Green Specimens Research Articles

Anisotropy in AISI 316L produced by Binder Jetting 3D printing: Sintering shrinkage and thermal conductivity

The inhomogeneous particle packing in green parts manufactured by Binder Jetting 3D printing is responsible for the anisotropy in several phenomena and properties. In this work, the anisotropy of the sintering shrinkage and of thermal conductivity of AISI 316L green specimens is investigated. Shrinkage was investigated by dilatometry. Moreover, the dimensional changes, density, and the thermal conductivity of specimens sintered at intermediate temperatures were measured. The microstructure of the specimens was analysed with the standard metallographic. Sintering shrinkage is basically isotropic during the heating step and becomes anisotropic on approaching the sintering temperature at 1370°C when the full density is achieved. A slight anisotropy in the building plane is observed. Contrarily, thermal conductivity is anisotropic during the heating step and becomes isotropic during the isothermal holding at the sintering temperature. Moreover, there is an inverse relationship between thermal conductivity in the debinded specimen and shrinkage. A hypothesis for this indirect correlation is proposed. The role of the large interlayer pores and the aligned pores caused by the ballistic effect of the binder jet is confirmed.

Characterization and utilization capabilities of industrial wastes for green bricks production

BackgroundThe goal of this study is to develop a feasible and sustainable solution to manage the use of industrial wastes of ground granulated blast-furnace steel slag (GGBS) activated by cement kiln dust (CKD) and quicklime (QL). Using activated GGBS in the manufacture of stabilized green bricks is still uncommon in Egypt in such applications. Five clay-based mixtures, each with varying replacement ratios (5–10, wt.%) of CKD and QL, were studied. Laboratory tests were conducted on cylindrical specimens made from these mixtures, which were left to cure for periods of up to 60 days. The raw materials and lab-made specimens were analyzed using particle size analysis, differential thermal analysis, X-ray fluorescence, and X-ray diffraction techniques. The physical and mechanical properties of the cured specimens were also determined and evaluated according to standard specifications. Furthermore, the durability of the cured specimens was evaluated against collapsibility in water.ResuItsIt has been observed that adding QL and CKD to the stabilized green specimens of different mixes can enhance their engineering properties with curing age increasing. This is due to the pozzolanic reaction, which fills the pore structure with calcium silicate hydrates and calcium aluminate hydrates gel. The ratio of QL and CKD used significantly affected the engineering properties of the specimens. The study found that using 20% GGBS and 5% QL led to an increase in compressive strength (266 kg/cm2) at the density of (2.15 g/cm3), while also water absorption was reduced (8%) to give superior results. When GGBS and CKD were combined, a higher content of CKD (10 wt.%) gave better results compared to (5 wt.%) CKD. Furthermore, the physical and mechanical properties of the tested specimens (MD 1, MD II, MD III and MD IV) met the acceptable limits of dry compressive strength (30–70 kg/cm2), water absorption (8–15%), and density (1.7–2 gm/cm3), as specified by the Egyptian standard specifications for buildings used compressed earth blocks.ConclusionThe CKD and QL act as alkali activators for GGBS and can be utilized in masonry construction.

Moldability and Solvent Debinding of Hydroxyapatite Micro-Part Processed through Micro-Powder Injection Molding

The development of the micro-powder injection molding (µPIM) process from the powder injection molding (PIM) process has been prompted by the demand of the worldwide market to produce micro-sized components. The need for µPIM-processed components is currently rising across a range of industries, including automotive, aerospace, food, biomedical, electronics, and telecommunications. In the current research work, homogeneous HA feedstock with a powder loading of 57 vol.% was prepared by mixing HA powder particles with palm stearin and low-density polyethylene (LDPE) binders at a mixing temperature of 150 °C for 6 h. Defect-free injection molded or green micro-sized components of HA were produced by employing injection pressure, injection time, mold temperature, and melt temperature of 12 bar, 5 s, 110 °C, and 180 °C, respectively. When mold temperatures less than 110 °C were used, short shot defects were frequently observed in green specimens. After solvent debinding at 60 °C for 50 min, 82.2% of the palm stearin was removed from the green part. No difference in dimension between the solvent debound part and the green part was noticed. An open-pore structure developed in the solvent debound HA microcomponent is helpful for eliminating the insoluble LDPE binder during the thermal debinding phase.

