Stuart Hampshire

University of Limerick | UL · The Bernal Institute

Oxynitride glasses combine a high refractoriness, with Tg typically >850°C, and remarkable mechanical properties in comparison with their parent oxide glasses. Their Young's modulus and fracture toughness reach 170 GPa and 1.4 MPa.m0.5, respectively. Most reports show good linear relationships between glass property values and nitrogen content. The...

This paper reviews investigations of silicon nitride‐silicon carbide micro‐nano‐composites from the original work of Niihara, who proposed the concept of structural ceramic nanocomposites, to more recent work on strength and creep resistance of these unique materials. Various different raw materials are described which lead to formation of nano‐siz...

The phase formation behaviour of β′-SiAlON with the general formula Si6-zAlzOzN8-z was studied comprehensively for z values from 1 to 3 using spark plasma sintering (SPS) as the consolidation technique at synthesis temperatures from 1400 to 1700 °C. The samples were prepared close to the β′-SiAlON composition line: Si3N4 − 4/3(AlN·Al2O3) in the pha...

Oxynitride glasses form in a number of M–Si–Al–O–N systems where up to 30 equivalent % (eq. %) nitrogen can be accommodated. Elastic modulus, hardness, glass‐transition temperature (T g), and viscosity all increase linearly with nitrogen content whereas thermal expansion coefficient decreases. For example, for glasses with constant cation ratio (in...

Coal fly ash, a solid state waste massively produced from coal combustion, is considered to be highly hazardous to the environment due to its persistently toxic trace elements. High-value added waste recycling is a promising technique to address this issue. In this work, a waste-to-resource strategy is proposed for design of highly porous whisker-s...

This article provides an overview of the effects of glass composition on properties and crystallization of oxynitride glasses. Oxynitride glass formation occurs in a number of M–Si–O–N, M–Si–Al–O–N and M–Si–Mg–O–N systems and was reviewed in the previous article. The effect of nitrogen substitution for oxygen in silicate and aluminosilicate glasses...

SiAlONs are solid solutions based on the α- and β-silicon nitride structures. β′-SiAlON is formed when oxygen (O²⁻) replaces nitrogen (N³⁻) and silicon (Si⁴⁺) is replaced by aluminum (Al³⁺) to maintain overall charge neutrality. In α′-SiAlON, partial replacement of Si⁴⁺ by Al³⁺ occurs if, at the same time, charge compensation is effected by the acc...

For all but 5 of his 94 years Kenneth Henderson Jack lived, studied, and worked within 10 miles of where he was born, in the North-East of England. Educated in chemistry, he became an X-ray crystallographer. He applied his knowledge of chemistry and his skills in crystallography to the three main areas of materials science: metals, glasses and cera...

This article gives an overview of surface and bulk matter transport processes occurring during the densification of ceramic powder compacts. Starting from purified or chemically synthesized raw materials, sintering takes place by either solid state or liquid phase mechanisms during heat treatment which can be supplemented by use of microwaves, exte...

This article outlines the use of silicon nitride and silicon carbide ceramics as biomaterials. Silicon nitride is densified using Y2O3 and Al2O3 as sintering additives and is fired in nitrogen at >1700°C followed by hot-isostatic pressing. Commercially, it has been developed for spinal reconstruction devices. Using various chemical or heat treatmen...

Ceramic materials are commonly fabricated by powder processing and a subsequent heat treatment, which results in the elimination of about 40 vol% of porosity during the sintering step. The densification occurs at high temperature allowing atom diffusion in the solid state or through a liquid phase but is always accompanied by grain growth occurring...

Oxynitride glasses are formed by the replacement of oxygen atoms by nitrogen in silicate and aluminosilicate glasses in various M-Si-O-N, M-Si-Al-O-N, and M-Si-Mg-O-N systems, where M is a modifying cation such as Mg, Ca, Ba, Sc, Y and the rare earth lanthanides. Representation of four and five-component systems are explained and glass forming regi...

