Rapid Temperature Ramping Research Articles

Pilot Quality-Assurance Study of a Third-Generation Batch-Mode Clinical-Scale Automated Xenon-129 Hyperpolarizer.

We present a pilot quality assurance (QA) study of a clinical-scale, automated, third-generation (GEN-3) 129Xe hyperpolarizer employing batch-mode spin-exchange optical pumping (SEOP) with high-Xe densities (50% natural abundance Xe and 50% N2 in ~2.6 atm total pressure sourced from Nova Gas Technologies) and rapid temperature ramping enabled by an aluminum heating jacket surrounding the 0.5 L SEOP cell. 129Xe hyperpolarization was performed over the course of 700 gas loading cycles of the SEOP cell, simulating long-term hyperpolarized contrast agent production in a clinical lung imaging setting. High levels of 129Xe polarization (avg. %PXe = 51.0% with standard deviation σPXe = 3.0%) were recorded with fast 129Xe polarization build-up time constants (avg. Tb = 25.1 min with standard deviation σTb = 3.1 min) across the first 500 SEOP cell refills, using moderate temperatures of 75 °C. These results demonstrate a more than 2-fold increase in build-up rate relative to previously demonstrated results in a comparable QA study on a second-generation (GEN-2) 129Xe hyperpolarizer device, with only a minor reduction in maximum achievable %PXe and with greater consistency over a larger number of SEOP cell refill processes at a similar polarization lifetime duration (avg. T1 = 82.4 min, standard deviation σT1 = 10.8 min). Additionally, the effects of varying SEOP jacket temperatures, distribution of Rb metal, and preparation and operation of the fluid path are quantified in the context of device installation, performance optimization and maintenance to consistently produce high 129Xe polarization values, build-up rates (Tb as low as 6 min) and lifetimes over the course of a typical high-throughput 129Xe polarization SEOP cell life cycle. The results presented further demonstrate the significant potential for hyperpolarized 129Xe contrast agent in imaging and bio-sensing applications on a clinical scale.

Batch-Mode Clinical-Scale Optical Hyperpolarization of Xenon-129 Using an Aluminum Jacket with Rapid Temperature Ramping

We present spin-exchange optical pumping (SEOP) using a third-generation (GEN-3) automated batch-mode clinical-scale 129Xe hyperpolarizer utilizing continuous high-power (~170 W) pump laser irradiation and a novel aluminum jacket design for rapid temperature ramping of xenon-rich gas mixtures (up to 2 atm partial pressure). The aluminum jacket design is capable of heating SEOP cells from ambient temperature (typically 25 °C) to 70 °C (temperature of the SEOP process) in 4 minutes, and perform cooling of the SEOP gas mixture to the temperature at which the hyperpolarized gas mixture can be released from the hyperpolarizer (with negligible quantity of Rb metal leaving the cell) in approximately 4 minutes-substantially faster (by a factor of six) than previous hyperpolarizer designs relying on air heat exchange versus aluminum as employed here. These decreases in temperature cycling time will likely be highly beneficial for the overall increase of production rates of batch-mode (i.e., stopped-flow) 129Xe hyperpolarizers, which is particularly beneficial for clinical applications. The additional advantage of the presented design is significantly improved thermal management of the SEOP cell. Accompanying the heating jacket design and performance, we also evaluate the repeatability of SEOP experiments conducted using this new architecture, and present typically achievable hyperpolarization levels exceeding 40% at exponential build-up rates on the order of 0.1 min-1.

A rotating fluidized bed reactor for rapid temperature ramping in two-step thermochemical water splitting

Two-step thermochemical water splitting (TWS) is a promising carbon-free/low-carbon technology for producing hydrogen in a mass production scale, in which water is dissociated in the presence of metal oxide-based catalysts via redox cycles driven by thermal energy. While active research is underway to develop high-performance metal oxide catalysts, less attention has been paid to reactor design and relevant system analysis, which are essential for constructing an actual system. The gas and solid flow configuration is one of the key design parameters in reactor design that determines thermodynamic and kinetic characteristics of the entire two-step TWS system. In this study, we propose a rotating fluidized bed reactor design wherein the rotating current flow configuration allows a much larger relative velocity between sweep gas and redox particles compared to conventional flow configurations. The rotating current flow configuration significantly improves the temperature ramp rate of redox particles via enhanced heat transfer between particles and sweep gas. Through thermodynamic and kinetics analysis of the reactor system, we show that the large temperature ramp rate of the proposed reactor results in a considerable improvement in the hydrogen yield per hour. This work adds a new dimension to the reactor design for two-step TWS.

