Search2011 Vol. 18, No. 1
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2011, vol. 18, no. 1, pp.
1-8.
https://doi.org/10.1007/s12613-011-0392-2
Abstract:
The stability and productivity concerning a modification on the traditional room and pillar for a new selective technique at the Portuguese Panasqueira Mine have been described. The traditional room-and-pillar stoping uses 5.0-m wide rooms with 3.0 m×3.0 m pillars, while the selective room-and-pillar mining technique consists in stoping with rooms of 4.0 m wide and pillars of 4 m×4 m with a subsequent selective cutting of the quartz veins at the mid pillar of approximately 0.5 m high, to obtain a pillar section with an area of 3.0 m×3.0 m. The stability and productivity analyses indicate that the selective technique obtains smaller average pillar safety factor, more rock mass displacement, more extraction and selectivity ratios, and ore grade improvement, compared with the traditional technique. These results show that the selective technique is also more convenient. This proposed selective room-and-pillar mining technique is applicable to any sub-horizontal narrow quartz veins with wolfram, gold, etc. such as the famous La Rinconada gold mine in the Peruvian Andes.
The stability and productivity concerning a modification on the traditional room and pillar for a new selective technique at the Portuguese Panasqueira Mine have been described. The traditional room-and-pillar stoping uses 5.0-m wide rooms with 3.0 m×3.0 m pillars, while the selective room-and-pillar mining technique consists in stoping with rooms of 4.0 m wide and pillars of 4 m×4 m with a subsequent selective cutting of the quartz veins at the mid pillar of approximately 0.5 m high, to obtain a pillar section with an area of 3.0 m×3.0 m. The stability and productivity analyses indicate that the selective technique obtains smaller average pillar safety factor, more rock mass displacement, more extraction and selectivity ratios, and ore grade improvement, compared with the traditional technique. These results show that the selective technique is also more convenient. This proposed selective room-and-pillar mining technique is applicable to any sub-horizontal narrow quartz veins with wolfram, gold, etc. such as the famous La Rinconada gold mine in the Peruvian Andes.
2011, vol. 18, no. 1, pp.
9-17.
https://doi.org/10.1007/s12613-011-0393-1
Abstract:
A comparative study of the dissolution kinetics of galena ore in binary solutions of FeCl3/HCl and H2O2/HCl has been undertaken. The dissolution kinetics of the galena was found to depend on leachant concentration, reaction temperature, stirring speed, solid-to-liquid ratio, and particle diameter. The dissolution rate of galena ore increases with the increase of leachant concentration, reaction temperature, and stirring speed, while it decreases with the increase of solid-to-liquid ratio and particle diameter. The activation energy (Ea) of 26.5 kJ/mol was obtained for galena ore dissolution in 0.3 M FeCl3/8.06 M HCl, and it suggests the surface diffusion model for the leaching reaction, while the Ea value of 40.6 kJ/mol was obtained for its dissolution in 8.06 M H2O2/8.06 M HCl, which suggests the surface chemical reaction model for the leaching reaction. Furthermore, the linear relationship between rate constants and the reciprocal of particle radius supports the fact that dissolution is controlled by the surface reaction in the two cases. Finally, the rate of reaction based on the reaction-controlled process has been described by a semiempirical mathematical model. The Arrhenius and reaction constants of 11.023 s-1, 1.25×104 and 3.65×102 s-1, 8.02×106 were calculated for the 0.3 M FeCl3/8.06 M HCl and 8.06 M H2O2/8.06 M HCl binary solutions, respectively.
