Corundum Particles Research Articles

Sintering of glass matrix composites with small rigid inclusions

We investigated the effect of dispersed crystalline particle volume content Φ on sintering of glass matrix composites (GMC) for low-temperature co-fired ceramics (LTCC) applications. Such composites typically consist of alumo-borosilicate glass and α-Al 2O 3 powders of similar average particle size ( D 50 ≈ 3 μm). Sintering shrinkage was observed by dilatometry and heating microscopy and was backed up by glass viscosity measurements. Microstructure analysis revealed that α-Al 2O 3 particles do neither show significant dissolution into the liquid phase nor detectable crystallization throughout LTCC firing schedules. Therefore, in this study α-Al 2O 3 particles were treated as small rigid inclusions. It was found that Φ lowers the shrinkage rate of GMC. While the lowering is small for small Φ and at the early stage of densification it progressively increases during sintering, and final shrinkage shifts up to 170 K to higher temperatures for Φ = 0.45. The behaviour observed could be explained assuming that sintering is controlled by the effective viscosity, which progressively increases non-linearly during densification due to the gradually wetting of the surface area of corundum particles. We could demonstrate that Al 2O 3 cluster can cause residual pores and reduce the attainable shrinkage. The reduction of attainable shrinkage is found to depend on Φ 3, reaching about 8% at Φ = 0.45.

Role of Oxide Surface Chemistry and Phospholipid Phase on Adsorption and Self-Assembly: Isotherms and Atomic Force Microscopy

We have examined the effects of metal oxide surface chemistry and lipid phase on phospholipid adsorption affinity and self-assembly. Adsorption isotherms of ditridecanoylphosphocholine (DTPC) at 40 °C and pH 7.2 on quartz (α-SiO2), rutile (α-TiO2), and corundum (α-Al2O3) particle suspensions indicated oxide-dependent adsorption affinity that decreased as rutile > corundum ≅ quartz at low concentrations and corundum > rutile ≅ quartz at higher concentrations. Significantly, atomic force microscopy of DTPC and dipalmitoylphosphocholine (DPPC) at high concentration on planar oxide surfaces at 25 °C in liquid-crystal and gel phases, respectively, also showed oxide-specific adsorption. Multiple bilayers formed on corundum (100), indicating greater coverage compared to single bilayers, bilayer patches, or supported vesicle layers on the negatively charged surfaces of mica (001), rutile (100), and amorphous silica glass (fused quartz plate). Thus, the amount and self-assembly of adsorbed phospholipid was found to be oxide-dependent regardless of the lipid phase. Significantly, both experimental methods show multiple bilayer formation as a unique feature of the positively charged alumina surface. The observed oxide affinity sequences are interpreted as controlled by van der Waals and electrostatic forces between the oxide surface and the negatively charged (−R(PO4−)R′−) portion of the phosphocholine headgroup. Our results have implications for the interactions of amphiphilic molecules with mineral surfaces in diverse biogeochemical, biomedical, and industrial processes, including membrane-bound biomineralization, cell membrane stability during early evolution of life, organic matter burial in ocean sediments, the design of supported lipid bilayers and biomimetic cell membranes for medical implant devices, enhanced oil recovery, and ore extraction by froth flotation.

Random lasing in porous scattering medium

The spectrum behavior evolution and the threshold of random lasing depending on the way of photon walk randomization in an active random medium were investigated. The following three ways of photon walk randomization were implemented: multiple light scattering by corundum and silica particles embedded into a solid polymer solution of dye (astrafloxin), multiple light reflection at sub-millimeter extensive air pores (mean diameter 200 μm) produced in the medium, and the combined action of both these effects. The most effective lasing is observed in the case of an active medium with air pores and scattering particles in the interpore space. Such a combined porous scattering medium acts as a network of dielectric waveguides transmitting effectively the random light. This spatial structure of the random active medium significantly increases the photon path in the medium, thereby promoting photon multiplication due to stimulated emission. In this combined medium the random lasing reveals the narrowest spectrum, the lowest threshold, and the highest density of spectral energy in the spectrum maximum.

