Removal and transformation of dissolved organic matter in secondary effluent during granular activated carbon treatment

This paper focused on the removal and transformation of the dissolved organic matter （DOM） in secondary effluent during the granular activated carbon （GAC） treatment. Using XAD-8/XAD-4 resins, DOM was fractionated into five classes： hydrophobic acid （HPO-A）, hydrophobic neutral （HPO-N）, transphilic acid （TPI-A）, transphilic neutral （TPI-N） and hydrophilic fraction （HPI）. Subsequently, the water quality parameters of dissolved organic carbon （DOC）, absorbance of ultraviolet light at 254 nm （UV-254）, specific ultraviolet light absorbance （SUVA） and trihalomethane formation potential （THMFP） were analyzed for the unfractionated and fractionated water samples. The results showed that the order of the DOC removal with respect to DOM fractions was observed to be HPI〉HPO-A〉HPO-N〉TPI-A〉TPI-N. During the GAC treatment, the THMFP of the unfractionated water samples decreased from 397.4 μg/L to 176.5 μg/L, resulting in a removal efficiency of 55.6%. The removal order of the trilaalomethanes （THMs） precursor was as follows： HPO-A〉TPI-A〉TPI-N〉HPO-N〉HPI. By the GAC treatment, the specific THMFP of HPO-A, TPI-A, TPI-N and the original unfractionated water samples had a noticeable decrease, while that of HPO-N and HPI showed a converse trend. The Fourier transform infrared （FTIR） results showed that the hydroxide groups, carboxylic acids, aliphatic C-H were significantly reduced by GAC treatment.

Processing of a low-costγ-γ'NiPtAl coating with improved oxidation resistance

A novelγ-γ'(Ni solid solution—Ni_(3)Al)NiPtAl coating was produced on advanced single-crystal(SC)superalloy N5 by electroplating of a thin Pt coating with~3μm in thickness followed by heat treatment at 1000℃in vacuum.For comparison,a traditionalγ-γ'NiPtAl coating was also produced by electroplating of a thick Pt coating with~6μm in thickness followed by heat treatment at 1100℃in vacuum.The novel coating has a mass gain of~0.5 mg·cm^(-2)after 100 h 1-h cyclic oxidation at 1150℃,showing better oxidation resistance than the traditional coating.An oxide scale mostly consisting ofα-Al_(2)O_(3)grew on the novel coating because the element Cr from the SC alloy substrate contributes to the formation ofα-Al_(2)O_(3).Pt content in the novel coating has significant effect on the oxidation resistance.The optimized Pt content in the coating is about 16 at%,which is helpful to reduce the diffusion of harmful elements from the substrate into the coating but also to reduce the cost of the coating.

Microstructural evolution,mechanical properties and degradation mechanism of PS-PVD quasi-columnar thermal barrier coatings exposed to glassy CMAS deposits

Thermal barrier coatings(TBCs) applied in aeroengines tend to be attacked by molten calcia-magnesiaalumino-silicate(CMAS) at high operating temperatures.Yttria-stabilized zirconia(YSZ) coatings with quasicolumnar microstructure were fabricated by plasma spray physical vapor deposition(PS-PVD) technique.The chemic al changes,micros tructural transform ation,mechanical properties and degradation mechanisms of the CM AS-interacted TBCs in the thermal cycling tests were investigated.Feathered YSZ grains were dissolved in the CMAS melts,and then the ZrO_(2) grains were reprecipitated with spherical shape,accompanying with phase transformation from tetragonal(t) to monoclinic(m).The thermal cycling tests reveal that the YSZ coating fails at the early stage due to the attack of CMAS.The fractures in intracolumns lead to partial spallation of the coatings.The failure of the coating occurs at the interfaces between thermally grown oxides(TGO) layer and YSZ topcoat;especially,the hardness and Young's modulus of the YSZ coatings increase intensively,as the coatings were infiltrated by the CMAS for a long time.

