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The cordierite is one of the most important phases within the MgO-Al 2 O 3 -SiO 2 (MAS) system. In this study, the crystallization and microstructure of cordierite was analyzed. Four samples were prepared, which were subjected to a thermal treatment at a temperature of 1200 °C with a permanence time of 2 h. The temperature of the thermal treatment...
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... to the α-cordierite and the β-cordierite; furthermore, it is perceived that the α-cordierite phase increases in the positive direction of the X axis, unlike β-cordierite. As it could be detected, Mullite is only found in sample M7 and cristobalite is formed from sample M7-1A. The percentages of the spinel and the vitreous phase are below 5%. Fig. 5 shows SEM micrographs for samples M7, M7-1A, M7-1B y M-1C. All samples were exposed to a thermal treatment of 1200 °C for 2 h. Fig. 5 (a) shows the micrographs of the M7 sample; the dendritic structure corresponds to the crystalline phase that is formed after the thermal treatment, so it is presumed that it can be a mixture of ...
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... of the X axis, unlike β-cordierite. As it could be detected, Mullite is only found in sample M7 and cristobalite is formed from sample M7-1A. The percentages of the spinel and the vitreous phase are below 5%. Fig. 5 shows SEM micrographs for samples M7, M7-1A, M7-1B y M-1C. All samples were exposed to a thermal treatment of 1200 °C for 2 h. Fig. 5 (a) shows the micrographs of the M7 sample; the dendritic structure corresponds to the crystalline phase that is formed after the thermal treatment, so it is presumed that it can be a mixture of α-Cordierite and β-cordierite mainly; the matrix contains the dendritic phase, and a phase of glass that did not crystallize during the heat ...
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... and β-cordierite mainly; the matrix contains the dendritic phase, and a phase of glass that did not crystallize during the heat treatment can be identified, this is supported by the results of XRD, due to the similarity in the crystalline structures, α-cordierite is hexagonal and the crystalline structure of β-cordierite is orthorhombic [45]. Fig. 5 (b) and 5 (c) show SEM micrographs for samples M7-1A and M7-1B. These two samples have a very similar morphology in their microstructure. In the micrographs, is clearly to see a dendritic structure for the most part, it is worth mentioning that the sample M7-1A and the sample M7-1B contain 1 %wt and 2 %wt of NiO respectively; in the ...
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... it is worth mentioning that the sample M7-1A and the sample M7-1B contain 1 %wt and 2 %wt of NiO respectively; in the grain boundaries, a small percentage of the phase different from the dendritic phase can be seen by contrasting colors, a phase that possibly corresponds to the vitreous phase without crystallizing after the thermal treatment. Fig. 5 (c) corresponds to the microstructure of sample M7-1C, where a non-dendritic microstructure is observed, unlike samples M7, M7-1A and M7-1B. It is important to mention that sample M7-1C contains 3 %wt of ...
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... of SEM analysis are shown in Fig. 5. Fig. 5 (a) corresponds to the sample M7 where it was observed that the morphology of the microstructure is constituted by a vitreous matrix (dark gray), according to the EDXS results, which are summarized in the table attached to the image. It could be observed that this phase contains %wt Si greater than the other regions of the ...
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... of SEM analysis are shown in Fig. 5. Fig. 5 (a) corresponds to the sample M7 where it was observed that the morphology of the microstructure is constituted by a vitreous matrix (dark gray), according to the EDXS results, which are summarized in the table attached to the image. It could be observed that this phase contains %wt Si greater than the other regions of the sample. Within ...
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... than the other regions of the sample. Within the matrix, is a crystalline phase that is composed of Cordierite α and β principally (light gray). The third crystalline phase identified can be attributed to the Mullite phase, which can be corroborated with the XRD results, as well as the presence of three crystalline phases. On the other hand, in Fig. 5 (b and C) corresponding to Sample M7-1A and M7-1B (1 %wt NiO and 2 %wt NiO respectively), a columnar (light gray) microstructure was observed, corresponding to the crystalline phase of the sample, in which a mixture of Cordierite α and β is mainly found. This columnar structure is delimited by a grain limit in which it was possible to ...
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... on the previous XRD results, it is assumed that the grains with the brightest appearance in Fig. 5 (c) corresponding to sample M7-1C (3 %wt NiO) correspond to the α-cordierite, which possesses the highest crystallinity and stability. Dendritic structure corresponding to a mixture of the α and β phases of the cordierite, extends uniformly over the entire surface. Furthermore, the microstructure of the glass was observed in gray contrast ...
