Ca Sheet Research Articles

Fabrication of cellulose acetate microfluidic devices using injection molding and CO2 laser ablation

AbstractCellulose acetate (CA) is a bio‐based polymer derived from natural resources and has unique physical and chemical properties, such as high transparency, chemical and mechanical stability, hydrophilicity, biocompatibility, and biodegradability. This study proposed an approach for the fabrication of CA‐based microfluidic devices with injection molded CA sheet and CO2 laser‐ablated microchannel. This study also provided a detailed study of the width and depth of the laser‐ablated microchannels with various scan speeds and laser energy settings. A droplet generator and a diffusion mixer were also fabricated and tested for the demonstration of the proposed fabrication technique. Biocompatibility test, biodegradability test, and spontaneous flow experiments were also conducted with the fabricated CA‐based microfluidic devices. The proposed fabrication method for CA‐based microfluidic devices has great application prospects in analytical chemistry, biological, and medical fields for the formation of environmentally friendly microfluidics devices.

Inherited effect of original loading direction on the annealing behavior of a hot-compressed Mg-1.0 wt%Ca sheet

This short communication reports the grain growth behaviors and static recrystallization mechanisms of Mg-1.0 wt%Ca sheet after hot-compression along rolling direction (RD) and normal direction (ND), respectively. The results strongly suggest that Mg-1.0 wt%Ca alloy owns excellent thermal stability and has the potential to serve as heat-resistant products.

Substantial improvement in cold formability of concentrated Mg–Al–Zn–Ca alloy sheets by high temperature final rolling

Poor formability at room temperature (RT) has been the main bottleneck for a wider range of applications of concentrated Mg–Al–Ca(–Zn) sheet alloys. Here, we report that RT stretch formability of concentrated Mg–Al–Zn–Ca alloy sheets can be improved substantially by increasing the final rolling temperature. A Mg–6Al–1Zn–1Ca alloy sheet subjected to 510 °C final rolling shows an index Erichsen (I.E.) value of 7.9 mm, which is significantly higher than that of the same sheet subjected to 450 °C final rolling (4.1 mm). More excitingly, 510 °C final rolled Mg–6Al–1Zn–2Ca (wt%) alloy sheet exhibits a large I.E. value of 8.0 mm which has never been achieved in 2 wt% Ca-containing Mg alloys. A systematic microstructural investigation indicates that the substantial improvement in stretch formability of Mg–6Al–1Zn–xCa (x=1, 2) alloy sheets is mainly associated with weakened basal textures. To clarify the mechanisms responsible for the weak basal textures developed in the high temperature rolled sheets, electron backscatter diffraction (EBSD) assisted slip trace analysis and quasi-in-situ EBSD method were employed. EBSD-assisted slip trace analysis on the side surface of as-rolled Mg–6Al–1Zn–1Ca alloy sheets indicates that the activity of pyramidal <c+a> slip increases significantly by increasing the final rolling temperature from 450 to 510 °C. During subsequent annealing, grains deformed by pyramidal <c+a> slip evolve into new recrystallized grains with a wide spectrum of orientations, which plays a key role in the development of the weaker basal texture.

Excellent age hardenability with the controllable microstructure of AXW100 magnesium sheet alloy

Age-hardenability and corresponding improvement of the mechanical properties of Mg–1Al–0.7Ca and Mg–1Al–0.7Ca–0.7Y alloy sheets are addressed with respect to the microstructure and texture evolution during thermomechanical treatments. A fine grain structure and weak texture with the basal pole split into the sheet transverse direction are retained in the Mg–1Al–0.7Ca–0.7Y sheet even after the homogenization at 500 °C, due to the grain boundary pinning by Y-containing precipitates possessing a high thermal stability. Contrarily, the Mg–1Al–0.7Ca sheet shows a coarse microstructure and basal-type texture after the homogenization. The peak-aged condition is attained after the aging at 250 °C for 1800 s of both homogenized sheets, while the Y-containing sheet shows a higher hardness than the Mg–1Al–0.7Ca sheet. TEM analysis and thermodynamic calculation show the formation of metastable precipitates composed of Al, Ca, Y and Mg in the Mg–1Al–0.7Ca–0.7Y sheet at the homogenized and peak-aged conditions. A significant increase in the yield strength is obtained in the peak-aged condition from 162 MPa after the homogenization to 244 MPa, which arises from the increased size and number density of the precipitates. The high age-hardenability of the Mg–1Al–0.7Ca–0.7Y sheet attributes to the superior mechanical properties with an improved ductility promoted by the weak texture.

