Carbon dioxide is a colorless gas with a barely perceptible odor, non-toxic, heavier than air. Carbon dioxide is widely distributed in nature. It dissolves in water, forming carbonic acid H 2 CO 3, giving it a sour taste. The air contains about 0.03% carbon dioxide. The density is 1.524 times greater than the density of air and is equal to 0.001976 g/cm 3 (at zero temperature and pressure 101.3 kPa). Ionization potential 14.3V. Chemical formula - CO 2.
In welding production the term is used "carbon dioxide" cm. . In the “Rules for the Design and Safe Operation of Pressure Vessels” the term "carbon dioxide", and in - term "carbon dioxide".
There are many ways to produce carbon dioxide, the main ones are discussed in the article.
The density of carbon dioxide depends on pressure, temperature and the state of aggregation in which it is found. At atmospheric pressure and a temperature of -78.5°C, carbon dioxide, bypassing the liquid state, turns into a white snow-like mass "dry ice".
Under a pressure of 528 kPa and at a temperature of -56.6 ° C, carbon dioxide can be in all three states (the so-called triple point).
Carbon dioxide is thermally stable, dissociating into carbon monoxide only at temperatures above 2000°C.
Carbon dioxide is first gas to be described as a discrete substance. In the seventeenth century, a Flemish chemist Jan Baptist van Helmont (Jan Baptist van Helmont) noticed that after burning coal in a closed vessel, the mass of ash was much less than the mass of the burned coal. He explained this by saying that coal was transformed into an invisible mass, which he called “gas.”
The properties of carbon dioxide were studied much later in 1750. Scottish physicist Joseph Black (Joseph Black).
He discovered that limestone (calcium carbonate CaCO 3), when heated or reacted with acids, releases a gas, which he called “bound air.” It turned out that “bound air” is denser than air and does not support combustion.
CaCO 3 + 2HCl = CO 2 + CaCl 2 + H 2 O
By passing “bound air” i.e. carbon dioxide CO 2 through an aqueous solution of lime Ca(OH) 2 calcium carbonate CaCO 3 is deposited to the bottom. Joseph Black used this experiment to prove that carbon dioxide is released through animal respiration.
CaO + H 2 O = Ca(OH) 2
Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O
Liquid carbon dioxide is a colorless, odorless liquid whose density varies greatly with temperature. It exists at room temperature only at pressures above 5.85 MPa. The density of liquid carbon dioxide is 0.771 g/cm 3 (20°C). At temperatures below +11°C it is heavier than water, and above +11°C it is lighter.
The specific gravity of liquid carbon dioxide varies significantly with temperature, therefore, the amount of carbon dioxide is determined and sold by weight. The solubility of water in liquid carbon dioxide in the temperature range 5.8-22.9°C is no more than 0.05%.
Liquid carbon dioxide turns into gas when heat is supplied to it. Under normal conditions (20°C and 101.3 kPa) When 1 kg of liquid carbon dioxide evaporates, 509 liters of carbon dioxide are formed. When gas is withdrawn too quickly, the pressure in the cylinder decreases and the heat supply is insufficient, the carbon dioxide cools, the rate of its evaporation decreases and when it reaches the “triple point” it turns into dry ice, which clogs the hole in the reduction gear, and further gas extraction stops. When heated, dry ice directly turns into carbon dioxide, bypassing the liquid state. To evaporate dry ice, it is necessary to supply significantly more heat than to evaporate liquid carbon dioxide - therefore, if dry ice has formed in the cylinder, it evaporates slowly.
Liquid carbon dioxide was first produced in 1823. Humphry Davy(Humphry Davy) and Michael Faraday(Michael Faraday).
Solid carbon dioxide "dry ice" resembles snow and ice in appearance. The carbon dioxide content obtained from dry ice briquettes is high - 99.93-99.99%. Moisture content is in the range of 0.06-0.13%. Dry ice, being in the open air, evaporates rapidly, so containers are used for its storage and transportation. Carbon dioxide is produced from dry ice in special evaporators. Solid carbon dioxide (dry ice), supplied in accordance with GOST 12162.
