Lithium Orthosilicate Research Articles

Lithium orthosilicate for CO2 capture with high regeneration capacity: Kinetic study and modeling of carbonation and decarbonation reactions

One of the most promising techniques for CO2 capture at high temperatures consists in its separation by the carbonation reaction with an inorganic solid. Lithium orthosilicate (Li4SiO4) is considered one potential material due to its high capture capacity and thermal stability. In this study, the kinetics of carbonation and decarbonation of Li4SiO4 was evaluated at atmospheric pressure, isothermal and non-isothermal conditions and in cycling experiments. According to the non-isothermal test, carbonation occurs within 500–715°C and decarbonation above it. Isothermal tests showed that the reaction rates increased with increasing temperature and at high temperatures it was possible to capture up to 35wt% CO2. Kinetics of both carbonation and decarbonation was adequately described by the shrinking core model. The Li4SiO4 presented an excellent durability comparing to other materials for CO2 capture, with an activity decay of 20% after 48 cycles.

Synthesis of Lithium Orthosilicate and Fabrication of Pebbles by the Solid-State Reaction Process

The fusion of deuterium and tritium is being considered for the energy source from fusion reactions, and on reaction each nuclei will produce one helium nuclei, one neutron and thermal energy. Deuterium is naturally available and the technologies to separate it from the compounds of hydrogen are well developed. Tritium can be produced by nuclear reaction of Li6 isotope with thermal neutrons, and natural lithium contains about 7.5% Li6. Lithium has a low melting point and readily reacts with oxygen, nitrogen and moisture present in air. So, lithium-containing ceramics, namely lithium orthosilicate and lithium titanate enriched in Li6 isotope, are being considered for tritium production by nuclear reaction with neutron. It was found that like lithium titanate, lithium orthosilicate can also be synthesised and pebbles can be fabricated by solid-state reaction process by using silica and lithium carbonate as raw materials. The advantage of this process is that the synthesis can be carried out at 800°C and fabricated pebbles can be sintered at 900°C to achieve the desired properties of the pebbles. Both these temperatures for synthesis and sintering are lower than that of the molten spray method. The experimental details and results are discussed in this paper.

First-principles study of electronic, dynamical and thermodynamic properties of γ-Li4SiO4

We have studied the structural, electronic and dynamic properties of γ- Li4SiO4(lithium orthosilicate) using density functional theory (DFT) with the generalized gradient approximation (GGA). The crystal structure is fully relaxed. The electronic band structure and Density of States (DOS) calculations indicate that γ- Li4SiO4is an insulator with an indirect band gap of 5.19 eV and it has a conduction band with the width of 5.92 eV and two valance bands with the width of 4.45 eV and 0.57 eV, respectively. In the partial DOS, Li and Si electronic densities increase more sharply than O atoms. Comparing with previous works, the phonon dispersion curves without negative frequencies are calculated along high symmetry points. By adding the Born effective charges in the phonon calculation, the LO–TO splittings are also calculated which indicate that γ- Li4SiO4is polar and anisotropic. The optical modes of phonon frequencies at Γ point are assigned as Raman and Infrared-active modes. Additionally, the thermodynamic functions (entropy, internal energy, Helmholtz free energies and constant-volume specific heats) were determined by using the phonon DOS. The calculated results may provide useful guidance of γ- Li4SiO4for future experimental studies in some degree.

Carbon Dioxide Absorption Behavior and Carbonate Ion Transport of Lithium Orthosilicate / Potassium Carbonate Coexistence System Prepared By Ball Milling

