Understanding the Effect of Stepwise Irrigation on Liquid Holdup and Hysteresis Behavior of Unsaturated Ore Heap

Liquid is a crucial medium to contain soluble oxygen, valuable metal ions, and bacteria in unsaturated heap leaching. Liquid retention behavior is the first critical issue to be considered to efficiently extract low-grade minerals or wastes. In this study, the residual liquid holdup of an unsaturated packed bed was quantitatively discussed by liquid holdup (θ), residual liquid holdup (θresidual), relative liquid holdup (θ’), and relative porosity (n*) using the designed measuring device. The detailed liquid holdup and the hysteresis behavior under stepwise irrigation are indicated and discussed herein. The results show that relative porosity of the packed bed was negatively related to particle size, and intra-particle porosity was more developed in the −4.0 + 2.0 mm packed bed. The higher liquid retention of the unsaturated packed bed could be obtained by using stepwise irrigation (incrementally improved from 0.001 to 0.1 mm/s) instead of uniform irrigation (0.1 mm/s). It could be explained in that some of the immobile liquid could not flow out of the unsaturated packed bed, and this historical irrigation could have accelerated formation of flow paths. The θ was sensitive to superficial flow rate (or irrigation rate) in that it obviously increased if a higher superficial flow rate (u) was introduced, however, the θresidual was commonly affected by n* and θ’. Moreover, the liquid hysteresis easily performed under stepwise irrigation condition, where θ and θresidual were larger at u of the decreasing flow rate stage (DFRS) instead of u of the increasing flow rate stage (IFRS). These findings effectively quantify the liquid retention and the hysteresis behavior of ore heap, and the stepwise irrigation provides potential possibility to adjust liquid retention conditions.

Effect of Desert Sand on the Mechanical Properties of Desert Sand Concrete (DSC) after Elevated Temperature

Building fires and shortage of medium sand resources have become two major issues in building domain. Desert sand was used to produce desert sand concrete (DSC), which was suitable for engineering utility. The mechanical properties tests of DSC with different desert sand replacement ratio (DSRR) were carried out after elevated temperature. The effects of elevated temperature and DSRR on DSC mechanical properties were analyzed. DSC microstructure was investigated by SEM and XRD. Research studies’ results showed that the relative compressive strength increased gradually with increasing temperature. The maximum value appeared at 200°C–300°C, and it began to decrease at 500°C. Compared with room temperature, the compressive strength at 700°C was about 70% of that at room temperature. Relative splitting tensile strength increased first and then decreased, and the value reached the maximum at 100°C. DSC relative flexural strength decreased with the temperature. Relative compressive strength, splitting tensile strength, and flexural strength of DSC enhanced first and then decreased with DSRR, and the maximum values were obtained with 40% DSRR. Based on the regressive analysis, the relative compressive strength was a quadratic polynomial with relative porosity. Relative splitting tensile strength and relative flexural strength were linear with relative porosity. Research results can provide the technical support for DSC engineering application and postfire assessment.

Microstructure characterization and properties of porous piezoceramics

In this paper, a comprehensive study of microstructure/properties interrelations for porous piezoceramics based on PZT composition was performed. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. Porosity dependencies of elastic, dielectric, piezoelectric and electromechanical coefficients of the porous ceramics in the relative porosity range 0–50% were obtained and analyzed. As a result of microstructure analysis, it was found that at any connectivity type (3–0, 3–3) and porosity up to 50% the real structures of porous piezoceramics were close to the matrix medium structure with continuous piezoceramic skeleton. It was also revealed that the microstructural features of porous piezoceramics define the character of the dependences of the dielectric, piezoelectric and electromechanical properties of porous piezoelectric ceramics on porosity. In conclusion, microstructure/properties interrelations, as well as new applications of porous piezoceramics were discussed.

Dispersion characteristics of complex electromechanical parameters of porous piezoceramics

In this paper, the results of experimental study of dispersion characteristics of complex electromechanical parameters of ferroelectrically “hard” porous piezoceramics based on PZT composition were presented. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. The complex constants of porous piezoceramics with relative porosity 16% and their frequency dependences were measured using the piezoelectric resonance analysis method. As a result of experimental studies, regions of elastic, piezoelectric and electromechanical dispersion, characterized by anomalies in the frequency dependences of the imaginary and real parts of the complex constants of porous piezoelectric ceramics were found. It was revealed also that the microstructural features of porous piezoceramics determine the character of frequency dependences of complex electromechanical parameters of porous piezoelectric ceramics. In conclusion, the microstructural and physical mechanisms of electromechanical losses and dispersion in porous piezoceramics were discussed.

The Effect of Relative Porosity on the Survivability of a Powder Metallurgy Part During Ejection

The desire to produce functional powder metallurgy (PM) components has resulted in higher compression forces during compaction. This in turn increases the ejection stresses and therefore the possibility of failure during ejection. This failure can be caused by sprig back during ejection due to frictional forces that are generated between the powder part and the die walls. In order to predict these factors a stress analysis of the powder part during ejection was done. Due to complexity, finite element analysis was used to model the powder during compaction and ejection. Since the ejection stage is the most critical stage of the PM process, it is essential to understand the factors that determine the survivability of a part during this stage. This work uses experimental data, finite element modeling and reliability analysis to determine the probability of failure of metallic powder components during the ejection phase. The results show that there is an increased possibility of failure during ejection as compaction pressure is increased. This information can be used by designers and process planners to determine the optimal process parameters that need to be adopted for optimal outcomes during powder metallurgy.

