title: Mechanical and Structural Properties of Microwave Sintered Tin-Copper-Antimony Alloys

authors: Ariff, Tasnim Firdaus Binti Mohamed

subjects: Pewter alloys

abstract: Tin-copper-antimony (pewter) alloys have been traditionally produced by a casting process which consumes large amounts of energy, time and as a result is expensive. This research aims to investigate the possibilities of implementing powder metallurgy for pewter production through a sintering process using microwave energy. The optimum sintering conditions using microwave sintering are also of interest. Pewter alloys were examined to determine the effect of green density, sintering time, and sintering temperature on the mechanical and structural properties of the sintered compacts. Samples were prepared by hydraulic pressing of a well mixed and blended tin alloy powder with three different compositions; 97wt%Sn 2wt%Cu 1wt%Sb, 94wt%Sn 4wt%Cu 2wt%Sb and 91wt%Sn 6wt%Cu 3wt%Sb. Two compaction loads were used to produce the samples with different green densities. Pellets pressed at 96 MPa had an average relative density of 80.7%, while those pressed at 129 MPa had an average green density of 84.6%.  

Sixteen different time-temperature combinations were used for the heat treatments at 160 and 220 C for both conventional and microwave sintering. However, the sintering times had to be restricted to 15 and 30 minutes for microwave heating. Meanwhile, 60 and 120 minutes were used for conventional heating. It was found that for all three compositions, samples with a higher green density had a higher sintered density, compared to samples with lower green density, for the same sintering time and temperature. The relative density of sintered pewter alloys increased on average by 13% after conventional sintering and by about 14% after microwave sintering, when the sintering was carried out for the longer of the two sintering times and at the higher of the sintering temperatures selected, for all three compositions. 

Moreover, the hardness increased by 25.6%, 23.5% and 7.0% when microwave sintered relative to the conventional sintering for 97Sn2Cu1Sb, 94Sn4Cu2Sb and 91Sn6Cu3Sb alloys respectively. Nevertheless, the grain size remained similar for all three compositions under the same sintering conditions. The degree of grain growth in microwave sintered samples was marginally smaller (up to 23-24 μm) than in conventionally sintered samples which reached a grain size of 26-27 μm. 

In terms of strength, microwave sintering produced samples with similar properties to those conventionally sintered under the same sintering conditions for all three compositions. The tensile strengths obtained compared well with the strengths obtained from the casting process. Nonetheless, tensile strengths for both conventionally and microwave sintered material was higher in the transverse direction than in the longitudinal direction. In conventionally sintered material, there was an increase in transverse strength of about 6.9%, 5% and 4%, while for the microwave sintered material, the strength increase was 9.1%, 5.6% and 4.5% for 97Sn2Cu1Sb, 94Sn4Cu2Sb and 91Sn6Cu3Sb alloys respectively when compared to the longitudinal direction. 

The microwave sintered samples in general have improved hardness, better densification and a finer microstructure compared with the conventionally sintered samples and traditionally cast pewter. Increasing the Cu and Sb content increases the hardness and strength but in return, decreases its ductility. Hence, a pewter alloy with a moderate amount of Cu and Sb, i.e. 97Sn2Cu1Sb, microwave sintered at 220 C for 30 minutes would be the best choice for optimum mechanical properties.

text: Mechanical and Structural Properties of Microwave Sintered Tin-Copper-Antimony Alloys Tin-copper-antimony (pewter) alloys have been traditionally produced by a casting process which consumes large amounts of energy, time and as a result is expensive. This research aims to investigate the possibilities of implementing powder metallurgy for pewter production through a sintering process using microwave energy. The optimum sintering conditions using microwave sintering are also of interest. Pewter alloys were examined to determine the effect of green density, sintering time, and sintering temperature on the mechanical and structural properties of the sintered compacts. Samples were prepared by hydraulic pressing of a well mixed and blended tin alloy powder with three different compositions; 97wt%Sn 2wt%Cu 1wt%Sb, 94wt%Sn 4wt%Cu 2wt%Sb and 91wt%Sn 6wt%Cu 3wt%Sb. Two compaction loads were used to produce the samples with different green densities. Pellets pressed at 96 MPa had an average relative density of 80.7%, while those pressed at 129 MPa had an average green density of 84.6%.  

Sixteen different time-temperature combinations were used for the heat treatments at 160 and 220 C for both conventional and microwave sintering. However, the sintering times had to be restricted to 15 and 30 minutes for microwave heating. Meanwhile, 60 and 120 minutes were used for conventional heating. It was found that for all three compositions, samples with a higher green density had a higher sintered density, compared to samples with lower green density, for the same sintering time and temperature. The relative density of sintered pewter alloys increased on average by 13% after conventional sintering and by about 14% after microwave sintering, when the sintering was carried out for the longer of the two sintering times and at the higher of the sintering temperatures selected, for all three compositions. 

