Some topical applications of plasma atomic spectrochemical methods for the analysis of ceramic powders

The scope of a number of plasma spectrochemical methods for the determination of the main components and impurities in ceramic powders is described. These methods meet the requirements for the analytical characterization of new structural and functional ceramics for modern industrial applications and electronic devices. For ceramic powders, spectrochemical analysis with direct methods as well as analysis subsequent to sample dissolution are discussed. Fusion is a powerful method for the dissolution of ZrO₂ ceramic powders, provided the fluxes are pure enough. For determinations in Al₂O₃, SiC and ZrO₂, it will be shown that ICP-MS is very useful. This is especially true for trace analysis after matrix removal. The latter can easily be performed on-line in the case of the analysis of Al₂O₃ powders. For direct analysis of ceramic powders, the direct insertion of samples into the plasma, spark and arc ablation, laser ablation, electrothermal vaporization and slurry nebulization are discussed. Particular attention is given to the direct analysis of ceramics in powder form (Al₂O₃, SiC, Si₃N₄, B₄, WC) using ICP-OES with slurry nebulization as well as with direct sample insertion (DSI) and with electrothermal vaporization (ETV). For the two latter methods, the use of chemical modifiers for volatile compound formation will be shown to be of great importance, and its features will be explained using thermochemical considerations. Received: 18 February 1998 / Revised: 13 May 1998 / Accepted: 9 June 1998     

Comparison of decomposition procedures for analysis of titanium dioxide using inductively coupled plasma optical emission spectrometry

The determination of impurities in titanium dioxide pigments, such as Al, Cd, Cr, Fe, Mn, P, Zn and Zr, is relevant because trace elements affect pigment properties. The critical step in the analysis of this pigment is the conversion of the solid sample to a representative solution. This study compared four acid decomposition procedures for TiO₂ for the determination of Al, P and trace impurities using inductively coupled plasma optical emission spectrometry. The decomposition procedures investigated involved acid digestion with: (i) (NH₄)₂SO₄/H₂SO₄; (ii) HF/H₂SO₄; (iii) H₃PO₄; and (iv) HCl/HNO₃/HF. This latter mixture was tested in a microwave-assisted procedure with closed vessels. Comparing the procedures using conventional conductive heating, the procedure using (NH₄)₂SO₄/H₂SO₄ was the most suitable for complete decomposition of TiO₂ samples, requiring approximately 30 min. Applying a paired t-test, it was shown that all strategies led to results in agreement at a 95% confidence level with those obtained using X-ray fluorescence. The accuracy for Cr, Fe, P and Zr was also checked using a certified reference material, and again all results were in agreement at a 95% confidence level. The performance of two ICP-OESs, one based on a mini-torch using a radial view configuration, and the other based on an axial view configuration, were compared. Both plasmas are intensely affected by matrix constituents. The mini-torch plasma is less able to cope with high amounts of solids; however this parameter also negatively affects the background level when using axial-viewed ICP-OES.     

Some topical applications of plasma atomic spectrochemical methods for the analysis of ceramic powders

The scope of a number of plasma spectrochemical methods for the determination of the main components and impurities in ceramic powders is described. These methods meet the requirements for the analytical characterization of new structural and functional ceramics for modern industrial applications and electronic devices. For ceramic powders, spectrochemical analysis with direct methods as well as analysis subsequent to sample dissolution are discussed. Fusion is a powerful method for the dissolution of ZrO₂ ceramic powders, provided the fluxes are pure enough. For determinations in Al₂O₃, SiC and ZrO₂, it will be shown that ICP-MS is very useful. This is especially true for trace analysis after matrix removal. The latter can easily be performed on-line in the case of the analysis of Al₂O₃ powders. For direct analysis of ceramic powders, the direct insertion of samples into the plasma, spark and arc ablation, laser ablation, electrothermal vaporization and slurry nebulization are discussed. Particular attention is given to the direct analysis of ceramics in powder form (Al₂O₃, SiC, Si₃N₄, B₄, WC) using ICP-OES with slurry nebulization as well as with direct sample insertion (DSI) and with electrothermal vaporization (ETV). For the two latter methods, the use of chemical modifiers for volatile compound formation will be shown to be of great importance, and its features will be explained using thermochemical considerations.     

