Liquid Phase Contact Research Articles

Microstructure and tribological properties of ZrB2-enhanced NiCrBSi coatings prepared by high-velocity oxy-fuel spraying

This paper presented a novel study of the preparation of ZrB2-enhanced NiCrBSi coatings and its microstructure and tribological properties. NiCrBSi-ZrB2 composite powder and coatings with ZrB2 contents of 20 %, 40 %, and 50 % were prepared by spray-drying and high-velocity oxygen-fuel (HVOF) spraying, respectively. The microstructure and high-temperature wear performance at 700 °C were compared with those of an NiCrBSi coating. The results showed that the NiCrBSi and ZrB2 powder exhibited good wetting properties in the solid-liquid sintering zone and the CrB phase was formed in the liquid phase contact zone in composite coatings with ZrB2 contents of 20 % and 40 %, while the CrB phase disappeared in the 50 %ZrB2 coating due to the pinning effect caused by excessive ZrB2. The microhardness of composite coatings tended to increase, then decrease, and the 40%ZrB2 coating reached a maximum hardness of 874 HV. The NiCrBSi coating presented oxidative wear and adhesive wear. Although the fracture toughness of composite coatings was lower than that of the NiCrBSi coating, the wear resistance in the composite coating was significantly enhanced due to the evenly distributed ZrB2 and CrB phases. The 20%ZrB2 coating with low fracture toughness and the 50 %ZrB2 coating with hardness mismatch caused by the absence of CrB produced severe abrasive wear. The hardness gradient with the matrix, ZrB2 and CrB phases reduced abrasive wear caused by peeling in 40%ZrB2 coating, and the ceramic phases acted as skeletons reducing the deformation of the load contact area. The formation of Cr2O3 during the friction process further improved the wear resistance. The wear mechanism of 40%ZrB2 coating underwent light adhesive wear, mild abrasive wear and oxidative wear, and the coating exhibited the best wear resistance with the lowest wear rate of 1.16 × 10−13 m3/N·m (a decreased of 56 %).

Conversion of Marine Plastic Litter into Chemicals and Fuels through Catalytic Pyrolysis Using Commercial and Coal Fly Ash-Synthesized Zeolites

A marine plastic litter (MPL) sample, collected during a beach cleanup campaign, underwent thermal and catalytic pyrolyses to demonstrate that valuable hydrocarbon oil and gas can be produced from heterogeneous plastic waste, partly aged and not mechanically recyclable. A low-cost H-X zeolite lab synthesized from coal fly ash (CFA) was tested and compared with two commercial zeolites (H-USY and H-ZSM-5) commonly used in the industrial cracking field. MPL characterization revealed it is mainly composed of polyethylene and polypropylene (52 and 45 wt %, respectively), and it has ideal physicochemical properties as feed for pyrolysis processes. Thermogravimetric analyses demonstrated that catalysts can reduce the degradation temperature of MPL from 472 to 425 °C and from 450 to 421, 342, and 380 °C for H-ZSM-5, H-X/CFA, and H-USY, respectively. These results were confirmed by thermal and catalytic pyrolyses tests performed in a bench-scale reactor. All the catalytic tests were carried out at 450 °C with a liquid phase contact mode. In particular, H-X/CFA, avoiding tar and wax formation, produced up to 87 wt % of light oil with a high content of short chain aliphatic hydrocarbons, obtaining results very similar to those gained with the expensive commercial H-USY. For all the catalytic pyrolysis tests, the produced gases proved to be more than sufficient to sustain the process heat requirement.

Effect of impregnated phenolic resin on the properties of Si–SiC ceramic matrix composites fabricated by SLS-RMI

Selective laser sintering (SLS) combined with reaction melt infiltration was used to fabricate Si–SiC ceramic matrix composites, and the effects of different concentrations of phenolic resin (PF) on the properties of the SLS green body and carbonized and final Si–SiC samples were investigated. The results showed that the impregnation with PF can increase the bulk density, reduce the porosity of the samples at all stages, and improve the mechanical properties of the reactive bonded samples. The degree of densification and mechanical properties of the sample gradually enhanced with an increase in PF concentration. The main phases of the Si–SiC composites were free Si, α-SiC, β-SiC, plus an extremely small amount of Al–Si alloy, and the SiC and the Si phase contents increased and decreased, respectively, as the concentration of PF increased when measured using Rietveld refinement and image analysis software. The macroscopic properties of the samples improved greatly after precursor infiltration pyrolysis (PIP) treatment with 66.7%vol PF-ethanol solution twice. According to the crystal nucleation-growth theory, it was inferred that the infiltrated PF could provide a certain amount of pyrolytic carbon in the carbonized specimen. During the reaction bonded process, the carbon formed by carbonization pyrolysis first dissolves into the molten Si and reaches saturation. With the further dissolution of carbon, [C] and [Si] in the liquid phase contact each other to form β-SiC nuclei, the nuclei that precipitate at the pore wall position and gradually form a continuous interfacial layer of β-SiC. The β-SiC layer prevents the liquid Si from direct contact with C inside the prefabricated body, therefore, further reactants diffuse through the layer. Finally, the fine crystalline β-SiC grains were fabricated inside the specimen.

