high quality large iron ore high frequency screen sell at a loss in washington

high quality large iron ore high frequency screen sell at a loss in washington

"Experimentation allows us to test theories about how we thinktechnological processes worked in antiquity," said Jeffery, a Ph.D.student in Materials Science and Engineering. "And quite frequentlyexperimental archaeology shows that the process didn't work the way wethought it did."

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In this case, Jeffery is studying bloomery furnaces that were usedto make iron and steel in Europe and the United States up until about200 years ago. These furnaces also have a long history in manycultures, stretching back more than 2,000 years

"Like a lot of ancient technologies, it gets treated as a simplistictechnology," Jeffery said. "But attempts to recreate it have proventhat it's not nearly as simple as people would like to believe. So far,we have conducted two separate smelts with bloomery furnaces andneither was terribly successful."

making iron the old-fashioned way is a tricky business

Iron from bloomery furnaces were used in Japan, Renaissance Europe,ancient Rome, Africa, and many other places to make iron and steel forarmor, swords, locks, tools and hundreds of other household items

"Iron has been a critical, fundamental part of human existence forcenturies," Jeffery said. "Understanding how iron was produced andhaving a clear concept of what it took to do that and replicating thatprocess today is significant from a scientific and human perspective."

Bloomery furnaces smelt iron in a direct reduction process, wherethe iron never becomes liquid. If the furnace gets too hot and the ironliquefies, it picks up a lot of carbon and becomes cast iron, which istoo brittle to be worked into tools, swords and other objects thatrequire a more flexible metal

"We're trying to quantify the operational characteristics ofbloomery furnaces," Jeffery said. "It's an intriguing and reallydifficult task because there are many variables in air-flow design,charcoal used, furnace materials, the original source of iron ore andconstruction of the furnace."

making iron the old-fashioned way is a tricky business

The furnace produces a "bloom," which is like a big sponge, with anetwork of glass-filled channels running through it. The iron hasloosely bonded together, leaving the glass that was produced from allthe impurities in the iron ore

Getting the right ratio of glass-to-iron is critical. If theoriginal ore is too iron rich, the furnace won't produce the glass slaguntil the iron has been heated past its melting point, producing castiron. If the furnace is too cool, or there isn't enough iron, the ironwill act as a flux and the bloom will be mostly glass

After the bloom is produced, a blacksmith starts working it while itis still hot, repeatedly hammering and reshaping it to drive the glassout, leaving the iron. With just a little manipulation, the iron isgood enough for tools, although they might break easily where largeglass inclusions make them weak. With lots of hammering, shaping andreheating, the blooms can be formed into the fine steel found insamurai swords, for instance

making iron the old-fashioned way is a tricky business

The process started when Tom Mclane, a local blacksmith, pulled amagnet through Tucson washes to gather magnetite sand. Then Jeffery,Mclane and others heated the ore in the furnace with mesquite charcoal.The result was a bloom with very little iron

Jeffery thinks the magnetite was too iron rich and dense. Most ironores used in ancient European bloomery furnaces (the furnaces Jefferyis basing his work on) came from boggy environments and were veryporous, unlike the dense magnetite

"Iron often is referred to as the 'democratic metal' because it isso available," he said. "Whereas copper is much scarcer and wasn'tdistributed to everyone. Once technology for smelting iron caught on,everybody had access to metal."

making iron the old-fashioned way is a tricky business

"We've involved a lot of people here in the materials sciencedepartment who probably would never have had experience with an ancienttechnology and with grasping what is involved in doing this," Jefferysaid. "Those students who came and saw the furnace in operation had achance to work the bellows, see the fire, and feel the heat. They gotsome concept of how this was done and learned about one aspect of whathelped us to be where we are today

Jeffery has a bachelor's degree in linguistics and a master's degreein archaeological science. He came to UA's Materials Science andEngineering program because "I decided I wanted a much better, harderscience background as I was proceeding down the archaeology road," hesaid

