scholarly journals Deposits in Gas-fired Rotary Kiln for Limonite Magnetization-Reduction Roasting: Characteristics and Formation Mechanism

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 764 ◽  
Author(s):  
Xianghui Fu ◽  
Zezong Chen ◽  
Xiangyang Xu ◽  
Lihua He ◽  
Yunfeng Song
Keyword(s):  
Melting Point ◽  
Liquid Phase ◽  
Formation Mechanism ◽  
Rotary Kiln ◽  
Coal Ash ◽  
Binder Phase ◽  
Reduction Roasting ◽  
Key Factor ◽  
Liquefaction Temperature ◽  
Melting Point Eutectic

The formation mechanism of deposits in commercial gas-fired magnetization-reduction roasting rotary kiln was studied. The deposits ring adhered on the kiln wall based on the bonding of low melting point eutectic liquid phase, and the deposit adhered on the air duct head by impact deposition. The chemical composition and microstructure of the deposits sampled at different locations varied slightly. Besides a small amount of quartz and limonite, main phases in the deposits are fayalite, glass phase and magnetite. The formation of the deposits can be attributed to the derivation of low melting point eutectic of fine limonite and coal ash, and the solid state reaction between them. Coal ash, originated from the reduction coal, combining together with fine limonite particles, results in the accumulation of deposits on the kiln wall and air duct. Fayalite, the binder phase, was a key factor for deposit formation. The residual carbon in limonite may cause an over-reduction of limonite and produce FeO. Amid the roasting process, SiO2, originated from limonite and coal ash, may combine with FeO and reduce the liquefaction temperature, therewith liquid phase generates at high temperature zone, which can significantly promote the growth of deposits.

Thermodynamics and Kinetic Considerations behind the Growth of AlN Whiskers Synthesized by Carbothermal Reduction

2007 ◽  
Vol 280-283 ◽  
pp. 1403-1408 ◽  
Author(s):  
Ren Li Fu ◽  
He Ping Zhou ◽  
Ke Xin Chen ◽  
José Maria F. Ferreira
Keyword(s):  
Melting Point ◽  
Liquid Phase ◽  
Carbothermal Reduction ◽  
Solid Phase ◽  
Dominant Role ◽  
Kinetic Studies ◽  
Synthesis Temperature ◽  
Screw Dislocations ◽  
Melting Point Eutectic ◽  
Kinetics Of

AlN whiskers have been successfully synthesized by carbothermal reduction. The thermodynamics and growth kinetics of AlN whiskers were studied at 1600°C using CaCO3 as a catalyst. The research indicated that AlN whiskers are more easily nucleated from the liquid phase than at the surface of solid phase. AlN whiskers are nucleated by VLS mechanism and the liquid, which plays a dominant role in the VLS mechanism, is formed by Al-Ca interphases, such as CaO×2Al2O3 and CaO×6Al2O3. Kinetic studies suggest that the catalyst reacts with Al2O3 to form a low melting point eutectic (1390°C). The liquid phase formed at this low melting point eutectic provides good conditions for nucleation of AlN whiskers. At the synthesis temperature, the liquid phase vaporizes, thus creating suitable conditions for the subsequent growing of whiskers by the VLS mechanism. This growing mechanism conforms to thermodynamics and a lot of proof indicates that screw dislocations play an important role in the process of the whiskers' formation.

scholarly journals A Robust Recovery of Ni From Laterite Ore Promoted by Sodium Thiosulfate Through Hydrogen-Thermal Reduction

2021 ◽  
Vol 9 ◽  
Author(s):  
Shoujun Liu ◽  
Chao Yang ◽  
Song Yang ◽  
Zhongliang Yu ◽  
Zhao Wang ◽  
...  
Keyword(s):  
Melting Point ◽  
Sodium Thiosulfate ◽  
Thermal Reduction ◽  
Metal Salts ◽  
Reduction Roasting ◽  
Alkali Metal Salts ◽  
Ni Content ◽  
Element Migration ◽  
Melting Point Eutectic ◽  
Laterite Ore

Laterite ore is one of the important sources of nickel (Ni). However, it is difficult to liberate Ni from ore structure during reduction roasting. This paper provided an effective way for a robust recovery of Ni from laterite ore by H2 reduction using sodium thiosulfate (Na2S2O3) as a promoter. . It was found that a Ni content of 9.97% and a Ni recovery of 99.24% were achieved with 20 wt% Na2S2O3 at 1,100°C. The promoting mechanism of Na2S2O3 in laterite ore reduction by H2 was also investigated. The thermogravimetric results suggested the formation of Na2Mg2SiO7, Na2SO3, Na2SO4, and S during the pyrolysis of laterite with Na2S2O3, among which the alkali metal salts could destroy the structures of nickel-bearing silicate minerals and hence release Ni, while S could participate in the formation of the low-melting-point eutectic phase of FeS-Fe. The formation of low-melting-point phases were further verified by the morphology analysis, which could improve the aggregation of Ni-Fe particles due to the capillary forces of FeS-Fe as well as the enhanced element migration by the liquid phase of sodium silicates during reduction.

