Low Process Pressure Research Articles

THERMOLYSIS OF FUEL OIL IN A FLOW-TYPE REACTOR OVER A TIN-LEAD MELT

A technology for thermolytic processing of fuel oil over a tin-lead melt in a flow-type reactor is proposed. Methods for fuel oil processing at oil refineries are currently too complicated and cost-demanding, so the development of effective technologies for fuel oil processing is an urgent task. The main advantages of the proposed technology are rather low process temperature and pressure close to atmospheric. The technological parameters of the process are constant over all points of the reactor, which ensures high-quality products. The formation of carbon deposits on the reactor walls is essentially eliminated. The technological process occurs simultaneously with auxiliary and transport operations, which increases the productivity of the installation. It becomes possible to completely automate technological process, eliminating the use of manual labour and simplifying installation maintenance. A schematic diagram of the flow-type installation is presented. The results of experiments on the thermal cracking of fuel oil over a tin-lead melt, carried out using two versions of destructive distillation, are presented. The first version involves minimal withdrawal of thermal gas oil (31 %), while in the second version it is maximal (77 %). It has been shown that the content of gasoline fraction (i.b.p.-180 °С, where i.b.p. is initial boiling point) and diesel fraction (180-360 °С) in the thermal gas oil obtained according to the second version is lower than that obtained according to the first version. Thermal gas oils have a high content of aromatic compounds, which makes them a promising raw material for the production of needle coke.

Separation of CH4 - CO2 gas mixture by gas hydrate crystallisation: A parametric study

In the present study a comprehensive experimental study of the CO2 gas hydrate recovery from the CH4 (81.70 mol.%) - CO2 (18.30 mol.%) experimental gas mixture was realised. The effect of the mode, temperature, pressure, and promoter on the CO2 gas hydrate recovery efficiency was investigated. The parametric study will optimise the technology of gas hydrate crystallisation to CO2 remove from natural gas. The gas mixture process separation factor and gas hydrate recovery were studied in SDS (0.30 wt%) aqueous solutions with and without THF (3.80 wt%). The separation simulation was performed for the two modes: pressure-dropping and constant pressure in the temperature range 272.15–283.15 К at the driving forces 1.00 and 2.00 MPa 8 h after the start of the gas hydrate formation. The different temperature dependence is shown for the CH4 and CO2 gas hydrate recovery in depending on the aqueous solution. The CO2 gas hydrate recovery maximum, equal to 63.92% (without THF) and 57.19% (with THF), is observed at the constant pressure separation at 272.15 K and 2.00 MPa. However, THF addition makes it possible to decrease the gas hydrate dissociation pressure of the experimental gas mixture in 7.87 times at 272.15 K. Thus, the choice of the aqueous solution was determined by the aim for the gas hydrate separation – high gas hydrate recovery (without THF) or low process pressure (with THF).

Mechanism of Chromium Separation and Concentration from Tannery Wastewater by Membrane Methods

The article specifies conditions for a nanofiltration process employing a diafiltration method with a constant volume diafiltration (NF-CVD) for exhausted chromium tannery wastewater treatment and describes a mechanism of the examined process carried out for model wastewater. The authors prove that a decrease in salt concentration in the NF-CVD process is an important factor that enables effective concentration of chromium. Based on the proposed chromium separation and concentration mechanisms, it was found that this effect may be achieved by (1) limiting the formation of an ionic adsorption-polarization layer and (2) reducing the increase in the osmotic pressure caused by a change in the separation properties of the membrane. The article shows that in the analyzed system a higher amount of the solvent introduced at the diafiltration stage and a lower process pressure that ensures a reduction in salt retention translate to a high level of salt removal. In regenerates, after the NF-CVD processes in which at least the same volume of a washing diluent as the volume of the retentate after the pre-concentration step was used, salt concentration below 10 g L-1 and chromium concentration about three times higher than in the case of the feed solution were obtained. Therefore, the proposed solution implements the circular economy strategy in the tannery.

