Which is more ductile copper or silver

Copper has a wide range of properties.

Copper is one of the most widespread materials in our everyday environment and is an important functional and construction material. However, copper is also a “carrier metal” for a wide range of other non-ferrous metals.

But it is also of crucial importance for the development of new technologies that will not reach their full potential until well into the 21st century. We encounter copper in many areas of life - whether in architecture, information and communication technology, electrical engineering, renewable energies or in numerous industrial applications of innovative engineering. The material owes this primarily to its extraordinary material properties. Because copper has excellent heat and electrical conductivity and is very durable. Copper is a relatively soft and ductile, but also resistant metal that can be easily processed and shaped. It is also extremely durable and - depending on the application - can be used for decades. Above all, it is 100 percent recyclable. Alloyed with other metals, it can develop further properties, including hardness, strength, relaxation behavior and much more.

advantages

Good electrical and thermal conductivity are important properties of copper as a material. The great importance of this material for technology only results from the combination of the various good properties that - also in connection with other metals - have been used and further developed for years. In addition, copper has excellent corrosion resistance and is 100 percent recyclable without any loss of quality.

Chemical symbolCu
Atomic number29
Relative atomic mass63,546
density8.93 g / cm3
Melting point1083 ° C
boiling point2595 ° C
Electrical conductivity at 20 ° C57 m / (Ω * mm2)
Thermal conductivity at 20 ° C394 W / m * K
Temperature coefficient of electrical conductivity0.0039 / K
Thermal expansion17 * 10-6 / K (from 25 to 300 ° C)
Specific warmth0.39 J / g * K (20 to 400 ° C)
Heat of fusion214 J / g
Crystal structureCubic area-centered
Physical Properties
Mechanical properties
Physiological properties

Physical Properties

Copper is the only metal that is salmon-red in color. Besides gold, it is the only colored metallic element.

In the periodic system of the elements, copper is in the first subgroup with silver and gold. The structure of pure copper consists of a homogeneous phase and crystallizes in a face-centered cubic lattice. Pure copper is a salmon-colored ductile metal with a melting point of 1083 ° C and a boiling point of 2595 ° C. In its chemical compounds, copper is practically always mono- and bivalent.

Individual physical properties of copper depend heavily on the degree of purity or on the impurities. On the other hand, there is the possibility of changing certain physical properties over a wide range by alloying the metals with one another, by hot and / or cold deformation or by heat treatment. In this way, many characteristic values ​​of the copper materials can be adapted to the respective purpose.

Copper is one of the specifically heavy utility metals. In the solid state, the density of pure copper at 20 ° C is 8.93 g / cm3.

As a result of the (failed) attempt at a technically and physically clear separation between "light" and "heavy" metals, the term "heavy metals" has been used in public for about 40 years and in so-called specialist literature for "heavy" metals with toxic properties at the same time . The distinction between a physical quantity (density = mass / volume = "heaviness") and a biological property (toxicity) was lost. Metals such as copper and zinc, on the other hand, which are also physically “heavy” and also biologically vital, are subsumed in such lists and put on an equal footing with elements that are actually critical to health such as cadmium or mercury. Physically and technically, no uniform definition could be found for a sharp separation between “heavy” and “light” metals, a fact that the renowned chemist and biologist John Diffus of the International Union of Pure and Applied Chemistry (IUPAC) has been pointing out for decades draws attention: According to this there is a tendency, which is not supported by the facts, that all so-called 'heavy metals' and their compounds have highly toxic or ecotoxic properties. This has no basis in chemical or toxicological data. According to IUPAC, there are almost 40 different definitions of the term in the literature. Diffus clearly advocates a new classification based on the chemical properties of the metals as the basis for classification.

Nowadays one speaks more of base or technology metals.

Depending on the type and proportion of alloying elements / s added, the density of the resulting copper alloys changes. The density decreases with the lighter elements silicon or aluminum, while it is hardly changed by nickel and less by tin or zinc.

When the temperature changes, the materials expand or shrink; their volume changes analogously. The change in length is calculated using the linear thermal expansion coefficient. The spatial expansion coefficient is around three times as large as the linear expansion coefficient. It should be noted that the expansion coefficient is temperature-dependent. The linear expansion coefficient of pure copper is reduced by the addition of nickel, hardly influenced by aluminum and increased by zinc and tin.

