Showing papers in "Journal of Materials Science in 1996"

Some physico-chemical aspects of hydroxylapatite

Abstract: A few significant physico-chemical aspects of hydroxylapatite, a biological material of extensive contemporary inter-disciplinary research, have been reviewed. Updated information on preparation techniques, characterization, isomorphous substitutions, and solubility equilibria is provided. Recent research trends and aspects which require further clarification have been emphasized.

Oxidation protection for carbon fibre composites

Abstract: Carbon fibre-reinforced ceramic matrix composites are promising candidate materials for high-temperature structural applications such as gas turbine blades. In oxidizing environments at temperatures above 400°C, however, carbon fibres are rapidly oxidized. There is, therefore, a need to coat the composite in order to protect it against oxidation. This review identifies the requirements of an effective oxidation protection system for carbon fibre-reinforced ceramics and summarizes the work which has been carried out towards this goal over the last 50 years. The most promising coatings are those composed of several ceramic layers designed to protect against erosion, spallation and corrosion, in addition to possessing a self-healing capability by the formation of glassy phases on exposure to oxygen.

Evaluation and extension of physical property-porosity models based on minimum solid area

Abstract: Physical property-porosity models based on minimum solid areas of idealized stackings of either: (1) spherical particles partially bonded (e.g. sintered), or (2) spherical pores in a solid matrix are shown to agree with appropriate physical property data for bodies whose porosity is reasonably represented by such stackings. Appropriate physical properties are those determined mainly by local stress or flux, e.g. elastic properties, strengths, and electrical and thermal conductivity. The minimum solid areas are, respectively, the: (1) bond (e.g. neck) area between particles defining pores smaller than the particles, or (2) minimum web thickness between adjacent pores being more than or equal to the surrounding particles (e.g. bubbles in a foam). Combinations of the models for mixtures of basic porosity types and changes in basic model parameters (e.g. stacking) over the significant porosity range covered, are shown to agree with the literature (mainly mechanical) property data for bodies of appropriate porosity combinations. Areas of further development and testing are noted.

Low-temperature synthesized aluminosilicate glasses

Abstract: The reaction below 100 °C of a dehydroxylated clay (metakaolinite: (Al2O3)(SiO2)2(H2O)005) suspended in an alkaline sodium silicate solution ((Na2O)(SiO2)14(H2O)x) leads to an amorphous glassy aluminosilicate, called in this work “low-temperature inorganic polymer glass” (LTIPG or IPG)

Polymer-clay nanocomposites: Free-radical grafting of polystyrene on to organophilic montmorillonite interlayers

Abstract: Vinyl monomer-montmorillonite intercalates, which are able to swell and disperse in organic solvents, have been prepared by a cation exchange process by the interaction between the Na+ or Ca2+ cations of montmorillonite and vinylbenzyltrimethylammonium chloride. The resulting vinyl monomer-montmorillonite materials have been identified by X-ray diffraction (XRD), elemental analysis and infrared absorption spectra. Free-radical solution polymerizations of the penetrated styrene between the interlayers of 5, 10, 25 and 50 wt% vinyl monomer-montmorillonite have resulted in grafted polystyrenemontmorillonite materials. The effect of montmorillonite amounts on the formed polystyrene was determined by extraction with organic solvents, which showed an increase in the grafted polymer formed (0.84–2.94 g/g MMT), and a decrease in the external polystyrene with increasing amounts of montmorillonite. The molecular weight of the external polystyrenes was found to be in the range of 22000. The vinyl monomer-montmorillonite and polymer-montmorillonite intercalates have been identified by XRD, elemental analysis and infrared spectroscopy. Examination of the polystyrene-montmorillonite materials by SEM, TEM and XRD showed spherical particles of nanosize about 150–400 nm, and basal spacings of 1.72–2.45 nm.

Characterization of dispersion state of filler and polymer-filler interactions in rubber-carbon black composites

Abstract: The physical properties of carbon black-filled rubbers are affected mainly by the distribution of filler, carbon black properties and polymer-filler interactions. A number of experimental methods and approaches for characterization of the dispersion state of filler in rubber-carbon black composites and an investigation of polymer-filler interactions are reviewed. The dispersion state characterization, electrical conductivity measurements, bound rubber evaluations, mechanical properties measurements, carbon black surface properties study, small angle X-ray scattering (SAXS) and nuclear magnetic resonance (NMR) spectroscopy are among the most important ones.

