Precipitation Of Crystalline Phase Research Articles

Elimination mechanism of voids caused by density differences in high crystallinity alumina/alumina joints bonded with dysprosium aluminum silicate glass ceramic filler

In this work, the Dy2O3-Al2O3-SiO2 (DASN) and Dy2O3-Al2O3-SiO2-TiO2 (DAST) glass fillers were used for joining alumina ceramic. During the cooling process of the alumina/DASN/alumina joints, Dy2Si2O7 and Al2O3 were precipitated simultaneously and gradually grown. As a result, voids were formed due to the poor flowability of the glass ceramic filler and the large density difference between the glass filler and Dy2Si2O7 crystals. On the contrary, the addition of TiO2 altered the sequence of the crystalline phase precipitation during the cooling process. During cooling from the joining temperature (1450 °C) to 1100 °C, only Dy2Si2O7 was formed in the brazing seam. Simultaneously, the flowing glass phase was able to fill the spaces caused by the density differences. When the growth of Dy2Si2O7 phase ceased, the Al2O3 phase began to precipitate. Therefore, the voids caused by density differences can be eliminated in the alumina/DAST/alumina joints with high crystallinity. The optimal flexural strength of alumina/DAST/alumina joints tested at room temperature and 1000 °C reached 350 MPa and 158 MPa, respectively.

One-step formation of ZrON thin film on surface of carbon fine particles for membrane electrode assembly

Zirconium nitride and oxynitride films were deposited on alumina or carbon particles by reactive sputtering using a magnetron sputtering apparatus with a Zr hollow cylindrical target and a vibrating equipment with heating capability. The vibrating equipment developed in this study was effective if the particles are spherical and highly monodisperse. Uniform film deposition was achieved over the entire surface of highly monodisperse spherical alumina particles using the vibrating equipment during deposition. Pure ZrN crystalline layers was deposited under Ar and N2 gas flows with heating on XC-72 carbon powder particles removed adsorbed oxygen. Energy dispersive x-ray spectroscopy mapping analysis for deposited XC-72 carbon particles showed ubiquitous film deposition on agglomerated particles regardless of vibration during sputtering. Uniform film deposition with vibrating equipment was achieved on the entire surface of CGB-10 particles with more spherical and monodisperse than XC-72 but precipitated crystalline phase depended on unintentional oxygen chemisorbed on the particles. Addition and increase in flow rate of oxygen to the sputtering gas resulted in the formation of desired crystalline phase, Zr2ON2, Zr7O8N4, and monoclinic ZrO2, precipitated in the film using CGB-10 particles with chemisorbed oxygen removed. Current density for oxygen reduction reaction measured for MEA made from CGB-10 particles with ZrON-based crystals deposited was larger than that for thin film deposited on a carbon plate substrate.

Effect of substituting Li2O with ZnO on the crystallization and properties of Li2O–Al2O3–SiO2 transparent glass ceramics

The transparent glass ceramic Li2O–Al2O3–SiO2 (LAS) was successfully prepared through a melting method. The impact of ZnO substitution for Li2O on the crystallization and properties of LAS glass ceramics was investigated. The results revealed that with the increase in ZnO substitution from 0% to 4%, the Q4 structural units in the base glass increased, reinforcing the integrity of the glass network structure. This led to an elevation in the glass transition temperature (from 533.5°C to 545.7°C), crystallization temperature (from 728.6°C to 832.3°C), and Vickers hardness (from 5.98 to 6.44 GPa). Additionally, the primary crystalline phases in the glass ceramics transformed from Li2Si2O5 and LiAlSi4O10 to cristobalite, and the multiphase crystalline structure transitioned to a single phase with a spherical morphology of the crystalline grains. The discussion delved into the size distribution of crystals in the glass ceramics, revealing that the increase in ZnO content refined the size and homogenized the distribution of the cristobalite crystals. Glass ceramics with 0% and 4% ZnO substitution, nucleated at 570°C for 4 h and crystallized at 700°C for 2 h, yielded lithium disilicate glass ceramic and cristobalite glass ceramic, respectively, with maximum transmittances (at 550 nm) of 86.92% and 88.79%. The study indicated that the type and size of precipitated crystalline phases significantly influenced the whiteness of the glass ceramics, with minimal impact on other color parameters. Moreover, the presence of fine grains in the glass ceramics, compared with the base glass, imparted a higher hardness. The addition of ZnO exhibited an increasing trend in the toughness of the glass ceramics. At a ZnO substitution of 4% and a crystallization temperature of 700°C, the glass ceramic with cristobalite as the crystalline phase demonstrated optimal comprehensive performance.