Semi-automatic standardized analysis method to objectively evaluate near-infrared fluorescent dyes in image-guided surgery.

Near-infrared fluorescence imaging still lacks a standardized, objective method to evaluate fluorescent dye efficacy in oncological surgical applications. This results in difficulties in translation between preclinical to clinical studies with fluorescent dyes and in the reproduction of results between studies, which in turn hampers further clinical translation of novel fluorescent dyes. Our aim is to develop and evaluate a semi-automatic standardized method to objectively assess fluorescent signals in resected tissue. A standardized imaging procedure was designed and quantitative analysis methods were developed to evaluate non-targeted and tumor-targeted fluorescent dyes. The developed analysis methods included manual selection of region of interest (ROI) on white light images, automated fluorescence signal ROI selection, and automatic quantitative image analysis. The proposed analysis method was then compared with a conventional analysis method, where fluorescence signal ROIs were manually selected on fluorescence images. Dice similarity coefficients and intraclass correlation coefficients were calculated to determine the inter- and intraobserver variabilities of the ROI selections and the determined signal- and tumor-to-background ratios. The proposed non-targeted fluorescent dyes analysis method showed statistically significantly improved variabilities after application on indocyanine green specimens. For specimens with the targeted dye SGM-101, the variability of the background ROI selection was statistically significantly improved by implementing the proposed method. Semi-automatic methods for standardized quantitative analysis of fluorescence images were successfully developed and showed promising results to further improve the reproducibility and standardization of clinical studies evaluating fluorescent dyes.

Phosphorescence and Tarnish Resistance Properties of Copper with Strontium Aluminate Addition

The purpose of this research is to examine the effect of strontium aluminate (SrAl2O4) in copper samples on phosphorescence and tarnish resistance properties. The samples were fabricated by powder metallurgy using the compression moulding technique and then sintered in argon atmosphere. Phosphorescence, hardness, microstructure and tarnish resistance were studied. In the process of the compression moulding, the samples contain 100, 90, 80 and 70 percent of copper powder, by weight, with the addition of 0, 10, 20 and 30 percent of strontium aluminate, by weight, respectively. Polyvinyl alcohol (PVA) was used as a binder and mixed with copper and strontium aluminate powder to produce the green specimens using a hydraulic machine. Then, the green samples were sintered at 900 °C for one hour. After sintering, PVA was eliminated and the samples became denser. It was found that the hardness of the sample without strontium aluminate (30.5 HV) is higher than that of the sample with 10% of strontium aluminate addition (12.84 HV). Furthermore, copper samples containing strontium aluminate were fluorescent under ultraviolet at 517 nm. The sample with the largest amount of strontium aluminate (70Cu-30SrAl2O4) has higher phosphorescence than 90Cu-10SrAl2O4. In sulphur atmosphere, the tarnish resistance was found to be improved when strontium aluminate was added into copper. The colour difference (DE*) of 100Cu, which has no strontium aluminate, was 6.42 and higher than that of 90Cu-10SrAl2O4 (DE*= 3.5), 80Cu-20SrAl2O4 (DE*= 1.37), and 70Cu-30SrAl2O4 (DE*= 0.49), when testing in sulphur atmosphere for 30 min. 70Cu-30SrAl2O4, containing the highest amount of strontium aluminate, has the least colour changing on its surface resulting in the resistance in tarnishing.