Lithium Orthosilicate (Li4SiO4), a type of ceramic CO2 absorbent has a large absorptive capacity (36.7 wt. %) and also has heat resistance. This material has some useful application as a separator in Molten Carbonate Fuel Cell and as a direct CO2 absorbent in large-scale emission sources, for example, thermal power stations; because the following equilibrium reaction at the temperature around 993 K; Li4SiO4 + CO2 ⇄ Li2CO3 + Li2SiO3. In this study, we focused on the absorption behaviors of CO2 at lower temperature into Li4SiO4 in combination of these two methods and evaluated the physiochemical dependence of surface properties of CO2 absorption reaction. Li4SiO4 was prepared from solid state reaction. SiO2 powder and Li2CO3 powder were mixed at the molar ratio Li/Si = 4.0. The mixture was calcined at 973 K for 20 h in air. The resulting powder (Li4SiO4) kept in an Argon atmosphere glove box and in order to confirm the effect of carbonate, was mixed with a given amount of K2CO3. Each mixture (2.5 g) was put in the grinding bowl with the grinding balls, it sealed up under the Ar atmosphere, and the grinding processing was done for 0-300 minutes in revolution speed 250 rpm using planetary ball mill. Also, the grinding process was done under the condition of one cycle for 15 minutes of the grinding processing and two minutes of rest time to prevent the samples temperature from rising. Samples were characterized with X-ray diffraction (XRD), N2-isotherm, SEM, SEM-EDX, TG-DTA and Electro spin resonance (ESR). It was found that samples whose surface was modified with ball milling method under Ar gas flow showed a tendency to increase the surface area estimated by BET method measured by N2-isotherm and increase of Si dangling bond measured by ESR. Also, it was found that there are two different absorption processes, one is a chemisorption at the surface (T<773 K) the other is a bulk diffusion (T>773 K) by the result of TG-DTA. As seen in isothermal analysis (Fig. 1), the CO2 absorb reaction rate improved by the coexistence of K2CO3 infiltrated in Li4SiO4 being promoted by not only the surface area was increased and activated by the ball milling but also absorbing CO2 of coexisting K2CO3. Furthermore, it was found that ΔG‡ decreased from the result of the isothermal analysis at 873 K. We would like to consider controlling transportation of carbonate ion electrochemically according to the CO2 absorption reaction as a separator in Molten Carbonate Fuel Cell. Figure 1

Facile synthesis of macroporous Li4SiO4 with remarkably enhanced CO2 adsorption kinetics

Lithium orthosilicate (Li4SiO4) has attracted extensive scientific attention due to its large CO2 adsorption capacity at high temperature (650–700°C) and low material cost. However, the conventional nonporous Li4SiO4 ceramic shows very poor CO2 adsorption performance below 600°C, which is a relevant condition for possible applications such as sorption-enhanced steam methane reforming. In the present work, in order to increase the CO2 adsorption kinetics below 600°C, Li4SiO4 was synthesized in the form of a macroporous structure by a simple solid-state transformation method using LiOH and fumed silica as a precursor for Li and SiO2, respectively. The use of LiOH substantially decreased the synthesis temperature of Li4SiO4 down to 600°C, compared with the conventional syntheses using other lithium precursors such as Li2CO3 and LiNO3 that require very high synthesis temperature (>700°C). The decrease of the material synthesis temperature circumvents undesirable sintering of initially formed small Li4SiO4 crystallites and leads to the formation of a highly macroporous (macropore volume >0.6mLg−1) Li4SiO4 framework that has a significantly higher BET surface area (15m2g−1) than conventional nonporous Li4SiO4 (<1.0m2g−1). The macroporous Li4SiO4 exhibited dramatically enhanced CO2 adsorption capacity (29.8wt%) and rate (56.1mgg−1min−1), compared with the CO2 adsorption capacities (1.40–7.79wt%) and rates (0.420–2.95mgg−1min−1) of nonporous Li4SiO4 materials. Adsorption–desorption cycles at 550°C could be repeated 10 times without a significant decrease in the adsorption capacity or the rate capability.

Electrical behaviour of ceramic breeder blankets in pebble form after γ-radiation

Lithium orthosilicate (Li4SiO4) ceramics in from of pebble bed is the European candidate for ITER testing HCPB (Helium Cooled Pebble Bed) breeding modules. The breeder function and the shielding role of this material, represent the areas upon which attention is focused. Electrical measurements are proposed for monitoring the modification created by ionizing radiation and at the same time provide information on lithium movement in this ceramic structure. The electrical tests are performed on pebbles fabricated by Spray-dryer method before and after gamma-irradiation through a 60Co source to a fluence of 4.8Gy/s till a total dose of 5∗105Gy. The introduction of thermal annealing treatments during the electrical impedance spectroscopy (EIS) measurements points out the recombination effect of the temperature on the γ-induced defects.

