Vacuum Removal Research Articles

An applicability study on various methods for determining the monomer conversion rate of polyamide 6

AbstractAnionic ring opening polymerization of ε‐caprolactam (CL) results in the formation of high molecular weight polyamide 6 (PA6) within a few minutes. The monomer conversion rate is an important characterization parameter for polymerization process as well as the end products. This paper used PA6 films with different polymerization degrees as research object for the first time, and systematically compared the performance of four methods for measuring CL conversion rate. The analytical methods were solvent extraction (methanol, ethanol, or water), vacuum removal, thermogravimetric analysis (TGA), and absorbance ratio respectively. For all PA6 products, solvent extraction based on methanol/water and vacuum removal were effective methods for determine their conversion rates. And TGA was only applicable for samples with high degree of polymerization. The CL conversion rate obtained by solvent extraction based on ethanol and absorbance ratio was slightly higher than the real value, especially the latter. Moreover, a new method was discovered and validated during the research process, namely atmospheric devolatilization. The methodology and results in this study can be employed for guiding the production and application of polymers, especially the reactive processing of PA6.

ВЫБОР ЖИДКОСТНОКОЛЬЦЕВОГО ВАКУУМНОГО НАСОСА ДЛЯ ШАРОВОЙ МЕЛЬНИЦЫ С ВАКУУМНЫМ ОТВОДОМ

The use of powders is of interest in many industries. At the same time, the degree of grinding of materials depends on the intended purpose; in particular, in the production of paints, it is necessary to ensure a certain fineness of grinding of the pigment. The smaller the particles, the higher its hiding power. However, excessively high grinding fineness may reduce the hiding power of the pigment. It is proposed to grind the pigment in a two-section cylindrical-conical ball mill with vacuum removal of particles of a given degree of grinding. The article describes the design of the mill and shows a diagram of the line for vacuum transportation of the crushed pigment. The purpose of the work is to determine the main parameters of the vacuum line of pneumatic transport when grinding solid organic materials using a ball mill with a vacuum outlet. A method for calculating the geometric, kinematic and dynamic parameters of the developed mill and pneumatic transport line is presented. A significant reduction in energy costs for excess grinding is achieved through timely vacuum removal of crushed particles. The vacuum in the system is created and maintained by a liquid ring vacuum pump. Various options for the operation of the developed installation are described: direct grinding; additional grinding and recirculation of additional liquid generated during the operation of the liquid ring vacuum pump, which further reduces energy costs during grinding

A new analytical model to predict the effect of suction removal on vacuum preloading of fine copper tailings

This research deals with the vacuum preloading of fine-grained soft tailings related to the Sungun copper mine through laboratory tests and theoretical analysis. Vacuum preloading tests are conducted in two groups using a newly configured radial consolidation apparatus. During the first group of tests, the suction intensity is maintained constant similar to conventional vacuum consolidation tests, and in the second group, the suction is removed at certain steps after starting the preloading to investigate the vacuum removal effect on consolidation behavior. The samples in the slurry form are tested under three suctions of 20 kPa, 30 kPa, and 40 kPa individually considering influences of the initial water content of samples, vacuum pressure distribution, smear zone parameters, well resistance, and the dimensions of the vertical drain. Experimental results indicated that the initial water content and suction intensity severely governed the ultimate vertical strain of the sample. Also, depending on removal time, the sample could experience settlement, swelling, or no volume change after removing the suction. In the second part of the study, the vacuum removal effect is included in a new analytical model for vacuum preloading based on the Darcian law to predict the excess pore pressure dissipation and vertical strains. The proposed solutions successfully led to highly accurate predictions for vertical strains observed through comparative tests on the copper tailings. Besides, the proposed model effectively reproduced measurements of an in-situ vacuum consolidation of soda-ash tailings on a site near Dalian Bay in China, and the results of a numerical study on vacuum removal for a project in Ballina, Australia, with maximum errors of approximately 7%.

