Peng Mou

A review of mechanochemistry applications in waste management

Mechanochemistry is defined to describe the chemical and physicochemical transformation of substances during the aggregation caused by the mechanical energy. Mechanochemical technology has several advantages, such as simple process, ecological safety and the possibility of obtaining a product in the metastable state. It potentially has a prospective application in pollution remediation and waste management. Therefore, this paper aims to give an overall review of the mechanochemistry applications in waste management and the related mechanisms. Based on our study, the modification of fly ash and asbestos-containing wastes (ACWs) can be achieved by mechanochemical technology. Waste metal oxides can be transformed into easily recyclable sulfide by mechanochemical sulfidization. Besides, the waste plastics and rubbers, which are usually very difficult to be recycled, can also be recycled by mechanochemical technology.

Products made from nonmetallic materials reclaimed from waste printed circuit boards

Abstract Printed circuit boards (PCBs) are in all electronic equipment, so with the sharp increase of electronic waste, the recovery of PCB components has become a critical research field. This paper presents a study of the reclaimation and reuse of nonmetallic materials recovered from waste PCBs. Mechanical processes, such as crushing, milling, and separation, were used to process waste PCBs. Nonmetallic materials in the PCBs were separated using density-based separation with separation rates in excess of 95%. The recovered nonmetals were used to make models, construction materials, composite boards, sewer grates, and amusement park boats. The PCB nonmetal products have better mechanical characteristics and durability than traditional materials and fillers. The flexural strength of the PCB nonmetallic material composite boards is 30% greater than that of standard products. Products derived from PCB waste processing have been brought into industrial production. The study shows that PCB nonmetals can be reused in profitable and environmentally friendly ways.

Simulation-Based Optimization of a Vector Showerhead System for the Control of Flow Field Profile in a Vertical Reactor Chamber

Optimization of a vector showerhead in a vertical reactor involves thousands of holes on the showerhead face plate and the spatial distribution of physical fields, so parameterizing the geometry configuration of the holes in high resolution is very difficult, which makes the conventional optimization methods hard to deal with. To solve this problem, a profile error feedback (PEF) optimization solution was proposed to optimize a vector showerhead gas delivery system for the control of mass transport. The gas velocity profile in the reactor and the continuous-feature impedance distribution profile on the showerhead face plate are defined as design objective and variables, respectively. A cyclic iterative approximation idea was implemented in this solution. The algorithm was started from a guessed initial design model and then cyclically adjusted the design variables by the constructed PEF iterative formula to generate a better model and to make the gas velocity profile in the critical domain of the new model continually approximate to the expected profile, until it could be accepted. Finally, the optimized impedance profile was mapped to the holes geometry configuration through the established equivalent impedance model for the showerhead face plate.

New simulation-based approach for the profile control in a process chamber: Fluid, thermal, and plasma profile:

Process chamber is the core unit of chemical vapor deposition and etching, and the physical fields in it have fatal effect on process quality. It is significant and difficult for improving the process performance to regulate the fields’ profiles finely. Two design solutions for the profile regulation are proposed: controllable type and resistance type. A novel profile error feedback method is presented, and a simulation-based auto-design framework is established. The profile error feedback method is in a quasi-closed-loop-control mode. It starts from an initial guessed sequence of the design/control variables and predicts a better sequence via feedback of the profile error between the output-targeted profile and the expected one. It never stops until the profile error is narrowed in the preset tolerance. Three kinds of numerical experiments about the regulation of the thermal, fluid, and plasma profile are set to test the effectiveness and feasibility of the profile error feedback method and the two kinds of design schemes.

Devulcanization of Waste Tire Rubber Vulcanizate through a Mechanochemical Pan Milling at Ambient Temperature

The partially devulcanization of waste tire rubber vulcanizate was carried out with the newly developed mechanochemical pan mill, which can exert fairly strong compressing and shearing force on the milling materials and avoid the agglomeration phenomenon. The experimental results indicate that the particle size is greatly reduced and the surface is fluffier, crosslink density is reduced to one half without large degradation and heavy damage of rubber backbones. The study of mechanical properties of revulcanizate of SBR and waste tire rubber blends at 1:1 ratio indicates that elongation at break increased from 302% to 447.6%. But the properties of tensile strength, modulus and hardness are reduced. The mechanochemical pan milling process is a simple, low cost and environmental-benign process for waste tire rubber devulcanization at ambient temperature without any use of chemicals and can be used at commercial-scale.

Modeling and case study of the regional e-waste reverse logistics system

This research proposed a variant Weber-triangle model based on various costs and industrial accumulation effect to analyze the location preference of e-waste reverse logistics system and to find out the actual and main factors that determine the regional development of an e-waste reverse logistics system. Finally, a PCB recycling industry is discussed as a case study.

