Alkali-activated cementitious materials: Alternative matrices for the immobilisation of hazardous wastes: Part II. Stabilisation of chromium and lead

This research focuses on the study of the stabilisation/solidification capacity of a cementing matrix, which has been made using alkali activation of fly ash, in the presence of toxic elements chromium and lead. Such capacity has been compared with that of Portland cement.Leaching tests carried out proved that this new matrix is able to stabilise and solidify lead in a very efficient way (analysed lead concentrations from leaching are in parts per billion). However, it does not present itself as efficient concerning chromium fixation since this element strongly disturbs the alkali-activation mechanism of the ash.     

废乙腈合成乙酸的工艺研究

本文报道了一种由废乙腈合成乙酸的工艺方法 ,并叙述了合成条件对产物收率的影响     

Lead recovery from waste frit glass residue of electronic plant by chemical-electrochemical methods

This work aims at recovering lead from frit glass waste of electronic plants by using the electrochemical method comprising two successive steps of lead leaching and electrodeposition. In the leaching step, it was found that nitric acid and acetic acid are better solutions for the dissolution of lead oxide compared with sodium hydroxide, hydrochloric acid, and sulfuric acid. More than 95% of the lead was leached by 0.1 M nitric acid or 0.5 M acetic acid at 0.5% weight by solid volume. In the electrodeposition step, more than 95% of lead can be removed with high current efficiency from the leaching solution at an optimum current density. The values of the optimum current density of 0.5 and 1 M acetic electrolytes were between 8.8–10 mA/cm², whereas those for 0.1 M and 0.5 M of nitric acid were 15 and 27.5 mA/cm², respectively.     

Technological and environmental behavior of sewage sludge ash (SSA) in cement-based materials

Sewage sludge ash (SSA) is a waste material obtained from the incineration of wastewater sludge. The physical, chemical and mineralogical characteristics of SSA, and the evaluation of its use in cement-based materials, are presented in this paper. Results show that SSA is composed of irregular grains having a high specific surface area and thus leading to a significantly high water demand. A fraction of the ash is rapidly soluble (sulfates, aluminum and silica) and can create new-formed products in presence of lime. SSA induces short delays of cement hydration, probably due to both minor elements of the ash and dilution effect. Compressive strengths of mortars containing 25% and 50% of SSA are always lower than those of reference mortars but it is shown that SSA has a long-term positive effect which might be related to a slight pozzolanic activity. The amount of elements leached from SSA mortars is slightly higher than from the reference mortar without residue but it remains of the same order of magnitude. An extensive literature review was performed in order to compare the residue used in this study with others included in the same category. This analysis highlighted the principal characteristics that must be taken into account to use SSA correctly in cement-based materials.     

Double polarization hysteresis and dramatic influence of small compositional variations on the electrical properties in Bi4Ti3O12 ceramics

This work reports the existence of double polarization hysteresis (P–E) loop in Aurivillius-phase ferroelectric Bi₄Ti₃O₁₂ (BiT) and reveals dramatic influence of small compositional variations on the electrical properties of it. The double polarization hysteresis is a characteristic of the interaction of defects with domain walls. This characteristic becomes more pronounced in Bi-deficient and Mg-doped BiT due to an increase in oxygen vacancy concentration at the lattices. Normal and saturated P–E loop is recalled by Nb donor doping, and associated composition Bi₄Ti_2.97Nb_0.03O_12.015 (BiT-0.03Nb) shows high remnant polarization (P_r = 12.5 μC/cm²) and large field-induced strain (S₃₃ = 5.6 × 10^?4). In addition, this doping results in bulk conductivity (σ_b) of BiT decreasing dramatically and associated activity energy (E_a) increasing significantly. In contrast, high oxide ion conductivity is induced with Mg²⁺ acceptor doping, and at 600 °C the optimum composition has ionic conductivity of ?0.65 × 10^?2 S cm^?1 in the bulk.     