Bio‐Based, Self‐Condensed Polyols

AbstractA new method for the synthesis of high‐molar‐mass (MM), bio‐based polyols for elastic polyurethanes is developed. This process is based on the self‐condensation of low MM polyols (Mn ≈ 1000) and vacuum removal of the resulting glycerol. Self‐condensation products are hyperbranched estolide polyols with average MMs close to 3000 and hydroxyl numbers in the range of 40–95 mg KOH g−1. Three polyols, one with primary and two with secondary hydroxyls and different functionalities, are studied. The transesterification proceeded much faster with primary hydroxyls, leading to high‐viscosity products. The effect of functionality and reactivity of starting polyols on properties is discussed.Practical applications: The process is useful for upgrading the existing natural oil‐based polyols to higher MM, lower OH number and variable‐functionality polyols, for expanding application in the urethane field. The process is simple, involving just an oil‐based polyol, a catalyst, and heating under vacuum.

Intensification of the Removal of Iron Impurities from Microporous Aluminum Oxide via Argon Blowing

A model is proposed for intensification of the process of high-temperature vacuum removal of iron impurities from microporous aluminum oxide via purging of the particle layer with argon. In the temperature range characteristic of this process, the pressure of saturating vapors above pure iron is on the order of 0.1 mm Hg. For an impurity with a concentration of several particles per million, the figure is proportionally smaller, and this creates problems with evacuation of the chamber. The use of argon as a carrier gas destroys the rigid connection between the partial vapor pressure of the impurity and the pressure in the vacuum chamber. Calculations show that the argon flow under moderate vacuum 10–5 mm Hg with a mass flow rate on the order of 10–7 kg/(m2 s) provides a very deep purification.

RETRACTED: Mechanism analysis on ground settlement induced by vacuum removal

Due to the settlement hazards induced by the soft clayey soils, vacuum preloading has been widely used all over the world. Many studies focus on the process of vacuum application but the process of vacuum removal is generally ignored. Different from observations on surcharge preloading, ground settlement rather than heave occurred during vacuum removal. In this study, a stress-controlled triaxial test was carried out to simulate both processes of vacuum application and removal applied on a clayey soil and hence the mechanism of ground settlement induced by vacuum removal is discussed. Compressive axial strain was observed during the decrease of isotropic stress that simulated vacuum removal. To better understand the observed deformation characteristics of the clayey soils during vacuum removal, in this study, a simple anisotropic elastic model was used. The happening of ground settlement of the clayey soil during vacuum removal is mainly because that the Young’s modulus in the vertical direction is higher than that in the horizontal direction. Lateral extension is dominant for the ground deformation during vacuum removal.

Технология заготовки кормов с досушкой прессованного сена вакуумным способом удаления влаги

Технология заготовки кормов с досушкой прессованного сена вакуумным способом удаления влаги

Effect of vacuum removal on consolidation settlement under a combined vacuum and surcharge preloading

The combined vacuum and surcharge preloading technique is extensively used to accelerate the consolidation process of subsoils. The effect of vacuum pressure is often considered as a loading/unloading cycle of mean effective stress, such that elastic rebound occurs after vacuum removal, which cannot explain the observed postconstruction settlement in the field. In this study, the stress state of subsoils subject to vacuum and surcharge preloading is analyzed and decomposed into two components: (a) geostatic consolidation at a different depth, and (b) loading/unloading in the minor principal stress direction. A series of consolidated drained triaxial tests is conducted to simulate the soil behaviour after vacuum removal. Results show that the contribution of unloading in the minor principal stress direction outweighs the magnitude of elastic rebound after vacuum removal, and hence continued settlement dominates. A field case for highways is provided to further demonstrate the proposed mechanism.

