scholarly journals Pressureless sintering behavior of injection molded alumina ceramics

2014 ◽  
Vol 46 (1) ◽  
pp. 3-13 ◽  
Author(s):  
W. Liu ◽  
Z. Xie
Keyword(s):  
Detrimental Effect ◽  
Pore Space ◽  
Critical Role ◽  
Solid Loading ◽  
Sintering Behavior ◽  
Alumina Powder ◽  
Pressureless Sintering ◽  
Alumina Ceramics ◽  
Injection Molded ◽  
Full Densification

The pressureless sintering behaviors of two widely used submicron alumina (MgOdoped and undoped) with different solid loadings produced by injection molding have been studied systematically. Regardless of the sinterability of different powders depending on their inherent properties, solid loading plays a critical role on the sintering behavior of injection molded alumina, which greatly determines the densification and grain size, and leads to its full densification at low temperatures. As compared to the MgO-doped alumina powder, the undoped specimens exhibit a higher sinterability for its smaller particle size and larger surface area. While full densification could be achieved for MgO-doped powders with only a lower solid loading, due to the fact that MgO addition can reduce the detrimental effect of the large pore space on the pore-boundary separation.

Effect of TiO2 and MgO on Microstructure of α-Alumina Ceramics and its Sintering Behavior

2015 ◽  
Vol 1112 ◽  
pp. 519-523 ◽  
Author(s):  
Jarot Raharjo ◽  
Sri Rahayu ◽  
Tika Mustika ◽  
Masmui ◽  
Dwi Budiyanto
Keyword(s):  
Mechanical Properties ◽  
Sintering Temperature ◽  
Physical And Mechanical Properties ◽  
Basic Material ◽  
Sintering Behavior ◽  
Pressureless Sintering ◽  
Alumina Ceramics ◽  
Density Measurements ◽  
Technical Alumina ◽  
Platelet Structure

Observation on the effect of adding titanium oxide (TiO2) and magnesium oxide (MgO) on the sintering of α-alumina (Al2O3) has been performed. In this study, technical alumina used as basic material in which the sample is formed by the pressureless sintering/cold press and sintered at 1500°C which is lower than alumina sintering temperature at 1700°C. Elemental analysis, observation of microstructure, hardness, fracture toughness and density measurements were carried out to determine the physical and mechanical properties of alumina. The results indicate a change in the microstructure where the content of the platelet structure are much more than the equilateral structure. At sintering temperature of 1500°C, neck growth occurs at ceramics grain, supported by the results of the density test which indicate perfect compaction has occurred in this process.

Milling and Sintering Behavior of the Metal-Ceramic Mixed Powders

2007 ◽  
Vol 534-536 ◽  
pp. 93-96
Author(s):  
Z. X. Yang ◽  
Sang Heum Youn ◽  
Kyu Hong Hwang ◽  
Seog Young Yoon ◽  
Jong Kook Lee ◽  
...  
Keyword(s):  
Sintering Behavior ◽  
Alumina Powder ◽  
Reaction Sintering ◽  
Alumina Ceramics ◽  
Mixed Powder ◽  
Attrition Milling ◽  
Alumina Particles ◽  
Metal Ceramic ◽  
Milling Characteristics ◽  
Firing Shrinkage

The reaction-sintered alumina ceramics with low firing shrinkage were prepared from Al/Al2O3 powder mixture by attrition milling and the effect of milling characteristics of raw powders on reaction sintering was investigated. Powder mixtures of flaky shape Al with coarse alumina was much more effectively comminuted by the attrition milling than the mixtures of globular shape Al with coarse alumina powders. Furthermore the coarse alumina was much more useful in pulverizing and grinding the ductile Al particles than fine alumina. After attrition milling and isopressing at 400MPa, the Al/Al2O3 specimen was oxidized at 1200°C for 8 hours followed by sintering at 1550°C for 3 hours. Because mixed powder of coarse alumina with flaky Al was much more effectively comminuted than the globular Al, sintered body of more than 97% theoretical density was achieved, but low contents of Al leads to relatively higher shrinkage of about 8%. As the coarse alumina particles are much more useful in cutting and reducing the ductile Al particles, the use of the coarse alumina powder was much more effective in reaction-sintering.

