Electrochemical polymerizatıon of hexachloroethane to form poly(hydridocarbyne): a pre-ceramic polymer for diamond production

Due to its structural similarity with diamond, poly(hydridocarbyne) (PHC), which is sp³-hybridized, is a unique polymer that can be easily converted to diamond and diamond-like-carbon ceramics upon heating. PHC can be easily synthesized via the electrochemical polymerization of chloroform as previously reported. Here, we report the electrosynthesis of PHC from hexachloroethane. Since hexachloroethane has six chlorine atoms in its structure, polymerization takes place through the carbons simultaneously. Thus, the polymer is bigger in chain length than PHC obtained from the polymerization of chloroform. UV-vis, FTIR, and NMR spectroscopy were utilized to determine the polymer structure. Conversion of the polymer to diamond was accomplished by heating at 1000 °C under a nitrogen atmosphere as confirmed by Optical Microscopy and Raman analysis. XRD studies showed that the product is an assortment of diamond forms.     

High speed CNC system design. Part III: high speed tracking and contouring control of feed drives

A servo control system capable of delivering rapid and accurate feed motion is a necessity for high speed machine tools. The control law must be designed to provide a high tracking bandwidth as well as adequate disturbance rejection and parameter variation robustness, in order minimize the following errors in each axis. This also contributes to the minimization of the contour errors in the machined part. This paper provides a systematic approach for designing such a control law. Position, velocity, and disturbance estimates are obtained using a Kalman filter. The feedback loop is closed using a pole placement controller with disturbance cancellation, in order to counteract the detrimental effects of friction, cutting forces, and drive parameter variations. The overall tracking bandwidth is widened by compensating for the closed loop dynamics in a feedforward manner. Also, the tracking errors due to friction transients at the corners and arc quadrants are reduced by precompensating for the expected friction forces. The contribution of each component in the control scheme to the contouring accuracy has been experimentally verified, and the overall contouring performance has been demonstrated in high speed machining tests. The experimental results were obtained using the smooth trajectory generation algorithm and identified axis and friction models which have been presented in Parts I and II respectively, of this paper.     

Study of threading dislocations in the plan-view sample of SiGe/Si(001) superlattices by transmission electron microscopy

Interfacial defects due to a mismatch of 1.378% between substrate and epilayer were examined in a Si_0.67Ge_0.33/Si(001) superlattice by transmission electron microscopy (TEM). Plan-view specimens from the superlattice were prepared to investigate the defects in the structure. It was observed that 60°C-type misfit dislocations associate with point contrast on and at their ends. This point contrast was found to represent threading dislocations by using tilt experiments in the microscope. Consequently, stereo electron microscopy was used to examine the threading dislocations. It was discovered that the threading dislocations are not on the {111} slip planes but can be almost parallel to the [001] zone axis.     

Hole effects on lateral buckling of laminated cantilever beams

In this study, the effects of hole diameter and hole location on the lateral buckling behaviour of woven fabric laminated composite cantilever beams have been investigated. In the experimental studies, two different groups of samples were used; samples with a single circular hole and samples with no hole. The critical buckling load for each sample was then determined experimentally. For the numerical analyses, ANSYS 10.0 finite element program was utilized. It has been noted that there is a good agreement between experimental results and those of finite element analyses. On the basis of this harmony, the numerical analyses of some models having different dimensions and fiber orientations have been done by changing length and width of the beam, diameter and location of the hole. It has been concluded that the effects of the hole diameter and hole location on the lateral buckling behaviours is very important, especially for the short beams.     

Conducting Copolymers of 3-Methylthienyl Methacrylate and p-Vinylbenzyloxy Poly(ethyleneoxide) and Their Electrochromic Properties

Summary A random copolymer (CP) containing 3-methylthienyl methacrylate (MTM) and p-vinylbenzyloxy poly(ethyleneoxide) (PEO-VB) units was synthesized. Further graft copolymerization of CP with pyrrole (Py) and thiophene (Th) were achieved in H₂O - sodium dodecyl sulfate (SDS), H₂O - p-toluenesulphonic acid (PTSA) and acetonitrile (AN) - tetrabutylammonium tetrafluoroborate (TBAFB) solvent electrolyte couples via constant potential electrolyses. Characterization was performed by cyclic voltammetry (CV), nuclear magnetic resonance spectroscopy (NMR), and fourier transform infrared spectroscopy (FTIR). The morphologies of the films were examined by scanning electron microscopy (SEM). Conductivities of the samples were measured by using four-probe technique. Moreover, spectroelectrochemical and electrochromic properties of the copolymer obtained from thiophene were investigated by UV-Vis spectrometry and colorimetry.     

