Formation Of ZrSiO4 Research Articles

Influence of sintering atmosphere on the formation of ZrSiO4 by solid‐state sintering method

AbstractExploring the influence of sintering atmosphere on the formation of ZrSiO4 is of great significance. Herein, ZrSiO4 ceramics were prepared by the solid‐state reactive sintering method under different atmospheres (air, N2, vacuum, and Ar + 5%H2). The influence of sintering atmosphere on the phase and microstructure evolutions of the obtained ceramics was investigated. It was found that ZrSiO4 ceramics could be prepared under air atmosphere, whereas ZrO2–SiO2 glass ceramics were obtained under N2, vacuum, and Ar + 5%H2 atmosphere, which may be due to the fact that the oxygen‐deficient environment inhibits the transformation of ZrO2 to tetragonal phase (t‐ZrO2) and the crystallization of amorphous SiO2. The results demonstrated that t‐ZrO2 and c‐SiO2 were beneficial for the formation of ZrSiO4. The ZrSiO4 conversion fraction was up to 96.16% under air atmosphere at 1450°C for 6 h. Furthermore, the predominant formation mechanism of ZrSiO4 was the reaction between t‐ZrO2 and c‐SiO2.

High capacity and aqueous stability immobilization of simulated trivalent actinides by zircon-based borosilicate glass-ceramics: Synergistic effect between the crystal lattice and glass network immobilization

The development of matrix with high capacity and stability immobilization of nuclear waste is highly desirable. Herein, new type of zircon-based borosilicate glass-ceramics (ZBGC) with high immobilization capacity and excellent aqueous stability was prepared and applied to immobilize simulated trivalent actinide (Nd). The effects of Nd doping and sintering temperature on the microstructure and phase composition of the obtained ZBGC were researched. The experimental suggested that high ZrSiO4 formation rate (97.49 wt%) was obtained by tuning the Nd content and sintering temperature. The record high immobilization capacity of Nd in ZGBC (18 at%) was achieved owing to the synergistic effect between the crystal lattice and glass network immobilization. Additionally, the obtained Nd-doped ZBGC exhibited excellent aqueous stability (∼10−6 g m−2 d−1) due to the high compactness. The results demonstrated that ZBGC with high immobilization capacity and aqueous stability could be potential matrix for actinides immobilization.

Rapid and low-temperature preparation of zircon ceramic by hydrothermal-assisted sol-gel process and microwave sintering

During the traditional preparation of zircon, higher sintering temperatures and longer holding times are inevitable. A novel hydrothermal-assisted sol-gel process and microwave sintering (HM, microwave sintering precursors derived from hydrothermal-assisted sol-gel process) were provided to prepare zircon ceramics hereof. The influences of sintering temperature and holding time on the phase composition, microstructure, and compactness of ceramics were investigated. Data display that the properties of the obtained ceramics were highly dependent on the temperature and time, and the ZrSiO4 formation efficiency can be improved by increasing these two factors. The sample prepared by the HM process has the formation efficiency of ZrSiO4 up to 91.74 wt% (HM-1350-300), which far exceeds that of conventional microwave sintering (M-1350-300, 45.02 wt%). The results demonstrate that the HM process can be employed to obtain ZrSiO4 ceramics rapidly at low temperatures.

Dual occupancy of Tb3+/PO43− at the tetragonal lattice of ZrSiO4 influenced through titanium addition. Synthesis, mechanical, optical and imaging characteristics

The salient features of zircon (ZrSiO4) display their application potential in hard tissue replacements. However, the formation of ZrSiO4 through synthetic approach at relatively low temperature requires the addition of mineralizers. Herein, titanium has been used as a mineralizer to promote the ZrSiO4 formation and further a series of dual substitution of Tb3+/PO43− have been undertaken to investigate their capability to accommodate at the tetragonal crystal lattice of ZrSiO4. The rationale to substitute Tb3+/PO43− is mainly based on tailoring the bioimaging capacity of ZrSiO4 by hosting Tb3+ whereas the accommodation of PO43− is due to its significance in forming a major component in inorganic bone mineral. The characterization studies revealed the dual occupancy of Tb3+/PO43− at the crystal lattice of ZrSiO4 until 10 mol%, beyond which the crystallization of TbPO4 is noticed. Tb3+ substitution has induced a series of fascinating features in ZrSiO4 namely the fluorescence in the visible region, computed tomography (CT) efficiency, paramagnetic response with T2 magnetic resonance imaging (MRI) characteristics. Nevertheless, the crystallization of TbPO4 as a secondary component signified a detrimental effect on the mechanical properties of ZrSiO4. The in vitro tests performed on MG63 cell lines accomplished the biocompatibility features of Tb3+/PO43− substituted ZrSiO4.

