Crystallization Of Magnesium Hydroxide Research Articles

Effects of titanium carbide on modified magnesium oxysulfate cement: Microstructure and mechanical properties

This study explores the effects of micro and nano titanium carbide (TiC) on the properties of magnesium oxysulfate cement with dosages of 1–5%. The flexural and compressive strength of composites were 15–21 MPa and 82–95 MPa at 28d. TiC reduced brittleness by improving displacement and energy absorption capability to 82 % and 114 %. Curing age influenced flexural strength by increasing both displacement and energy absorption capability, but the compressive strength development depends primarily on energy absorption capability. The 517 phases in clusters or rings grown from interfaces with gels contributed to high strength of cement. The poor performance of composites containing 5% nano-TiC was attributed to the formation of magnesium hydroxide crystals. TiC decreased the water resistance due to the formation of long needle crystals. Carbonization did not reduce compressive strength statistically but weakened flexural strength by 18%–56 %. Evaluation based on 15 indicators concluded the optimal sample with 1 % nano-TiC, providing insights into the design of magnesium oxysulfate cement products with high performance.

Phenolic resin-based nanoflower porous carbon synthesized by self-assembly of MgO hydrolysis for boosting supercapacitor performance

Although electrode materials with flower-like structures have showing promising achievement for battery energy storage for stable structure and rich specific surface area, there are still some challenges in precisely controlling their microstructure. Inspired by the hydrolysis and self-assembly of MgO into petal-like magnesium hydroxide crystals under alkaline critical micelle conditions, we have proposed to synthesize a unique phenolic resin with a 3D flower-like structure as a carbon precursor. After a series of treatments, the optimal sample consists of nanosheets (thickness ≈27 nm) extending in all directions from the core, with a porous structure, significant specific surface area of 2028 m2/g and pore volume of 1.79 m3/g. Electrochemical experiments confirmed that the sample exhibits satisfactory electrochemical performance as the electrode of supercapacitor. It shows an amazing unique capacitance of 320.1 F/g, and the charge–discharge capacity retention rate exceeds 94.6 % after 5000 cycles. Moreover, a high energy density of 9.44 Wh/kg at 126 W/kg is shown for the symmetrical supercapacitors. We believe that the 3D flower-like morphology formed by the unique lamellar structure can provide more active sites, promote ion transports and increase the stability of structure. These findings suggest a new strategy to control the morphology of phenolic resin-based carbon materials.

Preparation of durable magnesium oxysulfate cement with the incorporation of mineral admixtures and sequestration of carbon dioxide

To reduce the consumption of energy and raw materials caused by the production of Portland cement and enhance the carbon dioxide sequestration of building materials, this paper aims to manufacture durable and green magnesium oxysulfate cement based on incorporating mineral admixtures (fly ash (FA) or ground granulated blast-furnace slag (GGBFS)) and CO2 curing treatment. Compressive strength, flexural strength, resistance to water and wetting-drying cycles of magnesium oxysulfate (MOS) were evaluated. Phase compositions and microstructures of typical samples were measured by X-ray diffraction (XRD), differential scanning calorimetry (DSC-TG), and scanning electron microscope (SEM) techniques. The results showed that mechanical strength and strength retention after wetting-drying treatment of MOS cement was increased by the sequestration of carbon dioxide. Both FA and GGBFS could improve the water resistance due to restrainting the phase conversion of MgO into Mg(OH)2. However, the addition of FA or GGBFS deteriorated the compressive strength of MOS cement samples after wetting-drying treatment, owing to the formation of more magnesium hydroxide crystals and decomposition of 5 Mg(OH)2·MgSO4·7H2O (5·1·7 phase). Furthermore, about 5% carbon dioxide can be captured by MOS cement paste during 24 h accelerated carbonation treatment. Therefore, the incorporation of mineral admixtures and sequestration of carbon dioxide was suggested as an effective method in manufacturing the highly durable and cleaner magnesium oxysulfate cement.

