Active‐to‐Passive Transition in the Oxidation of Silicon Carbide and Silicon Nitride in Air

Vaughn, Wallace L.; Maahs, Howard G.

doi:10.1111/j.1151-2916.1990.tb09793.x

Cited by 249 publications

(107 citation statements)

References 7 publications

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“…Due to high viscocity of material fusant, gas volatilization causes general bulging of material. With decrease of sintering temperature, the "pits" formed after gas volatilization in fusant are preserved and dense closed pores appeared in material, thereby forming porous and light structure [9,10].…”

Section: Foaming Theorymentioning

confidence: 99%

Process and Properties Study of Porous Thermal Insulation Building Materials Based on Walnut Shell

YiShui¹,

Li²,

Xu³

et al. 2016

Proceedings of the 3rd International Conference on Material Engineering and Application (ICMEA 2016)

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Abstract. In this paper, shale and feldspar were regarded as matrix materials and sillcon carbide was added as foaming agent. After a quality ratio of walnut shell was mixed with as pore-forming agent,porous insulation materialswere made through high temperature foaming. The firing curve was developed by studying the thermal history. XRD and micro-morphology were used to study the effects of the amount of walnut shell on the density, thermal conductivity and mechanical properties of the products. The results show that when the amount of walnut shell was 10%, the sample density was 180 kg/m 3 , and the flexural strength and compressive strength could reach 1.031 MPa and 0.862 MPa respectively.Meanwhile, the thermal conductivity was 0.076 W/(m· K) and the water absorption could achieve 1.5%. It is concluded that adding walnut shell has no effect on the crystallization of the sample, but the walnut shell couldreplace a part of raw materials, resulting in the increase of density and strength. At the same time, the appearance of miscellaneous stomata could be attributed to the addition of walnut shell, and the number of open pores increased, leading to the increase of water absorption and thermal conductivity.

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Section: Foaming Theorymentioning

confidence: 99%

Process and Properties Study of Porous Thermal Insulation Building Materials Based on Walnut Shell

YiShui¹,

Li²,

Xu³

et al. 2016

Proceedings of the 3rd International Conference on Material Engineering and Application (ICMEA 2016)

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“…Tabla IV: condIcIones Para la TransIcIón de oxIdacIón acTIVa-PasIVa TeórIca del sIc (47)(48)(49)(50) MATERIALES COMPUESTOS C/SIC PARA APLICACIONES ESTRUCTURALES DE ALTA TEMPERATURA. PARTE I: ESTABILIDAD TERMODINÁMICA Y QUÍMICA La velocidad de disolución del SiC inmerso en agua a 290ºC depende del pH y de la cantidad de oxígeno disuelto en el agua.…”

Section: 2-estabilidad Termodinámica Del Sicunclassified

Materiales compuestos C/SiC para aplicaciones estructurales de alta temperatura. Parte I: estabilidad termodinámica y química

Aparicio¹,

Durán²

2000

Bol. Soc. Esp. Ceram. Vidr.

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El desarrollo de la industria aeroespacial se orienta actualmente hacia la tecnología hipersónica, el incremento en el rendimiento de las reacciones de combustión y la reducción de la emisión de contaminantes. Estos objetivos sólo pueden alcanzarse aumentando la temperatura de combustión, para lo cual es necesario desarrollar nuevos materiales que conserven sus propiedades mecánicas hasta temperaturas muy elevadas. Entre ellos se encuentran los materiales compuestos de matriz de SiC reforzada con fibra continua de carbono (C/SiC), cuyas propiedades más importantes son una elevada resistencia a flexión y al choque térmico desde temperatura ambiente hasta 1600ºCy su reducido peso específico. Sin embargo, el principal problema que acompaña a los materiales compuestos C/SiC es la elevada velocidad de oxidación de la fibra de carbono a partir de 450ºC. En la primera parte del trabajo se realiza una revisión de las características más relevantes del carbono y SiC, y de su comportamiento frente a la oxidación, tanto por separado como formando parte de materiales compuestos de matriz de SiC y fibra de C. Palabras clave: C/SiC, materiales compuestos, estabilidad termodinámica, oxidación. C/SiC composites for high temperature structural applications. Part I: thermodynamical and chemical stabilityThe development of aero-engine and aircraft industry is aimed to hypersonic technology, efficiency enhancements and pollutant emission reductions. This objective can only be reached by increasing the operating temperatures, utilising new materials which mechanical properties are retained up to high temperatures. SiC matrix composites reinforced with carbon fibres (C/SiC) are good examples with very good bending and thermal shock resistance at temperatures up to 1600ºC as well as low density. However, the fact which currently inhibits the application of these materials is the high oxidation rate of carbon fibres at temperatures above 450ºC. In the first part of the paper, a review of the most important properties and oxidation mechanisms of C and SiC has been carried out. The influence of each material disposition, individually and as composite, has been analysed.Keywords: C/SiC, composites, thermodynamical stability, oxidation. 1.-INTRODUCCIÓNLa necesidad de nuevos materiales estructurales capaces de trabajar a temperaturas cada vez mayores ha originado un desarrollo tecnológico intenso y sostenido en numerosos campos de la industria. Desde este punto de vista, sólo los materiales cerámicos avanzados ofrecen suficientes garantías, ya que su límite de aplicabilidad (fundamentalmente por el mantenimiento de sus propiedades mecánicas a alta temperatura) excede en muchos casos los 2000ºC. No es exagerado decir que industrias como la aeronáutica, y en general muchas industrias relacionadas con el espacio, dependen en gran medida del avance científico y tecnológico dentro del campo de los materiales cerámicos. La variedad de materiales cerá-micos avanzados es amplia, y abarca desde óxidos (Al 2 O 3 , TiO 2 , ZrO 2 , 3Al 2 O 3 ·2SiO 2 , ...

