Materials, Properties of

I INTRODUCTION

Materials, Properties of, characteristics of materials that determine their suitability for specific applications. Materials are anything from which products can be made. Materials science is the study of the properties, structure, and processing of materials.

II TYPES OF MATERIALS

Wood is a remarkable natural material. It is strong and relatively stiff and light. Its properties compete well with those of artificial materials. The fastest bomber in World War II, the British De Havilland Mosquito, was made of wood. When German intelligence discovered that the Allies were making aeroplanes out of wood, they thought that it was because supplies of metal had run out—not realizing that wood had been carefully chosen partly because it had excellent properties for this design. Wood remains the preferred material for many applications in the building industry throughout the world, and also for much furniture. Stone is another natural material, once used for making simple tools and weapons, and subsequently almost exclusively for buildings and sculptures.

Among the earliest materials to be put to use by human beings were ceramics, in the form of the clays used in pottery. Archaeologists date early civilizations by the pottery associated with them. Ceramic materials are chemical compounds of one or more metallic elements with oxygen or with other elements such as nitrogen. For a long time, ceramics were mainly used for plumbing or for cooking or eating utensils, but relatively strong engineering ceramics have now been developed with good mechanical properties, and others, called electroceramics, are essential for a wide range of electrical and electronic devices.

Metals are rarely found in the pure state in the crust of the Earth (although the centre of the planet is made of iron). They are good conductors of heat and electricity. When they are not tarnished or rusted they generally have a shiny surface. They are almost never used in their pure form for structural applications but are almost always mixed with other metals to form alloys. Iron is alloyed with controlled amounts of carbon and other elements to make steel, which was crucial to the Industrial Revolution, and is still by far the cheapest and most widely used metallic material. Aluminium alloys are widely used where weight-saving or corrosion resistance is more important than material cost—for example, in aeroplanes and to some extent in cars.

The whole of modern information and communication technology depends on semiconductors. These may be elements, such as silicon, or compounds, such as gallium arsenide, that have just enough electrical conductivity to make them useful for controlling and amplifying electrical signals. Silicon is universally used for digital switching devices such as those that are used in computers. For more difficult jobs, such as converting electrical signals to light or vice versa, semiconductoring compounds are used, and it is possible to tailor the properties of components by growing alternating layers of different materials. Every compact disc player contains a semiconductor laser. Long-distance communications are transmitted via fibre-optic links, using thin glass fibres, which were made possible by the development of extremely transparent types of glass.

Polymers are materials that are made of carbon, hydrogen, and other elements, with the carbon atoms connected to form long molecular chains. They can be made from crude oil, and they are usually formed into the desired shape while they are liquid. Thermoplastic polymers (from which we get the term “plastic“) become soft and mouldable when they are heated, and return to their solid form on cooling. Thermosetting polymers become solid owing to an irreversible chemical reaction. Cheap polymers are used for such common objects as shopping bags, but more sophisticated properties can be obtained. Polymer boxes can be made with integral hinges that can be flexed many thousands of times, and polymer roasting bags can survive high temperatures in ovens. Silk is a natural polymer that is stronger than many artificial materials. Polymers are usually electrically insulating, but they can also be made with useful conducting properties, and polymer transistors and light-emitting diodes have been produced.

Desirable properties of more than one material can be combined in composites. Glass-fibre-reinforced composites (fibreglass) are widely used to give high strength and stiffness without the fragility usually associated with glass. Many composites use carbon or polymer fibres in an epoxy matrix (the matrix is the material in which fibres or particles are embedded). The artificial material that is used in the greatest tonnage throughout the world is concrete, which is a composite of gravel, sand, and cement. Advanced composites are being developed that consist of ceramic fibres and different ceramic or metal matrix materials.

III MECHANICAL PROPERTIES

Density is the amount of mass in a unit volume. It is measured in kilograms per cubic metre or pounds per cubic foot. The density of water is very nearly 1,000 kg/cu m (62.4 lb/cu ft); most materials have a higher density and sink in water. Aluminium alloys, with densities typically around 2.8 times that of water, are considerably less dense than steels, which have densities typically around 7.8 times that of water. The density is significant in any application where the material must be supported or lifted off the ground.