Joining AlN ceramics by ZnO–Al2O3–B2O3–SiO2 (ZABS) glass-ceramic at low temperature

The ZnO–Al2O3–B2O3–SiO2 (ZABS) glass powder was designed and innovatively employed to join AlN ceramics. The crystallization, thermal expansion and wettability behavior of the ZABS glass and glass-ceramic were investigated. The results shows that Zn3B2O6, ZnSiO4 and Zn4B6O13 were precipitated after heat treatments at different temperature, respectively, resulting in a variation in the coefficient of thermal expansion (CTE) of the ZABS glass ceramic. Then guided by the wetting behavior on the AlN ceramic substrate, the joining of the AlN ceramics by ZABS glass at various temperatures and holding times were conducted. Notably, Zn3B2O6 was identified to be the primary product in the joints bonded at temperature of 700–800 °C due to the crystallization within the glass and no discernible reaction was observed between the substrate and the interlayer, while ZnSiO4 was observed at the periphery of Zn3B2O6 after 750 °C. Moreover, the crystalline phase Zn3B2O6 gradually grew with the temperature and holding time increasing as the glassy phase gradually diminished, resulting in a reduction of the strength and reliability of the joints. The optimal flexural strength of the joints was 156 ± 11 MPa at 700 °C for 30min. The reason for the high strength can be attributed to the interactions between the glass precipitated crystalline phase interlocking each other and the glass phase tightly bonded with the crystalline phase.

Enhancement of damage resistance of transparent Li2O-Al2O3-B2O3 glass by crystallization

Aluminoborate glasses exhibit remarkable crack-resistance properties, rendering them a promising material for cover glasses in portable electronic devices. However, their usage has been hindered by their relatively low hardness. To address this challenge, a parent glass with 11 Li2O-30 Al2O3-55 B2O3-2 TiO2-2 P2O5 (wt%) was prepared using a melt-cast method. Heat treatment at 575 °C yielded a glass-ceramic (G-575) with a Vickers hardness of 6.51 GPa, 40.91 % higher than the parent glass due to structural densification and Li(Al7B4O17) crystalline phase precipitation, improving indentation fracture toughness from 0.97 to 1.79 MPa·m1/2. Additionally, the glass-ceramics demonstrated a visible transmittance of approximately 85 % and a cracking resistance (CR) value of 14.8 N. Scratch tests conducted at a constant force revealed that the comprehensive damage resistance of glass-ceramics surpassed that of the parent glasses, making it a promising cover glass material.

Particle size modulation for effectively optimizing the dielectric and mechanical properties of La2O3–B2O3 based glass-ceramic/ceramic LTCC substrates

Lanthanum borate-based glass-ceramic has recently received considerable attention in the field of high-frequency communications as a sintering aid, due to the low sintering temperature and the precipitation of crystalline phases with excellent dielectric and mechanical properties. Importantly, the densification and crystallization behaviors of glass-ceramic are not only determined by its composition, but also affected by various processing parameters, such as the initial particle size, which is rarely explored for optimizing the dielectric and mechanical properties of lanthanum borate-based glass-ceramic/ceramic composites. Herein, La2O3–B2O3–CaO–P2O5–SiO2 (LBCPS) glass-ceramics with a series of initial particle sizes are achieved by ball milling method through controlling the milling time. Employing LBCPS glass-ceramics with different particle sizes as the sintering aid, various LBCPS/Al2O3 composites are fabricated, and the dielectric and mechanical properties of which are further investigated. Notably, the LBCPS/Al2O3 composite with a moderate glass-ceramic particle size of 2.7 μm exhibits the excellent comprehensive performance with a low dielectric loss of 8.6 × 10−4 at 9.8 GHz and a high flexural strength of 199 MPa. Moreover, the influencing mechanisms of the glass-ceramic particle size on the crystallization, microstructure, and densification of the LBCPS/Al2O3 composite have also been systematically explored and proposed. This research work provides an intriguing strategy for optimizing the dielectric and mechanical properties of the glass-ceramic/ceramic as the high-performance low-temperature co-fired ceramic (LTCC) substrate.

