Helium density in kg m3. What is the density of gold? How to distinguish real yellow metal from a fake

Today, many complex structures and devices have been developed that use metals and their alloys with different properties. To use the most suitable alloy in a particular structure, designers select it in accordance with the requirements of strength, fluidity, elasticity, etc., as well as the stability of these characteristics in the required temperature range. Next, the required amount of metal that is required for the production of products from it is calculated. To do this, you need to make a calculation based on its specific gravity. This value is constant - this is one of the main characteristics of metals and alloys, practically coinciding with density. It is easy to calculate: you need to divide the weight (P) of a piece of solid metal by its volume (V). The resulting value is denoted γ, and it is measured in Newtons per cubic meter.

Specific gravity formula:

Based on the fact that weight is mass multiplied by the acceleration of gravity, we get the following:

Now about the units of measurement of specific gravity. The above Newtons per cubic meter are in the SI system. If the GHS metric system is used, then this value is measured in dynes per cubic centimeter. To indicate specific gravity in the MKSS system, the following unit is used: kilogram-force per cubic meter. Sometimes it is acceptable to use gram-force per cubic centimeter - this unit lies outside all metric systems. The basic relationships are as follows:

1 dyne/cm3 = 1.02 kg/m3 = 10 n/m3.

The higher the specific gravity value, the heavier the metal. For light aluminum this value is quite small - in SI units it is equal to 2.69808 g/cm3 (for example, for steel it is equal to 7.9 g/cm3). Aluminum, as well as its alloys, is in high demand today, and its production is constantly growing. After all, this is one of the few metals needed for industry, the supply of which is in the earth’s crust. Knowing the specific gravity of aluminum, you can calculate any product made from it. For this, there is a convenient metal calculator, or you can make the calculation manually by taking the specific gravity of the desired aluminum alloy from the table below.

However, it is important to take into account that this is the theoretical weight of rolled products, since the content of additives in the alloy is not strictly defined and can fluctuate within small limits, then the weight of rolled products of the same length, but from different manufacturers or batches may differ, of course this difference is small, but it is there.

Here are some calculation examples:

Example 1. Calculate the weight of A97 aluminum wire with a diameter of 4 mm and a length of 2100 meters.

Let us determine the cross-sectional area of ​​the circle S=πR 2 means S=3.1415 2 2 =12.56 cm 2

Let's determine the weight of rolled products knowing that the specific gravity of grade A97 = 2.71 g/cm 3

M=12.56·2.71·2100=71478.96 grams = 71.47 kg

Total wire weight 71.47 kg

Example 2. Calculate the weight of a circle made of AL8 aluminum with a diameter of 60 mm and a length of 150 cm in the amount of 24 pieces.

Let's determine the cross-sectional area of ​​the circle S=πR 2 means S=3.1415 3 2 =28.26 cm 2

Let's determine the weight of the rolled product knowing that the specific gravity of the AL8 grade = 2.55 g/cm 3

Let us place iron and aluminum cylinders of the same volume on the scales (Fig. 122). The balance of the scales has been disrupted. Why?

Rice. 122

In lab work, you measured body weight by comparing the weight of weights to your body weight. When the scales were in equilibrium, these masses were equal. Disequilibrium means that the masses of the bodies are not the same. The mass of the iron cylinder is greater than the mass of the aluminum cylinder. But the volumes of the cylinders are equal. This means that a unit volume (1 cm3 or 1 m3) of iron has a greater mass than aluminum.

The mass of a substance contained in a unit volume is called the density of the substance. To find density, you need to divide the mass of a substance by its volume. Density is denoted by the Greek letter ρ (rho). Then

density = mass/volume

ρ = m/V.

The SI unit of density is 1 kg/m3. The densities of various substances are determined experimentally and are presented in Table 1. Figure 123 shows the masses of substances known to you in a volume V = 1 m 3.

Rice. 123

Density of solids, liquids and gases
(at normal atmospheric pressure)

How do we understand that the density of water is ρ = 1000 kg/m3? The answer to this question follows from the formula. The mass of water in a volume V = 1 m 3 is equal to m = 1000 kg.

From the density formula, the mass of a substance

m = ρV.

Of two bodies of equal volume, the body with the greater density of matter has the greater mass.

Comparing the densities of iron ρ l = 7800 kg/m 3 and aluminum ρ al = 2700 kg/m 3, we understand why in the experiment (see Fig. 122) the mass of an iron cylinder turned out to be greater than the mass of an aluminum cylinder of the same volume.

