Thermal Analysis of Magnesium Tris(maleato) Ferrate(III) Dodecahydrate. Physico-chemical studies

Thermal analysis of magnesium tris(maleato) ferrate(III) dodecahydrate has been studied from ambient to 700°C in static air atmosphere employing TG, DTG, DTA, XRD, Mössbauer and infrared spectroscopic techniques. The precursor decomposes to iron(II) intermediate species along with magnesium maleate at 248°C. The iron(II) species then undergo oxidative decomposition to give α-Fe₂O₃ at 400°C. At higher temperatures magnesium maleate decomposes directly to magnesium oxide, MgO, which undergoes a solid state reaction with α-Fe₂O₃ to yield magnesium ferrite (MgFe₂O₄) at 600°C, a temperature much lower than for ceramic method. The results have been compared with those of the oxalate precursor.     

Thermal and X-ray diffraction studies of the solid–solid interactions in CuO–MoO3/MgO system

The solid–solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.     

Preparation of anhydrous magnesium chloride in a gas-solid reaction with ammonium carnallite

Dehydrated ammonium carnallite was synthesized with bischofite from salt lake and ammonium chloride solution in a 1:1 molar ratio of MgCl₂:NH₄Cl, dehydrated at 160°C for about 4 h. The yield was above 85%. The product was then mixed with solid-state ammonium chloride with a 1:4 mass ratio for the further dehydration at 410°C. The decomposition of NH₄Cl made a pressure of NH₃ at 30.5 kPa to prevent the hydrolysis of ammonium carnallite. The anhydration of magnesium chloride was achieved at 700°C. The results showed that anhydrous magnesium chloride contains magnesium oxide in an amount that was less than 0.1% by weight. XRD pattern and SEM micrograph showed a good dispersion of ammonium carnallite and anhydrous magnesium chloride crystals with well-distributed big grains, just enough to meet the need for the production of magnesium metal in the electrolysis process. __________ Translated from Chinese Journal of Applied Chemistry, 2005, 22(8) (in Chinese)     

Production and properties of double potassium-ammonium sulfate

Process in which double potassium-ammonium sulfate is produced from potassium chloride and sulfuric acid was studied. A thermal analysis of the compound KNH₄SO₄ was made and the melting and decomposition points of double potassium-ammonium sulfate were determined. An X-ray phase analysis revealed the processes occurring when double potassium-ammonium sulfate is calcined at temperatures of 330, 370, and 580°C. The chemical processes in which double potassium-ammonium sulfate decomposes to give ammonium hydrosulfate were examined.     

Synthesis of nanosized zinc and magnesium chromites starting from PVA–metal nitrate solutions

In this article, we present a detailed study regarding the preparation of nanosized zinc and magnesium chromites starting from a 4% poly(vinyl)alcohol (PVA) aqueous solution and metal nitrates. The controlled thermal treatment of these solutions has permitted the isolation of an intermediary solid product, used as precursor of the preferred mixed oxides: zinc and magnesium chromites. The as-obtained precursors were characterized by FT-IR spectrometry and thermal analysis. FT-IR spectrometry has evidenced the disappearance of the NO₃ ^? anions at 140?°C, due to the redox interaction with PVA. The thermal decompositions of the synthesized precursors were different, as resulted from both thermal analysis and FT-IR spectrometry. Thus, while ZnCrPVA precursor decomposes up to 400?°C with formation of zinc chromite, the precursor MgCrPVA decomposes up to 500?°C, with formation of MgCrO₄ as intermediary amorphous phase. By thermal decomposition of MgCrO₄ at 500?°C, weakly crystallized MgCr₂O₄ powder is obtained. The obtained chromite powders consist of fine nanoparticles with diameters ranging from 10 to 30?nm at 500?°C; on raising the annealing temperature to 1000?°C, chromite particles become octahedral, with diameter up to 500?nm, but with no sign of sintering.     