Structural investigations of phosphate glasses: a detailed infrared study of the x(PbO)-(1−x) P2O5 vitreous system

Abstract: The results and detailed discussion of an extensive experimental study of infrared spectra of the x (PbO)-(1−x)P2O5 vitreous system (x=0.3–0.75) together with a brief review of infrared spectra of phosphate compounds, are presented. Theoretical models employed in the interpretation of infrared spectra of glasses have been reviewed. The frequency ranges of various infrared bands belonging to PO 4 3− and P2O 7 4− , observed in different phosphate compounds, are discussed. The glassy and quenched samples were prepared from PbO and NH4H2PO4 by the rapid quenching technique. The infrared spectra of the constituents of the system, PbO and P2O5, in their polycrystalline and glassy forms, have been discussed. The intensity and wavenumbers of the infrared bands around 1600 and 3300 cm−1, assigned to the bending and stretching modes in H2O trapped by the hygroscopic glasses, have been followed for different compositions with x<0.5. The changes observed in these infrared bands established the role of water as an additional glass modifier. The intensity and frequency variations of the infrared bands have been followed through all the compositions for characteristic phosphate group frequencies including P=O, P-O-P stretching and bending modes and P-O bending mode. The results clearly suggest that the x(PbO)-(1−x)P2O5 system undergoes gradual structural changes from metaphosphate (x=0.5), to pyrophosphate (x=0.66) and to orthophosphate (x=0.75). The continuing presence of the infrared band, in varying intensity, in the region 1200–1280 cm−1 attributed to P=O, suggests that the glass-forming ability of the binary system is extendable at least up to x=0.66 composition, and that no complete rupture of P=O bond by Pb2+ takes place. The ionic character of the phosphate groups, P-O(−), PO 4 3− is well revealed by significant changes with the PbO content in the spectral features of the infrared bands around 1120 and 980 cm−1 respectively. The maximum intensity of the P-O(−) band at 1120 cm−1 for 55 mol% PbO suggests a partial breakdown of the covalent vitreous network of the phosphates and formation of a crystalline phase consisting of ionic groups PO 4 3− , P2O 6 2− and P2O 7 4− for PbO greater than 55 mol%. The observed pattern of variation in the intensity of the infrared bands in the 940–1080 cm−1 region attributed to the v3-mode in PO 4 3− , suggests a gradual transformation of PO 4 3− units to PO 3 − groups in lead meta-phosphate glass and then their restoration to PO 4 3− groups of pyro- and ortho-phosphate quenched samples. The results indicate a gradual decrease in the number of bridging oxygens and increase in the resonance behaviour of non-bridging oxygens as the mole percentage of metal oxide (PbO) increases in the glass. The infrared spectra of several binary phosphate glasses have been reviewed in the context of the study of effect of the cation on the infrared spectra. It is found that the influence of the cation on the infrared spectra of phosphate glasses does not show any striking regularity. Theoretical calculations of these band frequencies were found to agree well only in the case of pure stretching (P=O and O-H) vibrations and pure bending (P-O-P and O-H) vibrations. The disagreement in the case of P-O(−), P-O-H and other modes of P-O-P groups, has been attributed to the mixed nature of modes occurring in glasses. The changes in the positions of the characteristic bands and their relative intensities are strongly dependent on the structural units and PbO content in the phosphate glasses and the results emphasize the role of PbO as a network modifier.

Electrical percolation phenomena in cement composites containing conductive fibres

Abstract: Electrical conductivity measurements on cement composites containing carbon fibres or steel fibres were conducted. Percolation phenomena associated with electrical conductivity were observed. The conductivity of the systems studied increased by several orders of magnitude, at a specific concentration of conductive fibre, i.e. the percolation concentration. The percolation concentration is shown to be dependent on conductive fibre geometry instead of system composition. The results provide an important guide for the manufacture of conductive cement composites containing conductive fibres.

Influence of ferrite-martensite microstructural morphology on tensile properties of dual-phase steel

Abstract: The influence of ferrite-martensite microstructural morphology, volume fraction of martensite, epitaxial ferrite on the tensile behaviour of dual-phase steels, was studied. It was observed that increasing the martensite content and its aspect ratio raised tensile strength and ductility. Epitaxial ferrite in rolled material strongly reduced the strength and improved the ductility, suggesting that substructure strengthening of material, as well as increased stress transfer to the hard phase, contribute to the strength of thermo-mechanically processed material. Mettallographic analysis of deformed samples revealed that void nucleation occurs predominantly along the ferrite-martensite interface. The void density in the necked region increased towards the fracture surface in all samples and was higher for samples which exhibited localized necking.

