High-temperature dilatometer with pyrometer measuring system and rate-controlled sintering capability

An optical pyrometer is used to measure and, in conjunction with temperature programmer and controller, control the temperature of the NETSZSCH Dilatometer DIL 402 E/7 up to 2400°C. This instrument is thus suitable to investigate sintering of technical ceramic materials such as SSiC and ZrO₂. Measurements carried out on these materials containing organic additives show that the sintering range of SSiC starts at 1800°C—although its final density is not reached at 2400°C at a heating rate of 20 deg·min^?1—and that the densification of ZrO₂ occurs between 1000° and 1800°C. Using rate controlled sintering (RCS) the sintering process can be extended on a time scale, but the same densities are obtained at the same temperatures when comparing the measurements with and without RCS.     

Investigation of Solid-Solid Interactions between Pure and Li2O-Doped Magnesium and Ferric Oxides

The results obtained showed that the addition of small amounts of LiNO₃ to the reacting mixed solids, consisting of equimolar proportion of Fe₂O₃ and basic MgCO₃ much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO₃ (6 mol% Li₂O) decreased the decomposition temperature of MgCO₃ from 525.5 to362°C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800°C yielding MgFe₂O₄. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the completion of this reaction required prolonged heating at elevated temperature above 1100°C. Doping with Li₂O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe₂O₄ phase at temperatures starting from 700°C. The addition of 6 mol% Li₂O to the mixed solids followed by precalcination at 1050°C for 4 h resulted in complete conversion of the reacting oxides into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050°C effected the disappearance of most of IR transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe₂O₄ structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility of the various reacting cations. The activation energy of formation (ΔE) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61 kJ mol⁻¹ for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li₂O, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dry Potassium-Based Sorbents for CO<Subscript>2</Subscript> Capture

Dry potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, CaO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property of various sorbents were measured in the presence of H₂O in a fixed bed reactor, during multiple cycles at various temperature conditions (CO₂ absorption at 50–100 °C and regeneration at 130–400 °C). The KAlI30, KCaI30, and KMgI30 sorbents formed new structures such as KAl(CO₃)₂(OH)₂, K₂Ca(CO₃)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely convert to the original K₂CO₃ phase at temperatures below 200 °C, during the CO₂ absorption process in the presence of 9 vol.% H₂O. In the case of KACI30, KTiI30, and KZrI30, only a KHCO₃ crystal structure was formed during CO₂ absorption. The formation of active species, K₂CO₃·1.5H₂O, by the pretreatment with water vapor and the formation of the KHCO₃ crystal structure after CO₂ absorption are important factors for absorption and regeneration, respectively, even at low temperatures (130–150 °C). In particular, the KTiI30 sorbent showed excellent characteristics with respect to CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (87 mg CO₂/g sorbent) without the pretreatment with water vapor, unlike KACI30, and a fast and complete regeneration at a low temperature condition (1 atm, 150 °C). In addition, the higher total CO₂ capture capacity of KMgI30 (178.6 mg CO₂/g sorbent) than that of the theoretical value (95 mg CO₂/g sorbent) was explained through the contribution of the absorption ability of MgO support. In this review, we introduce the CO₂ capture capacities and regeneration properties of several potassium-based sorbents, the changes in the physical properties of the sorbents before/after CO₂ absorption, and the role of water vapor and its effects on CO₂ absorption.     

碳酸盐共沉淀法制备Li[Li0.2Co0.13Ni0.13Mn0.54]O2中加料方式对产物性能的影响

采用碳酸钠和碳酸氢铵作为沉淀剂和络合剂,在水溶液中共沉淀Mn2+、Ni2+和Co2+以获得混合过渡金属元素的碳酸盐沉淀前驱体Mn0.675Ni0.1625Co0.1625CO3。并进一步合成高容量锂离子电池正极材料Li[Li0.2Co0.13Ni0.13Mn0.54]O2。考察了3种不同加料方式对共沉淀前驱体的结构、形貌和元素比例的影响,以及对最终产物的结构、形貌和电化学性能的影响。     

