Study of the material removal mechanism of glass-ceramics based on consecutive incremental loading in ductile-regime grinding

Glass-ceramics have many excellent properties and are widely used in various fields. During the grinding process,the workpiece surface is typically subject to material removal by grit of incremental heights, which has rarely been the focus of research. As such, it is necessary to study the material removal mechanism of glass-ceramics under consecutive incremental loading, which more closely reflects the actual grinding process. In this paper,to analyze the plastic deformation and residual stress of lithium aluminosilicate(LAS) glass-ceramics, a finite element model is established based on the Drucker–Prager yield criterion for ductile regimes. A nano-scratch test was also conducted and the test results show that both the residual depth and residual stress increase with an increase in the number of increments, and that consecutive incremental loading promotes the plastic deformation of glass-ceramics and increases the residual stress of the material in the ductile-regime process. These findings provide guidance for achieving higher dimensional accuracy in the actual grinding of glass-ceramics parts.

Fiber orientation effects on grinding characteristics and removal mechanism of 2.5D C_(f)/SiC composites

Carbon fiber reinforced silicon carbide(C_(f)/SiC)composites are widely used in aerospace for their excellent mechanical properties.However,the quality of the machined surface is poor and unpredictable due to the material heterogeneity induced by complex removal mechanism.To clarify the effects of fiber orientation on the grinding characteristics and removal mechanism,single grit scratch experiments under different fiber orientations are conducted and a three-phase numerical modelling method for 2.5D C_(f)/SiC composites is proposed.Three fiber cutting modes i.e.,transverse,normal and longitudinal,are defined by fiber orientation and three machining directions i.e.,MA(longitudinal and normal),MB(longitudinal and transverse)and MC(normal and transverse),are selected to investigate the effect of fiber orientation on grinding force and micro-morphology.Besides,a three-phase cutting model of 2.5D C_(f)/SiC composites considering the mechanical properties of the matrix,fiber and interface is developed.Corresponding simulations are performed to reveal the micro-mechanism of crack initiation and extension as well as the material removal mechanism under different fiber orientations.The results indicate that the scratching forces fluctuate periodically,and the order of mean forces is MA>MC>MB.Cracks tend to grow along the fiber axis,which results in the largest damage layer for transverse fibers and the smallest for longitudinal fibers.The removal modes of transverse fibers are worn,fracture and peel-off,in which normal fibers are pullout and outcrop and the longitudinal fibers are worn and push-off.Under the stable cutting condition,the change of contact area between fiber and grit leads to different removal modes of fiber in the same cutting mode,and the increase of contact area results in the aggravation of fiber fracture.

Removal mechanisms of heavy metal pollution from urban runoff in wetlands

Solid particles, particularly urban surface dust in urban environments contain large quantities of pollu- tants. It is considered that urban surface dust is a major pollution source of urban stormwater runoff. The storm- water runoffwashes away urban surface dust and dissolves pollutants adsorbed onto the dust and finally discharges into receiving water bodies. The quality of receiving water bodies can be deteriorated by the dust and pollutants in it. Polluted waters can be purified by wetlands with various physical, chemical, and biologic processes. These pro- cesses have been employed to treat pollutants in urban stormwater runoff for many years because purification of treatment wetlands is a natural process and a low-cost method. In this paper, we reviewed the processes involved during pollutants transport in urban environments. Parti- cularly, when the urban stormwater runoff enters into wetlands, their removal mechanisms involving various physical, chemical and biologic processes should been understood. Wetlands can remove heavy metals by absorbing and binding them and make them form a part of sediment. However, heavy metals can be released into water when the conditions changed. This information is important for the use of wetlands for removing of pollutants and reusing stormwater.

Bioremediation Process and Bioremoval Mechanism of Heavy Metal Ions in Acidic Mine Drainage

Acidic mine drainage（AMD） containing acidity and a broad range of heavy metal ions is classified as hazardous, and must be properly treated. The removal mechanism of heavy metal ions in acidic mine drainage containing Cu^2＋, Fe^2＋, and Zn^2＋ with biological method was studied here. Using 20 mmol/L ethanol as carbon source, Desulfovibrio marrakechensis, one of sulfate reducing bacteria（SRB） species, grew best at 35℃ and pH=6.72 with concentrations of 10, 55 and 32 mg/L for Cu^2＋, Fe^2＋ and Zn^2＋, respectively. The removal efficiency for each ion mentioned above was 99.99%, 87.64% and 99.88%, respectively. The mineralogy and surface chemistry of precipitates were studied by means of energy dispersive spectrometer（EDS）, X-ray photoelectron spectroscopy（XPS）, X-ray diffraction（XRD） combined with control tests. The experimental results demonstrate that the removal mechanism of heavy metal ions by Desulfovibrio marrakechensis is comprehensive function of chemical precipitation, adsorption and bioprecipitation. The biogenic iron sulfide solid was characterized as greigite（Fe3S4）, while the zinc sulfide solid was characterized as sphalerite（ZnS）.