Multielement trace determinations in A12O3 ceramic powders by inductively coupled plasma mass spectrometry with special reference to on-line trace preconcentration

The use of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of trace elements in Al₂O₃ powders is reported. Special interest is given to a preconcentration of the trace elements by on-line coupling of chromatography to ICP-MS. This is based on the complexation of Co, Cu, Cr, Fe, Ga, Mn, Ni, V and Zn with hexamethylene-dithiocarbamate (HMDC), their preconcentration on a C18 RP column by reversed phase liquid chromatography and their elution with CH₃OH-H₂O mixtures. A direct coupling of the HPLC system to the ICP-MS has been realized by high pressure pneumatic nebulization using desolvation. With the Chromatographie method developed, removal of the AI by at least 99% was achieved. For the trace elements V, Fe, Ni, Co, Cu and Ga, high and reproducible recoveries (ranging from 96–99%) were reached. The method developed has been shown to considerably enhance the power of detection as compared with direct procedures, namely down to 0.02–0.16 ( for V and Fe, respectively. The possibilities of the method are shown by the determinations of V, Mn, Fe, Ni, Co, Cu, Zn and Ga at the μg/g level in A1₂O₃ powders. The accuracy of the method at the 0.06 to 9.0 level for Co and Fe, respectively, is demonstrated by a comparison with results of independent methods from the literature.     

Studies on transport phenomena in electrothermal vaporization sample introduction applied to inductively coupled plasma for optical emission and mass spectrometry

In the present work electrothermal vaporization (ETV) was used in both inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (OES) for sample introduction of solution samples. The effect of (Pd + Mg)-nitrate modifier and CaCl₂ matrix/modifier of variable amounts were studied on ETV-ICP-MS signals of Cr, Cu, Fe, Mn and Pb and on ETV-ICP-OES signals of Ag, Cd, Co, Cu, Fe, Ga, Mn and Zn. With the use of matrix-free standard solutions the analytical curves were bent to the signal axes (as expected from earlier studies), which was observed in the 20–800 pg mass range by ICP-MS and in the 1–50 ng mass range by ICP-OES detection. The degree of curvature was, however, different with the use of single element and multi-element standards. When applying the noted chemical modifiers (aerosol carriers) in microgram amounts, linear analytical curves were found in the nearly two orders of magnitude mass ranges. Changes of the CaCl₂ matrix concentration (loaded amount of 2–10 μg Ca) resulted in less than 5% changes in MS signals of 5 elements (each below 1 ng) and OES signals of 22 analytes (each below 15 ng). Exceptions were Pb (ICP-MS) and Cd (ICP-OES), where the sensitivity increase by Pd + Mg modifier was much larger compared to other elements studied. The general conclusions suggest that quantitative analysis with the use of ETV sample introduction requires matrix matching or matrix replacement by appropriate chemical modifier to the specific concentration ranges of analytes. This is a similar requirement to that claimed also by the most commonly used pneumatic nebulization of solutions, if samples with high matrix concentration are concerned.     

Determination of trace impurities in high-purity zirconium dioxide by inductively coupled plasma atomic emission spectrometry using microwave-assisted digestion and wavelet transform-based correction procedure

This paper describes a rapid, accurate and precise method for the determination of trace Fe, Hf, Mn, Na, Si and Ti in high-purity zirconium dioxide (ZrO₂) powders by inductively coupled plasma atomic emission spectrometry (ICP-AES). The samples were dissolved by a microwave-assisted digestion system. Four different digestion programs with various reagents were tested. It was found that using a mixture of sulfuric acid (H₂SO₄) and ammonium sulfate ((NH₄)₂SO₄), the total sample dissolution time was 30 min, much shorter than that required for conventional digestion in an opening system. The determination of almost all of the target analytes suffered from spectral interferences, since Zr shows a line-rich atomic emission spectrometry. The wavelet transform (WT), a recently developed mathematical technique was applied to the correction of spectral interference, and more accurate and precise results were obtained, compared with traditional off-peak background correction procedure. Experimental work revealed that a high Zr concentration would result in a significant decrease in peak height of the analyte lines, which was corrected by standard addition method. The performance of the developed method was evaluated by using synthetic samples. The recoveries were in the range of 87-112% and relative standard deviation was within 1.1-3.4%. The detection limits (3σ) for Fe, Hf, Mn, Na, Si and Ti were found to be 1.2, 13.3, 1.0, 4.5, 5.8 and 2.0 μg g⁻¹, respectively. The results showed that with the microwave-assisted digestion and the WT correction, the detection limits have improved by a factor of about 5 for Fe, 4 for Mn and Ti, 3 for Si, and 2 for Hf and Na, respectively, in comparison with conventional open-system digestion and off-peak correction. The proposed technique was applied to the analysis of trace elements above-mentioned in three types of ZrO₂ powders.     

