Hydrothermal transformation of the calcium aluminum oxide hydrates CaAl2O4·10H2O and Ca2Al2O5·8H2O to Ca3Al2(OH)12 investigated by in situ synchrotron X-ray powder diffraction

The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl₂O₄·10H₂O converted to Ca₃Al₂(OH)₁₂ and amorphous aluminum hydroxide. Ca₂Al₂O₅·8H₂O transformed via the intermediate phase Ca₄Al₂O₇·13H₂O to Ca₃Al₂(OH)₁₂ and gibbsite, Al(OH)₃. The phase Ca₄Al₂O₇·19H₂O reacted via the same intermediate phase to Ca₃Al₂(OH)₁₂ and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.     

Effects of crystal structures on luminescent properties of Eu doped Ca–Al–O systems

To investigate the correlations between the structural transformations of calcium aluminates and luminescent properties, Eu doped Ca–Al–O system phosphors were synthesized by solid-state reaction process in H₂ atmosphere with CaCO₃, Al₂O₃, Eu₂O₃, and a flux, H₃BO₃ as starting materials. Various phases such as CaAl₂O₄, CaAl₄O₇, Ca₃Al₂O₆, and Ca₁₂Al₁₄O₃₃ were achieved depending on firing temperature, flux amounts, and the mixing ratio of CaO to Al₂O₃. Among various phases, only CaAl₂O₄ contributed to a strong blue emission at 440 nm with an excitation wavelength of 330 nm.     

High-performance cement matrices based on calcium sulfoaluminate–belite compositions

Cement clinkers with a mineralogy based on 4CaO·3Al₂O₃·SO₃, Ca₂SiO₄ (belite) and C₂(A,F) (ferrite) are made in China: annual production is >10⁶ tons/year. This cement is interground with 16–25% gypsum. The product has very rapid strength gain and examples removed from service in seawater are found to give remarkable protection to embedded steel after 14 years service in the intertidal zone. The chemistry and physics of sulfoaluminate cement hydration are described. Self-desiccation is more readily achieved in ettringite-rich cements than in traditional OPC formulations. It is concluded that the self-desiccated state, once achieved, is very difficult to resaturate and that the dry internal environment is partly responsible for the virtual absence of corrosion of embedded steel, even in chloride-rich environments.     

Oxidative coupling of methane over oxide catalysts with layered structure

The catalytic properties of complex oxides with a layered structure Bi₂GeO₅, Bi₂SiO₅, Bi₄Ti₃O₁₂, Bi₂CaSrCu₃O₈+x and YBa₂Cu₃O₆+δ in oxidative coupling of methane (OCM) have been studied. Bi₂EO₅ metastable compounds have been found to possess the high activity and C₂-selectivity 53–70%. It has been assumed that the intergrowth boundaries for the Bi₂EO₅ decomposition products, on which active catalytic sites may be located, play a specific role on the catalytic performance of the oxides. Bi₄Ti₃O₁₂ and Bi₂CaSrCu₃O₈+x have close catalytic activity values but Bi₂CaSrCu₃O₈+x as well as YBa₂Cu₃O₆+δ are not selective in OCM reaction.     

CaO含量对CBAS玻璃/Al2O3低温共烧陶瓷的影响

本文主要研究了CaO含量对CaO-B₂O₃-Al₂O₃-SiO₂(CBAS)玻璃/Al₂O₃低温共烧陶瓷结构和性能的影响。利用DSC、FTIR、XRD、SEM等测试方法对玻璃和低温共烧陶瓷的结构进行表征与分析。研究结果表明,CaO含量低于40%(质量分数,下同)时,由其引入的游离氧增加破坏了网络结构,降低玻璃黏度。CaO含量为40%及以上时,Ca²⁺与[SiO₄]四面体形成较大的阴离子基团,增大玻璃黏度,提高玻璃化转变温度。CaO会促进CaSiO₃和Ca₂SiO₄的析出和CaSiO₃向Ca₂SiO₄的转变。CaO含量增加导致陶瓷的致密度先增加后减少,晶相尺寸增大,使陶瓷的密度、抗折强度和介电常数先增大后减小。当CaO含量为40%时,样品综合性能最好,密度最大为2.94 g/cm³,抗折强度为153.44 MPa,介电常数为9.69。     

Modification on the tricalcium aluminate phase in cements by manganese substitution

The effect of manganese substitution into the crystal structure of the tricalcium aluminate Ca₃Al₂O₆ has been studied by X-ray, analytical electron microscopy, IR spectroscopy and electronic spin resonance. The limit of solid solution of manganese in this phase was determined. The formula proposed for this solubility is (Ca_2.984Mn_0.016)(Al_1.979Mn_0.021)O₆. In presence of CaO and Al₂O₃ the manganese reacts to give Ca₂AlMnO₅ phase, reducing appreciably tricalcium aluminate contents.     

