Silane formation. Chemical properties of silane. The course of the silane synthesis process

Thermal transformations Monosilane is the most stable of the silanes. It begins to noticeably decompose into silicon and hydrogen at a temperature of -380 C. Above 500 C, decomposition proceeds at a very high rate. Hydrogen formed by the reaction inhibits decomposition; but the reaction does not stop. SiH4 = SiH2 + H2 SiH2 = Si + H2 disilane and trisilane .. Monosilane ignites in air even at -180 C. Pure silane can be mixed in a certain ratio with air or oxygen at a temperature of 523 K and atmospheric pressure without explosion if these mixtures lie outside the upper and lower limits ignition. Under other conditions, especially in the presence of higher silanes, self-ignition or explosion is observed.

During the combustion of monosilane, depending on the amount of oxygen and temperature, SiO, Si02, and silicic acid derivatives are obtained. Interaction with water For the first time interaction of silane with water and aqueous solutions acids and alkalis have been studied in the works. Pure water in quartz vessels does not decompose silane, but the slightest traces of alkali (alkali extracted from glass by water is enough) accelerate decomposition. Hydrolysis proceeds very quickly and leads to the elimination of all hydrogen associated with silicon: SiH4 + 2H20 = Si02 + 4H2 SiH4 + 2NaOH + H20 = Na2Si03 + 4H2 Hydrolysis of silane is also catalyzed by acids, but not as vigorously as alkalis. Traces of moisture in combination with sufficiently active surfaces (for example, cylinders for storing silane) react almost completely with an excess of monosilane to form siloxanes and hydrogen according to the equation: 2SiH4+H20 = (H3Si)20+2H2 Interaction with halogens, halogen derivatives and some other substances.

Halogens react with silane very vigorously, with an explosion. At low temperatures, the reaction can be carried out at a controlled rate. Hydrogen chloride at atmospheric pressure in the absence of catalysts does not react with silane even at elevated temperatures. In the presence of catalysts, such as aluminum chloride, the reaction proceeds smoothly already at room temperature and leads to the formation of chlorine-substituted silanes. SiH4 + HCl = SiH3Cl + H2

SiH4 + 2HC1 = SiH2Cl2 + H2, etc. Silane reacts with phosphine at temperatures above 400 C to form SiH3PH2 and small amounts of SiH2(PH2)2, PH(SiH3)2, and Si2P; similar derivatives were also obtained with arsine. Interaction with organic compounds.

Silane does not interact with saturated hydrocarbons up to 600 C. Olefins, such as ethylene, are added to silane at 460-510 C and atmospheric pressure. The main reaction products are mono- and dialkylsilanes. At 100 C, the reaction proceeds only under pressure. Under normal conditions, the interaction is observed when irradiated with ultraviolet light. As a result of the thermal interaction of acetylene with silane, some vinylsilane is formed, but the main product of the reaction is ethynyldivinylsilane. As a result of the photochemical reaction, mainly vinyl silane is obtained.

Currently, dozens of methods for producing monosilane are described in the literature. Not all of them found industrial development. To industrial methods for obtaining silane include: 1. Decomposition of metal silicides. 2. Reduction of silicon halides with metal hydrides. 3. Catalytic disproportionation of trialkoxysilane. 4. Catalytic disproportionation of trichlorosilane. Decomposition of metal silicides Magnesium silicide is the most suitable raw material for the production of silane by the decomposition reaction of metal silicides. Reaction equation this method silane production is as follows: Mg2Si + 4H20 = SiH4 + 2Mg(OH)2 The total yield of silanes for silicon contained in the silicide is 25-30%. Of these, according to 37% - Sibi,; 30% - Si2H6; 15% - Si3H8 and 10% - Si io; the rest are liquid silanes Si5Hi2 and Si6H14, as well as solid compositions (SiHi, ): Mg2Si + 4NH4Br \u003d 2MgBr2 + SiH4 + 4NH3. In silane, the presence of more than 20 impurity substances is indicated, including silane homologues up to Si8Hi8, light hydrocarbons, ammonia, benzene, toluene, hydrogen chloride. Reduction of silicon halides with metal hydrides. This method is convenient, since the reaction proceeds at ordinary temperatures and atmospheric pressure and in almost quantitative yield.The resulting silane is not contaminated with impurities of higher silanes.

Silicon hydrides, the so-called silanes, form a homologous series, similar to the series of saturated aliphatic hydrocarbons, but characterized by the instability of polysilane chains -Si-Si-. Silane SiH4 is the most stable first representative of the entire homologous series; only at a red-hot temperature does it decompose into silicon and hydrogen. Disilane Si2H6 decomposes when heated above 3000 into silane and a solid polymer; hexasilane Si6H14, which is the highest known member of the homologous series, decomposes slowly already at normal temperature. All silanes have a characteristic odor and are highly toxic.

The main scheme for their production is the interaction of Mg2Si with hydrochloric acid. By fractionation of the resulting mixture, the corresponding silicic acid can be obtained. There are other methods for obtaining silanes. For example, the reduction of halosilanes with lithium hydride or lithium aluminum hydride, as well as the reduction of halosilanes with hydrogen in the presence of AICl3

SiH 3 CI + H2->SiH4 + HCI. In contrast to very inert hydrocarbons, silanes are extremely reactive compounds. An important property that distinguishes silanes from hydrocarbons is the ease of hydrolysis of the Si-H bond in the presence of alkaline catalysts. Hydrolysis proceeds very quickly, and this process can be depicted as follows:

SiH4 + 2H2O→SiO2 + 4H2

SiH4 + 2NaOH + H2O → Na2SiO3 + 4H2.

