Pub Date : 2022-02-15DOI: 10.36303/satnt.2021cosaami.49
T. Mashiyane, D. Desai, L. Tartibu
The high load-bearing ability of cylindrical roller bearing made its usage in rotating machinery popular. However, the performance of this bearing is impeded by the contact stress, stiffness and the temperature rise experienced operation. In this study, the thermomechanical behaviour of martensitic stainless steel (X20) fabricated roller bearing with polyamide pin type cage subjected to different rotating/operating speeds was simulated using finite element analysis software, Abaqus. The outcome of the analyses shows that the temperature, heat flux, contact or Hertzian stress and frictional energy developed in the bearing during operation increases with a corresponding increase in speed. It was further observed that a slight increase in the operating speed of the bearing leads to a significant rise in the temperature and frictional energy developed in the bearing. Also, the maximum Hertzian/contact stress was observed to developed on the outer ring of the roller bearing assembly (at the point of contact between the outer ring and the balls) in all the operational speeds considered. Thus, making this outer ring more susceptible to failure during operation as compared to the other components of the bearing.
{"title":"Influence of operating speed on the thermo-mechanical behaviour of cylindrical roller bearing","authors":"T. Mashiyane, D. Desai, L. Tartibu","doi":"10.36303/satnt.2021cosaami.49","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.49","url":null,"abstract":"The high load-bearing ability of cylindrical roller bearing made its usage in rotating machinery popular. However, the performance of this bearing is impeded by the contact stress, stiffness and the temperature rise experienced operation. In this study, the thermomechanical behaviour of martensitic stainless steel (X20) fabricated roller bearing with polyamide pin type cage subjected to different rotating/operating speeds was simulated using finite element analysis software, Abaqus. The outcome of the analyses shows that the temperature, heat flux, contact or Hertzian stress and frictional energy developed in the bearing during operation increases with a corresponding increase in speed. It was further observed that a slight increase in the operating speed of the bearing leads to a significant rise in the temperature and frictional energy developed in the bearing. Also, the maximum Hertzian/contact stress was observed to developed on the outer ring of the roller bearing assembly (at the point of contact between the outer ring and the balls) in all the operational speeds considered. Thus, making this outer ring more susceptible to failure during operation as compared to the other components of the bearing.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"124 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76623774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-02-15DOI: 10.36303/satnt.2021cosaami.50
WA Seya, A. Kolesnikov, I. Van der Walt, H. Bissett
The industrial application of the spheroidization process using high-temperature plasma is regarded as a good method for the conversion of irregularly shaped particles into a spherica shape. High temperature and controlled plasma conditions are required to obtain satisfactory results. Given this, a 3D model was used to simulate heat transfer from a source term to titanium-alloy particles using ANSYS Fluent software. Such models consider the effects of particle treatment on thermodynamic and transport properties of the plasma. This present study aims to investigate the impact of heat transfer on the particles and the effect of radiation energy loss on the particles, using numerical analysis. The results showed that the operating condition such mass flow was inversely proportional to the rate of heat transfer between plasma particles and the characteristics of the plasma gas, which was due to significant variation in radiation energy losses.