Moreover, the hardness increased by 25.6%, 23.5% and 7.0% when microwave sintered relative to the conventional sintering for 97Sn2Cu1Sb, 94Sn4Cu2Sb and 91Sn6Cu3Sb alloys respectively. Nevertheless, the grain size remained similar for all three compositions under the same sintering conditions. The degree of grain growth in microwave sintered samples was marginally smaller (up to 23-24 μm) than in conventionally sintered samples which reached a grain size of 26-27 μm. 

In terms of strength, microwave sintering produced samples with similar properties to those conventionally sintered under the same sintering conditions for all three compositions. The tensile strengths obtained compared well with the strengths obtained from the casting process. Nonetheless, tensile strengths for both conventionally and microwave sintered material was higher in the transverse direction than in the longitudinal direction. In conventionally sintered material, there was an increase in transverse strength of about 6.9%, 5% and 4%, while for the microwave sintered material, the strength increase was 9.1%, 5.6% and 4.5% for 97Sn2Cu1Sb, 94Sn4Cu2Sb and 91Sn6Cu3Sb alloys respectively when compared to the longitudinal direction. 

The microwave sintered samples in general have improved hardness, better densification and a finer microstructure compared with the conventionally sintered samples and traditionally cast pewter. Increasing the Cu and Sb content increases the hardness and strength but in return, decreases its ductility. Hence, a pewter alloy with a moderate amount of Cu and Sb, i.e. 97Sn2Cu1Sb, microwave sintered at 220 C for 30 minutes would be the best choice for optimum mechanical properties.

year: 2009

title: A pluralist and interdisciplinary approach to encryption regulation

authors: Dizon, Michael

abstract: The importance of trust in encryption is paramount, influencing user adoption and acceptance of the technology. A pluralist and interdisciplinary approach reveal that trust extends beyond the technology itself to include those who develop, provide, and regulate it. If encryption is perceived as unsafe or insecure, trust is compromised. Mandatory backdoors, allowing unauthorized access, face opposition as they erode trust in the technology, the government, and potential malicious actors. Trust is foundational to encryption, encompassing not only the technology but also providers and regulators.

Proposed encryption regulations must be evaluated based on their impact on trustworthiness. Questions should be raised: Does the regulation strengthen, maintain, or weaken trust in encryption and among relevant parties? Measures that diminish trust should be discarded, while those supporting or building trust should be explored. Trust emerges as a core consideration in crafting encryption laws and policies.

A comprehensive approach considers legal, social, and technical dimensions when addressing the complex task of regulating encryption. Relying solely on legal means is insufficient. Rejecting a legal-centric mindset allows acknowledgment of plural normative orders in a digital networked world. Understanding the critical technical and social principles and values surrounding encryption regulation becomes essential. Therefore, when formulating technology laws and policies, a pluralist and interdisciplinary approach, incorporating fundamental principles and values, is crucial to comprehensively address the legal, technical, and social aspects of the technology at hand.

text: A pluralist and interdisciplinary approach to encryption regulation The importance of trust in encryption is paramount, influencing user adoption and acceptance of the technology. A pluralist and interdisciplinary approach reveal that trust extends beyond the technology itself to include those who develop, provide, and regulate it. If encryption is perceived as unsafe or insecure, trust is compromised. Mandatory backdoors, allowing unauthorized access, face opposition as they erode trust in the technology, the government, and potential malicious actors. Trust is foundational to encryption, encompassing not only the technology but also providers and regulators.

Proposed encryption regulations must be evaluated based on their impact on trustworthiness. Questions should be raised: Does the regulation strengthen, maintain, or weaken trust in encryption and among relevant parties? Measures that diminish trust should be discarded, while those supporting or building trust should be explored. Trust emerges as a core consideration in crafting encryption laws and policies.

A comprehensive approach considers legal, social, and technical dimensions when addressing the complex task of regulating encryption. Relying solely on legal means is insufficient. Rejecting a legal-centric mindset allows acknowledgment of plural normative orders in a digital networked world. Understanding the critical technical and social principles and values surrounding encryption regulation becomes essential. Therefore, when formulating technology laws and policies, a pluralist and interdisciplinary approach, incorporating fundamental principles and values, is crucial to comprehensively address the legal, technical, and social aspects of the technology at hand.