Stiffness is a measure of the resistance to deformation such as stretching or bending. The Young modulus is a measure of the resistance to simple stretching or compression. It is the ratio of the applied force per unit area (stress) to the fractional elastic deformation (strain). Its SI units are MN/m2 (meganewtons per sq m) or, equivalently, MPa (megapascals). Stiffness is important when a rigid structure is to be made.

Strength is the force per unit area (stress) that a material can support without failing. The units are the same as those of stiffness, MN/m2, but in this case, the deformation is by definition irreversible. The yield strength is the stress at which a material first deforms plastically. For a metal, this may be somewhat less than the fracture strength, which is the stress at which it breaks. Many materials have a higher strength in compression than in tension; this is why steel reinforcement bars are used to support tensile (stretching) loads in concrete buildings and bridges.

Ductility is the ability of a material to deform without breaking. One of the great advantages of metals as materials lies in their ability to be formed into the desired shape, such as car body parts. Materials that are not ductile are brittle. Ceramics are generally quite brittle. Ductile materials can absorb energy by deformation but brittle materials cannot. Thus a metal teaspoon will survive being dropped on the floor while a ceramic teacup will break. High-impact polymers can similarly resist breakage.

Toughness is the resistance of a material to breaking when there is a crack in it. For a material of given toughness, the stress at which it will fail is inversely proportional to the square root of the size of the largest defect present. Toughness is different from strength: the toughest steels, for example, are different from the ones with highest tensile strength. Brittle materials have low toughness: glass can be broken along a chosen line by first scratching it with a diamond. Ceramic materials with a perfect crystalline structure can be extremely strong, but the presence of defects often limits the useful load that they can support; this is why they are generally weaker in tension than in compression. Composites can be designed to have considerably greater toughness than their constituent materials.

Creep resistance is the resistance to a gradual permanent change of shape and becomes especially important at higher temperatures. Lead pipes can sometimes creep at summer daytime temperatures. The hotter a gas-turbine engine is run, the more efficient it is, and a great deal of successful research has gone into developing materials for turbine blades that will enable them to operate at high temperatures and under high centripetal forces without gradually extending and scraping against the walls of the engine.

IV ELECTRONIC PROPERTIES

Electrical conductivity is the ability of a material to conduct electricity. It is the reciprocal of the resistivity, which is defined as the resistance between opposite faces of a cube of the material. The conductivity of metals decreases with increasing temperature, whereas the conductivity of semiconductors increases with increasing temperature. Most ceramics are insulators at room temperature, but many electroceramics acquire significant conductivity at higher temperatures. Metals can become superconductors (with zero resistance) at very low temperatures; several ceramics have been developed that exhibit superconductivity at the comparatively high temperature of liquid nitrogen (-196º C/-321º F).

Semiconducting properties are central to a huge range of electronic effects. By “doping” a semiconductor material with small amounts of impurities its properties can be dramatically changed. The junction between oppositely doped semiconducting materials is the basis of diodes and bipolar transistors, which are the fundamental components of all microchips. The gap between energy bands (see Condensed-Matter Physics) in a semiconductor determines the wavelength of light which that material can emit. Silicon has a bandgap corresponding to infrared radiation (although it can also emit visible light); for visible radiation, compound semiconductors are generally used.

Dielectric properties are measured by relative permittivity (dielectric constant), which is related to the static charge on the surface when an electric field is applied to insulators such as polymers and ceramics. Materials with high permittivity are good for capacitors, which store charge in circuits.

Piezoelectric properties are a material’s ability to generate a charge when its shape is changed, for example by an applied force. Some domestic gas spark igniters work this way. The quartz crystal oscillator in a digital watch depends on its piezoelectric properties to function. When a voltage is applied to a piezoelectric material, its shape changes and this property can be exploited in small actuators, as found in devices such as inkjet printers.

A pyroelectric material generates a voltage when its temperature changes. This is exploited in passive infrared detectors for automatic doors and burglar alarms, which can detect body heat at distances up to 100 metres (300 ft).

In a material with electro-optic properties, the propagation of light is altered by the influence of an applied electric field. Liquid crystals and certain transparent ceramics exhibit electro-optic properties, which make them useful for computer displays and for switching fibre-optic light signals.

Magnetic properties are traditionally associated with iron, but many other alloys and ceramics are also magnetic. “Soft” magnetic properties—properties that readily change as an applied magnetic field is changed—are required for transformers and for electromagnets that can be switched on and off. “Hard” magnetic properties—ones that are not easily changed—are required for permanent magnets; new materials of this kind have made possible compact yet powerful motors, such as those in electric screwdrivers.

