Effect of mechanical activation on the hydraulic properties of stainless steel slags

This work aims to assess the possibility of using ladle metallurgy and argon oxygen decarburization stainless steel slag as a hydraulic binder after mechanical activation. Prolonged milling in ethanol suspension resulted in 10-fold increase of the surface area and increase of the amorphous phase. Calorimetric analysis of slags mixed with water indicated the occurrence of exothermic reactions. XRD results revealed that periclase, merwinite, γ-C₂S and bredigite, decreased with hydration time. Thermogravimetric analyses indicated that the main hydration products are most probably C–S–H, CH and MH. The hydrated products in both slags were similar to C–S–H gel. WDS analysis demonstrated Ca and Si to be widespread in the structure. Formation of M–S–H gel or incorporation of Mg in the C–S–H gel remains uncertain. The 90 days compressive strength of mortars prepared from slags reached approximately 20% for LM and 10% for AOD of the compressive strength of mortars prepared from OPC.     

机械活化强化甘蔗渣铝酸酯表面改性

采用自制搅拌球磨机对甘蔗渣进行机械活化预处理,以改性甘蔗渣的活化度、润湿接触角及甘蔗渣/液体石蜡体系黏度为评价指标,分别研究了铝酸酯用量和机械活化时间对甘蔗渣改性效果的影响,并采用XRD、FTIR对甘蔗渣和改性产物进行了表征。研究结果表明：经铝酸酯处理后甘蔗渣的活化度、接触角增加,与液体石蜡体系的黏度降低,当铝酸酯用量为3%时效果最佳;机械活化明显强化了甘蔗渣与铝酸酯的反应,铝酸酯改性机械活化甘蔗渣的接触角和活化度明显增加,与液体石蜡组成的体系黏度降低,当机械活化120 min时效果最佳;甘蔗渣经表面偶联改性后,在有机相中的分散性明显增加,铝酸酯改性机械活化甘蔗渣效果更为显著;X射线衍射分析表明,机械活化降低了甘蔗渣纤维结晶度,提高了其对铝酸酯的反应活性;FTIR分析表明,甘蔗渣表面的羟基与铝酸酯中的烷氧基团发生化学反应,有新的官能团Al-O-C产生,并在甘蔗渣表面形成一层铝酸酯分子层。     

A Study on the Characterization of MASHS Processed Ti-Si-Al System

Many promising titanium aluminides and silicides could be synthesized in Ti-Si-Al system via mechanically activated self-propagating high-temperature synthesis (MASHS). The influence of mechanical activation and initial composition on phase formation, microstructure and synthesis behavior of mechanically activated Ti-rich mixtures in Ti-Si-Al system is investigated. Results indicate that Al can participate in the reaction and forms Ti₃Al and TiAl₃ phases beside Ti₅Si₃ phase by using mechanically activated reactants. Si and Al could be substituted each other in titanium aluminide and silicide to form solid solution of Ti₃(Si,Al) and Ti₅(Si,Al)₃. In Ti-Si-Al system, combustion temperature is increased by increasing Si amount in the system while, ignition temperature is decreased profoundly from 1100 to 800 ^°C by applying mechanical activation prior to reaction and increasing Al in the system. In addition, Mechanical activation prior to synthesis gives rise to narrow grain size distribution and more uniform microstructure in comparison with SHS products.     

Gel Composition and Strength Properties of Alkali‐Activated Oyster Shell‐Volcanic Ash: Effect of Synthesis Conditions

The gel composition and mechanical properties of alkali‐activated oyster shell‐volcanic ash were investigated at different NaOH concentrations (8, 12, and 15M) and curing temperatures (60°C and 80°C) in wet and dry conditions. XRD, FTIR, SEM‐EDS, and TGA‐DSC were used for microstructural characterization of the binder. The gel composition of the system was found to be influenced by NaOH concentration and was not affected when curing temperature was varied from 60°C to 80°C. The main phase was N,C–A–S–H for all alkali‐activated oyster shell‐volcanic ash, with C–S–H as secondary phase for some samples and contains high percentage of iron. The splitting at υ₃ = 1400–1494 cm^?1 on FTIR spectra corresponded to the elimination of the degeneracy due to the distortion of CO₃^2? group. The high degree of splitting indicated that this carbonate group is linked to Ca²⁺. The compressive strength was influenced by curing temperature and the formation of a secondary phase. The compressive strength in dry condition increased roughly between 28 and 180 d for some samples, while in wet condition, the partial dissolution of Si–O–Si bonds of some silicate phases resulted in a reduction of strength.     