Under the catalytic action of alkali on higher silanes, the Si-Si bond is broken

Н3Si-SiН3 + 6H2О→3SiО2 + 10H2.

With free halides, they react similarly to hydrocarbons, successively exchanging one hydrogen atom after another for a halogen. With hydrogen halides in the presence of a catalyst (АIСl3) there is a similar, but not analogous in hydrocarbon chemistry, reaction of the exchange of hydrogen for a halogen

SiН4 + HCI→H2 + SiН3СI.

Trichlorosilane SiH3CI can be obtained by direct synthesis from Si and HCl at elevated temperature.

Silanes do not react with concentrated sulfuric acid.

Compounds with its participation are used to protect the metal.

Monosilane- binary inorganic compound of silicon and hydrogen with the formula SiH4, colorless gas with an unpleasant odor, spontaneously ignites in air, reacts with water, poisonous

Other names: silane, silicon hydrogen, silicon hydride.

Monosilane is an inorganic compound with the chemical formula SiH 4 . Colourless, highly reactive gas, flammable in air.

Physical Properties

Chemical properties and preparation methods

Ways to get:

• Reaction between silicon(IV) chloride and lithium tetrahydridoaluminate.

Chemical properties:

• Starts to decompose above 400°C.

Storage

The gas can be stored in vessels with lubricated taps at room temperature without decomposition for several months. Silane is practically insoluble in vacuum grease. However, it should be noted that silicone-lubricated taps are difficult to open after prolonged standing. Storage of significant amounts of silane should be carried out in special steel cylinders with a special valve; material suitable for the manufacture of cylinders is alloy 40Mn - 4 steel.

List of used literature

1. Volkov, A.I., Zharsky, I.M. Big chemical reference book / A.I. Volkov, I.M. Zharsky. - Mn.: modern school, 2005. - 608 with ISBN 985-6751-04-7.
2. Hoffman W., Rüdorf W., Haas A., Schenk P. W., Huber F., Schmeiser M., Baudler M., Becher H.-J., Dönges E., Schmidbaur H., Erlich P., Seifert H. I Guide to inorganic synthesis: In 6 volumes. T.3. Per. with. German / Ed. G. Brouwer. - M.: Mir, 1985. - 392 p., ill. [with. 715-717]

The invention can be used in the chemical and electronic industries. Silicon hydride - monosilane is obtained by the interaction of magnesium silicide with mineral acids. The preparation of magnesium silicide is carried out by thermal interaction of a mixture containing 1 wt. part of the dispersed particles of silicon oxide, up to 10 wt. parts of silicon and from 3.5 to 4 wt. parts of lumpy fragments of magnesium, with continuous stirring. The particle size of silicon oxide does not exceed 3 mm, and the ratio of the particle size of silicon oxide and the size of lumpy fragments of magnesium is 1:(10-20). The interaction of the reacting components during the mixing process is carried out in the temperature range of 550-680°C. The proposed invention makes it possible to expand the raw material base for producing monosilane and reduce the cost of the product. 2 w.p. f-ly.

The invention relates to the production of silicon hydrides, including high purity monosilane, intended for the formation of semiconductor and dielectric layers, the synthesis of organosilicon compounds, thermal deposition (dissociation) of polycrystalline silicon.

A known method for producing silicon hydrides (monosilane) by catalytic disproportionation of trichlorosilane (US Pat. Germany No. 331165, dated 10/13/83), the essence of which is the catalytic hydrogenation (at a temperature of 400-500 ° C) of dispersed silicon and silicon tetrachloride according to the reaction:

Si + 2H 2 + 3SiCl 4 \u003d 4SiHCl 4

and subsequent dissociation of this compound according to the reaction:

4SiHCl 4 \u003d SiH 4 + 3SiCl 4

A significant disadvantage of this method is the presence of toxic chlorine involved in all reactions, which sharply limits (for environmental reasons) the production development of this method.

A known method of chloride-free production of silicon hydrides (Pat. No. RU 2151099, dated June 20, 2000, C01B 33/04), the technical essence of which lies in the thermal (at t - 450-600 ° C) interaction of dispersed quartzite with magnesium in a stoichiometric ratio , in the presence of aluminum salts, in a stream of atomic hydrogen, in a glow discharge. However, the complete reduction of silicon dioxide to pure silicon by the magnesium thermal method, at a stoichiometric ratio of the masses of SiO 2 and Mg, is difficult, due to the high reaction rate and significant heat release (~92 kcal/mol), at which the temperature in the reaction zone reaches values ​​above 3000°C , with the evaporation of the reaction products, leading to an uncontrolled explosion. The introduction of an inert additive - aluminum salt, designed to compensate for the heat of reaction, leads to a decrease in the likelihood of direct contact of magnesium particles with all quartzite particles, which causes a local deviation of the interacting reagents from stoichiometry, with the formation of magnesium silicide (Mg 2 Si), the heat of formation of which is ~19 kcal/mol. The formation of this compound leads to the fact that part of the silicon dioxide remains unreduced. Thus, the complete magnesium thermal recovery of silicon dioxide under the conditions given in the known technical solution is very difficult.