A simulation tool for ion exchange membrane crystallization of magnesium hydroxide from waste brine

Increasing attention is nowadays paid to the management and valorisation of industrial waste brines aiming also at the recovery of raw materials. Magnesium has been listed as a Critical Raw Material by EU, prompting researchers to investigate novel routes for its recovery. Within this framework, a novel Crystallizer with Ion Exchange Membrane (CrIEM), is proposed as an innovative way to recover magnesium from industrial waste brines exploiting low-cost alkaline reactants. In the present work, a novel mathematical model of the CrIEM process is proposed to provide a useful tool for its design in different working conditions. Batch and feed & bleed continuous configurations have been investigated taking into account: (i) the variation of the alkaline and brine concentration in their own collection tanks over time and (ii) the spatial mono-dimensional (1D) steady-state description of the main phenomena that occur inside the CrIEM. Original experimental data, from ad-hoc laboratory tests, and literature information were used to validate the proposed model both in the batch and continuous feed & bleed configuration. A good agreement between model predictions and experimental/literature data was found for both cases, thus proving the reliability of the proposed model for the design of the CrIEM reactor.

A Novel Ionic Exchange Membrane Crystallizer to Recover Magnesium Hydroxide from Seawater and Industrial Brines.

A novel technology, the ion exchange membrane crystallizer (CrIEM), that combines reactive and membrane crystallization, was investigated in order to recover high purity magnesium hydroxide from multi-component artificial and natural solutions. In particular, in a CrIEM reactor, the presence of an anion exchange membrane (AEM), which separates two-compartment containing a saline solution and an alkaline solution, allows the passage of hydroxyl ions from the alkaline to the saline solution compartment, where crystallization of magnesium hydroxide occurs, yet avoiding a direct mixing between the solutions feeding the reactor. This enables the use of low-cost reactants (e.g., Ca(OH)2) without the risk of co-precipitation of by-products and contamination of the final crystals. An experimental campaign was carried out treating two types of feed solution, namely: (1) a waste industrial brine from the Bolesław Śmiały coal mine in Łaziska Górne (Poland) and (2) Mediterranean seawater, collected from the North Sicilian coast (Italy). The CrIEM was tested in a feed and bleed modality in order to operate in a continuous mode. The Mg2+ concentration in the feed solutions ranges from 0.7 to 3.2 g/L. Magnesium recovery efficiencies from 89 up to 100% were reached, while magnesium hydroxide purity between 94% and 98.8% was obtained.

Ultrasound-assisted Crystallisation of Magnesium Hydroxide from Seawater

High purity magnesium hydroxide has been synthesised from seawater with the addition of dolomite lime as reagent. High intensity ultrasound-assisted crystallization of magnesium hydroxide was carried out during precipitation with the intention to obtain fine particles of Mg(OH)2 as well as to prevent their agglomeration. Investigations were conducted on magnesium hydroxide samples in the form of sludge and voluminous powder. The composition, morphology, and properties of the product were determined by chemical, XRD, FTIR, and SEM/EDS analysis. The particle size distribution was detected by the laser light scattering method. The results showed that the mean particle size of magnesium hydroxide sludge was 5.75 µm, while voluminous powder was 7.58 µm. The morphology of magnesium hydroxide voluminous powder was in the form of aggregated filamentous (up to 300 nm in size) or flake structures.

Modeling on the hydration and leaching of eco-friendly magnesium oxychloride cement paste at the micro-scale

Magnesium oxychloride cement (MOC) has been considered as a kind of eco-friendly cement in view of its significantly low calcination temperature and large capacity of carbon dioxide sequestration, compared with ordinary Portland cement (OPC). In this work, a computer model is established to simulate the hydration and leaching of MOC paste at the micro-scale. The composition of MOC paste in the ultimate hydration is investigated based on the thermodynamic method, and pore structure obtained from the computer simulation is compared with the one from experiments and literature, respectively. The simulated leaching results show that the original solid phase skeleton of MOC paste decomposes into magnesium hydroxide crystals. It is demonstrated that the simulation results are in good agreement with experimental data from literature and the proposed simulation can provide an effective method to reveal the hydration and leaching mechanism of MOC paste.