Influence of Ca and Zn synergistic alloying on the microstructure, tensile properties and strain hardening of Mg-1Gd alloy

Influences of Zn, Ca, and their synergistic additions on the microstructures, tensile properties, and strain hardening behaviors of extruded Mg-1Gd alloy sheets were investigated. The grain size of Mg-1Gd sheet was slightly refined with the sole addition of Zn or Ca, while a striking grain refinement was observed with the synergistic addition of Zn and Ca. Sole Zn addition resulted in an increase of both yield strength and ductility of Mg-1Gd sheet. Sole addition of Ca enhanced yield strength but decreased ductility of Mg-1Gd sheet, in which an inhomogeneous distribution of coarse Mg2Ca particles was observed. With the Zn and Ca synergistic addition, the alloy sheet showed much higher strengths. The ultimate tensile and yield strengths of Mg-1Gd-0.7Zn-0.7Ca sheet were ~339 MPa and ~135 MPa along extrusion direction, and ~329 MPa and ~172 MPa along transverse direction, respectively. Meanwhile, the ductility of Mg-1Gd-0.7Zn-0.7Ca sheet along extrusion and transverse direction were also increased up to ~28.5% and ~18.6%, respectively. The improved mechanical performance of Mg-1Gd-0.7Zn-0.7Ca sheet was ascribed to a combined effect of many factors such as fine grain size, homogenous distribution of fine Mg2Ca particles, high prismatic slip activity, suppression of grain boundary cracking, and enhancement of strain coordination capability.

Microstructure and Hot Deformation Behavior of Twin Roll Cast Mg-2Zn-1Al-0.3Ca Alloy.

In the present work, the microstructure, texture, mechanical properties as well as hot deformation behavior of a Mg-2Zn-1Al-0.3Ca sheet manufactured by twin roll casting were investigated. The twin roll cast state reveals a dendritic microstructure with intermetallic compounds predominantly located in the interdendritic areas. The twin roll cast samples were annealed at 420 °C for 2 h followed by plane strain compression tests in order to study the hardening and softening behavior. Annealing treatment leads to the formation of a grain structure, consisting of equiaxed grains with an average diameter of approximately 19 µm. The twin roll cast state reveals a typical basal texture and the annealed state shows a weakened texture, by spreading basal poles along the transverse direction. The twin roll cast Mg-2Zn-1Al-0.3Ca alloy offers a good ultimate tensile strength of 240 MPa. The course of the flow curves indicate that dynamic recrystallization occurs during hot deformation. For the validity range from 250 °C to 450 °C as well as equivalent logarithmic strain rates from 0.01 s−1 to 10 s−1 calculated model coefficients are shown. The average activation energy for plastic flow of the twin roll cast and annealed Mg-2Zn-1Al-0.3Ca alloy amounts to 180.5 kJ/mol. The processing map reveals one domain with flow instability at temperatures above 370 °C and strain rates ranging from 3 s−1 to 10 s−1. Under these forming conditions, intergranular cracks arose and grew along the grain boundaries.

Bake-hardenable Mg–Al–Zn–Mn–Ca sheet alloy processed by twin-roll casting

Mg–1.3Al–0.8Zn–0.7Mn–0.5Ca (wt.%) (AZMX1110) alloy sheet produced by low-cost twin-roll casting process exhibits excellent room temperature formability with a large Index Erichsen (I.E.) value of 7.8 mm at room temperature in a solution treated condition (T4). The large I.E. value is associated with a weak basal texture in the T4-condition. This alloy shows rapid age-hardening response at 170 °C, resulting in a significant increase of the flow stress from 198 MPa to 238 MPa within 20 min; such bake hardenability (BH) has never been explored in magnesium sheet alloys before. The microstructure of the bake-hardened sample, characterized by a correlative transmission electron microscopy and atom probe tomography (TEM-APT), reveals that Al, Zn and Ca atoms are segregated to basal <a> dislocations and contribute to the strengthening by pinning dislocation motions, along with the co-clustering of these atoms. This first BH Mg sheet alloy composed of only ubiquitous elements is highly attractive for application to automotive bodies.