Coal fly ash, a solid state waste massively produced from coal combustion, is considered to be highly hazardous to the environment due to its persistently toxic trace elements. High-value added waste recycling is a promising technique to address this issue. In this work, a waste-to-resource strategy is proposed for design of highly porous whisker-s...

The low strength of bioglasses have restricted their use to non‐load bearing applications and therefore improvements in mechanical properties are needed. One solution to this challenge is to incorporate nitrogen into the glass silicate network. This paper outlines the effect of nitrogen on properties and structure of two series of glasses: (1) a "b...

Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids. However, because of their poor strength their use is restricted to non-load-bearing applications. The effects of nitrogen addition on the physical and mechanical properties and structure of bioactive oxynitride glasses in the system Na–Ca–Si–P–...

This chapter gives an overview of surface and bulk matter transport processes occurring during the densification of ceramic powder compacts. Starting from purified or chemically synthesized raw materials, sintering takes place by either solid state or liquid phase mechanisms during heat treatment which can be supplemented by use of microwaves, exte...

The effects of fluorine and nitrogen substitution for oxygen in aluminosilicate glasses, effectively oxyfluoronitride (OFN) glasses, modified by calcium, calcium – yttrium or calcium – magnesium on thermal and physical / mechanical properties have been compared. Thus, forty-two glasses in the Ca–(Mg)–(Y)–Si–Al–O–(N)–(F) system have been prepared an...

This paper reports the effects of using nano-precursor powders, including α-Si3N4 or amorphous-Si3N4, and particularly the partial replacement of AlN by Al metal precursor, on the properties of a fixed Ca-α-SiAlON composition, consolidated by spark plasma sintering at 1450 °C and 1600 °C. The observed changes in mechanical properties are related to...

X-ray amorphous glasses of composition (in equivalent percent) 15Ca:15Mg: 55Si:15Al:(100-x-y)O: xN:yF with x = 0, 10, 15 and y= 0, 1, 3, 5, were prepared by melting and casting. The effects of oxygen substitution by fluorine and/or nitrogen on the physical, mechanical, thermal and optical properties of the glasses have been investigated. Molar volu...

5wt.% yttria doped mullite ceramics were sintered using nanocomposite powders which consisted of a Y2O3-SiO2 core coated with pseudoboehmite. Firstly, the powders were heated up to 1300°C; mullite began to form at 1050°C which is ∼150°C lower than in previous diphasic precursors. Then, the powders were sintered at 1550°C for 0.5, 5 and 48h, and cha...

With abundant bauxite mineral as starting material, a low-cost alumina-mullite composite hollow fiber ceramic membrane (HFCM) was fabricated via phase-inversion method followed by high temperature sintering. Process parameters, including bore fluid flow rate and air-gap distance, which affect structure and properties of the HFCM were systematically...

This chapter reviews one of the important engineering ceramics developed over the last 40 years, silicon nitride and the related SiAlONs, a "family" of structural materials with high flexural strength, good fracture toughness, excellent creep resistance, and wear resistance. Microstructure-property relationships are outlined. Oxide-sintering additi...

The low mechanical strength of bioactive glasses restricts their use to non load-bearing applications. One way to increase strength of glasses is to introduce nitrogen into the silicate network. Oxynitride bioactive glasses in the SiO2-CaO-Na2O-Si3N4 system were successfully prepared. Structural characterization using 29Si MAS-NMR shows that, as ni...

Ca-Sialon glasses have been known for some time [1] and they are effectively calciumalumino-silicate glasses containing nitrogen which improves their mechanical properties. Calcium alumino-silicate glasses containing fluorine are known to have useful characteristics as potential bioactive materials [2]. Therefore, the combination of both nitrogen a...

Recycling of industrial solid state waste is always the priority solution in the prospect of waste management. This work demonstrated a new method converting coal fly ash (CFA) industrial waste to anorthite-cordierite-based porous ceramic membrane supports (ACCMS), through high-temperature sintering with additions of dolomite mineral. Characterizat...

