C.S. Liu

The Study on Ductile Removal Mechanisms of Ultrasonic Vibration Grinding Nano-ZrO2 Ceramics

On the basis of analyzing the brittleness, ductileity, and the removal mechanisms of the^nano-ZrO2 Ceramics, the critical ductile grinding depth formula of the nano-ceramics was established. Due to superductileity of the nano-ZrO2 ceramics, it couldn’t apply the formula of the common engineering ceramic material according to experimental results. The value of material coefficient ζ has relations with not only the material characteristics but also the processing methods and the processing parameters. It was proved that ζ has great effects on the accuracy of theoretical calculation. Experimental results showed that the critical ductility grinding depth of the nano-ZrO2 ceramics is up to 12 µm in common grinding methods, while in ultrasonic grinding is up to 20µm. The grinding chips with and without ultrasonic vibration assistance were discussed.

Study on Ultrasonic Vibration Grinding Character of Nano ZrO2 Ceramics

Nano ceramics possessed ascendant mechanical property and physical characteristics contrast with engineering ceramics, so it has extensive application prospect in various industries. On the basis of applying the indentation fracture mechanics to analyze the removal mechanics of ceramic material, this paper analyzed the critical ductile grinding depth of the nano ZrO2 ceramics. Adopting ultrasonic composite processing we describe the influence of different processing parameters and grain size of diamond wheel on the grinding forces and surface roughness. Based on the grinding forces and surface roughness the grinding process with and without vibration is analyzed. By means of SEM and AFM the surface character and critical ductile grinding depth of nano ZrO2 ceramics are also discussed. The paper supplied the theoretical and experimental basis for the grinding of the large-sized ultraprecision plate structure of nano ZrO2 ceramics (nm).

Study on Motion Model of Abrasive Particle and Surface Formation Mechanics under Two Dimensional Ultrasonic Grinding

This paper worked on two dimensional ultrasonic grinding system with workpiece adhered to ultrasonic vibration. It analyzed the working locus of abrasive particle under two dimensional ultrasonic grinding (TDUG), and emulated the working course, and gave the key parameters affecting grinding efficiency and grinding locus’s characteristic under different grinding parameters, and brought forward the cutting course between abrasive particle and workpiece under TDUG belongs to an new rotating dynamic contact cutting model. At the same time, it put forward the theoretically critical speed condition under TDUG to obtain the optimum grinding effect, and verified good micro-feature of finished surface under TDUG by the means of grinding tests of nano ZrO2 ceramics.

Research on Relationships Between Surface Fracture States and Surface Roughness Dispersion Range in Ultrasonic Grinding ZrO2

On the basis of the relationship between machined surface roughness and cutting parameters of hard-brittle materials, experiments of common and ultrasonic honing ZrO2 engineering ceramics were carried out using coarse diamond grits to discuss the relationship between surface roughness and its dispersion range and surface fracture states. Experimental results show that the machined surface roughness value of hard-brittle materials and the characteristics of its dispersion range can be considered as the criteria of cutting state. Therefore, as the machined surface roughness value and its dispersion range are both rather small, the cutting goes in the ductile cutting state, whilst the machined surface roughness value and its dispersion range are both rather large, the cutting goes in the crack cutting state. When the machined surface roughness value is rather small and its dispersion range is rather large the cutting is in the transition cutting state. Introduction At present with combination to the special machining technology such as ultrasonic, the traditional ultra-precision machining technology for hard-brittle materials has developed a new way to obtain the ductile surface effectively. In 1993, Professor D. Prabhakar put forward a theoretical model of material removal rate for rotating ultrasonic machining engineering ceramics [1] to discuss the theoretical relationship between material removal rate and amplitude, rotating velocity, grit size and machining pressure, and proved that the rotating ultrasonic machining has a relatively lower cutting force and higher material removal rate with the same conditions as common grinding. In 1994, H. Frei and G. Grathwohl studied the microstructure and intensity of advanced ceramics after ultrasonic machining [2], and found out in the process of machining engineering ceramics such as Al2O3, ZrO2 and N4Si3, the material removal process includes both crack and mini-plastic deformation, and the later resulted in higher surface compressive stress and flexural strength. In the same year, Professor X. Ai and D.M. Kim studied the ultrasonic drilling of engineering ceramics [3] and found that ultrasonic machining has smaller cutting force, lower cutting temperature and better surface quality than common way. In 1995, Z.J. Pei investigated the material removal rate of rotating ultrasonic milling MgO and ZrO2 engineering ceramics, and forecasted the relation between removal rate and cutting parameters [4]. A.R Jones worked over the press distributing model of ultrasonic polishing using stamping die [5]. Z.Y. Wang put forward the dynamic model of material removal rate in ultrasonic machining metal accessories [6]. H. Dam studied the productivity, surface quality and dimension tolerance of ultrasonic machining ceramics [7]. In the 48th CIRP annual meeting, B. Varghese and S. Malkin gave a progress report of radial ultrasonic vibration machining, and the results shew contact press, loaded area, working cycle time, ultrasonic vibration and its direction, and slotted wheel have effort on the material removal rate of ZrO2 and Si3N4 [8]. E. Uhlman and G. Spur discussed the surface figuration mechanism of slow-feed grinding advanced ceramics assisted by ultrasonic, reviewed the cut-in mechanism of single grit imposed ultrasonic vibration in the normal direction of workpiece, and forecasted that the axial vibration could get a better machining effect [9]. Obviously these researches focused on the Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 239-243 doi:10.4028/www.scientific.net/KEM.259-260.239