Microstructure, Texture and Mechanical Properties of Mg-0.8 Zn-0.3 Gd-0.5 Ca Alloy Sheets

In this study, the microstructure, texture and mechanical properties of rolled Mg-0.8 Zn-0.3 Gd-0.5 Ca sheets have been investigated. It is shown that the as-cast microstructure of the Mg-0.8 Zn-0.3 Gd-0.5 Ca alloy is composed of coarse grains with fine intermetallic particles. The deformed microstructure of the as-rolled sheets results in the non-basal texture with triple peaks. Upon annealing treatment at different temperatures, the fraction of recrystallized microstructure is increased and the grains grow up. With the increase of annealing temperature, the (0002) basal pole of as-rolled sheets has transformed into texture with double peaks firstly and then into triple peaks. Accompanying the change of microstructure and texture, structure and mechanical anisotropy of the rolled sheets is modified.

Effects of Zinc and Calcium Concentration on the Microstructure and Mechanical Properties of Hot-Rolled Mg–Zn–Ca Sheets

Four kinds of Mg alloys with different Zn and Ca concentration were selected to analyze the effect of Zn and Ca concentration on the microstructure and the mechanical properties of Mg–Zn–Ca alloys. It was found that Zn and Ca concentration has a great influence on the volume fraction, the morphology and the size of second phase. The Mg–1.95Zn–0.75Ca (wt%) alloy with the highest volume fraction, continuous network and largest size of Ca2Mg6Zn3 phase showed the lowest elongation to failure of about 7%, while the Mg–0.73Zn–0.12Ca (wt%) alloy with the lowest volume fraction and smallest size of Ca2Mg6Zn3 phase showed the highest elongation to failure of about 37%. It was suggested that uniform elongations of the Mg–Zn–Ca alloys were sensitive to the volume fraction of the Ca2Mg6Zn3 phases, especially the network Ca2Mg6Zn3 phases; post-uniform elongations were dependent on the size of the Ca2Mg6Zn3 phase, especially the size of network Ca2Mg6Zn3 phase. Reduction in Zn and Ca concentration was an effective way to improve the room-temperature ductility of weak textured Mg–Zn–Ca alloys.

Electron cryotomography studies of maturing HIV-1 particles reveal the assembly pathway of the viral core.

To better characterize the assembly of the HIV-1 core, we have used electron cryotomography (ECT) to image infected cells and the viral particles cryopreserved next to them. We observed progressive stages of virus assembly and egress, including flower-like flat Gag lattice assemblies, hemispherical budding profiles, and virus buds linked to the plasma membrane via a thin membrane neck. The population of budded viral particles contains immature, maturation-intermediate, and mature core morphologies. Structural characteristics of the maturation intermediates suggest that the core assembly pathway involves the formation of a CA sheet that associates with the condensed ribonucleoprotein (RNP) complex. Our analysis also reveals a correlation between RNP localization within the viral particle and the formation of conical cores, suggesting that the RNP helps drive conical core assembly. Our findings support an assembly pathway for the HIV-1 core that begins with a small CA sheet that associates with the RNP to form the core base, followed by polymerization of the CA sheet along one side of the conical core toward the tip, and then closure around the body of the cone. During HIV-1 assembly and release, the Gag polyprotein is organized into a signature hexagonal lattice, termed the immature lattice. To become infectious, the newly budded virus must disassemble the immature lattice by proteolyzing Gag and then reassemble the key proteolytic product, the structural protein p24 (CA), into a distinct, mature hexagonal lattice during a process termed maturation. The mature HIV-1 virus contains a conical capsid that encloses the condensed viral genome at its wide base. Mutations or small molecules that interfere with viral maturation also disrupt viral infectivity. Little is known about the assembly pathway that results in the conical core and genome encapsidation. Here, we have used electron cryotomography to structurally characterize HIV-1 particles that are actively maturing. Based on the morphologies of core assembly intermediates, we propose that CA forms a sheet-like structure that associates with the condensed viral genome to produce the mature infectious conical core.

Comparison of static recrystallization behavior in hot rolled Mg–3Al–1Zn and Mg–3Zn–0.5Ca sheets

A comparative study has been performed between Mg–3Al–1Zn (in wt%, AZ31) and Mg–3Zn–0.5Ca (ZX31) to investigate the texture evolution during annealing of hot rolled sheets. ZX31 shows faster recrystallization kinetics than AZ31. During static recrystallization of as–rolled sheet, no significant change in texture takes place in AZ31, while much weaker basal texture develops in ZX31, indicating that discontinuous recrystallization occurs during annealing of ZX31 sheet. Such a development of weaker basal texture in the ZX31 sheet is related to the mode of twins generated during rolling process, i.e. the deformation bands consisted of compression and secondary twins induces accelerated nucleation of recrystallized grains during annealing. ZX31 exhibits significantly enhanced room temperature formability than AZ31. The enhanced formability is considered to be closely related with different texture evolution mode during annealing as well as typical strain hardening behavior in ZX31.