A comparative study of the dissolution kinetics of galena ore in binary solutions of FeCl3/HCl and H2O2/HCl has been undertaken. The dissolution kinetics of the galena was found to depend on leachant concentration, reaction temperature, stirring speed, solid-to-liquid ratio, and particle diameter. The dissolution rate of galena ore increases with the increase of leachant concentration, reaction temperature, and stirring speed, while it decreases with the increase of solid-to-liquid ratio and particle diameter. The activation energy (Ea) of 26.5 kJ/mol was obtained for galena ore dissolution in 0.3 M FeCl3/8.06 M HCl, and it suggests the surface diffusion model for the leaching reaction, while the Ea value of 40.6 kJ/mol was obtained for its dissolution in 8.06 M H2O2/8.06 M HCl, which suggests the surface chemical reaction model for the leaching reaction. Furthermore, the linear relationship between rate constants and the reciprocal of particle radius supports the fact that dissolution is controlled by the surface reaction in the two cases. Finally, the rate of reaction based on the reaction-controlled process has been described by a semiempirical mathematical model. The Arrhenius and reaction constants of 11.023 s-1, 1.25×104 and 3.65×102 s-1, 8.02×106 were calculated for the 0.3 M FeCl3/8.06 M HCl and 8.06 M H2O2/8.06 M HCl binary solutions, respectively.
2011, vol. 18, no. 1, pp.
18-23.
https://doi.org/10.1007/s12613-011-0394-0
Abstract:
The modification of MgO·Al2O3 spinel inclusions in Al-killed steel by Ca-treatment has been studied by industrial trials and thermodynamic calculations. In the industrial trials, samples were taken systematically during the refining process in which the molten steel was treated by calcium, and the characters of the inclusions were analyzed using scanning electron microscopy (SEM) and energy dispersive spectra (EDS). The effects of Ca-treatment were evaluated by tracking the compositions of the inclusions. The results show that the modification of MgO·Al2O3 spinel inclusions by Ca-treatment is effective and the transformation sequence of the inclusions during the refining is Al2O3→MgO·Al2O3→liquid complex inclusions. The modification of spinel inclusions by Ca-treatment was calculated by FactSage6.0 utilizing its free-energy minimization routines. The results of thermodynamic calculations indicate that spinel inclusions are easier to be modified than Al2O3 inclusions and the spinel inclusions in 30CrMo steel would transform to liquid complex inclusions when the content of dissolved Ca in the molten steel exceeds 1×10-6. Also, the results show that adding more calcium into the molten steel would lower the contents of Al2O3 and MgO and increase the CaO content of the inclusions, while the change in SiO2 content is little.
The modification of MgO·Al2O3 spinel inclusions in Al-killed steel by Ca-treatment has been studied by industrial trials and thermodynamic calculations. In the industrial trials, samples were taken systematically during the refining process in which the molten steel was treated by calcium, and the characters of the inclusions were analyzed using scanning electron microscopy (SEM) and energy dispersive spectra (EDS). The effects of Ca-treatment were evaluated by tracking the compositions of the inclusions. The results show that the modification of MgO·Al2O3 spinel inclusions by Ca-treatment is effective and the transformation sequence of the inclusions during the refining is Al2O3→MgO·Al2O3→liquid complex inclusions. The modification of spinel inclusions by Ca-treatment was calculated by FactSage6.0 utilizing its free-energy minimization routines. The results of thermodynamic calculations indicate that spinel inclusions are easier to be modified than Al2O3 inclusions and the spinel inclusions in 30CrMo steel would transform to liquid complex inclusions when the content of dissolved Ca in the molten steel exceeds 1×10-6. Also, the results show that adding more calcium into the molten steel would lower the contents of Al2O3 and MgO and increase the CaO content of the inclusions, while the change in SiO2 content is little.
2011, vol. 18, no. 1, pp.
24-34.
https://doi.org/10.1007/s12613-011-0395-z
Abstract:
The development of some computational algorithms based on cellular automaton was described to simulate the structures formed during the solidification of steel products. The algorithms described take results from the steel thermal behavior and heat removal previously calculated using a simulator developed by present authors in a previous work. Stored time is used for displaying the steel transition from liquid to mushy and solid. And it is also used to command computational subroutines that reproduce nucleation and grain growth. These routines are logically programmed using the programming language C++ and are based on a simultaneous solution of numerical methods (stochastic and deterministic) to create a graphical representation of different grain structures formed. The grain structure obtained is displayed on the computer screen using a graphical user interface (GUI). The chaos theory and random generation numbers are included in the algorithms to simulate the heterogeneity of grain sizes and morphologies.