Elevated Temperature Basic Oxygen Furnace Slag Stabilisation of Desilicated Foundry Sand

This study presents the use of Basic Oxygen Furnace slag (BOFS) as a stabilizer for disilicated waste foundry (DWF) sand and therefore provides an opportunity for high-volume use of waste material for low-cost, low-volume building and construction material. DWF was stabilized with BOFS to 40 %. The effect of composite moisture content, BOFS content, curing time and curing temperature was studied. A 50:50 DWF: BOFS composite cured at 80 °C for 96 h had the highest unconfined compressive strength (UCS) of 7.83 MPa, a 15.5 % water absorption after a 24 h soak with a corresponding 20.5 % reduction in UCS. The green specimen (70:30) was then used to stabilize expansive soil. The formation of hydration products was responsible for the strength gain in the stabilized DWF specimens. It was concluded that BOFS was successful in stabilizing DFS. The stabilised DWF for ASTM C34-13, C129-14a and South African standards (SANS227: 2007).

Sintering behavior of ultra-thin 3D printed alumina lattice structures

Ceramic stereolithography or vat photopolymerization is a process allowing the fabrication of ceramic objects with highly complex shapes. Lattices structures are particularly used together with advanced optimization topology tools for the design of printable lightweight shapes with optimized mechanical resistance. If the mechanical resistance of these lattices structures is well controlled at the polymeric state, they can be severely deformed at high temperatures during the sintering stage. The deformation sensitivity of the lattices structures during the sintering should then be determined to include this aspect at the conception stage. The finite element (FEM) simulation of lattices sintering is an interesting solution to anticipate numerically the deformation sensitivity of the lattices and determine their minimum wall thickness. This requires to determine the sintering behavior of the printed green specimens and to take into account the sintering anisotropy, which involves weaker resistance between the layers. In this study the sintering behavior is first determined by multiple-axis dilatometry, modeled analytically and then simulated by the FEM method. Afterward, the sintering simulation of lattices with different wall thicknesses is conducted. This allows testing the simulation tool predictability for each lattices wall thickness and to compare their deformation sensitivity at high temperatures.

Fabrication and Characterization of Cu/SiC‐Based Axially Functionally Graded Beam

Metal−ceramic based functionally graded materials (FGMs) are mainly used for thermal and structural applications in industry. A metal matrix‐based axially FGM beam is fabricated using a powder metallurgy manufacturing process. The main objective of this work is to develop a processing method for an axially graded beam made of Cu/SiC by stacking powder in the longitudinal direction. A three‐layered Cu/SiC FGM having a step‐wise gradation along the length is fabricated. The green specimens are prepared by the uniaxial compaction of powder mixture by the universal testing machine (UTM) followed by cold isostatic pressing (CIP). Further, a detailed microstructure analysis of the powders and the sintered specimens is conducted. The Vicker's microhardness test is also performed for each layer of the sintered specimen to analyze the effect of SiC content. A smooth transition of the ceramic content in the specimen along the length is observed. The effect of ball milling on the crystallite size is studied using Scherrer and Williamson−Hall approach. An uniform and consistent distribution of the SiC particles shows a reduction in porosities and increment in the hardness value with increase in SiC wt% is also observed. The present investigation helps to design functionally graded rotor blades, gears, and orthopedic implants.

Influence of the heating rate on sintering shrinkage of plain iron

ABSTRACT The effect of heating rate on shrinkage of plain iron was investigated on green specimens with different green densities: 6.5, 6.9 and 7.3 g cm−3. On increasing the heating rate, the anisothermal shrinkage in the alpha field starts at higher temperatures but its amount does not change. The activation energy corresponds to that of dislocation pipe diffusion, confirming the role of the structural defects accumulated in the particles during cold compaction. The isothermal shrinkage increases on increasing the heating rate, likely due to the effect of surface diffusion at lower temperatures that reduce the driving force, without a measurable effect on shrinkage. The effect of green density is the same for anisothermal and isothermal shrinkage, with a minimum (in absolute value) at the intermediate green density.