Inductively-coupled plasma atomic emission spectroscopic determination of trace impurities in ZrO2-powder

Four independent procedures including one using slurry nebulization ICP-AES were developed for the trace analysis of ZrO₂ powders. They were evaluated with respect to detection limits, blank values, interferences, accuracy and precision. For the procedures I–III ZrO₂ powder was decomposed by fusion with a 10-fold excess of NH₄HSO₄ and subsequent dissolution of the melt in either water or, after evaporation of NH₄HSO₄, in diluted HNO₃. In procedure I the solution was directly analyzed by ICP-AES, which was optimized with the aid of a simplex algorithm. In procedure II Zr was separated by extraction from 6 mol/l HNO₃ with a 0.5 mol/l solution of 2-thenoyltrifluoroacetone (TTA) in xylene. More than 99.5% of the Zr was removed and more than 95% of the trace elements retained. In procedure III the matrix was separated by its precipitation as ZrOCl₂·8 H₂O from a (1:4) HCl-acetone medium. More than 98% of Zr were removed and more than 90% of the trace elements were retained. In procedure IV the ZrO₂ powder was dispersed by ultrasonic treatment in water acidified with HCl (pH 2) and the slurry was directly analyzed by ICP-AES using a Babington nebulizer. The optimization and the analytical features of this procedure will be described in a subsequent paper. In all procedures the calibration was performed by standard addition and matrix matching was not necessary. The detection limits varied from 0.3 g/g (Ca) to 10 g/g (Al). The standard deviations obtained were 1–10% depending on the element and its concentration in the sample. The results of the procedures for 6 commercially available fine ZrO₂ powders were found to agree for Al, Ca, Fe, Mg, Na, Ti and Y. A good agreement between the results of the procedures using matrix separation was also observed for Cu, Mn, V, but the concentrations of these elements found by methods without matrix separation were considerably higher. Except for Ca and Mg the blank values encountered were below the detection limits.On leave from Department of Analytical Chemistry, Technical University, PL-00-664 Warsaw, Poland     

Direct solid sampling electrothermal vaporization of alumina for analysis by inductively coupled plasma optical emission spectrometry

A procedure based on electrothermal evaporation (ETV) and inductively coupled plasma atomic emission spectrometry (ICP-OES) for the determination of trace impurities in Al₂O₃ powders without any sample pretreatment is presented. With the aid of matrix modifier the transport and the evaporation efficiency for refractory compounds could be increased by forming halides with a lower boiling point. As calibration is still a problem in direct solid sample analysis, different calibration approaches including the use of certified reference materials from NIST and standard addition of aqueous solutions of analytes were discussed. The accuracy obtained with calibration and with the standard addition method was shown up for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni and V for the case of Al₂O₃ NIST standard reference material (SRM 699). The ETV–ICP-OES method was used for the analysis of Al₂O₃ powders with impurities in the low μg/g range and the results for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni and V obtained with evaporation of discrete powder amounts with ETV–ICP-OES and slurry evaporation under the use of ultrasonic homogenization during the sampling and ETV–ICP-MS were shown to be in a good agreement.     

