Experimental study on mitigating wind erosion of calcareous desert sand using spray method for microbially induced calcium carbonate precipitation

Wind erosion is one of the significant natural calamities worldwide, which degrades around one-third of global land. The eroded and suspended soil particles in the environment may cause health hazards, i.e. allergies and respiratory diseases, due to the presence of harmful contaminants, bacteria, and pollens. The present study evaluates the feasibility of microbially induced calcium carbonate precipitation (MICP) technique to mitigate wind-induced erosion of calcareous desert sand (Thar desert of Rajasthan province in India). The temperature during biotreatment was kept at 36 °C to stimulate the average temperature of the Thar desert. The spray method was used for bioaugmentation of Sporosarcina (S.) pasteurii and further treatment using chemical solutions. The chemical solution of 0.25 pore volume was sprayed continuously up to 5 d, 10 d, 15 d, and 20 d, using two different concentration ratios of urea and calcium chloride dihydrate viz 2:1 and 1:1. The biotreated samples were subjected to erosion testing (in the wind tunnel) at different wind speeds of 10 m/s, 20 m/s, and 30 m/s. The unconfined compressive strength of the biocemented crust was measured using a pocket penetrometer. The variation in calcite precipitation and microstructure (including the presence of crystalline minerals) of untreated as well as biotreated sand samples were determined through calcimeter, scanning electron microscope (SEM), and energy-dispersive X-ray spectroscope (EDX). The results demonstrated that the erosion of untreated sand increases with an increase in wind speeds. When compared to untreated sand, a lower erosion was observed in all biocemented sand samples, irrespective of treatment condition and wind speed. It was observed that the sample treated with 1:1 cementation solution for up to 5 d, was found to effectively resist erosion at a wind speed of 10 m/s. Moreover, a significant erosion resistance was ascertained in 15 d and 20 d treated samples at higher wind speeds. The calcite content percentage, thickness of crust, bulk density, and surface strength of biocemented sand were enhanced with the increase in treatment duration. The 1:1 concentration ratio of cementation solution was found effective in improving crust thickness and surface strength as compared to 2:1 concentration ratio of cementation solution. The calcite crystals formation was observed in SEM analysis and calcium peaks were observed in EDX analysis for biotreated sand.     

Research on slag-resistance of ZrN-SiAlON-SiC-C composite refractory in different atmospheres

The ZrN-SiAlON composite powder was synthesized using low-grade zircon and bauxite by carbothermal reduction nitridation at first and then ZrN-SiAlON-SiC-C composite refractory were fabricated with the ZrN-SiAlON powder, SiC particles, and a small amount of Si powder as raw materials and sucrose as the binder. The slag resistance of these composites in O₂, N₂ and Ar atmosphere was investigated by X-ray diffraction, scanning electron microscopy, and energy dispersion spectra. The results show that the pores in the inside of ZrN-SiAlON-SiC-C composite refractory were enlarged in oxygen atmosphere due to oxidation, which leads to the decrease in slag resistance. In argon atmosphere, blast furnace slag destroyed the sintered body of zircon, corundum, and cristobalite with the formation of CaZrO₃, then infiltrated into and filled the pores inside the refractory to form a dense layer, which hindered the further erosion of the blast furnace slag. In the reducing atmosphere, the interfacial energy of the gas-liquid phases became larger due to the reactions between blast furnace slag liquid and the gas, resulting in a larger wetting angle which prevented the erosion.     

钢包包衬侵蚀对内衬温度和钢水温降的影响

为了研究包衬侵蚀对钢水温降的影响规律,通过ANSYS有限元软件以及ParaMesh网格随移技术建立了考虑包衬侵蚀的钢包传热计算模型,研究并分析了包衬侵蚀对包衬及钢水温度的影响规律。结果表明,包衬侵蚀对包衬温度影响较大,在相邻两个修包周期内,包衬侵蚀造成渣线和包壁的包衬内部(工作层与永久层交界处)温差为14～114 K;包衬侵蚀导致包壳外表面温度升高,包壳向外散热增加,与此同时,包衬受侵蚀变薄,蓄热减少,两者同时作用导致包衬侵蚀对钢水温降影响不大,最高不超过1 K,在实际生产中可以适当地忽略钢包侵蚀对钢水温降的影响。     

