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Every year hundreds of millions of Euros are spent on building storage silos for particulate materials, or bulk solids, as they are also often called. Such materials are the basis of most land based industries, and it has been estimated that over half by volume, or a third by value, of materials handled by typical process industry companies are particulate in nature. It is, however, quite astonishing that in spite of the obvious advantages of obtaining an uninterrupted material flow in processing operations, most suppliers and users still fail to pay sufficient attention to the design of perhaps the most important items in such a process train i.e. the storage vessels and their charging and discharging systems. The results of this neglect are many: hang-up in silos, uncontrolled sudden discharge, dusting, product degradation etc. etc.
This paper insists that the design of reliable storage and discharge systems for particulate materials can only be undertaken after proper characterisation of the physical (and sometimes chemical) properties of the materials to be stored. It describes the differences between particulate materials on the one hand, and solids and liquids on the other, and points out how these differences influence the stress distribution in storage vessels and on discharge devices. It also highlights the tendency of mixtures of such materials to segregate, i.e. separate into fractions with similar properties in different zones, during the filling and discharging processes.
In the glass industry, the properties of glass contact refractories must be chosen to give glassmakers the possibility to maximise glass quality, to improve furnace productivity, and to increase campaign life. In recent years, high zirconia fused cast (HZFC) refractory was introduced with the aim of decreasing the number of glass defects and increasing the corrosion resistance of refractories for special glasses. There now exist many industrial applications of this product.
By comparative study of the properties of HZFC and fused AZS products in contact with different glasses, we offer furnace application guidelines for choosing between these two refractories. To provide effective information, extensive field results from glass furnaces have been collected. In addition, an experimental program involving corrosion tests with various glasses compositions will be reviewed. By using microstructural studies of the interface between the refractories and these glasses, we can understand the influence of the chemical analysis of both the glass and the refractories on the diffusion processes of the different components inside the refractories. The knowledge of diffusion processes at the glass-to-refractory interface for HZFC and fused AZS refractories, as a function of the glass composition, yields clues explaining both the corrosion resistance and defect generation mechanisms for the two refractory compositions.
Effects influencing properties
and structure of glass fibres
In the polymer industry, capillary
rheometry is a well-known method for investigation of both shear
and elongational viscosity. These data can e.g. be used for numerical
simulations or for quality control. The method has proven successful
in detecting very small structural changes. Due to the high shear
rates that can be obtained with this method (typically in the
range from 100-100 000 s-1), measurements are carried
out in a highly non-Newtonian range. Though the method at first
glance seems quite simple, it has been, and still is, subject
of numerous investigations. Because capillary rheometry is rare
in the glass industry, this paper will give an overview of the
method, the Bagley correction, the Rabinowitsch correction for
non-Newtonian fluids, and will focus on methods of obtaining
an elongational viscosity from capillary data, with a particular
emphasis on Cogswells model. This paper will also discuss recent
work on capillary die corner shape. Wall slip at sharp corners
at the die entrance has been reported earlier as well as a substantial
vortex enhancement compared with dies having a slight roundness
at the entrance. It is of great importance to get experimental
information on the influence of corner shape on vortex size and
entrance pressure drop, as this pressure drop is a parameter
in the calculation of the extensional viscosity. Experiments
have been conducted with an isotactic polypropylene on the effect
of rounding the die corner on entrance pressure drop. Shear viscosity
effects are quite small for this material, as is the vortex reduction
arising from rounding edges. Still there is a significant relationship
between the change in vortex shape and the entrance pressure
drop. Similar work on a NAPOLI glass (Na2O . Li2O
. 2P2O5) is in progress.
of geological melts and glasses
non-newtonian flow and the orientation of structure units of
both glass and polymer melts during extrusion process
The rheological properties of both inorganic and organic melts are determined by means of extrusion. It is observed that like polymer the calcium metaphosphate glass (Ca(PO3)2) melt is also subject to the non-Newtonian flow during extruding process, i.e. the viscosity decreases with increasing shear rate. The structural anisotropy of the extruded glass is verified by measuring the two-dimensional rotorsynchronized magic angle sample spinning nuclear magnetic resonance (2D MAS NMR), optical birefringence and thermal expansion. With regard to both the non-Newtonian flow behaviour and the anisotropy of structure, the Ca(PO3)2 melt is compared with the polymer melt. Such a comparison contributes to a better understanding of both structure and properties of inorganic glasses. The results indicate that not only the macroscopic structural anisotropy but also the local molecular alignment are present in the extruded Ca(PO3)2 glass. However, the extruded glass exhibits much lower extent of the non-Newtonian flow and also much lower degree of local alignment than the oriented polymer. The reason could be the following: the Ca(PO3)2 glass does not possess so stable and long molecular chains as polymer and therefore its oriented structure relaxes much faster than the polymer. Due to the slow cooling process of glass melt and due to the fact that the glass melt was not cooled down under load, the relaxation process is not totally hindered and therefore the oriented structure was only partially frozen-in.
Glass has been manufactured for thousands of years. In the early days it was used to make jewellery and highly prized jars. Today hand-cut crystal glass is valued for its refractive properties, not to speak about the value of high-performance glasses used in optical and electrical applications. However, at the end of the 20th century glass had to face quite an exciting and new challenge caused by the huge development of society during the previous decades.