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... produced at high temperature and for the addition of NiO, giving a glass-ceramic. The amount of NiO played an important role in the crystallization behavior of the ceramic through phase separation. α-cordierite are randomly oriented as already observed in M7-1C. However, in contrast to M7, M7-1A and M7-1B, the orientation information presented in Fig. 5 (c) gives no clue as to the preferred orientations of α-cordierite. The average size of the α-cordierite crystals is reduced and, therefore, it is much smaller than in the M7, M7-1A and M7-1B samples. In summary, the microstructure of M7-1C seems more homogeneous than that of the rest of the ...
Citations
... In [27][28][29], the expediency of introducing cations of transition elements for the formation of a cordierite phase and sintering of cordierite ceramics was shown. The Cu 2+ , Co 2+ , and Ni 2+ ions have an ionic radius close to the Mg 2+ ionic radius (0.74 Å) and form solid solutions when Mg 2+ ions are substituted in the cordierite structure. ...
The paper presents the results of a study of radio-transparent cordierite ceramics, in which a part of the components was introduced using the eutectic glass of the MgO-Al₂O₃-SiO₂ pseudoternary system. The formation of α-cordierite occurs during the sintering of ceramics due to the intensive interaction of components of the eutectic glass with crystalline fillers, as well as due to the crystallization of glass. At the same time, densely sintered material was obtained at relatively low temperatures (1300-1350 °С). The crystalline phase of α-cordierite fully forms the structural matrix of the ceramic material. Crystals of the cordierite phase are formed in the form of regular-shaped flat prisms, mostly 1-3 μm in size. The pores between cordierite crystals are completely filled with glassy phase, which ensures their strong connection, uniform and dense microstructure of the material, as well as high strength, dielectric and thermal characteristics.
... In [22,23], the effect of cations of transition elements Cu and Co is investigated; and in [24] -of Ni and Mo on the processes of formation of the cordierite phase and sintering of ceramics. The effective role of such cations has been established. ...
... Subsequently, the formation of cordierite from forsterite 2MgO·SiO 2 and clinoenstatite MgO·SiO 2 is likely. Forsterite interacts with mullite for (24). In the case of MgO·SiO 2 , cordierite formation is most likely according to (20) for composition C-5. ...
The search for effective modifiers of the structure of densely baked cordierite ceramics to reduce the firing temperature is a relevant task but typically requires a large amount of experimental research. The object of this study is the reaction of the formation of the cordierite phase with the participation of glass components of the eutectic compositions of the MgO– Al2O3–SiO2 system under low-temperature firing conditions. In this case, thermodynamic analysis was used as a tool to assess the probability of chemical reactions. Thermodynamic analysis can significantly reduce the volume of the experimental sample. This paper reports the results of theoretical and experimental studies into the features of the course of chemical reactions with the participation of glass components of eutectic compositions of the MgO–Al2O3–SiO2 system. It was revealed that once the stoichiometric ratio is maintained, the resulting product of the interaction between the components of eutectic glasses of the MgO–Al2O3–SiO2 system with charging components is cordierite. Changes in the mineralogical composition of cordierite compositions depending on the firing temperature have been determined. The formation of the cordierite phase is preceded by the process of transformation of meta kaolinite Al2O3·2SiO2, which is a product of kaolin dehydration, into mullite 3Al2O3·2SiO2. Subsequently, the formation of cordierite (in addition to crystallizing directly from eutectic glasses) occurs with the participation of the mullite phase. The formation of the cordierite phase occurs in several stages and is completed at a temperature of 1300 °C. The established features of the reactions of cordierite formation make it possible to determine the most optimal compositions for glasses of the MgO–Al2O3–SiO2 system to obtain low-temperature cordierite ceramics with a high degree of sintering. At the same time, it is also possible to control the phase composition of ceramics and its properties
... CaO is often used as flux to reduce viscosity and melting temperature of silicate slag by dissociating the silicon-oxygen tetrahedron structure Zalapa-Garibay et al., 2019). Fig. 4 shows the effect of CaO on the viscosity and melting behavior of smelting slag. ...
