Bryony James

Microhardness variation in relation to carbide development in heat treated Cr3C2-NiCr thermal spray coatings

Abstract Cr 3 C 2 –NiCr thermal spray coatings have been extensively used to mitigate high temperature wear. During deposition compositional degradation occurs through dissolution of the carbide phase into the matrix. High temperature exposure leads to transformations in the microstructure, which influences the coating microhardness. While such developments have been investigated in short-term trials, no systematic long-term investigations of the microhardness variation as a function of microstructural development have been presented. In this work, high velocity sprayed Cr 3 C 2 –NiCr coatings were heat treated at 900 °C for up to 60 days in air and argon. With treatment, matrix phase supersaturation was reduced, while widespread carbide nucleation and growth generated an expansive carbide skeletal network. An initial softening of the coatings occurred through matrix phase refinement, the subsequent hardness recovery was a function of carbide development. Treatment in air generated further hardness increases as a result of internal oxidation.

Membrane fouling during filtration of milk––a microstructural study

Abstract The surface morphology and internal microstructure of a membrane are the result of membrane manufacturing processes and subsequent use during fluid processing in industry. Both these structural factors have a great effect on fouling and filtration performance. In this study, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy were used to comprehensively characterise the surface of unused microfiltration and ultrafiltration membranes, the fouled layer on the surface of membranes used for milk filtration and the internal fouling within the used membranes. A simple and effective sample preparation method was developed to study the internal membrane structure using high-resolution field emission SEM with low-accelerating voltage. Various methods of structural characterisation were compared and the results showed that for flat sheet membranes AFM is an appropriate and convenient technique for examining the surface topography of membranes. In contrast SEM is a very appropriate technique for examining the cross-sectional and internal structure of a membrane, either unused or fouled. Using these complimentary techniques it has been shown that internal fouling, during filtration of skim milk, proceeds by protein–polymer and protein–protein interactions. A gel layer forms on the surface of the membrane and has been imaged using SEM. This layer is slightly compressible and densifies as it grows. Fouling initiation commences after a very short filtration time.

Long-term carbide development in high-velocity oxygen fuel/high-velocity air fuel Cr3C2-NiCr coatings heat treated at 900 °C

During the deposition of Cr3C2-NiCr coatings, compositional degradation occurs, primarily through the dissolution of the carbide phase into the matrix. Exposure at an elevated temperature leads to transformations in the compositional distribution and microstructure. While these have been investigated in short-term trials, no systematic investigations of the long-term microstructural development have been presented for high-velocity sprayed coatings. In this work, high-velocity air fuel (HVAF) and high-velocity oxygen fuel (HVOF) coatings were treated at 900 °C for up to 60 days. Rapid refinement of the supersaturated matrix phase occurred, with the degree of matrix phase alloying continuing to decrease over the following 20 to 40 days. Carbide nucleation in the HVAF coatings occurred preferentially on the retained carbide grains, while that in the HVOF coatings developed in the regions of greatest carbide dissolution. This difference resulted in a variation in carbide morphologies. Preferential horizontal growth was evident in both coatings over the first 20 to 30 days of exposure, beyond which spheroidization of the microstructure occurred. After 30 days, the carbide morphology of both coatings was comparable, tending toward an expansive structure of coalesced carbide grains. The development of the carbide phase played a significant role in the microhardness variation of these coatings with time.

Tracking crystallinity in siliceous hot-spring deposits

Siliceous hot spring deposits (sinters) entrap paleoenvironmentally significant components and are used as extreme-environment analogs in the search for early Earth and extraterrestrial life. However, sinters undergo a series of textural and mineralogical changes during diagenesis that can modify and overprint original environmental signals. For ancient hydrothermal settings including those close to the dawn of life, these transformations have long since occurred, so that study of diagenetic processes and effects is best undertaken in much younger deposits still undergoing change. Three young sinters preserve the entire diagenetic sequence of silica phases, from opal-A to quartz. The 6000 to ∼ 11,500 years BP ± 70 years sinter at Steamboat Springs, Nevada, the ∼ 1600 - 1900 ± 160 years BP Opal Mound sinter at Roosevelt Hot Springs, Utah, and the ∼ 456 ± 35 years BP deposit at Sinter Island, Taupo Volcanic Zone, New Zealand, provide an opportunity to track crystallographic, mineralogic and morphologic transitions of sinter diagenesis using standard and new analytical approaches. Worldwide, sinter forms from cooling, alkali chloride waters as noncrystalline opal-A, transforming first into noncrystalline opal-A/CT, then paracrystalline opal-CT ± moganite, paracrystalline opal-C, and eventually to microcrystalline quartz. In this study, these changes were identified by the novel and combined application of electron backscatter diffraction, X-ray powder diffraction, and scanning electron and optical microscopy techniques. We show that mineralogical changes precede morphological and accompanied crystallographic transformations. During this modification, silica particles grow and shrink several times from the micron- to nano-meter scales via dissolution, reprecipitation and recrystallization, and diagenesis follows the Ostwald Step rule. All deposits followed nearly identical diagenetic pathways, with time as the only variable in the march toward physicochemically stable quartz crystals. Diagenesis alters original environmental signatures trapped within sinters. After five silica phase changes, filamentous microfossils are modified but still remain recognizable within sinter from the Opal Mound and Steamboat Springs deposits, and during the opal-A to opal-CT silica phase transformations at Sinter Island. Therefore, delineating diagenetic components and how they affect sinters is necessary to accurately identify biosignals from ancient hot-spring deposits.

