Oxygen Acetylene Research Articles

A novel molecular structure design of liquid silicone rubber modified by ceramic precursors for high-performance flexible ablation

High ablation-resistant silicone rubber exhibits a significant role in the thermal protection of space vehicles. However, its limited by the low mechanical strength in practical heat protection applications. Herein, a novel molecular network structure is proposed, which links polycarboxysilane (PCS) rigid molecules onto polydimethylsiloxane molecular chains. The use of PCS rigid chains enhances the heat resistance while reducing the material's mass ablation rate. The addition of a small quantity of PCS (0.406 mmol) increases the tensile strength of the material by 10.4 % and augmentes the static ablation residual weight by 32.8 % compared with polydimethylsiloxane. Additionally, PCS molecular modification of polydimethylsiloxane is beneficial for maintaining the stability of the char layer after oxygen acetylene ablation, making the char layer denser, and improving the interface bonding between the ceramic layer, pyrolysis layer and matrix, ultimately improving the ablation performance of polydimethylsiloxane. This work provides a new approach for development of high-performance flexible ablative materials.

Flame Edge Detection Method Based on a Convolutional Neural Network.

In this study, an improved flame edge detector based on convolutional neural network (CNN) was proposed. The proposed method can generate edge graphs and extract edge graphs relatively effectively. Our network architecture was based on VGG16 primarily, the last two max-pooling operators and all full connection layers of the VGG16 network were deleted, and the rest was taken as the basic network. The images output by the five convolution layers were upsampled to the size of the input images and finally fused to the edge image. Error calculation and back propagation of the fusion image and label image are carried out to form a weakly supervised model. Using the open datasets BSDS500 to train the network, the ODS F-measure can reach 0.810. Various experiments were carried out on different flame and fire images, including butane–air flame, oxygen–ethanol flame, energetic material flame, and oxygen–acetylene premixed jet flame, and the infrared thermogram was also verified by our method. The results demonstrate the effectiveness and robustness of the proposed algorithm.

LC/8YSZ TBCs Thermal Cycling Life and Failure Mechanism under Extreme Temperature Gradients

The purpose of this paper is to study the thermal shock resistance and failure mechanism of La2Ce2O7/8YSZ double-ceramic-layer thermal barrier coatings (LC/8YSZ DCL TBCs) under extreme temperature gradients. At high surface temperatures, thermal shock and infrared temperature measuring modules were used to determine the thermal cycling life and insulation temperature of LC/8YSZ DCL TBCs under extreme temperature gradients by an oxygen–acetylene gas flame testing machine. A viscoelastic model was used to obtain the stress law of solid phase sintering of a coating system using the finite element method. Results and Conclusion: (1) Thermal cycling life was affected by the surface temperature of LC/8YSZ DCL TBCs and decreased sharply with the increase of surface temperature. (2) The LC ceramic surface of the failure coating was sintered, and the higher the temperature, the faster the sintering process. (3) Accelerated life test results showed that high temperature thermal cycling life is not only related to thermal fatigue of ceramic layer, but is also related to the sintering degree of the coating. (4) Although the high temperature thermal stress had great influence on the coating, great sintering stress was produced with sintering of the LC ceramic layer, which is the main cause of LC/8YSZ DCL TBC failure. The above results indicate that for new TBC ceramic materials, especially those for engines above class F, their sinterability should be fully considered. Sintering affects the thermal shock properties at high temperature. Our research results can provide reference for material selection and high temperature performance research.

Study the Effect of Laser Nozzle and Lens Design on the Oxygen Supply System for CNC Gas Cutting Machines

The process of laser cutting by (Nozzle C 20E) can detect the roughness of the surface from the upper side, while laser cutting by (Nozzle C30E) have less roughness detection according to the ability of constant speed with different metal thickness. The width of the Kerf and surface roughness are the most factors which needs for focusing during cutting process for various plate cutting operation by CNC machine. Such machines require oxygen and propane or acetylene gases with proper pressure controls. For the gas cutting machine, the volume of oxygen gas used is more than that of propane gas. The oxygen gas is used for heating and cutting the plates. It is necessary to supply the proper amount and quality of gas to the machine to obtain a good cutting quality surfces. However; the pressure of oxygen gas depends upon the thickness of cutting plates. Stainless steel is the most important metals in the industrial and manufacturing process, so the cutting conditions are very important. Its concluded from our result, that the characteristics of the main selecting factors which effects the laser machine performance such as, the focal lens nozzle height (0.6 to 1.0mm) and the ability and speed of cutting should be fixed and not changing.