Evaluation of different types of mannitol for dry granulation by roller compaction

Dry granulation by roller compaction (RC) is a continuous manufacturing technology increasingly used in the pharmaceutical industry for improving bulk density and flowability of powder mixtures or for preventing segregation issues of highly potent drugs prior to tableting. Dry granulation is ideally applied to moisture and heat sensitive drugs with added benefits also in terms of costs and lower equipment footprint. Mannitol is a polyol widely used in pharmaceutical formulations: particularly in orally dispersible tablets and powders and chewable tablets, where its high solubility and pleasant organoleptic properties make it an excipient of choice. Mannitol is available in several grades with different technological characteristics for adapting to various applications. In view of the use of mannitol for the formulation of active ingredients with poor flowability and compaction, the present work was aimed at analyzing the properties of the different commercial types of mannitol when used for dry granulation by roller compaction to obtain tablets. Mannitol raw materials and granules prepared by roller compaction at different pressure were characterized for particle size distribution, bulk density, flow properties, specific surface area and ability to tableting. Granules with proper size (500–1500 μm), increased bulk density and adequate flow properties could be obtained. Increased specific surface area of the granules suggested a fragmentation of the particles during roller compaction even at relatively low processing pressure confirming the brittleness of the materials. For all materials tested, satisfactory properties for enabling tableting process were shown.

Numerical simulation of airflow behaviour and nozzle geometry on commingling for thermoplastic composites

The current study highlights the superiority of nozzles with forwarding airflow to produce the commingled yarns for thermoplastic composite applications. A new cost-effective nozzle that can produce good quality commingled yarns at low air pressure is introduced. 3D CFD simulation and experimental studies are conducted to investigate the effect of aerodynamics of three different cylindrical nozzle configurations (CONF) on the commingling process efficiency. Nozzle CONF I and II work on backwards airflow principles among these configures, while CONF III functions with forwarding airflow. Commingling process efficiency of nozzle designs is analysed in terms of vorticity magnitude, turbulence kinetic energy, turbulence intensity and radial velocity values obtained from the simulation study. Additionally, the structure of hybrid yarns is qualitatively analysed to support the simulation study. The study concludes that nozzle CONF I and III holds the excellent potential of mixing both reinforcement and matrix filaments across the yarn structure. In addition, these nozzles can form stable nips in the yarn structure and make the textile preforming effortless. Nozzle CONF III offers better yarn quality parameters over other nozzles at low processing pressure.

Growth and characterization of Rhenium Nitride coatings produced by reactive magnetron sputtering

In this work, thin rhenium nitride (ReNx) films were deposited by reactive radio frequency (R. F.) magnetron sputtering on H13 steel and polished silicon substrates. To improve adhesion to the substrates, a Ti/TiN bilayer was deposited before the ReNx films. Substrate temperature, R.F. power, Ar and N2 gas flow, negative bias voltage, and working pressure were varied in the experiments when synthesizing the ReNx coatings. It was found that lower process pressure and nitrogen flow rate negatively affect the stabilization of coatings and lead to their delamination after they are extracted from the vacuum chamber. Meanwhile, higher nitrogen flow rate and work pressure increase the stability of the coatings by up to several days. Additionally, when the nitrogen flow rate and the negative bias voltage were increased, changes in the crystalline structure of the coatings were observed. However, when the work pressure and N2/Ar ratio were increased and the bias voltage was decreased, the stability of ReNx coatings continued even several weeks after their deposition. X-ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD) measurements validated the formation of ReN compound. The more stable deposited rhenium nitride coatings exhibited lower hardness values than the theoretical predictions for this compound, possibly due to the presence of metallic rhenium and thereby rhenium oxides, as seen in the XRD and XPS characterizations.

