Undissolved Particles Research Articles

Heat treatment and effects of Cr and Ni in low alloy steel

The effects of Cr and Ni on low carbon steel was observed. Undissolved carbide particles refine the austenite grain size. In the presence of nickel, chromium carbide is less effective in austenite grain refinement than chromium carbide in absence of nickel at temperature below 975°C. Nickel does not produce any austenite grain refinement but presence of nickel promotes the formation of acicular ferrites. It was also found that Ni and Cr as chromium carbide also refines the ferrite grain size and morphology. Cr as chromium carbide is more effective in refining ferrite grain size than nickel.

Laser gas assisted melting of preprepared alumina surface including TiC particles at surface

Laser gas assisted remelting of prepared alumina surface is carried out. In the prepreparation cycle, carbon film containing TiC particles of 50 μm thickness is formed at the alumina surface. Laser controlled melting is carried out on the preprepared alumina surface at high pressure nitrogen environment. The microstructural and morphological changes in the laser treated section are examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction (XRD). The microhardness of the resulting surface is measured, and the residual stress developed in the surface is determined from the XRD technique. ABAQUS code is used to predict the temperature and stress fields in the laser treated region. It is found that a dense structure containing undissolved TiC particles is formed in the surface region of the laser treated layer. The nitride compounds of AlN and Al(C, N) are formed at the surface during the laser treatment process. The columnar structure is formed beneath the dense structure. The predictions of residual stress agree with the results obtained from the XRD technique.

Austenite grain growth prediction coupling with drag and pinning effects in low carbon Nb microalloyed steels

A metallurgical model has been developed to predict the austenite grain growth in Nb microalloyed steels. The mutual effects of Nb(CN) particle pinning and Nb solute drag on grain growth kinetics are studied. The particle dissolution, the undissolved particle coarsening and the changes in Nb solute in solution during reheating or isothermal heat treatment process are taken into account in the model. It is shown that, besides the pinning exerted by the NbC precipitates, the solute drag of Nb in solid solution plays an important role in the inhibition of austenite grain growth in Nb microalloyed steels. The Nb solute drag effect on grain growth decreases with increasing temperature because the grain boundary can gradually break away from the solute atmosphere in the higher velocity region at high temperature. The mean austenite grain size sluggishly increases with temperature in the low temperature region, while it significantly increases in the relative high temperature region. The predicted austenite grain size concerning the combined effect of Nb drag and Nb(CN) pinning is in good agreement with the experimental results from the literature.

Effect of nano-Al2O3 on erosion–corrosion behaviour of composite alloying layer under two phase flow conditions

The present study was focused on understanding the effect of the added nano-Al2O3 on erosion–corrosion behaviour of composite alloying layer. The nano-Al2O3 reinforced composite alloying layer was prepared by duplex surface treatment, which consisted of Ni/nano-Al2O3 predeposited by brush plating and a subsequent surface alloying with Ni–Cr–Mo–Cu by double glow process on the surface of AISI 316L stainless steel. Current response with applied potential, potentiodynamic polarisation curve, electrochemical impedance spectroscopy and weight loss techniques were applied to evaluate the erosion–corrosion behaviour of composite alloying layer compared with the single alloying layer and 316L stainless steel under hydrodynamic conditions. Results of electrochemical measurements showed that the erosion–corrosion resistance of composite alloying layer was lower than that of single alloying layer when the rotating velocity of tested samples was below 2·51 m s−1, whereas the erosion–corrosion resistance of composite alloying layer was higher than that of single alloying layer when the rotating velocity of tested samples above 2·51 m s−1. The weight loss rate studies and surface analysis suggested that the dispersive undissolved nano-Al2O3 particles and γ′ prime (Ni3Al) phase were helpful to improve the erosion–corrosion resistance of composite alloying layer at high rotational speed, though the γ′ prime phase was deleterious to corrosion resistance of composite alloying layer.

Liquid-phase sintering of powder bodies of the Al-Si system

The liquid-phase sintering of the Al-Si system is performed in two stages, namely, an increase in the volume (growth) of the powder body (first) and then shrinkage (second). The bulk variations are caused by the diffusion nature of the interaction between two metals, one of which is in a liquid state. The formation mechanisms of the polyhedral structure are the dissolution of aluminum particles and the crystallization of the melt on undissolved particles upon cooling and the process of dissolution-precipitation under the conditions of holding at a constant temperature.

