Undissolved Particles Research Articles

Effect of scanning speeds on microstructure and wear behavior of laser-processed NiCr–Cr3C2–MoS2–CeO2 on 38CrMoAl steel

Self-lubricating wear-resistant NiCr–Cr3C2–MoS2–CeO2 layers were fabricated on 38CrMoAl extruder screws by laser processing. The effect of scanning speeds on microstructure, phases, microhardness, and wear behavior was investigated. The obtained results indicate that the laser-processed layers had fine and nonuniform microstructures with undissolved MoS2 particles distributed on the matrix. With an increase of the laser-scanning speeds, the microstructures changed from hypoeutectic to hypereutectic, volume fraction of martensite increased, microhardness increased, and thickness and friction coefficients of the layers decreased. Wear resistance of the optimized layer was increased by 29.76 times compared with that of the substrate. The undissolved MoS2 was separated from the matrix on loading. In addition to the grain-refining and solution-strengthening effects, oxide films formed on the surface of the layers shielded them and enhanced their wear resistance. The crack or fracture behavior of the laser-processed layers on loading was determined by its toughness, which also had an important effect on the wear behavior of the processed layers.

The Effect Of Homogenization Conditions On The Structure And Properties Of 6082 Alloy Billets

Abstract The paper presents the results of laboratory homogenization investigations of the 6082 grade alloys, differing in Mg and Si content. At the first stage, the microstructure of alloys was analysed after homogenization finished with water quenching. SEM/EDS investigations and DSC tests were applied to evaluate the dissolution of the Mg2Si particles and concentration of the main alloying additions in the grains interiors, depending on soaking conditions. In the case of alloy with lower Mg and Si content, homogenization the temperature of 535ºC for 8h is sufficient for significant Mg2Si particles dissolution. For the alloy with higher Mg and Si content, after homogenization the temperature of 550ºC for 8h, the amount of undissolved Mg2Si particles decreases visibly, compared to homogenization at 535ºC for 8h. However, an unfavourable tendency of dispersoids growth is observed and these soaking conditions are not found to be recommended. At the second research stage, the influence of homogenization cooling rate on the size and distribution of the Mg2Si particles observed in the alloys microstructure was analysed. The ability of the Mg2Si particles, precipitated during various homogenization coolings, to rapid dissolution was estimated. For this purpose, the hardness after solution heat treatment with short annealing and ageing was determined and the DSC tests were performed. It was found, that cooling after homogenization at 315ºC/h is sufficient for precipitation of fine Mg2Si particles, which dissolve during subsequent rapid heating. Cooling at 40ºC/h, causes precipitation of Mg2Si phase in the form of large particles, unable for further fast dissolution.

OPTIMIZATION OF GRADING ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Al13Fe4/Al COM- POSITES IN SITU SYNTHESIZED BY MECHANICAL ALLOYING AND SPARK PLASMA SINTERING

Al-Fe alloys are widely applied in automobile, aerospace, military industry and other fields owing to their high specific strength, high specific stiffness and good stability of the microstructure originating from the low diffusivity of Fe in Al. However, conventional casting method leads to inferior mechanical properties of Al-Fe alloys due to the coarse grain microstructure, which cannot meet application requirements. In this work, fully densed Al13Fe4/Al composites were fabricated by combination of mechanical alloying and spark plasma sintering(MA-SPS) approaches. Effect of gradation of grinding balls on microstructure and properties of composites was investigated by means of XRD, SEM, TEM, hardness and compressive test. The results showed that the size of powders became more uniform by ball gradation in MA treatment, and solid solubility was greatly enhanded as well.Furthermore, the Al-Fe powder after MA using a single grinding ball size showed the microstructure of tiny white Fe particles on the surface of each particle, while no white Fe particles were observed for the one with ball gradation, which confirmed that ball gradation was more beneficial to the mixture and solid solution of Al and Fe, resulting in more homogeneously distributed powders with smaller particle sizes of 10 μm. The composites after SPScontained a-Al phase and intermetallic compound Al13Fe4. Three types of Al13Fe4 were observed: large particles(1~2 μm), ultrafine particles(0.1~1.0 μm) and nano-particles(about 20 nm). The large particles and ultrafine Al13Fe4 formed by the reaction between undissolved Fe particles and the Al melt while nano-particles of Al13Fe4 originated from the precipitation of supersaturated Al(Fe) solid solutions. The sintered sample with ball gradation after SPS showed optimized microstructure with coarser a-Al particles and ultrafine Al13Fe4 particles, resulting in good comprehensive properties with 227 HV in microhardness, 845.8 MPa in compressive strength and 13.6% in plastic deformation. The combination of large quantities of coarse a-Al particles and ultrafine Al13Fe4 particles were considered as the reason for high strength and high toughness of Al-Fe alloy.

