Slurry Technique Research Articles

The structure and high temperature corrosion performance of medium-thickness aluminide coatings on nickel-based superalloy GTD-111

Simple and Si-modified aluminide coatings having medium-thickness (40–60 μm) have been applied on the superalloy GTD-111 by a slurry technique. Hot corrosion and cyclic oxidation performance of the uncoated and the coated superalloy were investigated by exposing samples to a molten film of Na 2SO 4-40 %wt NaVO 3-10%wt NaCl at 780 °C and 1 h cyclic oxidation at 1100 °C in air, respectively. The presence of silicon in the aluminide structure increased the oxidation resistance by a factor of 1.7 times. In addition, a SiO 2-containing scale, which formed on the Si-containing coating surface, was stable during of the hot corrosion testing.

Microstructure and properties characterisation of the double layered glass–ceramic coating on near-α titanium alloy

Abstract A protective double layered glass–ceramic coating was produced by slurry technique in order to improve the oxidation resistance of Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si-0.06C-0.09O, wt.%, at temperatures above 600 °C. A SiO 2 –P 2 O 5 –B 2 O 3 –CaO–K 2 O–Na 2 O layer was produced as the outer layer, with self-healing properties. Analytical scanning- and transmission electron microscopy were used for detailed analyses of the microstructure and phase composition of the coating. It was found that both layers contain several crystalline and amorphous phases. It was established that the double layered glass–ceramic coating formed on TIMETAL 834 shows higher hardness than the substrate alloy and better oxidation resistance at elevated temperature, since no weight change of the coated alloy was observed after oxidation for 300 h at 800 °C. The self-healing behaviour of the outer layer was also demonstrated.

Preparation of Asymmetric Tubular Oxygen Separation Membrane with Oxygen Permeable Pr2Ni0.75Cu0.25Ga0.05O4+δ

The electrical conductivities and oxygen permeation properties of Pr2Ni0.75Cu0.25Ga0.05O4+δ were measured by conventional DC four-probe method with Pt electrode and gas chromatography. The total conductivities increased with an apparent slope of 1/6, satisfied by the charge neutrality condition at the p-type regime of . A tubular-type, asymmetric, mixed-conducting oxygen separation membrane was fabricated by drain casting method. A microporous, ceramic support was prepared by slurry processing, because the use of a slurry technique and a suspension of dispersed particles provides a lower final porosity and a more homogeneous particle packing than dry-pressing does. The 30 cm long, tubular, porous alumina with a soft surface was successfully prepared by drain casting. The surface SEM images revealed a structure with reasonable porosity and well-necked particles. A mixed-conducting layer of Pr2Ni0.75Cu0.25Ga0.05O4+δ was applied inside of the support tube by drain casting. A dense separation layer was successfully fabricated inside the porous alumina tube by sintering at 1473 K for 8 h in air.

Microstructure characterization of erosion resistant coatings on carbon‐bonded carbon fibre composites

The microstructure of as received and surface treated carbon-bonded carbon fibre composites has been examined by light microscopy, scanning and transmission electron microscopy. The microstructure of the as received material consists of a bonded together layered carbon fiber network, identified as graphitic carbon (hexagonal close packed). To improve the erosion resistance of the carbon-bonded carbon fibre composites composite, the SiC and silicate glass-ceramic coatings from the system SiO(2)-Al(2)O(3)-Y(2)O(3) were produced on carbon-bonded carbon fibre composites composites by a low-cost slurry technique. Transmission electron microscopy investigations of cross-section thin foils allowed for detailed analysis of the coatings microstructure. It was found that the SiC coating was consisting mainly of a nanocrystalline SiC (fcc). The multilayered glass-ceramic coating showed a complex microstructure consisting of an external SiO(2)-Al(2)O(3)-Y(2)O(3) layer and an intermediate nanocrystalline SiC layer. The SiO(2)-Al(2)O(3)-Y(2)O(3) layer was composed of SiO(2) (fcc), Y(2)Si(2)O(7) (op) and Al(4.644)Si(1.357)O(9.68) (op).