A known method for producing silicon hydrides, used by the Japanese company Komatsu MFG CO LTD ("Monosilane in the technology of semiconductor materials." Overview, a series of "organoelement compounds and their applications", NIIETKhIM, Chemical industry, 1983). The technical essence of this method lies in the fact that in the first stage, magnesium silicide is formed by means of a reaction carried out at a temperature of 500-600 ° C in a neutral medium:

Si+2Mg=Mg 2 Si+19 kcal/mol

In the second stage, magnesium silicide is subjected to interaction with mineral acids or salts, with the release of gaseous silicon hydrides, for example, by the reaction acid hydrolysis:

Mg 2 Si + 2HCl \u003d MgCl 2 (L) + SiH 4 (G)

or acidolysis of magnesium silicide:

Mg 2 Si (T) + 4NH 4 Cl (T) \u003d 2MgCl 2 (T) + SiH 4 (G) + 6NH 3 (G)

This method is the closest in technical essence and the achieved effect to the claimed technical solution and is taken as a prototype.

A significant disadvantage of the prototype is that in order to obtain silicon that meets the properties applicable to its use in electronic or semiconductor technology (purity 99.9999%), raw materials in the form of silicon are used, with a purity of 98-99%, i.e. containing impurities. This significantly reduces the raw material base, i.e. eliminates the possibility of using other than silicon, its compounds, such as quartzite (SiO 2) or silicic acid (H 2 SiO 3).

The purpose of the proposed technical solution is to expand the raw material supply of the process by creating the possibility of participating in the reaction of obtaining magnesium silicide (Mg 2 Si), silicon dioxide (SiO 2), silica or quartzite, which is widespread in nature, and silicic acid (H 2 SiO 3).

The specified technical result is achieved by introducing into the reaction of obtaining magnesium silicide from silicon-containing compounds, including SiO 2 and H 2 SiO 3 , which is inert with respect to the interacting components of an additive that does not contribute to general reaction additional chemicals. Such an addition to the reaction

SiO 2 +2Mg=2MgO+Si+92 kcal/mol

is dispersed silicon. The addition of silicon is necessary to dissipate the heat released during this reaction, without introducing additional chemical elements capable of introducing "pollution" into the final product.

To reduce heat release during the simultaneous interaction of particles of silicon oxide (silicic acid) with magnesium, the latter is introduced into the reaction in the form of lumpy fragments, which prevents a complete volumetric reaction leading to an explosion, because only those particles of silicon dioxide that are in contact with the magnesium fragment participate in the reduction. To carry out a complete, bulk reaction, the mixture of particles must be stirred to renew the contacts of magnesium lumpy fragments with new, previously unreacted particles of silicon oxides. The mixing can be carried out, for example, in rotating or oscillating reactors. The mixing process, as the entire reaction process as a whole, is carried out until the complete disappearance ("eating") of lumpy fragments of magnesium.

The masses of the reacting components must correspond to the ratio:

Up to 10:(3.5÷4.0), because the heat capacity of silicon in the temperature range of 0-1000°C is equal to 3.58 cal/mol×deg, then for full compensation thermal energy of 92 kcal / mol released during the stoichiometric, magnesium-thermal reaction of silicon dioxide reduction, an additional addition of up to 20 moles of pure dispersed silicon or up to 10 parts by weight is required (the mass of one mole of SiO 2 is ~ twice as much as a mole of Si). The mass of added silicon particles is ballast and does not participate in the final reaction of obtaining silicon hydrides when the mixture interacts with mineral acids and salts. This silicon is a technological circulating raw material of the proposed method for producing silanes.

The addition of 3.5-4 parts of magnesium is justified by the fact that 1.5-2 parts of magnesium are needed to restore silicon from its dioxide according to the reaction:

SiO 2 + 2Mg \u003d 2MgO + Si,

the addition of two more parts of magnesium is necessary for the formation of magnesium silicide from reduced silicon by the reaction Si+2Mg=Mg 2 Si.

The maximum particle size of silicon dioxide is 3 mm and the ratio of the sizes of the latter with the sizes of lumpy fragments of magnesium:

was determined empirically, for reasons of minimizing the heat released during the reduction reaction, to optimize the time of the magnesium-thermal reaction. The interaction of magnesium with silicon dioxide particles larger than 3 mm leads to a local mini-explosion. The size of lumpy fragments of magnesium less than ten times the size of silicon dioxide also leads to a mini-explosion due to the large surface of interparticle interaction and insignificant heat absorption for the formation of magnesium silicide. More than a twenty-fold increase in the size of lumpy fragments of magnesium in relation to the particles of silicon dioxide leads to an unreasonable increase in the total reaction time.

The temperature range of the reaction for the synthesis of magnesium silicide 550-680°C is justified by the fact that an increase in the total mass of the reacting components compared to the stoichiometric ratio leads to the need to increase the heating intensity, as well as to create the possibility of changing the state of aggregation of magnesium fragments before melting. This leads to a reduction in the cost of the process by reducing the price of magnesium raw materials. The market price of magnesium castings is 80-90 rubles/kg, the price of dispersed magnesium (including magnesium shavings) is 400-600 rubles. kg. In a given temperature range lumpy magnesium is melted (t melt =620°C) due to external heating and heat release and evenly distributed in the reaction zone.

The analysis of the prior art showed that the claimed set of essential features set forth in the claims is unknown. This allows us to conclude that it meets the criterion of "novelty". To verify the compliance of the claimed invention with the criterion of "inventive step", an additional search for known technical solutions was carried out in order to identify features that match the distinguishing features of the claimed technical solution from the prototype. It has been established that the claimed technical solution does not follow explicitly from the prior art. Therefore, the claimed invention meets the criterion of "inventive step". The essence of the invention is illustrated by an example of the practical implementation of the method.

