Iron Oxide Samples Research Articles

Kinetic study of the redox process for separating and storing hydrogen: Oxidation stage and ageing of solid

The behaviour of an iron oxide sample (Fe 2O 3) during successive reduction–oxidation cycles (steam–iron process) has been investigated by means of a thermobalance system acting as a differential reactor. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, based on nucleation and growth mechanisms, has been used to describe the individual reoxidation processes as well as to predict the stability of the oxide after a high number of redox cycles. The effect of temperature, steam partial pressure and oxidation length has been discussed. The experimental results, as well as the parameters for the JMAK model, show that there is no significant effect of the temperature and the steam partial pressure used in the oxidation stages on the behaviour of the subsequent cycles (taking apart the first one). This conclusion applies also to the length of the oxidation period, if for such variable a value above a given threshold is used, which could be theoretically foreseen.

Relationship between temperature-programmed reduction profile and activity of modified ferrite-based catalysts for WGS reaction

A series of modified ferrites were prepared by doping iron oxide with various transition/non-transition/inner-transition metal ions [M = Cr, Mn, Co, Ni, Cu, Zn and Ce] in situ during synthesis. All the modified ferrites thus obtained exhibit remarkably high surface areas, greater than that of pure iron oxide (Fe 2O 3) sample. The efficacy of the dopant ions in modifying the resultant specific surface area, could be directly related to variations in the rate of crystal growth. The nature and concentration of the foreign cations present in the system govern this variation. Interestingly all the modified ferrites, exhibit a narrow pore size distribution in the range of 4.9–25 nm. XRD analysis revealed the existence of hematite (Fe 2O 3) phase in all the as-prepared samples. The X-ray diffraction experiments performed on activated catalysts, confirmed the existence of magnetite (Fe 3O 4) phase with a nominal composition of Fe 2.73M 0.27O 4. These inverse or mixed spinels with general formula A (1− δ) B δ [A δ B (2− δ) ]O 4, possess highly facile Fe 3+ ⇔ Fe 2+ redox couple, the degree of facileness depends on the extent of synergistic interaction between iron and the other substitutent metal ion. The rapid electron hopping between Fe 3+ ⇔ Fe 2+ in the Fe 3O 4 lattice system is essential to catalyze WGS reaction. From TPR it was observed that, incorporation of metal cations into the hematite (α-Fe 2O 3) crystal structure alters the reducibility of the hematite particles, which in turn depends on the nature of the incorporated metal cation. A plausible explanation for the WGS activity over various modified ferrites has been attempted with the help of TPR analysis.

Synthesis of α‐Fe2O3 Nanocubes

Nanocubes of α‐Fe2O3 were successfully synthesized by aqueous polymer thermolysis method in air. The synthesis of hematite nanoparticles has been carried out using a habit modifier polyvinyl alcohol of different molecular weights. The influence of annealing temperature from 300 to 500°C on structural and thermal properties of α‐Fe2O3 nanoparticles was investigated systematically using X‐ray diffraction and thermogravimetric analysis. The smallest grain size of 12 nm after calcinations was found in presence of PVA of 1,25,000 molecular weight. The binding and microstructural features of polycrystalline samples of iron oxide were studied by FTIR, SEM and TEM. Infrared spectra reveal the formation of α‐Fe2O3 and the removal of organic matter at higher temperatures.

Sulfate removal from aqueous solutions by hydrous iron oxide macroscopic, thermal and spectroscopic analyses

A series of hydrous iron oxide samples were prepared by homogeneous precipitation from FeCl 3 solution in the presence of SO 4 2− ions. Experiments were conducted to study the removal of sulfate ions by varying pH, SO 4 2−/Fe 3+ molar ratio and the nature of the associated cation. Conventional methods including Infrared Spectroscopy, X-ray Diffraction and Thermal Analyses were used for the characterization of sulfate ions interactions with the hydrous iron surface. The results of macroscopic studies show that the removal of sulfate is highly pH dependent, it is greater at pH range [3–4] and it decreases as the molar ratio enhances. Thermal and IR analyses demonstrate strong interactions of sulfate ions with the hydrous iron oxide. In the pH range studied, the results are consistent with innersphere surface complexes.