Effects of the incorporation of Municipal Solid Waste Incineration fly ash in cement pastes and mortars: I. Experimental study

This work falls within the scope of a general problem regarding the assessment of concrete manufactured from waste materials. The main objective is to study the long-term evolution of these materials during the leaching process, using the cellular automaton-based hydration model developed at the National Institute of Standards and Technology. The work is based on the analysis of mortars and cement pastes containing experimental waste: Municipal Solid Waste Incineration fly ash (MSWI fly ash). The study therefore aims to develop a methodology for assessing concrete manufactured from waste, and not to study a process or a formulation enabling the incorporation of the waste in concrete. The physical, chemical and mineralogical characteristics of MSWI fly ash were first analysed to introduce them into the model. A simplified quantitative mineralogical composition of the ash was proposed. The performance characteristics (setting times, compressive strengths, shrinkage, etc.) for mortars containing ash were then studied.     

Preparation of SiC layer with sub-micro grain structure in TRISO particles by spouted bed CVD

The previous studies showed that the SiC layer with sub-micro grain structure can prevent fission products release more effectively. Usually, the silicon carbide (SiC) layer in TRISO (Tristructural isotropic) particles was deposited at 1500–1600 °C by spouted bed chemical vapor deposition (CVD) from methyltrichlorosilane in H₂ environment. It has grain size in micro scale (1–10 μm). In this work, we proposed a novel method for preparation of sub-micro grained SiC layer by adjusting the deposition parameters. The as-prepared SiC layer had grain size about 200 nm and pure phase (β-SiC). The fined grain SiC layer also exhibited higher mechanical property than SiC layer with larger grain size.     

One-step solution combustion synthesis of K0.5Na0.5NbO3 powders at a large-scale

In this work, fine powders of K_0.5Na_0.5NbO₃ (KNN) are produced by a single step of solution combustion synthesis (SCS) using glycine as the reductant fuel and potassium & sodium nitrates as the oxidizers, which are mixed with niobium oxide. Single phase of KNN products can be successfully prepared in a one-step SCS by adjusting the glycine-nitrate ratio. It is concluded that the stoichiometric or slightly fuel-excess condition is good for the single step production of KNN. The one-step SCS of KNN also shows good scaling-up productivity, which can be ignited by both electric heating and microwave heating. This work may provide a feasible large-scale production of various functional oxides by a one-step SCS process.     

First-principles simulation of the growth of in situ synthesised β-Sialon and its effects on the thermo-mechanical properties of Al2O3-C refractory composites

Columnar β-Sialon bonding phases were in situ synthesised in Al₂O₃-C refractory composites and their growth mechanism was simulated based on first-principles calculations. The experimental results indicated that the addition of Fe₂O₃ as a catalyst accelerated the transformation of Si₃N₄ to β-Sialon, resulting in a well-developed columnar structure. The (100) facet was the primary surface for crystal growth during the transformation process of Si₃N₄ into β-Sialon. According to first-principles calculations, the surface energy of the (100) facet decreased greatly due to the substitution of (Si, N) pairs with (Al, O). The catalyst could promote the adsorption of gaseous phases on the (100) facet of Si₃N₄ and decreased the gas adsorption energy of both SiO and Al₂O. Owing to the presence of in situ synthesised columnar β-Sialon bonding phases, the residual crushing strength of Al₂O₃-C refractory composites after 5 thermal shock cycles increased by 25.1%.     

