Temperature- and pH-dependent morphology and FT-IR analysis of magnesium carbonate hydrates

Various morphologies of magnesium carbonate hydrates have been synthesized by carefully adjusting the reaction temperature and pH value of the initial reaction solution in the precipitation process. At lower temperatures (from room temperature to 328 K) and lower pH values (variation with the reaction temperature), magnesium carbonate hydrates are prone to display needlelike morphology, and the axis diameter of the particles decreases with the increase of reaction temperature and pH value. With the further increase of the reaction temperature (333-368 K) and pH value, the sheetlike crystallites become the preferred morphology, and at higher temperatures and pH values, these crystallites tend to assemble into layerlike structures with diverse morphologies, such as spherical-like particles with rosette-like structure and cakelike particles built from sheetlike structure. Fourier transform infrared (FT-IR) spectra show that these various morphologies are closely related to their compositions. The needlelike magnesium carbonate hydrate has a formula of MgCO3.xH2O, in which the value x is greatly affected by the experimental conditions, whereas with the morphological transformation from needlelike to sheetlike structure, their corresponding compositions also change from MgCO3.xH2O to Mg5(CO3)4(OH)2.4H2O in the interval of 328-333 K.     

Influence of Mg surface layer for induction period of Grignard reagent formation

Factors that affect the induction period of Grignard reagent formation, which involves heterogeneous reaction between magnesium metal (Mg) and an alkyl halide in ether solvent, has been clarified to achieve safer and more efficient operation in chemical processes. The influence of the Mg surface, especially the effects of carbonate, hydroxide, and oxide layers on the induction period were investigated by measuring the exothermic behavior of Grignard reagent formation by a differential reaction calorimeter. Mg powder was kept in water bubbled with CO₂ or N₂ gas to form a coating on the Mg surface. The calorimetry results for the reaction indicated that both treatments increased the induction period. Thermogravimetric analysis-mass spectrometry was conducted to identify the chemical species and quantify the amount of surface material on the Mg particles. It was found that basic magnesium carbonate and magnesium hydroxide were formed on Mg exposed to CO₂ and N₂, respectively. Subsequent heating the carbonate- or hydroxide-coated Mg at 500 °C caused a MgO layer to form on the surface, which was found to dramatically reduce the induction period.     

Synthesis and properties of a microtube photocatalyst with photoactive inner surface and inert outer surface

Synthesis of a photocatalyst with a novel particle form, its photoactivity, and the degradation of polyvinyl alcohol containing the photocatalyst were studied in detail. A microtube photocatalyst with titanium dioxide particles supported on the inner surface of the microtube was synthesized by adding fine titanium dioxide particles in the formation process of basic magnesium carbonate microtube. The photoactivity of the microtube photocatalyst was confirmed from the decomposition of 2-propanol under blacklight irradiation. Moreover, the microtube photocatalyst was found to cause no degradation of polyvinyl alcohol, whereas, it decomposed 2-propanol with its photoactivity when impregnated in a polyvinyl alcohol foam. This fact was considered to be derived from the unique structure of the microtube photocatalyst, which has a photoactive inner surface with titanium dioxide and an inert outer surface of basic magnesium carbonate.     

A new hydrate of magnesium carbonate,MgCO3·6H2O

During investigations of the formation of hydrated magnesium carbonates, a sample of the previously unknown magnesium carbonate hexahydrate (MgCO₃·6H₂O) was synthesized in an aqueous solution at 273.15 K. The crystal structure consists of edge‐linked isolated pairs of Mg(CO₃)(H₂O)₄ octahedra and noncoordinating water molecules, and exhibits similarities to NiCO₃·5.5H₂O (hellyerite). The recorded X‐ray diffraction pattern and the Raman spectra confirmed the formation of a new phase and its transformation to magnesium carbonate trihydrate (MgCO₃·3H₂O) at room temperature.     

Temperature driven morphological changes of hydrothermally prepared copper oxide nanoparticles

The size and shape of nanocrystals have a strong effect on the optical, electrical and catalytic properties. Therefore, controlling the size, shape and structure of nanocrystals is technically important. The controlled synthesis of CuO nanostructures was achieved using a hydrothermal process by simply controlling the precipitation reaction temperature between copper nitrate trihydrate and sodium hydroxide. The Scanning Electron Microscopy (SEM), EDS, XRD, and FTIR analysis revealed that the synthesized product at 200 °C is of pure copper oxide particles. From Scherrer formula, the prepared CuO particles varied approximately 3–7 nm in size simply by varying the reaction temperature. The synthesized particles exhibited a regular flake like morphology and had a uniform size distribution. The morphology and size depend on the reaction conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Nanobelt formation of magnesium hydroxide sulfate hydrate via a soft chemistry process

The nanobelt formation of magnesium hydroxide sulfate hydrate (MHSH) via a soft chemistry approach using carbonate salt and magnesium sulfate as reactants was successfully demonstrated. X-ray diffraction (XRD), energy dispersion X-ray spectra (EDS), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis revealed that the MHSH nanobelts possessed a thin belt structure (approximately 50 nm in thickness) and a rectangular cross profile (approximately 200 nm in width). The MHSH nanobelts suffered decomposition under electron beam irradiation during TEM observation and formed MgO with the pristine nanobelt morphology preserved. The formation process of the MHSH nanobelts was studied by tracking the morphology of the MHSH nanobelts during the reaction. A possible chemical reaction mechanism is proposed.     

