Reactivity of heat-treated coals in air at 500 °C

Twenty one US coals, of widely ranging rank, have been carbonized under controlled conditions to 1000 °C, and the reactivity in air at 500 °C of the resulting chars or cokes has been measured by a gravimetric method. The reactivities lie within a well-defined band when plotted against rank of the parent coal. The lower-rank coal chars are more reactive than those prepared from high-rank coals. In extreme cases, the reactivity found for a Montana lignite char is some 100 times as great as that obtained for a char produced from a Pennsylvania low-volatile coal. Variation of reactivity with heat-treatment temperature (600 to 1000 °C) has been studied for three coals. As heat-treatment temperature increases, there is a decrease in reactivity. Some results are reported on the effects which mineral matter and pore structure have on the reactivity parameter. Chars containing high concentrations of magnesium and calcium impurities are most reactive. The amount of macro and transitional porosity in a char has a marked influence on reactivity.     

Reactivity of heat-treated coals in carbon dioxide at 900 °C

Reactivities of sixteen 40 × 100 (U.S.) mesh U.S. coals charred to 1000 °C were measured in carbon dioxide at 900 °C. Chars derived from coals with less than 80% carbon, on a dry-ash-free basis, were the most reactive. These chars also gave the widest spread in reactivity. Plots of inorganic element content in the chars versus reactivity showed that magnesium and calcium are important to char reactivity. Six coals were acid-washed with hydrochloric acid and four coals were further demineralized with hydrofluoric acid. Most acid-treated coals showed a decrease in reactivity; but two coals of high rank increased in reactivity. This increase in reactivity is attributed to the creation of additional porosity as a result of mineral matter removal and thus a reduction in resistance to carbon dioxide diffusion to reactive sites. Two demineralized and two original coals were divided into four size ranges and chars were produced from each size of each coal. Gasification rates increased monotonically with decreasing particle size reacted.     

Solubility of potassium ferrate in 12 M alkaline solutions between 20°C and 60°C

The solubility of potassium ferrate (K₂FeO₄) was measured in aqueous solutions of NaOH and KOH of total concentration 12 M containing various molar ratios of KOH:NaOH in the range 12:0 to 3:9. Several analytical methods were tested for the determination of ferrate concentration. The final method chosen consisted of potentiometric titration of the ferrate sample with an alkaline solution of As₂O₃. The assumption was made that ferrate dissociates in concentrated KOH solutions predominantly to KFeO₄⁻. The solubility constant, S, defined as the product of the molar concentration of the potassium ion, K⁺, and the ferrate anion, KFeO₄⁻, was found to be 0·044 ± 0·006 mol² dm⁻⁶ for 20°C, 0·093 ± 0·004 mol² dm⁻⁶ for 40°C and 0·15 ± 0·09 mol² dm⁻⁶ for 60°C. From these results the heat of dissolution of K₂FeO₄ was calculated as −14·3 kJ mol⁻¹. At 60°C the enhanced decomposition of the ferrate at the higher temperature led to a greater deviation in solubility values compared with data for either 20°C or 40°C.     

Desulfurization of coal by air + steam at 400°C in a fixed bed

A high-volatile coal was treated by mixtures of air and steam at 400°C. The coal particle size, air/steam ratio and treatment time were varied. The degree of conversion of total sulfur depended on the particle size (but not proportionally) and the air/steam ratio (proportionally). The kinetics of the heterogeneous desulfurization by oxidation of FeS/FeS₂ was investigated. The kinetic data were well described by the model of an unreacted shrinking core in a coal particle of unchanging size. The coal particle size affected the external and internal diffusion of O₂ molecules only; the air/steam ratio affected the internal diffusion of O₂ molecules only. On average, the process was governed 14% by external diffusion, 76% by internal diffusion and 10% by chemical reaction. It was possible to elucidate the desulfurization mechanism merely from a knowledge of the experimental relation between total sulfur conversion degree and treatment time.     

Nickel catalysed steam gasification of chars obtained from coal-alkali reaction at 600 °C

Studies on the steam gasification of washed residual chars (obtained from coal-alkali reaction at 600 °C) were carried out at 500 °C and 100 kPa pressure in a fixed bed glass reactor with or without nickel (as nickel nitrate) as catalyst. The results when compared with the corresponding data on coal, revealed that under similar reaction conditions, the coals yielded more gas with higher H₂ and CO contents than their corresponding chars. It was concluded that presence of functional groups, especially oxygen containing is a requirement for nickel catalysed steam gasification of coals/lignites. The recovery of nickel achieved was about 80%.     

