Ablation resistance

During the ablation experiment, temperature within the char layer exceeds 1000°C and approach 2000-2500°C at the surface. At these temperatures, any carbonaceous residue from the pol3oner will contain graphite. Additionally, mica-type layered silicates, such as montmorillonite, irreversibly transform into other aluminosilicate phases. Between 600 and 1000 C, montmorillonite dehydroxylates and has been observed to initially transform into spinel, cristobolite, mullite and/or pyroxenes (enstatite) (24). At temperatures greater than 1300 C, mullite, cristobolite and cordierite form and subsequently melt at temperatures in excess of 1500 C (mullite 1850 C, pure cristobolite 1728°C and cordierite --ISSO C) (25). The presence of an inorganic that transforms into a high viscosity melt on the surface of the char will improve ablation resistance by flowing to self-heal surface flaws. This is known to occur in silica-filled ablatives (26). 

Structural silica or quartz fibers made by downdrawing have diameters ranging from 7 to 14 jm rovings are made with up to 4800 filaments. These fibers offer superior heat resistance since they retain useful strength at very high temperatures. They also possess the high ablation resistance and the dielectric, acoustic, optical and chemical properties of quartz from... 

Liu et al. [72] used POSS nanomodification in phenolic resin with carbon fiber reinforcement. SEM analysis showed the production of best charred surface on burnt samples that enhanced the ablation performance. Novel flake graphite was introduced into barium-phenolic resin by Yu and Wan [73]. Nanocomposites were made by roller-coating technology and its ablation property was tested under long pulse laser radiation. Nanocomposites showed better ablation performance compared to the control system. It was also observed that the size of the graphite flake affected the ablation rate [73]. Srikanth et al. [74] prepared ablative nanocomposites by introducing nanosilica into the phenolic resin with carbon fiber reinforcement. Ablation resistance of nanocomposites increased with the nanosilica content up to 2 wt%. However, beyond this point ablation resistance decreased. 

Ablation resistance is an important property of composites, with thinner ablative structures desired to reduce the overall weight of aerospace systems. Phenolic resins easily char during endothermic pyrolysis, leading to the application of phenolic composites as ablative materials for rocket nozzles (Srikanth et al, 2010). A phenolic matrix with a high content of carbon nanofibers (CNFs) was demonstrated to be highly appropriate for rocket nozzle applications (Yoonessi et al., 2008). 

G R (2010), Nano silica modified carbon-phenolic composites for enhanced ablation resistance , Scr Mater, 63, 200-203, and references therein. 

In the manufacture of the casings of solid rocket motor (SRM), the material requirements are bifunctional. They have to have high hoop strength on one side and high ablation resistance on the other. In order to prepare such materials, the technology of coextrusion is utilized. In a twin-screw extruder, both the materials are coextruded together. During the residence time of the polymers in the extruder, the interdiffusion of either material in the other occurs. Calculate the interlayer thickness as a function of the extruder residence time and diffusivities of the two materials. 

Earlier work on the applications carried out up to 2002 was concerned with mechanical and thermal properties and ablation resistance. Thus, vapor-grown carbon fiber-reinforced phenolic resin composites have been evaluated for use in soUd rocket motor nozzles. 

Corral, E. L., Walker, L. S. (2010). Improved ablation resistance of C-C composites using zirconium diboride and boron carbide. Journal of the European Ceramic Society, 30, 2357-2364. doi 10.1016/j.jeurceramsoc.2010.02.025. 

ZrC with high melting point (3445°C), low density and excellent ablation-resistance is one of the most promising candidates for ultra-high temperature applications (Stroms, 1997 Upadhyaetal., 1997). Especially, continuous carbon fiber reinforced ZrC composite (C/ZrC) against the brittleness of monolithic ZrC ceramic attracts much attention. 

RMI can achieve near-net shape manufacturing with quick processing time and low cost. The present investigations mainly focus on the fabrication process of simple shaped materials and property evaluation of the as-produced materials. Complex shaped components with excellent ablation resistance and high strength are needed in the future applications. Efforts should be made to fabricate these complex shaped components with excellent properties by RMI. 

Li, H., Zhang, L., Cheng, L., Wang, Y. (2009). Ablation resistance of different coating structures for C/ZrB,-SiC composite under oxyacetylene torch flame. Int. J. Appl. Ceram. TechnoL, 6,145-150. doi 10.1111/j.l744-7402.2008.02320.x. 

In this chapter, the pyrolysis of synthesized polymers, microstructure of their derived UHTC composite matrices, as well the preparation and properties of C/C-ZrB2-ZrC-SiC composites are investigated. Preparation and microstructures of the composites were studied in part I of the paper. The ablation behaviors and mechanical properties of the composites in a ground arc-jet wind tunnel and plasma torch with temperatures above 2000 °C and heating rate around 30K/s were studied in Part II. The major aims of these studies were to evaluate the possibility of producing a nano-size dispersed ZrB -ZrC-SiC matrix using these complex polymeric precursors, which are expected to exhibit improved oxidation and ablation resistance, compared to those composites with layered or large particle incorporated UHTC matrices. 

Plasma arc-jet and oxyacetylene torch ablation tests are much more convenient for operations and with much lower cost, which therefore are often used for primary evaluations of materials about their thermal shock resistance and ablation resistance properties . The difference between these two methods is their gaseous composition and flow speed. A plasma of air may exhibit ultra high temperatures above 5000°C and high velocities of 2 Mach but with ionized air atmosphere. On the other hand, the generally used oxyacetylene torch is of combustion gaseous products of carbon mono/dioxide, water vapor, OH and active hydrocarbon species with gas velocity less than 1 Mach and temperatures above 3000°C. A HVOF torch exhibits... 

The high-temperature ablation and thermal shock properties of ZrCAV and TiCAV composites are tested with an oxyacetylene equipment. Both TiC and ZrC increase remarkably tbe ablation resistance of tungsten composites. ZrCAV comoposites exhibit better ablation than TiCAV composites. 

Song, G. M., Wang, Y. J., Zhou, Y. (2001). Elevated temperature ablation resistance and thermophysical properties of tungsten matrix composites reinforced with ZrC particle. Journal of Materials Science, 3(5,4625 631. doi 10.1023/A 1017989913219. 

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