scholarly journals Effect of microwave conditions on sintering of hydroxyapatite ceramics

2020 ◽  
Vol 52 (4) ◽  
pp. 469-479
Author(s):  
A. Faeghinia ◽  
T. Ebadzadeh
Keyword(s):  
Phase Transformation ◽  
Conventional Method ◽  
Heating Temperature ◽  
Power Level ◽  
Isothermal Holding ◽  
Conventional Process ◽  
Hydroxyapatite Ceramics ◽  
Higher Power ◽  
Tcp Phase

In this work, Hydroxyapatite (HAp) was sintered by microwave and compared with the sintered samples by conventional method. The power levels of microwave were 450, 600, 900 W and the sintering temperatures were in the range from 750 to 1000 ?C without isothermal holding. It was shown that the using of higher power level at the same heating temperature increases the density of sintered samples. Samples sintered in microwave at 1000 ?C by 900 W power reached a higher density of 95 % compared to the conventional process (85 %), however in the case of using 450 W power, the densification trend was almost similar to the conventional one. HAp to TCP phase transformation was not detected at 1000 ?C; however, the preferred growth of (211) planes corresponded to circular morphology was observed. Microstructural observations showed larger grains (500 nm) and porosities (300 nm) in the traditional sintered samples compared to the samples, which were sintered by microwave (200 nm and 100 nm, respectively).

Influence of Zn and Mg Doping on the Sintering Behavior and Phase Transformation of Tricalcium Phosphate Based Ceramics

2014 ◽  
Vol 805 ◽  
pp. 706-711 ◽  
Author(s):  
Karen C. Kai ◽  
Carlos A.V.A. Machado ◽  
Luis Antonio Genova ◽  
Juliana Marchi
Keyword(s):  
Phase Transformation ◽  
Tricalcium Phosphate ◽  
Sintering Behavior ◽  
Drying Process ◽  
Zn Doping ◽  
Wet Chemical Synthesis ◽  
Mg Addition ◽  
Tcp Phase ◽  
Wet Chemical ◽  
Dilatometric Studies

β-tricalcium phosphate based ceramics (β-TCP) are resorbable biomaterials used as bone substitutive materials. Several ions can substitute specific Ca positions in the crystalline structure of TCP, so that general Me-TCP can be obtained. Particularly, magnesium can increase the temperature of β-α-TCP transformation while zinc stimulates the bone formation. In this work, the influence of magnesium or zinc ions on the sintering behavior of Me-TCP was investigated. The powders were produced through wet chemical synthesis with a freeze drying process. The powders were calcined and subsequently uniaxially pressed into pellets. The pellets were sintered up to 1300°C/1h. The influence of Mg or Zn doping was investigated by dilatometric studies, thermal analysis and XRD. The microstructure was evaluated through SEM. The results suggest that Mg increased temperature of β-α-TCP phase transformation. The Me-doped TCP samples can be considered as promising biomaterials, having stimulatory effect of Zn or suitable densification due to Mg addition.

NUMERICAL MODELING OF PHASE TRANSFORMATION DURING GRINDING PROCESS

2017 ◽  
Vol 79 (5) ◽  
Author(s):  
Syed Mushtaq Ahmed Shah ◽  
M. A. Khattak ◽  
Muhammad Asad ◽  
Javed Iqbal ◽  
Saeed Badshah ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Thermal Stresses ◽  
Heating Temperature ◽  
Temperature History ◽  
Grinding Process ◽  
Cooling Rates ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Heating And Cooling

