Thermal Decomposition Of Salts Research Articles

Double complex salts containing [Pt(NO3)6]2- anion and Rh(III) complex cations: Synthesis, structure and utilisation for preparing (Rh–Pt)/CeO2 catalysts

Three new double complex salts (DCSs) containing [Pt(NO3)6]2- anion and Rh(III) metalorganic cations [Rh(4-pic)4Cl2]2[Pt(NO3)6] (1,4-pic = 4-methylpyridine), [Rh(bpy)3]2[Pt(NO3)6]3 (2, bpy = 2,2′-bipyridiine) and [Rh(bpy)3][Pt(NO3)6](NO3)(CH3COCH3)(CH3CN)(H2O) (3) were prepared and characterised by elemental analysis and infrared spectroscopy. Crystal structures of 1 and 3 were determined using X-ray single crystal analysis. Thermal decomposition of salts 1 and 2 in various atmospheres (He, He/H2, air) was shown to yield Rh–Pt solid solutions with a Rh:Pt ratio inherited from the starting salt composition. The Rh0·67Pt0·33/CeO2 catalyst was prepared by thermal decomposition of salt 1 supported on a CeO2 surface. The catalyst was tested in a CO oxidation reaction and demonstrated full conversion of CO from about 145 °C at gas hourly space velocity of 200 000 ml g−1 h−1.

Tetraammineplatinum(II) and Tetraamminepalladium(II) Chromates as Precursors of Metal Oxide Catalysts.

[M(NH3 )4 ]A (M=Pt, Pd; A=CrO4 , Cr2 O7 ) and [Pt(NH3 )4 (NO2 )(Cr2 O7 )]NO3 complex salts were synthesized and characterized by a number of physicochemical methods of analysis (IR, single-crystal and powder XRD, and simultaneous thermogravimetry and differential scanning calorimetry with evolved gas analysis mass spectrometry). Thermolysis of the salts obtained in a hydrogen atmosphere proceeds with the partial reduction of chromium to a metallic state and the formation of Mx Cr1-x (M=Pt, Pd) metal solid solution with a chromium content of up to 22 at % and chromium(III) oxide. The thermal decomposition of salts in an inert and oxidizing atmosphere passes through the formation stage of the MCrO2 phase with the delafossite structure followed by its subsequent decomposition into chromium(III) oxide and noble metal. Nanosized Pt-Cr2 O3 and Pd-Cr2 O3 composites obtained by the thermolysis of precursor salts in air at 500 °C and being held at this temperature for 1 h showed a high catalytic activity in the CO total oxidation (TOX) and preferential oxidation in the excess of hydrogen (PROX) processes compared with that of monometallic Pt and Pd powders.

Novel method for additive manufacturing of metal-matrix composite by thermal decomposition of salts

Very limited Additive Manufacturing (AM) processes have been developed for production of Metal Matrix Composites (MMCs) reinforced by ceramic. Most of these processes use different mixing techniques to mix metal and ceramic powder particles in order to be used in an existing AM process such as Selective Laser Melting (SLM) process. The current AM techniques for MMCs fabrication have limitations due to material mixing and the AM process limitations itself. This paper introduces a novel AM method for fabrication of MMCs by Thermal Decomposition of Salts (TDS). In this method inorganic salts are printed on metal powder bed to fabricate green part. The green part undergoes bulk sintering. During bulk sintering the printed inorganic salts are decomposed to fine ceramic particles to form MMC. This process is capable of generating MMC structures with uniformly distributed and dispersed ultra-fine ceramic particles in the metal matrix with less limitations and lower cost compared to other existing AM techniques. In this paper, bronze-alumina MMC was fabricated and studied by the TDS process to validate the proposed process. It was also shown that the TDS process can be used to fabricate other types of MMCs besides bronze-alumina due to the nature of the process. Design of Experiments methodology was used to study and model the effects of sintering parameters on the properties of the bronze-alumina fabricated by the TDS process. Due to MMCs unique properties combined with AM benefits, this novel method will be of great interest to various industries such as aerospace applications.

Thermoelectric properties of a Pb0.2Sn0.8Te solid solution prepared through thermal decomposition of salts

We have studied the thermoelectric properties of microcrystalline samples of the Pb0.2Sn0.8Te solid solution prepared by hot-pressing fine powders obtained through the thermal decomposition of lead acetate trihydrate and tin oxalate in the presence of tellurium powder. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the samples have been measured at room temperature and in the temperature range 300–700 K and correlated with the particle size of the powders and heat-treatment conditions. We have compared the thermoelectric properties of hot-pressed samples from powders prepared through the thermal decomposition of salts and by mechanical grinding of ingots.