Oxygen transport in ferrite-based ceramic membranes: Effects of alumina sintering aid

Moderate additions of Al₂O₃ to strontium ferrite-based mixed conductors, such as SrFe_0.7Al_0.3O_3−δ and La_0.2Sr_0.8Fe_0.8Ga_0.2O_3−δ with the composition close to the solid solution formation limits, make it possible to improve ceramics sinterability, to increase oxygen permeability and to decrease thermal expansion. These effects are associated with the segregation of alumina-rich phases, primarily SrAl₂O₄, and the formation of A-site cation-deficient perovskite. The improved properties of the SrFe_0.7Al_0.3O₃-based material were used to fabricate high-quality tubular membranes for methane conversion reactors. Similar enhancement in sinterability is also observed for another promising parent material of mixed-conducting membranes, La_0.5Sr_0.5FeO_3−δ. However, extensive dissolution of Al³⁺ cations in the iron sublattice, creation of A-site vacancies and changing the La:Sr concentration ratio all lead to decreasing ionic transport in La_0.5Sr_0.5FeO_3−δ. As a result, additions of either Al₂O₃ or SrAl₂O₄ have a deteriorating influence on the oxygen permeation fluxes through La_0.5Sr_0.5FeO₃-based ceramics.     

Characterization of Al-doped spinel LiMn2O4 thin film cathode electrodes prepared by Liquid Source Misted Chemical Deposition (LSMCD) technique

A novel process called Liquid Source Misted Chemical Deposition (LSMCD) was used to synthesize Al-doped LiMn₂O₄ cathode films for Lithium microbatteries. The cathode films were characterized by XRD, SEM, cyclic volatmmetry, and charge/discharge test. LiMn_1.8Al_0.2O₄ film crystallized at 800 °C in rapid thermal annealing (RTA) for 5 min under oxygen atmosphere exhibited more improved electrochemical rechargeability than spinel LiMn₂O₄ film because the substitution of Al³⁺ for Mn³⁺ increased Mn---O bonding strength in the spinel framework and suppressed the two-phase behavior of the unsubstituted spinel during the intercalation/deintercalation that is the origin of the failure mechanism in the 4 V region. As a result, LiMn_1.8Al_0.2O₄ film showed an initial discharge capacity of 52 μAh/cm² μm and no capacity fade over 100 cycles.     

The simultaneous activation of methane and carbon dioxide to C2 hydrocarbons under pulse corona plasma over La2O3/γ-Al2O3 catalyst

The pulse corona plasma has been used as an activation method for reaction of methane and carbon dioxide, the product was C₂ hydrocarbons and by-products were CO and H₂. Methane conversion and the yield of C₂ hydrocarbons were affected by the carbon dioxide concentration in the feed. The conversion of methane increased with increasing carbon dioxide concentration in the feed whereas the yield of C₂ hydrocarbons decreased. The synergism of La₂O₃/γ-Al₂O₃ and plasma gave methane conversion of 24.9% and C₂ hydrocarbons yield of 18.1% were obtained at the power input of plasma was 30 W. The distribution of C₂ hydrocarbons changed by using Pd-La₂O₃/γ-Al₂O₃ catalyst, the major C₂ product was ethylene.     

温度对精炼渣碳酸化效果影响分析

为了有效改善精炼渣的安定性及致密性问题,采用正交试验探讨精炼渣碳酸化过程,以温度为单一影响因素,考察碳酸化粒度分布,结合XRD,SEM,FT-IR,TG-DTA等手段对精炼渣碳酸化效果进行探讨。结果表明,精炼渣碳酸化各因素主次关系为:粒径>CO₂通气量>反应温度>转速>液固比;碳酸化后精炼渣中f-CaO、Ca₂SiO₄、Ca₃SiO₅、12CaO·7Al₂O₃消失,CaCO₃晶型增加明显,且以方解石为主;不同温度(20 ℃、40 ℃、60 ℃、80 ℃)碳酸化后精炼渣总的热分解失重百分率分别为:35.26%、35.24%、34.36%和27.29%。     

Investigations on the structure of fully hydrated portland cement and tricalcium silicate pastes. II. Total porosity and pore size distribution

On a series of OPC pastes hydrated at 20 °C and 90 °C and Ca₃SiO₅ pastes hydrated at 20 °C the total porosity and pore size distribution were measured. Data obtained by mercury porosimetry and nitrogen adsorption did not agree well as the volumina of pores filled with Hg and N₂ differed. Regardless on the method employed the found pore size distribution depended on the starting water-solid ratio; as equal porosity, it was different in different hydrated materials.     