Effect of thermal history on high‐valence chromium ion dissolution in merwinite (3CaO·MgO·2SiO2)

Solubility and local structure of transmission elements in calcium silicate compounds has not been well understood. We investigate the local structure of chromium ions dissolved in merwinite (3CaO·MgO·2SiO₂) of a monoclinic crystal structure. The acceptance of doping elements into merwinite has not been reported before. We found that chromium ions are soluble in merwinite in air and that chemical valence of the dissolved Cr ions varies with annealing temperature. The absorption edge in the x‐ray absorption near edge structure (XANES) of Cr‐doped merwinite indicated that octahedrally coordinated Cr³⁺ ions were mainly formed when annealed at 1673 K in air. A pre‐edge peak was also detected, indicating the existence of tetrahedrally coordinated high‐valence Cr ions. Conversely, through annealing of merwinite at 1123 K in air, tetrahedrally coordinated Cr⁶⁺ ions were found to be the main form of chromium. XANES spectra simulated by first‐principle calculations were used to explain the structural features in the observed spectra. We propose the coexistence of Cr³⁺ ions in octahedral Mg²⁺ sites and high‐valence Cr ions in tetrahedral Si⁴⁺ sites. In addition, a change in the chromium ion oxidation state in tetrahedral coordination sites was suggested by XANES spectroscopy of Cr‐doped merwinite synthesized at 1673 K and reannealed at 1123 K.     

钢渣安定性与活性激发的研究进展

钢渣是炼钢过程中产生的废渣,高碱度钢渣中含有较多的C3S和C2S,因而具有一定的胶凝活性,可用于生产钢渣水泥.但高碱度钢渣中游离氧化钙含量较高,使钢渣水泥的安定性不良.必须对钢渣进行适当的处理,解决其安定性问题,并通过机械或化学的方法激发其活性.本文对钢渣膨胀的诱因与抑制措施、活性激发等问题进行了详细的探讨.     

Phosphoric and boric acid activation of pine sawdust

Chemical activation of pine sawdust using aqueous solutions of phosphoric and boric acid was studied. Thermogravimetric analyses of the impregnated lignocellulosic precursor as well as their reactivities are presented. The role of the activating agents in the thermal decomposition of the precursor and their effects on the development of porosity in activated carbons is discussed. The use of boric acid as activating agent and a final heat treatment temperature (HTT) of 600 °C produced some porosity and activated carbons with a surface area of 600 m² g^?1. With a HTT of 450 °C, molecular sieve‐like materials were produced. In contrast, phosphoric acid activation produced activated carbons with high surface areas. The amount of phosphoric acid retained in the precursor was, as expected, a function of the initial concentration as well as the impregnation time and temperature. The fact that the activated carbon porosity increases with the phosphoric acid content per gram of precursor was confirmed. The use of 6 M phosphoric acid solution and HTT of 450 °C produced the activated carbon with the highest surface area, about 1600 m² g^?1. The high degree of microporosity which developed in phosphoric acid‐activated carbons is related to the low reactivity during the thermal treatment of chemical activation. The presence of up to 10% oxygen during HTT with phosphoric acid activation caused only small textural changes. Copyright © 2003 Society of Chemical Industry     

Solid-state formation of lithium ferrites from mechanicallyactivated Li2CO3–Fe2O3 mixtures

The formation of lithium ferrites (LiFe₅O₈ and LiFeO₂) from mechanically activated mixtures of Li₂CO₃–Fe₂O₃ has been studied using thermal analysis (TGA, DSC), evolved gas analysis (TG/FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and particle size analysis. It is shown that mechanical activation of the precursors considerably enhances the reactivity of the solid system analysed and makes it possible to obtain reaction products with a much lower expense of thermal energy. In particular, lithium ferrites can be obtained at temperatures at least 160 °C lower than those necessary in the absence of mechanical activation. Moreover, both the microstructure and the allotropic ratio of the products, as well as the reaction path, are affected by mechanical activation.     

