Carbon, atomic properties, chemical and physical properties

Properties of the carbon atom:

Thermal conductivity of steel and other alloys of copper, brass and aluminum, heat transfer

The thermal conductivity of aluminum is more than 3 times higher than the thermal conductivity of iron, which leads to strong heat removal and a wide heating zone of the metal adjacent to the seam.  

The thermal conductivity of aluminum is five times greater than that of cast iron, and therefore aluminum alloys often replace cast iron in the manufacture of pistons for internal combustion engines. In addition, an aluminum alloy piston, being approximately three times lighter than a cast iron one, lightens the weight of the structure. Metals with high thermal conductivity are at the same time the best conductors of electricity.  

The high heat capacity and thermal conductivity of aluminum ensure uniform temperature along the entire length of the tube.  

Since the thermal conductivity of aluminum is almost five times higher than the thermal conductivity of steel, the heating time, and therefore the vulcanization time of rubber compounds in molds made of this material, is reduced. However, it should be noted that aluminum molds wear out quickly, which is their significant drawback.  

Impurities have a significant effect on the thermal conductivity of aluminum at low temperatures.  

The thermal conductivity of the oxide film is much worse than the thermal conductivity of aluminum, but due to the insignificant thickness of the film, this does not have a noticeable effect on the overall thermal conductivity of the product.  

Titanium has low thermal conductivity, which is 13 times less than the thermal conductivity of aluminum and 4 times less than the thermal conductivity of iron. With increasing temperature, the thermal conductivity of titanium decreases slightly and at 700 C is 0.0309 cal/cm sec CC.  

Titanium has low thermal conductivity, which is 13 times less than the thermal conductivity of aluminum and 4 times less than the thermal conductivity of iron. With increasing temperature, the thermal conductivity of titanium decreases slightly and at 700 C is 0.0309 cal/cm sec C.  

Therefore, for example, the thermal conductivity of titanium is 8–10 times less than the thermal conductivity of aluminum.  

The thermal conductivity coefficient of copper, silver and steel changes slightly with temperature, the thermal conductivity of aluminum increases in the range 0 - 400 C approximately 1 6 times.

At high temperatures, silver evaporates more intensely than copper, and copper oxidizes and interacts with tellurides vapors. Therefore, for copper busbars it is advisable to use protection with a layer of iron.

The contact of the tires with thermoelements is carried out through intermediate layers, which prevent the diffusion of the tire material into the thermoelectric material.  

Therefore, for example, the thermal conductivity of titanium is 8–10 times less than the thermal conductivity of aluminum.  

From a comparison of the given data for aluminum with the thermophysical characteristics of alkali metals, it follows that the boiling point and thermal conductivity of aluminum are much higher, and the thermal neutron capture cross section is much smaller than the corresponding values ​​for alkali metals.

Bearing in mind that the remaining thermophysical characteristics of the compared metals are approximately the same, and also taking into account the low elasticity of aluminum vapor at high temperatures, we can conclude that from the point of view of the thermophysical characteristics, aluminum, as a coolant, has certain advantages over alkaline materials. metals when solving problems associated with high coolant temperatures.  

It should be emphasized that since the actual transient electrical resistance of the welding points (RK) is very small (it is measured in fractions of a microhm), and the thermal conductivity of aluminum and copper is high, overheating never occurs at the welding site when current passes, even in cases where the total The cross-section of the weld points is significantly smaller than the working cross-section of the tire itself. This has been thoroughly verified through extensive laboratory and field testing.  

Characteristics of thermal conductivity of materials

The concept of thermal conductivity of materials is characterized by the ability to transfer thermal energy within a certain object from heated parts to cold ones. The process is carried out by atoms, molecules, electrons and occurs in any body with an uneven temperature distribution.

From the standpoint of kinetic physics, this process occurs as a result of the interaction of particles of molecules in hotter areas within the sample with other elements characterized by a lower temperature. The mechanism and rate of heat transfer depends on the state of aggregation of the substance.

https://.com/watch?v=z8JhdvjYrl8

The thermal conductivity category involves determining the heating rate of a material sample and the movement of a temperature wave in a certain direction. The indicator depends on physical parameters:

• density;
• temperature of phase transition to liquid state
• speed of sound propagation (for dielectrics).

Thermal Conductivity - Aluminum

The strength of the aluminum shell is several times higher than that of lead, aluminum is 4 2 times lighter than lead (specific gravity 2 7 and 11 4, respectively), the thermal conductivity of aluminum is approximately six times higher than that of lead, its resistance to vibration fatigue is 25 times greater than at lead. In four-wire AC networks with voltages up to 1000 V with a solidly grounded neutral, it is allowed to use an aluminum sheath as a neutral working wire.  

