L Losoba - Academia.edu (original) (raw)

Papers by L Losoba

International Journal of Materials Technology and Innovation (Online), Jun 1, 2023

Typical offshore area facilities impose stringent structural integrity and safety conditions, oft... more Typical offshore area facilities impose stringent structural integrity and safety conditions, often necessitating dissimilar welding (DMW) for joining structural fabrication. Although various combinations of material options have been explored in service and literature, none have been able to prevent or fully justify the failure mechanism observed in the process area. In this study, DMW joints produced from duplex stainless steel (DSS) and API 5L X60 material combination using gas tungsten arc (GTA) welding process were investigated for microstructure and mechanical property evaluation using low (0.73-0.88kJ/mm), medium (1.3-1.7kJ/mm), and high (2.1-2.8kJ/mm) heat inputs. Microstructural characterization of the welded samples suggests the presence of a type II boundary close to and parallel to the fusion boundary close to API 5L X60 base metal. Noticeable presence of macro-segregation at the interfaces between HAZ of the base materials and the weld metal, while high heat input weldment favored the formation of delta ferrite. Morphology of the grains in the HAZ transits from coarse to equiaxed showing typical post-solidification structure with varying grain morphologies. Microhardness evaluation of the HAZ region of both DSS and X60 DMW, indicated a comparable value in all conditions with the low (262/218 HV), high (257/206 HV) and medium (235/220HV) heat inputs, respectively. In the FZ, the medium (192HV) value is intermediate between high (180HV) and low (198HV) heat inputs. The tensile and yield strength of the weldments indicated that the medium heat input has an intermediate value of 439 and 585 HV, respectively.

The effect of antimony substitution for niobium on potassium sodium niobate (KNN) ceramic was inv... more The effect of antimony substitution for niobium on potassium sodium niobate (KNN) ceramic was investigated with respect to the densification behaviour at different sintering temperatures, microstructure and electrical properties. Sb 5+ was slightly added while simultaneously lowering the amount of Nb 5+ and in this study of the (K0.5Na0.5)(Nb1-xSbx)O3 system, x content was varied from 0 to 14 mol.% Our results show that Sb 5+ slightly increased the optimum sintering temperature for KNN but above 8 mol %, its resistivity and piezoelectric properties decreased. As the amount of Sb 5+ substituted is increased, the structure of the ceramic transformed from orthorhombic to pseudocubic which led to slight shrinkage in the unit cell volume. Microstructural examination revealed that above 10 mol %, a second phase (K2NaSb3O9) was formed which segregated mainly to the grain boundary while the quantitative EDX analysis showed that there was A-site vacancy due to loss of the alkali elements. The two phase transitions points, Curie temperature (TC) and the tetragonal to orthorhombic (TT-O) shifted to lower temperature with increasing Sb 5+ content and above 10 mol %, the TT-O shifted to below room temperature. The dielectric loss slightly increases with increasing Sb 5+ content up to 200°C. There was an improvement in the piezoelectric properties with ≤ 6 mol % Sb content while optimum properties were obtained with 4 mol % (KP = 0.46, Qm= 6.2, NP = 2296). piezoelectric properties can be obtained 7. Saito et al 8,9 showed that by using texture and isovalent substitution of both the A and B-site elements, the piezoelectric properties in the KNN system can be greatly improved. Combined Li + , Ta 5+ and Sb 5+ substitutions have been known to give the highest piezoelectric properties in the KNN system 10,11. The effect of Li + on the properties of KNN have also been widely reported in the literature 12,13 The effect of Ta 5+ which is expected to enter the B-site of the structure based on valence and ionic radius has also been reported by Matsubara et al 14. Li + and Ta 5+ 9,15 as well as Li + and Sb 5+ on the A and B-sites respectively of KNN have been reported 16,17. There is however very little report in the literature on the effect of adding only Sb 5+ on the structure and properties of KNN. KNN has been doped with Sb and MnO 2 and the authors reported that MnO 2 served only as a sintering aid but it is possible that it has other effects on KNN 18,19. In this work, we investigated the effect of substituting Nb 5+ with Sb 5+ on the piezoelectric, dielectric, crystallographic and microstructural properties of K 0.5 Na 0.5 NbO 3. The objective was to understand through experimental studies, what happens when only Nb 5+ is substituted with Sb 5+ in KNN.

