Properties of metals and alloys (general). Physical properties of metals - Knowledge Hypermarket Physical properties of metals chemistry 9

Lesson topic. "Physical properties of metals" grade 9

Chemistry teacher Vera Ivanova

Goals : to form students' understanding of the structural features of metal atoms, their general physical properties and the dependence of properties on the type of crystal lattice

Tasks:

Educational: to summarize information about the metallic chemical bond, and the crystal lattice of metals,

to form an idea of ​​the nature of physical properties

Developing: the ability to form, analyze, work with tables, text, observe, draw conclusions

Educational : to intensify the cognitive activity of students, independence, initiative

Equipment : collection of metal samples, tables containing materials on the physical properties of metals, cards with tasks, the periodic system of chemical elements of D.I. Mendeleev

Forms of work: individual, pair work

Lesson type : learning new material

Lesson motto “First and foremost, study chemistry as closely as possible! This is amazing science! Her piercing bold gaze penetrates into the darkness of the earth's crust ”M. Gorky.

During the classes:

1. Organizational moment

What substances is modern civilization unthinkable without?

Indeed, metals play an important role in human life.

The word metal in translation means mine, mine. V earth crust there are large reserves of metal and polymetallic ores, which are used to obtain metals.

2. Updating knowledge

Before moving on to the study of new material, let's find out what we already know about metals.

1. Where are the metals in the periodic table of elements

2. How does the radius of metal atoms change in groups, in periods

3. How metallic properties change in groups, periods

4. What are the structural features of metals?

3. Explanation of the new material

Teacher.

The nature of the metallic chemical bond was discussed earlier in the course of the 8th grade.

What is the nature of the metallic bond?

What are the features of the crystal metal lattice?

Make a diagram of the metal crystal lattice on the board.

At the sites of the crystal lattice are located both neutral atoms and metal cations, bound by means of shared electrons (also called electron gas) belonging to the entire crystal. These electrons move freely throughout and attract metal cations, which are located in the nodes of the crystal lattice, ensuring its stability.

Thus, a metal bond is a bond that occurs in crystals as a result of the electrostatic interaction of positively charged metal ions with negatively charged free electrons. The metallic bond is characteristic of metals and their alloys.

What do we mean by the physical properties of a substance?

What determines the physical properties?

The most important physical properties of metals are determined by the nature of the metal bond, the structure of the crystal lattice ..

Consider a collection of metal samples. Students work with metal samples.

1. Set color, transparency

2. How is the ability to reflect light expressed?

3. How do metal samples react to the action of a magnet?

4. What are the physical properties of metals?

What are the general physical properties of metals?

Students note: metallic luster, hardness, plasticity, electrical and thermal conductivity.

Students study the table of the physical properties of metals, then, using these tables, answer questions and write in a notebook

Physical properties of metals

Students write down physical properties in a notebook, give examples.

Density. By density, metals are divided into two groups:

lungs , density no more than 5 g / cm 3 –

heavy , density more than 5 g / cm 3 –

The lightest - lithium, density 0.53 g / cm 3 , the heaviest - osmium, density 22.6 g / cm 3

Temperature. Metals, depending on the melting point, are subdivided:

fusible , melting point is not higher than 1000° С -

refractory , melting point above 1000° С -

The lowest melting metal is mercury t = -39 ° С , the most refractory is tungsten

t = 3340 ° С

Hardness. The hardness of metals is compared with the hardness of diamond and is divided into groups:

soft -

solid -

the hardest metal - chrome, scratches glass, the softest - alkali metals, which are cut with a knife

Electrical conductivity.Electrical conductivity is explained by the presence of free electrons, under the action of an applied electric voltage, chaotically moving electrons acquire directional motion in the metal, and an electric current arises.

Silver, copper, gold, aluminum have high electrical conductivity.

Mercury, lead, tungsten have low electrical conductivity

Thermal conductivity... The thermal conductivity of metals, as a rule, coincides with the electrical conductivity.

Metallic luster... Metals are capable of reflecting light waves, magnesium and aluminum are capable of retaining a metallic luster even in powder.

Colour - most metals are silvery, with the exception of gold-yellow, copper - red-yellow.

Plastic. Plasticity - the ability to change shape upon impact, to be drawn into wire, rolled into thin sheets. In the series Au, Ag, Cu, Sn, Pb, Zn, Fe decreases.

