Preparation of Ca(OH)2 nanoparticles by impinging stream reaction precipitation method

In this paper, Ca(OH)₂ nanoparticles are prepared by impinging stream co-precipitation method. The process of preparing nanoparticles by impinging stream is optimized. The influence of process variable, such as dispersant type, dispersant dosage, circulating flow rate, reactant concentration ratio of OH⁻ and Ca²⁺, reaction temperature and circulation time, on the particle size of Ca(OH)₂ nanoparticle are investigated. The results show that the concentration ratio of reactants has a significant effect on the size of Ca(OH)₂ nanoparticles. The optimal process conditions are obtained by single factor experiment, PEG6000, 3.3% dispersant dosage, Q = 1000 L · h⁻¹, C = 1.88, T = 46.68°C and t = 60 min. The average particle size of Ca(OH)₂ nanoparticles prepared under these conditions is 107.67 nm. According to the microstructure analysis, the prepared Ca(OH)₂ nanoparticles samples have high purity and a good crystal structure. The powder dispersed with a marked hexagonal crystal shape and good thermal decomposition.     

On the nature of the crystallographic disorder in submicrometer particles of Ca (OH)2 produced by vapour phase hydration

Poor crystalline form of Ca(OH)₂ can be produced by reaction of water vapours at room temperature with CaO powders and are highly reactive towards liquids and gases. Nitrogen adsorption isotherms, X-ray broadening analysis and S.E.M. observations were made on different samples either before or after a thermal treatment (essentially an irreversible process) that transforms these hydroxides into more crystalline materials. It is shown that the vapour phase hydration yields not only small-size particles and high porosities but also crystallographic defects, and that the irreversible transformation is mainly connected to a recovery of defects.     

Al Surface Modification by a Facile Route

A facile route was used to modify Al particle surfaces by putting Al particles into an Al(OH)₃ suspension, which was produced by the reaction of Al powder with water under vacuum at a mild temperature, then drying and heat‐treating under vacuum at elevated temperature. The modified Al powder has a good reaction activity with water to generate hydrogen, and its reaction rate depends on the sizes of Al particles used to produce Al(OH)₃ suspension. The reaction induction time of the modified Al powder prepared using the Al(OH)₃ suspension produced by the reaction of Al with water is obviously shorter than that prepared using the Al(OH)₃ suspension formed by the direct addition of a commercial Al(OH)₃ powder, because the in situ formed Al(OH)₃ has a finer microstructure. As the present method has no complicated processing procedure and the Al‐water reaction byproduct can be reused to modify Al, it is an economically viable way to fabricate the activated Al powder for commercial applications.     

Synthesis of transparent oil dispersion of monodispersed calcium carbonate nanoparticles with high concentration

The preparation of monodispersed inorganic nanoparticles is of great interest for many applications. In this article, transparent oil dispersion of monodispersed amorphous CaCO₃ nanoparticles with high concentration and long‐term stability were controllably prepared by a reverse microemulsion method. The effects of the addition amount of extra minute water and (NH₄)₂CO₃ as novel assistant promoter, reaction temperature, Ca(OH)₂/CaO mole ratio were explored. The optimum synthesis conditions were achieved. The as‐prepared transparent oil nanodispersion had a good monodispersity, a uniform particle size of 8–10 nm, a high stability of over 12 months, a high solid content of 38 wt% (Ca content of about 15.5 wt%) and a high total base number of 416 mgKOH/g. The preparation process was further investigated by polarized optical microscope and Fourier transform infrared. This nanodispersion will find a promising applicability as an excellent nanodetergent in the fields of automobile and marine lubricants. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3663–3669, 2017     

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.     

Mineralogy and Microstructure of Hydrated Phases During the Pozzolanic Reaction in the Sanitary Ware Waste/Ca(OH)2 System

Despite technological improvements in its production process, the sanitary ware industry inevitably generates a certain volume of discards, products whose quality is not up to standard. The present paper is the first to scientifically explore clay‐based sanitary ware waste (SW) with a view to its valorization as an addition in the design of new, more environmentally friendly cements. The focus is on characterization of the waste and its pozzolanicity, as well as the structural and microstructural changes taking place in the pozzolan/Ca(OH)₂ system in the first 90 d of reaction. The findings show that pozzolanicity in clay‐based waste is comparable to the activity observed in silica fume (SF) and higher than that found in other clay‐based materials and fly ash (FA). The microstructural study of the clay‐based waste/Ca(OH)₂ system, in turn, reveals that the proportion of C–S–H gels rises with hydration time. These gels are characterized by long mean chain lengths (MCL) and low Ca/Si ratios. The intrinsic characteristics of this thermally activated clay‐based waste qualify it as a type Q pozzolans as defined in the European cement standards, making it apt for use in the manufacture of CEM II, IV, and V cements.     