Far from equilibrium ultrafast high‐temperature sintering of ZrO2–SiO2 nanocrystalline glass–ceramics

AbstractUltrafast high‐temperature sintering (UHS) is a novel sintering technique with ultrashort firing cycles (e.g., a few tens of seconds). The feasibility of UHS has been validated on several ceramics and metals; however, its potential in consolidating glass–ceramics has not yet been demonstrated. In this work, an optimized carbon‐free UHS was utilized to prepare ZrO2–SiO2 nanocrystalline glass–ceramics (NCGCs). The phase composition, grain size, densification behavior, and microstructures of NCGCs prepared by UHS were investigated and compared with those of samples sintered by pressureless sintering. Results showed that NCGCs with a high relative density (～95%) can be obtained within ～50 s discharge time by UHS. The UHS processing not only hindered the formation of ZrSiO4 and cristobalite but also enhanced the stabilization of t‐ZrO2. Meanwhile, owing to the ultrashort firing cycles, the UHS technology allowed the NCGCs to be consolidated in a far from equilibrium state. The NCGCs showed a microstructure of spherical monocrystalline ZrO2 nanocrystallites embedded in an amorphous SiO2 matrix.

Enhancing the zircon yield through the addition of calcium phosphates into ZrO2-SiO2 binary systems: synthesis and structural, morphological, mechanical and in vitro analysis.

The crystallization of ZrSiO4 is generally accomplished by the addition of mineralizers into ZrO2-SiO2 binary oxides. The current investigation aimed to investigate the effect of adding calcium phosphates into ZrO2-SiO2 binary oxides on the yield of ZrSiO4. The concentration of calcium phosphate additions were varied to obtain ZrSiO4 that fetches improved mechanical and biological properties for application in hard tissue replacements. The findings highlight the significant role of Ca2+ and P5+ in triggering the ZrSiO4 formation via their accommodation at the Zr4+ and Si4+ sites. Especially, calcium phosphate additions trigger the t- → m-ZrO2 transition beyond 1000 °C, which consequently reacts with SiO2 to promote ZrSiO4 formation. Calcium phosphates are accommodated at the lattice sites of ZrSiO4 with a maximum limit of 20 mol%, beyond which the crystallization of β-Ca3(PO4)2 is noticed. The optimum amount of 20 mol% of calcium phosphates displayed a better strength than that of all the investigated specimens. More than 80% of cell viability in MG-63 cells was invariably determined in all the calcium phosphate-added ZrSiO4 systems.

New insights into the formation mechanism of zircon in a ZrO2–SiO2 nanocrystalline glass-ceramic: A TEM study

We have previously observed that doping of Ca ions was beneficial to the formation of zircon (ZrSiO4). It is well known that synthetic ZrSiO4 is typically formed via a solid-state reaction between ZrO2 and SiO2, in which the interfaces between the reactant and resultant play an important role. However, the interfaces are lacking detailed microstructural observation. This follow-up study aims at exploring the formation mechanism of ZrSiO4 by inspecting the interfaces at the nano and atomic scales with TEM techniques. Results demonstrated that ZrSiO4 was formed in the Ca-doped sample after sintering at 1200 °C, whereas, no ZrSiO4 was formed in the undoped sample even after sintering at 1230 °C. The Ca-doped sample consisted of a continuous ZrSiO4 matrix with dispersed ZrO2 nanocrystallites. Doping of Ca ions promoted the formation of ZrSiO4 by causing lattice distortion and oxygen vacancies in ZrO2 lattices. Thin amorphous grain boundary complexions were found between ZrO2 nanocrystallites and between ZrO2 and ZrSiO4 crystallites. These amorphous complexions acted as reaction sites and an intermediate metastable state for the solid-state reaction. A detailed formation mechanism of ZrSiO4 at the nanometer scale and atomic scale has been proposed.