Temperature-dependent synchrotron powder diffraction measurements have been performed on leadfree... more Temperature-dependent synchrotron powder diffraction measurements have been performed on leadfree ferroelectric (K 0.37 Na 0.52 Li 0.03)(Nb 0.87 Ta 0.1 Sb 0.03)O 3 ceramics. The measurement was performed from 20 C to 400 C with 20 C steps. The diffraction patterns showed the existence of two phases from 20 C to 180 C while the ferroelectric to paraelectric phase transition occurred between 340 C and 360 C. Rietveld refinement using the Fullprof software was employed and the two-phase region was refined using a combination of the orthorhombic phase with space group Amm2 (38) and the tetragonal phase with space group P4mm (99) from 20 C to 180 C. The tetragonal phase was used for the refinement up to 340 C while the cubic phase was refined with space group Pm 3 3m (221). Good refinement structure parameters were obtained for all temperatures with the average G.O.F being approximately 4.0. Information about the cell parameters and weight fraction of the phases were obtained as a function of temperature.

Cogent Engineering, Feb 29, 2016

In the current study, the influence of delta (δ) ferrite on the corrosion susceptibility of AISI ... more In the current study, the influence of delta (δ) ferrite on the corrosion susceptibility of AISI 304 austenitic stainless steel was evaluated in 1Molar concentration of sulphuric acid (H 2 SO 4) and 1Molar concentration of sodium chloride (NaCl). The study was performed at ambient temperature using electrochemical technique—Tafel plots to evaluate the corrosive tendencies of the austenitic stainless steel sample. The as-received (stainless steel) specimen and 60% cold-worked (stainless steel) specimens were isothermally annealed at 1,100°C for 2 h and 1 h, respectively, and quenched in water. The results obtained show that the heat-treated specimen and the 60% cold-worked plus heat-treated specimen exhibited higher corrosion susceptibility than the as-received specimen, which invariably contained the highest fraction of δ ferrite particles. The finding shows that the presence of δ ferrite, in which chromium (Cr), the main corrosion inhibitor segregates, does not degrade and or reduces the resistance to aqueous corrosion of the austenitic stainless steel material.

… of the European Ceramic …, 2009

Lead free ferroelectric ceramics of the KNN-LiTaO 3-LiSbO 3 system were prepared using the mixed ... more Lead free ferroelectric ceramics of the KNN-LiTaO 3-LiSbO 3 system were prepared using the mixed oxide route. This work reports the effect of doping (K 0.44 Na 0.52 Li 0.04)(Nb 0.86 Ta 0.1 Sb 0.04)O 3 produced through the conventional solid state sintering method with different amounts of MnO 2. With 1 mol% of the dopant, ~ 96.5% of the theoretical density of the ceramics was achieved while grain growth inhibition was attained through pinning of the grain boundary movement. A polymorphic phase transition (PPT) was induced in the ceramic from the orthorhombic crystal structure to the tetragonal structure with increasing dopant amount. At lower temperatures, the doped samples had higher epsilon values but there was a decrease in both Tc (from 333 •C to 249 •C) and epsilon value at Tc (from ≈9500 to <6000). At temperatures below 300 •C however, the loss tangent in the doped samples (≈2.5 mol%) was much lower and steady when compared to the undoped one. The ferroelectric properties were slightly lowered with the addition of MnO2. The remnant polarisation (Pr) was lowered from ~18µC/cm2 to ~9µC/cm2, the coercive field (E c) from ~ 8.5 kV/cm to ~ 6.2 kV/cm and the piezoelectric charge coefficient (d 33) decreased as well.