Synergistic effects, gas evolution and ash interaction during isothermal steam co-gasification of biomass with high-sulfur petroleum coke

This work investigated the co-gasification behavior of rice straw (RS) and a high-sulfur petroleum coke (PC). An isothermal gasification experiment under a steam atmosphere was conducted on a self-designed thermogravimetry (TG) coupled with mass spectrometry (MS). The results indicate that the high sulfur content in PC seem to have no significant effect on co-gasification. RS showed obvious catalytic effect only after it was completely gasified into ash. Affected by the high concentration of steam, the main components of synthesis gas are H2 and CO2. The RS ash presents a violent melting state, and the lower RS addition ratio only shows a strong catalytic effect in the initial stage of the reaction. The high addition ratio makes the ash particles in the liquid phase contact and react well with the PC particles, and will not inhibit the gasification of the PC particles before the PC particles are completely wrapped.

Effect of mixing ratio on the adsorption behavior of low-rank coal surface using mixed collectors: Experimental and molecular dynamics simulation study

ABSTRACT The effect mechanism of mixing ratio on the adsorption behavior of low-rank coal surface using mixed collectors has not been systematically studied. In this study, dodecane (D) and n-valeric acid (N) were mixed into different collectors in different ratios, and their adsorption mechanism on the surface of LRC was studied by experiment and simulation calculation. The flotation results indicated that the sequence of the flotation clean coal yield was 8:2 > 6:4 > 5:5 > 7:3 > 9:1. The measurement results of the heat of adsorption, total organic carbon, and liquid phase contact angle all responded to the flotation results as a whole. The molecular dynamics simulation results revealed that when an appropriate ratio was used to form a mixed collector, the N molecules could make the D molecules form oil molecular layer thicken, thus increasing the hydrophobicity of the surface of the LRC molecules. The optimal mixing ratio could also create a large interaction energy between the mixed collector and LRC. Therefore, D and N need to be mixed at a proper ratio to maximize the LRC flotation efficiency.

High-temperature erosive wear characteristics and bonding requirements of hard carbides cast-in insertion multi-component white cast iron

This research investigated wear resistance characteristics of hard carbide cast-in insertion cast iron by high-temperature erosive test. Moreover, good bonding conditions between cast iron and hard carbide alloy were examined by using casting simulation CAE. Two types of multi-component white cast iron with Cr, Mo, W, V, and Nb for base metal, tungsten carbide (WC) and titanium carbide (TiC) for insert were prepared. High-temperature erosion tests were conducted using alumina ball (average diameter: 1.16 mm, hardness: 1140 HV) with impact angle of 30, 60, and 90 deg. at 873 K.The air velocity of 100 m/s (particle velocity about 30 m/s). The total particle loading was 8 kg. The mass of the test specimen was measured before and after each test to evaluate the erosive wear property by erosion rate which is volumetric removal divided by the total feed of impact particles.As a result of erosion tests, WC cast-in insertion multi-component white cast iron showed good wear resistance characteristics compared with TiC one. TiC cast-in insertion multi-component white cast iron increased wear amounts due to cracking on insert surfaces that occurred by heat shock when pouring.Temperature history of interfacial molten cast iron and insert on solidification process were acquired by using solidification analysis to compere condition of molten steel and insert at the bonding interface. To longer liquid phase contact time is the thicker diffusion and reaction layer of each cast-in insertion sample. Both diffusion and reaction layers were created in the bonding interface of WC cast-in insertion sample. On the other hand, only diffusion layer was created in TiC cast-in insertion sample. These differences in bondability are due to diffusion coefficient of insert elements and gibbs standard free energy of carbides.