Fluidization Behavior of Cohesive Ca(OH)2 Powders Mixed with Hydrophobic Silica Nanoparticles

Dry mixing with hydrophobic silica nanopowders was used to improve the fluidization quality of Ca(OH)₂ particles which belong to the Geldart C group and, thus, normally cannot be fluidized. Three parameters, i.e., sieved size of Ca(OH)₂ particles and sieved size and weight percentage of SiO₂ nanoparticles were selected for experiments. A direct proportionality was found between the coverage quality of materials over each other and the fluidization behavior of their corresponding adsorbents. Optimum SiO₂ size and concentration values were determined for the improvement of Ca(OH)₂ fluidizability. The sieved size of Ca(OH)₂ powder had no consequential effect on the coverage quality. The Richarson‐Zaki equation and fractal analysis combined with a modified Richardson‐Zaki approach were proposed for prediction of the fluidization quality and agglomerate size.     

Interfacial interaction in AI(OH)3/polypropylene composites modified by insitu‐functionalized polypropylene

To investigate the interfacial interaction of AI(OH)₃/polypropylene (PP) composites modified by in situ‐functionalized polypropylene (FPP), AI(OH)₃/polypropylene (PP) composites containing a low AI(OH)₃ content, modified by in situ‐grafted acrylic acid, were prepared by a one‐step melt‐extrusion process. The effect of in situ FPP on the crystallization and melting behavior, crystalline morphology of the composites, and interfacial interaction between the filler and PP was investigated. The crystallization and melting behavior and crystalline morphology of PP in the composites depended upon the interfacial physical [heterogeneous nucleation of AI(OH)₃; cocrystallization and compabilitization of PP with in situ FPP] and the interfacial chemical interaction between both the components in the composites. FTIR results indicated that there exists a chemical reaction between AI(OH)₃ and in situ FPP. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 110–120, 2002; DOI 10.1002/app.10270     

氯化镁溶液氨气鼓泡反应制备纳米氢氧化镁

引言 氢氧化镁(magnesium hydroxide,MH)具有分解温度较高、热稳定性好、无毒、无烟及抑烟等特点,适合作为无机添加型阻燃剂,国外已有六十余年的研究与生产历史[1].MH也是制备高纯MgO的主要原料[2-5],同时作为酸性废水的中和剂、重金属废水的吸附剂及烟气脱硫剂,在绿色环保领域应用广泛.     

Synthesis of Nano Calcium Hydroxide in Aqueous Medium

The present work reports a simple, inexpensive method for synthesis of calcium hydroxide [Ca(OH)₂] nanoparticles (CHNPs). The method involves chemical precipitation (CP) in aqueous medium at room temperature. Calcium nitrate dihydrate [Ca(NO₃)₂.2H₂O] and sodium hydroxide were used as precursors. The CHNPs were characterized by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), Rietveld analysis, field‐emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM), BET surface area evaluation as well as particle size distribution analysis techniques. The results confirmed the synthesis of CHNPs as the major phase. The CHNPs exhibited an average size of about 350 nm. In addition, some calcite phase formed due to the inevitable carbonation process. A very minor amount of aragonite phase was also present. A schematically developed new qualitative model is proposed to explain the genesis and subsequent evolution of the various phases at the nanoscale. The model helps to identify the rate‐controlling step. It also highlights the implication of reaction kinetics control in synthesis of predesigned nanophase assembly.     

Mineralogical Evolution of Kaolin‐Based Drinking Water Treatment Waste for Use as Pozzolanic Material. The Effect of Activation Temperature

This study reports on exhaustive scientific research into the influence of the activation temperature of inert waste from drinking water treatment plants for use as supplementary cementing material in cements. The effect of activation temperature on the mineralogy of the reactive products resulting from pozzolanic activity and on the evolution of the hydrated phases formed during the pozzolanic reaction at 28 d of curing was analyzed with the assistance of different instrumental techniques such as X‐ray fluorescence, X‐ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. The results show that all the activated products (based on metakaolinite) presented high pozzolanic activity at all ages of the reaction (up to 90 d), although 600°C at 2 h are the recommended ideal activation conditions from an energetic and economic viewpoint. The activation temperature (600°C–900°C for 2 h of retention) plays an important role in the reaction kinetics in activated drinking water waste/Ca(OH)₂ systems. The hydrated phases identified under these activation conditions were very similar, but with important differences in the crystalline aluminates phases content. Thus, the formation of stratlingite (C₂ASH₈) is favored at low temperatures (<800°C); whereas at higher temperatures (at 900°C), tetra calcium aluminate hydrate (C₄AH₁₃) appears as the only crystalline phase. Finally, this type of treatment of drinking water waste (based on kaolinite) is ideal to obtain future pozzolans based on recycled metakaoline, a product that is currently listed in international standards for the manufacture of commercial cements.     

