Diffusion Impregnation Research Articles

Enhancement of Ni-NiO-CeO2 Interaction on Ni-CeO2/Al2O3-MgO Catalyst by Ammonia Vapor Diffusion Impregnation for CO2 Reforming of CH4.

Ni-based catalysts have been widely used for the CO2 reforming of methane (CRM) process, but deactivation is their main problem. This study created an alternative electronic Ni-NiO-CeO2 interaction on the surface of 5 wt% Ni-5 wt% CeO2/Al2O3-MgO (5Ni5Ce(xh)/MA) catalysts to enhance catalytic potential simultaneously with coke resistance for the CRM process. The Ni-NiO-CeO2 network was developed on Al2O3-MgO through layered double hydroxide synthesis via our ammonia vapor diffusion impregnation method. The physical properties of the fresh catalysts were analyzed employing FESEM, N2 physisorption, and XRD. The chemical properties on the catalyst surface were analyzed employing H2-TPR, XPS, H2-TPD, CO2-TPD, and O2-TPD. The CRM performances of reduced catalysts were evaluated at 600 °C under ambient pressure. Carbon deposits on spent catalysts were determined quantitatively and qualitatively by TPO, FESEM, and XRD. Compared to 5 wt% Ni-5 wt% CeO2/Al2O3-MgO prepared by the traditional impregnation method, the electronic interaction of the Ni-NiO-CeO2 network with the Al2O3-MgO support was constructed along the time of ammonia diffusion treatment. The electronic interaction in the Ni-NiO-CeO2 nanostructure of the treated catalyst develops surface hydroxyl sites with an efficient pathway of OH* and O* transfer that improves catalytic activities and coke oxidation.

Results of steel microarc diffusion impregnation with boron combined with carbide-forming elements

Results of steel microarc diffusion impregnation with boron combined with carbide-forming elements

Surface modification of PVC by silica sol

One of the most important and widely used modern materials is polymeric composite materials based on PVC. One of the possible ways to improve the properties and increase the reliability of polymer products is their surface diffusion treatment with liquid nanomodifying components. The study investigated the possibility of using silica sol to strengthen the surface of rigid PVC. It is shown that as a result of diffusion impregnation of PVC in silica sol to a certain degree of saturation and subsequent heat treatment (in order to fix the modifier), the resulting composites have enhanced surface properties. As a result of the diffusion of silica sol into the PVC matrix and its physicochemical interaction with the latter, a modified surface layer is formed with a structure and properties that vary in its thickness. Modifying the surface of finished PVC products without changing the inner part, allows you to strengthen the whole material as a whole and increase its resistance to various external factors. At the same time, the consumption of the modifying additive is significantly reduced in comparison with the adding into the volume of the material, and its effectiveness increases due to the high local concentration on the surface.

Features of Thermal Diffusion Impregnation with Hydrogen of Porous Material Based on Titanium

The effect of bulk porosity on the kinetics of hydrogen thermal diffusion impregnation and on the structure of specimens prepared from different semiproducts, i.e., bars, wires, and fibers of commercially pure titanium, is studied. It is established that the rate of hydrogen absorption by porous titanium is at a maximum at 650°C and it increases with an increase in bulk porosity, pore size and a reduction in typical size of original semiproduct. Simultaneous thermal diffusion impregnation of monolithic and porous material leads to nonuniform distribution of hydrogen between them and correspondingly a change in structure.

Thermal diffusion zincing/aluminizing of steels and alloys under mechanical activation of sample surfaces

Possibility of producing zinc-aluminide coatings by thermal diffusion impregnation of steels under mechanical activation of the surface of samples in a rotating reactor was analyzed.

Control of the plasticity of organosilicon rubbers by their modification with polypyrrole

Modification of organosilicon rubbers SKTN and SKTV with polypyrrole was studied. The modifying agent was synthesized directly in the rubbers containing iron trichloride acting as oxidant and catalyst, using the diffusion procedure and impregnation of organosilicon rubbers with pyrrole-2-carboxylic acid in supercritical carbon dioxide. Changes in the ductility and viscosity of the composite materials were analyzed.

Development and creation of layered materials for tool purposes with a prescribed property gradient

Layered composite materials based on hard alloys grades VK and TK with graded surface properties are studied. The materials are prepared using standard procedures of thermal diffusion impregnation, deposition from the vapor phase, and ion-plasma deposition. In addition dispersion strengthened hard alloys are prepared by processing in Ti plasma between the stages of preliminary and final sintering.

Carboborosilicide and oxide composite coatings on carbon materials

Complex carboborosilicide and oxide coatings on carbon materials prepared by vacuum activated diffusion impregnation predominantly through a liquid phase, vacuum fusion, and enamelling are studied. It is established that coating formation from the vapor phase hardly reduces the original porosity of carbon materials. The complex protective coatings developed that are formed by vacuum activated diffusion impregnation through a liquid phase lead to a reduction in the original porosity and gas permeability of carbon materials thereby increasing their high-temperature strength and heat resistance at elevated temperatures. It is shown that higher heat resistance in the temperature range 1800–2000 °C is provided by multilayer coatings based on carbides and borides of silicon, titanium and zirconium, borosilicides of tungsten, hafnium, molybdenum, and also oxides of silicon, aluminum, zirconium, and hafnium. It is established that the protective properties of coatings depend markedly both on their composition, structure, preparation method and on the form of the original carbon materials.

