On investigating the soda-lime shot blasting of AZ31 alloy:Effects on surface roughness,material removal rate,corrosion resistance,and bioactivity

In the present study,a novel method of surface finish improvement is proposed using shot blasting of soda lime(SBSL)beads on the Mg-AZ31 alloy.The effect of the soda blasting process parameters,such as blast pressure,stand-off distance,and blast duration,have been studied in-response of material removal rate(MRR)and surface roughness(SR)and corresponding statistical models have been obtained.The multi-objective optimization has also been performed to obtain parameters for maximum MRR and minimum SR.The corrosion behavior of the treated specimens has been performed to study their in-vitro biodegradability in simulated body fluid(SBF)for 1,3,7,10,15,and 21 days.The wettability study of the SBSL treated samples has been investigated using sessile drop methodology.Further,cell adhesion test has also been performed to study the biocompatibility characteristics of the SBSL treated samples using Huh7 liver cell lines.Based on obtained quantitative data as well as scanning electron microscopy analysis of treated samples,the SBSL treatment of the AZ31 alloy has been found highly useful in producing biocompatibility surfaces along with desirable morphological features.

Ammonium Removal from Ammonium Rich Solution by Bio Char

When biochar made from waste pallet was added to treated livestock wastewater, the total nitrogen and ammonium ion concentrations decreased, with removal rates over 10 days of about 60% and 30%, respectively. Bacteria were isolated with high ammonium removal ability and they were identified based on their 16S rRNA gene sequences. Anaerobic denitrifying Cronobacter spp. was isolated from the biochar used for water purification. When each strain was cultured in a liquid medium containing ammonium sulfate (initial ammonium concentration 30 mg/L), the highest ammonium removal rates were 83.8% - 96.5%. Organic acids were more effective than carbohydrates as sole carbon sources for nitrogen removal from wastewater. The absorbance at 660 nm increased with nitrogen removal, indicating that cells proliferated, so it was presumed that ammonium was taken up by assimilation.

Powder mixed electrochemical discharge process for micro machining of C103 niobium alloy

This work demonstrates the viability of the powder-mixed micro-electrochemical discharge machining(PMECDM) process to fabricate micro-holes on C103 niobium-based alloy for high temperature applications.Three processes are involved simultaneously i.e.spark erosion,chemical etching,and abrasive grinding for removal of material while the classical electrochemical discharge machining process involves double actions i.e.spark erosion,and chemical etching.The powder-mixed electrolyte process resulted in rapid material removal along with a better surface finish as compared to the classical microelectrochemical discharge machining(MECDM).Further,the results are optimized through a multiobjective optimization approach and study of the surface topography of the hole wall surface obtained at optimized parameters.In the selected range of experimental parameters,PMECDM shows a higher material removal rate(MRR) and lower surface roughness(R_(a))(MRR:2.8 mg/min and R_(a) of 0.61 μm) as compared to the MECDM process(MRR:2.01 mg/min and corresponding Raof 1.11 μm).A detailed analysis of the results is presented in this paper.

Progress in Preparation Technology of Porous Ceramics for High Temperature Dust Filtration

With the rapid industrialization and urbanization,the demand for air quality management is more and more urgent.High temperature dust filtration is one important environmental management technology.Porous ceramics are used as filter materials in the field of high-temperature dust filtration because of their unique advantages such as high filtration efficiency,as well as high temperature stability,particle loss resistance,corrosion resistance and durability.This paper mainly introduced several common preparation techniques of porous ceramics,including the traditional organic foam impregnation method,foaming method,in-situ combustion method,pore-forming method and other new methods such as the template method,gel injection molding method,freeze-drying method,multi-component co-precipitation method and hydrogel method.The principle,advantages and disadvantages of these preparation technologies and their research status were described.The application of these technologies in the field of high temperature dust filtration was briefly reviewed.Finally,the application prospect of the porous ceramics in the field of high temperature dust filtration was prospected.

Improving energy utilization efficiency of electrical discharge milling in titanium alloys machining

Electrical discharge milling(ED-milling) can be a good choice for titanium alloys machining and it was proven that its machining efficiency can be improved to compete with mechanical cutting. In order to improve energy utilization efficiency of ED-milling process, unstable arc discharge and stable arc discharge combined with normal discharge were implemented for material removal by adjusting servo control strategy. The influence of electrode rotating speed and dielectric flushing pressure on machining performance was investigated by experiments. It was found that the rotating of electrode could move the position of discharge plasma channel, and high pressure flushing could wash melted debris out the discharge gap effectively. Both electrode rotating motion and high pressure flushing are contributed to the improvement of machining efficiency.