Effect of adding Er3+ on the precipitated crystalline phase of SrF2–ZnO–B2O3 glass and upconversion luminescence

Elucidating the relationship between nucleation and its structure in glasses is essential for the efficient development of new glass-ceramics. In this study, we developed new oxyfluoride nanocrystallized glass-ceramics with potential for upconversion luminescence, phosphor for LEDs, and fiber laser hosts. We investigated the glass-forming region in the SrF2–ZnO–B2O3 system and the crystallization behavior, glass structure, and optical properties of the xSrF2–(50−x)ZnO–50B2O3 system with the lowest quantity of glass-forming oxides. Whereas both the x = 10 and x = 20 samples precipitated more than 100 nm diameter of Zn4B6O13 by heat treatment, the Er3+-doped samples with x = 10 and x = 20 precipitated SrF2 nanocrystals of less than 20 nm. The resulting SrF2 nanocrystallized glass was transparent, and upconversion luminescence was observed by irradiating with a 980-nm LD. We found that the addition of Er3+ ions has a significant impact on crystallization, and the proposed mechanism for this is that the bond selectivity arising from the polarizability forms fluoride-rich domains, and Er3+ further assists the nucleation of SrF2 by serving as a crystal nucleation site. This study is expected to provide a guideline for the development of new transparent nanocrystallized glasses.

Optimizing dry-wear performance of a Ti-based high entropy bulk metallic glass via isothermal annealing

The evolution of microstructure, thermal stability, mechanical response behavior and tribological properties of the Ti20Zr20Cu20Hf20Be20 high entropy bulk metallic glass (HE-BMG) before and after isothermal annealing were systematically studied. The results demonstrate that isothermal annealing affects the mechanical and tribological properties by modifying the microstructure and the consumption of free volume in the structure. Although the strength/hardness of HE-BMG can be improved after the isothermal annealing before crystallization, the deterioration of shear plastic deformation leads to serious brittle fracture, thus cancelling out the contribution of strength to wear resistance and resulting in negligible variation of wear rates. When the crystallization isothermal annealing is performed, the wear resistance can be dramatically enhanced and the wear mechanism changes to slight abrasive and oxidation wear, which can be mainly attributed to the good co-deformation between the amorphous matrix and precipitated crystalline phases.

Confocal scanning laser microscopy investigation of crystallization behavior of hot blast furnace slag

The isothermal and non-isothermal crystallization behavior of blast furnace (BF) slag with varying CaO/SiO2 ratios was in-situ observed through a confocal scanning laser microscopy (CLSM). The crystallization kinetics was analyzed and precipitation of crystalline phases was discussed by theoretical analysis from FactSage 8.0 and X-ray Diffraction (XRD). The results showed that, with the increasing CaO/SiO2 ratio from 1.0 to 1.3, the crystals morphology changed first from rectangles and squares to small-size and irregular, and further to long strip shape at the cooling rate of 100 °C/min. The onset crystallization temperature in CTT diagram was higher at a larger CaO/SiO2 ratio due to the decrease of polymerization degree of the slag. For the isothermal crystallization process at 1250°C, the crystals morphology changed gradually from lamellar to long-trip or columnar, and the incubation period in TTT diagram became shorter with the increase of CaO/SiO2 ratio. Avrami index n decreased from appropriately 2.3 to 1.5, and the growth mode of crystals converted from two-dimensional to one- dimensional. XRD analysis showed that only merwinite existed in four slags at 1380°C. Akermanite and gehlenite were generated at 1350°C, and their amount first increased greatly and then decreased slightly with a continuous increase of CaO/SiO2 ratio. At the low temperature, the number of akermanite and gehlenite reduced, while that of merwinite increased obviously in the slags when CaO/SiO2 ratio was 1.2 and 1.3, indicating that increasing CaO/SiO2 ratio promoted the generation of merwinite.

