Thermal decomposition study of selected isopolymolybdates

The thermal decomposition of ammonium trimolybdate (NH₄)₂Mo₃O₁₀·H₂O, anilinium trimolybdate (C₆NH₈)₂Mo₃O₁₀·4H₂O and anilinium pentamolybdate (C₆NH₈)₂Mo₅O₁₆ in air and nitrogen has been investigated. The decomposition of molybdates was studied in situ by powder X-ray diffraction. Moreover, results of TG, as well as scanning microscopy studies, are presented. It was found that during thermal treatment in air phases of MoO_x type are obtained, while thermal treatment in nitrogen leads to obtaining a mixture of Mo_yC_z and Mo_pN_q. It is worth noting that even though chemical decomposition and formation of new compounds took place, in some cases needle-like or plate-like shapes of crystallites were preserved during thermal treatment.     

Effects of alkali metal ions on the thermal decomposition of ammonium heptamolybdate tetrahydrate

The thermal decomposition of pure ammonium heptamolybdate tetrahydrate (AHMT), and doped with Li⁺, Na⁺ and K⁺ ions was investigated using thermogravimetry, differential thermal analysis, infrared and X-ray diffraction techniques. Results obtained revealed that the decomposition of AHMT proceeded in three decomposition stages in which both NH₃ and H₂O were released in all stages. The presence of 0.5 mol % alkali metal ions enhances the formation of the intermediateb (NH₄)₂MO₇O₂₂·2H₂O while the decomposition of this intermediate into MoO₃ is slightly affected in the presence of all dopant concentrations used. The infrared absorption spectra of the thermal products of AHMT treated with 10 mol% alkali metal ions (AMI) at 350°C indicated a reduction of some Mo⁶⁺ ions. By heating of AHMT above 500°C in presence of 5 or 10 mol % of AMI, a solid-solid interaction between alkali metal oxides and MoO₃ giving rise to well crystallized alkali metal molybdates. finally the activation energies accompanied various decomposition stages were calculated.     

Was ist „Molybdänsäure”︁ oder „Polymolybdänsäure”︁?

What is “Molybdic Acid” or “Polymolybdic Acid”? According to a comparative study of the literature, supplemented by well-aimed experimental investigations and equilibrium calculations, the terms “molybdic acid” or “polymolybdic acid”, used for many substances, species, or solutions in the literature, are applicable to a species, a solution, and two solids:

• a) The monomeric molybdic acid, most probably having the formula MoO₂(OH)₂(H₂O)₂(? H₂MoO₄, aq), exists in (aqueous) solution only and never exceeds a concentration of ≈ 10^?3 M since at higher concentrations it reacts with other monomemeric molybdenum (VI) species to give anionic or cationic polymers.
• b) A concentrated (>0.1 M Mo^VI) aqueous molybdate solution of degree of acidification P = 2 (realized, e. g., by a solution of one of the Mo^VI oxides; by any molybdate solutions whose cations have been exchanged by H₃O⁺ on a cation exchanger; by suitable acidification of a molybdate solution) contains 8 H₃O⁺ and the well-known polyanion Mo₃₆O₁₁₂(H₂O)₁₆^8? exactly in the stoichiometric proportions.
• c) A glassy substance, obtained from an alkali metal salt-free solution prepared according to (b), refers to the compound (H₃O)₈[Mo₃₆O₁₁₂(H₂O)₁₆]·xH₂O, x = 25—29.
• d) A solid having the ideal composition [(H₃O)Mo₅O₁₅(OH)H₂O·H₂O]∞ consists of a polymolybdate skeleton (the well-known ?decamolybdate”? structure), in the tunnels of which H₃O⁺ and H₂O are intercalate. The structure is very unstable if only H₃O⁺ cations are present, but it is enormously stabilized by a partial exchange of H₃O⁺ by certain alkali or alkaline earth metal cations.

For the compounds MoO₃, MoO₃·H₂O, and MoO₃·2H₂O the term ?molybdic acid”? is unjustified. The commercial product ?molybdic acid, ≈85% MoO₃”? is the well-known polymolybdate (NH₄)₂O·4 MoO₃ with a layer structure of the polyanion.     

Diagramme de phases du système Tl2OMoO3

Six thallium(I) molybdates with numerous allotropic modifications have been found in the binary system Tl₂OMoO₃; Tl₄MoO₅, Tl₂Mo₂O₇, Tl₈Mo₁₀O₃₄ (three forms), and Tl₂Mo₇O₂₂ (two forms) melt incongruently; Tl₂MoO₄ and Tl₂Mo₄O₁₃ which are trimorphic melt congruently. For the most part, the compounds were characterized by their powder diagram and by their IR spectrum which allowed comparisons with alkaline molybdates.     

