Thermogravimetric analysis of wheatleyite Na<Subscript>2</Subscript>Cu<Superscript>2+</Superscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>·2H<Subscript>2</Subscript>O

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. The anhydrous oxalate mineral moolooite CuC₂O₄ as the natural copper(II) oxalate mineral is a classic example. Another example of a natural oxalate is the mineral wheatleyite Na₂Cu²⁺(C₂O₄)₂·2H₂O. High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition of wheatleyite at 255°C. Two higher temperature mass losses are observed at 324 and 349°C. Higher temperature mass losses are observed at 819, 833 and 857°C. These mass losses as confirmed by mass spectrometry are attributed to the decomposition of tennerite CuO. In comparison the thermal decomposition of moolooite takes place at 260°C. Evolved gas mass spectrometry for moolooite shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper(II) oxalate as compared to the synthetic compound which is the dihydrate.     

Thermal decomposition of humboldtine: A high resolution thermogravimetric and hot stage Raman spectroscopic study

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. Humboldtine as the natural iron(II) oxalate mineral is a classic example. Thermogravimetry coupled to evolved gas mass spectrometry shows dehydration takes place in two steps at 130 and 141°C. Loss of the oxalate as carbon dioxide occurs at 312 and 332°C. Dehydration is readily followed by Raman microscopy in combination with a thermal stage and is observed by the loss of intensity of the OH stretching vibration at 3318 cm^-1. The application of infrared emission spectroscopy supports the results of the TG-MS. Three Raman bands are observed at 1470, 1465 and 1432 cm^-1 attributed the CO symmetric stretching mode. The observation of the three bands supports the concept of multiple iron(II) oxalate phases. The significance of this work rests with the ability of Raman spectroscopy to identify iron(II) oxalate which often occurs as a film on a host rock.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal treatment of whewellite—a thermal analysis and Raman spectroscopic study

Thermal transformations of natural calcium oxalate monohydrate known in mineralogy as whewellite have been undertaken using a combination of thermal analysis and Raman microscopy with the use of a thermal stage. High resolution thermogravimetry shows that three mass loss steps occur at 162, 479 and 684 °C.Evolved gas mass spectrometry shows that water is evolved in the first step and carbon dioxide in the second and third mass loss steps. The changes in the molecular structure of whewellite can be followed by the use of the in situ Raman spectroscopy of whewellite at the elevated temperatures. The whewellite is stable up to around 161 °C, above which temperature the anhydrous calcium oxalate is formed. At 479 °C, the oxalate transforms to calcium carbonate with loss of carbon dioxide. Above 684 °C, calcium oxide is formed.     

Metal oxalates in paints: a Raman investigation on the relative reactivities of different pigments to oxalic acid solutions

One degradation phenomenon that occurs in artworks is the formation of metal oxalates on their surfaces. In order to gain insight into the inclination of pigments to produce oxalates, nine pigments including Na, Ca, Fe, Pb and Cu cations were selected to react with oxalic acid solutions at different concentrations (1 M, 0.1 M, 0.01 M and 0.005 M). Micro-Raman spectroscopy was used to detect the different reaction products. Pigments containing calcium (calcite, gypsum and Volterra gypsum) showed a high tendency to form weddellite as well as whewellite, especially at high acidic concentrations; among copper-based pigments (malachite, azurite, verdigris), the formation of moolooite was observed for high concentrations of acid and down to the lowest concentration (0.005 M) in the case of verdigris. Lead oxalate was detected on lead white. No iron oxalates were observed for hematite; the formation of calcium oxalate crystals was observed instead. Ultramarine blue reacted to produce elemental sulfur. According to the results obtained, calcite and verdigris showed the highest reactivity in oxalic acid environments, resulting in a high tendency to form calcium and copper oxalates, even at very low acidic concentrations; this behavior seems to arise from the high solubilities of these pigments in acidic environments.     