Material removal mechanisms and characteristics of potassium dihydrogen phosphate crystals under nanoscratching

Potassium dihydrogen phosphate(KDP)crystals are important materials in high-energy laser systems.However,because these crystals are brittle and soft,machining-induced defects often emerge in KDP components.This study aimed to investigate the material removal mechanisms and characteristics of KDP during nanoscratching using Berkovich,spherical,and conical indenters.We found that KDP surface layers could be removed in a ductile mode at the micro/nanoscale and that dislocation motion was one of the main removal mechanisms.Removal characteristics are related to the stress fields generated by indenter geometries.The spherical indenter achieved a ductile removal mode more easily.The lateral force of nanoscratching increased with an increase in the normal force.The coefficient of friction(COF)followed the same trend as the lateral force when spherical and conical indenters were used.However,the COF was independent of the normal force when using a Berkovich indenter.We found that these COF variations could be accurately described by friction models.

Surfactant-Modified Hydrophobic Biochar Derived from Laver (Porphyra haitanensis) with Superior Removal Performance for Kitchen Oil

In this study,a novel absorpent(MSAR600℃)with a hydrophobic surface and hierarchical porous structure for the removal of kitchen oil was facilely fabricated from the macroalgae,laver(Porphyra haitanensis)by incorpor-ating high-temperature carbonization and alkyl polyglucosides(APG)and rhamnolipid(RL)surfactants modifi-cation.The characterization results showed MSAR600℃ possessed a louts-leaf-like papillae microstructure with high contact angle(137.5°),abundant porous structure with high specific surface area(23.4 m^(2)/g),and various oxygen-containing functional groups(-OH,C=O,C-O).Batch adsorption experiments were conducted to inves-tigate the effect of adsorption time,temperature,pH,and absorbent dose on kitchen oil adsorption performance.Then the practical application for the removal of kitchen oil using MSAR600℃ was also performed.The results showed that MSAR600℃ had a higher removal efficiency for kitchen oil(75.98%),compared with the commercial detergent(72.3%).This study demonstrates an example of fabricating a green tableware detergent for enhanced removal performance of kitchen oil.

The technology and mechanism of removal of plastic mulch and land preparation

In this article,the characteristic of the field plastic mulch, the craft for mechanization removal and land preparation of plastic mulch and the mechanism frequently used in the removal and land preparation of plastic mulch were introduced, which offered references for the design of removal mechanism and land preparation of plastic mulch and structural optimization combination of working components.

Energy beam-based direct and assisted polishing techniques for diamond:A review

Diamond is a highly valuable material with diverse industrial applications,particularly in the fields of semiconductor,optics,and high-power electronics.However,its high hardness and chemical stability make it difficult to realize high-efficiency and ultra-low damage machining of diamond.To address these challenges,several polishing methods have been developed for both single crystal diamond(SCD)and polycrystalline diamond(PCD),including mechanical,chemical,laser,and ion beam processing methods.In this review,the characteristics and application scope of various polishing technologies for SCD and PCD are highlighted.Specifically,various energy beam-based direct and assisted polishing technologies,such as laser polishing,ion beam polishing,plasma-assisted polishing,and laser-assisted polishing,are summarized.The current research progress,material removal mechanism,and infuencing factors of each polishing technology are analyzed.Although some of these methods can achieve high material removal rates or reduce surface roughness,no single method can meet all the requirements.Finally,the future development prospects and application directions of different polishing technologies are presented.

Field-assisted machining of difficult-to-machine materials

Difficult-to-machine materials (DMMs) are extensively applied in critical fields such as aviation,semiconductor,biomedicine,and other key fields due to their excellent material properties.However,traditional machining technologies often struggle to achieve ultra-precision with DMMs resulting from poor surface quality and low processing efficiency.In recent years,field-assisted machining (FAM) technology has emerged as a new generation of machining technology based on innovative principles such as laser heating,tool vibration,magnetic magnetization,and plasma modification,providing a new solution for improving the machinability of DMMs.This technology not only addresses these limitations of traditional machining methods,but also has become a hot topic of research in the domain of ultra-precision machining of DMMs.Many new methods and principles have been introduced and investigated one after another,yet few studies have presented a comprehensive analysis and summarization.To fill this gap and understand the development trend of FAM,this study provides an important overview of FAM,covering different assisted machining methods,application effects,mechanism analysis,and equipment design.The current deficiencies and future challenges of FAM are summarized to lay the foundation for the further development of multi-field hybrid assisted and intelligent FAM technologies.