Preparation and characterization of Li4SiO4 ceramic pebbles by graphite bed method

Lithium-based ceramics have long been recognized as tritium breeding materials in fusion reactor blankets. Lithium orthosilicate (Li4SiO4) is one of these materials and has been recommended by many ITER research teams as the first selection for the solid tritium breeder. In this paper, the fabrication of Li4SiO4 pebbles used as tritium breeder by a graphite bed method was studied for the first time. Ceramic powders and deionized water were mixed and ball milled to obtain homogeneous suspensions. And then the ceramic suspensions were dispersed on spread graphite powder through nozzles. Spherical droplets with highly uniform size were formed by the surface tension of the liquid droplets. The droplets converted into green pebbles after drying. After calcination and sintering, Li4SiO4 pebbles with desired size and shape were prepared. The obtained Li4SiO4 pebbles had narrow size distribution and favorable sphericity. Thermal analysis, phase analysis and microstructure observation of the pebbles were carried out systematically. Properties of the prepared pebbles were also characterized for crushing load strength, density and porosity, etc. The values were found to be conforming to the desired properties for used as solid breeder.

CO2 absorption properties of Ti- and Na-doped porous Li4SiO4 prepared by a sol–gel process

To improve the carbon dioxide (CO2) absorption performance of lithium orthosilicate (Li4SiO4), tablet-like Li4Si1−x Ti x O4 and Li3.9Na0.1Si0.96Ti0.04O4 sorbents with loose and porous texture were prepared by a sol–gel process. The relationship between the Ti doping and volume expansion was studied for the first time. The results indicated that the Ti presence into the Li4SiO4 structure inhibited the growth of grains and abated the volume expansion. The X-ray diffraction and scanning electron microscopy results showed that the loose and porous solid solutions with similar phase crystallite but different grain sizes could obtain by heat treatment of precursor at 700 °C. The optimum Ti content of Li4Si1−x Ti x O4 seems to be 0.04 of Li4Si0.96Ti0.04O4. And the CO2 capture behaviors of Li3.9Na0.1Si0.96Ti0.04O4 were better than Li4Si0.96Ti0.04O4.

Thermally induced outdiffusion studies of deuterium in ceramic breeder blanket materials after irradiation

Based on a KIT–CIEMAT collaboration on the radiation damage effects of light ions sorption/desorption in ceramic breeder materials, candidate materials for the ITER EU TBM were tested for their outgassing behavior as a function of temperature and radiation. Lithium orthosilicate based pebbles with different metatitanate contents and pellets of the individual oxide components were exposed to a deuterium atmosphere at room temperature. Then the thermally induced release of deuterium gas was registered up to 800°C. This as-received behavior was studied in comparison with that after exposing the deuterium-treated samples to 4MGy total dose of gamma radiation. The thermal desorption spectra reveal differences in deuterium sorption/desorption behavior depending on the composition and the induced ionizing damage. In these breeder candidates, strong desorption rate at approx. 300°C takes place, which slightly increases with increasing amount of the titanate second phase. For all studied materials, ionizing radiation induces electronic changes disabling a number of trapping centers for D2 adsorption.

CFD Analysis for the Hydrodynamics and Heat Transfer in Packed Pebble Bed

Lithium titanate (Li2TiO3) and lithium orthosilicate (Li4SiO4) are the promising solid breeder materials for the fusion reactors. Packed bed of Li2TiO3 or Li4SiO4 pebbles is considered in the fusion reactor blanket for in situ production of tritium and for this a good effective thermal conductivity of the pebble bed is necessary. In recent past, Mandal et al. [26] studied the hydrodynamics and heat transfer properties of bed of lithium titanate pebbles at different operating conditions viz., gas flow rates, pebble sizes, bed wall temperatures, etc. In the present study laminar, k – ε and low Reynolds k – ε model have been used to simulate the hydrodynamics and heat transfer data of Li2TiO3 pebble bed. The computational fluid dynamics (CFD)-simulated hydrodynamics results have been compared with hydrodynamics and heat transfer results of bed of Li2TiO3 pebbles reported by Mandal et al. [26] and others. It was found that k – ε and low Reynolds number k – ε model shows better agreement with experimental results. The CFD study were carried out using low Reynolds k – ε model for pebble bed of different materials viz. Li2TiO3, Li4SiO4 and alumina (Al2O3). The effect of flow rate, pebble size, wall temperature, solid properties viz. thermal conductivity and specific heat on effective thermal conductivity and overall heat transfer coefficient has been discussed in this paper.

ChemInform Abstract: Recent Developments of Solid Breeder Fabrication

AbstractReview: 25 refs.

