Sinter Strength Research Articles

Flow and penetration behaviours of liquid phase on iron ore substrate and their effects on bonding strength of sinter

ABSTRACTThe flow and penetration behaviours of the liquid phase on nuclei ore play crucial roles in the bonding of the sinter. In this study, the flow and penetration tests of the liquid phase and simulation tests were conducted to study the effects of SiO2 and Al2O3 contents of the adhering fines on the flow area (FA) and maximum penetration depth (MPD) through the micro-sintering method. The effects of the FA and MPD on the bonding strength of the sinter were investigated by a bonding test of quasi-particles. The results show that during the assimilation between the primary liquid phase and haematite ore, the gangues dissolve in the primary liquid phase, promoting the transformation of quasi-calcium ferrite into quasi-calcium silicate liquid. After solidification and precipitation, the two liquids turn into the silico-ferrite of calcium and aluminium and Fe2O3-bearing silicates. Increasing SiO2 or Al2O3 content decreases the FA by raising the viscosity of the primary liquid phase. However, it increases the MPD by reducing the quaternary basicity of the adhering fines and elevating the wettability of the liquid phase. The FA has a positive effect on the bonding strength of the sinter, whereas the effect of the MPD may be indirectly negative.

Impacts of CO2 on the pyrite–kaolinite interaction and the product sintering strength

Interactions between pyrite and silicates are very critical to ash slagging in coal-fired boilers. However, no work has been reported regarding the impacts on such interactions of CO2, the dominant component in the oxy–fuel combustion gas. This was investigated in the present work by using mixtures of pyrite and kaolinite, a prevailing silicate mineral in coal. Furthermore, the sintering strength of the generated products was also evaluated. The pyrite–kaolinite mixtures were treated on a fixed bed reactor in both N2 and CO2 for comparison. The treating temperature was 1050, 1150 and 1250 °C while the reaction time was 3, 6 and 12 min, respectively. The solid products were characterized by techniques such as X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). Sintering tests of these products were carried out as well. It was found that some interactions between pyrite and kaolinite took place in the N2 atmosphere. This was evidenced by the formation of iron aluminosilicate and attributed to the effects of water vapor released from kaolinite dehydroxylation. Nevertheless, pyrite–kaolinite interactions in N2 were limited and had insignificant effects on product sintering strength development. In CO2, pyrite–kaolinite interactions were significantly enhanced, compared with those in N2. Although the kaolinite-derived water vapor had some effects, CO2 was found to play a dominant role. Enhanced pyrite–kaolinite interactions resulted in an increase of eutectic phases. Consequently, the product sintering strength development was greatly elevated. It was further found that, under the conditions investigated, the interactions between pyrite and kaolinite were actually through reactions between FeO, rather than other intermediates, and aluminosilicate. This new finding enabled us to develop the mechanisms for pyrite–kaolinite interactions in N2 and CO2.

An integrated approach for production of stainless steel master alloy from a low grade chromite concentrate

As an alternative process, the production of stainless steel master alloys in blast furnace (BF) exhibits high economic efficiency and great potential to use low-grade chromite resources. To produce desirable sinter products required by the blast furnace smelting process, sintering tests of ore mixtures made from a low grade South African chromite concentrate (Cr2O3/FeO = 1.99) and Chinese magnetite concentrate were performed in a sinter pot in terms of various sintering parameters including coke dosage, mix moisture, sinter basicity and proportion of magnetite concentrate, etc. An integrated process comprising “high pressure grinding rollers (HPGR) pretreatment, pelletizing, coke coating, pre-drying and non-fluxed sintering” steps was proposed based on the pellet-sintering technique. The quality of Cr-bearing sinters was evaluated. The results show that high quality Cr-bearing sinters can be obtained through the proposed process. Addition of 40% or more magnetite concentrate in ore blends promises to yield desirable sinters of proper chemical composition and good metallurgical properties required by the blast furnace smelting process. The smelting performance of the Cr-bearing sinter made from the 40% chromite and 60% magnetite mixture was assessed under simulated blast furnace smelting conditions. It is feasible to use the Cr-bearing sinters in blast furnace for stainless steel master alloy production. A stainless steel master alloy containing 71.75% Fe, 19.52% Cr and 7.84% C with phosphorus and sulfur contents (<0.015%) is obtained at Fe and Cr recovery rates of 92.55% and 87.53%, respectively, when smelting at 1550 °C for 60 min with slag compositions (10% Al2O3, 10% MgO and R2 = 1.0). The bonding mechanism of Cr-bearing sinters and the formation mechanism of liquid phase were further revealed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS). Both slag bonding (10 to 20% silicate) and solid bonding (recrystallization of spinel phase) contribute to the consolidation of the Cr-bearing sinters. Increasing the basicity of sinter made from 100% chromite concentrate or addition of magnetite concentrate in the ore blend at natural basicity lead to the formation of low-strength slag bonds, which generally reduces the sinter strength.

