Vaporization of atoms and molecules during heating of cadmium,lead and zinc salts in a carbon tube atomizer

Vaporization characteristics of atoms and molecules produced during heating of aqueous solutions of Cd, Pb and Zn salts in the carbon tube atomizer are described. Sulfates, nitrates and fluorides are decomposed completely to free atoms without losses. When concentrated halide solutions are employed, gaseous metal chlorides, bromides and iodides are removed partly from the atomizer in the initial atomization phase, and the atomic absorption response is decreased. This loss can be suppressed effectively by adding nitric or sulfuric acid to the halide solutions.     

Signal depression in electrothermal atomic absorption spectrometry by nitrate and sulfate ions

The effects of nitrates and sulfates, which decompose to generate oxidants on heating, on the gaseous atom concentration for Ag,Cu and Ga have been investigated with a graphite filament atomizer and an optical arrangement which allows spatial information above the atomizer surface to be gathered. For the potassium and sodium salts, the largest signal depression, caused by gaseous atom oxidation, was found with the largest relative decomposition at the particular temperature, which therefore gives the largest partial pressure of the oxidants formed above the oxidizer. For the calcium salts, Ca metal was vaporized from the atomizer and competed successfully with the analyte, for any oxidants generated, thereby preventing oxidation of the analyte, so that, in some cases, the analyte atom concentration was increased.     

Mechanism of Thermal Decomposition of d-metals Nitrates Hydrates

A series of six nitrates(V) hydrates of 4d-metals as well as mercury and cadmium thermal decomposition was examined by DTA, TG and EGA techniques. It was found that thermal decomposition of d-metals nitrate(V) hydrates proceeds in three stages: partial dehydration, oxo-nitrates and hydroxide nitrates formation and metal oxides formation. General chemical equations for all decomposition stages were proposed. It was found that dehydration of hydrated salts is accompanied by partial decomposition of nitrate(V) groups. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nanocomposites based on opal matrices and iron subgroup metal nanoparticles

Three-dimensional nanocomposites based on ordered opal matrices (OMs) and metal nanoparticles were prepared by the reduction of salts and oxides of iron subgroup metals (M = Ni, Co, and Fe) and their binary and ternary mixtures with isopropanol in a supercritical state. The effect of the composition of the initial salts (nitrates or chlorides) on the phase composition of OM/M composites was determined. For a binary system of Ni and Co nitrates (1 : 1), the particles of a NiCo solid solution in a cubic modification were formed in an opal matrix after treatment in supercritical isopropanol. For the Ni-Fe and Co-Fe systems, the nanoparticles of solid solutions based on nickel or ??-, ??-cobalt metal and also oxides or an MFe₂O₄ phase with the spinel structure were formed in opal matrices with the use of iron trichloride. The nanoparticles of iron metal and Ni₃Fe, NiFe, and CoFe intermetallic compounds with regular distributions of metal atoms were detected for the first time in addition to spinel phases upon the reduction of composites with Fe, Ni-Fe, and Co-Fe nitrates with supercritical isopropanol. The reduction of composites obtained by the thermal treatment of a ternary mixture of nickel and cobalt nitrates and iron chloride in supercritical isopropanol led to the formation of solid solution nanoparticles based on Ni, Co, and Fe with an fcc structure and an oxide phase with the spinel structure in the voids of opal matrices. In the composite based on an opal matrix and a ternary system of Ni-Co-Fe nitrates (1 : 1 : 1), the complete reduction of spinel phases to the intermetallic phases of Ni₃Fe, NiFe, and CoFe was noted.     

The compressibility of molten salts

Values of the adiabatic and isothermal compressibility, κ_S and κ_T, of some 80 molten salts at the corresponding temperature of T = 1.1T_m (T_m is the melting point) are obtained from literature data either directly or re-calculated here. For some of the series of salts: alkali metal halides and nitrates, divalent metal halides, and alkali metal sulfates and carbonates the κ_T values are inversely proportional to the corresponding cohesive energy densities ced (internal energies per unit volume, separately for each class of compounds). The ced values for 1:2 and 2:1 salts not previously evaluated are presented here too.     