Investigation on the structure of fully hydrated portland cement and tricalcium silicate pastes. III. Specific surface area and permeability

On a series of d-dried OPC pastes hydrated at 20 and 90 °C and Ca₃SiO₅ pastes hydrated at 20 °C the specific surface area was measured using four different methods i.e. BET_{N 2} and those calculated from adsorption isotherms and BET_{H 2 0} mercury porosimetry and water permeability data. Values found using different methods were not identical. In addition to that, the specific surface area of the same pastes in non-dried state was estimated from their permeability to water. A drying and resaturation of the pastes resulted in a decrease of the specific surface area indicating a coarsening of the pore structure in the course of drying.     

Transmittance and cathodoluminescence of AlN ceramics sintered with Ca3Al2O6 as sintering additive

Aluminum nitride ceramics were prepared by sintering with 0–4.8 mass% of Ca₃Al₂O₆ (C₃A) as a sintering additive. The transmittance in the range of 260–550 nm increased with increasing amount of C₃A. The cathodoluminescence intensity attributed to oxygen-induced defects decreased with increasing amount of C₃A. From the results, the increase of the transmittance in the range of 260–550 nm was considered to be related to the decrease of the oxygen-induced defect density.     

Kinetic analysis of extraction of calcium silicates with methanolic solution of salicylic acid. II. Extraction of dicalcium silicates

By applying the methods described in Part I. of the article, kinetic analysis for extractions of γ-, β- and '-modifications of Ca₂SiO₄ by methanolic solution of salicylic acid was carried out. According to the obtained results, surface interaction is the rate-determining process in all the three cases, and the values of the rate constants increase in the following order: β-, γ-, '-modification. The rate constants of the reaction were assessed for three temperatures, which made it possible to calculate the activation energy.     

Fabrication and conductivity of a new compound Ca2Cr2O5

A new brownmillerite-related compound. Ca₂Cr₂O₅, has been prepared. It has been indexed according to an orthorhombic lattice a = 5·750 Å, b = 14·398 Å and c = 5·483 Å. A series of experiments was performed in order to find the appropriate firing temperature. The total conductivity was measured by a four-point method in the range of 690–911°C. Impedance spectroscopy was also employed in the temperature range 343–785°C. Conductivity measurements at different oxygen pressures at 500°C suggest that Ca₂Cr₂O₅ is a predominantly ionic conductor at P_o2 = 1–10⁻²atm.     

Subsolidus phase relationships in part of the system Si, Al, Ca/N, O

Subsolidus phase relationships in the region bounded by Si₃N₄, SiO₂, CaSiO₃, 2CaO.Al₂O₃.SiO₂, CaO.Al₂O₃, Al₂O₃ and β'-Si₂Al₄O₄N₄(β₆₀) have been studied. A new quinary phase with composition near to CaO. 1·33Al₂O₃.0·67Si₂N₂O (designated as S-phase) and a complete series of solid solution between S-phase and CaO.2Al₂O₃ were found. Fourteen compatible tetrahedra, of which five contain S-phase, occur in the region explored. They are as follows: X₁-SiO₂-anorthite-mullite; X₁-anorthite-mullite-Al₂O₃; X₁-anorthite-Al₂O₃-β₆₀; X₁-anorthite-β₆₀-Si₃N₄; X₁-anorthite-Si₃N₄-Si₂N₂O; X₁-anorthite-Si₂N₂O-SiO₂; anorthite-Si₂N₂O-SiO₂-CaSiO₃; anorthite-Si₂N₂O-CaSiO₃-gehlenite; anorthite-Si₂N₂O-gehlenite-Si₃N₄; S-anorthite-Al₂O₃-β₆₀; S-Al₂O₃-CaO.2Al₂O₃-gehlenite; S-Al₂O₃-gehlenite-anorthite; S-gehlenite-anorthite-Si₃N₄; S-anorthite-Si₃N₄-β₆₀.     

