Min Zou

Investigation of the properties of plasma-enhanced chemical vapor deposited silicon nitride and its effect on silicon surface passivation

Silicon nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) are used for a variety of applications in integrated circuit and solar cell industries, such as surface passivation and insulation. The objective of this article is to investigate and understand the impact of the PECVD deposition parameters on the silicon surface passivation and establish the correlation between the properties of the silicon nitride and the ensuing silicon surface recombination velocity. All the films were annealed at 350 °C for 20 min in a rapid thermal annealer after the deposition. It is shown that bonded hydrogen and positive charge in the annealed PECVD silicon nitride films have the opposite effect on the surface passivation. The surface recombination velocity decreases with the increase in the positive charge density and the decrease in the bonded hydrogen content. It is found that the deposition temperature has the most influence on achieving low surface recombination velocity. Higher deposition tempe...

Wear-Resistant PTFE/SiO2 Nanoparticle Composite Films

Polytetrafluoroethylene (PTFE) is a polymer that is well known for its exceptional tribological properties and, as such, it is commonly used to reduce the coefficient of friction between surfaces. In recent years it has also been established that by incorporating nanoparticle fillers in PTFE, it is possible to extend the polymers life by reducing its wear rate. Although much study has been placed on bulk PTFE, very little study has been focused on thin films. This article demonstrates that SiO 2 nanoparticles can be used as a filler to significantly reduce the wear of PTFE thin films while also maintaining a low coefficient of friction. The wear resistance and coefficient of friction of PTFE/SiO 2 composite films on stainless steel substrates were tested using a linear reciprocating tribometer and compared to pure PTFE films and bare stainless steel to evaluate the benefit of incorporating the SiO 2 filler in the film. The composite films showed a significant improvement in wear resistance when compared to pure PTFE films. The coefficient of friction for the composite film remained low and stable during a 50 g normal load friction test for a duration of approximately 300 cycles, whereas that of PTFE showed an increasing trend at onset. In addition, of 1.7 and 3.3 wt% SiO 2 concentrations in solution, 3.3 wt% SiO 2 showed better performance, with a much higher wear resistance than that of 1.7% SiO 2 after being subjected to a 1,000-cycle abrasive wear test.

Clearance Control of a Mechanical Face Seal

Seal clearance control is an advancement in noncontacting mechanical face seal operation because seal clearance variation caused by process disturbances may cause either severe face contact or excessive leakage, each of which is regarded as seal failure. The objective of this research is to control the seal clearance at a desired value overcoming operation disturbances, including variations in shaft speed and sealed fluid pressure. A flexibly mounted rotor (FMR) noncontacting mechanical face seal test rig is used in this study. The clearance control concept is to adjust the closing force that acts upon the flexibly mounted rotor. The seal clearance is measured by an eddy current proximity probe. The seal axial dynamic model is experimentally determined for the design of a proportional-integral (PI) controller with anti-windup. The controller is then applied to the test seal. Results show that the controlled seal maintains or follows set-point clearance changes with and without disturbances in sealed water...

Contact elimination in mechanical face seals using active control

Wear and failure of mechanical seals may be critical in certain applications and should be avoided. Large relative misalignment between the seal faces is the most likely cause for intermittent contact and the increased friction that eventually brings failure. Adjustment of the seal clearance is probably the most readily implemented method of reducing the relative misalignment and eliminating seal face contact during operation. This method is demonstrated with the aid. of a noncontacting flexibly mounted rotor mechanical face seal test rig employing a cascade control scheme. Eddy current proximity probes measure the seal clearance directly. The inner loop controls the clearance, maintaining a desired gap by adjusting the air pressure in the rotor chamber of the seal. When contact is detected the outer loop adjusts the clearance set point according to variance differences in the probes signals. These differences in variance were found to be a reliable quantitative indication for such contacts. They are complimentary to other more qualitative phenomenological indications, and provide the controlled variable data for the outer loop. Experiments are conducted to test and verify this active control scheme and strategy. The analysis and results both show that contrary to intuition for the seal under investigation, reducing seal clearance can eliminate contact, and the outer cascade loop indeed drives the control toward this solution.