Biological response to micron‐ and nanometer‐sized particles known as potential wear products from artificial hip joints: Part II: Reaction of murine macrophages to corundum particles of different size distributions

Macrophages play a pivotal role in tissue reaction and immune response. They recognize, phagocytose particles and generate cytokines to influence local cellular reactions. Friction and wear of implant components usually generates microparticles (MP) in a size range of 1-10 mum and nanoparticles (NP) in the range of 10-1000 nm. To investigate the possible impact of MP or NP on cellular reactions, we exposed murine macrophages (RAW264.7) to corundum MP and NP. The same mass was used in both NP and MP cell culture solutions, i.e. there were more NP than MP per identical volumes of culture solution. After 4, 24, 48, 72, and 96 h aliquots of cell culture supernatants were tested for different cytokines, growth factors and nitric oxide. Macrophages were stained with MGG (May-Grünwald Giemsa), counted and morphologically characterized by scanning electron microscopy and transmission electron microscopy. Particles were attached to cell surfaces and phagocytosed within cells. Cells stimulated with particles or lipopolysaccharides for positive controls showed surface modifications indicating enhanced function. Although only marginal differences between negative controls and particle-stimulated cells were observed in respect to cytokine production, exposure to corundum particles led to a decrease in the number of vital macrophages and to an increase in the number of giant cells. Corundum NP formed micron-sized aggregates in the cell culture medium and led to the production of more giant cells than MP. Sodiumdodecylsulfate polyacrylamide gel electrophoresis of the cell culture medium with particles proved the adsorption of proteins to particles.

Interface Interactions of Osteoblasts with Structured Titanium and the Correlation between Physicochemical Characteristics and Cell Biological Parameters

Cellular behavior at the interface of an implant is influenced by the material's topography. However, little is known about the correlation between the biological parameters and the physicochemical characteristics of the biomaterial. We therefore modified pure titanium surfaces by polishing, machining, blasting with glass spheres, blasting with corundum particles, and vacuum plasma spraying to give progressively higher surface roughness. The material surface was characterized by SEM, surface profiling, and electrochemical methods. We revealed a correlation for integrin expression and formation, adhesion, spreading, proliferation, and bone sialo protein expression with the physicochemical parameters of the titanium surfaces.

Preparation and High Temperature Performance of β-Sialon Bonded Corundum Multiphase Material

β-Sialon bonded corundum multiphase ceramic refractory was prepared by the method of carbothermal reduction and nitridation reactions of clay mineral doped with corundum particle phase. The high-temperature oxidation resistance and the thermal-shock resistance behaviors of the material were tested and investigated. The results show that the oxidation reaction history at 1573K can be divided into two reaction kinetic phases. The circle times of the thermal-shock resistance ($=1473K) reached to more than 200 times and the thermal shock failure is not a brittle rupture but a desquamate damage.

Micro- and Nanoscaled Titanium Surface Structures Textured by Electrolytic Plasma and Etching Methods

The surface topography of Titanium implants modulates bone response and implant anchorage. For this reason great efforts yet will be made for new surface refinements. In this work Ti samples were surface structured by corundum blasting firstly and then chemically etched to remove the remaining corundum particles and further surface structuring. In following steps these samples were electrochemically etched or additionally structured and coated with various micro-plasma processes. As result we got various typical surface structures in micro- and nanoscale and also different coating layers in dependence on the composition of the electrolyte for the micro-plasma process. In all steps the properties of the modified Ti surfaces were characterised mechanically by surface profiling, optically by SEM and electrochemically by CV- (for testing the corrosion parameters), CA- (to give the enlargement of the real surface) and EIS-measurement in range of 100 kHz to 1 mHz (to give a survey of the changing of surface capacities and structures). A comparison of the measuring results demonstrated their reliability.