If the volume of a body is measured in cm 3, then to determine the body mass it is convenient to use the density value ρ, expressed in g/cm 3.

The substance density formula ρ = m/V is used for homogeneous bodies, that is, for bodies consisting of one substance. These are bodies that do not have air cavities or do not contain impurities of other substances. The purity of the substance is judged by the measured density. Is there, for example, any cheap metal added inside a gold bar?

Think and answer

1. How would the balance of the scales change (see Fig. 122) if instead of an iron cylinder a wooden cylinder of the same volume were placed on a cup?
2. What is density?
3. Does the density of a substance depend on its volume? From the masses?
4. In what units is density measured?
5. How to move from the unit of density g/cm 3 to the unit of density kg/m 3?

Interesting to know!

As a rule, a substance in the solid state has a density greater than in the liquid state. The exception to this rule is ice and water, consisting of H 2 O molecules. The density of ice is ρ = 900 kg/m 3, the density of water? = 1000 kg/m3. The density of ice is less than the density of water, which indicates a less dense packing of molecules (i.e., greater distances between them) in the solid state of the substance (ice) than in the liquid state (water). In the future, you will encounter other very interesting anomalies (abnormalities) in the properties of water.

The average density of the Earth is approximately 5.5 g/cm 3 . This and other facts known to science allowed us to draw some conclusions about the structure of the Earth. The average thickness of the earth's crust is about 33 km. The earth's crust is composed primarily of soil and rocks. The average density of the earth's crust is 2.7 g/cm 3, and the density of the rocks lying directly under the earth's crust is 3.3 g/cm 3. But both of these values ​​are less than 5.5 g/cm 3, i.e. less than the average density of the Earth. It follows that the density of matter located in the depths of the globe is greater than the average density of the Earth. Scientists suggest that in the center of the Earth the density of the substance reaches 11.5 g/cm 3, that is, it approaches the density of lead.

The average density of human body tissue is 1036 kg/m3, the density of blood (at t = 20°C) is 1050 kg/m3.

Balsa wood has a low wood density (2 times less than cork). Rafts and lifebelts are made from it. In Cuba, the Eshinomena prickly hair tree grows, the wood of which has a density 25 times less than the density of water, i.e. ρ = 0.04 g/cm 3 . The snake tree has a very high wood density. A tree sinks in water like a stone.

Do it yourself at home

Measure the density of the soap. To do this, use a rectangular shaped bar of soap. Compare the density you measured with the values ​​obtained by your classmates. Are the resulting density values ​​equal? Why?

Interesting to know

Already during the life of the famous ancient Greek scientist Archimedes (Fig. 124), legends were formed about him, the reason for which was his inventions that amazed his contemporaries. One of the legends says that the Syracusan king Heron II asked the thinker to determine whether his crown was made of pure gold or whether the jeweler mixed a significant amount of silver into it. Of course, the crown had to remain intact. It was not difficult for Archimedes to determine the mass of the crown. Much more difficult was to accurately measure the volume of the crown in order to calculate the density of the metal from which it was cast and determine whether it was pure gold. The difficulty was that it was the wrong shape!

Rice. 124

One day, Archimedes, absorbed in thoughts about the crown, was taking a bath, where he came up with a brilliant idea. The volume of the crown can be determined by measuring the volume of water displaced by it (you are familiar with this method of measuring the volume of an irregularly shaped body). Having determined the volume of the crown and its mass, Archimedes calculated the density of the substance from which the jeweler made the crown.

As the legend goes, the density of the crown’s substance turned out to be less than the density of pure gold, and the dishonest jeweler was caught in deception.

Exercises

1. The density of copper is ρ m = 8.9 g/cm 3, and the density of aluminum is ρ al = 2700 kg/m 3. Which substance is more dense and by how many times?
2. Determine the mass of a concrete slab whose volume is V = 3.0 m 3.
3. What substance is a ball with volume V = 10 cm 3 made of if its mass m = 71 g?
4. Determine the mass of window glass whose length a = 1.5 m, height b = 80 cm and thickness c = 5.0 mm.
5. Total mass N = 7 identical sheets of roofing iron m = 490 kg. The size of each sheet is 1 x 1.5 m. Determine the thickness of the sheet.
6. Steel and aluminum cylinders have the same cross-sectional area and mass. Which cylinder has the greater height and by how much?