A practical method for the restoration of clogged rural vertical subsurface flow constructed wetlands for domestic wastewater treatment using earthworm

This paper presents a simple method for the restoration of clogged vertical subsurface flow constructed wetland by earthworm. Since clogging always takes place at the top layer, epigeic earthworm is suitable for restoration of the clogged wetland. Earthworm can not only loosen the substrate, but also transform 80∼90% of undissolved organic particles into dissolved matters. Accordingly, the accumulated solids in substrate with earthworm are 50% less than the one without earthworm. The wetland with earthworm removed 2∼5 percentage points more nitrogen and 12 percentage points more phosphorous for its better ventilation conditions, while 2 percentage points less COD because the generation of dissolved organic matter from undissolved organic particles by earthworm. In general, the influence of earthworm on the effluent quality of the wetland could be ignored. Hydrology of six full-scale clogged wetlands was restored by Eisenia foetida. The optimal strength of earthworm addition is 0.5 kg/m2, which spend RMB six yuan/m2, less than € 0.75/m2. No specific training is required for the staffs on this method; it takes 10 days to restore the clogged wetland.

Biorelevant in vitro dissolution testing of products containing micronized or nanosized fenofibrate with a view to predicting plasma profiles

The ability of in vitro biorelevant dissolution tests to predict the in vivo performance of nanosized fenofibrate (Lipidil 145 ONE®) and microsized fenofibrate (Lipidil – Ter®) was evaluated in this study. In vitro dissolution was carried out using USP apparatus 2 (paddle method) with updated biorelevant media to simulate the pre- and postprandial states. Membrane filters with different pore sizes were evaluated for their ability to hold back undissolved, nanosized drug particles. It was shown that filters with pore sizes of 0.1μm and 0.02μm were able to separate molecularly dissolved drug from colloidal and undissolved particles. In vitro results obtained with a suitable filter were used to generate simulated plasma profiles in combination with two different models using STELLA® software: (a) under the assumption of no permeability restrictions to absorption and (b) under the assumption of a permeability restriction. The simulated plasma profiles were compared to in vivo data for the nanosized and the microsized formulation in the fasted and fed states. The first model approach resulted in good correlation for the microsized fenofibrate formulation, but the plasma profile of the formulation containing nanosized fenofibrate was overpredicted in the fasted state. The second model successfully correlated with in vivo data for both formulations, regardless of prandial state. Comparison of simulations with the two models indicates that in the fasted state, absorption of fenofibrate from the nanosized formulation is at least partly permeability-limited, while for the microsized formulation the dissolution of fenofibrate appears to be rate-determining.

Effect of microstructure on liquation cracking during AZ91 friction stir spot welding

Effect of microstructures on liquation cracking is investigated. Melted eutectic formation and cracking are observed in the stir zone region of friction stir spot welds made in squeeze cast and in incompletely solutionised AZ91 sections containing Mg17Al12 particles. Crack susceptibility in the stir zone region is dramatically decreased in AZ91 base material which has been forged and solution treated, and is completely free of Mg17Al12 particles. It is suggested that rapid heating during the tool penetration stage in friction stir spot welding creates undissolved Mg17Al12 particles, which facilitate eutectic melting when the temperature in the stir zone reaches 437°C, the (α-Mg+Mg17Al12) eutectic temperature in the binary Mg–Al equilibrium phase diagram.

Accessibility, reactivity and supramolecular structure of E. globulus pulps with reduced xylan content

The correlation of structural assembly on a molecular level with macroscale properties such as accessibility and reactivity was investigated. A series of TCF-bleached E. globulus kraft dissolving pulps was prepared aiming at a specification suitable for viscose application. The removal of xylan to a comparable level was achieved by different pre- and post-treatments. Solid-state CP-MAS 13C NMR was used to determine the degree of order and the lateral fibril dimensions of cellulose fibrils. The results of the NMR measurements were related to the processability of these pulps during viscose manufacture, expressed in terms of filterability of the viscose dope and its amount of undissolved particles. The cellulose crystallinity did not affect the pulp reactivity. It was noticed that the cold caustic extracted (CCE) pulps revealed both large fibril aggregate width as determined from NMR data and low reactivity toward xanthation at the same time. These pulps exhibited significantly higher amounts of alkali-resistant xylan than those prepared by prehydrolysis kraft cooking.