Fabrication of large-area interconnects by sintering of micron Ag paste

Organics are difficult to be decomposed from large-area interconnects, i.e., more than 12 mm × 12 mm, using sintered Ag nanoparticles. This is mainly due to the lack of contact with air, which leads to insufficient sintering and low shear strength. In this paper, we report robust bonding of large-area interconnects by sintering of 1–2 μm micron Ag paste. Organics could be removed rapidly from the large pores surrounded by coarse necks. At 250 °C, the content of residual organics in sintered silver joints with micron Ag paste was only 2.4%, which is 0.45 times lower than the one with nanoscale Ag paste. Roubus joints with high shear strength of 33.6 MPa were formed by coarse necks. The mechanism and morphological evolution of sintered silver joints with micron Ag paste were also studied. Interestingly, the cavities could be formed and enlarged inside the 1–2 μm Ag micron-flakes due to the increase of tensile stress around the micron-flakes. This may be the main reason for the formation of coarse necks with robust bonding.

Influence of Load Changes on the Deposit Behavior during Combustion of Five Different Hard Coals

This work focuses on the influence of cyclic temperature profiles on the sintering behavior of hard coal ashes. To extract mechanisms, all ashes are fully characterized concerning chemical and mineralogical composition and thermal behavior including the characterization of the decomposition species and the ash fusion test with two different setups. Also, the characterization should ensure a broad variability of chemical and mineralogical compositions. To determine sintering effects, the sintering strength test was used in combination with mass and density change analysis. All samples were investigated at 12 different temperature profiles, whereas four include different cycling conditions, four use isothermal short-term conditions, and four use isothermal long-term conditions. In addition, the effect of the preparation load for this experiment was examined. Although all ashes contain similar amounts of the common hard coal ash main components like SiO2, Al2O3, and Fe2O3, they still differ a lot in alkaline...

Structure and morphology evolution in solid-phase synthesis lithium ion battery LiNi0.80Co0.15Al0.05O2 cathode materials with different micro-nano sizes of raw materials

The LiNi0.80Co0.15Al0.05O2 (NCA) cathode is endowed with a high energy density and excellent cycling performance. However, the preparation conditions for this material are quite harsh. Therefore, it is rather significant to obtain well-qualified NCA by simple solid-phase synthesis. In this study, the solid-phase synthesis of NCA cathode material is carried out by mixing two types of raw materials via stirring or sand milling. The effects of different particle sizes on the structure and morphology of NCA materials are analyzed. Owing to the different particle sizes of the raw materials, the diffusion path of Li+ between the solid phases differs greatly. The XRD results show that the samples mixed by stirring have a worse cation mixture than those mixed by sand milling due to the larger particle size, smaller sintering surface energy, and insufficient sintering strength. The electrochemical results show that the sample mixed by sand milling has a higher specific capacity at a low rate, the initial discharge capacity is 199.22 mAh g−1, and the capacity retention rate is 86.9% after 50 cycles. In contrast, the initial discharge capacity of the sample mixed by stirring is 184.86 mAh g−1, and the capacity is 171.93 mAh g−1 after 50 cycles with a 93.0% capacity retention rate.

Impact of Oxy-fuel Combustion on Ash Properties and Sintering Strength Development

For a successful implementation of the oxy-fuel combustion technology, a good understanding of ash-related issues has to be achieved. Knowledge is still lacking on how oxy-fuel combustion can affec...

Factors influencing melt fluidity of iron ore

The melt fluidity (MF) of iron ore, which reflects the flow and bonding abilities of the melt, plays a significant role during sintering. In this study, the MF of iron ore was measured by the micro-sintering method, and the formation and flow of the melt were analyzed using Factsage 7.0. Additionally, chemical reagent simulation tests were conducted to determine the effects of chemical components and gangue mineral types on MF, and the effect of MF on sinter strength was studied by sinter pot tests. The results show that the sintering melt includes some non-miscible liquids and solids. The liquid phases of hematite and limonite ores include silico-ferrites of calcium and aluminum system (predominant) and silico-ferrites of calcium system, and those of the magnetite ores are CaO-FeO-Fe2O3-SiO2 systems. The MF of iron ore depends mainly on liquid amount and viscosity, which play opposite roles in increasing the MF. Moreover, SiO2 increases the MF, whereas Al2O3 and loss on ignition decrease the MF. Increasing the substitution proportion of quartz and gibbsite by kaolinite enhances the MF. The effect of MF of the ore blends on the shatter index of the sinter shows a trend of inverted “V”.