All metals have certain physical and mechanical properties, which, in fact, determine their specific gravity. To determine how suitable a particular alloy of ferrous or stainless steel is for production, the specific gravity of rolled metal is calculated. All metal products that have the same volume, but are made from different metals, for example, iron, brass or aluminum, have different mass, which is directly dependent on its volume. In other words, the ratio of the volume of the alloy to its mass - specific density (kg/m3) is a constant value that will be characteristic of a given substance. The density of the alloy is calculated using a special formula and is directly related to the calculation of the specific gravity of the metal.

The specific gravity of a metal is the ratio of the weight of a homogeneous body of this substance to the volume of the metal, i.e. this is density, in reference books it is measured in kg/m3 or g/cm3. From here you can calculate the formula for finding out the weight of a metal. To find this you need to multiply the reference density value by the volume.

The table shows the densities of non-ferrous metals and ferrous iron. The table is divided into groups of metals and alloys, where under each name the grade according to GOST and the corresponding density in g/cm3 are indicated, depending on the melting point. To determine the physical value of specific density in kg/m3, you need to multiply the tabulated value in g/cm3 by 1000. For example, this way you can find out what the density of iron is - 7850 kg/m3.

The most typical ferrous metal is iron. The density value of 7.85 g/cm3 can be considered the specific gravity of iron-based ferrous metal. Ferrous metals in the table include iron, manganese, titanium, nickel, chromium, vanadium, tungsten, molybdenum, and ferrous alloys based on them, for example, stainless steel (density 7.7-8.0 g/cm3), black steel ( density 7.85 g/cm3) cast iron (density 7.0-7.3 g/cm3) is mainly used. The remaining metals are considered non-ferrous, as well as alloys based on them. Non-ferrous metals in the table include the following types:

− light - magnesium, aluminum;

− noble metals (precious) - platinum, gold, silver and semi-precious copper;

− low-melting metals – zinc, tin, lead.

Specific gravity of non-ferrous metals

When rolling non-ferrous metal blanks, it is also necessary to know exactly their chemical composition, since their physical properties depend on it.
For example, if aluminum contains impurities (even within 1%) of silicon or iron, then the plastic characteristics of such a metal will be much worse.
Another requirement for hot rolling of non-ferrous metals is extremely precise temperature control of the metal. For example, zinc requires a temperature of strictly 180 degrees when rolling - if it is slightly higher or slightly lower, the capricious metal will sharply lose its ductility.
Copper is more “loyal” to temperature (it can be rolled at 850 – 900 degrees), but it requires that the melting furnace must have an oxidizing (high oxygen content) atmosphere - otherwise it becomes brittle.

Table of specific gravity of metal alloys

The specific gravity of metals is most often determined in laboratory conditions, but in their pure form they are very rarely used in construction. Alloys of non-ferrous metals and alloys of ferrous metals, which according to their specific gravity are divided into light and heavy, are much more often used.

Light alloys are actively used by modern industry due to their high strength and good high-temperature mechanical properties. The main metals of such alloys are titanium, aluminum, magnesium and beryllium. But alloys based on magnesium and aluminum cannot be used in aggressive environments and at high temperatures.

Heavy alloys are based on copper, tin, zinc, and lead. Among the heavy alloys, bronze (an alloy of copper with aluminum, an alloy of copper with tin, manganese or iron) and brass (an alloy of zinc and copper) are used in many industries. Architectural parts and sanitary fittings are produced from these grades of alloys.

The reference table below shows the main quality characteristics and specific gravity of the most common metal alloys. The list provides data on the density of basic metal alloys at an ambient temperature of 20°C.

The density of metals and alloys presented in the table will help you calculate the weight of the product. The method for calculating the mass of a part is to calculate its volume, which is then multiplied by the density of the material from which it is made. Density is the mass of one cubic centimeter or cubic meter of a metal or alloy. Mass values ​​calculated on a calculator using formulas may differ from real ones by several percent. This is not because the formulas are not accurate, but because in life everything is a little more complicated than in mathematics: right angles are not quite right, circles and spheres are not ideal, deformation of the workpiece during bending, embossing and hammering leads to unevenness of its thickness , and you can list a bunch more deviations from the ideal. The final blow to our desire for precision comes from grinding and polishing, which lead to unpredictable weight loss in the product. Therefore, the obtained values ​​should be treated as indicative.