Influence of fiber length on the mechanical properties of wood-fiber/polypropylene prepreg sheets

Abstract Natural fiber based composites have the potential to improve the mechanical properties of plastics while reducing the cost and weight. This study shows a practical method of blending natural-fiber with polypropylene to form a mat and then consolidated into a sheet by hot pressing. The natural fibers assessed were Pinus radiata and Eucalyptus regnan high temperature thermomechanical pulps and sisal (Agave sisalana) fibers. The tensile strength was shown to decrease with an increase in fiber content, while the tensile modulus was shown to increase. Tensile and flexural modulus were positively influenced by fiber length. The water performance tests of the sheets generally showed approximately 20% weight gain and approximately 3% thickness swell at 30% fiber content. The natural fiber surface chemical composition was determined by X-ray photoelectron spectroscopy and shown to be primarily covered with hydrophobic material such as lignin and extractives, while polypropylene was shown to be partially oxidized.

Characterization of Exhaust Particulates from a Dual Fuel Engine by TGA, XPS, and Raman Techniques

Particulate matter (PM) emitted from a dual fuel engine is characterized using thermogravimetry, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Thermogravimetric analysis (TGA) provides the mass fractions of elemental carbon and volatile materials in PM; XPS provides the possible chemical compositions in the topmost layer of PM surface and Raman analysis provides the possible structure of the carbon presented in PM. Dual fuel engine uses both liquid (diesel) and gaseous fuels simultaneously to produce mechanical power and can be switched to only diesel fueling under load. The dual fuel engine is operated with natural gas and simulated biogases (laboratory prepared) and results are compared between the dual fueling and diesel fueling under the same engine operating conditions. Significantly higher volatile fractions in PM are obtained for dual fueling compared to diesel fueling complementing the gravimetric results. The maximum contribution of the graphitic carbon or aliphatic carbon such as hydrocarbons and paraffins (C═C or C─C) are found in the topmost atomic layers of both the diesel and dual fuel PM samples. The other chemical states are found to be the carbon-oxygen functional groups indicating significant oxidation behavior in the PM surface. Lesser aromatic content is noticed in the case of dual fuel PM than diesel PM. The carbon in dual fuel PM is found to be more amorphous compared to diesel PM. These characterizations provide us new information how the PM from a diesel engine can be different from that from a dual fuel engine.

Multi-Layered Plasma-Polymerized Chips for SPR-Based Detection

The surface functionalization of a noble metal is crucial in a surface plasmon resonance-based biomolecular detection system because the interfacial coating must retain the activity of immobilized biomolecules while enhancing the optimal loading. We present here a one-step, room-temperature, high-speed, gas-phase plasma polymerization process for functionalizing gold substrates using siloxane as an adhesion layer and acrylic acid as a functional layer. Siloxane- and thiol-based coatings were compared for their performance as adhesion and the interfacial layer for subsequent functionalization. An in situ sequential deposition of siloxane and acrylic acid resulted in a 7-fold increase in carboxylic functionality surfacial content compared to films deposited with thiol-containing precursors. Grading of the layer composition achieved as a consequence of ion-induced mixing on the surface coating under the application of the plasma is confirmed through secondary ion mass spectroscopic studies. DNA hybridization assays were demonstrated on gold/glass substrates using surface plasmon enhanced ellipsometry and the applicability of this coating for protein immunoassays were demonstrated with plasma functionalized gold/plastic substrates in Biacore 3000 SPR instrument.

The effect of textural complexity of solid foods on satiation

Previous studies have shown that food texture affects satiation by influencing the eating rate, bite size and oral transit time. However, investigations into the direct effect of texture on satiation are limited. The objective of the current study was to investigate the effect of textural complexity on satiation, independent of oral processing time and energy density. A preload-test meal design was used in this study; model foods with three levels of textural complexity (low, medium and high) were consumed as preload foods followed by a two-course ad libitum meal. This study was a randomized cross-over trial with 38 subjects. The results clearly showed that food with greater textural complexity led to significantly lower food intake overall. The first course of the meal and total food intake was significantly reduced (p<0.05) although food intake at the second course did not differ between groups. Despite the differing total intake, all subjects rated to have the same sense of satiety after three hours post-trial and the time taken to the next eating occasion did not differ between different preload conditions. Increased textural complexity in food enhances satiation and may potentially impact on satiety however this needs to be further confirmed in future studies. The findings suggest that foods with more complex textures can be a helpful tool in reducing the short-term food intake and enhancing the satiation response.

In Situ ESEM Examination of Microstructural Changes of an Apple Tissue Sample Undergoing Low-Pressure Air-Drying Followed by Wetting

Low-pressure drying of apple tissue has been visualized in situ using an environmental scanning electron microscope (ESEM). Both freshly cut and pre-boiled sample tissues were tested for drying and followed by wetting processes and the differences between the two types of samples noted. Bubble formation was observed when drying the freshly cut sample and were found to form only around the intact cells (intracellular spaces or channels). Boiling produced a more uniform surface and no bubble formation could be observed. Air-drying of the two tissue samples was conducted as a complementary investigation so that the effect of boiling can be better ascertained.

Textural Complexity is a Food Property – Shown Using Model Foods

The aim of this study was to examine textural complexity by developing a model food with varying levels of textural complexity but comparable nutritional density. Embedding inclusions in a gel matrix and layering the samples created different levels of structural and textural complexity: low, medium, and high. Texture properties and textural complexity were analyzed by generic quantitative descriptive analysis and modified texture profiling. The total number of unique textural descriptors observed by the panellists was used as a rudimentary measure of textural complexity and an increasing trend of textural complexity, low complexity < medium complexity < high complexity was observed. Ten unique descriptors showed significantly greater intensity ratings (p < 0.05) for the high complexity sample. This suggested that these textural attributes may be more likely to be distinguished during consumption of a high complexity sample compared to the low complexity or medium complexity samples, leading to greater perceived textural complexity in the high complexity sample.