Thermal Decomposition and Dehydration Kinetics of Tetra(piperidinium) Octamolybdate Tetrahydrate in Air

Thermal decomposition of tetra(piperidinium) octamolybdate tetrahydrate, [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O, was investigated in air by means of TG‐DTG/DTA, DSC, TG‐IR and SEM. TG‐DTG/DTA curves showed that the decomposition proceeded through three well‐defined steps with DTA peaks closely corresponding to mass loss obtained. Kinetics analysis of its dehydration step was performed under non‐isothermal conditions. The dehydration activation energy was calculated through Friedman and Flynn‐Wall‐Ozawa (FWO) methods, and the best‐fit dehydration kinetic model function was estimated through the multiple linear regression method. The activation energy for the dehydration step of [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O was 139.7 kJ/mol. The solid particles became smaller accompanied by the thermal decomposition of the title compound.     

CoC2O4·2H2O在空气中的热分解动力学研究

纳米Co3O4具有尖晶石结构,Co3 占据八面体位,具有较高的晶体场稳定化能,在空气中低于800℃时十分稳定,是优良的催化材料[1]。Co3O4还可以作为高比能锂离子电池负极材料具有非常好的电化学活性,充放电容量高达960m A h·g-1。纳米Co3O4在紫外、可见及近红外区域都有良好的吸收效果,因此,在隐身技术、保温节能技术等领域具有潜在的应用前景。所以,Co3O4超细粉体的制备和应用研究具有十分重要的意义。我们合成了草酸盐先驱物制备纳米Co3O4用作隐身材料,因此对先驱物的热分解过程研究是十分必要的。热分析方法在了解先驱物热分解反应的物理…     

TG and DTA study of oxygen depletion and reoxidation of bismuth molybdates (2∶1;2∶3)

Oxygen depletion and reoxidation of bismuth molybdates (2∶1; 2∶3) have been studied by means of isothermal thermogravimetry and DTA measurements. From the isothermal curves, Arrhenius energies were obtained between 411 and 683 K. The activation energies for oxygen depletion from Bi₂O₃·MoO₃ were lower than those for Bi₂O₃·3MoO₃. Two kinetically different types of oxygen release were identified for both molybdates. Arrhenius plots were also obtained from reoxidation experiments: Bi₂O₃·MoO₃ was more easily reoxidable than Bi₂O₃·3MoO₃. The substantial closeness of the respective activation energies suggests that depletion and reoxidation follow the same mechanistic steps. Some DTA measurements confirm the existence of at least two types of reoxidation sites for both oxysalts.     

Mechanochemical synthesis of nanocrystalline nickel-molybdenum compounds and their morphology and application in catalysis: II. Effect of mechanochemical activation parameters—process power density and exposure time—on the composition and structure of nickel-molybdenum compounds

The effect of mechanochemical activation parameters-process power density and the time of treatment of a mixture of nickel hydroxocarbonate NiCO₃ · 2Ni(OH)₂ · nH₂O and ammonium paramolybdate (NH₄)₆Mo₇O₂₄ · 4H₂O -on the phase composition, specific surface area, and morphology of mechanically activated products at different Ni: Mo atomic ratios was studied. It was found that, at a mechanochemical activation process power density of 6.2 W/g, layered transition metal molybdates (LTM compounds) with different amounts of crystal water were the constituents of the products, whereas the products mechanically activated at a power density of 28.0 W/g contained a mixture of LTM compounds and heteropoly compounds with the Anderson structure regardless of activation time.     

草酸锌空心纳米结构的一步固相合成及其表征

本文利用醋酸锌和草酸的一步低热固相化学反应制备了草酸锌空心纳米球，并通过在该反应体系中加入表面活性剂聚乙二醇400得到了草酸锌空心纳米链。采用X-射线粉末衍射（XRD）、透射电镜（TEM）、高倍透射电镜(HRTEM)、扫描电镜(SEM)、红外(IR) 以及热重-差热(TG/DTA)分析对所合成的样品进行了表征.     