Development of iron oxide sorbents for Hg 0 removal from coal derived fuel gas: Sulfidation characteristics of iron oxide sorbents and activity for COS formation during Hg 0 removal

The aim of this study is to develop a process for the removal of Hg 0 using H 2S over iron oxides sorbents, which will be located just before the wet desulfurization unit and catalytic COS converter of a coal gasification system. It is necessary to understand the reactions between the iron oxide sorbent and other components of the fuel gas such as H 2S, CO, H 2, H 2O, etc. In this study, the sulfidation behavior and activity for COS formation during Hg 0 removal from coal derived fuel gas over iron oxides prepared by precipitation and supported iron oxide (1 wt% Fe 2O 3/TiO 2) prepared by conventional impregnation were investigated. The iron oxide samples were dried at 110 °C (designated as Fe 2O 3-110) and calcined at 300 and 550 °C (Fe 2O 3-300 and Fe 2O 3-550). The sulfidation behavior of iron oxide sorbents in coal derived fuel gas was investigated by thermo-gravimetric analysis (TGA). COS formation during Hg 0 removal over iron oxide sorbents was also investigated using a laboratory-scale fixed-bed reactor. It was seen that the Hg 0 removal activity of the sorbents increased with the decrease of calcinations temperature of iron oxide and extent of sulfidation of the sorbents also increased with the decrease of calcination temperature. The presence of CO suppressed the weight gain of iron oxide due to sulfidation. COS was formed during the Hg 0 removal experiments over Fe 2O 3-110. However, in the cases of calcined iron oxides (Fe 2O 3-300, Fe 2O 3-550) and 1 wt% Fe 2O 3/TiO 2, formation of COS was not observed but the Hg 0 removal activity of 1 wt% Fe 2O 3/TiO 2 was high. Both FeS and FeS 2 were active for Hg 0 removal in coal derived fuel gas without forming any COS.

Characterizing Swelling Behaviour of Iron Oxides during Solid State Reduction for COREX Application and their Implications on Fines Generation

Quality of iron feed source plays a critical role on the efficiency and productivity of advanced ironmaking processes such as COREX. A bench-scale study was conducted to characterize the effect of gas composition on solid state reduction and swelling behaviour of pellets and lumpy state of iron ore for COREX application. Swelling and reduction behaviour of five commercials iron oxides were analysed in a horizontal tube furnace and a thermogravimetric analysis (TGA) reactor respectively by simulating the reducing gas composition and thermal profile of the reduction shaft of COREX process. The degree of reduction and swelling were related to the initial porosity of iron oxide samples. The study demonstrated the strong influence of the initial porosity of iron feed samples on both reduction and swelling characteristics such that high porosity pellets indicated faster reduction and less swelling when compared to low porosity pellets. However, cracks formed in the iron pellets during different stages of reduction could modify the degree of the influence of the initial porosity on the reduction rates due to modification of surface area growth. The compressive strength of samples was found to change non-linearly with progressive reduction such that the crushing strength of pellets declined continuously up to 30% reduction followed by rapid strength increase as the degree of reduction exceeds 50% which can be attributed to increasing sintering of metallic phases. The study implies that as far as physical properties are concerned, the initial porosity of iron feed samples can be used to optimize the reduction kinetics, the swelling tendency and the associated implications for the stability of COREX operations including fines generations in the reduction shaft.

Formation and properties of the nanocluster structure of iron oxides

Nanostructures based on iron oxide clusters 1–300 nm in size were synthesized and studied. Thermodynamic models of nanocluster nucleation resulting in the formation of both primary nanoclusters and nanocluster aggregates with the sizes up to 70–80 nm were considered. Models of heat capacity of the nanoclusters were examined, and the twofold increase in the heat capacity of the iron oxide clusters 2–3 nm in size compared to that of the bulk iron oxide samples was found. The size of the primary nanoclusters and the intercluster interaction make it possible to vary the magnetic properties of the nanostructures in a wide range from paramagnetic to magnetically ordered α-Fe2O3-γ-Fe2O3 nanostructures with the first-order magnetic phase transitions, magnetic twinning, and a strong magnetic field (10 Oe) effect on the magnetization increase at low temperatures.

