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1.
Kinetics and Mechanism of Corrosion of SiC by Molten Salts 总被引:2,自引:0,他引:2
NATHAN S. JACOBSON 《Journal of the American Ceramic Society》1986,69(1):74-82
Corrosion of sintered α-SiC under thin films of Na2 CO3 /CO2 , Na2 SO4 /O2 , and Na2 SO4 /SO3 was investigated at 1000°C. Chemical analysis was used to follow silicate and silica evolution as a function of time. This information couples with morphology observations leads to a detailed corrosion mechanism. In all cases the corrosion reactions occur primarily in the first few hours. In Na2 CO3 /CO2 case, rapid oxidation and dissolution lead to a thick layer of silicate melt in ∼0.25 h. After this, silica forms a protective layer on the carbide. In the Na2 SO4 /O2 case, a similar mechanism occurs. In the Na2 SO4 /SO3 case, a porous nonprotective layer of SiO2 grows directly on the carbidem and a silicate melt forms above this. In addition due to reaction of silicate with SO3 and SO2 +O2 . The reaction slows when the lower silica layer becomes nonporous. 相似文献
2.
Deposits of S0 ; and Na2 SO4 together in bubbles within production float glass are generated by disproportionation of SO2 , derived from dissolved SO3 , in company with Na2 O from the interior bubble surfaces. This reaction proceeds rapidly in molten glass and also at temperatures well below Tg . 相似文献
3.
The hot corrosion of sintered α-Sic by thin films of Na2 SO4 and Na2 CO3 was studied at 1000°C in controlled gas atmospheres. Under all conditions corrosion led to 10 to 20 times the amount of SiO2 formed in pure oxidation after a 48-h exposure. In addition, small amounts of sodium silicate formed. Melts of Na2 SO4 /SO3 caused uniform pitting of the Sic substrate; Na2 CO3 /CO2 melts caused localized pitting and grain-boundary attack. In all cases the protective SiO2 layer dissolved to form silicate, leading to corrosion. In the sulfate case, free carbon in the Sic promotes this process. In all cases the presence of liquid films is responsible for rapid transport rates and the subsequent rapid reaction. 相似文献
4.
Chai Zhang Liang Jing-Kui Xu Xian-ting 《Journal of the American Ceramic Society》1988,71(10):C436-C438
The phase diagram of the pseudobinary system Li2 SO4 –La2 (SO4 )3 has been investigated by means of X-ray diffraction and differential thermal analysis. LiLa(SO4 )2 is formed by a peritectic reaction in this system; the peritectic temperature is 653±3°C. The eutectic reaction of Li2 SO4 and LiLa(SO4 )2 occurs at 553±3°C; the composition at the eutectic point is 17 mol% La2 (SO4 )3 . LiLa(SO4 )2 is monoclinic with a=1.375 nm, b=0.6744 nm, c=0.7068 nm, and β=105.4°. The ionic conductivity of LiLa(SO4 )2 has been studied from room temperature to 350°C and is found to be relatively low at room temperature or at lower temperatures. Its activation energy is 0.66 eV. Thus it is not suitable as a fast ion conductor. 相似文献
5.
Various Na2 SO4 -Na2 CO3 -CaCO3 -SiO2 combinations were studied by differential thermal analysis to elucidute the role of Na2 SO4 in soda-lime-silica glassmelting reactions. It was found that Na2 SO4 encourages the formation of wollastonite at 850° to 900°C. The solid-state reaction of Na2 Ca(CO3 )2 occurs very readily at temperatures in the vicinity of 400°C. The Na2 Ca(CO3 )2 must therefore be considered a major constituent in glass batches containing both soda ash and limestone . 相似文献
6.
Continuous weight-change measurements were used to determine the vaporization kinetics of Na2 SO4 from 900° to 1200°C in 150 torr O2 . Simple evaporation of the sulfate was indicated. An activation energy for vaporization of 71 kcal/mol was calculated. Vaporization results obtained for Na2 SO4 on oxide substrates indicated an Na2 SO4 -Cr2 O3 reaction; however, no Na2 SO4 -ZrO2 reaction was observed. 相似文献
7.
Yiguang Wang Yahui Wu Laifei Cheng Litong Zhang 《Journal of the American Ceramic Society》2010,93(1):204-208
Barium aluminosilicates (BAS) were coated on the carbon fiber-reinforced silicon carbide composites (C/SiC) as environmental barriers. The hot corrosion behavior of the coated composites was studied at 900°C in dry air and water vapor, respectively. The molten Na2 SO4 was used as the corrosion reactant. The results indicate that the BAS coatings can effectively block the attack of molten Na2 SO4 to C/SiC composites in dry air. However, the coated composites degrade rapidly when exposed to molten Na2 SO4 coupled with water vapor. It is found that the BAS is corroded by Na2 SO4 melt with the formation of BaSO4 , resulting in the destruction of BAS structure, which makes the coating lose its protection to the C/SiC composites in water vapor. 相似文献
8.