The role of reinforcement architecture on impact damage mechanisms and post-impact compression behaviour

Abstract: This review considers the link between the damage tolerance of composite laminates and the nature and organization of the fibre reinforcement. This embraces composites made from unidirectional prepregs through composites based on a variety of textile forms such as woven fabrics, multiaxial fabrics, braids and knits. The objective has been firstly to detail how the differing varieties of composite exhibit different properties under impact conditions and under subsequent loading after impact. This includes both fracture mechanisms and data such as energy absorption, and peak failure loads. The second objective is to describe the links that have been found between these properties and the specific fibre architectures and damage development processes in the various composite forms. The post impact compression properties are highlighted as this is the area of greatest interest by end-users. The review describes the different forms of textiles that are used for composite reinforcement, considers different impact conditions (e.g. low velocity and ballistics), general materials variables such as fibre and resin type, and ultimately looks at specific textile systems. Some consideration is also given to the value and role of numerical modelling in the field of damage formation and damage tolerance. Clear differences have been found in the literature between composites based on different textile forms in terms of damage states after impact and the consequences of this damage on subsequent properties. While the literature is clearly incomplete at this time there is sufficient information available to indicate that control of fibre organization by the use of textiles may be an effective method of optimizing composite properties for specific end use properties.

Comparison of physical property-porosity behaviour with minimum solid area models

Abstract: An extensive survey of the porosity dependence of (room temperature) physical properties shows that mechanical properties and electrical and thermal conductivity, i.e. properties dependent on the local flux or fields in the material, follow minimum solid area models. This is shown extensively for elastic properties and tensile (flexure) strength, but consistency with other properties, e.g. compressive strength, hardness, electrical and thermal conductivity is also shown. Although data for ceramics is most extensive, data for rocks, metals, and carbon are included, since the consistency of these, especially of metals with ceramics, provides important support for the minimum solid area concept. While porosity characterization is generally minimal, expected model trends with pore character are corroborated by correlating processing and resultant expected pore character with porosity-property results. It is argued that properties dependent on mass should be better fit by a linear, i.e. rule of mixture, relationship between such properties and porosity. Support for this is shown in dielectric constant-porosity data.

Dielectric behaviour of thin films of β-PVDF/PZT and β-PVDF/BaTiO3 composites

Abstract: Thin films of the composites formed between poly(vinylidene fluoride) (PVDF) and lead zirconium titanate (PZT) and also barium titanate with 0–3 connectivity, have been obtained by dispersion of the ceramic powder in a solution of PVDF in dimethylacetamide DMA Evaporation of the solvent at 65 °C allowed crystallization of PVDF predominantly in the polar β phase, regardless of the amount of PZT or BaTiO3 powder added upto 40 vol % The relative permittivity and loss index values were determined for the pure components and for the composites with different ceramic contents, in the frequency range of 100 Hz to 13 MHz An increase in PZT or BaTiO3 content resulted in an increase in the relative permittivity of the composites, and the experimental results are shown to be in good agreement with those calculated from the theoretical expression of Yamada et al [1] The de electrical conductivity of composites with different compositions was also determined

An evaluation of hydroxyapatite-based filters for removal of heavy metal ions from aqueous solutions

Abstract: Three hydroxyapatite(HA)-based materials have been investigated with respect to their potential for removing heavy metal ions from aqueous solutions. The materials have been evaluated as both loose powders and in the form of ceramic foams. The results have shown that all three grades of HA were found to be capable of removing a number of different ionic species although the more impure grades generally yielded the best performance. It is believed that the increased impurity levels resulted in increased numbers of lattice defects which were ideal adsorption/exchange sites. 100% removal could be achieved for some ions under the correct experimental conditions. For the ceramic foam filters, the optimum filtration parameters were found to be a high surface area, long filtration times, a low pH and a high filtrate temperature. Ion adsorption was positively detected as a mechanism of ion removal. Ion exchange was not observed but could not be completely ruled out.