{"title":"Impact of heat transfer on spheroidization of titanium alloys","authors":"WA Seya, A. Kolesnikov, I. Van der Walt, H. Bissett","doi":"10.36303/satnt.2021cosaami.50","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.50","url":null,"abstract":"The industrial application of the spheroidization process using high-temperature plasma is regarded as a good method for the conversion of irregularly shaped particles into a spherica shape. High temperature and controlled plasma conditions are required to obtain satisfactory results. Given this, a 3D model was used to simulate heat transfer from a source term to titanium-alloy particles using ANSYS Fluent software. Such models consider the effects of particle treatment on thermodynamic and transport properties of the plasma. This present study aims to investigate the impact of heat transfer on the particles and the effect of radiation energy loss on the particles, using numerical analysis. The results showed that the operating condition such mass flow was inversely proportional to the rate of heat transfer between plasma particles and the characteristics of the plasma gas, which was due to significant variation in radiation energy losses.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"98 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85899860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-24DOI: 10.36303/satnt.2021cosaami.39
B. Ngobe, M. Phasha, IA Mwamba
Density functional theory (DFT) based on the first-principles technique, CASTEP, was used to explore the possibility of inducing martensitic transformation (MT) in a stable B2 TiRu alloy by systematic introduction of palladium (Pd) on the ruthenium (Ru) site. The structural, mechanical and electronic properties of pure, as well as, Pd-doped TiRu were calculated. The elastic constants obtained show that the addition of Pd seems to induce MT in the ordered TiRu, as shown by mechanical instability (C΄= C11-C12 < 0) of the B2 phase against shear deformation at 0 K. This is an indication that B2 is likely to transform to low symmetry phases such as L10/B19/B19’. Moreover, the calculated total density of states (T-DOS) also indicated that the addition of Pd shifted the Fermi level (EF) from the centre of the pseudogap of the ordered pure TiRu towards the right (anti-bonding region), rendering the resulting B2 ternary phase unstable at certain Pd compositions higher than 10 atomic percent (at.%). The predicted induced martensitic transformation is one of the key characteristics of shape memory behaviour in B2 Ti-based alloys such as NiTi, TiPd and TiPt. Further work on the possible low temperature phases resulting from B2 Ti-Ru-Pd ternary alloys is underway.
{"title":"First-principles study to explore the possibility of inducing martensitic transformation in ordered B2 TiRu phase by alloying with Pd","authors":"B. Ngobe, M. Phasha, IA Mwamba","doi":"10.36303/satnt.2021cosaami.39","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.39","url":null,"abstract":"Density functional theory (DFT) based on the first-principles technique, CASTEP, was used to explore the possibility of inducing martensitic transformation (MT) in a stable B2 TiRu alloy by systematic introduction of palladium (Pd) on the ruthenium (Ru) site. The structural, mechanical and electronic properties of pure, as well as, Pd-doped TiRu were calculated. The elastic constants obtained show that the addition of Pd seems to induce MT in the ordered TiRu, as shown by mechanical instability (C΄= C11-C12 < 0) of the B2 phase against shear deformation at 0 K. This is an indication that B2 is likely to transform to low symmetry phases such as L10/B19/B19’. Moreover, the calculated total density of states (T-DOS) also indicated that the addition of Pd shifted the Fermi level (EF) from the centre of the pseudogap of the ordered pure TiRu towards the right (anti-bonding region), rendering the resulting B2 ternary phase unstable at certain Pd compositions higher than 10 atomic percent (at.%). The predicted induced martensitic transformation is one of the key characteristics of shape memory behaviour in B2 Ti-based alloys such as NiTi, TiPd and TiPt. Further work on the possible low temperature phases resulting from B2 Ti-Ru-Pd ternary alloys is underway.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"115 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80868858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-24DOI: 10.36303/satnt.2021cosaami.48
J. Negondeni, T. Ngwenya
As South Africa moves towards the production and storage of green energy sources, proton exchange membrane (PEM) fuel cells have been characterized as promising energy sources for transportation, heating, and power sources and have an efficient energy conversion that does not allow greenhouse gas emissions. However, to improve the energy efficiency and to reduce the system cost, and make it suitable for large-scale commercialization, precious metal catalyst needs to be developed with improved catalyst activities for PEM fuel cells. Due to the high cost of platinum, platinum alloy nanostructures have been investigated for use as an electrocatalyst in PEM fuel cells. Platinum-nickel alloy nanostructures in previous research studies have shown 36- and 22-times enhancement in mass and specific activity respectively, towards the cathodic oxygen reduction reaction (ORR) in PEM fuel cells and for the methanol oxidation reaction (MOR) in direct methanol fuel cell (DMFC) than the Pt/C catalyst. Therefore, this research focused on developing rich Pt-skin platinumnickel nanoframes which were synthesized using solvothermal and in-house developed methods. The intermediate products were etched to remove the interior using either a weak acid or an oxidative acid for comparison. The final product was supported by Vulcan XC-72 at a loading of 20 wt. % Pt-Ni. The properties of Pt-Ni/C will be characterized and evaluated to determine if the nanoframes are formed. The preliminary results for the X-ray diffraction pattern showed that the structure of Pt-Ni contracted and affected the catalyst properties. The catalytic activities were determined by electrochemical methods using thin-film RDE measurements, the results indicated that Pt-Ni as-synthesized has higher specific activity at 900 mV versus RHE. The specific and mass activity of the oxygen reduction reaction for Pt-Ni/C will be compared to the activities of the current high-performing Pt/C catalyst.
