scholarly journals Microstructural investigation of the coatings prepared by simultaneous aluminizing and siliconizing process on γ-TiAl

2019 ◽  
Vol 55 (2) ◽  
pp. 217-225
Author(s):  
S. Nouri ◽  
M. Azadeh
Keyword(s):  
Powder Mixture ◽  
Pack Cementation ◽  
Chemical Compositions ◽  
Powder Mixtures ◽  
Microstructural Investigation ◽  
Diffusion Coatings ◽  
Sequential Mechanism ◽  
First Time ◽  
Pack Cementation Process ◽  
Segregated Structure

In this research, formation of aluminide/silicide diffusion coatings on ?-TiAl[Ti-48Al-2Nb?2Cr (at.%)] alloy using gasphase diffusion pack cementation process has been investigated. The application of powder mixtures with various chemical compositions in the pack cementation process performed at 1000oC for 6 hours in order to achieve simultaneous diffusion of Al and Si, showed that the composition of the powder mixture could have a significant effect on the structure and thickness of the aluminide/silicide coatings. The identification and analysis of aluminide/silicide microstructures formed as a result of simultaneous diffusion of Al and Si, which was comprehensively and qualitatively done for the first time in this study, showed that the sequential mechanism is dominant in the formation of the above-mentioned coatings. Furthermore, Kirkendall phenomenon and volumetric changes caused by the formation of Ti5Si3 and Ti5Si4, were considered as the two dominant mechanisms in the formation of porous segregated structure in these coatings. In this study, the effect of decreasing the activity of Si, through two approaches of reducing the amount of Si in the powder mixture and using Al- 20wt.%Si alloyed powder instead of pure Al and Si depositing elements, on the microstructural modification coatings was investigated. The results showed that reducing the Si activity at the surface of the coating and, consequently, reducing the flux of active silicon atoms (JSi), has a significant effect on the formation of coating with an ideal structure.

Diffusion Layers with Ti and Ti+Al Formed on 316L Austenitic Steel by a Pack Cementation Procedure

2011 ◽  
Vol 312-315 ◽  
pp. 13-19 ◽  
Author(s):  
Iulia Mirela Britchi ◽  
Mircea Olteanu ◽  
Niculae Ene ◽  
Petru Nita
Keyword(s):  
Activation Energy ◽  
Powder Mixture ◽  
Pack Cementation ◽  
X Ray Diffraction ◽  
Powder Mixtures ◽  
X Ray ◽  
Diffusion Coatings ◽  
Diffusion Layers ◽  
316L Steel ◽  
Temperature Activation

Pack cementation procedure implies the use of a powder mixture containing the diffusive elements, which in our case are either Ti or Ti+Al, Al2O3 and NHCl as activator. In the case of titanizing the powder mixture contained 77% in weight Ti, while for alumino-titanizing Al/Ti = 1/5 ratio was employed. NH4Cl content was 3% in weight in all cases. Aluminium additions to the powder mixtures led to a decrease of the process temperature. Activation energy for the aluminizing of austenitic 316L steel is 73.87 KJ/mol, much smaller than for the titanizing, 257.86 KJ/mol. Activation energy for alumino-titanizing, in the same conditions, is 146.01 KJ/mol. All diffusion coatings, in the Ti – 316L and Ti+Al – 316L couples are formed of two layers having different structures and compositions. All couples were investigated by optical microscopy, electron microscopy (SEM and EDX), X-ray diffraction and microhardness trials.

scholarly journals High temperature gas extrusion of reactive powder mixture Ni + AL

2019 ◽  
Vol 489 (4) ◽  
pp. 358-361
Author(s):  
F. F. Galiev ◽  
I. V. Saikov ◽  
V. D. Berbentcev ◽  
A. V. Guliyutin ◽  
V. I. Bugakov ◽  
...  
Keyword(s):  
High Temperature ◽  
Powder Mixture ◽  
Model System ◽  
Steel Shell ◽  
Powder Mixtures ◽  
Reactive Powder ◽  
First Time ◽  
High Temperature Gas

The results of the study of intermetallic rods in a steel shell obtained by high-temperature gas extrusion for the first time used for reactive powder mixtures are presented. Tests were conducted on the basis of model system Ni-Al.

scholarly journals Microstructures and Oxidation Behaviors of Silicide Coated Nb Alloys by Halide Activated Pack Cementation Process

2020 ◽  
Vol 58 (8) ◽  
pp. 507-514
Author(s):  
Wonchul Yang ◽  
Choong-Heui Chung ◽  
Sangyeob Lee ◽  
Kyeong Ho Baek ◽  
Youngmoo Kim ◽  
...  
Keyword(s):  
Oxidation Resistance ◽  
Coating Layer ◽  
Pack Cementation ◽  
Powder Mixtures ◽  
Arc Melting ◽  
Static Oxidation ◽  
Coating Layers ◽  
Pack Cementation Process ◽  
Coating Layer Thickness ◽  
Oxidation Behaviors