Analysis of silicon carbide powders with ICP-MS subsequent to sample dissolution without and with matrix removal

ICP-MS has been employed for the analysis of silicon carbide powders in connection with high pressure acid decomposition without and with matrix removal by evaporation. The powder is decomposed by treatment of a 250 mg sample with a mixture of HNO₃, H₂SO₄ and HF. Prior to the analyses with ICP-MS the solutions have to be diluted to a matrix concentration of 500 g/ml related to SiC in order to realize full long-term precision. The results obtained for Li, B, Na, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Ag, Cd, In, Sn, Sb, Ba, La, Ce, Pr, Nd, Hf, Ta, W, Tl, Pb, Bi, Th and U in SiC powder S-933 are shown to be in good agreement with those of independent methods, such as INAA, ICP-AES with slurry atomization and ICP-AES subsequent to sample decomposition. For extending the use of ICP-MS to elements such as Mg, Ca, Sc and Ti at the relevant concentrations in SiC powders, a more effective matrix removal by evaporation of the decomposition solution to near dryness has been successfully applied. Its advantages have been proven by the results of high resolution ICP-MS. It has been found by analyses of the treated sample solutions for the residual Si and C with ICP-MS that over 99% of the matrix and also of the acids used for decomposition are removed. For B, Al and Fe losses were found to occur at concentration levels of some g/g, 200 g/g and 300 g/g, respectively, and all other elements were detected with very good recoveries. For all 36 elements investigated in this work the detection limits could be improved from the ng/g to the pg/g range by removal of the matrix. The analytical range could be improved, in particular for In, Tl, Bi and U.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Application of countercurrent chromatography to the purification of chemical reagents

Countercurrent chromatography has been employed for the purification of solid chemical reagents, such as (NH₄)₂SO₄, NH₄HSO₄, NH₄F and NH₄Cl from a number of most common metal impurities (Fe, Al, Zn, Cu, Co, Cd, Ni, Cr, Ca, Mg, K) in order to gain high-purity reagents. After evaporation these can be used for fusion decomposition purposes in trace analysis of various refractory materials (e.g. high tech ceramics). N,N-hexamethylenedithiocarbamic acid, 8-hydroxyquinoline, dibenzo-18-crown-6 and dicyclohexano-18-crown-6 were used as extracting reagents.     

Studies on the determination of trace elements in high-purity Sb using GFAAS and ICP-QMS

Trace element impurities in high-purity antimony were determined employing three different methods for the removal of matrix; on Dowex 50WX 8 by adsorption from 0.1 mol/L HF and elution with 4 mol/L HNO₃; on Chelex-100 resin (in NH₄ ⁺ form) Bi, Cd, Co, Cu, and Pb were separated in the presence of tartaric acid at a pH of 9.0 ± 0.1 with subsequent elution with 2 mol/L HCl; these determinations were carried out by GFAAS. The separation of trace impurities from Sb by volatilization of the matrix from H₂SO₄ and HBr medium was also investigated. ICP-MS was used for the determination in these cases. All the three procedures showed that the removal of the antimony matrix was nearly quantitative (> 99.99%). The recoveries of trace elements were found to be > 95%. The relative standard deviations were in the range 2–7%. Standard addition calibrations were used. The levels of process blanks indicate that with careful optimization, the volatilization procedure coupled with ICP-QMS can be used for trace impurity characterization of 6N+ Sb.     

Isotype Strukturen einiger Hexaamminmetall(II)-halogenide von 3d-Metallen: [V(NH3)6]I2, [Cr(NH3)6]I2, [Mn(NH3)6]Cl2, [Fe(NH3)6]Cl2, [Fe(NH3)6]Br2, [Co(NH3)6]Br2 und [Ni(NH3)6]Cl2

The Structures of some Hexaammine Metal(II) Halides of 3 d Metals: [V(NH₃)₆]I₂, [Cr(NH₃)₆]I₂, [Mn(NH₃)₆]Cl₂, [Fe(NH₃)₆]Cl₂, [Fe(NH₃)₆]Br₂, [Co(NH₃)₆]Br₂ and [Ni(NH₃)₆]Cl₂ Crystals of yellow [V(NH₃)₆]I₂ and green [Cr(NH₃)₆]I₂ were obtained by the reaction of VI₂ and CrI₂ with liquid ammonia at room temperature. Colourless crystals of [Mn(NH₃)₆]Cl₂ were obtained from Mn and NH₄Cl in supercritical ammonia. Colourless transparent crystals of [Fe(NH₃)₆]Cl₂ and [Fe(NH₃)₆]Br₂ were obtained by the reaction of FeCl₂ and FeBr₂ with supercritical ammonia at 400°C. Under the same conditions orange crystals of [Co(NH₃)₆]Br₂ were obtained from [Co₂(NH₂)₃(NH₃)₆]Br₃. Purple crystals of [Ni(NH₃)₆]Cl₂ were obtained by the reaction of NiCl₂ · 6H₂O and NH₄Cl with aqueous NH₃ solution. The structures of the isotypic compounds (Fm3 m, Z = 4) were determined from single crystal diffractometer data (see “Inhaltsübersicht”). All compounds crystallize in the K₂[PtCl₆] structure type. In these compounds the metal ions have high-spin configuration. The orientation of the dynamically disordered hydrogen atoms of the ammonia ligands is discussed.     

