title: Effects of high energy mechanical milling on the kinetics of solid state reactions

authors: Ying, Danyang

abstract: The effects of high energy mechanical milling on the kinetics of solid state reactions in two binary metallic systems, Al-Ni and Cu-Al, and two metal-oxide systems, Al-TiO₂ and Cu(Al)-CuO, have been investigated by using X-ray diffractometry (XRD), differential thermal analysis (DTA), differential scanning calorimetry (DSC), optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

A quantitative analysis of the Ni/Al system was performed to gain an understanding of the reaction behaviour during heating of the high energy mechanically milled powders. Results showed that nucleation and lateral growth along the interface region occurred at different temperatures from the diffusion controlled transverse growth. The amount of new phase formed through nucleation and lateral growth along the interface region increased in proportion to the interface area.

A two-step model for describing new phase nucleation and growth along the interface and transverse growth perpendicular to the interface was developed from the principles of classic heterogeneous nucleation and growth theories and the one-dimensional diffusion equation. The model was verified against the experimental results of Ni/Al system. It was found that the interface area, activation energy and pre-exponential factor are the major parameters affecting the kinetics of the solid state reactions of the powders.

It was found that, in the Cu/Al system, Cu(Al) solid solution or  γ-Cu₉Al₄ intermetallic compound could form after the powder mixture was milled for up to 8 hours. Upon heating the powder mixtures milled for shorter times, γ-Cu₉Al₄ formed first in the powder with a nominal composition of Cu-14at%Al, and then, γ-Cu₉A₄ dissolved into Cu forming Cu(Al) solid solution. Whereas, θ-CuAl₂ formed first for the powder with a nominal composition of Cu-37at%Al, and then, θ-CuAl₂ reacted with Cu forming γ-Cu₉Al₄ intermetallic compound. The solid solution or intermetallic compound formed by heating the powders milled for shorter times is the same as that produced by mechanical alloying.

In the Al/TiO₂ system, the effects of high energy milling on the phase formation and reaction kinetics was studied. It was found that the reaction between Al and TiO₂ also followed a two step reaction mechanism: interfacial reaction and bulk diffusional reaction. The first phase formed by the interfacial reaction was always Al₃Ti irrespective of the initial composition of the powder mixture. The reaction product for the subsequent reaction depends on the composition of the powder mixture. α-Ti phase could form at a higher temperature. The formation of α-Al₂O₃ phase is highly dependent on the reaction kinetics. It requires higher temperature or longer time to form detectable amount.

In the case of Cu(Al)-CuO system, two reactions occurred sequentially: Reaction 1, forming Cu₂O from the reaction between CuO and Cu-Al powders and Reaction 2, forming Cu from the reaction between Cu₂O and Cu-Al powders. High energy mechanical milling enhanced both reactions leading to a substantial decrease in the reaction temperatures.

Overall, high energy mechanical milling enhances the solid state reactions by establishing and refining composite microstructures of the powder particles. The reaction temperature could be substantially decreased. Prolonged mechanical alloying process can be replaced by a short time mechanical milling plus a well controlled heat treatment process.

text: Effects of high energy mechanical milling on the kinetics of solid state reactions The effects of high energy mechanical milling on the kinetics of solid state reactions in two binary metallic systems, Al-Ni and Cu-Al, and two metal-oxide systems, Al-TiO₂ and Cu(Al)-CuO, have been investigated by using X-ray diffractometry (XRD), differential thermal analysis (DTA), differential scanning calorimetry (DSC), optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

A quantitative analysis of the Ni/Al system was performed to gain an understanding of the reaction behaviour during heating of the high energy mechanically milled powders. Results showed that nucleation and lateral growth along the interface region occurred at different temperatures from the diffusion controlled transverse growth. The amount of new phase formed through nucleation and lateral growth along the interface region increased in proportion to the interface area.

A two-step model for describing new phase nucleation and growth along the interface and transverse growth perpendicular to the interface was developed from the principles of classic heterogeneous nucleation and growth theories and the one-dimensional diffusion equation. The model was verified against the experimental results of Ni/Al system. It was found that the interface area, activation energy and pre-exponential factor are the major parameters affecting the kinetics of the solid state reactions of the powders.

It was found that, in the Cu/Al system, Cu(Al) solid solution or  γ-Cu₉Al₄ intermetallic compound could form after the powder mixture was milled for up to 8 hours. Upon heating the powder mixtures milled for shorter times, γ-Cu₉Al₄ formed first in the powder with a nominal composition of Cu-14at%Al, and then, γ-Cu₉A₄ dissolved into Cu forming Cu(Al) solid solution. Whereas, θ-CuAl₂ formed first for the powder with a nominal composition of Cu-37at%Al, and then, θ-CuAl₂ reacted with Cu forming γ-Cu₉Al₄ intermetallic compound. The solid solution or intermetallic compound formed by heating the powders milled for shorter times is the same as that produced by mechanical alloying.

In the Al/TiO₂ system, the effects of high energy milling on the phase formation and reaction kinetics was studied. It was found that the reaction between Al and TiO₂ also followed a two step reaction mechanism: interfacial reaction and bulk diffusional reaction. The first phase formed by the interfacial reaction was always Al₃Ti irrespective of the initial composition of the powder mixture. The reaction product for the subsequent reaction depends on the composition of the powder mixture. α-Ti phase could form at a higher temperature. The formation of α-Al₂O₃ phase is highly dependent on the reaction kinetics. It requires higher temperature or longer time to form detectable amount.