Single ferromagnetic behaviour of nanopowders with [formula omitted

The magnetic properties of Fe 3 C nanopowders prepared by laser pyrolysis (Sample A) and reduction and carburization of a nanocrystalline iron oxide (Sample B) are investigated. Fe 3 C was recognized as the solely ferromagnetic phase with the crystallite mean size 20 and 12 nm for the Sample A and B, respectively. The nanopowders exhibit ferromagnetic behavior with a blurred transition to paramagnetic state nearby the Curie temperature of coarse grained Fe 3 C . This effect is explained by a grain size distribution and the influence of the surface/interface regions of the nanoparticles.

Thermal decomposition of iron(VI) oxides, K 2FeO 4 and BaFeO 4, in an inert atmosphere

The thermal decomposition of solid samples of iron(VI) oxides, K 2FeO 4·0.088 H 2O ( 1) and BaFeO 4·0.25H 2O ( 2) in inert atmosphere has been examined using simultaneous thermogravimetry and differential thermal analysis (TG/DTA), in combination with in situ analysis of the evolved gases by online coupled mass spectrometer (EGA–MS). The final decomposition products were characterized by 57Fe Mössbauer spectroscopy. Water molecules were released first, followed by a distinct decomposition step with endothermic DTA peak of 1 and 2 at 273 and 248 °C, respectively, corresponding to the evolution of molecular oxygen as confirmed by EGA–MS. The released amounts of O 2 were determined as 0.42 and 0.52 mol pro formula of 1 and 2, respectively. The decomposition product of K 2FeO 4 at 250 °C was determined as Fe(III) species in the form of KFeO 2. Formation of an amorphous mixture of superoxide, peroxide, and oxide of potassium may be other products of the thermal conversion of iron(VI) oxide 1 to account for less than expected released oxygen. The thermogravimetric and Mössbauer data suggest that barium iron perovskite with the intermediate valence state of iron (between III and IV) was the product of thermal decomposition of iron(VI) oxide 2.

Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

Abstract. This study examines the potential role of some types of mineral dust and mineral dust with sulfuric acid coatings as heterogeneous ice nuclei at cirrus temperatures. Commercially-available nanoscale powder samples of aluminum oxide, alumina-silicate and iron oxide were used as surrogates for atmospheric mineral dust particles, with and without multilayer coverage of sulfuric acid. A sample of Asian dust aerosol particles was also studied. Measurements of ice nucleation were made using a continuous-flow ice-thermal diffusion chamber (CFDC) operated to expose size-selected aerosol particles to temperatures between -45 and -60°C and a range of relative humidity above ice-saturated conditions. Pure metal oxide particles supported heterogeneous ice nucleation at lower relative humidities than those required to homogeneously freeze sulfuric acid solution particles at sizes larger than about 50 nm. The ice nucleation behavior of the same metal oxides coated with sulfuric acid indicate heterogeneous freezing at lower relative humidities than those calculated for homogeneous freezing of the diluted particle coatings. The effect of soluble coatings on the ice activation relative humidity varied with the respective uncoated core particle types, but for all types the heterogeneous freezing rates increased with particle size for the same thermodynamic conditions. For a selected size of 200 nm, the natural mineral dust particles were the most effective ice nuclei tested, supporting heterogeneous ice formation at an ice relative humidity of approximately 135%, irrespective of temperature. Modified homogeneous freezing parameterizations and theoretical formulations are shown to have application to the description of heterogeneous freezing of mineral dust-like particles with soluble coatings.

Mo/spl uml/ssbauer studies of nano-size controlled iron oxide for biomedical applications

We present the magnetic properties and the material characteristics of magnetite (Fe/sub 3/O/sub 4/), which was successfully prepared by using the reaction of iron(III) acetylacetonate [Fe(acac)/sub 3/] with surfactants at temperature (so called by high temperature decomposition method). According to the results of resolution transmission electron microscopy (HRTEM) analysis, the prepared iron oxide particles had the average particle sizes between 4 and 6 nm and very uniform size distributions. The crystal structure analyzed by using both XRD and Mo/spl uml/ssbauer spectra confirmed that the prepared iron oxide nanoparticles only have single magnetite (Fe/sub 3/O/sub 4/) crystal phase. The typical superparamagnetic behaviors were observed from the prepared iron-oxide nanoparticles. In addition, they showed the saturation magnetization, M/sub S/ of 59.5 emu/g for 4 nm, and of 59.7 emu/g for 6 nm, respectively at room temperature under the externally applied magnetic field of 10 kOe. The measured Mo/spl uml/ssbauer spectrum at 4.2 K was fitted using two magnetic components: (1) hyperfine fields H/sub hf/=514 and 492 kOe, (2) isomer shifts /spl delta/=0.35 and 0.73 mm/s. The fitted data apparently verified that the prepared iron oxide samples only have pure magnetite ([Fe/sup 3+/]/sub A/ [Fe/sup 2+/Fe/sup 3+/]/sub B/O/sub 4/).

