Magnesium Hydroxycarbonate Research Articles

Effect of Al and Ca Elements on the Atmospheric Corrosion of Field-Exposed Mg–Al–Zn–Ca–Mn Magnesium Alloys

Three different extruded Mg–Al–Zn–Ca–Mn magnesium alloys with varying alloying elements and a diecast AZ91D alloy were exposed to two coastal environments for five years. Under unsheltered exposure, Mg–Al type layered double hydroxide was primarily formed, and the mass loss corrosion rate was decreased with increasing Al content in the alloys. Under sheltered exposure, magnesium hydroxy carbonate was the main corrosion product. Additionally, Mg alloys with high Al content tended to exhibit localized corrosion. Furthermore, the negative impact of Ca addition on atmospheric corrosion occurred when the alloys were exposed under sheltered conditions.

New frontiers in sustainable cements: Improving the performance of carbonated reactive MgO concrete via microbial carbonation process

The low conversion of reactive MgO cement (RMC) into hydrated magnesium hydroxy carbonates (HMHCs) due to limited CO2 diffusion towards the sample core leads to inefficient RMC use and low strength development in RMC concrete. This study proposed a novel technique to enhance hydration and carbonation at both the exterior and core sections of RMC concrete via a synergistic combination of microbial carbonation process (MCP) with nucleation seeding (S). The production of CO32− ions via the introduction of urease-producing bacteria to catalyze the hydrolysis of urea enabled self-carbonation of RMC, leading to the formation of HMHCs under ambient conditions. Improvements in CO2 dissolution and formation of brucite with a low crystallinity further stimulated HMHC formation under accelerated carbonation conditions. The simultaneous use of MCP and S resulted in dense microstructures composed of HMHCs with improved morphologies, translating into strengths that were >3 times of the control (62 vs 20 MPa).

Use of microbial carbonation process to enable self‑carbonation of reactive MgO cement mixes

The low hydration and carbonation of reactive MgO cement (RMC) under ambient conditions causes prolonged setting and low compressive strengths (~4 MPa). This study proposed a unique technique which led to the enhancement of the hydration and carbonation processes via the synergistic combination of microbial carbonation process (MCP) with a hydration agent (HA) that enabled the self‑carbonation of RMC-based mixes without using of any special curing environments. Through hydrolysing urea (CO(NH2)2) using ureolytic bacteria, CO32− ions were produced to facilitate the carbonation of dissolved Mg2+ ions to form hydrated magnesium hydroxy carbonates (HMHCs). The self‑carbonation of RMC enabled by the MCP resulted in formation of brucite with a poor crystallinity and its rapid conversion into HMHCs, which improved the setting time and compressive strength of RMC-based samples. The simultaneous use of MCP with 2 M urea and HA revealed HMHCs with improved morphologies, resulting in the highest compressive strength (~15 MPa).

Electrical resistivity and thermopower of hole-doped delafossite CuCoO2 polycrystals

We have synthesized the polycrystalline samples of the delafossite oxide CuCo1−y Mg y O2 through the thermal decomposition of copper–cobalt–magnesium hydroxycarbonates. As is expected from the theoretical calculations, relatively large thermopower of S ∼ 700 μV K−1 is observed at room temperature in the parent compound CuCoO2, whereas the resistivity is too high even in the doped compounds compared with other thermoelectric oxides. The high-temperature transport is thermal-activation type characterized by two energy gaps, Δ ρ and Δ S , which are estimated from the resistivity and the thermopower, respectively. In the parent compound, we obtain Δ ρ ≃ 0.47 eV and Δ S ≃ 0.38 eV. We find that Δ ρ is larger than Δ S in all the samples, implying a mobility gap opening due to a grain-boundary scattering.

On the early stages of localised atmospheric corrosion of magnesium\u2013aluminium alloys

The surface film on pure magnesium and two aluminium-containing magnesium alloys was characterised after 96 h at 95% RH and 22 °C. The concentration of CO2 was carefully controlled to be either 0 or 400 ppm. The exposed samples were investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and electron microscopy. The results showed that when the alloys were exposed to the CO2-containing environment, aluminium cations (Al3+) was incorporated into a layered surface film comprising a partially “hydrated” MgO layer followed by Mg(OH)2, and magnesium hydroxy carbonates. The results indicated that aluminium-containing magnesium alloys exhibited considerably less localised corrosion in humid air than pure magnesium. Localised corrosion in the materials under investigation was attributed to film thinning by a dissolution/precipitation mechanism.

