Accelerated sintering and phase transformation of TiO2in microwave radiation

1998 ◽  
Vol 13 (12) ◽  
pp. 3417-3422 ◽  
Author(s):  
Zhi-Peng Xie ◽  
Xu-Dong Fan ◽  
Yong Huang
Keyword(s):  
Phase Transformation ◽  
Microwave Radiation ◽  
Dwell Time ◽  
High Density ◽  
Sintering Process ◽  
Grain Sizes ◽  
Refined Microstructure ◽  
Lower Temperature ◽  
Powder Compacts ◽  
Heating Behavior

The sintering process and phase transformation of submicrometer powder compacts of TiO2 were investigated using 2.45 GHz microwave radiation. The microwave-sintered samples were densified more rapidly and at much shorter time and lower temperature than that of the conventionally sintered samples. Also, an accelerated phase transformation from anatase to rutile was observed in microwave processing when the dwell time is cut down from 6 h in conventional to 30 min in microwave at 1000 °C. The samples sintered in microwave show a refined microstructure and smaller grain sizes at high density near 98–99% theoretical. In addition, the reasons for rapidly heating behavior and enhanced sintering on TiO2 in microwave are discussed.

The Governance of Sintering Regimes on the Properties and Ageing Resistance of Y-TZP Ceramic

2012 ◽  
Vol 545 ◽  
pp. 81-87 ◽  
Author(s):  
Sivakumar Sivanesan ◽  
Ramesh Singh ◽  
Chin Kong Leong
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Phase Transformation ◽  
Low Temperature ◽  
Dwell Time ◽  
Superheated Steam ◽  
Xrd Analysis ◽  
Sintering Process ◽  
Monoclinic Symmetry ◽  
The Poor

The retention of nanometric microstructures is a challenge in any presureless sintering process. Grain size influences mechanical properties and grain coarsening retards densification upon sintering, thus resulting in the poor overall product properties. Hence, it is important to select, among others a suitable sintering regime which promotes densification and retards microstructure coarsening. In this work, Y-TZP ceramic bodies were fabricated under four different sintering regimes to investigate the governance of conventional Single-Stage Sintering (SSS) with 1 min and 2 h dwell time, and comparing their performance with bodies produced by Two-Stage Sintering (TSS). It was revealed that TSS sintered samples, yielded better properties than the SSS samples sintered at 1400°C with a dwell time of 2 hours. In the hydrothermal ageing test, TSS samples did not undergo the low-temperature degradation via the martensitic phase transformation of tetragonal to monoclinic symmetry. Nevertheless, it was found by XRD analysis that Y-TZP ceramics sintered by the SSS method using a short dwell time of 1 minute was effective in maintaining the tetragonal phase stability after 50 hours of exposure in superheated steam conditions.

scholarly journals Phase Transformation of Kaolin-Ground Granulated Blast Furnace Slag from Geopolymerization to Sintering Process

2021 ◽  
Vol 7 (3) ◽  
pp. 32
Author(s):  
Noorina Hidayu Jamil ◽  
Mohd. Mustafa Al Bakri Abdullah ◽  
Faizul Che Pa ◽  
Mohamad Hasmaliza ◽  
Wan Mohd Arif W. Ibrahim ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Blast Furnace ◽  
Blast Furnace Slag ◽  
Room Temperature ◽  
Curing Temperature ◽  
Curing Process ◽  
Sintering Process ◽  
Granulated Blast Furnace Slag ◽  
Fluxing Agent ◽  
Furnace Slag

The main objective of this research was to investigate the influence of curing temperature on the phase transformation, mechanical properties, and microstructure of the as-cured and sintered kaolin-ground granulated blast furnace slag (GGBS) geopolymer. The curing temperature was varied, giving four different conditions; namely: Room temperature, 40, 60, and 80 °C. The kaolin-GGBS geopolymer was prepared, with a mixture of NaOH (8 M) and sodium silicate. The samples were cured for 14 days and sintered afterwards using the same sintering profile for all of the samples. The sintered kaolin-GGBS geopolymer that underwent the curing process at the temperature of 60 °C featured the highest strength value: 8.90 MPa, and a densified microstructure, compared with the other samples. The contribution of the Na2O in the geopolymerization process was as a self-fluxing agent for the production of the geopolymer ceramic at low temperatures.