High‐Resolution X‐ray Diffraction and Fluorescence Microscopy Characterization of Alkali‐Activated Slag‐Metakaolin Binders

The effect of the activator concentration on the structure of alkali silicate‐activated slag/metakaolin pastes is assessed through synchrotron radiation‐based X‐ray techniques. As main reaction products, both calcium aluminosilicate hydrate (C–A–S–H) and sodium/calcium aluminosilicate hydrate [(C,N)–A–S–H] type gels are formed in activated binders solely based on slag, along with the zeolitic products gismondine and garronite. In activated blended pastes, the inclusion of metakaolin in the binder hinders the formation of zeolite products, instead favoring the formation of a (C,N)–A–S–H type gel consistent with the activation of metakaolin in the presence of high concentrations of Ca. The formation of the two distinct binding products is confirmed by high‐resolution X‐ray fluorescence microscopy, where the “inner” products and the “outer” products have compositions consistent with (C,N)–A–S–H and C–A–S–H type gels, respectively. These results provide important new insights into the gel chemistry and micro/nanostructure of blended alkali‐activated binder systems.     

Preparation of Alkali‐Activated Slag‐Fly Ash‐Metakaolin Hydroceramics for Immobilizing Simulated Sodium‐Bearing Waste

The radioactive sodium‐bearing waste (SBW), which is mainly generated from spent nuclear fuel reprocessing activities, requires to be stabilized into a solid form for geological disposal. In this study, the alkali‐activated slag–fly ash–metakaolin hydroceramic (ASFMH) waste form for solidifying simulated SBW (S‐SBW) was prepared by hydrothermal process. The mineralogy, morphology, composition, compressive strength, and chemical durability of ASFMH waste form were investigated. It is shown that crystalline analcime phase was formed in the hydration products of ASFMH waste form after alkaline activation and hydrothermal process. The introducing of S‐SBW not only contributed to forming crystalline zeolite phase but also reduced the temperature and time for forming zeolite phase. Importantly, the cations including simulated radionuclides Sr²⁺ and Cs⁺ in S‐SBW could be immobilized as cationic components in the channels or voids of zeolitic structure during the formation of analcime phase. Moreover, when the loading content of S‐SBW in ASFMH waste form was 37.5 wt%, ASFMH waste form still exhibited superior mechanical strength, which was higher than 24 MPa. The product consistency test leaching results showed that ASFMH waste form possessed superior chemical durability after leaching test carried out for 7 d. It is suggested that ASFMH waste form is a promising candidate for application in immobilizing SBW.     

Formation of encapsulated molybdenum carbide particles by annealing mechanically activated mixtures of amorphous carbon with molybdenum

The investigation of morphological and structural changes during high-energy ball milling and thermal annealing of mixtures of amorphous carbon and molybdenum demonstrated that the activation leads to the formation of a nano-size carbide Mo₂C phase. Morphological characteristics of the annealed, mechanically activated amorphous carbon-molybdenum samples depend on the time of preliminary mechanical activation. Annealing of amorphous carbon-molybdenum samples after preliminary mechanical activation, at a temperature of 860 °C, caused the formation of nano-sized encapsulated particles of molybdenum carbide Mo₂C. The surface of the Mo₂C nanoparticles was coated with a shell composed of hexagonal polyaromatic carbon 5-20 nm thick. The size of the encapsulated particles varies within a rather broad range from 10 to 20 nm to several hundred nanometers.     

Effect of mechanical activation of coprecipitated precursor on synthesis of La2Zr2O7

A lanthanum zirconate (La₂Zr₂O₇, LZ) precursor has been prepared by coprecipitation of the relevant hydroxides from nitrate solution. The effect of the mechanical activation of the precursor on its thermal decomposition and LZ formation in the temperature range of 700–1100 °C has been investigated. After mechanical activation, the precursor releases volatile components (H₂O and CO₂) at lower temperatures. Mechanical activation accelerates the LZ crystallisation and results in the formation of phase-pure LZ without admixtures of unreacted zirconia and lanthana. The LZ powder prepared from the mechanically activated precursor is characterised by a larger BET surface area, in comparison to that synthesised from the as-prepared precursor under the same calcination conditions.     

