Heating In Argon Research Articles

In-situ monitoring of microstructure changes during the heating of amorphous ruthenia by means of Emanation Thermal Analysis

Results of Emanation Thermal Analysis (ETA), Thermogravimetry (TG) and Differential Thermal Analysis (DTA) of hydrous ruthenia measured during heating in argon from 20 to 1000°C are presented. The ETA results were interpreted using comparison with the results of TG, DTA, X-ray diffraction, transmission electron microscopy and surface area measurement. An agreement of the results was found. The ETA made it possible to monitor microstructure changes under in situ conditions of heat treatment of the samples.

Effect of Surface Modification by Heating in Argon on Charge/Discharge Characteristics of Mg<SUB>2</SUB>Ni Electrode

Charge/discharge characteristics of Mg 2 Ni electrodes were examined by focussing attention on the influence of surface modification by heating in argon. The initial activation was significantly easier for the electrodes heated at 550°C than un-heated ones. The surfaces of electrodes became porous by the heating because of the evaporation of magnesium. A MgO layer was formed during the heating. The improvement of charge/discharge characteristics by the heating was ascribed to the increase in the specific surface area and the porosity of the oxide film, and to the formation of MgNi 2 and nickel phases which should act as the local reaction sites for hydrogen during the charge and discharge processes.

Some investigations on the effective short time outgassing depth of metals

Outgassing rates of aluminium samples coated with Al, Fe, and B were studied as a function of the surface composition at and near room temperature. The surface was changed by diffusion processes caused by heating in argon at atmospheric pressure and in vacuum. Achieved effects of these preparations were studied by x-ray photoelectron spectroscopy depth profiling, scanning electron microscopy, and atomic force microscopy measurements. It can be shown that the outgassing rate is independent on the atomic concentration of O, C, Al, Fe, and B in the nanometer range for many 105 s, when the samples were prepared in this way. The samples coated and heated at 500 °C in vacuum and the aluminum surface cleaned with ethanol have nearly the same outgassing behavior after air exposure. Therefore it can be concluded that the short time outgassing is only controlled by contamination and desorption.

Thermogravimetric–differential thermal analysis of the solid-state decomposition of ammonium tetrathiomolybdate during heating in argon

The formation of MoS2 by thermal decomposition of ammonium tetrathiomolybdate (ATT) solids under an argon atmosphere has been studied by simultaneous thermogravimetric and differential thermal analysis. The sequential products for the decomposition upon heating to 700 °C is ATT (hydrated)→(NH4)2MoS4→(NH4)HMoS4→H2MoS4→MoS3→ Mo2S5→MoS2. MoS2 forms between 230 and 260 °C and remains stable up to about 360 °C when it tends to be oxidized by residual oxygen, if present in the atmosphere. These findings suggest that the synthesis of MoS2 from (NH4)2MoS4 via formation of MoS3 is not a direct process, as previously reported, but rather a complex process involving a number of intermediate products (NH4)HMoS4, H2MoS4 and Mo2S5 which have not been reported before. That these products are only specific to the very narrow temperature regimes as revealed suggests that they are very unstable and short lived, that their presence is transient in nature and thus that ex-situ characterization of them is normally difficult. The presence of these intermediate products, as justified experimentally, is further interpreted in terms of their mutual structural similarities which improve understanding as to why MoS2 can usually be prepared from ATT by thermal decomposition, as in this case, or by other techniques, such as anodizing. Laminar morphology of MoS2 is revealed by transmission electron microscopy and its crystal structure examined by selected-area diffraction. Further ex-situ examination by X-ray photoelectron spectroscopy of this end product supports the feasibility of preparing MoS2 from aqueous solutions by anodizing. © 1998 Kluwer Academic Publishers

Argon plasma coagulation (APC) vs heat probe (HP) for bleeding peptic ulcers: a prospective, randomized trial

Argon plasma coagulation (APC) vs heat probe (HP) for bleeding peptic ulcers: a prospective, randomized trial