Example of practical implementation

The proposed technical solution was specifically carried out in the production of silicon hydrides by acid hydrolysis in hydrochloric acid mixtures of silicon and magnesium silicide:

A mixture of silicon and magnesium silicide was previously obtained by calcining the following components in a hydrogen environment:

Si+SiO 2 +4Mg=2MgO+Mg 2 Si+Si

(the previous reaction does not show the dissolution reaction of magnesium oxide, which is formed during the magnesium thermal reduction of silicon dioxide according to the reaction). The particle size of silicon and silicon dioxide did not exceed 1 mm, and the size of magnesium fragments did not exceed 2.5 mm. The reaction was carried out at a temperature of 650°C in a rotary kiln with a nichrome heater. The furnace rotation speed was 5 rpm. The reaction mixture weighed included the following components: silicon dioxide 2 kg, dispersed silicon 20 kg, lump magnesium 8 kg. Baking time 2 hours. As a result of the reaction carried out with the indicated parameters, a mixture of Mg 2 Si and Si with a ratio of components of 1:4 was obtained. Residual silicon dioxide in the reaction (in the residue after acid hydrolysis) was not detected. The specified implementation example confirms the compliance of the claimed method with the condition of "inventive step"

1. A method for producing silicon hydride - monosilane from magnesium silicide obtained by thermal interaction of dispersed silicon with active magnesium in an inert medium, followed by interaction of this compound with mineral acids, characterized in that magnesium silicide is obtained by thermal interaction of a mixture containing 1 wt .h. dispersed particles of silicon oxide, up to 10 wt.h. silicon and from 3.5 to 4 wt.h. lumpy fragments of magnesium, with continuous stirring.

2. The method according to claim 1, characterized in that the particle size of silicon oxide does not exceed 3 mm, and the ratio of particle sizes of silicon oxide to the size of lumpy fragments of magnesium is 1: (10-20).

3. The method according to claim 1, characterized in that the interaction of the reacting components in the mixing process is carried out in the temperature range of 550-680°C.

Similar patents:

The invention relates to a method for producing high-purity and low-cost monosilane suitable for forming thin semiconductor and dielectric layers, as well as high-purity poly- and single-crystal silicon for various purposes (electronics, solar energy).

The invention relates to methods for separating mixtures of volatile substances in chemical engineering processes and can be used to separate mixtures of chlorosilanes, hydrides, fluorides, organic products and other products with the release of the target product.

The invention relates to a method for producing high purity monosilane suitable for the formation of thin-film semiconductor products, as well as high purity poly- and single-crystal silicon for various purposes (semiconductor technology, solar energy).

The invention relates to a technology for producing silane for the manufacture of high-purity semiconductor silicon used in power electronics, as well as silicon wafers for the production of ultra-large integrated circuits and for the formation of various silicon-containing layers and film coatings in microelectronics.

3.1. Physical and chemical properties

Silicon tetrafluoride was discovered by Scheele in 1771. It is a colorless gas with a pungent, irritating odor. Relative molecular weight - 104.08. The molar volume is 22.41 l/mol. Boiling point (sublimation) - -95˚C, melting point - -90.2˚C. The density in air under normal conditions is 3.6272, the mass of 1 liter of gas is 4.69g.

Silicon tetrafluoride is extremely temperature resistant. Under ordinary conditions, it hardly reacts with heavy metals, their oxides and glass, if they are completely dry; at elevated temperatures it is more reactive, especially with alkali, alkaline earth and rare earth metals. When dissolved in water, silicon tetrafluoride undergoes hydrolytic decomposition:

SiF 4 +2H 2 O→SiO 2 +4HF.

It smokes in humid air, as it easily interacts with water, giving fluorosilicic acid:

3SiF 4 +(x+2)H 2 O→2H 2 SiF 6 +SiO 2 *xH 2 O.

Forms a fluorosilicate with sodium fluoride:

SiF 4 +2NaF→Na 2 SiF 6 .

Many reactions of silicofluoride with organic substances are of great interest. It forms adducts with acetone and aromatic amines. Interaction with the Grignard reagent leads to the formation of triorganofluorosilanes, which are more stable than the corresponding chlorosilanes:

SiF 4 +3RMgX→R 3 SiF+3MgFX .

3.2. Preparation and use of silicon tetrafluoride

In the laboratory, silicon fluoride can be obtained by the reaction:

2CaF 2 + SiO 2 + 2H 2 SO 4 (c) → SiF 4 + 2CaSO 4 + 2H 2 O.

The reaction is carried out with heating and the gas evolved is of high purity.

Silicon tetrafluoride has limited use and is not produced on an industrial scale. However, it is contained in waste gases from the production of phosphate fertilizers and is considered as the most promising source of fluorine. By treating these exhaust gases with water, the SiF 4 contained therein can be recovered in the form of H 2 SiF 6 or Na 2 SiF 6 . They are beginning to be used as a source of fluorine in the synthesis of cryolite and aluminum trifluoride.

4. Silane

4.1. Physical and chemical properties of silane

Monosilane SiH 4 is a colorless gas that, when diluted, has a slight characteristic odor, reminiscent of the smell of antimony hydrogen; in high concentrations smells very bad. Its relative molecular weight is 32.12; boiling point - -111.2˚C; its melting point is -184.6˚C. The mass of 1 liter of gas under normal conditions is 1.4469g. Air density - 1.12. The density of liquid silane at the boiling point is 0.557g/cm3; at a melting point - 0.675g / cm 3.

