside the Al2O3·SiO2 and alkali oxide·Al2O3·SiO2 phase systems. Hence, the focus of this study was the use of geopolymer‐like processing to make preceramic bodies with magnesium, yttrium, and zinc aluminosilicate and silicate compositions. These preceramics were successfully fired into monolithic bodies of cordierite, mixed yttrium and aluminum silicates, yttrium disilicate, and willemite. The synthesis of these preceramics employed a guanidine silicate solution, a synthetic oxide powder, and in some cases metakaolin to reach the oxide composition of the ceramic. All solidified within 3 days at 20°C or 50°C, depending on the composition. For the first time, this study showed that Y2O3 and ZnO can react with silicate solutions to give some Y‐O‐Si and Zn‐O‐Si bonding analogous to Al‐O‐Si bonding in geopolymers. These results suggest that other silicate compositions may be possible, such as with the rare earth oxides, which might be valuable to process like a geopolymer rather than by traditional ceramic processing. However, the ceramics made here were generally porous due to the expansion of gases within the sample that were trapped by a viscous liquid phase during firing.

Influence of water vapor partial pressure on self-healing and oxidation of SiC-dispersed yttrium silicate composites

The self-healing and oxidation behavior of SiC-dispersed Y2Si2O7-Y2SiO5 composites were elucidated under various water vapor partial pressures PH2O. Samples were exposed in a furnace for self-healing experiments at 1100–1300°C and for high-temperature oxidation at 1200–1400°C, both for 1–24 h, under PH2O ranging from 2×104 to 5×104 Pa, while keeping PO2constant at 2×104 Pa. Water vapor promoted the self-healing effectiveness of the composites. A mechanism contributing to the closure of surface cracks was consistent with volume expansion derived from the oxidative conversion of SiC into SiO2 and the outward diffusion of yttrium cations. The formation of the internally oxidized zone signifies oxidation behavior, resulting from the inward diffusion of oxygen ions. Growth of the internally oxidized zone obeys the parabolic pattern. The influence of PH2O on the high-temperature oxidation of SiC/Y2Si2O7-Y2SiO5 is discussed in this study.

Corrosion behavior of Si-18at%Y alloy in air/water-oxygen environment

This work aimed to investigate the corrosion behavior of Si-18at%Y alloys in air oxidation and water-oxygen corrosion environments. The objective was to understand how different times, temperatures, and the presence or absence of water vapor affected the distribution and transformation of the alloy’s phases. The results revealed that extended duration facilitates growth of yttrium silicate, while higher temperature promotes stable phase transformation. The distribution and type of yttrium silicate are influenced by the presence of SiO2. At lower temperatures, water vapor facilitated the formation of SiO2, whereas at higher temperatures, it depleted SiO2 and inhibited the generation of yttrium silicate.

Synthesis and up-conversion luminescence of erbium-doped yttrium silicate single crystal nanoparticles tailored by the mesoporous silica template

Erbium-activated yttrium silicate nanoparticles were tailored using a mesoporous silica template. Transmission electron microscopy (TEM) revealed that the synthesized particles are single crystals of yttrium pyrosilicate (α−Y2Si2O7:Er), possessing a spherical shape (with an average size of about 210 nm) and a narrow size distribution. Up-conversion luminescence of the synthesized particles was investigated in the green spectral region under excitation by a laser diode operating at a wavelength of 808 nm. In the range of 510-580 nm, intense narrow lines with a Lorentzian shape were observed, attributed to radiative transitions from two thermally coupled energy levels of the Er3+ ion [2H11/2→4I15/2 (520–540 nm) and 4S3/2→4I15/2 (545–570 nm)]. It was experimentally demonstrated that within the temperature range of 250–520 K, the equilibrium populations of the 2H11/2 and 4S3/2 levels follow the Boltzmann distribution. This result provides a basis for the potential use of the synthesized particles as temperature sensors in various applications, including biomedical ones.

