Effect Of Thermal Pretreatment Research Articles

Effect of thermal pretreatment on the structural properties of [formula omitted] catalysts in hydrocarbon synthesis from CO and H 2

Two iron on MgO catalysts with the same iron content but subjected to different thermal pretreatments, prepared from magnesium hydroxycarbonate (MHC), have been studied. Chemisorption, Mössbauer spectroscopy and activity and selectivity measurements in a Fischer-Tropsch reaction have been combined to characterized them. The catalysts obtained show diverse structural properties and catalytic behaviour. When the supported crystallite size changed from 63 to 193 Å, the methane turnover frequency increased 3.5 times. For the reaction conditions used, 543 K, H( in2): CO = 3:1 and atmospheric pressure, the catalyst with larger iron particles produce a lower fraction of C 2+ in hydrocarbon products and showed a greater tendency to the deactivation and loss of C 2+ selectivity than the one with smaller particles. This behaviour is discussed in terms of the structural properties of Fe° microcrystals.

Effect of thermal pretreatment on the fracture behavior of polycarbonate in medium strain rate tensile tests

AbstractThe fracture properties of as‐received and annealed (48 h at 403 K) commericial polycarbonates (PC) were examined in tensile tests with an average strain rate of ė = 2 s−1. Both materials were subjected to tensile tests at temperatures ranging from 223 to 423 K. The results were processed by a computer interfaced to the testing machine. The tensile strength of the annealed (pretreated) PC was superior to that of the as‐received (untreated) material. The elongation at break and the fracture energy, then, decreased due to annealing at all temperatures, yet followed impact strength curves. Fracture analysis and fracture morphology revealed clear differences in the behavior of the materials. Fracture nucleation occurred commonly at several points in the pretreated specimens, whereas only one nucleation point was found in the untreated specimens. Shear yielding morphology, which indicated plastic deformation, started to appear at a lower temperature in the pretreated specimens than in the untreated ones.

余剰活性汚泥の嫌気性消化に及ぼす前熱処理と滞留時間の影響

余剰活性汚泥の嫌気性消化に及ぼす前熱処理と滞留時間の影響

A study of TiO 2 powders as a support for the photochemical synthesis of ammonia

TiO 2 powder in either the rutile or the anatase form do not generate ammonia when they are subjected to ultraviolet irradiation under a wet nitrogen flux. In order to undergo this photochemical reaction, the samples first have to be annealed under air at atmospheric, high temperature. This treatment generates defect states in the band gap of the semiconductor and in the hydroxyl groups on the surface. The effects of thermal pretreatment on the various characteristics of the TiO 2 powders such as specific area, crystal structure, morphology and stoichiometry have been studied. The nature of the hydroxyl groups on TiO 2 surface is determined by IR spectrometry and by temperature-programmed desorption.

Effect of thermal pretreatment on the surface reactivity of amorphous silica

Effect of thermal pretreatment on the surface reactivity of amorphous silica

Effects of Thermal Pretreatment on Coarsening of Nominally Monodispersed Titania

The coarsening of nominally nwnodisperscd, ∼0.35‐μm‐diameter titania powders produced by controlled hydrolysis of titanium tetraethoxide was studied. Thermal treatments prior to coarsening experiments had a minimal effect on the apparent particle size distribution, but significantly modified the coarsening behavior and microstructural characteristics. Explanations attributing these differences to the effects of preannealing on the microstructure (grain size and phase composition) within particles are proposed.

Effect of thermal pretreatment on electron irradiation induced defects in hydrogen-grown silicon

Wafers of float zone Si grown in hydrogen (Si[H]) were annealed at various temperatures in the range of 300–750 °C before irradiation with 5 MeV electrons. It was found that hydrogen-related deep levels were no longer observed, when the preannealing temperature was above 500 °C (450 °C) in the case of irradiated n-type Si[H] (p-type Si[H]) samples. Similarly, the convergence of annealing temperatures of different irradiation defects towards a common temperature normally observed in Si[H] was no longer observed, if the Si[H] sample had been annealed at or above 550 °C. A dynamic model is proposed to explain the experimental results.

Hydrogen adsorption on chromia-supported iridium catalyst

Effect of thermal pretreatment of chromia-supported iridium catalyst on hydrogen adsorption was studied. It was found that the hydrogen uptake by Ir/Cr2O3 was highly dependent on the reduction temperature. The catalyst proved to be resistant to sintering in oxygen atmosphere at temperatures up to 700 °C and it showed symptoms of redispersion even at 650 °C.