High-efficiency preparation of zircon ceramics using borosilicate glass as sintering additive

Synthesis of zircon (ZrSiO4) ceramics suffers from high sintering temperature and long holding time. Herein, we reported a novel method to synthesize ZrSiO4 ceramics using borosilicate glass as sintering additive, and the influences of the borosilicate glass content and sintering temperature on the phase evolution and microstructure of the obtained ceramics were investigated in detail. The results indicated that the addition of borosilicate glass had significant effect on the phase evolution and properties of the obtained ceramics. The formation of ZrSiO4 was enhanced with increasing the content of borosilicate glass and sintering temperature. At sintering temperature of 1400 °C and holding time of 6 h, the formation efficiency of ZrSiO4 phase was up to 91.27 wt%. Moreover, ZrSiO4 ceramic with high compactness was obtained with the weight ratio of borosilicate glass to zircon in the range of 0–0.25. The results demonstrated that ZrSiO4 ceramics can be effectively prepared by using borosilicate glass as sintering additive.

High temperature structure evolution of SiBZrOC quinary polymer derived ceramics.

SiBZrOC quinary ceramics were obtained through the modification of a SiOC precursor with B(OH)3 and Zr(OnPr)4. The results showed that both B and Zr atoms were involved in the SiOC network through Si–O–B and Si–O–Zr bonds, respectively. The combined effects of B and Zr on the chemical structure and the thermal stability of the SiBZrOC system were investigated in detail. The sp3–C/Si ratio of SiBZrOC ceramics was between the values for SiZrOC and SiBOC. The presence of B promotes the crystallization of t-ZrO2, which precipitated at 1000 °C and transformed to m-ZrO2 at 1400 °C. At 1600 °C, ZrO2 reacted with the matrix and formed ZrSiO4, which consumed SiO2 and thus inhibited the carbothermal reaction. The very small I(D)/I(G) ratio of 0.13 in the Raman spectra indicated the high graphitization of free carbon in SiBZrOC ceramics, which was observed by TEM with 10–20 graphene layers. The SiBZrOC ceramics showed excellent thermal stability in argon at 1600 °C for 5 h with a mass loss of 6%. Both the formation of ZrSiO4 and the highly graphitized free carbon play important roles in inhibiting the carbothermal reaction and thus improving the thermal stability of SiBZrOC ceramics.

Phase-engineering strategy of ZrO2 for enhancing the mechanical properties of porous cordierite ceramics

Porous cordierite ceramics, one of the major industrial materials used in heat transmission pipelines, have gained much attention due to their superior thermal properties. However, the unsatisfactory mechanical properties restrict their further application to some extent. In this work, the porous cordierite ceramics were prepared with fused magnesia, Al2O3, and SiO2 at different sintering temperatures from 1250 ℃ to 1400 ℃. To further reinforce the mechanical properties, ZrO2 characteristic of various phase types was regarded as sintering additives and then the enhancing mechanism was investigated. The phase evolution, microstructures, apparent porosity, bulk density, cold compressive strength, and thermal shock resistance of porous cordierite ceramics have been evaluated. The results indicated a great promotion on the mechanical (from 77.43 to 148.18 MPa) and thermal properties (from1.66 to 2.09 W m−1 K−1) by introducing the sintering additives. Furthermore, the strengthening mechanism of ZrO2 on porous cordierite ceramics was proposed, that is, the monoclinic phases facilitated the substitution reaction of Zr4+ and Mg2+ in cordierite, and the tetragonal phases were highly advantageous for the formation of ZrSiO4. Profiting from the delicate material phase composition modulation of ZrO2, the reinforced porous cordierite ceramics manifests outstanding mechanical properties and superior thermal stability.