International Journal of Evaluation and Research in Education (IJERE), Aug 23, 2017

The study investigated influence of some factors on the performance of selected West African Seni... more The study investigated influence of some factors on the performance of selected West African Senior School Certificate Examination (WASSCE) candidates. It also examined the relationship between these factors and candidates' performance. Factors investigated include socioeconomic background of the candidates (SEB), study hours (SH), attitude towards English Language (ATTENG) and attitude towards Mathematics (ATTMAT). Secondary schools in Lagos State were divided into private and public secondary schools. Simple random sampling was used to select five out of the six educational districts in Lagos State. Then one public and one private secondary schools were selected in each of the five educational districts earlier selected in stage one. Thereafter, 30 senior secondary school III students were selected in each of the ten schools (5 public and 5 private schools). A total of 600 candidates (consisting of male and female participants) were expected, however, only 564 participants with complete data were found suitable for the study. An instrument tagged "Candidates Rating Scale (CRS)" was developed and used to measure their SEB, SH, ATTENG and ATTMA which were the independent variables while candidates' scores at WASSCE was used as the dependent variable. Obtained data were analyzed by using multiple regressions. The results of the study indicate that there exists a positive correlation between WASSCE grades and all the variables in Mathematics but correlate with socio economic background only for English language.

Cogent Engineering, 2016

In the current study, the influence of delta (δ) ferrite on the corrosion susceptibility of AISI ... more In the current study, the influence of delta (δ) ferrite on the corrosion susceptibility of AISI 304 austenitic stainless steel was evaluated in 1Molar concentration of sulphuric acid (H 2 SO 4) and 1Molar concentration of sodium chloride (NaCl). The study was performed at ambient temperature using electrochemical technique—Tafel plots to evaluate the corrosive tendencies of the austenitic stainless steel sample. The as-received (stainless steel) specimen and 60% cold-worked (stainless steel) specimens were isothermally annealed at 1,100°C for 2 h and 1 h, respectively, and quenched in water. The results obtained show that the heat-treated specimen and the 60% cold-worked plus heat-treated specimen exhibited higher corrosion susceptibility than the as-received specimen, which invariably contained the highest fraction of δ ferrite particles. The finding shows that the presence of δ ferrite, in which chromium (Cr), the main corrosion inhibitor segregates, does not degrade and or reduces the resistance to aqueous corrosion of the austenitic stainless steel material.

International Journal of Materials Technology and Innovation (Online), Jun 1, 2023

Typical offshore area facilities impose stringent structural integrity and safety conditions, oft... more Typical offshore area facilities impose stringent structural integrity and safety conditions, often necessitating dissimilar welding (DMW) for joining structural fabrication. Although various combinations of material options have been explored in service and literature, none have been able to prevent or fully justify the failure mechanism observed in the process area. In this study, DMW joints produced from duplex stainless steel (DSS) and API 5L X60 material combination using gas tungsten arc (GTA) welding process were investigated for microstructure and mechanical property evaluation using low (0.73-0.88kJ/mm), medium (1.3-1.7kJ/mm), and high (2.1-2.8kJ/mm) heat inputs. Microstructural characterization of the welded samples suggests the presence of a type II boundary close to and parallel to the fusion boundary close to API 5L X60 base metal. Noticeable presence of macro-segregation at the interfaces between HAZ of the base materials and the weld metal, while high heat input weldment favored the formation of delta ferrite. Morphology of the grains in the HAZ transits from coarse to equiaxed showing typical post-solidification structure with varying grain morphologies. Microhardness evaluation of the HAZ region of both DSS and X60 DMW, indicated a comparable value in all conditions with the low (262/218 HV), high (257/206 HV) and medium (235/220HV) heat inputs, respectively. In the FZ, the medium (192HV) value is intermediate between high (180HV) and low (198HV) heat inputs. The tensile and yield strength of the weldments indicated that the medium heat input has an intermediate value of 439 and 585 HV, respectively.