Low roughness diamond films produced at temperatures less than 600°C

Recent progress has been made in the production of low-roughness Chemical Vapor Deposition (CVD) diamond films at temperatures less than 600°C. These films are particularly suitable for cutting tool applications. Such progress was achieved by simultaneously promoting the renucleation process and controlling the growth process at low temperatures. In this paper, we show that below 700°C (unlike what is usually observed at temperatures in the range of 750–900°C), secondary nucleation does not occur easily even on (111) faces. This makes the growth of low roughness films difficult. We also report on the role of a thin gold layer deposited on top of a diamond film in favoring smoother film formation. This observation was seen to be due to the ability of the thin gold layer in promoting renucleation. Furthermore, the effect of the percentage of methane introduced in the feed gas was studied.     

Oxidation Behavior of SiC Whiskers at 600–1400°C in Air

The oxidation behavior of SiC whiskers (SiC_W) with a diameter size of 50–200 nm has been investigated at 600°C–1400°C in air. Experimental results reveal that SiC_W exhibit a low oxidation rate below 1100°C while a significant larger oxidation rate after that. This can be attributed to the small diameter size of SiC_W, which determines that it is hard to form a protective SiO₂ layer thick enough to hamper the diffusion of oxygen effectively. Both nonisothermal and isothermal oxidation kinetics were studied and the apparent oxidation energy was calculated to further understand the oxidation behavior of the SiC_W.     

The thermal degradation of an amine-cured epoxide resin at temperatures between 200°C. and 310°C.

This paper describes the nonoxidative thermal degradation of an epoxide resin based on the diglycidyl ether of bisphenol A crosslinked with p,p′-diaminodiphenyl methane. Temperatures of degradation lay between 200 and 310°C. and the process was followed concurrently by three means: changes in dielectric properties, changes in infrared spectra, and weight loss. Dielectric properties support the contention that there is a dehydration step during degradation. It is proposed that vacuum curing at high temperature can produce optimum crosslinking. Evidence of phenol and N-methyl aniline as degradation products is advanced, and possible degradation mechanisms are discussed.     

Combined pyrolysis and radiochemical gas chromatography for studying the thermal degradation of epoxy resins and polyimides. I. The degradation of epoxy resins in nitrogen between 400°C and 700°C

The thermal degradation of a bisphenol A-based epoxy resin (EP 274) cured with 4,4′-diaminodiphenyl methane (DDM) and with phthalic anhydride (PA) was studied using a radiochemical pyrolysis gas chromatography technique. Conclusive evidence for some of the degradation mechanisms of these resins was obtained by pyrolyzing samples containing various ¹⁴C-labelled groups and analyzing the products using this method.     

Thermal shock behavior of Ti2AlC from 200°C to 1400°C

The thermal shock behavior of Ti₂AlC synthesized by means of self‐propagating high‐temperature combustion synthesis with pseudo hot isostatic pressing is investigated, with a focus on the effect of the quenching temperature and quenching times. In general, Ti₂AlC exhibits a better thermal shock resistance than typical brittle ceramics like Al₂O₃. Although the flexural strength decreases quickly in the temperature range of 300°C‐500°C, no discontinuous decrease in the retained strength is observed in Ti₂AlC which, as with other MAX phases, differs from the behavior of typical brittle ceramics. Overall, the initial strength (grain size) plays a determining role in the thermal shock behavior of Ti₂AlC and other MAX phases. On increasing quench times to 5 cycles, the retained flexural strength decreases further, however with a lower rate of decrease compared with the first quench. Quenching at 300°C and above, voids after the pullout of grains and cracks are present, which however are absent in the un‐quenched samples, indicating the weakening of bonding among grains and the induced damage around the grain boundary during the thermal shock.     

Wear of zirconia-dispersed alumina at ambient temperature, 140 °C and 250 °C

Commercial grade alumina along with 5, 10, 15 and 20 wt.% zirconia-dispersed aluminas were tested for their wear resistance at ambient temperature, 140 °C and 250 °C using a pin on disk tribotester fitted with a hot stage. The sample suite was investigated for physical characteristics including hardness, fracture toughness, bulk density, alumina grain size and zirconia grain size. The wear track and wear debris were investigated using profilometry, SEM as well as TEM.

The 5 wt.% zirconia-dispersed aluminas had the lowest wear volume loss over the temperature range. The alumina sample exhibited a wear dependence with relative humidity which is attributed to the formation of a tribochemical layer. Investigation of the tribochemical layer using SEM/EDS and TEM electron diffraction showed the tribochemical layer to be aluminium hydroxide. The major wear mechanism for all samples was brittle fracture.     

