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1.
Effects of Na+ substitution Cs+ on the microstructure and thermal expansion behavior of ceramic derived from geopolymer
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Jingkun Yuan Peigang He Dechang Jia Jinsong You Xuzhao Liu Yao Zhang Delong Cai Zhihua Yang Xiaoming Duan Shengjin Wang Yu Zhou 《Journal of the American Ceramic Society》2017,100(10):4412-4424
As part of a series of studies, effects of Na+ substitution on the thermal evolution of cesium‐based geopolymers on heating were studied. A series of sodium‐substituted cesium‐based geopolymers, Cs(1?x)NaxGPs (where x=0, 0.1, 0.2, 0.3, and 0.4), were prepared and treated at 1300°C for 2 hours to obtain the corresponding ceramic products. The thermal evolution process was disclosed by virtue of a variety of technical, including TG‐DTA, thermal shrinkage, XRD analysis, SEM, and TEM investigation. The results indicated that unheated Cs(1?x)NaxGPs was not completely amorphous after the substitution of Na+ and the crystallinity of Cs(1?x)NaxGPs gradually increased with the rise of sodium content. Meanwhile, the average particle sizes of Cs(1?x)NaxGPs also increased evidently with increases in sodium substitution. The final product after heat treatment mainly consisted of pollucite (CsAlSi2O6) and amorphous glass phase. The particle size of pollucite grain gradually decreased as more Cs+ were replaced maybe owing to the role of Na+ in the nucleation process of pollucite. Two forms of Na+ present in the final products: A small portion was present in the pollucite grains due to Na+ partial occupied the crystallographic sites of Cs+; and the rest were present in the amorphous glass phase among the pollucite grains. The average coefficient of thermal expansion (CTE) of resulting Cs(1?x)NaxGPs ceramics increased from 4.80×10‐6 K?1 (x=0) to 7.26×10?6 K?1 (x=0.4) with increases in sodium substitution, which could be due to the amorphous glass phase had a relatively higher CTE than that of pollucite. 相似文献
2.
Christophe Chlique David Lambertin Pascal Antonucci Fabien Frizon Philippe Deniard 《Journal of the American Ceramic Society》2015,98(4):1308-1313
The purpose of this work was to study the role of cesium in sodium‐based geopolymer and its thermal stability for nuclear waste management. A series of mixed sodium and cesium geopolymer samples (Na1?x Cs x )2O·Al2O3·SiO2·12H2O (referred to as (Na1? x Cs x )‐GP, where x = 0, 0.08, 0.15, 0.42, 1) have been prepared. All geopolymer samples were heated at 1100°C for 24 h. Pollucite (CsAlSi2O6) and feldspathoid (CsAlSiO4) were crystallized from Cs‐GP. Nepheline (NaAlSiO4) and a small amount of crystallized silica were obtained from Na‐GP. The other geopolymers (Na1? x Cs x )‐GP (x = 0.08, 0.15, 0.42) led to pollucite and nepheline main phases. Amorphous silica phase was observed in all the geopolymer samples with various amounts. Phase quantification and scanning electron microscope revealed that higher Cs concentrations in Na‐GP tend to decrease the amorphous phase while improving pollucite and nepheline phase quantification. The amorphous geopolymers have also been studied by pair distribution function analysis. Tetrahedral chains formed by T–O bonding (with T = Si, Al) were shown to be more tighten around Cs+ than around Na+. It led to shorter Cs–T bond than Na–T bond matching the higher solvation property of Na+. Furthermore, thermal study analysis pointed out the fact that geopolymer samples (Na1? x Cs x )‐GP, can be considered as solid solutions. 相似文献
3.