Effect of pulsed Nd:YAG laser re-melting on chromium surface alloyed AA6061-T6 aluminum

In this work, in situ formation of Al–Cr intermetallic compound on the surface of AA6061-T6 aluminum pre-placed chromium powder via pulsed Nd:YAG laser surface alloying was investigated. The effect of laser re-melting on microstructure and hardness of the treated layers was examined. Laser re-melting resulted in a significant reduction in the presence of cracks, pores, and undissolved Cr-rich particles along with a more uniform distribution of intermetallic compounds. The results showed that the alloyed layers mainly consisted of fine Al7Cr and Al4Cr intermetallic compounds in an α-Al solid solution matrix with cellular and dendritic morphologies. Hardness profiles along cross section and top surface of the alloyed layers indicated that laser re-melting enhanced homogeneity and increased the hardness value to more than six times of that of the base material.

Allergenic proteins in enology: a review on technological applications and safety aspects.

Proteinaceous products are widely used as fining agents during winemaking to remove unwanted insoluble particles and undissolved microscopic particles (colloidal material) from the must or wine to improve stability. Some of them (egg white, caseinates, and fish gelatine) have allergenic potential and the presence of their residues in the final product could represent a risk for allergic individuals. Moreover, lysozyme (an egg allergen) is included among wine additives to control the fermentation processes and avoid spoiling during winemaking. The aim of this paper is to review the experimental/clinical data on the use of allergenic products in enology and the measurement of relative risk for sensitized subjects. In addition, methods developed specifically for the quantification of allergenic residues in must and wine are described.

Improving mechanical properties of extruded Mg–Al alloy with a bimodal grain structure through alloying addition

This paper seeks to find an appropriate alloying method for improving the mechanical properties of wrought Mg alloys that have a bimodal structure of fine and coarse recrystallized grains created through insufficient precipitation. The addition of an alloying element with a high solid solubility in the a-Mg matrix of the base alloy is found to result in a fine, homogeneous grain structure of wrought material through a restriction of grain growth by newly formed fine precipitates. This consequently leads to a significant improvement in strength via enhanced precipitation/grain-boundary strengthening, without any major loss of ductility. However, excessive addition above the maximum solid solubility greatly deteriorates the material's ductility due to the creation of large, undissolved particles. The validity of this approach is demonstrated by varying the addition of Sn to AM80 alloy.

Mechanical, thermal, and antioxidant properties of composite films prepared from durum wheat starch and lignin

Lignin conveys several important and useful characteristics to starch films depending on the lignin MW, extraction procedure, and lignin botanical source. In this study, lignin was obtained from durum wheat straw through the organosolv process, followed by fractionation according to solubility in alcohol. The alcohol‐soluble lignin (ASL) was then used to prepare starch–ASL films. The mechanical properties, thermal stability, water solubility, color, and antioxidant activity of the resulting films were evaluated, and the starch–ASL films were also analyzed by means of SEM and attenuated total reflection infrared spectroscopy (ATR‐IR). A procedure, to incorporate ASL, was developed and used to produce homogenous surfaces in starch–ASL films; agglomerations or undissolved particles of lignin were not observed in the starch matrix at microscopic level. ASL promoted significant decrease of the tensile strength (TS) and elastic modulus (EM), but an increase of elongation at break (EB) in films. Thermal analysis of the starch–ASL films showed high resistance to thermal degradation, due to the incorporation of ASL. In addition, the starch–ASL films exhibited antioxidant activity (2,2‐diphenyl‐1‐picrylhydrazyl [DPPH]), which increased with increasing ASL content.