Central glucagon like peptide-1 inhibits reflex swallowing elicited by the superior laryngeal nerve via caudal brainstem in the rat

The effects of glucagon like peptide-1 (GLP-1) on reflex swallowing were examined using anaesthetized rats. GLP-1 was injected into the dorsal vagal complex (DVC) using glass micropipettes. Swallowing was induced by repeated electrical stimulation of the central cut end of the superior laryngeal nerve (SLN) and was identified by the electromyogram lead penetrated in the mylohyoide muscle through bipolar electrodes. Microinjection of GLP-1 into the medial DVC (M-DVC) increased the frequency of swallowing during the electrical stimulation of the SLN and extended the latency of the first swallowing. Microinjection of GLP-1 into the lateral DVC (L-DVC) did not change the frequency of swallowing or the latency of the first swallowing. Neither the injection of vehicle into the M-DVC nor L-DVC affected swallowing frequency. Pre-injection of exendin (5-39), a GLP-1 receptor antagonist, attenuated the degree of suppression of swallowing frequency induced by the administration of GLP-1 in addition to shortening the latency of the first swallowing. To identify the effective site of GLP-1, lesion experiments were performed. Electrical lesion of the commissural part of the NTS (cNTS) and the vacuum removal of the area postrema (AP) did not affect the inhibition of reflex swallowing induced by the injection of GLP-1 into the M-DVC. Electrical lesion of the medial nucleus of the NTS (mNTS) and its vicinity abolished the inhibitory effects of swallowing induced by the injection of GLP-1. These results suggest that GLP-1 inhibits reflex swallowing via the mNTS in the dorsal medulla.

Synthesis of Large Pore Carbon Nanoparticles for Removal of Malachite Green

In this work, we have synthesized high surface area and large pore volume carbon nanoparticles (CNP) by a simple and easy sol-gel approach. The sol was prepared by mixing Pluronic F127 and phloroglucinol-terephthalaldehyde in acidic ethanol solution and the gel was formed after the vacuum removal of ethanol. In the sol-gel process, hydrophobic segments of Pluronic F127 forms enhanced hydrogen bonding with trihydroxyl groups of phloroglucinol. A polymeric network of carbon precursor was also prepared by making the interconnectivity between four phloroglucinol and one terephthalaldehyde molecules. After thermal polymerization and carbonization of the gel, the CNP had a very high surface area (1441 m² g⁻¹) and large pore volume (1.7 cm³ g⁻¹) with narrow micropore (1.0 nm) and mesopore (2.3 nm) diameters. The mesopore was developed due to the enhanced hydrogen bonding between Pluronic F127 and phloroglucinol, while the micropores were generated due to hydrocarbon polymeric network of phloroglucinol-terephthalaldehyde. The CNP had a size about ca. 20 nm. The CNP were applied for the removal of the highly hazardous water pollutant malachite green (MG) and achieved a very high adsorption capacity (1892 mg g⁻¹). The commercials powder activated carbon (PAC) was also applied for the removal of MG and achieved an adsorption capacity of PAC was 1390 mg g⁻¹. It believes that shape and size of CNP and PAC played an important role in the adsorptive removal of MG.

Reverse Dissolution as a Route in the Synthesis of Poly(vinyl butyral) with High Butyral Contents

For applications in ultrafiltration membranes, cancer cell uptake, bioimaging, and diagnostics, a reverse dissolution approach, where swollen poly(vinyl alcohol) (PVA) particles are added to a butyraldehyde solution in ethanol, is employed to synthesize poly(vinyl butyral) (PVB) with high contents of butyral groups. The final butyral group content (up to 84%) of PVB is found to be dependent strongly on the initial condensed state of PVA, the degree of polymerization of PVA, the purity and volume of ethanol, and the pH value. A maximum of butyral group content may be obtained under conditions: swollen PVA particles, (95 vol %) ethanol of 125–150 mL, and pH 1. This reverse dissolution approach has advantages such as a mild reaction condition (70 °C), no predissolution of PVA at high temperatures, no vacuum removal of water during reaction, and low water consumption in post-treatment of the product.

