Ferroelectric properties of Li‐doped BaTiO3 ceramics

We prepared 3 kinds of Li⁺‐doped BaTiO₃ ceramics by the solid‐state reaction method: (i) (Ba_1?xLi_x)TiO_3?x/2 having A‐site Li⁺, (ii) Ba(Ti_1?xLi_x)O_3?3x/2 having B‐site Li⁺, and (iii) x/2 Li₂CO₃+BaTiO₃ mixed one, for which we investigated the stable site of Li. The density of all prepared ceramics is above 95%. The results show that the lattice structure, the grain size, and the electric properties of Li⁺‐doped BaTiO₃ ceramics are dependent on Li⁺ site. According to the increase in Li content, the cell volume of Ba_1?xLi_xTiO_3?x/2 decreases, but that of BaTi_1?xLi_xO_3?3x/2 increases. That of x/2Li₂CO₃+BaTiO₃ decreases by the small addition of Li, but increases by the large addition of Li. All Li⁺‐doped ceramics show antiferroelectric‐like double hysteresis loops. The shape of loops and the dielectric properties are also dependent on the Li site. We suggest that the role of oxygen vacancy accompanied by the Li‐doping is important. By comparison with the results of 3 type ceramics, it is concluded that at x/2Li₂CO₃+BaTiO₃ ceramics, the Li⁺ prefers to favorably substitute Ba²⁺ at A site for the low concentration of Li but its location was changed to Ti⁴⁺ site for the high concentration of Li.     

Kinetic study on carbonation of crude Li<Subscript>2</Subscript>CO<Subscript>3</Subscript> with CO<Subscript>2</Subscript>-water solutions in a slurry bubble column reactor

Investigations were conducted to purify crude Li₂CO₃ via direct carbonation with CO₂-water solutions at atmospheric pressure. The experiments were carried out in a slurry bubble column reactor with 0.05 m inner diameter and 1.0 m height. Parameters that may affect the dissolution of Li₂CO₃ in the CO₂-water solutions such as CO₂-bubble perforation diameter, CO₂ partial pressure, CO₂ gas flow rate, Li₂CO₃ particle size, solid concentration in the slurry, reaction temperature, slurry height in the column and so on were investigated. It was found that the increases of CO₂ partial pressure, and CO₂ flow rate were favorable to the dissolution of Li₂CO₃, which had the opposite effects with Li₂CO₃ particle size, solid concentration, slurry height in the column and temperature. On the other hand, in order to get insight into the mechanism of the refining process, reaction kinetics was studied. The results showed that the kinetics of the carbonation process can be properly represented by 1−3(1−X)^2/3+2(1–X)=kt+b, and the rate-determining step of this process under the conditions studied was product layer diffusion. Finally, the apparent activation energy of the carbonation reaction was obtained by calculation. This study will provide theoretical basis for the reactor design and the optimization of the process operation.     

Analysis of CO2 sorption/desorption kinetic behaviors and reaction mechanisms on Li4SiO4

The CO₂ sorption/desorption kinetic behaviors on Li₄SiO₄ were analyzed. The theoretical compositions of the sorption/desorption reactions were calculated using FactSage. The sorption/desorption process on Li₄SiO₄ was investigated by comparing the shrinking core, double exponential, and Avrami–Erofeev models. The Avrami–Erofeev model fits the kinetic thermogravimetric experimental data well and, together with the double‐shell mechanism, clearly explains the sorption/desorption mechanism. The sorption process is limited by the rate of the formation and growth of the crystals with double‐shell structure consisting of Li₂CO₃ and Li₂SiO₃. The whole desorption process is found to be controlled by the rate of the formation and growth of the Li₄SiO₄ crystals. Furthermore, the influence of steam on the CO₂ sorption process was analyzed. It has been observed that the presence of steam enhance the mobility of Li⁺ and, therefore, the rate of diffusion control stage. © 2012 American Institute of Chemical Engineers AIChE J, 59: 901–911, 2013     