Magnetic properties.Magnetic properties are determined by the ability of metals to be attracted to the external magnetic field and retain the ability to be magnetized. The strongest magnetic properties are: iron, nickel, cobalt. These metals are called ferromagnetic (from the Latin word ferrum - iron).

4. Consolidation of knowledge

Students receive assignment cards and answer the questions.

Quest cards.

Test instructions: choose one correct answer

Option 1

the answers

1. Select a group of elements that contains only metals

A) Cu K Mg C

B) Ba Zn Pb Li

B) Na Mn Br Fe

2, Indicate the common structure of Li and K

A) 1 electron at the last electronic level

B) the same number of electronic levels

B) 2 electrons at the last electronic level

3.For metals of group 1A, it is not typical

A) the oxidation state in compounds -1

B) the oxidation state in the compounds +1

B) the general formula of the higher oxide R 2 O

4. The metallic properties of calcium are weaker than

A) potassium

B) lithium

C) iron

5. Active metals include

A) Cu Ag Ca Fe

B) Mg K Ba Ca

B) Pb Li Zn Sn

6.Low-active metals include

A) Hg Ag Cu

B) Ca Sr Ba

C) Cs Mg K

5. Summing up the lesson

Teacher:

What new have you learned about the physical properties of metals?

How can you explain the presence of common physical properties in such a large number of simple substances?

6 homework

Prepare messages on the role of metals in our lives.

All metals and metal alloys have certain properties. Properties metals and alloys divided into four groups: physical, chemical, mechanical and technological.

Physical properties... To physical properties metals and alloys include: density, melting point, thermal conductivity, thermal expansion, specific heat, electrical conductivity and the ability to magnetize. The physical properties of some metals are given in the table:

Physical properties of metals

Density. The amount of a substance contained in a unit of volume is called density. The density of the metal can vary depending on the method of its production and the nature of the processing.

Temperaturemelting... The temperature at which the metal completely passes from a solid to a liquid state is called melting point. Each metal or alloy has its own melting point. Knowledge of the melting point of metals helps to correctly conduct thermal processes during the heat treatment of metals.

Thermal conductivity. The ability of bodies to transfer heat from warmer particles to less heated ones is called thermal conductivity. . The thermal conductivity of a metal is determined by the amount of heat that passes through a metal rod with a cross section of 1 cm 2 , length 1cm within 1sec. with a temperature difference of 1 ° C.

Thermalextension. Heating the metal to a certain temperature causes it to expand.

The magnitude of the elongation of the metal upon heating is easy to determine if the coefficient of linear expansion of the metal α is known. The coefficient of volumetric expansion of the metal ß is equal to Zα.

Specificheat capacity... The amount of heat needed to raise the temperature 1 G substances per 1 ° C, is called the specific heat. Metals, in comparison with other substances, have a lower heat capacity, therefore they are heated without large expenditures of heat.

Electrical conductivity. The ability of metals to conduct electric current is called electrical conductivity. The main quantity characterizing the electrical properties of a metal is the electrical resistivity ρ, that is, the resistance that a wire made of a given metal with a length of 1 m has to current and section 1 mm 2. It is defined in ohms. The reciprocal of the electrical resistivity is called elekconductivity.

Most metals have high electrical conductivity, such as silver, copper and aluminum. With an increase in temperature, the electrical conductivity decreases, and with a decrease, it increases.

Magnetic properties. The magnetic properties of metals are characterized by the following values: residual induction, coercive force and magnetic permeability.

Residual induction (Vr) is called the magnetic induction that remains in the sample after its magnetization and removal of the magnetic field. Residual induction is measured in gauss.

Coercive force (NS) is the strength of the magnetic field that must be applied to the sample in order to nullify the residual induction, that is, to demagnetize the sample. Coercive force is measured in oersteds.

Magnetic permeability μ characterizes the ability of a metal to magnetize under it is determined by the formula

Iron, nickel, cobalt and gadolinium are attracted to the external magnetic field much more strongly than other metals, and constantly retain the ability to magnetize. These metals are called ferromagnetic (from the Latin word ferrum - iron), and their magnetic properties are called ferromagnetism. When heated to a temperature of 768 ° C (Curie temperature), ferromagnetism disappears and the metal becomes non-magnetic.

