Ammonium Phosphate Solution Research Articles

Electrochemical Recovery of N and P from Municipal Wastewater

Phosphorus, P, is a vital element of paramount importance for both humans and for the Environment. Wastewater contains often relatively high concentrations of P which can be recovered as crystalline struvite (MgNH4PO4·6H2O, MAP). This option is quite attractive in assisting sustainable development because struvite can be used as a slow-release fertilizer. Domestic wastewater is usually high in P and nitrogen, N, but relatively poor in magnesium, Mg. It is necessary to develop low-cost solutions for the enrichment of wastewater with Mg. In the present work, sacrificial magnesium anodes were used, which dissolve upon anodic polarization, releasing sufficient magnesium for the selective precipitation of MAP. The application of constant current between two electrodes of which the anode is a low-cost magnesium cylindrical rod (4 cm2 exposed surface area) and the other a platinum cathode electrode, both immersed in ammonium phosphate solutions, without adjustment of the solution pH, was investigated. Constant current density over the range 10–100 A·m−2, between the Mg- Pt electrodes immersed in solutions of ammonium hydrogen phosphate of exactly known initial concentration, was applied using a potentiostat. In the presence of sodium chloride solutions, on the magnesium anode and in the bulk solution, Mg(OH)2 (brucite) formed because of the passivation of the Mg electrode. In dilute ammonium hydrogen phosphate solutions, the magnesium anode dissolution resulted in struvite precipitation, even at a low applied current (10 mA). Struvite crystals with an average size of 20 μm were precipitated. The behavior of the cell for the electrolyte solutions used was Faradaic as long as the surface coverage of the anode was relatively low. The anodic dissolution of Mg resulted in high pH values (pH 11) eliminating the need for alkali addition.

Synchrotron small-angle X-ray scattering study of flame retardants based on ammonium sulfate and disubstituted ammonium phosphate

The use of wood in structural and finishing materials can significantly reduce the time of building construction, but the high flammability of wood limits its use in the building industry. To increase fire resistance, wooden structures are impregnated with flame retardants and the penetrating ability depends on their structure. We present the results of a small-angle X-ray scattering study of the structure of flame retardants based on ammonium sulfate and phosphate. The radii of inertia of hydrated complexes formed when flame retardants are dissolved in water, their shape and type of chains along which hydrated ions are located are determined. It is revealed that the presence of diffraction maxima indicates the presence of an ordering in the arrangement of hydrated ions. Aqueous solutions of ammonium sulfate and disubstituted ammonium phosphate contain two types of hydrated complexes of the same shape but different radius of inertia. At the same time, hydrated ions in complexes are located along persistent chains, and ordering revealed in the arrangement of ions, depended on their type. The results obtained can be used in developing flame retardants with a reduced radius of inertia, which will increase the penetrating capacity of the processing solution and increase the fire safety of wooden structures.

Preparation of Calcite-Precipitating Bacteria-Embedded Magnesium Phosphate Cement for Self-Healing Application

The present study was undertaken to check the feasibility of magnesium phosphate cement (MPC) for the immobilization of calcite-precipitating bacteria. An aqueous route of MPC synthesis was followed using magnesium phosphate Mg3(PO4)2 powder and ammonium phosphate solution. The Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis confirmed the synthesis of MPC. The thermal decomposition analysis (TGA) showed decomposition of struvite between 50–60 °C - Paenibacillus sp. NCIM 5410 was used due to its urea hydrolysis ability. pH 9 was found to be optimum for urea hydrolysis. The urea hydrolysis steadily decreased with an increase in temperature from 30 °C to 60 °C. The hydrolysis was seen to increase with an incubation time of up to 72 h and subsequently reduced. The bacteria showed 90% urea hydrolysis at pH 9, 30 °C temperature, and after 72 h. The bacterial spores were incorporated during MPC synthesis, which helped their immobilization. The bacterial spore-containing MPC decomposed around 70 (±0.48)% of urea. Further, calcite precipitation was studied. The precipitate formed due to bacterial action in the MPC crack showed the presence of calcium. The calcite precipitation helped to reduce the water absorption by MPC specimens. The spore containing MPC specimens showed around 2.62 (±0.55) % water absorption. These results suggest that it is possible to synthesize bioactive MPC by immobilizing bacterial spores in MPC.