Effect of CaO/SiO2 mass ratio and Li2O on structure and phase precipitation behaviors of CaO–SiO2–MgO–Al2O3 oxide inclusions

The crystallization behaviors and structure of CaO-SiO2-MgO-Al2O3 melts representing the oxide inclusions in Si-Mn-killed steel were investigated. Raman spectroscopy analysis indicates that the degree of polymerization of oxide melts is lowered with increasing the CaO/SiO2 mass ratios or Li2O contents. Lowering the CaO/SiO2 mass ratios decreases the crystallization temperatures and suppresses crystallization of the oxide melts. Two crystalline phases precipitate (4CaO·MgO·Al2O3·3SiO2 and 3CaO·MgO·2SiO2 in sequence) during continuous cooling of oxide melts with the CaO/SiO2 mass ratios of 1.55 and 1.15. Only one crystalline phase (4CaO·MgO·Al2O3·3SiO2) was precipitated during the continuous cooling of the oxide melts with CaO/SiO2 mass ratio of 0.77. The crystallization ability of oxide melts was retarded with increasing the Li2O content. The crystalline phases precipitated sequentially are blocky 4CaO·MgO·Al2O3·3SiO2 and faceted 3CaO·MgO·2SiO2 irrespective of the Li2O content of oxide melts.

Behavior of Glass-like and Mineral-like Phosphate Compounds with an Immobilized Chloride Mixture in Hydrogen Peroxide Solutions

A new type of high-level waste (HLW) is generated during pyrochemical reprocessing of mixed nitride spent uranium–plutonium nuclear fuel. Such waste is a spent electrolyte, which is a mixture of chloride salts containing approximately 25.7 wt.% LiCl + 31.6 wt.% KCl + 4.1 wt.% CsCl + 5.1 wt.% BaCl2 + 3.8 wt.% SrCl2 + 29.7 wt.% LaCl3, and its immobilization in reliable matrices is an actual radiochemical problem. The structure and hydrolytic stability of sodium aluminoironphosphate (NAFP) glass and a low-temperature mineral-like magnesium potassium phosphate (MPP) matrix, which are promising for spent electrolyte immobilization in the presence of hydrogen peroxide solutions simulating natural water radiolysis products, were studied in this work. The structure of the samples was studied using the SEM-EDS method. It was shown that the initial samples of NAFP glass after leaching in hydrogen peroxide solutions are prone to precipitation of crystalline phases on the surface, which are mainly represented by a mixture of sodium–iron–aluminum pyrophosphates. It was established that the leaching rate of structure-forming components of NAFP and MPP matrices generally increase, but remain at a low level, meeting modern requirements for HLW immobilization. This confirms the effectiveness of the studied matrices for the industrial use of the spent electrolyte.

Effect of forced cooling on the microstructure and properties of Fe-based amorphous composite coatings prepared by laser remelting

A forced cooling system with three cooling plates was designed to assist laser remelting, and the effects of forced cooling on the microstructure and properties of Fe-based amorphous composite coatings prepared by laser remelting were studied. Results show that the content and size of the precipitated crystalline phase decrease, and the crystallites become finer with an increase in the temperature gradient of the forced cooling device. When the temperature of the cooling plate drops to 200 K, the precipitation of the strengthening phase M23(CB)6 is inhibited, and only the α-Fe phase precipitates, which has a good toughening effect. The hardness of the coating decreases because the precipitation of the strengthening phase is inhibited. The wear and corrosion resistances of the coatings are significantly improved because of an increase in the content of the amorphous phase and solid solution strengthening of the α-Fe phase. However, lowering the temperature of the cooling plate does not result in better performance. At a cooling plate temperature of 200 K, the wear resistance of the coating is the best because the appropriate amount of α-Fe phase plays a toughening effect.

Optimisation of Thermal Processes with Plasma Nitriding on Vanadis 4 High Speed Steel.