Molecular dynamics simulation of the material removal in the scratching of 4H-SiC and 6H-SiC substrates

Single crystal silicon carbide(SiC)is widely used for optoelectronics applications.Due to the anisotropic characteristics of single crystal materials,the C face and Si face of single crystal SiC have different physical properties,which may fit for particular application purposes.This paper presents an investigation of the material removal and associated subsurface defects in a set of scratching tests on the C face and Si face of 4H-SiC and 6H-SiC materials using molecular dynamics simulations.The investigation reveals that the sample material deformation consists of plastic,amorphous transformations and dislocation slips that may be prone to brittle split.The results showed that the material removal at the C face is more effective with less amorphous deformation than that at the Si face.Such a phenomenon in scratching relates to the dislocations on the basal plane(0001)of the SiC crystal.Subsurface defects were reduced by applying scratching cut depths equal to integer multiples of a half molecular lattice thickness,which formed a foundation for selecting machining control parameters for the best surface quality.

Material Removal Behavior and Surface Integrity in Grinding of UltrafineGrained WC-Co Materials

Due to the excellent combination of wear resistance and fracture toughness,the ultrafine-grained WC-Co composites can significantly improve the durability and reliability of industrial tools.However,the grinding of ultrafine-grained WC-Co remains a challenge.In order to provide an experimental basis for improving grinding quality of ultrafine-grained WC-Co,a series of surface grinding experiments on ultrafine-grained WC-Co hardmetals were conducted by diamond wheel under various grinding conditions,and the material removal behavior and surface integrity in grinding of ultrafine-grained WC-Co materials were characterized by means of scanning electron microscopy(SEM),X-ray microstress analyzer and surface roughness analyzer in this paper.The results indicate that the material removal behavior in grinding of ultrafine-grained WC-Co materials is determined not only by the abrasive grain size on the wheel,but also by the depth of cut.The roughness values of ground surface increase with increasing grit size of diamond wheel,and increase initially,then decrease with increase in depth of cut.Grinding causes the residual compressive stress in the surface layer of ground cemented carbides under various grinding conditions;the magnitude of residual surface stress increases with increasing grit size of diamond wheel,and isn't changed obviously along with the change of depth of cut.

Formation and Removement Mechanism of Haze Defects on（111）p－type Silicon Wafers

The haze defects on p-type (111) silicon wafers were investigated by means of chemical etching, Fouriertransform infra-red microscopy (FTIR), spreading resistance measurement. secondary ion mass spectroscopy(SLMS), transmission electron microscopy (TEM) equipped with an energy-dispersive X-ray spectrometer(EDX). The haze defects are the precipitates of silicide of metal impurities (Fe, Ni) on the wafer surface.The formation of haze defects can efficiently be inhibited by utilizing the technology of fast neutronirradiation combined with the internal gettering (IG), and then, the formation and removement mechanismof the haze defects have been discussed in this paper.

Effect of tool geometry on ultraprecision machining of soft-brittle materials:a comprehensive review

Brittle materials are widely used for producing important components in the industry of optics,optoelectronics,and semiconductors.Ultraprecision machining of brittle materials with high surface quality and surface integrity helps improve the functional performance and lifespan of the components.According to their hardness,brittle materials can be roughly divided into hard-brittle and soft-brittle.Although there have been some literature reviews for ultraprecision machining of hard-brittle materials,up to date,very few review papers are available that focus on the processing of soft-brittle materials.Due to the‘soft’and‘brittle’properties,this group of materials has unique machining characteristics.This paper presents a comprehensive overview of recent advances in ultraprecision machining of soft-brittle materials.Critical aspects of machining mechanisms,such as chip formation,surface topography,and subsurface damage for different machining methods,including diamond turning,micro end milling,ultraprecision grinding,and micro/nano burnishing,are compared in terms of tool-workpiece interaction.The effects of tool geometries on the machining characteristics of soft-brittle materials are systematically analyzed,and dominating factors are sorted out.Problems and challenges in the engineering applications are identified,and solutions/guidelines for future R&D are provided.

