Formation Of Molten Phase Research Articles

Valorization of oil‐based drilling cuttings as a substitute for bauxite in fracturing proppants application

AbstractThis study aimed to increase the scale of oil‐based drilling cuttings (OBDCs) resource utilization in the ceramic industry. The sintering process and mechanism were explored based on the analysis of physicochemical properties, phase transitions, and microstructure. The results showed that (1) The main ceramic‐technological characteristics of the OBDC were determined, which belonged to high‐silica solid waste with a high Si–Al ratio and a low acid–base ratio of oxides. (2) The low meltability temperature of the OBDC could largely influence the determination of the sintering temperature range for ceramic products. (3) The chemical components OBDC provided were involved in the formation of molten phases, which could affect dimensional accuracy and mechanical properties. Meanwhile, the dolomite promoted the formation of closed pores and enhanced lightweight performance. (4) Before 800°C, dolomite decomposed and reacted with SiO2 to form silicate, and then a new feldspar crystal appeared. After 1000°C, orthoclase completely melted into the molten phase, only two phases of quartz and diopside existed in the material until 1150°C. When the temperature was higher than 1350°C, the glass transition of the phase was basically intensified. (5) In the analyzed scenarios, the results indicated OBDC can only be doped in low contents and degrades the ceramic material properties.

Li4SiO4 pellets templated by rice husk for cyclic CO2 capture: Insight into the modification mechanism

Li4SiO4 stands out among various solid sorbents for CO2 capture. The commonly used mechanical granulation process for Li4SiO4 sorbents causes the destruction of the microstructures. Therefore, with the characteristics of huge production and low cost, an agricultural waste (rice husk) was employed as a pore former to improve the structures of Li4SiO4 pellets and, thus, enhance the cyclic CO2 sorption performance. The rice husk templating greatly enhanced the CO2 sorption capacity of Li4SiO4 pellets. Especially, 20 wt% rice husk-templated Li4SiO4 exhibited the capacity of 0.21 g/g, which was nearly twice that of the unmodified sorbent. The quick release of the combustion gases from burning rice husk could create porosity for the sorbents. In addition, the alkaline compositions in rice husk promoted the CO2 sorption due to the decreased CO2 diffusion resistance by the formation of molten phases. Moreover, the ashes of rice husk after high-temperature combustion were found to block the pores of the sorbents, leading to the capacity reduction. The comprehensive function of rice husk templating for Li4SiO4 pellets was the tradeoff between the positive effects of pore creation and alkaline doping and the negative effects of pore blockage by the ashes.

Volumetric Shrinkage Characteristics and Kinetics Analysis of Vanadium Titanomagnetite Carbon Composite Hot Briquette during Isothermal Reduction

The volumetric shrinking characteristics and kinetics of vanadium titanomagnetite carbon composite hot briquette (VTM-CCB) during isothermal reduction were investigated in this paper. It was found that the volumetric shrinking occurs as a combination of a loss of carbon and oxygen from VTM-CCB as well as sintering of iron oxide, suppression of growth of iron whiskers, formation of molten phases, and residual solid carbon content. In the temperature range from 900°C to 1100°C, the carbon gasification is viewed as the primary factor for the shrinking behavior. In the temperature range higher than 1100°C, the shrinking of VTM-CCB is mainly caused by the formation of molten slag, liquid iron, and residual solid carbon. It also should be pointed out that, in the higher temperature range, the volumetric shrinkage of VTM-CCB decreased with increasing FC/O ratio, which is mainly due to the fact that a higher FC/O ratio leads to a decreasing of molten slag generation proportion and a suppression of aggregation growth of liquid iron by the increasing of residual solid carbon. Based on the kinetics analysis, The formula for the shrinkage of VTM-CCB during reduction can be obtained, and the value of shrinking activation energy of VTM-CCB decreased obviously from 337.86 kJ/mol to 84.85 kJ/mol with increasing FC/O ratio from 0.8 to 1.4.

Long-time ablation protection of carbon/carbon composites with different-La2O3-content modified ZrC coating

Long time oxidation protection at ultra-high temperatures or ablation protection has been a choke point for C/C composites. In this study, long time ablation protection of different-La2O3-content (5–30vol.%) modified ZrC coating for SiC-coated carbon/carbon (C/C) composites was investigated. Results showed that ZrC coating with 15vol.% La2O3 had good ablation resistance and could protect C/C composites for at least 700 s at 2160°C. A high-thermal-stability and low-oxygen-diffusivity oxide scale containing m-ZrO2 particles and molten phases with La0.1Zr0.9O1.95 and La2Zr2O7 was formed during ablation, offering the ablation protection. La could erode grain boundaries of ZrO2 to refine ZrO2 by short-circuit diffusion and m-ZrO2 particles were retained due to less bulk diffusion than grain-boundary diffusion of La into ZrO2. The erosion resulted in the formation of molten phases containing fine nano-ZrO2, which served as viscous binder among m-ZrO2 particles and crack sealer for the oxide scale.

Thorium as a carbon oxidation catalyst

A large number of metal oxides are known to catalyze the gasification of carbon by molecular oxygen [1,2] and very small concentrations of the most active materials are capable of reducing the temperature at which carbon begins to oxidize in air by several hundred degrees [3]. Although active catalytic species come from every Group of the Periodic Table, the majority of catalysts appear to function via a redox cycle, being reduced to lower oxidation states by reaction with the carbon substrate and then reoxidizing back to the original state by reaction with ambient oxygen [3,4]. A few catalysts, such as Cr,O,, silver metal and possibly transition metal carbides [5], appear to accelerate the oxidation reaction by providing sites for the dissociation of molecular oxygen to give absorbed oxygen atoms, which then diffuse across the carbon surface to active sites where the carbon is gasified. In some cases the catalytic effect may be enhanced by the formation of a molten phase, followed by spreading and wetting of the carbon surface [6]. The actinide elements and their compounds have not been studied as catalysts for this reaction, although their behavior is somewhat predictable based on the above considerations. Uranium, which forms a series of oxides, has been found to be active catalytically, when present as UO, or U,O, [7]. Sampath et al. [8] have, however, recently reported that thorium oxide, ThO,. is an active catalyst for the oxidation of graphite in air in the temperature range 600-900°C. As the single oxide of thorium is very stable (AH&R = -293 kcal mol-‘), it would not be reduced to metal by heating with carbon in this temperature range and hence it would not be expected to participate in oxidation-reduction cycles on the graphite surface. ThO, is also much more stable in the presence of oxygen than the known carbides, ThC and ThC,, and hence carbide formation during carbon gasification would not be expected. In addition, the very high melting point (3220 o C) of ThO, would preclude the formation of molten phases and the wetting of the graphite substrate. For all these reasons a demonstrated catalytic activity for thoria would disqualify the usual redox process as the likely mechanism of the catalyzed gasification of carbon in this case, and as ThO, is only an indifferent catalyst for gas phase oxidation reactions (e.g., oxidation of CO) [9], it is also improbable that this oxide would bring about the dissociation

Effects of doping on the thermal decomposition of potassium perchlorate

The effects of impurities and additives on the thermal decomposition of potassium perchlorate have been investigated by thermoanalysis. The results indicate that the predominant effect of the impurities in altering the thermal stability of the potassium perchlorate is the formation of molten phases.