水合盐的几种脱水过程探讨

通过差热/热重联机 (DTA/TGA)和差示扫描量热法 (DSC)测定几种盐(Na2SO4·10H2O、CuSO4·5H2O、Na2S2O3·5H2O)的失水过程 ,对水合盐脱水过程几种可能的类型进行探讨。研究表明低温 (100℃以下 )水合盐脱水有两种类型 ,一种直接失去气态水 ,另一类先脱去液态水再进一步变为气态水。并从热力学上理论分析两类脱水过程的原因。     

Crystal structures of some crystal hydrates of binary molybdates

The structures of a series of binary molybdates with the lithium cation LiM(MoO₄) · H₂O (M = K⁺, Na⁺, Rb⁺, NH ₄ ⁺ ) are analyzed and compared. Except for LiNa(MoO₄) · 2H₂O, in all other compounds the lithium cations have a tetrahedral coordination formed by the oxygen atoms of the water molecules and molybdate groups. The structure of LiNa(MoO₄) · 2H₂O was found to contain a unique coordination polyhedron of lithium, i.e., a trigonal bipyramid formed by the O atoms of the water molecules and oxo anions.     

A series of Mixed-Valent Molybdenum Monophosphates,isotypic with leucophosphite represented by CsMo2P2O10 and K1.5Mo2P2O10 · H2O

The structure of two mixed valent molybdenum phosphates, CsMo₂P₂O₁₀ and K_1.5Mo₂P₂O₁₀ · H₂O has been solved from single crystals by X-ray diffraction in the space group P2₁/c with a = 9.428(1), b = 9.943(2), c = 12.348(2) Å and β = 127.38(1)° for CsMo₂P₂O₁₀ and a = 9.721(2), b = 9.805(3), c = 12.329(3) Å and β = 128.73(2)° for K_1.5Mo₂P₂O₁₀ · H₂O. These compounds isotypic with NH₄Mo₂P₂O₁₀ · H₂O and RbMo₂P₂O₁₀ · (1 ? x)H₂O exhibit the leucophosphite structure. The possibility of cationic non stoichiometry in this structure is also shown by the synthesis of two isotypic compounds A_1.5Mo₂P₂O₁₀ · xH₂O (A = Rb, Tl). In these monophosphates, one site Mo(1) is fully occupied by Mo^V, whereas the other octahedral site Mo(2) exhibits a variable valency Mo^III? Mo^IV to Mo^V. The main difference between these different phosphates deals with the distribution of the A cations inside the tunnels, depending upon their size and their content.     

Keggin-type cesium salt of first series transition metal-substituted phosphomolybdates: one-pot easy synthesis,structural, and spectral analysis

The Keggin-type cesium salt of transition metal-substituted phosphomolybdates, Cs₅[PCo(H₂O)Mo₁₁O₃₉]?·?6H₂O (1) and Cs₅[PMn(H₂O)Mo₁₁O₃₉]?·?6H₂O (2), were synthesized from commercially available H₃PMo₁₂O₄₀. The compounds were characterized by thermal, structural, and spectroscopic techniques. X-ray structural analysis reveals that, in these isostructural disordered compounds, the transition metal (Co/Mn) and Mo atoms are distributed over 12 positions. The presence of Co/Mn atoms was confirmed by powder XRD, FT-IR, DR-UV-Vis, ESR, and ³¹P NMR studies.     

Characterization and TG-MS studies of lactato and bipyridine-lactato complexes of Co(II) and Ni(II)

Two lactates and four new mixed ligand complexes with formulae Co(lact)₂·2H₂O, Ni(lact)₂·3H₂O, Co(4-bpy)(lact)₂, Co(2,4'-bpy)₂(lact)₂, Ni(4-bpy)(lact)₂·2H₂O and Ni(2,4'-bpy)₂(lact)₂ (where 4-bpy=4,4'-bipyridine, 2,4'-bpy=2,4'-bipyridine, lact=CH₃CH(OH)COO^-) were isolated and investigated. The thermal behaviour of compounds was studied by thermal analysis (TG, DTG, DTA). In the case of hydrated complexes thermal decomposition starts with the release of water molecules. The compounds decompose at high temperature to metal(II) oxides in air. A coupled TG-MS system was used to analyse the principal volatile products of thermolysis and fragmentation processes of obtained complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

(Zn1-xMnx)C2O4·2H2O在空气中的热分解动力学研究

用热分析（TG-DTG/DTA）、X射线衍射（XRD）技术和透射电镜（TEM）研究了固态物质Zn_1-xMn_xC₂O₄•2H₂O在空气中热分解的过程。热分析结果表明，Zn_1-xMn_xC₂O₄•2H₂O在空气中分两步分解，其失重率与理论计算失重率相吻合。 XRD和TEM结果表明，Zn_1-xMn_xC₂O₄•2H₂O分解的最终产物为Zn_1-xMn_xO,其颗粒大小约为10-13 nm。在非等温条件下对Zn_1-xMn_xC₂O₄•2H₂O的热分解动力学进行了分析。用Friedman法和Flynn-Wall-Ozawa(FWO)法求取了分解过程的活化能E，并用多元线性回归给出了可能的机理函数。Zn_1-xMn_xC₂O₄•2H₂O两步热分解的活化能分别为155.7513 kJ/mol 和215.9397 kJ/mol。     