随着南非向绿色能源的生产和储存迈进，质子交换膜(PEM)燃料电池被认为是一种很有前途的能源，可用于运输、加热和发电，并且具有高效的能量转换，不允许温室气体排放。然而，为了提高能源效率和降低系统成本，使其适合大规模商业化，需要开发具有更高催化剂活性的贵金属催化剂用于PEM燃料电池。由于铂的高成本，铂合金纳米结构已被研究用于PEM燃料电池的电催化剂。在以往的研究中，铂镍合金纳米结构在PEM燃料电池中的阴极氧还原反应(ORR)和直接甲醇燃料电池(DMFC)中的甲醇氧化反应(MOR)的质量和比活性分别比Pt/C催化剂提高36倍和22倍。因此，本研究的重点是利用溶剂热法和自行开发的方法合成富铂镍纳米框架。中间产物蚀刻去除内部使用弱酸或氧化酸进行比较。最终产品由火神XC-72支撑，负载为20wt . % Pt-Ni。将对Pt-Ni/C的性质进行表征和评价，以确定是否形成纳米框架。x射线衍射图的初步结果表明，Pt-Ni的结构收缩，影响了催化剂的性能。采用薄膜RDE测量电化学方法测定了Pt-Ni的催化活性，结果表明，合成的Pt-Ni在900 mV时比RHE具有更高的比活性。将Pt- ni /C的氧还原反应的比活性和质量活性与目前高性能Pt/C催化剂的活性进行比较。
{"title":"Synthesizing Pt-Ni/C Nanoframes electrocatalyst using the solvothermal and in-house developed method for PEM fuel cells","authors":"J. Negondeni, T. Ngwenya","doi":"10.36303/satnt.2021cosaami.48","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.48","url":null,"abstract":"As South Africa moves towards the production and storage of green energy sources, proton exchange membrane (PEM) fuel cells have been characterized as promising energy sources for transportation, heating, and power sources and have an efficient energy conversion that does not allow greenhouse gas emissions. However, to improve the energy efficiency and to reduce the system cost, and make it suitable for large-scale commercialization, precious metal catalyst needs to be developed with improved catalyst activities for PEM fuel cells. Due to the high cost of platinum, platinum alloy nanostructures have been investigated for use as an electrocatalyst in PEM fuel cells. Platinum-nickel alloy nanostructures in previous research studies have shown 36- and 22-times enhancement in mass and specific activity respectively, towards the cathodic oxygen reduction reaction (ORR) in PEM fuel cells and for the methanol oxidation reaction (MOR) in direct methanol fuel cell (DMFC) than the Pt/C catalyst. Therefore, this research focused on developing rich Pt-skin platinumnickel nanoframes which were synthesized using solvothermal and in-house developed methods. The intermediate products were etched to remove the interior using either a weak acid or an oxidative acid for comparison. The final product was supported by Vulcan XC-72 at a loading of 20 wt. % Pt-Ni. The properties of Pt-Ni/C will be characterized and evaluated to determine if the nanoframes are formed. The preliminary results for the X-ray diffraction pattern showed that the structure of Pt-Ni contracted and affected the catalyst properties. The catalytic activities were determined by electrochemical methods using thin-film RDE measurements, the results indicated that Pt-Ni as-synthesized has higher specific activity at 900 mV versus RHE. The specific and mass activity of the oxygen reduction reaction for Pt-Ni/C will be compared to the activities of the current high-performing Pt/C catalyst.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82370872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-24DOI: 10.36303/satnt.2021cosaami.19
TM Ledwaba, RG Diale, P. Ngoepe, H. Chauke
Fe-Co alloys are considered good candidates for high-temperature applications due to their high saturation magnetisation and Curie temperature. However, these alloys show low levels of ductility at room temperature. In this study, cluster expansion was employed to probe the thermodynamic stability of the FeCo1-XVX and Fe1-XCoVX alloys. Ten new stable structures were found from both FeCo1-XVX and Fe1-XCoVX systems. Their stability was observed by deducing the heats of formation, and it was found that VFeCo2 and VFe2Co (P4/mmm) are the most thermodynamically stable phases. The results also showed that vanadium prefers the Co-site rather than the Fe-site substitution. The calculated Pugh’s ratio and Poisson’s ratio confirm that alloying with V effectively improved the ductility. It was also found that VFeCo2, VFe2Co, VFe4Co3 and FeCo showed a positive shear modulus condition of stability for the structures. The ternary addition of V in the FeCo system resulted in enhanced magnetic properties. Thus, ternary systems with vanadium addition enhance the ductility of the Fe-Co systems, and these alloys could be used to develop future magnets.