Effect of temperature and oxidative atmosphere on the oxidation behavior of yttrium-containing ceramics

Yttrium-containing ceramics exhibit excellent resistance to water-oxygen corrosion, making them an attractive choice as the modified matrix for SiCf/SiC composites. However, the oxidation products of yttrium-containing ceramics are complex and vary widely in performance. In this study, YSOC ceramics, which are composed of yttrium silicate, SiO2, and SiC, were prepared using Y2O3, SiO2, SiC, and Li2CO3. This research investigated the effects of high temperatures, air oxidation, and water-oxygen corrosion on the phase compositions of YSOC ceramics. The influence of environmental factors on the synthesis and decomposition of yttrium silicate was analyzed. Moreover, the study explored the compatibility of different oxidation products with SiC. The results suggest that Y2SiO5 and Y2Si2O7 are formed through the low eutectic of SiO2, Y2O3, and Li2CO3. The high SiO2 content likely contributes to the relatively low formation temperature of Y2Si2O7. In the oxidizing environment, Y2SiO5 reacts with SiO2 to produce Y2Si2O7. Conversely, in the water vapor-containing atmosphere, Y2Si2O7 undergoes hydrolysis to form Y2SiO5. Y2Si2O7 displays a reduced elastic modulus in comparison to SiC fibers and exhibits favorable physical and chemical compatibility with SiC fibers. However, the hydrolysis of Y2Si2O7 may potentially affect the water-oxygen corrosion resistance of the ceramics. These findings will significantly advance research and enhance understanding of the water-oxygen corrosion behaviors of yttrium-containing matrix-modified composites.

Significant impact of carbon source on microstructure and water–oxygen corrosion behavior of Si–Y alloy modified SiC/SiC composite

This study investigated the influence of carbon source on the microstructure and water–oxygen corrosion behavior of Si–Y alloy modified SiC/SiC composites. The results indicated that incorporating a small-sized and diffusely distributed carbon source within the matrix not only facilitates the preparation of a highly dense matrix, but also enables a uniform dispersion of the reaction-generated SiC. Furthermore, with the assistance of residual Si–Y alloy, the dispersed SiC enhanced the matrix strength, leading to a stepwise fracture behavior of the composites. Yttrium silicate with a gradient structure formed around the dispersed SiC could effectively exert its water–oxygen corrosion resistance. After 100 h of water–oxygen corrosion test at 1300 °C, the flexural strength of the composites with this structure reached 416 MPa, with a retention rate of 85 %. Both bending strength and retention were found to be at a high level in the current research on matrix modification.

Significantly improved water-oxygen corrosion resistance of SiC/SiC composite modified by Si-B-Mo-Y using reactive melt infiltration

Si-B-Mo-Y modified SiC/SiC composites were prepared by reactive melt infiltration (RMI) process to study their high-temperature water-oxygen corrosion resistance, and to compare them with SiC/SiC composites prepared by RMI using Si. The results show that the corrosion rates of the modified composites are only 1/9, 1/10 and 1/3 of those of the comparison samples at 1200°C, 1300°C and 1400°C, respectively, which is attributed to the higher densification of the modified composites. More importantly, the modified composites were able to form borosilicates, which effectively healed the oxide film defects; meanwhile, yttrium silicate inhibited the reaction between borosilicates and water vapor.

Theoretical Determination of the Electronic Structures and Energy-Level Splitting for Pr3+-Doped Y2SiO5 Crystals.

Trivalent praseodymium (Pr3+)-doped yttrium silicate (Y2SiO5) crystals have been widely used in various phosphors owing to their excellent luminescence characteristics. Although a series of studies have been carried out on its application prospects, the electronic structures and energy-transfer mechanisms of Pr3+-doped Y2SiO5 (Y2SiO5:Pr) remain an exploratory topic. Herein, the crystal structure analysis by the particle swarm optimization structure search method is used to study the structural evolution of Y2SiO5:Pr. Two novel structures with local [PrO7]-11 and [PrO6]-9 [Y2SiO5:Pr (I) and Y2SiO5:Pr (II)] are successfully identified. The impurity Pr3+ ions occupy the Y3+ sites and successfully integrate into the Y2SiO5 host crystal with a Pr3+ concentration of 6.25%. The calculated electronic band structures show that the doping of Pr3+ induces a reduction in band gaps for the host Y2SiO5 crystal. The conduction bands near the Fermi level are completely composed of f states. For the atomic energies of Pr3+ in Y2SiO5, the Stark levels and transitions are properly simulated based on a new set of crystal field parameters (CFPs) at the C1 site symmetry. A satisfactory r.m.s. dev. of 15.57 cm-1 with 9 free ion parameters (plus 27 fixed CFPs as obtained from ab initio calculation) fitted to the 33 observed levels is obtained for the first time. The plentiful energy-level transition lines, from the visible light to the near-infrared region, are deciphered for Pr3+ in Y2SiO5. Blue 3P0 → 3H4 at 465 nm is calculated to be a strong emission line, and it might be an ideal channel for laser actions. These results could not only provide important insights into the rare-earth-doped crystals but also lay the foundation for future research studies of designing the new laser materials.