Novel high-entropy alloys with high-density ε-D019 and abnormal phase transformation

2021 ◽  
Vol 199 ◽  
pp. 113893
Author(s):  
G.H. Xia ◽  
Z.L. Ma ◽  
Z.Q. Xu ◽  
M. Wang ◽  
X.W. Cheng ◽  
...  
Keyword(s):  
Phase Transformation ◽  
High Density ◽  
High Entropy Alloys ◽  
High Entropy

Effects of nano-AlN on phase transformation of low temperature vitrified bond during sintering process

2009 ◽  
Vol 19 ◽  
pp. s706-s710 ◽  
Author(s):  
Yong SHANG ◽  
Yong-gai HOU ◽  
Gui-ying QIAO ◽  
Wen-jun ZOU ◽  
Fu-ren XIAO ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Low Temperature ◽  
Sintering Process ◽  
Vitrified Bond

scholarly journals Effects of temperatures on pressure-induced structural changes in amorphous Si: A molecular-dynamics study

10.29007/6kp3 ◽  
2020 ◽  
Author(s):  
Renji Mukuno ◽  
Manabu Ishimaru
Keyword(s):  
Molecular Dynamics ◽  
Phase Transformation ◽  
Amorphous Phase ◽  
Structural Changes ◽  
Interatomic Potential ◽  
Activation Barrier ◽  
Distribution Functions ◽  
High Density ◽  
Angle Distribution ◽  
Dynamics Simulations

The structural changes of amorphous silicon (a-Si) under compressive pressure were examined by molecular-dynamics simulations using the Tersoff interatomic potential. a-Si prepared by melt-quenching methods was pressurized up to 30 GPa under different temperatures (300K and 500K). The density of a-Si increased from 2.26 to 3.24 g/cm3 with pressure, suggesting the occurrence of the low-density to high-density amorphous phase transformation. This phase transformation occurred at the lower pressure with increasing the temperature because the activation barrier for amorphous-to-amorphous phase transformation could be exceeded by thermal energy. The coordination number increased with pressure and time, and it was saturated at different values depending on the pressure. This suggested the existence of different metastable atomic configurations in a-Si. Atomic pair-distribution functions and bond-angle distribution functions suggested that the short-range ordered structure of high-density a-Si is similar to the structure of the high-pressure phase of crystalline Si (β-tin and Imma structures).

scholarly journals Effect of porosity and particle size on microwave heating of copper

2010 ◽  
Vol 42 (2) ◽  
pp. 169-182 ◽  
Author(s):  
A. Mondal ◽  
A. Shukla ◽  
A. Upadhyaya ◽  
D. Agrawal
Keyword(s):  
Particle Size ◽  
Particle Sizes ◽  
Metallic Materials ◽  
Bulk Materials ◽  
Microwave Furnace ◽  
Particulate Form ◽  
Heating Profiles ◽  
Powder Compacts ◽  
Heating Behavior ◽  
Difference Time

The present study investigates the effect of varying particle size and porosity on the heating behavior of a metallic particulate compact in a 2.45GHz multimode microwave furnace. Experiments on copper suggest that unlike monolithic (bulk) materials, metallic materials do couple with microwaves when they are in particulate form. The powder compacts having higher porosity and smaller particle sizes interact more effectively with microwaves and are heated more rapidly. A dynamic electromagnetic-thermal model was developed to simulate the temporal temperature distribution using a 2-D finite difference time domain (FDTD) approach. The model predicts the variation in temperature with time during heating of copper powder compacts. The simulated heating profiles correlate well with those observed from experiments.

scholarly journals Sintering of a fine-grained BaCeO3 powder obtained from a co-precipitation method

2018 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Precursor Powder ◽  
Coarse Grained ◽  
Precipitation Method ◽  
Fine Grained ◽  
Grain Sizes ◽  
Three Phase ◽  
Sintering Behaviour ◽  
Co Precipitation ◽  
Precursor Powders ◽  
Powder Compacts