Plasma Nitriding Mechanisms of Low-Density Sintered Metal Products

Abstract The mechanism of plasma nitriding include the formation of various active species generating nitrogen atoms reacting with the metal. Which species prevail in supplying nitrogen depends on nitriding conditions as well as the nature of the treated metal. Plasma nitriding of low-density powder metal (PM) products results in a formation of the layers whose thicknesses may depend on the gas pressure used for the process. Higher pressure can cause locally deeper penetration of the surface by active nitrogen species formed from ammonia compounds generated by the plasma. While a low processing pressure reduces this effect significantly. The formation mechanism of a locally thicker layer relies on the presence of open porosities in the surface as they can be penetrated by the ammonia species generated by the plasma. The same porosities cannot be penetrated by the ions of nitrogen formed at the same time since their mean free life is much shorter than that of ammonia species. ◼

Clitic-doubled left dislocation in L2 Spanish: The effect of processing load at the syntax-discourse interface

ABSTRACT This project examines whether second-language (L2) learners can converge on a native-like pattern at the interface between syntax and discourse under low and high processing pressure, using Spanish clitic-doubled left dislocation (CLLD) as a test case. The original version of the Interface Hypothesis (IH) predicts that L2 competence on syntax-discourse interface structures may diverge from that of L1 speakers , yet there is experimental evidence of native-like offline judgments of clitic-doubling and its correlation to relevant discourse contexts in L2 Spanish. However, the most updated version of the IH argues that problems at the syntax-discourse interface are not due to divergent competence but rather to L2 processing limitations. To isolate the potential source of divergence, in the present study L2 Spanish learners completed an Acceptability Judgment Task (low processing pressure) and a Speeded Production Task (high processing pressure). Group results show convergence on the native-like pattern on the Acceptability Judgment Task and divergence on the Speeded Production Task. The first finding suggests that L2 learners have linguistic knowledge of discourse-related clitic-doubling, challenging the original version of the IH. The second finding suggests that the processing pressure induced by time constraints and production is correlated with L2 divergence, as predicted by the new version of the IH. We conclude by considering whether this divergence is most appropriately attributed to processing at the interfaces or could alternatively be explained as a result of real-time production specifically.

Evolution of etch profile of copper thin films in high density plasmas of alcohol-based gases

Dry etching of copper thin films patterned with SiO2 masks was performed using inductively coupled plasmas of CH3OH/Ar, C2H5OH/Ar, and O2/C2H5OH gases. The etch rates of copper films in CH3OH/Ar plasma were slightly faster than those in C2H5OH/Ar plasma while the etch profiles in C2H5OH/Ar plasma were better than those in CH3OH/Ar plasma. Upon varying the etch parameters, high coil RF power, high dc-bias voltage to substrate, and low process pressure were found to cause increased redeposition of the etched materials on the copper sidewalls and increased etch slopes. Optical emission spectroscopy, energy dispersive X-ray spectroscopy, and the evolution of the etch profiles revealed the etch mechanism of copper films in C2H5OH/Ar gas. X-ray photoelectron spectroscopy confirmed that the etching of copper films by C2H5OH/Ar takes place via a chemical mechanism involving the formation of copper compounds and a sputtering mechanism by the ions, depending on the C2H5OH concentration. Good etch profiles of copper films without the redeposition were achieved using the optimized O2/C2H5OH gas.

Ultrahigh-yield growth of GaN via halogen-free vapor-phase epitaxy

The material yield of Ga during GaN growth via halogen-free vapor-phase epitaxy (HF-VPE) was systematically investigated and found to be much higher than that obtained using conventional hydride VPE. This is attributed to the much lower process pressure and shorter seed-to-source distance, owing to the inherent chemical reactions and corresponding reactor design used for HF-VPE growth. Ultrahigh-yield GaN growth was demonstrated on a 4-in.-diameter sapphire seed substrate.

Cure Cycle Optimization of Rapidly Cured Out-Of-Autoclave Composites.