Rare earth mineralization in volcanic-sedimentary rocks of the Shatak complex (Southern Urals)

The paper presents materials on the study of rare earth mineralization in rocks of the Shatak complex, which belongs to the Mashak formation (RF2). Numerous rare earth minerals have been discovered and characterized in detail in terrigenous rocks, metabasalts and rhyodacites: allanite-(Ce), monazite-(Ce), monazite-(La), monazite-(Nd), nioboeschinite-(Y), aeshinite-(Y) , talenite-(Nd), talenite-(Dy), synchysite-(Ce), Ce–La–Fe oxide, cerite and unidentified compounds: yttrium silicate, cerium silicate, Ce–Fe compound, as well as REE-containing minerals: epidote and fluorapatite. In the contact zone between metabasalts and quartz sandstones, oxyfluoride – (La, Ce) (OnFm)3 mineralization, represented by compounds of variable composition, forming an isomorphic series: trifluoride (La, Ce)F3 – oxyfluoride (La, Ce)OF, is described for the first time in the world literature –oxide (La, Ce)2O3.
 It has been established that the determining factors in the formation of rare earth mineralization in the rocks of the Shatak complex are the conditions and nature of metamorphism and the chemistry of the mineral formation environment.
 The species diversity of rare earth minerals and the peculiarities of their chemical composition make the Shatak volcanic-sedimentary complex a unique object for studying the processes of rare earth mineral formation in various petrotypes of rocks formed in a single geotectonic setting and united by common thermobaric parameters of metamorphism.

Effect of Y2O3 Concentration on the Surface and Bulk Crystallization of Multicomponent Silicate Glasses

Multicomponent silicate glasses are crystallized by Y2O3 addition. Depending on the Y2O3 concentration, different crystalline phases evolve. In the absence of Y2O3, a multicomponent glass crystallizes as ZnSnO3, while with the addition of just 3% of this oxide, ZnSnO3 no longer crystallizes and ZrSiO4 appears instead. Different yttrium silicate crystals are formed in all glasses containing Y2O3, but, while α-Y2Si2O7 and β-Y2Si2O7 are favored at low Y2O3 concentrations, the γ-Y2Si2O7 and y-Y2Si2O7 phases are favored at the maximum Y2O3 content. At a 12% Y2O3 concentration, barium and calcium silicate crystalline phases also evolve. Interestingly, the crystalline phases appearing on the surface of the material present different microstructures compared to crystals developed in the bulk. While the crystallized surface presents a tabular-shape type, crystallization in the bulk is of a prismatic type at low Y2O3 concentrations and of a globular (spherical) type at higher concentrations. The main crystal size ranges between 0.85 and 0.75 micrometers, but most of the crystals coalesce to form larger superstructures depending on the Y2O3 concentrations.

A thermodynamic study of the influence of the Al2O3 content on the CaO-SiO2-YO1.5 system

In aircraft engines applications, the interactions between rare earth silicates (mainly yttrium silicates) used as Environmental Barrier Coatings (EBCs) on turbine blades and liquid calcium-magnesium-aluminosilicates (CMAS) due to the particles ingested by the engines may lead to severe damages at high temperature. Due to the large range of composition of CMAS, simplified model systems must be used to have a good comprehension of the thermochemical phenomena leading to degradation. The interaction between ceramics and CMAS can lead to the precipitation of phases as apatite Ca2Y8(SiO4)6O2 and cyclosilicate Ca3Y2(Si3O9)2 which might provide protection to the EBC. However, their thermodynamic stability depends on many parameters. In the present work, the influence of alumina Al2O3 addition to the ternary system CaO-SiO2-YO1.5 has been studied in order to verify the equilibrium with the liquid field at 1300 °C.

Sol-Gel Synthesis and Characterization of Cerium-Doped Yttrium Silicate

Sol-Gel Synthesis and Characterization of Cerium-Doped Yttrium Silicate

The impact of water and oxygen contents on the corrosion performance of yttrium silicate modified SiCf/SiC composites under high temperature conditions

SiCf/SiC composites have emerged as a prominent research area in the field of structural materials for engine hot-end applications. However, SiCf/SiC composites exhibit susceptibility to oxidation and corrosion when exposed to oxygen and water vapor. The yttrium silicate ceramic in the SiCf/SiC composite (SiCf/SiC-YS composite) serves as corrosion-resistant matrix. The corrosion behavior of SiCf/SiC-YS composites was assessed by examining the phase composition, microstructure, and bending strength after exposure to different water and oxygen environments. The results show that SiCf/SiC-YS composites exhibit excellent resistance to water and oxygen at temperatures below 1300 °C. Above 1300 °C, the decomposition of yttrium disilicate affects the internal structure and bending strength of the composites. Temperature- and water vapor concentration-dependent crystal transformation of yttrium silicate is a crucial factor that influences the microstructure and water-oxygen corrosion resistance of SiCf/SiC-YS composites.