The most important physical property of pure copper is its high thermal and electrical conductivity. After silver, copper has the highest electrical conductivity of all metals. It is customary to state the electrical conductivity of metals in% I.A.C.S (International Annealed Copper Standard) or in MS / m. 100% I.A.C.S. correspond to 58.00 MS / m (= 58.00 m / W mm2). The electrical conductivity of pure copper is severely reduced by even minor impurities. The specific electrical resistance depends on the temperature. The influence of unalloyed copper is greater than that of copper alloys. Cold forming reduces the conductivity of the copper materials. Hardenable copper alloys, on the other hand, have a higher conductivity in the quenched and tempered condition than in the solution-annealed condition. The thermal conductivity of pure copper decreases slightly with increasing temperature, while it increases with temperature in copper alloys.

Mechanical properties

Soft copper has a tensile strength of approx. 200 MPa, a yield strength of 40-80 MPa and an elongation at break of over 40%. If cold deformation takes place, the tensile strength increases to at least 350 MPa and the yield strength to at least 320 MPa, but then the elongation at break drops to values ​​below 5%. Pure copper does not have a warm, brittle area and can be easily formed even when it is warm. At the same time, copper does not become brittle even at low temperatures. Since copper also has considerable fatigue strength characteristics, it is also suitable as a material for vibrating loads without fear of brittle fractures. The mechanical properties of the various pure types of copper practically do not differ from one another. Only the creep behavior can be positively influenced by adding small amounts of alloy, such as silver. Alloys can be used to achieve strength values ​​of up to approx. 700 MPa, in special cases even up to 1500 MPa, but the conductivity can then drop considerably.

Chemical properties

In its chemical compounds, copper occurs in monovalent and bivalent form, in some exceptional cases - e.g. B. in the K3[CuF6] - also trivalent, in one case - namely in the Cs2(CuF6) - even tetravalent. In aqueous solutions, copper is the only utility metal that shows a normal potential that is more noble than that of hydrogen. In relation to acids, the corrosion behavior of copper depends not only on its type and concentration but also on the amount of oxygen or an oxidizing agent present. Copper is stable in non-oxidizing acids that do not contain dissolved oxygen. Alkaline aqueous solutions of the hydroxides and carbonates of the alkaline earth and alkali metals - with the exception of NH3 - have little effect on copper.

In the atmosphere - also in sea air - copper is very stable. Its surface is initially covered with a dark brown to almost black protective layer, which over time mostly changes into the green patina known from old copper roofs. Patina is a mixture of basic copper salts (sulfate, carbonate, near the sea also chloride), the proportion of which is determined by the concentration of the corresponding basic substances in the air. Moist ammonia and hydrogen sulfide vapors have an unfavorable effect. Copper is also very resistant to drinking and service water (cold and warm water). That is why it is an excellent material for water pipes. Resistance is linked to the formation of a uniform protective layer.

Physiological properties

Copper is not only a naturally occurring element that can be found in various forms and concentrations in the earth's crust, oceans, lakes and rivers, it is also a vital trace element. The life of flora and fauna has evolved within the framework of this natural presence of copper. Hence, most organisms have an intrinsic mechanism for their use. For the human organism, copper is an essential trace element, i.e. humans need copper in order to survive. The daily requirement of around 2 milligrams for an adult is usually achieved by eating a balanced diet with a large proportion of grain, meat, root vegetables, legumes, nuts or even chocolate. Since copper is particularly important for the metabolism, a copper deficiency can lead to serious health problems.

Corrosion behavior

Copper is the only utility metal that is more noble than hydrogen in the normal range of voltages. The good corrosion resistance of copper materials is based on their ability to form stable cover layers that protect the material from further corrosive attack (the green church roofs are a visible example of this). The formation of the top layer is positively influenced by adding alloying elements.

In the atmosphere, these compact and protective layers consist of oxides and poorly soluble basic salts. In solutions, the corrosion behavior is primarily influenced by the presence of oxygen or other oxidizing agents. Depending on the environmental parameters, the medium can be permanently corrosive or lead to the formation of a protective layer. However, the copper can only be attacked if the attack agent contains oxygen or oxidizing agent or is itself oxidizing, and in weakly corrosive agents (e.g. oxygen-containing water) the protective layers mentioned inhibit or prevent the progress of corrosion.

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