Studies on the thermal decomposition of the silver group of alkali metal nitritocobaltates(III)

The thermal decomposition of nitritocobaltate(III) of the silver group of general formula M₂Ag[Co(NO₂)₆] (where M = K⁺, NH⁺₄, Rb⁺ or Cs⁺) has been investigated. Based on the thermal curves of the investigated compounds and chemical and diffractometric analysis, the mechanism of thermal decomposition has been determined. The results obtained indicate that the decomposition proceeds in three stages. As a result of decomposition in the first stage (300°C), nitrates of alkali metals, metallic silver and Co₃O₄ are formed. In the second stage (500°C), a partial decomposition of nitrates to alkali metal oxides occurs, and in the third stage the products are alkali metal oxides, silver and Co₃O₄. This paper also presents the dependence of the decomposition temperature of nitritocobaltates(III) of the silver group on the ionic radius of the outer-sphere cation.     

Explosive degradation of woody biomass under the presence of metal nitrates

The influence of various metal nitrates (Fe, Ni, Cu, Zn, etc.) has been studied in the pyrolysis of woody biomass under inert atmosphere. Pyrolysis samples have been prepared by impregnation of wood with aqueous solution of the salts as well as by mechanical mixing of powders of wood and nitrates. Thermogravimetric analysis showed that the addition of nickel, copper and zinc nitrates reduced significantly the decomposition temperature of wood below 150 °C. The decomposition of wood completes explosively at the temperature. The pyrolysis products have been analysed by GC–MS and XRD methods. Preliminary result of the quantitative analysis of emitted NO_x gas in the pyrolysis treatment is also presented.     

Long-chain dicarboxylic acids : II. Precipitation of aqueous 5-(and 6-)carboxy-4-hexyl-2-cyclohexen-1-yl octanoic acid solutions with metal ions

Aqueous dispersions of heavy-metal salts of 5-(and 6-)carboxy-4-hexyl-2-cyclohexen-1-yl octanoic acids, denoted by H₂D, were prepared by direct mixing of solutions of the metal nitrates with solutions of Na₂D. With any particular concentration of D²⁻ ion, it was found that the turbidity increased sharply when the concentration of a metal ion exceeded a certain value. This transition from low to high turbidity defined the boundary between stable and unstable soap suspensions, and the concentration of the added salt at which it occurred was labeled as critical transition concentration (ctc). Complete domains, showing the ctc values for different concentrations of dicarboxylate for thallium(I), magnesium, calcium, and lanthanum counterions, have been given. These transition boundaries are strongly dependent on pH. The mixing of calcium and lanthanum nitrates with a solution of Na₂D gave a suspension of solid particles, whereas immediate spontaneous emulsification occurred when thallium(I) and magnesium nitrates were used.     

Thermal behavior of Co(II) and Ni(II) hydroxycarboxylate complexes obtained by two original synthesis methods

This paper presents a facile and rapid synthesis route of metallic Ni and Co nanocrystallites at ~150 °C in the mixture composed of the corresponding metal nitrates and 1,3-propanediol, as reducing agent. The metal oxides NiO, CoO, Co₃O₄ nanocrystallites were, also, successfully synthesized by thermal decomposition at 300 °C of the hydroxycarboxylate coordination products, obtained in the redox reaction between 1,3-propanediol and Ni(II) and Co(II) nitrates. The formation of the Ni(II) and Co(II) hydroxycarboxylate complexes depends on the diol which generates the carboxylate anion, the transition metal and the process parameters. Ni(II) and Co(II) nanocomposites were also synthesized by thermal decomposition of the complex combinations formed within the pores of the hybrid silica gels. One of the purposes of the present study was to investigate the phase constitution of the composites obtained in similar synthesis conditions, from Ni(II) and Co(II) complex combinations embedded in silica gels. These gels were submitted to various thermal treatments and the changes occurring during these treatments were described by X-ray diffraction. Thermal analysis is an excellent tool for the study of the processes implied in the formation and decomposition of the Co(II) and Ni(II) carboxylate complexes. X-ray diffraction evidenced the nanometer sized metal and/or metal oxide phases.     