Jeffery's research is part of UA's Heritage Conservation ScienceProgram. Students in this program learn to stabilize, preserve andbetter understand ancient artifacts and how they were created and used

making iron the old-fashioned way is a tricky business

The curriculum, which combines engineering, anthropology,architectural history and art history, is particularly important todaybecause many of the material links to our past are disintegrating,while the ancient technologies that created them are disappearing

flexible and reconfigurable radio frequency electronics

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Smart materials that can change their properties based on an applied stimulus are in high demand due to their suitability for reconfigurable electronics, such as tunable filters or antennas. In particular, materials that undergo a metal–insulator transition (MIT), for example, vanadium dioxide (VO2) (M), are highly attractive due to their tunable electrical and optical properties at a low transition temperature of 68 °C. Although deposition of this material on a limited scale has been demonstrated through vacuum-based fabrication methods, its scalable application for large-area and high-volume processes is still challenging. Screen printing can be a viable option because of its high-throughput fabrication process on flexible substrates. In this work, we synthesize high-purity VO2 (M) microparticles and develop a screen-printable VO2 ink, enabling the large-area and high-resolution printing of VO2 switches on various substrates. The electrical properties of screen-printed VO2 switches at the microscale are thoroughly investigated under both thermal and electrical stimuli, and the switches exhibit a low ON resistance of 1.8 ohms and an ON/OFF ratio of more than 300. The electrical performance of the printed switches does not degrade even after multiple bending cycles and for bending radii as small as 1 mm. As a proof of concept, a fully printed and mechanically flexible band-pass filter is demonstrated that utilizes these printed switches as reconfigurable elements. Based on the ON and OFF conditions of the VO2 switches, the filter can reconfigure its operating frequency from 3.95 to 3.77 GHz without any degradation in performance during bending

flexible and reconfigurable radio frequency electronics

In recent years, smart electronics have gained tremendous attention in both scientific and industrial fields1 due to their ability to transform, change their shape or tuning, and modulate their properties in response to external stimuli, such as mechanical deformation2, thermal heating3, an electrical field4, or a magnetic force5. Creating smart electronics and exploring their versatile applications in smart energy devices4,6, smart skins7,8, smart wearables9,10,11, reconfigurable electronics12,13,14, and even smart cities15, has raised new requirements for functional materials that can tune their properties according to specific demands6,13,16,17. Despite a diverse cluster of new materials, such as carbon-based materials2,10, transition metal dichalcogenides18, and metal oxide nanocrystals19, metal insulator transition (MIT) materials have great promise due to their easy and reversible tunability between the metal and insulator via various external stimuli20,21,22,23. For example, vanadium dioxide (VO2) (M) exhibits MIT behavior by possessing an insulating state at room temperature and a metallic state at a critical temperature (~68 °C)24 and is attracting a substantial amount of interest for optical and electrical electronic applications12,17,25,26,27,28,29. Currently, a variety of techniques, such as radio frequency (RF) sputtering30,31, pulsed laser deposition32, and electron beam evaporation29, have been evaluated to fabricate high-quality VO2 films with an ON/OFF ratio of over 104. Unfortunately, these previously reported deposition methods operate under high vacuum conditions. They either consist of complex steps or deposit VO2 thin films with a limited size, which is not favorable for efficient fabrication. In addition, a high processing temperature is typically required during deposition, limiting compatibility with flexible polymer substrates

Recently, printed electronics have made rapid progress. By depositing functional materials via conventional printing techniques (e.g., inkjet printing and screen printing), printed electronics offer a new method for achieving high-throughput and roll-to-roll production of electronic devices and integrated systems at low cost33,34,35,36,37,38. Despite the great progress made in printable materials and printing technologies, few reports have succeeded in developing printable VO2 ink to deposit high-quality VO2 films. Ji et al. prepared an inkjet-printable VO2 ink, fabricated VO2 films, and studied the infrared thermochromic properties39. Our group reported a VO2 nanoparticle-based ink for the inkjet printing of VO2 films. The printed VO2 films demonstrated an electrical conductivity of ~1 S m−1 in the insulating state and 150–200 S m−1 in the metallic state, resulting in a conductivity ratio of 10217. The ink has also been used to fabricate RF switches, exhibiting decent RF performance from low frequencies (10 MHz) up to 40 GHz12, which is comparable to that of nonprinted VO2 switches29. However, these inkjet printable VO2 inks suffer from low VO2 loading, possible nozzle clogging, unstable printing, and slow deposition. The printed VO2 films exhibit poor adhesion to substrates and less flexibility due to the absence of polymer additives. In addition, to achieve improved electrical performance, thick films (tens of micrometers) are typically required; thus, tens or hundreds of printing passes are necessary to generate high-quality VO2 films, which is not favorable for high-efficiency fabrication, especially for large-area printing

