Nitrogen desorption from pure iron melts under reduced pressure

More recently, lower nitrogen contents of steel are required in view of its workability and applicability. The present study covers basic investigations on the improvement of mass transfer in denitrogenation of steel melts under vacuum. Extensive reduction of the contents of the surface-active elements oxygen and sulfur is a precondition to increase the rate of nitrogen desorption. Kinetics of nitrogen transfer is reliably described by a mixed control model which includes diffusion in the melt, interfacial reaction and diffusion in the gas phase. Particularly at low oxygen and sulfur contents, mass transfer of nitrogen during desorption from steel melts is markedly accelerated. A convincing explanation of this phenomenon has not been found yet.     

Physico–chemical and Dyeing Properties of Disperse Dyes containing Phthalimide Residues

The relationship between the constitution and the physico–chemical and dyeing properties of disperse dyes containing phthalimide residues has been studied. The influence of the –NH or –NCH₃ group in the phthalimide residues on the thermal and spectral properties of dyes has been investigated. Their influence on the dyeing process and on the colour and fastness properties of dyed polyester have also been studied.     

A New Route to Highly Stretchable and Soft Inorganic–Organic Hybrid Elastomers Using Polydimethylsiloxane as Crosslinker of Epoxidized Natural Rubber

Sulfur or peroxide crosslinking is the most common and conventional method to develop elastomeric materials. A new approach to crosslink epoxidized natural rubber (ENR) by aminopropyl terminated polydimethylsiloxane (AT-PDMS) is described, intending to develop a new kind of hybrid organic–inorganic elastomers. The curing reaction is accelerated by using hydroquinone as a catalyst. The formation of the hybrid structure is evident from the appearance of two glass transition temperatures, at −1 and −120 °C, for the ENR and PDMS phases, respectively. The curing reaction is found to be of first order with respect to amine concentration with the estimated activation energy of ≈62 kJ mol⁻¹. Comparing the mechanical properties to a typical ENR-sulfur system leads to the conclusion that the ENR/AT-PDMS hybrid structure is highly stretchable and soft, as demonstrated by its relatively higher strain at failure (up to ≈630%), and lower hardness and modulus values. The higher stretchability and soft nature of the material are achieved by introducing flexible PDMS chains during the curing process resulting to a hybrid elastomer networks. This kind of soft but robust materials can find several applications in diverse fields, such as soft robotics, flexible, and stretchable electronics.     

A STUDY ON THE BEHAVIOUR OF GALLIUM IN THE IRONMAKING PROCESS

Gallium is a valuable rare metal which is mainly being used in the production of GaAs. The demand for gallium is increasing but production is limited since gallium is extracted only as a by-product of bauxite processing. On the other hand coal, ironmaking coke and iron ore gangue contain traces of gallium. However little is known about the behaviour of gallium in ironmaking. The aim of the study is to clarify the distribution of gallium between hot metal, slag and top gas by means of laboratory experiments. It was found that Ga2O3 is not stable in blast furnace slags and that gallium is retained in hot metal. Vacuum distillation experiments with hot metal showed that gallium is not transferred to the gas phase. Data on the input and output of gallium at two industrial blast furnaces, as well as chemical analyses of the gallium content of several cokes are presented, too.     

Dephosphorization equilibria between pure molten iron and CaO-saturated FeOn–CaO–CaF2 slags

Metal-slag refining reactions have been investigated to determine dephosphorization equilibria in steelmaking using CaO-saturated FeO_n–CaO–CaF₂ slags low in P₂O₅ content. Slag compositions have been optimized to achieve maximum partition ratios wt.%(P₂O₅)/wt.%[P] and minimum phosphorus contents in pure molten iron at 1 550 and 1 600°C. FeO_n–CaO–CaF₂ slags prove to be most effective dephosphorizers. Optimal slag compositions are between 10 and 20 wt.% FeO_n. Attempts were also made to present phosphate capacities fractions of free oxygen ions and theoretical optical basicities Λ as a function of the FeO_n content of slags. Dephosphorization capacity of FeO_n–CaO–CaF₂ slags is compared with that of FeO_n–CaO–SiO₂ and FeO_n–CaO–Al₂O₃ slags.     