Nitrous oxide production kinetics during nitrate reduction in river sediments

A significant amount of nitrogen entering river basins is denitrified in riparian zones. The aim of this study was to evaluate the influence of nitrate and carbon concentrations on the kinetic parameters of nitrate reduction as well as nitrous oxide emissions in river sediments in a tributary of the Marne (the Seine basin, France). In order to determine these rates, we used flow-through reactors (FTRs) and slurry incubations; flow-through reactors allow determination of rates on intact sediment slices under controlled conditions compared to sediment homogenization in the often used slurry technique. Maximum nitrate reduction rates ( R m) ranged between 3.0 and 7.1 μg N g −1 h −1, and affinity constant (K m) ranged from 7.4 to 30.7 mg N-NO 3 − L −1. These values were higher in slurry incubations with an R m of 37.9 μg N g −1 h −1 and a K m of 104 mg N-NO 3 − L −1. Nitrous oxide production rates did not follow Michaelis–Menten kinetics, and we deduced a rate constant with an average of 0.7 and 5.4 ng N g −1 h −1 for FTR and slurry experiments respectively. The addition of carbon (as acetate) showed that carbon was not limiting nitrate reduction rates in these sediments. Similar rates were obtained for FTR and slurries with carbon addition, confirming the hypothesis that homogenization increases rates due to release of and increasing access to carbon in slurries. Nitrous oxide production rates in FTR with carbon additions were low and represented less than 0.01% of the nitrate reduction rates and were even negligible in slurries. Maximum nitrate reduction rates revealed seasonality with high potential rates in fall and winter and low rates in late spring and summer. Under optimal conditions (anoxia, non-limiting nitrate and carbon), nitrous oxide emission rates were low, but significant (0.01% of the nitrate reduction rates).

Alternative Solid Sample Pretreatment Methods in Green Analytical Atomic Spectrometry

ABSTRACT A review of recent literature utilizing alternative sample pretreatment methods for solid environmental and biological materials analysis to assess total metals content by atomic spectrometry is provided. All the selected treatments coincide with all or some of the fundamentals of Green Chemistry policy such as prevention of waste generation; safer and less toxic solvents and reagents; and designs for energy efficiency. The review covers the classic slurry sampling technique, mainly, its current trends, as well as developments based on the use of diluted acids, chelating agents solutions, or even water for leaching (extraction) methods assisted by ultrasounds, microwave energy, or pressurization. In addition, the use of conventional or assisted enzymatic hydrolysis procedures is also discussed.

Microstructure, properties and oxidation behavior of the glass–ceramic based coating on near-α titanium alloy

Protective SiO 2–Al 2O 3–CaO–Na 2O glass–ceramic based coating produced on TIMETAL 834 by slurry technique was investigated. Analytical scanning and transmission electron microscopy as well as X-ray diffraction were used for detailed analyses of a microstructure and chemical composition of the coating. It was found that the coating contains crystalline phases: CaSiO 3, NaAlSiO 4, Na 2CaSiO 4 and amorphous phase containing mainly O, Si and Al. It was established that glass–ceramic coating formed on TIMETAL 834 essentially improves the alloy selected properties, e.g. its hardness and high temperature oxidation resistance.

Performance and testing of glass-ceramic sealant used to join anode-supported-electrolyte to Crofer22APU in planar solid oxide fuel cells

This work describes the performance and testing of a glass-ceramic sealant used to join the ceramic electrolyte (anode-supported-electrolyte (ASE)) to the metallic interconnect (Crofer22APU) in planar SOFC stacks. The designed glass-ceramic sealant is a barium and boron free silica-based glass, which crystallizes by means of the heat-treatment after being deposited on substrates by the slurry technique. Joined ASE/glass-ceramic seal/Crofer22APU samples were tested for 500 h in H 2–3H 2O atmosphere at the fuel cell operating temperature of 800 °C. Moreover, the joined ASE/glass-ceramic seal/Crofer22APU samples were submitted to three thermal cycles each of 120 h duration, in order to evaluate the thermomechanical stability of the sealant. The microstructures and elemental distribution at Crofer22APU/glass-ceramic and ASE/glass-ceramic interfaces were investigated. SEM micrograph observations of joined samples that underwent cyclic thermal tests and exposure for 500 h in H 2–3H 2O atmosphere showed that the adhesion between the glass-ceramic and Crofer22APU at either interface was very good and no microstructural changes were detected at the interfacial boundaries. The study showed that the use of the glass-ceramic was successful in preventing strong adverse corrosion effects at the Crofer22APU/glass-ceramic sealant interface.