In this equation, di 15 5 - 10 - 3 ( m) is the outer diameter of the graphite cylinder; d0 1 1 45 - 10 - 3 ( m) - cross-sectional diameter of the molten metal being tested; q ( ​​z) ( kcal / m2 - hour) - heat flow on the outer surface of the graphite cylinder; K AI and gr (kcal / m - hour - deg) are the thermal conductivity coefficients of aluminum and graphite, respectively.  

The best metals to conduct heat are silver and copper. The thermal conductivity of aluminum is approximately 2 5 times, iron 1 time, lead 12 times less than copper.  

The corrosive effect of some flux components on aluminum is neutralized by washing the seam and surfaces of parts with a 10% solution of nitric acid in warm water and subsequently with hot water.

The thermal conductivity of aluminum is almost 5 times, and the heat capacity is 2 times greater than steel, so when welding aluminum it is necessary to maintain a higher flame temperature than the melting point of aluminum.

The thermal conductivity of aluminum is 3 times greater than that of steel, the expansion coefficient is 2 times higher than the expansion coefficient of steel.  

The crystal lattice of aluminum consists, like many other metals, of face-centered cubes (see page. The thermal conductivity of aluminum is twice the thermal conductivity of iron and equal to half the thermal conductivity of copper. Its electrical conductivity is much higher than the electrical conductivity of iron and reaches 60% of the electrical conductivity of copper.  

The best metals to conduct heat are silver and copper. The thermal conductivity of aluminum is approximately 2 5 times less, that of iron is 6 times less, that of lead is 12 times less, and that of copper.  

As the purity of aluminum decreases, thermal conductivity decreases, and with increasing temperature it increases slightly. At 100, the thermal conductivity of aluminum is 66 5% of the thermal conductivity of silver.  

If this amount of heat is known, then for section z, from the measured value of the temperature gradient in it, it is possible to calculate the value of the thermal conductivity coefficient of the sample. The final calculation of the desired value of the thermal conductivity coefficient of aluminum consists of calculating the correction for the thermal conductivity coefficient of the sample for the heat passing through the walls of the graphite cylinder.  

The atomic structure of titanium and its high electron affinity have a strong influence on properties such as electrical and thermal conductivity. Its thermal conductivity is 8 - 10 times less than the thermal conductivity of aluminum. This is of significant importance, for example, when cutting metal.  

The modulus of elasticity of titanium is almost half that of iron, is on the same level as that of copper alloys and is significantly higher than that of aluminum.

The thermal conductivity of titanium is low: it is about 7% of the thermal conductivity of aluminum and 16-5% of the thermal conductivity of iron. This must be taken into account when heating metal for pressure treatment and welding.

The electrical resistance of titanium is approximately 6 times greater than that of iron and 20 times greater than that of aluminum.  

The modulus of elasticity of titanium is almost half that of iron, is on the same level as that of copper alloys and is significantly higher than that of aluminum.

The thermal conductivity of titanium is low: it is about 7% of the thermal conductivity of aluminum and 16-5% of the thermal conductivity of iron.  

Fiberglass based on phenolic resins have thermal conductivity of the same order. For comparison, it should be noted that the thermal conductivity of steel is 40, and the thermal conductivity of aluminum ranges from 175 to 200 kcal/m-h-deg.  

(not yet) Loading...

Chemical properties of carbon:

Application

Graphite is used in the pencil industry. It is also used as a lubricant at particularly high or low temperatures.

Diamond, due to its exceptional hardness, is an indispensable abrasive material. The grinding attachments of drills are coated with diamond. In addition, cut diamonds are used as gemstones in jewelry. Due to its rarity, high decorative qualities and a combination of historical circumstances, a diamond is invariably the most expensive gemstone. The exceptionally high thermal conductivity of diamond (up to 2000 W/m•K) makes it a promising material for semiconductor technology as substrates for processors. But the relatively high price (about $50/gram) and the difficulty of diamond processing limit its use in this area. In pharmacology and medicine, various carbon compounds are widely used - derivatives of carbonic acid and carboxylic acids, various heterocycles, polymers and other compounds. Thus, carbolene (activated carbon) is used to absorb and remove various toxins from the body; graphite (in the form of ointments) - for the treatment of skin diseases; radioactive carbon isotopes—for scientific research (radiocarbon dating).

Carbon plays a huge role in human life. Its applications are as varied as this many-sided element itself.