Jingkun Yuan Peigang He Xiaomin Liang Dechang Jia Lingyu Jia Delong Cai Zhihua Yang Xiaoming Duan Shengjin Wang Yu Zhou 《Ceramics International》2018,44(9):10047-10054
In this paper, a high temperature treatment procedure was designed to evaluate the effect of holding temperature on thermal evolution process of Li+ substituted Cs-based geopolymer (Cs0.7Li0.3GP), including the thermal analysis, phase composition and microstructure evolution. With rising of holding temperature, amorphous unheated Cs0.7Li0.3GP gradually transformed into a multiphase system during the high temperature treatment process, which consisted of pollucite (CsAlSi2O6), spodumene (LiAlSi2O6) and amorphous glass phase. In the multiphase system, Cs+ ions were in the form of pollucite grains, while Li+ ions were in the form of spodumene nanocrystallines distributed in amorphous matrix. The pollucite grains gradually coarsened with rise in holding temperature, and the densification of the resulting products were also improved synchronously, which were related to the presence of amorphous glass phases. The amorphous glass phase would be in a molten state when holding temperature over 800?°C. And the presence of molten amorphous phase would make the mass transfer process easier, which could contribute to the growth of the crystal grains and the elimination of the pores. 相似文献
4.
Low‐temperature sintering of β‐spodumene ceramics with low coefficient of thermal expansion (CTE) was attained using Li2O–GeO2 sintering additive. Single‐phase β‐spodumene ceramics could be synthesized by heat treatment at 1000°C using highly pure and fine amorphous silica, α‐alumina, and lithium carbonate powders mixture via the solid‐state reaction route. The mixture was calcined at 950°C, finely pulverized, compacted, and finally sintered with or without the sintering additive at 800°C–1400°C for 2 h. The relative density reached 98% for the sample sintered with 3 mass% Li2O–GeO2 additive at 1000°C. Its Young's modulus was 167 GPa and flexural strength was 115 MPa. Its CTE (from R.T. to 800°C) was 0.7 × 10?6 K?1 and dielectric constant was 6.8 with loss tangent of 0.9% at 5 MHz. These properties were excellent or comparative compared with those previously reported for the samples sintered at around 1300°C–1400°C via melt‐quenching routes. As a result, β‐spodumene ceramics with single phase and sufficient properties were obtained at about 300°C lower sintering temperature by adding Li2O–GeO2 sintering additive via the conventional solid‐state reaction route. These results suggest that β‐spodumene ceramics sintered with Li2O–GeO2 sintering additive has a potential use as LTCC for multichip modules. 相似文献
5.
The thermal evolution of cesium-substituted potassium-based geopolymer ((K1−xCsx)2O·Al2O3·5SiO2·11H2O, x = 0, 0.1, 0.2, 0.3, and 0.4) on heating is studied by a variety of techniques. Phase compositions and thermal expansion behaviors of the ceramics derived from the geopolymer are characterized. All of the geopolymer specimens with or without cesium substitution exhibit similar thermal evolution trends. Major weight losses before 600 °C from all the geopolymer specimens are observed and are resulted from evaporation of free water and hydroxyl groups. Thermal shrinkage of these specimens can be divided into four stages, i.e. structural resilience, dehydration, dehydroxylation and sintering, according to the dilatometer results. For these specimens, significant difference is observed in the viscous sintering stage and the effect of cesium is to reduce the thermal shrinkage in this stage due to the increased matrix viscosity. In the ceramics derived from geopolymer, the amount of stabilized leucite increases with the amount of cesium and with 20% cesium substitution leucite is fully stabilized in cubic phase. 相似文献
6.
Jian Fang Liangbo Sun Songsong Guo Chunfeng Liu Jie Zhang 《Journal of the European Ceramic Society》2021,41(3):1817-1827
Various glass-ceramics were prepared based on the CaO-Al2O3-SiO2 system with the addition of Li2O in an attempt to develop a suitable sealant for SiC ceramic. The effects of Li2O content on crystallization behavior and thermal expansion properties were systematically investigated. The results revealed that the addition of Li2O significantly reduced the crystallization activation energy of glass. Besides, as the Li2O content increased, the precipitation of spodumene and wollastonite was promoted while the precipitation of anorthite was suppressed. By controlling the Li2O content and crystallization treatment, the coefficient of thermal expansion (CTE) of glass-ceramic could be adjusted in a certain range, from 8.5 × 10?6/°C to 2.8 × 10?6/°C. When the content of Li2O was 3 wt.%, the CTE of the formed glass-ceramic was well-matched with that of SiC ceramic. Furthermore, it was confirmed that this glass-ceramic possessed an excellent wettability and weldability to SiC ceramic. 相似文献
7.