Peracetic acid as a single endodontic irrigant: effects on microhardness,roughness and erosion of root canal dentin

The aim was to assess the effects of 1% peracetic acid (PAA) as a single endodontic irrigant on microhardness, roughness, and erosion of root canal dentin, compared with 2.5% sodium hypochlorite (NaOCl) and with 2.5% NaOCl combined with 17% EDTA. Forty human, single‐rooted tooth hemisections were submitted to Knoop microhardness test, before and after the following irrigation protocols: PAA = 1% PAA; NaOCl = 2.5% NaOCl; NaOCl‐EDTA‐NaOCl = 2.5% NaOCl +17% EDTA +2.5% NaOCl; and SS = saline. Another 40 roots were instrumented, irrigated with the same protocols, and sectioned longitudinally. The roughness analysis was performed on the mesial section using a confocal laser scanning microscope, whereas erosion was analyzed on each third of the distal section, using a scanning electron microscope. The data were analyzed using ANOVA and Tukey post‐tests, and Kruskal‐Wallis and Dunn post‐tests (α = .05). The PAA and NaOCl‐EDTA‐NaOCl groups showed no significant differences (p > .05); both promoted reduction in microhardness and increase in roughness, compared with the NaOCl and SS groups (p < .05). NaOCl‐EDTA‐NaOCl promoted higher erosion in the cervical and middle thirds than the other groups (p < .05); there was no difference among PAA, NaOCl, and SS (p > .05). There was also no difference among the groups regarding the apical third (p > .05). PAA used as a single endodontic irrigant caused reduction in root canal dentin microhardness and increase in roughness in a similar way to NaOCl‐EDTA‐NaOCl; however, PAA caused less erosion than NaOCl‐EDTA‐NaOCl.     

Microstructure and corrosion behaviors of FeCrNiBSiMox stainless steel fabricated by laser melting deposition

In this paper, FeCrNiBSiMo_x (x = 1.0, 1.5, 2.0, 2.5) stainless steels were successfully prepared using a laser melting deposition technology, with the aim to investigate the effect of Mo content on microstructure and corrosion behaviors. The results showed that the as-deposited specimens were composed mostly of α-Fe and a small amount of (Cr, Mo)₇C₃, and (Cr, Mo)₇C₃ existed in the inter-dendritic (ID) region. As the Mo content increased, grain refinement could be clearly observed, and the area of the ID region increased from 27% to 54%. The low-angle boundaries accounted for 60–70% of the grain boundaries of the as-deposited specimens. Increasing the content of Mo improved the microhardness of the as-deposited specimens from 652 HV to 813 HV. The corrosion current density of the as-deposited specimens with the Mo mass fractions of 1.0%, 1.5%, 2.0%, and 2.5% were 1.37 × 10⁻⁶, 1.02 × 10⁻⁷, 6.19 × 10⁻⁷, and 3.06 × 10⁻⁷ A/cm², respectively. The as-deposited specimen with Mo content of 1.5% had lower cumulative erosion loss and erosion loss rate than other as-deposited specimens. The FeCrNiBSiMo_x (x = 1.5) specimen exhibited excellent resistance to electrochemical corrosion and cavitation erosion.     

伞帽用高铬铸铁在热强碱腐蚀环境下的磨损分析

针对氧化铝行业中常用的Cr28和Cr20高铬铸铁伞帽在相同工况条件下的磨损机理进行分析,并对比研究了实际生产中两种失效材料的成分、组织及性能。结果表明,伞帽部件在高温强碱腐蚀条件下受到外界冲刷时,磨损量由微切削磨损与变形磨损这两种机制共同决定。含铬量较高的Cr28高铬铸铁,其冲刷和抗腐蚀磨损性能均优于Cr20高铬铸铁。伞帽服役寿命主要受浆料和表层的铸铁材料两大因素影响。两种试验材料经淬火+回火处理后,基体组织中主要为回火马氏体+M₇C₃型碳化物+少量残留奥氏体,其中含铬量较高的Cr28高铬铸铁中共晶碳化物含量更高,且分布更加弥散,其平均硬度值为64.0 HRC,高于Cr20高铬铸铁的60.2 HRC。最终确定Cr28高铬铸铁作为伞帽材质更能满足氧化铝生产及设备检修周期的需要。     

