title: Generation and Langmuir probe analysis of a DC glow discharge and the deposition of chromium from a carbonyl precursor

authors: Pilling, L.S.

abstract: Experimental investigations detailed in this thesis fall into two distinct areas: Diagnostics of a nitrogen DC discharge with Langmuir probes and spectroscopy, and experiments designed to deposit chromium metal from a chromium hexacarbonyl precursor (Cr(C0)6). New diagnostic equipment was designed, tested and implemented to record Langmuir probe data with high resolution and accuracy. A monochromator was employed to record the light emission from the plasma. This identified which ionized species were present as well as the ion temperature from the resulting band structures present. The monochromator analysis was necessary to validate the assumptions of the Langmuir probe theory and to allow a choice of which theories applied. 
The Langmuir probe analysis of the recorded data for many plasmas have been well covered in the literature but few papers give a comprehensive coverage of the main probe theories using the one set of data and fewer still make use of double as well as single probes. The majority simply assume the particular theory used is relevant to the plasma conditions and the resulting temperatures and densities are correct. 
During the experiments and subsequent analysis it was found, similar to other researchers, that the ion densities were consistently higher than the electron densities even though the theoretical analysis applied in the saturation regimes appeared to be valid. Rather than ignoring this issue, and assuming ion collisions or secondary electron emission were the cause, new methods were developed to analyse the data. By determining the gradient of the saturation regimes and comparing them to those expected experimentally, it was found that the ion saturation regime neither followed the orbital nor radial motion theories investigated. However, the electron current did follow the orbital motion theory and it is demonstrated that the densities obtained from the ion currents, using these theories, were incorrect. This had been previously shown to be true only with non-probe methods. 
Using the same discharge configuration, impurity-free chromium films were deposited onto stainless steel substrates from a chromium hexacarbonyl precursor. This had been attempted by previous researchers, using a variety of discharge configurations, who invariably deposited similar metallic films with significant levels of oxygen and carbon impurities. The combination of the carbonyl precursor and the carrier gases (nitrogen and argon) with the discharge configuration resulted in these impurity-free films even when a negative bias of up to 50 V was applied to the sample.

text: Generation and Langmuir probe analysis of a DC glow discharge and the deposition of chromium from a carbonyl precursor Experimental investigations detailed in this thesis fall into two distinct areas: Diagnostics of a nitrogen DC discharge with Langmuir probes and spectroscopy, and experiments designed to deposit chromium metal from a chromium hexacarbonyl precursor (Cr(C0)6). New diagnostic equipment was designed, tested and implemented to record Langmuir probe data with high resolution and accuracy. A monochromator was employed to record the light emission from the plasma. This identified which ionized species were present as well as the ion temperature from the resulting band structures present. The monochromator analysis was necessary to validate the assumptions of the Langmuir probe theory and to allow a choice of which theories applied. 
The Langmuir probe analysis of the recorded data for many plasmas have been well covered in the literature but few papers give a comprehensive coverage of the main probe theories using the one set of data and fewer still make use of double as well as single probes. The majority simply assume the particular theory used is relevant to the plasma conditions and the resulting temperatures and densities are correct. 
During the experiments and subsequent analysis it was found, similar to other researchers, that the ion densities were consistently higher than the electron densities even though the theoretical analysis applied in the saturation regimes appeared to be valid. Rather than ignoring this issue, and assuming ion collisions or secondary electron emission were the cause, new methods were developed to analyse the data. By determining the gradient of the saturation regimes and comparing them to those expected experimentally, it was found that the ion saturation regime neither followed the orbital nor radial motion theories investigated. However, the electron current did follow the orbital motion theory and it is demonstrated that the densities obtained from the ion currents, using these theories, were incorrect. This had been previously shown to be true only with non-probe methods. 
Using the same discharge configuration, impurity-free chromium films were deposited onto stainless steel substrates from a chromium hexacarbonyl precursor. This had been attempted by previous researchers, using a variety of discharge configurations, who invariably deposited similar metallic films with significant levels of oxygen and carbon impurities. The combination of the carbonyl precursor and the carrier gases (nitrogen and argon) with the discharge configuration resulted in these impurity-free films even when a negative bias of up to 50 V was applied to the sample.