Synthesis and characterization of solid molybdenum(VI) complexes with glycolic,mandelic and tartaric acids. Photochemistry behaviour of the glycolate molybdenum complex

The complexes (NH₄)₂[MoO₂(C₂H₂O₃)₂]·H₂O, (NH₄)₂[MoO₂(C₈H₆O₃)₂] and (NH₄)₂[MoO₃(C₄H₄O₆)]·H₂O were prepared by reaction of MoO₃ with glycolic, mandelic and tartaric acids, respectively. The complexes were characterized by elemental and thermal analysis, IR spectroscopy and X-ray diffraction. Crystals of the glycolate and tartarate complexes are orthorhombic and the mandelate complex is monoclinic. Elemental and thermal analysis data showed that the glycolate and tartarate complexes are monohydrated. Hydration water is not present in the structure of the mandelate complex. IR spectra showed COO^? is involved in coordination as well as the oxygen atom of the deprotonated hydroxyl group of the α-carbon. The glycolate molybdenum complexes with general formula M₂[MoO₂(C₂H₂O₃)₂]·nH₂O, where M is an alkali metal and n?=?1 or ½, were also prepared and characterized. Aqueous solutions of the glycolate complex become blue and mandelate and tartarate complexes change to yellow or brown when exposed to UV-radiation.     

Two pillared-layer architectures constructed from copper molybdate sheets and linear organonitrogen ligands

In this article, we report the syntheses and structures of two new inorganic–organic hybrid copper molybdates with organonitrogen ligands, [Cu₂(bpe)(Mo₂O₈)]?·?3H₂O (1) (bpe?=?1,2-bis(4-pyridyl)ethene) and [{Cu(4,4′-bpy)}₂(Mo₂O₈)] (2) (bpy?=?4,4′-bipyridine). Elemental analyses, IR spectra, EPR spectra, XPS spectra, TG analyses and single crystal X-ray diffraction were used to characterize these compounds. The structure of 1 exhibits a pillared-layer framework built up from unusual bimetallic two-dimensional sheets pillared by linear bpe ligands. Compound 2 features a pillared-layer structure constructed from copper molybdate 4,8-net sheets connected by 4,4′-bpy ligands.     

A metal-oxo cluster-supported transition metal complex: synthesis,structure and properties of [Cu(phen)2]2[{Cu(phen)}2Mo8O26]·H2O

[Cu(phen)₂]₂[{Cu(phen)}₂Mo₈O₂₆]·H₂O has been synthesized from MoO₃, H₂MoO₄, Cu(Ac)₂·H₂O and 1,10-phenanthroline in aqueous solution using the hydrothermal method and characterized by single-crystal X-ray structure analysis. The title compound consists of a centrometric β-octamolybdate-supported complex anion [{Cu(phen)}₂Mo₈O₂₆]²⁻, two bis-phenanthroline Cu(I) cations, and one water molecule of crystallization.     

Thermal behaviour and vibrational spectra of (NH4)3Ga(C2O4)3 · 3H2O and (NH4)3Al(C2O4)3 · 3H2O

The IR and Raman spectra and the thermal behaviour of the isomorphous compounds (NH₄)₃Ga(C₂O₄)₃·3H₂O and (NH₄)₃Al(C₂O₄)₃·3H₂O were investigated. Detailed stoichiometries, sustained by TG, DTA and IR spectroscopic analyses, were found in both cases. Different results, associated with the different polarizing powers of the metal cations, were obtained. The first evidence was found of the formation of basic gallium carbonates.     

Partial thermal reduction of ammonium paratungstate tetrahydrate

Thermal decomposition of ammonium paratungstate tetrahydrate, (NH₄)₁₀[H₂W₁₂O₄₂]·4H₂O has been followed by simultaneous TG/DTA and online evolved gas analysis (TG/DTA-MS) in flowing 10% H₂/Ar directly up to 900°C. Solid intermediate products have been structurally evaluated by FTIR spectroscopy and powder X-ray diffraction (XRD). A previously unexplained exothermic heat effect has been detected at 700–750°C. On the basis of TG/DTA as well as H₂O and NH₃ evolution curves and XRD patterns, it has been assigned to the formation and crystallization heat of γ-tungsten-oxide (WO_2.72/W₁₈O₄₉) from β-tungsten-oxide (WO_2.9/W₂₀O₅₈) and residual ammonium tungsten bronze.