CHAPTER 1 CERAMICS PROCESSING AND CERAMIC PRODUCTS

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CHAPTER 1CERAMICS PROCESSING ANDCERAMIC PRODUCTS
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• 1. This book is concerned primarily with
  understanding the scientific principles and
  technology involved in processing particulate
  ceramic materials into fabricated products.
• 2. Our topic is commonly referred to as ceramics
  fabrication processes, ceramics processing
  technology, or simply ceramics processing.
• Ceramics processing technology is used to produce
  commercial products that are very diverse in
  size, shape, detail, complexity, material
  composition, structure, and cost.

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Several examples of both modern advanced ceramics
and traditional ceramics are shown in Fig. 1.1.
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• The applications of these products, as are
  indicated in Table 1.1, are also diverse and are
  dependent on the func-
• tions indicated in Table 1.2.

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• The functions of ceramic products are very
  dependent on their chemicalcomposition and their
  atomic and microscale structure, which determines
  their properties.
• Compositions of ceramic products vary widely, and
  both oxide and nonoxide materials are used.
• Today the composition and structure of grains and
  grain boundary phases and the distribution and
  structure of pores is more carefully controlled
  to achieve greater product performance and
  reliability (Fig.1.2).

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• In the development and production of the more
  advanced ceramics, extraordinary control of the
  materials and processing operations is requisite
  to minimize microstructural defects.

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1.1 A BRIEF HISTORY OF CERAMIC TECHNOLOGY
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• The history of ceramic processing technology is
  very interesting in that both simple processes
• developed in ancient times for natural materials,
  
• and recently developed, relatively sophisticated
  processes dependent on synthetic materials are
  used extensively near the end of the 20th
  century.

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• Hand mixing, hand building, and scratch and slip
  decorating of earthenware date back to before
  5000 BC.
• The first forming machine was probably the
  potter's wheel, which was used earlier than 3500
  BC for throwing a plastic earthenware body and
  later for turning a somewhat dried, leather, hard
  body.
• Shaping by pressing material in fired molds and
  firing in a closed kiln were subsequent
  developments.

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• The most notable achievement early in the
  Christian era was the development in China of
  pure white porcelain of high translucency.
• Duplication in the West was frustrated until
  1708, when a young German alchemist, Frednch
  Bottger, under the direction of the celebrated
  physicist Count von Tschimhaus, discovered that
  fine porcelain could be produced on firing a body
  containing a fireresistant clay with fusible
  materials.

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• Other inventions in the eighteenth century
  included the use of a template for forming, slip
  casting in porous molds, auger extrusion,
  transfer decoration, and firing in a tunnel kiln.

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• The introduction of steam power in the nineteenth
  century led to the mechanization of mixing,
  filter pressing, dry pressing, and pebble mill
  grinding.
• Near the end of that century, separate phases of
  silica were distinguished using optical
  microscopy, and silicon carbide was synthesized
  in an electric furnace.
• Pyrometric cones were developed by Seager to
  control firing.

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• The first half of the twentieth century saw the
  rapid development of x-ray techniques for the
  analysis of the atomic structure of crystals and
  later electron microscopy for examining
  microstructure beyond the limit of the optical
  microscope.
• Material systems became more refined, and special
  compounds were developed, synthesized, and
  fabricated into products for refractory and
  electronic applications. Refined organic
  additives were purposefully introduced to improve
  the processing behavior.

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• Industrial production became mechanized, and
  several stages of manufacturing were automated.
  Thermocouples were used routinely to monitor
  temperatures during firing.
• The second half of the twentieth century has
  witnessed major advances in the synthesis,
  characterization, and fabrication of ceramic
  products.

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• Scanning electron microscopy is now used for
  routine microstructural analysis for quality
  control in manufacturing.
• Several different instrumented techniques have
  been
• developed for bulk chemical analysis at a
  concentration of less than a fraction of one part
  in a million and surface concentrations a few
  atomic layers in thickness

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• The particle size distribution of a material can
  be determined to below 0.1µm in a few minutes.
  The flow behavior during forming is developed and
  controlled using a multi component system of
  additives.
• Testing apparatus and processing machinery are
  much more advanced. Computers are now used
  throughout the industry to monitor and/or control
  raw-matenal handling and preparation,
  fabrication, and firing.

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1.2 INDUSTRIAL CERAMICS PROCESSING
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• The realization of a product depends on material
  factors and nonmaterial factors such as the
  economics of the marketplace,consumer response.
• The manufacture of ceramics is a complex
  interaction of raw materials, technological
  processes, people, and financial investment.
• Manufacturing managers are involved with all of
  these aspects.

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• Ceramics processing commonly begins with one or
  more ceramic materials, one or more liquids, and
  one or more special additives called processing
  aids.
• The starting materials or the batched system may
  be beneficiated chemically and physically using
  operations such as crushing, milling, washing,
  chemical dissolving, settling, flotation,
  magnetic separation, dispersion, mixing,
  classification, de-airing, filtration, and
  spray-drying.

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• The forming technique used will depend on the
  consistency of the system (i.e., slurry, paste,
  plastic body,or a granular material) and will
  produce a particular unfired shape with a
  particular composition and microstructure.
• Drying removes some or all of the residual
  processing liquids.

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• Additional operations may include green machining
  surface grinding, surface smoothing and cleaning,
  and the application of surface coatings such as
  electronic materials or glaze.
• The finished material is then commonly
  heat-treated to produce a sintered
  microstructure.
• The sintered product may be a single component or
  a multi component composite structure.
• A general processing flow diagram indicating the
  sequences of operations used in forming a product
  is shown in Fig. 1.3.

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1.3 SCIENCE IN CERAMICS PROCESSING
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• Up to about the first half of the twentieth
  century, processing engineers depended on
  empirical correlations and practical intuition
  for innovating new process designs and process
  controls.
• Most new products were seen as inventions rather
  than the planned outcome of research and
  development.
• Material systems were typically complex, and
  laboratory tests and analyses were tedious and
  time consuming.

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• Before the development of scientific insights of
  ceramics processing, the properties of the
  product were often correlated with changes in a
  processing operation to identify the more
  important superficial variables (Fig. 1.4).

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• The objectives of the science of ceramics
  processing are to identify the important
  characteristics of the system and understand the
  effects of processing variables on the evolution
  of these characteristics.
• The objectives in process engineering should be
  to change these characteristics purposefully to
  improve product quality.

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• SUMMARY
• 1. Ceramic products are used in applications
  where the performance and reliability of the
  product must be predictable and assured and the
  product must be fabricated successfully in a
  productive manner.
• 2.The manufacture of these products from a
  complex batch containing ceramic materials and
  processing additives into a finished product
  involves many operations.

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SUMMARY

• 3. All of the materials and operations must be
  carefully controlled.
• 4. Principles of science should be used in
  addition to empirical tests for understanding,
  improving, and controlling ceramics processing.

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