Vanadis 4 steel is a tool steel processed by powder metallurgy (PM). Its main alloying elements are Cr, V and Mo. Through the application of a design of experiments with six factors and eight experiments, the parameters of the process related to the thermal treatment of these steels are deliberately varied. Those thermal parameters related to the destabilisation of austenite were analysed: the cooling method in quenching, tempering and the application of an ionic nitriding treatment. Through XRD, the percentage and types of precipitated crystalline phases were determined, and, through SEM-EDX, the microstructure was revealed. At the same time, through a pin-on-disc test, those factors with a significant influence on resistance to wear were determined. It has been concluded that, in order to increase resistance to wear, treatments of destabilisation of the austenite at 900 °C with oil quenching, tempering at 550 °C for 4 h and a subsequent treatment of plasma nitriding would be very favourable. This tempering favours a second destabilisation of the austenite and its transformation into martensite, as well as the joint precipitation of type M7C3 and MC carbides. The thickness of the nitrided layer exceeds 100 microns and generates a fully adhesive wear mechanism.

An investigation about crystallization properties of vermiculite based machinable glass-ceramics

This study investigated the crystallization kinetics of a vermiculite-based glass-ceramic system prepared by the melt-quench technique. Four compositions with different boron content consisting of SiO2–Al2O3–K2O–B2O3–MgF2 components were prepared, and then vermiculite mineral was added to these as 50/50 wt%. Differential scanning calorimetry (DSC), Differential thermal analysis (DTA), X-ray Diffraction (XRD), Scanning electron microscopy (SEM), and field emission scanning electron microscopy (FESEM) were used for characterization. The activation energies for the precipitation of crystalline phases have been evaluated, and DSC results have studied the crystallization mechanisms. Furthermore, a machinability test was performed to understand the machining performance of the samples. Density function theory (DFT) was used to calculate the interactions between SiO4-BO3 and SiO4-BO4. The glass-ceramics exhibited excellent performance in machinability tests without cracking or deforming. While the boron additive had different effects on crystallization, it caused the machinability to be negatively affected.

Fabrication of magnetically controllable glass ceramics with completely dense microstructure by hot pressing

AbstractCompletely dense magnetite‐based aluminosilicate glass ceramics with adjustable magnetic properties were successfully synthesized by method of hot pressing. The influences of sintering conditions and magnetite contents on magnetic properties and microstructure of samples were analyzed. It was found that increases in sintering temperature and time could improve the densification degree of samples. However, precipitation of crystalline phases from glass would worsen the densification of samples. The optimum parameters of hot pressing were 950°C for 1 h, under which condition, the glass ceramics containing 10–65 wt.% magnetite showed a fully dense microstructure. As the magnetite content increased from 10 to 65 wt.%, magnetization and area of hysteresis loops of glass ceramics increased, while coercivity showed an opposite trend. However, when the magnetite content increased to 70 wt.%, pores appeared and the degree of densification decreased.

Preparation of monolithic transparent mullite-based glass-ceramics by the sol–gel method

Monolithic transparent mullite-based glass ceramics were prepared in the system SiO2–Al2O3–B2O3–ZnO–K2O by the sol–gel method. Heat treatment of the resulted monolithic xerogels at 950 °C for 6 h, in air atmosphere resulted dense, homogeneous and transparent glass-ceramics. The activation energy for crystallization, the Avrami constants and the mechanism of crystallization were determined by the Marotta, Augis-Bennet and the modified Kisinger methods, using the differential thermal analysis. X-ray diffraction and transmission electron microscope were also used to determine the crystallinity of the specimens, and the morphology of the precipitated crystalline phase. Also, transparency of the prepared sol and the synthesized glass and glass ceramics were evaluated by UV–vis spectrophotometer. In addition, the volume percent of the precipitated mullite, which was calculated by the internal standard method, was 34%. The transmission of the samples in the range of visible wavelengths was about 79%. According to the results, the Avrami constant for crystallization was 1.24 that means mullite was precipitated in the glassy phase through the surface crystallization mechanism.