Analysis of the Rotary Ultrasonic Machining Mechanism

Ultrasonic machining (USM) is considered as an effective method for machining hard and brittle materials such as glass, engineering ceramics, semiconductors, diamonds, metal composites and so on. However, the low material removal rate due to using abrasive slurry limits further application of USM. Rotary ultrasonic machining (rotary USM) superimposes rotational movement on the tool head that vibrates at ultrasonic frequency (20 kHz) simultaneously. The tool is made of mild steel coated or bonded with diamond abrasive. Therefore, abrasive slurry is abandoned and coolant is used to carry debris out of working area. Compared with USM, rotary USM can obtain much higher material removal rate, deep holes, and fine precision, which leads to its further application. Combined with CNC technology, rotary USM can be used to conduct contour machining of hard and brittle materials. In this paper, the movement of abrasive particles in tool tip of rotary ultrasonic machining is analyzed. The impacting and grinding of abrasive in tool tip to machined surface are considered as main factors to material removal rate. The process of crack forming and growing in one loading and unloading cycle can be described as following stages: a) When abrasive particle acts the pressure on work-piece, the macro cracks in periphery of contact area are exerted increasing tensile stress. b) As the tensile stress increase to the critical of material tension, the one of cracks in periphery of contact area begins to propagate around contact area and develop beneath the surface to certain depth. c) Indentation area varies with increasing of load, the circle crack around contact area steadily or dynamical propagates towards inside of work-piece. d) As tensile stress in crack increases to critical of crack steady failure, circle crack suddenly becomes conic crack. e) Further increase load, the crack continues to grow while contact area is surrounded by conic cracks. f) During unloading, conic crack begins to close, some of cracks continue their extension towards the surface and forms a circle groove. The mathematical model for material removal rate shows that the factors affecting on material removal rate are static load, grid and concentration of abrasive, mechanical properties of machined materials, rotational speed of tool and feed speed of work-piece.

The effects of electrical heating and additives on the microbial remediation of petroleum-contaminated soils

Although petroleum is an important source of energy and an economic driver of growth,it is also a major soil pollutant that has destroyed large swathes of vegetation and forest cover.Therefore,it is vital to develop affordable and efficient methods for the bioremediation of petroleum-contaminated forest soils to restore vegetation and improve tree survival rates.In this study,bioremediation experiments were performed in an electrically heated thermostatic reactor to test the effects of organic matter additives,surfactants,and oxygen providers of nine hydrocarbon-degrading fungal strains on crude oil removal rates.In the three soil temperatures tested(20℃,25℃,and 30℃),the highest average crude oil removal rate was at 25℃(74.8%)and the lowest at 30℃(49.4%).At each temperature,variations in the addition of organic matter and oxygen providers had significant effects on crude oil removal rate.Variations in surfactant addition was significant at 20℃ and 25℃ but insignificant at 30℃.Given the same surfactant treatment,variations in temperature,organic additives,and oxygen providers was significant for crude oil removal rate.Treatments without surfactants and treatments with Tween80 exhibited their highest crude oil removal rates at 25℃.However,treatments that included the SDS surfactant exhibited their highest crude oil removal rates at 30℃.Amongst the treatments without surfactants,treatments with corn cob addition had the highest crude oil removal rates,and with surfactants,treatments that included the organic fertilizer exhibited the highest crude oil removal rates.Given the same organic fertilizer treatment,the highest crude oil removal rate was at 25℃.At each level of oxygen availability,the maximum crude oil removal rate always occurred at 25℃,and the treatments that included organic fertilizer exhibited the highest crude oil removal rates.Amongst the treatments without oxygen providers,treatments without surfactants had the highest crude oil removal rates,and with an oxygen provider,treatments with SDS addition exhibited the highest crude oil removal rates.Based on the crude oil removal rates of the treatments,we determined that S_(1)W_(1)O_(1)(addition of Tween80,organic fertilizers,and H_(2)O_(2))was optimum for remediating petroleum-contaminated forest soils in cold,high-altitude regions.This study is helpful to vegetation restoration and reforestation on petroleum contaminated forestlands.