Study of Fe Addition on the Thermal Decomposition of Coprecipitated Oxalates for the Bi-based Superconductor Synthesis

This work introduces results obtained during the preparation of a Bi-based material with superconducting properties by oxalate coprecipitation. The influence of Fe presence on the precursors thermal stability and on the superconducting phases formation mechanism are presented. The thermal decomposition and the stability in air of FeC₂O₄×2H₂O and also of the components mixture were studied by DTA/TG. It was evidenced that iron oxalate decomposes at the lowest temperature compared to the decomposition temperatures of the individual oxalates. XRD, IR and TEM/ED studies were approached to investigate the individual oxalates and the mixture coprecipitates for the high-T _c superconducting material synthesis. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Raman spectroscopic study of thermally treated glushinskite--the natural magnesium oxalate dihydrate

Raman spectroscopy has been used to study the thermal transformations of natural magnesium oxalate dihydrate known in mineralogy as glushinskite. The data obtained by Raman spectroscopy was supplemented with that of infrared emission spectroscopy. The vibrational spectroscopic data was complimented with high resolution thermogravimetric analysis combined with evolved gas mass spectrometry. TG-MS identified two mass loss steps at 146 and 397 degrees C. In the first mass loss step water is evolved only, in the second step carbon dioxide is evolved. The combination of Raman microscopy and a thermal stage clearly identifies the changes in the molecular structure with thermal treatment. Glushinskite is the dihydrate phase in the temperature range up to the pre-dehydration temperature of 146 degrees C. Above 397 degrees C, magnesium oxide is formed. Infrared emission spectroscopy shows that this mineral decomposes at around 400 degrees C. Changes in the position and intensity of the CO and CC stretching vibrations in the Raman spectra indicate the temperature range at which these phase changes occur.     

Crystal structures and topological aspects of the high-temperature phases and decomposition products of the alkali-metal oxalates M2[C2O4] (M=K, Rb, Cs)

The high-temperature phases of the alkali-metal oxalates M2[C2O4] (M = K, Rb, Cs), and their decomposition products M2[CO3] (M = K, Rb, Cs), were investigated by fast, angle-dispersive X-ray powder diffraction with an image-plate detector, and also by simultaneous differential thermal analysis (DTA)/thermogravimetric analysis (TGA)/mass spectrometry (MS) and differential scanning calorimetry (DSC) techniques. The following phases, in order of decreasing temperature, were observed and crystallographically characterized (an asterisk denotes a previously unknown modification): *alpha-K2[C2O4], *alpha-Rb2[C2O4], *alpha-Cs2[C2O4], alpha-K2[CO3], *alpha-Rb2[CO3], and *alpha-Cs2[CO3] in space group P6(3)/mmc; *beta-Rb2[C2O4], *beta-Cs2[C2O4], *beta-Rb2[CO3], and *beta-Cs2[CO3] in Pnma; gamma-Rb2[C2O4], gamma-Cs[C2O4], gamma-Rb2[CO3], and gamma-Cs2[CO3] in P2(1)/c; and delta-K2[C2O4] and delta-Rb2[C2O4] in Pbam. With respect to the centers of gravity of the oxalate and carbonate anions, respectively, the crystal structures of all known alkali-metal oxalates and carbonates belong to the AlB2 family, and adopt either the AlB2 or the Ni2In arrangement depending on the size of the cation and the temperature. Despite the different sizes and constitutions of the carbonate and oxalate anions, the high-temperature phases of the alkali-metal carbonates M2[CO3] (M = K, Rb, Cs), exhibit the same sequence of basic structures as the corresponding alkali-metal oxalates. The topological aspects and order-disorder phenomena at elevated temperature are discussed.     