Effect of the type of matrix on the electronic state of cobalt cations in impregnated catalytically active nanostructures

Physicochemical methods are used to study the electronic state of cobalt cations in nanostructures produced by thermal decomposition of salts on the surface and in the bulk of ZSM-5, Al2O3, SiO2, and ERI matrices. It is shown that the electronic state of cobalt is influenced by the type of matrix and cobalt–adsorbed oxygen ratio. It is established that cobalt cations can be immobilized in the tetrahedral and octahedral oxygen environment of the matrix and the oxidation state can change (Co2+ → Co3+) because of the transition from tetrahedral to octahedral coordination.

Fabrication of bulk materials from fine particles of PbTe-SnTe solid solutions prepared through thermal decomposition of salts

A process has been proposed for the fabrication of microcrystalline thermoelectric materials based on PbTe-SnTe solid solutions by compacting and hot-pressing fine powders prepared through the thermal decomposition of lead acetate trihydrate and tin oxalate in the presence of tellurium powders. We analyze the mechanism of the thermal decomposition of the powder mixtures, resulting in the formation of Pb1 − x Sn x Te particles, and examine the influence of cold compaction, heat treatment, and hot pressing on the grain composition, electrical conductivity, and Seebeck coefficient of materials prepared by pressing the powders.

Principal component analysis of thermal decomposition of magnesium salts used as drugs

Thermal decomposition of magnesium salts of organic acids used in medicine (Mg acetate, Mg valproate, Mg lactate, Mg citrate, Mg hydrogen aspartate, Zn hydrogen aspartate) was analyzed by thermoanalytical, calorimetrical, and computational methods. Thermoanalytical studies were performed with aid of a derivatograph. 50-, 100-, and 200-mg samples were heated in a static air atmosphere at a heating rate of 3, 5, 10, and 15 °C min−1 up to the final temperature of 700–900 °C. By differential thermal analysis (DTA), thermogravimetry (TG), and derivative thermogravimetry (DTG) methods, it has been established that thermal decomposition of the salts under study occurs via two stages. The first stage (dehydratation) was distinctly marked on the thermoanalytical curves. Calorimetrical studies were carried out by using of a heat-flux Mettler Toledo differential scanning calorimetry (DSC) system. Ten milligram samples of compounds under study were heated in the temperature range from 20 to 400 °C at a heating rate of 10 and 20 °C min−1 under an air stream. The studies showed that the values of transitions heats and enthalpies of dehydration for investigated salts varied with the increasing of heating rate. For chemometric evaluation of thermoanalytical results, the principal component analysis (PCA) was applied. This method revealed that points on PC1 versus PC2 diagrams corresponding to the compounds of similar chemical constitution are localized in the similar ranges of the first two PC’s values. This proves that thermal decomposition reflects similarity in the structure of magnesium salts of organic acids.

Double complex salts of Pt and Pd ammines with Zn and Ni oxalates – promising precursors of nanosized alloys

Double complex salts [M(NH 3) 4][M′(Ox) 2(H 2O) 2] · 2H 2O (M = Pd, Pt, M′ = Ni, Zn) were synthesized by combination of solutions containing corresponding cations [M(NH 3) 4] 2+ and anions [M′(Ox) 2(H 2O) 2] 2−. The salts obtained were characterized by IR spectroscopy, thermal analysis, powder and single crystal X-ray diffraction. The prepared compounds are isostructural and crystallize in the orthorhombic crystal system (space group I222, Z = 2). Thermal decomposition of the salts in helium or hydrogen atmosphere at 200–400 °C results in formation of nano-sized bimetallic powders. Depending on the phase diagram of the respective bimetallic system and temperature conditions, they can be single phase or multiphase products. In particular, thermal decomposition of double complex salts [M(NH 3) 4][Zn(Ox) 2(H 2O) 2] · 2H 2O (M = Pd, Pt) results in formation of PdZn and PtZn intermetallic compounds, correspondingly. Decomposition of [Pd(NH 3) 4][Ni(Ox) 2(H 2O) 2] · 2H 2O affords a disordered solid solution Pd 0.5Ni 0.5. Disordered Pt 0.5Ni 0.5 was obtained from [Pt(NH 3) 4][Ni(Ox) 2(H 2O) 2] · 2H 2O in helium atmosphere, while in hydrogen atmosphere – a two-phase mixture of disordered Pt 0.5Ni 0.5 and ordered PtNi. In all cases crystallite sizes of bimetallic particles varied within 50–250 Å.

