Awais Qadir | Technische Universität Bergakademie Freiberg (original) (raw)

Papers by Awais Qadir

Research paper thumbnail of Tribology of Si3N4 containing in-situ grown Si2N2O processed from oxidized α - Si3N4 powders

Ceramics International, 2021

Silicon nitride ceramics containing in-situ grown Si 2 N 2 O were prepared from oxidized silicon ... more Silicon nitride ceramics containing in-situ grown Si 2 N 2 O were prepared from oxidized silicon nitride powders by hot isostatic pressing (HIP) at 1500 • C and 1700 • C in a nitrogen gas environment under 20 MPa for 3 h. In case of systems sintered at 1700 • C, the volume fraction of the silicon oxynitride (Si 2 N 2 O) increased, and the β-Si 3 N 4 phase decreased with the increase of oxidation time. The tribological behavior of the materials was studied by the ball-on-disc method under dry sliding conditions at room temperature under an applied load of 5 N with a sliding speed of 0.05 m/s using Si 3 N 4 ball as a tribo-partner. For the systems sintered at 1700 • C, the coefficient of friction (COF) values were between 0.8 and 0.76 at the start, and started decreasing with the increasing sliding distance, at 1000 m of sliding distance the values were between 0.65 and 0.6. The lowest COF value was measured for the system with unoxidized α-Si 3 N 4 powder sintered at 1700 • C with the value of 0.65. The lowest wear rate, 1.224 x 10-4 mm 3 /N•m, was measured for the system with 10 h oxidized α-Si 3 N 4 powder sintered at 1500 • C. Fractographical analyses of the wear track revealed that the main wear mechanisms were abrasive wear with grain pull-out, micro-cracking, and debris formation together with tribo-film formation. Lin et al. [14] produced porous Si 2 N 2 O ceramics from α-Si 3 N 4 and SiO 2 powders with different amounts of Li 2 CO 3 as a sintering aid

Research paper thumbnail of Silicon Nitride-Based Composites with the Addition of CNTs—A Review of Recent Progress, Challenges, and Future Prospects

Materials

In this overview, the results published to date concerning the development, processing, microstru... more In this overview, the results published to date concerning the development, processing, microstructure characteristics, and properties of silicon nitride/carbon nanotube (Si3N4 + CNTs) composites are summarized. The influence of the different processing routes on the microstructure development of the Si3N4 + CNTs is discussed. The effects of the CNTs addition on the mechanical properties—hardness, bending strength and fracture toughness—and tribological characteristics—wear rate and coefficient of friction—are summarized. The characteristic defects, fracture origins, toughening and damage mechanisms occurring during the testing are described. The influence of the CNTs’ addition on the thermal and functional properties of the composites is discussed as well. New trends in the development of these composites with significant potential for future applications are outlined.

Research paper thumbnail of Effect of the oxidization of Si3N4 powder on the microstructural and mechanical properties of hot isostatic pressed silicon nitride

Ceramics International, Aug 1, 2018

The effect of nanosized oxidized silicon nitride powder particles on the microstructural and mech... more The effect of nanosized oxidized silicon nitride powder particles on the microstructural and mechanical properties of hot isostatic pressed silicon nitride was studied. The starting Si 3 N 4 powders were oxidized for 10 and 20 h at 1000 ˚C in ambient air environment. An amorphous oxide layer was observed on the surface of Si 3 N 4 powder particles using high resolution transmission electron microscopy (HRTEM) whose thickness increased with the oxidation time. The powders were hot isostatic pressed at 1500 ˚C and 1700 ˚C in nitrogen gas environment under 20 Mpa for 3h. Complete to transformation was observed in Si 3 N 4 samples sintered at 1700 C under 20 MPa for 3 h compared to Si 3 N 4 samples sintered at 1500 ˚C. Silicon oxynitride (Si 2 N 2 O) was found in sintered samples whose amount increased with the oxidation time. The phase decreased with the increase of Si 2 N 2 O phase in the sintered samples. The flexural strength of samples sintered at 1700 ˚C is higher due to the higher amount of -Si 3 N 4 phase than for samples sintered at 1500 ˚C. Decreasing flexural strength was observed with the oxidation time. Higher amount of oxygen in the base powders resulted in a higher Si 2 N 2 O content in the sintered Si 3 N 4 .