Synthesis and Sintering-wet Carbonation of Nano-sized Carbonated Hydroxyapatite

Synthetic carbonated apatite ceramics are considered as promising alternative to auto- and allograft materials for bone substitute. In this study, Carbonated hydroxyapatite (CHA) was synthesized by nanoemulsion method. The powder produced was B-type CHA in nano-sized and had 8.25% carbonate content. The CHA samples were made into pellets and were sintered to 800 °C. Upon cooling down to 150, 200, 250 and 300 °C, carbonation with wet CO₂ was performed on the CHA in a desiccator to re-compensate the carbonate loss due to sintering and improve densification. The aim of this study was to investigate and compare the effect of cooled down temperatures on dense CHA with two kind of wet CO₂ atmospheres: direct wet CO₂ and dry CO₂ through water. Sintered CHA carbonated by using dry CO₂ through water had overall higher amount of carbonate content as compared to carbonation from wet CO₂ directly from tank. D200, sample undergone carbonation by carbonated by dry CO₂ through water at 200 °C had the highest carbonate content (3.35%).     

Aldol Condensations Catalyzed by PEG400 and Anhydrous K2CO3 Without Solvent

Abstract

Aldol condensations of aromatic aldehydes with ketones under solvent‐free conditions to synthesize α,β‐unsaturated ketones in good to excellent yields using PEG400 and powdered anhydrous K₂CO₃ as catalysts at 90 °C and 120 °C are described.     

The solid state reaction between lanthanum oxide and strontium carbonate

The reaction between lanthanum oxide and strontium carbonate was studied non-isothermally between 350 and 1150 °C at different heating rates, intermediates and the final solid product were characterized by X-ray diffractometry (XRD). The reaction proceeds through formation of lanthanum oxycarbonate La₂O(CO₃)₂, lanthanum dioxycarbonate La₂O₂CO₃, and non-stoichiometric strontium lanthanum oxide La₂SrO_x (x = 4 + δ). La₄SrO₇ was found to be the final product which begins to form at ∼700 °C. Li⁺ doping enhances the formation of the final product as well as commencement of the reactions at lower temperatures.     

Termal decomposition of carbonated calcium phosphate apatites

The thermal stability of AB-type carbonated calcium phosphate apatites prepared by precipitation from aqueous media was studied. The behavior of powders was investigated using temperature programmed XRD, infrared spectroscopy and thermogravimetry. In N₂ atmosphere, two successive peaks of decarbonatation with maxima at about 700 and 950°C occurred. This behavior is explained by different substitution modes for carbonates in the apatite. The decarbonatation peaks were shifted to higher temperature under CO₂ (around 900 and 1150°C). The analysis of the thermal stability allowed further densification of carbonate apatite ceramics without important carbonate loss. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of sol–gel derived Ag(Nb,Ta)O<Subscript>3</Subscript> nanopowder

Perovskite-type Ag(Nb_0.6Ta_0.4)O₃ nanopowder was prepared by the sol–gel process from the AgNO₃, Ta₂O₅ and Nb₂O₅, with help of K₂CO₃, avoiding use of strong corrosive acid or expensive niobium ethoxide and tantalum ethoxide. The results suggested that thermal decomposition of the xerogel took place when the xerogel was heated at 450 °C. Well-crystallized single-phased powder was obtained at low temperature about 680 °C. With the heat-treatment temperature increasing (680–1,100 °C), the intensity of the diffraction peaks increased. The crystallite size determined by Scherer formula and the result suggested that higher temperature lead to larger crystallite size. Moreover, the average grain size 30–50 nm was estimated by a field emission scanning electron microscope. The influence of holding time on microstructures indicated that the homogeneous and small grains were obtained at 800 °C for 2–4 h while larger ones for 8–16 h.     

Microwave-Assisted Synthesis of Dimethyl Carbonate

Microwave assisted synthesis of dimethyl carbonate directly from CO₂ and methanol can be completed in a relative short time, at lower temperature and fewer by-products compared with conventional heating mode. This revised version was published online in June 2006 with corrections to the Cover Date.     