... This was because, on the one hand, the existence of Na 2 CO 3 promoted the formation of low-viscosity glassy phases (e.g., albite and nepheline), decreasing the viscosity of slag (Ichimura et al., 2017;Liao and Huang, 2012;McClane et al., 2019). On the other hand, the addition of Na 2 CO 3 could lower the surface tension of the smelting system (Zalapa-Garibay et al., 2019), speeding up the sedimentation of PGMs-enriched nickel matte (Min et al., 2019). However, adding Na 2 CO 3 excessively would increase the alkalinity of the smelting system, resulting in higher dissolution loss of nickel matte in slag and thereby lower collection of PGMs (Liao and Huang, 2012). ...
The necessity, economics, and sustainability of recycling platinum-group metals (PGMs) from spent automotive catalysts (SAC) have stimulated the emergence of many relevant treatment technologies. Considering the industrial feasibility and recovery efficiency of smelting, this study provided an in-depth review of smelting technologies for recovering PGMs from SAC. Based on the understanding of the characteristics and deactivation mechanisms of automotive catalysts, the effects of various factors on the performance of slagging, collection and separation of PGMs and the features of main smelting processes involving using lead, iron, copper, matte, and wastes as collectors of the metals were reviewed and discussed. The measures for improving the recovery efficiency of PGMs by smelting were proposed from the perspectives of selection of additives and collectors, regulation of slag properties, and optimization of smelting conditions, introduction of microwave field, etc. In addition, the solutions for reducing the dependence of catalysts on PGMs were discussed to further resolve the supply and demand conflict of PGMs.
... Stable β-cordierite forms hydrothermally below 830 • C. µ-cordierite is obtained meta-stably below 925 • C by crystallizing the glassy phase and then slowly turning to the α form when heated above this temperature. [3][4][5] The standard production method of the most preferred single-phase cordierite is synthesis by the solid-state sintering of SiO 2 , Al 2 O 3 , and MgO mixture prepared according to cordierite stoichiometry at high temperatures. [6][7][8] However, cordierite ceramics are difficult to sinter by the solid-state process because of having a very narrow sintering range. ...
In this study, h‐BN was added to the cordierite composition obtained from zeolite, which was prepared by the determined stoichiometry to facilitate machinability and increase thermal conductivity. Sintering behavior, hardness, machinability, and thermal/electrical properties of the samples obtained by sintering the compounds at different times were investigated. Thanks to these features, it is aimed to use cordierite as an alternative material to integrated circuit substrates and electronic packaging materials. The produced samples were analyzed by X‐ray diffraction analysis, examined by scanning electron microscopy, and field emission scanning electron microscopy. Afterward, thermal properties such as thermal diffusivity, thermal conductivity, and electrical properties such as electrical conductivity and dielectric permittivity were measured. The hardness and machinability of samples were investigated. Cordierite, spinel, glassy phase, and h‐BN phase were detected, and it was observed that the blocky cordierite grains turned into equiaxed grains with the increase of the h‐BN. According to the results obtained from the thermal conductivity test, it was seen that the h‐BN additive increased the thermal conductivity value in general. In addition, it was determined that with the increase of h‐BN, the hardness decreased, and the machinability properties of the samples improved.
... Perhaps as a consequence of more limited glass formation tendencies, exhibited as restricted stabilization temperature range (difference between glass transition temperature, T g and crystallization temperature, T c ), the MAS system is widely used as a foundation for glass-ceramics with various crystallization agents. [27][28][29] A structural argument for the reduction in the glass formation region may be related to the oxygen coordination of magnesium ions within aluminosilicate glasses. Magnesium is proposed to sometimes exhibit tetrahedral oxygen coordination, 30-32 but more preferably fivefold coordination, because the size of Mg 2+ . ...
The glass formation boundary defines a chemistry space within which compositions prefer to remain amorphous when cooled from a melt. Several studies on alkali aluminosilicates and alkaline earth aluminosilicates have demonstrated that the alumina edge of the glass formation boundary was independent of cooling rate and defined by a fixed molar ratio of 1.2 (±0.1) moles of Al2O3‐1.0 mole of flux – R2O (Na2O or K2O) or RO (CaO or MgO) – over a broad range of silica levels. These results were consistent with the glass composition in porcelains, the grain boundary chemistry in sintered alumina, and the gloss‐matte boundary in whiteware glazes with mixed fluxes.
... This result is completely consistent with the results obtained by West et al., [8]. They found that as the addition of nickel increases, the crystal size formed in the MgO-Al 2 O 3 -SiO 2 glass system decreased [30]. The addition of nickel oxide with different amounts led to oriented crystallization of phases in one direction as needle-like growths [31]. ...