The development of some computational algorithms based on cellular automaton was described to simulate the structures formed during the solidification of steel products. The algorithms described take results from the steel thermal behavior and heat removal previously calculated using a simulator developed by present authors in a previous work. Stored time is used for displaying the steel transition from liquid to mushy and solid. And it is also used to command computational subroutines that reproduce nucleation and grain growth. These routines are logically programmed using the programming language C++ and are based on a simultaneous solution of numerical methods (stochastic and deterministic) to create a graphical representation of different grain structures formed. The grain structure obtained is displayed on the computer screen using a graphical user interface (GUI). The chaos theory and random generation numbers are included in the algorithms to simulate the heterogeneity of grain sizes and morphologies.
2011, vol. 18, no. 1, pp.
35-41.
https://doi.org/10.1007/s12613-011-0396-y
Abstract:
In order to get the controlled methods of microstructure homogenization and high strengthening-toughening combination by compact strip production (CSP) rolling, the dynamic recrystallization characteristics of each pass were obtained during CSP rolling using a Gleeble-1500 thermal mechanical simulator. Then, the CSP process was simulated by laboratory rolling experiment. Through thermal mechanical simulation experiment and laboratory rolling experiment, a design idea of Nb-bearing pipeline steel by CSP can be obtained as the following: the level of dynamic recrystallization behavior should be increased through the reasonable balance of high deformation temperature and deformation amount in F1 and F2 passes, and F3-F7 passes should be controlled in the austenite non-recrystallization zone. Finally, X65 pipeline steel with microstructure uniformity and good properties was produced by CSP. The yield strength is up to 497 MPa, the tensile strength is up to 563 MPa, the elongation is 30% on average, and the toughness is very good whose Charpy impact value is 110 J on average and drop-weight tear test shearing areas are all 100% at -60, -40, -20, 0, and 20℃.
2011, vol. 18, no. 1, pp.
42-47.
https://doi.org/10.1007/s12613-011-0397-x
Abstract:
The passive film formed on 2205 duplex stainless steel (DSS) in 0.5 M NaHCO3+0.5 M NaCl aqueous solution was characterized by electrochemical measurements, including potentiodynamic anodic polarization and dynamic electrochemical impedance spectroscopy (DEIS). The results demonstrate that there is a great difference between the passive film evolutions of ferrite and austenite. The impedance values of ferrite are higher than those of austenite. The impedance peaks of ferritic and austenitic phases correspond to the potential of 0.15 and 0.25 V in the low potential range and correspond to 0.8 and 0.75 V in the high potential range. The evolutions of the capacitance of both phases are reverse compared to the evolutions of impedance. The thickness variations obtained from capacitance agree well with those of impedance analysis. The results can be used to explain why pitting corrosion occurs more easily in austenite phase than in ferrite phase.
The passive film formed on 2205 duplex stainless steel (DSS) in 0.5 M NaHCO3+0.5 M NaCl aqueous solution was characterized by electrochemical measurements, including potentiodynamic anodic polarization and dynamic electrochemical impedance spectroscopy (DEIS). The results demonstrate that there is a great difference between the passive film evolutions of ferrite and austenite. The impedance values of ferrite are higher than those of austenite. The impedance peaks of ferritic and austenitic phases correspond to the potential of 0.15 and 0.25 V in the low potential range and correspond to 0.8 and 0.75 V in the high potential range. The evolutions of the capacitance of both phases are reverse compared to the evolutions of impedance. The thickness variations obtained from capacitance agree well with those of impedance analysis. The results can be used to explain why pitting corrosion occurs more easily in austenite phase than in ferrite phase.
2011, vol. 18, no. 1, pp.
48-52.
https://doi.org/10.1007/s12613-011-0398-9
Abstract:
Pitting corrosion of 316L stainless steel in NaCl solution was investigated by means of staircase potential electrochemical impedance spectroscopy (SPEIS). The investigation focused on the transition of stainless steel from the passive state to pitting corrosion. Based on the evolution of electrical parameters of the equivalent electrical circuit, it is suggested that the most probable mechanism of pit creation is the film breaking model. The result demonstrates that staircase potential electrochemical impedance spectroscopy is an effective method for the investigation of pitting corrosion.