The life span of humans has increased and it is today much longer than mother nature originally planned. Moreover, the unfortunate tendency of man to make wars and get into accidents has tremendously extended the need for skeletal "spare parts". Many special materials have been developed and used successfully as implants. There are, however, several options to meet the problem considering the implant-tissue response. Tissue close to a toxic material will die. A non-toxic but biologically inactive material will be encapsulated by a fibrous tissue of varying thickness. A non-toxic and resorbable material will be replaced by time by host tissue. The problem with this particular biomaterial type is the matching resorption rate to the repair rate of body tissue. The problem is especially complicated because the individual rates of tissue healing vary enormously with age and health. There is, however, one group of biomaterial consisting of non-toxic ceramics, which are biologically active and form an interfacial bond to the host tissue. A subgroup of these ceramics is established by a group of special glasses that are known to possess the highest rate of bioactivity among all biomaterials. A firm chemical bond is formed between the glass implant and tissue as a result of the chemical reactions occurring at the interface. These glasses have been used clinically already for years to replace small bones in the middle ear and as a filling material in odontology, orthopaedics and in facial surgery. The implants have been used as crushed bioactive glass or non-porous blocks. Unfortunately, working on the glass by remelting it has been impossible because of devitrification of the material resulting in loss of bioactivity.
Introduction of novel bioactive glasses during the 90's in Turku, Finland, highly changed the profile of bioactive glasses. It widened the possibilities for development of more advanced clinical applications for bioactive glasses. Now, for example, micro spheres, fibres, etc. can be manufactured of bioactive glass without risk of loosing of the bioactivity of the material. By sintering bioactive glass micro spheres it is possible to obtain porous bioactive structures, in which the reactive area is a manifold compared with non-porous bioactive glass blocks. Additionally, in porous bioactive implants reactions between the bioactive glass and host tissue occur inside the three-dimensional matrix and provide an anchoring surface for the ingrown new bone. Further, the bioactivity of the material can be controlled by changing the composition of the glass. Therefore, a bioactive glass can be designed to bond to soft tissue as well. Not surprising, porous texture made by sintering bioactive micro spheres is considered to be an exciting option for biological tissue guiding of a human body.
on soda-lime type II glass containers by concentrated salt solutions
Following the European and American Pharmacopeia, the glass used for injectables is devided into three classes: I (borosilicates), II (dealcalized soda-lime glasses), III (normal soda-lime glass). The chemical resistance is decreasing from type I to III.
For what concerns the durability of type II glasses there are a lot of papers and information on their behaviour when the attacking liquids are water or diluted salt solutions. Less is known when the attack on these glasses is made by concentrated salt solutions. In this study we report the behaviour of Type II glasses when leached by LiCl, NaCl, NaBr, KCl, KBr, CsCl, BaCl2, CaCl2.
The chemical attack has been simulated in laboratory by means of an autoclave treatment at 121 °C for 1 hour. The total number of analysed samples was 1120. We measured an hydrolytic dissolution and studied the surface by means of AFM and SEM microscopy. By using a fixed pH of the starting solutions, we confirmed that the chemical attack depends on the salt concentration, as expected, and at a fixed concentration, on the salt type in the following order: KCl<LiCl<NaCl<KBr<CsCl = NaBr<BaCl2, CaCl2.
The latest developments in
the field of combustion to reach environmental regulations and
Lead crystal producers like Nachtmann company have to handle a significant amount of waste and residues. The costs for disposal are an important economic factor for the production of lead crystal. In recent years Nachtmann made many efforts to avoid or reuse waste, not only to lower the cost but also to meet the demands of the new German environmental protection laws. The topics of this paper is one result of these efforts achieved in recent years.
Typical residues originating from different steps in the glass production are filter dust, dirty or coloured cullet and grinding sludge. The main target of our research was the vitrification of non-avoidable waste, especially of all residues which cause high costs for disposal, for example filter dust. To keep the cost of the waste treatment low, an expensive pre-treatment of the batch and also the admixture of additional agents, for example for refining and colouring, is not desired. Last but not least the melting products should be saleable.
The carried out investigations point out to some special problems with remelting of the residues. First of all the varying compositions and properties of each residue and the high water content of the grinding sludge require an optimised melting technology especially if a continuous melting in a tank furnace is projected.
With the developed waste-melting-furnace now it is possible to transform most of the waste and residues into recycling-glass. The produced recycling-glass has a composition similar to that of normal lead crystal. It is coloured and not free of streaks and bubbles. Nevertheless it is suitable for the manufacture of a variety of saleable products. By using this technology the melting cost is clearly lower than the cost for waste disposal.
Isostatically pressed chromic oxide blocks were first introduced to the container glass industry almost 12 years ago. By this time, use of our special products in the construction of glass furnaces for production of glass containers and float glass has proved excellent performance in many installations. The technical characteristics of this refractory material are being described. Results of industrial applications in critical glass melt contact areas show that the material meets customer requirements. The unique product is compatible with conventional fused AZS materials and glass properties are not being affected. The overall corrosion of the furnace becomes more uniform and the service life of the production unit can be extended significantly.
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