Sulphide inhibition of methanogenic activity at various pH levels at 55°C

The purpose of this study was to evaluate the toxic effect of sulphide on thermophilic methanogenic bacteria, pre-cultivated in UASB-reactors fed with and without sulphate, at 55°C and different pH levels. For granular sludge, precultivated in the presence of sulphate, the inhibition caused by hydrogen sulphide was dependent on the pH imposed. At alkaline pH the inhibitory effect of hydrogen sulphide was higher than at neutral or acidic pH. The effect of sulphide could not be described in terms of free hydrogen sulphide level only. For dispersed sludge, pre-cultivated in the absence of sulphate, the inhibition caused by free hydrogen sulphide was independent of the pH, and the toxic effect of sulphide could be described in terms of free hydrogen sulphide.     

Cyclic Oxidation of Ternary Layered Ti2AlC at 600–1000°C in Air

The cyclic oxidation of bulk Ti₂AlC at intermediate temperatures of 600–1000°C in air was studied by thermogravimetric analysis. It was demonstrated that Ti₂AlC exhibited good cyclic‐oxidation resistance at temperatures above 700°C. The cyclic‐oxidation kinetics approximately follows a parabolic rate law at 700–1000°C range. The surface scales are dense, resistant to spalling and adhesive to Ti₂AlC substrate. An abnormal oxidation whose cyclic‐oxidation kinetics obeys a linear law is observed at 600°C. As revealed by scanning electron microscope (SEM), oxidation‐induced cracks present at 600°C results in poor protectivity and accounts for the abnormal oxidation. The cracks are caused by the stress associated with the volume expansion due the formation of anatase TiO₂ in the scale.     

Thermal degradation of poly(methyl methacrylate) at 50°C to 125°C

Small but significant numbers of chain scissions occur in a commercial poly(methyl methacrylate) sheet exposed to temperatures between 50 and 125°C. The scission rate is initially high and then levels off to a constant rate. The short-time rate of chain scissions is temperature dependent, while the long-time rate of chain scissions appears to be temperature independent. Four possible sources of random chain scission initiation were considered: (1) the presence of unreacted initiators of polymerization, (2) free radicals generated from additives in the commercial film, (3) weak links in the polymer chain, and (4) free radicals generated from the thermal decomposition of an oxidation product of methyl methacrylate (MMA) monomer. The source most consistent with our results is the one involving free radicals generated from the oxidation product of MMA monomer.     

The pyrolysis of acrylic fiber in inert atmosphere. I. Reactions up to 400°C

The pyrolysis of acrylic fiber up to 400°C in an inert atmosphere at 1° and 6°C/min was studied by means of thermogravimetric and differential thermal analysis. The exothermic reaction occuring at 180–300°C was shown to be due to the reaction of nitrile groups by comparing the extent of exotherm with the number of nitrile groups present, determined by infrared spectroscopy. In addition, results of single-fiber tensile measurements, density, and elemental analysis of the pyrolyzed fibers are interpreted in terms of possible molecular structures. The gases evolved on pyrolysis were analyzed for both ammonia and hydrogen cyanide and the liberation of ammonia was attributed to a termination reaction of the polymerization of nitrile groups. The critical conditions necessary for the production of high strength and modulus carbon fiber are discussed briefly in ralation to the chemical changes occurring on pyrolysis.     

Specific heat of glassy carbon between 0.4° and 4.5°K—II

Glassy Carbon heat-treated to 3000°C (GC30), for which the specific heat follows from 5°K down to 0·4°K the relation C = γT + αT³, was neutron irradiated in the Western New York reactor to different doses (20, 50, 125, 300 and 1250 hr.). In the He⁴ range of temperature, the coefficient γ increases fast with the dose, with α decreasing at the same time. The combined effect results in a surprizing behavior above 2·5°K, where the specific heat decreases at first with dose and then increases after having passed through a minimum. In the lowest temperature range (below 2°K) a tail of a peak located below 0·4°K appears after irradiation with an increasing intensity. Presumably the peak is formed at about the same place as it is created in process of carbonization, the response of Glassy Carbon to irradiation being similar in this respect to the behavior of soft carbons. The relationship between the linear term γ, the height of the peak and the concentration of localized spins is discussed and problems and difficulties to be solved are indicated.     

