PIP cycle

The Raman spectroscopic work of Ja-covitz [31], Comilsen et al. [32, 33], and Audemer et al. [34] is the most direct spectroscopic evidence that the discharge product in battery electrodes, operating of the pip cycle, is different from well-crystallized yS-Ni(OH)2. The O-H stretching modes and the lattice modes in the Raman spectra are different from those found for well-crystallized Ni(OH)2, prepared by recrystallization from the ammonia complex, and are more similar to those... 

Recent ECQM work and X-ray diffraction have confirmed the conversion of the cdy cycle to the piP cycle up on electrochemical cycling in concentrated alkali. Earlier ECQM studies of -Ni(OH)2 films had shown a mass inversion in the microgravimetric curve after prolonged cycling [64] there is a mass decrease in charge instead of a mass increase. More recent work has confirmed that this mass... 

A systematic effort is therefore required to investigate the effect of porosity < i the durability performance of ceramic matrix composites. A Polymer Infiltration Pyrolysis (PIP) CMC system was chosen for this effort based on past work of the authors [5-7]. The PIP system also should allow different porosity levels as most PIP systems require multiple infiltrations. By stopping the manufacturing process at different infiltration cycles, different porosity levels will be produced in the material. The results of mechanical and durability testing on composite material produced at four different PIP cycles are explored in this paper. 

The material system used for this effort was the SiC/SiNC system with CG-Nicalon fibers (a non>stoichiometric SiC fiber). The matrix of Si, N and C was arrived at by set iterations via the polymer pyrolysis process. The initial processing step was compression molding followed by repeated infiltration cycles. For the present worfc, material subjected to 5,7,9 and 11 PIP cycles were considered. The lay-up of all the panels considered here is [0/90]2s resulting in an 8 ply composite. Additional material information has been published by the authors [3,5]. For this test series, each panel was 150 mm x 150 mm x the as-received thickness of the material. This allowed 8 tensile bars to be machined out of the panel as well as 4 interlaminar tensile buttons. 

For each of the 4 different PIP cycles, two tensile tests were done at room temperature and two tests were done at 982 C. The results of the testing are shown in Table I. The trend in the data is that the proportional limit and tensile modulus increase with increasing number of PIP cycles with only a slight difference between 9 and 11 PIP cycle materials. The ultimate tensile strength and strain to failure is the lowest for the 5-PIP cycle panel and relatively constant for the other three PIP cycles. 

There were two fatigue and two creep samples from each of the PIP cycle panels. The creep testing has not been completed and will not be discussed iurther. The results of the fatigue testing are shown in Table III. This table clearly shows that the highest number of cycles to failure is seen for the 7-PIP cycle panel. 

PIP Cycles ( ) Siiinple ID Test Temperaluio ( < ) Peak Cyclic Stress (MPa) R Ratio Cycles to Failure... 

A typical micro-structural cross section of the CMC material is shown in Figure 1. As can be seen, there are large and medium size pores present in the matrix of the material as well as smaller pores within the fiber tows. A porosity analysis was done on material from several tab regions from various samples and the percent porosity from this effort is found in Table IV. This table shows that there is not a clear trend in lower porosity with increasing number of PIP cycles. 

PIP Cycles ( ) Test Temperature C F) Tensile Modulus (MPa) Optical Porosity (%) X-ray CT Porosity (%)... 

A series of panels were made with differing number of PIP cycles with the expectation that this would result in different overall porosity levels. The optical and x-ray porosity analysis did not confirm this trend and some of the properties did not follow the expected trend with increasing number of infiltration cycles. It was found fiom fast fracture studies that the overall diffusivity is controlled by the microstructure and therefore the porosity correlates with tensile properties. No clear correlation between porosity and properties was observed from the durability testing done. Durability appears to be controlled by the location and distribution of the porosity. Additional testing and analysis is needed to shed insight on the material performance. 

The advancement of PIP method of the porous C/C composites with an initial bulk density of 0.68g/cm and open porosity of 60% was examined by density measurements. The bulk density of the C/C-ZrB -ZrC-SiC composites produced according to the number of PIP cycles is shown in Figure 7, which corresponds volume ratios of the formed ZrB 2 ZrC SiC matrix of 20 30 50 (Table 3). It shows a gradual decrease in the impregnation efficiency with increasing of the number of PIP cycles. After 16 PIP cycles, the bulk density increases by less than 2%. 

Figure 7. Bulk density versus numbers of PIP cycles of the composite showing a finial bulk density of 2.1 g/crn was obtained...

Therefore, further impregnations will not significantly increase its bulk density. The composites were prepared after 16 PIP cycles with a bulk density of 2.06 g/cm and open porosity of 9.6%. 

Preparation process and microstructure investigation of the novel C/C-ZrB -ZrC-SiC have been reported in the previous chapter The composite contained a 2D carbon fiber non-woven architecture with fiber volume fraction of 17.6%, with pyrolytic carbon deposited on carbon fiber by CVI as interphase with a volume fraction of 22.3%. The obtained porous C/C composite exhibited a bulk density of 0.68g/cm, 50 vol% ZrB2-ZrC-SiC matrix and 9.6 vol% open porosity. The homogeneous dispersed ZrB2-ZrC-SiC complex ceramic matrix was formed inside this porous C/C composites by PIP technique using a blending ZrB -ZrC-SiC pre-ceramic polymeric precursors solution in xylene. The finial bulk density of the fabricated composite is 2.06 g/cm (details were reported in Part 1) after 16 PIP cycles. Finther densi-fication was difficult because of limitation of low residual porosity and ceramic yields from these precursors. PIP under ultra high pressure may further decrease the residual porosity of the composite but this was not conducted in this study due to the lack of this device. 

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