Effect of homogenization temperature on the microstructure and mechanical properties of extruded Mg–7Sn–1Al–1Zn alloy

The effect of homogenization temperature (HT) on the microstructure and tensile properties of extruded Mg–7Sn–1Al–1Zn (TAZ711) alloy was investigated by conducting homogenization heat-treatment at 400, 450, and 500°C for 24h, followed by indirect extrusion. The results obtained through this revealed that second phases are nearly fully dissolved by homogenization at 500°C, but undissolved Mg2Sn particles remain after homogenization at 450 and 400°C. Furthermore, the increase in large undissolved particles with decreasing HT helped to promote dynamic recrystallization (DRX) during extrusion by particle stimulated nucleation (PSN), thus resulting in an increase in the area fraction of DRXed grains in the extruded alloy. A decrease in the amount of Sn supersaturated in the matrix, however, suppressed the formation of fine Mg2Sn precipitates during extrusion, which in turn led to an increase in the size of DRXed grains due to a reduction in grain boundary pinning by precipitates. Ultimately, this meant that although the yield and ultimate tensile strengths gradually improved with increasing HT due mainly to a decrease in the DRXed grain size, an increase in texture intensity, and an increased number of fine Mg2Sn precipitates, the elongation deteriorated due to crack initiation at twins formed within coarse non-DRXed grains.

Alkaline corrosion properties of laser-clad aluminum/titanium coatings

Purpose– The purpose of this paper is to study the use of titanium as a protecting element for aluminum in alkaline conditions.Design/methodology/approach– Aluminum coatings containing up to 20 weight per cent Ti6Al4V were produced using laser cladding and were investigated using light optical microscope, scanning electron microscope – energy-dispersive X-ray spectroscopy and X-Ray Diffraction, together with alkaline exposure tests and potentiodynamic measurements at pH 13.5.Findings– Cladding resulted in a heterogeneous solidification microstructure containing an aluminum matrix with supersaturated titanium (<1 weight per cent), Al3Ti intermetallics and large partially undissolved Ti6Al4V particles. Heat treatment lowered the titanium concentration in the aluminum matrix, changed the shape of the Al3Ti precipitates and increased the degree of dissolution of the Ti6Al4V particles. Corrosion testing showed significant localized dissolution of the aluminum matrix.Research limitations/implications– Increased titanium concentration and heat treatment gave improved alkaline corrosion properties. At pH 13.5, the Al3Ti phases were protected, while the aluminum matrix corroded.Practical implications– For alkaline corrosion-protection of aluminum in the automobile industry, titanium might be useful at pH values below 13.5 or by using other coating techniques.Originality/value– This is the first study testing the use of titanium as a protective element of aluminum in stringent alkaline conditions.

Cocrystallization Behavior of Hdpe/Uhmwpe Blends Prepared by Two-Step Processing Way

Blends of high density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMWPE) were prepared by two-step processing way. Middle molecular weight polyethylene (MMWPE) as the lubricant was added into UHMWPE in the first processing step. Cocrystallization behavior of the blends was examined by DSC, XRD and light microscope (LM). A single endotherm peak in DSC curves revealed that cocrystallization probably formed between HDPE and UHMWPE. Moreover reducing heating rate didn't make the single endotherm separate. The enhancing of diffractive strength on 110 and 200 crystal face manifested that the UHMWPE molecular chains taken part in the crystallization of the blends. Reducing of the diameter of the undissolved UHMWPE particles in LM manified that the dispersion of UHMWPE in the blends obviously improved. Therefore two-step processing way could improve the dissolved degree and contribute to form the cocrystallization.