A Comparative Study on the Efficacy between Minimally Invasive Caries Removal Technique involving Carisolv and Traditional Mechanical Caries Removal in Treating Dental Caries in Children

Objective:To explore the curative effect of Carisolv,a minimally invasive caries removal technique and traditional mechanical caries removal treatment on children’s dental caries.Methods:A total of 97 children with dental caries who were treated in the Department of Stomatology in Affiliated Hospital of Chifeng University,Chifeng from September 2017 to May 2019 were selected and recruited as the research subjects.They were divided into two groups by random number table method.Forty-nine individuals were assigned in the control group while the remaining 48 individuals in the observation group.The control group was treated with traditional mechanical caries removal method,and the observation group was treated with minimally invasive caries removal technique,i.e.Carisolv.Both groups were followed up for six months.The degree of pain,recovery time of dental function and complications after six months of treatment were observed in the two groups of children.Results:During the treatment,compared with the control group,the children in the observation group experienced lower degree of pain and had shorter recovery time of dental function.After six months of treatment,the incidence of complications in the observation group was lower than that in the control group.The difference was statistically significant(P<0.05).Conclusion:Compared with traditional mechanical caries removal method,Carisolv,a minimally invasive caries removal technique could reduce the pain of children during the treatment process,shorten the time to restore dental function,reduce the occurrence of complications,and had a better therapeutic effect in treating children’s dental caries.

Synergetic catalytic removal of chlorobenzene and NOχfrom waste incineration exhaust over MnNb0.4Ce0.2Oχcatalysts:Performance and mechanism study

Nb doped MnCe0.2Ox complex oxides catalysts prepared via a homogeneous precipitation method were investigated for synergistic catalytic removal of NOx and chlorobenzene(CB)at low temperatures.The MnNb0.4Ce0.2Ox catalyst with a molar ratio of Nb/Mn=0.4 exhibits excellent activity and the NOx and CB removal efficiency reaches 94.5%and 96%at 220℃,respectively.Furthermore,the NOx and CB removal efficiency of MnNb0.4Ce0.2Ox still remains above 80%after injecting 300 ppm SO2 and 7 vol%H2 O for 36 h.In addition,the presence of CB and NOx+NH3 can improve the NOx and CB removal efficiency of MnNb0.4Ce0.2Ox,respectively.The analysis results from N2-BET,Py-IR,H2-TPR and NH3-TPD reveal that the introduction of Nb increases the average pore size,pore volume and surface area,promoted the growth of Lewis acid amount obviously,and enhances redox ability of MnCe0.2Ox at 100-250℃.Moreover,the molecular migration process of NOx,NH3,CB and SO2 in NH3-SCR and CB oxidation reaction over MnNb0.4Ce0.2Ox catalysts were systematically studied.In situ DRIFTS,FT-IR and XPS also confirm that the adsorption of sulfate species and SO2 on the surface of MnNb0.4Ce0.2Ox is inhibited effectively by the introduction of Nb in the presence of SO2 and H2 O.Moreover,Nb additives also enhance the structural stability of MnNb0.4Ce0.2Ox,due to the interactions among Mn,Nb and Ce.The NH3-TPD,H2-TPR and in situ DRIFTS results also confirm that the MnNb0.4Ce0.2Ox still retains abundant acid sites and high redox ability in the presence of SO2 and H2O.In summary,MnNb0.4Ce0.2Ox catalysts represent a promising and effective candidate for controlling NOx and CB at low temperatures.

Precision Grinding of Reaction Bonded Silicon Carbide Using Coarse Grain Size Diamond Wheels

Reaction bonded SiC（RBSiC） is attractive for optical application because of its favorable properties and low fabrication cost. However, the difficultness and cost involved in RBSiC grinding limit its application. The investigation on high efficient and low-cost machining with good grinding quality is desired. Generally, high efficient machining for RBSiC is realized by using coarse grain size grinding wheels, but serious grinding damage is inevitable. In this paper, monolayer nickel electroplated coarse grain size diamond grinding wheels with grain sizes of 46 μm, 91 μm, and 151 μm were applied to the grinding of RBSiC. An electrolytic in-process dressing（ELID） assisted conditioning technique was first developed by using cup shape copper bonded conditioning wheels with grain sizes of 15 μm and 91 μm to generate the conditioned coarse grain size wheels with minimized wheel run-out error within 2 μm, constant wheel peripheral envelop as well as top-flattened diamond grains. Then, the grinding experiments on RBSiC were carried out to investigate the grinding performance and material removal mechanism. The experimental results indicate that the developed conditioning technique is applicable and feasible to condition the coarse grain size diamond wheels under optimal conditioning parameters, and the material removal mechanism involved in RBSiC grinding is the combination of brittle fracture and ductile deformation to generate smooth ground surface. This research is significant for the high efficient and low-cost precision grinding of RBSiC with good ground surface quality.