アルカリ水溶液中における褐炭の酸素酸化によるベンゼンポリカルボン酸の生成に対する熱処理の効果

アルカリ水溶液中における褐炭の酸素酸化によるベンゼンポリカルボン酸の生成に対する熱処理の効果

The effect of thermal pretreatment on the anaerobic biodegradability and toxicity of waste activated sludge

The management of sludges generated by biological treatment of wastewaters has become an increasingly severe problem in recent years. The objective of this study was to examine the effect of thermochemical pretreatment on the anaerobic biodegradability and toxicity of waste activated sludge (WAS). In order to accomplish this, the degradability and toxicity of pure nitrogenous organic compounds present in WAS, and mixtures of these compounds, were also evaluated. The anaerobic bioconvertibility and toxicity of the various organics were determined using batch bioassay techniques. It was found that WAS bioconvertibility increased with increasing pretreatment temperature up to a maximum at 175°, and this resulted in an increase in methane production of 27% over the control. With the compounds and cultures used, mesophilic bioconvertibility and toxicity were found to be significantly higher than the corresponding values under thermophilic conditions. Finally, it was found that most of the pure individual nitrogen compounds and simple mixtures tested were quite biodegradable, although at the concentrations evaluated (20 gl −1) most were toxic. It was also noted that small changes in structure could have a significant effect on both toxicity and bioconvertibility. In most cases thermochemical pretreatment of these individual compounds resulted in decreased bioconvertibility and increased toxicity. In conclusion it can be stated that thermochemical pretreatment enhances WAS bioconvertibility, while under identical treatment conditions, resulted in a considerable reduction in the bioconvertibility of individual nitrogen compounds and mixtures. This effect appears to be due to the conversion of biodegradable organics to refractory ones. Further, the toxicity of WAS after thermochemical pretreatment appears to be due to its solubilization, and conversion of these soluble products to toxic compounds under more extreme treatment conditions.

The effect of thermal pretreatment on the creep of hardened cement paste

Miniature, saturated, hardened cement paste specimens were pretreated for 2 days at various temperatures in the range 20–92°C. Specimens were then loaded for 6 days and unloaded; immediate, creep and recovery strains were monitored, as were changes in the microstructure -- polysilicate and nitrogen sorption analyses were used for this purpose. For both young (28d) and mature (2.5y) specimens, thermal pretreatment resulted in significant changes in the microstructure; polysilicate content and average pore size increased while surface area decreased. In young specimens, the pretreatment resulted in a reduction in subsequent creep deformation; good correlation was found between creep and the polysilicate content at the time of load. The results for mature specimens showed a different trend; in these, pretreatment resulted in an increased creep response. Polysilicate measurements made before and after loading showed significant differences. In young specimens polysilicate content increased during loading. In contrast, depolymerisation appeared to result from loading mature specimens.

Annealing of polycarbonate below the glass transition: quantitative interpretation of the effect on yield stress and differential scanning calorimetry measurements

This paper is concerned with the effect of thermal pre-treatments (below the glass transition) on the yield stress and on the enthalpy change of polycarbonate. A treatment is proposed which accounts quantitatively for experimental results. It relies both on free volume and activation concepts and makes use of classical equations and simple assumptions, chiefly that the same free energy is associated with the molecular motions giving rise to deformation at yield and densification during annealing.

Track-profile and range studies of heavy and light ions in CR-39: Effect of thermal pre-treatment on etching characteristics

ABSTRACT Sheets of CR 39 have been irradiated with 20 Ne, 32 S, 40 Ar, 56 Fe and 63 Cu ions at normal incidence to the surface of the sheets and at normal incidence to the edges. The profiles of the etched tracks have been observed side-on and measurements made of the variation of V (the ratio of track to bulk etching velocities) along the tracks and of the fully etched range of the tracks. Heating the plastic at 100 °C prior to etching produces zones within the plastic having different bulk etching rates V B . An outer zone of low V B is followed by a zone of much higher V B . This allows tracks to be readily etched to very large diameters, comparable in size to the breakdown spots produced by electrochemical etching.

The relationship between the effect of thermal pre-treatment and the viscoelastic behaviour of polycarbonate in the glassy state

The viscoelastic behaviour of three different samples of polycarbonate, with differing pre-treatment, is described here by a generalized non-linear Maxwell system, proposed previously. This model gives the variation of the tensile yield stress related to each sample as a function of temperature and strain rate. The response is checked over a large range of strain rates, at temperatures from 20 to 80° C. The model allows the determination of the damping peak arising from the molecular movements which it expresses. A correspondence is found with the intermediate loss peak location, which occurs for each sample just below the α transition. Results obtained from dynamic mechanical tests and differential scanning calorimetry show that the structure of the samples changes in the range of temperatures where the intermediate loss peak arises at 1 Hz.