The rapid heating and cooling in a grinding process may cause phase transformations. This will introduce thermal strains and plastic strains simultaneously in a workpiece with substantial residual stresses. The properties of the workpiece material will change when phase transformation occurs. The extent of such change depends on the temperature history experienced and the instantaneous thermal stresses developed. To carry out a reliable residual stress analysis, a comprehensive modelling technique and a sophisticated computational procedure that can accommodate the property change with the metallurgical change of material need to be developed. The objective of this work is to propose a simplified model to predict phase evolution during given temperature history for heating and cooling as encountered during grinding process. The numerical implementation of the proposed model is carried out through the developed FORTRAN subroutine called PHASE using the FEM commercial software Abaqus®/standard. Micro-structural constituents are defined as state variables. They are computed and updated inside the subroutine PHASE. The heating temperature is assumed to be uniform while the cooling characteristics in relation to phase transformations are obtained from the continuous cooling transformation (CCT) diagram of the given material (here AISI 52100 steel). Four metallurgical phases are assumed for the simulations: austenite, pearlite, bainite, and martensite. It was shown that at low cooling rates high percentage of pearlite phase is obtained when the material is heated and cooled to ambient temperature. Bainite is formed usually at medium cooling rates. Similarly at high cooling rates maximum content of martensite may be observed. It is also shown that the continuous cooling transformation kinetics may be described by plotting the transformation temperature, directly against the cooling rate as an alternative to the continuous cooling transformation diagram. The simulated results are also compared with experimental results of Wever [20] and Hunkle [21] and are found to be in a very good agreement. The model may be used for further thermo-mechanical analysis coupled with phase transformation during grinding process.

Ultra-Wideband Solutions for Last Mile Access Network

2009 ◽  
pp. 1443-1452
Author(s):  
Sabira Khatun ◽  
Rashid A. Saeed ◽  
Nor Kamariah Nordin ◽  
Borhanuddin Mohd Ali
Keyword(s):  
Wireless Communications ◽  
Power Efficiency ◽  
Orthogonal Frequency Division Multiplexing ◽  
Mesh Networks ◽  
Power Level ◽  
Average Power ◽  
Ultra Wideband ◽  
Digital Data ◽  
Higher Power ◽  
Power Limit

Ultra-wideband (UWB) is an alternative wireless communications technology that offers high bandwidth wireless communications without the constraints of spectrum allocation. Fundamentally different from conventional radio frequency communications, UWB relies on a series of narrow, precisely timed pulses to transmit digital data. Transmitters and receivers that use UWB can be much simpler to build than their conventional counterparts, resulting in lower cost and higher power efficiency. Moreover, the inherent properties of UWB emissions allow them to potentially coexist with conventional wireless systems on a noninterfering basis. In April 2002, the Federal Communications Commission (FCC) released UWB emission masks and introduced the concept of coexistence with traditional and protected radio services in the frequency spectrum, which allows the operation of UWB systems mainly in the 3.1 to 10.6 GHz band, limiting the power level emission to -41dBm/MHz. Within the power limit allowed under the current FCC regulations, Ultra-wideband can not only carry huge amounts of data over a shortto- medium distance at very low power (this range can be extended by using ad-hoc or mesh networks), but it also has the ability to carry signals through doors and other obstacles that tend to reflect signals at more limited bandwidths and a higher power (Reed, 2005). At higher power levels, UWB signals can travel to significantly greater ranges. In March 2005, the FCC granted the waiver request, filed by the multiband Orthogonal Frequency Division Multiplexing (OFDM) alliance (MBOA), in which it approved the change in measurement for the all UWB technologies (neutral approach) (Barret, 2005). The FCC’s waiver grants effectively removes the previous transmit power penalties for both frequency-hopping (OFDM) and gated UWB technologies (TH and DS). Hence, they are allowed to transmit at higher power levels and then become idle for some time, as long as they meet the limits for average power density. This new rules allow those technologies to achieve up to four times better performance and double the range.

Microwave-Assisted Synthesis of Zinc Oxide Nanoparticles on Paper

2018 ◽  
Vol 775 ◽  
pp. 163-168
Author(s):  
Saberina I. Saberon ◽  
Monet Concepcion Maguyon-Detras ◽  
Maria Victoria P. Migo ◽  
Marvin U. Herrera ◽  
Ronniel D. Manalo
Keyword(s):  
Zinc Oxide ◽  
Zinc Oxide Nanoparticles ◽  
Power Level ◽  
Microwave Assisted Synthesis ◽  
Chemical Transformations ◽  
Paper Substrate ◽  
Microwave Assisted ◽  
Higher Power ◽  
Particle Size And Structure ◽  
Scanning Electron

Nanostructured zinc oxide (ZnO) particles were grown on paper substrate made from Abaca hybrid 7 pulp. Microwave irradiation technique was used at power levels (180 and 540W) and exposure times (5, 10, 20 and 25 minutes). Chemical transformations were observed using Fourier Transform Infrared (FTIR) Spectroscopy. The effects of the power levels and exposure times on the morphology of the nanostructures were determined using scanning electron microscopy. FTIR spectra proved the embedment of ZnO on the paper substrate. Power levels and exposure times affected the distribution, particle size and structure of the ZnO nanoparticles. Higher power level and longer exposure resulted to the formation of more ZnO with larger particles. Grainlike and flowerlike ZnO nanostructures were formed at lower and higher levels, respectively.