Carbon is the basis of all organic substances. Any living organism consists largely of carbon. Carbon is the basis of life. The source of carbon for living organisms is usually CO2 from the atmosphere or water. Through photosynthesis, it enters biological food chains in which living things devour each other or each other's remains and thereby obtain carbon to build their own bodies. The biological cycle of carbon ends either by oxidation and return to the atmosphere, or by burial in the form of coal or oil.

Carbon in the form of fossil fuels: coal and hydrocarbons (oil, natural gas) is one of the most important sources of energy for humanity.

Physical properties of carbon:

Story

Carbon in the form of charcoal was used in ancient times to smelt metals.
Allotropic modifications of carbon—diamond and graphite—have long been known. At the turn of the XVII-XVIII centuries. The phlogiston theory arose, put forward by Johann Becher and Georg Stahl. This theory recognized the presence in each combustible body of a special elementary substance - a weightless fluid - phlogiston, which evaporates during the combustion process. Since when a large amount of coal is burned, only a little ash remains, phlogistics believed that coal was almost pure phlogiston. This is what explained, in particular, the “phlogisticating” effect of coal—its ability to restore metals from “limes” and ores. The later phlogistics, Reaumur, Bergman and others, had already begun to understand that coal was an elemental substance. However, “clean coal” was first recognized as such by Antoine Lavoisier, who studied the process of combustion of coal and other substances in air and oxygen. In the book “Method of Chemical Nomenclature” (1787) by Guiton de Morveau, Lavoisier, Berthollet and Fourcroix, the name “carbon” (carbone) appeared instead of the French “pure coal” (charbone pur). Under the same name, carbon appears in the “Table of Simple Bodies” in Lavoisier’s “Elementary Textbook of Chemistry.”

In 1791, the English chemist Tennant was the first to obtain free carbon; he passed phosphorus vapor over calcined chalk, resulting in the formation of calcium phosphate and carbon. It has been known for a long time that diamond burns without leaving a residue when heated strongly. Back in 1751, the German Emperor Franz I agreed to provide diamond and ruby ​​for combustion experiments, after which these experiments even became fashionable. It turned out that only diamond burns, and ruby ​​(aluminum oxide with an admixture of chromium) can withstand prolonged heating at the focus of the ignition lens without damage. Lavoisier conducted a new experiment on burning diamond using a large incendiary machine and came to the conclusion that diamond is crystalline carbon. The second allotrope of carbon - graphite - in the alchemical period was considered a modified lead luster and was called plumbago; It was only in 1740 that Pott discovered the absence of any lead impurity in graphite. Scheele studied graphite (1779) and, being a phlogistician, considered it a special kind of sulfur body, a special mineral coal containing bound “aerial acid” (CO2) and a large amount of phlogiston.

Twenty years later, Guiton de Morveau turned the diamond into graphite and then into carbonic acid by careful heating.

origin of name

In the 17th-19th centuries, the term “carbon solution” was sometimes used in Russian chemical and specialized literature (Schlatter, 1763; Scherer, 1807; Severgin, 1815); Since 1824, Solovyov introduced the name “carbon”. Carbon compounds have the carbo(n)

- from lat.
carbō (gen. carbōnis
) “coal”.

Carbon crystal lattice:

Thermal conductivity of graphite and copper - Metalworker's Handbook

So what is thermal conductivity? From a physics point of view, thermal conductivity

– this is the molecular transfer of heat between directly contacting bodies or particles of the same body with different temperatures, in which the energy of movement of structural particles (molecules, atoms, free electrons) is exchanged.

To put it simply, thermal conductivity

is the ability of a material to conduct heat. If there is a temperature difference inside the body, then thermal energy moves from the hotter part of the body to the colder part.

Heat transfer occurs due to the transfer of energy when molecules of a substance collide. This happens until the temperature inside the body becomes the same.

This process can occur in solid, liquid and gaseous substances.

In practice, for example in construction for the thermal insulation of buildings, another aspect of thermal conductivity is considered, associated with the transfer of thermal energy. Let's take an “abstract house” as an example.

In the “abstract house” there is a heater that maintains a constant temperature inside the house, say, 25 ° C. The temperature outside is also constant, for example, 0 °C.

It is quite clear that if you turn off the heater, then after a while the house will also be 0 °C. All the heat (thermal energy) will go through the walls to the street.

To maintain the temperature in the house at 25 ° C, the heater must be constantly running. The heater constantly creates heat, which constantly escapes through the walls to the street.

Coefficient of thermal conductivity

The amount of heat that passes through the walls (and according to science, the intensity of heat transfer due to thermal conductivity) depends on the temperature difference (in the house and outside), on the area of ​​the walls and the thermal conductivity of the material from which these walls are made.