Recovery of Lithium Hydroxide from Spent Lithium Carbonate using Crystallizations

Abstract

Recovery of LiOH from the spent Li₂CO₃ used as absorbent for carbon dioxide in breathing apparatus was successfully explored by precipitation and crystallization. A lithium hydroxide solution was prepared by precipitation of calcium carbonate using reaction of spent Li₂CO₃ and calcium hydroxide. The effects of the operating conditions on the reaction were investigated. Conversion of calcium carbonate was about 95%. Lithium hydroxide monohydrate from lithium hydroxide solution was obtained in batch evaporative crystallization. The effect of the evaporation rate on crystal morphology was investigated. The evaporation rates were affected to control size and yield of crystals. Eventually, the purity of crystals was above 99 wt% and yield was about 80%.     

Kinetics of carbon dioxide sorption on potassium-doped lithium zirconate

Potassium-doped lithium zirconate (Li₂ZrO₃) sorbents with similar crystallite but different aggregate sizes were prepared by a solid-state reaction method from mixtures of Li₂CO₃, K₂CO₃, and ZrO₂ of different particle sizes. Carbon dioxide sorption rate on the prepared Li₂ZrO₃ sorbents increases with decreasing sorbent aggregate size. It is the size of the aggregate, not the crystallite, of Li₂ZrO₃ that controls the sorption rate. Temperature effect on CO₂ sorption is complex, depending on both kinetic and thermodynamic factors. A mathematical model based on the double-shell sorption mechanism was established for CO₂ sorption kinetics and it can fit experimental data quite well. Above 500°C, the rate-limiting step of CO₂ sorption is the diffusion of oxygen ions through the ZrO₂ shell formed during the carbonation reaction. Oxygen ion conductivities in the ZrO₂ shell were obtained by regression of the experimental CO₂ uptake curves with the model and are consistent with the literature data.     

Synthesis,characterization and sintering of Li2TiO3 nanoparticles via low temperature solid-state reaction

Synthesis of fine Li₂TiO₃ powders via low-temperature solid-state reaction (LTSSR) was studied. Solid Li₂CO₃ and H₂TiO₃ were blended by planetary ball mill with deionized water as medium. Calcination of the milled powder at low temperature of 500 °C resulted in the formation of pure Li₂TiO₃ nanoparticles. Another Li₂TiO₃ powder was also prepared by the conventional solid-state reaction (SSR) and a good comparison between different routes was realized. The results show that the particle size of LTSSR powder is significantly decreased to 19.6 nm while the one obtained by SSR is 146.6 nm. Low temperature calcined powders have less agglomeration and higher sinterability, which can be sintered at lower temperature. Pebbles sintered from the LTSSR powders at 750 °C exhibit small grain size (650 nm), high relative density (85.1%) and satisfactory crush load (42.8 N), whereas the SSR pebbles can only be sintered above 950 °C with the relative density close to 80%. Besides, the LTSSR samples also have a higher conductivity at room temperature, indicating the lower tritium diffusion barrier in ceramics. It is confirmed that H₂TiO₃ rather than TiO₂ is more appropriate for the solid-state reaction to produce Li₂TiO₃ powders with nano-size particles and favorable properties.     

Low Temperature Liquid State Synthesis of Lithium Zirconate and its Characteristics as a CO2 Sorbent

Abstract

In this study, a new preparation method providing greatly improved CO₂ sorption is introduced. Li₂ZrO₃ sorbent was prepared by low temperature co‐precipitation and compared in CO₂ sorption performance with a sorbent prepared by the conventional high temperature solid‐state reaction method. The two sorbents were characterized using scanning electron microscopy, X‐ray diffraction and thermo‐gravimetric analysis. The Li₂ZrO₃ powder prepared by the relatively simple co‐precipitation method showed significantly better performance than the one prepared by solid‐state reaction with respect to both kinetics and CO₂ sorption capacity. Extensive study of the powder prepared by co‐precipitation has been performed at various conditions.     