Synthesis and Crystal Structure of Ammonium Cyanimide NH4HCN2

The compound NH₄HCN₂ ( 1 ) was prepared by the reaction of H₂CN₂ with liquid ammonia. The ammonium salt 1 was characterized by a low temperature single‐crystal X‐ray structure analysis. The anionic part of the structure consists of HCN₂^? anions, which are connected via N–H···N bonds (H···N distance: 2.47Å, DHA: 165°). The N–H···N hydrogen bonds of the ammonium ion to the anions range from 2.00 to 2.14Å (DHA = Donor···Acceptor angles: 165–176°), all N–H···N interactions together give rise to a three‐dimensional network. 1 decomposes quantitatively to dicyandiamide at room temperature.     

Carbon nanostructures in an ammonium medium

The reaction of fullerene C₆₀, single- and multi-walled carbon nanotubes (SWNTs and MWNTs, respectively), as well as a mixture of these carbon nanomaterials with 8–10 wt% of ammonium chloride (reaction promoter) with ammonia as a source of hydrogen and nitrogen, at an initial ammonium pressure of 0.6–0.8 MPa in the temperature range 20–550°C was studied. The reaction at 450°C is accompanied by hydrogenation and nitrogenation of the fullerite matrix, and at 500°C decomposition of the fullerene carcass occurs. Physicochemical properties of the hydride-nitride phases formed by the reaction were studied. Single- and multiwalled nanotubes were shown to be stable in an ammonium medium at 20–450°C, while at 500°C their ends are opened.     

Physico–chemical properties of CdO–Al2O3 catalysts. I – Structural characteristics

Alumina gels AN6 and AN7 were prepared by precipitation with NaOH from hydrated aluminum sulfate at pH 6 and 7, respectively. A third alumina gel AA7 was similarly prepared, but by precipitation with 30% ammonia. Pure cadmia C8 and C9 were precipitated from cadmium sulfate at pH 8 and 9 using NaOH. Five mechanically mixed gels ACM (1:0.25), ACM (1:0.5), ACM (1:1), ACM (0.5:1) and ACM (0.25:1) were prepared by thoroughly mixing the appropriate molar ratios of AN7 and C8. Also, five coprecipitated gels ACC (1:0.25), ACC (1:0.5), ACC (1:1), ACC (0.5:1) and ACC (0.25:1) were coprecipitated by dropping simultaneously the appropriate volumes of 1 M aluminum sulfate, 1 M cadmium sulfate and 3 M NaOH. Calcination products at 400, 500, 600, 800 and 1000 °C were obtained from each preparation.TG–DTA patterns of uncalcined samples were analyzed and the XRD of all 1000 °C-products and some selected samples calcined at 400–800 °C were investigated. The thermal behaviors of pure and mixed gels depend on the precipitating agent, pH of precipitation, chemical composition and method of preparation. Generally, calcination at temperatures below 800 °C gave poorly crystalline phases. Well crystalline phases are obtained at 800 and 1000 °C. For pure alumina γ-Al₂O₃ was shown as 400 °C-calcination product that transforms into the δ form around 900 °C and later to θ-Al₂O₃ as a major phase and α-Al₂O₃ as a minor phase at 1000 °C. CdO was shown by 500 °C-calcined cadmia gel that showed color changes with rise of calcination temperature. The most stable black cadmium oxide phase (Monteponite) is obtained upon calcination at 1000 °C. Thousand degree celsius- calcined mixed oxides showed θ-Al₂O₃, α-Al₂O₃, CdAl₂O₄ and monteponite which dominate depending on the chemical composition.     