The formation of BaCeO3 by a co-precipitation method is described herein. The coprecipitationroute leads to an orange (BaCe)-precursor powder (1). To improve the sinteringbehaviour, a small amount of Ge4+ was incorporated, leading to a (BaCe0.95/Ge0.05)-precursor(2). Both precursor powders results in fine-grained preceramic powders (1A, 2A) aftercalcination. The shrinkage and sintering behaviour of resulting powder compacts were studiedin comparison to a coarse-grained mixed-oxide BaCeO3 powder (3). Compacts of 2A reach arelative density of 90 % after sintering at 1350 °C with grain-sizes between 0.9−3.2 μm. Onthe other hand ceramics of 1A and 3 have, after sintering at 1500 °C (10 h), relative densitiesof 85 % and 76 %, respectively. Ceramic bodies of 1A consisted of phase-pure orthorhombicBaCeO3, whereas bodies of 2A show reflections of BaCeO3 and a Ba2GeO4 phase. DTAinvestigations of samples 1A and 2A reveal three phase transitions at 255 °C (1A) and 256 °C (2A) as well as 383 °C (1A) and 380 °C (2A). A very weak one can be obtained in the range880−910 °C

Mechanochemical Polymorphic Transformation of Photocatalyst Material TiO2 and its Dependence on the Milling Operation

2011 ◽  
Vol 675-677 ◽  
pp. 283-286
Author(s):  
Guo Min Mi ◽  
Fumio Saito
Keyword(s):  
Phase Transformation ◽  
Titanium Dioxide ◽  
Polymorphic Transformation ◽  
Metastable Phase ◽  
Planetary Mill ◽  
Wet Grinding ◽  
Dry Grinding ◽  
Milling Operation ◽  
Lower Temperature ◽  
Tumbling Mill

Some dry and wet grinding experiments have been respectively conducted on titanium dioxide which is a noble photocatalyst material in a mortar, a tumbling mill and a planetary mill. Anatase is apt to transform to rutile via a metastable phase brookite in every kind of mills in the case of dry grinding. And it hardly takes place for phase transformation from rutile to other forms. It is shown that the kind of mill has not decisive effect on the mechanochemical polymorphic transformation of titanium dioxide, which merely influences the rate of phase transformation. On the other hand, the addition of other liquid media, such as water and acetone, is helpless for phase transformation of anatase. Only anatase can transform to metastable phase brookite by wet grinding. When ground titanium dioxide is heated, the amorphous phase is easier to transform to rutile than metastable phase brookite at lower temperature.

scholarly journals Flame Retardancy of High-Density Polyethylene Composites with P,N-Doped Cellulose Fibrils

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 336 ◽  
Author(s):  
Shuai Zhang ◽  
He Chen ◽  
Yin Zhang ◽  
Yi-meng Zhang ◽  
Weiyan Kan ◽  
...  
Keyword(s):  
Flame Retardancy ◽  
High Density Polyethylene ◽  
High Density ◽  
One Pot ◽  
Peak Heat Release Rate ◽  
Cellulose Fibrils ◽  
Acid Catalyzed ◽  
Lower Temperature ◽  
Cellulose Surface ◽  
Phosphate Groups

To derive P,N-doped cellulose fibrils, phosphoric acid and aqueous ammonia were placed in a one-pot reaction, and the phosphate groups and ammonium phosphates were successfully introduced into the cellulose surface. The obtained P,N-doped cellulose fibrils with high liberation were thereafter incorporated into a high-density polyethylene (HDPE) matrix to improve the flame retardancy of HDPE composites, and they had a significant improvement on flame retardancy of HDPE composites. In particular, 7 wt % P,N-doped cellulose fibrils considerably reduced the average and peak heat release rate (HRR) by 29.6% and 72.9%, respectively, and increased the limited oxygen index (LOI) by 30.5%. The presence of phosphate groups and ammonium phosphates within P,N-doped cellulose fibrils was found to promote the thermal degradation of HDPE composites at a lower temperature (i.e., 240 °C). The released acid catalyzed the dehydration of cellulose to form an aromatic carbonaceous structure with a higher crystalline orientation, which improves the flame retardancy of HDPE composites.

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