Effect of WC Addition on Phase Formation and Microstructure of TiC-Ni Composites

2008 ◽  
Vol 55-57 ◽  
pp. 353-356
Author(s):  
Nawarat Wora-uaychai ◽  
Nuchthana Poolthong ◽  
Ruangdaj Tongsri
Keyword(s):  
Liquid Phase ◽  
Tungsten Carbide ◽  
Phase Formation ◽  
Liquid Phase Sintering ◽  
Precipitation Process ◽  
Solid Solution Phase ◽  
Binder Phase ◽  
Sintering Process ◽  
X Ray Diffraction ◽  
X Ray

In this research, titanium carbide-nickel (TiC-Ni) composites, with tungsten carbide addition, were fabricated by using a powder metallurgy technique. The TiC-Ni mixtures containing between 0-15 wt. % tungsten carbide (WC), were compacted and then sintered at 1300°C and 1400°C, respectively. The phase formation and microstructure of the WC-added TiC-Ni composites have been investigated by X-ray diffraction and scanning electron microscopy techniques. Mechanical properties of these composites were assessed by an indentation technique. The X-ray diffraction patterns showed no evidence of tungsten rich phases in the sintered WC-added cermets. This indicates that during the sintering process, tungsten carbide particles were dissolved in metallic binder phase (Ni phase) via dissolution/re-precipitation process during liquid phase sintering. The liquid phase formed during sintering process could improve sinterability of TiC-based cermets i.e., it could lower sintering temperatures. The TiC-Ni composites typically exhibited a core-rim structure. The cores consisted of undissolved TiC particles enveloped by rims of (Ti, W)C solid solution phase. Hardness of TiC-Ni composites increased with WC content. Sintering temperature also had a slight effect on hardness values.

Carbon Capture From Natural Gas via Polymeric Membranes

2018 ◽  
pp. 3043-3055
Author(s):  
Nayef Mohamed Ghasem ◽  
Nihmiya Abdul Rahim ◽  
Mohamed Al-Marzouqi
Keyword(s):  
Liquid Phase ◽  
Low Temperature ◽  
Gas Flow ◽  
Polymeric Membrane ◽  
Co2 Absorption ◽  
Membrane Contactor ◽  
Liquid Temperature ◽  
Liquid Phase Boundary ◽  
Key Factor ◽  
Absorption Performance

Polymeric membrane is a promising energy effective and an active alternative for conventional CO2 absorption column. The type of absorption liquid and operating parameters plays an efficient role in the ultimate absorption/stripping performance using gas-liquid membrane contactor. The gas flow rate has a significant effect on CO2 absorption performance, by contrast, it has no effect on stripping performance. Further the CO2 absorption performance in membrane contactor could be enhanced by high liquid flow rates. Because the gas–liquid contact time was a key factor to enhance the stripping flux at low temperature while liquid phase boundary layer thickness and associated mass transfer resistance is important at elevated temperature. So by controlling the liquid phase velocity and the length of module at low temperature better stripping performance can be achieved. The effect of liquid temperature on absorption performance in gas-liquid is not straightforward, since the liquid temperature cooperatively influence several factors.

scholarly journals Markov Chain Simulation of Coal Ash Melting Point and Stochastic Optimization of Operation Temperature for Entrained Flow Coal Gasification

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4245
Author(s):  
Zhang ◽  
Guan ◽  
Hou ◽  
Zhang ◽  
Li ◽  
...  
Keyword(s):  
Markov Chain ◽  
Melting Point ◽  
Stochastic Programming ◽  
Optimization Model ◽  
Coal Gasification ◽  
Coal Ash ◽  
Entrained Flow ◽  
Sample Data ◽  
Ash Melting ◽  
Mc Simulation

In the entrained flow coal gasification process, the gas production is critically affected by the operating temperature (OT) and coal ash melting point (AMP), and the AMP is one of key factors for the determinations of OT. Considering the fact that coal is a typical nonhomogeneous substance and the coal ash composition varies from batch to batch, this paper proposes the application of the Markov Chain (MC) method in simulation of the random AMP series and the stochastic optimization of OT based on MC simulation for entrained flow coal gasification. The purpose of this paper is to provide a more accurate optimal OT decision method for entrained flow coal gasification practice. In this paper, the AMP was regarded as a random variable, and the random process method, Markov Chain, was used to describe the random AMP series of feed coal. Firstly, the MC simulation model about AMP was founded according to an actual sample data, 200 sets of AMP data from an industrial gasification plant under three simulation schemes (the sample data were individually divided into 16, eight and four state groups,). The comparisons between the simulation results and the actual values show that the founded MC simulation model descries the AMP series very well. Then, a stochastic programming model based on MC simulation for OT optimization was developed. Finally, this stochastic programming optimization model was optimized by genetic algorithm (GA). Comparing with the conventional OT optimization method, the proposed stochastic OT optimization model integrated MC simulation can ascertain a more accurate OT for guiding the coal gasification practice.