V CHEMICAL PROPERTIES

Corrosion resistance is the ability of a material to resist degradation through oxidation. With prolonged exposure to the atmosphere ordinary steels rust and copper develops a green oxide which eventually turns black. Stainless steels are alloys containing chromium that have high resistance to rusting and other forms of chemical attack. Aluminium is a chemically reactive element, but it forms a stable oxide that is well bonded to the metal, thus inhibiting further corrosion.

Colour is a property that is important in textiles and in paints, inks, and so on. In gemstones, the colour is controlled by microscopic defects in the crystal lattice known as colour centres.

Biocompatibility describes the ability of materials to be used inside the human body, for example as prosthetics (artificial spare parts) in replacement surgery. The materials must not be chemically attacked by substances naturally present in the body, and they must not give off harmful chemicals or debris from wear. Biocompatible materials are being developed that can be organically incorporated into natural tissues such as bone.

VI MICROSTRUCTURAL PROPERTIES

Under everyday conditions of temperature and pressure, all materials are made of atoms. In polymers, the atoms are arranged in large groupings called molecules, which are bound together to give the material its properties. The molecules in many polymers and the atoms in most other artificial materials are arranged in crystals, in which the atoms repeat themselves in regular arrangements. The crystal structure plays a key role in giving a material its mechanical, electrical, and, to some extent, chemical properties.

Microchips are made, hundreds at a time, in the form of semiconductor wafers, which are large single crystals as much as 20 cm (8 in) in diameter. The whole of modern electronic and computer engineering has been made possible by engineers’ ability to make silicon material of extremely high purity and crystal perfection.

Almost all metals and ceramics are polycrystalline: consisting of many individual crystal grains adjoining one another. Grains of zinc on the surface of galvanized iron are often large enough to be seen with the naked eye. In most alloys, the grain structure can be seen with a standard microscope if the metal is first polished and then etched with a suitable acid. Much of the understanding of the structure and properties of materials has come about through the use of microscopes.

In order to see the structure within a grain, the transmission electron microscope is used (see Microscope: Electron Microscope). This instrument uses magnetic lenses to focus electrons, rather as glass lenses focus light. The mechanical behaviour of metals is found to be controlled by dislocations, which are defects in an otherwise perfect crystal lattice. It would be difficult to move one whole plane of atoms over another in a metal crystal, but a dislocation enables the planes to slide a little bit at a time, rather as a caterpillar moves over a leaf by making a hump in its back so that at that point its legs do not touch the surface on which it is standing. Ceramics are brittle because the dislocations in them cannot easily move. In a pure metal, the dislocations can move rather easily (unless they get tangled by work hardening); much of the design of alloys is concerned with making it more difficult for the dislocations to move.

Several kinds of microscopes enable individual atoms of a solid to be imaged. High-resolution electron microscopes can resolve single columns of atoms along a chosen crystal direction. Field ion microscopes can image the atoms on the end of a sharp needle of a material; it is even possible to pull atoms off the surface and weigh them one at a time in a mass spectrometer to find out what they are made of. Scanning tunnelling microscopes enable the positions and electronic structure of individual atoms and molecules on a flat surface to be seen. See Microscope: Scanning Probe Microscope.

Contributed By:
Andrew Briggs

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Intellectual Property

Intellectual Property, defined as those creations of the mind that can be protected by law once they take tangible form. An idea for a story, a recipe handed down through generations of a family, a tune whistled in the street—none of these can be protected by law: but once they are written down, recorded, or even performed in public, then the laws protecting copyright, designs, or patents, can be invoked to protect the rights and interests of the creator—the copyright holder, or the owner of the intellectual property.

The copyright system in most countries of the world rests on this fundamental principle of intellectual property. This provides a mechanism for the orderly buying and selling of rights, their transfer or assignment, and the control of their use nationally and, to some extent, internationally.

Intellectual property covers all works that are original or novel, whether they are literary, dramatic, artistic, or musical—but nothing qualitative is implied in the meaning of any of those words: any work of whatever quality is protected.

Laws protecting intellectual property are drawn up nationally. However, a number of international conventions have attempted to create a system of common protection. The most important for owners of intellectual property are the Berne Convention of 1886 and the Universal Copyright Convention which dates from 1952. Other agreements to protect performers and recording companies were drawn up in Paris and Geneva.