In the case of Cu(Al)-CuO system, two reactions occurred sequentially: Reaction 1, forming Cu₂O from the reaction between CuO and Cu-Al powders and Reaction 2, forming Cu from the reaction between Cu₂O and Cu-Al powders. High energy mechanical milling enhanced both reactions leading to a substantial decrease in the reaction temperatures.

Overall, high energy mechanical milling enhances the solid state reactions by establishing and refining composite microstructures of the powder particles. The reaction temperature could be substantially decreased. Prolonged mechanical alloying process can be replaced by a short time mechanical milling plus a well controlled heat treatment process.

year: 2000

title: Willing workers on organic farms (WWOOF): The alternative farm stay experience

authors: McIntosh, Alison J.

subjects: farm tourism

abstract: This paper aims to contribute to knowledge about the farm stay experience by providing exploratory insights into the characteristics that are common to a hosted stay on a WWOOF farm and to investigate whether the experiences provided for visitors by WWOOF hosts are notably different from those offered by other farm hosts. The paper reports the findings of in-depth interviews conducted with 12 WWOOF hosts and 22 visitors staying at WWOOF farms located in the rural region of Canterbury in the south island of New Zealand. The findings of the study, while indicative, show that the hosted experience on an organic (WWOOF) farm may be notably different from that provided at a commercial farm stay, with four key dimensions: the rurality of the experience; the opportunity to learn about organics; the personal meaningfulness of the experience; and the element of sincerity in the experience.

text: Willing workers on organic farms (WWOOF): The alternative farm stay experience This paper aims to contribute to knowledge about the farm stay experience by providing exploratory insights into the characteristics that are common to a hosted stay on a WWOOF farm and to investigate whether the experiences provided for visitors by WWOOF hosts are notably different from those offered by other farm hosts. The paper reports the findings of in-depth interviews conducted with 12 WWOOF hosts and 22 visitors staying at WWOOF farms located in the rural region of Canterbury in the south island of New Zealand. The findings of the study, while indicative, show that the hosted experience on an organic (WWOOF) farm may be notably different from that provided at a commercial farm stay, with four key dimensions: the rurality of the experience; the opportunity to learn about organics; the personal meaningfulness of the experience; and the element of sincerity in the experience.

year: 2006

title: Pōuri: Two original screenplays

authors: Kohere, Anthony

subjects: Screenplays

abstract: Pōuri, as defined on Te Aka Māori Dictionary, means “regret, mournful, gloomy, in the dark.” It is an apt description of the following stories: Unprivate Moments, and Haytham; or, The Māori Gothic. A common thematic tie between the characters is that they regret past actions, have become disheartened, and experience severe distress. As a thesis, the aim is to expand on what a “Māori story” is beyond the familiar, or dare I say, expected.

'Unprivate Moments' is about an estranged father and son reconciling their differences, disguised as a low-level spy film. I see this as an opportunity to take a well-defined genre and treat it in a realistic fashion in terms of location and character, although not necessarily in believability. Set in Whanganui it can play with many tropes and preconceptions, almost with self-awareness without falling into parody or metacommentary. The formatting does not follow industry standards but inverts the layout of the scene descriptions and dialogue. While I cannot say for certain, Stanley Kubrick is the only one I am aware of that has done this when he adapted 'A Clockwork Orange'. His rationale for this break in style was to draw the eye to the visual storytelling rather than the dialogue.

'Haytham' is centred on a young Byronic Māori man during the late 1880s. Like the archetype he is derived from, Haytham is a tall, dark, and mysterious man. As he reveals himself both to the audience and to the other characters, we come to find someone who has been  damaged and corrupted. This issue of childhood trauma is the central crux of the story and is explored through his relationships with the women in his life. And finally, despite the script’s setting and intentional use of familial names, this is not a biographical work.

text: Pōuri: Two original screenplays Pōuri, as defined on Te Aka Māori Dictionary, means “regret, mournful, gloomy, in the dark.” It is an apt description of the following stories: Unprivate Moments, and Haytham; or, The Māori Gothic. A common thematic tie between the characters is that they regret past actions, have become disheartened, and experience severe distress. As a thesis, the aim is to expand on what a “Māori story” is beyond the familiar, or dare I say, expected.

'Unprivate Moments' is about an estranged father and son reconciling their differences, disguised as a low-level spy film. I see this as an opportunity to take a well-defined genre and treat it in a realistic fashion in terms of location and character, although not necessarily in believability. Set in Whanganui it can play with many tropes and preconceptions, almost with self-awareness without falling into parody or metacommentary. The formatting does not follow industry standards but inverts the layout of the scene descriptions and dialogue. While I cannot say for certain, Stanley Kubrick is the only one I am aware of that has done this when he adapted 'A Clockwork Orange'. His rationale for this break in style was to draw the eye to the visual storytelling rather than the dialogue.

'Haytham' is centred on a young Byronic Māori man during the late 1880s. Like the archetype he is derived from, Haytham is a tall, dark, and mysterious man. As he reveals himself both to the audience and to the other characters, we come to find someone who has been  damaged and corrupted. This issue of childhood trauma is the central crux of the story and is explored through his relationships with the women in his life. And finally, despite the script’s setting and intentional use of familial names, this is not a biographical work.

year: 2022