{"title":"Structural and stability of B2 FeCo1-XVX and Fe1-XCoVX systems: Cluster expansion approach","authors":"TM Ledwaba, RG Diale, P. Ngoepe, H. Chauke","doi":"10.36303/satnt.2021cosaami.19","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.19","url":null,"abstract":"Fe-Co alloys are considered good candidates for high-temperature applications due to their high saturation magnetisation and Curie temperature. However, these alloys show low levels of ductility at room temperature. In this study, cluster expansion was employed to probe the thermodynamic stability of the FeCo1-XVX and Fe1-XCoVX alloys. Ten new stable structures were found from both FeCo1-XVX and Fe1-XCoVX systems. Their stability was observed by deducing the heats of formation, and it was found that VFeCo2 and VFe2Co (P4/mmm) are the most thermodynamically stable phases. The results also showed that vanadium prefers the Co-site rather than the Fe-site substitution. The calculated Pugh’s ratio and Poisson’s ratio confirm that alloying with V effectively improved the ductility. It was also found that VFeCo2, VFe2Co, VFe4Co3 and FeCo showed a positive shear modulus condition of stability for the structures. The ternary addition of V in the FeCo system resulted in enhanced magnetic properties. Thus, ternary systems with vanadium addition enhance the ductility of the Fe-Co systems, and these alloys could be used to develop future magnets.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"22 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82680107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-24DOI: 10.36303/satnt.2021cosaami.25
R. van der Merwe, H. Bissett, I. Van der Walt, L. Cornish
Copper alloys are typically produced by conventional casting processes, including spark plasma sintering (SPS), which often produce inhomogeneous mixtures of Cu or Al precipitates and unwanted intermetallic phases in solid products. Induction melting should provide good mixing, controlled heating and melt stirring, potentially improving homogeneity. Homogeneous melts should produce homogeneous powders, giving better properties in additive manufacturing (AM). To ascertain homogeneity, a density test was developed. After comminution, homogeneous powders can be used to produce high quality components. To manufacture dense AM components, spheroidised powders are needed because they increase particle packing and powder flow. An Al-50Cu (at.%) button was produced by high-frequency (HF) induction melting, to give better mixing and hence phase distributions. To identify the phases and their distributions, the as-cast sample was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), as well as absolute density using helium pycnometry. Results indicated inhomogeneity in the samples, due to Al loss, complex solidification and the densest phase settling at the bottom of the button.