year: 2003

title: The temperature response of nitrate removal in denitrification beds

authors: Carter, Anna Marie

subjects: nitrate removal

abstract: The addition of reactive nitrogen (Nᵣ) to agricultural systems has helped crop production match human population growth. However, the addition of Nᵣ comes at a cost to environment in the form of ozone destruction, habitat degradation and biodiversity loss. Denitrification beds represent an effective method for the removal of Nᵣ from a range of wastewaters and groundwater with high nitrate (NO₃¯) concentrations. Beds are lined containers filled with a carbon (C) source to enhance denitrification: the conversion of NO₃¯ to unreactive dinitrogen (N₂). 

In general, the rate of NO₃¯ removal in denitrification beds increases with increasing temperature. However, the temperature response of NO₃¯ removal in beds is poorly constrained as other controlling factors (e.g. NO₃¯ concentration and C source availability) can obscure the effect of temperature. The objective of this study was to measure the rates of NO₃¯ removal in three denitrification beds as temperature changed seasonally. The beds were located in the North Island of New Zealand and were loaded with NO₃¯ from wastewater from a hydroponic glasshouse (Karaka), domestic effluent from a campground (Motutere) and wastewater and domestic effluent from a research station (Newstead). Water samples were collected from wells installed along the length of each bed every month and were analysed for NO₃¯ concentration by ion chromatography. Rates of NO₃¯ removal were calculated using the change in NO₃¯ concentration and the flow rate. The temperatures of the beds were also measured at each sampling. 

Nitrate concentrations declined along the length of each denitrification bed and rates of NO₃¯ removal were calculated to average 3.6, 4.3 and 1.7 g N m¯³ day¯¹ for Karaka, Motutere and Newstead, respectively. The rates of removal increased with increasing temperature at Karaka and Motutere and the Q₁₀ values (the factor by which the rate of removal increased for a 10 °C increase in temperature) were calculated as 4.1 and 2.2 for Karaka and Motutere, respectively. The rates of NO₃¯ removal and Q₁₀ values were similar to those reported in previous studies of denitrification beds both in New Zealand and overseas. However, the rate of NO₃¯ removal at Karaka was less than the rate of removal of 7.6 g N m¯³ day¯¹ previously measured at Karaka in a study 5 years ago. Similarly, the temperature response at Karaka was higher than the Q₁₀ of 2 reported in this previous study at Karaka. The decrease in removal and increase in Q₁₀ may have been due to a decline in C source quality. 

There was no evidence of an increase in the rate of NO₃¯ removal with temperature at Newstead, with a Q₁₀ calculated as 1.0. The denitrification bed had been recently installed and was in a start-up phase. It was likely that the pretreatment system, in particular the nitrifying component responsible for converting ammonium (NH4+) in the effluent to NO₃¯, was not functioning effectively which resulted in low NO₃¯ concentrations entering the bed at Newstead. Nitrate was depleted within the beds at Motutere and Newstead which indicated that the rates of removal were NO₃¯ limited and that the temperature response may not have been adequately measured. 

This study confirmed that the rate of NO₃¯ removal increased with increasing temperature in the denitrification beds at Karaka and Motutere. The temperature response of NO₃¯ removal was similar to the response reported in previous studies of denitrification beds. However, additional research is required to further constrain the range of Q₁₀ values from which future denitrification beds can be designed to optimise NO₃¯ removal. Whether Q₁₀ values increase as wood chips age and C quality decreases also requires further investigation.

text: The temperature response of nitrate removal in denitrification beds The addition of reactive nitrogen (Nᵣ) to agricultural systems has helped crop production match human population growth. However, the addition of Nᵣ comes at a cost to environment in the form of ozone destruction, habitat degradation and biodiversity loss. Denitrification beds represent an effective method for the removal of Nᵣ from a range of wastewaters and groundwater with high nitrate (NO₃¯) concentrations. Beds are lined containers filled with a carbon (C) source to enhance denitrification: the conversion of NO₃¯ to unreactive dinitrogen (N₂). 