Less than one minute low-pressure gas chromatography - mass spectrometry

Conventional gas chromatography - mass spectrometry (GC-MS) takes 20–40 min per sample, which is undesirably slow in any application if speed can be increased while still meeting analytical needs. In this study, we achieved reasonably good separations with full analysis cycle times of less than 1 min by combining for the first time low-pressure (LP) GC-MS with low thermal mass (LTM) resistive-heating for rapid temperature ramping and cooling of the capillary column. The analytical column is threaded into the LTM thin-walled metal tubing in an instrumental device known as “LTM Fast GC” that is mounted at the top of the gas chromatograph in a detector port. The column inlet and outlet are connected to the GC injector and MS transfer line as usual. For LPGC-MS, a 40 cm, 0.1 mm. i.d. uncoated flow restrictor capillary connected at the injector is coupled with a 2.6 m, 0.25 mm i.d., 0.25 µm film thickness analytical column leading to the MS. Thus, the inlet operates at normal GC pressures, but the analytical column is under vacuum, which increases the optimal helium carrier gas flow velocity thereby increasing speed of full range separations while maintaining acceptable quality of chromatography. This column configuration in LTM-LPGC-MS trades a 64-fold gain in speed of analysis vs. standard GC-MS for a 4-fold loss in chromatographic peak capacity, thereby converting analysis time from minutes into seconds in common applications. For example, jet fuel containing fatty acid methyl esters (akin to biofuel) was separated in 25 s with <1 min full analysis cycle time. An EPA Method 8270 mixture of 76 analytes was also analyzed in <1 min full cycle time by LTM-LPGC-MS. Other examples include very fast analysis of heroin in a street drug powder and elucidation of a new organic synthetic compound. In this report, we describe and discuss the several advantageous and practical features of LTM-LPGC-MS, as well as its trade-offs.

Detachable Trap Preconcentrator with a Gas Chromatograph-Mass Spectrometer for the Analysis of Trace Halogenated Greenhouse Gases.

A detachable trap preconcentrator coupled with a gas chromatograph-mass spectrometer (GC-MS) was developed for measuring trace amounts of anthropogenic halogenated greenhouse gases such as hydrofluorocarbons (HFCs) and nitrogen trifluoride (NF3). Hayesep D cooled to -135 °C was used as an adsorbent for preconcentrating the target analytes. A differential trapping method was applied to remove major interfering substances such as CO2, N2, and O2 in order to ensure sufficient sampling volume of secondary injection trap. This was accomplished without using any CO2-removal agent such as molecular sieve adsorbents. Consequently, the temperature of the primary transfer trap was set to -75 °C for selective desorption of a significant amount of CO2 that could be vented out. In the meantime, the major components of air, e.g., N2 and O2, were vented out before transferring the analytes to the secondary injection trap, in order to protect the gas plumbing from pressure shock induced by rapid temperature ramping over 100 °C/min in the secondary trap. When the traps were heated, linear motion was operated to detach them from the copper baseplate on the freezer, thereby restricting heat transfer to the freezer and maintaining the freezer close to the background temperature of -135 °C. This trap design is a key improvement to address the insufficient cooling capacity of the employed freezer, allowing sensitive detection of trace halogenated greenhouse gases in GC-MS. NF3 and various HFCs at ambient levels were quantitatively and qualitatively measured with a precision of 0.35% at rates below 45 min/cycle. In particular, the limit of detection for NF3 was evaluated to be 0.2 pmol/mol, with linear responses at ambient concentration.

Synthesis of Vertical MoO2/MoS2 Core–Shell Structures on an Amorphous Substrate via Chemical Vapor Deposition

Vertical MoO2/MoS2 core–shell structures were synthesized on an amorphous surface (SiO2) by chemical vapor deposition at a high heating rate using a configuration in which the vapor phase was confined. The confined reaction configuration was achieved by partially covering the MoO3-containing boat with a substrate, which allowed rapid buildup of the partially reduced MoO3–x crystals in an early stage (below 680 °C). Rapid temperature ramping to 780 °C enabled spontaneous transition of the reaction environment from sulfur-poor to sulfur-rich, which induced a sequential phase transition from MoO3–x to intermediate MoO2 and finally to MoO2/MoS2 core–shell structures. The orthorhombic crystal structure of MoO3–x contributed to the formation of vertical crystals on the amorphous substrate, whereas the nonvolatility of the subsequently formed MoO2 enabled layer-by-layer sulfurization to form MoS2 on the oxide surface with minimal resublimation loss of MoO2. By adjustment of the sulfurization temperature and time...