Microstructural changes in building materials after various consolidation treatments studied by small-angle neutron scattering, mercury intrusion porosimetry and scanning electron microscopy

Stone or rendered facades of historical buildings often encounter loss of cohesion after long-term weathering. Specialist consolidating agents containing nanoparticles which can penetrate the degraded layer are used to extend the lifetime of such facades. Clay mortar prepared in the laboratory was used in the present study as a material for testing the effectiveness of several consolidating agents. Changes in porosity after treatment of the sample layers were assessed using small-angle neutron scattering, mercury intrusion porosimetry and scanning electron microscopy techniques. The scattering differed for the various samples, mainly in the medium range of scattering vector magnitudes. The cause of the scattering was ascribed to three populations of pores: large (micrometres), medium-sized (thousands of ångströms) and small (hundreds of ångströms). While the non-treated sample and the sample treated with a silicic acid ester-based product do not exhibit significant differences, the sample treated with a nano-lime suspension shows a decrease of 16% in the volume fraction of medium-sized pores. A difference was also observed in the sample treated with a dihydrogen ammonium phosphate solution: the size of the medium pores increased while their volume fraction decreased, and a change in the large pores was observed. The modelled small pores remained unaffected by the consolidating treatment.

Electrochemical recovery of phosphate from synthetic wastewater with enhanced salinity

Electrochemical recovery of phosphorus from synthetic wastewater using a sacrificial Mg anode has been explored as a function of key parameters, including pH, voltage, and salinity. The effect of chloride (NaCl) concentrations in the range of 0–1500 mM on both Mg corrosion and phosphate precipitation was investigated in acidic and alkaline (i.e., pH 4 and 8) solutions of dihydrogen ammonium phosphate. The primary phosphate precipitate was expected to be struvite (MgNH4PO4·6H2O), and collected precipitates were characterized to determine composition and phase. Batch experiments were run at selected potentials identified by linear sweep voltammetry experiments. Higher corrosion current densities (jcorr), which indicated higher Mg dissolution and corrosion rates (υcorr), were achieved in solutions with higher pH and salt concentrations. Both Mg corrosion and phosphate recovery were proportional to [Cl−], so 1500 mM Cl− at pH 8 resulted in increased Mg dissolution and phosphate recovery by ∼5x and 2x, respectively, compared to the solution without chloride. Elemental composition analysis (ion chromatography), crystallography (X-ray diffraction), surface chemical composition analysis (Fourier-transform infrared spectrometry) and characterization (scanning electron microscopy images) of precipitates suggested the presence of struvite. The Mg/P composition of precipitates formed in 1000 mM Cl− solution showed a greater extent of deviation from the theoretical molar ratio in struvite when the electrochemical cell was operated at more positive anodic overpotential and low initial solution pH. The elevated Mg/P ratio could indicate the presence of mixed precipitates. Simulation of product distribution analysis and specific energy requirement results suggest optimum electrochemical struvite production in the pH range of 8–10 in the presence of chloride.

Extrusion-Based 3D Printing of Calcium Magnesium Phosphate Cement Pastes for Degradable Bone Implants.

This study aimed to develop printable calcium magnesium phosphate pastes that harden by immersion in ammonium phosphate solution post-printing. Besides the main mineral compound, biocompatible ceramic, magnesium oxide and hydroxypropylmethylcellulose (HPMC) were the crucial components. Two pastes with different powder to liquid ratios of 1.35 g/mL and 1.93 g/mL were characterized regarding their rheological properties. Here, ageing over the course of 24 h showed an increase in viscosity and extrusion force, which was attributed to structural changes in HPMC as well as the formation of magnesium hydroxide by hydration of MgO. The pastes enabled printing of porous scaffolds with good dimensional stability and enabled a setting reaction to struvite when immersed in ammonium phosphate solution. Mechanical performance under compression was approx. 8–20 MPa as a monolithic structure and 1.6–3.0 MPa for printed macroporous scaffolds, depending on parameters such as powder to liquid ratio, ageing time, strand thickness and distance.