Study on the Key Influencing Factors in Atmospheric Pressure Plasma Processing of Fused Silica

In order to get ultra-smooth fused silica surface without subsurface damage efficiently, the atmospheric pressure plasma processing( APPP) method has been developed. It is based on chemical reaction between active radicals excited by plasma and workpiece surface atoms,so the subsurface damage caused by contact stress can be avoided and atomic-level precision can be ensured. In this paper,based on the spectral quantitative analysis theory,the influence laws on material removal rate by the key factors of APPP including the flow rate of reaction gases,the input power,the processing distance and time are discussed. In addition,the results that APPP can remove the damaged surface layer and do not introduce secondary damage are proved via the nanoindentation technology.

Treatment of Shrimp Effluent by Integrated Culture of Bivalves and Macroalgae

[Objectives]To provide a theoretical basis for constructing the best species suitable for local shrimp-bivalves-algae IMTA through the screening of different bivalves and the determination of seaweed density.[Methods]The preliminary studies of different kind of bivalves and macroalgae(Gracilaria lichevoides)used for the purification of shrimp effluent were described.Through the screening of benthic bivalves,the best ratio of integrated culture of bivalves and algae was determined.[Results]Both bivalves and macroalgae had certain purification effects on aquaculture wastewater,but the effects significantly differed from species and breeding density.The removal rate of nutrient declined from Potamocorbula laevis,Sinonovacula constricta,Tegillarca granosa.The mixotrophic culture of 8 ind/L P.laevis and 120 g G.lichevoides had the highest efficiency of purification and removal rates of nutrient:NH4-N:90.67%,TP:86.18%,TN:72.66%,NO3-N:51.85%,respectively.There was a significant difference between the blank control group and the other three groups(P<0.01).The 8 ind/L+120 g group was significantly higher than the 4 ind/L+120 g group(P<0.05)in TP removal rate.Additionally,the difference between four groups was significant in the removal rate of NH4-N and TN(P<0.05),but 2 ind/L+120 g group and 8 ind/L+120 g group in the removal rate of NO3-N had no significant difference(P>0.05).[Conclusions]This research provides a reference for the use of filterable shellfish and large seaweed to treat aquaculture wastewater,and also provides the theoretical basis for constructing the local multi-level breeding structure.

Preparation of CeO_(2) abrasives by reducing atmosphere-assisted molten salt method for enhancing their chemical mechanical polishing performance on SiO_(2)substrates

Ce^(3+)as the active site on the CeO_(2)abrasive surface is the key to enhancing the material removal rate(MRR).The CeO_(2)abrasives with high chemical activity were prepared by the molten salt method under a reducing atmosphere.The crystal structure and morphology of CeO_(2)abrasive s were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FT-IR),ultraviolet—visible diffuse reflectance spectroscopy(UV-Vis DRS),and X-ray photoelectron spectroscopy(XPS).The CeO_(2)abrasives were obtained under different atmospheres(Air,Ar,and Ar/H_(2)).With the enhancement of the reducing atmosphere,the morphology of the abrasives transforms from spherical to octahedral,while more oxygen vacancies and Ce^(3+)are generated on the surface of CeO_(2)abrasives.The CMP experiments show that the MRRs of the CeO_(2)-Air,CeO_(2)-Ar,and CeO_(2)-Ar/H_(2)abrasives on SiO_(2)substrates are 337.60,578.74,and 691.28 nm/min,respectively.Moreover,as confirmed by atomic force microscopy(AFM),the substrate surfaces exhibit low roughness(20.5 nm)after being polished using all of the prepared samples.Especially,the MRR of CeO_(2)-Ar/H_(2)abrasives is increased by 104.76%compared with CeO_(2)-air abrasives.The improved CMP performance is attributed to the increased Ce^(3+)concentration and the octahedral morphology of the abrasives enhancing the chemical reaction and mechanical removal at the abrasive-substrate interface.

Novel model of material removal rate on ultrasonic-assisted chemical mechanical polishing for sapphire

Ultrasonic-assisted chemical mechanical polishing(UA-CMP)can greatly improve the sapphire material removal and surface quality,but its polishing mechanism is still unclear.This paper proposed a novel model of material removal rate(MRR)to explore the mechanism of sapphire UA-CMP.It contains two modes,namely two-body wear and abrasive-impact.Furthermore,the atomic force microscopy(AFM)in-situ study,computational fluid dynamics(CFD)simulation,and polishing experiments were conducted to verify the model and reveal the polishing mechanism.In the AFM in-situ studies,the tip scratched the reaction layer on the sapphire surface.The pit with a 0.22 nm depth is the evidence of two-body wear.The CFD simulation showed that abrasives could be driven by the ultrasonic vibration to impact the sapphire surface at high frequencies.The maximum total velocity and the air volume fraction(AVF)in the central area increased from 0.26 to 0.55 m/s and 20%to 49%,respectively,with the rising amplitudes of 1–3μm.However,the maximum total velocity rose slightly from 0.33 to 0.42 m/s,and the AVF was nearly unchanged under 40–80 r/min.It indicated that the ultrasonic energy has great effects on the abrasive-impact mode.The UA-CMP experimental results exhibited that there was 63.7%improvement in MRR when the polishing velocities rose from 40 to 80 r/min.The roughness of the polished sapphire surface was R_(a)=0.07 nm.It identified that the higher speed achieved greater MRR mainly through the two-body wear mode.This study is beneficial to further understanding the UA-CMP mechanism and promoting the development of UA-CMP technology.