Processing and Analysis of Ceramic Mesoscale Combustors Fabricated by Co-Extrusion

2013 ◽  
Author(s):  
Khurshida Sharmin ◽  
Ingmar Schoegl
Keyword(s):  
Solvent Extraction ◽  
Carbon Black ◽  
Crack Formation ◽  
Pore Space ◽  
Thermo Gravimetric Analysis ◽  
Functionally Graded ◽  
Full Density ◽  
Alumina Powder ◽  
Gravimetric Analysis ◽  
Thermal Debinding

In this work, millimeter-scale tubular combustion channels were fabricated from ceramic precursor materials. Co-extrusion of structured feedrods holds promise for the development of multi-layered, functionally graded and/or textured combustor walls, but requires a polymer binder that is difficult to remove before structures can be sintered to full density. In conventional thermal debinding, cracking is a major issue, where crack formation is attributed to a lack of pore space for outgassing of pyrolysis products. The main focus of this study is to validate a manufacturing process that uses a combination of solvent de-binding and thermal debinding, which is applied to a simple combustor geometry. Alumina powder was batched with a mixture of polyethylene butyl-acrylate (PEBA) and polyethylene glycol (PEG) in a torque rheometer. A 19mm feedrod, consisting of a carbon-black/binder mixture as core, and a surrounding ceramic/binder mixture forming the wall, was extruded through a 5.84 mm die. The binder removal involves two processing steps, where the PEG content was removed by solvent extraction (SE) to initiate pore formation, after which thermal de-binding by pyrolysis removes the remaining binder and carbon-black. Solvent extraction was performed in water at three different temperatures for various times. The 1:1 mixture of PEG:PEBA showed the highest PEG removal of 80wt% for 6 hrs extraction. The thermal de-binding cycle was designed based on thermo-gravimetric analysis (TGA) and successfully performed with a ramping rate of 1.25°C/min to 1000°C without any crack formation. After de-binding, samples were sintered at 1600°C for 1 hr. SEM analysis showed some void spaces in the solvent extracted samples but confirmed that solvent extraction followed by thermal de-binding yielded the best results. The viability of sintered ceramic tubes was tested for conditions typical for thermal cycling in a combustion environment.

scholarly journals Synthesis and Research of Alumina Ceramics Properties

2020 ◽  
Vol 8 (1) ◽  
pp. 20218102
Author(s):  
Evgeniy I. Frolov ◽  
Polina V. Notina ◽  
Sergey V. Zvonarev ◽  
Evgeniya A. Il'ina ◽  
Vyacheslav Yu. Churkin
Keyword(s):  
Optical Properties ◽  
Sol Gel ◽  
Aluminum Nitrate ◽  
Alumina Powder ◽  
Alumina Ceramics ◽  
Powder Synthesis ◽  
Gel Method ◽  
Varying Parameters ◽  
Luminescence Efficiency ◽  
F Center

The article describes in detail alumina powder synthesis by different methods at varying parameters. The technique of obtaining ceramics and the research of the optical properties for determining the materials with the maximum luminescence efficiency is presented. The concentration of the luminescence intrinsic centers and various defects differ for ceramics synthesized by different methods. It is determined that ceramics based on the powder synthesized by a sol-gel method has the maximum thermoluminescence intensity in the F-center peak, whereas for the peak of 360 °C it is obtained with the powder prepared by precipitation of aluminum nitrate with a PEG‑20000 stabilizer.