EXAFS study of Nd(III) uptake by amorphous calcium silicate hydrates (C–S–H)

Calcium silicate hydrate (C–S–H) phases control the immobilization of many metal cations in cementitious materials. In this study Nd binding to amorphous C–S–H phases with different Ca/Si (C/S) mol ratios (0.56, 0.87 and 1.54) and Nd loadings (7 and 35 μmol/g), and which had been aged up to 270 days, has been investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. The structural parameters derived from EXAFS were compared with those predicted from bond-valence calculations. The study reveals that Nd may form several species in contact with C–S–H phases. The EXAFS parameters determined in samples after one day of reaction indicate the formation of inner-sphere surface complexes. The Nd–Ca and Nd–Si bond-distances tend to increase with time at both Nd loadings. Changes in the coordination numbers N Si and N Ca were found to be dependent on the (C/S) ratio. At the lowest C/S ratio the number of neighboring Si atoms tends to increase with time while the number of neighboring Ca atoms tends to increase with time at highest C/S ratio. No clear trend was observed for the medium C/S ratio. Nd incorporation into the structures of C–S–H phases is assumed to be the dominant immobilization process based on comparison with bond-distances predicted from structural considerations. After prolonged reaction times (⩾45 days) Nd is expected to be predominantly incorporated into the Ca sheets of the C–S–H structure while small portions of Nd might also be taken up by the interlayer. The study suggests that, in the long term, amorphous C–S–H phases are capable of taking up Nd via exchange processes with Ca 2+ in the Ca sheets and the interlayer.

The thermal behaviour of fluorapophyllite from the Mieedzyrzecze sill near Bielsko-Biala in the Polish Carpathians

Fluorapophyllite, (K 0 . 9 6 Na 0 . 0 3 ) 0 . 9 9 Ca 3 . 9 6 (Si 7 . 9 5 Al 0 . 0 4 P 0 . 0 3 ) 8 . 0 2 O 1 9 . 9 8 (F 0 . 8 3 OH 0 . 1 7 ) 1 . 0 0 . 8.02 H 2 O has been found in the Miedzyrzecze sill. The apophyllite crystals were collected in the complex veins cross cutting small pectolite skarn body at the top of picrite sill. Apophyllite from Miedzyrzecze exhibits no signs of abnormal optical properties; it is tetragonal with lattice parameters: a = 8.974 (2) A, c = 15.798 (6) A. The dehydration behaviour of apophyllite from Miedzyrzecze was studied by means of X-ray diffraction, thermal analysis and infrared spectroscopy; also its dielectric properties were measured. The DTA curve shows two distinct endothermic peaks connected with irreversibly removal of water molecules from K + (OH 2 ) 8 polyhedron, centred at about 348 and 454 °C, respectively. All analytical data obtained confirm suggestion, that amorphous layers on the outer parts of apophyllite grains form a diffusion barrier causing moderation of H 2 O molecule migration and the second endothermic peak origin. The ring diffusion of H 2 O starts at about 160 °C, when the water molecules begin to migrate from the outside parts of apophyllite grains through 4- and 8- membered rings along [001] direction. Expulsion of the water molecule from the K, Ca sheets causes initiation of the non-diffracting amorphous phase origin. The subsequent water loss gives occasion to permanent distortion of sillicate layers with simultaneous K and Ca coordination collapse. The IR data obtained was useful to discuss the structural property of amorphous form of dehydrated apophyllite.

A study on the etching properties of electron-irradiated plastic track detectors

Abstract The variations of the bulk etching rate of electron-bombarded CN, CA, CAB, PC and PET sheets were studied as a function of electron dose and etching temperature. A conclusion was made that in the plastics under study a radiation-damaged region produced, either by an electron beam or a heavily ionizing nuclear particle display, to a certain extent, analogous etching properties. It was shown that the ratio of the etching rates of an electron-bombarded and an unirradiated sheet increases with the increase of the etching temperature for PC and PET, and with the decrease of etching temperature for CN and CA. Similar temperature dependences were obtained for the ratio of track– and bulk-etching rates (i.e. for registration sensitivity) if the plastic sheets were irradiated with heavier nuclear particles. Our results seem to confirm the assumption that the delta electrons may play an important role in the formation of primary nuclear particle tracks in plastic track detectors.