Atomistic Fabrication Technology to Enhance Accuracy

Atomistic Fabrication Technology to Enhance Accuracy Importance of Atomistic Fabrication Technology to Enhance Machining Accuracy During Electrochemical Machining of Metals Ritesh Upadhyay, Arbind Kumar P.K. Srivastava Abstract Atomistic fabrication technology fully utilizes physical and chemical phenomena with atomistic and electronic understanding. In the case of mechanical machining many defects are introduced when pushing the tool on the workpiece surface and then atoms on the workpiece surface are removed by the displacement and multiplication of such defects. Therefore many defects remain on the workpiece surface after mechanical machining. Machining accuracy is considerably affected by disturbances such as thermal deformation and external vibration because removal depth is dependent on the cutting depth of the tool and is very difficult to manufacture precision products by mechanical machining. In the case of atomistic fabrication technology surface atoms are naturally removed by chemical reaction caused by reactive species and therefore no deformed layer on the workpiece surface. A very high-precision product can be easily manufactured with stable physical and chemical phenomenon used for removal re action. In this paper possibility of atomic level removal of work piece (Iron workpiece) have been explored. The current and voltage requirements for removal of few thousand atoms will be calculated along with. the mechanism of removal of metals in relation with over-voltage and conductivity. Introduction The essence of nanotechnology is the ability to work at the molecular level, atom by atom, to create large structures with fundamentally new molecular organization. Compared to the behavior of isolated molecules of about 1 nm (10 -9 m) or of bulk materials, behavior of structural features in the range of about 10-9 to 10-7 m exhibit important changes. Nanotechnology is concerned with materials and systems whose structures and components exhibit novel and significantly improved physical and chemical processes due to their nanoscale size. The goal is to exploit these properties by gaining control of structures and devices at atomic, molecular, and supramolecular levels and to learn efficient manufacturing and use these devices 1-4. Maintaining the stability of interfaces and the integration of these nanostructures at micron-length and macroscopic scales are all keys to success. New behavior at the nanoscale is not necessarily predictable from that observed at large size scales.The most important changes in behavior are caused not by the order of magnitude size reduction, but by newly observed phenomena intrinsic to or becoming predominant at the nanoscale5-6. These phenomena include size confinement, predominance of interfacial phenomena and quantum mechanics. Once it becomes possible to control feature size, it will also become possible to enhance material properties and device functions Being able to reduce the dimensions of structures down to the nanoscale leads to the unique properties of carbon nanotubes, quantum wires and dots Nanotechnology is the exploitation of the novel and improved physical, chemical, mechanical, and biological properties, phenomena, and processes of systems that are intermediate in size between isolated atoms/molecules and bulk materials, where phenomena length and time scales become comparable to those of the structure. It impl ies the ability to generate and utilize structures, components, and devices with a size range from about 0.1 nm (atomic and molecular scale) to about 100 nm by control at atomic, molecular and macromolecular levels. Novel properties occur compared to bulk behavior because of the small structure size and short time scale of various processes7-8. Electrochemical Reaction When the current passed through a NaCl electrolyte solution following reaction occure NaCl = Na+ + Cl H2O = H + + OH The positive ions moves towards cathode and negative ions moves towards anode. Each Na+ ions gain an electron and is converted to Na . Hence Na+ ions are reduced at the cathode by means of electrons. Cathode Reaction: Na+ + e = Na Na +H2O = NaOH + H+ 2H+ + 2e = H2 It shows that only hydrogen gas evolve at cathode and there will be no deposition Anode Reaction: Fe = Fe2+ +2e Fe2+ + 2Cl = FeCl2 Fe2+ + 2OH = Fe (OH)2 FeCl2+ 2OH = Fe(OH)2 + 2Cl 2Cl →Cl2 + 2e 2FeCl2 + Cl2 = 2FeCl3 H+ + Cl = HCl 2Fe(OH)2 +H2O +O2 = 2Fe(OH)3 Fe(OH)3 + 3HCl = FeCl3 + 3H2O FeCl3 + 3NaOH = Fe(OH)3↓ + 3NaCl Theoretical Aspects Building block atoms play an important role in future atmostic fabrication technology. Material removal rate for removal of Fe work piece at atomic level have been calculated by using Faraday’s law. Where MRR = Metal Removal Rate , A = Atomic weight, I = Current, Z = valency, F = faraday’s constant . The results are shown in figure 1, Fig 1 Plot of Metal Removal Rate against Current Density, A=55.85,Z=2,F=96500 It is clear from the figure that very low current is needed for atomic scale removal of iron atoms from the iron work piece. The requirement of voltage for removal of iron at atomic scale have been calculated using ohm’s Law and shown in figure 2 Fig 2 Plot of Metal Removal Rate against Voltage, where specific conduction=0.0387ohm-1 cm-1others  parameter are same as in figure 1. It is clear from the figure that voltage requirement is very low. The current and voltage data for removal of few thousand atoms shows that conductivity and over-voltage play important role in current carrying process. Effect of electrolyte conductivity on MRR: Electrolytes are substances that become ions in solution and having capacity to conduct electricity. The electrolyte has three main functions in the ECM process. It carries the current between the tool and the workpiece, it removes the product of the reaction from the cutting region, and it removes the heat produced by the current flow in the operation. Electrolytes must have high conductivity, low toxicity and corrosivity, and chemical and electrochemical stability. The rate of material removal in ECM is governed by Faraday’s laws and is function of current density which depends upon the concentration of electrolyte with increase in concentration of electrolyte the MRR increases continuously up to a limiting value after which if further increase in concentration is made the MRR decreases due to decrease in ionic mobility. Effect of Over voltage: The over-voltage is the important parameter which restrict the material removal rate and is sensitive to tool feed rate and equilibrium machining gap. Material removal rate decreases due to increase in over voltage and decrease in current efficiency, which is directly related to the conductivity of the electrolyte solution. 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The variation of over voltage with equilibrium gap is shown in Figure 3 which indicate that over-voltage decreases linearity with increase in equilibrium gap. When equilibrium gap approaches to zero, over voltage approaches to applied voltage. Figure 4 shows variation of tool feed rate with overvoltage, which shows that over voltage decreases sharply with penetration rate and goes to negative side after a certain tool feed rate. Negative value of V, seems to be unreal because un-matching long range values of penetration rate for single fixed value of equilibrium gap. Fig 3. Plot of Over voltage against equilibrium machining gap Fig 4. Plot of over voltage against penetration gap Conclusion: The effort is made to focus on the importance of atomistic fabrication technology with the effect of key factors like over voltage and electrolyte concentration influencing the quality of machined surface and dimensional accuracy. 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