Preparation and ablation resistance of carbon fiber with yttrium silicate coating

AbstractIn order to solve the shortcoming of fiber oxidation in a high‐temperature environment and improve the antiablative performance, yttrium silicate is coated on the carbon fibers’ surface by the sol‐gel process. In the present work, investigations of the ablation resistance of carbon fiber composites with yttrium silicate coatings (YS‐CFs) prepared by different sol contents and sintering temperatures are reported. The results show that YS‐CFs exhibit excellent ablation resistance in the oxyacetylene test with a heat flow of 1.5 MW/m2. The surface coating of carbon fiber is composed of a mixture of cristobalite, yttrium monosilicate, and yttrium disilicate. The best ceramic coating could be obtained by dipping 20% silica sol and 14% yttrium sol in turn and sintering at 1300°C. In this case, the linear and mass ablation rates reach the minimum values of .667 μm/s and 2.975 mg/s, respectively. YS‐CFs could be used as reinforcements for thermal protection materials in high‐temperature environments.

Thermal aging and CMAS corrosion behaviors of Y2SiO5 ceramic for environmental barrier coatings

Yttrium silicate (Y2SiO5) is considered as one of the most promising candidate materials for environmental barrier coatings. In this paper, Y2SiO5 powder with a single phase were successfully prepared by high-temperature solid phase reaction method. The influence of sintering behavior on the microstructure, phase composition and mechanical properties of Y2SiO5 ceramics was studied at 1400 °C. In addition, the corrosion behavior and mechanism of Y2SiO5 against CMAS at 1250 °C and 1350 °C were also investigated. The results showed that the grain size of the prepared Y2SiO5 ceramic was about 1.28 µm with relatively uniform, and there were many pore structures. Although Y2SiO5 was still the main phase, a new small amount of Y4.67(SiO4)3O phase was formed in Y2SiO5 ceramics after sintering at 1400 °C for 25 h. The sintering phenomenon of Y2SiO5 ceramics occurred at 1400 °C: the porosity decreased and the grain size grew. With the increase of sintering time, fracture toughness first increased and then decreased. The maximum fracture toughness was 4.84 MPa m1/2 after 50 h sintering. Part of Y2SiO5 was dissolved in CMAS melt and Ca4Y6(SiO4)6O rare-earth oxyapatite phase was generated after CMAS corrosion for 24 h. The corrosion zone could be divided into loose corrosion area (about 93 µm thickness) and dense reaction layer with Ca4Y6(SiO4)6O phase (about 16 µm thickness) at 1250 °C for 24 h. With the increase of corrosion time and corrosion temperature, both the corrosion depth of CMAS and the thickness of dense reaction layer increases. The dense Ca4Y6(SiO4)6O layer can effectively resist the further corrosion of CMAS melt.

Y/YbB4-modified SiCf/SiC composites with enhanced water-oxygen corrosion resistance

Silicon carbide fibers-reinforced silicon carbide matrix (SiCf/SiC) composites, which are commonly used as thermal structural materials in different components, e.g., combustion chamber liners, are susceptible to water-oxygen corrosion, resulting in rapid performance degradation and structural collapse. To enhance their resistance to water-oxygen corrosion, the incorporation of rare-earth silicates (RE silicates) has been explored. In this study, novel Y/YbB4-modified SiCf/SiC composites, with superior resistance to water-oxygen corrosion, are fabricated using a combination of slurry infiltration (SI) and reactive melt infiltration (RMI) process. Results demonstrate that Y/YbB4-modified SiCf/SiC composites exhibit open porosity of 3.2 ± 0.4%, corresponding to remarkable reduction of 69.8% compared to CVI-SiCf/SiC composites. Furthermore, after being exposed to water-oxygen environment at 1200 °C for 100 h, the surface of Y/YbB4-modified SiCf/SiC composites displays various yttrium silicates and ytterbium silicates. The material exhibits strength retention of 76.84%, indicating a notable improvement of 15.71% over the CVI-SiCf/SiC composites.