Cobalt-Chromium Powder Alloys and Retention Coatings Made from Them for Orthopaedic Stomatology

An alloy of Co-Ni-Mo-Cr is prepared by diffusion impregnation with chromium from point sources of cobalt-nickel-molybdenum alloy powder synthesized by combined reduction. Optimum regimes are determined for preparing alloy powder by combined reduction of cobalt, nickel, and molybdenum oxides (reduction temperature 1325 K, isothermal soaking time 3 h) and diffusion impregnation with chromium (temperature 1373 K, isothermal soaking time 4 h). The adhesive strength of a facing coating with material of a dental prosthesis manufactured using the alloy developed is studied. It is shown that with application of retention layers the adhesive strength increases by a factor of three to five compared with using cast spheres (beads).

Simulation of Wood Impregnation with Oligomer Solutions

An adequate model is developed for the impregnant distribution along the fibers of a small-dimension crosscut end under conditions of isothermal diffusion impregnation with oligomer solutions.

Diffusion Interaction during Preparation of Nanocrystalline Powders in the System ZrO2-Y2O3

The properties of ZrO2 - 3 mole% Y2O3 nanocrystalline powder prepared by diffusion impregnation are studied. The original nanocrystalline powder of M-ZrO2 is prepared with hydrothermal treatment of aqueous zirconium hydroxychloride solution by different regimes. It is found that after diffusion impregnation for all of the powders with yttrium oxide two solid solutions are formed (F-ZrO2 and M-ZrO2) in mixture. It is established that the morphological features typical for the original powders are retained. The efficiency of diffusion impregnation is determined by the slightly-agglomerated powder with a high degree of crystallinity.

SURFACE IMPROVEMENT OF DUCTILE CAST-IRON

Diffusion impregnation with chromium is widley used as a surface treatment for steel and gray cast-iron, but very limited in ductile cast-iron. Two types of ductile cast-iron, ferretic and 60 % pearlitic, are surface chromised under different conditions using powder pack method. The maximum attaind chromised layer thickness of 22 um with surface micro-hardness of 1950 HV. is achived after treatment at 1000.0 for 30 hours. The rate controlling of the carbide layer growth process during chromising is being the diffusion of the chroium element and the direction of layer growth is determined to be inward chromium diffusion. The evaluation of the newly formed layers by corrosion, oxidation and wear resistance are carried out and discussed in the light of the obtained results.

Structure formation processes in sintering of stainless-steel-base heterophase materials 1. Sintering of austenitic stainless-steel-base materials with additions of Cr3C2

Earlier [1-3], a series of basic and applied investigations of the processes of pressing, sintering, and hot compacting of chromium and chromium-nickel stainless steel powders were presented. These works are devoted primarily to powdermetallurgy steels with a single-phase homogeneous structure basically not differing from the structure of the stainless steels produced by traditional methods. Of interest is development of stainless-steel-base materials with a heterophase structure. Together with good corrosion resistance such materials may possess such specific properties as increased wear resistance. This is obtained by addition to the metallic matrix of various additions such as carbides, intermetallides, nitrides, borides, sulfides, etc. However, certain additions reduce the corrosion and certain mechanical properties of stainless steels, particularly plasticity. In order to provide the optimum combination of properties of such materials it is necessary to optimize their composition and structure. In this work the structure and properties of austenitic chromium-nickel stainless-steel-base materials with additions of chromium carbide Cr3C 2 in a quantity of up to 10% were studied. The powders of types Khl8N12, Khl8N15, Khl8N12, Khl8N12M2, and K.h23N18 stainless steels were prepared by atomization, calcium hydride reduction, and diffusion impregnation [4]. The specimens for tensile, bend, and impact mechanical tests were prepared by a single pressing and sintering in hydrogen and vacuum at 1200~ After sintering the microstructure was investigated and the density and hardness of the specimens and the microhardness of the structural constituents were determined. In addition, selective micro-x-ray spectral and x-ray structural analyses were made for the purpose of studying the composition of the matrix and the carbide inclusions and also of establishing the crystalline lattice parameters of the base. In order to study the influence of the degree of dispersion of the chromium carbide additions on the character of their interaction with the matrix a preliminary investigation including use of types Khl8N15, Kh18N12, and Khl8N12M5 stainless steel powders obtained by the above methods was made. Monodispersed chromium carbide powder with average particle sizes of 30, 80 130, and 200 #m (sifted through -0056, -0100 + 0063, -0160 + 0100, and -0250 + 0160 screens) was used. In all cases the quantity of Cr3C 2 was 10 wt. %. The specimens were sintered in vacuum at 1200~ It was established that the hardness and microhardness of the base of the specimens containing carbides are higher and their density somewhat lower than of the standard specimens. At the same time the microhardness of the carbides themselves also drops significantly as the result of sintering (Fig. 1). With a decrease in carbide inclusion size, all of these rules are strengthened, which is an indication of the more active interaction of the more dispersed carbides with the base. The nature of the powders of the base has significantly less influence on the character of its interaction with the carbides than their degree of dispersion. The more active interaction with the metallic matrix of specimens of atomized type Khl8N12M2 powder is confirmed by the higher absolute and relative increase in microhardness of the base of the these specimens in compared with those prepared from Khl8N12 and Kh18N15 powders prepared by methods of diffusion impregnation and calcium hydride reduction (Figs. 1, 2). The increase by several percent in the chromium content in the metallic matrix and the increase in its crystallin lattice parameters in comparison with the standard specimens simultaneously established by methods of micro-x-ray spectral and xray structural analyses (Table I) are apparently caused by diffusion of chromium and carbon from the carbides into the base. The greatest change in the crystalline lattice parameters of the base is observed with use of dispersed additions with an average