In the present work, the authors partially introduce NiO in the place of CaO into the 23.5Li2O-11.5CaO-55SiO2 eutectic (954 ± 4 °C) glass system to study the effect of composition modification on crystallization characteristics and magnetic behavior. Also, the effects of NiO contents on density, microhardness and chemical durability were examined. Lithium-based silicate glasses were prepared by a conventional melt-quenching technique, followed by a two-step heat-treatment to prepare glass-ceramics. The DTA results indicated that Tg of the synthesised glasses decreased with the increase of NiO content. The XRD indicated that Li-disilicate and their solid solution (Li,Ni)2Si2O5, Li2Ca3Si6O16 and quartz phases were crystallized, in addition to Niopside-CaNiSi2O6 and Ni2SiO4 phases. Adding NiO instead of CaO in the prepared glass-ceramics led to the formation of a dense structure with density values rising from 2.48 to 2.62 g/cm³ and greatly improved in hardness number from 4410 to 5311 MPa. The chemical durability has also improved dramatically. The examined glass-ceramics had excellent magnetic properties with saturation magnetization (0.053 –0.44 emu/g), remanence magnetization (1.7–5.4 emu/g), and coercivity force (50–157 G).The study shows glass-ceramic with excellent properties that have attracted considerable attention in electronic devices, wear-resistance uses, and biomedicine applications.
... All the values of transition probability and cross-section about the emission of the present series of materials show the highest value for glass with 0.6 mol% of NiO concentration due to the highest interionic balance and resultant force between Ni 2+ ions to Ba 2+ La 3+ and Si 4+ ions. Linear relation between D.C. Conductivity with increased inverse temperature in the present series of materials suggesting that the linear thermally exciting movement of the charge carriers for conduction[43,44]. An increase in the values of D.C. Conductivity and decrease in the values of A.E. up to 0.6 mol% of NiO concentration suggest a higher rate of polaron hopping and ionic transport phenomenon within the present series of materials. ...
Past three decades to current literature, lanthanum silicates embedded with nickel ions are notable for different opto-electronic and semiconducting use. Current days of opto-electronics, including advanced semiconducting resources, need different assemblies of glass resources employing elastic, luminescent, and electronic characteristics. In this view, the opto-electronic resource of chemical composition Ba (10-x) Ni x La 30 Si 60 has planned for synthesis followed by mechanical, thermoluminescent, and opto-electronic characterization. The materials developed are showing glassy behavior, and which was confirmed by the structural characterization. The glass with 0.6 mol% NiO concentration exhibiting better thermal stability. Observations made on the elastic characterization of glasses suggested covalent structure. DTA results which include thermal stabilities of glasses, suggest materials are capable of high thermal stability. Molecular structure of glasses studied with the help of FT-IR spectra. Different structural units and their waves number positions are identified and analysed. Which also suggested glassy behavior. D.C. Conductivity reports suggest that the materials are electrically active, and they are showing few orders of ionic conductivity. A decrease in optical basicity with increasing NiO mol% of glasses suggests high order of covalence. Trap depth parameters (T m , E 𝛕 , E 𝛅 , E 𝛚 & m s ) under thermoluminescence studies suggest glass with 0.6 mol% NiO concentration is a beneficial TL resource. Optical absorption spectra of glasses is recorded, and which helps to calculate the Racah parameters of glasses. Refractive index, emissive cross-section, optical band gap, and transition probability of nickel hosted present glasses evaluated with the help of photoluminescence characterization. This suggests glasses embedded with nickel ions are highly photonic. All the outcomes from the various characterization of glasses which include mechanical, thermoluminescent, and photo-electronic results, suggest a glass with 0.6 mol% NiO concentration is a helpful thermoelement and opto-electronic resource.
... CaO is often used as flux to reduce viscosity and melting temperature of silicate slag by dissociating the silicon-oxygen tetrahedron structure Zalapa-Garibay et al., 2019). Fig. 4 shows the effect of CaO on the viscosity and melting behavior of smelting slag. ...
... This was because, on the one hand, the existence of Na 2 CO 3 promoted the formation of low-viscosity glassy phases (e.g., albite and nepheline), decreasing the viscosity of slag (Ichimura et al., 2017;Liao and Huang, 2012;McClane et al., 2019). On the other hand, the addition of Na 2 CO 3 could lower the surface tension of the smelting system (Zalapa-Garibay et al., 2019), speeding up the sedimentation of PGMs-enriched nickel matte (Min et al., 2019). However, adding Na 2 CO 3 excessively would increase the alkalinity of the smelting system, resulting in higher dissolution loss of nickel matte in slag and thereby lower collection of PGMs (Liao and Huang, 2012). ...