Correlation between the reactivity and the structural and thermal properties of supported metal nitrates

Montmorillonite-supported iron(III) nitrate and copper(II) nitrate reagents, and other supported metal nitrates prepared in the same way, were investigated by thermal and X-ray powder diffraction methods. The metal nitrates are present on the support in the form of crystalline hydrate and not as acetone solvate as supposed earlier. Thermal decomposition of metal nitrates that are active in model reactions proceeds in a different way from that of the practically inactive nitrates. In the former case, water release and nitrate decomposition itself are simultaneous process. These and other results contributed to determination of suitable reaction conditions for the montmorillonite-supported reagents.     

A thermogravimetric study of phosphonium halides

The TG/DTG thermal curves for a series of phosphonium halides are presented. The stability of phosphonium salts increases in the order chloride < bromide ≈ iodide. While phosphonium salts with only nonpolar groups in the cation volatilize completely, increasing substitution by polar cyanoethyl groups results in residue formation. The kinetics of the thermal decomposition can be obtained using isothermal thermogravimetry.     

Thermal stability of quaternary ammonium hexafluorophosphates and halides

Thermal decomposition of hexafluorophosphates of short-chain tetraalkylammonium salts of the general formula R₃R’NPF₆, where R₃ = R’ = CH₃, C₂H₅, C₄H₉; R₃ = C₂H₅, R’ = CH₂C₆H₆ or CH₂CH=CH₂, was studied by thermal gravimetric analysis. Measurements were performed in air in the temperature interval 20–500°C. The thermal stability of halides with the same cations in the same temperature interval was studied for comparison. The effect of cation on the thermal stability of the halides and hexafluorophosphates was examined. The mechanism of thermal decomposition of quaternary ammonium hexafluorophosphates was suggested.     

Gamma-radiolysis of solid zirconium nitrate and its binary mixtures with potassium halides

Gamma-radiolytic decomposition of zirconium nitrate and its binary mixtures with potassium halides viz. KCl, KBr and KI has been studied at different compositions up to an absorbed dose of 550 kGy. Radiolytic decomposition has been found to decrease with the absorbed dose. It also varies with the concentration of zirconium nitrate in the binary mixtures. G(NO ₂ ^– ) values are enhanced by the addition of halides but only at 75% composition. It is not affected so significantly by KI. A plot of G(NO ₂ ^– ) vs. composition of the binary mixtures of the nitrates shows a somewhat parabolic curve with a minimum at 75% Zr(NO₃)₄+25% KX composition. A part of the energy absorbed by the system is being taken up by the halides depending upon their nature and concentration. Thermal decomposition shows slow decomposition, finally yielding an oxynitrate of indefinite composition.     

Synthesis and characterization of Mn-, La-Mn- and La-Ca-Mn-citrates as precursors for LaMnO<Subscript>3</Subscript> and La<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>MnO<Subscript>3</Subscript>

Mn-, LaMn- and LaCaMn-citrates were synthesized at 60–120°C in ethylene glycol medium using chlorides or nitrates as metal sources. Their composition, IR spectra and thermal decomposition were studied. Equimolar La/Mn ratio has been established in the complex, prepared from chloride solution with the same initial composition of the metals. In the isolated three-metallic complex the molar ratio of the metals deviates from the composition in the initial solution. The final products of the heating of Mn- and mixed-metal LaMn-citrates at 1000°C are phase-homogeneous Mn₃O₄ (hausmannite) and LaMnO₃ respectively. Parasitic phase(s) are observed in La_xCa_1−xMn_yO₃, produced from LaCaMn-citrate.     

Effects of metal salts on the thermal decomposition of edta-gel precursors for ferroelectric ceramic powders

Raw chemicals such as metal nitrates and chlorides were found to affect the thermal decomposition behaviour of EDTA-gel precursors used for the production of ceramic powders. Fine, homogeneous ceramic powders were produced from nitrate solutions while chlorides gave segregated phases. In studies on the production of lead zirconate titanate (PZT) using chlorides, the segregation and loss of lead was observed and shown to be caused by the formation and evaporation of PbCl₂. Thermal analysis (DTA/TG) quantitatively proved the suggested reaction mechanism for this phase segregation. Crystallization of the desired perovskite phase of lead zirconate titanate (PZT) and barium titanate (BT) initiated at temperatures as low as 250°C in the nitrate-EDTA precursors. Water of crystallization and formation of BaCO₃ in the barium titanate precursor were suggested to account for differences in the observed decompositional behaviours of the BT and PZT precursors.     