Specific heat of glassy carbon between 0.4° and 4.5°K—I

The specific heat of Glassy Carbon was investigated in the temperature range from 0.4°–4.5°K. Samples of Glassy Carbon heat-treated to 1000°C (GC10) were prepared in form of tubes by the Tokai Electrode Manufacturing Company of Japan. They were heat-treated to various temperatures up to 3200°C in our graphite tube furnace. It was found that above 2°K, all samples follow the relation C = γT + αT³, with γ going through a strong maximum and α varying only slightly with increase in heat-treatment temperature. On the average the cubic term α is about the same as for soft carbons heat-treated to 1000–1250°C. In the lower temperature range evidence of a specific heat peak located below 0·4°K is obtained. The observed high temperature tail of the peak increases and then decreases in parallel with changes of the linear term γ. The room temperature specific heat of Glassy Carbon changes very little with heat-treatment giving evidence of the nongraphitizability of this material.     

A Comparison of 0°–0° and 45°–45° bridge‐Seeded,YBCO single grains

A variety of multiseeding techniques have been investigated over the past 20 yr in an attempt to enlarge bulk (RE)BCO superconducting samples fabricated by the top‐seeded melt growth (TSMG) process for practical applications. Unfortunately, these studies have failed to establish whether technically useful values of trapped field can be achieved in multiseeded bulk samples. In this work specially designed, 0°–0° and 45°–45° bridge seeds of different lengths have been employed to produce improved alignment of the seeds during the TSMG process. The ability of these bridge‐seeded samples to trap magnetic field, which is the key superconducting property for practical applications of bulk (RE)BCO, is compared for the samples seeded using 0°–0° and 45°–45° bridge seeds of different lengths. The grain boundaries produced by these bridge seeds are analyzed in detail, and the similarities and differences between the two bridge‐seeding processes are discussed.     

The start‐up of anaerobic sequencing batch reactors at 20 °C and 25 °C for the treatment of slaughterhouse wastewater

The objective of this research was to evaluate the feasibility, the stability and the efficiency of a start‐up at 20 °C and 25 °C of anaerobic sequencing batch reactors (ASBRs) treating slaughterhouse wastewater. Influent chemical oxygen demand (COD) and suspended solids concentrations averaged 7500 and 1700 mg dm^?3, respectively. Reactor start‐up was completed in 168 and 136 days at 20 °C, and 25 °C, respectively. The start‐up process was stable at both temperatures, except for a short period at 20 °C, when effluent volatile fatty acid (VFA) concentrations increased from an average of 40 to 400 mg dm^?3. Effluent quality varied throughout start‐up, but in the last 25 days of the experiment, as the ASBRs were operated under organic loading rates of 2.25 ± 0.21 and 2.86 ± 0.24 kg m^?3 d^?1 at 20 °C and 25 °C, respectively, total COD was reduced by 90.3% ± 1.3%. Methanogenesis was not a limiting factor during start‐up. At 20 °C, the limiting factor was the acidification of the soluble organics and, to a smaller extent, the reduction of propionic, isobutyric and isovaleric acids into lower VFAs. At 25 °C, the limiting factor was the hydrolysis of particulate organics. To minimize biomass loss during the start‐up period, the organic loading rate should be increased only when 75 –80% of the COD fed has been transformed into methane within the design hydraulic retention time. © 2001 Society of Chemical Industry     

Effective Thermal Conductivity of Soda‐Lime Silicate Glassmelts with Different Iron Contents Between 1100°C and 1500°C

This study presents a simple method for retrieving the effective thermal conductivity of semitransparent glassmelts from measured temperature profiles. Effective thermal conductivity of molten glass at high temperature is an important thermophysical property that affects the glassmelting and forming processes and thus the quality of the final glass products. In semitransparent glassmelts, heat is transferred by both conduction and radiation. In the limiting case of optically thick glassmelts, typically featuring high iron content, thermal radiation can be treated as a diffusion process. The total heat flux can be expressed as the sum of a phononic and a radiative heat fluxes based on Fourier's law. For weakly absorbing glassmelts, the temperature profile may be strongly nonlinear particularly neat container walls due to the contribution from emission and absorption. Steady‐state measurement techniques, such as the linear heat flux method, have been developed to measure glassmelt effective thermal conductivity at high temperatures. However, they typically use only three temperatures measurements and assume linear temperature profile in the glassmelt. The new retrieval method addresses these drawbacks particularly for weakly absorbing glassmelts featuring nonlinear temperature profiles. It is demonstrated with experimental data collected for soda‐lime silicate glasses with iron content ranging from 0.008 to 1.1 wt% and temperatures between 1100°C and 1550°C.