The feasibility of a facile route to recover platinum-group metals (PGMs) from spent catalyst by microwave smelting of spent catalyst with the additions of nickel matte as metal collector and sodium salts as fluxes was verified, based on the thermodynamic and experimental analyses which evaluated the dielectric properties, conductivities/resistances and viscosities of the materials involved in the smelting process. The results showed that the combined use of sodium salts (Na2B4O7 and Na2CO3) reduced the viscosity and smelting temperature effectively by breaking the silicon-oxygen tetrahedron structure which facilitated the collection of PGMs and the separation of PGMs-enriched nickel matte from smelting slag. In association with the eddy current loss and swirling sedimentation effect produced by microwave heating, 98.59% of Pt, 97.91% of Pd and 97.16% of Rh were collected under the optimal smelting conditions of the mass ratios of nickel matte, Na2B4O7 and Na2CO3 to spent catalyst of 1.25, 0.575 and 0.125, respectively, temperature of 1250 °C, time of 2 h, and N2 atmosphere. This new strategy enabled rapid collection of PGMs from spent catalyst at the low temperature within a short time, contributing to energy conservation and environmental protection.
... In comparison, A3_2 has a slightly smaller mean grain size than that of A3_3. Having said that, previous studies revealed an inversed relationship between microhardness and grain size of glass-ceramic [44][45][46], which was attributed by the Hall-Petch effect. It can be deduced that the microhardness of the A3_2 was improved by the refinement of grain size. ...
In order to determine the correlation of flexural strength and thermal shock resistance properties, the sintering behavior of Li2O-Al2O3-SiO2 (LAS) glass-ceramics at different sintering treatment times and the effect of thermal shock cycles on LAS glass-ceramics were investigated. The LAS glass-ceramics were isothermally treated at 1100°C from 1.5 to 4.5 h. Phase transformation of major crystalline of β-spodumene and minor crystalline of ZrTiO4 revealed unchanged as sintering treatment time increased. The physical properties of LAS glass-ceramics that were sintered for 3.5 h demonstrated an increased density (2.45 g/cm³) and less porosity percentage (0.62%). The prolonged sintering treatment affected the microstructure whereby the mean grain size increased from 0.55 to 0.67 µm which also demonstrated the increase of microhardness in the range between 3.90 and 5.47 GPa. The flexural strength of LAS glass-ceramics revealed an enhancement of 158 MPa when sintered for 3.5 h. The thermal shock resistance properties were assessed at 500°C from one to seven cycles via thermal shock tests. After four thermal shock cycles, LAS glass-ceramics showed an improvement of 82% of residual strength from its original strength, due to a decrease in the formation of pores and an increase in the crystallinity and percentage of β-spodumene.
... Manuela et al. [58] Studied the analysis of mechanical properties the crystallization and microstructure of cordierite is one of the most important phases within the MgO-Al 2 O 3 -SiO 2 model. The cordierite was prepared for four samples, which were thermal treatment at a temperature of 1200 °C with a permanent time of 2 h. ...
This review studied the mechanical behaviors of Glass ceramics (GC) based on the Al2O3 /SiO2 system. Glass ceramics are great interest due to their wide variety of applications, which have the ability to fulfil the recent demands of advanced mechanical, optical and biomedical applications. Glass-ceramics are typically heat-stable and have greater mechanical features than glasses. In addition, mechanical properties can be customized to provide variable volume fractions of crystalline phases by regulating nucleation and growth of the crystalline phases. The distribution of these crystalline phases in the glass matrix increases the consistency of the material and, in comparison, effectively limits the growth of cracks. The crystallization process resulted in substantial improvements in micro-hardness and density values such as sodium calcium phosphate (Na4Ca(PO3 )6 and calcium pyrophosphate (βCa2P2O7 ) had sufficient properties for bone grafts and dental applications. This article outlines recent developments in the field of doping Oxides as reinforced with SiO2 -Al2O3 -based Glassceramics, to enhance the mechanical properties of Glassceramics combination. The research focused on the mechanical and the tribological behaviour of Biomedical, Electronics applications and selection of fabrication methods