The effect of new LED lighting systems on the colour of modern paints

This research focuses on the investigation of the effect of a new light emitting diode (LED)-lighting system which reproduces indoor museum conditions, on some self-made art paint colours (acrylic-, alkyd-, and linseed oil-based paints) often used in modern-contemporary art. A halogen lamp representing a traditional light source for museum lighting was also considered. Lighting-set-up and lighting optimization parameters were considered while Ultraviolet/Visible/Near Infrared (UV/Vis/NIR) spectrophotometry was used for investigating the colour change of the paint samples. Univariate analyses allowed determining the highest effect of the lighting systems on the linseed oil binder and ultramarine blue PB29 mixture upon ageing, according to the highest total colour change ΔE*ab. In a more specific and detailed way, variance analyses not only demonstrated the strong correlation between the type of binder and pigment used for the paint samples with the colour variation, but also showed that the short-wavelength blue LEDs influenced the change along the yellow–blue b* axis of the yellow and blue samples, whereas the halogen lamp mostly had an impact towards the red–green a* axis of mostly the green specimens.

Study on the indirect selective laser sintering (SLS) of WC-Co/PA12 powders for the manufacturing of cemented carbide parts

A new approach for the manufacturing of cemented carbide parts with a high degree of complexity via indirect selective laser sintering (SLS), using commercial WC-12Co with different amounts of polyamide (PA12) and using low-cost standard equipment is proposed. After debinding, vacuum sintering and sinter-HIP at 1400 °C with 50 bar Ar of the green specimens, the samples showed low relative densities in the range of 60–66%, while the shrinkage after sintering ranged between 35% and 42%, being constant within the volume. This method enables the production of complex shape parts which retained their shape even with respect to the cooling channels after sintering, showing good surface quality and geometry definition. The 3D scan of a WC-12Co end mill sample with 20% PA12 showed low dimensional deviation compared to the 3D model (.stl), proving the capability of the SLS to manufacture near-net-shape cemented carbide parts. The obtained results are indicating that, by adopting a better suited WC-Co powder, indirect SLS followed by Sinter-HIP, can become an interesting method for the Additive Manufacturing of complex cemented carbide parts.

Sintering shrinkage of cold compacted iron: effect of thermodynamic driving force, structural and geometrical activity

ABSTRACT The sintering shrinkage of tapped powders and prior cold compacted specimens of sponge and water atomised iron powders was investigated. The behaviour of the tapped powders is only determined by the driving force and that of the green compacts is strongly affected by modifications caused by cold compaction, which introduce a structural and a geometrical activity that enhance the kinetics of shrinkage. While the tapped powders display only an isothermal shrinkage, the green specimens display an additional large and anisotropic anisothermal shrinkage which is independent on the surface area of the powders. The effect of prior cold compaction tends to run out during the heating step of the sintering cycle.

Osseointegration of Cylindrical Zirconia–Alumina Functionally Graded materials, Dental implant by Electrophoretic Deposition

Electrophoretic deposition (EPD) technique is used to prepare zirconia–alumina composite layers based on the principle of functionally graded materials (FGM). The FGM were prepared with five layers. The outer layer was composed of pure α-alumina to promote biocompatibility while the inner layer was stabilised zirconia (3Y-TZP), to benefit from its tough properties. The intermediate layers were stepwise graded layers. The stability of the EPD suspensions was the main challenge during the preparation steps. Due to availability and low cost, alcoholic solutions of polyethylene glycol (PEG) and toluene were used to control conductivity, dielectric constant and the viscosity of the suspension. The appropriately applied potential, (ζ), for the deposition of each layer, was achieved via gradation of the applied voltage, which was to optimise the packing of each layer and avoid cracking after sintering at 1500 °C. The cylindrical-shaped green specimens were obtained via deposition on graphite electrodes. A small amount of acetic acid was added during the deposition of the final outer alumina layer to introduce porosity, via the bubbling of acetic acid, to encourage osseointegration. The sintered specimens were implanted in rabbit tibial bone. In vivo histological tests showed the successful osseointegration of the implants to the rabbit bone.