Unit

Aluminum Density and any other material is a physical quantity that determines the ratio of the mass of the material to the occupied volume.

• The unit of measurement for density in the SI system is kg/m3.
• For the density of aluminum, a more descriptive dimension g/cm 3 is often used.

Density of aluminum in kg/m3a thousand times more than in g/s m 3.

Specific gravity

To estimate the amount of material per unit volume, such a non-systemic, but more visual unit of measurement as “specific gravity” is often used. Unlike density, specific gravity is not an absolute unit of measurement. The fact is that it depends on the magnitude of gravitational acceleration g, which varies depending on the location on Earth.

Dependence of density on temperature

The density of the material depends on temperature. It usually decreases with increasing temperature. On the other hand, specific volume—volume per unit mass—increases with increasing temperature. This phenomenon is called thermal expansion. It is usually expressed as a coefficient of thermal expansion, which gives the change in length per degree of temperature, for example mm/mm/ºC. Change in length is easier to measure and apply than change in volume.

Specific volume

The specific volume of a material is the reciprocal of density. It shows the volume of a unit of mass and has the dimension m 3 / kg. Based on the specific volume of the material, it is convenient to observe the change in the density of materials during heating and cooling.

The figure below shows the change in specific volume of various materials (pure metal, alloy and amorphous material) with increasing temperature. The flat sections of the graphs represent temperature expansion for all types of materials in solid and liquid states. When a pure metal is melted, there is a jump in the increase in specific volume (a decrease in density); when an alloy is melted, it rapidly increases as it melts in the temperature range. Amorphous materials, when melted (at the glass transition temperature), increase their coefficient of thermal expansion.

Aluminum Density

Theoretical density of aluminum

The density of a chemical element is determined by its atomic number and other factors such as atomic radius and the way the atoms are packed. T The theoretical density of aluminum at room temperature (20 °C) based on the parameters of its atomic lattice is:

• 2698.72 kg/m3.

Density of aluminum: solid and liquid

A graph of aluminum density versus temperature is shown in the figure below:

• As the temperature increases, the density of aluminum decreases.
• When aluminum transitions from a solid to a liquid state, its density decreases abruptly from 2.55 to 2.34 g/cm 3 .

The density of aluminum in the liquid state - molten 99.996% - at various temperatures is presented in the table.

Aluminum alloys

Effect of doping

Differences in the density of different aluminum alloys are due to the fact that they contain different alloying elements and in different quantities. On the other hand, some alloying elements are lighter than aluminum, others are heavier.

Alloying elements lighter than aluminum:

• silicon (2.33 g/cm³),
• magnesium (1.74 g/cm³),
• lithium (0.533 g/cm³).

Alloying elements heavier than aluminum:

• iron (7.87 g/cm³),
• manganese (7.40 g/cm³),
• copper (8.96 g/cm³),
• zinc (7.13 g/cm³).

The effect of alloying elements on the density of aluminum alloys is demonstrated by the graph in the figure below.

Density of industrial aluminum alloys

The densities of aluminum and aluminum alloys that are used in industry are presented in the table below for the annealed state (O). To a certain extent, it depends on the state of the alloy, especially for heat-hardening aluminum alloys.

Aluminum-lithium alloys

The famous aluminum-lithium alloys have the lowest density.

• Lithium is the lightest metal element.
• The density of lithium at room temperature is 0.533 g/cm³ - this metal can float in water!
• Every 1% lithium in aluminum reduces its density by 3%
• Every 1% lithium increases the elastic modulus of aluminum by 6%. This is very important for aircraft construction and space technology.

Popular industrial aluminum-lithium alloys are 2090, 2091 and 8090:

• Alloy 2090 has a nominal lithium content of 1.3% and a nominal density of 2.59 g/cm3.
• Alloy 2091 has a nominal lithium content of 2.2% and a nominal density of 2.58 g/cm3.
• Alloy 8090 with a lithium content of 2.0% has a density of 2.55 g/cm 3 .

Density of metals

Density of aluminum compared to the density of other light metals:

• aluminum: 2.70 g/cm 3
• titanium: 4.51 g/cm 3
• magnesium: 1.74 g/cm3
• beryllium: 1.85 g/cm 3

Sources:
1. Aluminum and Aluminum Alloys, ASM International, 1993.
2. FUNDAMENTALS OF MODERN MANUFACTURING – Materials, Processes, and Systems / Mikell P. Groover – JOHN WILEY & SONS, INC., 2010