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“…The formation of a protective layer of SiO2 protects Si-based materials and coatings from further oxidation under conditions of moderate temperature (up to ≈1600°C) [57]. For both SiC and Si3N4, Vaughn and Maahs found the transition from passive oxidation protection to gaseous production of SiO (and mass loss) occurred at conditions of 1,347°C for an oxygen partial pressure of 2.5Pa and 1,543°C at 123.2Pa, indicating that increases in oxygen pressure elevated the maximum use temperature of the binary compounds [58]. Scramjet engines typically operate with dynamic pressures in the range of 24kPa to 96kPa [23].…”

Section: Figure 27 the Specific Yield Strength Of Some High Temperamentioning

confidence: 99%

Thermal Management at Hypersonic Leading Edges

Kasen

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The intense heat flux incident upon the leading edges of hypersonic vehicles traveling through the low earth atmosphere at speeds of Mach 5 and above requires creative thermal management strategies to prevent damage to leading edge components. Conventional thermal protection systems (TPSs) include the ablative coatings of NASA's Mercury, Gemini, and Apollo vehicles and the reusable reinforced carbon-carbon (RCC) system of the Space Shuttle Orbiter. The ablative approach absorbs heat by endothermic transformation (phase and/or chemical change to the polymeric coating). The heat is dissipated from the vehicle as the single-use coating eventually vaporizes. The RCC approach manages the intense heat by operating at high temperatures and radiating heat to its surroundings. The effectiveness of both approaches is predicated on keeping the heat flux that impinges upon the susceptible aluminum airframe below a critical level.ii ________________________________________________________________________ This dissertation has explored an alternative metallic TPS concept which seeks to redistribute the heat from the leading edge, thereby eliminating local hot spots. It makes use of high thermal conductance heat pipes coupled to the leading edge so that the thermal load may be redistributed from a high heat flux location (at the stagnation point) to regions where it can be effectively radiated from the vehicle. The sealed system concept is based upon the evaporation of a fluid near the heat source that sets up a region of elevated vapor pressure inside the pipe. The latent heat is transported down the resulting pressure gradient by the vapor stream where it condenses at cooler regions, releasing the heat for removal.Replenishment of the condensed working fluid to the evaporator region is accomplished through the capillary pumping action of a porous wick which lines the interior surface of the pipe.A design methodology for a wedge-shaped heat pipe is presented which uses a coupled flow-wall temperature model to construct design maps which relate design parameters of the leading edge system (overall length, wall thickness, and alloy) to its operating conditions (isothermal temperature, maximum temperature, maximum thermal stress). Potential bounds on heat transport due to physical phenomena linked to the sound speed within a chamber (sonic limit), capillarity, and boiling nucleation are considered by extending models developed for tube designs to the wedge geometry. A new heat flux limit is proposed which, should it be exceeded, subjects the leading edge to thermally-induced plastic deformation of the TPS. iii ________________________________________________________________________To investigate the validity of the design approach and thermal spreading effectiveness of the proposed concept, a low temperature wedge-shaped leading edge was designed and constructed using stainless steel as the case material and water as the working fluid. Under localized tip heating, the maximum temperatures were significantly reduced compa...

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Active‐to‐Passive Transition in the Oxidation of Silicon Carbide and Silicon Nitride in Air

Cited by 249 publications

References 7 publications

Process and Properties Study of Porous Thermal Insulation Building Materials Based on Walnut Shell

Process and Properties Study of Porous Thermal Insulation Building Materials Based on Walnut Shell

Materiales compuestos C/SiC para aplicaciones estructurales de alta temperatura. Parte I: estabilidad termodinámica y química

Thermal Management at Hypersonic Leading Edges

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