Sintering behavior and mechanical properties of a metal injection molded Ti–Nb binary alloy as biomaterial

2015 ◽  
Vol 640 ◽  
pp. 393-400 ◽  
Author(s):  
Dapeng Zhao ◽  
Keke Chang ◽  
Thomas Ebel ◽  
Hemin Nie ◽  
Regine Willumeit ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Binary Alloy ◽  
Sintering Behavior ◽  
Injection Molded

Stability of alumina ceramics bonded with nanoscaled alumina powder

1999 ◽  
Vol 12 (5-8) ◽  
pp. 1041-1044 ◽  
Author(s):  
R.J. Hellmig ◽  
J.-F. Castagnet ◽  
H. Ferkel
Keyword(s):  
Alumina Powder ◽  
Alumina Ceramics

Debinding Behaviors and Mechanism of Injection Molded ZrO2 Ceramics Using Kerosene as Solvents

2012 ◽  
Vol 512-515 ◽  
pp. 431-434 ◽  
Author(s):  
Wei Liu ◽  
Zhi Peng Xie ◽  
Li Li Zhang ◽  
Xian Feng Yang
Keyword(s):  
Reaction Rate ◽  
Low Cost ◽  
Controlling Factor ◽  
Solid Loading ◽  
Concentration Difference ◽  
Initial Stage ◽  
Low Toxicity ◽  
Injection Molded ◽  
Increasing Temperature ◽  
Main Factor

In this study, low-cost kerosene with low toxicity was used as organic solvent to research the solvent debinding behavior of ceramic compact produced by injection molding. The Influences of time, temperature and solid loading on the debinding rate were investigated, the mechanism of which was also discussed. The results show that: The debinding rate increased with increasing temperature and decreased with extended time; Diffusion is the controlling factor at the initial stage and temperature was the main factor influencing the reaction rate; Dissolution is the controlling factor and concentration difference was the main factor at the later stage; The higher the solid loading of green body, the slower the debinding rate and the lower the final proportion of binder removal.

scholarly journals Factors influencing test porosity in planktonic foraminifera

2018 ◽  
Vol 15 (21) ◽  
pp. 6607-6619 ◽  
Author(s):  
Janet E. Burke ◽  
Willem Renema ◽  
Michael J. Henehan ◽  
Leanne E. Elder ◽  
Catherine V. Davis ◽  
...  
Keyword(s):  
Fossil Record ◽  
Pore Space ◽  
Planktonic Foraminifera ◽  
Critical Role ◽  
Environmental Drivers ◽  
Geochemical Data ◽  
Test Surface ◽  
Metabolic Rates ◽  
Pore Characteristics ◽  
Test Volume

Abstract. The clustering of mitochondria near pores in the test walls of foraminifera suggests that these perforations play a critical role in metabolic gas exchange. As such, pore measurements could provide a novel means of tracking changes in metabolic rate in the fossil record. However, in planktonic foraminifera, variation in average pore area, density, and porosity (the total percentage of a test wall that is open pore space) have been variously attributed to environmental, biological, and taxonomic drivers, complicating such an interpretation. Here we examine the environmental, biological, and evolutionary determinants of pore characteristics in 718 individuals, representing 17 morphospecies of planktonic foraminifera from 6 core tops in the North Atlantic. Using random forest models, we find that porosity is primarily correlated to test surface area, test volume, and habitat temperature, key factors in determining metabolic rates. In order to test if this correlation arose spuriously through the association of cryptic species with distinct biomes, we cultured Globigerinoides ruber in three different temperature conditions, and found that porosity increased with temperature. Crucially, these results show that porosity can be plastic: changing in response to environmental drivers within the lifetime of an individual foraminifer. This demonstrates the potential of porosity as a proxy for foraminiferal metabolic rates, with significance for interpreting geochemical data and the physiology of foraminifera in non-analog environments. It also highlights the importance of phenotypic plasticity (i.e., ecophenotypy) in accounting for some aspects of morphological variation in the modern and fossil record.

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