Application of a water based nanofluid for wettability alteration of sandstone reservoir rocks to preferentially gas wetting condition

Condensate and water banking around gas condensate wells result in vital well deliverability issues. Wettability alteration of near wellbore region to gas wetting condition is known to be the most novel and the only permanent method, to improve condensate well productivity. In this work, a water based nanofluid is used to change the wettability of sandstone reservoir rocks from strongly liquid wetting to intermediate gas wetting condition. Static contact angle measurements demonstrated significant increase of liquid phase contact angle as a result of chemical treatment with SurfaPore M nanofluid. The characteristics of SurfaPore M adsorption on sandstone rock are quantified through kinetic and equilibrium adsorption studies, as well as the stability of the used chemical against NaCl brine salinity in ambient condition,. Air/liquid spontaneous imbibition tests along with core flooding experiments were utilized to study the effect of wettability on two phase fluid flow through porous media. It has been concluded that kinetic behavior of SurfaPore M-sandstone system conforms pseudo-second order, while Freundlich isotherm matches the equilibrium adsorption data; these results eventuate multilayer chemisorption of NPs on sandstone surface. The results of spontaneous imbibition tests showed remarkable decrease of the ultimate amount of imbibed liquid by factors of 0.09 and 0.17 for n-decane and water, respectively. Also, the results of water injection experiments demonstrated the increase in liquid phase mobility by a factor of 3.2 as a result of surface modifiers in high permeability sandstone core plug. Furthermore, it is concluded that the utilized nanofluid is better to be used in high permeability sandstone rocks. The results of this research pave the way for possible future field applications of SurfaPore M nanofluid chemical in gas condensate reservoirs to alleviate production difficulties.

Pyrolysis of municipal plastic wastes II: Influence of raw material composition under catalytic conditions

In this work, the results obtained in catalytic pyrolysis of three plastic waste streams which are the rejects of an industrial packing wastes sorting plant are presented. The samples have been pyrolysed in a 3.5 dm 3 reactor under semi-batch conditions at 440 °C for 30 min in nitrogen atmosphere. Commercial ZSM-5 zeolite has been used as catalyst in liquid phase contact. In every case, high HHV gases and liquids which can be useful as fuels or source of chemicals are obtained. A solid fraction composed of the inorganic material contained in the raw materials and some char formed in the pyrolysis process is also obtained. The zeolite has shown to be very effective to produce liquids with great aromatics content and C3–C4 fraction rich gases, even though the raw material was mainly composed of polyolefins. The characteristics of the pyrolysis products as well as the effect of the catalyst vary depending on the composition of the raw material. When paper rich samples are pyrolysed, ZSM-5 zeolite increases water production and reduces CO and CO 2 generation. If stepwise pyrolysis is applied to such sample, the aqueous liquid phase can be separated from the organic liquid fraction in a first low temperature step.

Individual and simultaneous degradation of brominated high impact polystyrene and brominated acrylonitrile-butadiene-styrene and removal of heteroelements (Br, N, and O) from degradation oil by multiphase catalytic systems

Brominated high-impact polystyrene (HIPS-Br), which contained decabromodiphenyl ether flame retardant, and brominated acrylonitrile butadiene styrene (ABS-Br), which contained bromine-containing epoxy-type flame retardant, were degraded at 450°C individually and in a 1/1 mixture by a thermal and catalytic procedure using folded sheet mesoporous (FSM) and ZSM-5 zeolite in liquid phase contact mode. The two polymers produced similar degradation oils but at a higher yield for HIPS-Br. However, the composition and distribution of Br-, N-, and O-containing compounds depended on the type of flame retardant in HIPS-Br and ABS-Br. Multiphase catalytic systems consisting of FSM in liquid phase contact mode and various CaH-, FeO-, CoMo-, and NiMo-based catalysts, or combinations of these catalysts, in vapor phase contact mode were used to decrease the amount of heteroatoms (Br, N, and O) in the degradation oils. Each system gave particular results in terms of mass balance and concentrations of heteroatoms. A FSM (liquid phase contact)/CaHC (vapor phase contact) combination was the best catalytic system to remove Br-, N-, and O-containing compounds from degradation oils.