year: 2021-11

title: Māori men's positive and interconnected sense of self, being and place

authors: Rua, Mohi

subjects: Maori men, interconnected self, pluralistic identities, relational health

abstract: Māori  men are on the wrong side of the ledger when it comes to illness and crime rates. Correspondingly, there is a significant amount of research into issues such as abuse and premature death involving Māori men, who are also often characterised in public discourse as inarticulate, deviant and incapable of maintaining positive relationships. There is very little research on positive practices among Māori men who are caring and expressive, and who do not harm their partners, families, and communities. This thesis explores how Māori men negotiate a positive sense of self, relationships and a place in our society, which is awash with negative characterisations of Māori men. I document how Māori men's identities are pluralistic and on-going projects. These identities are negotiated within the settler society through interactions with other people and media characterisations. These identities are also negotiated within the Māori world through interactions with whānau (immediate and extended family) and participation in cultural rituals, including tangihanga (traditional Māori death ritual/funeral process). This research involves two separate, yet interrelated studies, and is guided by kaupapa Māori research, Māori cultural concepts, Māori relational understandings of being and health, and relevant social science theory and research. Study one explores Māori men’s relationships with other men, their families and media depictions of men in the settler society. The participants from study one are working class men who were also part-time members of a Territorial Army unit within which Māori and Pākehā  men come together through mutual interests and negotiate meaningful relationships, and various cultural similarities and differences. Study one drew upon an ethnographic orientation that included direct observations, narrative interviews, media diaries and photo elicitation projects to understand the everyday lived realities of participants’ in settler society. Study two explores the constructive engagement of working class ex-Army Māori men back in their communities of origin in order to investigate key aspects of their identities and relationships as men within the Māori world. An ethnographic approach was also used in study two and involved direct observations, participation in shared practices and narrative interviews. Overall, findings from these studies demonstrate how Māori men construct a positive sense of self that extends beyond the deficit-orientated characterisations offered by academic research and mainstream media depictions. In constructing understandings of themselves and their place in the world, my participants emphasise their meaningful relationships with partners, children, colleagues, friends and communities. These men invoke a positive sense of self through accounts of belonging, reciprocity, dialogue, intimacy, and care for themselves, their whānau, and traditions. Participants’ positive Māori self-constructions are fundamentally interconnected with other people, cultural traditions, physical and symbolic places, and shared practices. My research sheds light on Māori men’s ways of belonging and being that span, but manifest in unique ways within, the settler society and the Māori world. This research also contributes to scholarship on men that takes a strengths-based approach by considering the valuable everyday functions men serve within their families and communities.

text: Māori men's positive and interconnected sense of self, being and place Māori  men are on the wrong side of the ledger when it comes to illness and crime rates. Correspondingly, there is a significant amount of research into issues such as abuse and premature death involving Māori men, who are also often characterised in public discourse as inarticulate, deviant and incapable of maintaining positive relationships. There is very little research on positive practices among Māori men who are caring and expressive, and who do not harm their partners, families, and communities. This thesis explores how Māori men negotiate a positive sense of self, relationships and a place in our society, which is awash with negative characterisations of Māori men. I document how Māori men's identities are pluralistic and on-going projects. These identities are negotiated within the settler society through interactions with other people and media characterisations. These identities are also negotiated within the Māori world through interactions with whānau (immediate and extended family) and participation in cultural rituals, including tangihanga (traditional Māori death ritual/funeral process). This research involves two separate, yet interrelated studies, and is guided by kaupapa Māori research, Māori cultural concepts, Māori relational understandings of being and health, and relevant social science theory and research. Study one explores Māori men’s relationships with other men, their families and media depictions of men in the settler society. The participants from study one are working class men who were also part-time members of a Territorial Army unit within which Māori and Pākehā  men come together through mutual interests and negotiate meaningful relationships, and various cultural similarities and differences. Study one drew upon an ethnographic orientation that included direct observations, narrative interviews, media diaries and photo elicitation projects to understand the everyday lived realities of participants’ in settler society. Study two explores the constructive engagement of working class ex-Army Māori men back in their communities of origin in order to investigate key aspects of their identities and relationships as men within the Māori world. An ethnographic approach was also used in study two and involved direct observations, participation in shared practices and narrative interviews. Overall, findings from these studies demonstrate how Māori men construct a positive sense of self that extends beyond the deficit-orientated characterisations offered by academic research and mainstream media depictions. In constructing understandings of themselves and their place in the world, my participants emphasise their meaningful relationships with partners, children, colleagues, friends and communities. These men invoke a positive sense of self through accounts of belonging, reciprocity, dialogue, intimacy, and care for themselves, their whānau, and traditions. Participants’ positive Māori self-constructions are fundamentally interconnected with other people, cultural traditions, physical and symbolic places, and shared practices. My research sheds light on Māori men’s ways of belonging and being that span, but manifest in unique ways within, the settler society and the Māori world. This research also contributes to scholarship on men that takes a strengths-based approach by considering the valuable everyday functions men serve within their families and communities.

year: 2015