Pitting corrosion of 316L stainless steel in NaCl solution was investigated by means of staircase potential electrochemical impedance spectroscopy (SPEIS). The investigation focused on the transition of stainless steel from the passive state to pitting corrosion. Based on the evolution of electrical parameters of the equivalent electrical circuit, it is suggested that the most probable mechanism of pit creation is the film breaking model. The result demonstrates that staircase potential electrochemical impedance spectroscopy is an effective method for the investigation of pitting corrosion.
2011, vol. 18, no. 1, pp.
53-58.
https://doi.org/10.1007/s12613-011-0399-8
Abstract:
316L stainless steel (SS 316L) is quite attractive as bipolar plates in proton exchange membrane fuel cells (PEMFC). In this study, graphite-polypyrrole was coated on SS 316L by the method of cyclic voltammetry. The surface morphology and chemical composition of the graphite-polypyrrole composite coating were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). A simulated working environment of PEMFC was applied for testing the corrosion properties of graphite-polypyrrole coated SS 316L. The current densities in the simulated PEMFC anode and cathode conditions are around 3×10-9 and 9×10-5 A·cm-2, respectively. In addition, the interfacial contact resistance (ICR) was also investigated. The ICR value of graphite-polypyrrole coated SS 316L is much lower than that of bare SS 316L. Therefore, graphite-polypyrrole coated SS 316L indicates a great potential for the application in PEMFC.
316L stainless steel (SS 316L) is quite attractive as bipolar plates in proton exchange membrane fuel cells (PEMFC). In this study, graphite-polypyrrole was coated on SS 316L by the method of cyclic voltammetry. The surface morphology and chemical composition of the graphite-polypyrrole composite coating were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). A simulated working environment of PEMFC was applied for testing the corrosion properties of graphite-polypyrrole coated SS 316L. The current densities in the simulated PEMFC anode and cathode conditions are around 3×10-9 and 9×10-5 A·cm-2, respectively. In addition, the interfacial contact resistance (ICR) was also investigated. The ICR value of graphite-polypyrrole coated SS 316L is much lower than that of bare SS 316L. Therefore, graphite-polypyrrole coated SS 316L indicates a great potential for the application in PEMFC.
2011, vol. 18, no. 1, pp.
59-65.
https://doi.org/10.1007/s12613-011-0400-6
Abstract:
The effects of gravity on nickel electrodeposition, the morphology and mechanical properties of deposits were studied in a super gravity field. Predictions in a microgravity field were also presented based on the obtained experimental tendency. Linear sweep voltammetry reveals that the nickel electrodeposition process is enhanced by increasing the gravity coefficient (G). The limiting current density changes from 10.2 to 293.0 mA·cm-2 with the increase of the G value from 10-4 to 354. The morphology of deposits was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The images show that the morphology deposited in the super gravity field has finer grain sizes and denser and smoother surfaces. The roughness reduces from 48.3 to 4.9 nm with the increase of the G value from 10-4 to 354. Meanwhile, mechanical tests indicate that the mechanical properties of nickel foils are greatly improved due to introducing a super gravity field during electrodeposition.
The effects of gravity on nickel electrodeposition, the morphology and mechanical properties of deposits were studied in a super gravity field. Predictions in a microgravity field were also presented based on the obtained experimental tendency. Linear sweep voltammetry reveals that the nickel electrodeposition process is enhanced by increasing the gravity coefficient (G). The limiting current density changes from 10.2 to 293.0 mA·cm-2 with the increase of the G value from 10-4 to 354. The morphology of deposits was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The images show that the morphology deposited in the super gravity field has finer grain sizes and denser and smoother surfaces. The roughness reduces from 48.3 to 4.9 nm with the increase of the G value from 10-4 to 354. Meanwhile, mechanical tests indicate that the mechanical properties of nickel foils are greatly improved due to introducing a super gravity field during electrodeposition.