High temperature reactions of titanium(IV) oxide with some alkali persulfates and their decomposition products

The solid state reactions between TiO₂ and Na₂S₂O₈ or K₂S₂O₈ have been investigated using TG, DTG, DTA, IR, and X-ray diffraction studies in the range of 20 to 1000°C.It has been shown that TiO₂ reacts stoichiometrically (1 : 1) with Na₂S₂O₈ in the range of 160 and 220°C forming the complex sodium monoperoxodisulfato—titanium(IV) as characterized by IR and X-ray analysis. The new complex then decomposes into the reactants above 190°C.An exothermic reaction has been observed between TiO₂ and molten K₂S₂O₇ at mole ratio 1:2 respectively and higher, in the range of 280 and 350°C. The IR and X-ray analyses have shown the formation of a complex namely, potassium tetrasulfato titanium(IV) for which the formula and structure have been proposed. This complex decomposes at higher temperatures into K₂SO₄ and a mixed sulfate of potassium and titanium. The mixed sulfate melts at 620°C and decomposes into K₂SO₄, TiO₂, and the gaseous SO₃.On the other hand, Na₂S₂O₈ decomposes in a special mode producing a polymeric product of Na₁₀S₉O₃₂. Decomposition of this species occurs after melting at 560°C into Na₂SO₄ and sulfur oxides. The decomposition reaction has been proved to be catalysed by TiO₂ itself.     

The thermal decomposition of (NH4)4V2O11 in a nitrogen atmosphere and the kinetics of the first decomposition step

Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min^?1 ammonium peroxo vanadate, (NH₄)₄V₂O₁₁, decomposes to (NH₄)[VO (O₂)₂ (NH₃)] (above 93°C); this in turn decomposes to (NH₄) [VO₃ (NH₃)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol^?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol^?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.     

THERMAL REACTIONS IN SYNTHETIC APATITE–AMMONIUM SULFATE MIXTURE

The thermal reactions in the mixtures of hydroxylapatite or fluorapatite and (NH₄)₂SO₄up to 500°C were studied with the purpose of elaborating the conditions of obtaining calcium–ammonium cyclophosphate that could be used as fertilizer. Thermal analysis with a simultaneous FTIR analysis of the evolved gases as well as the analyses of chemical and phase composition of solid products were performed. The thermal changes in the mixtures could be divided into three steps: (1) decomposition of (NH₄)₂SO₄and reactions of apatite with these products at 250–420°C, (2) calcium ammonium polyphosphate formation at 290–450°C, and (3) reaction of CaSO₄with CaNH₄P₃O₉at 320–500°C. Higher concentrations of NH₃in the gas phase promote the formation of CaNH₄P₃O₉and increase its stability. Calcination at temperatures above 350°C causes decomposition of CaNH₄P₃O₉with a decrease in the content of water-soluble phosphorus and evolvement of SO₂.     

Crosslinking of polystyrene under friedel–crafts conditions in dichloroethane and carbon tetrachloride solvents through the formation of strongly colored polymer–AlCl3–solvent complexes

Polystyrene was crosslinked in either 1,2-dichloroethane or carbon tetrachloride in the presence of aluminum chloride. Apparently, the reactions involve Friedel–Crafts substitution of phenyl ring with CH₂CH₂Cl or CCl₃ groups, which than participate in crosslinking, giving CH₂CH₂ or CCl₂, CCl, and C bridges. In the first stage a charge-transfer complex is formed between AlCl₃, polystyrene and the solvent. After heating this complex above 35–40°C a rapid formation of HCl occurs and a crosslinked polymer is formed. This final product is insoluble, infusible, and inflammable. It decomposes at 400°C without melting.     

Effect of preparative conditions on the surface characteristics of mixed zirconium and titanium oxides