Stimulation of hydrogen production in algal cells grown under high CO2 concentration and low temperature

When cells ofChlamydomonas sp. MGA 161, a marine green alga, were cultivated at a high CO₂ concentration (15% CO₂) and low temperature (15°C), the growth lag time was much longer, but the starch accumulated was two times higher than under the basal conditions (5% CO₂ 30°C). When the cells grown in the high-CO₂/low-temperature conditions were incubated under dark anaerobic conditions, the degradation of starch and production of hydrogen and ethanol were remarkably higher than those grown under the basal conditions. The lag time of cell growth was shortened, whereas the high capacity of starch accumulation and hydrogen production was maintained, by cultivating the cells alternately every 12 h under the basal and high-CO₂/low-temperature conditions. Using this dual system, in which the cultivation was alternated between the two conditions, the total productivity was significantly improved.     

Phase evolution of sol-gel CaO-ZrO2 using sulfuric acid as hydrolysis catalyst

Several compositions in the CaO-ZrO₂ system were synthesized from zirconium n-butoxide and calcium methoxide, by the sol-gel method. Hydrolysis and gelation occurred at pH 3, using H₂SO₄ as hydrolysis catalyst. Fresh gels were annealed in air at 100 to 900°C, in 100°C steps every 20 h, for a total annealing time of 140 h. Analysis by X-ray diffraction showed the formation of hydrated calcium sulfate together with amorphous zirconia up to 400°C. At the ZrO₂ rich-end, tetragonal and monoclinic zirconia solid solutions were stabilized in the presence of Ca ions. When 20 and 30 wt% of CaO were added, cubic zirconia and CaZrO₃ solid solutions were observed above 700°C. At the CaO rich-end, the coexistence of calcium carbonate polymorphs as vaterite and calcite were observed. Anhydrite was present across the entire range of compositions studied from 300 to 900°C.     

Thermal and X-ray diffraction studies of the solid–solid interactions in CuO–MoO3/MgO system

The solid–solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.     

Studies on the effects of coated Li2CO3 on lithium electrode

Although a lithium metal anode has a high energy density compared with a carbon insertion anode, the poor rechargeability prevents the practical use of anode materials. A lithium electrode coated with Li₂CO₃ was prepared as a negative electrode to enhance cycleability through the control of the solid electrolyte interface (SEI) layer formation in Li secondary batteries. The electrochemical characteristics of the SEI layer were examined using chronopotentiometry (CP) and impedance spectroscopy. The Li₂CO₃-SEI layer prevents electrolyte decomposition reaction and has low interface resistance. In addition, the lithium ion diffusion in the SEI layer of the uncoated and the Li₂CO₃-coated electrode was evaluated using chronoamperometry (CA).     

Chromium(III) Hydroxide Solubility in the Aqueous K+-H+-OH?-CO2-HCO 3? -CO 32? -H2O System: A?Thermodynamic Model

Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures of CO₂(g) (0.003 or 0.03 atm.), and as functions of K₂CO₃ concentrations (0.01 to 5.8 mol⋅kg⁻¹) in the presence of 0.01 mol⋅dm⁻³ KOH and KHCO₃ concentrations (0.001 to 0.826 mol⋅kg⁻¹) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions. A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used to interpret the solubility data. Only two aqueous species [Cr(OH)(CO₃)₂²⁻ and Cr(OH)₄CO₃³⁻] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO₂(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log ₁₀ K° values of reactions involving these species [{Cr(OH)₃(am) + 2CO₂(g)⇌Cr(OH)(CO₃)₂²⁻+2H⁺} and {Cr(OH)₃(am) + OH⁻+CO₃²⁻ ⇌Cr(OH)₄CO₃³⁻}] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available for comparisons.     