In air, silane ignites with an explosion. When heated to 300 - 400˚C, it decomposes at a high rate.

4.1.1. Thermal transformations

Monosilane is the most stable of the silanes. Hydrogen formed during decomposition inhibits the process of further decomposition, but the reaction does not stop. The silicon film deposited on the surface during the decomposition of silane is a silver-colored metal mirror, which at low temperatures has a pronounced crystalline structure, and at higher temperatures it is amorphous.

In the presence of 1% arsine, the rate of silane decomposition increases.

At 470˚C, silane is partially converted to disilane, apparently through the formation of SiH 3 radicals. In the presence of ethylene at 450 - 500˚C, Si 3 H 8 is formed along with Si 2 H 6 . SiD 4 decomposes more slowly than SiH 4 .

4.1.2. Oxidation

Monosilane ignites in air even at -180˚C. Careful oxidation of monosilane with oxygen highly diluted with nitrogen at a temperature of -110˚C produces a white, sometimes brown, flaky precipitate, consisting mainly of proloxane (H 2 SiO) x .

During the combustion of silane, depending on the amount of oxygen and temperature, SiO, Si and other products are obtained. Thermodynamic calculations show that the amount of SiO increases with increasing temperature. Increasing the pressure helps to reduce the formation of SiO.

4.1.3. Interaction with water and alcohols

Pure water in quartz vessels does not decompose the silane, but the slightest trace of alkali accelerates the decomposition. Hydrolysis proceeds very quickly and leads to the elimination of all hydrogen associated with silicon:

SiH 4 +2H 2 O→SiO 2 +4H 2; SiH 4 +2NaOH+H 2 O→Na 2 SiO 3 +4H 2 .

Silane hydrolysis is also catalyzed by acids, but not as vigorously as by alkalis.

Alcohols, in the presence of alkali metal ions, react with silane to form orthosilicic acid esters Si(OR) 4 along with more or less HSi(OR) 3 and H 2 Si(OR) 2 .

4.1.4. Interaction with halogens, halogen derivatives and ammonia

Halogens react with silane very vigorously, with an explosion. At low temperatures, the reaction can be carried out at a controlled rate.

Hydrogen chloride at atmospheric pressure in the absence of catalysts does not react with silane even at elevated temperatures. In the presence of catalysts, for example, aluminum chloride, the reaction proceeds smoothly already at room temperature and leads to the formation of chlorine-substituted silanes:

SiH 4 +HCl→SiH 3 Cl+H 2 ; SiH 4 +2HCl→SiH 2 Cl 2 +2H 2 ;

SiH 4 +3HCl→SiHCl 3 +3H 2 ; SiH 4 +4HCl→SiCl 4 +4H 2.

Hydrogen bromide reacts with silane more easily than hydrogen chloride. Hydrogen iodide reacts even more easily with silane.

Monosilane does not interact with ammonia at ordinary temperatures, but in the presence of amide, the following reaction occurs:

SiH 4 +4NH 3 →1/x x +4H 2 .

4.1.5. Interaction with organic compounds

The reaction with sodium tetramethoxyborate is:

SiH 4 +NaB(OCH 3) 4 →NaBH 4 +Si(OCH 3) 4.

With diethylmagnesium in ether, silane interacts with the simultaneous splitting of the ether:

SiH 4 + Mg (C 2 H 5) 2 + (C 2 H 5) 2 O→HMgOC 2 H 5.

4.2. Preparation and application of silane

4.2.1. Decomposition of metal silicides

For the production of silane by this method, magnesium silicide is most suitable: Mg 2 Si+4H 2 O→SiH 4 +2Mg(OH) 2 .

Simultaneously with monosilane, higher silanes are obtained. The yield and relative amount of individual silanes depend on the conditions for the preparation of magnesium silicide, in particular, on the temperature and time of fusion of the components. The maximum yield (~38%) is achieved when silicon powder is alloyed with magnesium at 650˚C.

4.2.2. Disproportionation reactions of trialkoxysilanes

In industrial production, the interaction of hydrogen chloride with silicon produces trichlorosilane, which with alcohol gives triethoxysilane:

SiHCl 3 + 3C 2 H 5 OH → SiH (OC 2 H 5) 3 + 3HCl.

Disproportionation of the latter

4SiH(OC 2 H 5) 3 →SiH 4 +3Si(OC 2 H 5) 4

goes in the presence of a catalyst - metallic sodium.

4.2.3. Reduction of silicon halides with metal hydrides

This method is convenient because the reaction proceeds at ordinary temperatures and atmospheric pressure. The resulting silane is not contaminated with impurities of higher silanes.

Recovery with lithium aluminum hydride is usually carried out in an ethyl ether medium, adding silicon chloride to the ether suspension of aluminum hydride upon cooling (~0˚):

SiCl 4 + LiAlH 4 → SiH 4 + LiCl + AlCl 3 . Yield ~99%.

Calcium hydride begins to react with silicon fluoride to form silane at a temperature of ~250˚C:

2CaH 2 +SiF 4 →SiH 4 +2CaF 2 . Yield 80 - 90%.

To increase the reaction surface, calcium hydride is ground into powder. The hydride is then loaded into the reactor. The reactor is evacuated and purged with hydrogen. Silicon fluoride is fed into the reactor up to a predetermined pressure. The exiting silane is collected in traps cooled with liquid nitrogen. The process is unlimited in time. At the end of the reaction, the silane is transferred from the traps to a receiving cylinder and weighed.