Charring depth and charring rate of cross-laminated bamboo slabs exposed to a one-sided standard fire

In recent years, inspired by cross-laminated timber (CLT), cross-laminated bamboo (CLB) has been proposed to promote the development of high-rise bamboo structures. To better understand the charring properties of CLB, three groups of CLB slabs treated with different fire-resistant methods, including no treatment, painting fire-retardant coatings and impregnating flame retardants, were exposed to fire on one side with furnace temperatures following the requirements of ISO 834-1. The test results indicated that under the same fire-exposure duration, the charring degree of the CLB slabs treated with different fire-resistant methods showed a decreasing order as follows: no fire-resistant treatment > impregnating a monobasic ammonium phosphate (MAP) solution > painting fire-retardant coatings. A modified theoretical calculation method (time-location model) was proposed to calculate the charring depth considering the difference in the average charring rates between layers in which the grain direction is parallel or perpendicular to the major longitudinal direction. Furthermore, the temperature versus fire-exposure duration curves were divided into four stages: a slow rising stage, a platform stage, a rapid rising stage and a furnace temperature stage. A modified temperature profile model was proposed and was applicable for the temperature prediction of CLB slabs.

Ammonium-to-sodium ion-exchange process at the interlayer of octacalcium phosphate.

Octacalcium phosphate (OCP) has been considered as the layer component of calcium phosphate, but whether it achieves the ionic-exchange ability of conventional layer components is unclear. As OCP is highly biocompatible, understanding its ionic-exchange properties would potentially expand its pharmaceutical and medical applications. Herein, we demonstrate that the substituted cations in ammonium (NH4)-substituted octacalcium phosphate (OCP-NH4) and sodium (Na)-containing ammonium phosphate solutions undergo ion exchanges with OCP interlayers. Replacing NH4+ with Na+ did not alter the crystal structure of OCP, confirming that a substituted cation exchange process similar to that in other layered compounds occurs in OCP.

Electrochemical Synthesis of Struvite from Wastewater: Implications of Chloride Ion and Initial pH

Electrochemical precipitation of magnesium ammonium phosphate (MAP) compounds, specifically as struvite (NH4MgPO4.6H2O) from wastewater is gaining importance as one of the techno-economically feasible pathways of sustainable development [1]. However, systematic exploration of the optimal range of anode potential for maximizing phosphate recovery under varied parametric conditions of pH and ion concentrations, other than NH4 + and PO4 3- has not been attempted so far. Additionally, ion dissolution from sacrificial magnesium anode over stipulated potential range between pitting and secondary passivation needs to be investigated for maximum struvite production with minimal consumption of magnesium. In this study, we have characterized the role of initial pH (4 and 8) and chloride ion concentration (1 M) on phosphate recovery and magnesium dissolution by conducting batch electrochemical experiments with three different anode potentials covering the entire range of feasible potential window. Linear Sweep Voltammetry (LSV) was performed at two different initial pHs to identify the aforementioned potential range. Subsequently, batch experiments at different anode potentials were conducted in an electrochemical cell consisting of pure magnesium sheet as sacrificial anode and stainless steel cathode. 77 mM solution of dihydrogen ammonium phosphate (NH4H2PO4) and 1M sodium chloride was used as electrolyte. Lower value of Pitting potential in presence of chloride ions with respect to that with baseline NH4H2PO4 solution was indicative of the favorable effect of chloride in rupturing the passive layer of magnesium hydroxide that normally forms on anode surface and hinders magnesium dissolution. Higher magnesium dissolution rate and phosphate recovery were recorded above and over respective pitting potentials for both pHs. Moreover, monotonic increasing profiles of precipitate masses with increasing anode potential unambiguously indicates higher dissolution of magnesium with as alternatively reflected in terms of elevated charge transfer as per Faraday’s law. In both cases of different initial pHs, final pH was recorded in alkaline range. Nevertheless, ammonia loss was observed to increase with anode potentials and increasing pH. Precipitates, formed at the surface of anode and in bulk solution, on characterization revealed the presence of several MAP and other magnesium phosphate precipitates including Struvite (MgNH4PO4.6H2O), Dittmarite (MgNH4PO4.H2O), Magnesium phosphate tribasic (Mg3(PO4)2) and Newberyite (MgHPO4.3H2O). Magnesium hydroxide was detected at higher pH. Simulation of saturation indices and product distribution using Visual Minteq 3.1 predicted optimal recovery of Struvite (MgNH4PO4.6H2O) in the pH range 8-10. Reference: [1] Cid, C. A.; Jasper, J. T.; Hoffmann, M. R., Phosphate Recovery from Human Waste via the Formation of Hydroxyapatite during Electrochemical Wastewater Treatment. ACS Sustainable Chem. Eng. 2018, 6 (3), 3135-3142.