Prediction of sinter yield and strength in iron ore sintering process by numerical simulation

Sinter yield and strength were predicted by the method of numerical simulation in this study. An unsteady two-dimensional mathematical model for the iron ore sintering process was developed by taking most of the significant physical phenomena and chemical reactions into consideration. By employing FLUENT software and C language programming via custom code, numerical simulation was carried out. A sinter pot test was performed and experimental data reasonably agreed with the numerical results, which validated the model. By analyzing temperature profile and melt fraction, parameters including peak temperature, residence time, cooling rate, melt formation heat and melt fraction were analyzed. Relationship between cooling rate and sinter strength was discussed as well as relationship between melt fraction and the yield of product sinter. Results indicated that sinter strength and yield could be predicted by simulation. The effects of different coke contents and additional heat supplement on sinter strength and yield were discussed. Results showed that increasing coke content improves sinter strength. Lower coke content will lead to increasing of under-melted sinter while higher coke content will lead to increasing of over-melted sinter and decreasing of the yield. Additional heat supplement technology can not only enhance sinter strength, but also promote sinter yield significantly.

Densification and properties investigation of W-Cu composites prepared by electroless-plating and activated sintering

W-20Cu composites were fabricated by electroless plating and low-temperature hot pressure sintering (850°C) with different content of Ag particles range from 0 to 2.5wt% as additives. The impacts of Ag additives on the densification and properties of W-Cu composites were investigated. X-ray diffraction and Field emission scanning electron microscope coupled with energy dispersive spectrum were used to analyze the phase and microstructure of powder and sintered composites. Relative density, electrical conductivity, Vickers hardness and bending strength were measured. W-20Cu composite powders prepared by electroless plating exhibited dense and uniform structure. The results showed that the addition of Ag had significant effect on the microstructure and properties of W-Cu composites, and the optimal content of Ag particles is 2wt%. After added of 2wt% Ag, the relative density of sintered W-Cu composites can achieved to 98.57%, the electrical conductivity reached 46.5% IACS, mechanical properties improved greatly due to the formation of solid solution during activated sintering, Vickers hardness and bending strength can reached 227.6HV and 894.72MPa, respectively.

Effects of Dolomite on Mineral Compositions and Metallurgical Properties of Chromium-Bearing Vanadium–Titanium Magnetite Sinter

Chengde chromium-bearing vanadium–titanium magnetite (CCVTM) has been used as an important mineral resource in sinter making. The MgO content of this sinter can be enhanced by adding dolomite, which improved operation of the blast furnace. The effects of MgO in the form of dolomite on metallurgical properties, microstructure and mineral compositions of CCVTM sinter were studied by a sinter pot test, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and mineral phase microanalysis. The results were as follows: The flame front speed and sinter coefficient decreased with an increase in MgO content from 2.66 to 3.86% by adding dolomite. With an increase in MgO content from 2.66 to 3.86%, the flame front speed, sintering utilization factor, and the value of RI decreased, while RDI and the softening–melting properties improved. In addition, the value of sinter strength (TI) reached a maximum value at MgO = 3.56%. In addition, an increase in the abundance of magnetite, magnesium ferrite, and silicate phase, as well as a decrease in hematite, was found with an increase in MgO content. We concluded that the most appropriate MgO content in the sinter is 3.56%.

Predicting iron ore sinter strength through partial least square regression (PLSR) analysis of X-ray diffraction patterns

The decrease in quality of Australian iron ore, coupled with the demand for more efficient energy use, means that closer monitoring and optimisation of process conditions for iron ore sinter production is required. Here, the suitability of using partial least-squares regression analysis of powder X-ray diffraction data, collected for iron ore sinter samples, for the prediction of iron ore sinter strength has been further assessed. In addition, a preliminary assessment of the effect of 2θrange on the quality of prediction has been made. For the purposes of process control, the level of correlation between predicted strength and actual sinter strength would inform an operator whether or not the process was operating within the acceptable limits, or whether there was a potential problem requiring further investigation or rapid intervention. Reducing the 2θrange was found to reduce the level of correlation between predicted and actual strength, to a point where the particular analysis may no longer be suitable for process control.