Recycling MoSi2 heating elements for preparing oxidation resistant multilayered coatings

Spent MoSi2 heating elements were used to fabricate MoSi2, ZrB2/MoSi2 and MoSi2-ZrB2/MoSi2 oxidation resistant coatings via a two-step process of slurry painting and spark plasma sintering. Cracks appeared in simple MoSi2 and ZrB2/MoSi2 coatings, whilst MoSi2-ZrB2/MoSi2 coating was crack-free as CTE mismatch was reduced. Mo5Si3 and MoB diffusion layers formed under MoSi2-ZrB2 transition layer in MoSi2-ZrB2/MoSi2 coating, revealing good metallurgical combination between the substrate and coating. On one side the silica layers covering MoSi2 and ZrB2/MoSi2 coatings displayed diffused cracks after oxidation at 1773 K for 100 h, on the other side it was dense and continuous for MoSi2-ZrB2/MoSi2 coating, showing low oxidation rate constant at 1773 K. Furthermore, MoSi2-ZrB2 transition layer in MoSi2-ZrB2/MoSi2 coating possessed good short-term oxidation protective properties at 1873 and 1973 K since the formation of ZrSiO4 improved the stability of Si-O-Zr composite oxide scale and diminished the oxygen permeability, therefore demonstrating good high-temperature oxidation resistance.

Unusual temperature-dependent reactivity of ultra-high temperature ceramic (UHTC) borides with calcia-magnesia-alumina-silicate (CMAS)

The resistance of ultra-high temperature ceramic (UHTC) borides to calcia-magnesia-alumina-silicate (CMAS) attack is evaluated for the first time. ZrB2 and HfB2 are reacted with 23 mol% of CMAS 1000 °C, 1300 °C and 1600 °C, respectively, for 1 h, 10 h and 100 h, respectively, in atmosphere. Interestingly, borides first oxidize before reacting with CMAS to form ZrSiO4 and HfSiO4, respectively, which peaks at 1300 °C. At 1600 °C, the reaction with CMAS to form HfSiO4 is greatly suppressed; moreover, ZrB2 exhibits only oxidation and no reaction with CMAS nor formation of ZrSiO4 or any other CMAS induced reaction product. This unusual inertness at temperatures above 1600 °C could enable new approaches to addressing the CMAS problem in thermal and environmental barrier coatings.

A study of zircon crystallization, structure, and chemical resistance relationships in ZrO2 containing ceramic glazes

This study aims to investigate zircon (ZrSiO4) formation during thermal treatment and its influence on the structure and properties of the ceramic glazes. Four raw ceramic glazes with the addition of 5, 9, 13, and 17wt% of ZrO2 (<5μm) at the expense of SiO2 were prepared by the ceramic traditional route. To obtain homogeneous melting and consequently a high-quality surface, 5wt% of colemanite (2CaO·3B2O3·5H2O) was added to the ceramic glazes formulation. XRD, NMR, Raman spectroscopy and FTIR measurements revealed the formation of ZrSiO4. An increase of ZrSiO4 from 35 to 86wt% with an increase of ZrO2 content in the composition of ceramic glazes was observed. 29Si solid-state MAS NMR measurements also showed that with successive increases of ZrO2 concentration the relative intensity of zircon resonance increases. The evaluation of the chemical resistance revealed the beneficial effect of ZrSiO4 on this property.

Low temperature synthesis of green submicro Cr‐ZrSiO4 ceramic pigments by solid‐state method

AbstractA green submicro Cr‐ZrSiO4 pigment was successfully synthesized with Li2CO3 used as mineralizer by a simple solid‐state method at low temperature. The formations of the samples with and without mineralizer were investigated by X‐ray diffraction, scanning electron microscope, and thermogravimetry differential thermal analysis, respectively. The reflectance spectrum and color properties of the Cr‐ZrSiO4 pigments were characterized and analyzed. The XRD results show that Li2CO3 as a mineralizer can significantly promote the formation of ZrSiO4 and decrease the synthesis temperature to 900°C, which is 500°C lower than without mineralizer. The SEM revealed that the Li2CO3 containing ceramic powders are more homogeneous than undoped samples and have uniform particle size between 100 and 500 nm. It is indicated that Li2CO3 as a mineralizer can effectively destroy the Si‐O bond of random network structure, reduce the viscosity and accelerate the formation of ZrSiO4 at low temperature. The results from CIE L*a*b* characterization indicate that the samples exhibit high doping limitation (x = 0.06) and green hue (a* = −10.13) at 900°C. In addition, the method used in this work has the advantages of simple process, low cost, and large‐scale production, and is expected to synthesize other types of high‐temperature ceramic pigments.

