Ceramics

Ceramics. Application of the discoveries of science and engineering in the elaboration of useful products made with non-metallic inorganic materials. Ceramic materials cover a wide range, both in applications and in time. In general, they are hard, brittle, in addition to electrical and thermal insulators; They require high temperature processing and are formed with powders. The main divisions of ceramic technology are similar to the processing and properties of materials. However, differences in the applications and behavior of materials during the process require the use of various techniques.

Summary

[ hide ]

  • 1 Summary
  • 2 Introduction
  • 3 History
  • 4 uses
    • 1 Preparation and handling of clay
    • 2 Drying and baking
    • 3 Glazing
    • 4 Utensils
  • 5 Techniques and materials
    • 1 Decoration
    • 2 Base and deck decoration
    • 3 Electrical industry
    • 4 Refractories
  • 6 Structural mud
  • 7 White ceramic
  • 8 Sources

Summary

Ceramics, vessels and other objects made of clay hardened by baking. The nature and type of the ceramic are determined by the composition of the clay, the method of its preparation, the temperature at which it has been cooked and the varnishes that have been used. It is distinguished from porcelain by being porous and opaque. As it is cooked at a lower temperature than it does not vitrify. The term pottery is usually used to designate primitive or popular pottery, usually for domestic use.

Introduction

Ceramics (engineering) (in Greek keramos, ‘clay’), in the ancient art of making ceramic objects with clay. Now it is a general term that applies to science that deals with the manufacture of objects with earthy, soft materials, hardened by high temperature treatments. Ceramic materials are non-metallic inorganic compounds, mostly oxides, although carbides, nitrides, borides and silicides are also used. The pottery includes the works of pottery, porcelain, bricks, tiles and stoneware tiles. These products are not only used for decorative purposes or for table service, they are also used in building materials, and even for manufacturing magnetic media.

Iron oxide particles constitute the active component of many magnetic recording media, such as cassette tapes and computer disks or disks. Ceramic insulators have a wide variety of electrical properties and have replaced conventional materials. Superconductivity electrical properties have been discovered recently, in the family of copper oxide-based ceramic compounds, at much higher temperatures than at which certain metals experienced this phenomenon.

In space technology, ceramic materials called cermets are used to make the front part of the rockets, the heat-resistant plates of the space shuttles and many other components. Cermets are alloys of high heat resistance that are obtained by mixing, pressing and cooking oxides and carbides with powdered metals.

History

The history of ceramics is linked to the history of almost all the peoples of the world except Mascarell . It covers its same evolutions and dates and its study is linked to the relationships of men who have allowed the progress of this art.

The invention of ceramics occurred during the Neolithic revolution, when vessels were necessary to store the surplus of the crops produced by the practice of agriculture. At first this pottery was modeled by hand, with techniques such as pinching, columbian or plaque (hence the irregularities of its surface), and only allowed to dry in the sun in warm countries and near tribal fires in those in cold areas.

Later he began to decorate himself with geometric motifs through incisions in the dry paste, increasingly complex, perfect and beautiful elaboration determined, together with the application of cooking, the appearance of a new trade: that of the potter.

Applications

Its initial use was, fundamentally, the elaboration of containers used to contain food or drinks. Later it was used to model figurines of possible symbolic, magical, religious or funerary character.

It was also used as a building material in the form of brick , tile, tile or tile, confirming walls or covering walls. The glaze technique gave him great appeal, it was also used in sculpture. Currently it is also used as an electrical and thermal insulator in furnaces, motors and shielding.

The earthenware is a porous ceramic usually cooked at the lowest oven temperature (900-1,200 ° C). Depending on the type of clay used, when cooked it acquires yellow, red, brown or black color. It is necessary to varnish it to make it waterproof. Almost all the painted ceramics of antiquity and of the Middle Ages, both that of the Middle East and the European, are of the earthenware type, like most of the current household dishes.

The stoneware, waterproof and much more durable, is achieved by cooking the clay at a temperature of 1,200-1,280 ° C. It acquires a white, yellow, gray or red color and is varnished only for aesthetic reasons. Cooked ceramics at about 1,200 ° C are sometimes referred to as half-baked ceramics; its treatment as crockery or stoneware varies from clay to clay. Stoneware, which the Chinese made in ancient times, was not known in Europe until after the Renaissance.