Optimal Anode Potential Range for Electrochemical Synthesis of Struvite from Wastewater

Electrochemical recovery of phosphorous and nitrogen from wastewater as struvite (NH4MgPO4.6H2O) is progressively gaining importance as one of the innumerable pathways of sustainable development. However, the optimal range of anode potential that maximizes struvite purity under varied parametric conditions of pH and ion concentrations other than NH4 +and PO4 -3 has not been methodically explored so far. Additionally, corrosion behavior of a sacrificial magnesium anode under an anode potential range needs to be investigated because according to techno-economic feasibility criterion, it is advantageous to produce struvite with minimal consumption of magnesium. In this study, we will report on the effects of pH (4 and 8) and chloride ion concentration (0.1 M to 1 M) on struvite production and magnesium dissolution rates through performing a systematic investigation using Linear Sweep Voltammetry (LSV) and Potentiodynamic Polarization (PDP) techniques. Aqueous solutions of dihydrogen ammonium phosphate with varied chloride ion concentration are used as simulated wastewater. Electrochemical experiments are conducted in batch mode with a sacrificial magnesium anode and a stainless-steel cathode. Furthermore, bulk and electrode surface (both anode and cathode) precipitates are analyzed for elemental composition, crystallinity,and morphological features. The present research outcomes are expected to serve as a baseline protocol to select an optimal anode potential window in electrochemical struvite production from wastewater.

Lime and cement mortar consolidation by ammonium phosphate

The present study investigates the strengthening ability and the compatibility of two different ammonium phosphate solutions used for consolidation of mortars based on slaked lime, natural hydraulic lime or cement, to resemble historic and modern mortars. After impregnation for 24 h, new calcium phosphate phases were detected in all types of mortar. New calcium phosphates induced significant mechanical consolidation, with only slight alterations in the pore system and in water transport properties. In lime-based mortars (initially white) no color alteration was visible after treatment, while colored mortars experienced some color change when the more concentrated phosphate solution was used.

Phase relations in the calcium carbonate/ammonium phosphate system under aqueous conditions and 25°C

AbstractA theoretical and experimental approach was applied to investigate phase relations in a system containing calcium carbonate and different ammonium phosphate solutions. Using laboratory experiments and thermodynamic modeling, this paper provides an insight into the formation of stable phase assemblages in the calcium carbonate and mono‐, di‐, triammonium phosphate aqueous system. Focus is placed on the morphological and mineralogical characterization and thermodynamic calculation of calcium phosphates precipitating due to the reaction between the calcium carbonate and ammonium phosphate solutions. Correlations between the formed stable calcium phosphate phases and the ammonium phosphate precursors are provided. Advantages and limitations of various analytical and modeling techniques used in this study such as geochemical equilibrium‐based modeling, X‐ray diffraction, scanning electron microscopy, and thermal analysis, are critically evaluated. Additionally, possible impacts of the ammonium phosphate solution type on the kinetics of phase transformations are discussed.

Pilot-scale demonstration of nitrogen recovery in the form of ammonium phosphate (AP) from anaerobic digestate

Nitrogen in anaerobic digestate was recovered as ammonium phosphates (APs), a valuable fertilizer, in a pilot-scale system consisting of ammonia stripper, absorber and crystallizer. The dissolved ammonium concentration in the anaerobic digestate was stripped and then absorbed into the phosphoric acid (42.5 wt%) with 95% absorbing efficiency. As the NH3 stripping continued, both the N/P ratio and pH, key operating parameters in the absorber are optimized N/P = 0.6 and pH = 1.7. The residual AP solution after crystallization was reused to enhance the crystallization efficiency up to 88%. The overall recovery efficiency of APs was estimated at 72% of the input nitrogen mass. Analyses of SEM and XRD revealed that the recovered AP crystals were mainly composed of mono-ammonium phosphate (MAP). This pilot-scale study demonstrated that nitrogen load in anaerobic digestates could be effectively recovered as a valuable fertilizer source of AP crystals.