Localized Atmospheric Corrosion of Magnesium-Aluminum Alloys Produced by Semisolid Casting: A 2D and 3D Investigation

The localized corrosion of the two magnesium-aluminum alloys AM50 and AZ91 produced by a semisolid casting method was investigated under atmospheric corrosion conditions, in the presence of NaCl. Gravimetry confirmed the beneficial effect from ambient levels of carbon dioxide (CO2) in suppressing corrosion through the formation of magnesium hydroxy carbonates. Both 2D and 3D characterization revealed that ambient CO2 has a strong influence on the morphology and rate of localized corrosion. In CO2-free atmosphere, the alloys suffered localized corrosion resulting in clustered and interconnected cavities that extended deep into the material. In contrast, corrosion in the presence of ambient levels of CO2 (400 ppm) resulted in evenly distributed shallow corrosion sites. The results indicate that CO2 neutralizes the cathodic areas resulting in diminished cathodic activity and inhibiting NaCl(aq) droplet coalescence.

Effect of molten sodium nitrate on the decomposition pathways of hydrated magnesium hydroxycarbonate to magnesium oxide probed by in situ total scattering

Effect of molten sodium nitrate on the decomposition pathways of hydrated magnesium hydroxycarbonate to magnesium oxide probed by in situ total scattering

Chemical precipitation of heavy metals from wastewater by using the synthetical magnesium hydroxy carbonate.

Heavy metal pollution has become one of the most serious environmental problems today. The preparation of magnesium hydroxy carbonate from low-grade magnesite, and the chemical precipitation of heavy metal wastewater with magnesium hydroxy carbonate as precipitating agent were undertaken. The removal efficiencies of heavy metals were improved by increasing the dose of magnesium hydroxy carbonate, and the applicable dose of magnesium hydroxy carbonate was 0.30 g for 50 mL of the wastewater (6,000 mg/L). The precipitation reactions proceeded thoroughly within 20 min. At this time, the removal efficiencies of heavy metals were above 99.9%. The final pH value was 7.1, the residual VO2 +, Cr3+ and Fe3+ concentrations were 0.01, 0.05 and 1.12 mg/L, respectively, which conformed to the limit of discharge set by China (0.5-2.0 mg/L, GB 8978-1996). The precipitate was mainly composed of Fe2O3, V2O5 and Cr2O3, which can be recycled as secondary raw material for metallurgical industry. The treatment of the heavy metal wastewater with magnesium hydroxy carbonate was successful in decreasing the concentrations of VO2 +, Cr3+ and Fe3+ in wastewater.

РАЗРАБОТКА СОСТАВА И ТЕХНОЛОГИИ ТАБЛЕТОК, ПОКРЫТЫХ ОБОЛОЧКОЙ, С ЭКСТРАКТОМ RHEUM CORDATUM LOSINSK

Objective: Development of a rational composition, optimal technology, standardization criteria for tablets with Rheum cordatum extract, establishing the stability of the composition and storage conditions. Methods: As an active pharmaceutical substance, a standardized extract of Rheum cordatum was used. Pharmacopoeial excipients for the production of tablet mass are magnesium hydroxycarbonate, croscarmellose sodium, microcrystalline cellulose, Plasdone S-630, magnesium aluminum metasilicate, calcium stearate, purified water and film coating Opadry 85F18422 White. To obtain tablets qualified equipment was used in the technological process: a tablet mass mixer, a rotary tablet press, highly efficient film coating equipment, a packaging machine / blister machine. When developing the tablets, we were guided by the «Quality by design» concept of medicines, based on ICH guidelines: ICH Q11 «Development and manufacture of medicinal substances», ICH Q8 «Pharmaceutical Development» and ICH Q10 «Pharmaceutical Quality System». Standard pharmacopoeial research methods were used. Results: 50 experimental mass models for tableting have been developed in the variants of combining excipients and active substance in an effective single dose of 300 mg. Only 4 models of the core tablets obtained met the selection criteria (abrasion, crush resistance, disintegration, and dissolution). The optimal tableting method using wet granulation is substantiated, which makes it possible to obtain tablets of the proper pharmacopoeial quality and the following composition: soft rhubarb root extract, magnesium hydroxycarbonate, croscarmellose sodium, microcrystalline cellulose 102, Plasdone S-630, magnesium aluminum metasilicate, calcium stearate. To coat the obtained tablet cores, the following film coating composition was selected: Opadry 85F18422 White, consisting of polyvinyl alcohol, titanium dioxide E 171, macrogol 4000 and talc. Conclusions: The pharmaceutical development of coated tablets with an extract of Rheum cordatum has been done. The rational composition and optimal technology for producing tablet cores coated with a film coating of Opadry 85F18422 White were established. The quality of the obtained tablets was evaluated, the stability of the composition for 9 months was studied, the results of quality indicators are within acceptable standards, and research in this direction is going on. Keywords: Extract, coated tablets, pharmaceutical development, composition, technology, stability.

