Deformation and fracture of single-crystal and sintered polycrystalline silicon carbide produced by cavitation

An investigation was conducted to examine the deformation and fracture behavior of single-crystal and sintered polycrystalline SiC surfaces exposed to cavitation. Cavitation erosion experiments were conducted in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (1 mm) to the surface of SiC. The horn frequency was 20 kHz, and the double amplitude of the vibrating disk was 50 microns. The results of the investigation indicate that the SiC (0001) surface could be deformed in a plastic manner during cavitation. Dislocation etch pits were formed when the surface was chemically etched. The number of defects, including dislocations in the SiC (0001) surface, increased with increasing exposure time to cavitation. The presence of intrinsic defects such as voids in the surficial layers of the sintered polycrystalline SiC determined the zones at which fractured grains and fracture pits (pores) were generated. Single-crystal SiC had superior erosion resistance to that of sintered polycrystalline SiC

Prediction of cavitation erosion based on the measurement of bubble collapse impact loads

The prediction of cavitation erosion rates is important in order to evaluate the exact life of components in fluid machineries. The measurement of impact loads in bubble collapses helps us to predict the life under cavitation erosion. In this study, we carried out the erosion tests and measured impact loads in bubble collapses with a cavitating liquid jet apparatus which complies with the ASTM G134-95 standard. The bubble collapse impact loads were measured by a piezo ceramic transducer in a cavitating liquid jet apparatus. To produce various cavitation conditions, the flow velocity was changed from 184 down to 80 m/s. We evaluated the incubation period based on a cumulative damage rule by measuring the impact loads of cavitation acting on the specimen surface and by using the constant impact load number of impact curve similar to the modified Miner s rule which is employed for fatigue life prediction. We found that the parameter ?(Fi?×ni) (Fi: impact load, ni: number of impacts and ?:constant) is suitable for the evaluation of the erosion life. After the constant ? has been obtained under two different cavitation conditions, we can predict the incubation period with the cavitating liquid jet method under yet another condition, provided that the bubble collapse impact loads are measured.http://deepblue.lib.umich.edu/bitstream/2027.42/84234/1/CAV2009-final33.pd

Comparison of cavitation erosion rate with liquid impingement erosion rate.

Both cavitation erosion and liquid impingement erosion are phenomena that can cause pipe wall thinning in power plants. The Code for Power Generation Facilities, Rules on Pipe Wall Thinning Management, was published by the JSME (Japan Society of Mechanical Engineers) in 2005. The code says that cavitation erosion shall be prevented either in the design stage or by daily inspection. On the other hand, liquid impingement erosion can occur in any location where a working fluid attacks a pipe wall at high flow velocities. Therefore, it is very important to evaluate the amount of erosion by liquid impingement for pipe steels quantitatively from the viewpoint of aging management. In this study, we carried out both cavitation erosion and liquid impingement erosion tests, and clarified the relation between the two erosion rates. As a result, we found that the erosion rate by cavitation increases in proportion with the 5.2th to 6.8th power of the flow velocity and that by liquid impingement with the 6.0th to 7.4th power. Moreover, a good correlation was obtained between erosion rates by cavitation and by liquid impingement. We also discussed the erosion mechanism with SEM photography, and proposed an erosion model.http://deepblue.lib.umich.edu/bitstream/2027.42/84233/1/CAV2009-final32.pd

Evaluation of incipient cavitation erosion for pipe wall at downstream of an orifice

Cavitation induced vibration and the consequent erosion of pipes are the potential damaging factors in the piping systems. In order to prevent such trouble, it is preferable to develop a detection method for cavitation occurrence. Especially, in power plants, it is necessary to detect cavitation from the outside of the piping during operation. In this paper, in order to evaluate incipience of cavitation erosion, we carried out cavitation erosion experiments using aluminium specimens and we measured impulsive force induced by cavitation bubbles collapse using impact force detectors. In the cavitation erosion experiments, the incipient cavitation numbers, where cavitation erosion pits occured, were 0.8 at 50mm and 75mm downstream from the orifice and 0.7 at 100mm downstream. At those cavitation numbers, the states of cavitation was in a developed state or nearly so. In the measurements of impulsive force, the cavitation number, where impulsive force began to increase, was almost with the same as cavitation numbers at the occurrence of erosion pits.http://deepblue.lib.umich.edu/bitstream/2027.42/84261/1/CAV2009-final64.pd