Molecular Vibration Theoretical Analysis of Two-Dimensional Photoelectric Conversion Material WSe2

Monolayer WSe2 is flexible, nearly transparent and direct band-gap semiconductor with the potential to be new generation thin film photoelectric conversion materials. The molecule vibration modes of monolayer and bulk WSe2 was analyzed by factor group and the phonons dispersion and vibration frequency was calculated by first-principles based on density functional theory. Furthermore, the comparison between the above calculations and experiment values of Raman shift of monolayer and bulk WSe2 was made to verify the accuracy of theoretical analysis and theoretically explain the differences of monolayer and bulk WSe2 materials in Raman spectra.

Avoidance of boron rich layer formation in the industrial boron spin-on dopant diffused n-type silicon solar cell without additional oxidation process

In the present work, the properties of boron rich layer (BRL) formed in the boron spin-on dopant diffusion as well as the avoidance of BRL formation without additional oxidation process are studied. The boron concentration distributions characterized by SIMS exhibit the formation and avoidance of BRL with the variation of oxygen content in the boron diffusion process. The existence of BRL can degrade the minority carrier lifetime due to the enhancement of recombination as well as weaken the anti-reflection effect due to the unmatched refractive index of BRL and SiO2/SiNx stack layers. The decreased minority carrier lifetime together with the increased surface reflectance eventually deteriorates the electrical behavior of solar cell with a maximum power conversion efficiency loss of 0.55%. Significantly, the formation of BRL is found to be avoided due to the complete oxidation of excess elemental boron atoms when the oxygen content increases to 10%, contributing to the recovery of solar cells’ electrical performance with an average efficiency of 19.47%. The present work will be helpful to deepen the understanding of BRL and simplify the boron diffusion process for massive cell production.

Rapid and accurate characterization of silver-paste metallization on crystalline silicon solar cells by contact-end voltage measurement

Contact-end voltage measurement was applied to characterize the contact-formation process of silver paste metallization on p- and n-type crystalline silicon solar cells under different temperatures with well-designed fixtures and test patterns based on the circular transmission line model. The contact-end voltage values were found to be sensitive to sintering temperature, and the current density and contact end voltage curves of both contacts were linear, stating that the contacts were ohmic contacts. Their symbols on the n-type emitter reversed from negative to positive under the established connection mode, which indicated conductive-path changes manifested in the form of macroscopic electrical properties under insufficient, optimal, and over-fired conditions. We inferred that the conductive channel variations were mainly caused by the silver crystallites that precipitated on the emitter surface from the combination of the cross-sectional and interface morphology analyses. No similar phenomenon was observed on the p-type emitter for the few silver crystallites or silver-aluminum alloy without conductive-path alternation. Their values were much greater than those of the n-emitter, which agreed with the present industrial n-type cell characteristics. The measurement improved our understanding of the contact formation process, and can be used as a flexible approach for researchers to optimize the silver-paste formula and sintering processes for high-efficiency solar cells.Contact-end voltage measurement was applied to characterize the contact-formation process of silver paste metallization on p- and n-type crystalline silicon solar cells under different temperatures with well-designed fixtures and test patterns based on the circular transmission line model. The contact-end voltage values were found to be sensitive to sintering temperature, and the current density and contact end voltage curves of both contacts were linear, stating that the contacts were ohmic contacts. Their symbols on the n-type emitter reversed from negative to positive under the established connection mode, which indicated conductive-path changes manifested in the form of macroscopic electrical properties under insufficient, optimal, and over-fired conditions. We inferred that the conductive channel variations were mainly caused by the silver crystallites that precipitated on the emitter surface from the combination of the cross-sectional and interface morphology analyses. No similar phenomenon was obse...