Thermal decomposition of mixed oxalates

The thermogravimetric analysis of several coprecipitated zinc-copper oxalates in nitrogen is reported. The thermal decompositions of these mixed oxalates show a separate single step for dehydration and decomposition in the mass loss versus temperature curve. It is found that the onset temperature decreases with composition. For example, it decreases from 380 for zinc oxalate to 260 for copper oxalate. The end-product is mixed oxides and copper metal. These studies indicate the formation of an interpenetrating structure or mixed crystals during coprecipitation. Rate parameters have been calculated for dehydration and decomposition.One of us (B. D. D.) is grateful to the University Grants Commission, New Delhi, India, for the award of a research fellowship.     

Analysis of a coloured Dutch map from the eighteenth century: the need for a multi-analytical spectroscopic approach using portable instrumentation

A Dutch map from the eighteenth century was multi-analytically analysed making use of energy dispersive X-ray fluorescence (EDXRF), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), Raman and scanning electron microscopy coupled to energy dispersive spectrometry (SEM-EDS). The cellulosic support was characterised and its state of conservation was evaluated. Besides, paramagnetic impurities were detected together with copper metallic chips. The colours present in some areas of the map were also analysed. Vermilion, carbon black and organic pigments were found. Surprisingly, in the green areas, the rare presence of the mineral moolooite (copper oxalate) was detected. A possible biological attack is discussed in order to explain the presence of such compound. Almost all of the techniques used in the analysis were portable, non-destructive and non-invasive, which is very desirable when analysing objects belonging to Cultural Heritage. The need for a multi-analytical approach using portable instrumentation is also discussed.     

Multianalytical approach to the analysis of English polychromed alabaster sculptures: μRaman, μEDXRF,and FTIR spectroscopies

A complete study of several English polychromed alabaster sculptures is presented. The support, pigment, and binders were characterised by combining μEDXRF, μRaman, and FTIR spectroscopies. Among the pigments, minium, vermilion, lead white, carbon black, red iron oxide, and a degraded green copper pigment were determined, together with gold leaf. The presence of the rare mineral moolooite (copper oxalate) was also found as a degradation product in the green areas, where weddellite (calcium oxalate dihydrate) was also determined. These facts, together with degradation of the green copper pigment, suggest microbiological degradation of the original materials. Remains of glue and a varnish were also determined by FTIR spectroscopy and principal-components analysis (PCA) of the spectra. Finally, PCA analysis was carried out to confirm whether the pieces came from the same quarry.     

Old acid,new chemistry. Negative metal anions generated from alkali metal oxalates and others

A brief search in Sci Finder for oxalic acid and oxalates will reward the researcher with a staggering 129,280 hits. However, the generation of alkali metal and silver anions via collision-induced dissociation of the metal oxalate anion has not been previously been reported, though Tian and coworkers recently investigated the dissociation of lithium oxalate [18]. The exothermic decomposition of alkali metal oxalate anion to carbon dioxide in the collision cell of a triple quadrupole mass spectrometer leaves no place for the electron to reside, resulting in a double electron-transfer reaction to produce an alkali metal anion. This reaction is facilitated by the negative electron affinity of carbon dioxide and, as such, the authors believe that metal oxalates are potentially unique in this respect. The observed dissociation reactions for collision with argon gas (1.7−1.8 × 10⁻³ mbar) for oxalic acid and various alkali metal oxalates are discussed and summarized. Silver oxalate is also included to demonstrate the propensity of this system to generate transition-metal anions, as well.     

Thermal behavior of Ca2+ and Cu2+ oxalates obtained by precipitation in homogeneous solution from dimethyl oxalate hydrolysis

Mixed calcium and copper oxalates, with different proportions of Ca²⁺ and Cu²⁺ ions, were precipitated by dimethyl oxalate hydrolysis in homogeneous solution. The compounds were evaluated by means of scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetry (TG), and differential thermal analysis (DTA). The results suggested quantitative precipitation without solid solution formation. From the TG and DTA curves, it was possible to evaluate the Ca²⁺ ion proportion in the solid phase and to confirm the precipitation of the individual species.     