4.2.4. Application

High-purity monoisotopic silane is used to produce polycrystalline silicon and to coat quartz crucibles with a layer of silicon dioxide in order to grow monoisotopic silicon single crystals from them by the Czochralski method.

High purity silane is one of the main strategic materials of the modern industrialized state.

II. experimental part

1. Scheme and technical description of the installation

The installation diagram is shown in the figure. Cylindrical reactors 1 and 2, made of stainless steel, are mounted vertically and placed in a resistive electric furnace. The reactors work alternately. The switching of the reactors into the flow system is carried out by taps 19 - 22, the connection with the vacuum line by taps 17,18. The upper ends of both reactors are placed in a hermetically sealed Plexiglas box with a lock and an inert gas purge device.

When carrying out the process, the reactor used is connected to the system for forming the flow of the gaseous reagent I and the system for receiving the gaseous target product II. The process temperature in the reactor is set and maintained by the temperature control system III. Temperature control in the reactor is carried out by a temperature measurement system IV.

The gaseous reactant flow formation system I consists of two identical branches operating in parallel and forming flows of silicon tetrafluoride and hydrogen. Each branch consists of a cylinder with a substance 24, 28, a gas pressure stabilizer (SDG) 25, 29, a leak valve 26, 30 and a gas flow regulator (RRG) 27, 31, connected by stainless steel tubes. The pressure at the outlet of the SDG is measured by pressure and vacuum meters 32, 33. Through valves 2, 4, each branch is independently connected to the forevacuum line. After leaving the RRG, the flows of hydrogen and silicon tetrafluoride are mixed, forming a gaseous reagent. The latter is fed into the reactor through a line mounted in the bottom flange of the reactor. The pressure of the gas mixture at the outlet of the RRG is determined by the pressure vacuum gauge 34.

The mixture of the gaseous target product with hydrogen flows out of the reactor through a line built into the upper flange and enters the system for receiving the gaseous target product II. The pressure at the outlet of the reactor is determined by a vacuum pressure gauge 35. The system for receiving the gaseous target product II consists of three metal traps 36 cooled with liquid nitrogen and two receiving cylinders 37. The traps are used to separate the gaseous target product from the hydrogen flow by condensing (“freezing”) the latter . As can be seen from the figure, the system of communications and valves 11-16 allows you to implement various ways to include traps in the flow. The outgoing hydrogen flow is discharged through the rheometer 38 into the exhaust ventilation. After the end of the process, the target product is reloaded from the traps into receiving cylinders, which later serve to store and transport the target product.

The pressure in the receiving system during reloading is controlled by a vacuum pressure gauge 39. Through valves 3 and 5, the receiving system is connected to the forevacuum line.

The reactor is heated and the process temperature is maintained by the temperature control system III. It consists of two control thermocouples placed at the ends of each of the reactors, a temperature control unit 40 and an amplifier 41, the output of which is connected to the reactor heating furnace.

Temperature control inside the reactor is carried out by a temperature measurement system IV. It consists of six measuring thermocouples,

located along the axis of the reactor in a tube introduced into the reactor coaxially, signal converter 42 and a personal computer. The change in temperature during the process at the points of location of each of the six thermocouples is displayed on the computer monitor.

The foreline allows different parts of the plant to be connected to it independently. The pressure in the foreline is recorded by a manometer 44, a rotameter 45 makes it possible to record even insignificant flows of residual gases.

2. Method of work on the installation

The initial state. The reactor is cleaned from solid-phase reaction products, it contains air diluted with an inert gas - nitrogen. The top flange of the reactor has been removed. The box is closed and purged with nitrogen evaporating from the Dewar. All taps on the plant are closed. The line of silicon tetrafluoride of the flow formation system I and the system for receiving the gas-phase target product II are evacuated.

Before loading the solid-phase reagent, the reactor is purged with hydrogen. To do this, open the tap on the hydrogen cylinder, set the pressure to 1 atm on the gearbox. izb. (control by pressure and vacuum gauge “H 2” - 33), open the valves “leakage” -30, 7, 20 (19), set the desired flow of 33-35 divisions on RRG 31.

Banks with calcium hydride are placed through the gateway into the box. After filling the reactor with hydrogen (~15 min.), calcium hydride powder is poured into the reactor. During the filling process, it is necessary to lightly tap the reactor to achieve a more uniform filling of the reactor volume with the reagent. The required filling level is controlled by a special meter.

After the loading of calcium hydride into the reactor, the box cover is removed, the upper flange of the reactor is installed and bolted, and valves 22(21), 23, 9, 8 are opened. 0.3 atm. The pressure is controlled by a pressure vacuum gauge "SiН 4 +H 2" 35.

2.2. Installation start

The start-up of the installation begins with the heating of the reactor. To do this, turn on the temperature controller, increase the reference voltage - "task" - manually, first smoothly, then discretely to a predetermined value. Then, pumping out of the system for forming the flow of silicon tetrafluoride and the system for receiving the gas-phase target product are turned on. To do this, open taps 4, 3, 6, 16, 14, 12.

Next, hydrogen is let into the traps using a vacuum line for this. For this purpose, the valves 4, 1 are closed, the valves on the hydrogen cylinder 28, on the reducer 29 and 2 are opened. The hydrogen pressure is controlled by a pressure and vacuum gauge "SiH 4" 39. In this case, the traps are cooled with liquid nitrogen.