Research paper thumbnail of Visible thermochromism in vanadium pentoxide coatings

ACS applied materials & interfaces, Jan 31, 2017

Although di-vanadium pentoxide (V2O5) has been a candidate of extensive research for over half a ... more Although di-vanadium pentoxide (V2O5) has been a candidate of extensive research for over half a century, its intrinsic thermochromism has not been reported so far. Films of V2O5 grown on silicon, glass and metal substrates by MOCVD in this study, exhibit a thermally induced perceptible color change from bright yellow to deep orange. Temperature-dependent UV-Vis spectroscopy and XRD allow the correlation between the reversible continuous red shift of the absorption and the anisotropic thermal expansion along the (001) direction, i.e. perpendicular to the sheets constituting the layered structure. Furthermore, the possibility of tuning the thermochromic behavior was demonstrated via a chemical doping with chromium.

Research paper thumbnail of Properties of MWCNTs added Si3N4 composites processed from oxidized silicon nitride powders

Processing and Application of Ceramics, 2020

Si 3 N 4 /3 wt.% multi-walled carbon nanotubes (MWCNTs) composites were prepared from oxidized α-... more Si 3 N 4 /3 wt.% multi-walled carbon nanotubes (MWCNTs) composites were prepared from oxidized α-Si 3 N 4 powders and sintering additives by hot isostatic pressing (HIP). The Si 3 N 4 powders were oxidized at 1000°C in ambient air environment for 10 and 20 h and the powder mixture was sintered at 1700°C for 3 h under the pressure of 20 MPa in nitrogen. The relationship between oxidation, microstructure, tribology and mechanical properties was studied. The dispersion of MWCNTs was not optimal, as they were found mainly in the form of bundles between the β-Si 3 N 4 grains. Neither Si 2 N 2 O nor other oxide phase were observed after the sintering. This was probably caused by the presence of MWCNTs at the grain boundaries of the Si 3 N 4 grains causing reduction of oxide phases. The density, hardness, bending strengths and friction coefficient of the composites increased with the oxidation time of the Si 3 N 4 powder.

Research paper thumbnail of Tribology of Si3N4 containing in-situ grown Si2N2O processed from oxidized α - Si3N4 powders

Ceramics International, 2021

Silicon nitride ceramics containing in-situ grown Si 2 N 2 O were prepared from oxidized silicon ... more Silicon nitride ceramics containing in-situ grown Si 2 N 2 O were prepared from oxidized silicon nitride powders by hot isostatic pressing (HIP) at 1500 • C and 1700 • C in a nitrogen gas environment under 20 MPa for 3 h. In case of systems sintered at 1700 • C, the volume fraction of the silicon oxynitride (Si 2 N 2 O) increased, and the β-Si 3 N 4 phase decreased with the increase of oxidation time. The tribological behavior of the materials was studied by the ball-on-disc method under dry sliding conditions at room temperature under an applied load of 5 N with a sliding speed of 0.05 m/s using Si 3 N 4 ball as a tribo-partner. For the systems sintered at 1700 • C, the coefficient of friction (COF) values were between 0.8 and 0.76 at the start, and started decreasing with the increasing sliding distance, at 1000 m of sliding distance the values were between 0.65 and 0.6. The lowest COF value was measured for the system with unoxidized α-Si 3 N 4 powder sintered at 1700 • C with the value of 0.65. The lowest wear rate, 1.224 x 10-4 mm 3 /N•m, was measured for the system with 10 h oxidized α-Si 3 N 4 powder sintered at 1500 • C. Fractographical analyses of the wear track revealed that the main wear mechanisms were abrasive wear with grain pull-out, micro-cracking, and debris formation together with tribo-film formation. Lin et al. [14] produced porous Si 2 N 2 O ceramics from α-Si 3 N 4 and SiO 2 powders with different amounts of Li 2 CO 3 as a sintering aid

Research paper thumbnail of Silicon Nitride-Based Composites with the Addition of CNTs—A Review of Recent Progress, Challenges, and Future Prospects

Materials

In this overview, the results published to date concerning the development, processing, microstru... more In this overview, the results published to date concerning the development, processing, microstructure characteristics, and properties of silicon nitride/carbon nanotube (Si3N4 + CNTs) composites are summarized. The influence of the different processing routes on the microstructure development of the Si3N4 + CNTs is discussed. The effects of the CNTs addition on the mechanical properties—hardness, bending strength and fracture toughness—and tribological characteristics—wear rate and coefficient of friction—are summarized. The characteristic defects, fracture origins, toughening and damage mechanisms occurring during the testing are described. The influence of the CNTs’ addition on the thermal and functional properties of the composites is discussed as well. New trends in the development of these composites with significant potential for future applications are outlined.