Mark A. Rodriguez Terry J. Garino David X. Rademacher Xiaoyi Zhang Tina M. Nenoff 《Journal of the American Ceramic Society》2013,96(9):2966-2972
Barium‐substituted CsAlSi2O6 pollucites, CsxBa(1?x)/2AlSi2O6, and barium‐ and iron‐substituted pollucites, CsxBa(1?x)/2AlxFe1?xSi2O6 and CsxBa1?xAlxFe1?xSi2O6 were synthesized with 1 ≥ x≥ 0.7 using a hydrothermal synthesis procedure. Rietveld analysis of X‐ray diffraction data confirmed the substitution of Ba for Cs and Fe for Al, respectively. The crystallographic analysis also describes the effects of three different types of pollucite substitutions on the pollucite unit cell: Ba2+ for Cs1+ cation results in little effect on cell dimensions, intermediate concentrations of Ba2+ and Fe3+ substitution result in net minor expansion due to Fe3+ addition, and large Ba and Fe substitutions result in overall framework contraction. Elemental analysis combined with microscopy further supports the phase purity of these new phases. These materials can be used to study the stability of CsAlSi2O6 as a durable ceramic waste form, which could accommodate with time Cs and its decay product, Ba. Furthermore, success in iron substitution for aluminum into the pollucite lattice predicts that redox charge compensation for Cs cation decay is possible. 相似文献
8.
Crystal Structure and Thermodynamic Stability of Ba/Ti‐Substituted Pollucites for Radioactive Cs/Ba Immobilization
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Hongwu Xu Manuel E. Chavez Jeremy N. Mitchell Terry J. Garino Haiqing L. Schwarz Mark A. Rodriguez David X. Rademacher Tina M. Nenoff 《Journal of the American Ceramic Society》2015,98(8):2634-2640
As an analogue of the mineral pollucite (CsAlSi2O6), CsTiSi2O6.5 is a potential host phase for radioactive Cs. However, as 137Cs and 135Cs transmute to 137Ba and 135Ba, respectively, through the beta decay, it is essential to study the structure and stability of this phase upon Cs → Ba substitution. In this work, two series of Ba/Ti‐substituted samples, CsxBa(1?x)/2TiSi2O6.5 and CsxBa1?xTiSi2O7?0.5x, (x = 0.9 and 0.7), were synthesized by high‐temperature crystallization from their respective precursors. Synchrotron X‐ray diffraction and Rietveld analysis reveal that while CsxBa(1?x)/2TiSi2O6.5 samples are phase‐pure, CsxBa1?xTiSi2O7?0.5x samples contain Cs3x/(2+x)Ba(1?x)/(2+x)TiSi2O6.5 pollucites (i.e., also two‐Cs‐to‐one‐Ba substitution) and a secondary phase, fresnoite (Ba2TiSi2O8). Thus, the CsxBa1?xTiSi2O7?0.5x series is energetically less favorable than CsxBa(1?x)/2TiSi2O6.5. To study the stability systematics of CsxBa(1?x)/2TiSi2O6.5 pollucites, high‐temperature calorimetric experiments were performed at 973 K with or without the lead borate solvent. Enthalpies of formation from the constituent oxides (and elements) have thus been derived. The results show that with increasing Ba/(Cs + Ba) ratio, the thermodynamic stability of these phases decreases with respect to their component oxides. Hence, from the energetic viewpoint, continued Cs → Ba transmutation tends to destabilize the parent silicotitanate pollucite structure. However, the Ba‐substituted pollucite co‐forms with fresnoite (which incorporates the excess Ba), thereby providing viable ceramic waste forms for all the Ba decay products. 相似文献
9.