Identification of minerals and meteoritic materials via Raman techniques after capture in hypervelocity impacts on aerogel

Abstract— Mineral particles analogous to components of cosmic dust were tested to determine if their Raman signatures can be recognized after hypervelocity capture in aerogel. The mineral particles were accelerated onto the silica aerogel by light‐gas‐gun shots. It was found that all the individual minerals captured in aerogel could be identified using Raman (or fluorescence) spectra. The laser beam spot size was ˜5 micrometers, and in some cases the captured particles were of a similar small size. In some samples fired into aerogel, a broadening and a shift in the wave numbers of some of the Raman bands was observed, a result of the trapped particles being at elevated temperatures due to laser heating. Temperatures of samples were also estimated from the relative intensities of Stokes and anti‐Stokes Raman bands, or, in the case of corundum particles, from the wave number of fluorescence bands excited by the laser. The temperature varied greatly, dependent upon laser power and the nature of the particle. Most of the mineral particles examined had temperatures below 200 °C at a laser power of about 3 mW at the sample. This temperature is sufficiently low enough not to damage most materials expected to be found captured in aerogel in space. In the worst case, some particles were shown to have temperatures of 500–700 °C. In addition, selected meteorite samples were examined to obtain Raman signatures of their constituent minerals and were then shot into aerogel. It was possible to find Raman signatures after capture in aerogel and obtain a Raman map of a whole grain in situ in the aerogel. It is concluded that Raman analysis is indeed well suited for an in situ analysis of micrometer‐sized materials captured in aerogel.

Comparative surface examinations on corund blasted titanium implants and explants in total hip arthroplasty

Blasting techniques using corundum to create rough surfaces are used in many different processes for the surface treatment of hip implants. Recent evidence points an association between residual particles and early loosenings in the sense of third-body wear. The surfaces of five unused, original-packaged CLS stems and ARR-Titan supporting rings, respectively, were compared with five explanted CLS stems and ARR-Titan supporting rings. The surface of the ARR-Titan supporting rings was adhered to Al2O3 particles at 23.2+/-2.5% on the implants and 12.3+/-3.0% on the explants (P < 0.0001). For the CLS stem, the surface to which Al2O3 particles adhered was 16.4+/-2.2 % on the implants, whereas the surface to which Al2O3 particles adhered was 12.4+/-3.3% on the explants (P = 0.0275). The results of this study show that corundum particles can be found to cover a high percentage on rough-blasted titanium surfaces of ready-to-use devices. In contrast, this contamination is significantly less on the explants treated in an identical fashion prior to implantation.

In Situ Characterization of Aluminum-Containing Mineral−Microorganism Aqueous Suspensions Using Scanning Transmission X-ray Microscopy

In situ characterization of colloidal particles under hydrous conditions is one of the key requirements for understanding their state of aggregation and impact on the transport of pollutants in aqueous environments. Scanning transmission X-ray microscopy (STXM) is one of the few techniques that can satisfy this need by providing element- and chemical-state-specific 2-D maps at a spatial resolution better than 50 nm using soft X-rays from synchrotron radiation wiggler or undulator sources tuned to the absorption edges of different elements. X-ray absorption near-edge structure (XANES) spectra can also be collected simultaneously at a similar spatial resolution and can provide phase identification in many cases. In this study, we report STXM images and XANES spectroscopy measurements at or above the Al K-edge (E = 1559.6 eV) of various Al-containing minerals and synthetic oxides [alpha-Al2O3 (corundum), gamma-Al2O3, gamma-AlOOH (boehmite), alpha-Al(OH)3 (bayerite), KAl2(AlSi3O10)(OH)2 (muscovite), (Al,Mg)8(Si4O10)4(OH)8.nH2O (montmorillonite), and Mg6Al2(OH)16CO3.4H2O (hydrotalcite)] and demonstrate the capability of this spectromicroscopic tool to identify different Al-containing mineral colloids in multiphase mixtures in aqueous solution. We also demonstrate that STXM imaging at or above the C K-edge (E = 284.2 eV) and Al K-edge can provide unique information on the interactions between bacteria and Al-containing nanoparticles in aqueous suspensions. STXM images of a mixture of Caulobacter crescentus and montmorillonite and corundum particles just above the C and Al K-edges show that the mineral particles and bacteria are closely associated in aggregates, which is likely due to the binding of bacteria to clay and corundum particles by extracellular polysaccharides.