Electrical discharge and arc milling with automatic tracking of optimal flushing direction:A novel high-efficiency compound machining method

The arc milling method has the advantages of high machining efficiency and low cost and is independent of the strength and hardness of machined materials.However,frequent electrode back-offs and the risk of workpiece burning may occur if erosion products are not removed promptly.In this study,it was found that the flushing method of the working medium had a significant impact on the machining performance of arc milling.Based on this,a novel highefficiency compound machining method of electrical discharge and arc milling with automatic tracking of the optimal flushing direction was proposed.An automatic tracking optimizer for external working medium injection was designed to determine the optimal external flushing direction according to the feed direction.The influence of flushing methods,working mediums,and machining parameters on the machining efficiency,tool electrode wear rate,machining error,and surface integrity of titanium alloys were investigated.The results indicated that better machining performance and environmental friendliness were achieved using the compound flushing method of outer compressed air and inner deionized water.Additionally,the automatic tracking flushing method in the opposite direction of the feed direction showed superior results compared to other directions.The material removal rate with the opposite direction injection could be increased up to 1.62 times that of the same direction,and the relative electrode wear rate could be reduced by 14.76%.This novel method has broad application prospects for machining parts with difficult-to-cut materials in aerospace and military industries.

Flat jet electrochemical milling of TC4 alloy with tailoring backward parallel flow

In flat jet electrochemical milling, the electrolyte forms a backward parallel flow after impacting the workpiece, resulting in a weak current density distribution on the workpiece. Poor surface quality usually occurs on the machined titanium alloy surface because it inevitably suffers from the weak current density. In this study, a method of flat jet electrochemical milling with tailoring the backward parallel flow was proposed to eliminate the negative effects caused by the weak current density. Multiphysics simulations are carried out to comprehend the mechanism of flat jetEC milling with tailoring backward parallel flow and better construct the novel tool electrode.Experiments on flat jet electrochemical milling of TC4 alloy with and without tailoring backward parallel flow are conducted. The results reveal that, compared with flat jet electrochemical milling without tailoring backward parallel flow, the recommended tool reduces the surface roughness by86% to 93%, and improves the material removal rate by 93% to 163% with different feed rates.Additionally, the recommended tool is more conducive to maintaining the inherent hardness of the material. Finally, a surface with low Sa of 0.37 μm is obtained.

Experimental investigation of rotary sinking electrochemical discharge milling with high-conductivity salt solution and non-pulsed direct current

Electrochemical milling is a modified technique of traditional electrochemical machining(ECM)that can be used to manufacture some helicopter transmission system parts.The use of rotary tools and an inner-jet electrolyte supply pattern can greatly improve the material removal rate(MRR)in a single pass.However,the feed speed is generally limited to minimize the tool wear.To increase the MRR,electrical discharge machining(EDM)is introduced into the electrochemical milling process.The tool rotation is employed to interrupt the discharge and the high-conductivity salt solution and non-pulsed direct current power supply are also adopted to increase ECM,eventually,a new machining method is proposed,which can be called rotary sinking electrochemical discharge milling(RSECD milling).The mechanism of it is explored in this study by analyzing the machined current,MRR,surface morphology,and tool wear at different applied voltages and feed speeds.Besides,the RSECD milling using the tool with a larger diameter is also conducted to further verify the effectiveness.In particular,the MRR can be increased by 742.5%when using the tool with a diameter of 20 mm at the applied voltage of 20 V.