Carbon dioxide is most often used:
- to create a protective environment for metals;
- in the production of carbonated drinks;
- refrigeration, freezing and storage of food products;
- for fire extinguishing systems;
- for cleaning surfaces with dry ice.
The density of carbon dioxide is quite high, which allows the arc reaction space to be protected from contact with air gases and prevents nitriding at relatively low carbon dioxide consumption in the jet. Carbon dioxide is, during the welding process, it interacts with the weld metal and has an oxidizing and also carburizing effect on the metal of the weld pool.
Previously obstacles to the use of carbon dioxide as a protective medium were in the seams. The pores were caused by boiling of the solidifying metal of the weld pool from the release of carbon monoxide (CO) due to its insufficient deoxidation.
At high temperatures, carbon dioxide dissociates to form highly active free, monoatomic oxygen:
Oxidation of the weld metal released free from carbon dioxide during welding is neutralized by the content of an additional amount of alloying elements with a high affinity for oxygen, most often silicon and manganese (in excess of the amount required for alloying the weld metal) or fluxes introduced into the welding zone (welding).
Both carbon dioxide and carbon monoxide are practically insoluble in solid and molten metal. The free active oxidizes the elements present in the weld pool depending on their oxygen affinity and concentration according to the equation:
Me + O = MeO
where Me is a metal (manganese, aluminum, etc.).
In addition, carbon dioxide itself reacts with these elements.
As a result of these reactions, when welding in carbon dioxide, significant burnout of aluminum, titanium and zirconium is observed, and less intense burnout of silicon, manganese, chromium, vanadium, etc.
The oxidation of impurities occurs especially vigorously at . This is due to the fact that when welding with a consumable electrode, the interaction of the molten metal with the gas occurs when a drop remains at the end of the electrode and in the weld pool, and when welding with a non-consumable electrode, it occurs only in the pool. As is known, the interaction of gas with metal in an arc gap occurs much more intensely due to the high temperature and larger contact surface of the metal with the gas.
Due to the chemical activity of carbon dioxide in relation to tungsten, welding in this gas is carried out only with a consumable electrode.
Carbon dioxide is non-toxic and non-explosive. At concentrations of more than 5% (92 g/m3), carbon dioxide has a harmful effect on human health, since it is heavier than air and can accumulate in poorly ventilated areas near the floor. This reduces the volume fraction of oxygen in the air, which can cause oxygen deficiency and suffocation. Premises where welding is carried out using carbon dioxide must be equipped with general supply and exhaust ventilation. The maximum permissible concentration of carbon dioxide in the air of the working area is 9.2 g/m 3 (0.5%).
Carbon dioxide is supplied by . To obtain high-quality seams, gaseous and liquefied carbon dioxide of the highest and first grades is used.
Carbon dioxide is transported and stored in steel cylinders or large-capacity tanks in a liquid state, followed by gasification at the plant, with a centralized supply to welding stations through ramps. A standard one with a water capacity of 40 liters is filled with 25 kg of liquid carbon dioxide, which at normal pressure occupies 67.5% of the volume of the cylinder and produces 12.5 m 3 of carbon dioxide upon evaporation. Air accumulates in the upper part of the cylinder along with carbon dioxide gas. Water, which is heavier than liquid carbon dioxide, collects at the bottom of the cylinder.
To reduce the humidity of carbon dioxide, it is recommended to install the cylinder with the valve down and, after settling for 10...15 minutes, carefully open the valve and release moisture from the cylinder. Before welding, it is necessary to release a small amount of gas from a normally installed cylinder to remove any air trapped in the cylinder. Some of the moisture is retained in carbon dioxide in the form of water vapor, worsening the welding of the seam.
When gas is released from the cylinder, due to the throttling effect and heat absorption during the evaporation of liquid carbon dioxide, the gas cools significantly. With intensive gas extraction, the reducer may become clogged with frozen moisture contained in carbon dioxide, as well as dry ice. To avoid this, when extracting carbon dioxide, a gas heater is installed in front of the reducer. The final removal of moisture after the gearbox is carried out with a special desiccant filled with glass wool and calcium chloride, silica gel, copper sulfate or other moisture absorbers
The carbon dioxide cylinder is painted black, with the words “CARBON ACID” written in yellow letters..