The effect of antimony substitution for niobium on potassium sodium niobate (KNN) ceramic was inv... more The effect of antimony substitution for niobium on potassium sodium niobate (KNN) ceramic was investigated with respect to the densification behaviour at different sintering temperatures, microstructure and electrical properties. Sb 5+ was slightly added while simultaneously lowering the amount of Nb 5+ and in this study of the (K0.5Na0.5)(Nb1-xSbx)O3 system, x content was varied from 0 to 14 mol.% Our results show that Sb 5+ slightly increased the optimum sintering temperature for KNN but above 8 mol %, its resistivity and piezoelectric properties decreased. As the amount of Sb 5+ substituted is increased, the structure of the ceramic transformed from orthorhombic to pseudocubic which led to slight shrinkage in the unit cell volume. Microstructural examination revealed that above 10 mol %, a second phase (K2NaSb3O9) was formed which segregated mainly to the grain boundary while the quantitative EDX analysis showed that there was A-site vacancy due to loss of the alkali elements. The two phase transitions points, Curie temperature (TC) and the tetragonal to orthorhombic (TT-O) shifted to lower temperature with increasing Sb 5+ content and above 10 mol %, the TT-O shifted to below room temperature. The dielectric loss slightly increases with increasing Sb 5+ content up to 200°C. There was an improvement in the piezoelectric properties with ≤ 6 mol % Sb content while optimum properties were obtained with 4 mol % (KP = 0.46, Qm= 6.2, NP = 2296). piezoelectric properties can be obtained 7. Saito et al 8,9 showed that by using texture and isovalent substitution of both the A and B-site elements, the piezoelectric properties in the KNN system can be greatly improved. Combined Li + , Ta 5+ and Sb 5+ substitutions have been known to give the highest piezoelectric properties in the KNN system 10,11. The effect of Li + on the properties of KNN have also been widely reported in the literature 12,13 The effect of Ta 5+ which is expected to enter the B-site of the structure based on valence and ionic radius has also been reported by Matsubara et al 14. Li + and Ta 5+ 9,15 as well as Li + and Sb 5+ on the A and B-sites respectively of KNN have been reported 16,17. There is however very little report in the literature on the effect of adding only Sb 5+ on the structure and properties of KNN. KNN has been doped with Sb and MnO 2 and the authors reported that MnO 2 served only as a sintering aid but it is possible that it has other effects on KNN 18,19. In this work, we investigated the effect of substituting Nb 5+ with Sb 5+ on the piezoelectric, dielectric, crystallographic and microstructural properties of K 0.5 Na 0.5 NbO 3. The objective was to understand through experimental studies, what happens when only Nb 5+ is substituted with Sb 5+ in KNN.

Temperature-dependent synchrotron powder diffraction measurements have been performed on leadfree... more Temperature-dependent synchrotron powder diffraction measurements have been performed on leadfree ferroelectric (K 0.37 Na 0.52 Li 0.03)(Nb 0.87 Ta 0.1 Sb 0.03)O 3 ceramics. The measurement was performed from 20 C to 400 C with 20 C steps. The diffraction patterns showed the existence of two phases from 20 C to 180 C while the ferroelectric to paraelectric phase transition occurred between 340 C and 360 C. Rietveld refinement using the Fullprof software was employed and the two-phase region was refined using a combination of the orthorhombic phase with space group Amm2 (38) and the tetragonal phase with space group P4mm (99) from 20 C to 180 C. The tetragonal phase was used for the refinement up to 340 C while the cubic phase was refined with space group Pm 3 3m (221). Good refinement structure parameters were obtained for all temperatures with the average G.O.F being approximately 4.0. Information about the cell parameters and weight fraction of the phases were obtained as a function of temperature.

Cogent Engineering, Feb 29, 2016

In the current study, the influence of delta (δ) ferrite on the corrosion susceptibility of AISI ... more In the current study, the influence of delta (δ) ferrite on the corrosion susceptibility of AISI 304 austenitic stainless steel was evaluated in 1Molar concentration of sulphuric acid (H 2 SO 4) and 1Molar concentration of sodium chloride (NaCl). The study was performed at ambient temperature using electrochemical technique—Tafel plots to evaluate the corrosive tendencies of the austenitic stainless steel sample. The as-received (stainless steel) specimen and 60% cold-worked (stainless steel) specimens were isothermally annealed at 1,100°C for 2 h and 1 h, respectively, and quenched in water. The results obtained show that the heat-treated specimen and the 60% cold-worked plus heat-treated specimen exhibited higher corrosion susceptibility than the as-received specimen, which invariably contained the highest fraction of δ ferrite particles. The finding shows that the presence of δ ferrite, in which chromium (Cr), the main corrosion inhibitor segregates, does not degrade and or reduces the resistance to aqueous corrosion of the austenitic stainless steel material.