Immobilization of Separated Tc and Cs/Sr in Synroc

AbstractIn some radwaste applications, such as immobilization of U.S. Tank wastes using vitrification, Tc and Cs/Sr are likely to be separated out from HLW supernates. Simplified Synroc preparations can be devised for the immobilization of separated Tc and Cs/Sr, either together or individually. Under suitably reducing processing conditions, Tc can be immobilized, as metal or Tc4+. The volatility of Tc and Cs/Sr in Synroc processing is very restricted.In Synroc-C, designed for Purex high-level reprocessing wastes, Tc exists as a metal alloy. In air-saturated water, normalized MCC-1 type total differential leach rates at 90°C decreased with leaching time and after 90 days were <10-4 g/m2/d, decreasing by a factor of ∼100 in anoxic conditions. The corresponding results in a pH=6.1 buffer solution were fairly similar to those in deionised water, but in anoxic conditions, the leach rates were higher in the buffer solution than in the deionised water.A single perovskite phase was loaded with ∼40 wt% of TcO2 to form CaTc0.5Ti0.5O3 by a combination of graphite-die hot-pressing and heating in argon. Rutile, intended to be doped with ∼35wt% TcO2, was fabricated by bellows hot-pressing at 1200°C; aproximately 75% of the Tc formed a solid solution with rutile, but some metallic Tc was also present due to imperfect redox control. Results of both MCC-1 and PCT-type leach tests are presented on a preparation containing 70 wt% hollandite + 20 wt% perovskite + 10 wt% rutile containing about 5 wt% of Cs and Sr respectively. Phase distributions resulting from incorporating Cs and Sr in Synroc-B precursor were studied.

Enhancement of T c and the irreversibility line in argon pretreated LnSrBaCu 3O 6+z (Ln=Nd,Eu,Sm)

LnSrBaCuO (Ln=Nd,Eu,Sm) samples were prepared by oxygen annealing [O] and by heating in argon followed by oxygen annealing [AO]. This treatment resulted in an increase in T c and in the irreversibility line. A rearrangement of the oxygen atoms in the basal plane due to [AO] treatment may explain the data.

Crystallization in a Barium-Containing Magnesium Aluminosilicate Glass-Ceramic

Crystallization in a Ba-containing magnesium aluminosilicate (Ba-MAS) glass-ceramic was studied using transmission electron microscopy. Ba-MAS slabs were hot-pressed at 1000°C to form dense glassy bodies, which were crystallized by further heating in air or argon between 850° and 1300°C. Heterogeneous nucleation of a metastable highquartz solid solution (μ-cordierite) occurred at crystallization temperatures below 1100°C, followed by dendritic growth; the interdendrite phase was Ba-rich silicate glass. The high-quartz solid solution generally acted as a precursor for the nucleation of the stable β-phase, which was the final crystallization product. Surprisingly, slower crystallization kinetics were observed in argon than in air. Further morphological changes at the higher temperatures and longer annealing, times resulted from a Rayleigh type instability, which led to breakup of the interdendrite silicate rods, and simultaneous polygonization of β-cordierite.

Thermal decomposition of silver cyano complex and characterization its decomposition products by ETA, DSC, DTA and TG

It was found by DTA and TG that [Phenyl2I][Ag(CN)2] in the solid state is chemically stable on heating in argon up to 160°C. During heating to higher temperatures it decomposes, forming volatile products such as [Phenyl]I, [Phenyl]NC and (CN)2 [1]. After heating the sample to 500°C metallic silver resulted. The volatile and intermediate solid products were analysed by IR-spectroscopy.

Thermal stability of [phenyl 2I] + cyano complexes containing silver, chromium and cobalt

The thermal stability of the complexes [Ph 2I][Ag(CN) 2], [Ph 2I] 3[Cr(CN) 6] and [Ph 2I] 3 [Co(CN) 6] on heating in argon were studied by means of DTA and TG-DTG. The morphological changes taking place during the heating of these solid samples were indicated by means of emanation thermal analysis.

Interaction between oxidation and mechanical properties of 20Cr–25Ni–Nb stabilised stainless steel

The influence of oxidation in carbon dioxide and of heat treatment in an inert gas (argon) for up to 2000 h at 1000°C on the metallurgical structure of a 20Cr–25Ni–Nb (wt-%) stabilised stainless steel, annealed before these exposures at 930°C, has been investigated. The effect of oxidation for varying periods and of the corresponding argon heat treatments on the subsequent creep rupture properties of the steel at 750°C has also been studied. The influence of concurrent strain, from a constant applied load, on the oxidation behaviour of the same type of steel has also been examined during 100 h oxidation, in carbon dioxide at 1000°C.MST/1176

Studies on a high temperature regenerative heat exchanger for closed cycle MHD power generation. (6th report. Heat transfer analysis in the combustion chamber during the evacuation and argon heating periods).

A two-dimensional unsteady heat transfer analysis in the combustion chamber of a pebble bed regenerative heat exchanger for high temperature argon heating has been performed for the evacuation and argon heating periods. The analysis well explains the measured time history of the temperature of the top of the pebble bed facing the combustion chamber during both periods. The analysis also shows that optimization of the height of the combustion chamber is important for maximizing the argon temperature at the exit of the heat exchanger.

Studies on a high temperature regenerative heat exchanger for closed cycle MHD power generation. (7th report. Unsteady thermal performance under cyclic continuous operation).

