Ceramic materials reasons

The expert tried to optimise the design of unbreakable crockery. First he wanted to find reasons for using ceramic as the main material in terms of desired properties. From this first step, he concluded that ceramic had some advantages over metals or composites. The expert made a sharp distinction between intrinsic and extrinsic properties. The choice of type of ceramics was not relevant becanse the desired properties are extrinsically determined. Thns relevant properties cannot be much influenced by the difference in bonding strength due to the different types of ions of the material. Consequently, the properties of ceramic crockery are not mnch inflnenced by the actual choice of ceramic material. Because of this, the expert did not inclnde the ionic stmcture in his reasoning. When he was asked why he did not nse this snb-microscopic level, he explained it was not necessary becanse this [the desired properly] is not imdeigoing influences at atomic level at all . 

For these and other reasons, it has become commonplace to compare fired ceramic material with fired ceramic material assumed to be representative of a particular production centre. Material of assumed provenance can be used, but, for preference, kiln wasters are often used as comparative material. These are vessels that have failed in the firing for some reason, and... 

Middleton, A.P. (1987) Technological investigation of the coatings on some hematite-coated pottery from Southern England. Archaeometry 29 250-261 Middleton, A.P. (1992) Ceramics Materials for all reasons. In Bowman, S. (ed.) Science and the past. British Museum Press, 16-36 Mijirtskii, A.V. Langelaar, M.H. Boerma,... 

In testing the abrasiveness of floor finish of man-made materials, special variations of Shore s scleroscope are commonest. For ceramic and rock floor tiles, the commonest testers are Bohme s disc and the Teledyne Abra-der. For sewage and chemical stoneware, the standards now in force recommend abrasiveness tests with the use of a sandblasting jet blower. For technical reasons, a more precise Mackensen blower method for stoneware testing has been in use in Poland for several years. From the experience gained over years, a standard recommending Mackensen s method has been laid down for stoneware abrasiveness tests. Research results proved the usefulness of this method also for other ceramic materials. 

Why are geology and mineralogy discussed in a book on ceramics The main reason is the fact that nature shows us which materials might be suitable ceramic materials for various applications. Over the past millions of years nature has produced an enormous variety of rocks and minerals with numerous properties. Researching these products has taught us how nature shaped them and what their structure are like. Nowadays these production processes can be imitated in the laboratory, very often within a short period of time. In addition, most ceramic raw materials are obtained from nature and sometimes altered chemically or physically in the laboratory. This means that the ceramicist must have a good knowledge of these raw materials. 

Aluminium oxide is the oldest ceramic material used in medicine. Bauxite and corundum are the main natural sources of aluminium oxide. Bauxite is a mixture of diaspore, gibbsite, iron hydroxides, clay minerals and quartz. It is formed by the tropical weathering of silicate rocks during which quartz and the elements sodium, calcium, magnesium and potassium are largely washed away. This is the reason why the remaining material becomes richer in the resistant elements titanium, iron and aluminium. The latter is extracted from this mixture in the form of aluminium hydroxide. In its turn this compound is converted into aluminium oxide by heating the mixture to 1200-1300 °C, this is called calcination. The hydroxide is thus made anhydrous. 

The book is aimed at ceramics in the year 2000 and the subject is introduced via two routes, i.e. the period of approximately 25,000 BC until about 1850 AD in which clay and related natural raw materials prevailed, and the period from 1850 until 2000 with clay and other, mainly synthetic raw materials. Despite the length of the period in which only clay was used, this book will pay relatively little attention to it. The reason for this is the fact that the number of application of ceramic materials increased considerably with the introduction of synthetic raw materials. Moreover, natural sciences have boomed enormously after World War II and consequently so did the education in ceramics. The main part of this book is therefore devoted to ceramics after 1945. Because one of the applications of this book is in the field of education, the text is occasionally illustrated with simple experiments. 

Despite their overawing complexity, clay minerals are to receive particular emphasis in this book as model systems. They are of high abundance and of key importance in sedimentary and soil systems (63-64), as ceramic materials (65) and as industrial fillers (66) they exhibit essentially all of the generic spectroscopic and surface chemical properties of reactive minerals in general and there are good reasons to believe that many of the spectroscopic and chemical attributes of minerals as a whole may be exaggerated in clays. 

This chapter gives an introduction to the preceramic polymer route to ceramic materials and focuses on the reasons why this new approach was needed and on the chemical considerations important in its implementation, with examples from research on organosilicon polymers. Novel polysilazanes have been prepared by the dehydro-cyclodimerization reaction, a new method for polymerizing suitably substituted cyclooligosilazanes. The living polymer intermediate in this reaction has been used to convert Si-H-containing organosilicon polymers that are not suitable for pyrolytic conversion to ceramics into useful preceramic polymers. 

One can easily summarize the requirements that should be fulfilled before the titanium-based ceramic materials can be obtained through an aqueous solution synthesis method. First, the precursor compound should possess good solubility in water, and preferably it should be stable over a wide pH range. In ideal case such compound should be a weighing form for titanium however, from the practical considerations it is sufficient to have a stock solution stable for a reasonably long period of time. Second, the reagent should be non-toxic, relatively cheap and its impact on the environment should be small. Its composition and chemistry should be simple and the reactions with other cations that will be introduced to the system must be well-predictable. The tendency to form precipitates with many cations, like in the case of oxalate ions, must be avoided. Finally, from an industrial point of view, the overall process should be cost effective and environmentally benign. 

According to their chemical composition, fireclay products belong to the clay ceramic materials. However, their preferred utilization for refractory furnace linings makes it more reasonable to discuss them with the other refractory products. 

Ionic conductivity (although somewhat lower) is reasonably isotropic in polycrystalline ceramic materials, which can be fabricated economically with excellent mechanical properties. 

The Silver Coulometer. The silver coulomcter consists, essentially, of a platinum dish or crucible as cathode, and a silver anode with a silver nitrate solution as electrolyte. Surrounding the anode is, in the latest types of the instrument, a porous cup of ceramic material, for reasons to be explained below. A convenient form of silver coulometer is shown diagrammatically in Fig. 3. A dish, Pt, holds a solution of silver nitrate... 

Supported metal clusters play an important role in nanoscience and nanotechnology for a variety of reasons [1-6]. Yet, the most immediate applications are related to catalysis. The heterogeneous catalyst, installed in automobiles to reduce the amount of harmful car exhaust, is quite typical it consists of a monolithic backbone covered internally with a porous ceramic material like alumina. Small particles of noble metals such as palladium, platinum, and rhodium are deposited on the surface of the ceramic. Other pertinent examples are transition metal clusters and atomic species in zeolites which may react even with such inert compounds as saturated hydrocarbons activating their catalytic transformations [7-9]. Dehydrogenation of alkanes to the alkenes is an important initial step in the transformation of ethane or propane to aromatics [8-11]. This conversion via nonoxidative routes augments the type of feedstocks available for the synthesis of these valuable products. 

When an oil-bearing formation consists of loose, uncemented sand, a ceramic niter should be installed on the wellbottom (Fig. 64). The niter protects the bottomhole equipment from intensive wear that would be caused otherwise by the sand carried into the well with hot oil and gas. These niters are made for different permeabilities, they can withstand temperatures of up to 3,000°C, and they effectively stop sand penetration into the well. Because the surface of the niter is coarse-grained and has sharp unrounded edges, a turbulent Bow is created in the oil entering from the bed. For this reason the filter practically never plugs up. Moreover, the ceramic material is chemically inert therefore, the niter resists very well the action of low pH liquids and of other corrosive agents in the bottomhole. At the same time, the niter acts as a good heat insulator. 

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