Research paper thumbnail of Effect of the oxidization of Si3N4 powder on the microstructural and mechanical properties of hot isostatic pressed silicon nitride

Ceramics International, Aug 1, 2018

The effect of nanosized oxidized silicon nitride powder particles on the microstructural and mech... more The effect of nanosized oxidized silicon nitride powder particles on the microstructural and mechanical properties of hot isostatic pressed silicon nitride was studied. The starting Si 3 N 4 powders were oxidized for 10 and 20 h at 1000 ˚C in ambient air environment. An amorphous oxide layer was observed on the surface of Si 3 N 4 powder particles using high resolution transmission electron microscopy (HRTEM) whose thickness increased with the oxidation time. The powders were hot isostatic pressed at 1500 ˚C and 1700 ˚C in nitrogen gas environment under 20 Mpa for 3h. Complete to transformation was observed in Si 3 N 4 samples sintered at 1700 C under 20 MPa for 3 h compared to Si 3 N 4 samples sintered at 1500 ˚C. Silicon oxynitride (Si 2 N 2 O) was found in sintered samples whose amount increased with the oxidation time. The phase decreased with the increase of Si 2 N 2 O phase in the sintered samples. The flexural strength of samples sintered at 1700 ˚C is higher due to the higher amount of -Si 3 N 4 phase than for samples sintered at 1500 ˚C. Decreasing flexural strength was observed with the oxidation time. Higher amount of oxygen in the base powders resulted in a higher Si 2 N 2 O content in the sintered Si 3 N 4 .

Research paper thumbnail of Visible thermochromism in vanadium pentoxide coatings

ACS applied materials & interfaces, Jan 31, 2017

Although di-vanadium pentoxide (V2O5) has been a candidate of extensive research for over half a ... more Although di-vanadium pentoxide (V2O5) has been a candidate of extensive research for over half a century, its intrinsic thermochromism has not been reported so far. Films of V2O5 grown on silicon, glass and metal substrates by MOCVD in this study, exhibit a thermally induced perceptible color change from bright yellow to deep orange. Temperature-dependent UV-Vis spectroscopy and XRD allow the correlation between the reversible continuous red shift of the absorption and the anisotropic thermal expansion along the (001) direction, i.e. perpendicular to the sheets constituting the layered structure. Furthermore, the possibility of tuning the thermochromic behavior was demonstrated via a chemical doping with chromium.

Research paper thumbnail of Properties of MWCNTs added Si3N4 composites processed from oxidized silicon nitride powders

Processing and Application of Ceramics, 2020

Si 3 N 4 /3 wt.% multi-walled carbon nanotubes (MWCNTs) composites were prepared from oxidized α-... more Si 3 N 4 /3 wt.% multi-walled carbon nanotubes (MWCNTs) composites were prepared from oxidized α-Si 3 N 4 powders and sintering additives by hot isostatic pressing (HIP). The Si 3 N 4 powders were oxidized at 1000°C in ambient air environment for 10 and 20 h and the powder mixture was sintered at 1700°C for 3 h under the pressure of 20 MPa in nitrogen. The relationship between oxidation, microstructure, tribology and mechanical properties was studied. The dispersion of MWCNTs was not optimal, as they were found mainly in the form of bundles between the β-Si 3 N 4 grains. Neither Si 2 N 2 O nor other oxide phase were observed after the sintering. This was probably caused by the presence of MWCNTs at the grain boundaries of the Si 3 N 4 grains causing reduction of oxide phases. The density, hardness, bending strengths and friction coefficient of the composites increased with the oxidation time of the Si 3 N 4 powder.