Effect of molten sodium nitrate on the decomposition pathways of hydrated magnesium hydroxycarbonate to magnesium oxide probed by in situ total scattering.

The effect of NaNO3 and its physical state on the thermal decomposition pathways of hydrated magnesium hydroxycarbonate (hydromagnesite, HM) towards MgO was examined by in situ total scattering. Pair distribution function (PDF) analysis of these data allowed us to probe the structural evolution of pristine and NaNO3-promoted HM. A multivariate curve resolution alternating least squares (MCR-ALS) analysis identified the intermediate phases and their evolution upon the decomposition of both precursors to MgO. The total scattering results are discussed in relation with thermogravimetric measurements coupled with off-gas analysis. MgO is obtained from pristine HM (N2, 10 °C min-1) through an amorphous magnesium carbonate intermediate (AMC), formed after the partial removal of water of crystallization from HM. The decomposition continues via a gradual release of water (due to dehydration and dehydroxylation) and, in the last step, via decarbonation, leading to crystalline MgO. The presence of molten NaNO3 alters the decomposition pathways of HM, proceeding now through AMC and crystalline MgCO3. These results demonstrate that molten NaNO3 facilitates the release of water (from both water of crystallization and through dehydroxylation) and decarbonation, and promotes the crystallization of MgCO3 and MgO in comparison to pristine HM. MgO formed from the pristine HM precursor shows a smaller average crystallite size than NaNO3-promoted HM and preserves the initial nano-plate-like morphology of HM. NaNO3-promoted HM was decomposed to MgO that is characterized by a larger average crystallite size and irregular morphology. Additionally, in situ SEM allowed visualization of the morphological evolution of HM promoted with NaNO3 at a micrometre scale.

Assessment of the Total Volume Membrane Charge Density through Mathematical Modeling for Separation of Succinic Acid Aqueous Solutions on Ceramic Nanofiltration Membrane

Nanofiltration of aqueous solutions of succinic acid with the addition of sodium hydroxide or magnesium hydroxycarbonate has been investigated experimentally and modeled with the comprehensively described Donnan–Steric partitioning model. The experimental retentions of acid at the same pH varied between 16% and 78%, while the estimated total volume membrane charge densities were in the range of −35.73 and +875.69 mol/m3. This work presents a novel insight into the modeling of nanofiltration and investigates the relations between the estimated total volume membrane charge densities, ionic strength, and component concentration on the performance of ceramic membrane. In addition, this study takes into consideration other parameters such as pH regulation and viscosities of solutions.

Characterization and Structure⁻Property Relationships of Organic⁻Inorganic Hybrid Composites Based on Aluminum⁻Magnesium Hydroxycarbonate and Azo Chromophore.

In this study, novel organic–inorganic composites were prepared by the complexation of dicarboxylic azo dye (AD) with aluminum–magnesium hydroxycarbonate (AlMg–LH). This procedure provides an effective method for the stabilization of dicarboxylic organic chromophores on an AlMg−LH host. The structures of the hybrid composites were examined by X-ray diffraction (XRD), secondary ion mass spectrometry (TOF-SIMS), 27-Al solid-state nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA) and scanning transmission electron microscopy (STEM). The TOF-SIMS method was applied to investigate the metal–dye interactions and to monitor the thermal stability of the organic–inorganic complexes. Secondary ion mass spectrometry confirmed the presence of a characteristic peak for C18H10O5N2Mg22+, indicating that both carboxylic groups interacted with AlMg−LH by forming complexes with two Mg2+ ions. Modification with hybrid pigments affected the crystal structure of the AlMg−LH mineral, as shown by the appearance of new peaks on the X-ray diffraction patterns. Adsorption of the dicarboxylic chromophore not only led to significantly enhanced solvent resistance but also improved the thermal and photostability of the hybrid pigments. We propose a possible arrangement of the azo dye in the inorganic matrix, as well as the presumed mechanism of stabilization.