Low-temperature synthesized aluminosilicate glasses. Part II Rheological transformations during low-temperature cure and high-temperature properties of a model compound

Abstract: The reaction below 100 °C of a dehydroxylated clay (metakaolinite) suspended in an alkaline sodium silicate solution leads to an amorphous aluminosilicate, called low-temperature inorganic polymer glass (LTIPG or IPG). Some rheological transformations during the isothermal hardening process are followed with dynamic mechanical analysis (DMA) and compared with differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC). It can be concluded that the change in storage modulus (DMA) during the formation of the inorganic network can be characterized quantitatively with the evolution of the heat capacity (MDSC), and that the reaction rate is not decreased by the vitrification process. During the first heating after polymerization up to 1000°C, the material shrinks due to the evaporation of residual water from the reaction mixture as illustrated by thermogravimetric analysis (TGA) and thermomechanical analysis (TMA). The low-temperature synthesized inorganic polymer glass is thermomechanically stable up to a temperature of at least 650°C. In that temperature zone, the glass transition can be detected with TMA and DMA.

Grain size and porosity dependence of ceramic fracture energy and toughness at 22 °C

Abstract: A review of the fracture energy and toughness data for dense ceramics at 22 °C shows maxima commonly occurring as a function of grain size. Such maxima are most pronounced for non-cubic materials, where they are often associated with microcracking and R-curve effects, especially in oxides, but often also occur at too fine a grain size for association with microcracking. The maxima are usually much more limited, but frequently definitive, for cubic materials. In a few cases only a decrease with increasing grain size at larger grain size, or no dependence on grain size is found, but the extent to which these reflect lack of sufficient data is uncertain. In porous ceramics fracture toughness and especially fracture energy commonly show less porosity dependence than strength and Young's modulus. In some cases little, or no, decrease, or possibly a temporary increase in fracture energy or toughness are seen with increasing porosity at low or intermediate levels of porosity in contrast to continuous decreases for strength and Young's modulus. It is suggested that such (widely neglected) variations reflect bridging in porous bodies. The above maxima as a function of grain size and reduced decreases with increased porosity are less pronounced for fracture toughness as opposed to fracture energy, since the former reflects effects of the latter and Young's modulus, which usually has no dependence on grain size, but substantial dependence on porosity. In general, tests with cracks closer to the natural flaw size give results more consistent with strength behaviour. Implications of these findings are discussed.

The effect of indentation-induced cracking on the apparent microhardness

Abstract: The phenomenon of apparent microhardness increase with increasing applied indentation test load, the reverse indentation size effect (RISE), was addressed from the viewpoint of indentation-induced cracking. The apparent microhardness when the cracking occurs was found to be related to the applied indentation test load as P5/3. Previously published results on single crystals of silicon, GaAs, GaP and InP, which differ by a factor of four, all fall on the same line when analysed through this concept. It is concluded that the RISE is a result of the specimen cracking during the indentation.

Sapphire matrix composites reinforced with single crystal YAG phases

Abstract: An investigation of fabrication technology on eutectic composites consisting of Al2O3 phases and YAG (Y3Al5O12) phases was carried out by applying the unidirectional solidification process. Unidirectionally solidified eutectic composites consisting of 〈110〉 sapphire phases and 〈420〉 single crystal YAG phases could be fabricated successfully by lowering a Mo crucible at a speed of 5 mm h−1 under a pressure of 10−5 mmHg of argon. These eutectic composites have excellent high-temperature properties up to 1973 K. For example, the flexural strength is 360–500 MPa independent of testing temperature from room temperature to 1973 K. Oxidation resistance at 1973 K in an air atmosphere is superior to SiC and Si3N4 and the microstructure of these eutectic composites is stable even after heat treatment at 1773 K for 50 h in an air atmosphere.

Fracture mechanisms of the Strombus gigas conch shell: implications for the design of brittle laminates

Abstract: Flexural strength, crack-density evolution, work of fracture, and critical strain energy release rates were measured for wet and dry specimens of the Strombus gigas conch shell. This shell has a crossed-lamellar microarchitecture, which is layered at five distinct length scales and can be considered a form of ceramic “plywood”. The shell has a particularly high ceramic (mineral) content (99.9 wt%), yet achieves unusually good mechanical performance. Even though the strengths are modest (of the order 100 MPa), the laminated structure has a large strain to fracture, and a correspondingly large work of fracture, up to 13 kJ m−2. The large fracture resistance is correlated to the extensive microcracking that occurs along the numerous interfaces within the shell microstructure. Implications of this impressive work of fracture for design of brittle laminates are considered.

Indentation size effect: reality or artefact?