The influence of surface roughness of titanium on β1- and β3-integrin adhesion and the organization of fibronectin in human osteoblastic cells

Mechanisms of cell adhesion and extracellular matrix formation are primary processes in the interaction with the material surface of an implant which are controlled by integrin receptors. The aim of our study was to find out whether β1- and β3-integrins of osteoblastic cells sense the surface topography of titanium, and if structural alterations of integrin adhesions were involved in the organization of fibronectin. Pure titanium surfaces were modified by polishing (P), machining (NT), blasting with glass spheres (GB), and blasting with corundum particles (CB) resulting in increasing roughness. Confocal microscopic investigations revealed fibrillar adhesions of β1- and α5-integrins on P, NT, and GB, but on CB with its sharp edges these integrin subunits did not form fibrillar adhesions. β3 generally appeared in focal adhesions. We observed aligned fibrillar structures of fibronectin on NT not only on the basal site but interestingly, also on the apical cell surface. In contrast, on CB, fibronectin appeared apically clustered. We suggest that this alignment of fibronectin fibrils depends on the directed actin cytoskeleton and in particular, on the capability of the β1-integrins to form fibrillar adhesions, which is affected by the surface roughness of titanium.

The thermally induced transformation of pseudoboehmite gels—a comparison of the effects of corundum seeding and iron doping

The transformation of doped or seeded pseudoboehmite to corundum was studied by combining thermal analysis, X-ray diffraction, transmission electron microscopy, and electron paramagnetic resonance spectroscopy. The temperature of phase transformation to corundum was lowered by about 130 °C when Fe 3+ or corundum seeds were added to the sols. Action of Fe 3+ ions depends on the actual degree of thermally induced transformation of pseudoboehmite via transition aluminas to corundum and the ability of these alumina phases to incorporate Fe 3+ ions. These ions tend to aggregate with increasing iron concentration of the alumina phases and can work as nucleation centers. Small (∼20 nm) corundum particles act as active nucleation sites whereas larger grains (200–400 nm) also present in the samples are less effective. For the first time trapping and stabilization of NO 2 molecules in transition aluminas formed by a sol–gel route was shown.

Calorimetric studies of refractory corundum

Calorimetry has been used in the investigations of calcium aluminate materials produced as a binder for aluminate-corundum composites of high refractoriness. The kinetics and of hydration process was thus characterized and the optimum compositions of initial binders and cement-corundum refractory filler blends could be selected for further tests. The acceleration of heat evolution - the shortening of so-called induction period and relatively high heat output in the presence of corundum was observed. It means the acceleration of hydration process, that is early crystallisation of hydration products and subsequent further dissolution of initial anhydrous aluminate phases. In the presence of fine grained corundum particles these phenomena should be attributed to the nucleating effect of fine corundum particles.

Hercynite-Free Ceramic Liner for Composite Steel Pipe Made Using a Self-Propagating High-Temperature Synthesis Gravitational-Thermite Process

A ceramic-lined steel pipe was fabricated using a self-propagating high-temperature synthesis gravitational-thermite process. Some rare-earth oxides and glass powders were added to the aluminothermite. The experimental results showed that the ceramic liner consisted of three phases: corundum (Al2O3), glass, and iron particles. Neither hercynite (FeO·Al2O3) nor iron ions existed in the liner of the composite pipe.