Protection of carbon materials from high-temperature gas corrosion

A study is made of composite carbon -borosilicide on carbon materials prepared by gas phase deposition, diffusion impregnation, liquid-phase impregnation, and fusion. It is shown that muldlayer coatings prepared from carbon-borosilicide materials, particularly silicon and titanium carbides, and molybdenum, tungsten, and hafnium borides and silicides have greater heat resistance in the temperature range 1500–2000°C in air. Their protective properties are strongly dependent on composition, coating structure, and preparation methods as well of the grade of the original carbon materials.

Chemical heat treatment of powder materials based on iron

Diffusion chromizing and boriding of iron-base powder materials SP30, SP90, and SP90D3 are studied. The growth kinetics for diffusion layers are determined depending on diffusion impregnation conditions, and material composition and porosity. Comparative bending and tensile strength tests as well as wear- and heat-resistance tests for materials after sintering by standard conditions or boriding and chromizing are performed. It is shown that the mechanical properties of materials after different types of processing are approximately the same whereas the wear and heat resistance after diffusion impregnation increase markedly. This makes it possible to conclude that a combination of sintering and boriding (or chromizing) is possible under the following conditions: boriding at 1000°C for 2–3 h; chromizing at 1100°C for 3–4 h.

Nitriding of martensitic-austenitic steel with a different original structure

Hardening heat treatment of a number of promising martensitic-austenitic steels [i, 2] predetermines presence in the structure of different amounts of martensite, equilibrium quench austenite, and phase-hardened (forming during aging as a result of ~ + y-transformation) austenite. Optimization of the quantitative ratio of these structural components is important not only in order to obtain the required mechanical properties, but also creation of favorable conditions for diffusion impregnation of the surface layer in the case, for example, of additional nitriding of these steels with the aim of improving surface hardness and wear resistance. It is well known [3] that formation of nitrided layers and their properties depend in many cases on the original structure of the steel being nitrided.

Cladding of diamond powders by thermal diffusion impregnation. II. The structure and properties of metallized diamond powders

Cladding of diamond powders by thermal diffusion impregnation. II. The structure and properties of metallized diamond powders

Hardening of die sintered carbide parts by thermal diffusion impregnation of their surface with titanium from a coating

Hardening of die sintered carbide parts by thermal diffusion impregnation of their surface with titanium from a coating

Increasing the heat resistance of vanadium by siliciding

The purpose of this article was to evaluate the influence of modifier metals on the protective properties of silicide coatings in heating of vanadium in air and also on the mechanical properties of type VnM-2 unalloyed vanadium and VTsU alloy. Coatings were produced by diffusion impregnation from molten sodium with silicon or silicides of the modifying elements. The silicides of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, chromium, tungsten, rhenium, and nickel were investigated using x-ray spectrometric and hardness investigations and x-ray diffractometric analysis. The protective properties of the coatings were determined from the relative change in weight of the samples with and without coatings during isothermal oxidation in air at 1073/sup 0/K and also by differential thermal analysis. The influence of the coating on the mechanical properties of the material was also investigated using a borosilicide coating. High-temperature vacuum annealing was assessed as a method for restoring the plastic properties and relieving the stresses of vanadium and VTsU alloy subsequent to coating.

Influence of a palladium coating on the mechanical properties of KhN67MVTYu alloy

Depending upon which of the structural constituents predominates in the coating, single phase (solid solutions) or heterophase(chemical compounds such as intermetallides, carbides, etc.) plastification or embrittlement, respectively, will occur. In single component diffusion impregnation of a multicomponent system (or in multicomponent impregnation of a singlecomponent matrix) with the use of an active transport medium the structural transformations in the surface layer are difficult to predict. Therefore in each specific case it is necessary to investigate the influence of the diffusion layer on the mechanical properties of the material in general.