2011, vol. 18, no. 1, pp.
66-69.
https://doi.org/10.1007/s12613-011-0401-5
Abstract:
Martensitic stabilization caused by deformation in a TiNi shape memory alloy was studied. Special attention was paid to the deformed microstructures to identify the cause of martensitic stabilization. Martensitic stabilization was demonstrated by differential scanning calorimetry for the tensioned TiNi shape memory alloy. Transmission electron microscopy revealed that antiphase boundaries were formed because of the fourfold dissociation of [110]B19’ super lattice dislocations and were preserved after reverse transformation due to the lattice correspondence. Martensitic stabilization was attributed to dislocations induced by deformation, which reduced the ordering degree of the microstructure, spoiled the reverse path from martensite to parent phase compared with thermoelastic transformation, and imposed resistance on phase transformation through the stress field.
Martensitic stabilization caused by deformation in a TiNi shape memory alloy was studied. Special attention was paid to the deformed microstructures to identify the cause of martensitic stabilization. Martensitic stabilization was demonstrated by differential scanning calorimetry for the tensioned TiNi shape memory alloy. Transmission electron microscopy revealed that antiphase boundaries were formed because of the fourfold dissociation of [110]B19’ super lattice dislocations and were preserved after reverse transformation due to the lattice correspondence. Martensitic stabilization was attributed to dislocations induced by deformation, which reduced the ordering degree of the microstructure, spoiled the reverse path from martensite to parent phase compared with thermoelastic transformation, and imposed resistance on phase transformation through the stress field.
2011, vol. 18, no. 1, pp.
70-76.
https://doi.org/10.1007/s12613-011-0402-4
Abstract:
An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration (with a frequency of 15 kHz and a maximum output of 2 kW) during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31. The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared. It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects: the softening effect which reduces the flow resistance and improves the plasticity, and the hardening effect which decreases the formability. When a lower amplitude or vibration energy is applied to the tensile sample, the softening effect dominates, leading to a decrease of AZ31 deformation resistance with an increase of formability. Under the application of a high-vibrating amplitude, the hardening effect dominates, resulting in the decline of plasticity and brittle fracture of the samples.
An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration (with a frequency of 15 kHz and a maximum output of 2 kW) during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31. The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared. It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects: the softening effect which reduces the flow resistance and improves the plasticity, and the hardening effect which decreases the formability. When a lower amplitude or vibration energy is applied to the tensile sample, the softening effect dominates, leading to a decrease of AZ31 deformation resistance with an increase of formability. Under the application of a high-vibrating amplitude, the hardening effect dominates, resulting in the decline of plasticity and brittle fracture of the samples.
2011, vol. 18, no. 1, pp.
77-82.
https://doi.org/10.1007/s12613-011-0403-3
Abstract:
The oxidation behavior of different SiAlON phases (β-SiAlON, X-phase SiAlON and 12H powders) synthesized from coal gangue in air atmosphere was investigated using isothermal thermogravimetry (TG) and field-emission scanning electron microscopy (FE-SEM). The effect of ferric oxide impurities in coal gangue was studied. The results show that ferric oxide contributes to the growth of SiAlON crystalline during the synthesis process. In the oxidation experiment, the existence of ferric oxide decreases the oxidation resistance of SiAlON. The reason is that the impurity causes the formation of a liquid phase at a higher temperature. At 1423–1623 K, the oxidation of SiAlON powders is diffusion controlled and it can be described by Chou’s model. A fair agreement is found between theoretical calculations and the experimental data.
The oxidation behavior of different SiAlON phases (β-SiAlON, X-phase SiAlON and 12H powders) synthesized from coal gangue in air atmosphere was investigated using isothermal thermogravimetry (TG) and field-emission scanning electron microscopy (FE-SEM). The effect of ferric oxide impurities in coal gangue was studied. The results show that ferric oxide contributes to the growth of SiAlON crystalline during the synthesis process. In the oxidation experiment, the existence of ferric oxide decreases the oxidation resistance of SiAlON. The reason is that the impurity causes the formation of a liquid phase at a higher temperature. At 1423–1623 K, the oxidation of SiAlON powders is diffusion controlled and it can be described by Chou’s model. A fair agreement is found between theoretical calculations and the experimental data.