Investigations on poly(vinyl chloride). IV. Effects of metal chlorides on the thermal decomposition of poly(vinyl chloride)

The effects of various metal oxides upon the thermal decomposition of poly(vinyl chloride) (PVC) were previously reported. In this work, 23 metal chlorides were investigated to determine their effects on the thermal decomposition of PVC by pyrolysis–gas chromatography at 500°C. Each metal chloride exhibits influences on the course of thermal decomposition of PVC almost similar to the corresponding metal oxide except for a few elements; the metal chlorides from acidic metal oxides accelerate the thermal decomposition of PVC, but the metal chlorides from basic metal oxides do not. On comparing the effects of metal oxides and metal chlorides on the thermal decomposition of PVC, most metal chlorides were found to accelerate the thermal decomposition of PVC more than the corresponding metal oxides, owing to ease of addition of the chlorine atoms released from metal chloride to the dehydrochlorinated chains. It is concluded from these results that the thermal decomposition of PVC containing metal salts is markedly influenced by the ease with which chlorine atoms are released from the corresponding metal chloride.     

Decomposition study of Ni–La–Mg–O precursors using thermal analysis

The thermal decomposition process of La₂O₃/MgO (La/Mg = 2, 1 and 0.5) supported nickel (15% mass/mass Ni) precursor was investigated. Thermal analysis results show distinct processes of decomposition of the samples in accordance with the composition. The mass loss at higher temperature is associated to distinct stages of decomposition of lanthanum precursors. The thermal analysis results agree with the FTIR spectra showing change in the band corresponding to carbonates and nitrates species. XRD results also confirmed the precursor’s decomposition. It can be concluded that the thermal decomposition of La₂O₃–MgO-nickel precursor depends on the La/Mg ratio and of the residual species.     

Electric conductivity of porous glass modified by oxides of bivalent cobalt, nickel, and copper

Multiply repeated operations of porous glass impregnation by aqueous solutions of bivalent cobalt, nickel, and copper nitrates followed by the thermal decomposition of the deposited salts provide a gradual accumulation of oxides in the carrying agent. In all cases, as the surface of glass open channels is filled with oxides, a section of substantial increase in conductance is detected, in which a tentative oxide monolayer is formed. Relations established between conductivity and its activation energy are treated on the basis of the conception of intervalence mechanism of electron transfer in the systems under consideration.     

Structural characterization of mono- and bisphosphonium salts by fast atom bombardment mass spectrometry and tandem mass spectrometry

Positive-ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono- and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium salts typically contain abundant intact cations that can be used to establish the cationic relative molecular mass and diagnostic fragment ions that allow the characterization of structural subgroups. Depending on the functional group substitution on the alkyl group, additional fragment ions are observed which are formed by loss of small neutral molecules from the intact cation and that can be used for the differentiation of isomeric phosphonium salts. Molecular dication are typically observed in the FAB mass spectra of the bisphosphonium salts when they are analysed in 3-nitrobenzyl alcohol. In addition, production of singly charged ions by clustering with a counter ion, decomposition involving removal of one of the charge centres and one-electron reduction are generally observed. Structurally diagnostic fragments are also obtained. The fragmentation pathways of the ions derived from the phosphonium salts were elucidated by precursor ion and product ion tandem mass spectrometric experiments. For the phosphonium salts containing a long-chain hydrocarbon alkyl group, high-energy collision-induced decomposition of the intact cation is needed to obtain unambiguous structural information.     

Powder X-ray diffraction study of the double complexes [M(NH3)5Cl][M"Cl4] as precursors of metal powders (M = Ir,Rh, Co; M" = Pt,Pd)

According to the results of powder X-ray diffraction study of the complex salts of composition [M(NH₃)₅Cl][M"Cl₄] (M = Ir, Rh, or Co and M" = Pt or Pd), the anhydrous salts crystallize in the orthorhombic system (space group Pnma) and are isostructural to the [Ir(NH₃)₅Cl][PtCl₄] complex studied previously. The unit cell parameters of the resulting salts were refined. The metal powders, which were obtained by thermal decomposition of these salts under an atmosphere of hydrogen, were studied by powder X-ray analysis.