Out-of-autoclave prepreg typically needs a long cure cycle to guarantee good properties as the result of low processing pressure applied. It is essential to reduce the manufacturing time, achieve real cost reduction, and take full advantage of out-of-autoclave process. The focus of this paper is to reduce the cure cycle time and production cost while maintaining high laminate quality. A rapidly cured out-of-autoclave resin and relative prepreg were independently developed. To determine a suitable rapid cure procedure for the developed prepreg, the effect of heating rate, initial cure temperature, dwelling time, and post-cure time on the final laminate quality were evaluated and the factors were then optimized. As a result, a rapid cure procedure was determined. The results showed that the resin infiltration could be completed at the end of the initial cure stage and no obvious void could be seen in the laminate at this time. The laminate could achieve good internal quality using the optimized cure procedure. The mechanical test results showed that the laminates had a fiber volume fraction of 59–60% with a final glass transition temperature of 205 °C and excellent mechanical strength especially the flexural properties.

Synthesis of ScAlN thin films on Si (100) substrates at room temperature

Scandium aluminum nitride alloy (ScAlN) thin films have been synthesized using reactive sputtering of a scandium aluminum alloy (Sc0.40Al0.60) target on Si (100) substrates. We have investigated the effects of two sputtering control factors, namely sputtering process pressure and discharge power, on the c-axis growth of the piezoelectric layers. According to our X-ray diffraction analysis, the films are highly textured in the [001] direction at low process pressures and moderate to high discharge powers. X-ray energy dispersive spectroscopy data reveal that the Sc content in the synthesized ScAlN thin films is proportional to the Sc content in Sc0.40Al0.60 alloy target. Finally, surface acoustic wave resonators have been manufactured to demonstrate the feasibility of this material for micro electro mechanical systems applications based on ScAlN/Si bilayer systems.

Designing a low-temperature curable phenolic/benzoxazine-functionalized phthalonitrile copolymers for high performance composite laminates

A low-temperature curable phenolic/benzoxazine-functionalized phthalonitrile (SH/BZ-CN) copolymer system with well processability is designed and applied in high performance glass fiber (GF) composite laminates. Differential scanning calorimetry (DSC) results showed that plenty of phenolic hydroxyl groups on SH could catalyze the oxazine ring-opening and triazine/phthalonitrile ring-forming reaction of BZ-CN. The ring-opening peak and ring-forming peak of SH/BZ-CN systems are reduced by 47.1 °C and 17.0 °C than those of BZ-CN, respectively. The processability of SH/BZ-CN copolymers were improved and could be controlled by tuning SH content, processing temperature and time. These parameters provided ground for preparing SH/BZ-CN/GF composite laminates under a relatively mild condition. All SH/BZ-CN/GF composite laminates exhibit excellent flexural strength more than 500 MPa and flexural modulus over 22.0 Gpa. SH/BZ-CN/GF composites showed immiscible structures and double Tgs, and they could stand high temperature up to 350 °C. Low temperature curing, short processing time and low processing pressure are beneficial to large-scale manufacturing and application of SH/BZ-CN/GF composites.

Highly anisotropic etching of Ta thin films using high density plasmas of halogen based gases

Inductively coupled plasma reactive ion etching of Ta thin films masked with photoresist was performed using C2F6/Ar, HBr/Ar and Cl2/Ar gases. The etch characteristics such as etch rate, etch selectivity and etch profile were investigated in different gas concentrations of each gas. The Cl2 chemistry showed high degree of anisotropy in etch profile as well as fastest etch rate and highest etch selectivity of Ta films among these gases. Optical emission spectroscopy revealed that the increase in chlorine radicals with increasing Cl2 concentration was responsible for the increase in the Ta etch rate. The etch rate of Ta films increased with increasing ICP rf power and dc-bias voltage, and decreasing process pressure. Good etch profiles were obtained at high rf power and dc-bias voltage, and low process pressure. X-ray photoelectron spectroscopy confirmed the existence of a chemical reaction of Ta with chlorine radicals by forming tantalum chlorides. These results suggested that Ta etching in Cl2/Ar follows the typical reactive ion etching mechanism. It was concluded that a high degree of anisotropy and high etch rate of Ta films were achieved using Cl2/Ar gas.

