Abstract: The mineral assemblage, gold occurrence and characteristics of process mineralogy of Nongruri Gold Deposit were discussed on the basis of geology, petrography, ore microscopy, SEM/EDS, EPMA and LA-ICP-MS results. All native gold, with fine grains and a high fineness of 992 to 996, was found in the clay minerals and between the clay minerals and quartz. The native gold is a dominant occurrence state in this deposit. Minor invisible gold was confirmed in the pyrite and arsenopyrite, and the contribution of invisible gold to the ore grade is small. All the silver was found in the phosphate minerals as micro-enclaved silver. According to the statistic results of native gold and gold-bearing minerals, the mass fractions of different ore types were estimated.
Abstract: By using an underground high-precision micro-seismic monitoring system, the dynamic development law and the distribution pattern of micro-seismic events (MS events) were analyzed, and the movement law of roof strata in extra-thick coal seams in the fully mechanized top-coal caving mining workface was inferred in combination with the mine pressure and strata movement theory and the rock mechanics theory. Monitoring results show that MS events in higher strata and lower strata are of low-density distribution and high-density distribution, respectively. Comparative studies on the horizon and maximum amplitude energy sum of micro-seismic waves indicate that MS events reveal periodical distribution in height and time. Further more, the movement law of roof strata in extra-thick coal seams in the fully mechanized top-coal caving mining workface was inferred. Macro-observations of support pressure show the conclusion of periodic movement of roof strata is reasonable.
Abstract: The effects of the water table, the ultimate pullout force of the rockbolt, the soil friction angle, and the penetration depth of the diaphragm wall on the stability of the wall under seismic conditions were investigated. The earth pressure, the groundwater pressure and the inertial force of the wall were calculated using "general wedge earthquake analysis". The pseudo-static method was used for analyzing the stability of the wall from the perspective of the safety factors against overturning and sliding. The calculated results show that the stability of the diaphragm wall decreases as the horizontal seismic acceleration coefficient increases;the water table on the non-excavation side, the soil friction angle, the ultimate pullout force of the rockbolt, and the penetration depth of the diaphragm wall play an important role on the stability;moreover, the soil friction angle has greater effect on the safety factor against sliding than on the safety factor against overturning, but the ultimate pullout force of the rockbolt has greater effect on the safety factor against overturning than on the safety factor against sliding.
Abstract: Based on an analysis of existing thermodynamic data, a two-parameter model for estimating the specific heat of a dual intermetallic is developed. It can estimate the specific heats of dual intermetallics composed of simple metals involving Fe, Si, Nb, Ti, Cu, Co, Mg, etc. The specific heats of 132 intermetallics are estimated, such as AlCa, AlCo, CrNi, FeTi, FeSi, FeNb, and MoSi. It is found that the average error of specific heat is about 2.74J·mol-1·K-1 and the standard deviation is 3.84J·mol-1·K-1. The precision of standard entropy estimated by the two-parameter model is higher than that estimated by the ion binding model.
Abstract: The change process of MnS inclusions in YF45MnV steel was in-situ observed by confocal laser scanning microscope. The result shows that during the continuous heating process, slender MnS inclusions firstly change into string-like inclusions composed of subsphaeroidal sulfides, then these subsphaeroidal sulfides diffuse and grow up with the number decreasing. When the temperature increases to some extent, MnS inclusions dissolve to the steel and the areas of corresponding sulfides decrease.
Abstract: Precipitation behaviors of Ti-containing inclusions and inclusion-induced intragranular ferrite were investigated by thermodynamic calculations and laboratory experiments. The results show that there are six forms about position relations of inclusions to ferrite grains and pearlite grains. The effects of inclusion types and size on the inclusion-inducing ability were analyzed quantificationally by defining the index of inducing ability. It is indicated that the ability of Ti-containing complex oxide-inclusions inducing intragranular ferrite is the best, but that of Al2O3 is the worst. The optimal size of Ti-containing complex oxide-inclusions is 4 to 6μm and that of other inclusions is 2 to 4μm. Intra-granular ferrite is induced to precipitate by controlling the inclusion types and size, leading to grain refinement.