Preparation of nanosized iron oxide and its application in low temperature CO oxidation

A method to prepare iron oxide material which has a higher surface area and nanosized particle was developed. It was used as a catalyst for CO oxidation at low temperature. Iron oxide materials were prepared by precipitation under constant pH value. The effects of preparation parameters, such as iron salt (FeCl3, Fe(NO3)3 and FeCl2), pH value (between 8 and 12), drying temperature (between 120°C and 300°C), and feeding rate of the aqueous solution of the iron salt, on the characteristics of iron oxide have been investigated. The materials were characterized by N2 sorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The surface area of iron oxide was greater than 400 m2/g using FeCl3 as the starting material with very low feeding rate of 10 ml/min, the pH value of 11, and drying at 120°C. The XRD patterns indicated that the iron oxide samples heated at a temperature below 180°C was either amorphous or of a particle size too small (<4 nm) for the samples prepared with FeCl3. Depending on the preparation conditions, the iron oxide samples showed a phase transition from amorphous to various crystalline phases. Large amount of hydroxyl groups were preserved if the drying temperature was below 200°C. TEM images showed that the particle diameters were less than 4 nm for the samples prepared with FeCl3 at pH value of 11 with a low feeding rate of 10 ml/min, and heated below 200°C. XPS Fe 2p3/2 spectra showed the phase transition of iron oxide from Fe3O4 to FeO. The feeding rate of starting material and pH value during precipitation played the important roles to obtain iron oxide with high surface area. The nanosized iron oxide demonstrated high activity for CO oxidation even at ambient condition. The higher activity of Fe x O y nanoparticles in CO oxidation was attributed to a small particle size, high surface area, high concentration of hydroxyl groups, and more densely populated surface coordination unsaturated sites.

Mobilization of arsenic by dissolved organic matter from iron oxides, soils and sediments

The arsenic contamination of aquifers has been linked to the input of dissolved organic matter (DOM). In light of this suggestion, the aim of this study was to quantify chemical effects of DOM on desorption and redox transformations of arsenic bound to synthetic iron oxide and natural samples from different geochemical environments (soils, shallow aquifer, lake sediment). In batch experiments, solutions containing 25–50 mg/L of two different types of DOM (purified peat humic acid and DOM from a peat drainage) were used as extractants in comparison to inorganic solutions. DOM solution was able to mobilize arsenic from all solid phases. Mobilization from iron oxides (maximum: 53.3%) was larger than from natural samples (maximum: 2.9%). The mobilization effect of extractants decreased in the order HCl > NaH 2PO 4 > DOM > NaNO 3. DOM solutions, therefore, mainly targeted weakly sorbed arsenic. Mobilization was complete within 24–36 h and DOM was sorbed during incubation indicating competition for sorption sites. The same patterns were observed for different DOM types and concentrations. Addition of DOM lead to (a) enhanced reduction (maximum 7.8%) and oxidation (6.4%) of arsenic in aqueous solution and (b) the appearance of arsenite in aqueous phase of soil samples (5.5%). As the primary mechanism for the arsenic release from solid phases we identified the competition between arsenic and organic anions for sorption sites, whereas redox reactions were probably of minor importance. The results of this study demonstrate that sorption of DOM has a strong potential to mobilize arsenic from soils and sediments.