Article 9 of the Berne Convention states that “authors of literary and artistic works protected by this Convention shall have the exclusive right of authorizing the reproduction of these works in any manner or form”.

Intellectual property of any kind—whether literary, dramatic, musical, or artistic—must be in tangible form. Neither the idea behind the creation nor the ink in a book or the paint of a painting constitutes property that can be protected by copyright legislation.

There is no copyright in a name or in the title of a book. However, the owners of brand names and devices, or commercial catchphrases, may well have registered them as trademarks, which are protected in the United Kingdom by the Trademark Acts of 1938 and 1994. In addition, the law of passing off prevents misuse of someone’s name, or of the design and overall appearance of a product, where the confusion is caused or deception can be proved.

Scientific inventions or commercial designs are also protected by the 1988 Copyright, Designs, and Patents Act in the United Kingdom, or in the case of registered designs by the Registered Designs Act of 1949. Further protection may be gained by taking out a patent, under the terms of the Patents Act 1977.

Most forms of protection for intellectual property give a period of time in which owners can exercise their rights. Typically, copyright lasts for 50 years from the date a work was first issued to the public, although in the case of an author of a literary, dramatic, artistic, or musical work, the 50-year period begins after the author’s death. In some countries, the period is longer—70 or even 75 years.

As electronic publishing and electro copying play an increasing part in the cultural, social, academic, and professional world in which we live, rights of owners of intellectual property have become threatened. The main reason for this is that detection of copying or misuse is becoming more difficult, and the means of registering and collecting payment for exploitation of the tangible forms of intellectual property are not easy to monitor and control.

Designs can be transferred via a Standard Generalized Markup Language (SGML) system, instructions for a computer software programme can be copied in microseconds, and the ways of defining originality become ever harder. The Internet system is one example of a network on which it is impossible safely to control exploitation or misappropriation of intellectual property.

The argument that the free flow of information is important to the academic and intellectual health of the world takes no account of the commercial imperative of the creator. If the creators—authors— can no longer be rewarded for their creativity or originality, then it will soon not be worth their while to create in the first place.

The situation in countries such as China, where it is politically (and financially) expedient to disseminate all intellectual property, whether or not it belongs to the individual concerned, can only lead to electronic and intellectual anarchy. The trading system becomes corrupt, the standard value of original creative work disappears, and the world’s store of intellectual property—both current and future—is permanently and irreversibly bankrupted.

Contributed By:
Richard Balkwill

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Distributive Property

Distributive Property, trait of two mathematical operations that allows one operation to be distributed across the other. According to the general distributive law, for example, multiplication may be distributed across addition without changing the value of the overall expression. This law states that x(y + z) = xy + xz for any numbers x, y, and z. For instance, to find the value of the expression 5(3 + 4), add 3 plus 4 to get 7, and then multiply 5 times 7 to get 35. The distributive property allows the expression to be rewritten, with the multiplication by 5 distributed to each of the terms that were added together: 5(3 + 4) = (5 × 3) + (5 × 4). Multiplying 5 times 3 gives 15, and 5 times 4 gives 20. Adding 15 and 20 gives 35, the same value as that of the first calculation. The distributive property works no matter how many instances of the second operation are involved: x(w + y + z) = xw + xy + xz, x(v + w + y + z) = xv + xw + xy + xz, and so on.

The distributive law is useful for simplifying algebraic expressions such as:
Applying the distributive property to the top part of the expression yields:
The y + 3 terms cancel each other because (y + 3)/(y + 3) = 1, leaving x = 7.

Multiplication also distributes over subtraction: x(y – z) = xy – xz. For example, 6(4 – 2) = (6 × 4) – (6 × 2) = 12. Not all operations, however, are distributive. Addition and subtraction, for example, do not distribute over multiplication: 6 + (4 × 2) = 14, while (6 + 4)(6 + 2) = 80.

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Community Property

Community Property, in law, possessions held jointly by a married couple. Except for inheritances or gifts to either spouse, all property acquired by the husband or wife during the marriage is usually considered community property. This includes money, real estate, household furnishings, investment securities, cars, and other types of consumer goods that people have accumulated together. Property owned prior to the marriage and any income from such property remains separate and apart. Contractual agreements may also be made by the couple to allow them to maintain an individual property.