Recovery of Cerium Dioxide from Spent Glass-Polishing Slurry and Its Utilization as a Reactive Sorbent for Fast Degradation of Toxic Organophosphates

The recovery of cerium (and possibly other rare earth elements) from the spent glass-polishing slurries is rather difficult because of a high resistance of polishing-grade cerium oxide toward common digestion agents. It was shown that cerium may be extracted from the spent polishing slurries by leaching with strong mineral acids in the presence of reducing agents; the solution may be used directly for the preparation of a ceria-based reactive sorbent. A mixture of concentrated nitric acid and hydrogen peroxide was effective in the digestion of partially dewatered glass-polishing slurry. After the removal of undissolved particles, cerous carbonate was precipitated by gaseous NH3and CO2. Cerium oxide was prepared by a thermal decomposition of the carbonate precursor in an open crucible and tested as reactive sorbent for the degradation of highly toxic organophosphate compounds. The samples annealed at the optimal temperature of approximately 400°C exhibited a good degradation efficiency toward the organophosphate pesticide fenchlorphos and the nerve agents soman and VX. The extraction/precipitation procedure recovers approximately 70% of cerium oxide from the spent polishing slurry. The presence of minor amounts of lanthanum does not disturb the degradation efficiency.

Applying Spectral Unmixing to Determine Surface Water Parameters in a Mining Environment

Compared to natural waters, mine waters represent an extreme water type that is frequently heavily polluted. Although they have been traditionally monitored by in situ measurements of point samples taken at regular intervals, the emergence of a new generation of multispectral and hyperspectral (HS) sensors means that image spectroscopy has the potential to become a modern method for monitoring polluted surface waters. This paper describes an approach employing linear Spectral Unmixing (LSU) for analysis of hyperspectral image data to map the relative abundances of mine water components (dissolved Fe—Fediss, dissolved organic carbon—DOC, undissolved particles). The ground truth data (8 monitored ponds) were used to validate the results of spectral mapping. The same approach applied to HS data was tested using the image data resampled to WorldView2 (WV2) spectral resolution. A key aspect of the image data processing was to define the proper pure image end members for the fundamental water types. The highest correlations detected between the studied water parameters and the fractional images using the HyMap and the resampled WV2 data, respectively, were: dissolved Fe (R2 = 0.74 and R2vw2 = 0.6), undissolved particles (R2 = 0.57 and R2vw2 = 0.49) and DOC (R2 = 0.42 and R2vw2 < 0.40). These fractional images were further classified to create semi-quantitative maps. In conclusion, the classification still benefited from the higher spectral resolution of the HyMap data; however the WV2 reflectance data can be suitable for mapping specific inherent optical properties (SIOPs), which significantly differ from one another from an optical point of view (e.g., mineral suspension, dissolved Fe and phytoplankton), but it seems difficult to differentiate among diverse suspension particles, especially when the waters have more complex properties (e.g., mineral particles, DOC together with tripton or other particles, etc.).

Effect of bubbles and silica dissolution on melter feed rheology during conversion to glass.

Nuclear-waste melter feeds are slurry mixtures of wastes with glass-forming and glass-modifying additives (unless prefabricated frits are used), which are converted to molten glass in a continuous electrical glass-melting furnace. The feeds gradually become continuous glass-forming melts. Initially, the melts contain dissolving refractory feed constituents that are suspended together with numerous gas bubbles. Eventually, the bubbles escape, and the melts homogenize and equilibrate. Knowledge of various physicochemical properties of the reacting melter feed is crucial for understanding the feed-to-glass conversion that occurs during melting. We studied the melter feed viscosity during heating and correlated it with the volume fractions of dissolving quartz (SiO2) particles and the gas phase. The measurements were performed with a rotating spindle rheometer on the melter feed heated at 5 K/min, starting at several different temperatures. The effects of undissolved quartz particles, gas bubbles, and compositional inhomogeneity on the melter feed viscosity were determined by fitting a linear relationship between the logarithm of viscosity and the volume fractions of suspended phases.

The effect of silicon on precipitation and decomposition behaviors of M6C carbide in a Ni–Mo–Cr superalloy

The effect of silicon addition on the precipitation and decomposition behaviors of M6C carbide in a Ni–Mo–Cr based superalloy and the tensile properties of this alloy have been investigated. Silicon increases the amount of undissolved M6C carbide particles obviously in Ni–Mo–Cr superalloy. Composition analyses reveal that primary M6C carbides in the standard heat are highly enriched in silicon. The addition of silicon widens the temperature range of M6C carbide existence to 1335°C, while the M6C carbide in non-silicon heat was completely decomposed when heated to 1260°C. According to the calculation results using Thermal-calc software, the Gibbs free energy of M6C carbide decreases with the silicon content, and the silicon-riched M6C carbide is more stable than that in non-silicon heat samples. In tensile tests, it is found that silicon-rich M6C carbide particles act as cracking origin sites, and further give rise to the degradation of the high temperature tensile properties of standard heat samples as compared to non-silicon heat ones.