Corrosion behavior of AZ31 magnesium alloy in the chloride solution containing ammonium nitrate

Corrosion behavior of AZ31 magnesium alloy in NH4NO3-containing chloride solution was investigated by immersion tests, hydrogen evolution collection, electrochemical measurements, and microscopic observation. Addition of NH4NO3 accelerates corrosion due to the deterioration of Mg(OH)2 by NH4+ and the promotion of cathodic NO3− reaction, which is supported by the buffering effect of NH4+. Hydrogen evolution is suppressed with addition of high concentrations of NH4NO3, attributed to the preferential occurrence of NO3− reduction. Loose and cracked corrosion products, which are mainly composed of Mg2(OH)3Cl·4H2O and magnesium hydroxy carbonates, form in the NH4NO3-containing environment. When the NH4NO3 concentration is between 0.005 and 0.03 M, autocatalytic pitting corrosion occurs due to the synergistic effects of Cl−, NH4+, and NO3− at the specific concentration range. The H+ (supplied by NH4+ hydrolysis), Cl− in combination with the depolarization effect of NO3− support the autocatalytic growth and eventually perforate the alloy. With the addition of NH4NO3 higher than 0.05 M, corrosion pits with shallow-dish shape form initially and then evolves into general corrosion, because general corrosion is promoted by the decrease of solution pH, suppression of Mg(OH)2 precipitation, and enhancement of cathodic reactions.

Sequestering CO2 by Mineralization into Useful Nesquehonite-Based Products

The precipitation of magnesium hydroxy-carbonate hydrates has been suggested as a route to sequester CO2 into solids. We report the development of self-cementing compositions based on nesquehonite, MgCO3·3H2O, that are made from CO2-containing gas streams, the CO2 being separated from other gases by its high solubility in alkaline water, while magnesium is typically provided by waste desalination brines. Precipitation conditions are adjusted to optimize the formation of nesquehonite and the crystalline solid can readily be washed free of chloride. Products can be prepared to achieve self-cementation following two routes: (i) thermal activation of the nesquehonite then rehydration of the precursor or (ii) direct curing of a slurry of nesquehonite. The products thus obtained contain ~ 30 wt% CO2 and could form the basis for a new generation of lightweight, thermally insulating boards, blocks and panels, with sufficient strength for general construction.

Influence of temperature on the atmospheric corrosion of the Mg–Al alloy AM50

The effect of temperature on the NaCl-induced atmospheric corrosion of the Mg–Al alloy AM50 has been investigated in the laboratory. The corroded samples were analyzed gravimetrically and by SEM, EDX, XRD, and FTIR. The atmospheric corrosion of 99.97% Mg was also studied for reference. While the NaCl-induced atmospheric corrosion of AM50 is strongly reduced with decreasing temperature, 99.97% Mg does not exhibit such a trend. The temperature dependence of the atmospheric corrosion of alloy AM50 is attributed to the aluminum content in the alloy. Several crystalline magnesium hydroxy carbonates formed at 4 and 22°C but were absent at −4°C.

Initial formation of corrosion products on pure zinc and MgZn2 examinated by XPS

A corrosion behaviour study of pure phases of zinc and zinc–magnesium (MgZn2) exposed to humid air at 35°C for 4days is presented. For zinc, hydroxide formation at the surface and zinc oxide in the first innerlayers is observed. The corrosion of the MgZn2 leads to the segregation of magnesium at the surface to mainly form magnesium hydroxycarbonate: the presence of magnesium modifies the corrosion products. At larger depths, metallic zinc coexists with magnesium oxide and hydrozincite. The higher reactivity of MgZn2 alloy can be attributed to the interaction with carbonate ions.