苯酚和草酸二甲酯酯交换合成碳酸二苯酯反应产物的气相色谱-质谱分析

采用气相色谱-质谱联用、程序升温方法对苯酚和草酸二甲酯酯交换合成碳酸二苯酯反应产物进行了分析。实现了对钛酸四丁酯催化苯酚和草酸二甲酯二甲酯酯交换合成草酸二苯酯反应的主产物草酸二苯酯、中间产物甲基苯基草酸酯、副产物丁基苯基草酸酯、2-甲基丁醛、正丁醚及草酸二苯酯脱羰基生成碳酸二苯酯反应产物的定性，验证了苯酚和草酸二甲酯酯交换合成碳酸二苯酯反应分三步进行的反应模式。     

聚亚苯基苯并二噻唑与聚亚苯基苯并二噁唑的热分解

用高分辨裂解气相色谱 质谱（ＨＲＰｙＧＣ ＭＳ）研究了聚亚苯基苯并二噻唑、聚亚苯基苯并二唑的热分解行为,鉴定了相应裂解产物的组成、分布及其与高分子结构的关系,并用热重法（ＴＧ）测定了它们的热分解反应动力学参数,提出了其热分解反应机理     

Kinetic study of Y, Ba, Cu oxalates and coprecipitated Y-Ba-Cu oxalate

The kinetics of the decomposition of Y, Ba and Cu oxalates and coprecipitanted Y-Ba-Cu oxalate was investigated under a nitrogen atmosphere on the basis of dynamic thermogravimetric data, the average activation energies of the decomposition of Y, Ba and Cu oxalates were obtained from the slopes of the T. Ozawa plot. The average activation energies for the dehydration of these oxalate and coprecipitated Y-Ba-Cu oxalate were also evaluated from the thermogravimetric curves.     

Peculiarities of polythermic decomposition of iron,cobalt and nickel oxalates within pores of photonic crystals based on SiO<Subscript>2</Subscript> in atmosphere with oxygen lack

Iron(II), cobalt(II) and nickel(II) oxalates were synthesized as nanofractals inside the voids of the photonic crystals based on SiO₂. Guest substances undergone polythermic decomposition within the pores of the photonic crystals in helium atmosphere containing of oxygen traces (∼1 Pa) under static conditions. Pyrolysis of Fe(COO)₂·2H₂O, Co(COO)₂·2H₂O and Ni(COO)₂·2H₂O studied by TG and DSC techniques results in the formation of the metal oxides. The nanoparticles of Fe₂O₃, CoO (Co₃O₄) and NiO populated the interspheric voids of the photonic crystals exhibited no ferromagnetic effects indicating that no metallic inclusions were formed in helium in the presence of O₂ traces. The exothermic effect was observed by the thermal decomposition of the cobalt(II) oxalate only under oxygen lack.     

Dimorphism of a new CuI coordination polymer:synthesis,crystal structures and properties of catena[CuI(2-iodopyrazine-N)] and poly[CuI(mu2-2-iodopyrazine-N,N')

Two modifications of the new copper(I) iodide coordination polymer CuI(2-iodopyrazine) were obtained by the reaction of CuI and 2-iodopyrazine in acetonitrile. During this reaction, intensely yellow crystals of form I appear first which transform within several minutes to intensely red crystals of form II which is the thermodynamically most stable form at room temperature. In catena[CuI(2-iodopyrazine-N)] (form I; a = 4.1830 (6) A; b = 10.814 (1) A; c = 17.961 (4) A; V = 812.5 (2) A(3); orthorhombic; P2(1)2(1)2(1); Z = 4), corrugated CuI double chains are found in which each copper atom is coordinated by one additional 2-iodopyrazine ligand. In poly[CuI(mu-2-iodopyrazine-N,N')] (form II; a = 4.2679 (5) A; b = 13.942 (2) A; c = 13.017 (2) A; b = 92.64 (1) degrees; V = 773.76 (2) A(3); monoclinic; P2(1)/c; Z = 4), CuI single chains occur which are connected via mu-N,N' coordination by the 2-iodopyrazine ligands to layers parallel to (010). The thermal behavior of both forms was investigated using simultaneous differential thermoanalysis, thermogravimetry, and mass spectrometry as well as differential scanning calorimetry and temperature resolved X-ray powder diffraction. On heating, both forms decompose to copper(I) iodide, and the decomposition temperature of form I is significantly lower than that of form II. From all experiments, there is no indication of a phase transition of one form into the other or for the formation of a phase with lower amine content.     