New solid-state synthesis routine and mechanism for LiFePO4 using LiF as lithium precursor

Li₂CO₃ and LiOH·H₂O are widely used as Li-precursors to prepare LiFePO₄ in solid-phase reactions. However, impurities are often found in the final product unless the sintering temperature is increased to 800 °C. Here, we report that lithium fluoride (LiF) can also be used as Li-precursor for solid-phase synthesis of LiFePO₄ and very pure olivine phase was obtained even with sintering at a relatively low temperature (600 °C). Consequently, the product has smaller particle size (about 500 nm), which is beneficial for Li-extraction/insertion in view of kinetics. As for cathode material for Li-ion batteries, LiFePO₄ obtained from LiF shows high Li-storage capacity of 151 mAh g⁻¹ at small current density of 10 mA g⁻¹ (1/15 C) and maintains capacity of 54.8 mAh g⁻¹ at 1500 mA g⁻¹ (10 C). The solid-state reaction mechanisms using LiF and Li₂CO₃ precursors are compared based on XRD and TG-DSC.     

以氨水和碳酸铵为沉淀剂制备氧化铝的对比研究

γ-Al2O3，是一种常用的催化剂载体，它具有比表面大和价廉易得等优点。但对于很多高温反应体系，如汽车尾气催化净化，其热稳定性在很大程度上影响了汽车尾气净化催化剂的活性和稳定性，因此提高γ-Al2O3的高温热稳定性对保持汽车尾气净化催化剂的反应活性、延长催化剂的使用寿命非常重要。     

Preparation and Application of Ca0.8 Sr0.2 TiO3 for Plasma Activation of CO2

Despite a large interest in plasma-assisted catalytic technology (PACT), very little has been reported about the catalytic effects of different dielectric barriers on a dielectric barrier discharge (DBD) reaction. In the present study, Ca_0.8Sr_0.2TiO₃, that possesses a high permittivity, was prepared by liquid phase sintering and used as a dielectric barrier in a DBD reactor to break CO₂. The mechanical and dielectric properties of Ca_0.8Sr_0.2TiO₃ were greatly enhanced by adding 0.5 wt.% Li₂Si₂O₅. A DBD plasma was successfully generated by using this Ca_0.8Sr_0.2TiO₃ as a dielectric barrier and 18.8% CO₂ conversion was achieved with the residence time of 0.17 s at the frequency of 8 kHz, which was much higher than with those using an alumina or a silica glass barrier. It was found that the plasma power increased with the increasing of the permittivity, and finally very dense and strong microdischarges were initiated to decompose CO₂.     

Electrical Properties of Sm‐doped Ceria (SDC) and SDC Carbonate Composite

This study prepared a dense Sm‐doped ceria (SDC) and an SDC carbonate composite (abbreviated as SDC‐C). The latter was prepared by immersing porous SDC with a formula of (Ce_0.8Sm_0.2)O_1.9 and a relative density of approximately 65‐70% into a molten mixture of carbonates containing 1:1 molar ratio of Li₂CO₃ and Na₂CO₃ at 500 °C. The relative density of the SDC‐C was close to 100%. In addition, SDC oxide without carbonates, which also has a relative density of close to 100%, was heat treated at 1600 °C. At 500 °C, the electrical conductivity and ionic transference number (t_i) of the SDC oxide were 1.79(5) × 10^?3 S·cm^?1 and 0.99(2), respectively, such that electronic conduction could be disregarded. Increasing the temperature caused a gradual decrease in the t_i of SDC. Following the addition of carbonates to SDC, the electrical conductivity reached 1.23(9) × 10^?1 S·cm^?1 at 500 °C. After 14 days (340 h), the electrical conductivity of the SDC‐C at 490 °C, leveled off at about 6 × 10^?2 S·cm^?1. SDC‐C could be used as a potential electrolyte in solid oxide fuel cells (SOFCs) at temperatures below 500 °C.     

Short Range Order Evolution in the Preparation of SnO2 Based Materials

The evolution of Eu³⁺ doped SnO₂ xerogels to the cassiterite structure observed during sintering was studied by means of Eu³⁺ spectroscopy, XRD and EXAFS at the Sn K-edge. Eu³⁺ ions adsorbed at the surface of colloidal particles present a broad distribution of sites, typical of oxide glasses. With sintering at 300°C, this distribution is still broadened. Crystallization is clearly observed by the three techniques with increasing sintering temperature. It is found that the addition of Eu³⁺ limits the crystallite growth.