To quantify thermal conductivity, there is a coefficient of thermal conductivity of materials . This coefficient reflects the property of a substance to conduct thermal energy. The higher the thermal conductivity coefficient of a material, the better it conducts heat.

If we are going to insulate a house, then we need to choose materials with a small value of this coefficient. The smaller it is, the better. Nowadays, the most widely used materials for insulating buildings are mineral wool insulation and various foam plastics.

A new material with improved thermal insulation properties – Neopor – is gaining popularity.

The thermal conductivity coefficient of materials is designated by the letter ? (Greek small letter lambda) and is expressed in W/(m2*K). This means that if you take a brick wall with a thermal conductivity coefficient of 0.67 W/(m2*K), a thickness of 1 meter and an area of ​​1 m2.

, then with a temperature difference of 1 degree, 0.67 watts of thermal energy will pass through the wall. If the temperature difference is 10 degrees, then 6.7 watts will pass. And if, with such a temperature difference, the wall is made 10 cm, then the heat loss will already be 67 watts.

More details about the methodology for calculating heat loss in buildings can be found here.

It should be noted that the values ​​of the thermal conductivity coefficient of materials are indicated for a material thickness of 1 meter. To determine the thermal conductivity of a material for any other thickness, the thermal conductivity coefficient must be divided by the desired thickness, expressed in meters.

In building codes and calculations the concept of “thermal resistance of a material” is often used. This is the reciprocal of thermal conductivity. If, for example, the thermal conductivity of foam plastic 10 cm thick is 0.37 W/(m2*K), then its thermal resistance will be equal to 1 / 0.37 W/(m2*K) = 2.7 (m2*K)/ Tue

Thermal conductivity coefficient of materials

The table below shows the values ​​of the thermal conductivity coefficient for some materials used in construction.

Thermal conductivity of metals

Among the large number of parameters characterizing metals, there is such a concept as thermal conductivity. Its importance is difficult to overestimate. This parameter is used when calculating parts and assemblies. For example, gear transmissions. In general, a whole branch of science called thermodynamics deals with thermal conductivity.

Thermal conductivity of metals

What is thermal conductivity and thermal resistance

The thermal conductivity of metals can be characterized as follows - this is the ability of materials (gas, liquid, etc.) to transfer excess thermal energy from heated areas of the body to cold ones. Transfer is carried out by freely moving elementary particles, which include atoms, electrons, etc.

Note:

201* The range of atomic mass values ​​is indicated due to the varying abundance of isotopes of a given element in nature.

206* According to [1], the covalent radius of carbon is 77 pm for sp3, 73 pm for sp2, 69 pm for sp, and 77 pm according to [3].

401* The density of graphite according to [3] is 2.25 g/cm3 (at 0 °C and other standard conditions, the state of the substance is a solid).

410* The molar heat capacity of graphite according to [3] is 8.54 J/(K mol).

Being in nature

The carbon content in the earth's crust is 0.1% by mass. Free carbon is found in nature in the form of diamond and graphite. The bulk of carbon is in the form of natural carbonates (limestones and dolomites), fossil fuels - anthracite (94-97% C), brown coal (64-80% C), bituminous coal (76-95% C), oil shale (56- 78% C), oil (82-87% C), flammable natural gases (up to 99% methane), peat (53-56% C), as well as bitumen, etc. In the atmosphere and hydrosphere it is found in the form of carbon dioxide CO2, in the air there is 0.046% CO2 by mass, in the waters of rivers, seas and oceans it is ~60 times more. Carbon is included in the composition of plants and animals (~18%). The human body enters carbon through food (normally about 300 g per day). The total carbon content in the human body reaches about 21% (15 kg per 70 kg body weight). Carbon makes up 2/3 of muscle mass and 1/3 of bone mass. Excreted from the body mainly through exhaled air (carbon dioxide) and urine (urea). The carbon cycle in nature includes the biological cycle, the release of CO2 into the atmosphere during the combustion of fossil fuels, from volcanic gases, hot mineral springs, from the surface layers of ocean waters, etc. Biological The cycle is that carbon in the form of CO2 is absorbed from the troposphere by plants. Then from the biosphere it returns again to the geosphere: with plants, carbon enters the body of animals and humans, and then, when animal and plant materials rot, into the soil and in the form of CO2 into the atmosphere.

In a vapor state and in the form of compounds with nitrogen and hydrogen, carbon is found in the atmosphere of the Sun, planets, and is found in stone and iron meteorites.

Most carbon compounds, and above all hydrocarbons, have a pronounced character of covalent compounds. The strength of simple, double and triple bonds of C atoms with each other, the ability to form stable chains and cycles from C atoms determine the existence of a huge number of carbon-containing compounds studied in organic chemistry.