Thermal analysis of transition metal salts of carboxylic acids

The thermal decomposition of salts (both normal and acid) of transition metals with carboxylic acids (maleic, ortho-phthalic and terephthalic) was studied in inert atmosphere. The residues after pyrolysis (up to 450°C) are composites including two structural components: an organic polymer matrix and spherical conglomerates from metal grains coated with polymer. Thermal decomposition of solid solutions of metal bimaleates (Co-Ni, Fe-Ni, Zn-Ni) was investigated. Thermogravimetric data (obtained at different rates of linear heating) were processed with 'Netzsch Thermokinetics' computer program. Kinetic parameters were calculated only for the first decomposition step, and the process is described by Prout-Tompkins equation of nth order with autocatalysis. Some properties of the resulting composites have been studied qualitatively.

Synthesis and characterization of 3-methoxydiphenylamine-4-diazonium salt and its diazoresin

3-Methoxydiphenylamine-4-diazonium salt (MDDS) and its diazoresin were synthesized. The photo- and thermal decomposition of salt and the resins were investigated. The results show that MDDS exhibits excellent thermostability as well as high photosensitivity. A series of diazoresins with different organic counteranions, which dissolve in common solvents and usually were chosen to manufacture the negative presensitized plate, were also synthesized The kinetics of the photo- and thermal decomposition of MDDS in ethanol is reported. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1975–1982, 1998

Preparation of palladium-based alloy powders by the thermal decomposition of binary complex ammonium oxalate salts

The possibility of obtaining powder alloys (solid solutions) by thermal decomposition of salts of the types [Pd(NH3)4[M(C2O4)2] and (M(NH3)n[Pd(C2O4)2] was investigated. Salts of the desired compositions were synthesized by double decomposition of the ammonium and oxalate complexes of the metals in aqueous solution. The production of new compounds was confirmed by x-ray diffraction analysis. It was shown that pyrolysis of the salts (Pd(NH3)4][M(C2O4)2] occurs in stages: initially one of the oxalate groups migrates to the cationic part, and later the products obtained, (Pd(NH3)2](C2O4)] and MC2O4, decompose. The decomposition temperatures of the salts obtained correlated with those of MC2O4. Pyrolysis of [Pd(NH3)4] [M(C2O4)2] produced highly dispersed solid solution powders of palladium with copper, nickel, and copper, respectively, with the atom ratio Pd:M = 1:1, and the intermetallic compound PdZn. The powder particle sizes did not exceed 1 μm. Initial salts, intermediate products, and oxides were not detected in the powders.

Electrocatalyse sur oxydes métalliques

The electrocatalysis on metallic oxide for oxygen reactions (ORR, oxygen reduction reaction, and OER, oxygen evolution reaction) is reviewed. The emphasize is put on the spinel and perovskite families. The properties of the oxides depend on the preparation procedure. Some methods of preparation of powders and films of mixed oxides are briefly presented: thermal decomposition of salts, freeze dryin8, spray pyrolysis, sol-gel, sputtering and electrochemical. Characterization of the products by X-ray diffractometry is not sufficient. Surface optical methods like, for instance, near grazing X-ray diffraction are useful with very thin films, together with UV-vis-NIR reflectance spectroscopy for their identification. Transmission and/or reflexion NIR spectroscopy is also useful, as the thickness detection lower limit can be as low as 5 nm in the best case with this technique. Optical spectra of Co 3 O 4 and NiCo 2 O 4 are presented. The knowledge of the cationic distribution in the mixed oxide is essential to a better understanding of the electrocatalytic properties. Cyclic voltammetry provides an electrochemical mean of characterization of the oxide/solution interface. A double electrode flow through cell has been designed to investigate the ORR on films and to determine the ratio of the direct reduction rate constant (k 1 ) to the indirect (peroxide) reduction rate constant (k 2 ). This will be exemplified with the copper manganite spinel Cu 1+x Mn 2-x O 4 on which k 1 /k 2 increases from 2 to 9 when x increases from 0.2 to 0.4

A contribution to the thermal decomposition of salts and metal complexes of 1,1-dithiolates

The thermal decomposition of salts and metal complexes (binary and mixed ligand) of dithiocarbamates, xanthates, dithiocarbazates and dithiophosphates has been studied thermogravimetrically. The activation energies of decomposition for some of them were calculated adopting the Coats and Redfern equation. In most cases the binary complexes decompose in a single sharp stage whereas the mixed ligand complexes are characterised by decompositions having more than one stage.