Feasibility of Contact Elimination of a Mechanical Face Seal Through Clearance Adjustment

The feasibility of eliminating contact in a noncontacting flexibly mounted rotor (FMR) mechanical face seal is studied. The approach for contact elimination is based on a parametric study using FMR seal dynamics. Through clearance adjustment it is possible to reduce the maximum normalized relative misalignment between seal faces and, therefore, eliminate seal face contact. Clearance is measured by proximity probes and varied through a pneumatic adjustment mechanism. Contact is determined phenomenologically from pattern recognition of probe signals and their power spectrum densities as well as angular misalignment orbit plots, all calculated and displayed in real-time. The contact elimination strategy is experimentally investigated for various values of stator misalignment and initial rotor misalignment. Contrary to intuition but compliant with the parametric study, the experimental results show that for the seal under consideration contact can be eliminated through clearance reduction.

Dynamic simulation and monitoring of a non-contacting flexibly mounted rotor mechanical face seal

Abstract Mechanical face seal rotor dynamics is investigated through both simulation and real-time monitoring of a non-contacting flexibly mounted rotor (FMR) mechanical face seal in a seal test rig. Dynamic simulation is performed to investigate the seal rotor angular response to the stator misalignment, the stator angle, the initial rotor misalignment and clearance. Rotor angular response orbit is introduced and is able to characterize the rotor dynamic response. A real-time monitoring system is constructed in the test rig to monitor the instantaneous dynamic behaviour of the seal rotor, including its angularresponse, precession angle and angular response orbit. Experimental results agree qualitatively well with those of the dynamic simulation. Potential applications of the monitoring system for detecting seal face contact and for seal control are stated.

Real-time Condition Monitoring of Mechanical Face Seal

Mechanical face seals are the most versatile type of rotating shaft seal. Despite their wide applications in industry, mechanical face seals generally have unpredictable life and their premature and random failure is not uncommon. Seal failure is often characterized by worn faces caused by rubbing contact between the rotor and the stator. In critical applications, such as nuclear reactor cooling pumps or liquid oxygen (LOX) turbopumps seal failure may have severe implications. There is, therefore, a need to detect, monitor and control the unwanted contact between the rotor and stator during seal operation. In this research, methods of detecting contact between the rotor and the stator in real-time have been developed for a FMR noncontacting mechanical face seal test rig. The rotor angular misalignment orbit is introduced for mechanical seal condition monitoring. A monitoring system has been constructed to detect seal contact and monitor the dynamic behavior of mechanical face seal in real-time.

Silicon Nanowires by Aluminum-Induced Crystallization of Amorphous Silicon

This paper discusses controlled studies on the effect of stress on the formation of silicon nanowires (SiNWs) produced by aluminum-induced crystallization (AIC) of plasma-enhanced chemical vapor deposited amorphous silicon (a-Si:H). The impact of stress on the growth of SiNWs was completely decoupled from other factors such as a-Si:H and Al deposition parameters and rapid thermal annealing conditions. This study shows, that AIC of a-Si:H can be used to fabricate SiNWs through the combination of rapid thermal annealing and stress adjustment.

Diamond-like carbon coatings with zirconium-containing interlayers for orthopedic implants

Six types of diamond-like carbon (DLC) coatings with zirconium (Zr)-containing interlayers on titanium alloy (Ti-6Al-4V) were investigated for improving the biotribological performance of orthopedic implants. The coatings consist of three layers: above the substrate a layer stack of 32 alternating Zr and ZrN sublayers (Zr:ZrN), followed by a layer comprised of Zr and DLC (Zr:DLC), and finally a N-doped DLC layer. The Zr:ZrN layer is designed for increasing load carrying capacity and corrosion resistance; the Zr:DLC layer is for gradual transition of stress, thus enhancing layer adhesion; and the N-doped DLC layer is for decreasing friction, squeaking noises and wear. Biotribological experiments were performed in simulated body fluid employing a ball-on-disc contact with a Si3N4 ball and a rotational oscillating motion to mimic hip motion in terms of gait angle, dynamic contact pressures, speed and body temperature. The results showed that the Zr:DLC layer has a substantial influence on eliminating delamination of the DLC from the substrates. The DLC/Si3N4 pairs significantly reduced friction coefficient, squeaking noise and wear of both the Si3N4 balls and the discs compared to those of the Ti-6Al-4V/Si3N4 pair after testing for a duration that is equivalent to one year of hip motion in vivo.

Production of a superhydrophilic surface by aluminum-induced crystallization of amorphous silicon

The wettability of glass substrates textured via aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) was studied. It was found that a stable superhydrophilic surface could be produced by AIC of a-Si. This research suggests that densely distributed micron-sized silicon islands with nanoscale silicon spikes produced by the technique of AIC of a-Si are responsible for the stable superhydrophilicity. The study also shows that these superhydrophilic surfaces can be easily converted to superhydrophobic ones by means of coating with C(4)F(8).