mehri mashhadi | Tarbiat Modares University (original) (raw)
Papers by mehri mashhadi
مواد و فناوری های پیشرفته, Nov 22, 2017
In the present paper, ZrB 2-SiC nanocomposite was developed by pressureless sintering method. Mic... more In the present paper, ZrB 2-SiC nanocomposite was developed by pressureless sintering method. Micro sized AlN powder and SiC powderes at nano and micro-sized scale were used as additive. In order to produce composite samples, the primary powders were milled and blended in planetary ball mill apparatus with rotational speed of 200rpm and then processed using hot pressing (80ᵒC and 100MPa), cold isostatic press and sintering at 2150ᵒC. The values of relative density and porosity of samples were measured to evaluate the effect of presence of micro-sized SiC and SiC nano particles simultaneously on the pressureless sintering behavior of ZrB 2-SiC. In order to compare the microstructure and mechanical properties of samples Scanning Electron microscopy (SEM), equipped with EDS spectroscopy, XRD analysis, hardness and toughness tests were used. The results show that as the volume percentage of nano SiC decreases to 15 vol.% and AlN increases to 7.5 vol.% the hardness (17.1 GPa), toughness (5.7 MPa.m 1/2) and relative density (98.1%) increase.
Journal of Ceramic Processing Research, Apr 1, 2019
استقلال, May 1, 2015
In this study, AlN whiskers were prepared in a tube furnace at 1000˚C for 1h with 500 cc min nitr... more In this study, AlN whiskers were prepared in a tube furnace at 1000˚C for 1h with 500 cc min nitrogen gas flow. Al powders with particle size of 3 μm and 45 μm and NH 4 Cl were used as raw materials. SEM, TEM and XRD analysis were used to characterize AlN whiskers. The results showed that the diameters of AlN whiskers would range from 140 nm to 340 nm if different amounts of NH 4 Cl and 3 μm Al powder were used. In the case of using NH 4 Cl more than 40wt%, pure AlN without any unreacted Al was formed as the final product. Using NH 4 Cl and Al with particle size of 45 μm led to AlN whiskers with 630 nm to 870 nm in diameter. By adding 50%wt NH 4 Cl, pure AlN was formed. The diameter of the whiskers was increased by increasing NH 4 Cl content in starting materials (about 200 nm). Also, an increase in the diameter of AlN whisker resulted from coarse Al powder. By adding NH 4 Cl to Al, thermodynamically spontaneous cholororination-nitridation reactions were increased in vapor phase and whiskers and pure AlN powder were produced.
International Journal of Ceramic Engineering & Science
The reason of this study is to synthesize ZrB2 nano powder utilizing boric acid and phenolic resi... more The reason of this study is to synthesize ZrB2 nano powder utilizing boric acid and phenolic resin. Within the study of zirconia as a source of zirconium, boric acid was used as a source of boron and phenolic resin as a carbon source. The theoretical and experimental studies of ZrB2 were synthesized by boro/carbothermal diminishment from the novel sol–gel technology. The zirconia powder was crushed for 8 h and in conjunction with different molar proportions of boric acid, in this consider, a kinetic demonstrate for reactions creating ZrB2 was built up based on thermodynamic analysis. The resultant powder was synthesized in a neutral atmosphere controlled in 1450°C and 1550°C. After it was also observed that, with the increase of molar proportion of H3BO3, the reaction delivered ZrB2 powders in high amount of the boron reaction. The compound was analyzed by an X‐ray diffraction technique and found to be ZrB2 powder that was synthesized with the purity of approximately 98%.