Comparison of sintering performance of typical specular hematite ores with distinct size distributions

AbstractThe sintering performance of three typical specular hematite ores (coarse SO-A, intermediate SO-B and ultrafine SO-C) was compared in an industrial ore blend through pilot-scale sinter pot tests. The effect of particle size of specular hematite ores on their granulation and sintering performance was revealed. Compared with the coarse SO-A fine and ultrafine SO-C concentrate, the intermediate SO-B showed inferior granulation and sintering performance characterized with poorer bed permeability and productivity, lower sinter strength and higher fuel rates. A new material preparation method was hence proposed and verified at both pilot and industrial scales. The proposed method by mixing SO-B with a high amount of goethite-type iron ore fines was found to be an effective way in improving the granulation and assimilative characteristics of ore blend comprising 31% intermediate SO-B, leading to improved sinter productivity and lowered fuel rates. The metallurgical properties and microstructure of sinters were also investigated. The sinters obtained through the proposed preparation method were generally stronger and more reducible on account of better sinter structure with more relict hematite ultimately connected with needle-like silico-ferrite of calcium and aluminum and lower porosity.

Improvement of heat pattern and sinter strength at high charcoal proportion by applying ultra-lean gaseous fuel injection in iron ore sintering process

Using biomass for partial replacement of coke breeze in iron-ore sintering process is an effective technique as a countermeasure against global warming. However, the sinter strength would be weakened due to the damaged heat pattern at high biomass proportion. In this paper, the gaseous fuel injection method was experimentally investigated with the aim at solving this problem. Eleven cases were arranged to examine the ultra-low concentration of methane combustion and its effect on the improvement of heat pattern at high charcoal proportion. The temperature in the sintering bed was recorded by both thermocouples and infrared thermography. The thermocouple data indicated that the melt quantity index was significantly increased by employing the gaseous fuel injection method. Moreover, the infrared images show that the red-hot region was expanded at each moment in the methane injection cases. The influencing mechanism of gaseous fuel injection on the heat pattern in sintering process was revealed in this paper. As the premixed methane/air approaching to the solid fuel combustion zone, it was preheated by the hot sintered ores, then ignited and self-sustained near the solid fuel combustion zone. A newly generated gaseous fuel combustion zone coupled with the solid fuel combustion zone was used to control the heat pattern in sintering bed. The results showed that the heat pattern and sinter strength kept increasing until the methane concentration increased to 0.4–0.5% under the lab conditions. The stable interval of secondary combustion zone in the sintering bed was also analyzed. Finally, comprehensively considering the sinter strength, yield, productivity and sintering time, the recommended equivalent methane concentration at high charcoal proportion was 0.5% where the shatter strength grew 3.78% and solid fuel rate reduced 7.52%, compared with 100% coke sintering case. Generally, the gaseous fuel injection offers a technical support for the iron ore sinter production using cheap or carbon neutral solid fuel. More importantly, this method can also reduce solid fuels (the main contributor of contamination dust during the production, transportation and storage) consumption by partial substitution of cleaner gaseous fuel.

Optimization of gaseous fuel injection for saving energy consumption and improving imbalance of heat distribution in iron ore sintering

It has been widely reported that the sinter strength and heat pattern would be weakened when adopting the low grade solid fuels, such as biomass, semi-coke and anthracite. Moreover, the imbalance of heat distribution in the sintering bed is considered to be problematic on the energy efficiency. To solve the above problems simultaneously, the gaseous fuel segregation method was firstly proposed in this paper. The gaseous fuel was injected to the melting zone from the top and auto-ignited near the solid fuel combustion zone. Firstly, methane concentrations of 0.0% and 0.5% vol. were tested, keeping the total calorific heat input unchanged. The heat pattern in melting zone was recorded by both contact thermocouples and non-contact thermal infrared imager. The results indicated that the methane injection could significantly extend the melting zone from the upstream and raise the sinter strength higher than that of coke sintering, without increasing the energy consumption. Then, the energy saving potential of the novel method was evaluated by reducing the calorific heat input 4, 6 and 8%. Furthermore, in the segregation case, the gaseous fuel injecting concentration was increased in the upper bed to enhance the weak heat pattern, and decreased in the lower bed to avoid the energy waste. It was observed that the melting zone became much more uniform in the infrared images. Finally, the optimum segregation degree of 1.0%/mm was recommended, where the sinter strength grew 2.31%. The present study provides an effective way for optimizing the energy efficiency in the sintering process.