Electrochemical cycling behaviour of lithium carbonate (Li2CO3) pre-treated graphite anodes – SEI formation and graphite damage mechanisms

Graphite electrode surfaces were treated using a simple process of sedimentation in aqueous solutions containing 0.5 and 1.0 wt.% Li₂CO₃ with particle sizes of ∼1–2 μm. During the first cycle of voltammetry tests (vs. Li/Li⁺), the graphite surface was subjected to electrochemical degradation as a result of fracture and removal of near-surface graphite particles. Surface degradation was accompanied by a 0.4% strain in the graphite lattice as determined by in situ Raman spectroscopy. Pre-treated electrodes experienced a capacity drop of 3% in the first cycle, compared to a 40% drop observed in case of untreated graphite electrodes. After testing for 100 cycles, a capacity of 0.54 mAh cm⁻² was recorded for the pre-treated electrodes as opposed to a significant drop to 0.11 mAh cm⁻² for the untreated graphite. Cross-sectional HR-TEM indicated that the SEI formed on the pre-treated electrodes primarily consisted of Li₂CO₃ crystals of 14.6 ± 6.9 nm in size distributed within an amorphous matrix. The results suggested that the Li₂CO₃ enriched SEI formed on the pre-treated electrodes reduced the intensity of solvent co-intercalation induced surface damage. It is proposed that the Li₂CO₃ enriched SEI facilitated Li⁺ diffusion and hence improved the capacity retention during long-term cycling.     

Effects of the starting materials and mechanochemical activation on the properties of solid-state reacted Li4Ti5O12 for lithium ion batteries

Li₄Ti₅O₁₂ was synthesized by a solid-state reaction between Li₂CO₃ and TiO₂ for applications in lithium ion batteries. The effects of the TiO₂ phase and mechanochemical activation on the Li₄Ti₅O₁₂ particles as well as the corresponding electrochemical properties were investigated. Rutile TiO₂ was more desirable in acquiring high purity Li₄Ti₅O₁₂ than anatase due to the anatase to rutile phase transformation, which was found to be more rigid in the solid-state reaction than the intact rutile phase. Mechanochemical activation of the starting materials was effective in decreasing the reaction temperature and particle size as well as increasing the Li₄Ti₅O₁₂ content. The specific capacity depended significantly on the Li₄Ti₅O₁₂ content, whereas the rate capability improved with decreasing particle size due to the enhanced contact area and reduced diffusion path. Overall, a 200 nm-sized Li₄Ti₅O₁₂ powder with a specific capacity of 165 mAh/g could be synthesized by optimizing the milling method and starting materials.     

Synthesis,kinetic study,and reaction mechanism of Li4SiO4 with CO2 in a slurry bubble column reactor

Abstract

This study was performed to investigate the synthesis, kinetic and reaction mechanism of Li₄SiO₄ with CO₂ in a slurry bubble column reactor. The Li₄SiO₄ powder sample was prepared via a solid-state reaction. The sample was characterized via X-ray diffraction (XRD) analysis and verified as a single phase. The median diameter of the sample was measured using the laser diffraction and scattering method as about 20?μm. The synthesized sample was suspended in binary molten carbonate of Li₂CO₃–K₂CO₃ having a molar ratio of 38:62. The experimental results show that Li₄SiO₄ in the slurry bubble column absorbed approximately a stoichiometric amount of CO₂. The kinetic study shows that the CO₂ reaction behavior on the Li₄SiO₄ surface was fitted to a double exponential model and the limiting step of the reaction was lithium diffusion. The mass transfer coefficient of CO₂ and rate constant of reaction with Li₄SiO₄ were studied to understand the overall absorption mechanism in the reactor. The resistance for the direct reaction of CO₂ on the Li₄SiO₄ was much smaller than the resistance for the mass transfer of CO₂ to the Li₄SiO₄. We can conclude that the direct contact of CO₂ with Li₄SiO₄ was the main path for the reaction.     