The surface characteristics of mixed zirconium and titanium oxides prepared from different starting materials are investigated. One mode of preparation entailed the use of zirconium sulfate and titanium oxysulfate as starting materials and ammonium hydroxide as precipitating agent. The produced oxides were washed to different extents to obtain samples with different sulfate content. A second preparative mode used zirconium oxychloride and titanous chloride as starting materials also with ammonium hydroxide as precipitating agent. The oxidation of the titanous to the titanic form for these oxides was carried out by means of oxygen gas. Resulting samples were heat treated at 400 °C and 600 °C, and textural characteristics determined from the adsorption of N₂ at 77 K, complemented by infrared and thermal studies. The samples precipitated from the oxychloride and chloride salts of zirconium and titanium, as well as those precipitated from the sulfate and oxysulfate salts and washed free of the sulfate ions displayed quite similar textural characteristics. The unheated samples and those heat-treated at 400 °C were mesoporous, with some microporosity, and relatively large surface areas in the order of 200–300 m²/g. Heat treatment to 600 °C led to a relative decrease in surface area, in the order of 100 m²/g, and to the disappearance of microporosity. The mixed zirconium and titanium oxides with a sulfate content of ≈17% displayed significantly lower surface areas, smaller than 10 m²/g, with a prevalence of micro and mesoporosity. Infrared and thermal studies indicated the presence of differently bounded sulfato groups, which seem to have a blocking effect on the pores, resulting in the observed smaller surface areas.     

Sulfate intercalated layered double hydroxides prepared by the reformation effect

The removal of the sulfate anion from water using synthetic hydrotalcite (Mg/Al LDH) was investigated using powder X-ray diffraction (XRD) and thermogravimetric analysis (TG). Synthetic hydrotalcite Mg₆Al₂(OH)₁₆(CO₃)·4H₂O was prepared by the co-precipitation method from aluminum and magnesium chloride salts. The synthetic hydrotalcite was thermally activated to a maximum temperature of 380 °C. Samples of thermally activated hydrotalcite where then treated with aliquots of 1000 ppm sulfate solution. The resulting products where dried and characterized by XRD and TG. Powder XRD revealed that hydrotalcite had been successfully prepared and that the product obtained after treatment with sulfate solution also conformed well to the reference pattern of hydrotalcite. The d₍₀₀₃₎ spacing of all samples was found to be within the acceptable region for a LDH structure. TG revealed all products underwent a similar decomposition to that of hydrotalcite. It was possible to propose a reasonable mechanism for the thermal decomposition of a sulfate containing Mg/Al LDH. The similarities in the results may indicate that the reformed hydrotalcite may contain carbonate anion as well as sulfate. Further investigation is required to confirm this.     

Über Kupfer(I)-sulfat Cu2SO4. Darstellung und thermische Eigenschaften

Preparation and Thermal Properties of Copper(I) Sulfate Cu₂SO₄ Copper(I) sulfate Cu₂SO₄ can be prepared in high purity by reaction of Cu₂O with dimethyl sulfate (CH₃)₂SO₄ at 160°C in an argon atmosphere. Using an extremely fine grained Cu₂O, as obtained by reduction of cupric acetate with hydrazine, and a reaction time of 10 minutes a Cu₂SO₄ is obtained that contains less than 1% Cu₂O. Longer reaction times lead to partial decomposition of the Cu₂SO₄ to Cu(met.) and CuSO₄. In a closed system Cu₂SO₄ melts at about 400°C, however, the melt rapidly decomposes to Cu and CuSO₄, solidifying simultaneously. When heated in a thermoanalyzer in flowing argon or in a vacuum, Cu and CuSO₄ react under liberation of SO₂. Increasing the temperature leads to CuO in three steps, which converts to Cu₂O when heated to 1000°C. The question of formation of Cu₂SO₄, occasionally mentioned in the literature, being responsible for the liquid phases observed in the system Cu? S? O at temperatures below 500°C, is discussed.     

Surface characteristics and corrosion resistance of sol–gel derived CaO–P2O5–SrO–Na2O bioglass–ceramic coated Mg alloy by different heat-treatment temperatures

