Effect of Bimodal Granularity Distribution on the Properties of Silica-Based Ceramic Cores

2017 ◽  
Vol 898 ◽  
pp. 1724-1731
Author(s):  
Xiao Guang Liu ◽  
Xin Li ◽  
Ding Zhong Tang ◽  
Jian Sheng Yao ◽  
Shu Xin Niu
Keyword(s):  
Flexural Strength ◽  
Creep Deformation ◽  
Fine Particles ◽  
Process Condition ◽  
Sharp Decrease ◽  
Casting Process ◽  
Phase Evolution ◽  
Fused Silica ◽  
Coarse Particles ◽  
Granularity Distribution

In this work, the effects of the bimodal particle size distribution of fused silica on the properties of silica-based ceramic cores have been investigated. In order to simulate a casting process condition, the core specimens were sintered at 1220°C, tested at above 1500°C. Three point bending tests were carried out on all the prepared specimens. Phase evolution and microstructure were investigated by XRD and SEM respectively. The results showed that with the bimodal granularity distribution broaden and the content of coarse particles increasing, the contraction, flexural strength and creep deformation of ceramic cores decreased linearly, as the content of mineralizer was determined. Coarse particles served as the skeleton to relieve the contraction in ceramic matrix and avoided sharp decrease of flexural strength. The high temperature properties were largely determined by the combined effects of crystallization and skeleton network. The crystallization depended mostly on the fine particles, and the skeleton network was prerequisite to avoid creep deformation.

Investigation on Nano-Fused Silica in Silica-Based Ceramic Cores for Investment Casting

2015 ◽  
Vol 816 ◽  
pp. 266-270 ◽  
Author(s):  
Shu Xin Niu ◽  
Shu Cai ◽  
Ding Zhong Tang ◽  
Xiao Guang Liu ◽  
Guo Hong Gu ◽  
...  
Keyword(s):  
Flexural Strength ◽  
Investment Casting ◽  
Process Condition ◽  
Casting Process ◽  
Phase Evolution ◽  
Silica Content ◽  
Fused Silica ◽  
Comprehensive Properties ◽  
Micro Cracks ◽  
Heat Treated

In this work, nanofused silica and its effect on mechanical and chemical behavior of injection moulded silica-based ceramic cores were investigated. In order to simulate casting process condition, the sintered samples at 1180 °C were also heated up to 1500 °C. Flexural strength test was carried out on both sintered and heat treated samples. Phase evolution and microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the samples with 0.5 wt.% nanofused silica content had an optimal comprehensive properties for investment casting. The flexural strength of sintered samples with 0.5 wt.% nanofused silica at room temperature and at 1500 °C for 30 min were 30.3 MPa and 24.4 MPa, respectively, and the creep deformation at 1500 °C was 0.8 mm. The addition of nanofused silica was favorable for cristobalite transformation and the samples had a good leachability for the micro-cracks introduced by crystallization.

Microstructure and Performance of Fused Silica-Based Ceramic Core Reinforced by Mullite Fiber

2016 ◽  
Vol 848 ◽  
pp. 228-232
Author(s):  
Xin Li ◽  
Jian Sheng Yao ◽  
Xiao Guang Liu ◽  
Hong Na Fan ◽  
Shu Xin Niu
Keyword(s):  
Flexural Strength ◽  
Creep Test ◽  
Casting Process ◽  
Fused Silica ◽  
Strength Test ◽  
Ceramic Core ◽  
The Core ◽  
Mullite Fiber ◽  
And Performance ◽  
Microstructure And Performance

Fused silica-based ceramics are often used as sacrificial cores in investment castings to produce hollow, precise, and complex-shaped blades. In this work, the content of mullite fiber and its effects on mechanical and dimension behavior of silica-based ceramic cores were investigated. In order to simulate the single crystal blades casting process, the sintered samples were also heated up to 1540°C and kept for 0.5 h. Flexural strength test at 1540°Cwas carried out for the samples. The shrinkage, creep behavior and erode behavior were characterized. The results showed that in the premise of maintaining strength of materials, mullite fiber could decrease significantly the shrinkage. Many gains appeared on the surface of fiber after creep test of the core samples at 1540°C.

scholarly journals Contribution of Fine Particles to Air Emission at Different Phases of Biomass Burning

Atmosphere ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 278 ◽  
Author(s):  
Niloofar Ordou ◽  
Igor E. Agranovski
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Fine Particles ◽  
Combustion Process ◽  
Coarse Particles ◽  
Biomass Smoke ◽  
Smoke Particles ◽  
Air Emission ◽  
Entire Duration ◽  
Diffusion Properties

Particle size distribution in biomass smoke was observed for different burning phases, including flaming and smouldering, during the combustion of nine common Australian vegetation representatives. Smoke particles generated during the smouldering phase of combustions were found to be coarser as compared to flaming aerosols for all hard species. In contrast, for leafy species, this trend was inversed. In addition, the combustion process was investigated over the entire duration of burning by acquiring data with one second time resolution for all nine species. Particles were separately characterised in two categories: fine particles with dominating diffusion properties measurable with diffusion-based instruments (Dp < 200 nm), and coarse particles with dominating inertia (Dp > 200 nm). It was found that fine particles contribute to more than 90 percent of the total fresh smoke particles for all investigated species.