Plasma-enhanced chemical vapor deposition of nitrides on fluidized particles

A new plasma jet fluidized bed reactor working at atmospheric pressure is presented. The plasma arc is created inside the bed of particles in order to improve the reactivity between excited gaseous species and the particles to be coated. Metal chlorides, nitrogen and hydrogen were used as precursors of deposited layers. TiN, Si 3N 4 and SiO x coatings were deposited on silica and corundum particles by this plasma-assisted CVD process. Optical emission spectroscopy and electron microanalysis characterized the plasma and the layer composition, respectively.

Effect of adhesion strength of DLC to steel on the coating erosion mechanism

The wear of DLCs deposited onto steel substrates using a graphite arc-pulse sputtering technique in a corundum particle jet was studied. Two sample sets had different adhesion strength to the substrate due to different adhesive sublayer structures. It was found that the DLC itself does not wear, so that coating destruction occurs due to peeling. Analysis of the wear results for coatings having different (0.4–2.6 μm) thickness revealed that peeling is a result of two basic crack systems: (i) from the DLC surface inside the coating; and (ii) along the DLC–substrate interface.

Calculation of the elastic-stressed state under concentrated loading in diamond-like–metal substrate system

A model is proposed which reduces the contact problem of a coating to that of an elastic semi-space with modified boundary conditions. The model takes into account mechanical (difference in elastic modulus of the coating and substrate) and geometric (ratio of contact area to coating thickness) properties of a coating–substrate system, and conditions of their interface conjugation. A comparison of the model outcomes with calculation results for the problem without a coating is carried out in a simple case of uniaxial load. Experiments on the shock action of corundum particles on the surface of two mechanically different metals (aluminium and steel) with diamond-like coating are considered.

Effect of chilling on soundness and ultimate tensile strength (UTS) of aluminium alloy –corundum particulate composite

An investigation has been carried out to fabricate and evaluate the strength and soundness of chilled composites consisting of aluminium matrix and corundum particles (size 20–50 μm) in the matrix. The dispersoid added ranged from 3 to 9 vol.% in steps of 3%. The resulting composites cast in moulds containing metallic and non-metallic chill blocks were tested for their strength and soundness. Results of the investigation reveal the following: (1) Strength of the composite developed is highly dependent on the location of the casting from where the test specimens are taken and also on the dispersoid content of the composite. (2) Chill thickness and chill material, however, does significantly affect the strength and soundness of the composite. (3) Soundness of the composite developed is highly dependent on the chilling rate as well as the dispersoid content. An increase in the rate of chilling and increase in the dispersoid content of the material both result in an increase in the ultimate tensile strength (UTS) of the material. The temperature gradient developed during solidification and volumetric heat capacity (VHC) of the chill used are the important parameters controlling the soundness of the composite. (4) Maximum interface temperature attained by the chill decreases with the increase in their VHC and the total heat absorbed by the chill increases with increase in VHC. (5) Thermal properties of the end chills are used to determine the magnitude of the temperature gradient developed along the length of the casting solidifying under the influence of chills.

A three-dimensional model of diffusion-controlled sintering

A three-dimensional diffusional model is used to describe sintering of powder compacts composed of monosized corundum particles. The sintering process is thought of as consisting of four stages. The duration of each stage and the corresponding shrinkage and porosity are evaluated. The results agree reasonably well with experimental data on the sintering of corundum ceramics.

Investigation of impact of solid particles against hardmetal and cermet targets

The objective of the present work is to investigate and discuss some features of the surface damage and material removal process during particle-wall collision of the solid particles and hardmetal and cermet targets. The restitution parameters of TiC-base cermets, WC–Co hardmetals and glass of different composition and properties have been investigated. In order to clarify the details of the impact of glass spheres and corundum particles of irregular shape on a solid half-space, the process of interaction of solid particle with target was studied using a Laser Doppler Anemometer (LDA) measuring technique. Targets were impacted with particles over the range of impact velocities (7–50 m s −1) at impact angle 67°. The experimentally observed variations of the coefficient of velocity restitution as a function of the test material properties, impact velocity and hardness ratio ( H m/ H a) are adequately explained on the basis of a theoretical model. Systematic studies of the influence of the impact variables on the collision process have been carried out.