Microbeam x-ray absorption spectroscopy study of chromium in large-grain uranium dioxide fuel

Synchrotron-based microprobe x-ray absorption spectroscopy (XAS) has been used to study the local atomic structure of chromium in chromia-doped uranium dioxide (UO2) grains. The specimens investigated were a commercial grade chromia-doped UO2 fresh fuel pellet, and materials from a spent fuel pellet of the same batch, irradiated with an average burnup of ~40 MW d kg-1. Uranium L3-edge and chromium K-edge XAS have been measured, and the structural environments of central uranium and chromium atoms have been elucidated. The Fourier transform of uranium L3-edge extended x-ray absorption fine structure shows two well-defined peaks of U–O and U–U bonds at average distances of 2.36 and 3.83 Å. Their coordination numbers are determined as 8 and 11, respectively. The chromium Fourier transform extended x-ray absorption fine structure of the pristine UO2 matrix shows similar structural features with the corresponding spectrum of the irradiated spent fuel, indicative of analogous chromium environments in the two samples studied. From the chromium XAS experimental data, detectable next neighbor atoms are oxygen and uranium of the cation-substituted UO2 lattice, and two distinct subshells of chromium and oxygen neighbors, possibly because of undissolved chromia particles present in the doped fuels. Curve-fitting analyses using theoretical amplitude and phase-shift functions of the closest Cr–O shell and calculations with ab initio computer code FEFF and atomic clusters generated from the chromium-dissolved UO2 structure have been carried out. There is a prominent reduction in the length of the adjacent Cr–O bond of about 0.3 Å in chromia-doped UO2 compared with the ideal U–O bond length in standard UO2 that would be expected because of the change in effective Coulomb interactions resulting from replacing U4+ with Cr3+ and their ionic size differences. The contraction of shortest Cr–U bond is ~0.1 Å relative to the U–U bond length in bulk UO2. The difference in the local chromium environment between fresh and irradiated UO2 is discussed based on the comparison of quantitative structural information obtained from the two chromia-doped fuel samples analyzed.

Guar gum solutions for improved delivery of iron particles in porous media (Part 2): Iron transport tests and modeling in radial geometry

In the present work column transport tests were performed in order to study the mobility of guar-gum suspensions of microscale zero-valent iron particles (MZVI) in porous media. The results were analyzed with the purpose of implementing a radial model for the design of full scale interventions. The transport tests were performed using several concentrations of shear thinning guar gum solutions as stabilizer (1.5, 3 and 4g/l) and applying different flow rates (Darcy velocity in the range 1·10−4 to 2·10−3m/s), representative of different distances from the injection point in the radial domain. Empirical relationships, expressing the dependence of the deposition and release parameters on the flow velocity, were derived by inverse fitting of the column transport tests using a modified version of E-MNM1D (Tosco and Sethi, 2010) and the user interface MNMs (www.polito.it/groundwater/software). They were used to develop a comprehensive transport model of MZVI suspensions in radial coordinates, called E-MNM1R, which takes into account the non Newtonian (shear thinning) rheological properties of the dispersant fluid and the porous medium clogging associated with filtration and sedimentation in the porous medium of both MZVI and guar gum residual undissolved particles. The radial model was run in forward mode to simulate the injection of MZVI dispersed in guar gum in conditions similar to those applied in the column transport tests. In a second stage, we demonstrated how the model can be used as a valid tool for the design and the optimization of a full scale intervention. The simulation results indicated that several concurrent aspects are to be taken into account for the design of a successful delivery of MZVI/guar gum slurries via permeation injection, and a compromise is necessary between maximizing the radius of influence of the injection and minimizing the injection pressure, to guarantee a sufficiently homogeneous distribution of the particles around the injection point and to prevent preferential flow paths.