In general, the rate of NO₃¯ removal in denitrification beds increases with increasing temperature. However, the temperature response of NO₃¯ removal in beds is poorly constrained as other controlling factors (e.g. NO₃¯ concentration and C source availability) can obscure the effect of temperature. The objective of this study was to measure the rates of NO₃¯ removal in three denitrification beds as temperature changed seasonally. The beds were located in the North Island of New Zealand and were loaded with NO₃¯ from wastewater from a hydroponic glasshouse (Karaka), domestic effluent from a campground (Motutere) and wastewater and domestic effluent from a research station (Newstead). Water samples were collected from wells installed along the length of each bed every month and were analysed for NO₃¯ concentration by ion chromatography. Rates of NO₃¯ removal were calculated using the change in NO₃¯ concentration and the flow rate. The temperatures of the beds were also measured at each sampling. 

Nitrate concentrations declined along the length of each denitrification bed and rates of NO₃¯ removal were calculated to average 3.6, 4.3 and 1.7 g N m¯³ day¯¹ for Karaka, Motutere and Newstead, respectively. The rates of removal increased with increasing temperature at Karaka and Motutere and the Q₁₀ values (the factor by which the rate of removal increased for a 10 °C increase in temperature) were calculated as 4.1 and 2.2 for Karaka and Motutere, respectively. The rates of NO₃¯ removal and Q₁₀ values were similar to those reported in previous studies of denitrification beds both in New Zealand and overseas. However, the rate of NO₃¯ removal at Karaka was less than the rate of removal of 7.6 g N m¯³ day¯¹ previously measured at Karaka in a study 5 years ago. Similarly, the temperature response at Karaka was higher than the Q₁₀ of 2 reported in this previous study at Karaka. The decrease in removal and increase in Q₁₀ may have been due to a decline in C source quality. 

There was no evidence of an increase in the rate of NO₃¯ removal with temperature at Newstead, with a Q₁₀ calculated as 1.0. The denitrification bed had been recently installed and was in a start-up phase. It was likely that the pretreatment system, in particular the nitrifying component responsible for converting ammonium (NH4+) in the effluent to NO₃¯, was not functioning effectively which resulted in low NO₃¯ concentrations entering the bed at Newstead. Nitrate was depleted within the beds at Motutere and Newstead which indicated that the rates of removal were NO₃¯ limited and that the temperature response may not have been adequately measured. 

This study confirmed that the rate of NO₃¯ removal increased with increasing temperature in the denitrification beds at Karaka and Motutere. The temperature response of NO₃¯ removal was similar to the response reported in previous studies of denitrification beds. However, additional research is required to further constrain the range of Q₁₀ values from which future denitrification beds can be designed to optimise NO₃¯ removal. Whether Q₁₀ values increase as wood chips age and C quality decreases also requires further investigation.

year: 2014

title: Frozen rights?: The right to develop Maori treaty and aboriginal rights

authors: Joseph, Robert

subjects: Maori

abstract: Bishop Manuhuia Bennett often asked the question: "What did Maori call New Zealand before the arrival of the Pakeha [Europeans]?" After a deliberate pause, he would then simply utter: "Ours".

text: Frozen rights?: The right to develop Maori treaty and aboriginal rights Bishop Manuhuia Bennett often asked the question: "What did Maori call New Zealand before the arrival of the Pakeha [Europeans]?" After a deliberate pause, he would then simply utter: "Ours".

year: 2011