Intermediate Thermal Treatment Research Articles

Synthesis of Bimetallic Catalysts on the Basis of Y Type Zeolite

In this work, it is shown that based on powder zeolite type Y, mono metallic and bimetallic catalysts have been developed that are promising for petroleum chemistry processes. The method is based on the preparing hydrogen form of Y zeolite by ion exchange with a solution of ammonium nitrate at a starting concentration of 70 g.l-1 and nickel nitrate solution which provides Ni cations. Then after preparation of bimetallic catalysts by impregnating second metal by incipient wetness. All samples and catalysts were characterized using X-ray diffraction (XRD) analysis techniques, adsorption methods, and elemental analysis. The research results showed that in order to reach the degree of exchange of Na+ for H+ cations no less than 0.73, it is necessary to carry out four exchanges of Na+ by NH4+ and three intermediate thermal treatments at 540 °C for 3 to 4 hours in air atmosphere.

In vitro evaluation of drug release and antibacterial activity of a silver-loaded wound dressing coated with a multilayer system

The goal of the study was to elaborate an antibacterial silver wound dressing covered by a protective coating that would prevent silver diffusion toward skin without losing its biocide properties. Therefore, non woven polyethyleneterephtalate (PET) textiles were pre-treated by two types of polysaccharides – chitosan and cyclodextrin – both crosslinked with citric acid by a pad/dry/cure process. Both types of resulting thermofixed textiles carrying the citrate crosslinks were then impregnated in silver solution followed by a thermal treatment and were finally coated by Layer-by-Layer (L-b-L) deposition of a polyelectrolyte multilayer (PEM) film consisting of anionic water-soluble poly-cyclodextrin and cationic chitosan. The influence of the process parameters was investigated in terms of silver adsorption capacity, PEM system build-up, silver kinetics of release and antibacterial activity. We demonstrate i) the utility of the intermediate thermal treatment step in the reduction of silver leakage in the polyelectrolyte solutions used in the L-b-L process, ii) that silver adsorption on the preliminary thermofixed layers did not affect the PEM system build-up, iii) the slowing down of silver release kinetic thanks to the PEM coating, iv) the preservation of the antibacterial activity despite the PEM coating.

Crystal growth direction-controlled antimony selenide thin film absorbers produced using an electrochemical approach and intermediate thermal treatment

Sb2Se3 is an emerging material among alternative light absorbers for photovoltaic applications. Unlike typical chalcogenides, Sb2Se3 is particularly appealing due to its single stable crystal phase, layered structure with loose binding of no dangling bonds. Nevertheless, a cost-effective electrochemical approach for the synthesis of Sb2Se3 compounds has not been identified, and the Sb2Se3 film with the most favorable [001] preferred orientation has only just been developed. In this study, Sb-rich precursors were prepared electrochemically at −950mV (vs. Ag/AgCl), and homogeneous Sb2Se3 thin films were produced using a pre-thermal treatment process prior to the typical selenization process with additional Se coating. This novel procedure notably suppresses potential Sb dissolution into liquid Se due to the formation of polycrystalline Sb-related crystals. As a result, the Sb-rich precursor was successfully transformed into Sb2Se3 thin films with an enhanced perpendicular orientation of the [001] direction. Unfortunately, a high density of voids was produced in the precursor film with two distinguishable layers, and their size increased after selenization. The voids were formed through evolution of H2Se gas after the initial electrochemical reaction. The resulting photovoltaic cells demonstrated an energy conversion efficiency of 1.8% in a substrate structure consisting of Mo/Sb2Se3/CdS/ZnO/ITO.

Powder metallurgically manufactured cellular metals from carat gold alloys for decorative applications

This paper explores the possibilities of producing visually attractive cellular gold structures via two different powder metallurgical approaches: sintering of loosely packed gold fibers and replication of polymeric templates. In the latter case, two different templates were used: reticulated polyurethane (PU) foam and expanded polystyrene (EPS) spheres which were coated with atomized gold powder. In contrast to the fiber route, replication techniques require an intermediate thermal treatment for the removal of the templates prior to sintering. Typical carat gold alloys lend themselves for supersolidus liquid phase sintering due to a sufficient difference between solidus and liquidus temperature. This approach was applied to all three manufacturing routes and rigid cellular gold structures were obtained successfully in all cases.