Mechanism and threshold fluence of nanosecond pulsed laser paint removal

In this paper, the nanosecond pulse laser surface treatment of the waterborne anti-rust paint on HT250 gray cast iron was carried out. The area and depth of the per-pulse laser ablation paint layer were measured. The threshold of laser energy density was determined through the relations with ablation area and depth. The paint removal mechanism was discussed by analyzing the ablation features of the paint layer on laser cleaning. The features of the paint removal under various laser energy densities were characterized, and the process parameters in the experiments were investigated.The results showed that there were four thresholds and three kinds of mechanisms in the paint removal process with nanosecond pulsed laser. The ablation threshold of substrate was deepened on the laser parameters. The ablation processes were included thermal ablation, thermal vibration and paint ionization concurrently, respectively. The surface cracks and paint debris were observed at the edge of the cleaning path, which were ascribed to the vibration effect by laser. In addition, the vibration effect could significantly increase the width of paint removal. Paint ionization has also a significant influence on the substrate morphology. Paint ionization would have an obvious impact on the formation of the substrate morphology. It is desirable to fabricate approach to remove the paint layer without damaging the substrate under optimized laser parameters by nanosecond pulse laser.

Efficient removal of tetracycline by H_(2)O_(2) activated with iron-doped biochar: Performance, mechanism, and degradation pathways

In this study,novel iron-doped biochar(Fe-BC) was produced using a simple method,and it was used as an H_(2)O_(2)activator for tetracycline(TC) degradation.Generally,iron loading can improve the separation performance and reactivity of biochar(BC).In the Fe-BC/H_(2)O_(2)system,92% of the TC was removed within 30 min with the apparent rate constant(k_(obs)) of 0.155 min^(-1),which was 23.85 times that in the case of the BC/H_(2)O_(2)system(0.0065 min^(-1)).The effects of the H_(2)O_(2) and Fe-BC dosage,initial pH,and TC concentration on the TC removal were investigated.The radical quenching and electron paramagnetic resonance(EPR) measurements demonstrated that the removal of TC using the Fe-BC/H_(2)O_(2)process involved both radical(^(*)OH and O_(2)^(-)) and non-radical pathways(^(1)O_(2) and electron transfer).In addition,the performance of the catalyst was also affected by the persistent free radicals(PFRs) and defective sites on the catalyst.Moreover,the degradation pathways of TC were proposed according to the intermediate products detected by LC-MS and the ecotoxicity of intermediates was evaluated.Finally,the Fe-BC/H_(2)O_(2)showed high resistance to inorganic anions and natural organic matter in aquatic environments.Overall,Fe-BC is expected to be an economic and highly efficient heterogeneous Fenton catalyst for removing the organic contaminants in wastewater.

Plasma-enabled electrochemical jet micromachining of chemically inert and passivating material

Electrochemical jet machining(EJM)encounters significant challenges in the microstructuring of chemically inert and passivating materials because an oxide layer is easily formed on the material surface,preventing the progress of electrochemical dissolution.This research demonstrates for the first time a jet-electrolytic plasma micromachining(Jet-EPM)method to overcome this problem.Specifically,an electrolytic plasma is intentionally induced at the jet-material contact area by applying a potential high enough to surmount the surface boundary layer(such as a passive film or gas bubble)and enable material removal.Compared to traditional EJM,introducing plasma in the electrochemical jet system leads to considerable differences in machining performance due to the inclusion of plasma reactions.In this work,the implementation of Jet-EPM for fabricating microstructures in the semiconductor material 4H-SiC is demonstrated,and the machining principle and characteristics of Jet-EPM,including critical parameters and process windows,are comprehensively investigated.Theoretical modeling and experiments have elucidated the mechanisms of plasma ignition/evolution and the corresponding material removal,showing the strong potential of Jet-EPM for micromachining chemically resistant materials.The present study considerably augments the range of materials available for processing by the electrochemical jet technique.

High Efficiency Axial Deep Creep-Feed Grinding Machining Technology of Engineering Ceramics Materials

Axial deep creep-feed grinding machining technology is a high efficiency process method of engineering ceramics materials, which is an original method to process the cylindrical ceramics materials or hole along its axis. The analysis of axial force and edge fracture proved the cutting thickness and feed rate could be more than 5-10 mm and 200 mm/min respectively in once process, and realized high efficiency, low-cost process of engineering ceramics materials. Compared with high speed-deep grinding machining, this method is also a high efficiency machining technology of engineering ceramics materials as well as with low cost. In addition, removal mechanism analyses showed that both median/radial cracks and lateral cracks appeared in the part to be removed, and the processed part is seldom destroyed, only by adjusting the axial force to control the length of transverse cracks.