Microstructure and mechanical behavior of novel rare earth-containing Pb-Free solders

Sn-rich solders have been shown to have superior mechanical properties when compared to the Pb-Sn system. Much work remains to be done in developing these materials for electronic packaging. In this paper, we report on the microstructure and mechanical properties of La-containing Sn-3.9Ag-0.7Cu alloys. The addition of small amounts of La (up to 0.5 wt.%) to Sn-Ag-Cu refined the microstructure by decreasing the length and spacing of the Sn dendrites and decreased the thickness of the Cu₆Sn₅ intermetallic layer at the Cu/solder interface. As a result of the change in the microstructure, Sn-Ag-Cu alloys with La additions exhibited a small decrease in ultimate shear strength but significantly higher elongations compared with Sn-Ag-Cu. The influence of LaSn₃ intermetallics on microstructural refinement and damage evolution in these novel solders is discussed. Our results have profound implications for improving the mechanical shock resistance of Pb-free solders.     

Effect of fluoride on root resorption of autogenous dental replants. Clinical study

One hundred and fifty teeth were replanted using three procedures and it was found that greater success occurred in teeth when the periodontal membrane had been removed prior to treatment with two per cent sodium fluoride solution before replantation. Retention of the periodontal membrane on the root surface of the alveolar bone was not significant in the success of replants and reduced the success of those replants which were treated with fluoride. Endodontic procedures were found to be time consuming without contributing to the success of the end result.     

The influence of microstructure on thermal response of glass ionomers

This study was designed to determine the dimensional changes caused by thermal stimuli of glass ionomers with different glass/matrix ratios. Four cylindrical specimens were made for each of four powder/liquid ratios (3:1, 2.5:1, 2:1 and 1.5:1) for a conventional luting glass ionomer, two high viscosity restorative glass ionomers and a restorative resin-modified glass ionomer. The thermal characteristics were determined using a thermal mechanical analyzer (TMA) by heating the samples from 25 °C to 70 °C at 10 °C per minute. All glass ionomers and the resin-modified glass ionomer lost water on heating. The results of the thermal response of these materials were explained in terms of the opposing effects of thermal expansion and desiccation on heating. The contraction on heating of glass ionomer and related materials was found to relate to the glass/matrix ratio but not directly proportional to it. Materials with lower P/L ratios contracted the most when heated to 70 °C. The water loss from conventional and resin-modified glass ionomer with different glass/matrix ratios compensated for their thermal expansion and led to a minimal dimensional change when heated up to 50 °C. This outcome may be interpreted as an example of smart behaviour of these materials.     

Formation of aluminium carbide by cast iron and liquid aluminium interaction

Abstract

Aluminium carbide (Al₄C₃) has been identified in ex service and laboratory test specimens of cast irons exposed to liquid aluminium. In cast iron/aluminium couples, the formation of Al₄C₃ and κ-Fe₃AlC was confirmed for the first time. The growth kinetics of Al₄C₃ were parabolic with an activation energy 145±23 kJ mol^?1 (1023–1223 K), which is consistent with the reported activation energy for growth in graphite/liquid aluminium couples. The aim of this work is to shed light upon the origin and growth of Al₄C₃ in cast iron/liquid aluminium couples in the temperature range of 1023–1223 K.     

Prevalence of human pathogens and indicators in stormwater runoff in Brisbane,Australia

Elevated numbers of enteric pathogens in the receiving waters following a storm event can be a serious public health concern. The purpose of this study was to conduct a preliminary investigation into the presence of human pathogens of concern in urban stormwater runoff. The involvement of a human sewage as a potential source of contamination was also investigated by using microbial source tracking methods. Water samples (20 L) were collected after storm events and during the dry weather from six sites in Brisbane, Australia. Collected samples were analyzed for fecal indicator bacteria (FIB), and then concentrated using hollow fiber ultrafiltration followed by molecular detection of selected enteric pathogens. The levels of FIB were found to frequently exceed the upper limit of Australian guidelines for managing risks in recreational water, during the dry periods and by further several orders of magnitude in the stormwater runoff. Enterococcus spp. numbers as high as 3 × 10⁴ 100 mL^?1 were detected in the stormwater runoff at the Fitzgibbon site. Human adenovirus and polyomavirus were frequently detected from all six sampling sites during wet and dry weather conditions suggesting their wide spread presence in the urban aquatic environments. Campylobacter jejuni, Campylobacter coli and Salmonella enterica were also detected during both dry and wet weather conditions. Presence of human-specific HF183 Bacteroides marker in most of the samples tested suggests ubiquitous sewage contamination in the urban environment. Since stormwater runoff routinely contains high numbers of FIB and other enteric pathogens, some degree of treatment of captured stormwater would be required if it were to be used for non-potable purposes.     