Synthesis and Characterization of Silicon Carbide Powders Converted from Metakaolin‐Based Geopolymer
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Cengiz Bagci Gregory P. Kutyla Kevin C. Seymour Waltraud M. Kriven 《Journal of the American Ceramic Society》2016,99(7):2521-2530
Silicon carbide (SiC) ceramic powders were synthesized by carbothermal reduction in specific geopolymers containing carbon nanopowders. Geopolymers containing carbon and having a composition M2O·Al2O3·4.5SiO2·12H2O+18C, where M is an alkali metal cation (Na+, K+, and Cs+) were carbothermally reacted at 1400°C, 1500°C, and 1600°C, respectively, for 2 h under flowing argon. X‐ray diffraction and microstructural investigations by SEM/EDS and TEM were made. The geopolymers were gradually crystallized into SiC on heating above 1400°C and underwent significant weight loss. SiC was seen as the major phase resulting from Na‐based geopolymer heated to ≥1400°C, even though a minor amount of Al2O3 was also formed. However, phase pure SiC resulted with increasing temperature. While a slight increment of the Al2O3 amount was seen in potassium geopolymer, Al2O3 essentially replaced cesium geopolymer on heating to 1600°C. SEM revealed that SiC formation and a compositionally variable Al2O3 content depended on the alkaline composition. Sodium geopolymer produced high SiC conversion into fibrous and globular shapes ranging from ~5 μm to nanosize, as seen by X‐ray diffraction as well as SEM and TEM, respectively. 相似文献
10.
Yaqun Wu Yuming Tian Yaqiao Wu Mei Qing Ming Feng Dongcheng Ye Baoshun Zhu 《International Journal of Applied Ceramic Technology》2022,19(3):1702-1712
In this work, spodumene/mullite ceramics with low thermal expansion were successfully prepared from spodumene, quartz, talc, and clay. The effects of spodumene content and sintering temperature on the mechanical properties of spodumene/mullite ceramics were investigated. The formed phases were then detected by X-ray diffraction analysis and the microstructures of the sintered bodies were determined by scanning electron microscopy. The interaction effects of the spodumene content and sintering temperature on the apparent porosity and bulk density were studied by response surface methodology. The results demonstrate that an appropriate sintering temperature and spodumene content can promote densification, improve the mechanical properties, and reduce the coefficient of thermal expansion (CTE) of spodumene/mullite ceramics. At the spodumene content of 40 wt.%, the sintering temperature of 1270°C, and the holding time of 90 min, the bending strength was 60.45 MPa, the CTE was 1.73 × 10–6/°C (α[25–650°C] < 2 × 10–6/°C), the bulk density was 2.28 g cm-3, and the apparent porosity was 0.43%. Therefore, this study was of guiding significance for reducing the production cost of spodumene low thermal expansion ceramics and improving product quality. 相似文献
11.
Effect of P2O5 on the Nonisothermal Sinter‐Crystallization Process of a Lithium Aluminum Silicate Glass
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Viviane Oliveira Soares Edgar Dutra Zanotto 《International Journal of Applied Ceramic Technology》2016,13(5):948-955
Dense (~98.5%), lithium aluminum silicate glass‐ceramics were obtained via the sinter‐crystallization of glass particle compacts at relatively low temperatures, that is, 790–875°C. The effect of P2O5 on the glass‐ceramics' sinter‐crystallization behavior was evaluated. We found that P2O5 does not modify the surface crystallization mechanism but instead delays the crystallization kinetics, which facilitates viscous flow sintering. Our glass‐ceramics had virgilite (LixAlxSi3‐xO6; 0.5 < x < 1), a crystal size <1 μm, and a linear thermal expansion coefficient of 2.1 × 10?6°C?1 in the temperature range 40–500°C. The overall heat treatment to obtain these GCs was quite short, at ~25 min. 相似文献
12.