Storage and supply of hydrogen by means of the redox of the iron oxides modified with Mo and Rh species

The redox performance of iron oxides containing Mo and/or Rh species (Fe 3O 4 + 4H 2 ⇆ 3Fe + 4H 2O) was investigated. The redox cycle of the reduction of Fe 3O 4 with hydrogen and the subsequent oxidation of iron metal with water vapor can be applied for the storage and supply of pure hydrogen. Addition of Rh to the iron oxide samples improved the reactivity for the redox at a low temperature. The addition of Rh to iron oxide samples decreased apparent activation energy for the oxidation of iron metal with water vapor. However, Rh species added to iron oxides promoted sintering of iron species during the redox. The addition of Mo cations to iron oxides containing Rh prevented the sintering of iron species during the redox. Therefore, iron oxides containing both Rh and Mo species could form hydrogen repeatedly through the redox. The local structures of Mo and Rh species added to the iron oxide samples were investigated by Mo and Rh K-edge XANES and EXAFS. Mo cations added to the iron oxide samples were always stabilized in the ferrites Mo x Fe 3− x O 4 during the repeated redox reactions. Rh species added to the iron oxide samples were present as Rh–Fe alloys after the reduction with hydrogen, while they were present as Rh metal after the oxidation with H 2O.

Carburization of iron using CO−H2 gas mixture

Iron carbides formed on the surface of iron and iron oxide samples at 640 °C in a gas mixture of CO−H2 were characterized by scanning electron microscopy (SEM), Mossbauer spectroscopy, X-ray diffraction patterns (XRD), and by measuring mass change. The Fe3C amount of the samples has been quantitatively evaluated by the weight change during carburization. While Fe2O3 powder was mostly completed to Fe3C in the early stage, within 5 min after reduction reactions, the conversion of Fe powder sample to Fe3C (iron carbide) was almost finished after 10 min. The carburization rate of a Fe sheet was very slow and intermediate products (Fe2C, Fe5C2) were observed. This phenomenon is largely due to the difficulty of carbon diffusion into its dense surface. It was found that the carburization rate was affected by change of surface conditions and surface area by reduction, degradation, and cracks at high temperature. This study should help provide a fundamental understanding of carburization in the field of iron-making and suggest a direction for its further development.

Selective hydrogenation of α, β-unsaturated ketones to α, β-unsaturated alcohols on gold-supported catalysts

The liquid-phase reduction of α, β-unsaturated ketones [ trans,4-phenyl,3-buten,2-one (benzalacetone C 6H 5CHCHCOCH 3), 4-methyl,3-penten,2-one (CH 3) 2CCHCOCH 3, and 3-penten,2-one CH 3CHCHCOCH 3] to the corresponding α, β-unsaturated alcohols has been investigated on gold-supported catalysts. Au/Fe 2O 3 and Au/Al 2O 3 have been prepared by coprecipitation and deposition-precipitation. The catalytic behavior of a Au/Fe 2O 3 “reference” catalyst supplied by the World Gold Council has been also investigated. In the hydrogenation of benzalacetone and 4-methyl,3-penten,2-one on the “homemade” Au/Fe 2O 3 catalysts the unsaturated alcohol is the main reaction product. Chemoselectivity higher than 60% was achieved. On Au/Al 2O 3, the selectivity is 10%. It is noteworthy that within the gold supported on iron oxide samples, the reference catalyst shows the lowest selectivity toward the formation of the unsaturated alcohol. In the hydrogenation of 3-penten,-2-one on the homemade Au/Fe 2O 3, the saturated ketone is the main reaction product and the selectivity toward the formation of the unsaturated alcohol is 15% at conversion >90%. It is likely that the absence of bulky substituents on the conjugated CC double bond favors its adsorption on the catalytic sites, leading to the formation of the saturated carbonyl compounds as the main reaction product. A detailed characterization of the investigated catalysts by TEM and XRD is also reported.

The reactivity of ethylene oxide in contact with iron oxide fines as measured by adiabatic calorimetry

Samples of various iron oxides suspended above ethylene oxide in an adiabatic calorimeter exhibit exothermic activity at temperatures as low as room temperature. A γ-Fe 2O 3 sample was found to show the highest reactivity with ethylene oxide. Ethylene oxide in combination with most of the iron oxide fines tested displayed exothermic activity below 100 °C. Self-heat rates near 2000 °C/min were observed for the γ-Fe 2O 3 fines while rates in excess of 100 °C/min were found for other fines (α-Fe 2O 3 and hydrated α-Fe 2O 3). In two cases (α-Fe 3O 4 and α-Fe 2O 3), pressurization rates above 1000 psi/min took place. No reactivity was observed for ethylene oxide with the FeO. Thermal inertia effects in commercial operation, such as heat uptake by the equipment to which fines are attached, are presumed to be a factor in limiting the occurrence of related exotherms in ethylene oxide manufacturing facilities.