Enhanced adhesion resistance of an 8YSZ thermal barrier coating trough the formation of zircon and mullite as self-healing reaction products under cyclic oxidation conditions

The formation of ZrSiO4 (zircon), 3Al2O3·2SiO2 (mullite), and amorphous SiO2 as healing products from the oxidation reaction of the SiC (silicon carbide) self-healing agent, occurred after 250 h of thermal exposition (ten thermal cycles of 25 h at 1100 °C). By SEM and TEM analysis of adhesion fracture surfaces, both zircon and mullite complex oxides were identified mainly along micro-cracks adjacent to theTGO-TC interface and forming bridges-like bonds with the ZrO2-TC and Al2O3-TGO compounds. Then adherence resistance seems to be enhanced by the formation of these bonds and by the mere presence of self-healing products retarding or blocking crack propagation.

Effect of Moist Air and Minor Zr Addition on Oxidation Behavior of Arc-Melted Multiphase Mo–Si–B Alloys in the Temperature Range of 1000 °C–1300 °C

Arc-melted multiphase intermetallic alloys, Mo76Si14B10, Mo74Si14B10Zr2, Mo79.5Si12B8.5 and Mo77.5Si12B8.5Zr2 with microstructures containing Moss, Mo3Si and Mo5SiB2 were isothermally exposed for 1 h or 24 h at 1000 °C, 1150 °C and 1300 °C in dry or moist air. The residual area fraction was found to be the highest on exposure at 1150 °C in dry air, but the least at this temperature in moist air. Examination of dry air formed oxide scales by X-ray diffraction, and scanning electron microscopy with energy-dispersive spectroscopy showed the presence of Mo, and MoO2 with a continuous, protective glassy B2O3–SiO2 top layer. Formation of Zr(MoO4)2 in the Zr-containing alloys had lowered mass loss by arresting MoO3 vaporization, and had enhanced the B2O3–SiO2 scale formation kinetics. Further, Si(OH)4, cristobalite, H3BO3 and MoO3·(H2O)2 appeared to be constituting the oxidation products formed in moist air. Alloying with Zr enhanced the kinetics of protective scale formation by lowering the Moss content, and microstructural refinement. The deterioration of oxidation resistance in moist air was conjectured to be due to longer duration required for protective scale to form, formation of β-cristobalite permitting grain boundary diffusion of oxygen anions, as well as volatile hydrated oxidation products as mentioned above. Formation of ZrSiO4 and dissolved ZrO2 in B2O3–SiO2 scale of the Mo-Si-B-Zr alloys in both dry air and moist air is considered to have contributed to the enhanced protective character of oxide scale by stabilizing the glassy scale.

Low temperature synthesis and performance investigation of co-doped (Cr, Co)–ZrSiO4 ceramic pigments

In this paper, a green (Cr, Co)-codoped ZrSiO4 pigment was successfully prepared with Li2CO3 as mineralizer via solid-state reaction method at low temperature. The samples were characterized by X-ray diffraction, thermogravimetry and differential scanning calorimeter analysis, respectively. The XRD results reveal that the Li2CO3 as mineralizer can promote the formation of ZrSiO4 and decrease the synthesis temperature to 1000 °C that is 400–500 °C lower than the without mineralizer. The TG-DSC curve doped with Li2CO3 shows that zirconia and silica react to form zircon at 1000 °C. It is indicated that the Li2CO3 can reduce reaction activation energy and Si-O bond degree to promote zircon formation. After calcining at 1000 °C for 2h, the intensity of the colour in the samples varies from light green to dark green, depending on the co-doping content. The sample with 8mol% (Co, Cr) particles exhibit brilliant green (a*=-19.33), the value of a* is almost as good as commercial pigments, which indicates it is a potential candidate for ceramic pigments application. More importantly, the preparation method has the advantages such as reduce color ion doping, simplicity of process, and can also be used for preparing other zircon-based high-temperature colorants.