Oxynitride glasses and glass ceramics are increasingly recognized as potential materials in specialist applications in modern industrial sectors. Oxynitride glasses have superior mechanical, rheological and optical properties to their oxide glass counterparts. Properties of these glasses can be tailored by changes in nitrogen content and additions...

Different whiskers on characterized improved high additives. structure © from traditional particle packing structure, a porous structure of ceramic membrane support was fabricated, featuring elongated mullite with enhanced porosity, permeance and sufficient mechanical strength. The effect of additives (MoO3and AlF3) and sintering procedure open por...

Glasses with cation composition of M:Si:Al = 3.45:3:2 (where M = Er and Y) with varying nitrogen contents (0, 5, 8, 15 and 22 eq.%) have been prepared by ball milling in alcohol media. These Er- and Y-sialon glasses were heat-treated at temperatures in the range of 950–1200 °C for 10 h to study the crystal phase(s) obtained. Samples were characteri...

Low-cost porous mullite ceramic membrane supports were fabricated from recycling coal fly ash with addition of natural bauxite. V2O5 and AlF3 were used as additives to cause the growth of mullite crystals with various morphologies via an in situ reaction sintering. Dynamic sintering, microstructure and phase evolution of the membrane supports were...

Glasses in the Na2O–CaO–SrO–ZnO–SiO2 system have previously been investigated for suitability as a reagent in Al-free glass polyalkenoate cements (GPCs). These materials have many properties that offer potential in orthopedics. However, their applicability has been limited, to date, because of their poor strength. This study was undertaken with the...

The development of SiAlON-based ceramics has shown great impact in the cutting/drilling tool industry and for other engineering applications. It is highly desirable to reduce the cost of the cutting tools by increasing their service lifetime. Potential ways to improve tool life is by preparing these SiAlON-based ceramics adopting non-conventional s...

Calcium alumino-silicate glasses of general composition (in eq.%) 28Ca:57Si:15Al:[100 − (x + y)]O:xN:yF (x = 0 or 20 and y = 0, 3 or 5) and their glass–ceramic counterparts were immersed in simulated body fluid (SBF) at 37 ± 0.5 °C for 28 days to assess their potential bioactivity. The glasses showed no Ca release or surface calcium phosphate depos...

The effects of increasing bioactive glass additions, SiO2-TiO2-CaO-Na2O-ZnO up to 25 wt% in increments of 5 wt%, on the physical and mechanical properties of hydroxyapatite (HA) sintered at 900, 1000, 1100 and 1200 °C for 2 h was investigated. Increasing both the glass content and the temperature resulted in increased HA decomposition. This resulte...

This chapter is an overview of the fundamental aspects of hard ceramics. Following an introduction to bonding and crystal structure of ceramics, an outline on processing directed particularly to near-net shaping techniques is given. High-temperature consolidation techniques discussed include surface and bulk transport processes, mechanisms of densi...

Reduction in weight of ceramics has been achieved by using a specific porous agent, starch, to achieve porosity ranging from 10% to 35%. Two incorporation routes of the porous agent have been investigated. For different levels of weight reduction, ceramics are characterized by microstructural analysis and mechanical testing. It is shown that the fe...

Silicon nitride is recognized as a high performance material for both wear resistant and high temperature structural applications. Oxide sintering additives, such as yttrium or rare earth oxides plus alumina or magnesia, are used in processing the ceramic to provide conditions for liquid phase sintering. The oxynitride liquid promotes densification...

Different kinds of bioactive materials are used as bone substitutes. In particular, bioglasses containing Si, Ca, Na and P, bind to host tissues with a stable chemical bond. The phenomenon of bioactivity is associated with the formation of a crystallized hydroxycarbonated apatite (HCA) layer on the bioglass surface, when soaked in a simulated physi...

Nano-sized Ce0.79Sm0.2Cu0.01O2−δ (CSCO) and Ce0.80Sm0.2O2−δ (CSO) electrolyte powders were synthesized by the PVA-assisted combustion method, sintered at various temperatures and electrochemical properties, mechanical properties and microstructures were characterized in detail. The results demonstrate that besides a considerable lowering of sinteri...