Guar gum solutions for improved delivery of iron particles in porous media (Part 1): Porous medium rheology and guar gum-induced clogging

The present work is the first part of a comprehensive study on the use of guar gum to improve delivery of microscale zero-valent iron particles in contaminated aquifers. Guar gum solutions exhibit peculiar shear thinning properties, with high viscosity in static conditions and lower viscosity in dynamic conditions: this is beneficial both for the storage of MZVI dispersions, and also for the injection in porous media. In the present paper, the processes associated with guar gum injection in porous media are studied performing single-step and multi-step filtration tests in sand-packed columns. The experimental results of single-step tests performed by injecting guar gum solutions prepared at several concentrations and applying different dissolution procedures evidenced that the presence of residual undissolved polymeric particles in the guar gum solution may have a relevant negative impact on the permeability of the porous medium, resulting in evident clogging. The most effective preparation procedure which minimizes the presence of residual particles is dissolution in warm water (60°C) followed by centrifugation (procedure T60C). The multi-step tests (i.e. injection of guar gum at constant concentration with a step increase of flow velocity), performed at three polymer concentrations (1.5, 3 and 4g/l) provided information on the rheological properties of guar gum solutions when flowing through a porous medium at variable discharge rates, which mimic the injection in radial geometry. An experimental protocol was defined for the rheological characterization of the fluids in porous media, and empirical relationships were derived for the quantification of rheological properties and clogging with variable injection rate. These relationships will be implemented in the second companion paper (Part II) in a radial transport model for the simulation of large-scale injection of MZVI-guar gum slurries.

Facile pulping of lignocellulosic biomass using choline acetate.

Treating ground bagasse or Southern yellow pine in the biodegradable ionic liquid (IL), choline acetate ([Cho][OAc]), at 100°C for 24h led to dissolution of hemicellulose and lignin, while leaving the cellulose pulp undissolved, with a 54.3% (bagasse) or 34.3% (pine) reduction in lignin content. The IL solution of the dissolved biopolymers can be separated from the undissolved particles either by addition of water (20 wt% of IL) followed by filtration or by centrifugation. Hemicellulose (19.0 wt% of original bagasse, 10.2 wt% of original pine, containing 14-18 wt% lignin) and lignin (5.0 wt% of original bagasse, 6.0 wt% of original pine) could be subsequently precipitated. The pulp obtained from [Cho][OAc] treatment can be rapidly dissolved in 1-ethyl-3-methylimidazolium acetate (e.g., 17 h for raw bagasse vs. 7h for pulp), and precipitated as cellulose-rich material (CRM) with a lower lignin content (e.g., 23.6% for raw bagasse vs. 10.6% for CRM).

グラファイト粉末を用いたレーザ合金化処理によるTi/TiC 表面複合層の形成と微細組織の評価

Titanium and its alloys have various excellent properties, such as good corrosion resistance and high specific strength. However, they have not been applied to the sliding parts under sever wear condition due to their poor tribological properties.In this study, laser alloying using graphite powder was carried out to form Ti/TiC composite surface layer on commercial pure titanium substrate for improving wear resistance. The effects of graphite powder size and laser irradiation parameters on the microstructure of laser alloyed zone were mainly investigated. In the laser alloyed zone, dendritic primary TiC and fine particles of eutectic TiC were observed. In the condition of higher laser traverse speed and larger size of graphite powder, undissolved graphite particles were observed.

Laser controlled melting of Hastelloy X alloy with presence of B4C particles at surface

Laser controlled melting of pre-prepared Hastelloy X alloy surface is carried out at high nitrogen gas pressure environment. The pre-prepared workpiece surface consists of 40 μm carbon film with uniformly distributed 5%B4C particles. The carbon film enhances the absorption of the incident laser irradiation and holds B4C particles at the workpiece surface prior to the laser treatment process. The morphological and metallurgical changes in the treated layer are characterised using scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. The microhardness at the treated surface and the residual stress formed in the surface vicinity are measured. It is found that dense layer consists of fine grains are formed at the surface because of the high cooling rates. Locally distributed undissolved B4C particles are observed at the surface due to high melting temperature of B4C. Although thermal expansion coefficients of B4C and the base material are different, no microcracks are took place in the close neighbourhood of the particles. The microhardness of the surface increased almost 2·2 times of the base material hardness and the residual stress formed at the surface is on the order of −1·4 GPa, which is compressive.