In this work, we synthesize high-crystal VO2 (M) microparticles and report a simple route to produce VO2 ink suitable for screen-printing techniques. With this ink, we demonstrate high-throughput printing of VO2 switches on both flexible polymers (Kapton and poly[ethylene terephthalate] (PET)) and rigid sapphire wafers with high resolution (down to 60 µm) at high speed (220 mm s−1) over a large area. The printed VO2 switches exhibit excellent electrical performance (ON/OFF ratio of 300 and conductivity as high as 1037 S m−1 after heating at 120 °C), excellent mechanical stability (bending radius down to 1 mm), satisfactory air stability (negligible performance change after 1 month), and decent RF performance (−1 dB isolation and −2.6 dB insertion loss up to 20 GHz). Finally, we demonstrate fully screen-printed reconfigurable RF electronic devices, including series switches, band-stop filters, and band-pass filters

flexible and reconfigurable radio frequency electronics

In our previous study17, we determined that as-prepared VO2 (M) nanoparticles do not have high quality due to a low crystallinity, which resulted in poor electrical performance. In this work, we prepared highly crystalline VO2 microparticles using an autoclave reactor in an aqueous environment using a commercially available V2O5 powder (≥98%, Sigma-Aldrich) as the precursor and oxalic acid as the reducing agent. Initially, X-ray diffraction (XRD) analysis and morphological observations were conducted for V2O5 powder, as presented in Fig. S1. It is clearly shown that the V2O5 powder consisted of micron-sized particles, and multiple crystalline peaks were observed in the XRD pattern. We designed experiments using a constant weight percentage of precursor materials with different reaction times (i.e., 3, 6, and 24 h), and the products were investigated by XRD analysis. As displayed in Fig. S2, the as-synthesized samples were a mixture of undesired VO2 (A) and desired VO2 (M) phases that produced low-intensity XRD peaks. To achieve a pure VO2 (M) phase, we exposed the as-synthesized samples to different annealing environments. The XRD spectra demonstrated in Fig. 1a clearly reveal that a pure VO2 (M) phase was obtained for all the samples synthesized for 3-, 6- and 24‑h reaction times after annealing at 300 °C in vacuum. The XRD peaks observed at 27.84°, 37.01°, 42.19°, and 55.56° were indexed to the [011], [200], [210] and [−222] crystal planes, which is consistent with JCPDS No. 72–0514. It is interesting to note that the sample synthesized for 3 h followed by annealing demonstrated low-intensity XRD peaks, while the 6- and 24‑h reaction time samples demonstrated higher intensity peaks. Thus, VO2 particles synthesized with a reaction time of 6 h and an annealing temperature of 300 °C were used for further study. It is noteworthy that the reaction time is much shorter than those reported in the literature, where more than one day has been used for the synthesis40,41,42