Inhibition of Homogeneous Formation of Magnesium Hydroxide by Low-Molar-Mass Poly(acrylic acid) with Different End-Groups

The homogeneous crystallization of magnesium hydroxide (Mg(OH)2) was carried out at 97 °C in the absence and presence of low molar mass (Mn ≤ 2000) poly(acrylic acid) (PAA) terminated with different end groups. A significant decrease in Mg(OH)2 crystal growth was found in the presence of PAA, with relatively hydrophobic end-groups being most effective. The end-groups that were most effective were decyl isobutyrate which are more hydrophobic than the hexyl isobutyrate end-groups previously shown to be maximally effective in inhibiting calcium carbonate and calcium oxalate scaling.

The Properties of Modified Polysulfonamide Fabrics with Lamellar Magnesium Hydroxide Crystals

Lamellar magnesium hydroxide crystals were prepared successfully on the surface of polysulfonamide fibers with carboxylic acid groups. The polysulfonamide fabrics with Mg(OH)2 crystals were characterized by Scanning electron microscopy, Inductively coupled plasma atomic absorption spectrometer X-ray diffraction, Vertical flammability test and Thermalgravimetric analysis. The vertical flammability test showed that the damaged length of original polysulfonamide fabrics was 34mm, while that of the polysulfonamide fabrics with Mg(OH)2 crystals (treated by 7.5% NaOH solutions) was 14mm. In addition, the Mg (OH)2 crystals played a critical role in the improvement of thermal stability and heat insulation of polysulfonamide fabrics.

Controlled growth of magnesium hydroxide crystals and its effect on the high-temperature properties of cotton/magnesium hydroxide composites

Controlled magnesium hydroxide particles were assembled successfully on the surface of cotton fibers for the improvement of flammability and thermal stability of cotton/magnesium hydroxide composites. Unlike previous researches where magnesium hydroxide particles have been blended into polymer matrix, self-assembly of particles onto the fiber surface demonstrated in this research provided substantially excellent properties. The morphology, structure and properties of cotton/magnesium hydroxide composites were characterized. Here, the fibers exhibited a swelling surface after the urea-modification, resulting in the more amounts of magnesium hydroxide crystals growing. Without the presence of sodium chloride, the particles self-assembled into lamellar-like structure on the surface of cotton fibers and into rod-like structures with the presence of sodium chloride thereby enabling us to control the growth of the particles. The vertical flammability test showed that the introduction of sodium chloride resulted in the change of morphology of magnesium hydroxide crystals, which had the important effect on the fire-proofing properties of cotton/magnesium hydroxide composites. The weight loss of origin fabrics, citric acid-modified cotton fabrics with Mg(OH)2 crystals grew with salts and urea/citric acid-modified cotton fabrics with Mg(OH)2 crystals grew with salts were 81.5%, 57.4% and 48.9% respectively when heated to a temperature of 500 °C.

Influence of magnesium source on the crystallization behaviors of magnesium hydroxide

The crystallization of magnesium hydroxide [Mg(OH) 2] from the aqueous solutions of magnesium chloride (MgCl 2) or magnesium dodecyl sulfate [Mg(DS) 2] was conducted by means of the slowly diffusing of ammonia gas at 30 °C. When the aqueous solution of 5.0×10 −3 mol/L MgCl 2 was used as a reaction medium, the sunflower-shaped superstructures of thin and branched Mg(OH) 2 sheets were obtained at 2 d; the prolongation of reaction time and the increase of MgCl 2 concentration caused the formation and the consequent agglomeration of Mg(OH) 2 platelets. Interestingly, the aqueous solution of 5.0×10 −3 mol/L Mg(DS) 2 could be referred as the counterpart of 5.0×10 −2 mol/L MgCl 2 at the surface nucleation of Mg(OH) 2. The precipitates sampled from Mg(DS) 2 solutions at 2 or 3 d presented the lamellar aggregates of Mg(OH) 2 platelets; while these sampled at 6 and 12 d showed the column-shaped structures of Mg(OH) 2 under the transmission electron microscopy (TEM) observation, suggesting the further growth of Mg(OH) 2 platelets along the c-axis perpendicular to the [0 0 1] face. Meanwhile, the nucleation, the crystal orientation, and the crystallographic defect were also discussed, indicating the different crystallization habits of Mg(OH) 2 in the aqueous solutions of different magnesium sources.