The Effect of Relative Porosity on the Survivability of a Powder Metallurgy Part During Ejection

The desire to produce functional powder metallurgy (PM) components has resulted in higher compression forces during compaction. This in turn increases the ejection stresses and therefore the possibility of failure during ejection. This failure can be caused by sprig back during ejection due to frictional forces that are generated between the powder part and the die walls. In order to predict these factors a stress analysis of the powder part during ejection was done. Due to complexity, finite element analysis was used to model the powder during compaction and ejection. Since the ejection stage is the most critical stage of the PM process, it is essential to understand the factors that determine the survivability of a part during this stage. This work uses experimental data, finite element modeling and reliability analysis to determine the probability of failure of metallic powder components during the ejection phase. The results show that there is an increased possibility of failure during ejection as compaction pressure is increased. This information can be used by designers and process planners to determine the optimal process parameters that need to be adopted for optimal outcomes during powder metallurgy.

The Effect of Electrolytic Solution Composition on the Structure, Corrosion, and Wear Resistance of PEO Coatings on AZ31 Magnesium Alloy

Plasma electrolytic oxidation coatings were prepared in aluminate, phosphate, and silicate-based electrolytic solutions using a soft-sparking regime in a multi-frequency stepped process to compare the structure, corrosion, and wear characteristics of the obtained coatings on AZ31 magnesium alloy. The XRD results indicated that all coatings consist of MgO and MgF2, while specific products such as Mg2SiO4, MgSiO3, Mg2P2O7, and MgAl2O4 were also present in specimens based on the selected solution. Surface morphology of the obtained coatings was strongly affected by the electrolyte composition. Aluminate-containing coating showed volcano-like, nodular particles and craters distributed over the surface. Phosphate-containing coating presented a sintering-crater structure, with non-uniform distributions of micro-pores and micro-cracks. Silicate-containing coating exhibited a scaffold surface involving a network of numerous micro-pores and oxide granules. The aluminate-treated sample offered the highest corrosion resistance and the minimum wear rate (5 × 10−5 mm3 N−1 m−1), owing to its compact structure containing solely 1.75% relative porosity, which is the lowest value in comparison with other samples. The silicate-treated sample was degraded faster in long-term corrosion and wear tests due to its porous structure, and with more delay in the phosphate-containing coating due to its larger thickness (30 µm).

Fractal Characteristics of Porosity of Electrospun Nanofiber Membranes

In this paper, the method of measuring the porosity of electrostatic nanofiber membrane by VC++ and Matlab is introduced. It is found that the ratio of the calculated porosity to the porosity measured by the mercury intrusion method accords with the famous Feigenbaum constant (α=2.5029078750957⋯). The porosity distribution of nanofiber membranes was studied by VC++ and Matlab based on the image obtained by using a scanning electron microscope. The porosity distribution calculated by using a computer is magnified by eα times which was named as relative porosity distribution. According to the relative porosity distribution, we use the algorithm proposed by Grassberger and Procaccia (briefly referred to as the G-P algorithm) to calculate the correlation fractal dimension. The correlation fractal dimension calculated from the relative porosity distribution series was between 1 and 2, consistent with geometric characteristics of coincidence samples. The fractal meaning of the Feigenbaum constant was verified again. In the end, we obtained the relationship between the associated fractal dimension and the filtration resistance by fitting in accordance with the secondary function relationship and reached the maximum correlation fractal dimension when the filtration resistance was 15–20 pa.

Comparison of Porosity Evaluation Methods Using the Example of Dissimilar Metal Joints

Welded metal porosity significantly influences the mechanical properties of dissimilar metal joints. In this study, the comparison of porosity evaluation methods was held using the sample of welded-brazed zinc coated steel and Al-Mg-alloy plates joint. Relative porosity was measured through cross-sections’ images area analysis, as well as it was evaluated through 3D-fitting of spotted on these images pores. Area and size of pores was measured, volume and distribution were evaluated. It was found that relative porosity values estimated by 2D and 3D methods are equal.

Microstructure-Property Relationships in Powder Bed Fusion of Type 304L Austenitic Stainless Steel

Additive manufacturing (AM) includes a diverse suite of innovative manufacturing processes for producing near-net shape metallic components, typically from powder or wire. Reported mechanical properties of materials produced by these processes varies significantly and can usually be correlated with the relative porosity in the materials. In this study, relatively simple test components were manufactured from type 304L austenitic stainless steel by powder bed fusion (PBF). The quality of the components depends on a host of manufacturing parameters as well as the characteristics of the feedstock. In this study, the focus is the bulk material response. Tensile properties are reported for PBF type 304L produced in similar build geometries on two different machines with independent operators. Additionally, the effect of hydrogen on the tensile properties of the AM materials is evaluated. The goal of this study is to provide a benchmark for tensile properties of PBF 304L material in the context of wrought type 304L, and to make a preliminary assessment of the effects of hydrogen on tensile properties.