scholarly journals Effects of Boron Addition on the Microstructure and Mechanical Properties of (Ti,Ta)(C,N)-Co Based Cermets

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 787
Author(s):  
Ernesto Chicardi ◽  
Francisco José Gotor Martínez
Keyword(s):  
Mechanical Properties ◽  
Liquid Phase ◽  
Intermetallic Compound ◽  
Solid Solutions ◽  
General Trend ◽  
Liquid Phase Sintering ◽  
Binder Phase ◽  
Boron Addition ◽  
Sintering Additive ◽  
Microstructure And Mechanical Properties

In this work, a titanium–tantalum carbonitride based cermet, with cobalt as the binder phase and boron as a sintering additive, was developed by a mechanically induced self-sustaining reaction process using two different methodologies. The boron additive was added to prevent the formation of brittle intermetallic compounds generally formed during the liquid phase sintering step due to the excessive ceramic dissolution into the molten binder phase. A systematic study was carried out to understand the effects of boron addition on the nature of the phases, microstructure, and mechanical properties of cermets. With the boron addition, the formation of two different boride solid solutions, i.e., (Ti,Ta)B2 and (Ti,Ta)3B4, was observed. Moreover, the nature of the binder was also modified, from the (Ti,Ta)Co2 brittle intermetallic compound (for cermets without boron addition) to ductile and tough (Ti,Ta)Co3 and α-Co phases (for cermets with boron addition). These modifications caused, as a general trend, the increase of hardness and toughness in cermets.

Phase Evolution and Formation Mechanism in Acicular Mullite Prepared from Kaolinite via Wet Chemistry Method

2010 ◽  
Vol 152-153 ◽  
pp. 643-647
Author(s):  
Xiao Chun Dai ◽  
Zhu Fa Zhou ◽  
Shu Mei Wang ◽  
Ran Ran Tian ◽  
Chun Rong Wang ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Formation Mechanism ◽  
Phase Evolution ◽  
Molar Ratio ◽  
Wet Chemistry ◽  
Chemistry Method ◽  
Acicular Mullite

Mullite was synthesized by firing precursors prepared from kaolinite via a wet chemistry method at various temperatures. The acicular mullite grains were formed in samples with addition of AlF3 by this process. The phase evolution and morphology of the fired samples were investigated. For the samples without AlF3, the mullitization began to occur at 1300 and almost completed at 1550 , the grains formed were normal-shaped. For the samples with AlF3, acicular mullite was formed, and mullitization began to occur at 1100 and completed at 1250 . The growth of the acicular mullite was associated with a liquid phase. The formed acicular mullite was alumina-rich and had a composition of about 73.4 wt% Al2O3 and 26.6 wt% SiO2 (Al2O3/SiO2=1.65, molar ratio).

Entire Symmetric Structure Inchworm-Type Piezoelectric Linear Actuator

2011 ◽  
Vol 480-481 ◽  
pp. 1061-1064 ◽  
Author(s):  
Hong Zhuang Zhang ◽  
Jiang Tian Shi ◽  
De Xin Sun
Keyword(s):  
Melting Point ◽  
Magnesium Alloy ◽  
Tensile Stress ◽  
Liquid Film ◽  
Solidification Process ◽  
Solidification Cracking ◽  
Necessary Condition ◽  
Welding Joint ◽  
Solidification Cracks ◽  
Melting Point Eutectic

The feature of the hot cracks of the welding joint of the MIG welded magnesium alloy AZ91D was studied systematically. The result indicates that the weld of the magnesium alloy displays a high cracking susceptibility. The cracks are mainly formed on the centerline of the weld and in the arc crater at the end of the weld. These cracks propagate along the α-Mg grain boundary, and they belong to the solidification cracking. These solidification cracks are resulted by the joint function of the low melting point liquid film in the weld and the tensile stress suffered by the weld metal during the solidification process. The low melting point liquid film is the internal cause to form the solidification cracks, while the tensile stress is a necessary condition. Limiting the amount of the low melting point eutectic and decreasing the tensile stress of the welding joint are two effective methods to improve the solidification cracking susceptibility of the Mg alloy weld.

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