Youichi Shimizu Miho Okimoto Noriko Souda 《International Journal of Applied Ceramic Technology》2006,3(3):193-199
All solid-state sulfur oxides (SO x ) sensor devices combined with a sodium ionic conductor (Na5 DySi4 O12 ) disk and metal sulfide-sensing electrodes synthesized via solution routes have been systematically investigated for the detection of SO2 in the range of 20–200 ppm at 150–400°C. Among the various sulfide-sensing electrodes tested, the metal monosulfide-based electrodes gave good SO2 sensitivity at 400°C. The Pb1− x Cd x S ( x =0.1, 0.2)-based solid electrolyte sensor element showed the best sensing characteristics, i.e., the EMF response was almost linear to the logarithm of SO2 concentration in the range between 40 and 400 ppm, with a 90% response time to 100 ppm SO2 of about 3–15 min, and also showed high selectivity to SO2 at 400°C. 相似文献
9.
Yang Yu-Xiang Qu Xu-Ping Chen Ya-Ru Jia Xiang-Chen Zhang Jian-Bo Liu Xiang-Nong 《Journal of the American Ceramic Society》2007,90(7):2050-2056
Mesoporous silica materials with ordered hexagonal and parallel-arranged pore channel have been synthesized using cetyl trimethylammonium bromide as a template and Na2 SO4 as counterions. Their ordered mesostructures were characterized by infrared spectroscopy, X-ray diffraction patterns, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption analysis. The effects of Na2 SO4 concentration on variations of morphology, specific surface area, and pore size were discussed; the results show that a high concentration of Na2 SO4 induces the formation of crystal threads with a "tubules-within-tubule" structure, and also leads to mesoporous silica materials with spherical, fabaceous, sheet-like, or prismatic shapes. The results also show that a high concentration of Na2 SO4 can make the pore size decrease, but cannot change pore wall thickness, demonstrating the stability of the hexagonal-shaped pores. 相似文献
10.
Stress rupture testing was performed in four-point flexure at 1000°C to determine the effects of Na2 SO4 -induced corrosion on the static-fatigue life of a Ce-TZP and a MgO-doped Si3 N4 . The results showed that the static-fatigue life of the Ce-TZP was unaffected by this corrosive environment. However, the static-fatigue life of a MgO-doped Si3 N4 was reduced by the introduction of Na2 SO4 . 相似文献
11.
α-Al2 O3 platelet powders were synthesized in molten Na2 SO4 flux. The size of α-Al2 O3 platelets was significantly reduced when partially decomposed rather than pure Al2 (SO4 )3 was used as the source of Al2 O3 ; a further reduction in the platelet size was realized through additional seeding with nanosized α-Al2 O3 seeds. The addition of microsized α-Al2 O3 platelet seeds significantly influenced the platelet morphology of the final powder, as well. The platelet size of the final powder was in direct proportion to the size of the platelet seeds, and was in reverse proportion to the cube root of the platelet seed content. 相似文献
12.
γ-Y2 Si2 O7 is a promising candidate material both for high-temperature structural applications and as an environmental/thermal barrier coating material due to its unique properties such as high melting point, machinability, thermal stability, low linear thermal expansion coefficient (3.9 × 10−6 /K, 200°–1300°C), and low thermal conductivity (<3.0 W/m·K above 300°C). The hot corrosion behavior of γ-Y2 Si2 O7 in thin-film molten Na2 SO4 at 850°–1000°C for 20 h in flowing air was investigated using a thermogravimetric analyzer (TGA) and a mass spectrometer (MS). γ-Y2 Si2 O7 exhibited good resistance against Na2 SO4 molten salt. The kinetic curves were well fitted by a paralinear equation: the linear part was caused by the evaporation of Na2 SO4 and the parabolic part came from gas products evolved from the hotcorrosion reaction. A thin silica film formed under the corrosion scale was the key factor for retarding the hot corrosion. The apparent activation energy for the corrosion of γ-Y2 Si2 O7 in Na2 SO4 molten salt with flowing air was evaluated to be 255 kJ/mol. 相似文献
13.
India as a Hot Corrosion-Resistant Stabilizer for Zirconia 总被引:2,自引:0,他引:2
After showing that india (In2 O3 ) resisted high-temperature reaction with SO3 /Na2 SO4 and vanadate melts, we prepared india-stabilized zirconia (ISZ) by a proprietary sol–gel process, and tested the material for corrosion resistance to 700–900°C molten vanadates. ISZ was superior to yttria-stabilized zirconia (YSZ) in vanadate resistance at 700°C, and essentially equivalent at 900°C. Certain differences were observed between the vanadate-induced corrosion/destabilization of ISZ and that of YSZ. 相似文献
14.