Application of carbon dioxide. G. Cavendish was the first to draw attention to the fact that an aqueous solution of carbon dioxide has, although weak, a pleasant sour taste. He demonstrated at the Royal Society a glass of extremely pleasantly sparkling sparkling water, hardly different from seltzer water, and received the society's gold medal for this discovery.
This was the first practical use of carbon dioxide; American entrepreneurs became interested in it when D. Priestley was already in exile, after one doctor began prescribing carbonated water with the addition of fruit juices to his patients. This is where the carbonated drink industry began to develop, which is still one of the most important consumers of carbon dioxide. Carbon dioxide is used for carbonating fruit and mineral waters, for the production of sugar, beer, and in medicine for carbon dioxide baths. It is filled with lifebelts and rafts made from small steel cylinders containing a liquid mass of carbon dioxide.
Liquid carbon anhydride is used 1 in portable fire extinguishers 2 in fire extinguishing systems of aircraft and ships, carbon dioxide fire engines.
Such widespread use in fire extinguishing is due to the fact that in some cases water is not suitable for extinguishing, for example, when extinguishing ignited flammable liquids or when there is unswitched electrical wiring in the room, unique equipment that can be damaged by water. The use of pressed solid carbonic anhydride, which we call dry ice, is also quite widespread. Thus, it is used to maintain low temperatures in refrigerator cars for the transport of perishable products, as well as in the production of ice cream.
Why, the question arises, cannot be used with ordinary ice. But it turns out that dry ice has a number of advantages: 1. it allows you to maintain a much lower temperature in the refrigerator, the role of which is played by a simple cardboard box for ice cream sellers, up to -78.2C 2. it absorbs three times more heat per unit mass during evaporation than ice during melting 3 . does not pollute the refrigerator, like ordinary ice, with a liquid melting product 4. creates an atmosphere of carbon dioxide in the refrigerator, which additionally protects food products from spoilage.
Dry ice is also used for cooling and hardening rivets made of aluminum alloys and when putting bandages - metal rings or belts on machine parts. Carbon dioxide is also used as a coolant in graphite reactors. A very interesting application of carbon monoxide IV to modify the weather is when dry ice powder is dispersed from an aircraft flying over a supercooled cloud, creating artificial snowfall over airfields at a consumption of only about 100 g of ice per 1 km3 of cloud. At the same time, thick wet flakes of snow begin to fall, and soon the sky begins to shine through the continuous clouds. The gaps quickly expand and merge into the wide blue sky. As a result of strong cooling, only a few water droplets freeze.
The rest remain in a hypothermic state. But since at the same temperature supercooled water has a higher vapor elasticity than ice, the growth of ice crystals immediately begins due to droplets of liquid water, which leads to snowfall.
In many cases, carbonic anhydride is not used in finished form, but is obtained during use. In such cases, the starting materials are used either separately - as sulfuric acid and sodium dicarbonate in conventional fire extinguishers, or as a mixture of two dry powders as in some baking powders, for example, a mixture of sodium bicarbonate with potassium tartrate, ammonium tartrate or ammonium chloride.
As long as the mixture remains dry, no reaction occurs. When water is added, the salts dissolve, dissociate, and an ionic reaction occurs, releasing carbon dioxide. Similar reactions occur when baking powders are mixed with dough to leaven the dough chemically.
End of work -
This topic belongs to the section:
Interdisciplinary connections in the course of the school subject of chemistry on the subject of carbon and its compounds
A physicist is blind without mathematics, a dry hand without chemistry. I set the following goals for myself: 1. To trace and study interdisciplinary connections in the school course.. To give an answer in the form of bar graphs about the relative error of determination. To identify the most accessible way to obtain it in a university laboratory regarding the availability of chemicals..
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You already know that when you exhale, carbon dioxide comes out of your lungs. But what do you know about this substance? Probably a little. Today I will answer all your questions regarding carbon dioxide.
Definition
This substance under normal conditions is a colorless gas. In many sources it can be called differently: carbon monoxide (IV), and carbon anhydride, and carbon dioxide, and carbon dioxide.