Effect of interconnect pre‐oxidation on high‐temperature wettability and mechanical properties of glass seals in SOFC

AbstractMetallic interconnect oxidation has a significant influence on shear strength between interconnect and sealing glass in SOFC stack operation. This is attributed to high‐temperature mutual wettability. In this work, the glass having different crystallization kinetics was chosen to evaluate wettability and shear strength on Fe–16Cr alloy, which was heated treated at 750°C for 0, 50, and 100 h, forming oxide scale with a varying rough surface. Visual observation was used to quantify equilibrium contact angles between glass and substrates. The results illustrated that alloy oxidized for 50 h exhibited better wettability and shear strength, implying that thickness and roughness of the oxide scale are critical to enhancing interface joint strength. Long‐term testing indicated that thermally stable glass possesses higher joint shear strength and more consistent properties. It was found that precipitated crystalline phases limited improvement of glass wettability, resulting in interfacial delamination of the glass/alloy layer over long‐term operation.

Preparation of fully dense and magnetically controllable CaO-Al2O3-SiO2-Na2O-Fe3O4 glass ceramics by hot pressing

Fully dense and magnetically controllable glass ceramics was successfully synthesized by method of hot pressing using CaO-Al2O3-SiO2-Na2O glass powder and Fe3O4 powder as raw materials. The influences of sintering temperature and time, content and particle size of Fe3O4, as well as particle size of glass powder on the densification and magnetic properties of samples were investigated. It was found that the saturation magnetization gradually increased with increasing magnetite content. In addition, the samples containing smaller size magnetite particles had a higher coercivity. However, for samples using smaller size glass powder, magnetite particles could partially dissolve into the glass matrix, which led to the decrease of saturation magnetization and the increase of coercivity. It was also concluded that the precipitation of crystalline phase from smaller size glass powder caused the decrease of degree of densification, and after decreasing the sintering temperature, the degree of densification of product was enhanced.

Comparison of hot pressing sintering and conventional powder-sintering in preparation of CaO-Al2O3-SiO2-Fe3O4-R2O glass ceramics

The influences of different alkali metal oxides, sintering methods, process conditions on the crystallization behavior and densification of CaO-Al2O3-SiO2-Fe3O4-R2O (R=Na, K) glass ceramics were investigated. It can be concluded that the initial crystallization temperature and crystallization peak temperature of glass containing K2O were higher than those of glass containing Na2O, respectively. The increase of sintering temperature promoted the precipitation of crystalline phase in glass ceramics, meanwhile, the crystalline phases transformed from single magnetite to magnetite and CaFeSi2O6. The glass ceramics obtained by powder-sintering showed a low degree of densification. The fully dense glass ceramics containing Na2O can be obtained by hot pressing sintering above 680 °C for 2 h. However, due to the high viscosity of the glass containing K2O, the degree of densification of K2O containing glass ceramics was relatively low even after the hot pressing sintering. Magnetite based glass ceramics can be used as candidates for magnetic materials.

Microstructure evolution and corrosion mechanism of laser cladded Zr-Cu-Ni-Al in-situ metallic glass matrix composite coatings

Laser cladding provides a widely applicable method for the preparation of metallic glass matrix composite (MGMC) coatings, where the mechanical property and the corrosion resistance can be tailored by the in-suit precipitated crystalline phases. Thus, the investigation on the microstructure evolution and corrosion mechanism of MGMC coating to achieve superior performance is of great importance. In the presented work, Zr50.7Cu28Ni9Al12.3 MGMC coatings, which are constituted by Zr&Cu enriched dendrites and Ni&Al enriched metallic glass (MG) matrix, were prepared by laser cladding. The effect of the laser power on the microstructure and the corrosion property of the MGMC coatings was investigated. It has been found that the MG content increases and the size of the dendrites decreases with decreasing laser power. Increasing MG content in the coating can decrease the self-etching current density due to the rapid surface oxidation, and decrease the open-circuit-potential due to the higher chemical activity of MG. Besides that, a probable corrosion mechanism of the Zr-Cu-Ni-Al MGMC coating in the NaCl solution was proposed. The segregation of Cu could be the main inducement for pitting. The increasing MG phase content can suppress the segregation of Cu and therefore increase the pitting corrosion resistance of the coating.