Chemical properties. The chemical properties of metals and metal alloys are called the properties that determine their relationship to the chemical effects of various active media. Each metal or metal alloy has some ability to resist these environments.

Chemical influences environments are manifested in different forms: iron rusts, bronze is covered with a green oxide layer, steel, when heated in quenching furnaces without a protective atmosphere, oxidizes, turning into scale, and dissolves in sulfuric acid, etc. Therefore, for the practical use of metals and alloys, you need to know them Chemical properties... These properties are determined by the change in the weight of the test samples per unit time per unit surface. For example, the resistance of steel to scale formation (heat resistance) is established by the increase in the weight of the samples for 1 hour by 1 dm surface in grams (weight gain is obtained due to the formation of oxides).

Mechanical properties. Mechanical properties determine performance metal alloys when exposed to external forces. These include strength, hardness, elasticity, plasticity, impact strength, etc.

To determine the mechanical properties metal alloys they are subjected to various tests.

Trialtensile(break). This is the main test method used to determine the proportionality limit σ pts, the yield strength σ s, tensile strength σ b relative elongation σ and relative contraction ψ.

For tensile testing, special specimens are made - cylindrical and flat. They can be of various sizes, depending on the type of tensile testing machine on which the metal is tensile tested.

The tensile testing machine works as follows: the test specimen is fixed in the clamps of the heads and gradually stretched with increasing force R before the break.

At the beginning of the test at light loads the sample is deformed elastically, its elongation is proportional to the increase in the load. The dependence of the elongation of the sample on the applied load is called proportionality law.

The greatest load that a sample can withstand without deviating from the law of proportionality is called beforeproportionality scrap:

σ pc = PP /Fo

FO mm 2.

With increasing load, the curve deviates to the side, i.e., the proportionality law is violated. To the point P p the deformation of the sample was elastic. Deformation is called elastic if it completely disappears after unloading the sample. In practice, the elastic limit for steel is taken equal to the proportional limit.

With a further increase in load (above the point P e) the curve begins to deviate significantly. The smallest load at which the sample is deformed without a noticeable increase in the load is called yield point:

σ s=Ps / Fo

where , kgf;

F o - initial cross-sectional area of ​​the sample, mm 2. After the yield point, the load increases to the point P e, where it reaches its maximum. By dividing the maximum load by the cross-sectional area of ​​the sample, determine tensile strength:

σb = Pb / Fo,

F o - initial cross-sectional area of ​​the sample, mm 2. At the point P to the sample bursts. The change in the sample after rupture is judged on the ductility of the metal, which is characterized by the relative elongation δ and contraction ψ.

Elongation is understood as the ratio of the increment in the length of the sample after rupture to its initial length, expressed as a percentage:

δ= l 1 - l 0 / l 0 · 100%

where l 1 is the length of the sample after rupture, mm;

l 0 is the initial length of the sample, mm.

Relative constriction is the ratio of the decrease in the cross-sectional area of ​​the sample after rupture to its initial cross-sectional area

φ= F o- F 1 / F 0 · 100%,

where F o - initial cross-sectional area of ​​the sample, mm 2;

F 1 - cross-sectional area of ​​the sample at the point of rupture (neck), mm 2.

Creep test. Creep is a property metal alloys slowly and continuously plastically deform under constant load and high temperatures. The main purpose of the creep test is to determine the creep limit - the magnitude of the stress applied for a long time at a certain temperature.

For parts working long time at elevated temperatures, take into account only the creep rate in a steady state process and set the boundary conditions, for example, 1 ° / o per 1000 hours. or 1 ° / o for 10,000 hours.

Trialimpact strength. The ability of metals to resist shock loads is called toughness. Structural steels are mainly subjected to impact testing, since they must have not only high static strength values, but also high impact toughness.

A sample of a standard shape and size is taken for testing. The sample is cut in the middle so that it breaks at this point during the test.

The sample is tested as follows. A test sample is placed on the support of the pendulum copra notch to bed . Pendulum weight G rise to a height h 1 . When falling from this height, the pendulum with a knife edge destroys the sample, after which it rises to a height h 2 .

The work expended is determined by the weight of the pendulum and the height of its rise before and after the destruction of the sample. A.

Knowing the work of destruction of the sample, we calculate the impact strength:

α To= A /F

where A- the work spent on the destruction of the sample, kgcm;

F - cross-sectional area of ​​the sample at the notch, cm 2.