Visualization Study on the Methane Segregation Injection Technology in Iron Ore Sintering Process

It is widely reported that sinter strength would be weakened due to the damaged heat condition adopting low grade solid fuels, such as biomass. Moreover, the unevenly distributed heat in sintering bed is considered to be problematic on the quality of sintered ores. Aiming at solving these problems, the gaseous fuel (methane) injection method is experimentally investigated. Furthermore, the methane segregation injection method is firstly proposed. In this paper, the heat pattern in melting zone is recorded by the thermal infrared imager. The premixed air and methane is injected to the melting zone from the top surface of sintering pot and burned near the solid fuels combustion zone. Methane concentrations of 0.0% and 0.5% are tested, keeping the total calorific heat input unchanged. The non-segregation (0.5%-0.5%) and segregation (0.8%-0.2%) injection cases are also compared. The results indicate that methane injection method could extend the melting zone from the upstream without increasing the energy consumption, which is helpful to the improvement of sinter strength. From the infrared images, it is observed the melting zone becomes much more uniform after employing the segregation injection method. The present study provides an effective way to maintain the sinter quality when using low grade fuels in sinter plant, and minimize the imbalance of heat distribution in sintering bed.

Spark plasma sintering and high-temperature strength of B6O–TaB2 ceramics

Tantalum diboride – boron suboxide ceramic composites were densified by spark plasma sintering at 1900°C. Strength and fracture toughness of these bulk composites at room temperature were 490MPa and 4MPam1/2, respectively. Flexural strength of B6O–TaB2 ceramics increased up to 800°C and remained unchanged up to 1600°C. At 1800°C a rapid decrease in strength down to 300MPa was observed and was accompanied by change in fracture mechanisms suggestive of decomposition of boron suboxide grains. Fracture toughness of B6O–TaB2 composites showed a minimum at 800°C, suggestive a relaxation of thermal stresses generated from the mismatch in coefficients of thermal expansion.Flexural strength at elevated temperatures for bulk TaB2 reference sample was also investigated.Results suggest that formation of composite provides additional strengthening/toughening as in all cases flexural strength and fracture toughness of the B6O–TaB2 ceramic composite was higher than that reported for B6O monoliths.

Sintering behaviours of iron ore with flue gas circulation

ABSTRACTFlue gas circulation is an important method for energy conservation and pollutant emission reduction in iron ore sintering. In this paper the effects of flue gas recirculation ratio on sintering of different iron ores including haematite, magnetite and limonite were studied by illustrating the variation of sinter bed temperature, atmosphere and mineralisation characteristics of different types of iron ores induced by the circulation. It shows that the proper flue gas circulation ratios for haematite, magnetite and limonite are 37, 30 and 25%, respectively. For magnetite ore, preheating and high consumption of oxygen in combustion zone caused more silicate minerals and less acicular calcium ferrite, thereby lowering sinter tumbler strength. As for haematite ore, the rapid change of temperatures of combustion, melting and solidification zones leads to elevated combustion efficiency and increased formation of acicular calcium ferrite, which enhances the sinter strength. When using limonite ore as the main raw material, high oxygen consumption, lower maximum temperature of sintering bed, higher cooling rate and larger porosity of sinter are observed.

Effects of Matrix Densification Based on Particle Packing on Lightweight Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-MgO Castables

The property of refractory matrix was dominated by both the maineral composition and particle packing behaviors. In this study, the theoretical packing density of refractory castables was calculated to design the particle size distribution (PSD) of its matrix. Four lightweight Al2O3-MgO castables with different matrix PSD (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q ( &gt; 0.31). For the sample with q = 0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favorable compromise among sintering characteristics (apparent porosity = 14.8%, bulk density = 3.02g∙cm-3, permanent linear change &lt; 0.6%), strength (cold modulus of rapture = 12.4MPa, cold crashing strength=155.5MPa), and resistance against both slag corrosion (Ic = 22.4%) and penetration (Ip = 11.5%). The sample with q = 0.25 showed the highest strength and resistance against slag corrosion, but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.

Study on liquid phase formation and fluidity of iron ores

The sinter strength is guaranteed by liquid phase formation and agglomeration of the unmelted materials. Liquid phase formation and fluidity of iron ores are the basic which have significant influence on the yield and quality of the sinter. In this study, first the thermodynamic analysis of liquid phase formation was carried out with FactSage on seven kinds of domestic and overseas iron ores. Second, the generation speed, the amount of liquid phase and fluidity index of the sinters were measured and analyzed. The results indicated that the sinter liquid formation increased with rising temperature. When the reaction temperature was 1050 °C, a part of iron ore generated some liquid phase at a rapid speed, and the production of the liquid phase of most iron ores reached the highest level at about 1350 °C. As there is a large difference about liquid phase fluidity between different iron ores, the iron ores with worse fluidity could be used for matching with the iron ores of better fluidity in order to meet the quality requirements of the sinter.