Thermal degradation of organic material by portable laser Raman spectrometry

2012 ◽  
Vol 11 (3) ◽  
pp. 177-186 ◽  
Author(s):  
Sanjoy M. Som ◽  
Bernard H. Foing
Keyword(s):  
Thermal Degradation ◽  
Biological Samples ◽  
Signal To Noise Ratio ◽  
Power Level ◽  
Laser Wavelength ◽  
Planetary Exploration ◽  
Integration Time ◽  
Raman Spectrometry ◽  
Laser Raman ◽  
Higher Power

AbstractRaman spectrometry has been established as an instrument of choice for studying the structure and bond type of known molecules, and identifying the composition of unknown substances, whether geological or biological. This versatility has led to its strong consideration for planetary exploration. In the context of the ExoGeoLab and ExoHab pilot projects of ESA-ESTEC & ILEWG (International Lunar Exploration Working Group), we investigated samples of astrobiological interest using a portable Raman spectrometer lasing at 785 nm and discuss implications for planetary exploration. We find that biological samples are typically best observed at wavenumbers >1100 cm−1, but their Raman signals are often affected by fluorescence effects, which lowers their signal-to-noise ratio. Raman signals of minerals are typically found at wavenumbers <1100 cm−1, and tend to be less affected by fluorescence. While higher power and/or longer signal integration time improve Raman signals, such power settings are detrimental to biological samples due to sample thermal degradation. Care must be taken in selecting the laser wavelength, power level and integration time for unknown samples, particularly if Raman signatures of biological components are anticipated. We include in the Appendices tables of Raman signatures for astrobiologically relevant organic compounds and minerals.

scholarly journals Inactivation of Salmonella enteritidis on raw poultry using microwave heating

2005 ◽  
Vol 48 (6) ◽  
pp. 939-945 ◽  
Author(s):  
Amanda B. Pucciarelli ◽  
Fernando O. Benassi
Keyword(s):  
Microwave Heating ◽  
High Power ◽  
Salmonella Enteritidis ◽  
Power Level ◽  
Heating Time ◽  
Higher Power ◽  
Power Setting ◽  
High Power Level ◽  
Raw Poultry ◽  
The Relationship

The effect of microwave heating on Salmonella Enteritidis inoculated on fresh chicken was investigated using a microwave oven (800 w) to determine the destruction of Salmonella Enteritidis isolated from chicken carcasses, in relation to the time of heating at two power settings: high (power level 10) and medium (power level 6); The relationship between heating time and temperature was also been studied. The destruction was 6.4 log cycles at time 95 sec for the high power level, and 5 log cycles at time 140 sec for medium power setting. After 110 sec for higher power level, no survival of Salmonella Enteritidis was detected in samples (100g), but at 140 sec for medium power level, these food pathogens were still present.

scholarly journals Feasibility study of the university of Utah TRIGA reactor power upgrade - part II: Thermohydraulics and heat transfer study in respect to cooling system requirements and design

2013 ◽  
Vol 28 (4) ◽  
pp. 352-361
Author(s):  
Philip Babitz ◽  
Dongok Choe ◽  
Tatjana Jevremovic
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Power Level ◽  
Flow Simulation ◽  
Nucleate Boiling ◽  
Reactor Power ◽  
Convection Current ◽  
Triga Reactor ◽  
Higher Power ◽  
The University

The thermodynamic conditions of the University of Utah's TRIGA Reactor were simulated using SolidWorks Flow Simulation, Ansys, Fluent and PARET-ANL. The models are developed for the reactor's currently maximum operating power of 90 kW, and a few higher power levels to analyze thermohydraulics and heat transfer aspects in determining a design basis for higher power including the cost estimate. It was found that the natural convection current becomes much more pronounced at higher power levels with vortex shedding also occurring. A departure from nucleate boiling analysis showed that while nucleate boiling begins near 210 kW it remains in this state and does not approach the critical heat flux at powers up to 500 kW. Based on these studies, two upgrades are proposed for extended operation and possibly higher reactor power level. Together with the findings from Part I studies, we conclude that increase of the reactor power is highly feasible yet dependable on its purpose and associated investments.