Molecular dynamics simulation of methane hydrate dissociation by depressurisation

Methane (CH4) hydrate dissociation and the mechanism by depressurisation are investigated by molecular dynamics (MD) simulation. The hydrate decomposition processes are studied by the ‘vacuum removal method’ and the normal method. It is found that the hydrate decomposition is promoted by depressurisation. The quasi-liquid layer is formed in the hydrate surface layer. The driving force of dissociation is found to be controlled by the concentration gradient between the H2O molecules of the hydrate surface layer and the H2O molecules of the hydrate inner layer. The clathrates collapse gradually, and the hydrate decomposes layer by layer. Relative to our previous MD simulation results, this study shows that the rate of the hydrate dissociation by depressurisation is slower than that by the thermal stimulation and the inhibitor injection. This study illustrated that MD simulation can play a significant role in investigating the hydrate decomposition mechanisms.

Evolution of Microstructure During Solidification of an Aluminium Alloy Under Stirring

In the present work, the evolution of microstructure during solidification of A356 alloy under stirring is performed experimentally in a high temperature concentric viscometer. The stirring during solidification results a semisolid slurry in the annular space between the cylinders. This slurry is removed periodically during processing using a vacuum removal quartz tube and quenched in water for micrograph analysis. From the micrograph analysis, the shape, stacking arrangement and corresponding microstructural evolution of the suspended primary particles in the slurry are studied. The work also predicts the fraction of solid present in the extracted slurry. Finally, the effect of microstructure and the solid-fraction on the slurry viscosity is presented.

Vacuum Refining of Molten Silicon

AbstractMetallurgical fundamentals for vacuum refining of molten silicon and the behavior of different impurities in this process are studied. A novel mass transfer model for the removal of volatile impurities from silicon in vacuum induction refining is developed. The boundary conditions for vacuum refining system—the equilibrium partial pressures of the dissolved elements and their actual partial pressures under vacuum—are determined through thermodynamic and kinetic approaches. It is indicated that the vacuum removal kinetics of the impurities is different, and it is controlled by one, two, or all the three subsequent reaction mechanisms—mass transfer in a melt boundary layer, chemical evaporation on the melt surface, and mass transfer in the gas phase. Vacuum refining experimental results of this study and literature data are used to study the model validation. The model provides reliable results and shows correlation with the experimental data for many volatile elements. Kinetics of phosphorus removal, which is an important impurity in the production of solar grade silicon, is properly predicted by the model, and it is observed that phosphorus elimination from silicon is significantly increased with increasing process temperature.

Kinetics and Mechanism of Phosphorus Removal from Silicon in Vacuum Induction Refining

AbstractVacuum induction refining is a process that can be applied to remove phosphorus from molten silicon for the production of solar grade silicon. Pure silicon was doped by phosphorus to make molten silicon containing around 17 ppmw phosphorus. The kinetics of phosphorus removal from this silicon was studied at 0.5 Pa through the application of vacuum induction refining. It was observed that vacuum removal of phosphorus occurs through a first-order reaction. The rate constants of phosphorus evaporation were determined as 2.28

Surgical treatment of squamous cell carcinoma of tongue with carbon dioxide laser radiation (CO2)

In this clinical study, we proposed to observe the efficacy of the treatment of squamous cell carcinoma of the tongue (SCCT) by carbon dioxide (CO2) laser surgery. Twelve patients with SCCT were treated with excisional surgery using the CO2 laser with a spot size of 0.8 mm, 10 W, power density of 2.5 W/cm2 in continuous mode, and under constant vacuum removal of the plume. The post surgical clinical evaluations were done every day until the sutures were removed and then every 7 days up to 1 month postoperatively. Subjects were re-examined quarterly until the fifth year post surgery. After 5 yr of follow-up for all subjects, there was no recurrence of the SCCT at the involved sites. The functional and aesthetic results observed were excellent. It is concluded that CO2 laser ablation of SCCT is an extremely useful surgical technique that can provide a clean field and is capable of providing surgical results consistent with accepted principles of oncological surgery.