2011, vol. 18, no. 1, pp.
83-88.
https://doi.org/10.1007/s12613-011-0404-2
Abstract:
Surface modification of wollastonite particles using titanate as a modification agent incorporated by simultaneous wet ultra-fine grinding in a laboratory stirred mill was investigated. The physical, physic-chemical and application properties of the modified wollastonite were measured and evaluated. The results showed that grinding intensity markedly influences the modification effect because of the mechano chemical effect. The hydrophilic surface of wollastonite was turned into a hydrophobic one after modification. The interaction between titanate and wollastonite under wet grinding circumstances was studied. It was suggested that physical adsorption and chemical adsorption of titanate coexisted on the wollastonite surface. The mechanical properties of polyethylene (PE) filled with the modified wollastonite powder were markedly improved.
Surface modification of wollastonite particles using titanate as a modification agent incorporated by simultaneous wet ultra-fine grinding in a laboratory stirred mill was investigated. The physical, physic-chemical and application properties of the modified wollastonite were measured and evaluated. The results showed that grinding intensity markedly influences the modification effect because of the mechano chemical effect. The hydrophilic surface of wollastonite was turned into a hydrophobic one after modification. The interaction between titanate and wollastonite under wet grinding circumstances was studied. It was suggested that physical adsorption and chemical adsorption of titanate coexisted on the wollastonite surface. The mechanical properties of polyethylene (PE) filled with the modified wollastonite powder were markedly improved.
2011, vol. 18, no. 1, pp.
89-93.
https://doi.org/10.1007/s12613-011-0405-1
Abstract:
Heavy concrete currently used for construction contains special materials that are expensive and difficult to work with. This study replaced natural aggregate (stones) in concrete with round steel balls, which are inexpensive and easily obtainable. The diameters of the steel balls were 0.5 and 1 cm, and their density was 7.8 kg/m3. Dense packing mixture methods were used to produce heavy concrete with densities of 3500 and 5000 kg/m3. The various properties of this concrete were tested according to the standards of the American Society for Testing and Materials (ASTM). The results indicated that the construction slump of the concrete could reach 260–280 mm and its slump flow could reach 610–710 mm. More important, its compressive strength could reach 8848 MPa. These results will significantly alter traditional construction methods that use heavy concrete and enhance innovative ideas for structural design.
Heavy concrete currently used for construction contains special materials that are expensive and difficult to work with. This study replaced natural aggregate (stones) in concrete with round steel balls, which are inexpensive and easily obtainable. The diameters of the steel balls were 0.5 and 1 cm, and their density was 7.8 kg/m3. Dense packing mixture methods were used to produce heavy concrete with densities of 3500 and 5000 kg/m3. The various properties of this concrete were tested according to the standards of the American Society for Testing and Materials (ASTM). The results indicated that the construction slump of the concrete could reach 260–280 mm and its slump flow could reach 610–710 mm. More important, its compressive strength could reach 8848 MPa. These results will significantly alter traditional construction methods that use heavy concrete and enhance innovative ideas for structural design.
2011, vol. 18, no. 1, pp.
94-99.
https://doi.org/10.1007/s12613-011-0406-0
Abstract:
The electrical conductivity and dielectric property of fly ash geopolymer pastes in a frequency range of 100 Hz-10 MHz were studied. The effects of the liquid alkali solution to ash ratios (L/A) were analyzed. The mineralogical compositions and microstructures of fly ash geopolymer materials were also investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The 10 mol sodium hydroxide solution and sodium silicate solution at a sodium silicate-to-sodium hydroxide ratio of 1.0 were used in making geopolymer pastes. The pastes were cured at 40℃. It is found that the electrical conductivity and dielectric constant are dependent on the frequency range and L/A ratios. The conductivity increases but the dielectric constant decreases with increasing frequency.