Microcrystalline silicon thin films deposited by matrix-distributed electron cyclotron resonance plasma enhanced chemical vapor deposition using an SiF4 /H2 chemistry

For the growth of hydrogenated microcrystalline silicon (μc-Si:H) thin films by low temperature plasma-enhanced chemical vapor deposition (PECVD), silicon tetrafluoride (SiF4) has recently attracted interest as a precursor due to the resilient optoelectronic performance of the resulting material and devices. In this work, μc-Si:H films are deposited at high rates (7 Å s−1) from a SiF4 and hydrogen (H2) gas mixture by matrix-distributed electron cyclotron resonance PECVD (MDECR-PECVD). Increased substrate temperature and moderate ion bombardment energy (IBE) are demonstrated to be of vital importance to achieve high quality μc-Si:H films under such low process pressure and high plasma density conditions, presumably due to thermally-induced and ion-induced enhancement of surface species migration. Two well-defined IBE thresholds at 12 eV and 43 eV, corresponding respectively to SiF+ ion-induced surface and bulk atomic displacement, are found to be determinant to the final film properties, namely the surface roughness, feature size and crystalline content. Moreover, a study of the growth dynamics shows that the primary challenge to producing highly crystallized μc-Si:H films by MDECR-PECVD appears to be the nucleation step. By employing a two-step method to first prepare a highly crystallized seed layer, μc-Si:H films lacking any amorphous incubation layer have been obtained. A crystalline volume fraction of 68% is achieved with a substrate temperature as low as 120 °C, which is of great interest to broaden the process window for solar cell applications.

Strain-Controlled of Compressive/Tensile Ge Epilayers on Si by Electron Cyclotron Resonance Chemical Vapor Deposition

In this study, we use electron cyclotron resonance chemical vapor deposition to investigate the strain behavior in Ge epilayers grown on silicon at a low temperature of 220°C. The strain in the Ge epilayers is transformed from compressive (−0.567%) to tensile (0.15%) as the process pressure decreases and main coil current increases. This tensile strain is due to intrinsic stress in the Ge epilayers at high process pressure and low main coil current. Besides, the Ge atoms have higher kinetic energy and shorter mean free path at low process pressure and high main coil current, which causes atomic bombardment effect on the Ge surfaces frequently. Thus, the intrinsic stress in Ge epilayers become compressive. The absorption coefficient of tensile and compressive strain in Ge films are measured using a UV–VIS-NIR spectrophotometer. The results show the absorption coefficients of the tensile strain Ge epilayer has a redshift condition on the absorption edge compare with compressive strain Ge epilayers. Finally, the structure information of the Ge epilayers is identified by atomic force microscopy and transmission electron microscopy. This strain control technology is modulated by film growth parameter, which can adjust the Ge bandgap for the device requirement.

Nucleation and growth of ultrathin BaTiO3 films on single terminated Nb:SrTiO3 (100) substrates for ferroelectric tunnel junctions

The authors report on a new table top radio frequency (RF)-magnetron sputtering unit and process for the sputter deposition of barium titanate thin films. Like silicon substrate in conventional electronics, strontium titanate (SrTiO3) is the substrate of choice in the emerging field of oxide electronics and hence Nb doped SrTiO3 n-type semiconducting substrates were considered. The authors observe substrate etching and nonstoichiometry in the film composition at high RF-power and low processing pressure, respectively. However, films deposited at 20 mTorr and 10 W of RF power resulted in stoichiometric BaTiO3. Layer by layer (two-dimensional) growth, prerequisite for epitaxial BaTiO3 on Nb:SrTiO3 (100) substrates, were realized at 600 °C. Hysteresis loops (phase angle versus applied voltage) in piezoresponse force microscopy confirm ferroelectricity of the films. Ultrathin epitaxial BaTiO3 on Nb:SrTiO3 (100) is of great interest as a ferroelectric tunnel junction with pronounced contrast between the ON/OFF tunnel resistance.