Optimal application of the Contura multilumen balloon breast brachytherapy catheter vacuum port to deliver accelerated partial breast irradiation

Purpose The impact of using the Contura multilumen balloon (MLB) (SenoRx, Inc., Irvine, CA) breast brachytherapy catheter’s vacuum port in patients treated with accelerated partial breast irradiation (APBI) was analyzed. Methods and Materials Data from 32 patients at two sites were reviewed. Variables analyzed included the seroma fluid (SF):air volume around the MLB before and after vacuum port use and on its ability to improve ( 1) the eligibility of patients for APBI and ( 2) dose coverage of the planning target volume for evaluation (PTV_EVAL) in eligible patients. Results The median SF/air volume before vacuum removal was 6.8 cc vs. 0.8 cc after vacuum removal (median reduction in SF/air volume was 90.5%). Before vacuum port use, the median SF/air volume expressed as percentage of the PTV_EVAL was 7.8% (range, 1.9–26.6) in all patients. After application of the vacuum, this was reduced to 1.2%. Before vacuum port use, 10 (31.3%) patients were not considered acceptable candidates for APBI because the SF/air volume:PTV_EVAL ratio (SF:PTV) was greater than 10% (range, 10.1–26.6%; median, 15.2%). After vacuum port use, the median SF:PTV ratio was 1.6% for a median reduction of 91.5%. In addition, the percentage of the prescribed dose covering greater than or equal to 90% of the PTV_EVAL proportionally increased a median of 8% (range, 3–10%) in eligible patients. Conclusion Use of the Contura MLB vacuum port significantly improved the conformity of the target tissue to the balloon surface, leading to reproducible dose delivery and increased target volume coverage. In addition, application of the vacuum allowed the safe treatment of unacceptable patients with APBI.

Mechanics and Robust Coordinated Control of the Automated Roadway Debris Vacuum Robotic Manipulator

This paper discusses the development of a redundant, long-reach robotic device aimed at the vacuum removal of debris from roadways and roadsides. The future Automated Roadway Debris Vacuum (ARDVAC) system will include trajectory tracking, an advanced controller combining a PID joint controller with a robust H ∞ task-space controller, and a trajectory generation method related to the coverage problem. The manipulator control is coordinated with the vehicle's speed to track task-space end-effector trajectories, exploiting redundancies to achieve the required motion. The controller is robust with respect to external disturbances, including the end-effector forces created by the vacuuming process, thus maintaining the ideal fly-height for optimal vacuum efficiency. Both the theoretical development of the controller and simulation results are presented, which show the efficacy of the approach.

Vacuum removal of the template in MCM-41 silica studied by the positron annihilation method

Positron annihilation lifetime spectra were measured for ordered silica before template (octadecyltrimethyl ammonium) removal. An intermediate lifetime component, well pronounced in the spectra, indicates the presence of structural defects in the template being the size of a surfactant molecule. At the temperature near 420 K a radical change of template structure occurs, consisting in appearance of disorder and the degradation of template; evaporation of the fragments begins. It seems that moderate heating (up to about 500 K only) in vacuum for several hours is an effective and simple method of template removal, leaving no pure carbon residue in the pore structure. The results are compared with the data from the liquid nitrogen adsorption/desorption method and elemental analysis, confirming the positron annihilation results.

Management of the Whitefly Bemisia tabaci (Genn.) on Melon by Vacuum Removal

The efficacy of a field vacuum unit for the management of Bemisia tabaci was evaluated on melon (Cucumis melo L.) during two summer seasons. The tractor-mounted unit was designed to dislodge insects by blowing air from lateral vents onto the plants while simultaneously vacuuming from above. Field observations, collection of leaf samples, and hand-vacuum sampling before and after the field vacuuming were used to evaluate the efficacy of removal. Bemisia tabaci population reductions were significant (30–60%) and lasted from week to week when vacuumed weekly. Parasitoid populations were slightly affected, but were not significantly different from populations in the untreated control plot. Field vacuuming was found to be as effective as insecticide applications for the control of B. tabaci in melons.