Native Oxide Transport and Removal During Atomic Layer Deposition of TiO2 Films on GaAs(100) Surfaces

In this work, we studied the evolution and transport of the native oxides during the atomic layer deposition (ALD) of TiO2 on GaAs(100) from tetrakis dimethyl amino titanium and H2O. Arsenic oxide transport through the TiO2 film and removal during the ALD process was investigated using transmission Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Experiments were designed to decouple these processes by utilizing their temperature dependence. A 4 nm TiO2 layer was initially deposited on a native oxide surface at 100 °C. Ex situ XPS confirmed that this step disturbed the interface minimally. An additional 3 nm TiO2 film was subsequently deposited at 150 to 250 °C with and without an intermediate thermal treatment step at 250 °C. Arsenic and gallium oxide removal was confirmed during this second deposition, leading to the inevitable conclusion that these oxides traversed at least 4 nm of film so as to react with the precursor and its surface reaction/decomposition byproducts. XPS measurements confirmed the relocation of both arsenic and gallium oxides from the interface to the bulk of the TiO2 film under normal processing conditions. These results explain the continuous native oxide removal observed for alkyl-amine precursor-based ALD processes on III-V surfaces and provide further insight into the mechanisms of film growth.

Study of GTD-111 Superalloy Microstructural Evolution During High-Temperature Aging and After Rejuvenation Treatments

Nickel-based superalloys are normally present in mechanical components requiring resistance to high temperatures and extreme mechanical stresses, e.g., gas turbine blades. The large amount of γ′-precipitates coherent with the γ-matrix in these superalloys ensures excellent properties at high operating temperatures. Nevertheless, after long service periods, the γ′-precipitates grow and lose coherence with the matrix. Intermediate thermal treatments are a potential solution to recover the microstructure, extending the component lifetime. Thermal cycles for γ′-dissolution and reprecipitation define the efficiency of such thermal treatments. The objectives of this work are to analyze the aging kinetics of the nickel-based superalloy GTD-111 (used in gas turbine blades for thermoelectric energy generation) and to study the effects of solution and preprecipitation treatment temperatures on the microstructure and hardness obtained by rejuvenation thermal treatment. For the experiments, samples were previously aged under laboratory conditions during 2,000 h at 1,000 °C. The subsequent rejuvenation thermal treatments consisted of four steps: solution (at 1,150, 1,175, and 1,190 °C), preprecipitation (at 1,055 and 1,120 °C), and reprecipitation (at 845 °C). The resulting microstructures were analyzed using scanning electron microscopy and Vickers hardness measurements. During the aging treatment, the average size of γ′-particles changed from 0.20 µm2, as found in virgin material, to 0.99 µm2 after 2,000 h of aging; the hardness changed from 417 to 320 HV, respectively. For solution treatment at 1,150 °C, total dissolution of γ′-particles did not occur and they presented a bimodal size distribution of coarse and fine particles. For solution treatment at 1,175 and 1,190 °C, the γ′-particles were fine and homogeneous, and the maximum hardness obtained after reprecipitation was 460 HV for 1,190 °C solution treatment and 1,120 °C preprecipitation.

MnO x -Al2O3 catalysts for deep oxidation prepared with the use of mechanochemical activation: The effect of synthesis conditions on the phase composition and catalytic properties

The catalytic activity of alumina-manganese catalysts in the oxidation of CO was studied. The MnOx-Al2O3 catalysts were prepared by an extrusion method with the introduction of mechanically activated components (manganese oxide and its mixtures with aluminum oxide, aluminum hydroxide, and a mixture of a manganese salt with aluminum hydroxide) into a paste of aluminum hydroxide followed by thermal treatment in air or argon at 1000°C. In the majority of cases, the catalysts contained a mixture of the phases of β-Mn3O4 (Mn2O3), α-Al2O3, and δ-Al2O3. The presence of low-temperature δ-Al2O3 suggested the incomplete interaction of manganese and aluminum oxides. It was found that the catalytic activity of MnOx-Al2O3 depends on the degree of interaction of the initial reactants, and its value is correlated with the amount of β-Mn3O4 in the active constituent. The intermediate thermal treatment of components at 700°C negatively affects the catalytic activity as a result of the formation of Mn2O3 and the coarsening of particles, which levels the results of mechanochemical activation. The greatest degree of interaction between Al- and Mn-containing components was reached in the selection of mechanochemical activation conditions by decreasing the size of grinding bodies, optimizing the time of mechanochemical activation, and using the mechanochemical activation of precursor mixtures. As a result of mechanochemical activation, the initial reactants were dispersed, the amounts of MnO2 and Mn2O3 changed, and defects were formed; this strengthened the interaction of components and increased catalytic activity.