The as-annealed products were further characterized for their morphological and thermal behavior. It can be seen in the scanning electron microscopy (SEM) image in Fig. 1b that the VO2 particles were uniformly grown and comprised micron-scale sheets that were arranged in a flower-shaped morphology, with an average particle size from 4–6 µm (inset in Fig. 1b). It is interesting to note that the morphology of the as-annealed products is similar to that of the V2O5 precursor powder. Thus, the shape and size of the VO2 particles can be further optimized by selecting the finest V2O5 powder with regular sizes either from commercially available sources or through custom in-house preparation of V2O5 particles. A micron-thick sheet was also characterized by transmission electron microscopy (TEM), as illustrated in Fig. 1c, d. The inset in Fig. 1c displays a selected-area electron diffraction (SAED) pattern of the sheet, which confirmed its crystalline nature with interplanar distances of 0.15, 0.25, 0.3, and 0.48 nm. The high-resolution TEM (HR-TEM) image displayed in Fig. 1d indicates that the distance between two crystal planes was 0.32 nm, which corresponds to (011) crystal planes. The existence of an MIT temperature is an attractive property of VO2, and it was assessed via thermal analysis using differential scanning calorimetry (DSC), as displayed in Fig. 1e. The annealed VO2 particles were exposed to heating and cooling from room temperature to 90 °C. Two clear MIT peaks at ~65.6 °C during heating and ~58.5 °C during cooling are observed. The calculated thermal width was ~7 °C, which corresponds to a first-order phase transition. The thermal width is lower than that of previously reported VO2 nanoparticles (~18 °C)17 because of the high quality of the as-annealed VO2 particles, which is of importance in smart optical and electrical switches43. It should be noted that the MIT temperature is an inherent property of the VO2 (M) phase, and its bulk value is ~68 °C. In our case, we observed that the MIT temperature of the as-annealed VO2 particles is slightly lower than that of the bulk VO2 particles, which is most likely due to the impurity of the precursor (i.e., V2O5, ≥ 98%) used for the synthesis. It is well known that impurities and doping have prominent effects on the MIT temperature, and even 1–2% impurities/doping can decrease the MIT temperature44,45,46. We observed that the MIT temperature of the as-synthesized VO2 particles (without annealing) was not distinct because the phase was not in a pure state, as confirmed by the DSC spectrum in Fig. S3a. Once the pure VO2 (M) phase was achieved after annealing, similar MIT temperatures were observed. This was confirmed by the sample with a long reaction time of 24 h, where an MIT temperature of 65.69 °C was obtained (Fig. S3b)

It is clear from the results in Fig. 1 that pure VO2 (M) particles were obtained. To develop a screen-printable VO2 ink, a mixed solvent of terpineol and ethanol (Fig. 2a) was selected due to its high viscosity and low surface tension. Ethyl cellulose (EC) (Fig. 2a) was used as an organic binder, dispersing agent, and rheological modifier. In a typical ink formulation, EC was first mixed with terpineol and ethanol at a weight ratio of 1:4:0.4 to form a viscous solution. Then, the VO2 particles were mixed with the prepared solution at a weight ratio of 3:5, followed by agitation to obtain a homogenous and stable VO2 ink with a VO2 content of 37.5 wt.% (Fig. 2a). The viscosity of the resultant ink was measured using a rheometer at a shear rate from 0.1 to 1000 s−1, and the curve is displayed in Fig. 2b. We clearly observed a shear thinning behavior of the formulated VO2 ink. The viscosity decreased from 12,492 to 58 Pa s as the shear rate increased from 0.1 to 10 s−1. This type of fluid behavior and high viscosity are essential to provide favorable printability. This ink was directly used for screen printing to deposit VO2 switches on various substrates. What should be noted is that the single-pass thickness of the printed VO2 film was affected by many factors, such as the screen mesh parameters (i.e., mesh count, mesh diameter, and emulsion thickness), printing parameters (i.e., printing speed, squeegee pressure, and snap-off distance), and ink properties (i.e., solid content and viscosity)47,48. Typically, a smaller mesh count, thinner wire, thicker emulsion, slower speed, larger pressure, larger snap-off distance, more solid content, and higher viscosity print thicker films. However, among all these factors, the mesh count and the solid content (i.e., VO2 particles and EC) of the ink are critical for controlling the thickness of the printed films. Specifically, a smaller mesh count means fewer openings per inch and a larger size of each opening in the screen, which results in a thicker film. In our experiment, the mesh count was fixed as 325. Thus, the dominant factor controlling the single-pass thickness was the solid content. A low solid content results in a thin layer. However, this might produce additional pores in the film due to the high amount of solvent. As a result, the electrical performance (i.e., ON/OFF ratio) of the printed VO2 films worsened, as shown in Fig. S4. After considering the optimized ink formulation (i.e., solid content and viscosity) and the printing parameters (i.e., printing speed and mesh count), the resultant thickness of the printed VO2 film in a single pass was ~8–10 µm. After the screen-printing process, the printed VO2 switches were baked in an oven at 120 °C for 1 h to evaporate the solvents and sinter the VO2 film. It is noteworthy that the printed VO2 films without polymer binders contained particle aggregates and cracks after thermal sintering, as can be observed from the optical images in Fig. S5. The limited addition of the polymer binder (the weight ratio of VO2 to binder is ~3.3) was favorable for dispersing the VO2 particles and achieving flexibility of the printed VO2 film