Application of Taguchi methods in the optimization of cutting parameters for surface finish and hole diameter accuracy in dry drilling processes

The aim of the work reported here was to utilize Taguchi methods to optimize surface finish and hole diameter accuracy in the dry drilling of Al 2024 alloy. The parameters of hole quality are analyzed under varying cutting speeds (30, 45, and 60 m/min), feed rates (0.15, 0.20, and 0.25 mm/rev), depths of drilling (15 and 25 mm), and different drilling tools (uncoated and TiN- and TiAlN-coated) with a 118° point angle. This study included dry drilling with HSS twist drills. The settings of the drilling parameters were determined by using Taguchi’s experimental design method. Orthogonal arrays of Taguchi, the signal-to-noise (S/N) ratio, the analysis of variance (ANOVA), and regression analyses are employed to find the optimal levels and to analyze the effect of the drilling parameters on surface finish and hole diameter accuracy values. Confirmation tests with the optimal levels of machining parameters are carried out in order to illustrate the effectiveness of the Taguchi optimization method. The validity of Taguchi’s approach to process optimization is well established.     

Photoinitiation of cationic polymerization by visible light activated titanocene in the presence of onium salts

Summary A visible light photoinitiating system for cationic polymerization of cyclic ethers such as cyclohexene oxide (CHO) and vinyl monomers such as n-butyl vinyl ether (BVE) and N-vinyl carbazole (NVC) has been developed, using a fluorinated titanocene free radical photoinitiator, Irgacure 784, together with an onium salt, such as diphenyl iodonium hexafluoro antimonate and N-ethoxy-2-methyl-pyridinium hexafluoro-antimonate. Based on the reported photochemistry of fluorinated titanocenes, a mechanism for generating cationic species is proposed based on electron transfer between photoproducts of titanocene and onium salt. Evidence against the incorporation of an aromatic titanocene moiety in the resulting polymers is presented. Inhibition by a specific proton scavenger suggests that protons may initiate the polymerization. Received: 26 April 2001/Revised version: 6 June 2001/Accepted: 6 June 2001     

Fuzzy logic method to investigate grinding of alumina ceramic using minimum quantity lubrication

The use of nanofluid in lubrication during machining of advanced engineering ceramics has been found to be highly efficient and eco-friendly. This work involves experimental investigation of grinding Alumina (Al₂O₃) ceramic to determine the effect of the grinding variables. The grinding variables considered include depth of cut, feed rate, type of diamond wheel, and lubrication type. Moreover, the response parameters considered include grinding power, coefficient of friction, and surface quality. The responses obtained during the experiments were used to develop a fuzzy logic prediction model. The findings from this work can be concluded as follows: (a) The depth of cut and feed rate have direct proportional relationship with the grinding power and coefficient of friction. (b) The metallic bonded diamond wheel was found to have higher machining efficiency than the resinoid bonded one. (c) Higher number of diamond grits produces lower frictional coefficient. (d) The carbon nanotube based nanofluid when used in the minimum quantity lubrication (MQL) process proffers better lubrication capability than conventional flood cooling system. (e) The developed fuzzy logic models were found to have high prediction accuracies of 97.22%, 98.60%, and 96.8%, respectively, for grinding power, grinding force ratio, and surface roughness.     

Synthesis and in vitro antimicrobial characterization of Boron-PVA Electrospun nanofibers

Polyvinyl alcohol (PVA) electrospun nanofibers and boric acid (BA) complexes of these nanofibers were synthesized with and without using TritonX-100(TX-100) as a water soluble surfactant (PVA, PVA/BA, PVA/TX-100, PVA/TX-100/BA). The electrospun nanofibers were characterized by SEM, FTIR and TGA. Preliminary results showed that certain amount of boric acid decreased the number of Stapylococcus aureus from 6,8x10⁷(CFU/mL) to 3x10⁷(CFU/mL). In the preparation of polymer, boric acid was used as a crosslinker and antimicrobial agent whereas TX-100 was used as surfactant. The viscosity and conductivity measurements indicated that the BA increased viscosity but decreased conductivity. In contrast, TX-100 increased conductivity without considerable effect on viscosity, which affects the production and resulting nanofiber properties such as diameter and bead formation. The antimicrobial activities of the nanofibers were assayed in vitro by Gram-negative (E. coli) and Gram-positive(S. aureus) bacteria. It was observed that PVA/TX-100/BA showed better antibacterial activity against S.aureus bacteria compared to PVA and PVA/TX-100 nanofibers.