Solvent Extraction of Li+ using Organophosphorus Ligands in the Presence of Ammonia

In this work, the selective extraction of Li⁺ with the aid of organophosphorus ligands (H-OP) including phenylphosphonic (H-PHO), phenylphosphinic (H-PHI) and bis(2-ethylhexyl) phosphoric (H-BIS) acids in the absence and presence of ammonia was studied. Adding NH₃ to the aqueous phase resulted in significant improvement in the % extraction of Li⁺ into the organic phase containing H-OP ligands. The highest % extraction values obtained in the case of H-PHO, H-PHI, and H-BIS were 43.2%, 45.7%, and 90.0%, respectively. Two mechanisms were inferred; the first was that the extraction equilibrium reaction of LiCl + H-OP ? Li-OP + HCl shifted forward due the reaction of the produced HCl with NH₃. The second mechanism was that the Li⁺/NH₄⁺ exchange of NH₄-OP (produced from the reaction of H-OP with NH₃) was easier than Li⁺/H⁺ exchange of H-OP itself. Competitive extraction experiments indicated that the selectivity factors of Li⁺ over Na⁺ and K⁺ were strongly dependent on the concentration of H-OP ligands which suggested that aggregation of ligand molecules via hydrogen bonding is the limiting factor for selectivity.     

Reaction mechanisms of lithium garnet pellets in ambient air: The effect of humidity and CO2

Li₇La₃Zr₂O₁₂ (LLZO) has been reported to react in humid air to form Li₂CO₃ on the surface, which decreases ionic conductivity. To study the reaction mechanism, 0.5‐mol Ta‐doped LLZO (0.5Ta–LLZO) pellets are exposed in dry (humidity ~5%) and humid air (humidity ~80%) for 6 weeks, respectively. After exposure in humid air, the formation of Li₂CO₃ on the pellet surface is confirmed experimentally and the room‐temperature ionic conductivity is found to drop from 6.45×10^?4 S cm^?1 to 3.61×10^?4 S cm^?1. Whereas for the 0.5Ta–LLZO samples exposed in dry air, the amount of formed Li₂CO₃ is much less and the ionic conductivity barely decreases. To further clarify the reaction mechanism of 0.5Ta–LLZO pellets with moisture, we decouple the reactions between 0.5Ta–LLZO with water and CO₂ by immersing 0.5Ta–LLZO pellets in deionized water for 1 week and then exposing them to ambient air for another week. After immersion in deionized water, Li⁺/H⁺ exchange occurs and LiOH H₂O forms on the surface, which is a necessary intermediate step for the Li₂CO₃ formation. Based on these observations, a reaction model is proposed and discussed.     

Rapid low‐temperature synthesis of tetragonal single‐phase Li7La3Zr2O12

The formation of Li₇La₃Zr₂O₁₂ (LLZ), a Li ion conducting oxide with a garnet‐type crystal structure, from a powder mixture of Li₂CO₃, La(OH)₃, and ZrO₂ was investigated, and two possible reaction pathways were identified. Based on the obtained results, LLZ was synthesized at low temperatures and short reaction times, using Li₂CO₃, La(OH)₃, and La₂Zr₂O₇ (instead of ZrO₂) as starting materials. According to the proposed method, single‐phase LLZ was obtained by heating the initial mixture to 800°C for 1 hour in air, which eliminated possible Li losses. The produced LLZ species exhibited a tetragonal crystal structure with the lattice parameters a=1.3189(3) nm and c=1.2694(1) nm, while their transmission electron microscopy images confirmed that LLZ formation occurred through the dissolution of La₂Zr₂O₇ and La(OH)₃ in a Li₂CO₃ melt followed by LLZ precipitation from solution.     