Abstract: The scanning Kelvin probe (SKP) technique, in combination with energy dispersive spectrum (EDS) analysis of corrosion products, was employed to investigate the initial corrosion behavior and potential distribution of Q235 carbon steel and Q450 weathering steel during salt spray test. The results showed that Q235 carbon steel was severely attacked by Cl-. During the initial period of salt spray test, anodic and cathodic areas formed on the surface of the specimens and the surface potential became more and more positive in the corrosion procedure with a distinct character of localized corrosion. The SKP results showed that Q450 weathering steel was inclined to uniform corrosion, whose surface potential was more positive than that of Q235 carbon steel, probably being due to the effect of alloying elements. The product layer of Q450 was more compact, which indicated that Q450 was more resistive to atmospheric corrosion than Q235.
Abstract: Taking batch annealed SPCD steel sheets as an example, orange peel defects in the surface of sheet stamping concerning with their formation mechanism and dependence on grain orientation were investigated by means of SEM, XRD and electron backscatter diffraction (EBSD) techniques. The results show that the orange peel defects are resulted from excessively coarse ferrite grains, whereas weak favorable {111} texture and a larger stamping value might be the key factors aggravating the formation of orange peel defects. Different morphologies featured by smooth and rough zones on the free surface of orange peel do not show remarkable dependence on grain orientation, and both display orientation feature with dominant {112}〈110〉 and {111}〈110〉 textures. The surface contact condition plays an important role in the surface morphology.
Abstract: In order to research the effect of alloy elements on the phase transformation of transformation-induced plasticity (TRIP) steels, continuous cooling transformation (CCT) diagrams of four kinds of C-Mn-Al-P TRIP steels, with different aluminum contents and with or without microalloy element P, were studied by using optical microscopy and microhardness measurements. Al makes the ferrite forming and pearlite forming temperatures to the left side, and the bainite forming and martensite forming to the higher temperatures of the diagram, as Al narrows the austenite phase region strongly and increases the Ac3 point and Ms point. P can reduce the kinetics of cementite precipitation, and when its mass fraction reaches 0.14%, it causes a shift of the pearlite forming and bainite forming temperatures to the right side significantly. However, P has no significant effect on ferrite transformation and martensite transformation. The results also reveal that the microhardness increases as the cooling rate increases, and the microstructure will be fully martensitic when the cooling rate reaches the critical rate of the steel.
Abstract: A low-carbon Mn-Mo-Nb-Cu-B ultra high strength structural steel for construction machinery was designed and the effect of TMCP (thermo-mechanical control process) + tempering (TMCP+T) technology and controlled rolling + direct quenching and tempering (CR+DQ+T) technology on its microstructure and mechanical properties under the same composition was studied. The changes in mechanical properties and microstructures of the steel plates before and after heat treatment were comparatively analyzed. The results show that after tempering from 500℃ to 620℃ for 1h, there is a substantial increase of the steel plates in yield strength. The performance of the steel plates treated by CR+DQ+T process is obviously superior to that by TMCP+T process, and the yield strength of the former is still more than 1000MPa after tempering at 600℃. Besides, the elongation can reach 18% and the impact energy at-40℃ is more than 30J. However, the plasticity of the latter is better but the strength slightly lower. With the tempering temperature increasing, the evolution speed of microstructures under the condition of CR+DQ+T is more quickly than that under the condition of TMCP+T.
Abstract: The effects of Ce on the inclusions and the impact toughness of 2Cr13 stainless steel were studied by metallographic examination, scanning electron microscope (SEM) and energy spectrum analysis. The results show that adding Ce into the steel improves the shape and size of inclusions. The fracture mode of 2Cr13 stainless steel is typical cleavage fracture, but quasi-cleavage and dimple fracture after adding Ce into the steel, and the spherical inclusions of rare earth oxysulfide in the dimple are the main factor for this transformation. The transverse impact toughness of 2Cr13 stainless steel is improved obviously by rare earth. In comparison with 2Cr13 stainless steel without Ce, the transverse impact toughness of 2Cr13 stainless steel with Ce is increased 54.55% at -40℃.
Abstract: A speed control model for continuous dieless drawing process of tapered pipes is established on the basis of the volume incompressibility principle of metal. The effects of drawing speed and other deformation process parameters on the volume of the deformation zone and the size of the tapered pipe were analyzed and verified by experiment. The results show that the drawing speed is related to the feed speed, the size of the blank pipe, the size of the tapered pipe and the hot-to-cold source distance. The drawing speed increases with time non-linearly. With an increase of drawing speed, the volume of the deformation zone declines;but with the hot-to-cold source distance lengthening and the feed speed increasing, the volume of the deformation zone changes significantly. When the proportion of feed speed to drawing speed is fixed, reducing the feed speed and enlarging the hot-to-cold source distance can reduce the dimension error and increase the control precision.