The electrical conductivity and dielectric property of fly ash geopolymer pastes in a frequency range of 100 Hz-10 MHz were studied. The effects of the liquid alkali solution to ash ratios (L/A) were analyzed. The mineralogical compositions and microstructures of fly ash geopolymer materials were also investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The 10 mol sodium hydroxide solution and sodium silicate solution at a sodium silicate-to-sodium hydroxide ratio of 1.0 were used in making geopolymer pastes. The pastes were cured at 40℃. It is found that the electrical conductivity and dielectric constant are dependent on the frequency range and L/A ratios. The conductivity increases but the dielectric constant decreases with increasing frequency.
2011, vol. 18, no. 1, pp.
100-104.
https://doi.org/10.1007/s12613-011-0407-z
Abstract:
The shrinkage of fly ash geopolymers was studied in the present study. Fly ash was used as the source material for making the geopolymers. The effects of the concentration of NaOH, sodium silicate-to-NaOH ratio, liquid-to-ash ratio, curing temperature, and curing time on shrinkage were investigated. The geopolymers were cured at 25, 40, and 60℃, respectively. The results indicate that the shrinkage of geopolymers is strongly dependent on curing temperature and liquid-to-ash ratio. The increase in shrinkage is associated with the low strength development of geopolymers. It is also found that NaOH concentration and sodium silicate-to-NaOH ratio also affect the shrinkage of geopolymers but to a lesser extent.
The shrinkage of fly ash geopolymers was studied in the present study. Fly ash was used as the source material for making the geopolymers. The effects of the concentration of NaOH, sodium silicate-to-NaOH ratio, liquid-to-ash ratio, curing temperature, and curing time on shrinkage were investigated. The geopolymers were cured at 25, 40, and 60℃, respectively. The results indicate that the shrinkage of geopolymers is strongly dependent on curing temperature and liquid-to-ash ratio. The increase in shrinkage is associated with the low strength development of geopolymers. It is also found that NaOH concentration and sodium silicate-to-NaOH ratio also affect the shrinkage of geopolymers but to a lesser extent.
2011, vol. 18, no. 1, pp.
105-114.
https://doi.org/10.1007/s12613-011-0408-y
Abstract:
Magnesia (MgO) is widely used in the production of refractory materials due to its high melting point, high thermal shock, and excellent slag resistance. The properties of refractory materials depend upon magnesia sources and processing parameters. In this work, three different magnesium sources, namely, magnesium hydroxide concentrate, magnesium carbonate concentrate, and intermediate flotation concentrate, were obtained from the Zinelbulak talc-magnesite, Uzbekistan, by causticization-hydration and flotation processes, respectively. A series of refractory materials were prepared on the basis of these magnesium sources, and their effects on physico-mechanical properties and microstructures were investigated as a function of sintering temperature, molding pressure, and the particle size of magnesium sources. The experimental results showed that a refractory material obtained from the magnesium hydroxide concentrate at 1600℃ for 4 h demonstrated favorable parameters due mainly to a higher degree of contact among fine particles. The results obtained from X-ray diffraction and optical microscopy confirmed the presence of periclase and forsterite as the predominant phases in refractory specimens. The prepared refractory materials meet the requirements of the State Standards (Nos.4689-94 and 14832-96) for magnesia and forsterite refractories, respectively. It is, therefore, suggested herein that the use of different magnesium sources derived from the Zinelbulak talc-magnesite will offer the potential to provide economic benefits in the refractory industry.
Magnesia (MgO) is widely used in the production of refractory materials due to its high melting point, high thermal shock, and excellent slag resistance. The properties of refractory materials depend upon magnesia sources and processing parameters. In this work, three different magnesium sources, namely, magnesium hydroxide concentrate, magnesium carbonate concentrate, and intermediate flotation concentrate, were obtained from the Zinelbulak talc-magnesite, Uzbekistan, by causticization-hydration and flotation processes, respectively. A series of refractory materials were prepared on the basis of these magnesium sources, and their effects on physico-mechanical properties and microstructures were investigated as a function of sintering temperature, molding pressure, and the particle size of magnesium sources. The experimental results showed that a refractory material obtained from the magnesium hydroxide concentrate at 1600℃ for 4 h demonstrated favorable parameters due mainly to a higher degree of contact among fine particles. The results obtained from X-ray diffraction and optical microscopy confirmed the presence of periclase and forsterite as the predominant phases in refractory specimens. The prepared refractory materials meet the requirements of the State Standards (Nos.4689-94 and 14832-96) for magnesia and forsterite refractories, respectively. It is, therefore, suggested herein that the use of different magnesium sources derived from the Zinelbulak talc-magnesite will offer the potential to provide economic benefits in the refractory industry.