固相配位化学反应研究(ⅩⅩⅤ)——草酸高铁与路易氏间碱的固相反应

用气相色谱法研究了草酸铁(Ⅲ)与路易氏碱在氢气氛和氦气氛中的固相反应。结果表明草酸铁与氢氧化钠在室温下明显发生固相反应,其产物随温度升高而变化。同时发现α-Fe对草酸钠有催化分解作用,与四硫化钾低于220°C时发生固相反应,生成KFeS₂,但只有1/4草酸铁参加了固相反应,反应不完全,对固相反应的机制及反应气氛的影响也进行了探讨。     

Nanorods of transition metal oxalates: A versatile route to the oxide nanoparticles

A versatile route has been explored for the synthesis of nanorods of transition metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates using reverse micelles. Transmission electron microscopy shows that the as-prepared nanorods of nickel and copper oxalates have diameter of 250 nm and 130 nm while the length is of the order of 2.5 μm and 480 nm, respectively. The aspect ratio of the nanorods of copper oxalate could be modified by changing the solvent. The average dimensions of manganese, zinc and cobalt oxalate nanorods were 100 μm, 120 μm and 300 nm, respectively, in diameter and 2.5 μm, 600 nm and 6.5 μm, respectively, in length. The aspect ratio of the cobalt oxalate nanorods could be modified by controlling the temperature.The nanorods of metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates were found to be suitable precursors to obtain a variety of transition metal oxide nanoparticles. Our studies show that the grain size of CuO nanoparticles is highly dependent on the nature of non-polar solvent used to initially synthesize the oxalate rods. All the commonly known manganese oxides could be obtained as pure phases from the single manganese oxalate precursor by decomposing in different atmospheres (air, vacuum or nitrogen). The ZnO nanoparticles obtained from zinc oxalate rods are ～55 nm in diameter. Oxides with different morphology, Fe₃O₄ nanoparticles faceted (cuboidal) and Fe₂O₃ nanoparticles (spherical) could be obtained.     

Should acid ammonium oxalate replace hydroxylammonium chloride in step 2 of the revised BCR sequential extraction protocol for soil and sediment?

The revised, four-step BCR sequential extraction for soil or sediment has been compared with an alternative procedure in which 0.2 mol l⁻¹ ammonium oxalate (pH 3) replaced 0.5 mol l⁻¹ hydroxylammonium chloride (pH 1.5) in step 2, the reducible step. A variety of substrates were studied: BCR CRM601, a sewage sludge amended soil, two industrial soils, and a steel manufacturing by-product (basic oxygen furnace filter cake). Greater amounts of iron were recovered in step 2 when acid ammonium oxalate was used, for all substrates. Similar trends were observed for copper. Manganese and zinc were not strongly affected by the procedural modification, except for zinc in the two industrial soils, where oxalate extraction proved more efficient than use of hydroxylammonium chloride. A large proportion of the calcium and lead isolated in step 2 of the BCR procedure was not released until step 3 when the alternative procedure with oxalate in step 2 was used. This is probably due to rapid precipitation of analyte oxalates from solution. Thus, whilst oxalate offers superior dissolution of iron-containing matrix components, it should not be used if calcium or lead concentrations are to be measured. Selection of the most appropriated sequential extraction protocol for use in a particular study must always be carried out on the basis of “fitness for purpose” criteria. However, the revised BCR protocol, involving use of 0.5 mol l⁻¹ NH₂OH·HCl in the reducible step, appears to be more generally applicable than procedures involving acid ammonium oxalate.