Cementation by the carbonation of hydrated lime

In this study, the factors which control carbonate cementation have been examined and several hypothesis developed to explain their interaction. These factors include the pressure, concentration, temperature and velocity of the carbonating gas as well as the thickness, temperature, gas permeability, moisture and Ca(OH)₂ contents of the compact. Of these factors, the greatest limitation for the more popular application of the cement is related to the diffusion of the carbonating gas into thicker or less permeable products. A possible reaction mechanism for the cementing process has been outlined and the matrix examined by electron optics, X-ray diffraction, thermal analysis and mercury intrusion porosimetry. These methods have shown that, in general, the matrix is composed of mostly amorphous or very poor crystalline forms of calcium carbonate. The only phases detected by X-ray diffraction methods were a small percentage of unreacted portlandite Ca(OH)₂, and calcite. Less than half of the calcium carbonate formed was present as crystalline calcite.     

Chemical Sequence and Kinetics of Alkali‐Silica Reaction Part I. Experiments

The deterioration induced by alkali‐silica reaction (ASR) is initiated by complicated heterogeneous chemical reactions. This study describes the experimental results obtained from the model reactant experiments focused on the kinetics of physical and chemical changes in the reactive aggregate‐simulated pore solution system undergoing ASR. Specifically, the study investigated the products formed by exposing reactive silica mineral (α‐cristobalite) to two alkali solutions in the presence of solid calcium hydroxide [Ca(OH)₂]. The experimental results showed that, as long as the Ca(OH)₂ remains in the system, the dissolution of the silica mineral proceeds at a constant rate and the only reaction product formed is the tobermorite‐type C–S–H. However, once the supply of Ca(OH)₂ in the system is exhausted, the level of dissolved silica ions starts to increase. At the same time, the previously formed C–S–H changes in composition by incorporating silicon and alkali ions from the solution. Continuous increase in the concentration of silica leads to formation of the ASR gel as a result of interaction between silica and alkali ions.     

Synthesis of Polystyrene/Hydrophobic SiO2 Composite Particles via Oil‐in‐Water Pickering Emulsion Polymerization

The aim of this work is to present a facile Pickering emulsion polymerization method for the synthesis of submicron polystyrene/SiO₂ core/shell composite particles. The commercial hydrophobic SiO₂ nanoparticles were used as stabilizing agent for creating a stable oil‐in‐water emulsion. Although the adsorption of hydrophobic SiO₂ nanoparticles in the emulsion system was unfavorable in terms of thermodynamics, by ultrasound treatment, self‐assembly of hydrophobic SiO₂ nanoparticles effectively stabilized oil‐in‐water Pickering emulsions during polymerization. Using 3 wt.% SiO₂ nanoparticles (based on styrene monomer) and 1:10 volume ratio of styrene monomer:water, the composite particles having average size of 790 nm and relatively narrow particles distribution were produced. With decreasing the volume ratio, smaller composite particles were created. Results from scanning electron microscope revealed that SiO₂ nanoparticles were located exclusively at the surface of the polystyrene latex particles. The SiO₂ content, determined by thermogravimetric analysis, was 12.6 wt.% in the composite particles. The route reported here may be used for the preparation of other composite nanostructures. POLYM. ENG. SCI., 59:E195–E199, 2019. © 2018 Society of Plastics Engineers     

Biopolymer-assisted green synthesis and characterization of calcium hydroxide nanoparticles

The use of biopolymers in the synthesis of different nanostructures can be a cost effective and eco-friendly approach. In the present study, a facile and “green” sol–gel method was employed for preparing calcium hydroxide nanoparticles (Ca(OH)₂-NPs) in gelatin matrix as a bio-template. Prepared nanoparticles were characterized by different instruments such as powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), and Fourier transform infrared spectroscopy (FTIR). The PXRD analysis revealed hexagonal Ca(OH)₂-NPs with preferential orientation in (101) reflection plane. They are hexagonal in shape with a mean particle size of approximately 42 nm in thickness. The synthesized Ca(OH)₂-NPs using gelatin were found to be comparable to those obtained from conventional methods using hazardous capping/stabilizing polymeric agents or surfactants and this route can be an excellent alternative for the synthesis of Ca(OH)₂-NPs using biomaterials.     