In the process of filling the traps with hydrogen, the pressure in the reactor is lowered to atmospheric, bypassing excess hydrogen into the traps. To do this, the valve 11 is opened. The pressure in the reactor is controlled by a pressure and vacuum gauge "SiH 4 + H 2" 35. When atmospheric pressure is reached in the reactor, the valve 11 is closed.

Upon reaching the hydrogen pressure in the traps, equal to atmospheric, valves 6, 2 are closed, valves 30, 20(19), 11, 8 are opened and the hydrogen flow is released through the reactor into the exhaust ventilation.

Upon reaching the initial temperatures on the first and second thermocouples from the bottom of the reactor (~100-105 o C and ~115-120 o C, respectively), a flow of silicon tetrafluoride is formed. To do this, we slightly open the valve of the cylinder with silicon tetrafluoride, the pressure at the outlet of the SDG increases to 1 atm., control by the vacuum pressure gauge "SiF 4" 32. Next, open the "leak valve SiF 4" 26 and the valve of the cylinder with silicon tetrafluoride completely. pressure gauge high pressure on the SDG shows the pressure of silicon tetrafluoride in the cylinder. Crane on SDG

gradually set to a position corresponding to an overpressure at the outlet of ~0.9 atm. according to the pressure vacuum gauge “SiF 4 “ 32, which corresponds to the indication of the flow value on the RRG ~ 23-25%. In this case, the hydrogen flow decreases to ~26–28%. The above parameters determine the technological mode of operation of the installation.

2.3. The course of the silane synthesis process

In normal mode, the process proceeds stationary. Control over the course of the process and registration of possible deviations is carried out using the following instruments.

1. Vacuum gauge "H 2" 33 - carrier gas pressure at the RRG inlet. Mode ~1 atm.

2. Pressure vacuum gauge ”SiF 4 “ 32 – pressure of silicon tetrafluoride at the outlet of the LDH. Mode - 0.9 atm. izb.

3. High pressure gauge on SDG - coarse control of silicon tetrafluoride consumption.

4. Pressure vacuum gauge "SiF 4 +H 2" 34 - pressure at the inlet to the reactor. Mode - 0.1-0.2 atm. izb.

5. Pressure vacuum gauge "SiH 4 +H 2" - pressure at the entrance to the traps. Atmospheric pressure mode.

6. Outlet rheometer - slight overpressure.

The flow index on the RRG is the share of the flow from the maximum under the conditions of the experiment. Mode - H 2: 27-29%; SiF4: 23-25%.

During the course of the process, it is possible for the condensate of gaseous reagents to overlap the passage section of the first trap along the flow. This is recorded by an increase in pressure at the inlet to the traps, determined by the “SiH 4 +H” 2 35 pressure and vacuum meter, and a decrease in flow, determined by the rheometer 38. To restore the normal mode of the process, valve 13 is opened, directing the flow of gaseous reaction products into the second trap. At the same time, valves 11 and 12 are left open so that the condensation process continues in the first trap. Similar actions are taken when closing the second trap by opening the tap 15.

2.4. End of the silane synthesis process

To complete the process, the flow of silicon tetrafluoride is blocked by a valve on the cylinder 24, the SDG valve is fully opened. Then the hydrogen flow is increased to 40%, the purge is carried out for about 20 minutes.

Next, the reactors are pumped out through the traps. To do this, close valves 8, 30 and open valve 3 and slowly valve 6. The pumping speed is controlled by a rheometer - the ball should not rise above 70 divisions. The depth of pumping and its end is determined by the pressure vacuum meters "SiH 4 +H 2" 35 and "SiF 4 "32. After the pumping is completed, the heating of the reactor is turned off, the valve on the SDG 25, the SiF 4 leak valve 26 and valves 21(22) are closed. The reactor is filled with hydrogen to a slight overpressure (0.1-0.15 atm. el.). After that, the valves 20(19), “leak H 2” 30, the valve on the hydrogen cylinder are closed. The traps are pumped out for some more time (~5 min), then valves 11, 12, 14, 16, 5, 23 are closed.

2.5. Transfer of gaseous target product from traps to a receiving cylinder

Receiving cylinders 37 are pre-cooled with liquid nitrogen. Traps 36 are unloaded in turn, starting with the third one closest to the receiving cylinders 37. Each trap is unloaded through the outlet line, if the section of the trap is blocked by condensate, then unloading is performed simultaneously through the inlet and outlet lines. The method of unloading the gaseous product is as follows.

The valve on the receiving cylinder 37 is opened. The trap is heated with a jet of warm air. Heating starts from the top of the trap, then the heating zone is slowly moved down. The reloading speed is controlled by the pressure on the SiH 4 pressure and vacuum gauge 39. If unloading is carried out along the inlet line, then the pressure is also controlled on the SiH 4 +H 2 vacuum gauge 35. After this trap is unloaded, the previous one is unloaded along the line, repeating similarly all methodical actions described above. At the end of the reloading of the gaseous target product, the valve on the receiving cylinder 37 is closed, the traps are pumped out to the forevacuum through the valve 3. After the pumping of the traps is completed, the valves 3, 6, 16 are closed.

2.6. Unloading the solid-phase reaction product from the reactor

To unload the solid-phase reaction product from the reactor, excess hydrogen pressure is released, a box is opened at the upper end of the reactor, and the upper flange is removed. Then, three bolts are unscrewed at the lower flange, a stud is inserted into one of the mounting holes, nuts are screwed onto both ends of it. Next, a receiving vessel (a glass jar 3 l) is substituted under the lower end of the reactor so that the flange enters the neck of the vessel. The fourth bolt is unscrewed, and the flange gently slides down. Removal of solid phase product powder is intensified by tapping a metal object against the reactor. The remains of the powder of the solid phase product are removed with a brush. Upon completion of unloading, the lower flange is put in place, the box is closed and put on purge with gaseous nitrogen evaporating from the Dewar vessel.