Chemical Processes During Energy‐Saving Preparation of Lightweight Ceramics

Lightweight glass‐ceramic material similar to foam glass was obtained at 700°C–800°C directly from alkali‐activated silica clay and zeolitized tuff without preliminary glass preparation. It was characterized by low bulk density of 100–250 kg/m³ and high pore size homogeneity. Chemical processes occurring in alkali‐activated silica clay and zeolitized tuff were studied using X‐ray diffraction, thermal gravimetry, IR‐spectroscopy, and scanning electron microscopy. Pore formation in both compositions is caused by dehydration of hydrated sodium polysilicates (Na₂O·mSiO₂·nH₂O), formed during alkali activation. Additional pore‐forming gas source in alkali‐activated zeolitized tuff is trona, Na₃(CO₃)(HCO₃)·2H₂O, formed during interaction between unbound NaOH and CO₂ and H₂O from air. Influence of mechanical activation of raw materials on chemical processes occurring in alkaline compositions was also studied.     

Mechanical Activation of Tetracalcium Phosphate

It was found that prolonged high-energy ball-milling of Hilgenstokite (tetracalcium phosphate, TTCP) resulted in a decrease in both particle and crystallite size, leading to a mechanical activation of the compound. This mechanically activated material demonstrated a high reactivity such that, in contrast to highly crystalline TTCP, a setting reaction with water to nanocrystalline hydroxyapatite (HA) and Ca(OH)₂ could be achieved at 37°C. However, crystalline TTCP is practically unreactive at physiologic temperatures because of the formation of a thin HA layer on the particle surface preventing further reaction.     

Al2O3·2SiO2 powders synthesized via sol–gel as pure raw material in geopolymer preparation

Geopolymers are inorganic aluminosilicates mainly proposed as environmentally friendly building materials, which are obtained by alkali activation of natural minerals, calcined clay (e.g., metakaolin) and other aluminosilicate sources. The wide range of chemical and mineralogical compositions of these raw materials influences several properties of the obtained geopolymers. In the present work, pure Al₂O₃·2SiO₂ powders were synthesized via the sol–gel technique and proposed as pure aluminosilicate sources to prepare alkali activated geopolymers. Samples differing in the ratio between the SiO₂ precursor and the H₂O used in the sol–gel process were prepared, in order to study the effect of water content on the material structure and reactivity. The chemical structure of all the obtained Al₂O₃·2SiO₂ powders were characterized by Fourier transform infrared (FT‐IR) and solid‐state nuclear magnetic resonance (²⁷Al and ²⁹Si MAS NMR) spectroscopies and compared to that of a reference metakaolin. Moreover, material reactivity was evaluated by alkali activation of the samples. After 28 days of ageing, ²⁷Al and ²⁹Si MAS NMR and FT‐IR spectra ascertained the formation of a geopolymeric network in the activated samples. The results showed that lower water content allows obtaining a homogeneous Al‐rich geopolymer similar to that obtained, using metakaolin as raw material.     

Influence of calcium additions on the compressive strength and microstructure of alkali‐activated ceramic sanitary‐ware

The ceramic sanitary‐ware market generates large amounts of waste, both during the production process and due to construction and demolition practices. In this paper, the effect of different amounts and calcium sources (calcium hydroxide Ca(OH)₂, calcium aluminate cement CAC, Portland cement PC) on the alkaline activation of ceramic sanitary‐ware waste (CSW) was assessed. Blended samples were activated with NaOH and sodium silicate solutions and cured for 3 and 7 days at 65°C. The maximum amount of calcium source‐type added to the system varied according to its influence on the compactability of the mortars.CSW was physico‐chemically characterized and the compressive strength development of activated samples was assessed on the mortars. The nature of the reaction products was analyzed in pastes, by X‐ray diffraction, thermogravimetric analysis, infrared spectroscopy and microscopic studies. The results show a great positive influence with the addition of moderate amounts of Ca(OH)₂, PC and CAC on the mechanical properties. Among the typical hydrates usually observed in plain water‐hydrated PC or CAC, only AH₃ and a small amount of C₃AH₆ were identified in the alkali‐activated CSW/CAC blended pastes, which indicates that Al and Ca from PC, CAC and Ca(OH)₂ are taken up in the newly formed (N,C)‐A‐S‐H or C‐A‐S‐H gels.     