High‐Temperature Capture of CO2 on Lithium‐Based Sorbents Prepared by a Water‐Based Sol‐Gel Technique

A convenient water‐based sol‐gel technique was used to prepare a highly efficient lithium orthosilicate‐based sorbent (Li₄SiO₄‐G) for CO₂ capture at high temperature. The Li₄SiO₄‐G sorbent was systematically studied and compared with the Li₄SiO₄‐S sorbent prepared by solid‐state reaction. Both sorbents were characterized by X‐ray diffraction, scanning electron microscopy, nitrogen adsorption, and thermogravimetry. The CO₂ sorption stability was investigated in a dual fixed‐bed reactor. Li₄SiO₄‐G exhibited a special Li₄SiO₄ structure with smaller crystalline nanoparticles, larger surface area, and higher CO₂ adsorption properties as compared with Li₄SiO₄‐S. The Li₄SiO₄‐G sorbent also maintained higher capacities during multiple cycles.     

High Speed Imaging of TATB‐ and HMX‐Based Energetic Material Decomposition in Molten Salts

Immersion of energetic materials into high‐temperature molten‐salt baths, where the energetic materials decompose, is being considered as a method for their safe destruction. In the present research, behaviors of the high explosives LX‐17 (92.5 wt% 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB), 7.5 wt% KeI‐F 800 plastic binder) and LX‐04 (85 wt% octahydro‐,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX), 15 wt% Viton A plastic hbinder) were studied when these materials were immersed into molten salt baths. Pressed cylindrical samples initially 6.35 mm in diameter and length were immersed in molten salt baths, and data were taken photographically. Sample decomposition behaviors were observed for varied salt temperatures in a molten LiCl‐NaCl‐KC1 eutectic and then separately in a molten Li₂CO₃‐Na₂CO₃‐K₂CO₃ eutectic. Bath temperatures ranged from 650 to 750°C. General combustion behaviors such as bubble formation characteristics, gas evolution, and sample lifetimes were observed. Results indicated that sample lifetimes decreased as bath temperatures increased, and that the carbonate eutectic increased initial decomposition rates and decreased sample lifetimes relative to the chloride eutectic.     

Salting‐out of acetone, 1‐butanol,and ethanol from dilute aqueous solutions

The salting‐out phase equilibria for acetone, 1‐butanol, and ethanol (ABE) from dilute aqueous solutions using potassium carbonate (K₂CO₃) and dipotassium hydrogen phosphate trihydrate (K₂HPO₄?3H₂O) as outstanding salting‐out agents were investigated. Increasing the salt concentration strengthened the salting‐out effects and improved the distribution coefficients of all three solvents (ABE) significantly. Temperature had a slight effect on the phase equilibria. The K₂HPO₄ solution (69 wt %) showed a stronger salting‐out effect than the K₂CO₃ solution (56 wt %) on recovering ABE from dilute aqueous solutions. Dilute aqueous solutions containing more solvents increased the recoveries of acetone and 1‐butanol, while the results showed a negligible effect on the solubility of ABE. The solubility of ABE was also correlated well with the molar number of salt per gram of water in the aqueous phase. A new equation demonstrated this satisfactorily. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3470–3478, 2015     

Phase Structure and Property Evaluation of (Ba,Ca)(Ti,Sn)O3 Sintered with Li2CO3 Addition at Low Temperature

A series of Li₂CO₃‐added (Ba_0.95Ca_0.05)(Ti_0.90Sn_0.10)O₃ (BCTS) ceramics were prepared by normal sintering at a low temperature of 1300°C; Their microstructure and electrical property evaluation were investigated with special emphases on the effect of Li₂CO₃ addition. Adding Li₂CO₃ significantly improves the sinterability of BCTS ceramics, resulting in a reduced sintering temperature by more than 150°C. The coexistence of R and T phases is confirmed by the Raman spectrum at room temperature for all samples and at a temperature range from ?80°C to 40°C for sample with 3% mol Li₂CO₃ addition. The specific ratio of R to T phase decreases with increasing temperature or Li₂CO₃ addition. A higher ε_r is observed in T phase compared to R phase in the studied BCTS system. Better properties with d₃₃ = 485 pC/N, k_p = 39%, and Q_m = 191 were obtained for BCTS sample with 3% mol Li₂CO₃ addition, which is attributed to the increased grain size and density along with the variation in the specific ratio of R to T phase.     