Abstract: An anti-oxidation coating, mainly composed of MgO and Cr2O3, was prepared by a mixing method. XRD and SEM were used to study the difference of mass increment, oxidative products and element distribution between samples with and without coatings at 1400℃. The results show that the coatings are environmental-friendly and cost effective and also have good effect on grain-oriented silicon steel, with a wide range of anti-oxidation applications.
Abstract: Different base oils and additives were used to compound emulsions for strip rolling. The influences of base oils and additives on the tribological properties of the rolling emulsions were investigated with a four-ball friction and wear testing machine. The lubricating effect of the rolling emulsions was actually verified by cold rolling experiment. It is shown that kinematical viscosity and saponification number are still the main parameters for choosing base oils, and the compatibility of based oils and additives has a certain impact on the performance of the rolling emulsions. Additives can highly influence the tribological properties of the rolling emulsions. Nano-hexagonal boron nitride (nano-h-BN) not only has excellent tribological properties by itself, but also plays a good collaborative role with traditional additives. In the cold-rolling process lubricated by rolling emulsions with nano-h-BN additives, all the rolling characteristic parameters such as rolling pressure and rolling power significantly decrease, and the good effects of nano-lubrication are initially embodied.
Abstract: The microstructure and microsegregation of nickel base corrosion resistant alloy C-276 vacuum-induction-melting and electroslag-remelting ingots were studied by optical microscope, scanning electron microscopy and energy dispersive X-ray spectroscopy. Based on the calculated results of the residual segregation parameter model, four homogenizing treatments were tested. Microstructure analysis and thermal compression test with a Gleeble 1500 machine were used to verify the effect of homogenizing treatment. The results show that the severest segregated elements in C-276 is Mo, and 1170℃/20h is the most appropriate treatment for C-276 alloy in the study as it ensures homogenizing effect and reasonable grain size for optimizing the hot-working plasticity of the alloy. It is also proved that homogenization process of C-276 alloy can be effectively predicted and evaluated by the residual segregation parameter model, which basically agrees with the experimental results.
Abstract: The hydrogenated tests of Ti-6Al-4V alloy were carried out at 750℃ and the hydrogen absorption kinetics was analyzed. The effect of holding time on the hydrogen distribution was studied by optical microscope and secondary ion mass spectrometry. The results show that the hydrogen absorption kinetics of Ti-6Al-4V alloy obeys the two-dimensional diffusion mechanism, in agreement with the Valensi equation g(α)=α+(1-α)ln(1-α), and thus the hydrogen diffusion is a rate-controlling step in the diametric direction of the sample. When the holding time is more than 60min, the hydrogen pressure becomes stable, hydrogen stops diffusing in the diametric direction of the sample, and the microstructure and hydrogen ion intensity at the center are the same as those at the brim during hydrogenation process, which proves that hydrogen distributes uniformly within the sample.
Abstract: Bismuth sulfide nanorods were synthesized from bismuth citrate and thiourea by microwave irradiation in the presence of surfactants. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The influence of surfactants on the morphology and crystallization of Bi2S3 nanorods was discussed. It is found that cetyltrimethyl ammonium bromide (CTAB) and β-cyclodextrin (β-CD) benefit the formation of Bi2S3 nanorods. Low concentration of β-CD (~0.005 mol·L-1) is favorable to the synthesis of well-separated Bi2S3 nanorods. The effect of preparation methods on the synthesis of Bi2S3 nanorods was also discussed. The results show that microwave irradiation saves about 80% of reaction time in comparison with the refluxing method, and Bi2S3 nanorods exhibit different crystal lattice growth directions in these two methods.