Formation of colloidal assemblies in suspensions for Pb(Mg1/3Nb2/3)O3 synthesis: Monte Carlo simulation study

We study numerically the aggregation processes with three types of charged colloidal particles, PbO–lead oxide, MHC–magnesium hydroxy carbonate, and Nb2O5–niobium oxide, interacting in the aqueous suspensions for Pb(Mg1/3Nb2/3)O3 ceramic synthesis. Using the Monte Carlo simulations we focus on the kinetics and structure of various types of precursor clusters that may form at different pH conditions. The parameters of the interaction potentials and the particle sizes are taken to closely correspond to the experimental situations in [Trefalt et al., J. Am. Ceram. Soc., DOI: 10.1111/j.1551-2916.2011.04443.x, 2011], where it was shown that the pyrochlore phase, which deteriorates the electrical properties of the Pb(Mg1/3Nb2/3)O3 ceramics, results from the suspension with pH = 11.4, while the pure perovskite powder is formed when pH = 12.5. Our simulations reveal a large population of clusters with close contacts between PbO and Nb2O5 at pH = 11.4, which thus enable the pyroclore phase to form. Whereas, at pH = 12.5 the competition between the repulsive and the attractive interactions changes in favor of the assembly of the equilibrium clusters in which MHC particles effectively separate PbO and Nb2O5. We also explore how the varying size of MHC particles affects the cluster assembly at both experimentally relevant pH conditions.

Iron-Magnesium Hydroxycarbonate (Fermagate)

This phase II study tested the safety and efficacy of fermagate, a calcium-free iron and magnesium hydroxycarbonate binder, for treating hyperphosphatemia in hemodialysis patients. A randomized, double-blind, three-arm, parallel-group study compared two doses of fermagate (1 g three times daily or 2 g three times daily with placebo). Sixty-three patients who had been on a stable hemodialysis regimen for > or =3 mo were randomized to the treatment phase. Study medication was administered three times daily just before meals for 21 d. The primary endpoint was reduction in serum phosphate over this period. In the intention-to-treat analysis, mean baseline serum phosphate was 2.16 mmol/L. The fermagate 1- and 2-g three-times-daily treatment arms were associated with statistical reductions in mean serum phosphate to 1.71 and 1.47 mmol/L, respectively. Adverse event (AE) incidence in the 1-g fermagate arm was statistically comparable to the placebo group. The 2-g arm was associated with a statistically higher number of patients reporting AEs than the 1-g arm, particularly gastrointestinal AEs, as well as a higher number of discontinuations, complicating interpretation of this dose's efficacy. Both doses were associated with elevations of prehemodialysis serum magnesium levels. The efficacy and tolerability of fermagate were dose dependent. Fermagate showed promising efficacy in the treatment of hyperphosphatemia in chronic hemodialysis patients as compared with placebo in this initial phase II study. The optimal balance between efficacy and tolerability needs to be determined from future dose-titration studies, or fixed-dose comparisons of more doses.

Structural, physical and mechanical properties of modified wood–magnesia composite

The results of research about the structural, physical and mechanical properties of wood–magnesia composites based on magnesium binder (caustic magnesia) and filler of wood sawdust modified with chemical industry waste fluorine anhydrite (fluoranhydrite) are described. It was found that during the hydration of caustic magnesia containing fluorine anhydrite additive in composition with magnesium chloride, magnesium oxychlorides with different morphologies are formed depending on the initial components. The structure examination after 9 years of products maintenance showed the intensive carbonization of caustic magnesia hydration products with the formation of magnesium hydroxycarbonates that caused the increase of the material density, strength, water resistance and decrease of the wood–magnesia constructional beam creeping deformations.

Study of montmorillonite and cationic activators sistem rheological characteristic change mechanism

The aim of this work is to examine changes of the montmorillonite mineral rheological characteristics during its activation with sodium carbonate and magnesium hydroxy carbonate. In order to foresee the mechanism of these processes, it was necessary to study the following: • The change of the rheological characteristics of the investigated system, i.e. viscosity and thixotropy, with respect to the initial montmorillonite and water system, • structural changes caused by migration of Al 3+ ions from the octaedric positions into the interlamellar region, by using the structural analysis methods and by monitoring the cation exchange capacity increase during the activation of this mineral, • formation of the new anionic clay types, as well as their synthesis and structure in an independent system and • formation and emergence of new structures during particle interaction, during which various products are created, in the form of “card house”, “band type”, “networked band type” or connected by a “latching” mechanism. The changes in rheological characteristics has been studied for the montmorillonite obtained from “Jelenkovac” bentonite by separating fractions smaller than 2 μm, with Ca 2+ and Mg 2+ mostly being the exchangeable cations.