Studies on lithium salts to mitigate ASR-induced expansion in new concrete: a critical review

This paper provides a critical review of the research work conducted so far on the suppressive effects of lithium compounds on expansion due to alkali-silica reaction (ASR) in concrete and on the mechanism or mechanisms by which lithium inhibits the expansion. After a thorough examination of the existing literature regarding lithium salts in controlling ASR expansion, a summary of research findings is provided. It shows that all the lithium salts studied, including LiF, LiCl, LiBr, LiOH, LiOH·H₂O, LiNO₃, LiNO₂, Li₂CO₃, Li₂SO₄, Li₂HPO₄, and Li₂SiO₃, are effective in suppressing ASR expansion in new concrete, provided they are used at the appropriate dosages. Among these compounds, LiNO₃ appears to be the most promising one. Although the mechanism(s) for the suppressive effects of lithium are not well understood, several mechanisms have been proposed. A detailed discussion about these existing mechanisms is provided in the paper. Finally, some recommendations for future studies are identified.     

Cost‐effective Synthesis of α‐LiAlO2 Powders for Molten Carbonate Fuel Cell Matrices

Lithium aluminate (α‐/β‐LiAlO₂) particles were fabricated using three methods. The first method used organic glycerin and triethylene glycol which functioned as a catalyst for fabrication of α‐LiAlO₂ particles with Al(OH)₃ and LiOH·H₂O as the starting materials. As a result of the heat‐treatment of the starting materials, α‐/β‐LiAlO₂ particles could be obtained. The amount of α‐LiAlO₂ particles in α‐/β‐LiAlO₂ increased slightly as more organics were added. Additionally, when synthesised α‐/β‐LiAlO₂ particles were heat‐treated in a CO₂ gas flow, β‐LiAlO₂ was partially transformed to α‐LiAlO₂. In the second method, molten salts (Li₂/Na₂/K₂CO₃) were used as a catalyst to fabricate α‐LiAlO₂ as a major phase, however, this method requires a washing process which can produce unexpected impurities. In the third method, pure α‐LiAlO₂ was obtained by heat‐treatment of cheap sources such as Li₂CO₃ and Al(OH)₃ at 600–800 °C. The mean particle size (604 nm–11.85 μm) and the specific surface area (3.22–11.4 m² g^–1) of α‐LiAlO₂ were suitable for reinforcing the matrix and tape casting. Lastly, this study examined the effect of CO₂ for the synthesising of α‐LiAlO₂ particles.     

Plasma dissociation reaction kinetics. I. Methyl methacrylate

Fourier transform infrared spectroscopy (FTIR) was utilized to study the plasma gas‐phase reaction kinetics and reaction mechanisms in capacitively coupled glow discharges of methyl methacrylate (MMA) under zero monomer flow rate conditions. The gas‐phase study shows two major electron‐impact‐induced dissociation pathways in MMA plasmas: the C—O bond cleavage reaction and decarboxylations. The C—O bond cleavage reaction accounts for approximately one‐half of the MMA dissociation, and neutral formaldehyde and dimethyl ketene (DMK) are produced via intramolecular rearrangement. Decarboxylations produce CO, CO₂, and a number of radicals that subsequently stabilize to form neutrals, including propylene, allene, and methanol. These intermediate species then further dissociate in the plasma to small hydrocarbons (methane, acetylene, and ethylene), CO, CO₂, and H₂. Plasma power and initial monomer pressure have only minor effects on the MMA fragmentation chemistry. However, the reaction rate increases at higher‐power and lower initial monomer pressure conditions. The modeling also reveals the relative reactivities of the neutrals. A time‐scale transformation technique based on the MMA decomposition half‐life significantly reduces the effects of the reactor condition on the kinetics. In addition, mass balance ratios are utilized to calculate the portion of plasma species that have been accounted for by the in situ technique. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1–16, 1999