Microstructures and Creep of AM50-Sb-Gd Alloys

2005 ◽  
Vol 488-489 ◽  
pp. 749-752 ◽  
Author(s):  
Su Gui Tian ◽  
Keun Yong Sohn ◽  
Hyun Gap Cho ◽  
Kyung Hyun Kim
Keyword(s):  
Activation Energy ◽  
Creep Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Deformation Mechanism ◽  
Creep Resistance ◽  
Fine Particles ◽  
Dislocation Climb ◽  
The Matrix

Creep behavior of AM50-0.4% Sb-0.9%Gd alloy has been studied at temperatures ranging from 150 to 200°C and at stresses ranging from 40 to 90 MPa. Results show that the creep rate of AM50-0.4%Sb-0.9%Gd alloy was mainly controlled by dislocation climb at low stresses under 50 MPa. The activation energy for the creep was 131.2 ± 10 kJ/mol and the stress exponent was in the range from 4 to 9 depending on the applied stress. More than one deformation-mechanism were involved during the creep of this alloy. Microstructures of the alloy consist of a–Mg matrix and fine particles, distinguished as Mg17Al12, Sb2Mg3, and Mg2Gd or Al7GdMn5 that were homogeneously distributed in the matrix of the alloy, which effectively reduced the movement of dislocations, enhancing the creep resistance. Many dislocations were identified to be present on non-basal planes after creep deformation.

scholarly journals Ambient Particulate Matter Air Pollution in Mpererwe District, Kampala, Uganda: A Pilot Study

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Stephan Schwander ◽  
Clement D. Okello ◽  
Juergen Freers ◽  
Judith C. Chow ◽  
John G. Watson ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Air Quality ◽  
Pilot Study ◽  
Fine Particles ◽  
Airborne Particulate Matter ◽  
Personal Exposure ◽  
Ambient Air ◽  
Combustion Products ◽  
Carbonaceous Aerosol ◽  
Coarse Particles

Air quality in Kampala, the capital of Uganda, has deteriorated significantly in the past two decades. We made spot measurements in Mpererwe district for airborne particulate matter PM2.5(fine particles) and coarse particles. PM was collected on Teflon-membrane filters and analyzed for mass, 51 elements, 3 anions, and 5 cations. Both fine and coarse particle concentrations were above 100 µg/m3in all the samples collected. Markers for crustal/soil (e.g., Si and Al) were the most abundant in the PM2.5fraction, followed by primary combustion products from biomass burning and incinerator emissions (e.g., K and Cl). Over 90% of the measured PM2.5mass can be explained by crustal species (41% and 59%) and carbonaceous aerosol (33%–55%). Crustal elements dominated the coarse particles collected from Kampala. The results of this pilot study are indicative of unhealthy air and suggest that exposure to ambient air in Kampala may increase the burden of environmentally induced cardiovascular, metabolic, and respiratory diseases including infections. Greater awareness and more extensive research are required to confirm our findings, to identify personal exposure and pollution sources, and to develop air quality management plans and policies to protect public health.

scholarly journals Characteristics of atmospheric mercury deposition and size-fractionated particulate mercury in urban Nanjing, China

2014 ◽  
Vol 14 (5) ◽  
pp. 2233-2244 ◽  
Author(s):  
J. Zhu ◽  
T. Wang ◽  
R. Talbot ◽  
H. Mao ◽  
X. Yang ◽  
...  
Keyword(s):  
Dry Deposition ◽  
Wet Deposition ◽  
Fine Particles ◽  
Unit Area ◽  
Atmospheric Mercury ◽  
Anthropogenic Sources ◽  
Deposition Flux ◽  
Coarse Particles ◽  
Mercury Deposition ◽  
Particulate Mercury

Abstract. A comprehensive measurement study of mercury wet deposition and size-fractionated particulate mercury (HgP) concurrent with meteorological variables was conducted from June 2011 to February 2012 to evaluate the characteristics of mercury deposition and particulate mercury in urban Nanjing, China. The volume-weighted mean (VWM) concentration of mercury in rainwater was 52.9 ng L−1 with a range of 46.3–63.6 ng L−1. The wet deposition per unit area was averaged 56.5 μg m−2 over 9 months, which was lower than that in most Chinese cities, but much higher than annual deposition in urban North America and Japan. The wet deposition flux exhibited obvious seasonal variation strongly linked with the amount of precipitation. Wet deposition in summer contributed more than 80% to the total amount. A part of contribution to wet deposition of mercury from anthropogenic sources was evidenced by the association between wet deposition and sulfates, as well as nitrates in rainwater. The ions correlated most significantly with mercury were formate, calcium, and potassium, which suggested that natural sources including vegetation and resuspended soil should be considered as an important factor to affect the wet deposition of mercury in Nanjing. The average HgP concentration was 1.10 ± 0.57 ng m−3. A distinct seasonal distribution of HgP concentrations was found to be higher in winter as a result of an increase in the PM10 concentration. Overall, more than half of the HgP existed in the particle size range less than 2.1 μm. The highest concentration of HgP in coarse particles was observed in summer, while HgP in fine particles dominated in fall and winter. The size distribution of averaged mercury content in particulates was bimodal, with two peaks in the bins of < 0.7 μm and 4.7–5.8 μm. Dry deposition per unit area of HgP was estimated to be 47.2 μg m−2 using meteorological conditions and a size-resolved particle dry deposition model. This was 16.5% less than mercury wet deposition. Compared to HgP in fine particles, HgP in coarse particles contributed more to the total dry deposition due to higher deposition velocities. Negative correlation between precipitation and the HgP concentration reflected the effect of scavenging of HgP by precipitation.