flexible and reconfigurable radio frequency electronics

a Molecular structures of binder (ethyl cellulose) and solvents (terpineol and ethanol) and digital photograph of the prepared VO2 ink. b The measured viscosity of the VO2 ink at a shear rate from 0.1 to 1000 s−1. c Digital photographs of the screen-printed VO2 switches on a Kapton substrate. Inset: Bent VO2 switches. d Digital photographs of the screen-printed VO2 switches on a PET substrate. Inset: Bent VO2 switches. e The printed VO2 line width as a function of the designed line width on the screen mesh. f Digital photograph of the screen-printed VO2 film on a 2-inch sapphire wafer. Inset: profilometry data from the printed VO2 layer

The low processing temperature enabled our VO2 ink to be suitable for various substrates, such as flexible polymers or even paper, largely widening its applications. Fig. 2c, d display digital photographs of the large-area VO2 switches printed on flexible Kapton and PET substrates in flat and bent states, respectively. We investigated the printed VO2 line features by comparing the printed line widths with the designed lines on the screen mesh. As presented in Fig. 2e, a linear behavior was observed between the printed and designed lines over the whole line width range (from 50 µm to 1.5 mm), demonstrating the excellent reliability of the screen-printed VO2 switches. The narrowest line width was ~65 µm. In addition, we found that the printed VO2 lines were slightly wider (~30 µm) than the designed lines, which was attributed to ink spreading after transfer to the substrates. We further printed a thick and large VO2 film on a 2-inch sapphire wafer with 15 printing passes to demonstrate high-throughput printing, as displayed in Fig. 2f. The printed VO2 film had a thickness of ~120 µm, as identified by the profile curve (inset in Fig. 2f), which was obtained by scanning the film with a profilometer (from the edge to the center). From the curve, we can also observe that the surface of the printed VO2 film was not smooth, which was attributed to the micron-sized particles. Notably, the printed wafer-scale VO2 film was of high quality, as confirmed by XRD pattern (Fig. S6), where four distinct diffraction peaks were indexed to pure VO2 (M) without any impurities. It should be noted that this film was printed at a high speed of 220 mm s−1, and it took only a few minutes to print the VO2 film. In comparison, tens of hours or even days are necessary to deposit the same VO2 film using the inkjet printing technique. All these results imply that our developed screen-printable VO2 ink and the conducted screen-printing process are ideal for mass production of VO2-based switches for tunable and reconfigurable RF electronics

We then evaluated the electrical properties of the screen-printed VO2 switches. Figure 3a presents the apparatus for the current–voltage (I–V) measurements, in which two probe tips were connected to the samples and a source measurement unit to measure the resistance of the VO2 switches. VO2 was printed between two silver (Ag) electrodes. The electrode width and the gap between the electrodes were marked as the width and length of the VO2 switches, respectively. Figure 3b displays the measured resistance of the printed VO2 switches (width and length were 0.5 and 0.3 mm, respectively) with increasing printing passes from one to nine at 25 °C (called the OFF state) and 90 °C (called the ON state). The resistance at both the OFF and ON states decreased rapidly for a larger printing pass, as a thicker and denser VO2 layer was formed. Specifically, the OFF resistance was 1976 ohm, while the ON resistance was 7.3 ohms after seven printing passes, yielding an ON/OFF ratio of 270, which is much higher than that of inkjet-printed VO2 films12,17. The reason for this was attributed to the (1) high quality of the VO2 particles, as confirmed by the intense XRD peaks; (2) well-dispersed VO2 particles in the ink system; and (3) dense VO2 layer via polymer binding. We then investigated the resistance of the VO2 switches with various lengths. As presented in Fig. 3c, when the VO2 film width was fixed as 0.5 mm, the measured ON resistance linearly increased from 1.8 to 10.3 ohms as the VO2 length increased from 0.035 to 0.4 mm, respectively. Thus, VO2 switches with varying ON and OFF resistances (within the bound of the best-case scenarios) can be designed by selecting different geometric parameters of the VO2 film, such as length, width, and thickness. The electrical conductivity (σ) of the printed VO2 switches in the ON state was calculated based on the measured ON resistance (R) and the VO2 geometries, such as VO2 length (l), VO2 width (w), and VO2 thickness (t), through the following equation, σ = l/(Rwt). The measured thicknesses and the calculated conductivities are displayed in Fig. S7 and Fig. 3d, respectively. Various samples for each length were measured, and an average conductivity value was obtained for each length. Generally, the average conductivity values in the ON state for all the samples are almost similar with some minor fluctuations (in the range of 852 to 1037 S m−1). These values are superior to the value of 200 S m−1 obtained for inkjet-printed VO2 films12. The slight fluctuation in the calculated conductivity can be attributed to fabrication tolerances because the samples with different lengths had slightly different thicknesses and widths. Furthermore, the edges of printed films are typically not smooth, and the surfaces are relatively rough, which can further affect the calculated results. Nevertheless, such a high ON/OFF ratio and electrical conductivity are promising for printed VO2 films that have been reported. Note that the achieved ON/OFF ratio (~102) is low compared to the typical values achieved from the VO2 films deposited through nanofabrication techniques (~104) due to the irregular VO2 particles during synthesis, partially covering of VO2 particles by polymer binders (Fig. S8), and the pores in the printed films. However, printed films have the advantages of easy processing, direct patterning, and roll-to-roll production capability. With the advancement of printing techniques and inks, it is expected that in the near future, printed films will have a comparable performance to films deposited through nanofabrication techniques