In the past, marital property laws were biased in favour of the husband, who usually held title to the couple’s major assets. In English common law, wives were originally unable to hold and dispose of property, but a series of 19th-century acts of parliament, culminating in the Married Women’s Property Act 1882, gave wives the right to their own property.

The question of who owns what is one of fact, so it varies from case to case. There are now provisions for the court to exercise wide discretion in adjusting the property ownership between divorcing parties (See Divorce; Maintenance). There are no such provisions in English law for couples who live together, and one partner may have to rely on proving that property in the name of the other partner is really shared between them.

Reviewed By:
Simon Levene

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Colligative Properties

I INTRODUCTION

Colligative Properties, properties of solutions that depend on the number of particles in a given volume of solvent and not on the mass of the particles. Colligative properties include: lowering of vapour pressure; elevation of a boiling point; depression of freezing point; osmotic pressure (see Osmosis; Reverse Osmosis). Measurements of these properties for a dilute aqueous solution of a non-ionized solute such as urea or glucose can lead to accurate determinations of relative molecular masses. Alternatively, measurements for ionized solutes can lead to an estimation of the percentage of ionization taking place.

II VAPOUR PRESSURE

The relationship between the lowering of vapour pressure and concentration is given by Raoult’s law, which states that the relative lowering of the vapour pressure is equal to the mole fraction of the solute in the solution.

Here p0 is the vapour pressure of pure solvent; p is the vapour pressure of solution; n is the number of moles of solute, and N is the number of moles of solvent.

As this relationship is true only for very dilute solutions, in which n is very small by comparison with N, it can be approximated by:
The left-hand side of the equation corresponds to the relative lowering of vapour pressure—that is the actual lowering divided by the original vapour pressure. The right-hand side of the equation is the ratio of the number of solute particles to the number of solvent particles.

III BOILING POINT AND FREEZING POINT

Both the elevation of the boiling point and the depression of the freezing point are proportional to the lowering of vapour pressure, provided only dilute solutions are considered.

IV OSMOTIC PRESSURE

For a fixed mass of 1 kg of solvent, the change in temperature is given by ΔT = K m / M
where m is the mass of solute, M is the relative molecular mass of solute, and K is the boiling-point constant or freezing point constant. K is a constant for a particular solvent.

Two laws governing the osmotic pressure of a dilute solution were discovered by the German botanist W. F. P. Pfeffer and the Dutch chemist J. H. van’t Hoff:

The osmotic pressure of a dilute solution at constant temperature is directly proportional to its concentration.The osmotic pressure of a given solution is directly proportional to its absolute temperature.

These are analogous to Boyle’s law and Charles’ law for gasses. A similar equation can be used: pV = n RT
where: p = osmotic pressure; V is the volume containing 1 mole of solute; T is absolute temperature; n is the number of moles of solute; R = 8.3145 J K-1mol-1, the molar gas constant.

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Estate

I INTRODUCTION

Estate, in law, the degree of interest or ownership that a person has in the property. The term “estate” is also used in a more general sense to denote the whole property possessed by an individual, for example, the estate of a deceased person. Sometimes debts are also included in this wide meaning, with all rights and duties regarded as a single entity. Estate in this sense of the total belongings of a person is divided into realty, or real estate, and personal estate (anything other than real estate, usually less permanent fixtures).

II DERIVATION

The term “estate”, in the sense of interest that a person has in the property, applies especially but not exclusively to realty. Much of the law of realty in England and the United States stems from the feudal institutions developed in England after the Norman Conquest (1066). The basic premise of feudalism was that the monarch enjoyed ultimate power over all the land in the realm. From the monarch, the lawful occupants and users of land had tenure, the right to occupancy and use, either directly or indirectly, through a lord. One’s tenure, or estate, determined one’s social status.

III TYPES

Estates are classified into two types: freehold and non-freehold. The freehold estates found in modern property law are further divided into the fee simple and the life fee. The fee simple estate is essentially absolute ownership of land, including the power to bestow by will or to sell it. The life fee estate is the right to control property during one’s lifetime only; the grantor of a life estate designates the party who is to come into possession on the death of the life tenant. A freehold estate in fee tail, or entail, is a grant to a person and his or her descendants forever in a direct line. The objective of entailing is to preserve family estates from the division.