Drawing of continuous sections with a regular polygon profile

When designing the drawing process of sections with a regular polygon profile, it is convenient to use analytical expressions that make it possible to operatively evaluate the effect of different manufacturing factors. A calculation procedure for stress in this process is proposed. The relationships are derived for the calculation of the drawing stress, the optimal angle for the drawing-tool channel, the limiting deformation rate with the use of a standard tool, and the stress-state characteristic in the axial part of the deformation zone. The application of a drawing tool with optimum angles decreases the accumulation rate for defects of the metal structure and makes it possible to decrease the number of intermediate thermal treatments during multiple drawing.

Effectiveness of heat treatment to protect introduced denitrifying bacteria from eukaryotic predatory microorganisms in a pilot-scale bioreactor

Bioaugmentation of bioreactor systems with pre-cultured bacteria has proven difficult because inoculated bacteria are easily eliminated by predatory eukaryotic-microorganisms. Here, we demonstrated an intermediate thermal treatment was effective for protecting introduced denitrifying bacteria from eukaryotic predators and consequently allowed the inoculated bacteria to survive longer in a denitrification reactor.

V6O13films by control of the oxidation state from aqueous precursor to crystalline phase

An aqueous deposition process for V(6)O(13) films is developed whereby the vanadium oxidation state is continuously controlled throughout the entire process. In the precursor stage, a controlled wet chemical reduction of the vanadium(V) source with oxalic acid is achieved and monitored by (51)Vanadium Nuclear Magnetic Resonance ((51)V-NMR) and Ultraviolet-Visible (UV-Vis) spectroscopy. The resulting vanadium(IV) species in the aqueous solution are identified as mononuclear citrato-oxovanadate(IV) complexes by Electron Paramagnetic Resonance (EPR) and Fourier Transform Infra-Red (FTIR) spectroscopy. This precursor is successfully employed for the deposition of uniform, thin films. The optimal deposition and annealing conditions for the formation of crystalline V(6)O(13), including the control of the vanadium oxidation state, are determined through an elaborate study of processing temperature and O(2) partial pressure. To ensure a sub 100 nm adjustable film thickness, a non-oxidative intermediate thermal treatment is carried out at the end of each deposition cycle, allowing maximal precursor decomposition while still avoiding V(IV) oxidation. The resulting surface hydrophilicity, indispensable for the homogeneous deposition of the next layer, is explained by an increased surface roughness and the increased availability of surface vanadyl groups. Crystalline V(6)O(13) with a preferential (002) orientation is obtained after a post deposition annealing in a 0.1% O(2) ambient for thin films with a thickness of 20 nm.

Acidity properties of Ni-exchanged mordenites prepared with and without microwaves

We prepared several Ni,Na-mordenites by ion-exchange of commercial Na-mordenite in the liquid phase under microwaves irradiation and by conventional heating for comparison. After one exchange at 333 K, similar amounts of exchanged Ni 2+ (around 47%) were achieved with and without microwaves but faster under microwave irradiation. Making an intermediate thermal treatment under microwaves between two exchanges, also made under microwaves, the exchanged Ni 2+ increased up to 84%. Interestingly, microwaves strongly affect the acidity of the exchanged samples since they showed the appearance of new weak acid sites, which increased as longer the microwaves treatment was (NH 3-TPD). This agrees with the higher amounts of Lewis acid centres observed by adsorbed pyridine FTIR for these samples. These new sites were not observed for the conventional exchanged sample. From these results, we believe that microwaves could interact with nickel cations inducing the formation of weak-acid hydrolised nickel species [Ni(OH)] + for the microwaved samples. These acid characterization results were confirmed by testing several of these Ni,Na-mordenites in two reactions catalysed by different acid sites.