Journal of Ceramic Processing Research, Oct 1, 2019
Materials Chemistry and Physics, 2022
Ceramics International, 2014
هديكچ ا رد ي قحت ن ي زوپماک ،ق ي ت ZrB2-HfB2 شور هب فت يشوج لوت راشف نودب ـ ي د و اـهردوپ زا ي Si... more هديكچ ا رد ي قحت ن ي زوپماک ،ق ي ت ZrB2-HfB2 شور هب فت يشوج لوت راشف نودب ـ ي د و اـهردوپ زا ي SiC ، MoSi2 و B4C ـ ندوزفا ناوـنع هـب ي دش هدافتسا . يارب هنومن تخاس اه ي زوپماک ي ت ي ردوپ ادتبا ، ZrB2 تدم هب ۲ سآ تعاس ي وقت تارذ سپس و با ي هفاضا نآ هب هدننک ت دـش . طوـلخم زوپماک ي ت ي زا هدافتسا اب لصاح دنيارف سرپ راشف مه درس (CIP) پ زا سپ و دش هداد لکش ي لور ي اـمد ود رد ،ز ي C ۲۱00 و C ۲۱۵0 لمع تـحت ـ ي تا فت يشوج تفرگ رارق . يارب اقم ي ندوزفا تارثا هس ي اه ي راتفر رب فلتخم فـت يـشوج دـب ناـکم صاوـخ و راـشف نو ي ک ي زوپماک ـ ي ت ZrB2-HfB2 زا م ي نورتکلا پوکسورک ي شبور ي (SEM) ط هب زهجم ي ف جنس EDS و شمخ نومزآ ، گ هزادنا ي ر ي نوسارتلا شور هب توص تعرس ي ک ) يارب هزادنا گ ي ر ي تسلاا لودم ي ک ( دش هدافتسا . اتن هب هجوت اب ي هنومن ،هدمآ تسد هب ج اه ي واح ي تارذ MoSi2 و SiC ان ب ون ي ش رت ي م ن ي ـ شمخ ماکحتـسا ناز ي اراد ار دندوب . ا رب هولاع ي شمخ ماکحتسا ،ن ي هنومن ازفا اب اه ي امد ش ي فت يشوج زا C ۲۱00 هب C ۲۱۵0 ازفا ي ش ي ب هک تفا ي دوبهب رگنا دنيارف فت يشوج رد امد ي C ۲۱۵0 تسا .
Composites: Mechanics, Computations, Applications: An International Journal
International Journal of Refractory Metals and Hard Materials
International Journal of Refractory Metals and Hard Materials
Journal of Materials Research and Technology
In the present paper, ZrB 2-HfB 2 composite was produced by pressureless sintering method and SiC... more In the present paper, ZrB 2-HfB 2 composite was produced by pressureless sintering method and SiC, MoSi 2 and B 4 C particles were used as additive. In order to produce composite samples, ZrB 2 powder was first milled for 2 hours and then the reinforcing particles were added to milled powder. The mixture was formed by cold isostatic press (CIP) and after pyrolysis, was sintered at 2100⁰C. In order to compare the effect of different additives on pressureless sintering behavior of ZrB 2-HfB 2 composite, the shrinkage percentage of samples were measured before and after sintering and the microstructure of samples were examined using Scanning Electron microscopy (SEM), equipped with EDS spectroscopy. Bending test was used to measure the strength and the elastic modulus of samples was measured by resonance frequency method. The results show that samples containing MoSi 2 and SiC nano-particles have the maximum flexural strength and elastic modulus. The reason is the better effect of MoSi 2 particles on sintering process and densification comparing to B 4 C particles.
International Journal of Refractory Metals and Hard Materials, 2014
Journal of Materials Research and Technology, 2015
International Journal of Refractory Metals and Hard Materials, 2015
ABSTRACT
Materials Research
In this research, electrical conductivity, thermal conductivity and mechanical properties of the ... more In this research, electrical conductivity, thermal conductivity and mechanical properties of the Al-TiC composites which were sintered via microwave-assisted process were investigated. The specimens were sintered for 3, 5 and 8 minutes. The results have shown that the sample which contains 4 vol. % TiC and was sintered for 8 minutes, has the highest electrical and thermal conductivities among the other obtained ones. Besides that, the sample which contains 8 vol. % TiC and was sintered for 3 minutes, has dedicated the highest hardness and density to itself. Scanning electron microscopy (SEM) micrographs have illustrated that by increasing the amount of TiC up to 12 vol. %, the agglomeration of particles occurs. The X-ray diffraction (XRD) investigations have shown that due to the short duration of the sintering process in the microwave method, there is no trace of TiO 2 and Al 4 C 3 as pernicious phases. According to the obtained results, it becomes clear that increasing the amount of TiC powder leads to the reduction of electrical and thermal properties of the samples and increasing the sintering duration, leads to the increase of the mentioned properties.