2011, vol. 18, no. 1, pp.
115-120.
https://doi.org/10.1007/s12613-011-0409-x
Abstract:
Au nanoparticles dispersed NiO composite films were prepared by a chemical solution method. The phase structure, microstructure, surface chemical state, and optical absorption properties of the films were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Uv-vis spectrometer. The results indicate that Au particles with the average diameters of 35–42 nm are approximately spherical and disperse in the NiO matrix. The optical absorption peaks due to the surface plasmon resonance of Au particles shift to the shorter wavelength and intensify with the increase of Au content. The bandwidth narrows when the Au content increases from 8.4wt% to 45.2wt%, but widens by further increasing the Au content from 45.2wt% to 60.5wt%. The band gap Eg increases with the increase of Au contents from 8.4wt% to 45.2wt%, but decreases by further increasing the Au content.
Au nanoparticles dispersed NiO composite films were prepared by a chemical solution method. The phase structure, microstructure, surface chemical state, and optical absorption properties of the films were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Uv-vis spectrometer. The results indicate that Au particles with the average diameters of 35–42 nm are approximately spherical and disperse in the NiO matrix. The optical absorption peaks due to the surface plasmon resonance of Au particles shift to the shorter wavelength and intensify with the increase of Au content. The bandwidth narrows when the Au content increases from 8.4wt% to 45.2wt%, but widens by further increasing the Au content from 45.2wt% to 60.5wt%. The band gap Eg increases with the increase of Au contents from 8.4wt% to 45.2wt%, but decreases by further increasing the Au content.
2011, vol. 18, no. 1, pp.
121-125.
https://doi.org/10.1007/s12613-011-0410-4
Abstract:
Oxide eutectic ceramic in situ composites have attracted significant interest in the application of high-temperature structural materials because of their excellent high-temperature strength, oxidation and creep resistance, as well as outstanding microstructural stability. The directionally solidified ternary Al2O3/YAG/ZrO2 hypereutectic in situ composite was successfully prepared by a laser zone remelting method, aiming to investigate the growth characteristic under ultra-high temperature gradient. The microstructures and phase composition of the as-solidified hypereutectic were characterized by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the composite presents a typical hypereutectic lamellar microstructure consisting of fine Al2O3 and YAG phases, and the enriched ZrO2 phases with smaller sizes are randomly distributed at the Al2O3/YAG interface and in Al2O3 phases. Laser power and scanning rate strongly affect the sample quality and microstructure characteristic. Additionally, coarse colony microstructures were also observed, and their formation and the effect of temperature gradient on the microstructure were discussed.
Oxide eutectic ceramic in situ composites have attracted significant interest in the application of high-temperature structural materials because of their excellent high-temperature strength, oxidation and creep resistance, as well as outstanding microstructural stability. The directionally solidified ternary Al2O3/YAG/ZrO2 hypereutectic in situ composite was successfully prepared by a laser zone remelting method, aiming to investigate the growth characteristic under ultra-high temperature gradient. The microstructures and phase composition of the as-solidified hypereutectic were characterized by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the composite presents a typical hypereutectic lamellar microstructure consisting of fine Al2O3 and YAG phases, and the enriched ZrO2 phases with smaller sizes are randomly distributed at the Al2O3/YAG interface and in Al2O3 phases. Laser power and scanning rate strongly affect the sample quality and microstructure characteristic. Additionally, coarse colony microstructures were also observed, and their formation and the effect of temperature gradient on the microstructure were discussed.
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