A novel process for the preparation of thick porous silicon layers with very high porosity

AbstractA novel process for the preparation of thick porous silicon layers having very high porosities is proposed. Starting with thick layers of intermediate porosity the porosity is further increased in an additional step. This is done by means of controlled partial oxidation of the silicon skeleton followed by selective removal of the oxide film in an HF vapor phase etching process. Due to this, porosities beyond 90% are accessible since any further liquid phase contact is avoided and therefore no additional drying steps are necessary. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The role of temperature program and catalytic system on the quality of acrylonitrile-butadiene-styrene degradation oil

Thermal and catalytic degradation of acrylonitrile-butadien-styrene copolymer (ABS) was performed at 450°C by semi-batch operation. Four different temperature programs were used for thermal degradation. SA4 silica alumina and three SA4/iron oxide combinations (γ-Fe 2O 3, a Fe 3O 4-C composite and α-FeOOH) were used for catalytic degradation. The heating rate affects the quality of the degradation oil, the following heating program giving the lowest amount of heavy nitrogen-containing compounds: room temperature→400°C (heating rate β=10°C min −1)→450°C ( β=1°C min −1; then isothermally hold at 450°C for 210 min). SA4 catalyst used in liquid phase contact mode has a cracking effect on ABS degradation. The SA4/iron oxide catalytic systems give better results than the separate use of the catalysts, converting the heavy nitrogen (N)-containing compounds into light aliphatic nitriles that can be easily removed from the degradation oil by distillation. With SA4/α-FeOOH system the amount of 4-phenylbutyronitrile, the main N-containing compound from ABS thermal degradation, was strongly decreased in oil, from 17.5 to 1.7 wt.%.

The enhancing effect of surface coatings on cast-in bonding of steel and titanium inserts in aluminium castings

Insertion bonding of mild steel and titanium pipes in aluminium castings was performed in two ways; either by holding paired pipe and aluminium cylinder specimens at constant high temperatures, or by pouring molten aluminium into sand moulds containing inserts. The surfaces of the inserts were electroplated using Ag or Au, or spray coated with Al-Si alloy. The bonding was evaluated by shear strength measurements and microstructure observations. To verify the effect of surface coatings, the contact between the molten aluminium and the specimens was observed. At constant high temperatures, coated steels showed good metallurgical bonding when they were maintained for about 200 s in contact with molten aluminium. The time necessary for bonding was shorter with titanium inserts. In bonded specimens, alloyed microstructures were observed at the interfaces. There was no bonding with uncoated specimens. All coatings used were effective when poured, but preheating of the moulds was necessary to allow sufficient solidification time for the melt/insert volume ratios which were 32 and 36. Process analysis by the finite difference method showed that bonding required a period of liquid phase contact of the melt with the inserts. Observation of aluminium droplet contact with the inserts showed that uncoated surfaces of steel and titanium are not wetted by the melt due to stable oxide skins. With Ag electroplating, aluminium droplets can make wet contact with the specimens. The contact angle decreased from about 140° in uncoated specimens to 15°-45° with Ag plating. The plating prevents surface oxidation of the inserts and promotes wet contact when the active aluminium liquid surface is exposed. The Al-Si alloy spray coating has some effect in promoting wettability, but it is inferior to Ag plating.

Degradation of polyethylene and polypropylene into fuel oil by using solid acid and non-acid catalysts

The thermal and catalytic degradation of plastic polymers, polyethylene (PE) at 430°C and polypropylene (PP) at 380°C into fuel oil were carried out by batch operation. The catalysts employed were acid-catalysts silica–alumina (SA-1, SA-2), zeolite ZSM-5 and non acidic mesoporous silica catalysts (silicalite, mesoporous silica gel and mesoporous folded silica (FSM). The yields of product gas, liquid and residues; recovery rate of liquid products, and boiling point distribution of liquid products by catalytic degradation were compared with those of non-catalytic thermal degradation. The present work is divided into three sections: (1) a study of effect of catalytic contact mode and (2) a study of effect of types of catalysts on plastic degradation, and (3) the evaluation of catalysts during the degradation of PE and PP by repeating batch operation. For PP degradation in liquid phase contact with SA-1, the yield of liquid hydrocarbons was obtained with 69 wt.%, and the boiling point (bp) of the oil ranged between 36 and 270°C, equivalent to the bp of normal paraffins n-C 6 to n-C 15. The liquid products from catalytic degradation have a carbon number distribution very similar to commercial automobile gasoline. For vapor phase contact, the yield of liquid products was much lower (54%) and the rate of liquid recovery (or formation) was much slower. Catalysts possessing strong acid sites such as zeolite ZSM-5 accelerated the degradation of PP and PE into gases which resulted in low liquid yields. For FSM, which possesses no acid sites, the initial rates of PP and PE degradation into liquid were as fast as that over an acid catalyst (SA-1) and the liquid yields were higher. The liquid products from catalytic degradation over FSM have a carbon number distribution similar to a mixture of kerosene and diesel oil. Upon repeated use SA-1 deactivated very rapidly due to coke deposition on the catalyst, whereas FSM deactivated much more slowly. These findings concerning the FSM catalyst strongly suggest that the mesopores surrounded by the silica sheet may act as reservoir for radical species and the radical species accelerate the degradation of plastic melt.