WayBrinell. The essence of this method is , that, using a mechanical press, a hardened steel ball is pressed into the test metal under a certain load and the hardness is determined from the diameter of the resulting print.

Rockwell's way. To determine the hardness by the Rockwell method, a diamond cone with an apex angle of 120 ° is used, or a steel ball with a diameter of 1.58 mm. In this method, it is not the indentation diameter that is measured, but the indentation depth of the diamond cone or steel ball. The hardness is indicated by an indicator arrow immediately after the end of the test. When testing hardened parts with high hardness, use a diamond cone and a weight of 150 kgf. In this case, the hardness is measured on a scale WITH and denote HRC. If the test takes a steel ball and a weight of 100 kgf, then the hardness is measured on a scale V and denote HRB. When testing very hard materials or thin products, use a diamond cone and a weight of 60 kgf. In this case, the hardness is measured on a scale A and denote HRA.

Rockwell hardness tester parts must be well cleaned and free from deep scratches. The Rockwell method allows accurate and fast metal testing.

Vickers way . When determining the hardness by the Vickers method, a tetrahedral diamond pyramid with an angle between the faces of 136 ° is used as a tip pressed into the material. The resulting print is measured using a microscope in the device. Then, according to the table, the number of hardness is found HV. When measuring hardness, apply one of the following loads: 5, 10, 20, 30, 50, 100 kgf. Small loads make it possible to determine the hardness of thin products and surface layers of nitrided and cyaninated parts. The Vickers device is commonly used in laboratories.

Method for determining microhardness . This method is used to measure the hardness of very thin surface layers and some structural components. metal alloys.

Microhardness is determined using the PMT-3 device, which consists of a mechanism for indenting a diamond pyramid under a load of 0.005-0.5 kgf and a metallographic microscope. As a result of the test, the length of the diagonal of the obtained impression is determined, after which the hardness value is found from the table. Microsections with a polished surface are used as samples for determining microhardness.

Method of elastic recoil... To determine the hardness by the elastic recoil method, Shor's device is used, which works as follows. On a well-cleaned surface of the test piece from a height N the firing pin, equipped with a diamond tip, falls. Striking the surface of the part, the firing pin rises to a height h. The hardness numbers are counted along the bounce height of the striker. The harder the test metal, the greater the rebound height of the striker, and vice versa. Shor's device is mainly used to test the hardness of large crankshafts, connecting rod heads, cylinders and other large parts, the hardness of which is difficult to measure with other devices. Shor's device allows you to check the ground parts without compromising the surface quality, however, the results of the check are not always accurate.

Hardness conversion table

Scratching method. This method, in contrast to those described, is characterized by the fact that during testing, not only elastic and plastic deformation of the test material occurs, but also its destruction.

At present, a device, an inductive flaw detector DI-4, is used to check the hardness and quality of heat treatment of steel billets and finished parts without destruction. This device operates on eddy currents excited by alternating electromagnetic field, which is created by sensors in the controlled parts and the standard.

Density. This is one of the most important characteristics of metals and alloys. by density, metals are divided into the following groups:

lungs(density no more than 5 g / cm 3) - magnesium, aluminum, titanium, etc.:

heavy- (density from 5 to 10 g / cm 3) - iron, nickel, copper, zinc, tin, etc. (this is the most extensive group);

very heavy(density over 10 g / cm 3) - molybdenum, tungsten, gold, lead, etc.

Table 2 shows the values ​​of the density of metals. (This and the following tables characterize the properties of those metals that form the basis of alloys for artistic casting).

Table 2. Density of the metal.

Melting temperature. Depending on the melting point, the metal is divided into the following groups:

fusible(melting point does not exceed 600 o C) - zinc, tin, lead, bismuth, etc .;

medium melting(from 600 o C to 1600 o C) - these include almost half of the metals, including magnesium, aluminum, iron, nickel, copper, gold;

refractory(more than 1600 o C) - tungsten, molybdenum, titanium, chromium, etc.

Mercury is a liquid.

In the manufacture of artistic castings, the melting point of the metal or alloy determines the choice of the melting unit and refractory molding material. When additives are introduced into the metal, the melting point, as a rule, decreases.

Table 3. Melting and boiling points of metals.