Properties
Carbon dioxide (formula CO 2) is a colorless gas, has an acidic odor and taste, and is soluble in water. If it is cooled properly, it forms a snow-like mass called dry ice (photo below), which sublimates at a temperature of -78 o C.
It is one of the products of decay or combustion of any organic matter. It dissolves in water only at a temperature of 15 o C and only if the water:carbon dioxide ratio is 1:1. The density of carbon dioxide may vary, but under standard conditions it is equal to 1.976 kg/m3. This is if it is in gaseous form, and in other states (liquid/gaseous) the density values will also be different. This substance is an acidic oxide; adding it to water produces carbonic acid. If you combine carbon dioxide with any alkali, the subsequent reaction results in the formation of carbonates and bicarbonates. This oxide cannot support combustion, except for certain exceptions. These are reactive metals, and in this type of reaction they take oxygen away from it.
Receipt
Carbon dioxide and some other gases are released in large quantities when alcohol is produced or natural carbonates decompose. The resulting gases are then washed with dissolved potassium carbonate. This is followed by their absorption of carbon dioxide; the product of this reaction is bicarbonate, upon heating the solution of which the desired oxide is obtained.
But now it is successfully replaced by ethanolamine dissolved in water, which absorbs carbon monoxide contained in the flue gas and releases it when heated. This gas is also a byproduct of those reactions that produce pure nitrogen, oxygen and argon. In the laboratory, some carbon dioxide is produced when carbonates and bicarbonates react with acids. It is also formed when baking soda and lemon juice or the same sodium bicarbonate and vinegar react (photo).
Application
The food industry cannot do without the use of carbon dioxide, where it is known as a preservative and leavening agent, code E290. Any fire extinguisher contains it in liquid form.
Also, tetravalent carbon oxide, which is released during the fermentation process, serves as a good feed for aquarium plants. It is also found in the well-known soda, which many people often buy at the grocery store. Wire welding occurs in a carbon dioxide environment, but if the temperature of this process is very high, then it is accompanied by the dissociation of carbon dioxide, which releases oxygen, which oxidizes the metal. Then welding cannot be done without deoxidizing agents (manganese or silicon). Carbon dioxide is used to inflate bicycle wheels; it is also present in the cans of air guns (this type is called a gas cylinder). Also, this oxide in a solid state, called dry ice, is needed as a refrigerant in trade, scientific research and when repairing some equipment.
This is how beneficial carbon dioxide is for humans. And not only in industry, it also plays an important biological role: without it, gas exchange, regulation of vascular tone, photosynthesis and many other natural processes cannot occur. But its excess or shortage in the air for some time can negatively affect the physical condition of all living organisms.
As you know, we all come from childhood. And one of the sweet memories of the first years of life, which we often carry throughout our lives, is the taste of sweet soda from a bottle. In order for children and adults to enjoy their favorite carbonated drinks, it is necessary carbon dioxide in cylinders, which, through simple manipulations, fills the contents of the bottle with magical bubbles. And there is no greater pleasure than exploding bubbles in the nose, mouth, stomach... We grow, mature. We begin to give preference to other carbonated and non-carbonated drinks that also “hit” the nose and head. But as we age, the answer to the question often remains a mystery to us:
How does carbon dioxide in cylinders end up in a bottle?
Carbon dioxide is a colorless gas with a slightly sour taste, non-toxic, which has many names such as: carbon dioxide, carbon dioxide, carbonic anhydride, CO2 and others. This gas does not support respiration and in high concentrations causes suffocation, but is essential in the metabolic process of living cells. It is obtained as a by-product during the production of alcohol, ammonia or fuel combustion. The gas density, under normal conditions, is 1.98 g/l. Therefore, carbon dioxide is transported in cylinders under a pressure of about 70 atmospheres, for greater capacity. Special equipment is used to compress gas. In the production of carbonated water, acid from a cylinder is added to the bottles of the drink, immediately before capping. And if you release carbon dioxide into the atmosphere, some of it will turn into dry ice. But the food industry is not the only area where carbon dioxide is used.
Where else is carbon dioxide used in cylinders?