A study on martensitic phase transformation in 9Cr–1W–0.23V–0.063Ta–0.56Mn–0.09C–0.02N (wt.%) reduced activation steel using differential scanning calorimetry

The salient characteristics of martensite formation kinetics in 9Cr–1W–0.23V–0.063Ta–0.09C–0.02N (wt.%) reduced activation steel have been investigated using differential scanning calorimetry and supplemented by microscopy characterisation. Accurate determination of the martensite start ( M S) and finish ( M f) temperatures as a function of cooling rate (1–99 K min −1) and holding time (1–120 min) in the γ-austenite phase field have been made. The critical cooling rate to form nearly 100% martensite is found to be of the order of 5–6 K min −1. The measured latent heat for the martensite transformation is found to be in the range 62–75 J g −1. In the case of austenitisation at 1323 K, it is found that the grain size of the parent austenite exhibited significant growth and the observed M S temperature too exhibited a systematic increase with austenite grain size. However, for those samples that are solution treated at a slightly lower temperature of 1253 K, the M S is found to be initially insensitive to the increase in holding time for up to about 30 min. This trend is followed later on by the usual increasing character of M S for further rise in the holding periods, up to about 120 min. This unusual initial behaviour is also reflected by the corresponding variation in the hardness values of the quenched in martensite. Moreover, the growth of parent austenite grains has also been restricted during the initial phase of solution annealing at 1253 K. This is attributed to the presence of undissolved carbide particles, which exert a pinning influence on the movement of austenite grain boundaries. The observed athermal martensite formation kinetics is described well by the Koistinen–Marburger relation.

Tensile strength and creep behaviour of austenitic stainless steel type 18Cr – 12Ni with niobium additions at 700°C

The effect of niobium additions up to 2.36 wt% on the creep behavior of a series of seven extra low carbon 18Cr-12Ni austenitic stainless steels at 700°C has been investigated. Grain size and hardness measurements, hot tensile tests and constant stress creep tests from 90 to 180 MPa were carried out for each alloy, in the solution treated condition at 1050, 1200 and 1300°C followed by quench in water. The mechanical behavior at high temperature was related to the amount of NbC precipitation occurring during the tests. Solid solution and intermetallic compound effects were also considered. Creep data analysis was done to determine the parameters of the creep power-law equation ϵ̇ = A.σn and the Monkman-Grant relation ϵ̇.tmR = K. Niobium-carbide precipitation in these steels reduces the secondary stage dependence of strain rate with applied stress, resulting in n-values which indicate the possibility of operation of various creep mechanisms. The creep strength during the secondary stage is primarily controlled by the amount of NbC available for precipitation. However, the rupture times increase progressively with niobium content, as the amount of undissolved carbide particles in grain boundaries and the Laves phase precipitation increase.

Microstructure and Wear Behavior of Laser-Aided Direct Metal Deposited Co-285 and Co-285 + WC Coatings

The laser-aided direct metal deposition technique was used to form Co-285 superalloy (A) and Co-285 + 30 wt pct WC (B) wear-resistant coatings on 1018 mild steel. Microstructure, element distribution, phases, microhardness distribution, and wear properties of the two coatings were investigated using scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectrometry, scanning transmission electron microscopy (TEM), X-ray diffractometry (XRD), microhardness testing, and wear testing. Results indicate that both of the coatings had dense structures, as well as a metallurgical bonding with the substrate. In addition, coating B had microcracks and randomly distributed undissolved WC particles in it. Coating A was composed of α-Co dendrites, Co3W precipitates, and eutectics, while coating B was composed of undissolved WC, Co-rich dendrites, eutectics, and the W-rich third phases with various shapes. Crack behavior in coating B was also discussed. The average microhardness of the matrix in coating B was 751 HV0.5, which was almost 1.8 times that of coating A (420 HV0.5). Wear results indicate that the wear resistance of coating B was improved by 6.8 times compared with that of coating A. The improvement in wear resistance is believed to be partially due to the undissolved WC and the formation of large numbers of carbides in the matrix working as wear-resistant phases and partially due to the good bonding between the hard phases and the tough matrix.

Purification and production of monospecific antibody to the hemagglutinin from subtype H5N1 influenza virus.