Temperature scanning stress relaxation behavior of water responsive and mechanically adaptive elastomer nanocomposites

The decrease of stress at constant strain, that is, the stress relaxation process as a function of temperature, is a central mechanical characteristics of elastomer nanocomposites for their potential applications. However, in the conventional stress relaxation test, the relaxation behavior is usually determined as a function of time at constant temperature. The present work reports the temperature scanning stress relaxation (TSSR) characteristics of a new kind of mechanically adaptive elastomer nanocomposite by monitoring the nonisothermal relaxation behavior as a function of temperature. This kind of adaptive elastomer nanocomposite was prepared by introducing calcium sulfate (CaSO₄), as the water-responsive phase into the hydrophilic elastomer matrix. The influence of water-induced structural changes on TSSR behavior was investigated. Water treatment had a strong effect on the shape of the relaxation spectrum of the nanocomposite. It was revealed that the in situ development of hydrated nano-rod crystal structures of CaSO₄ in the elastomer matrix was responsible for the changes in the mechanical relaxation behavior of the composites. Atomic force microscopy was used to verify this nano-rod crystal morphology in the elastomer matrix. The mechanism of water-induced mechanical reinforcement of the composite was explored from dynamic mechanical analysis of the material and correlated with its stress relaxation behavior. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48344.     

Adsorption of finite polymers in different thermodynamic ensembles

We investigate the cooperative effects of a single finite chain of monomers near an attractive substrate by first constructing a conformational pseudo-phase diagram based on the thermal fluctuations of energetic and structural quantities. Then, the adsorption transition is analyzed in more detail. This is conveniently done by a microcanonical analysis of densities of states obtained by extensive multicanonical Monte Carlo simulations. For short chains and strong surface attraction, the microcanonical entropy turns out to be a convex function of energy in the transition regime. This is a characteristic physical effect and deserves a careful consideration in analyses of cooperative macrostate transitions in finite systems.     

Structurally Based Assessment of the Influence of Fluorides on the Characteristics of Continuous Casting Powder Slags

The use of fluorides in continuous casting powder leads to the desired reduction of melting temperature to less than 1573 K (1300 °C) as well as to lowering the viscosity below 10 dPas. With an equilateral use of alkalis, the tendency to form volatile fluorine compounds rises. The effect of these components on the structure of the casting slags can be described with the NBO/T-ratio. Should the full effect of fluorides to be used for structural modification of the slags, the other components have to be inhibited by compound formation so as to prevent them from forming gaseous fluoride. If the fluoride content in the continuous casting slag is represented by means of fluorspar, the influence on the NBO/T-ratio can be described with the impact factor 4.0.     

Flame characteristics of pulverized torrefied-biomass combusted with high-temperature air

In this work, the flame characteristics of torrefied biomass were studied numerically under high-temperature air conditions to further understand the combustion performances of biomass. Three torrefied biomasses were prepared with different torrefaction degrees after by releasing 10%, 20%, and 30% of volatile matter on a dry basis and characterized in laboratory with standard and high heating rate analyses. The effects of the torrefaction degree, oxygen concentration, transport air velocity, and particle size on the flame position, flame shape, and peak temperature are discussed based on both direct measurements in a laboratory-scale furnace and CFD simulations. The results primarily showed that the enhanced drag force on the biomass particles caused a late release of volatile matter and resulted in a delay in the ignition of the fuel–air mixture, and the maximum flame diameter was mainly affected by the volatile content of the biomass materials. Furthermore, oxidizers with lower oxygen concentrations always resulted in a larger flame volume, a lower peak flame temperature and a lower NO emission. Finally, a longer flame was found when the transport air velocity was lower, and the flame front gradually moved to the furnace exit as the particle size increased. The results could be used as references for designing a new biomass combustion chamber or switching an existing coal-fired boiler to the combustion of biomass.     

Reactive polytetrafluoroethylene/polyamide compounds. I. Characterization of the compound morphology with respect to the functionality of the polytetrafluoroethylene component by microscopic and differential scanning calorimetry studies

Compounds of electron‐beam‐irradiated polytetrafluoroethylene (PTFE) and polyamide (PA) were produced by reactive extrusion. During extrusion, both a breakdown process of the PTFE agglomerates and a chemical reaction between PTFE and PA took place. The morphology of the compounds was characterized with differential scanning calorimetry using fractionated crystallization, with atomic force microscopy and scanning electron microscopy, and with dynamic light scattering. The particle size of the dispersed PTFE phase decreased as the irradiation dose increased. A simple theoretical model of the breakdown process of PTFE agglomerates was made for the discussion of the development of the observed degree of dispersion. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1308–1316, 2005