多泥沙河流水电站水轮机转轮内部流动数值模拟

针对多泥沙水电站水轮机转轮的泥沙磨损问题,以HLA351-LJ-275水轮机为模型,对水轮机在设计工况下,运用N-S方程和标准κ-ε湍流模型,利用CFX求解器进行仿真流动模拟。水轮机转轮进口沿叶高20%、50%、80%流面的压力、泥沙速度及泥沙体积分数分布的数值结果表明,水轮机转轮叶片工作面压力大于背面且最小压力高于气化压力。泥沙速度在叶片进水边和出水口位置普遍较高。水轮机转轮叶片工作面的泥沙体积分数大于背面,叶片工作面的泥沙体积分数在叶片出水口普遍较高,叶片背面的泥沙体积分数在叶片进水边普遍较高。研究结果对多泥沙河流水轮机转轮叶片的泥沙磨损评估及维修具有指导意义。     

New anti-ablation candidate for carbon/carbon composites: Preparation,composition and ablation behavior of Y2Hf2O7 coating under an oxyacetylene torch

Y₂Hf₂O₇ possesses low thermal conductivity and high melting point, which make it promising for a new anti-ablation material. For evaluating the thermal stability and the potential applications of Y₂Hf₂O₇ on anti-ablation protection of C/C composites, Y₂Hf₂O₇ ceramic powder was synthesized by solution combustion method and Y₂Hf₂O₇ coating was prepared on the surface of SiC coated C/C composites using SAPS. Results shown that the coating exhibits good ablation resistance under the heat flux of 2.4?MW/m² with the linear and mass ablation rates are 0.16?μm?s^?1 and ?0.028?mg?s^?1, respectively, after ablation for 40?s. With the prolonging of the ablation time, the increasing thermal stress causes the increase of cracks. Moreover, the chemical erosion from SiO₂ and the physical volatilization of low temperature molten products aggravate failure of the Y₂Hf₂O₇ coating.     

机械密封腔流场内粒子对密封腔壁面及波纹管冲蚀分析

为研究机械密封腔内混有固体颗粒的流体,在复杂工况下对密封腔壁面及波纹管表面冲蚀的影响,以CFD理论及方法,采用k-ε湍流模型和离散项DPM模型,对固液混合流场进行模拟分析,获得密封腔内流体中介质作用下密封腔壁面及波纹管外表面的压力场分布,分析不同工作状态下固体颗粒作用下密封腔内壁和波纹管外表面的冲蚀区域分布、固体颗粒在流场中的运动轨迹,以及机械密封工作过程中流场内固体颗粒的逃逸量、运动状态的变化。结果表明:粒子主要受颗粒阻力、浮重力、压力梯度力及波纹管和密封腔表面反作用力的影响;在旋转流场中,粒子作与旋转方向一致的螺旋方式前进;无转速时,冲蚀多发生在靠近入口处的波纹管外表面,旋转流场中,冲蚀多发生在密封腔靠后位置的壁面;随着转速增加,粒子逃逸率下降。研究结论为机械密封腔的设计布局及机械密封装置的优化提供理论依据。     

Leading edge erosion of wind turbines: Effect of solid airborne particles and rain on operational wind farms

Leading edge erosion (LEE) affects almost all wind turbines, reducing their annual energy production and lifetime profitability. This study presents results of an investigation into 18 operational wind farms to assess the validity of the current literature consensus surrounding LEE. Much of the historical research focuses on rain erosion, implying that this is the predominant causal factor. However, this study showed that the impact of excessive airborne particles from seawater aerosols or from adverse local environments such as nearby quarries greatly increases the levels of LEE. Current testing of leading edge protection coatings or tapes is based on a rain erosion resistivity test, which does little to prove its ability to withstand solid particle erosion and may drive coating design in the wrong direction. Furthermore, it was shown that there is little correlation between test results and actual field performance. A method of monitoring the expected level of erosion on an operational wind turbine due to rain erosion is also presented. Finally, the energy losses associated with LEE on an operational wind farm are examined, with the average annual energy production dropping by 1.8% due to medium levels of erosion, with the worst affected turbine experiencing losses of 4.9%.