Enhanced energy density and thermal stability in relaxor ferroelectric Bi0.5Na0.5TiO3-Sr0.7Bi0.2TiO3 ceramics

Sr_0.7Bi_0.2TiO₃ (SBT) was introduced into Bi_0.5Na_0.5TiO₃ (BNT) via a standard solid-state route to modulate its relaxation behaviour and energy storage performance. With increasing SBT content, the perovskite structure of BNT transforms from a rhombohedral phase to a weakly polarized pseudo-cubic phase, and the relaxation behaviour is enhanced. In particular, the E_DBS is improved from 120 kV/cm of BNT to 160 kV/cm of 0.6BNT-0.4SBT, which displays a large recoverable energy storage density (W_rec = 2.20 J/cm³), implying a large potential ability of energy storage for the 0.6BNT-0.4SBT ceramic. Moreover, both dielectric properties (28–326 °C) and energy storage properties (20–140 °C) exhibit a good thermal stability for the same 0.6BNT-0.4SBT composition. These characteristics suggest 0.6BNT-0.4SBT ceramic could be a promising candidate to be applied in a pulse power system over a broad temperature range.     

托普索法乙酸生产新工艺

扼要介绍托普索公司（ＨａｌｄｅｒＴｏｐｓφｅＡ／Ｂ）新开发成功的以合成气为原料直接生产乙酸新工艺。提出以渣油或沥青为原料加压气化制合成气直接合成乙酸的技术路线。论述新工艺与甲醇羰基化工艺比较在技术上与经济上的独特优点     

Effect of ZnO/K2O ratio on the crystallization sequence and microstructure of lithium disilicate glass-ceramics

The effect of ZnO/K₂O (Z/K) ratio on the crystallization sequence and microstructure of lithium disilicate (Li₂Si₂O₅: LS2) glass-ceramics was carefully investigated for the SiO₂-Li₂O-K₂O-ZnO-P₂O₅ system. The Z/K ratios of precursor glasses were varied from 0 to 3.5 while the nucleating agent of P₂O₅ and glass modifiers of ZnO plus K₂O were fixed to have 1.5 and 4.5 mol% relative to LS2, respectively. For the samples prepared by two-stage heat treatments of 500 °C for 1 h and 800 °C for 2 h in air, the LS2 nucleation rate was increased with increasing the Z/K ratio due to the variation in crystallization sequence from type II (Li₂SiO₃: LS) to type I (LS + LS2) in addition to an amorphous phase separation in base glass. Consequently, with increasing the Z/K ratio, the LS2 crystalline phase within the glass matrix continuously changed from larger acicular ones to smaller equiaxed ones.     

Improving the sinterability of CeO2 by using plane-selective nanocubes

CeO₂ nanocubes with (100) surface orientation are successfully synthesized and found to facilitate the sinterability of CeO₂ material. The CeO₂ nanocubes show a much-improved sinterability relative to CeO₂ nanoparticles prepared by the conventional citric-nitrate method. The nanocubes can be successfully sintered at a relatively low temperature of 1200 °C without using any sintering aids. In contrast, a pellet using conventional CeO₂ nano-powder obtained from the conventional citric-nitrate method can be densified only after sintering at 1400 °C, which is 200 °C higher than that for the CeO₂ nanocube sintering, although the starting particle size of both CeO₂ samples is similar. Density functional theory indicates that the surface energy of the (100) plane is significantly higher than that of the (111) plane, which is the more typical surface presentation of conventional CeO₂ particles. This high surface energy allows fast growth of the CeO₂ nanocubes during sintering, contributing to their improved sinterability.     

Ablation resistance and mechanism of ZrC-SiC-Yb2O3 ternary composite coatings fabricated by vacuum plasma spray

In this work, ZrC-SiC-Yb₂O₃ ternary composite coatings with different contents of Yb₂O₃ (0, 5, 15 and 30 wt.%) were fabricated by vacuum plasma spray and the anti-ablation property above 2000 °C was evaluated. The results showed that the microstructures of the oxide scales were changed with different Yb₂O₃ contents and then greatly modified the ablation resistant property of the composite coatings. The composite coating with 15 wt.% Yb₂O₃ exhibited the best ablation resistance. The disappearance of SiC-depleted layer and formation of ZrC_xO_y were observed. The mechanism of Yb₂O₃ on the oxidation products and ablation behaviors of ZrC-SiC system was analyzed.