Microstructure of laser clad Ni- Cr- Al- Hf alloy on a γ′ strengthened ni- base superalloy

Alloys and coatings for alloys for improved high temperature service life under aggressive atmo-spheres are of great contemporary interest. There is a general consensus that the addition of rare earths such as Hf will provide many beneficial effects for such alloys. The laser cladding technique was used to produce Ni-Cr-AI-Hf alloys with extended solid solution of Hf. A 10 kW CO₂ laser with mixed powder feed was used for laser cladding. Optical, scanning electron (SEM) and scanning transmission electron (STEM) microscopy were employed to characterize the microstructure of alloys produced during laser cladding processes. Microstructural studies revealed grain refinement, considerable in-crease in solubility of Hf in the matrix, Hf-rich precipitates, and new metastable phases. The size and morphology of γ′ (Ni₃Al) phase were discussed in relation to its microchemistry and the laser processing conditions. This paper will report the microstructural development in this laser clad Ni-Cr-AI-Hf alloy. Formerly Visiting Assistant Professor, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign.     

Spinodal decomposition of a Co-Ti-Nb alloy

The microstructural evolution on aging a Co-3 wt pct Ti-2 wt pct Nb alloy has been followed by transmission electron microscopy and diffraction to show that the solid solution decomposed by the spinodal mode. The strengthening observed has been correlated with the differences in lattice parameters of the coexisting phases. The several stages of coarsening have been documented to yield information about their kinetics and morphological changes. Formerly Visiting Assistant Professor, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801, is with .     

Laser-clad Ni70Al20Cr7Hf3 alloys with extended solid solution of Hf: Part II. Oxidation behavior

Ni-Al-Cr-Hf coatings with an extended solid solution of Hf were fabricated by laser cladding a premixed powder with a Ni-Al-Cr-Hf ratio of 70∶20∶7∶3 onto a substrate of RENé 80. Isothermal oxidation tests in slowly flowing air reveal that the claddings have a lower weight-gain rate than the substrate itselt. Microchemistry and microstructures of the oxidized samples were examined using scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The improvement in oxidation resistance is believed to be at least partially due to the formation of large numbers of hafnium-rich oxide spikes penetrating the unoxidized sample.     

Chemical Investigations on Celastrus paniculatus Seed Oil I

Fatty acid compositions of four lipid fractions of Celastrus paniculatus seed namely normal triglycerides (20.2%), polar triglycerides (44.4%), polar nonglyceridic ester (23.5%), and nonpolar nonglyceridic ester (11.9%), have been determined by gas liquid chromatography. Percentage contents of major component acids in these fractions are: palmitic, 25.1, 42.0, 12.7, 58.2; stearic, 6.7, 4.5, 15.8; oleic, 46.1, 24.8, 4.7, 14.2; linoleic, 15.4, 14.7, 10.0; and linolenic, 3.0, 13.1, 43.0, respectively. The major molecular species constituting the normal triglycerides are: palmitooleopalmitin, 6.8%; palmitooleostearin, 5.6%; palmitodiolein, 14.7; palmitooleolinolein, 7.0%; stearodiolein, 6.1%; triolein, 8.0% and dioleolinolein 7.6%. Lipolysis of the polar triglyceride indicated as high as 59.6% of saturated acids linked to the 2-position of glycerol.     

Twenty-first century research needs in electrostatic processes applied to industry and medicine

From the early 20th century Nobel Prize winning (1923) experiments with charged oil droplets, resulting in the discovery of the elementary electronic charge by Robert Millikan, to the early 21st century Nobel Prize (2002) awarded to John Fenn for his invention of electrospray ionization mass spectroscopy and its applications to proteomics, electrostatic processes have been successfully applied to many areas of industry and medicine. Generation, transport, deposition, separation, analysis, and control of charged particles involved in the four states of matter: solid, liquid, gas, and plasma are of interest in many industrial and biomedical processes. In this paper, we briefly discuss some of the applications and research needs involving charged particles in industrial and medical applications including: (1) generation and deposition of unipolarly charged dry powder without the presence of ions or excessive ozone, (2) control of tribocharging process for consistent and reliable charging, (3) thin film powder coating and powder coating on insulative surfaces, (4) fluidization and dispersion of fine powders, (5) mitigation of Mars dust, (6) effect of particle charge on the lung deposition of inhaled medical aerosols, (7) nanoparticle deposition, and (8) plasma/corona discharge processes. A brief discussion on the measurements of charged particles and suggestions for research needs are also included.     