Evaluation of the nifH gene marker of Methanobrevibacter smithii for the detection of sewage pollution in environmental waters in Southeast Queensland, Australia

This study aimed at evaluating the host-specificity and -sensitivity of the nifH gene marker of Methanobrevibacter smithii by screening 272 fecal and wastewater samples from 11 animal species including humans in Southeast Queensland (SEQ), Australia. In addition, environmental water samples (n = 21) were collected during the dry and wet weather conditions and tested for the presence of the nifH marker along with other sewage-associated markers, namely, enterococci surface protein (esp) found in Enterococci faecium, Bacteroides HF183, adenoviruses (AVs), and polyomaviruses (PVs). The overall host-specificity of the nifH marker to differentiate between human and animal feces was 0.96 (maximum value of 1), while the overall sensitivity of this marker in human sourced feces and wastewater was 0.81 (maximum value of 1). Among the 21 environmental water samples tested, 2 (10%), 3 (14%), 12 (57%), 6 (29%), and 6 (29%) were positive for the nifH, esp, HF183, AVs and PVs markers, respectively. The prevalence of the nifH marker in environmental water samples, however, was low compared to other markers, suggesting that the use of this marker alone may not be sensitive enough to detect fecal pollution in environmental waters. The nifH marker, however, appears to be sewage-specific in SEQ, Australia, and therefore, it is recommended that this marker should be used as an additional marker in combination with the HF183 or viral markers such as AVs or PVs for accurate and sensitive detection of fecal pollution in SEQ waterways.     

Fracture of Sn-Ag-Cu Solder Joints on Cu Substrates: I. Effects of Loading and Processing Conditions

During service, microcracks form inside solder joints, making microelectronic packages highly prone to failure on dropping. Hence, the fracture behavior of solder joints under drop conditions at high strain rates and under mixed-mode conditions is a critically important design consideration for robust joints. This study reports on the effects of joint processing and loading conditions on the microstructure and fracture response of Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates. The impact of parameters which control the microstructure (reflow condition, aging) as well as loading conditions (strain rate and loading angle) are explicitly studied. A methodology based on the calculation of the critical energy release rate, G _C, using compact mixed-mode (CMM) samples was developed to quantify the fracture toughness of the joints under conditions of adhesive (i.e., interface-related) fracture. In general, higher strain rate and increased mode-mixity resulted in decreased G _C. G _C also decreased with increasing dwell time at reflow temperature, which produced a thicker intermetallic layer at the solder–substrate interface. Softer solders, produced by slower cooling following reflow, or post-reflow aging, showed enhanced G _C. The sensitivity of the fracture toughness to all of the aforementioned parameters reduced with an increase in the mode-mixity. Fracture mechanisms, elucidating the effects of the loading conditions and process parameters, are briefly highlighted.     

A FUNDAMENTAL ANALYSIS OF CONTINUOUS FLOW BIOREACTOR AND MEMBRANE REACTOR MODELS WITH TESSIER KINETICS

In this research we analyze the steady-state operation of a continuous flow bioreactor, with or without recycle, and an idealized or nonidealized continuous flow membrane reactor. The model extends to include a fixed bed reactor where a fraction of the biomass is detached by the flow. The reaction is assumed to be governed by Tessier growth kinetics. We show that a flow reactor with idealized recycle has the same performance as an idealized membrane reactor and that the performance of a nonidealized membrane reactor is identical to that of an appropriately defined continuous flow bioreactor with nonidealized recycle. The performance of all three reactor types can therefore be obtained by analyzing a flow reactor with recycle. The steady states of the recycle model are found and their stability determined as a function of the residence time. The performance of the reactor at large residence times is obtained.     

Microstructural and Mechanical Studies of T91/T22 Welded Joints

Comparative studies have been performed to decide an appropriate combination of welding process and filler material by virtue of microstructural evolution, micro-hardness studies, tensile strength and fractographic analysis. Manual arc welding and tungsten inert gas welding processes are used along with different filler materials to manufacture T91/T22 welded joints. Studies with the purpose of comparison and evaluation of different zones of the weldments have been carried out. The highest value of micro-hardness observed on the T91 HAZ of the weldments may be attributed to martensitic structure of the region. The fracture morphology of both the weldments obtained from T22 BM has revealed the ductile fracture. Comparatively higher tensile strength (578 MPa) of T91/T22, GTAW combination is noticed by virtue of lower heat input. The better performance of T91/T22, GTAW weldment can be quoted on the basis of better joint integrity, tensile strength and ductility (26.4%).     

Characterization and In Vitro Corrosion Investigations of Thermal Sprayed Hydroxyapatite and Hydroxyapatite-Titania Coatings on Ti Alloy

In the current investigation, hydroxyapatite (HA) powder was mixed with titania (TiO₂) in 50:50?wt?pct for depositing composite coatings on a Ti-alloy substrate using a thermal-spray coating technique. The coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) analyses. The corrosion behavior of the coatings was studied by electrochemical corrosion testing in simulated human body fluid. After the corrosion testing, the samples were analyzed by XRD and SEM/EDS analyses. HA and TiO₂ (rutile) were the main phases observed in the developed coatings. Bulk HA coating was amorphous; however, the addition of TiO₂ effectively improved the crystallinity of HA in HA-TiO₂ coating. The SEM analysis confirmed the formation of a well-formed HA-TiO₂ composite coating. HA coating exhibited higher bond strength (67.8?MPa) compared with HA-TiO₂ composite coating (37.6?MPa). The electrochemical study showed a significant improvement in the corrosion resistance of the Ti alloy after the deposition of the coatings.