Influence of calcium and aluminum on crystallization of vivianite, [formula omitted

The iron(II) phosphate vivianite, Fe3(PO4)2·8H2O, has been precipitated at 37 °C from solution of ammonium iron(II) sulfate (Mohr’s salt) and ammonium phosphate, to which a small amount of calcium nitrate or aluminum potassium sulfate (alum) was added. The relatively high temperature was chosen to minimize the formation of crystal aggregates, which would otherwise complicate study of morphology. Crystallization kinetics was determined by pH recording, and the resulting crystals were studied by polarization microscopy. The main effect of Al observed was formation of small, irregular crystals. In contrast, Ca had little or no effect on morphology, but in three cases at intermediate additive concentrations kinetics changed from the usual combination of spiral growth and surface nucleation to pure spiral growth. It is proposed that the screw dislocations leading to growth spirals originate either from calcium phosphate crystallites acting as heteronuclei or from nuclei containing both Fe and Ca and with structure deviating from that of pure vivianite.

Production of laccase by repeated batch semi-solid fermentation using wheat straw as substrate and support for fungal growth.

Repeated batch semi-solid fermentation (sSF) process using wheat straw substrate and fungal growth of Ganoderma lucidum on solid substrate was studied for production of laccase. pH showed significant effect on laccase production. Highest laccase activity with pH controlled to 5.0 in batch sSF was 15257.2 ± 353.4UL- 1 on 9th day. In repeated batch process at pH 5.0, insoluble biomass substrate and fungal growth were reused after liquid part of medium was replaced with glucose, ammonium phosphate (best nitrogen source) and combined glucose and ammonium phosphate solution separately. Refilled to 80%wv- 1 of initial soluble sugar of first batch resulted in highest laccase production with peak activity after 4days from replacement. Production of enzyme increased from 15257.2UL- 1 in first batch to cumulative 90164.4UL- 1 in 29days after six repeated batches, productivity increased from 1680.2 to 3110.3UL- 1day- 1 (∼ 1.9 times) due to reductions in inhibitory effects and time required for fungal growth. Utilization of wheat straw in repeated batch sSF was supported by composition analysis and morphological changes (scanning electron microscopy) of substrate. Economic production of laccase using agricultural residues in repeated batch sSF could be possible.

Chemical poisoning by zinc and phosphorous of Pt/Ba/Al2O3 NOx storage catalysts

The effects of phosphorous and zinc on the performance of Pt/Ba/Al2O3 catalysts were investigated through wet impregnation of ammonium phosphate and zinc acetate aqueous solutions. Six different sample combinations were studied; 1 wt-% P, 1 wt-% Zn, 1 wt-% P with 1 wt-% Zn, 2 wt-% P, 2 wt-% Zn, 2 wt-% P with 2 wt-% Zn. NOx storage and reduction (NSR) activity and NO2 temperature programmed desorption (TPD) profiles were measured before and after impregnation of P and Zn. Samples containing P performed significantly worse than samples only containing Zn in both NSR activity and TPD measurements. The increased NOx slip during lean phase in activity measurements for P-poisoned samples is mainly related to an increased slip of NO2. This was found for both NO and NO2 in the gas feed during lean phase and suggests that it is mainly the storage component that is poisoned and not the noble metal. Furthermore, the combination (1 wt-% P and 1 wt-% Zn) proved to result in slightly worse performance than only 1 wt-% P, however this was not the case for samples containing 2 wt-%, where the addition of zinc reduced the negative effect of phosphorous. Measurements from NO2-TPD experiments showed that NOx release at low temperature was not affected by the addition of P, while desorption in the temperature range 425–475 °C was significantly reduced. It can therefore be concluded that the poisoning mainly is related to barium NOx storage sites and not to alumina sites. Moreover, X-ray diffraction measurements indicate that some of the barium species are affected by phosphorous. Images from scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX) mapping were in line with the results seen in both the activity tests and NO2-TPD experiments. Phosphorous was concentrated at the same position as barium in the observed images, whereas zinc was more evenly distributed over the surface. For the sample with both 2 wt-% P and 2 wt-% Zn, X-ray photoelectron spectroscopy measurements indicate that Zn and P have a low interaction and this suggests that most of the zinc and phosphorous are separated. However, STEM-EDX showed agglomerates of some zinc and phosphorous, which could be zinc phosphates. This is a plausible explanation of the decreased deactivation observed after introducing 2 wt-% Zn compared to the sample only containing 2 wt-% P.