Micro-homogeneity studies of boron carbide powders

We have studied the micro-homogeneity of boron carbide powders by inductively coupled plasma optical emission spectrometry (ICP-OES) and total reflection X-ray fluorescence spectrometry (TXRF) using slurry sampling. To get information on the particle size distributions of the powders, the stabilized slurries of boron carbide powders were nebulized, the aerosols were transported into a Batelle impactor and the droplets were collected on the impactor stages bearing TXRF sample holders. In a first series of measurements, parameters of the impaction like the duration of the impaction and the use of glutinous substance on the sample holders were optimized. The different mass size fractions for industrial boron carbide powders were determined by weight measurements of the fractions collected on the different stages. The established particle size distributions were in the range of 0.5 to >16 μm and found similar to those determined by laser diffraction reported elsewhere. Analyses of the mass fractions by slurry sampling TXRF showed that Ca, Ti, Cr, Mn, Fe, Ni and Cu within the measurements errors were homogeneously distributed over the mass fractions between 0.5 and 4 μm and that their concentrations agreed with the bulk composition, as determined with ICP-OES subsequent to digestion. However, light underestimates were found at the 5 (Mn) up to 150 μg g^?1 (Fe) level. Finally, boron carbide powders were washed out with nitric acid with different concentrations and leaching solutions and the residues were analyzed by ICP-OES and TXRF respectively. It is shown that up to 60% of the residual trace impurities in the powder studied can be removed by leaching with 34% (v/v) of nitric acid.

Studies on the determination of trace elements in high-purity Sb using GFAAS and ICP-QMS

Trace element impurities in high-purity antimony were determined employing three different methods for the removal of matrix; on Dowex 50WX 8 by adsorption from 0.1 mol/L HF and elution with 4 mol/L HNO₃; on Chelex-100 resin (in NH₄ ⁺ form) Bi, Cd, Co, Cu, and Pb were separated in the presence of tartaric acid at a pH of 9.0 ± 0.1 with subsequent elution with 2 mol/L HCl; these determinations were carried out by GFAAS. The separation of trace impurities from Sb by volatilization of the matrix from H₂SO₄ and HBr medium was also investigated. ICP-MS was used for the determination in these cases. All the three procedures showed that the removal of the antimony matrix was nearly quantitative (> 99.99%). The recoveries of trace elements were found to be > 95%. The relative standard deviations were in the range 2–7%. Standard addition calibrations were used. The levels of process blanks indicate that with careful optimization, the volatilization procedure coupled with ICP-QMS can be used for trace impurity characterization of 6N+ Sb. Received: 25 May 1998 / Revised: 23 September 1998 / Accepted: 26 September 1998     

Optimization of slurry nebulization inductively-coupled plasma atomic emission spectrometry for the analysis of ZrO2-powder

The optimization and use of ICP-AES with slurry nebulization for the direct analysis of ZrO₂-powder is described. The powder samples are dispersed in water, acidified to pH 2 and the slurry is fed into a Babington nebulizer. The effects of grain size, pH of the suspending medium and standing time on the stability of the slurry are discussed. For the optimization of the ICP operating conditions, a simplex technique is applied and for this purpose three types of objective functions were examined. Identical behaviour of slurries and solutions with the same matrix concentrations in the ICP-AES is achieved for powders with particle sizes lower than 10 m; in the latter case calibration can be performed by standard addition with aqueous solutions. The detection limits for Al, B, Ca, Cu, Fe, Mg, Mn, Na, Ti, V. Y are 0.03 g/g to 10 g/g and the standard deviation is generally lower than 10%. Six commercially available ZrO₂ powders are analyzed by slurry nebulization ICP-AES and the results were found to agree well with those obtained by ICP-AES after chemical decomposition of the samples.On leave from Department of Analytical Chemistry, Technical University, PL-00-664 Warsaw, Poland     