Master–Slave Current-Sharing Control of a Parallel DC–DC Converter System Over an RF Communication Interface

Using analog wireless communication, we demonstrate a master-slave load-sharing control of a parallel dc-dc buck converter system, thereby eliminating the need for physical connection to distribute the control signal among the converter modules. The current reference for the slave modules is provided by the master module using radio-frequency (RF) transmission, thereby ensuring even sharing of the load current. The effect of delay due to RF transmission on system stability and performance is analyzed, and regions of operation for a stable as well as satisfactory performance are determined. We experimentally demonstrate a satisfactory performance of the master-slave converter at 20-kHz switching frequency under steady state as well as transient conditions in the presence of a transmission delay. The proposed control concept, which can potentially attain redundancy that is achievable using a droop method, may lead to more robust and reconfigurable control implementation of distributed converters and power systems. It may also be used as a (fault-tolerant) backup for wire-based control of parallel/distributed converters.     

Modeling and Optimization for a Comprehensive Gas Processing Plant with Sensitivity Analysis and Economic Evaluation

Sweetening, dehydration, natural gas liquid (NGL) recovery, and sale gas compression are four major treatment stages for the general natural gas processing. Here, a comprehensive gas processing plant (CGPP) coupling sweetening, dehydration, NGL recovery, and compression subsystems have been conceptually designed, modeled, and optimized based on field data. The development includes four major stages of work: (i) CGPP process development with Aspen HYSYS simulator; (ii) sensitivity studies for all distillation columns involved in the CGPP process to optimize their performances; (iii) sizing of major equipment of the CGPP; and (iv) economic evaluations with Aspen process economic analyzer to calculate the expected capital and operating expenditures for the developed CGPP process. Valuable insights of natural gas monetization from the viewpoint of large-scale process system integration, modeling, and optimization are provided.     

A novel 0.9KNbO3–0.1BaNi0.5Nb0.5O3(KBNNO):Ag2O/Bi2O3 heterojunction photocatalyst: synthesis,characterization and excellent photocatalytic performance

In the present study, first 0.9KNbO₃–0.1BaNi_0.5Nb_0.5O₃(KBNNO) nanosized powder was synthesized by solution combustion method and then a series of KBNNO:Ag₂O and KBNNO:Bi₂O₃ composites with varying weight ratios (75:25, 50:50, and 25:75) were prepared by a simple precipitation technique/solid-state method. Preparation method and processing temperature have significant effect on phase stability and interface formation. The structural, morphological and photoabsorption behaviour of the synthesized powders were studied systematically by XRD, TEM, XPS and UV–visible spectroscopy. The photocatalytic performance of the photocatalysts was evaluated for the degradation of rhodamine B (RhB) solution under visible light exposure. In particular, KBNNO:Ag₂O composites exhibited better photodegradation of RhB. KBNNO:Ag₂O (50:50) nanocomposite can completely mineralize the RhB in 25 min, whereas KBNNO:Bi₂O₃ (25:75) can mineralize 96% of RhB in 45 min. The rate constant (k) for dye degradation of KBNNO:Ag₂O (50:50) (0.113 min^?1) sample showed the highest value which was 4.71 and 5.94 times better than that of KBNNO and Ag₂O under visible light irradiation. The rate constant for KBNNO:Bi₂O₃ (25:75) (0.048 min^?1) exhibited the highest k value which is 1.94 and 3.13 times greater than that of KBNNO and Bi₂O₃ under similar irradiation condition. The significant absorption in visible region and reduced recombination time of charge carriers in the composite than the parent materials were responsible for excellent photocatalytic properties. The mechanism for degradation was also studied in detail. Moreover, a reasonable degradation of 95% (on an average) was observed after five cycles, suggesting a good photocatalytic stability of the composites.