Glasses with composition (in eq.%) (30 − x)Ca:xM:55Si:15Al:80O:15N:5F have been prepared with different levels of substitution of Ca2+ cations by Mg2+, Y3+, Er3+, or Nd3+. The properties of these glasses are examined in detail and changes observed in molar volume (MV), free volume, fractional glass compactness, Young's modulus, microhardness, glass...

Oxynitride glasses exist as grain boundary phases in Si3N4 ceramics. This paper provides an overview of oxynitride glasses outlining effects of composition on properties. A review of the effects of grain boundary glass chemistry on fracture resistance of silicon nitride is given. A knowledge of overall additive compositions and their quantities in...

Thirty glasses of composition (in equivalent percent) 20-xCa: xY:50Si:30Al:(100-y-z)O:yN:zF, with x = 0, 10; y = 0, 10, 20, and z = 0, 1, 3, 5, 7 were prepared by melting and casting. All glasses were X-ray amorphous. Glass molar volumes (MV) decreased with nitrogen substitution for oxygen for all fluorine contents and, correspondingly, glass fract...

Noble-metal-free Cu(OH)2/TNTs (TNTs: TiO2 nanotubes) nanocomposite photocatalysts were successfully prepared by loading nano-Cu(OH)2 on TNTs via a hydrothermal-precipitation process. These were then characterized in terms of morphology and physicochemical properties by employing TEM, XRD, XPS, BET, UV–Vis DRS and PL. The effects of Cu(OH)2 loading,...

Bioglasses are used as bone substitutes and prosthetic coatings. Following implantation, they are predisposed to generate a series of physicochemical reactions at the glass-bone interface. Bioglasses with molar composition: 55SiO2–8.5CaO–31.5Na2O–5CaF2 have been synthesized and characterized. However, because of their poor strength, doping with nit...

Silicon nitride, one of the major structural ceramics, is sintered using additives such as Al2O3+MgO to provide conditions for liquid phase sintering to full density. The final microstructure contains high aspect ratio β-Si3N4 grains and intergranular glass. In this study, Spark Plasma Sintering (SPS) of silicon nitride, using Al2O3+MgO or MgF2 as...

The effects of fluorine and nitrogen substitution for oxygen in a calcium aluminosilicate glass have been examined. Twelve glasses in the Ca–Si–Al–O–N–F system, with constant cation ratio, have been prepared and characterized with respect to density, molar volume (MV), fractional glass compactness (C), Young's modulus (E), microhardness (μHv), and...

The effects of fluorine and nitrogen substitution for oxygen in a calcium aluminosilicate glass have been examined. Twelve glasses in the Ca–Si–Al–O–N–F system, with constant cation ratio, have been prepared and characterized with respect to density, molar volume (MV), fractional glass compactness (C), Young's modulus (E), microhardness (lHv), and...

Uniformly dispersed Ni catalysts supported on SiO2 wash-coated Ni foams were synthesized by the wet impregnation method and successfully applied for methane catalytic decomposition (MCD) at atmospheric pressure. All the prepared catalysts exhibited high catalytic stability. The effects of reaction temperature, space velocity, Ni loading on the MCD...

SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in silicon nitride ceramics and these grain boundary phases affect their fracture behavio...

Silicon nitride for engineering applications is densified by liquid phase sintering using oxide additives such as yttria and alumina. The oxynitride liquid remains as an intergranular glass. This paper provides a review of microstructural development in silicon nitride, grain boundary oxynitride glasses and effects of chemistry on properties. Nitro...

Amorphous alumino–silicophosphate materials containing up to 1.70wt.% nitrogen have been successfully prepared by aluminium nitride solution in Na–Li–Si–Al–P–O melts at 850°C thus preventing phosphorus volatilisation. Although the solubility limit for nitrogen in these glasses was limited to 8.31wt.%, the presence of nitrogen in the materials great...