The effects of thermal pre-treatment and molecular weight on the impact behaviour of polycarbonate

Notched impact fracture experiments have been conducted on specimens of polycarbonate in three different conditions, (a) as received, (b) annealed at 125° C, and (c) electron beam irradiated to reduce the molecular weight. By consideration of the behaviour of a wide range of notch geometries four different failure modes were identified which were present in different proportions for each material. (1) Razor notched specimens failed in a completely brittle manner, well described by linear elastic fracture mechanics. (2) Small notch tip radii specimens failed in an apparently brittle manner through the formation of a single craze. (3) Some intermediate notch tip radii specimens failed in a predominantly brittle manner with small shear lips indicative of plane stress yielding. A fracture mechanics approach was used here, the measured toughness correlating with the extent of plane stress yielding. (4) Fully ductile failure was observed for large notch tip radii for all materials. It has been established that the embrittlement of polycarbonate caused by annealing is due to an increase in the yield stress, whereas that caused by reducing the molecular weight is due to a reduction of the crazing stress. In both cases, more specimens of intermediate notch tip radius are caused to fail in the low energy brittle mode designated (2) above. By varying the yield stress and crazing stress independently we have thus been able to distinguish clearly how both influence the brittle-ductile transition.

Thermally stimulated discharge current studies on the effect of thermal treatment on the strength of polycarbonate

AbstractIt is well known that polycarbonate annealed at 80–130°C undergoes gradual changes in mechanical properties. Annealing below Tg (ca. 150°C) results in a decrease in impact resistance and an increase in strength. Polycarbonate has three single relaxation processes and some distributed relaxation processes in the temperature range between 100 and 250°K (the β transition region). The effect of thermal pretreatment on the relaxation has been investigated by the thermally stimulated discharge current technique. Partial heating, peak cleaning, and theoretical fitting have also been performed and the activation parameters associated with the relaxation processes have also been calculated to assist in the analysis of the relationship between effects of annealing and structural motions in polycarbonate.

Interactions of Nonaqueous Solvents with Textile Fibers

Pretreatment of polyester yarns with a strongly interacting solvent (dimethylformamide) leads to modifications of the fiber structure which permit rapid diffusion of even “high-energy” disperse dyes under atmospheric conditions without the addition of carriers. A comparison of the effects of solvent pretreatments with the effects of thermal pretreatments on the dyeing behavior has been carried out. Pretreatment in a strongly interacting solvent leads to a high degree of swelling and at higher temperature to the formation of crystallites within the swollen structure. It appears that the swollen structure can be stabilized, depending on the size and stability of the crystallites formed, leading to cavitation and void formation upon subsequent removal of the interacting medium. It is suggested that a rigid pore mechanism of dye diffusion becomes operative in this structure, as opposed to the free volume mechanism of diffusion in thermally-treated polyester yarns.

The effect of thermal pretreatment on the mechanical properties of polycarbonate

The effect of annealing on the mechanical and thermal properties of polycarbonate resin has been investigated. The previously observed increases in yield strength and decreases in impact strength have been confirmed and it has been shown further that annealed polymer shows a larger strain softening effect after yield than untreated material. This is reflected in an increased negative slope in the stress-strain curve. After yielding the endothermic D.S.C. peak due to annealing is largely eliminated. The extra mechanical energy required to deform the annealed polymer is similar in magnitude to the thermal energy associated with the D.S.C. peak. The reduction in impact strength during annealing is ascribed to greater plastic instability and to the consequent reduction in volume of the zone of plastic yielding in the impact test. This conclusion is confirmed by the examination of annealed and untreated impact test pieces in polarized light.

The effect of Thermal Pre‐treatment on the Reactivity of Fe2O3

AbstractThe effect of thermal pre‐treatment of iron(III) oxides on thier reactivity has been studied together with the studies of some of their physical properties.Cadmium ferrite formation slightly increased when the iron(III) oxide was sintered between 550 and 680°C and markedly decreased above 700°C. The effect of thermal pretreatment appeared more pronouncedly when reactions were carried out at the temperature of the sintering. Between 550 and 750°C the highest conversion was found when iron(III) oxide was sintered and brought into reaction at about 700°C. The reactivity of iron(III) oxide was investigated also in other reactions: solubility in HCl and catalytic decomposition of H2O2.On the basis of density and electric conductivity data the high reactivity of Fe2O3 exhibited between 675 and 700°C was interpreted by the great increase of iron vacancies.

The effect of thermal pretreatment on the strength of polycarbonate

AbstractThe effect of preheat treatment at temperatures below the glass transition for various periods of time on selected properties of molded polycarbonate has been studied. Changes in tensile and flexural strength as functions of time and preheat temperature (80–140°C.) were determined and these are discussed in relation to changes in the nature of the β‐transition region and the influence of the glass transition region. It is suggested that the preheat treatment produces a greater degree of order within the amorphous region of the polymer, resulting in an increase in strength at temperatures up to 132°C. The strength of the polycarbonate before and after heat treatment appears to be independent of the presence of the equilibrium water content.