Cast-in insertion of steel pipes in cast iron with internal air and nitrogen cooling

When using cast-in inserts of pipes in molten metal with large melt/insert volume ratios, the pipe may suffer structural damage such as grain growth and excessive diffusion of melt elements, and may even melt locally due to the heat of the melt. In this research, air and nitrogen gas cooling was applied to mild steel pipe inserted in grey cast iron. Experiments showed that an adequate amount of air flow improves grain growth, decreases carburized layers, and still gives good metallurgical bonding, although excessive cooling harms bonding. Nitrogen has a cooling effect similar to air, and prevents oxidation and decarburization of inner surfaces of the steel pipe. Solidification analysis of the interface melt by the finite difference method and the concept of liquid phase contact time, LCT, gave a good explanation of the experimental results. Internal cooling was successfully applied to ductile cast iron, and was also found to improve the microstructure of castings.

Catalytic Degradation of Polypropylene into Liquid Hydrocarbons Using Silica-Alumina Catalyst

Abstract The degradation of polypropylene (PP) was carried out at 380 °C by batch operation using silica-alumina catalyst in 1) liquid phase contact and 2) vapor phase contact. For liquid phase contact, the liquid hydrocarbon products with a yield of 69 wt% had a boiling points (BP) range of 36 to 270 °C, equivalent to the BP of normal paraffins n-C6 to n-C15. For vapor phase contact, the yield of liquid products was much lower (54 wt%) and the rate of liquid recovery was much slower.

Kinetics and Thermodynamics of Surfactant Adsorption at Model Interfaces: Evidence of Structural Transitions in the Adsorbed Films

An in situ method, based on two liquid phase contact angle measurements, is developed to investigate the mechanisms of simultaneous adsorption of surfactant at solid−liquid and liquid−liquid interfaces. Well-characterized model systems (methyl-terminated monolayer−hydrocarbon drop−aqueous surfactant solution) and (methyl-terminated monolayer−air bubble−aqueous surfactant solution) have been used to allow reliable connection between surface characteristics and observed phenomena. The adsorption kinetics at such complex interfaces was analyzed through the balance of interfacial forces. For both nonionic surfactants (C8E10 and C12E7) and air bubble used in these studies, we have found that the adsorption kinetics exhibit intermediate transition plateaus at some critical bulk concentrations (around the cmc). These transitions were related to structural rearrangements in the adsorbed surface phase.

Evaluation of Thermal Conditions for Bonding in Cast-In Inserts of Steel to Cast Iron.

Thermal conditions for metallurgical bonding in cast-in inserts of steel and cast iron were discussed based on experiments and solidification analyses performed on three types of castings, pipes and bars inserted in melt, and melt poured into pipes. The liquid phase contact time, LCT, was determined from the calculated solid fraction vs. time curve of the interface melt. It was concluded, that a LCT larger than 100 sec results in good metallurgical bonding, 20-50-sec LCT yields partial bonding, and there is no bonding at LCT less than 10 sec in the atmosphere without surface treatment. The criterion was also applied to cast-in inserts of pipes with inside air cooling at various volume ratios and air flow rates that changed the cooling and solidification rates. Thermal spraying of Ni based self-fluxing alloy decreases the minimum required LCT to less than 5 sec.

Gas absorption accompanied by a two-step chemical reaction

Film and penetration theory solutions are presented for gas absorption accompanied by a two-step chemical reaction involving a transient intermediate species. For the case of equal diffusivities, the two theories agree with each other within 6 per cent. When the intermediate species is relatively long-lived, φ, the factor by which the chemical reaction enhances the absorption rate, goes through a maximum as liquid phase contact time increases, and φ approaches its ultimate asymptote from above. This unique behaviour is not found in gas absorption accompanied by a single chemical reaction, but aspects of this interesting behaviour have been observed in published experimental data for the carbon dioxide-monoethanolamine system and for the chlorine-ferrous chloride system.