Oncosaccus: a rare green alga endemic to China belongs to Chaetopeltidales (Chlorophyceae, Chlorophyta)

ABSTRACT The green algal genus Oncosaccus, endemic to China, has previously been classified in Chlamydomondales (Chlorophyceae). In the present study, two green algal specimens from west China were identified as Oncosaccus tetrasporoides due to their unique colonial form with numerous cells embedded in a thick gelatinous envelope without perforations and pseudocilia. Molecular data from two nuclear loci (18S rDNA and ITS) were used to test the hypothesised membership of this taxon. The molecular data clearly showed that Oncosaccus did not have close affinities to the Chlamydomondales, but instead belonged to the order Chaetopeltidales in the family Chaetopeltidaceae, and had a close relationship with Chaetopeltis and Pseudulvella. The ultrastructure of Oncosaccus tetrasporoides resembled Chaetopeltis and Pseudulvella, and adjacent cells lacked plasmodesmata, and the pyrenoid matrix was traversed by a cytoplasmic channel instead of the thylakoid membrane were present. This morphology supported the molecular data and confirmed this group’s placement in the Chaetopeltidales. The present study expanded our understanding of the morphological features of green algae, particularly those of the poorly studied Chaetopeltidales. Nonetheless, a phylogenetic re-evaluation based on large samples in conjunction with molecular analyses is needed.

Effect of Ball Milling Time on Strengths of Hybrid Fiber-reinforced Plaster Molds for Investment Casting

In order to prepare high strength plaster molds for investment casting, polypropylene and aluminum silicate hybrid fibers of contents 0.50 wt% were introduced into powder mixture of gypsum and mullite. The effects of different ball milling times on strengths of plaster molds were investigated in this work. To this end, modified mullite and gypsum powder were mixed and treated by ball milling for 2.0–8.0 min. The hybrid fibers were added to the solid mixture to prepare reinforced plaster molds with high strengths. The green, fired, and residual strengths of plaster mold specimens were all tested. The results showed a positive effect of ball milling on the strengths of plaster molds, in which strength could effectively be improved by raising the ball-milled time regardless of the presence or absence of the fiber. The strength increased by at least 29.7% when compared to un-milled specimen. However, the ball milling time should not be too long since exceeding 6.0 min resulted in a slow declining trend of the strength of the plaster molds until reaching a stable plateau. Shorter ball milling periods could refine the crystal size of refractory materials. For green specimens, the morphology of plaster crystal changed from short rods to fine needles and then to column crystals as milled time rose, promoting changes in strength. The microscopic morphologies of fired specimens were slightly impacted by the increase in milling time. Overall, ball milling periods of 4.0–6.0 min were identified as optimum for fiber-reinforced plaster molds. These findings look promising for future preparation of solid shell for investment casting.

Isotomurus graminis Fjellberg (Collembola: Isotomidae) new for Iran, key to Iranian species in genus with comment on the validity of photographic records

As part of a comparison of the collembolan fauna in soil of forest, grasslands and broadacre agriculture in north east Iran, several pale green specimens were found that complied with all characters of Isotomurus prasinus (Reuter, 1891) and keyed out as such in Potapov (2001) except that the body covering consisted of smooth mesochaetae and not ciliated chaetae as are present in prasinus according to Potapov (2001). On a more extensive examination of the recent literature, it was clear that the Iranian specimens belonged to the species Isotomurus graminis Fjellberg, 2007 described six years later. In his description, Fjellberg (2007) notes that some specimens of the new species could have previously been identified as I. prasinus in spite of having a different chaetotaxic covering. He also notes that, in a number of characters, it is identical with Isotomurus unifasciatus (Börner, 1901) but the colour differentiates them as this latter species usually has a broad, pigmented, longitudinal dorsal stripe.

Influence of the forming method on flash sintering of ZnO ceramics

This work aimed to investigate different forming techniques used in the ceramic industry when applied to flash sintering. The way the density gradient interferes with the final densification and microstructural heterogeneity development of ZnO specimens was studied. For this purpose, ZnO cylindrical specimens were formed by uniaxial pressing, isostatic pressing, and slip casting. All experiments were conducted isothermally at 800 °C in an adapted tube furnace, with an applied electric field of 60 V/cm and maximum current density of 200 mA/mm2. Samples formed by isostatic pressing showed better control in the development of microstructural homogeneity. The ones formed by slip casting had lower apparent densities and longer incubation times among all the forming methods. Also, slip casting samples showed the largest detachment of average grain size in the central region compared to the other regions. One outstanding result is related to differences between the regions close to the upper and lower electrodes in the samples formed by uniaxial pressing, even when using alternating current mode. These results showed that the density distribution along the green specimen should be considered a decisive factor when evaluating flash sintered samples. The chosen forming technique causes significant differences in incubation time, densification, and the development of microstructural heterogeneity.