To improve the initial corrosion resistance and then make the degradation rate of magnesium alloys to meet the biomedical application, crack-free CaO–P₂O₅–SrO–Na₂O bioglass-ceramic coatings were synthesized on AZ31 magnesium alloy substrates using a sol–gel dip-coating technique followed by a heat-treatment in the temperature range of 400–500 °C. The effects of heat-treatment on the phase constituents, surface characteristics and corrosion resistances of the coatings were investigated. It was shown that the crystallization of Ca₂P₂O₇ occurred after the glass was treated at 400 °C. As the temperature increased from 400 °C to 450 °C, besides main phase Ca₂P₂O₇, β-Ca(PO₃)₂ and Ca₄P₆O₁₉ were identified as minor crystal phases in the glass–ceramic. No new phase was detected with the temperature increasing to 500 °C except for the further crystallization. Meanwhile, the water contact angles of the coatings decreased with the increase of heat-treatment temperature due to the great crystallization. The corrosion resistances of the coated magnesium alloys were studied by electrochemical corrosion techniques in the simulated body fluid. The results revealed that the coating heat-treated at 400 °C exhibited superior corrosion resistance because of less crystallization, suggesting that the calcium phosphate bioglass–ceramic coating can provide effective protection for magnesium alloy substrate to control its initial degradation in vivo and maintain the desired mechanical properties.     

Thermal Characterization and Physico-Chemical Properties of Fe2O3−Mn2O3/Al2O3 Systems

The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al₂O₃ and Fe₂O₃/Al₂O₃ systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe₂O₃ at 350°C and shows thermal stability up to1000°C. Crystalline Fe₃O₄ and Mn₃O₄phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al₂O₃ phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al₂O₃ phase at1000°C. Crystalline MnAl₂O₄ and MnFe₂O₄ phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products was tested using the decomposition of H₂O₂ reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structure and electric conductivity of vapor deposition polymerization products of cyanoacetylene

Cyanoacetylene can be polymerized from the vapor state onto an inactive surface of substrate at a temperature as low as 200°C. The polymerization first occurs by way of the carbon–carbon triple bond. The reaction product obtained at 1000°C contains nitrogen at a concentration as high as 13.7%. At least some of this nitrogen is in naphtiridine ring or rings similar to it. The product obtained at 400°C is amorphous, while the product obtained at 1000°C has at least partly graphite-like crystalline structures with an apparent crystallite size (L_c) of about 17 Å. The electric conductivities of the products obtained at 400, 700, and 1000°C are 7.7 × 10^?2, 91, and 1600 S/cm, respectively. These values are extremely high compared to the pyrolized PAN treated at the same temperature. Electric conductivity of the product obtained at 400°C is well explained by the variable range hopping model in 3-dimensional amorphous materials. With the products obtained at the higher temperatures, conductivity cannot be accounted for by the hopping model. This is probably due to the development of graphite-like structure.     

Kinetics of the catalytic decomposition of dichloromethane and trichloromethane

The kinetics of the catalytic decomposition of dichloromethane and trichloromethane in a single row plug flow reactor at 400–500°C has been studied. Dichloromethane decomposes into carbon and hydrogen chloride (presumably via the intermediate formation of monochlorocarbene). Trichloromethane decomposes mainly into carbon, hydrogen chloride and tetrachloromethane (presumably via the intermediate formation of dichlorocarbene).     

V-Ce/TiO2脱硝催化剂的SO2中毒机理研究

通过表相、体相硫组分的表征分析,结合不同温度下含硫气氛下的活性演变及原位红外研究,获得了VCe(0.1)/TiO2催化剂在180、240和300℃下含硫氛围的NH3-SCR反应中毒机理. 180℃下催化剂上沉积了大量的硫酸氢铵和少量的金属硫酸盐,共同导致在8 h内活性从77.8%降至51.2%,热再生后的活性测试结果表明硫酸氢铵的沉积导致了催化剂活性降低8.3%,金属硫酸盐的沉积导致了催化剂活性降低18.3%.原位红外结果表明中毒后催化剂在180℃下的NH3-SCR反应遵循L-H反应路径.随着温度升高至240、300℃,催化剂上沉积的硫酸氢铵逐渐减少,金属硫酸盐含量增加.不同温度下的抗硫活性结果表明,低温NH3-SCR反应需要较高的氧化还原性能,中高温NH3-SCR反应则需要较高的酸性,金属硫酸盐的生成导致了氧化还原性能降低、酸性增加,因此低温NH3-SCR活性大幅降低,中高温活性则能保持在100%.