Carbon Dioxide Uptake by Hydrated Lime Aerosol Particles

The reaction of the greenhouse gas, CO₂, with Ca(OH)₂ was explored using single-particle Raman spectroscopy to track the chemical reaction. Single particles were levitated in an electrodynamic balance (EDB) to maintain the particle in a laser beam. The levitation voltage provided gravimetric data. The humidity in the EDB chamber was varied to determine the effects of humidity on the reaction. It is demonstrated that no appreciable reaction occurs at low relative humidities (RH < 70%). This is evidenced by no disappearance of the Raman peak associated with the [OH]^? vibrational bond, but at high humidities (RH > 70%) the Raman spectrum of CaCO₃ developed as the reaction proceeded. The results are consistent with results from packed-bed studies of the reaction and are in agreement with similar findings for the SO₂/Ca(OH)₂ reaction used for desulfurization, that is, the reaction does not proceed until multiple monolayers of water are adsorbed on the particle surface.     

Controllable preparation of nano-CaCO3 in a microporous tube-in-tube microchannel reactor

In this work, nano-CaCO₃ particles with tunable size have been synthesized via CO₂/Ca(OH)₂ precipitation reaction in a microporous tube-in-tube microchannel reactor (MTMCR) with a throughput capacity up to 400 L/h for CO₂ and 76.14 L/h for liquid. The overall volumetric mass-transfer coefficient (K_La) of CO₂ absorption into Ca(OH)₂ slurry in the MTMCR has been deduced and analyzed. To control the particle size, the effect of operating conditions including initial Ca(OH)₂ content, gas volumetric flow rate, liquid volumetric flow rate, micropore size, and annular channel width was investigated. The results indicated that the mass transfer in the MTMCR can be greatly enhanced in contrast with a stirred tank reactor, and the particle size can be well controlled by tuning the operating parameters. The nano-CaCO₃ particles with an average size of 28 nm and a calcite crystal structure were synthesized, indicating that this process is promising for mass production of nanoparticles.     

Modification of Calcium Hydride as Solid Hydrogen Source for Fuel Cell System

The on‐site type hydrogen generator was developed. Among the various hydride materials, calcium hydride (CaH₂) was selected as hydrogen source because of less reactivity with moisture compared to other alkaline hydride compounds. By mixing CaH₂ with the thermosetting resin, inorganic–organic hybrid material was prepared. Pure CaH₂ reacts vigorously with water to form hydrogen gas and Ca(OH)₂, while this hybrid material moderately produces hydrogen by reacting with water keeping high reaction rate.     

Size-controlled high magnetization CoFe2O4 nanospheres and nanocubes using rapid one-pot sonochemical technique

Highly crystalline single phase spherical and monodisperse cobalt ferrite (CoFe₂O₄) nanoparticles (NPs) with uniform shape and size distribution have been synthesized by one pot-rapid sonochemical method. The effect of different solvents, such as aqueous, alcoholic, and a mix of water/ethanol in 1:1 volume ratio on the shape, size, and crystalline structure of CoFe₂O₄ NPs were studied using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. The size of CoFe₂O₄ nanoparticle was controlled in the range from 20 to 110 nm based on the solvent medium used in the synthesis process. Furthermore, the evolution from spherical to cubic morphology of cobalt ferrite NPs is achieved by simply changing the solvent medium from aqueous to alcoholic medium. The magnetic properties of all the synthesized CoFe₂O₄ NPs were studied by vibrating sample magnetometer (VSM) at room temperature. The magnetization value was found to be particle size dependent, and high magnetization (Ms) of 92.5 emu/g was obtained for the CoFe₂O₄ NPs sample synthesized in a mixed solution of water and ethanol. A possible reaction mechanism for the formation of cobalt ferrite NPs by the sonochemical technique was discussed. The facile method adopted in our study appears to be a promising route for synthesis of highly crystalline nanoparticles within short times and without the need for using any calcination process.     

Rapid Carbonation for Calcite from a Solid-Liquid-Gas System with an Imidazolium-Based Ionic Liquid

Aqueous carbonation of Ca(OH)₂ is a complex process that produces calcite with scalenohedral calcite phases and characterized by inadequate carbonate species for effective carbonation due to the poor dissolution of CO₂ in water. Consequently, we report a solid-liquid-gas carbonation system with an ionic liquid (IL), 1-butyl-3-methylimidazolium bromide, in view of enhancing the reaction of CO₂ with Ca(OH)₂. The use of the IL increased the solubility of CO₂ in the aqueous environment and enhanced the transport of the reactive species (Ca²⁺ and CO₃²⁻) and products. The presence of the IL also avoided the formation of the CaCO₃ protective and passivation layer and ensured high carbonation yields, as well as the production of stoichiometric rhombohedral calcite phases in a short time.