Preparation of fluoropolymer structures for orthogonal processing of diverse material by Micro-Contact Printing

Micro-Contact Printing (μCP), one of the soft lithography techniques, has been widely used to fabricate patterns of various materials on inorganic or organic substrates because of its low process temperature and pressure. In this paper, using a poly(dimethylsiloxane) (PDMS) mold, poly(1H,1H,2H,2H-perfluorodecyl methacrylate) polymer (PFDMA) films is patterned and deposited on various substrates such as silicon wafer, silicon oxide on silicon wafer, glass, poly(methylmethacrylate) (PMMA), and poly (vinyl pyrrolidone) (PVP). Because of the soft nature of PFDMA containing HFE-7500 as a casting solvent, the μCP can be done at room temperature without surface treatment or external pressure. The driving force of μCP of PFDMA is the very low adhesion force of 0.52mN/m between PFDMA film and PDMS mold compared to those between PFDMA and the substrate materials. For surface energy estimation of PFDMA contact angle measurements are performed and the adhesion forces among various materials are calculated. It can be shown that the solubility of PFDMA in fluorine-containing solvents can settle down the solvent orthogonality problem. A complementary image can be formed by the subsequent embossing of the remaining PFDMA layers in the recess areas of the hard PDMS mold after the μCP processing. Lift-off deposition of Cr lines is demonstrated using the PFDMA polymer structure.

Analysis of Heat Transfer Mechanism for Shelf Vacuum Freeze-Drying Equipment

Vacuum freeze-drying technology is applicable to the process of high heat-sensitive products. Due to the long drying period and extremely low processing temperature and pressure, the uniform and efficiency of heat transfer fluid temperature in shelf are critical for product quality. Therefore, in this study, the commercial computer fluid dynamics (CFD) software, FLUENT, was utilized for three-dimension numerical simulation of the shelf vacuum freeze-drying process. The influences of different inlet and outlet positions for shelves on the uniformity of the flow rate and temperature were discussed. Moreover, it explored the impacts on the temperature gradient of shelves after heat exchange of different flow rates and low temperature materials. In order to reduce the developing time and optimize the design, the various secondary refrigerants in different plies of shelves were investigated. According to the effect of heat exchange between different flow rates and low temperature layer material shelves on the temperature gradient of shelves surface, the minimum temperature gradient was 20 L/min, and the maximum was 2.5 L/min.

Optimal design and operation of polymer electrolyte membrane reactors for pure hydrogen production

Carbon monoxide (CO) in the hydrogen (H2) stream diminishes the performance of a low-temperature polymer electrolyte membrane (PEM) fuel cell. An on-board CO removal unit is essential in any fuel processor system to be developed for production of hydrogen with low CO concentration (<10ppm). Low process temperature (80°C or lower) and pressure are critical for such a gas clean-up unit. The existing gas clean-up units operate at high temperatures and pressures and often require on-board oxygen or air supply for CO oxidation. An attractive solution for on-board/site production of pure hydrogen is the electrochemical approach. This method removes the CO molecules in the synthetic gas stream after they have been adsorbed onto the catalyst surface in the anode side of a polymer electrolyte membrane reactor. In this process, some additional hydrogen is also produced through the water-gas shift reaction at the cathode side of the reactor offsetting the energy required to drive the electrolysis. In this study, through a parametric study, the optimal geometrical design and operation conditions of the CO removal reactor are determined with an attempt of maximizing the adsorption capacity and minimizing the catalyst consumption.