SiAlONs are silicon aluminium oxynitride ceramic materials with a range of technically important applications, from cutting tools to specialised refractories and the properties of SiAlONs can be tailored for specific purposes. In this study, different β-SiAlON compositions were prepared using fluoride (MgF2 as fluorine source plus Y2O3) and oxide (...

Previous work has shown that some RE-Si–Al–O–N glasses are coloured. In particular, oxynitride glasses containing Ytterbium were observed to display a wide range of colours depending on their composition. The reasons for this were not immediately evident. As Ytterbium and Europium have been reported to display valency variations in silicate glasses...

Y–Si–Al–O–N glasses are intergranular phases in silicon nitride based ceramics in which the composition and volume fraction of oxynitride glass phases determine the sintering/shrinkage behaviour. Several investigations on oxynitride glass formation and properties have shown that addition of nitrogen increases glass transition and softening temperat...

Presented at 7th International Symposium on Nitrides, St. Malo, France, June 2012 Effects of Nitrogen and Fluorine on Properties of Sr-aluminosilicate Glasses Stuart Hampshire, Z. Lyons, R. Guang, C. Crowley, M. J. Pomeroy Materials and Surface Science Institute, University of Limerick, Limerick, Ireland ABSTRACT Incorporation of nitrogen into rar...

The effect of nitrogen and fluorine substitution on the crystallisation of a new generation of oxyfluoronitride glasses in the Ca–Si–Al–O–N–F system has been studied. Glasses were nucleated for 5 h at the nucleation temperature of Tg + 50 °C and crystallised for 10 h at the maximum crystallisation temperature (900–1050 °C depending on the glass com...

Bioglasses have been developed for use in surgery because of their ability to form a hydroxy-carbonate apatite (HCA) layer on their surface which facilitates bonding to natural bone. However, they do not have sufficient strength for use in load-bearing situations and therefore improving their mechanical properties would allow their use in more robu...

The NZP-type crystal structure allows a large number of ionic substitutions which leads to ceramics with adjustable thermal expansion properties or interesting ionic conductivity. However, NZP is difficult to fabricate into monoliths because it requires both high temperatures and long sintering times. An alternative low temperature route to obtain...

This research explores the use of a variety of carbon nanostructures as reinforcing agents for Si3N4 matrix composites. We have chosen highly promising families of carbon materials: multiwall, singlewall carbon nanotubes (MWCNTs, SWCNTs), graphene, carbon black nanograins and graphite micrograins for use as fillers. These materials were dispersed w...

Comparisons of microwave and conventional sintering of zirconia and hydroxyapatite (HA)—zirconia bodies were investigated in order to understand how microwave energy may affect the physical and mechanical properties of the materials for use in biomedical applications. Powder compacts of commercial nano-sized ZrO2, with 2 to 5 mol% Y2O3, and mixture...

Nano-sized CSO (Ce0.80Sm0.20O2−δ) and CSCO (Ce0.79Sm0.20Cu0.01O2−δ) were synthesized by the PVA assisted combustion method, and then characterized by the structure of PVA–cation complexes and nano-powders, as well as mechanical and electrical performance after sintering. The results indicate that the PVA–cation complexes (PVA–(Ce3+,Sm3+) and PVA–(C...

The biological response of strontium (Sr) doped hydroxyapatite (HA) and hydroxyapatite-zirconia (HA-ZrO₂) composites produced by employing sol-gel technology, minimal ZrO₂ loadings, and novel microwave-sintering regimes thereby retarding decomposition, is reported. In vitro evaluations indicate that all materials induce a favorable response from ra...

Silicon nitride is recognised as a high performance material for both wear resistant and high temperature structural applications. Oxide sintering additives such as yttrium oxide and alumina are used to provide conditions for liquid phase sintering, during which the additives react with surface silica present on the Si3N4 particles and some of the...