Altering Reactivity of Aluminum with Selective Inclusion of Polytetrafluoroethylene through Mechanical Activation

Micrometer‐sized aluminum is widely used in energetics; however, performance of propellants, explosives, and pyrotechnics could be significantly improved if its ignition barriers could be disrupted. We report morphological, thermal, and chemical characterization of fuel rich aluminum‐polytetrafluoroethylene (70–30 wt‐%) reactive particles formed by high and low energy milling. Average particle sizes range from 15–78 μm; however, specific surface areas range from approx. 2–7 m² g⁻¹ due to milling induced voids and cleaved surfaces. Scanning electron microscopy and energy dispersive spectroscopy reveal uniform distribution of PTFE, providing nanoscale mixing within particles. The combustion enthalpy was found to be 20.2 kJ g⁻¹, though a slight decrease (0.8 kJ g⁻¹) results from extended high energy milling due to α‐AlF₃ formation. For high energy mechanically activated particles, differential scanning calorimetry in argon shows a strong, exothermic pre‐ignition reaction that onsets near 440 °C and a second, more dominant exotherm that onsets around 510 °C. Scans in O₂‐Ar indicate that, unlike physical mixtures, more complete reaction occurs at higher heating rates and the reaction onset is drastically reduced (approx. 440 °C). Simple flame tests reveal that these altered Al‐polytetrafluoroethylene particles light readily unlike micrometer‐sized aluminum. Safety testing also shows these particles have high electrostatic discharge (89.9–108 mJ), impact (>213 cm), and friction (>360 N) ignition thresholds. These particles may be useful for reactive liners, thermobaric explosives, and pyrolants. In particular, the altered reactivity, large particle size and relatively low specific surface area of these fuel rich particles make them an interesting replacement for aluminum in solid propellants.     

Preparation of a Novel Cementitious Material from Hydrothermally Synthesized C–S–H Phases

New cementitious materials based on calcium hydrosilicate hydrates were recently developed as potential substitutes for ordinary portland cement, but with a reduced CO₂ footprint. The materials are produced by hydrothermal processing of SiO₂ and Ca(OH)₂, giving rise to calcium silicate hydrates, followed by mechanical activation of the latter via cogrinding with various siliceous materials. Thus, the chemical composition in terms of C/S ratio could be adjusted over a broad range (1–3). In this study the synthesis of a previously unknown cementitious material produced via the combination of mechanical activation in a laboratory mill and thermal treatment of a mixture of quartz and hydrothermally synthesized calcium silicate hydrates: α‐Ca₂[HSiO₄](OH) (α‐C₂SH) and Ca₆[Si₂O₇](OH)₆ (jaffeite) are reported. It forms independently of the type of mill used (eccentric vibrating mill, vibration grinding mill) after thermal treatment of the ground materials at 360°C–420°C. The new material is X‐ray amorphous and possesses a CaO/SiO₂ ratio of 2. A characteristic feature in regards to the silicate anionic structure is the increased silicate polymerization (up to 27% Si₂O₇ dimers) as revealed by the trimethylsilylation method. Infrared (IR) spectra show a very broad absorption band centered at about 935 cm^?1. Another characteristic feature is the presence of ~2.5 wt% H₂O as shown by thermogravimetry (TG) coupled with IR spectroscopy. As this water is bound mostly as hydroxyl to Ca, we refer to this new cementitious material as calcium‐oxide–hydroxide–silicate (C–CH–S). Calorimetric measurements point to a very high hydraulic reactivity which is beyond that for typical C₂S materials. The influence of the type of grinding on the thermal behavior of α‐C₂SH upon its transformation into water‐free Ca₂SiO₄ modifications is discussed.     

Dependence of Silicon Carbide Product Morphology on the Degree of Mechanical Activation

Mechanical activation before carbothermic reduction can substantially enhance the formation of SiC from SiO₂and carbon mixtures. However, the morphology (e.g., particles or whiskers) of SiC formed from mechanically activated SiO₂and carbon mixtures is dependent of the degree of mechanical activation and the condition of the subsequent carbothermic reduction. These phenomena are investigated and rationalized based on the increased reactivity of the reactants and SiC formation mechanisms.     

Palladium‐Catalysed Intramolecular Direct Arylation of 2‐Bromobenzenesulfonic Acid Derivatives

A palladium‐catalysed intramolecular direct arylation of 2‐bromobenzenesulfonic acid derivatives was found to proceed using 1 mol% of palladium acetate as the catalyst. The influence of the substituents on the phenol moiety of 2‐bromobenzenesulfonic acid phenyl esters reveals that electron‐donating substituents favour the reaction while electron‐withdrawing ones are unfavourable. The reactivity of sulfonamides was also studied and, in all cases, a selective activation at sp² C H vs. sp³ C H was observed. A sulfonamide bearing both phenyl and benzyl substituents on nitrogen gave selectively the six‐membered ring product.