The purpose of this study was to purify the hemagglutinin from H5N1 virus and to generate monospecific antibody appropriate for production of sensitive and specific immunoassay for H5N1 avian influenza. For this purpose, a local isolate H5N1 virus (A/Ck/West Java/Hamd/2006) was propagated in chicken embryos. The viral pellet was dissolved in a Triton-X-100 solution, undissolved viral particles were pelleted by ultracentrifuge, and the supernatant containing viral surface glycoproteins (Hemagglutinin and neuraminidase) was collected. The neuraminidase in the supernatant was absorbed by passing the supernatant through an Oxamic-acid-superose column. After dialyzing extensively, the filtrate was further fractionated with an anion exchange chromatography (Q-sepharose) column. Proteins adsorbed by the column were eluted stepwisely with 0.10, 0.25, 0.25 and 0.75 M NaCl in 20 m M Tris, ph 8. Hemagglutinin (H5) was found to be eluted from the column with the 0.5 M NaCl elution buffer. The purified H5 was free from other viral proteins based on immunoassays using commercial antibodies to H5N1 nucleoprotein and neuraminidase. When used as ELISA’s coating antigen, the purified H5 proved to be sensitive and specific for hemagglutinin H5. Cross reactions with other type-A-influenza virus, H6, H7 dan H9, were negligibly low. For the production of monospecific antiserum, the purified H5 was separated with SDS-PAGE, the band containing the H5 monomer was cut out , homogenised and injected into rabbits. The antiserum was capable of detecting the presence of inactivated H5N1 virus in a very dilute suspension, with a detection limit of 0.04 heagglutination (HA) unit. The purified hemagglutinin and the serum raised against it should be useful for developing specific, sensitive and affordable immunoassay for H5N1 avian influenza. Key Words : H5N1, Hemagglutinin, Triton, Oxamic-acid Sepharose, Q sepharose, ELISA

Extraction of Beryllium from Refractory Beryllium Oxide with Dilute Ammonium Bifluoride and Determination by Fluorescence: A Multiparameter Performance Evaluation

Beryllium exposure can cause a number of deleterious health effects, including beryllium sensitization and the potentially fatal chronic beryllium disease. Efficient methods for monitoring beryllium contamination in workplaces are valuable to help prevent dangerous exposures to this element. In this work, performance data on the extraction of beryllium from various size fractions of high-fired beryllium oxide (BeO) particles (from < 32 μ m up to 212 μ m) using dilute aqueous ammonium bifluoride (ABF) solution were obtained under various conditions. Beryllium concentrations were determined by fluorescence using a hydroxybenzoquinoline fluorophore. The effects of ABF concentration and volume, extraction temperature, sample tube types, and presence of filter or wipe media were examined. Three percent ABF extracts beryllium nearly twice as quickly as 1% ABF; extraction solution volume has minimal influence. Elevated temperatures increase the rate of extraction dramatically compared with room temperature extraction. Sample tubes with constricted tips yield poor extraction rates owing to the inability of the extraction medium to access the undissolved particles. The relative rates of extraction of Be from BeO of varying particle sizes were examined. Beryllium from BeO particles in fractions ranging from less than 32 μ m up to 212 μ m were subjected to various extraction schemes. The smallest BeO particles are extracted more quickly than the largest particles, although at 90°C even the largest BeO particles reach nearly quantitative extraction within 4 hr in 3% ABF. Extraction from mixed cellulosic-ester filters, cellulosic surface-sampling filters, wetted cellulosic dust wipes, and cotton gloves yielded 90% or greater recoveries. Scanning electron microscopy of BeO particles, including partially dissolved particles, shows that dissolution in dilute ABF occurs not just on the exterior surface but also via accessing particles' interiors due to porosity of the BeO material. Comparison of dissolution kinetics data shows that as particle diameter approximately doubles, extraction time is increased by a factor of about 1.5, which is consistent with the influence of porosity on dissolution.

Processing of sewage sludge: Dependence of sludge dewatering efficiency on amount of flocculant

Paper presents results of experimental dewatering of stabilized sludge analysis and study. The experiments were carried out at a small waste water treatment plant (15,000 population equivalent). Experiment focused on impact of consumption of flocculant and centrifuge load on quality of dewatered sludge and centrate. Dry solids in dewatered sludge and content of undissolved particles in the centrate were observed in particular for proper evaluation of the experiment. It was proven that specific consumption of flocculant has greater impact on centrate quality than on dry solids content in dewatered sludge. It was possible to increase dry solids content in dewatered sludge only by 10% at most. However, amount of undissolved particles dropped more than ten-fold. Regarding quality of dewatered sludge and centrate, optimum specific consumption of flocculant during the experiment amounts to 8 g/kg of dry solids of sludge with flocculant concentration being 0.16% and centrifuge load reaching 110 kg/h of dry solids. Specific consumption of flocculant amounting to 5.4 g/kg of dry solids of sludge (calculated value) under identical operational conditions proves to be the best economical option.