Specific heat. This is the amount of energy required to raise the temperature of a unit of mass by one degree. The specific heat capacity decreases with an increase in the ordinal number of the element in the periodic table. The dependence of the specific heat capacity of an element in the solid state on the atomic mass is described approximately by the Dulong and Petit law:

m a c m = 6.

where, m a- atomic mass; c m- specific heat (J / kg * o C).

Table 4 shows the values ​​of the specific heat of some metals.

Table 4. Specific heat of metals.

Latent heat of melting of metals. This characteristic (Table 5), along with the specific heat capacity of metals, largely determines the required power of the melting unit. Sometimes more heat energy is required to melt a low-melting metal than a refractory one. For example, heating copper from 20 to 1133 o C requires one and a half times less thermal energy than heating the same amount of aluminum from 20 to 710 o C.

Table 5. Latent heat of metal

Heat capacity. Heat capacity characterizes the transfer of thermal energy from one part of the body to another, or rather, the molecular transfer of heat in a continuous medium, due to the presence of a temperature gradient. (table 6)

Table 6. Coefficient of thermal conductivity of metals at 20 o С

The quality of artistic casting is closely related to the thermal conductivity of the metal. In the smelting process, it is important not only to ensure sufficient high fever metal, but also to achieve a uniform temperature distribution throughout the entire volume of the liquid bath. The higher the thermal conductivity, the more evenly the temperature is distributed. In electric arc melting, despite the high thermal conductivity of most metals, the temperature drop across the cross section of the bath reaches 70-80 o С, and for metal with low thermal conductivity this drop can reach 200 o С and more.

Favorable conditions to equalize temperatures are created by induction melting.

Thermal expansion coefficient... This value, which characterizes the change in the dimensions of a sample with a length of 1 m when heated by 1 o C, is important for enamel work (table 7)

The coefficients of thermal expansion of the metal base and the enamel should be as close as possible so that the enamel does not crack after firing. Most enamels, which represent the hard coefficient of silicon oxides and other elements, have a low coefficient of thermal expansion. As practice has shown, enamels adhere very well to iron, gold, less firmly - to copper and silver. It can be assumed that titanium is a very suitable material for enameling.

Table 7. Coefficient of thermal expansion of metals.

Reflectivity. This is the ability of a metal to reflect light waves of a certain length, which is perceived by the human eye as a color (table 8). Metal colors are shown in table 9.

Table 8. Correspondence between color and wavelength.

Table 9. Colors of metals.

Pure metals are practically not used in arts and crafts. For the manufacture of various products, alloys are used, the color characteristics of which differ significantly from the color of the base metal.

Over the course of a long time, a huge experience has been accumulated in the use of various casting alloys for the manufacture of jewelry, household items, sculptures and many other types of artistic casting. However, the relationship between the structure of the alloy and its reflectivity has not yet been disclosed.

1. How are metals located in the periodic table of DI Mendeleev? What is the difference between the structure of metal atoms and the structure of non-metal atoms?
Metals are predominantly located on the left and bottom of the periodic table, i.e. mainly in groups I-III. And at the external energy level, metals usually have from one to three electrons (although exceptions are possible: antimony and bismuth have 5 electrons, and polonium has 6).

2. How do the crystal lattices of metals differ in structure and properties from ionic and atomic crystal lattices?
In the nodes of the metal crystal lattice there are positively charged ions and atoms, between which electrons move, and in the molecular and atomic crystal lattice molecules and atoms are located at the nodes, respectively.

3. What are the general physical properties of metals? Explain these properties based on your understanding of the metallic bond.

4. Why are some metals ductile (for example, copper), while others are brittle (for example, antimony)?
Antimony has 5 electrons at the external energy level, copper has 1. With an increase in the number of electrons, the strength of individual layers of ions is provided, preventing their free sliding, reducing plasticity.

5. When "dissolving" in hydrochloric acid 12.9 g of an alloy consisting of copper and zinc, received 2.24 liters of hydrogen (NU). Calculate the mass fractions (in percent) of zinc and copper in this alloy.

6. Copper-aluminum alloy was treated with 60 g of hydrochloric acid (mass fraction of HCl - 10%). Calculate the mass and volume of gas evolved (n.o.).