Multi-element determinations of N,N-dimethylformamide (DMF) coal slurries using ICP-OES

A slurry nebulisation technique was applied for elemental analysis of bituminous coals SARM 18, SARM 19 and four coals from three different seams in Witbank, South Africa, by inductively coupled plasma optical emission spectroscopy (ICP-OES). Major elements (Al, Ca, Fe, Mg, S, Si and Ti) and trace elements (Ba, Cr, Mn, Ni, Sr, V, Zn and Zr) in coal were determined. Various slurry preparations were evaluated using two dispersants (glycerol and Triton X-100) and by varying the concentration of dispersants, between 0.1% and 1.0% (v/v). The effect of initially solubilising the ground coal in N,N-dimethylformamide (DMF) was investigated by varying the volume of DMF added. The effect of wet grinding with DMF was investigated. Wet grinding with DMF was shown to drastically reduce particle sizes (50.0% < 0.28 μm and 90.0% < 6.17 μm) as compared to dry grinding (50.0% < 5.25 μm and 90.0% < 11.1 μm). The reduced particle sizes and increased transport efficiency of the coal slurries led to improved analytical recoveries of elements in the reference coal, SARM 18. The best analytical recoveries for all elements were achieved using 0.1% Triton X-100 with 10.0% DMF. Results obtained by ICP-OES after wet grinding of the coal with DMF, using 0.1% Triton X-100, also gave excellent recoveries (Al, 100%; Ca, 103%; Cr, 106%; Fe, 102%; Mg, 100%; Mn, 104%; Ni, 109%; Si, 102%; Ti, 95.0%; and V, 108%). The results obtained with 10.0% DMF and 0.1% Triton X-100 were in agreement with certified values for all selected elements according to paired t-test at the 95.0% confidence level. Selected elements (Al, Ca, Fe, Mg, Mn, Si, Ti and V) were also analysed with X-ray fluorescence for comparison with results obtained from ICP-OES. Analysis by ICP-OES of microwave digested coal was also carried out. It is suggested that the DMF slurry technique could be used for routine analysis of bituminous coals.

Manufacturing of Porous Alumina Scaffolds with Bio-Glass and HAp Coating: Mechanical and &lt;i&gt;In Vitro&lt;/i&gt; Evaluation

The objective of this study was to manufacture porous scaffolds with bioinert and bioactive materials to join mechanical properties and bony integration. Porous alumina ceramic matrices were produced using the slurry technique followed by isostatic pressing, leaching and sintering. Porous alumina samples presented 75.0vol% porosity and 52.27MPa of compressive strength. Bioglass/hydroxyapatite ceramic slurry was used as coating on alumina matrices. The infiltration was performed by dipping the alumina porous samples into bio-glass/hydroxyapatite ceramics slurry under vacuum and followed by sintering. The evaluation of the alumina ceramic scaffolds samples were made using EDX, mechanical and in vitro tests. For the in vitro tests, fibroblastic VERO cell line was employed. The porous alumina ceramic coated acquired a higher strength and more pronounced cell interaction than the non coated alumina scaffolds.

Aluminide Coating Formation on Internal Passages of GTD-111 Superalloy by Slurry Technique

The diffusion aluminide coatings are widely used in the air-cooling passages to protect their surfaces against high temperature corrosion. In this study plain and Si-modified aluminide coatings were applied by slurry technique on internal surfaces of Ni-base GTD-111 superalloy cylindrical specimens derived from a gas turbine air-cooled blade. The slurries containing Al or Al plus Si powders were applied on internal surfaces by injection method. Then, the samples were heated to high temperature (800-1000°C) to form the coatings. Optical, SEM-EDS, and XRD were utilized for characterizing microstructures and phase compositions of the coatings. The thicknesses of applied coatings on internal surfaces were in the range of 30-50 μm that meets specifications for diffusion coatings in such application (i.e. 25-756m). The examinations demonstrated that both coating types were contained β-NiAl phase as the matrix. The uniformities of coatings applied on different surface positions of passageway were determined. In addition, the effects of time and temperature of coating process as well as mass of dried slurry on the coating thickness were also discussed.