The segmented non-uniform dielectric module design for uniformity control of plasma profile in a capacitively coupled plasma chamber

Low-temperature plasma technique is one of the critical techniques in IC manufacturing process, such as etching and thin-film deposition, and the uniformity greatly impacts the process quality, so the design for the plasma uniformity control is very important but difficult. It is hard to finely and flexibly regulate the spatial distribution of the plasma in the chamber via controlling the discharge parameters or modifying the structure in zero-dimensional space, and it just can adjust the overall level of the process factors. In the view of this problem, a segmented non-uniform dielectric module design solution is proposed for the regulation of the plasma profile in a CCP chamber. The solution achieves refined and flexible regulation of the plasma profile in the radial direction via configuring the relative permittivity and the width of each segment. In order to solve this design problem, a novel simulation-based auto-design approach is proposed, which can automatically design the positional sequence with multi independent variables to make the output target profile in the parameterized simulation model approximate the one that users preset. This approach employs an idea of quasi-closed-loop control system, and works in an iterative mode. It starts from initial values of the design variable sequences, and predicts better sequences via the feedback of the profile error between the output target profile and the expected one. It never stops until the profile error is narrowed in the preset tolerance.

Analysis and Modeling of Wafer Thermal Transfer in a PECVD Reactor

The temperature distribution in the reactor, especially on the surface of the wafer, is the important factors influencing the chemical reaction in CVD and PECVD process. This paper focused on a typical cylindrical PECVD reactor carrying with a wafer, and established the combination calculation model, which divided the chamber system into two calculation domains according to the rarefied degree of the gases. A one-dimensional thermal model was developed to calculate the temperature profiles in the narrow gap between the wafer and the heater, considering the heat conduction, radiation and thermal accommodation phenomenon between the gas and the surfaces in low pressure conditions; a two-dimensional axisymmetric model was applied to calculate the temperature profiles in the chamber above the wafer, considering the heat conduction, radiation and mass transfer. We verified the validity of the model through the experimental measurement in different pressure with the aluminum matrix pedestal and the one without. The experiment and numerical calculation both pointed out that there are 15~30K temperature drop in the narrow gap between the wafer and heater with the pressure of 1~10Torr at the outlet of the chamber, the mass flow of 5000sccm at the inlet, and the fixed temperature of 673K within the heater. The lower the pressure was, the greater the differences were, and it presented a negative exponential relation. In addition, this paper predicted the response of the wafer surface temperature to the change of the narrow gap height and chamber pressure via numerical calculation model. The results showed a negative linear relationship between the wafer top surface temperature and the narrow gap height. When the narrow gap height was changed in the range of 0.15~2mm and chamber pressure of 1~10Torr, the temperature of wafer will drop 0.5~5.5K.

The Disassembly Process and Apparatus of Waste Printed Circuit Board Assembly for Reusing the Components

Printed Circuit Board Assembly (PCBA), is an important basic part of Electric and Electronic Equipment, which has lots of high-value components and toxic substances. Normally, when Electric and Electronic Equipment (EEE) is scraped, some components on waste PCBA still keep good performances. Therefore, it is feasible and economical to environment-friendly reuse the high-value components on waste PCBA. In order to guarantee the quality of the disassembled components, the components reuse-oriented disassembly process is proposed, in which the mechanical and physical characteristics of solder and the joint type of PCBA are considered comprehensively. In the process, through the analysis and measurement of the temperature distribution of PCBA, the optimized heating mode and heating temperature curve can be drawn up for the different joint type of PCBA. For getting the disassembly mode of PCBA, the disassembly force and separating displacement of components on PCBA are defined and the disassembly energy models for different kinds of components are set up. On the basis of the heating mode, heating temperature curve and disassembly energy, two kinds of disassembly apparatus and a performance testing procedure for certain kinds of old components are developed. In the end the components reuse-oriented disassembly process parameters are optimized to get a high separation ratio and reuse ration of components with orthogonal test.

Mathematical and Simulation Modelling of Moisture Diffusion Mechanism during Plastic IC Packages Disassembly

Reuse of plastic IC packages disassembled from printed circuit boards (PCBs) has significant environmental benefits and economic value. The interface delamination caused by moisture diffusion is the main failure mode of IC packages during the disassembling process, which greatly reduces the reusability and reliability of disassembled IC packages. Exploring moisture diffusion mechanism is a prerequisite to optimize prebaking processes before disassembling that is an effective way to avoid the interface delamination. To this end, a computational model with variable boundary conditions is developed based on the different combination state of water in IC packages. The distribution characteristics and mechanism of moisture diffusion behavior are analyzed including the humidity distribution field and the relation among baking temperature, water loss rate, and baking time during baking process, and then the results are validated by FEA simulation based on the improved definition of relative moisture concentration. Baking under variable temperature is proposed and compared with the baking process and baking efficiency under constant temperature to find out the optimized baking parameters. Finally, a set of curves which indicate the relation between baking energy consumption and temperature are determined under actual industrial baking experiments, which could be used as references to develop industrial standards for PCB disassembling process.