Determination of ruthenium and tin on electrochemical anodes by energy-dispersive X-ray fluorescence

“Dimensionally Stable Anodes” (DSA)® have gained wide acceptance in electrochemical production of chlorine and caustic soda. The DSAs are usually composed of electrocatalytic layers of precious and non-precious metal oxides produced by thermal decomposition of salts on a valve-metal substrate ( e.g., titanium). They have long lifetimes (some years) in commercial service, and accelerated aging is used in testing them. In these tests the cell potential is stable for most of the anode life. Failure of an anode is characterized by a rapid increase in potential to beyond the point of practical operation of the cell. Non-destructive X-ray techniques have been utilized to investigate the mechanism involved. It has been established that the precious metal content has been reduced by 50–60% when the anodes fail. Although present DSA coatings are more than adequate for commercial applications, there is continuing interest in improving them. The materials for DSA formulation include the precious metals iridium, ruthenium and rhodium, the non-precious metals tin, antimony and manganese, and the valve metals titanium and tantalum.

Thermal properties of thiocyanatothiocarbamidobismuthates(III) with alkaline elements

The thermal decomposition of complex salts of thiocyanatothiocarbamidobismuthates(III), having the general formula Me[Bi(SCN) 4(TM) 2] where Me = Li, Na, K, Rb, Cs, NH 4 and TM = thiourea, was studied. On the basis of the results of derivatographic studies and chemical analysis, both infrared spectrophotometric and diffractometric, the compositions of the intermediate and final products obtained during the thermal decomposition of those salts were established. On the strength of the experimental data obtained (without analyzing the gaseous products), the most probable overall equation was established of the decomposition reaction of thiocyanatothiocarbamidobismuthates(III) in air at a temperature of 480°C.

The effect of cations on the thermal decomposition of salts with oxyanions: A semi-empirical correlation

It is the purpose of this paper to reexamine the stability problem in a more quantitative way than has been previously done, particularly be examining relations between measures of thermal stability and ionic properties.

The thermal decomposition of salts of mellitic acid. Part III. Chromic, manganous, cupric, and zinc mellitates

Kinetic measurements for the thermal decomposition reactions of manganous, cupric, and zinc mellitates and a chromic–mellitic acid complex are reported. None of these substances melted during decomposition in vacuo but the kinetic data for rate processes fitted equations which were characteristic of reactions occurring in the homogeneous phase. The manganous and chromic compounds decomposed through two rate processes occurring in different temperature ranges; the complete decomposition of the cupric and zinc salts occurred in a single reaction. Mechanisms to account for these observations are discussed.Evidence is presented which demonstrates that activation energies for the decomposition of mellitates can be correlated with the heat of formation of the appropriate metallic oxide. From this it is concluded that the rate-determining step in mellitate decomposition involves rupture of the carboxyl group–metal bond. The results obtained for mellitates are compared with available measurements for the reactions of bivalent metal oxalates.

Mechanism of thermal decomposition of salts of carboxylic acids

1. The thermal decomposition of Ca, Ba, Li, Rb, Ag, and Cu acetates at 473–873°K was analyzed thermodynamically. In all cases apart from Ag and Cu acetates, and regardless of the nature of the acid radical, the decomposition of the salt to the anhydride and the metal oxide was thermodynamically forbidden. The results of the calculations are confirmed by experimental data. 2. The characteristics of the topochemical decomposition of Ca, Ba, Cd, Mg, and Zn acetates were examined: they were the lack of an induction period, the fact thatn in Erofeev's equationα=1−e−kτn is close to unity, the planar form of the reaction nucleus, and the fact that the reaction proceeds in the kinetic region. The decomposition proceeds by the growth of initial centers present in the substance and the activation energy determined experimentally is the activation energy of the growth of the reaction nuclei. 3. In the case of the decomposition of Li, Na, K, and Rb acetates, which occurs in the melt, an interpretation is given for the effect of the nature of the metal on the activation energy and pre-exponent. The effect of thermodynamic factors on the course of the change in activation energy is discussed.