Grain nucleation and formation in Mg–Zr alloys

Zirconium is the most potent nucleant discovered to date for magnesium. This work reports the grain nucleation and formation characteristics in zirconium-inoculated magnesium melts. It was found that nucleation of magnesium grains occurred on two types of zirconium nucleants, where the first type were small and round, suggesting that they were formed by precipitation, and the other type were larger and irregularly shaped, similar to undissolved particles. Subsequent growth of the magnesium halo structures after nucleation could occur either spherically or dendritically under similar cooling conditions but under well-inoculated conditions they grew spherically in general. Hence, achieving a high level of dissolved Zr content is not only essential to the nucleation process but also important for control of the subsequent growth morphologies of the halo structures. The nucleation process can be understood by an adsorption mechanism.

Polymerization in sodium silicate solutions: a fundamental process in geopolymerization technology

Geopolymerization is an innovative technology that can transform several solid aluminosilicate materials into useful products called geopolymers or inorganic polymers. Although the geopolymerization mechanism is not well understood, the most proposed mechanism includes four parallel stages: (a) dissolution of solid aluminosilicate materials in alkaline sodium silicate solution, (b) oligomerization of Si and/or Si–Al in aqueous phase, (c) polymerization of the oligomeric species, and (d) bonding of undissolved solid particles in the polymer. It is obvious that polymerization in sodium silicate solutions comprises a fundamental process in geopolymerization technology. Therefore, this article aims at studying experimentally the polymerization stage in synthetic pure sodium silicate solutions. The structure of sodium silicate gels as a function of the SiO2/Na2O molar ratio is examined and their hardness as well as hydrolytic stability are determined. In addition, the effect of aluminum incorporation in the hydrolytic stability of these gels is also examined. Finally, the structure of sodium silicate and aluminosilicate gels is correlated to the measured properties drawing very useful conclusions that could be applied on geopolymerization technology.

Effect of size and density on the thermodynamic predictions of coal particle phase formation during coal gasification

When coal is ground for use in a gasifier, the resulting particles will vary in physical and chemical make-up, in particular, the mineral amount and composition. The resulting ash composition distribution, by particle size and density, of ground Pittsburgh Seam coal was determined. The thermodynamically stable phases were calculated for each particle classification for a range of temperatures, with attention paid to the form of the non-slag phases, which must dissolve in the slag layer on the gasifier wall. Undissolved particles can be carried with the gas, resulting in fouling of downstream components. Results are separated into a comparison of the liquid versus solid phases formed, and a comparison of the phases formed for each particle type. Certain particle compositions form stable crystalline oxide phases that are usually incorporated into the slag at higher temperatures, while others can form metallic iron, which is stable even at high temperatures.

Laser clad Cr3C2–Ni composite coating on titanium alloys

Cr3C2–Ni composite coatings were fabricated on Ti–6Al–4V substrate by laser cladding using powder mixture of NiCrBSiC alloy and Cr3C2. Results of the analysis show that the microstructure and microhardness of the coatings depend strongly on the specific laser energy. With a relatively low specific laser energy (133·3 J mm−2), Cr3C2 particles were partially dissolved into melted Ni based alloy, and the coating was formed of undissolved Cr3C2 particles and cannular Cr23C6 uniformly distributed in cellular γ-Ni and eutectic matrix. With a higher specific laser energy (266·7 J mm−2), more Cr3C2 particles were dissolved, and the coating consisted of γ-Ni, TiC dendrites and lamellar CrB. When the specific laser energy is 133·3 and 266·7 J mm−2, the microhardness of the coating is 500–700 HV and 700–1000 HV, respectively.

Highly Supersaturated Solutions from Dissolution of Amorphous Itraconazole Microparticles at pH 6.8

Dry powders from aqueous dispersions, formed by antisolvent precipitation, dissolved to form solutions with supersaturation values up to 12 in 10 min at pH 6.8 with sodium dodecyl sulfate micelles. Itraconazole/hydroxypropylmethylcellulose (HPMC) aqueous particle dispersions were salt flocculated and filtered to produce medium surface area (2-5 m2/g) particles or lyophilized to produce high surface area (13-36 m2/g). Over 4 h, the decay in supersaturation was much slower for the medium surface area versus high surface area particles, since the smaller excess surface area of undissolved particles led to slower nucleation and growth from solution. A slow decay in supersaturation was also achieved by initially dissolving part of the drug at pH 1.2, and then shifting the pH to 6.8 thereby reducing the excess surface area of undissolved particles in the pH 6.8 media. This pH shift mimics the transition from stomach to intestines. The ability to generate and sustain high supersaturation at pH 6.8 by minimizing undissolved excess surface area may be expected to be beneficial for raising bioavailability by gastrointestinal delivery.