Mark G. Lawson Hei R. Kim Fred S. Pettit Jean R. Blachere 《Journal of the American Ceramic Society》1990,73(4):989-995
The high-temperature corrosion of bulk silica glass was studied in pure oxygen and in SO3 -containing oxygen atmospheres in the presence of liquid sulfate deposits at temperatures of 700° and 1000°C. No reaction and devitrification were observed without Na2 SO4 on the surface. The wetting of the silica by the sulfate, the tendency toward basic fluxing, and the crystallization of the silica incrased with the activity of Na2 O. The most extensive degradation of vitreous silica occurred by crystallization, and the resulting spalling under basic conditions and thermal cycling at basic conditions were parabolic. This behavior is explained by a model in which the crystallization is controlled by sodium at the glass-crystal interface and its diffusion into the glass. This sodium diffuses into the glass before crystallization and is swept ahead of the crystallization front. 相似文献
15.
Hot isostatically pressed Si3 N4 was coated with chemically vapor-deposited Ta2 O5 , and subjected to oxidative and corrosive environments to determine the feasibility of using a Ta2 O5 coating for protecting Si3 N4 from hot corrosion. The coated structure was relatively stable at 1000deg; C in pure O2 . However, the Ta2 O5 -Si3 N4 system became unstable in an environment containing Na2 SO4 and O2 at 1000deg; C because (1) Ta2 O5 and Na2 SO4 reacted rapidly to form NaTaO3 and (2) subsequently NaTaO3 interacted destructively with the underlying Si3 N4 substrate to form a molten phase. 相似文献
16.
LUBOMlAR NMEC 《Journal of the American Ceramic Society》1977,60(9-10):436-440
Refining mechanisms for a soda-lime glassmelt containing bubbles are proposed, based on photographic observations and data in literature. The equation expressing the removal of bubbles from the glassmelt by ascension has been derived from a linear relation between bubble size and time. Experimental and theoretical studies have shown that heterogeneous bubble nucleation occurs during refining. An additive relation between SiO2 (sand) dissolving tune and the theoretical refining time resulting from heterogeneous bubble nucleation has been verified for As2 O3 + NaNO3 , Na2 SO4 , and NaCl additions to a soda-lime glass batch. 相似文献
17.
Bruno Mottet Michel Pichavant Jean-Michel Bény Jean-André Alary 《Journal of the American Ceramic Society》1992,75(9):2515-2519
Monoclinic zirconia has been synthesized hydrothermally from zirconium oxychloride in the range 20–100 MPa, 250–650°C, for run duration from 20 to 100 h and in the presence of NaOH, Na2 CO3 , Na2 SO4 , NH4 F, HNO3 , and H2 SO4 additives. Isometric, platelike, and elongated crystal morphologies were obtained depending on the additive. Both spherulitic and isolated textures were encountered with H2 SO4 . Growth of isometric crystals follows a general dissolution–precipitation mechanism. For H2 SO4 , two growth steps were identified: an early spherulitic step followed by an isolated crystals step resulting from Ostwald ripening of preexisting spherulites. The formation of spherulites is consistent with the specific properties of the sulfuric hydrothermal medium. 相似文献
18.
Anatase nanocrystallites showing high surface area (∼62 m2 /g) and good photocatalytic property have been obtained by pyrolyzing at 600°C for 4 h an ammonium titanyl double sulfate precursor (α-(NH4 )2 TiO(SO4 )2 ) synthesized via a redox approach, that is, by oxidizing an aqueous solution of titanium trichloride (TiCl3 ) with ammonium peroxodisulfate ((NH4 )2 S2 O8 ), followed by reacting with ammonium sulfate ((NH4 )2 SO4 ). 相似文献
19.
The corrosion mechanism of Si3 N4 + Na2 SO4 /O2 at 1000°C was investigated. Corrosion of both pure and additive-containing Si3 N4 was studied. The reaction of Si3 N4 + Na2 SO4 consists of an initial period of slow weight loss due to Na2 SO4 vaporization and oxidation-dissolution. This initial period was the same for all forms of Si3 N4 . A second region consisted of further oxidation or near termination of reaction, depending on the additive in the Si3 N4 . A 5- to 10-μm yttrium depletion zone was found after corrosion for the Si3 N4 with yttria additives. For comparison, Si and SiC were corroded under similar conditions. These materials corroded substantially faster than all forms of Si3 N4 . 相似文献
20.
Burner Rig Hot Corrosion of Silicon Carbide and Silicon Nitride 总被引:1,自引:0,他引:1
A number of commercially available SiC and Si3 N4 materials were exposed to 1000°C for 40 h in a high-velocity, pressurized burner rig as a simulation of an aircraft turbine environment. Na impurities (2 ppm) added to the burner flame resulted in molten Na2 SO4 deposition, attack of the SiC and Si3 N4 , and formation of substantial Na2 O. x (SiO2 ) corrosion product. Room-temperature strength of the materials decreased as a result of the formation of corrosion pits in SiC and grain-boundary dissolution and pitting in Si3 N4 . 相似文献