An overview on the novel heat-resistant ferritic stainless steels

Heat-resistant ferritic stainless steels are widely used in many high-temperature applications such as power plants,automotive exhaust manifolds and solid oxide fuel cell interconnects due to their low price,low coefficient of thermal expansion,high thermal conductivity,high thermal fatigue resistance,high creep performance and excellent corrosion resistance.High-temperature strength,formability,high-temperature oxidation resistance and creep performance are the main evaluation criteria for the application.With the development of relevant industries,higher requirements are proposed for the performance of ferritic stainless steels.Therefore,the development of a new generation of heat-resistant ferritic stainless steel has received extensive attention.In this presentation,we summarized the research progress of heat-resistant ferritic stainless steels including high-temperature strength,formability,high-temperature oxidation resistance and creep performance.Meanwhile,some suggestions are given for alloy composition design and microstructure optimization.The future research direction of heat-resistant ferritic stainless steels also prospected.

Processing and oxidation behavior of Pt-diffused coatings

Pt-diffused coatings were synthesized on Ni10 Al alloy by electroplating a thin layer of Pt(1-5μm)followed by a diffusion treatment in vacuum at 1000-1100℃.Effects of processing parameters(Pt thickness and vacuum diffusion temperature)on the microstructures and chemical composition of Pt-diffused coatings were investigated.Also,the oxidation behavior of the coatings was studied at1100℃.Pt film reveals nano-sized grain size of 93-113 nm.Vacuum diffusion treatment leads to the grain growth.1-μm Pt film with 1000℃/1 h vacuum diffusion fabricates nano-sized Pt-diffused coating which exhibits the best oxidation resistance.And a single continuous Al2O3 scale forms on the coating with low Al(~9 at%)and Pt(~6 at%)contents.Increasing initial Pt thickness would introduce more defects and cracks,leading to a duplex scale and decreasing the oxidation resistance of Ptdiffused coatings.

Effect of W addition on hot deformation and precipitation behaviors of 19Cr2Mo ferritic stainless steel

The hot deformation behavior of 19Cr2Mo and 19Cr2Mo1W ferritic stainless steels was studied by using uniaxial hot compression tests on a thermomechanical simulator. The hot deformation was carried out at temperature ranging from 800 to 1150℃ and strain rates from 0.01 to 10 s^-1. Microstructure change and precipitation behavior during hot deformation were investigated by optical microscopy, electron probe microanalysis and transmission electron microscopy. The effects of temperature and strain rate on deformation behavior were obtained by a classical equation in Zener-Hollomon parameter. Since W addition to 19Cr2Mo1W steel could refine the size of the precipitates to enhance the precipitation strengthening and also had the effect of solution strengthening, the dynamic recrystallization, dynamic recovery and grain growth of 19Cr2Mo1W ferritic stainless steel were inhibited to a certain extent. The precipitate size of 19Cr2Mo1W steel was finer than that of 19Cr2Mo steel under the same deformation condition, which is due to the fact that the atomic diffusion is suppressed by W addition. W addition increased the amount of Laves phase in 19Cr2Mo1W steel, and thus Laves phase in 19Cr2Mo1W steel could be formed at higher temperature than that in 19Cr2Mo steel.

Microstructure stability of γ’+β Ni-Al coated single-crystal superalloy N5 annealed at 1100℃

γ’+β Binary-phase Ni-Al coatings were prepared on second-generation single-crystal superalloy Rene N5(N5) substrates by electron beam physical vapor deposition.Inter-diffusion behavior between coatings and substrates at 1100℃ and its effects on microstructure stability of the substrates were investigated.A 3-μm-thick substrate diffusion zone(SDZ) layer forms beneath the coating/substrate interface after 5-h heat treatment.The SDZ layer is composed of γ’-Ni_(3) Al phases and needle-like precipitates growing along(100)(110) or(100) <■> direction.After100-h annealing,the thickness of the SDZ layer increases to~17 μm,much lower than that of the single β-NiAl-coated substrate,while keeping single-crystal microstructure.