Bright visible luminescence of self-organized ZrO2 nanotubes

Self-organized nanotubular layers of ZrO₂ are electrochemically grown by tailored anodization in an (NH₄)₂SO₄ electrolyte containing small amounts of fluoride ions. The structure and morphology of these nanotubular layers were characterized by electron microscopy. XRD-measurements revealed anodic ZrO₂ films to be crystalline. Luminescence properties were investigated by photoluminescence and cathodoluminescence measurements. In both methods a very bright white luminescence of as-grown ZrO₂ nanotubes is observed. While the origin of this luminescence is not entirely clear, the findings may provide a path towards optoelectronic applications of ZrO₂ nanotubes.     

Über einen Isokonzentrationsschnitt in bezug auf Schwefelsäure im Dreistoffsystem Ammoniumsulfat-Eisen(III)sulfat-Wasser bei 25 °C

Zusammenfassung Untersucht wird ein Isokonzentrationsschnitt in bezug auf Schwefelsäure im Dreistoffsystem (NH₄)₂SO₄–Fe₂(SO₄)₃–H₂O bei 25 °C. Es wird ein Kristallisationsbereich von anomalen Mischkristallen auf der Basis (NH₄)₂SO₄ bei einem Eisen(III)-sulfatgehalt von 1,5% des Ammoniumsulfatgehalts ermittelt. Außerdem wird ein Kristallisationsbereich von Mischkristallen auf der Basis NH₄Fe(SO₄)₂·12 H₂O, ein Kristallisationsbereich von reinem NH₄Fe(SO₄)₂·12 H₂O und ein Kristallisationsbereich von Fe₂(SO₄)₃·9 H₂O festgestellt. Die Anwesenheit von Schwefelsäure in der Lösung vermindert die Löslichkeit aller Phasen im obigen System.Untersucht wird teilweise das Dreistoffsystem NH₄Fe(SO₄)₂–H₂SO₄–H₂O bei 25 °C. Es wird ein Kristallisationsbereich von NH₄Fe(SO₄)₂·12 H₂O, welches als feste Phase bis etwa 12% Schwefelsäure in der Lösung existiert, ermittelt. Es wird bewiesen, daß die anomalen Mischkristalle auf der Basis (NH₄)₂SO₄ metastabile, mit der Zeit langsamen Veränderungen unterliegende Systeme sind.

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An isoconcentration section with respect to sulphuric acid of the ternary system ammonium sulphate-ferric sulphate-water at 25 °C

The system (NH₄)₂SO₄–Fe₂(SO₄)₃–H₂O was investigated at 25 °C with an excess of H₂SO₄. The crystallization ranges of the anomalous mixed crystals based on ammonium sulphate, the mixed crystals on the basis of the double-salt NH₄Fe(SO₄)₂· ·12 H₂O, the crystallization ranges of Iron(III)-ammonium sulphate and Fe₂(SO₄)₃·9 H₂O were determined. The presence of H₂SO₄ in the solution lowers the solubilities of the different phases occurring in the said system. The system NH₄Fe(SO₄)₂–H₂SO₄–H₂O was partially studied at 25 °C. The crystallization range of iron-ammonium alum existing as a solid phase at equilibrium at sulphuric acid concentrations up to ca. 12% in the solution is described. It was shown that the anomalous mixed-crystals based on ammonium sulphate undergoe slow changes with time.