{"title":"Induction melting of an Al-50Cu alloy for improved homogeneity required for powder spheroidisation","authors":"R. van der Merwe, H. Bissett, I. Van der Walt, L. Cornish","doi":"10.36303/satnt.2021cosaami.25","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.25","url":null,"abstract":"Copper alloys are typically produced by conventional casting processes, including spark plasma sintering (SPS), which often produce inhomogeneous mixtures of Cu or Al precipitates and unwanted intermetallic phases in solid products. Induction melting should provide good mixing, controlled heating and melt stirring, potentially improving homogeneity. Homogeneous melts should produce homogeneous powders, giving better properties in additive manufacturing (AM). To ascertain homogeneity, a density test was developed. After comminution, homogeneous powders can be used to produce high quality components. To manufacture dense AM components, spheroidised powders are needed because they increase particle packing and powder flow. An Al-50Cu (at.%) button was produced by high-frequency (HF) induction melting, to give better mixing and hence phase distributions. To identify the phases and their distributions, the as-cast sample was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), as well as absolute density using helium pycnometry. Results indicated inhomogeneity in the samples, due to Al loss, complex solidification and the densest phase settling at the bottom of the button.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78010701","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-24DOI: 10.36303/satnt.2021cosaami.15
TM Phaahla, P. Ngoepe, RA Catlow, H. Chauke
Transition metal nanoclusters have been greatly investigated in various areas such as catalysis, energy conversion and sensing due to their unique chemical, optical, structural, and electronic properties. Doping monometallic clusters with other metals offer the opportunity to enhance these properties. Extensive work has been done on late transition metal clusters i.e., noble and platinum metals. However, less work has been done on titanium metal clusters. The structural properties of TiN-1Pt (N = 2 – 16) clusters have been investigated using the density functional theory method with the PBEsol exchange-correlation functional. Our results showed that the binding energies for both systems decrease with cluster size N. The Ti12Pt cluster was found to be more enhanced in comparison with pure Ti revealed by the binding energy, relative stability and dissociation energy. Furthermore, binding, relative stability and dissociation energies were found to be enhanced as compared to the energies for Ti monometallic clusters.
{"title":"The effect of doping with pt impurity on ti clusters: a density functional theory study","authors":"TM Phaahla, P. Ngoepe, RA Catlow, H. Chauke","doi":"10.36303/satnt.2021cosaami.15","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.15","url":null,"abstract":"Transition metal nanoclusters have been greatly investigated in various areas such as catalysis, energy conversion and sensing due to their unique chemical, optical, structural, and electronic properties. Doping monometallic clusters with other metals offer the opportunity to enhance these properties. Extensive work has been done on late transition metal clusters i.e., noble and platinum metals. However, less work has been done on titanium metal clusters. The structural properties of TiN-1Pt (N = 2 – 16) clusters have been investigated using the density functional theory method with the PBEsol exchange-correlation functional. Our results showed that the binding energies for both systems decrease with cluster size N. The Ti12Pt cluster was found to be more enhanced in comparison with pure Ti revealed by the binding energy, relative stability and dissociation energy. Furthermore, binding, relative stability and dissociation energies were found to be enhanced as compared to the energies for Ti monometallic clusters.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80201568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-24DOI: 10.36303/satnt.2021cosaami.26
P. Ngobeni, P. Ngoepe, KP Maenetja
MnO2 is presently under massive review for its capacitance properties. MnO2 recrystallizes into several crystallographic structures such as α, β, γ, δ, and λ structure. These structures vary in the way MnO6 octahedra are connected, they possess tunnels or interlayers with gaps of different magnitudes. However, upon lithium intercalation in β-MnO2, LiMnO2 suffers from capacity loss due to undesirable structural phase transformation into spinel like LixMn2O4. One of the major demands is to modify and strengthen the structural stability of MnO2 to prevent phase transformation during lithium intercalation and rapid capacity fading during cycling. DMol3 is a density functional theory-based program used to calculate the lattice parameter of ferromagnetic MnO2. After successfully parameterized MnO2, the lattice parameters were compared with the results from experiments. Density functional tight-binding (DFTB) was employed to investigate the electronic properties of MnO2 such as density of states (DOS) and band structures. The DOS was calculated to check the conductivity of MnO2. The electronic band structures calculated indicate the absence of a gap at the Fermi level, thus MnO2 is metallic. These findings are important in preserving the crystal structure of LiMnO2 and the maintenance of capacity during cycling.