Modern construction is entirely based on metal structures. To obtain a strong metal frame, welding is necessary. Carbon dioxide is an acid oxide that reacts with water to form carbonic acid. Reacts with alkalis to release bicarbonates and carbonates. This property of the acid is the basis for its use in the welding process: carbon dioxide in cylinders turns into a protective layer that ensures the strength of the weld. Fire extinguishers, which are designed to extinguish electrical installations, are also filled with carbon dioxide.
And if you decide to buy a gas cylinder, remember that there are special requirements for its transportation and use. Working with carbon dioxide can be dangerous; for example, if it gets on your hands, it can cause burns.
Where can I buy a gas cylinder?
Purchasing cylinders for storing and transporting gases from unknown sellers who cannot document their rights does not guarantee their safe use! Safely buy a gas cylinder from trusted manufacturers can be found here. Our cylinders for transporting carbon dioxide come in industrial volumes of 50 liters. and small cans for siphon. Their safe operation is ensured by manufacturing taking into account all GOST requirements.
An alternative use for carbon dioxide has been developed by chemical scientists. Scientists have developed a new catalyst material and design that produces liquid fuel from carbon dioxide, a huge contributor to greenhouse gas emissions.
The results show that existing technologies can convert carbon dioxide (CO2) and thus not add emissions to the atmosphere.
Carbon dioxide fuel
The proposed catalyst provides a new use for carbon dioxide to convert carbon dioxide (CO 2 ) to carbon monoxide (CO). This is the first step towards converting CO 2 into other chemicals, including fuels. Chemists have already established methods for converting CO and oxygen into various liquid fuels and other energy products.
The carbon monoxide can then be further processed into the desired material.
And if hydrogen and CO are produced using solar or other manufactured energy, then the new application of carbon dioxide could be carbon neutral. As a result of the decomposition reaction, carbon dioxide (CO 2) is formed into carbon monoxide (II) (CO) and oxygen (O 2) at a sufficiently high temperature.
2CO 2 → 2CO + O 2
Tunable Transformation
Scientists know that tuning catalysts affects the desired proportion of CO in the final product. 
Most of the efforts of technologists and designers are aimed at producing catalysts for the production of CO, taking into account different chemistry of the active surface. This material can be produced by depositing tiny beads of polystyrene on conductive electrodes of a substrate, and then electrochemically silvering the surface. This method creates a honeycomb-like hexagonal cell structure in industrially produced ones.
It turns out that the varying thickness of this porous catalyst produces a dual effect: the porous structure of the catalyst strongly promotes the production of CO from CO 2 by a factor of three, while also suppressing the alternative reaction of producing H 2 (hydrogen) by a factor of ten. Using this combined effect, CO production can be easily modified. The study results provide fundamental insights that may be applicable to the development of other catalyst materials for energy production from carbon dioxide CO 2 .
This represents just one step in the conversion of carbon dioxide into usable forms of energy, and initial demonstrations in small laboratory settings. Thus, a lot of work remains for chemists to find a practical approach to using carbon dioxide to produce carbon dioxide transport fuels.
But because the selectivity and efficiency of this initial conversion has an upper limit to the overall efficiency of energy production from CO 2 , in technical terms, the work provides the basic fundamental principles in carbon-neutral technology to replace existing fossil fuel systems.
It is necessary to be able to use everything from the existing infrastructure of gas stations, delivery vehicles and storage capacity.
Using carbon dioxide as in nature
Ultimately, the use of carbon dioxide is converted by plants. These devices can be connected directly to the flow of fossil fuel emissions from power plants.
When developing the final technology, it is possible, for example, to use CO 2 to produce fuel instead of releasing carbon dioxide into the atmosphere.
If developed, this could represent a closed anthropogenic carbon cycle by using generated electricity and converting greenhouse gas emissions into fuel. 
In essence, this is true: a clean process would do the same thing that plants and cyanobacteria did on earth millions of years ago to produce fossil fuels.
First of all: taking carbon dioxide from the air and turning it into more complex molecules. But in this case, the process does not have to last for thousands of years, the process must be replicated very quickly in a laboratory or factory. This is the same as natural photosynthesis, but much faster.