Microstructure and Corrosion Behavior of Aluminum Coatings Prepared by High-Efficiency Supersonic Plasma Spraying and Oxygen–Acetylene Flame Spraying

Thermal spraying aluminum coatings have been widely used in the corrosion protection of mild steel in seawater. In this study, high-efficiency supersonic plasma spraying (HESP) and oxygen–acetylene flame spraying (FS) were used to prepare aluminum coatings. The micromorphology of the coatings was analyzed by a scanning electron microscope equipped with an energy-dispersive x-ray spectrometer. The phase identification of the coatings was conducted by an x-ray diffractometer. The Vickers hardness and bonding strength of the coatings were measured by an HMV-2000 Vickers hardness tester and MTS809 universal tensile tester. The corrosion resistance of the coatings was tested by an IM6ex electrochemical workstation. The results show that the aluminum coatings prepared by HESP have a denser structure, higher microhardness, higher bonding strength, and better corrosion resistance than those prepared by the traditional FS. After 480-h immersion in 3.5 wt.% NaCl solution, a dense corrosion product formed on the surface of aluminum coatings prepared by HESP prevents further corrosion of the coatings, but the aluminum coatings sprayed by FS demonstrate a serious pitting phenomenon.

Timekeeping strategy in the oxygen acetylene welding practicum through attendance ranking approach

The culture of industry in vocational schools needs to be applied optimally to shape the work character of graduates who are increasingly fierce in competition. The trade starts to look at graduates with a better attitude than hard skills. This research is directed at how the fundamental problem of timely attendance is a phenomenon that deserves to be studied as part of the formation of soft skills. This study has objectives including (1) observing students’ participation at Oxygen Acetylene Welding (OAW) lectures and (2) reading of student attendance patterns after the implementation of timekeeping strategy-based ranking. The research method uses quantitative descriptive by collecting data by observing student attendance directly. The continuing collection was carried out for 14 weeks at the OAW practicum. Based on the results of the study showed that there was a significant increase in timely attendance and was gradually consistent until the end of the meeting. Besides, the presence sequence builds the habits of students to arrive on time.

Analysis of Equivalence Ratio in an Oxygen Acetylene Mixture

The paper presents an exclusive approach to analyze the oxygen and acetylene mixture in a Pulse Detonation Engine setup at PEC. The experiment was carried out by varying the amount of mass flow of acetylene and oxygen into the tube at different pressures in the settling chamber. The equivalence ratio of the acetylene-oxygen mixture with respect to the valve opening time of acetylene and oxygen was plotted. The analysis of equivalence ratio also defines the procedure which involved the cycle of valves and pressure supply to attain different values of filling fraction of the tube. The results experimentally predicted the feasible range of operation at different pressures in the settling chamber of the pulse detonation engine.

Highly branched phenolic resin‐grafted silicone rubber copolymer for high efficiency ablation thermal protection coating

ABSTRACTHighly branched phenolic resin‐grafted silicone rubber (PGS) was synthesized by grafting allyl ether phenolic resin onto silicone rubber with Si─H groups via hydrosilylation. The chemical structure of the copolymer was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography, and its microphase morphology was observed via scanning electron microscopy (SEM). The mechanical properties and thermal stability of the material were also characterized. Thereafter, an ablation thermal protection coating (ATPC) based on PGS as the polymer matrix was prepared. In comparison with silicone rubber‐based ATPC, the PGS‐based ATPC showed better thermal stability and a stronger char layer. After oxygen–acetylene testing, the micromorphology and chemical composition of the PGS‐based ATPC were characterized via SEM, energy‐dispersive spectrometry, and X‐ray diffraction. Finally, the PGS‐ and silicone rubber‐based ATPCs were subjected to a heat flow of 370 kW m−2 for 70 s, the background temperature of the PGS‐based ATPC was only 70 °C. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48353.