Effect of some thermally unstable magnesium compounds on the yield of char formed from poly(ethylene terephthalate)

Mixtures of poly(ethylene terephthalate) (PET) with magnesium compounds including carbonate, hydroxide, and oxide, with different weight ratios of the components, were subjected to thermogravimetric measurements up to 850 °C in argon atmosphere. For reference, pure components of the examined mixtures were analyzed at the same conditions. During the heating, PET underwent carbonization and magnesium carbonate and hydroxide decomposed to MgO with evolution of gaseous products (CO₂ and/or H₂O). As found, carbon yields calculated from the residual masses depended on the qualitative and quantitative composition of the starting mixture. Yields of carbon obtained from PET mixed with MgO did not depend on MgO/PET ratio. However, yields of carbon formed through pyrolysis of PET contained in the mixture with either magnesium carbonate or magnesium hydroxide were in general higher and depended on the weight ratio of components in the starting material. Reasons of these inconsistent results are discussed and explained. An influence of gasification of char on the carbon yield is explained.     

X-Ray Diffraction Analysis and Luminescent Study of the Structure of the Tb2(CF3COO)6(H2O)6 Dimer Obtained from Terbium(III) Carbonate

The molecular and crystal structure of the terbium(III) trifluoroacetate trihydrate dimer synthesized from terbium(III) carbonate was studied by X-ray diffraction (XRD) analysis. Luminescent data unambiguously show that the compound is one of the isomers of Tb₂(CF₃COO)₆(H₂O)₆ composition. Evidence has been found for the presence of another isomer in the terbium(III) dimer obtained from terbium(III) hydroxide.     

Effect of production conditions on physicochemical properties of aluminum and magnesium hydroxides

A study has been made of the effect of production conditions on chemical and phase composition, morphological structure, and surface area of aluminum and magnesium hydroxides synthesized in equilibrium and nonequilibrium conditions. Preliminary polycondensation in concentrated solutions of nitrate salts of aluminum and magnesium at different temperatures does not affect the properties of the resulting hydroxides substantially. The determining factors are the conditions of precipitation (pH, temperature and length of aging) and how pH is maintained (variable or constant). Conditions have been established for formation of pseudoboehmite with a particle size of 30 Å, isotropic in all directions, of an amorphous aluminum hydroxide with different composition, and of magnesium hydroxide with particular morphological structures (needles and plates) and surface area.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2169–2176, October, 1989.     

Hydrothermal Synthesis of Porous Al2O3/Al Metal Ceramics: II. Mechanism of Formation of a Porous Al(OH)3/Al Composite

The formation of a porous layer of aluminum hydroxide on the surface of aluminum particles and the aggregation of Al(OH)₃/Al composite particles were analyzed theoretically. It was found that the diffusion mass transfer of the hydroxo complexes of aluminum through the porous structure of a growing layer of aluminum hydroxide to the outer surface is a rate-limiting step in the synthesis of the porous composite. A model mechanism of formation of the porous composite was developed, and rate equations were derived for describing the growth of an aluminum hydroxide layer on the surface of an aluminum particle and changes in the degree of aluminum conversion and the contact radius between composite particles. Based on the developed mathematical model and experimental data, the diffusion coefficient of the hydroxo complexes of aluminum in the porous structure of aluminum hydroxide was calculated.     

Effect of inorganic anions on the morphology and structure of magnesium calcite

Calcium carbonate was precipitated from calcium hydroxide and carbonic acid solutions at 25 degrees C, with and without addition of different magnesium (MgSO(4), Mg(NO(3))(2) and MgCl(2)) and sodium salts (Na(2)SO(4), NaNO(3) and NaCl) of identical anions, in order to study the mode of incorporation of magnesium and inorganic anions and their effect on the morphology of calcite crystals over a range of initial reactant concentrations and limited c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios. The morphology, crystal size distribution, composition, structure, and specific surface area of the precipitated crystals, as well as the mode of cation and anion incorporation into the calcite crystal lattice, were studied by a combination of optical and scanning electron microscopy (SEM), electronic counting, a multiple BET method, thermogravimetry, FT-IR spectroscopy, X-ray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. In the systems of high initial relative supersaturation, precipitation of an amorphous precursor phase preceded the formation of calcite, whereas in those of lower supersaturation calcite was the first and only polymorphic modification of calcium carbonate that appeared in the system. The magnesium content in calcite increased with the magnesium concentration in solution and was correlated with the type of magnesium salt used. Mg incorporation caused the formation of crystals elongated along the calcite c axis and, in some cases, the appearance of new [011] faces. Polycrystalline aggregates were formed when the c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios in solution were increased. Addition of sulfate ions, alone, caused formation of spherical calcite polycrystalline aggregates.     