Effect of excess Li2S on electrochemical properties of amorphous li3ps4 films synthesized by pulsed laser deposition
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Zhen Quan Masaaki Hirayama Daichi Sato Yueming Zheng Taka‐aki Yano Kosuke Hara Kota Suzuki Masahiko Hara Ryoji Kanno 《Journal of the American Ceramic Society》2017,100(2):746-753
Amorphous Li3PS4 films were synthesized by pulsed laser deposition (PLD) at room temperature using Li3PS4 targets with excess lithium and sulfur. Raman and X‐ray photoemission spectroscopies indicated that the Li3PS4 film synthesized with a stoichiometric amount of Li3PS4 target contained lithium‐deficient phases such as Li4P2S6, Li2?xS and sulfur due to composition deviation caused during the ablation process. The film synthesized with a 14% Li2S‐excess target (Li3.42PS4.21) contained fewer impurities, and exhibited a higher ionic conductivity of 5.3 × 10?4 S/cm at 298 K than the lithium‐deficient film (3.1 × 10?4 S/cm). The target composition is an important factor for the fabrication of highly conductive Li3PS4 films for electrolytes in thin‐film batteries. 相似文献
13.
Optimization of Lithium Content and Sintering Aid for Maximized Li+ Conductivity and Density in Ta‐Doped Li7La3Zr2O12
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Narayanasamy Janani Sampathkumar Ramakumar Subramanian Kannan Ramaswamy Murugan 《Journal of the American Ceramic Society》2015,98(7):2039-2046
Ta‐doped cubic phase Li7La3Zr2O12 (LLZ) lithium garnet received considerable attention in recent times as prospective electrolyte for all‐solid‐state lithium battery. Although the conductivity has been improved by stabilizing the cubic phase with the Ta5+ doping for Zr4+ in LLZ, the density of the pellet was found to be relatively poor with large amount of pores. In addition to the high Li+ conductivity, density is also an essential parameter for the successful application of LLZ as solid electrolyte membrane in all‐solid‐state lithium battery. Systematic investigations carried out through this work indicated that the optimal Li concentration of 6.4 (i.e., Li6.4La3Zr1.4Ta0.6O12) is required to obtain phase pure, relatively dense and high Li+ conductive cubic phase in Li7?xLa3Zr2?xTaxO12 solid solutions. Effort has been also made in this work to enhance the density and Li+ conductivity of Li6.4La3Zr1.4Ta0.6O12 further through the Li4SiO4 addition. A maximized room‐temperature (33°C) total (bulk + grain boundary) Li+ conductivity of 3.7 × 10?4 S/cm and maximized relative density of 94% was observed for Li6.4La3Zr1.4Ta0.6O12 added with 1 wt% of Li4SiO4. 相似文献
14.
Sealing Glass‐Ceramics with Near Linear Thermal Strain,Part I: Process Development and Phase Identification
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Steve Dai Mark A. Rodriguez James J. M. Griego 《Journal of the American Ceramic Society》2016,99(11):3719-3725
A widely adopted approach to form matched seals in metals having high coefficient of thermal expansion (CTE), e.g. stainless steel, is the use of high CTE glass‐ceramics. With the nucleation and growth of Cristobalite as the main high‐expansion crystalline phase, the CTE of recrystallizable lithium silicate Li2O–SiO2–Al2O3–K2O–B2O3–P2O5–ZnO glass‐ceramic can approach 18 ppm/°C, matching closely to the 18 ppm/°C–20 ppm/°C CTE of 304L stainless steel. However, a large volume change induced by the α‐β inversion between the low‐ and high‐ Cristobalite, a 1st order displacive phase transition, results in a nonlinear step‐like change in the thermal strain of glass‐ceramics. The sudden change in the thermal strain causes a substantial transient mismatch between the glass‐ceramic and stainless steel. In this study, we developed new thermal profiles based on the SiO2 phase diagram to crystallize both Quartz and Cristobalite as high expansion crystalline phases in the glass‐ceramics. A key step in the thermal profile is the rapid cooling of glass‐ceramic from the peak sealing temperature to suppress crystallization of Cristobalite. The rapid cooling of the glass‐ceramic to an initial lower hold temperature is conducive to Quartz crystallization. After Quartz formation, a subsequent crystallization of Cristobalite is performed at a higher hold temperature. Quantitative X‐ray diffraction analysis of a series of quenched glass‐ceramic samples clearly revealed the sequence of crystallization in the new thermal profile. The coexistence of two significantly reduced volume changes, one at ~220°C from Cristobalite inversion and the other at ~470°C from Quartz inversion, greatly improves the linearity of the thermal strains of the glass‐ceramics, and is expected to improve the thermal strain match between glass‐ceramics and stainless steel over the sealing cycle. 相似文献
15.