Properties and Fracture Surface Features of Plaster Mold Reinforced with Short Polypropylene Fibers for Investment Casting

In this work, plaster molds for investment casting, reinforced with short polypropylene fibers, were prepared and their properties and fracture surface features were investigated. Fiber contents ranging from 0.10 to 0.50 wt% were introduced into a powder mixture of gypsum and mullite (ratio of 3:7) as reinforcements in order to prepare thin-walled plaster molds with high strength and permeability. The strength of green and fired plaster mold specimens was tested, the permeability was also tested, and their fracture surfaces were observed by scanning electron microscopy (SEM). The results show that the strength of the molds increases initially and then decreases with increasing fiber content. The green flexural strength of the specimens containing 0.20 wt% polypropylene fibers reached the maximum, c.a. 1.94 MPa, increased by 36.6%, and particularly, there was a slight increase in their fired strength, a maximum value of 0.45 MPa, in comparison with the fiber-free specimen. This low increase in the fired strength the reinforced specimen will produce a favorable effect on the collapsibility of shells in the casting cleaning process. In addition, the fired permeability of fiber-reinforced fired specimens exhibited significant enhancement, compared to that of the unreinforced ones. With increasing fiber content, the permeability of specimens increased from 8.6 to 11.5%. The improvement of green permeability was limited substantially. SEM observations indicate that the failure of the green specimens is a result of brittle fracture of the plaster substrate and/or fiber debonding from the matrix during loading. On the contrary, in fired specimens, the failure occurs by holes in the plaster substrate resulted from fiber ablation in the matrix during the firing process. The arrangement of polypropylene fibers can also affect the fracture behavior of molds. This proposed approach can reduce mold thickness without loss of strength and provide defined judgment basis for fracture features.

Direct ink writing additive manufacturing of porous alumina-based ceramic cores modified with nanosized MgO

Alumina-based ceramic cores, widely applied to cast alloy, have been restricted by the increased complexity of castings, the resultant complex equipment and cost. In this research, to address the aforesaid disadvantages, direct ink writing, a green additive manufacturing method, is utilized to directly fabricate a new kind of nanosized MgO strengthened alumina-based ceramic cores. Slurries with various compositions exhibits ideal shear-thinning behaviors, owing to the hydrogen bond formed between polyvinylpyrrolidone and kaolin molecules. We notice that introducing nanosized MgO reduces drying shrinkage of green specimens and greatly promotes liquid-phase sintering, leading to rather more densified samples. Overall, it is anticipated that the current approach is effective in rapidly manufacturing alumina-based ceramics and some other ceramics with high strength, low shrinkage and high quality.

Effect of Yttrium Oxide on Mechanical and Physical Properties of Fe–10%Cu Composite

Iron-based composites have found a lot of industrial applications such as bearings, camshafts, connecting rods, pulleys, various valves, oil pump gears and many other applications in the automotive and other industries due to their low cost, availability, and high strength. The present study aims to prepare Fe-10 vol.% Cu - (0 – 5) wt.% nano Y2O3 composites by powder metallurgy technique and studying their physical and mechanical properties. The powders were mixed into ball mill for 30 minutes, followed by room temperature uniaxial compaction at 700 MPa for 3 minutes. The green specimens were sintered at 1000 oC for 1 hour. The results of the present study showed that nano yttrium oxide has significant effects on both physical and mechanical properties of Fe-10%Cu composite. The bulk density was increased by 0.92% and the true porosity was decreased by 6.4% on increasing the nano oxide content from 0% to 3% respectively. Vickers microhardness was increased by 5.9% on increasing Y2O3 up to 1% followed by gradual decrease on further increase above 1%. Wear rate was decreased by 21% on increasing the nano oxide content from 0% to 3%. On the other hand, the compressive strength was decreased by 47% on increasing Y2O3 up to 5%.