III. The discussion of the results

The results obtained are displayed on a personal computer monitor and represent a system of graphs with pronounced maxima. Each curve corresponds to a certain measuring thermocouple, the maximum of the curve indicates the passage of the reaction front through the junction of this thermocouple.

As can be seen from the figure, as a result of the exothermic effect of the reaction, the temperature in the reaction zone rises to ~280˚C. The next task is to reduce the temperature of the maximum, since an increase in temperature can lead to decomposition of the resulting silane and a decrease in its yield.

The synthesis process is interrupted when the reaction front passes through the zone of the sixth thermocouple, since the continuation of the synthesis process can lead to a breakthrough of unreacted silicon tetrafluoride through the reactor.

IV. List of sources used

Myshlyaeva, L.V., Krasnoshchekov, V.V. Analytical chemistry of silicon. – M.: Nauka, 1972. – 210p.

Bezrukov, V.V., Guryanov, M.A., Kovalev, I.D., Ovchinnikov, D.K. Determination of gas-forming impurities in high-purity silicon using a tandem laser mass reflectron // High-purity substances and materials. Obtaining, analysis, application: Proceedings. report XII Conf., Nizhny Novgorod, May 31 - June 3, 2004 / Ed. ak. G.G. Ninth, corr. M.F. Churbanova. - Nizhny Novgorod: Publisher Yu.A. Nikolaev, 2004. - 368s.

Zhigach, A.F., Stasinevich, D.S. Chemistry of hydrides. - L .: Chemistry, Leningrad branch, 1969. - 676 ​​p., With hell.

Ishikawa, N., Kobayashi, E. Fluor. Chemistry and application / Per. from Japanese M.V. Pospelova / Ed. A.V. Fokin. - M.: Mir, 1982. - 280s.

Rapoport, F.M., Ilyinskaya, A.A. Laboratory methods for obtaining pure gases. – M.: Goshimizdat, 1963. – 420p.

Bulanov, A.D., Troshin, O.Yu., Balabanov, V.V., Moiseev, A.N. Synthesis and deep purification of monoisotopic silane // High-purity substances and materials. Obtaining, analysis, application: Proceedings. report XII Conf., Nizhny Novgorod, May 31 - June 3, 2004 / Ed. ak. G.G. Ninth, corr. M.F. Churbanova. - Nizhny Novgorod: Publisher Yu.A. Nikolaev, 2004. - 368s.

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Silica- a colorless crystalline substance with high strength and hardness. Formula SiO2.

Properties:

• melting point 1713 – 1728 °C
• interacts with basic oxides and alkalis (when heated)
• belongs to the group of acidic oxides
• soluble in hydrofluoric acid
• is a glass-forming oxide (it tends to form a supercooled melt - glass)
• dielectric (electronic current does not conduct)
• does not react with water
• durable

Application:

• production of glass, concrete products, ceramics, silica refractories, silicon, rubber, etc.
• electronics, radio electronics, ultrasonic devices
• amorphous non-porous silicon dioxide is used in Food Industry(E551), pharmaceutical and parapharmaceutical industries.
• fiber optic cables

Obtaining silicon dioxide

You will need:

• liquid glass (sodium silicate);
• acid (sulfuric, hydrochloric or nitric);
• water;
• soda.

Pour sodium silicate into a glass and add acid.

When the acid is added, a precipitate of silicon dioxide immediately begins to form. Acid is added until a sufficient amount of silicon dioxide is formed.

In another glass, we dilute a 5% soda solution and place the resulting precipitate there. Thus, we will get rid of the rest of the acid.
After, the silicon dioxide must be rinsed several times with clean water to get rid of the soda residue.

After washing, filter the precipitate through a paper filter.

magnesium silicide- inorganic binary compound of magnesium and silicon. Formula Mg2Si.

Properties:

• thermally stable
• melting point 1102 °C
• molar mass 76.7 g/mol
• density 1.988 g/cm3
• hydrolyzed by water
• decompose in acids

Application:

• silane gas production

Obtaining magnesium silicide

You will need:

• silica;
• magnesium (proshkoobrazny).

Grind silicon dioxide in a mortar.

We mix 4 g of silicon dioxide and 6 g of magnesium. If you have black magnesium powder, then you need to grind it in a mortar with silicon dioxide.

Pour the mixture into a test tube fixed on a tripod and heat it with a gas burner.
Important! All components must be well dried before heating! If even a small amount of moisture is present in the mixture, then selane will begin to be released during the reaction, which will subsequently ignite.

Under influence high temperature Magnesium silicide (a dark-colored substance) begins to form in the test tube.

Separate the parts of the tube from the powder.

Silane- pyrophoric gas. Formula SiH4.

Properties:

• molar mass 32.12 g/mol
• gaseous state
• colorless
• poisonous
• ignites on contact with air
• easily oxidized
• stable in neutral and acid environment
• dissolves in gasoline, standard
• density 0.001342 g/cm3
• melting point - 185 °C
• boiling point - 112 °C
• decomposition temperature 500 °C

Application:

• in reactions organic synthesis(obtaining valuable organosilicon polymers, etc.)
• microelectronics
• production of ultrapure polysilicon
• relationship between organic matrix and inorganic filler in composite dental materials