scholarly journals Experimental study on acidification effect of tailing sand

2021 ◽  
Vol 248 ◽  
pp. 01048
Author(s):  
Wenzhao Chen ◽  
Kai Yang ◽  
Jiaqing Fan ◽  
Xiqi Liu ◽  
Xiaoqing Wei
Keyword(s):  
Fine Particles ◽  
Iron Concentration ◽  
Chemical Properties ◽  
Surface Friction ◽  
Friction Angle ◽  
Immersion Test ◽  
Coarse Particles ◽  
Natural Conditions ◽  
Lead Zinc ◽  
Reaction Processes

Sulfide minerals (mainly FeS2) contained in lead-zinc tailings are easy to be acidified in the air. The acidification mechanism is that the tailing sand generates sulfuric acid and sulfate under the catalysis of oxidant, water and oxygen. The acidic liquid generated by the reaction will continue to react with metal oxides to form an insoluble precipitate.In order to reveal the corresponding changes of chemical properties and physical properties of lead-zinc tailing sand during acidification, a series of reaction processes of tailings under natural conditions were simulated by immersion test in laboratory.It is found through the test that with the deepening of acidification, the coarse particles of tailing sand dissolve, resulting in the decrease of iron concentration in the compound, the increase of fine particles, the increase of specific surface area, the decrease of surface friction and occlusion friction between particles, resulting in the decrease of internal friction angle, and the decrease of the safety of tailings dam. words.

A Study of Airborne Wear Particles Generated From a Sliding Contact

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Ulf Olofsson ◽  
Lars Olander ◽  
Anders Jansson
Keyword(s):  
Ultrafine Particles ◽  
Fine Particles ◽  
Urban Environments ◽  
Airborne Particles ◽  
Wear Particles ◽  
Coarse Particles ◽  
Sliding Velocity ◽  
Airborne Particle ◽  
Particle Generation ◽  
Pin On Disk

Recently, much attention has been paid to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environments. In this study airborne particles generated from a sliding steel-on-steel combination are studied using a pin-on-disk tribometer equipped with airborne-particle counting instrumentation. The instrumentation measured particles in size intervals from 0.01μm to 32μm. The result shows three particle size regimes with distinct number peaks: ultrafine particles with a size distribution peak around 0.08μm, fine particles with a peak around 0.35μm, and coarse particles with a peak around 2 or 4μm. Both the particle generation rate and the wear rate increase with increasing sliding velocity and contact pressure.

scholarly journals Morphological, chemical and optical absorbing characterization of aerosols in the urban atmosphere of Valladolid

2005 ◽  
Vol 5 (10) ◽  
pp. 2739-2748 ◽  
Author(s):  
S. Mogo ◽  
V. E. Cachorro ◽  
A. M. de Frutos
Keyword(s):  
Mass Fraction ◽  
Fine Particles ◽  
Aerosol Particles ◽  
Cascade Impactor ◽  
Urban Atmosphere ◽  
Coarse Particles ◽  
X Ray ◽  
Illumination System ◽  
Inverse Power Law

Abstract. Samples of atmospheric aerosol particles were collected in Valladolid, Spain, during the winter of 2003-2004. The measurements were made with a Dekati PM10 cascade impactor with four size stages: greater than 10 µm, between 2.5 to 10 µm, 1 to 2.5 µm and less than 1 µm. The size and shape of the particles were analyzed with a scanning electron microscope (SEM) and elemental analysis was done with an energy dispersive x-ray analysis (EDX). We present an evaluation by size, shape and composition of the major particulate species in the Valladolid urban atmosphere. The total aerosol concentration is very variable, ranging from 39.86 µg·m-3 to 184.88 µg·m-3 with the coarse particles as the dominant mass fraction. Emphasis was given to fine particles (<1 µm), for which the visible (400 nm to 650 nm) light absorption coefficients were measured using the integrating plate technique. We have made some enhancements in the illumination system of this measurement system. The absorption coefficient, σa, is highly variable and ranges from 7.33×10-6 m-1 to 1.01×10-4 m-1 at a wavelength of 550 nm. There is an inverse power law relationship between σa and wavelength, with an average exponent of -0.8.

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