Growth of the IMC at the interface of SnAgCuBi (Bi = 0,5; 1,0) solder joints with Cu substrate

Ovdje se analizira utjecaj dodavanja Bi na stvaranje intermetalne faze u bezolovno lemljenim spojevima od Sn-Ag-0.5Cu0.5Bi (SAC0,5B) i Sn-Ag-0.5Cu-1.0Bi (SAC1,0B), sastav dan u težinskim %, na bakrenoj podlozi. Lemljenje bakrene ploče je provedeno na 255 °C u trajanju od 5 s. Spojevi su zatim ostavljeni na temperaturi od 100 °C, 130 °C i 160 °C u trajanju od 1, 3, 7, 15 dana u konvekcijskoj peći. Međupovršine su tada analizirane optičkim mikroskopom i energetskom disperzivnom rendgenskom spektrometrijskom mikroanalizom (EDX, JEOL-JXA-840A). Dva intermetalna sloja su zapažena na međupovršini - Cu3Sn i Cu6Sn5. Sloj Cu6Sn5 je nastao tijekom lemljenja. Sloj Cu3Sn je nastao tijekom sazrijevanja u čvrstom stanju. Dodavanjem Bi smanjuje se nastanak Cu3Sn jer se tako sprječava širenje Sn duž granica zrna. U članku se dalje raspravlja mehanizam nastanka sloja Cu6Sn5 i daju se zaključci za optimalni kemijski sastav lemila.The effects of Bi addition on the intermetallic phase formation in the lead-free solder joints of Sn-Ag-0.5Cu0.5Bi (SAC0,5B) and Sn-Ag-0.5Cu-1.0Bi (SAC1,0B), composition given in weight (measured in %), with copper substrate are studied. The soldering of the copper plate was conducted at 255 °C for 5 s. The joints were subsequently aged at temperatures of 100 °C, 130 °C and 160 °C for 1, 3, 7, 15 days in a convection oven. The aged interfaces were analysed by the optical microscopy and energy dispersive x-ray spectrometry (EDX, JEOL-JXA-840A) microanalysis. Two intermetallic layers are observed at the interface – Cu3Sn and Cu6Sn5. Cu6Sn5 is formed during soldering. Cu3Sn is formed during solid state ageing. Bi decreases the growth rate of Cu3Sn since it can possibly inhibit Sn diffusion along the grain boundaries. The mechanism of the Cu6Sn5 layer growth is discussed and the conclusions for the optimal solder chemical composition are presented

Shear Strength of Copper Joints Prepared by Low Temperature Sintering of Silver Nanoparticles

In this work, mechanical properties of Cu-to-Cu joint samples prepared by low temperature sintering of Ag nanoparticle paste have been investigated. The silver nanopaste was prepared by a controlled thermal decomposition of an organometallic precursor. The as-synthesized Ag particles were spherical, with an average diameter of 8.5 nm. The Cu-to-Cu joint samples were made by placing a small amount of Ag nanopaste between two polished Cu plates and sintering at 150C, 200C, 220C and 350C in air. A normal load was applied to aid sintering. Mechanical properties were measured by imposing a uniform stress across the sample bond area and measuring the corresponding strain. The application of external load was found to have a positive effect on the material’s mechanical properties. Furthermore, interestingly high values of shear strength were observed.Byly zkoumány mechanické vlastnosti Cu-to-Cu spojů připravených nízkoteplotní sintrací pasty Ag nanočástic. Ag nanopasta byla připravena řízeným tepelným rozkladem organokovových prekurzorů. Syntetizované Ag NPs byly kulovité, o středním průměru 8,5 nm. Cu-to-Cu spoje byly vyrobeny umístěním malého množství Ag nanopasty mezi dvě leštěné Cu desky a sintrováním při 150C, 200C, 220C and 350C na vzduchu. Zatížení bylo použito na k podpoře sintrace. Mechanické vlastnosti byly měřeny stanovením napětí lomu a deformace. Bylo zjištěno, že aplikace vnějšího zatížení má pozitivní vliv na mechanické vlastnosti spoje