N2O emission contributions by different pathways and associated microbial community dynamics in a typical calcareous vegetable soil

Nitrous oxide, one of the powerful long-lived greenhouse gases, is emitted mainly through biological processes, especially from fertilized soil. It is critical to partition the contribution of different pathways to N2O emissions and the relevant characteristics of microbial communities to identify the key N2O processes. An microcosm was conducted to partition the N2O emissions from different pathways, and the changes in soil mineral nitrogen and various nitrifiers (amoA bacteria and amoA archaea) and denitrifiers (nirS, nirK, and nosZ) were also determined using qPCR and high-throughput sequencing methods. Different gas inhibitor combinations (i.e., 0.06% acetylene, pure oxygen, 0.06% acetylene in pure oxygen, and pure helium) were used to partition the N2O pathways. A 5% oxygen treatment, with and without acetylene, was also included so that the N2O emissions could be measured under lower oxygen partial pressure. Results showed that ammonia-oxidation (AO) and successive nitrifier denitrification (NiD) were the main pathways contributing to N2O emissions at the earlier period after ammonium sulfate application with the cumulative N2O emissions accounting for 30.9% and 59.2% of the total N2O emissions, respectively. The higher NiD N2O contributions occurred when the soil nitrite concentration appeared higher, especially under the lower oxygen conditions. Higher N2O emissions from AO and NiD were associated with the compositional proportion of some dominant AOB species. Denitrification contributed more N2O (63.6%–69.3%) in the later period during incubation, coinciding with the following characteristics for denitrifiers: a) lower nosZ/(nirS + nirK) ratio, b) more diversity in nirS, and c) different proportions of some dominant species in nirK. Our results demonstrated that higher AO and successive NiD were the main N2O emission pathways, suggesting that controlling the ammonium content and weakening the AO are critical in decreasing N2O emissions.

Mechanical, thermal, and ablative properties between graphene oxide and graphitic carbon nitride based carbon/phenolic composites: a comparative study

In this article, we investigated the interfacial, thermal and ablative properties of two nanofillers‐filled carbon/phenolic (CF/PR) composites. In particular, graphene oxide (GO) and graphitic carbon nitride (g‐C3N4) were used to produce lowly loaded (0.1 wt%) composites. The ablative properties of the composites were researched through an oxygen–acetylene flame torch test and were characterized through analysis of the post‐burning morphology, ablation depth and width. GO‐ and g‐C3N4‐filled composites showed 62.02 and 22.36% improvement in ablation resistance compared with the pristine, respectively, even with different mechanisms. The proposed mechanism of GO‐filled composite is that GO may significantly contribute to increasing the graphitization of the fiber surface and further improving the thermal resistance to high‐temperature ablation. However, thicker fiber diameter and charred layer of ablative zone in g‐C3N4‐filled composite can dissipate the flammable gases and improve the anti‐oxidation. POLYM. COMPOS., 39:E1928–E1938, 2018. © 2018 Society of Plastics Engineers

B4C-MODIFIED SiO2-PHENOLIC COMPOSITES FOR ENHANCED ABLATION RESISTANCE

In the present paper, the silica-phenolic composite (S-Ph) composites with different amount of B4C were prepared, and the ablation tests of these composites were carried out using oxygen–acetylene jet. The ablation process was systematically investigated. The addition of B4C with appropriate amount can efficiently improve the ablation resistance of S-Ph. The results showed that S-Ph containing B4C powder of 2[Formula: see text]wt.% exhibited the lowest linear and mass ablation rate. The influence mechanism for the results was analyzed deeply. The surface morphologies, phase composition, density and thermal conductivity of composites were characterized using a scanning electron microscope (SEM), X-Ray Diffraction (XRD), Archimedes method, and thermal conductivity meter, respectively. The present investigation will provide a theoretical basis for the preparation of the ablation resistant material.

Fabrication and Characterization of Nanocarbon-Based Nanofluids by Using an Oxygen-Acetylene Flame Synthesis System.

In this study, an oxygen–acetylene flame synthesis system was developed to fabricate nanocarbon-based nanofluids (NCBNFs) through a one-step synthesis method. Measured in liters per minute (LPM), the flame’s fuel flows combined oxygen and acetylene at four ratios: 1.5/2.5 (P1), 1.0/2.5 (P2), 0.5/2.5 (P3), and 0/2.5 (P4). The flow rate of cooling water (base fluid) was fixed at 1.2 LPM to produce different nanocarbon-based materials (NCBMs) and various concentrations of NCBNFs. Tests and analyses were conducted for determining the morphology of NCBMs, NCBM material, optical characteristics, the production rate, suspension performance, average particle size, zeta potential, and other relevant basic characteristics of NCBNFs to understand the characteristics and materials of NCBNFs produced through different process parameters (P1–P4). The results revealed that the NCBMs mainly had flaky and spherical morphologies and the diameters of the spherical NCBMs measured approximately 20–30 nm. X-ray diffraction and Raman spectroscopy revealed that the NCBMs contained graphene oxide (GO) and amorphous carbon (AC) when the oxygen flow rate was lower than 1.0 LPM. In addition, the NCBMs contained reduced GO, crystalline graphite (graphite-2H), and AC when the oxygen flow rate was higher than 1.0 LPM. The process parameters of P1, P2, P3, and P4 resulted in NCBMs produced at concentrations of 0.010, 0.013, 0.040, and 0.023 wt%, respectively, in NCBNFs. All the NCBNFs exhibited non-Newtonian and shear-thinning rheological properties. The P4 ratio showed the highest enhancement rate of thermal conductivity for NCBNFs, at a rate 4.85 % higher than that of water.