《Ceramics International》2021,47(20):28951-28959
The volatization of cesium at high temperatures makes its immobilization challenging to the nuclear scientists. Present work reports the feasibility of cesium incorporation into an orthorhombic langbeinite phosphosilicate. The structural flexibility, leachability and thermal expansion of K2-xCsxZr2P2SiO12 (x = 0, 0.5, 1.0, 1.5, 2.0) have been investigated. Powder X-ray results authenticates the accommodation of cesium into a single phasic orthorhombic langbeinite structure up to 29.17 wt %. Morphological study reveals the particle agglomeration and poor crystallinity, and vibrational spectral analysis shows peak broadening and peak shift upon increasing the cesium concentration. The static leach test has been performed on the pellet sample and the normalized leaching of Cs is found to be in the order of 101 g/m2. The average coefficient of thermal expansion for K0.5Cs1.5Zr2P2SiO12 is registered as 7.45 × 10−6/K between 303 and 873 K. Cesium insertion into K2Zr2P2SiO12 displays a large deviation in thermal expansion due to the size effect as observed by several researchers for other phosphate and phosphosilicate members. 相似文献
16.
Tunable negative thermal expansion and structural evolution in antiperovskite Mn3Ga1−xGexN (0 ≤ x ≤ 1.0)
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Huiqing Lu Ying Sun Sihao Deng Kewen Shi Lei Wang Wenjun Zhao Huimin Han Shenghua Deng Cong Wang 《Journal of the American Ceramic Society》2017,100(12):5739-5745
The negative thermal expansion (NTE) and structural evolution of antiperovskite compounds Mn3Ga1?xGexN (0 ≤ x ≤ 1.0) were systematically investigated. Our results indicate the crystal structure of Mn3Ga1?xGexN changes from cubic (C) to tetragonal (T4) with increasing Ge content by X‐ray diffraction (XRD).The negative thermal expansion from x = 0 (operation‐temperature range ?T = 20 K) to x = 0.4 (?T = 60 K) becomes broad and shifts to higher temperature, and then it became positive from x = 0.5 in Mn3Ga1?xGexN. Typically, Mn3Ga0.5Ge0.5N shows low thermal expansion behavior between 300 and 450 K (?T = 150 K), and thermal expansion coefficient α is estimated to be 2 × 10?6 K?1. Furthermore, variable temperature XRD was measured to reveal the origin of NTE. The cubic I ‐ cubic II phases coexistence (x = 0.2) and cubic I ‐ tetragonal coexistence (x = 0.5, 0.6) was observed at low temperature. The tunable NTE is highly valuable for practical applications in precision devices. 相似文献
17.
Glass‐Ceramics in the System BaO–SrO–ZnO–SiO2 with Adjustable Coefficients of Thermal Expansion
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Christian Thieme Gabriel Buzatto de Souza Christian Rüssel 《Journal of the American Ceramic Society》2016,99(9):3097-3103
Glasses from the system BaO–SrO–ZnO–SiO2 with different Ba/Sr ratios were characterized regarding crystallization behavior as well as the thermal expansion of almost fully crystallized glasses. Depending on the SrO concentration, different crystalline phases precipitate from the glasses. Those with low SrO concentrations precipitate crystals with the structure of low‐temperature BaZn2Si2O7 as one of the major phases. Higher SrO concentrations cause the formation of Ba1?xSrxZn2Si2O7 solid solutions with the structure of high‐temperature BaZn2Si2O7. Both, the low‐ as well as the high‐temperature phase exhibit very different thermal expansion behaviors ranging from a very high coefficient of thermal expansion in the case of the low‐temperature phase to a very low coefficient of thermal expansion in the case of the high‐temperature phase. The glass‐ceramics with the highest and that with the lowest coefficient of thermal expansion measured between 100°C and 800°C show a difference of 7.9 × 10?6 K?1, which is caused solely by a substitution of BaO with SrO. In contrast, the maximum variation in the thermal expansion of the glasses was only 1.5 × 10?6 K?1. The microstructure of sintered and afterward crystallized glass powders was analyzed via scanning electron microscopy and showed crack‐free samples with low porosity. 相似文献
18.
