NaCl In Air Research Articles

Novel oxide based anti-corrosion composite coating for gas turbines

In the present study glass-ceramic−8YSZ based multilayered functionally graded corrosion resistant coating was developed for gas turbine applications. Corrosion resistance property of developed coating was evaluated by exposing coating to molten mixture of 80 wt% Na2SO4 + 20 wt% NaCl in air at 1000 °C up to 100 h. It was found that coating morphology was gradually changed with respect to time at 1000 °C. No thermally grown oxide (TGO) layer was observed within different layers of TBC. However, thin reaction film was developed at substrate-coating interface, which helped to increase adherence of coating with substrate. Tetragonal zirconia to monoclinic zirconia phase transformation was not occurred in top coat even after long corrosive salt attack that strengthened TBC system. Developed coating showed good potential to be used as corrosion resistant coating for actual superalloy based gas turbine engine components.

PbO-SiO2 Based Glass Coating of PbI2 Doped PbTe

Thermoelectrics is one promising way of increasing the efficiency of machines and devices by reusing some of the waste heat produced. One obstacle for commercialization is the need to coat the materials to prevent sublimation and oxidation of the thermoelectric materials. Such coatings were designed for PbI2 doped PbTe using a (SiO2)0.68(PbO)0.3(B2O3)0.01(Na2O)0.01 based glass designed for operation at 500 °C. In this research various conditions of the coating process were examined. The effect of the atmosphere on the bonding and densification of the coating was studied using argon, vacuum and air. From the three air shows, the best bonding characteristics were from a better flow of glass and increased bonding between the oxidized PbTe layer and glass. This also created a PbO rich glass in the interface between the glass and the PbTe sample. The effect of 0, 3, and 6 wt. % NaCl additive to the solution was tested and showed that NaCl achieves better coverage due to high green body density, reaction of NaCl with the glass and removal of remaining CO2 from the glass in the form of decomposing Na2CO3. In addition, when testing the time and temperature, it was shown that the temperature of 520 °C was the minimum needed for high densification of the glass, but a duration shorter than 30 min did not allow for bonding of the glass to the substrate despite adequate densification. Finely, to obtain a well bonded coating with full coverage over the sample, the glass was coated with 6% NaCl in air at 520 °C for 30 min.

Hot Corrosion of Co-based Alloys with 25%NaCl+75%Na2SO4 Coating at 1173 K

AbstractHot corrosion behavior of pure Co, Co-10Cr and Co-10Cr-5Al alloys in the presence of a salt coat of Na2SO4+NaCl in air at 1173 K was studied. The results indicated that among the three samples, the mass gain of Co-10Cr-5Al alloy is the smallest, while that of Co-10Cr is biggest. The corrosion products of Co-10Cr-5Al can be divided into three layers, of which the outside layer is CoO, the middle layer consists of Cr2O3 and Al2O3, and the inside layer is a small amount of Chromium sulfide and aluminum sulfide. The corrosion products of Co-10Cr can also be divided into three layers, from the outermost to the innermost layer are CoO, Cr2O3, and small amount of Cr2S3. The corrosion resistance of Co-10Cr-5Al alloy is better than that of Co-10Cr alloy.

Crystal Structure of β-Fe2O3 and Topotactic Phase Transformation to α-Fe2O3

β-Fe2O3 is the scarce polymorph of Fe2O3 phases and is transformed easily into α-Fe2O3 at high temperature. However, its crystal structure and the transformation mechanism to α-Fe2O3 are still unclear because of the difficulty in obtaining monophasic β-Fe2O3 crystals. We established a synthesis method of the monophasic β-Fe2O3. It was synthesized by a two-step reaction: heating a mixture of Na2SO4 and Fe2(SO4)3 in air at 250 °C to form NaFe(SO4)2, and subsequent heating the resultant phase with NaCl in air at 500 °C. The crystal structure was refined to a bixbyite-type cubic structure (Ia3̅) with a = 9.4039(1) Å by the Rietveld method. Single crystalline β-Fe2O3 particles of approximately 1 μm in size were topotactically transformed into single α-Fe2O3 crystals. Electron diffraction analysis revealed the crystallographic orientation relationships between β-Fe2O3 and α-Fe2O3 to be [100]β//[0001]α, [010]β//[101̅0]α, and [001]β//[1̅21̅0]α.

Mechanisms of simultaneous oxidation–chloridation of austenitic stainless steels by NaCl in air

Mechanisms of simultaneous oxidation–chloridation of austenitic stainless steels by NaCl in air

Mechanisms of simultaneous oxidation-chloridation of austenitic stainless steels by NaCl in air

Simultaneous oxidation-chloridation behavior of austenitic stainless steels by NaCl in air was investigated at 650°C. Surface oxide scales of the test alloys had double-layered structures that consisted of inner spinel layer and outer Fe2O3 layer. Condensed and gaseous chlorides were formed below the scale surface by NaCl vapor diffusing inward via pores or cracks of the scales. The rate of internal and uniform attack mainly depended on the porosity of the inner spinel layer. In order to predict the complex mixed oxidation behavior of alloys, new types of thermodynamic stability diagrams were utilized, which was constructed by computer-assisted calculations of phase equilibria of the multi-component reacting systems using the Thermo-CaIc program. The overall mixed oxidation process including the initial stage of reaction, the rapid formation and growth of the scale and the transport of gaseous species through the oxide scale was elucidated.

Sintering kinetics of pure and CdCl2—doped NaCl in air

Sintering kinetics of pure and CdCl2—doped NaCl in air

Sintering kinetics of pure and CdCl2—doped NaCl in air

Sintering kinetics of pure and CdCl2—doped NaCl in air