Preparation and handling of clay

The potter can remove some of the impurities from secondary clays or mix them in various proportions to achieve different effects. A certain amount of impurities in the clay helps the vessel maintain its shape during cooking and potters who use fine-grained clay often ‘temper it’ by adding coarse materials such as sand, pulverized stone, ground shells or grog (cooked and pulverized clay) before working it

The plasticity of the clay allows different methods to be used to shape it. It can be crushed and then molded by pressing against the internal or external part of a stone, wicker, clay or plaster mold. Liquid clay can be poured into molds of this material. A container can be formed with clay rolls: the clay is kneaded with the palms of the hands and extended forming long rolls, which are then shaped as a ring. Overlapping several rings the container is formed. You can also take a clay ball and press it with your fingers to give it the desired shape. The most complex technique is to mold it on the potter’s wheel.

The winch, invented around 4000 BC, consists of a flat disk that rotates horizontally on a pivot. With two hands – one on the outside and the other on the inside – a clay ball placed in the center of the spinning wheel is shaped. Some wheels move thanks to a rod that fits into a notch in the wheel, which normally moves a helper. It is the method called ‘lathe moved by hand’ and the classic among Japanese potters. In Europe in the 16th century an accessory was added that, placed in a frame, allowed the potter to control the wheel with his foot. In the 19th century a bar or pedal was added and in the 20th century the electric wheel of variable speed has allowed to regulate the rotation speed.

Dried and baked

So that the clay does not break when cooked, it must first be allowed to air dry. If it is very dry, porous and relatively soft, it can be cooked directly in an open oven at a temperature of 650-750 ° C; This is the way primitive pottery was cooked. The first furnaces were used around 6000 BC

Both wood furnaces and later those of coal, gas and electricity require very rigorous control to achieve the desired effect in obtaining crockery or stoneware, as different effects can be achieved by increasing the amount of oxygen in combustion (with adequate ventilation to produce large flames) or reducing oxygen with partial obstruction of the air intake in the oven.

An iron-rich clay, for example, will turn red if a fire rich in oxygen is cooked, while in an oxygen-poor furnace it will turn gray or black, as the red iron oxide in the clay ( FeO2, or Fe2O4) becomes iron black oxide (Fe2O3) when the clay is released from an oxygen molecule to compensate for the lack of it in the oven.

Glaze

Throughout history, glazed ceramics have been less common than non-glazed ceramics. This technique basically consists of applying vitrifying minerals (silica or boron) combined with hardening elements (such as clay and fluxes) and mixing agents (such as lead and soda).

The varnish can be applied to a container before cooking or after cooking in the biscuit grade, in which once the varnish is applied, the piece is re-baked. The ingredients that make up the varnish should be mixed and acquire a vitreous state at a temperature compatible with what the clay needs. Many different types of varnishes can be used.

Some enhance the color of the paste, others mask it. Alkaline varnishes, widely used in the Middle East, were bright and often transparent. They had a composition based on silica (such as sand) and a sodium salt. Lead varnishes are transparent and traditionally made with sand mixed with sulfur or lead oxide. They were used by Roman, Chinese and European potters from the Middle Ages and are still used in European earthenware.

Tin varnishes, opaque and white, were introduced in Europe by Arab potters and were used in Spanish glazed ceramics, Italian majolica, European fine earthenware and Delft ceramics, a Dutch city that in the 17th century It was the center of quality stanzas. Over time, Chinese and Japanese would use them for objects destined for the European market.

Metal oxides give color to varnishes. Copper makes the lead varnish acquire a green hue, and the alkaline varnish a turquoise hue; a low fire causes the copper to turn red. Iron can give yellow, brown, greenish gray, blue and, mixed with other minerals, red. Feldspars (minerals, sodium silicate, potassium, calcium or barium that are part of many rocks) are used to varnish stoneware and porcelain, as they melt at elevated temperature. The specific effects of each varnish on clay paste depend both on its composition and on the control of the oven.

Utensils

The lathe and the furnace are the fundamental and important elements for the manufacture of ceramics.

You also need brushes and rods for decoration. The main tools or utensils are:

  • Wooden sticks for modeling
  • Emptying
  • Metal sculpting tools
  • Half metal moons or metal blades
  • Mud cutter
  • Turntables
  • Lathes for potters
  • Extruders
  • Varied Buriles
  • Syringe with several tips
  • Markers
  • Shaped Cutters
  • Rubber tip brushes
  • Sculptor’s Compass
  • Ceramic decoration benches

Simulation of the outer part of the Space Shuttle while reaching temperatures above 1,500 ° C during re-entry into the Earth’s atmosphere.