S0810104 充填効率と拡散抵抗を考慮したCO_2吸収セラミックスの形状設計

In order to combat global warming CO_2 emission reduction from the iron and steel making industry is necessary. The Active Carbon Recycling Energy System for the iron making process (iACRES) has been developed as a technical option for substantial CO_2 reduction. Lithium ortho-silicate (Li_4SiO_4, LS), which can separate high purity CO_2 at high temperatures, is a suitable solid sorbent to capture CO_2 from the iACRES process. In our previous studies, a spherical LS pellet was analyzed via numerical analysis using the unreacted core model. The diffusion resistance resulting from decreased porosity as CO_2 absorption occurred was found to be the dominant factor inhibiting the CO_2 absorption rate. In this study, the effect of a cylindrical LS pellet was analyzed using commercial FEM software with diffusion resistance and chemical reaction incorporated into the model. The result of the numerical analysis showed a trade-off between CO_2 loading capacity and absorption rate.

ICONE23-1090 SINGLE STEP FABRICATION OF NANO-SIZED Li4SiO4 BREEDER BY MICROWAVE-INDUCED SOLUTION COMBUSTION SYNTHESIS

Li_4SiO_4 (lithium orthosilicate) is a promising ceramic tritium breeder for the future D-T fusion reactor, which is also considered as a candidate material for Helium Cooled Pebble Bed Test Blanket Module (HCPB TBM) of China. Simple and efficient microwave-induced solution combustion synthesis (MSCS) approach was adopted to prepare Li_4SiO_4 powder by using lithium nitrate and tetraethyl orthosilicate as raw materials. In MSCS, microwave power is a key factor, which controls the combustion mode, flame temperature, phase composition, and microstructure of the product. The synthesized Li_4SiO_4 particles are homogeneous distributed with an average crystalline size of 20 nm when the microwave power is 1100 W. The Li_4SiO_4 powder shows comparable sinterability to the conventional solid state reaction, which reaches 89.2% of theoretical density at 1173 K with a small grain size of 2 μm.

Thermal conversion of a tailored metal-organic framework into lithium silicate with an unusual morphology for efficient CO₂ capture.

The conversion reaction of metal-organic frameworks (MOFs) was adopted as a synthetic method to produce an advanced CO2 absorbent. A Li- and Si-containing MOF is a good precursor for lithium orthosilicate (Li4SiO4); the resulting solid has an unusual coral-like morphology, which provides an enhanced CO2-sorption performance (high uptake and fast absorption).

The effect of γ-radiation in Li4SiO4 ceramic breeder blankets

Lithium orthosilicate (Li4SiO4) is considered one of the best candidates for the solid breeder blanket system (BBs) of future thermonuclear reactors. During reactor operation it will be bombarded by neutrons and gamma radiation which may alter its composition and properties, affecting its shielding role. The electrochemical impedance spectroscopy (EIS) is here used as a non-destructive tool for monitoring the electrical bulk conductivity of Li4SiO4 ceramic after different ionizing damaging treatments. The compound fabricated in our laboratories, was irradiated by a 60Co in the Nayade-facility (CIEMAT-Spain). Several studies with slight experimental variations were realized and here presented to understand the dynamic of the charge carriers’ movement and the role of intrinsic and extrinsic defects on the electrical properties of this candidate ceramic.

Studies on Evaluation of Reaction Rate of Lithium Ortho-Silicate for Chemical Heat Storage

Lithium ortho-silicate is a suitable solid sorbent for capturing CO2. This reversible chemical reaction is applicable to CHP. Reaction rate of Lithium ortho-silicate are studied by TG ( Thermogravimetry) and volumetric method that the influence of heat and mass transfer limitations at packed bed is designed as small as possible. CO2 adsorption reaction rate depends on the temperature. During continual operation, maximum reaction rate do not decrease for 10cycle and it turned out that the reaction system is repeated with from kept .The adsorbent utilization is higher than 60% at every condition. It turn out that lithium ortho-silicate is applicable to CHP.