XPS study of the effect of aluminium on the atmospheric corrosion of the AZ31 magnesium alloy

The surface characteristics and corrosion behaviour of the AZ31 magnesium alloy exposed to a high relative humidity (RH) atmosphere were investigated. During the first 15 days of humidity test at 98% RH and 50 °C, a significant increase of magnesium carbonate and a decrease of magnesium oxide were detected on the surface film by XPS; after this stage, increased exposure times did not produce substantial changes on the relative amounts of these compounds. The surface film of commercially pure magnesium, also examined for comparison purposes, revealed more magnesium carbonate and less magnesium oxide compared with the AZ31 alloy. Unlike the AZ31 alloy, the surface of pure Mg disclosed almost complete substitution of MgO by magnesium carbonate after 30 days of exposure time. Mass gain values of tested specimens and scanning electron microscope characterisation of corroded surfaces indicated lower corrosion susceptibility of the AZ31 alloy compared with the commercially pure Mg, suggesting superior chemical stability of the oxide/hydroxide film formed over the magnesium–aluminium alloy surface. XPS and energy dispersive X‐ray (EDX) analyses did not revealed any substantial enrichment of aluminium in the corrosion products film on the AZ31 alloy after 30 days of testing. Copyright © 2008 John Wiley & Sons, Ltd.     

Colloidal magnesium aluminum hydroxide and heterocoagulation with a clay mineral. II. Heterocoagulation with sodium montmorillonite

Montmorillonite dispersions were completely coagulated ¶by magnesium aluminum hydroxide when the hydroxide mass fraction, χ, was 0.2 or greater. The hydroxide dispersion required only a montmorillonite mass fraction of 0.06 for total coagulation. Thus, heterocoagulates were formed for 0.2<χ<0.94. At an excess of montmorillonite, network formation between the oppositely charged particles led to maxima of the yield value and the storage modulus at 0.4<χ<0.5. At higher hydroxide contents, χ>0.5, both properties decreased steeply, indicating the reduced mechanical stability of the network. Divalent anions at concentrations above 1 mmol/l acted as liquefying agents for the dispersed heterocoagulates. The specific surface area of the freeze-dried dispersions increased to a maximum value at χ = 0.65. The pore size distributions revealed that montmorillonite lamellae and hydroxide particles were not homogeneously distributed.     

Interphase structure development in impact modified PP/Mg(OH)2 composites reactively processed with 1,3‐phenylene dimaleimide

Interphase modification of impact modified isotactic poly(propene) (IMPP)/magnesium hydroxide (Mg(OH)₂) composites, via use of the reactive modifier 1,3 phenylene dimaleimide (BMI) has led to the formation of composites that have strength and toughness more than twice that of the unmodified composite. These significant improvements in properties were found (via response surface analysis, DSC and matrix extraction‐DRIFTS studies) to be due to encapsulation of the filler particles with the elastomeric poly(ethene‐co‐propene) impact modifier phase of the IMPP. Acceptable processing characteristics can be realised together with excellent mechanical properties, via judicious addition of a lubricant (a fatty acid amide/ester blend) to the formulation.     

Carboxyterfenadine antacid interaction monitoring by UV spectrophotometry and RP-HPLC techniques

Carboxyterfenadine, a primary metabolite of terfenadine, a second generation antihistaminic compound was introduced in therapy as a successor of terfenadine due to its cardiac arrhythmia. There are number of drug interactions of fexofenadine with erythromycin, ketoconazole and alike reported in the literature. In this paper, fexofenadine antacid interaction has been studied in presence of sodium bicarbonate, megaldrate, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium trisilicate, simethicone (dimethylpolysiloxane) and calcium hydroxide by UV–Vis spectrophotometer and high performance liquid chromatography (HPLC). These in vitro fexofenadine–antacid interactions were carried out in simulated gastric and intestinal juices and in buffer of pH 7.4 (simulating blood pH) on BP 2005 dissolution apparatus. The results show non-concordant availability of fexofenadine envisaged due to formation of unstable charge transfer complexes.     