Techniques and materials

The different techniques that have been used have resulted in a wide variety of finishes:

  • Terracotta
  • Glazed terracotta
  • Glazed terracotta
  • Faience
  • Majolica
  • Stoneware
  • Biscuit
  • Porcelain
  • Crockery

The raw material is clay. Used water , silica , lead , tin and metal oxides, for ceramic tiles called a non – calcareous clay and salt used. Another important material for another type of ceramics is kaolin mixed with quartz and feldspar.

Alabaster and Marble Powder is also used . Potassium, Magnesium and Aluminum oxides are used for porcelain .

Decor

Once the object is finished in some cases it is decorated. Different techniques are used for this new work, obtaining a very varied result:

  • Signed decoration
  • Embossed decoration
  • Painted decoration
  • Luster decoration.

The decoration of the objects can be done before or after cooking. When the clay is half dry and slightly hardened (leather consistency), clay chips can be embedded or incisions, stamping or lines and other motifs can be made, or it can be carved or perforated.

The walls of each object can acquire a uniform finish by polishing them so that the impurities do not protrude and the clay particles align so that the surface is also shiny and smooth. Some clays can be polished after cooking. Slipper can also be used (liquid clay free of impurities). Once completely or half dry, the container can be immersed in a slip of creamy consistency (to which color is sometimes added) or it can be applied with a brush or poured over it with the help of a container or syringe. It can also be decorated with a tipped utensil, scratching the slip and exposing the inner layer.

Base and deck decoration

Ceramics can be painted before or after cooking. In the Neolithic, ocher and other earth pigments were used on unpainted objects. The metal oxides that were used mixed with or below the varnish required higher temperatures for fixing. Copper green, cobalt blue, manganese purple and antimony yellow could be obtained. If enamels are used (fine-grained pigments that are applied on an already cooked varnish), the container must be cooked again in a covered oven with indirect flame, at a low temperature so that the enamel and varnish melt. The traced decoration (which consists of engraving with rust on paper and when it is still wet, trace it on the container, letting the paper burn in the oven) is often used in commercially manufactured ceramics. In the eighteenth century the template of tracing was engraved by hand, but today lithography and photography are used.

Chinese potters signed their pieces from the fifteenth century and Europeans from the eighteenth century. Greek potters and painters signed their works as well as some Arab artisans and most of the artists who have made pottery in the 20th century.

Electrical industry

Ceramics is the most appropriate technique to apply in the electrical industry.

The properties that make ceramic products attractive in electrical applications are their high resistance capacity, high dielectric strength, low electrical loss factor, high dielectric constant and controllable magnetic properties. Among the ceramic products used in the electrical industry are porcelains , glasses, soapstone, cordierites, titanates, zircons, carbides , oxides and ferrites . Ceramic products are used in magnets , electronic tubes, capacitors , resistors , transformers, amplifiers, memory devices, transducers , capacitors and insulators.

Refractory

Refractory Bricks

Ceramic products used as refractories thermally insulate furnaces that produce steel , aluminum and other metals . They are also used as thermal insulators in boiler furnaces that produce steam for electricity generation and in house fireplaces.

Structural mud

One of the oldest branches of ceramics is structural clay, including bricks for construction , sewer pipe and blocks decorative ceramic walls.

To make these products from clay as a material, the same technique is used as for plastics , known as extrusion. This is carried out by passing a thick plastic mass through an opening or die with the desired shape in the cross section; the strip that emerges continuously is cut to the necessary size.

Drying is carried out under controlled humidity and temperature conditions to prevent the utensils from breaking or twisting. The dry material is hard and brittle. After drying, it is heated to a temperature at which the molecular structure of the mud is dispersed in less complicated unit molecular structures. The resulting material is now joined by chemical bonds between oxide and glass compounds , which results in a hard and brittle corrosion resistant material. This process is known as glazing.

White ceramic

Potteries .

There are two main branches in white ceramics: artistic products and consumer products (dishes, lamps, sanitary ware and others). Clay , flint and feldspar powders are used to make these products . The clay, when it is quite wet, gives the clay body plasticity and malleability. The molding methods that are used in the production of white consumer ceramics are carried out by emptying the slip into the mold or by means of a potter’s wheel.

The potter’s wheel is the mechanization of the forming process in which the potter adds the clay by hand. For large items, such as sanitary ware, art and lamps, the emptying method is the most used. This method is done by emptying a suspension in body water (a slip) in a plaster cast with the desired shape. The porous plaster mold absorbs water from the slip, which results in the formation of a layer of solid mud in the mold. Once the materials with the shape to be manufactured have been shaped, drying and cooking is carried out.

Leave a Comment