Non-freehold estates, for the most part, are those established by lease of real property. Two common types are the estate for years and the periodic estate. In the former the right to occupy the realty terminates at a fixed time; in the latter, the lease period is for a definite term that is renewed automatically if neither party signifies an intention to terminate the tenancy.

Today the term “estate” generally refers to the property of every sort that is owned by an individual and that may be passed on to another at the owner’s discretion. A deceased person’s estate is disposed of according to law and to instructions given prior to death. An executor or administrator is responsible for carrying out the disposition of the estate. See Will.

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Real Estate Definition

I INTRODUCTION

Real Estate, in broad definition, land and everything built on it, and the nature and extent of one’s interest therein. Though chiefly an American usage, the term has the advantage of distinguishing between such landed property and the broader classes of property in general, unlike the common British usage. The word “real”, as it relates to property, means land as distinguished from personal property; and “estate” is defined as the interest one has in property.

Real estate may be acquired, owned, and conveyed (or transferred) by individuals; business corporations; charitable, religious, educational, and various other non-profit corporations; fiduciaries, such as trustees and executors; partnerships; and generally by any legal entity as determined and defined by the law. Limitations are established in connection with sales of real estate by children, incompetents, and certain types of corporations, and generally in cases involving some form of legal disability or lack of capacity. In such instances, it is necessary in some jurisdictions to make application to the courts for permission to sell; in other jurisdictions such transfers are governed by statute.

Real property is generally acquired by purchase, by descent and devise (the bequest of such property in a will), or by gift. When acquired by purchase, a deed is given by the seller, or grantor, to the purchaser, or grantee. The deed contains a legal description of the property conveyed; it must be drawn, executed, and acknowledged in proper form to be effective, and usually the change of ownership has to be registered or recorded with the relevant authority. It is customary for the seller and the purchaser to enter into a contract, at which time the purchaser makes a deposit on account of the purchase price. The purchaser engages a specialist (usually a lawyer) to search the title to the property to ensure that the seller can convey clear title and to find out other material information about the property. The transaction is then completed or closed; that is, the property title is transferred and the balance of the purchase price is paid.

When an owner of real property has died intestate, or without leaving a will, title to the property is said to pass by descent to the heirs; when he or she has died testate, or leaving a will, the property passes to the person or persons designated in the will.

Transfer of real property by gift, as, for instance, to Churches or educational institutions, is easily accomplished merely by the execution and delivery of a deed.

The greatest and most extensive interest that may be acquired in realty is described in law as a freehold, a term that implies a proprietary ownership, free and clear of conditions. There is also leasehold ownership, the commonest form of ownership for those owning part of a larger property, where the owners purchase a lease on the property from the freeholder, acquiring ownership of it for a designated period of time and within certain restrictions. However, precise terms and legal norms vary between countries.

II MULTIPLE OWNERSHIP

Multiple ownership, which has been widely adopted under the leasehold system, implies separate ownership of individual apartments or units in a multi-unit building. The purchaser becomes the owner of a particular unit and of a proportionate share in the common elements and facilities. The unit may be separately mortgaged; the owner pays taxes and a fixed monthly sum to maintain the common elements. In the sale of a unit, the seller executes and delivers to the buyer a deed conveying all right, title, and interest in and to the share of the whole as well as the particular unit.

III COOPERATIVE OWNERSHIP

Cooperative ownership, which on the surface seems similar to multiple ownership, is in fact quite different. In cooperative ownership, title to the multi-unit building usually is vested in a corporation. The purchaser of an apartment or a unit actually buys stock of the corporation; in addition to a stock certificate, a cooperative member receives a lease to the apartment, in which he or she is named lessee.

As a holder of stock, each cooperative member has an ownership interest in the corporation, which in turn owns all the units and common areas. Each tenant pays to the corporation a fixed rent, which is applied to the payment of a single blanket mortgage and real-estate taxes covering the entire building, and to the payment of insurance premiums and maintenance costs for the upkeep of the common areas and facilities, which each tenant uses in common with all other unit owners. In the sale of a cooperative unit, the seller surrenders his or her stock and lease to the corporation, which in turn issues a new stock certificate and lease to the purchaser. The form and structure of cooperatives vary, and in some countries are regulated by law. This form of property ownership, however, is not common in the United Kingdom.

Apart from actual ownership, an interest in real estate may consist of a lease, a mortgage, a lien, or other encumbrance on the property.

 

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