Oxidation behavior and kinetics of SiC/alumina–borosilicate coating for carbon–carbon composites

A SiC/alumina–borosilicate double-layer coating was prepared by a two-step slurry technique for the protection of carbon–carbon composites from oxidation. SEM, XRD and EDX analysis showed that the inner layer coating obtained from the first step consisted of β-SiC, Si and SiO 2. The outer layer consisted of B 4C, Al, amorphous SiO 2 and quartz. The oxidation behavior and kinetics of the SiC/alumina–borosilicate coating were investigated. It was found that the as-prepared coating could effectively protect carbon–carbon composites from oxidation at 1300 °C for 100 h. The isothermally oxidation kinetics could be described by Microflaws Model and Diffusion Model. During short-time oxidation, the overall oxidation kinetics was determined by the transport processes through microflaws, which resulted in a linear growth law. While during oxidation of longer time, the weight loss rate was controlled by the diffusion processes in the coating with growing oxide layer, which led to a parabolic growth law.

Cocrystal Screening of Stanolone and Mestanolone Using Slurry Crystallization

A slurry crystallization technique was used in cocrystal screening of two nonionizable pharmaceutical host compounds, stanolone and mestanolone, with 11 pharmaceutically acceptable guest acids. Crystallization was performed simply by adding crystallization solvents to solid mixtures of a host and a guest, which had been prepared using lyophilization of their dimethyl sulfoxide solution. Powder X-ray diffraction and thermogravimetric/differential thermal analysis were used to identify new solid forms. Two resultant new forms, stanolone l-tartaric acid 1:1 cocrystal and mestanolone salicylic acid 1:1 cocrystal, were characterized using single-crystal X-ray diffraction. The hosts, despite having the same steroidal skeleton and the same functional groups that form strong hydrogen bonds, each formed a cocrystal with a different guest molecule. All functional groups of the host and guest molecules that form strong hydrogen bonds were engaged in hydrogen bonding, but, despite the highly analogous molecular structures of the hosts, the two cocrystals exhibited dissimilar crystal structures. The present study shows the slurry technique to be viable and practical for cocrystal screening and demonstrates the importance not only of hydrogen bonding but also of geometric fit in cocrystal formation.

Characterization and performance of glass–ceramic sealant to join metallic interconnects to YSZ and anode-supported-electrolyte in planar SOFCs

This work describes the design, development and performance of a glass–ceramic sealant used to join the ceramic electrolyte (YSZ wafer and anode-supported-electrolyte (ASE)) to the metallic interconnects (Crofer22 APU and AISI 430) in planar SOFC stacks. The designed glass–ceramic sealant is a barium-free silica-based glass, which crystallizes by means of the heat treatment after being deposited on substrates by the slurry technique. The sealing process of the glass–ceramic was optimized and joined ceramic/seal/metal samples were morphologically characterized and tested for 400 h in air atmosphere followed by 200 h in H 2–3H 2O atmosphere at the fuel-cell operating temperature of 800 °C. The study showed that the use of the glass–ceramic was successful in joining the ceramic electrolyte to the metallic interconnect and in preventing adverse corrosion effects at the interface.

PERFORMANCE AND STABILITY OF MODERN GUN PROPELLANTS

ABSTRACTDifferent RDX based gun propellant compositions were prepared using slurry technique. Ballistic performance of the compositions was evaluated on the basis of closed vessel test. Heat of combustion was measured using a calorimetric bomb. Sensitivity, some thermal characteristics and thermal stability of the compositions were investigated. The obtained results reveal that gun propellant compositions based on approximately 58 percent RDX could provide relatively high level of powder force, acceptable maximum pressure and good stability.