A heat transfer analysis code for predicting the performance of a regenerative heat exchanger for high temperature argon heating has been developed which simulates heat transfer processes in the combustion chamber coupled with those in the storage bed of a pebble bed. The thermal performance of heat exchangers under cyclic operation is predicted by this code, and the results show that optimization of geometries for both the combustion chamber and the heat storage bed is important for improving the thermal performance. Unsteady response of heat exchangers to the change of the external load of a closed cycle MHD electrical power generator is investigated by the computer code. The results show that the response time is almost the same as the cyclic operational period of heat exchangers.

Thermal decompositions of some transition metal polyacrylates

Polyacrylales of Fe, Cr, Ni, Co and Mn were synthesized by the reaction of poly(sodium)acrylatc with metal halides. The salts obtained were investigated by thermal analysis. During heating in argon or air, all the salts behaved in a similar way. The initial decomposition temperature of the investigated salts increased in the following sequence: Fe<Cr<Ni<Co<Mn. The solid residues of the decompositions of the salts were also analysed.

Structural changes in coals during pyrolysis

Derivative thermogravimetry (DTG), emanation thermal analysis (ETA), gas adsorption methods for surface area and microporosity measurements, helium pycnometry and mercury porosimetry have been used for the characterization of structural changes in two bitumenous coals of British origin (Manvers Wath and Markham Main), during heating in argon up to 980 °C (heating rate 5 °C/min). The results are compared and advantages of the ETA for the assessment of the surface area and porosity changes in dynamical conditions of thermal treatment are demonstrated.

Preparation of BaTiO 3 by thermal decomposition of barium titanyl oxalate simultaneously investigated by emanation thermal analysis, TG-DTA and EGA

The decomposition reactions of Ba-titanyl oxalate and behaviour of the reaction product - BaTiO 3 - during heating in oxygen, carbon dioxide, argon, and helium were studied during heating up to 1500°C by Emanation Thermal Analysis, TG, DTA and EGA. The results are discussed and the ETA is recommended for the assessment of changes in the surface area, porosity and structure of the intermediate and final reaction products.

Creep behaviour and structural characterization at high temperatures of Nicalon SiC fibres

Two types of Nicalon SiC fibres having different structures have been examined. Their mechanical properties and their microstructures have been studied up to 1300° C. The fall in strength above 1000° C has been shown to be due to the microcrystallization of the fibre structure. Under low loads this change in structure led to a shrinkage of the fibre. The fibres were found to creep at temperatures above 1000° C when loads greater than a threshold level were applied. The creep of the fibres has been shown to be controlled by the changes which occur to the fibre structure. Degradation of the fibres on heating in air or argon has been shown to depend on SiO2 and free carbon, which have been shown to exist in the fibre.

Thermal properties of halogen-containing organic antipyrenes for polymers

Thermal properties were studied of many compounds inhibiting the combustion of polymers-compounds with chloro- and bromo-substituted aromatic and cycloaliphatic fragments in the molecule. The ability of antipyrenes to undergo distillation and decomposition with the liberation of gaseous halogen-containing products during isothermal and dynamic heating in argon was determined both in the free state and in radation-modified binary and ternary (with addition of Sb 2O 3) mixtures with PE. It was found that the type of halogen and the chemical structure of antipyrene have a marked effect on the temperature range, type and rate of liberation of halogen in the form of hydrogen halide and antimony trihalide, which basically determines the fire-resistance of polymer materials containing these antipyrenes.

ChemInform Abstract: A COMPARISON OF REDUCING AND OXIDIZING HEAT TREATMENTS OF HOT‐PRESSED SILICON NITRIDE

AbstractErhitzen eines heißgepreßten Si‐nitrids der Zusammensetzung (I) vor seiner Weiterverarbeitung auf 1400°C in Ar führt zum Verschwinden der interkristallinen Glasphase sowie zu einer Reduzierung des Gehalts an Si‐oxynitrid, was eine weiche, leicht abreibbare Oberfläche zur Folge hat.

X-ray and XPS studies of evaporated CuxS thin films

The structural changes in CuxS films have been monitored by x-ray diffraction and correlated to the chemical changes taking place on the CuxS surface, the latter monitored by XPS. The results show: evaporated CuxS films contained chalcocite, free copper phases, and probably a third phase (of sulfur); resistivity is related to the amounts of free Cu and S in the film; air heat treatments converted chalcocite to Cu deficient phases and resulted in the disappearance of the sulfide and predominance of CuSO4⋅nH2O and CuO; argon heat treatment tended to react Cu and S to form CuxS; Cd is detected on the surface of CuxS deposited onto CdS and is significantly increased in amount by heat treatments. These results can be related to chemical processes occurring on CuxS/CdS and CuxS/(Zn,Cd)S solar cells. For the CdS cell, oxides and sulfates of Cu and Cd are found on the CuxS surface and the sulfates are enhanced by the heat treatment in moist air. CuO and CuSO4 are formed in the absence of Cd, and dominate the CuxS surface.