Elemental analysis for iron, cobalt, copper and zinc decorated hydroxyapatite synthetic bone dusts by EDXRF and SEM

Iron, cobalt, copper and zinc decorated hydroxyapatite nanoparticles were produced with using ultrasonically assisted wet chemical method. Calcium nitrate tetra hydrate and dibasic ammonium phosphate were used as calcium and phosphorous source, respectively. Calcium nitrate tetra hydrate and dibasic ammonium phosphate solutions were prepared by dissolving the salts in distilled water and at different concentrations of decorated elements (iron, cobalt, copper and zinc) were appended to the calcium nitrate tetra hydrate solution. Stoichiometric decorated hydroxyapatite nanoparticles were analysed by energy dispersive X-ray fluorescence (EDXRF) with using standard method and the element analysis was determined with looking at the grain structures by Energy Dispersive X-Ray (EDX) and scanning electron microscopy (SEM). Not only have the concentrations of decorated metals but also calcium and phosphorus ratio for artificial bone powders been determined. As a result, calcium and phosphor ratio and metal decorated contents were evaluated according to the production values and compared previous studies. The answer to the question of how much of the contribution amounts was searched.

New insights on protective treatments for marble by FIB-SEM

In this study, we investigated by FIB-SEM the microstructure of protective coatings formed by two inorganic treatments (namely, ammonium oxalate and ammonium phosphate solutions), with the aim of identifying the factors limiting the protective efficacy of the coatings and outlining possible improvement strategies. In the case of the oxalate treatment, the resulting layer of whewellite was found to contain vertical channels, which can allow water to reach the marble surface and trigger dissolution. Possible prevention of the formation of these channels by addition of a calcium source to the oxalate solution was attempted, but even micromolar additions led to rapid precipitation in the solution. In the case of the phosphate treatment, the resulting hydroxyapatite and octacalcium phosphate coating was found to be cracked and porous. To prevent cracks and pores, diminishing the ammonium phosphate concentration and adding ethanol to the solution were found to be effective strategies, as cracks were prevented and pores were reduced almost to zero. The resulting protective efficacy of the coating was found to be significantly improved, although still not perfect.

Preparation of porous hybrid adsorbents based on fluor(calcium silicate)/activated carbon and its application in the removal of iron (III) from ammonium phosphate solutions

The high concentration of Fe3+ ions present in ammonium phosphate solutions have a significant effect on product quality and product morphology. Herein, hybrid adsorbents fluor(calcium silicate)/activated carbon (FCS/AC) combined with fluor(calcium silicate) (FCS) and activated carbon (AC) were prepared, characterized, and applied in the removal of Fe3+ ions from ammonium phosphate solutions. FCS/AC held both advantages of FCS and AC indicating a significant adsorption for Fe3+ ions. The adsorption kinetics, isotherms and thermodynamics of Fe3+ onto FCS/AC were investigated. The effect of solution pH, initial Fe3+ concentration, temperature and contact time on the adsorption of Fe3+ onto FCS/AC were also investigated. Desorption-resorption experiments of FCS/AC for Fe3+ ions were examined by the batch method using different eluents. The results showed that FCS/AC was an excellent, low cost and reusable adsorbent for the removal of Fe3+ ions from ammonium phosphate solutions, and the adsorption process appeared to follow the pseudo-second-order kinetic model and Langmuir isotherm model with a maximum Fe3+ adsorption of 15.41 mg/g. Various thermodynamic parameters such as △G0, △H0 and △S0 were calculated indicating the feasibility of the process and spontaneous nature of the adsorption.

Kinetics of solution crystal growth of strengite, FePO4,2H2O

The iron(III) phosphate strengite, FePO4,2H2O, has been precipitated at 25 °C by mixing solutions of iron alum and ammonium phosphate. The rate of crystallization has been determined by pH recording. Three stages of crystal growth kinetics could be distinguished: (1) mononuclear growth, (2) polynuclear growth and, in a few cases, (3) spiral growth (BCF mechanism). From the first two, the value of edge free energy λ = 87 ± 1 pJ/m was found. The identity of the precipitate was verified by SEM, XRD and Mössbauer spectroscopy.