Qian Wan Feng Rao Shaoxian Song Carlos A. Leon-Patino Yingqiang Ma Wanzhong Yin 《Journal of the American Ceramic Society》2019,102(5):2451-2461
Mine tailings-based geopolymers were prepared at ambient temperature. The evolution of their microstructure and the immobilization of lead were studied. Characterizations include measurements in compressive strength, scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and toxicity characteristic leaching procedure (TCLP) tests. With increasing the ratio of metakaolin from 0% to 50%, geopolymer gel in the mine tailings-based geopolymers increased from 33.92% to 79.45%, leading to the compressive strength that increased from 2 to 15.5 MPa. With addition of Pb(NO3)2, a three-stepped changes in the compressive strength and microstructure of the geopolymers were observed. As increasing Pb(NO3)2 dosage from 0% to 6%, geopolymer gel was kept constant, while lead silicate glass increased from 0% to 10.51%, and Si sites in calcium silicate hydrate (CSH) gel decreased from 20.55% to 11.3%. Pb2+ was effectively immobilized in the geopolymers. This study first presents the evolution of geopolymer gel, belite, lead silicate glass, and CSH gel in mine tailings-based geopolymers as the functions of metakaolin and Pb(NO3)2 additions. 相似文献
19.
Lithium Diffusion in Lithium Niobate Crystals with Different Initial Li2O Content at High Temperature
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Qinglian Li Jun Sun Jinfeng Yang Jifang Shang Ling Zhang Jingjun Xu 《Journal of the American Ceramic Society》2016,99(9):3055-3059
Lithium diffusion in lithium niobate crystals with different initial Li2O content (Cinitial) was investigated under Li‐rich environment at 1100°C. Lithium niobate crystals with widely varying diffusion‐limited Li2O content profiles were prepared through the vapor transport equilibration (VTE) technique using congruent lithium niobate crystals with different Cinitial, and the profiles were measured through Curie temperature by a thermal analyzer. A Boltzmann‐Matano analysis was employed to those profiles to estimate the Li+ diffusivity as a function of Li2O content in lithium niobate crystals. A trigonometric function method was applied to those profiles to correlate diffusion time and Li2O content. The results show that at the same composition of lithium niobate crystals after diffusing treatment, the less the Cinitial, the larger the Li+ diffusivity. The relation between diffusion time and Li2O content of the samples which have different Cinitial and thickness was derived. Based upon the Boltzmann‐Matano result, diffusion time can be estimated easily from the relation. It is concluded that increasing Cinitial contributes to shorten the diffusion time for preparing near‐stoichiometric lithium niobate crystals through the VTE technique, especially for thick crystal wafers. 相似文献
20.
Jun Yoshida Shinji Nakanishi Hideki Iba Hiroya Abe Makio Naito 《International Journal of Applied Ceramic Technology》2013,10(5):764-772
High‐voltage and high‐capacity cathode‐active materials are required to increase the energy density of rechargeable lithium‐ion batteries for hybrid vehicles. The olivine‐type LiMnPO4 is considered as a good candidate for the next‐generation lithium‐ion battery due to its high voltage (4.1 V vs Li+/Li), low cost, and lower toxicity compared with the currently used layered materials. However, recent research has demonstrated that the thermal stability of delithiated phase of Li1?xMnPO4 (0 ≤ x <1) was less than that of Li1?xFePO4. These reports verified that the delithiated MnPO4 decomposed and changed into Mn2P2O7 with O2 release at high temperature. In this study, we focused on the particle and crystal changes in LiMnP O4/MnPO4 at high temperature on a nanoscale. As a result, we have succeeded to observe directly the particle and crystal changes using transmission electron microscope (TEM) with heating. It revealed that MnPO4 was a thermally unstable phase because dendrites of Mn2P2O7 began to generate around 200°C. 相似文献