Abstract: The purpose of this investigation was to study the load dependence of the microhardness, typically in the range 5–500 gf. This well known phenomena is called the indentation size effect (ISE) and was investigated for two sets of specimens: titanium and aluminium alloys. Variation of the hardness with applied load was first compared with various existing models and the surface profile, near the indent, was measured by confocal microscopy. The formation of pile-ups near the indentation print led to the correction of the indent diagonal which is found to fit well with our experimental data as well as with other results in the literature. For the materials investigated, the ISE effect is an artefact, i.e. the variation of hardness with the applied load is only a consequence of the variation of the contact surface between the specimen and the indenter.

Observations on the formation of β-Al5FeSi phase in 319 type Al-Si alloys

Abstract: In Al-Si alloys, the properties are influenced by the shape and distribution of the eutectic silicon particles in the matrix, as also by the iron intermetallics and copper phases that occur upon solidification The β-Al5FeSi iron intermetallic phase, in particular, is known for its detrimental effect on the properties, and is controlled variously by the iron content and the melt/solidification conditions of the alloy The formation of the iron intermetallics has been observed in commercial 319 alloy end-chilled castings, obtained from non-treated and treated melts, where the effects of cooling rate, strontium modification and grain refinement have been studied The volume fraction of β-phase formed was seen to increase with the decrease in cooling rate (ie with increasing distance from the chill) in the untreated alloy Sympathetic (preferential) nucleation of the β-iron needles was also observed, in which the branching of β-needles from a parent needle resulted in the formation of large β-needle entities that can cover distances of ∼ 1200 μm across the matrix surface The beneficial effect of modification, ie strontium addition to the melt, was manifested through its influence on the fragmentation and dissolution of the β-needles The strontium “poisons” the sites where sympathetic nucleation takes place Dissolution was accelerated with increasing strontium content, the optimum level being ∼ 300 ppm Grain refining, on the other hand, negated the beneficial effect of modification, in that the β-needles underwent thickening and the sympathetic nucleation/branching also occurred The modified alloy was found to possess the lowest volume fraction of β-Al5FeSi phase among the unmodified, modified, grainrefined, and modified/grain-refined alloys

Martensitic transformations in Ti-(16–26 at%) Nb alloys

Abstract: Martensitic phase transformations in the solution-treated and water-quenched binary Ti-Nb alloys in the range of 16–26 at% Nb, were examined. An ordered, base-centred orthorhombic martensite was observed for alloys containing up to 23.4 at% Nb. The substructure of this martensite was generally composed of twins and stacking faults, the presence of antiphase boundaries observed in the plates indicating that the martensite underwent ordering during quenching. Both order-disorder and Ms temperatures were observed to be affected by total interstitial content, higher contents increasing both temperatures. Increasing the niobium content to above 23.4% resulted in retention of the β phase, this phase containing either athermal ω or “diffuse” ω depending upon niobium and total interstitial concentration. Finally, the microhardness of the Ti-Nb alloys examined was observed to decrease with increase in niobium and decrease in total interstitial content.

Effect of powder structure on the structure of thermally sprayed WC-Co coatings

Abstract: Five representative types of WC-Co powders were selected to clarify the dependence of the structure of sprayed coatings on the structure of powders themselves. The WC-Co coatings were sprayed with the Jet-Kote process and plasma spraying as well. The structure of WC-Co coatings was primarily characterized by X-ray diffraction. The X-ray diffraction patterns of the sprayed coatings were illustrated compared with those of powders, which aims at a better understanding of the structure of thermally sprayed WC-Co coatings. The selected coating was also analysed by differential scanning calorimetry (DSC). The decarburizing process, and the effects of powder structure and spray conditions on the crystal structure of sprayed WC-Co coatings are discussed in detail.

Silicon nitride crystal structure and observations of lattice defects

Abstract: In view of the considerable progress that has been made over the last 40 years on the microstructural design of silicon nitride and related materials of tailored properties for specific applications, a clear review of the current understanding of the crystal structure and crystal chemistry of silicon nitride is timely. The crystal structures, crystal chemistry, and lattice defect nature of silicon nitride are critically reviewed and discussed, with emphasis placed firstly on the structural nature of α-silicon nitride (whether it is a pure silicon nitride, or should better be regarded as an oxynitride); and secondly on the space group of β-silicon nitride (whether it is P63/m or P63). In conjunction with recent observations of vacancy clusters in α-silicon nitride, a comprehensive view compatible with all the experimental facts with respect to the structural nature of α-silicon nitride is tentatively presented.