     

Spectroscopic and analytical characteristics of an inductively coupled argon plasma combined with hydride generation with or without simultaneous introduction of the sample aerosol for optical emission spectrometry

A radially viewed inductively coupled argon plasma was used for optical emission spectrometry of volatile species formed by reaction with NaBH₄ (hydride generation). The volatile hydrides were either introduced into the plasma alone or at the same time as a sample aerosol generated by pneumatic nebulization with a commercially available Concomitant Metals Analyzer. The effects of the forward power, the presence of pre-reducing agents [(NH₂)₂SC, KI, KBr and hot HCl], the occurrence of easily ionized elements (Ca, K, Mg and Na) in the analyte solutions on the excitation temperature (as measured via Ar atomic lines) and the electron number density were investigated for both of the sample introduction modes applied. The detection limits and the signal-to-background intensity ratios for As, Bi, Sb, Se and Sn lines were also evalutated and were observed to deteriorate with increasing power. When simultaneous hydride generation and pneumatic nebulization was employed under optimized experimental conditions, detection limits of 3.5, 2.9, 4.3, 1.5 and 2.1 μg L⁻¹ for As, Bi, Sb, Se and Sn, respectively, were obtained, and the intensities of the analytical lines for elements that do not form volatile hydrides were found to be 40% (Cd), 30% (Ni), 20% (Co, Cr, Fe, Mn and Zn) and 10% (Cu, Mg, V) greater than those obtained when only pneumatic nebulization was used.     

Structural and IR Spectroscopic Analysis of Sol-Gel Processed CuFeMnO4 Spinel and CuFeMnO4/Silica Films for Solar Absorbers

Black colored CuFeMnO₄ spinel powders and films were prepared using sol-gel process from Mn-acetate and Fe- and Cu-chloride precursors. Films were deposited by dip-coating technique and heat-treated at 500°C. For CuFeMnO₄/silica films 3-aminopropyl-triethoxysilane (3-APTES) or tetraethoxysilane (TEOS) were used in molar proportion (Mn : Cu : Fe) : silica = 1 : 1. Films and powders were prepared by heating at 500°C. IR spectroscopic measurements were employed to follow the hydrolysis-condensation reactions in (Mn : Cu : Fe)/3-APTES sols hydrolysed with water, and (Mn : Cu : Fe)/TEOS sols hydrolysed with (NH₃)_aq (Stöber processing). The resulting coatings were examined with transmission electron microscopy (TEM) combined with electron dif-fraction analyses, Rutherford back scattering (RBS) and proton induced X-ray emission (PIXE) techniques. Results revealed that (Mn : Cu : Fe)/3-APTES films had a composite structure consisting of the upper Cu_1.4Mn_1.6O₄ spinel and the lower amorphous SiO₂ layer. RBS measurements confirmed the composite structure, showing also that the composition of the film was Mn : Cu : Fe = 1 : 0.96 : 0.29, i.e. close to the precursors ratio Mn : Cu : Fe = 3 : 3 : 1. (Mn : Cu : Fe)/TEOS films prepared from sols which were catalysed with (NH₃)_aq consisted of amorphous monodispersed spherical SiO₂ particles with a size of about 400–420 nm. Solar absorbance (a _s) and thermal emittance (e _T) values of CuFeMnO₄ (500°C) and (Mn : Cu : Fe)/TEOS films (500°C) showed that CuFeMnO₄ films could be used as potential selective coatings for solar absorbers in solar collector systems.     

DSC investigation of the thermal behaviour of (NH4)2SO4, NH4HSO4 and NH4NH2SO3

Gaseous products evolved from (NH₄)₂SO₄, NH₄HSO₄ and NH₄NH₂SO₃ during successive heating and cooling cycles were flushed with inert gas into analyzer Dräger tubes hooked tightly to the terminal port of the DSC cell base. This simple procedure allowed the starting temperature of the decomposition to be determined and the amount of the individual gases in the mixture to be identified and even estimated. NH₄NH₂SO₃ at 523 K in humid air produced HNH₂SO₃ initially and, on further cycling, (NH₄)₂SO₄ and NH₄HSO₄ also appeared. The ΔH_f values for NH₄HSO₄ were (kJ mole^?1): in an airtight sample holder 12.67, in a dry argon atmosphere 11.93, and in a static air atmosphere 10.92. Endothermic peaks for (NH₄)₂SO₄ and 498 and 411 K represented the incongruent melting point and the polymorphic transition of (NH₄)₂SO₄·NH₄HSO₄. After the first heating in air to 530 K, (NH₄)₂SO₄ and NH₄HSO₄ exhibited closely similar cyclic DSC curves. The endothermic peaks at about 393–420 K may be assigned to different combinations of (NH₄)₂SO₄ and NH₄HSO₄.