flexible and reconfigurable radio frequency electronics

a The setup diagram (top panel) to measure the resistance of the printed VO2 switch. Bottom panel: VO2 switch under test. b The measured resistance of the VO2 switches as a function of printing passes at 25 °C (OFF state) and 90 °C (ON state). c The measured ON resistance and ON/OFF ratio of the VO2 switches as a function of switch length. d The calculated electrical conductivity of the printed VO2 switches as a function of switch length. e The measured resistance of the printed VO2 switch at different temperatures in the heating and cooling process. f The measured resistance of the printed VO2 switch at different bias currents of 10 nA and 150 mA. Inset: the resistance as a function of cyclic electrical triggering

As a material with an MIT, VO2 could be stimulated by various external stimuli. Here, we evaluated the electrical response of the printed VO2 switches by applying heat and a bias current. We selected a typical VO2 switch for further study that had a length of 0.2 mm, a width of 0.5 mm, and an ON resistance of ~5 ohms. As displayed in Fig. 3e, at room temperature (25 °C), the measured resistance was ~1300 ohms, exhibiting insulating behavior. Then, the resistance slowly decreased to 200 ohms as the temperature increased to 60 °C. When the temperature reached 65 °C, the resistance dropped dramatically to 33 ohms, exhibiting an 83.5% decrease compared with the resistance at 60 °C. This is consistent with the transition temperature of 65.6 °C observed in the DSC result (Fig. 1e). With a further increase in the temperature, the resistance decreased to 5.5 ohms at 80 °C and remained constant at a value of approximately 5 ohms at 90 °C. During the cooling process, the resistance increased from 5 ohms to ~1300 ohms when the temperature decreased from 90 °C to 25 °C, respectively. Notably, this resistance change with temperature was highly repeatable, as the hundredth heating and cooling of the same sample demonstrated a similar electrical response in both the trend for the resistance change and the OFF and ON resistances, despite a slight variation in some of the resistance values. A similar resistance response was observed by applying different bias currents to the VO2 switches, as presented in Fig. 3f. The initial resistance at an applied current of 10 nA was ~1351 ohms, which was in the OFF state. The resistance dropped dramatically to 254 ohms at a supplying current of 3.6 mA and finally reduced to 5.1 ohms when the current was 150 mA. As the current further increased to 160 mA, the VO2 switch was burned, implying that careful selection of the applied current is important and that the current should be increased step by step. Similar to heat triggering, the resistance response of the VO2 switches with electrical triggering demonstrated excellent repeatability via the cyclic application of currents of 10 nA and 150 mA (inset in Fig. 3f). What should be noted is that the geometric parameters of a VO2 switch, such as its length, width, and thickness, determine the biasing current applied to the switch. Typically, a wider, longer, and thicker VO2 switch requires a higher biasing current12,29

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