Mullite ceramics were fabricated at relatively low sintering temperatures (1500–1550 °C) from recycled flyash and bauxite with MgO addition as raw materials. The densification behavior was investigated as function of magnesia content and sintering temperature. The results of thermal analysis, bulk density and pore structure indicate that MgO additi...

Porous cordierite ceramics were prepared using sepiolite source of MgO and SiO2 and alumina as starting materials by simple dry-pressing/sintering. The sepiolite/alumina green bodies were sintered at 1100–1350°C for 2h. The characterization was focused on thermal analysis, phase evolution, sintering behavior, thermal expansion and micro-structural...

Tubular porous alumina ceramic membrane supports were fabricated by an extrusion–drying–sintering process and then characterized in detail in terms of corrosion resistance in both H2SO4 and NaOH aqueous solutions. Variations in the properties of the alumina supports such as mass loss percent, mechanical strength, open porosity and pore size distrib...

Nano-sized Ce0.8Gd0.2O2−δ and Ce0.79Gd0.2Cu0.01O2−δ electrolyte powders were synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by powder characteristics, sintering behaviors and electrical properties. The results demonstrate that the as-synthesized Ce0.8Gd0.2O2−δ and Ce0.79Gd0.2Cu0.01O2−δ possessed similar powd...

This paper reports on improvement of the physical and mechanical properties of Y2O3–ZrO2 ceramics through compositional optimization, the use of nanograined powders and utilization of microwave sintering. ZrO2 with 2–5 mol% Y2O3, prepared from nanopowders, was sintered in both conventional and microwave furnaces under exactly the same heating sched...

The silicon oxynitride glasses take advantage of nitrogen bonding to attain high elastic modulus, increased softening temperatures and viscosities, greater slow crack growth resistance, and modest gains in fracture resistance. Of the oxynitride glasses, the Si–Y–Al-based oxynitride glasses have been most extensively studied and a degree of success...

μ-silicon nitride forms a range of solid solution M x (Si,Al) 12 (0,N) 16 where x = 2 and M is Li ⁺ , Ca 2+ , y ³⁺ or certain lanthanide cations. This paper reports the formation of Ln-α'-sialons by the reaction of Si 3 N 4 with AIN and Ln 2 O 3 where Ln=Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. Transformation reactions of Nd, Sm, Gd, Ho, E...

Silicon nitride based ceramics contain oxynitride glass phases at the grain boundaries which can impair subsequent high temperature properties. Investigations of bulk glasses in various M-Si-Al-O-N systems have been carried out and it has been shown that up to 15 atomic % N can be incorporated into these oxynitride glasses. Studies have revealed th...

Ca–Si–Al–O–N–F glass formation regions have been mapped on 6Ca2+–3Si4+–4Al3+ ternary diagrams at fixed O:N:F of 79:20:1 and 75:20:5 (in eq%). For both fluorine contents, glass formation regions extend toward more Ca-rich compositions at 1650°C compared with the Ca–Si–Al–O–N system at 1700°C. Ca–Si–Al–O–N–F melting temperatures are 150°–800°C lower...

Nano-sized Ce0.79Gd0.2Cu0.01O2−δ electrolyte powder was synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by crystalline structure, powder morphology, sintering micro-structure and electrical properties. The results demonstrate that the as-synthesized Ce0.79Gd0.2Cu0.01O2−δ was well crystalline with cubic fluori...

In order to effectively utilize industrial waste fly ash, porous mullite ceramic membrane supports were prepared from fly ash and calcined bauxite with chemically pure titania as sintering additive. The effects of TiO(2) on the sintering behaviors and main properties of porous mullite were studied in detail. Due to the addition of titania, the sint...

Following liquid phase sintering of silicon nitride ceramics with yttria and alumina densification additives, a Y-SiAlON glass remains at the grain boundaries. Crystallisation of such a glass in bulk form has been studied using both differential thermal analysis (DTA) and separate isothermal heat treatments in a tube furnace under nitrogen. The act...

Oxynitride glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in silicon nitride ceramics and these grain boundary phases affect their fracture beh...