Ceramics International, 2010
The processing of boron carbide by pressureless sintering with and without additives to obtain de... more The processing of boron carbide by pressureless sintering with and without additives to obtain dense pellets for use as neutron absorber in fast breeder reactors is reported. The effect of particle size and sintering temperature on density and microstructure was studied. Pressureless sintering of boron carbide powder (0.5 mm) at 2375 8C yielded a pellet of 93% r th . Addition of zirconium dioxide was found to be beneficial in lowering the sintering temperature. A typical sample with 5 wt% zirconia addition sintered at 2275 8C resulted in a density of 93% r th and a micro hardness value (HK 100 ) of 32 GPa. #
مواد و فناوری های پیشرفته, Nov 22, 2017
In the present paper, ZrB 2-SiC nanocomposite was developed by pressureless sintering method. Mic... more In the present paper, ZrB 2-SiC nanocomposite was developed by pressureless sintering method. Micro sized AlN powder and SiC powderes at nano and micro-sized scale were used as additive. In order to produce composite samples, the primary powders were milled and blended in planetary ball mill apparatus with rotational speed of 200rpm and then processed using hot pressing (80ᵒC and 100MPa), cold isostatic press and sintering at 2150ᵒC. The values of relative density and porosity of samples were measured to evaluate the effect of presence of micro-sized SiC and SiC nano particles simultaneously on the pressureless sintering behavior of ZrB 2-SiC. In order to compare the microstructure and mechanical properties of samples Scanning Electron microscopy (SEM), equipped with EDS spectroscopy, XRD analysis, hardness and toughness tests were used. The results show that as the volume percentage of nano SiC decreases to 15 vol.% and AlN increases to 7.5 vol.% the hardness (17.1 GPa), toughness (5.7 MPa.m 1/2) and relative density (98.1%) increase.
Journal of Ceramic Processing Research, Apr 1, 2019
استقلال, May 1, 2015
In this study, AlN whiskers were prepared in a tube furnace at 1000˚C for 1h with 500 cc min nitr... more In this study, AlN whiskers were prepared in a tube furnace at 1000˚C for 1h with 500 cc min nitrogen gas flow. Al powders with particle size of 3 μm and 45 μm and NH 4 Cl were used as raw materials. SEM, TEM and XRD analysis were used to characterize AlN whiskers. The results showed that the diameters of AlN whiskers would range from 140 nm to 340 nm if different amounts of NH 4 Cl and 3 μm Al powder were used. In the case of using NH 4 Cl more than 40wt%, pure AlN without any unreacted Al was formed as the final product. Using NH 4 Cl and Al with particle size of 45 μm led to AlN whiskers with 630 nm to 870 nm in diameter. By adding 50%wt NH 4 Cl, pure AlN was formed. The diameter of the whiskers was increased by increasing NH 4 Cl content in starting materials (about 200 nm). Also, an increase in the diameter of AlN whisker resulted from coarse Al powder. By adding NH 4 Cl to Al, thermodynamically spontaneous cholororination-nitridation reactions were increased in vapor phase and whiskers and pure AlN powder were produced.
International Journal of Ceramic Engineering & Science
The reason of this study is to synthesize ZrB2 nano powder utilizing boric acid and phenolic resi... more The reason of this study is to synthesize ZrB2 nano powder utilizing boric acid and phenolic resin. Within the study of zirconia as a source of zirconium, boric acid was used as a source of boron and phenolic resin as a carbon source. The theoretical and experimental studies of ZrB2 were synthesized by boro/carbothermal diminishment from the novel sol–gel technology. The zirconia powder was crushed for 8 h and in conjunction with different molar proportions of boric acid, in this consider, a kinetic demonstrate for reactions creating ZrB2 was built up based on thermodynamic analysis. The resultant powder was synthesized in a neutral atmosphere controlled in 1450°C and 1550°C. After it was also observed that, with the increase of molar proportion of H3BO3, the reaction delivered ZrB2 powders in high amount of the boron reaction. The compound was analyzed by an X‐ray diffraction technique and found to be ZrB2 powder that was synthesized with the purity of approximately 98%.