Design and experimental implementation of an effective control system for thin film Cu(InGa)Se2 production via rapid thermal processing

Copper indium gallium diselenide, Cu(InGa)Se2 (CIGS) solar cells have achieved efficiencies of 22.3% at the cell level and 17.5% at the module level. CIGS-based modules are also in the early stages of commercialization, with>1 GW annual production capacity. The most common method for producing CIGS in industry is via precursor reaction, which consists of depositing Cu-In-Ga precursor films and reacting them with gas-phase H2Se at 450–550°C for 60min or longer, and is commonly called selenization. Recently, interest has been growing in selenization by Rapid Thermal Processing (RTP), which is characterized by rapid temperature ramping, approximately 550°C or higher temperature reactions, and improved process throughput. However, it has been difficult to commercialize RTP for CIGS film production in part because implementing a rapid, linear temperature ramp in the reacting thin film is complicated by two intrinsic process characteristics: (i) the temperature of the CIGS film cannot usually be measured directly; and (ii), the process is significantly nonlinear due to the dominance of radiative heat transfer at high temperatures. In this paper, we present the design and modeling, construction, and successful operation of a pilot-scale RTP selenization reactor utilizing a novel temperature control system.Our two-fold approach to the unique temperature control challenges involves the design and implementation of (i) a first-principles, model-based observer to estimate the desired surface temperature; and (ii) a specialized controller to enable effective tracking of the desired linear temperature ramp set point. Our experimental results demonstrate that the control system is effective in tracking rapid temperature ramps accurately, with performance limited only by the physical constraints of the experimental system.

Microwave-Assisted Hydrothermal Synthesis of α-MnO2: Lattice Expansion via Rapid Temperature Ramping and Framework Substitution

Cobalt-doped cryptomelane-type manganese oxide (K-OMS-2) microwires have been successfully synthesized and characterized. Their catalytic activity was tested in an oxidation reaction with benzyl alcohol as the substrate, and the cobalt-doped OMS-2 materials showed 100% selectivity toward benzyl aldehyde with a conversion of 55%. The cobalt-doped OMS-2 materials were also investigated as a desulfurization sorbent in a fixed bed reactor at 250 °C where high sulfur sorption capacities (49.4 g of sulfur/100 g of sorbent) were observed. Here, structure-controlled synthesis was performed using a facile one-step microwave-assisted hydrothermal method (MWHY) associated with a rapid temperature ramping (200 °C/min). The structural effects induced by the compositional control of transition metal dopants on the cryptomelane (space group I4/m) body centered tetragonal structure were identified with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD and TEM results showed that the systematic v...

NiO/YSZ Reduction for SOFC/SOEC Studied In Situ by Environmental Transmission Electron Microscopy

SOFCs/SOECs are typically composed of ceramic materials, which are highly complex at the nano-scale. Scanning and transmission electron microscopy (SEM and TEM) are routinely applied for studying these nano-scaled structures post mortem, but only few SOFC/SOEC studies have applied environmental TEM (ETEM). ETEM offer the possibility to record image series (movies) of the ceramic nanostructures with atomic scale resolution during exposure to a reactive gas environment at elevated temperatures. The present contribution focuses on the typical reduction preparation step for the state-of-the-art Ni/YSZ (YSZ = Y2O3-stabilized ZrO2) based anodes for SOFC and cathodes for SOEC. Specifically, the reduction of nickel oxide to form the catalytically active nickel surface is monitored directly at the nano- and atomic scale by using an ETEM. The reduction process was followed while exposing NiO/YSZ and pure NiO to H2 at temperatures from room temperature to ca. 800°C. The NiO/YSZ was prepared by crushing down a tape casted and sintered model anode/cathode into a fine powder. Previous studies based on averaging techniques have shown that the reduction of pure NiO is a relatively rapid process, while the reduction of NiO/YSZ is slower, which indicates that the presence of YSZ inhibits the reduction of NiO. In the presents in situ experiments the temperature dependent reduction profile are found similar for the both nano-scaled NiO and NiO/YSZ sample. The apparent inhibitive effect of YSZ on NiO reduction is therefore not caused by a direct interaction between NiO and YSZ, but is an indirect effect depending on the NiO being integrated in a macroscopic network of NiO/YSZ. A Titan E-Cell 80-300ST TEM was used for the in situ work in combination with the chip-based heating holder from Protochips which facilitated rapid temperature ramping for example from room temperature to 800°C in only 1 s. The ETEM results are compared to complementary averaging techniques such as thermo-gravimetric analysis (TGA) and X-ray diffraction analysis (XRD).The figure presents a TEM image series of NiO during exposure to 2 mbar H2 and constant temperature ramping rate of 1°C/min. The NiO observed in the first image at 320°C is dense. From the lower left corner a front of porous Ni is progressing until full reduction at 340°C.