A novel method of water bath heating assisted small ball-end magnetorheological polishing for hemispherical shell resonators

Hemispherical shell resonator(HSR)is the core component of hemispherical resonator gyro.It is aφ-shaped small-bore complex component with minimum curvature radius less than 3 mm.Thus,traditional polishing methods are difficult to polish it.Small ball-end magnetorheological polishing method can polish the small components with complicated three-dimensional surface and obtain non-destructive surface.Therefore,this method is suitable for polishing HSR.However,the material removal rate of the ordinary small ball-end magnetorheological polishing is low,leading to long polishing time and low output of HSR.To solve this problem,a water bath heating assisted small ball-end magnetorheological polishing method is proposed in this research.The influence rule of processing parameters on the material removal rate is studied experimentally.A set of optimal processing parameters is obtained to maximize the material removal rate.Compared with the ordinary method,the material removal rate of the new method can be improved by 143%.Subsequently,an HSR is polished by the new method.The results show that the polishing time can be reduced by 55%,and the polished surface roughness can reach 7.7 nm.The new method has the great potential to be used in actual production to improve the polishing efficiency of HSR.

Microbial community characterization,activity analysis and purifying efficiency in a biofilter process

The growth and metabolism of microbial communities on biologically activated carbon(BAC) play a crucial role in the purification of drinking water.To gain insight into the growth and metabolic characteristics of microbial communities and the efficiency of drinking water treatment in a BAC filter,we analyzed the heterotrophic plate count(HPC),phospholipid,dehydrogenase,metabolic function and water quality parameters during start-up and steady-state periods.In the start-up process of the filter with natural biofilm colonization,the variation in heterotrophic plate count levels was S-curved.The total phospholipid level was very low during the first 5 days and reached a maximum value after 40 days in the filter.The activity of dehydrogenase gradually increased during the first 30 days and then reached a plateau.The functional diversity of the microbial community in the filter increased,and then reached a relatively stable level by day 40.After an initial decrease,which was followed by an increase,the removal rate of NH4+-N and COD Mn became stable and was 80% and 28%,respectively,by day 40.The consumption rate of dissolved oxygen reached a steady level after 29 days,and remained at 18%.At the steady operation state,the levels of HPC,phospholipid,dehydrogenase activity and carbon source utilization had no significant differences after 6 months compared to levels measured on day 40.The filter was shown to be effective in removing NH4+-N,NO2--N,COD Mn,UV 254,biodegradable dissolved organic carbon and trace organic pollutants from the influent.Our results suggest that understanding changes in the growth and metabolism of microorganisms in BAC filter could help to improve the efficiency of biological treatment of drinking water.

Abrasive-free polishing of hard disk substrate with H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry

The effect of tert-butyl hydroperoxide-sodium pyrosulfite((CH3)3COOH-Na2S2O5)as an initiator system in H2O2-based slurry was investigated for the abrasive-free polishing(AFP)of a hard disk substrate.The polishing results show that the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry exhibits a material removal rate(MRR)that is nearly 5 times higher than that of the H2O2 slurry in the AFP of the hard disk substrate.In addition,the surface polished by the slurry containing the initiator exhibits a lower surface roughness and has fewer nano-asperity peaks than that of the H2O2 slurry.Further,we investigate the polishing mechanism of H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry.Electron spin-resonance spectroscopy and auger electron spectrometer analyses show that the oxidizing ability of the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry is much greater than that of the H2O2 slurry.The results of potentiodynamic polarization measurements show that the hard disk substrate in the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry can be rapidly etched,and electrochemical impedance spectroscopy analysis indicates that the oxide film of the hard disk substrate formed in the H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry may be loose,and can be removed easily during polishing.The better oxidizing and etching ability of H_(2)O_(2)-C_(4)H_(10)O_(2)-Na_(2)S_(2)O_(5) slurry leads to a higher MRR in AFP for hard disk substrates.

Experimental investigation and finite element simulation of AISI 304 during electro discharge machining

In this paper,a two-dimensional axisymmetric thermal model using finite element method(FEM)has been established for predicting the temperature distribution pro-file on the work piece during electro discharge machining(EDM)and obtained material removal rate(MRR)from the temperature isotherm.For prediction of MRR,the model utilizes some important features viz.size and shape of the heat source(Gaussian heat distribution),thermal properties of workpiece,amount of heat distribution among the dielectric fluid,workpiece and tool,material flushing efficiency and pulse off/on time,etc.ANSYS software was used for developing the thermal model for the single spark operation.For this investigation,AISI 304 stainless steel and tungsten carbide was used as workpiece and electrode material,respectively.A comparison study has been carried out for theoretical and experimental MRR for the effect of each process parameter viz.gap voltage,pulse on time and peak current.The temperature distribution along the radial and depth direction of the workpiece has been reported.The model was validated by comparing the theoretical MRR with the experimental MRR and found a good correlation between them.