Improved ablation resistance of carbon–phenolic composites by introducing zirconium silicide particles

The effect of ZrSi2 on the thermal degradation behavior of phenolic and the role of ZrSi2 on the ablation resistance of carbon–phenolic (C–Ph) composites are investigated by introducing ZrSi2 particles into phenolic, and then ZrSi2 particles into C–Ph composites. Thermogravimetry (TG) analysis illustrates that the residue yield of phenolic at high temperatures is increased by the introduction of ZrSi2 particles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses reveal that the increased residue yield is attributed to the reactions between ZrSi2 particles and pyrolysis volatiles. Therefore, partial carbon and oxygen elements in the volatiles remain in the thermal residue in the forms of amorphous carbon, ZrO2 and SiO2, respectively. Moreover, the ablation resistance of C–Ph composites is significantly improved by the introduction of ZrSi2 particles with formation ZrO2 and SiO2 during the oxygen–acetylene ablation process. The average linear and mass ablation rates of ZrSi2 modified carbon–phenolic (Z/C–Ph) composites evidently reduce by comparison with those of C–Ph composites under similar conditions. As depicted in the microstructure, the ablation occurs in volume in C–Ph composites. The oxygen-containing molecules penetrate deeply inside the matrix, thus the ablation by oxidation is accelerated. However, the ablation occurs in surface in Z/C–Ph composites. ZrSi2 reacts with the oxygen-containing molecules to form SiO2–ZrO2 layer and molten SiO2 cover on the ablated surface, thus the ablation by the oxidation of matrix and fibers in the interior has been inhibited.

Numerical simulation of silica particle trajectory in flow field and silica particle spheroidizing in oxygen–acetylene flame spheroidization process

A numerical simulation was developed for particle trajectory in flow field and spheroidizing of silica particle in oxygen–acetylene flame spheroidization process. Gas flow field and silica particle behavior in oxygen–acetylene flame spheroidization process was simulated using a Computational Fluid Dynamics (CFD) package FLUENT. A model was proposed for optimizing spheroidization process of silica particle. Oxygen gas and acetylene gas were used as the continuous phase. Silica particle was used as the dispersed phase. The three-dimensional, steady and isothermal flow field was showed for illustrating the continuous phase and the dispersed phase. Conservation equations of mass and momentum for each phase were solved using the finite volume numerical technique. Various gas conditions were discussed systematically. The injected silica particle trajectories were simulated by using dispersed particle surface trajectory. The trajectories and spheroidizations of different size particles were analyzed. The results of numerical simulation reveal that the flame length was reasonable and overall temperature was highest when acetylene gas flow rate was 10L·min−1, oxygen gas flow rate was 20L·min−1 and powder carrying gas flow rate was 5L·min−1 and 40μm silica particles were difficult to finish spheroidizing within 5×10−4s. The comparison shows that temperature distribution, velocity distribution, particle trajectories, and deformation which were predicted by simulation, were in good agreement with the corresponding experimental results.

Microstructure and corrosion resistance of rare earth NiCrMoY alloy coatings

The microstructure and corrosion of rare earth NiCrMoY alloy made by atomisation and oxygen–acetylene flame spray and high-frequency induction remelting technique were investigated by means of scanning electron microscopy, energy spectrum, X-ray diffraction, uniform corrosion of laboratory immersion tests and anodic polarisation curve of three-electrode potentiodynamic scans. The results showed that compared to the coatings of Ni60A, the microstructure of NiCrMoY alloy coatings was finer, some bulk- and needle-like hard microstructures were precipitated, and a new phase MoB was produced. The corrosion rate of NiCrMoY alloy coatings is better than that of Ni60A coatings in HCl, H2SO4, HNO3 and artificial seawater.

니켈기 용사코팅의 스플랫 형성에 관한 연구

Thermal spray coatings developed by deposition of splats, it formed by impacting molten droplets on substrates during thermal spray process. In this study, the Ni-based coatings were fabricated by thermal spray process with two different process parameters, oxygen gas flow and acetylene gas flow, with three different levels of each parameters. The morphology of splats and microstructure were observed by optical microscope. Hardness test were performed on the Ni-based coatings. It was confirmed that process parameters of thermal spray process have effect in morphology of splats. These effects also have important implications on the deposit microstructure and properties of Ni-based coatings.