Infrared Spectroscopy Analysis of Oxyhydroxides as Intermediate Species in the Formation of Iron Oxides-Silica Xerogels

A detailed infrared spectroscopy analysis in the 2500 to 3800 cm−1 region has been used to study the formation of species in samples of iron oxides embedded in silica xerogel matrix. We report the presence of α, β, and γ forms of iron oxyhydroxides as intermediate species in the formation of α-Fe2O3, γ-Fe2O3 and e-Fe2O3 starting from three different iron precursors: iron nitrate, iron chloride and nanometric Fe particles prepared by chemical reduction. Our results show that under thermal dehydration α and γ forms of iron oxyhydroxides transform into hematite and maghemite, respectively, whereas the β form transform to the e-Fe2O3 without going through an intermediate iron oxide phase.

Immobilisation of molybdate by iron oxides: effects of organic coatings

It has been suggested that molybdate penetrates into micropores and interdomains of iron oxides. This process will cause immobilisation of molybdate. The influence of organic matter that may occlude the pores by adsorptive cover has not yet been examined. Thus, the aim of our study is to elucidate the role of organic coatings around iron oxides for intraparticular molybdate diffusion. We used two synthetic goethites of different crystallinity (specific surface G13: 13 m 2 g −1 and G83: 83 m 2 g −1), in pure form and equilibrated with dissolved organic matter (DOM), that has been extracted from forest floor samples. The iron oxide samples that were characterised by N 2 adsorption, X-ray diffraction analysis and scanning electron microscopy were preincubated with molybdate solution (5 g iron oxide l −1, 0.2 mM molybdate, pH 4) for 12, 24 and 48 h. To follow the molybdate immobilisation, molybdate desorption kinetics (desorption periods 0.5–48 h) were determined with ion exchange resins in batch systems after the different incubation times. In addition, the preincubated iron oxides were examined by XPS. Fractional coverage of DOM-treated iron oxides estimated according to the enthalpy of N 2 adsorption was 0.33 m 2 m −2 for G83 and 1.19 m 2 m −2 for G13. The pore volume of G13 decreased after DOM treatment. Furthermore, SEM images show that DOM treatment results in microaggregation of the iron oxides. A combination of the first-order equation and a diffusion term was applicable to the Mo desorption data of both, the pure and the DOM-treated iron oxides. Desorbability and apparent diffusion constants of molybdate decreased with increasing residence time. However, the decrease was less distinct for the DOM treated than for the pure goethites. The Mo/Fe XPS ratios of the iron oxides indicate that in the presence of organic matter a higher percentage of molybdate is sorbed to outer surfaces. The results confirm the hypothesis that molybdate diffuses into the pores of iron oxides. Organic coatings slow down the molybdate immobilisation probably by decreasing the accessibility of diffusion pathways. This mechanism may be relevant even at low molybdate and C concentrations, where no competition effect of sorbed organic molecules can be observed.

A time-of-flight resonance ionization mass spectrometer for elemental analysis of precious metals in minerals

An instrument for time-of-flight resonance ionization mass spectrometry (TOF-RIMS) developed at the Advanced Mineral Technology Laboratory (Ontario, Canada) is described which has been applied to the quantitative trace analysis of metals in minerals. The instrument incorporates new pulsed ion optics which provide fast switching of polarity and potentials of acceleration and ion lens optics between the two consecutive laser ablation and laser photoionization steps. Pulsed mode operation allows the time-of-flight mass spectrometer to be operated at higher laser ablation powers with more efficient suppression of the primary ions which are a source of noise that degrades the ultimate sensitivity of detection. The performance of the TOF-RIMS apparatus was assessed by analyzing trace amounts of gold (Au) in sulphide, iron oxide, and silicate mineral samples. Quantification of the TOF-RIMS measurements was established on the basis of calibration curves obtained using reference samples covering three orders of magnitude in concentration. Reproducible minimum detection limits (2σ) of ⩽10 parts per billion with a precision of ∼±15% were obtained.