… of the European Ceramic …, 2009

Lead free ferroelectric ceramics of the KNN-LiTaO 3-LiSbO 3 system were prepared using the mixed ... more Lead free ferroelectric ceramics of the KNN-LiTaO 3-LiSbO 3 system were prepared using the mixed oxide route. This work reports the effect of doping (K 0.44 Na 0.52 Li 0.04)(Nb 0.86 Ta 0.1 Sb 0.04)O 3 produced through the conventional solid state sintering method with different amounts of MnO 2. With 1 mol% of the dopant, ~ 96.5% of the theoretical density of the ceramics was achieved while grain growth inhibition was attained through pinning of the grain boundary movement. A polymorphic phase transition (PPT) was induced in the ceramic from the orthorhombic crystal structure to the tetragonal structure with increasing dopant amount. At lower temperatures, the doped samples had higher epsilon values but there was a decrease in both Tc (from 333 •C to 249 •C) and epsilon value at Tc (from ≈9500 to <6000). At temperatures below 300 •C however, the loss tangent in the doped samples (≈2.5 mol%) was much lower and steady when compared to the undoped one. The ferroelectric properties were slightly lowered with the addition of MnO2. The remnant polarisation (Pr) was lowered from ~18µC/cm2 to ~9µC/cm2, the coercive field (E c) from ~ 8.5 kV/cm to ~ 6.2 kV/cm and the piezoelectric charge coefficient (d 33) decreased as well.

International Journal of Evaluation and Research in Education (IJERE), Aug 23, 2017

The study investigated influence of some factors on the performance of selected West African Seni... more The study investigated influence of some factors on the performance of selected West African Senior School Certificate Examination (WASSCE) candidates. It also examined the relationship between these factors and candidates' performance. Factors investigated include socioeconomic background of the candidates (SEB), study hours (SH), attitude towards English Language (ATTENG) and attitude towards Mathematics (ATTMAT). Secondary schools in Lagos State were divided into private and public secondary schools. Simple random sampling was used to select five out of the six educational districts in Lagos State. Then one public and one private secondary schools were selected in each of the five educational districts earlier selected in stage one. Thereafter, 30 senior secondary school III students were selected in each of the ten schools (5 public and 5 private schools). A total of 600 candidates (consisting of male and female participants) were expected, however, only 564 participants with complete data were found suitable for the study. An instrument tagged "Candidates Rating Scale (CRS)" was developed and used to measure their SEB, SH, ATTENG and ATTMA which were the independent variables while candidates' scores at WASSCE was used as the dependent variable. Obtained data were analyzed by using multiple regressions. The results of the study indicate that there exists a positive correlation between WASSCE grades and all the variables in Mathematics but correlate with socio economic background only for English language.

Cogent Engineering, 2016

In the current study, the influence of delta (δ) ferrite on the corrosion susceptibility of AISI ... more In the current study, the influence of delta (δ) ferrite on the corrosion susceptibility of AISI 304 austenitic stainless steel was evaluated in 1Molar concentration of sulphuric acid (H 2 SO 4) and 1Molar concentration of sodium chloride (NaCl). The study was performed at ambient temperature using electrochemical technique—Tafel plots to evaluate the corrosive tendencies of the austenitic stainless steel sample. The as-received (stainless steel) specimen and 60% cold-worked (stainless steel) specimens were isothermally annealed at 1,100°C for 2 h and 1 h, respectively, and quenched in water. The results obtained show that the heat-treated specimen and the 60% cold-worked plus heat-treated specimen exhibited higher corrosion susceptibility than the as-received specimen, which invariably contained the highest fraction of δ ferrite particles. The finding shows that the presence of δ ferrite, in which chromium (Cr), the main corrosion inhibitor segregates, does not degrade and or reduces the resistance to aqueous corrosion of the austenitic stainless steel material.