铵盐体系电解锰渣中石膏的转变规律

电解锰渣已成为阻碍电解锰行业发展的瓶颈,其中锰渣含有的大量石膏是限制其资源化利用的关键。针对锰渣中石膏浸出问题,本文研究了NH₄HCO₃和NH₄Cl用量、浸出初始pH、浸出时间、浸出温度对锰渣中石膏转变规律的影响。研究结果表明,当锰渣与NH₄HCO₃和NH₄Cl之间的质量比为20∶8∶1.5、固液比为1∶5、浸出初始pH为7.5、浸出温度为70℃、浸出时间为120min时,石膏的浸出率达到90.0%;浸出锰渣主要物相含有CaCO₃、SiO₂、Ca₂Mn₂(OH)₄Si₄O₁₁·2H₂O、Mg_5.0Al₆Fe₄Si_2.5Al_1.5O₁₀(OH)₈以及KAl₃Si₃O₁₀(OH)₂等,其中浸出锰渣中MnO含量由未浸出前的7.45%提高到14.71%。转变规律表明,NH₄HCO₃与锰渣中的石膏反应转变成(NH₄)₂SO₄和CaCO₃,而NH₄Cl作为盐试剂可进一步促进石膏的溶解,从而提高石膏的浸出率。     

Carbon reduction reaction in the Y2O3–SiO2 glass system at high temperature

In order to assess the role of carbon with respect to the grain boundary chemistry of Si₃N₄-based ceramics model experiments were performed. Y₂O₃–SiO₂ glass systems with various amount of carbon (from 1 to 30 wt.%) were prepared by high-temperature treatment in a graphite furnace. High carbon activity of the furnace atmosphere was observed. EDX analysis proved the formation of SiC by the carbothermal reduction of SiO₂ either in the melt or in the solid state. The melting temperature of the Y₂O₃–SiO₂ system is strongly dependent on the amount of reduced SiO₂. XRD analysis of the products documented the presence of Y₂Si₂O₇, Y₂SiO₅ and Y₂O₃ crystalline phases in that order with an increasing amount of free C in the starting mixture. The reduction of Y₂O₃ was not confirmed.     

Reforming of methane with carbon dioxide to synthesis gas over supported Rh catalysts

Reforming of methane with carbon dioxide to synthesis gas (CO/H₂) has been investigated over rhodium supported on SiO₂, TiO₂, γ-Al₂O₃, MgO, CeO₂, and YSZ (ZrO₂ (8 mol% Y₂O₃)) catalysts in the temperature range of 650–750°C at 1 bar total pressure. A strong carrier effect on the initial specific activity, deactivation rate, and carbon accumulation was found to exist. A strong dependence of the specific activity of the methane reforming reaction on rhodium particle size was observed over certain catalysts. Tracing experiments (using ¹³CH₄) coupled with temperature-programmed oxidation (TPO) revealed that the carbon species accumulated on the surface of the Rh/Al₂O₃ catalyst during reforming reaction at 750°C are primarily derived from the CO₂ molecular route. The amount of carbon present on the working catalyst surface which is derived from the CH₄ molecular route is found to be very small.     

Mechanistic evidence of the partial oxidation of methane to formaldehdye over silica based oxide catalysts by temperature programmed reaction studies

The catalytic behaviour of SiO₂ supported MoO₂ and V₂O₅ catalysts in the partial oxidation of methane to formaldehyde with O₂ (MPO) in the range 400–800°C has been investigated by temperature programmed reaction (TPR) tests. Both the sequence of the onset temperature of product formation and the product distribution patterns signal that MPO on silica based oxide catalysts occurs mainly via a consecutive reaction path: CH₄ → HCHO → CO → CO₂. At T >/ 700°C a parallel surface assisted gas-phase reaction pathway leads to the formation of minor amounts of C₂ products both on SiO₂ and MoO₃/SiO₂ catalysts. The redox properties of MoO₃/SiO₂ and V₂O₅SiO₂ catalysts have been systematically evaluated by H₂ and CH₄ temperature programmed reduction (H₂-TPR, CH₄-TPR) measurements. H₂-TPR results do not account for the reactivity scale of oxide catalysts in the MPO. CH₄-TPR measurements indicate that the enhancement in the specific activity of the silica is controlled by the capability of MoO₃ and V₂O₅ promoters in providing ‘active’ lattice oxygen species.