Fundamental Study on Cavitatit Erosion Using a NiTi Shape Memory Alloy

In order to clarify the role of slip deformation on cavitation erosion, vibratory cavitation tests were carried out for a NiTi shape memory alloy in martensitic phase and austenitic phase. This alloy deforms plastically by the combination of slip and twinning deformation, and the erosion resistance of NiTi shape memory alloy is 500 to l 000 times higher than that of SUS316 stainless steel. The erosion resistance of austenitic phase is superior to martensitic phase, because the accumulation of slip in the austenitic phase is slower due to the superelasticity than that in the martensitic phase. The martensitic phase test with intermittent shape recovery shows a better resistance without the shape recovery, since the deformation twins produced by cavitation erosion test are eliminated by shape recovery, resulting in the delay of slip accumulation. However, the amount of shape recovery was decreased with test duration. The decreasing rate of shape recovery has a good linear relationship with the volume loss rate. It was concluded that the accumulation of slip deformation corresponds well with the volume Ivss rate

Cavitation erosion of silver plated coating considering thermodynamic effect

SUMMARY Cavitation often occurs in inducer pumps of space rockets. Silver plated coatings on the inducer liner face the damage of cavitation. In this study, we carried out cavitation erosion tests using silver plated coatings with different thermodynamic parameters at a constant cavitation number. Then we carried out cavitation erosion tests using some liquids with the same thermodynamic parameter and cavitation number as liquid oxygen. The thermodynamic parameter proposed by Brennen was used. The liquids used for the cavitation erosion tests were water, ethanol and hexane. We discuss the relation between the thermodynamic parameter and the mass loss rate, and the relation between acoustic impedance and the mass loss rate

Urinary ACE2 in pediatric IgA nephropathy

Background : Our previous studies demonstrated that the intrarenal renin-angiotensin system (RAS) status was activated in pediatric patients with chronic glomerulonephritis. In the present study, we tested the hypothesis that angiotensin-converting enzyme 2 (ACE2) expression in the kidney is associated with the development of pediatric IgA nephropathy. Methods : We analyzed urinary ACE2 levels and ACE2 expression in the kidney tissues of pediatric patients with IgA nephropathy treated with RAS blockade. Paired tests were used to analyze changes from the first to the second biopsy. Results : Urinary ACE2 levels were significantly decreased after RAS blockade treatment, accompanied by decreased ACE2 expression levels in kidney tissues, urinary protein levels and mesangial hypercellularity scores. Urinary ACE2 levels at the first biopsy were positively correlated with the ACE2 expression levels. Conclusions : These data suggest that urinary ACE2 is associated with ACE2 expression in the diseased kidney, which correlates with the pathogenesis of IgA nephropathy in pediatric patients

An application of bubble collapse pulse height spectra to venturi cavitation erosion of 1100-o aluminum

Venturi cavitation erosion tests were performed and correlated with bubble collapse pulse height spectra measured by a microtransducer. The effects of the throat velocity and the cavitation number [sigma] (referred to the downstream pressure and throat velocity) on the erosion rate (MDPR) were studied. The velocity damage exponent was 4.11 for 0.62 [les] [sigma] [les] 0.80, while the MDPR is almost independent of velocity for [sigma] = 0.85. The MDPR decreases with increased [sigma] for 0.62 [les] [sigma] [les] 0.85. The data were reduced to "acoustic power" (from pulse height spectra) and "erosion power" (the ultimate resilience multiplied by the MDPR). A near-linear relationship was found between these. Their reciprocal ratio [eta]cav [approximate] 7 x 10-11. For [sigma] = 0.62, the data deviated from the others, possibly because of the work hardening of the eroded surface.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25661/1/0000213.pd

Synthesis of carbon nanotubes by microwave heating: Influence of diameter of catalytic Ni nanoparticles on diameter of CNTs

We rapidly synthesized multi walled carbon nanotubes (MWCNTs) by calcination of granulated polystyrene with nickel nanoparticles having different average diameter (D-Ni = 10, 20, 50 or 90 nm) under nitrogen gas at a certain temperature and time (700 degrees C, 15 min or 800 degrees C, 10 min), using a domestic microwave oven in order to systematically investigate the influence of the diameter of nickel nanoparticles on the diameter of MWCNTs. The MWCNTs synthesized here were characterized by a transmission electron microscope, a Raman spectrophotometer and a wide angle X-ray diffractometer. We found that for the calcination condition of (800 degrees C, 10 min), a relationship between the outer diameter of the resulted carbon nanotubes (D-CNT) and the diameter of catalytic nickel nanoparticles (D-Ni) can be described as a linear function, D-CNT = 1.01D(Ni) + 14.79 nm with the correlation coefficient R = 0.99, and that for the calcination condition of 700 degrees C, 15 min, D-CNT = 1.12D(Ni) + 7.80 nm with R = 0.95. Thus, we revealed that when the diameter of the catalytic nickel nanoparticles (D-Ni) increases by 1 nm, the outer diameter of the obtained MWCNTs (D-CNT) increases by about 1 nm.ArticleJOURNAL OF MATERIALS CHEMISTRY A. 2(8):2773-2780 (2014)journal articl