Journal of Ceramic Processing Research, Oct 1, 2019
Materials Chemistry and Physics, 2022
Ceramics International, 2014
هديكچ ا رد ي قحت ن ي زوپماک ،ق ي ت ZrB2-HfB2 شور هب فت يشوج لوت راشف نودب ـ ي د و اـهردوپ زا ي Si... more هديكچ ا رد ي قحت ن ي زوپماک ،ق ي ت ZrB2-HfB2 شور هب فت يشوج لوت راشف نودب ـ ي د و اـهردوپ زا ي SiC ، MoSi2 و B4C ـ ندوزفا ناوـنع هـب ي دش هدافتسا . يارب هنومن تخاس اه ي زوپماک ي ت ي ردوپ ادتبا ، ZrB2 تدم هب ۲ سآ تعاس ي وقت تارذ سپس و با ي هفاضا نآ هب هدننک ت دـش . طوـلخم زوپماک ي ت ي زا هدافتسا اب لصاح دنيارف سرپ راشف مه درس (CIP) پ زا سپ و دش هداد لکش ي لور ي اـمد ود رد ،ز ي C ۲۱00 و C ۲۱۵0 لمع تـحت ـ ي تا فت يشوج تفرگ رارق . يارب اقم ي ندوزفا تارثا هس ي اه ي راتفر رب فلتخم فـت يـشوج دـب ناـکم صاوـخ و راـشف نو ي ک ي زوپماک ـ ي ت ZrB2-HfB2 زا م ي نورتکلا پوکسورک ي شبور ي (SEM) ط هب زهجم ي ف جنس EDS و شمخ نومزآ ، گ هزادنا ي ر ي نوسارتلا شور هب توص تعرس ي ک ) يارب هزادنا گ ي ر ي تسلاا لودم ي ک ( دش هدافتسا . اتن هب هجوت اب ي هنومن ،هدمآ تسد هب ج اه ي واح ي تارذ MoSi2 و SiC ان ب ون ي ش رت ي م ن ي ـ شمخ ماکحتـسا ناز ي اراد ار دندوب . ا رب هولاع ي شمخ ماکحتسا ،ن ي هنومن ازفا اب اه ي امد ش ي فت يشوج زا C ۲۱00 هب C ۲۱۵0 ازفا ي ش ي ب هک تفا ي دوبهب رگنا دنيارف فت يشوج رد امد ي C ۲۱۵0 تسا .
Composites: Mechanics, Computations, Applications: An International Journal
International Journal of Refractory Metals and Hard Materials
International Journal of Refractory Metals and Hard Materials
Journal of Materials Research and Technology
In the present paper, ZrB 2-HfB 2 composite was produced by pressureless sintering method and SiC... more In the present paper, ZrB 2-HfB 2 composite was produced by pressureless sintering method and SiC, MoSi 2 and B 4 C particles were used as additive. In order to produce composite samples, ZrB 2 powder was first milled for 2 hours and then the reinforcing particles were added to milled powder. The mixture was formed by cold isostatic press (CIP) and after pyrolysis, was sintered at 2100⁰C. In order to compare the effect of different additives on pressureless sintering behavior of ZrB 2-HfB 2 composite, the shrinkage percentage of samples were measured before and after sintering and the microstructure of samples were examined using Scanning Electron microscopy (SEM), equipped with EDS spectroscopy. Bending test was used to measure the strength and the elastic modulus of samples was measured by resonance frequency method. The results show that samples containing MoSi 2 and SiC nano-particles have the maximum flexural strength and elastic modulus. The reason is the better effect of MoSi 2 particles on sintering process and densification comparing to B 4 C particles.
International Journal of Refractory Metals and Hard Materials, 2014
Journal of Materials Research and Technology, 2015
International Journal of Refractory Metals and Hard Materials, 2015
ABSTRACT
Materials Research
In this research, electrical conductivity, thermal conductivity and mechanical properties of the ... more In this research, electrical conductivity, thermal conductivity and mechanical properties of the Al-TiC composites which were sintered via microwave-assisted process were investigated. The specimens were sintered for 3, 5 and 8 minutes. The results have shown that the sample which contains 4 vol. % TiC and was sintered for 8 minutes, has the highest electrical and thermal conductivities among the other obtained ones. Besides that, the sample which contains 8 vol. % TiC and was sintered for 3 minutes, has dedicated the highest hardness and density to itself. Scanning electron microscopy (SEM) micrographs have illustrated that by increasing the amount of TiC up to 12 vol. %, the agglomeration of particles occurs. The X-ray diffraction (XRD) investigations have shown that due to the short duration of the sintering process in the microwave method, there is no trace of TiO 2 and Al 4 C 3 as pernicious phases. According to the obtained results, it becomes clear that increasing the amount of TiC powder leads to the reduction of electrical and thermal properties of the samples and increasing the sintering duration, leads to the increase of the mentioned properties.
Ceramics International, 2010
The processing of boron carbide by pressureless sintering with and without additives to obtain de... more The processing of boron carbide by pressureless sintering with and without additives to obtain dense pellets for use as neutron absorber in fast breeder reactors is reported. The effect of particle size and sintering temperature on density and microstructure was studied. Pressureless sintering of boron carbide powder (0.5 mm) at 2375 8C yielded a pellet of 93% r th . Addition of zirconium dioxide was found to be beneficial in lowering the sintering temperature. A typical sample with 5 wt% zirconia addition sintered at 2275 8C resulted in a density of 93% r th and a micro hardness value (HK 100 ) of 32 GPa. #