What is Ceramic?

Definition of Ceramic

A ceramic is an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous (a glass).

Explanation of Ceramics

The word ceramic comes from the Greek word κεραμικός (keramikos) meaning pottery, which is said to derive from the Indo-European word ker, meaning heat. Ceramic may be used as an adjective describing a material, product or process; or as a singular noun, or, more commonly, as a plural noun, ceramics.

The earliest ceramics were pottery objects made from clay, later it has been used for manufacturing domestic, industrial and building products and art objects as well. In the 20th century, new ceramic materials were developed for use in advanced ceramic engineering e.g. in semiconductors.

Types of Ceramic Products

Ceramic products are divided into four categories including:

Structural Ceramic including bricks, pipes, floor and roof tiles.

Refractories including kiln linings, gas fire radiants, steel and glass making crucibles.

Whitewares Ceramic including tableware, wall tiles, pottery products, and sanitary ware

Technical Ceramic is also known as Engineering, Advanced, Special, and in Japan, Fine Ceramics. Such items include tiles used in the Space Shuttle Program, gas burner nozzles, ballistic protection, nuclear fuel uranium oxide pellets, bio-medical implants, jet engine turbine blades, and missile nose cones. Frequently the raw materials do not include clays.

Technical ceramics are further classified into three distinct material categories:

1- Oxides: Alumina, Zirconia.
2- Non-oxides: Carbides, Borides, Nitrides, Silicides.
3- Composites: Particulate reinforced combinations of oxides and non-oxides.

Each one of these classes can develop unique material properties.

Types of Ceramic Material

A ceramic material is often understood as restricted to inorganic crystalline oxide material. It is solid and inert. Ceramic materials are brittle, hard and strong in compression, weak in shearing and tension. They withstand chemical erosion that occurs in other materials subjected to acidic or caustic environment. Ceramics generally can withstand very high temperatures such as temperatures that range from 1,000 °C to 1,600 °C (1,800 °F to 3,000 °F). Exceptions include inorganic materials that do not include oxygen such as silicon carbide or silicone nitride.

A glass is often not understood as a ceramic because of its amorphous (non-crystalline) character. However, glass making involves several steps of the ceramic process and its mechanical properties are similar to ceramic materials.

Traditional ceramic raw materials include clay minerals such as kaolinite, whereas more recent materials include aluminium oxide, more commonly known as alumina. The modern ceramic materials, which are classified as advanced ceramics, include silicon carbide and tungsten carbide. Both are valued for their abrasion resistance, and hence find use in applications such as the wear plates of crushing equipment in mining operations. Advanced ceramics are also used in the medicine, electrical and electronics industries.

Crystalline Ceramics

Crystalline ceramic materials are not amenable to a great range of processing. Methods for dealing with crystalline ceramics tend to fall into one of two categories including making the ceramic in the desired shape, by reaction in situ and by "forming" powders into the desired shape, and then sintering to form a solid body.

Ceramic forming technique include shaping by hand (including a rotation process called "throwing"), Slip casting, tape casting (for making thin ceramic capacitors), injection moulding, dry pressing, and other variations.

Non-Crystalline Ceramics

Non-crystalline ceramics, being glasses, tend to be formed from melts. The glass is shaped when either fully molten, by casting, or when in a state of toffee-like viscosity, by methods such as blowing to a mold. If later heat-treatments cause this glass to become partly crystalline, the resulting material is known as a glass-ceramic.

What is Acid Rain?

Definition of Acid Rain

Acid rain describes any form of precipitation with high levels of nitric and sulfuric acids. It can occur in the form of fog, snow and tiny bits of dry material that settle to Earth.

Rotting vegetation and erupting volcanoes release some chemicals that can cause acid rain, but the main factor behind acid rain is human activities including burning of fossil fuels by coal-burning power plants, factories, and automobiles. By burning fossil fuels, sulfur dioxide (SO2) and nitrogen oxides (NO2) are released into the atmosphere. These gases react with water, oxygen, and other substances to form sulfuric and nitric acid. When acid rain reaches Earth, it flows across the surface in runoff water, enters water channels and absorbs into the soil.

Wet Deposition

Wet deposition of acids occurs when any form of precipitation (rain, snow) removes acids from the atmosphere and delivers it to the Earth's surface. This can result from the deposition of acids produced in the raindrops or by the precipitation removing the acids either in clouds or below clouds. Wet removal of both gases and aerosols are both of importance for wet deposition.

Dry Deposition

Acid deposition also occurs via dry deposition in the absence of precipitation. This can be responsible for 20% to 60% of total acid deposition. This occurs when particles and gases stick to the ground, plants or other surfaces.

Ecological Effects of Acid Rain

Acid rain has been proved to have adverse impacts on waters, aquatic life, soils, forests, buildings and human health.

Effect of Acid Rain on Water and Aquatic Life

Acid rain makes waters acidic and causes them to absorb the aluminum that makes its way from soil into lakes and streams. This combination makes waters toxic to crayfish, clams, fish, and other aquatic animals. Some species can tolerate acidic waters better than others. However, in an interconnected ecosystem, what impacts some species eventually impacts many more throughout the food chain—including non-aquatic species such as birds.

Both the lower pH and higher aluminum concentrations in surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals. At pHs lower than 5 most fish eggs will not hatch and lower pHs can kill adult fish. As lakes and rivers become more acidic biodiversity is reduced. The United States Environmental Protection Agency's (EPA) website states: "Of the lakes and streams surveyed, acid rain caused acidity in 75 percent of the acidic lakes and about 50 percent of the acidic streams".

Effect of Acid Rain on Soil

Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to tolerate changes to low pHs and are killed. The enzymes of these microbes are denatured by the acid. The hydronium ions of acid rain also mobilize toxins such as aluminium, and leach away essential nutrients and minerals such as magnesium.

2 H+ (aq) + Mg2+ (clay) 2 H+ (clay) + Mg2+ (aq)

Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are leached by acid rain thereby affecting sensitive species, such as sugar maple (Acer saccharum).

Effect of Acid Rain on Forests

Adverse effects may be indirectly related to acid rain, like the acid's effects on soil or high concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain. It robs the soil of essential nutrients and releases aluminum in the soil, which makes it hard for trees to take up water. Trees' leaves and needles are also harmed by acids. The effects of acid rain, combined with other environmental stressors, leave trees and plants less able to withstand cold temperatures, insects, and disease. The pollutants may also inhibit trees' ability to reproduce. Some soils are better able to neutralize acids than others. In areas where the soil's "buffering capacity" is low, the harmful effects of acid rain are much greater.

Other plants can also be damaged by acid rain, but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands. When calcium is leached from the needles of red spruce, these trees become less cold tolerant and exhibit winter injury and even death.

Effect of Acid Rain on Buildings

Acid rain can also cause damage to certain building materials and historical monuments. This results when the sulfuric acid in the rain chemically reacts with the calcium compounds in the stones (limestone, sandstone, marble and granite) to create gypsum, which then flakes off.

CaCO3 (s) + H2SO4 (aq) CaSO4 (aq) + CO2 (g) + H2O (l)

This result is also commonly seen on old gravestones where the acid rain can cause the inscription to become completely illegible. Acid rain also causes an increased rate of oxidation for metals, and in particular copper and bronze. Visibility is also reduced by sulfate and nitrate aerosols and particles in the atmosphere.

Effect of Acid Rain on Human Health

Scientists have suggested direct links to human health. Fine particles, a large fraction of which are formed from the same gases as acid rain (sulfur dioxide and nitrogen dioxide) have been shown to cause illness and premature deaths such as cancer and other diseases.