Synthesis of magnesium hydroxide nanoneedles and short nanorods on polymer dispersant template

Magnesium hydroxide nanoneedles and nanorods were synthesized by reverse precipitation in the presence of polyethylene glycol (MW 1000) at ambient temperature. The obtained magnesium hydroxide crystals were characterized in terms of morphology, particle size, crystal structure, and thermal stability by high-resolution transmission electron microscopy, x-ray diffraction, infrared spectroscopy, and thermogravimetric and differential thermal analysis. The experimental results show that the growth of magnesium hydroxide crystals and the dispersivity of the nanostructures were greatly influenced by polymer dispersant. The mechanism of the formation of magnesium hydroxide nanorods and nanoneedles was also proposed.

Volume stabilisation of high MgO cement: effect of curing conditions and fly ash addition

Hydration of high MgO cement paste under autoclave conditions causes the rapid formation and crystallization of magnesium hydroxide and leads to the creation of larger pore sizes. This results in the loss of mechanical strength and higher expansion values. Under ambient water curing, precipitation and distribution of gelatinous calcium silicate hydrates into the finer network causes a homogeneous morphology and the development of smaller pores. The resultant higher mechanical strength associated with partial hydration of MgO yields reduced expansion. High MgO cement paste containing fly ash also showed considerable pore refinement and improved hydrate morphology favouring volume stability under both autoclave and ambient water curing.

Reactive Crystallization of Magnesium Hydroxide

Reactive Crystallization of Magnesium Hydroxide

The crystallization of magnesium hydroxide, a constant composition study

A new method has been developed for studying the kinetics of precipitation of magnesium hydroxide, an important scalant in flash evaporation processes in which the activities of the ionic species in the precipitating medium were maintained constant. The results are in good agreement with those of conventional seeded growth experiments. As the concentration of magnesium hydroxide is increased, the effective kinetic order of the precipitation reaction induced by a number of different seed surfaces, changes from 3–7 at a relative supersaturation of approximately unity. In contrast to numerous other scale formation reactions, the induced precipitation of magnesium hydroxide is unaffected by the presence of a number of potential scale inhibitors.

The growth of Mg(OH) 2 crystals from MgCI 2 and Ca(OH) 2 in a brine environment

Magnesium hydroxide crystals of 0.03–4.0 μm diameter were precipitated by continuous stoichiometric reaction between MgCI 2 and Ca(OH) 2 in stirred 3.46 M CaCI 2 aqueous solution at constant temperature. The pH was recorded. Transmission electron microscopy was used to characterize the crystals. At 60°C, with 0–4.5 gpl excess Ca(OH) 2 present, sheetlike crystals of up to 4.0 μm diameter formed. This was attributed to Ca 2+ adsorption on the basal surface. At 43–77°C, with excess MgCl 2 present, a transition occurred below ∼8.5 pH from plates to a “stacked plate” (pyramidal) layered-crystal morphology, as observed previously [1,2] in the MgCl 2/NH 4OH system at 60°C. At 91°C, with 4.5 gpl excess Ca(OH) 2 present, trigonal plates which formed initially, grew preferentially along the c-axis forming triangular prisms. This is attributed to Ca desorption, which is supported by the results of ESCA/Auger analysis. Regardless of the amount of excess reagent present, increase in temperature lowered the pH and significantly changed the morphology.

Davydov splitting and multipole interactions

Davydov's theory of factor group splitting in molecular crystals has been revisited. It is observed that the dipole-dipole interaction alone is not sufficient to account for the splitting in some simple crystals. The effect of multipole interactions in the electrostatic energy including those which may be present even before the vibrational excitation must be investigated. It is shown that in case of calcium hydroxide and magnesium hydroxide crystals the quadrupolar interactions have a preponderant role in the Davydov splitting.

The crystallization of magnesium hydroxide

The thermodynamic association constant for the formation of the ion-pair MgOH + in solutions of magnesium hydroxide has been studied by potentiometric and conductometric methods. The growth of magnesium hydroxide seed crystals in supersaturated solutions over a range of concentrations of magnesium and hydroxide ions and in the presence of phosphonate additives has been investigated by a precision conductance method. After a rapid initial surge of growth, an equation first order with respect to supersaturation can be used to explain the experimental data. A surface diffusion process is proposed as the controlling step in the crystallization process.