Crystallographic Orientations and Electrical Properties of Bi3.47La0.85Ti3O12 Thin Films on Pt/Ti/SiO2/Si and Pt/SiO2/Si Substrates

We report on the crystallization and electrical properties of Bi3.47La0.85Ti3O12 (BLT) thin films for possible ferroelectric non-volatile memory applications. The film properties were found to be strongly dependent on process conditions especially on the intermediate heat treatment conditions. The crystallographic orientation of the films showed sharp changes at the intermediate rapid thermal annealing (RTA) temperature of 450°C. Below 450°C, BLT thin films have <117 > orientation while they have preffered c-axis orientation above 450°C. We found that RTA conditions of the first coating layer play a major role in determining the entire crystallographic orientation of the films. The films also showed of ferroelectric hysterisis behavior strongly dependent on RTA treatment. In fact, the remanent polarization of Bi3.465La0.85Ti3O12 thin films having <001> preferred crystallographic orientation showed much smaller value compared to those having <117> orientation. The BLT films also exhibited good fatigue characteristics under bipolar stress up to 1011 cycles regardless of their intermediate thermal treatments.

OVERVIEW ON THE ELECTROCHEMICAL DEPOSITION OF Bi-2212 FILMS

In the framework of the coated tape superconductors, the electrolytic deposition is one of the chemical routes to obtain highly textured films either of the precursors or of the fully superconducting oxides. The technology will be reviewed with particular emphasis on the growth of Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212) film on Ag tape. For this system, recent advancements have been achieved combining the electrolytic deposition with intermediate thermal treatments and with an adequate optimisation of the initial stoichiometry of the deposited elements. A careful control of the morphology and amount of the not superconducting alkaline earth cuprates phases, grown in the film, allows to reach high critical current density, up to 40.000 A cm -2, in self-field at 77 K. A qualitative analysis by optical and electron microscopy, as well as a more quantitative analysis by x-ray diffraction reveals that the alignment of the Bi-2212 lamellas with the substrate as well as the decrease of the amount of the cuprates correlate with the superconducting transport properties.

Critical current in NbTi wires irradiated by neutrons at 20 K

In the present paper the results of experimental investigations of NbTi superconducting wires are given with two different treatments: cold-deformed (CD), intermediate thermal treatment (ITT) and also NbTi multiwire of factory treatment. The influence of neutron irradiation on the critical current I c dependence on magnetic field was studied in the cryochannel of nuclear reactor. Integral neutron fluence of 3 × 10 18 cm −2 in one core wires increases I c for CD samples, but doesn't change for ITT samples. Integral neutron fluence of 1.6 × 10 18 cm −2 leads to substantial I c-degradation for multiwire, its value undergoes twofold reduction, that is due to the decrease of the working cross-section of the optimized superconducting buses at the expense of its presurface layer `spoiling' as a result of enrichment by foreign atoms from the matrix of stabilizer.

Sol–gel preparation and characterization of Ni–SiO 2 nanocomposites

A series of Ni–SiO 2 composites, in the range 7–80 mol% of nickel, were prepared by two gelation methods with tetraethylorthosilicate (TEOS) and nickel(II) nitrate as starting materials. In the first method an aqueous solution of the salt was used while the second employed an alcoholic solution. The methods also differed in the intermediate thermal treatments of the gels. All the systems were reduced at temperatures around 500°C in flowing hydrogen and were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Nanometre sized nickel particles, homogeneously dispersed over the silica support, were observed in the samples with the smaller Ni content obtained by both methods, but only the one which made use of the alcoholic solution was successful in providing nanometre sized particles with size increasing with increasing concentration.