Effect of the Europium during spark plasma sintering of yttrium silicate powder

Spark plasma sintering process was used to densify yttrium silicate powder doped with Europium, at temperature of 1673 K. Densification rate was evaluated during spark plasma sintering of yttrium silicate powder doped with 0, 1, 2.5 and 5 Eu weight percent. The activation energy for densification of the powder was determined at early stage of the sintering. After sintering the microstructure was analysed from sintered coupons doped with Europium+3, identifying an yttrium silicate second phase present.

Color-tunable persistent luminescence phosphor for multimode dynamic anti-counterfeiting

Using a solid-state approach, the persistent luminescence property in sodium yttrium silicate which was single-doped or co-doped by europium or cerium was studied. The orthorhombic structure with the space group P212121 could be indexed to all samples, according to X-ray powder diffraction. The luminescence characteristics of these phosphors, including photoluminescence, luminescence degradation, and temperature-dependent emission, were systematically investigated. Under UV (∼365 nm) irradiation, blue/green emissions with broad bands peaking at 450/510 nm attributed to the characteristic 5d→4f/4f65d→4f7 transitions of Ce3+/Eu2+ could be observed in Na3LuSi3O9:Ce3+ and Na3LuSi3O9:Eu2+, respectively. Moreover, blue and green persistent luminescence was also observed in Ce3+ or Eu2+ single-doped samples. Thermoluminescence curve of Na3LuSi3O9:Eu2+, Ce3+ reveals that Na3LuSi3O9:Ce3+ and Na3LuSi3O9:Eu2+ have similar trap distribution. Tunable persistent luminescence can be realized via ratio control of Ce3+ and Eu2+. A possible afterglow mechanism was presented and discussed. The prepared materials have the potential of multimode dynamic luminescence, because they are highly sensitive to the composition, the excitation wavelength, and the detecting time. The outstanding abilities of Na3LuSi3O9:Ce3+, Eu2+ demonstrate the practical capability of this material for fingerprint identification and anti-counterfeiting.

Thermodynamic analysis of processes in the high-temperature polycomponent Fe–Y–Si–O–C system

In the production of low-carbon and high-quality steels, it is recommended to use special complex alloys of rare earth metals for deoxidation, microalloying and modification. To elucidate the mechanism of action of each of the components of the alloy, it is necessary to differentiate the action of each individual element. Yttrium is usually classified as a rare earth metal, but its deoxidizing and modifying ability deficiency studies. The use of yttrium applica-tion is known to increase in density, ductility, scale resistance, resistance to high-temperature corrosion of steel, effec-tively affects the shape, size and distribution of non-metallic inclusions. This paper consider the interaction of yttrium, silicon, and carbon with oxygen dissolved in liquid iron. Nonmetallic inclusions formed in this case can be identified on the state diagram of the FeO–Y2O3–SiO2 oxide system. This diagram is absent in the literature; therefore, it was mod-eled on the basis of the available binary phase diagrams of the FeO–Y2O3, FeO–SiO2, and Y2O3–SiO2 systems. Com-plex deoxidation by yttrium and silicon is possible only at yttrium concentrations in liquid iron less than 0.0001% (ox-ide melt or yttrium silicates are formed as non-metallic inclusions). If the concentration of yttrium is higher than this value, then it is the only deoxidizer. In the presence of carbon, liquid non-metallic inclusions can form in a very narrow range of liquid metal compositions, and the main oxide non-metallic inclusion is yttrium oxide. At yttrium concentra-tions below 0.0001% and silicon concentrations up to 1%, only carbon is the deoxidizer. Taking into account the previ-ously studied Fe–Y–Me–O–C (Me–Ca, Mg, Al, Cr) systems, a thermodynamic data base was created for designing the compositions of complex yttrium-containing ligatures.

Identification of paramagnetic centers of gadolinium and iron in scandium and yttrium orthosilicates

The study of grown Sc2SiO5 : Gd and Sc2SiO5 : Fe crystals was carried out by the paramagnetic resonance method. It has been established that Fe3+ ions replace Sc3+ in both crystallographic positions, while Gd3+ ions exhibit a single center localized in a larger position with a coordination number of 7. Measurement of the orientational behavior of the positions of transitions of Fe3+ and Gd3+ centers in two orthogonal planes made it possible to determine the parameters of their triclinic spin Hamiltonians. To determine the localization of impurity ions Cr3+, Fe3+ and Gd3+ in scandium and yttrium silicates, the orientation of the main Z axes of the fine structure tensors of the second rank was used. Keywords: scandium and yttrium silicates, impurity ions, paramagnetic resonance.