{"title":"Structural and electronic properties of β-MnO2 employing DFTB technique","authors":"P. Ngobeni, P. Ngoepe, KP Maenetja","doi":"10.36303/satnt.2021cosaami.26","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.26","url":null,"abstract":"MnO2 is presently under massive review for its capacitance properties. MnO2 recrystallizes into several crystallographic structures such as α, β, γ, δ, and λ structure. These structures vary in the way MnO6 octahedra are connected, they possess tunnels or interlayers with gaps of different magnitudes. However, upon lithium intercalation in β-MnO2, LiMnO2 suffers from capacity loss due to undesirable structural phase transformation into spinel like LixMn2O4. One of the major demands is to modify and strengthen the structural stability of MnO2 to prevent phase transformation during lithium intercalation and rapid capacity fading during cycling. DMol3 is a density functional theory-based program used to calculate the lattice parameter of ferromagnetic MnO2. After successfully parameterized MnO2, the lattice parameters were compared with the results from experiments. Density functional tight-binding (DFTB) was employed to investigate the electronic properties of MnO2 such as density of states (DOS) and band structures. The DOS was calculated to check the conductivity of MnO2. The electronic band structures calculated indicate the absence of a gap at the Fermi level, thus MnO2 is metallic. These findings are important in preserving the crystal structure of LiMnO2 and the maintenance of capacity during cycling.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"61 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90336930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-24DOI: 10.36303/satnt.2021cosaami.32
T. Van Rhijn, W. du Preez, M. Maringa, D. Kouprianoff
Various researchers have investigated the use of experimental melt pool characterization to speed up the optimisation process of selective laser melting parameters and found this to be possible. From their studies, it has become clear that the incorporation of modelling into this approach could provide efficient and predictable results that would minimise the experimental validation work required. This paper reports on progress made towards characterising the melt pool through simulation. The development of a numerical model is discussed. Subsequently, experimental validation of the numerical model is presented. This is done through a comparison of the simulation results with the experimentally determined cross-sectional geometry of single tracks created with various sets of process parameters. Melt pool size and shape are considered. Based on these results, it is concluded that using an identical simulation setup, verified simulation method, and verified material properties, it was possible to accurately determine the melt pool geometry for some, but not all process parameters.
{"title":"Towards predicting process parameters for selective laser melting of titanium alloys through the modelling of melt pool characteristics","authors":"T. Van Rhijn, W. du Preez, M. Maringa, D. Kouprianoff","doi":"10.36303/satnt.2021cosaami.32","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.32","url":null,"abstract":"Various researchers have investigated the use of experimental melt pool characterization to speed up the optimisation process of selective laser melting parameters and found this to be possible. From their studies, it has become clear that the incorporation of modelling into this approach could provide efficient and predictable results that would minimise the experimental validation work required. This paper reports on progress made towards characterising the melt pool through simulation. The development of a numerical model is discussed. Subsequently, experimental validation of the numerical model is presented. This is done through a comparison of the simulation results with the experimentally determined cross-sectional geometry of single tracks created with various sets of process parameters. Melt pool size and shape are considered. Based on these results, it is concluded that using an identical simulation setup, verified simulation method, and verified material properties, it was possible to accurately determine the melt pool geometry for some, but not all process parameters.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"50 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90495468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-24DOI: 10.36303/satnt.2021cosaami.23
KP Maenetja, H. Chauke, P. Ngoepe
We investigate the structural stability of metal oxides β-MnO2, TiO2 and VO2 (MO2) which are used as catalyst in metal air batteries, using the density functional theory (DFT) within the generalized gradient approximation (GGA). Their mechanical property was determined to show the stability trend of the metal oxides catalyst. Cell parameters of the bulk structures of the MO2 are in reasonable agreement with the experimental values (deviations of approximately 0.8% and -3.1% for a and c, respectively, and of 1.6 % in the cell volume). Phonon dispersion curves show that rutile (R) TiO2 is the most stable structure since it does not have vibrations in the negative frequencies.
{"title":"Density functional theory study of MnO2, TiO2 and VO2","authors":"KP Maenetja, H. Chauke, P. Ngoepe","doi":"10.36303/satnt.2021cosaami.23","DOIUrl":"https://doi.org/10.36303/satnt.2021cosaami.23","url":null,"abstract":"We investigate the structural stability of metal oxides β-MnO2, TiO2 and VO2 (MO2) which are used as catalyst in metal air batteries, using the density functional theory (DFT) within the generalized gradient approximation (GGA). Their mechanical property was determined to show the stability trend of the metal oxides catalyst. Cell parameters of the bulk structures of the MO2 are in reasonable agreement with the experimental values (deviations of approximately 0.8% and -3.1% for a and c, respectively, and of 1.6 % in the cell volume). Phonon dispersion curves show that rutile (R) TiO2 is the most stable structure since it does not have vibrations in the negative frequencies.","PeriodicalId":22035,"journal":{"name":"Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81323968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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