Synthesis and Characterization of [NH2C(I)NH2]2ASnI5 with A = Iodoformamidinium or Formamidinium: The Chemistry of Cyanamide and Tin(II) Iodide in Concentrated Aqueous Hydriodic Acid Solutions

Crystals of the organic−inorganic compounds [NH2C(I)NH2]2ASnI5 (A = NH2C(I)NH2+ and NH2CHNH2+) have been grown in an inert atmosphere from slowly cooled aqueous hydriodic acid solutions, each with the same starting concentration of dissolved cyanamide and tin(II) iodide. Each compound can be achieved in high purity and yield simply by varying the thermal history of the solution during cooling. If one starts from lower temperatures, cyanamide rapidly undergoes an addition reaction to generate the iodoformamidinium cation, yielding crystals of [NH2C(I)NH2]3SnI5. At higher temperatures, iodoformamidinium is reduced to formamidinium and is ultimately hydrolyzed if heated further or left for long periods of time. When the solution is subjected to an intermediate thermal treatment of 24 h at 80 °C before slow cooling, both cations can be stabilized in the solid-state compound [NH2C(I)NH2]2(NH2CHNH2)SnI5. The [NH2C(I)NH2]3SnI5 structure has recently been reported in the monoclinic space group P21/c and consists of highly distorted SnI6 octahedra which share opposite corners to form extended one-dimensional chains separated by iodoformamidinium cations. The new mixed-cation compound adopts a very similar triclinic (P1) structure, with the lattice parameters a = 6.3635(3) Å, b = 8.8737(5) Å, c = 10.8782(6) Å, α = 111.616(5)°, β = 92.938(4)°, γ = 95.358(4)°, and Z = 1 and with much less distorted SnI6 octahedra and shorter average Sn−I bond lengths. The different local coordination translates into a substantially darker coloration for crystals with A = formamidinium relative to those having A = iodoformamidinium (dark red versus orange). In addition to examining the stability of cyanamide and derivative species in aqueous hydriodic acid solutions, thermal analysis indicates that in an inert atmosphere the iodoformamidinium cation decomposes exothermally in the solid state at approximately 178(2) °C. Ultraviolet illumination studies on the title compounds also demonstrate the photosensitivity of the iodoformamidinium cation within the tin(II) iodide framework.

Interface study of physical vapour deposition TiN coatings on plasma-nitrided steels

To improve the surface hardness of steel, the substrate can be plasma nitrided prior to the deposition of a TiN layer. The success of this combined treatment depends very strongly on the intermediate thermal treatments carried out between plasma nitriding and TiN deposition. In this paper, some additional steps carried out after plasma nitriding and prior to TiN deposition, have been investigated to reveal the effect of the resulting interface on the adhesion of the coating. These combined treatments are carried out on austenitic stainless steel AISI 304 and on cold work tool steel 1.2379. If the plasma-nitrided steel surface is only coated with a thin Ti intermediate layer before the deposition of the TiN layer 1.5 μm thick—as it is usually the case for a standard TiN coating—flaking of the TiN coating is observed with AISI 304, even if no external load is applied. For the cold work tool steel, the TiN coating flakes when a small external load is applied in a scratch adhesion test. However, if the nitrided specimen is first cooled down, subsequently plasma heated and then sputter etched before the deposition of the Ti-TiN layer, no flaking is observed for both steel types. X-Ray diffraction (XRD) measurements and a transmission electron microscopy (TEM) study are carried out to reveal the interfacial phases which could cause this different behaviour. Scratch tests are carried out to correlate the adhesion of the TiN coating for different intermediate treatments with the results of the XRD and TEM studies.

Production and superconducting properties of laboratory scale NbTi and NbTiTa multifilamentary cables

A comparison of high field, low temperature superconducting properties between a Nb47 w/o Ti and two NbTiTa alloys as bases of laboratory scale cables was carried out Optimization cycles needed to obtain fair superconducting properties imply intermediate thermal treatments in the range 380–400°C during deformation at cold-work of 70%. The ternary alloys exhibit excellent ductile properties as do NbTi alloys. After an adequate optimization cycle the alloy Nb38 w/o Ti34 w/o Ta showed the best high field superconducting properties with values of more than 600 A mm −2 at 12 Tesla and 2.15 K.

Study of the kinetics of 1,4‐trans‐polymerization of isoprene with vanadium catalysts

AbstractThe kinetic peculiarities of 1.4‐trans‐polymerization of isoprene with vanadium catalyst systems being activated by intermediate thermal treatment have been investigated. The rate propagation and chain transfer constants have been determined by two independent methods, namely by kinetic and radiochemical ones. It is supposed that the peculiarities of the polymerization on kinetic catalysts systems are connected with the formation of mixed crystal structures of vanadium and aluminium during the period of thermal treatment of the catalyst.