Sulfentrazone Adsorption and Mobility in Surface Soil of The Southern United States

Sulfentrazone adsorption and mobility in six soils with varying soil properties were evaluated under laboratory conditions. Adsorption was evaluated using a modified slurry technique. Mobility was evaluated using packed-soil columns under saturated flow conditions. The order of adsorption to soil was Sequatchie loam > Dothan loamy sand = Bosket fine sandy loam > Malden loamy sand > Commerce silty clay loam > Harkey clay loam. Greater sulfentrazone adsorption occurred in soils with lower pH. Sulfentrazone movement under saturated flow conditions in 27-cm soil-packed columns was greater in soils with low adsorption, high pH, and coarse texture. Sulfentrazone movement was limited in the Sequatchie loam but was greater in the other soils examined. No clear relationship was evident between sulfentrazone mobility and adsorption in these soils. Nomenclature: Sulfentrazone

The approaches to thin film preparation and TEM observations on slurry Si‐modified aluminide coatings

AbstractTransmission electron microscopy (TEM) can be used as a precision characterization tool to identify very small precipitates in diffusion aluminide coatings. However, in order to successfully prepare the appropriate samples for TEM observation, often non‐traditional thin film preparation techniques need to be employed. In this work, two sample preparation methods of twin jet electro‐polishing and ion milling were experienced to characterize fine precipitates (&lt; 1 μm), in Si‐aluminide coatings applied on Ni‐base superalloy In‐738LC by slurry technique. These precipitates are concentrated throughout the topcoat zone. It was found that the preparation of thin film exactly from the outer zone of the coating is only possible using ion milling process. The ion‐milled specimens were utilized to observe by JEOL high resolution TEM operating at an accelerating voltage of 300 kV. Electron diffraction patterns, bright field and EDS were used to identify the precipitate phases as well as the coating matrix. The results showed that the fine precipitates are typically chromium silicides in nature, mostly as Cr3Si and CrSi, distributed in the β‐NiAl matrix phase.

High temperature oxidation resistance coating on niobium

An ultrahigh temperature oxidation resistance MoSi2 coating on niobium substrate was prepared by a slurry sintering technique. The static antioxidation property was tested at 1600°C. The microstructure and phase composition of the coating were investigated by SEM, EDS, and XRD analysis. Results were correlated to the coating oxidation resistance. The results indicated that, when exposed to a high temperature oxidation atmosphere, the MoSi2 coatings oxidised selectively to form an oxide glass with a self healing function on the coating surface. Any impurities existing in the slurry deteriorated the integrity of the surface, and hence the antioxidation properties of the coating. A transitional layer formed by diffusion was found at the interface between the coating and the substrate.

Multielement analysis of tea leaves by inductively coupled plasma optical emission spectrometry using slurry nebulisation

In order to evaluate the slurry nebulization method as an alternative method for the analysis of tea, the metal ion content of tea samples of different origins was determined. The concentrations of six elements, Al, Ba, Ca, Mg, Mn and Zn, were determined by introducing tea as a slurry into an inductively coupled plasma optical emission spectrometer (ICP-OES). Calibration was performed by using either aqueous standard solutions or by using the simplified generalized standard additions method (GSAM). The simplified GSAM is an expansion of the conventional standard additions method, based on the principle of varying both the sample mass and the amount of standard solution added. Initially the tea was ground for 3 h prior to slurry preparation. A carbonization procedure was included before the sample was ground. The grinding time was reduced to only 30 min. For comparison, tea was also digested by boiling in acid and being introduced into the plasma as an aqueous solution. The results obtained using slurry analysis were much higher than the results obtained from digested tea using aqueous standards for calibration. The metal content of the tea samples was found to be suitable for differentiating amongst the tea samples studied. The accuracy of the method was checked by analyzing a tea certified reference material. The Student's t-test showed that values obtained using slurry nebulization were close to the certified values at a 95% confidence level. The simplified GSAM was applied to further confirm the accuracy of the slurry technique, and the values obtained using this method were comparable with those obtained using the slurry method with aqueous calibration. The slurry method can, therefore, be successfully applied to the analysis of tea leaves without the need to pre-dissolve them. This could avoid the use of hazardous chemicals, incomplete dissolution and loss of volatile analytes.

Catalytic Hydrogenation in the Liquid Phase

Catalytic hydrogenation in the liquid phase is a very common reaction type in the production of fine chemicals and pharmaceuticals. Among the various reaction techniques, it is the slurry technique (stirred tank or venturi type loop reactor) in a semi-batch mode which is most frequently used. General safety aspects of catalytic hydrogenations will be discussed und exemplified for a typical three-phase semi-batch catalytic hydrogenation.