Preparation of low radioactivity spherical silicon oxide powders via chemical-flame spheroidizing process

In this work, a chemical-flame spheroidizing method was proposed to facilely prepare low radioactivity spherical silicon oxide powders. Firstly, the rice husks, composed of silicon oxide frame, were employed as the raw materials to prepare high-purity colloidal silica nanoparticles with the size 24 nm via a simple “pyrolyzation–ashing–dissolvation” process. Then, the silica colloid was further treated by a spraying–drying process to mainly form mushroomhead-shaped silica particles with particle size 0.5–10 μm. Most of the powders were hollow, the thickness of the walls of hollow silicon oxide powders was about 50–100 nm. The surfaces were rough, the powders had poor fluidity and the apparent density was only 0.21 g/cm 3. Finally, almost all these submicro and microparticles were densified by an oxygen–acetylene flame spheroidizing process to get low radioactivity spherical silicon oxide powders with the size 0.5–5 μm. The fluidity, the apparent density and the content of U of the as-prepared spherical silicon oxide powders reached 94 s/50 g, 0.721 g/cm 3 and 0.05 × 10 −9g/g, respectively. Such silicon oxide material originating from rice husks could potentially be used in very large scale integration field.

Effects of spherical silica on the properties of an epoxy resin system

AbstractThe spherical silica powders were prepared by using an oxygen–acetylene flame method. After spheroidization, a scanning electron microscope investigation revealed that the spheroidization efficiency of the powder was nearly 100%, XRD patterns indicated that the raw crystal silica became amorphous silica. In this study, composites of spherical silica and an epoxy resin were prepared with a homogenizer, followed by a stepwise thermal curing process. The thermal stability and thermal degradation behavior of the composites were studied by a thermogravimetric analyzer. Meanwhile, the effects of spherical silica powder on dynamic mechanical, coefficient of thermal expansion, and mechanical properties of epoxy/silica composites were also investigated. The initial decomposition temperature and mechanical properties increased significantly after adding the spherical silica into the composite. The maximum properties of thermal stability and mechanical properties were observed when spherical silica accounted for 30% of the system. The thermal expansion had been significantly reduced by the addition of silica. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Numerical Simulation of Oxy-Acetylene Testing Procedure of Ablative Materials for Re-Entry Space Vehicles

A testing apparatus for flame exposure of ablative, high thermal flux-resistant materials has been designed and manufactured according to the ASTM E 285-80 standard. The test is useful for the selection of thermal protection systems (TPS) working as ablators and for the evaluation of their shielding performance. In order to support the material/component design and to offer new and differentiated tools for the screening phase of TPS materials, a CFD (computational fluid-dynamics) model of the burning test was developed. The model simulates the combustion of an oxygen—acetylene mixture occurring in a conventional welding torch, and calculates the heat flux incident on the sample and the related temperature fields. The validation of the model was obtained performing suitable instrumented tests enabling direct measurements of both incident heat flux and temperatures of the front and back surfaces of an ablative sample. Good agreement was found between numerical results and experimental measurements, encouraging the use of simulations for the design of the test environmental conditions.

Preparation of spherical silica powder by oxygen–acetylene flame spheroidization process

A novel economic oxygen–acetylene flame spheroidization process and special equipments to prepare spherical silica powders are presented. Before spheroidization treatment, the raw silica is purified by mixed acids. In this spheroidization process, oxygen is used both as the carrier gas to transport the purified silica powders to the flame region, and as the combustion-supporting gas. The crystallized silica powders are melted and then transformed to amorphous silica after oxygen–acetylene flame spheroidization treatment. The powder size analysis indicates that the powder size increases and the size distribution become narrower after spheroidization treatment. By optimizing the process parameters, spherical silica powders were obtained. A scanning electron microscope (SEM) investigation reveals that the spheroidization efficiency of the 5 μm diameter powder is more than 95% at feeding rates below 60 g/min. The closer the length–diameter ratio of raw silica powder is to 1, the higher the spheroidization efficiency of the sample is. The fluidity value and apparent density of the powder with the spheroidization efficiency 95% is 70 s/50 g and 0.88 g/cm 3, respectively. Oxygen–acetylene flame spheroidization process is a promising low-cost alternative for large-scale production of spherical silica powder.