Fabrication of βTCP Foam Using αTCP Foam as a Precursor by Heat Treatment

2012 ◽  
Vol 529-530 ◽  
pp. 15-18
Author(s):  
Taro Nikaido ◽  
Kanji Tsuru ◽  
Giichiro Kawachi ◽  
Melvin L. Munar ◽  
Shigeki Matsuya ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Compressive Strength ◽  
Phase Transformation ◽  
Transition Temperature ◽  
Bone Growth ◽  
Bone Cells ◽  
Heating Temperature ◽  
Extended Period ◽  
Heating Period ◽  
Bone Replacement

The present study reports the synthesis of βTCP foam with fully interconnecting pores based on phase transformation of αTCP foam precursor by employing heat treatment. First, the αTCP foam precursor was fabricated by sintering the ceramics slurry-coated polyurethane foam template at 1,500°C. The resultant αTCP foam was again heated below α,β transition temperature for an extended period of times. After heating at 800°C for 150 hours, 900°C for 100 hours and 1,000°C for 300 hours, βTCP foam was obtained. The compressive strength of βTCP foam was approximately 46 kPa and the porosity was approximately 93%. The long heating period as well as heating temperature were the key to the transformation of βTCP phase. βTCP foam could be an ideal bone replacement since the invasion of bone cells into the pores provides optimum bone growth or repair.

scholarly journals High-Frequency Heat Treatment of AISI 1045 Specimens and Current Calculations of the Induction Heating Coil Using Metal Phase Transformation Simulations

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1484
Author(s):  
Jinkyu Choi ◽  
Seoksoon Lee
Keyword(s):  
Heat Treatment ◽  
Phase Transformation ◽  
Induction Heating ◽  
High Frequency ◽  
Heating Temperature ◽  
Cooling Water ◽  
Metal Phase ◽  
Aisi 1045 ◽  
Simulation And Experiment ◽  
High Frequency Induction

AISI 1045 specimen was compared through a high-frequency heat treatment simulation and experiment considering metal phase transformation. Hardening zone predictions were confirmed through cooling and metal phase transformation simulations after obtaining the results from electromagnetic heat transfer simulations. The cooling process was modeled by applying the cooling coefficient of the cooling water in the same way as the actual heat-treatment process. To obtain the current flowing through the coil during high-frequency induction heating, the voltage was measured and applied using the resistance–inductance–capacitance circuit calculation method. Experimental and simulated results of the heating temperature and curing depth of an AISI 1045 specimen with a carbon content of 0.45% were compared; the comparison indicated good agreement between the two. Using the simulation results, we established a method for obtaining the current flowing through the induction coil for predicting the extent and depth of the hardening zone during high-frequency induction heat treatment.

Research on Heating Element of the Air Heater in the Industrial Practice

2012 ◽  
Vol 461 ◽  
pp. 211-214
Author(s):  
Wei Sheng Liu
Keyword(s):  
High Efficiency ◽  
Heating Temperature ◽  
Heating Element ◽  
Surface Load ◽  
Special Requirement ◽  
Industrial Practice ◽  
Air Heater ◽  
Short Period ◽  
Higher Power ◽  
Industrial Machine

The article introduces a high efficiency heating element of the air heater used in the industrial machine area, which can be used for high power low volume high efficiency air heater. The traditional air heater normally use tubular heating element or nickel-chrome alloy resistive wire wrapped around the mica rack as the heating element. Due to the constraint of the surface load, the power cannot meet the requirement of the industrial machine practice. Meanwhile, the movable air heater has special requirement for the volume and the power. Secondly, the metal sleeve heat resistance wire cannot release heat in the short period, and the life span at high temperature is relative short, this also restraint the heating temperature. The energy loss is quite significant due to the longer heating period. The higher power industrial air heater can effectively solve all the above mentioned problems.

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