Solders in electronics

Abstract: The metallurgy and mechanical behaviour of the principal solder types based on lead-tin alloys are reviewed. Particular emphasis is placed upon their performance under simulated service conditions, fatigue, creep and ageing, and life prediction. Requirements for improved and more environmentally compatible solders are explored.

Characterization of PAN-based carbon fibres with laser Raman spectroscopy

Abstract: Laser Raman spectroscopy (LRS) has been employed to characterize the structure and morphology of a series of carbon fibres, to assess the combined effects of ultimate firing temperature (UFT) and pre-graphitization drawing during manufacture and, finally, to investigate the influence of oxidative treatment upon the integrity of the fibre surface. Ten types of PAN-based carbon fibres of varying modulus, diameter and manufacturing method, were examined. All their spectral features were recorded and analysed in terms of position, bandwidth and band intensity. Low-modulus fibres, produced at low graphitization temperatures, exhibit weak and broad Raman bands in the 1200–1700 cm−1 frequency region. With the increase of the firing temperature, the spectral features sharpen and new lines appear at higher frequencies. The observed changes in the Raman spectra are discussed in detail and related to alterations in the conditions of manufacture.

Stresses and failure in the diametral compression test

Abstract: The validity of the diametral disc test with a small flat ground has been established. The stress distribution was determined by a finite element method for a range of loading conditions. The results show that for the case of a point load, the failure is due to shear and compressive stresses at the loading point. Application of the diametral disc test for a ground flat was proposed and tested. The width of the flattened area must be less than 0.2 times the diameter of the disc to obtain accurate tensile strength.

The failure of fibre composites and adhesively bonded fibre composites under high rates of test

Abstract: The dynamic effects which are commonly encountered during high-rate DCB tests with fibre composite and adhesively bonded fibre composite arms have been studied in detail. This paper, Part II of the series, follows Part I, which described the experimental aspects of the high-rate testing. Part III will report the results from mode II and mixed-mode I/II tests on the fibre-composite materials.

Synthesis of ultrafine LiCoO2 powders by the sol-gel method

Abstract: Ultrafine high-temperature (HT) LiCoO2 powders were synthesized by the sol-gel method using polyacrylic acid (PAA) as a chelating agent. The decomposition process of the gel precursor was examined to determine the crystallization temperature and the dependence of the physicochemical properties of HT-LiCoO2 powders on the PAA quantity was extensively investigated. Polycrystalline HT-LiCoO2 powders, composed of very uniformly sized ultrafine particulates with an average particle size of 30–50 nm and a specific surface area of 2.3–17 m2g−1, could be obtained at the lower calcination temperature of 550 °C and the shorter calcination time of 1 h compared to the solid-state reaction.

Control of calcium hexaluminate grain morphology in in-situ toughened ceramic composites

Abstract: The influence of processing conditions on the morphology of calcium hexaluminate (CA6) grains in Al2O3: 30 vol% CaO·6Al2O3 (CA6) ceramic composites was investigated. Specimens were prepared by in-situ reaction sintering using precursor powders of alumina, and either calcium carbonate or calcium oxide. In some samples, 1 vol% anorthite glass was added as a sintering aid. X-ray diffraction was used to study the phase development in the as-calcined and sintered states. The resultant microstructures were characterized using both scanning electron microscopy (SEM), and imaging secondary ion mass spectrometry (SIMS). It was found that the CA6 grains developed a platelike morphology when CaCO3 was used as the starting calcium-rich powder. In contrast, samples prepared using CaO resulted in equiaxed CA6 grains. This result was observed to be independent of the anorthite glass addition. The findings are rationalized in terms of distinct CA6 reaction mechanisms, resulting from differences in the reactivity of the powders during the early stages of calcining.

An X-ray photoelectron spectroscopic investigation into the chemical structure of deposits formed from hexamethyldisiloxane/oxygen plasmas

Abstract: The effect of oxygen addition to microwave-sustained plasmas of hexamethyldisiloxane (HMDSO) has been investigated. Attention was directed to the solid products formed on aluminium substrates (plasma deposits). To enable a quantitative analysis of these, X-ray photoelectron spectroscopy (XPS) of standard silicon-containing materials was carried out. When suitable charge correction is applied to the XP spectra of HMDSO/O2 plasma deposits, a number of very clear trends emerge. From changes in elemental composition, core line binding energies (Si2p, C 1s, and O 1s) and widths, we show how oxygen addition to the plasma affects the chemical nature of the plasma deposit. The data reported also provide (some limited) information on the reactions taking place in the plasma.