Solution based synthesis of mixed-phase materials in the Li2TiO3–Li4SiO4 system

As candidate tritium breeder materials for use in the ITER helium cooled pebble bed, ceramic multiphasic compounds lying in the region of the quasi-binary lithium metatitanate–lithium orthosilicate system may exhibit mechanical and physical advantages relative to single phase materials. Here we present an organometallic solution-based synthesis procedure for the low-temperature fabrication of compounds in the Li2TiO3–Li4SiO4 region and investigate phase stability and transformations through temperature varied X-ray diffraction and scanning calorimetry. Results demonstrate that the metatitanate and metasilicate phases Li2TiO3 and Li2SiO3 readily crystallise in nanocrystalline form at temperatures below 180°C. Lithium deficiency in the region of 5% results from Li sublimation from Li4SiO4 and/or from excess Li incorporation in the metatitanate phase and brings about a stoichiometry shift, with product compounds exhibiting mixed lithium orthosilicate/metasilicate content towards the Si rich region and predominantly Li2TiO3 content towards the Ti rich region. Above 1150°C the transformation of monoclinic to cubic γ-Li2TiO3 disordered solid-solution occurs while the melting of silicate phases indicates a likely monotectic type system with a solidus line in the region 1050–1100°C. Synthesis procedures involving a lithium chloride precursor are not likely to be a viable option for breeder pebble synthesis as this route was found to yield materials with a more significant Li-deficiency exhibiting the crystallisation of the Li2TiSiO5 phase at intermediate compositions.

Size-Dependent Crush Analysis of Lithium Orthosilicate Pebbles

The crushing strength of the breeder material [lithium orthosilicate (Li4SiO4 or OSi)] in the form of pebbles to be used for EU solid breeder concept is investigated. The pebbles are fabricated using a melt-spray method, and hence, a size variation in the pebbles produced is expected. Knowledge of the mechanical integrity (crush strength) of the pebbles is important for a successful design of a breeder blanket. In this paper, we present the experimental results of the crush (failure) loads for spherical OSi pebbles of different diameters ranging from 250um to 800um. The ultimate failure load for each size shows a Weibull distribution. Furthermore, the mean crush load increases with increase in pebble diameter. It is also observed that the level of opacity of the pebble influences the crush load significantly. The experimental data presented in this paper and the associated analysis could possibly help us to develop a framework for simulating a crushable polydisperse pebble assembly using discrete element method.

Thermal Discrete Element Analysis of EU Solid Breeder Blanket Subjected to Neutron Irradiation

Due to neutron irradiation, solid breeder blankets are subjected to complex thermo-mechanical conditions. Within one breeder unit, the ceramic breeder bed is composed of spherical-shaped lithium orthosilicate pebbles, and as a type of granular material, it exhibits strong coupling between temperature and stress fields. In this paper, we study these thermo-mechanical problems by developing a thermal discrete element method (Thermal-DEM). This proposed simulation tool models each individual ceramic pebble as one element and considers grain-scale thermo-mechanical interactions between elements. A small section of solid breeder pebble bed in a helium-cooled pebble bed (HCPB) is modelled using thousands of individual pebbles and subjected to volumetric heating profiles calculated from neutronics under ITER-relevant conditions. We consider heat transfer at the grain scale between pebbles through both solid-to-solid contacts and the interstitial gas phase, and we calculate stresses arising from thermal expansion of pebbles. The overall effective conductivity of the bed depends on the resulting compressive stress state during the neutronic heating. The Thermal-DEM method proposed in this study provides access to the grain-scale information, which is beneficial for HCPB design and breeder material optimization, and a better understanding of overall thermo-mechanical responses of the breeder units under fusion-relevant conditions.

Enhanced CO2absorption kinetics in lithium silicate platelets synthesized by a sol–gel approach

Platelet-shaped lithium orthosilicate particles synthesized by a sol–gel approach employing the precursors lithium nitrate and colloidal silica displayed enhanced absorption kinetics for CO2 compared to the powders prepared by a solid-state reaction process involving Li2CO3 and silica. The sol–gel samples showed a CO2 absorption capacity of 350 mg g−1 at an absorption rate of 22.5 mg g−1 min−1, a value 70% higher than the rate of 13.2 mg g−1 min−1 measured with the solid-state samples under similar conditions. The higher sorption kinetics of CO2 by the sol–gel derived lithium orthosilicate could be attributed to the unique platelet morphology of the particles, which have a very small thickness. A porous carbon mesh coated with the sol–gel based particles exhibited CO2 absorption capacity of 150 mg g−1 at an absorption rate of 37.5 mg g−1 min−1. This supported absorbent also showed stable absorption and desorption performance for the 8 cycles examined in this study. The excellent absorption characteristics of the sol–gel prepared powders, more specifically the coated strips, provide a successful pathway for the commercialisation of these materials.