TEST PROBLEMS

1. The most strikingly metallic properties are manifested by a simple substance, the atoms of which have the structure of an electron shell
1) 2e, 1e

2. The most vividly metallic properties are manifested by a simple substance, the atoms of which have the structure of an electron shell
4) 2e, 8e, 18e, 8e, 2e

3. A solid substance with a crystal lattice conducts electric current well
3) metal

Density. This is one of the most important characteristics of metals and alloys. by density, metals are divided into the following groups:

lungs(density no more than 5 g / cm 3) - magnesium, aluminum, titanium, etc.:

heavy- (density from 5 to 10 g / cm 3) - iron, nickel, copper, zinc, tin, etc. (this is the most extensive group);

very heavy(density over 10 g / cm 3) - molybdenum, tungsten, gold, lead, etc.

Table 2 shows the values ​​of the density of metals. (This and the following tables characterize the properties of those metals that form the basis of alloys for artistic casting).

Table 2. Density of the metal.

Melting temperature. Depending on the melting point, the metal is divided into the following groups:

fusible(melting point does not exceed 600 o C) - zinc, tin, lead, bismuth, etc .;

medium melting(from 600 o C to 1600 o C) - these include almost half of the metals, including magnesium, aluminum, iron, nickel, copper, gold;

refractory(more than 1600 o C) - tungsten, molybdenum, titanium, chromium, etc.

Mercury is a liquid.

In the manufacture of artistic castings, the melting point of the metal or alloy determines the choice of the melting unit and refractory molding material. When additives are introduced into the metal, the melting point, as a rule, decreases.

Table 3. Melting and boiling points of metals.

Specific heat. This is the amount of energy required to raise the temperature of a unit of mass by one degree. The specific heat capacity decreases with an increase in the ordinal number of the element in the periodic table. The dependence of the specific heat capacity of an element in the solid state on the atomic mass is described approximately by the Dulong and Petit law:

m a c m = 6.

where, m a- atomic mass; c m- specific heat (J / kg * o C).

Table 4 shows the values ​​of the specific heat of some metals.

Table 4. Specific heat of metals.

Latent heat of melting of metals. This characteristic (Table 5), along with the specific heat capacity of metals, largely determines the required power of the melting unit. Sometimes more heat energy is required to melt a low-melting metal than a refractory one. For example, heating copper from 20 to 1133 o C requires one and a half times less thermal energy than heating the same amount of aluminum from 20 to 710 o C.

Table 5. Latent heat of metal

Heat capacity. Heat capacity characterizes the transfer of thermal energy from one part of the body to another, or rather, the molecular transfer of heat in a continuous medium, due to the presence of a temperature gradient. (table 6)

Table 6. Coefficient of thermal conductivity of metals at 20 o С

The quality of artistic casting is closely related to the thermal conductivity of the metal. In the smelting process, it is important not only to ensure a sufficiently high temperature of the metal, but also to achieve a uniform temperature distribution throughout the entire volume of the liquid bath. The higher the thermal conductivity, the more evenly the temperature is distributed. In electric arc melting, despite the high thermal conductivity of most metals, the temperature drop across the cross section of the bath reaches 70-80 o С, and for metal with low thermal conductivity this drop can reach 200 o С and more.

Induction melting creates favorable conditions for temperature equalization.

Thermal expansion coefficient... This value, which characterizes the change in the dimensions of a sample with a length of 1 m when heated by 1 o C, is important for enamel work (table 7)

The coefficients of thermal expansion of the metal base and the enamel should be as close as possible so that the enamel does not crack after firing. Most enamels, which represent the hard coefficient of silicon oxides and other elements, have a low coefficient of thermal expansion. As practice has shown, enamels adhere very well to iron, gold, less firmly - to copper and silver. It can be assumed that titanium is a very suitable material for enameling.

Table 7. Coefficient of thermal expansion of metals.

Reflectivity. This is the ability of a metal to reflect light waves of a certain length, which is perceived by the human eye as a color (table 8). Metal colors are shown in table 9.

Table 8. Correspondence between color and wavelength.

Table 9. Colors of metals.

Pure metals are practically not used in arts and crafts. For the manufacture of various products, alloys are used, the color characteristics of which differ significantly from the color of the base metal.

Over the course of a long time, a huge experience has been accumulated in the use of various casting alloys for the manufacture of jewelry, household items, sculptures and many other types of artistic casting. However, the relationship between the structure of the alloy and its reflectivity has not yet been disclosed.