In this study, we tried to improve the oxidation resistance of Nb-12Si (wt%) alloys at 1200 °C or higher through pack cementation coatings. Nb-12Si (wt%) alloys were prepared by arc-melting under Ar atmosphere. When the alloys were coated using pack powder mixtures composed of Si, Al2O3 and NaF, two silicide layers composed of NbSi2 and Nb5Si3 phases were successfully produced on the substrate. The Si-pack coatings were performed with various heat treatment temperatures and time conditions. The microstructures and thickness changes of the coating layers were analyzed to determine the growth behaviors of the coating layer. The growth constant of 8.4 10–9 cm2/sec was obtained with a diffusion growth mode. In addition, in order to examine the resistance of the Si-pack coated alloys, isothermal static oxidation tests were performed at 1200 °C and higher temperatures. As a result, the oxidation resistance of the alloys was determined by protecting the surface of the alloys with silicide oxide layers formed by the silicide coatings. The uncoated specimens exhibited an abnormal weight increase due to the formation of Nb oxide. The coated specimen showed excellent oxidation resistance at 1200 °C for up to 12 hrs, while the previous reports on the same alloy verified oxidation resistance only up to 1100 °C. It appears that the excellent oxidation resistance is closely related to the NbSi2 coating layer thickness. The oxidation behaviors of the coating layers after the oxidation tests were discussed in terms of microstructural and phase analyses.

scholarly journals Comparative Study of Chemical Compositions and Antioxidant Capacities of Oils Obtained from 15 Macadamia (Macadamia integrifolia) Cultivars in China

Foods ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 1031
Author(s):  
Xixiang Shuai ◽  
Taotao Dai ◽  
Mingshun Chen ◽  
Ruihong Liang ◽  
Liqing Du ◽  
...  
Keyword(s):  
Palmitoleic Acid ◽  
Linear Regression Analysis ◽  
Monounsaturated Fatty Acids ◽  
Multiple Linear Regression Analysis ◽  
Chemical Compositions ◽  
Macadamia Integrifolia ◽  
Antioxidant Capacities ◽  
Squalene Content ◽  
First Time ◽  
Insight Into

The planting area of macadamia in China accounted for more than one third of the world’s planted area. The lipid compositions, minor components, and antioxidant capacities of fifteen varieties of macadamia oil (MO) in China were comparatively investigated. All varieties of MO were rich in monounsaturated fatty acids, mainly including oleic acid (61.74–66.47%) and palmitoleic acid (13.22–17.63%). The main triacylglycerols of MO were first time reported, including 19.2–26.1% of triolein, 16.4–18.2% of 1-palmitoyl-2,3-dioleoyl-glycerol, and 11.9–13.7% of 1-palmitoleoyl-2-oleoyl-3-stearoyl-glycerol, etc. The polyphenol, α-tocotrienol and squalene content varied among the cultivars, while Fuji (791) contained the highest polyphenols and squalene content. Multiple linear regression analysis indicated the polyphenols and squalene content positively correlated with the antioxidant capacity. This study can provide a crucial directive for the breeding of macadamia and offer an insight into industrial application of MO in China.

scholarly journals Thermodynamic Behavior of Fe-Mn and Fe-Mn-Ag Powder Mixtures during Selective Laser Melting

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 234
Author(s):  
Jakob Kraner ◽  
Jožef Medved ◽  
Matjaž Godec ◽  
Irena Paulin
Keyword(s):  
Selective Laser Melting ◽  
Manganese Oxides ◽  
Elevated Temperatures ◽  
Manganese Content ◽  
Chemical Compositions ◽  
Metal Powders ◽  
Laser Melting ◽  
Powder Mixtures ◽  
Ε Martensite ◽  
The Impact

Additive manufacturing is a form of powder metallurgy, which means the properties of the initial metal powders (chemical composition, powder morphology and size) impact the final properties of the resulting parts. A complete characterization, including thermodynamic effects and the behavior of the metal powders at elevated temperatures, is crucial when planning the manufacturing process. The analysis of the Fe-Mn and Fe-Mn-Ag powder mixtures, made from pure elemental powders, shows a high susceptibility to sintering in the temperature interval from 700 to 1000 °C. Here, numerous changes to the manganese oxides and the αMn to βMn transformation occurred. The problems of mechanically mixed powders, when using selective laser melting, were highlighted by the low flowability, which led to a less controllable process, an uncontrolled arrangement of the powder and a large percentage of burnt manganese. All this was determined from the altered chemical compositions of the produced parts. The impact of the increased manganese content on the decreased probability of the transformation from γ-austenite to ε-martensite was confirmed. The ε-martensite in the microstructure increased the hardness of the material, but at the same time, its magnetic properties reduce the usefulness for medical applications. However, the produced parts had comparable elongations to human bone.