Cation diffusion in LaMnO3, LaCoO3 and LaFeO3 materials

PhD i materialteknologiPhD in Materials Technolog

Temperature Measurement—Inquiry-Based Learning Activities for Third Graders

The article presents our Inquiry-Based Learning (IBL) activities in the project-based Science education of third graders (8–9-year-old pupils) in the Slovak Republic. Individual tasks of project assignment titled “Temperature Measurement” were conceived for “guided inquiry”. We also supported the IBL of pupils by interactive education strategy–Integrated e-Learning (INTe-L). The strategy was built on the role of interactive simulations and experimenting at the knowledge acquisition. The following INTe-L components were used: (a) on-site and remote experiments, (b) interactive simulations and (c) electronic study materials. The research was based the hypothesis that the project-based teaching of the topic “Temperature Measurement” using the IBL activities is significantly more efficient than traditional (instructivist) way of teaching. To verify the hypothesis, we carried out a pedagogical experiment on a sample of 60 respondents. The third graders were divided into two parallel groups: an experimental group (EG, 30 pupils) and control group (CG, 30 pupils). To get a relevant feedback, pre-test and post-test were developed and applied. The results attained in the EG were statistically processed, evaluated, and subsequently compared with those in the CG. The analysis of the results attained by the EG showed that their knowledge acquisition has been increased by 24% compared to CG. We have created a methodology for making simple scientific project assignments with the implementation of all components of the new integrated e-learning education strategy (real and real remote experiment, e-simulation, e-learning material). On a specific example of the topic “Temperature Measurement” in primary education, we have presented the possibility of using a “guided inquiry” in the implementation of individual experimental tasks. We have introduced a form of teamwork that allows to harmonize the teaching requirements with individual learning approach and helps to prepare pupils for planned work and independent knowledge acquisition and problem solving. The study has shown that complex IBL activities can be successfully applied at primary school 3rd grade level already. Our form of education with the wider use of modern information and communication technologies (ICT) was attractive for the learners and helped them to develop interdisciplinary relationships. The integrated e-learning has helped third grades to develop a deeper conceptual understanding of temperature and allowed them to prepare presentations to demonstrate their conceptual knowledge. The approach allowed pupils to gain key competencies in Science (discussion and presentation of results). It has also increased the pupils’ interest in Science in general and helped them to understand links between different subjects

Project-Based Teaching of the Topic “Energy Sources” in Physics via Integrated e-Learning—Pedagogical Research in the 9th Grade at Two Primary Schools in Slovakia

This work presents the results of two-year-long pedagogical research, the aim of which was to demonstrate the applicability of the usage of a new strategy in education—Integrated e-Learning (INTe-L)—through its introduction into project-based physics teaching in Slovakia. The INTe-L strategy is built around the role of experiments and interactive simulations in knowledge acquisition and on the possibility of integrating scientific methods in education. The elements of INTe-L are the following: (a) real on-site and real remote experiments, (b) interactive virtual experiments (e-simulations) and (c) educational e-materials. The primary objective of our study was to determine the suitability of project-based teaching with INTe-L elements for the topic “Energy Sources”. The research was based on the following hypothesis: project-based teaching via INTe-L of the topic “Energy Sources” in physics is more effective than the traditional (instructionist) way of teaching. To verify the hypothesis, we performed a pedagogical experiment on a sample of 155 respondents in the 9th grade at two primary schools in Slovakia. The pupils were divided into two working groups: an experimental group (EG) of 85 pupils and a control group (CG) of 70 pupils. The pupils with worse grades were included in the EG. To get relevant feedback, pre-test and post-test studies and an interview were developed and applied. The results attained in both groups were statistically processed, evaluated and subsequently compared. A two-phase test with dispersion equality proved that differences in the pre-test scores in the EG and CG were not statistically significant. The differences in the final didactic test (post-test) results achieved by the EG and CG, on the other hand, were statistically significant and better scores in the EG were obtained. A positive change of pupils’ attitude in the EG towards physics after the execution of our project-based teaching was noted. The evaluation of the results attained by the pupils proved that the introduction of project-based teaching via INTe-L was an effective strategy to improve Physics teaching. As such, the implementation of this interactive strategy into the instructional education process at primary schools is recommended

Effect of Heat Treatment on the Resulting Dimensional Characteristics of the C45 Carbon Steel after Turning

The presented article deals with the influence of the heat treatment of C45 steel on the surface quality after turning. Turning is a machining technology used to prepare specific geometrical characteristics of surface and dimensional quality. In the present paper, the same turning conditions were used for the turning treatment of differently heat-treated steels. The soft annealed state, normalized state, hardened state, quenched and tempered at 530 °C state and quenched and tempered at 660 °C state have been analyzed. By using this approach, it has been possible to evaluate the effects of hardening and machining on the resulting parameters after turning (roughness, cylindricity and circularity). The highest hardness was observed in the steel after the hardening process (694 ± 9 HV 10). The hardening has negatively influenced the surface quality. The high hardness was related to martensite formation and caused a damage to the cutting edge of the cut insert used, leading to a significant change in geometrical accuracy. The cylindricity change achieved 0.15 ± 0.03 mm which was significantly higher compared to the theoretical value of the diameter of the machined steel bar. An inaccuracy was also observed in diameter dimension. These inaccuracies were caused by the wear of the cutting edge of the tool used in cutting parameters setting