High temperature interaction of volcanic ashes with 7YSZ TBC's produced by APS: Infiltration behavior and phase stability

High-temperature infiltration behavior and phase stability of yttria-stabilized zirconia (7YSZ) thermal barrier coatings (TBC) produced by atmospheric plasma spray interacting with volcanic ashes (VAs) are presented here. Three VAs from the Colima, Popocatepetl, and Eyjafjallajökull volcanoes have been used in this work. Previous to infiltration experiments, physicochemical characterization of the VAs was carried out including thermal analyses by DSC, structural studies by XRD, and ICP chemical composition measurements. TBCs' infiltration tests were carried out at 1250 °C for different times. Results showed that infiltration depth as a function of time behaves in a non-linear way. Mainly two important infiltration behaviors were identified corresponding to high- and slow-speed infiltration regimes. Higher infiltration kinetics was detected for VAs with lower SiO2 content. The extent of chemical degradation of the 7YSZ is directly related to the silica content. For greater SiO2 values, a higher content of monoclinic ZrO2 was observed leading to maximum values at intermediate annealing times between 2 and 5 h. This behavior can be correlated with the high-speed tetragonal to monoclinic ZrO2 transformation at short times (between 2 and 5 h) until a maximum monoclinic content is reached. After that, the reaction follows by the interplay of ZrSiO4 formation at the expense of previously formed m-ZrO2 together with the incorporation of Y and Zr to the glass melt.

Effect of ZrO2 types on ZrSiO4 formation

The effect of various types of ZrO2 on ZrSiO4 formation was evaluated by the calcination of three types of nanosized ZrO2 (unstabilized ZrO2, 3Y–ZrO2, and 8Y–ZrO2) and amorphous SiO2 powders. Reaction was conducted in vacuum and air atmosphere. Results indicated that under a vacuum atmosphere, the yield of ZrSiO4 during synthetic reaction markedly varied when different types of ZrO2 were used. When 3Y–ZrO2 was used, the reaction reached equilibrium after only 6 h. This occurrence was facilitated by the stabilized ZrO2 tetragonal structure. ZrSiO4 synthetic mechanism by which SiO2 diffuses into a t-ZrO2 crystal structure and then ZrSiO4 nucleates and grows along on t-ZrO2 (101) planes was confirmed. That is, t-ZrO2 acts as a host for ZrSiO4 formation. However, the investigation under air atmosphere demonstrated that ZrSiO4 could be synthesized using unstabilized ZrO2 as previously reported; meanwhile, ZrSiO4 formation was nearly suppressed in samples containing Y2O3-stabilized ZrO2. This suppression was attributable to the oxygen absorption of Y2O3-stabilized ZrO2, affecting its internal micro-chemical environment and impeding ZrSiO4 nucleation.

Kinetics of zircon formation in yttria partially stabilized zirconia as a result of oxidation of embedded molybdenum disilicide

Recently MoSi2 sacrificial particles embedded in yttria partially stabilized zirconia (YPSZ) have been proposed as attractive healing agents to realize significant extension of the lifetime of the thermally loaded structures. Upon local fracture of the YPSZ, the embedded healing particles in the path and in the vicinity of the crack react with the oxygen atoms transported via the crack and first fill the crack with a viscous glassy silica phase (SiO2). The subsequent reaction between this freshly formed SiO2 and the existing tetragonal ZrO2 of the YPSZ leads to the formation of rigid crystalline zircon (ZrSiO4), which is key in the crack-healing mechanism of YPSZ based materials. The isothermal kinetics of the self-healing reaction and the mechanism of zircon formation from the decomposing MoSi2 and the surrounding YPSZ were assessed via X-ray diffraction (XRD). The obtained results revealed that at 1100 °C the reaction between amorphous SiO2 and YPSZ is completed after about 10 h. For a more accurate determination of the kinetics of the self-healing reaction, bilayer samples of YPSZ – MoSi2 (with and without boron addition) were annealed in air over a temperature range of 1100–1300 °C. This led to the formation of a MoSi2/amorphous (boro)silica/zircon/YPSZ multi-layer, which was investigated with scanning electron microscopy (SEM) and electron probe X-ray microanalysis (EPMA). Kinetic modeling of the growth of zircon and silica or borosilicate layers showed that zircon growth was dominated by the diffusion of Si4+ in zircon whereas the growth of the silica or borosilicate layer was controlled by oxygen diffusion. Moreover, a significant increase in the rate of ZrSiO4 formation was observed due to the presence of B in the MoSi2 particles.