Automated chip-based device for simple and fast nucleic acid amplification

A chip-based PCR device is presented that is capable of rapid temperature ramping and handling sample volumes in the microliter range. The PCR chip comprises a microchannel thermally connected to three temperature zones. Inside this microchannel, the PCR sample plug is driven and precisely positioned by a ferrofluidic actuator for more than 40 cycles within 5 min. Computer simulations predict that the sample plugs are thermally equilibrated on a time scale of some 10 ms when transported to a different temperature zone. Hence, the thermal limitations on the cycle speed of the system are considerably reduced compared with conventional cyclers. The system was developed on a modular platform suitable for handling further microfluidic tasks such as DNA extraction and preparation of the PCR mix. Thus, the aspired chip-based platform represents not only a PCR system but a complete analysis system, from the injection of a patient’s blood sample to its final appraisal.

Solid-phase micro extraction (SPME) and headspace derivatization of clenbuterol followed by GC-FID and GC-SIMMS quantification.

Solid-phase micro extraction (SPME) and on-fiber derivatization followed by Gas Chromatography coupled with Flame Ionization Detection (GC-FID) or Selected Ion Monitoring Mass Spectrometry (GC-SIMMS) allows for simple yet sensitive quantification for the hexamethyldisilazane derivative of the beta-agonist clenbuterol. Using an 85- micro m polyacrylate fiber, the analysis method is optimized with respect to extraction time, derivatization time and temperature, and solution pH. In addition, the use of a rapid temperature ramping injection port allows for optimization of fiber desorption conditions. Under optimal conditions, the limits of detection for the hexamethyldisilazane derivative of clenbuterol are 1.1 ppb by FID and 0.20 ppb by SIMMS.

Construction of a low-cost automated chromatographic system for the measurement of ambient methane

A fully automated gas chromatographic system was constructed to perform in situ measurement of atmospheric methane. To reduce cost, this system avoided the use of a conventional gas chromatography (GC), instead a direct resistive heated molecular sieve packed column with precise temperature control was constructed to permit rapid temperature ramping and cooling and, therefore, shorter turn-over time. No heat-cut or back-flush of high boiling residue was necessary, which often requires a pre-column and additional flow of carrier gas. The precision ( n=47) of the system was better than 0.20% at near background level (1.8 ppmv), and the linearity of the system was better than 0.9990. The system was deployed in the field to perform on-site unattended measurement of ambient methane. The fast cycled measurement facilitated detailed observation of diurnal concentration variation caused by temperature inversion, which could induce nearly two-fold of concentration enhancement.

Comparison of uranium and zirconium cobalt for tritium storage

Abstract The utility of ZrCo for tritium storage has been studied and a comparison with uranium has been made. Loading, unloading, and delivery operations typically required in tritium handling loops were conducted using two identical beds: one containing 25.0 g of ZrCo and the other 25.8 g of uranium powder. Hydrogen was the working gas. The two beds have similar performance characteristics although the bed containing uranium has faster loading kinetics and can attain a lower vacuum at room temperature. Particulates are transported into the loop by both beds and appear to be more difficult to contain in the ZrCo case. The temperature ramp rate to the unloading temperature for ZrCo must be controlled if operating at high H/M ratios. A transformation of the ZrCo alloy into a phase which has inferior loading rate characteristics may be induced by rapid temperature ramping.