scholarly journals Soil and Leaf Nutrients Drivers on the Chemical Composition of the Essential Oil of Siparuna muricata (Ruiz & Pav.) A. DC. from Ecuador

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2949
Author(s):  
Juan I. Burneo ◽  
Ángel Benítez ◽  
James Calva ◽  
Pablo Velastegui ◽  
Vladimir Morocho
Keyword(s):  
Gas Chromatography ◽  
Chemical Composition ◽  
Secondary Metabolites ◽  
Essential Oil ◽  
Chemical Elements ◽  
Climatic Conditions ◽  
Gas Chromatography Mass Spectrometry ◽  
Chemical Compositions ◽  
Leaf Nutrients ◽  
First Time

Chemical compositions of plants are affected by the initial nutrient contents in the soil and climatic conditions; thus, we analyzed for the first time the effects of soil and leaf nutrients on the compositions of the essential oils (EOs) of Siparuna muricata in four different localities in Ecuador. EOs were obtained by hydrodistillation and analyzed by gas chromatography/mass spectrometry (GC/MS) and a gas chromatography/flame ionization detector (GC/FID). Enantiomeric distribution by GC/MS was determined, modifying the enantiomeric separation of β-pinene, limonene, δ-elemene, β-bourbonene, cis-cadina-1 (6), 4-diene and atractylone. A total of 44 compounds were identified. The most representative for L1 were guaiol, atractylone and 4-diene; for L2, cis-cadina-1(6),4-diene and myrcene; for L3, atractylone, myrcene and germacrene B; and finally, L4 germacrene B, myrcene and cis-cadina-1(6),4-diene. Correlations between soil- leaf chemical elements such as Al, Ca, Fe, Mg, Mn, N and Si in the different localities were significant with chemical composition of the essential oil of Siparuna muricata; however, correlations between soil and leaf K, P, and Na were not significant. Cluster and NMDS analysis showed high dissimilarity values of secondary metabolites between four localities related with changes in soil- leaf nutrients. Thus, the SIMPER routine revealed that not all secondary metabolites contribute equally to establishing the differences in the four localities, and the largest contributions are due to differences in guaiol, cis-cadina-1(6),4-diene, atractylone and germacrene. Our investigation showed for the first time the influences of altitude and soil- leaf chemical elements in the chemical composition of the EOs of S. muricata.

Theoretical Analysis on the Constitution of Calorific Values of Biomass Fuels

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Fengqi Yao ◽  
Haihui Wang
Keyword(s):  
Chemical Species ◽  
Energy Utilization ◽  
Chemical Compositions ◽  
Chemical Bonds ◽  
Biomass Fuels ◽  
Conversion Model ◽  
Negative Role ◽  
First Time ◽  
Mass Increase ◽  
Heat Released

The present work explored the constitution of the calorific values of biomass fuels and the mechanism by which basic chemical compositions affect the fuel calorific data. For the first time, an energy conversion model was developed for the functional groups stored in biomass fuels by combustion. Validation of the model was performed by testing with various types of substances. By analyzing the effect of mass increase of individual chemical species on the amount of heat released by a fuel, it was confirmed that for ligno-cellulosic fuels, the species containing C–H, C–C and C=C bonds positively affect the fuel calorific values, whereas the species containing O–H, C–N, C–O, and C=O bonds have negative role in the increase of the fuel calorific values. A ratio parameter was then developed to quantitatively evaluate the potential of individual chemical bonds to contribute to the calorific values of biomass fuels, which well explained the existing techniques for treating biomass as fuels. The outcomes of this work serve as a theoretical basis for improving the efficiency in energy utilization of biomass fuels.

scholarly journals Малогазовая детонация в низкоплотных механоактивированных порошковых смесях

2019 ◽  
Vol 89 (6) ◽  
pp. 821
Author(s):  
С.А. Рашковский ◽  
А.Ю. Долгобородов
Keyword(s):  
Experimental Data ◽  
Shock Wave ◽  
Energy Release ◽  
Powder Mixture ◽  
Powder Compaction ◽  
Mutual Friction ◽  
Low Density ◽  
Powder Mixtures ◽  
Release Wave ◽  
Fuel Particles

Experimental data on supersonic self-sustaining propagation of the energy release wave in low-density mechanically activated powder mixtures are analyzed. Various mechanisms that may be responsible for this process are analyzed, and a mechanism for the detonation-like propagation of the reaction in powder mixtures is proposed. It is shown that under certain conditions this process has all the signs of detonation and should be recognized as one of the types of detonation. It is shown that this type of detonation is fundamentally different from the classical "ideal" detonation, for example, in gases: instead of a shock wave, a compaction wave propagates through the powder mixture, in which there is basically no compression of the particle material, but powder compaction occurs due to the mutual rearrangement of particles. In this case, the initiation of a chemical reaction occurs due to the mutual friction of the oxidizer and fuel particles in the powder compaction wave.

Sign in / Sign up

Export Citation Format

Share Document