Abstract: Modified zeolite with better nitrogen removal effect was used to prepare antibacterial adsorption materials for treating the secondary effluent of high-concentration coliform and ammonia nitrogen. Among Ag+, Zn2+ and Cu2+ ions, silver-supported antibacterial adsorption materials have the best antibacterial properties and are beneficial to nitrogen removal. The optimal preparation conditions are the following:AgNO3 concentration of 85mg·g-1, pH 6-7, preparation time of 120min, reaction temperature of 40℃, and reaction speed of 150r·min-1. After the optimization, the silver content in the prepared materials is 49.79mg·g-1. 0.5g·L-1 of silver-supported antibacterial adsorption materials and 2g·L-1 of zeolite were applied to treat renewable water under the optimal conditions. The results show that the reaction time is 120min, the sterilizing rate is 98.87%, the removal rate of ammonia nitrogen is 66.54%, the mass concentration of residual nitrogen is 8.36mg·L-1, which achieve the water-quality indexes of the urban miscellaneous water.
Abstract: Based on the mechanism of precision forming of camshafts by cross wedge rolling (CWR), the precision forming process of a simple and typical camshaft by CWR was numerically simulated with DEFORM-3D finite element software and an ideal shape was obtained. The FEM result was used to analyze the strain distribution in the work piece during the whole process. The metal flow laws in the axial, radical and circumferential directions were systematically discussed. It is shown that the simulation result is in agreement with CWR experimental data by comparison, indicating that the method of camshaft forming by CWR is feasible.
Abstract: The rolling deformation of high-intensity and thin tinplates was investigated for an HCM skin pass mill by FEM method and field experiment. Some reasons for higher actual roll force and poor flatness were revealed, and the solutions to these problems were determined. Based on the FEM analysis and roll profile design software, a new polynomial curve of the intermediate roll profile was proposed. Practical applications showed that the forced-contract was mitigatory, i. e., the actual roll force decreases by 10% to 20% and the actual elongation increases by 0.1% to 0.2%.
Abstract: A method of discontinuous purge with appropriate interrupt frequency and interrupt time was proposed to obtain higher oxygen recovery and concentration. The effects of purge steps on the oxygen recovery and concentration during pressure swing adsorption (PSA) oxygen concentration process were investigated experimentally. The results showed that both of oxygen recovery and product purity in the process with discontinuous purge are greater than those with continuous purge. Under the experimental conditions, when the optimized interrupt frequency is 2 and interrupt time is 0.3s, the oxygen recovery and concentration increase by 9.2% and 4.0%, respectively.
Abstract: It is still a problem to choose a crown feedback control strategy. In combination with Jigang 1700 ASP control project, a method of calculating the adjustable range of crown at each stand exit was studied in theory. By using the method the choice of a crown feedback control strategy was realized, the strategy that all stands take part in control was gained and a formula of crown deviation distribution was deduced. On the basis of the formula, a crown feedback control model for hot tandem rolling was built, and it was on-line programmed, debugged and put into use. Up to now, the crown feedback control system has already run stably for about two months. Statistical results show that the crown control precision is improved with this crown feedback control system.
Abstract: The security of a cryptosystem proposed in the article of Chaotic image scrambling algorithm based on sort transformation was analyzed. The whole key space of the image scrambling cryptosystem is too small to prevent the ciphertext-only attack when realizing in finite computing precision. The address codes of transposition can reappear by chosen-plaintext attack or chosen-ciphertext attack. A key recovery algorithm was presented by reverse iterating the Logistic chaotic map. The theoretical and experimental results verify that the key recovery algorithm is feasible and efficient. Two primary reasons for the unsafe problem are the restriction of finite computing precision and the weakness of linear transformation. Five possible improved methods and their effects were also discussed.
Abstract: A shaking table testing study on a 1/20 scale model of a hybrid high-rise building with irregularity was carried out with the Fulong Building in Xiamen as the project background. In the test, the model's dynamic properties, damp ratio, as well as the reaction of acceleration and deformation in frequent earthquake, basic seismic intensity and rare earthquake of 7 degree were examined, and the cracking pattern and failure mechanism of the model were studied. The result of this test demonstrates that the frequencies of the first three modes of the model are 1.74Hz (Y direction translation), 2.28Hz (X direction translation) and 3.12Hz (over rotation), and the damp ratio corresponded to X direction and Y direction is 6.3% and 6.5% respectively. Under the function of frequent earthquake and rare earthquake, the maximum story drift angle of the prototype in X direction is 1/956 and 1/147 respectively, and in Y direction is 1/570 and 1/83 respectively. Therefore a rational arrangement of structural elements with good overall anti-seismic behavior was presented. Finally, some suggestions for the seismic design of the structure are put forward in this paper.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