Synthesis of size-controlled acid-resistant hybrid calcium carbonate microparticles as templates for fabricating "micelles-enhanced" polyelectrolyte capsules by the LBL technique

Size-controlled, low-dispersed calcium carbonate microparticles were synthesized in the presence of the amphiphilic block copolymer polystyrene-b-poly(acrylic acid) (PS-b-PAA) by modulating the concentration of block copolymer in the reactive system. This type of hybrid microparticles have acid-resistant properties. By investigating the aggregation behaviors of PS-b-PAA micelles by transmission electron microscopy (TEM), the mechanism of hybrid calcium carbonate formation illustrated that the block copolymer served not only as "pseudonuclei" for the growth of calcium carbonate nanocrystals, but also forms the supramicelle congeries, a spherical framework, as templates for calcium carbonate nanocrystal growth into hybrid CaCO(3) particles. Moreover, this pilot study shows that the hybrid microparticle is a novel candidate as a template for fabricating multilayer polyelectrolyte capsules, in which the block copolymer is retained within the capsule interior after core removal under soft conditions. This not only facilitates the encapsulation of special materials, but also provides "micelles-enhanced" polyelectrolyte capsules.     

The Application of Ammonium Hydroxide and Sodium Hydroxide for Reagent Softening of Water

The calcium carbonate crystallization from aqueous solutions in the presence of alkali additives such as sodium hydroxide and ammonium hydroxide has been researched. It is found CaCO₃ crystallizes predominantly in the modification of aragonite in the presence of ammonium hydroxide. The calcium carbonate formation rate in an alkaline medium and the gaseous reaction products due to sorption of gas bubbles on crystal surfaces, affect the aragonite structure formation. It is shown use of ammonium hydroxide for water treatment can solve two urgent tasks such as water softening and exclusion sediment of deposits on the equipment surfaces by a calcium carbonate crystallization in the form of aragonite.     

Study of In Situ Formation of Magnesium Hydroxide Whisker via Basic Magnesium Chloride Whisker Regulated by Organic Parcels at Low Temperature

In this work, we demonstrate an in situ phase conversion from basic magnesium chloride（BMC） into magnesium hydroxide whisker by using polar organic solvent at low temperature. The morphology and phase composition of magnesium hydroxide whiskers prepared at different reaction temperature, alkali concentration and organic solvent were analyzed by X-ray diffraction（XRD） and scanning electronic microscope（SEM）. It was found that when one of the organic solvents such as absolute ethyl alcohol, butanol, polyethylene glycol（PEG-400）, acetone, et al. was selected as the template, the precursor BMC can transform into whisker-like magnesium hydroxide through precipitate transformation in low temperature and non-hydrothermal system. It can be reasonably explained that the regulation of Mg^2＋ solubility by those organic solvents and the sustained release of Mg^2＋ dissolution by organic adsorption played a significant role in the formation of magnesium hydroxide whisker via BMC whisker as the precursor.     

Textural and chemical characterizations of adsorbent prepared from palm shell by potassium hydroxide impregnation at different stages

Preparation and characterization of activated carbon from palm shell, a carbonaceous agricultural solid waste, by potassium hydroxide treatment at different stages were studied. The effects of activation temperature and chemical to sample ratio on the characteristics of the activated carbon were investigated. Fixed-bed adsorption of sulfur dioxide (SO(2)) gas was carried out to evaluate the adsorptive capacity of the samples. Desorption tests were conducted to verify the occurrence of chemisorption due to some surface functional groups or of chemical reaction between SO(2) and KOH. It was found that pre-impregnation of raw palm shell was involved in replacement of some hydrogen ions with potassium ions to form cross-linked complexes, which retarded the tar formation during carbonization, resulting in a relatively high yield. Moreover, these potassium ions accelerated the reaction as catalysts during gasification of chars by carbon dioxide. For chars with mid-impregnation, potassium hydroxide acted in two ways: (i) formation of metallic potassium by dehydration and (ii) conversion into potassium carbonate. Metallic potassium intercalated to the carbon matrix accounted for pore development and potassium carbonate layer prevented the sample from over burn-off. Post-impregnation of final products modified the textural characteristics of the sample as some pore entrances were blocked by chemicals. However, potassium hydroxide enhanced the amount of SO(2) uptaken via formation of potassium sulfite.     

Single-crystal structure of the 2H-related perovskites (A(3-x)Nax)NaBO6 (A = La, Pr, Nd; B = Rh, Pt)

Single crystals of La(2.47)Na(1.53)RhO6, Pr(2.45)Na(1.55)RhO6, Nd(2.45)Na(1.55)RhO6, La2Na2PtO6, and Nd2Na2PtO6 were grown from carbonate and "wet" hydroxide fluxes. All were found to crystallize in the trigonal space group R3c and adopt the K4CdCl6 structure.