THE PHYSICAL-CHEMICAL CHARACTERISATION OF COMPOUNDS BASED ON SILICON WITH ALUMINIUM CHLORIDE USING SULPHUR, DERIVED USING THE MOLECULAR STRATIFICATION METHOD

Zh.S.Yessenamanova, T.K.Ahmedzhanov, M.S. Yessenamanova,

C.C.Nurkeev , B.M.Nuranbaeva

K. I. Satpayev Kazakh National Technical University, Almaty

Kh.Dosmukhamedov Atyrau State University, Atyrau

Thesis

This work considers the possibility of deriving nanostructure and sulphurous compounds using an electrophilic reagent, aluminium chloride, using sulphur by the molecular stratification method.

Molecular stratification technology makes it possible to derive active centres of nanostructures of chlorides chemically bound to transitional d-elements on the surface of amorphous silicon.

1. Introduction. One of the new chemical nano-technological processes which is well known both in Russia and abroad, based on the carrying out of chemical reactions on the surface of various solid phase matrices is the molecular stratification method (MS) [1-3] which has been named in the work of foreign authors by the not totally adequate name of atomic layer epitaxy (ALE), and atomic layer deposition (ALD).

Based on the chemical assembly of nano-structures on the surface of solid bodies using the molecular stratification method (MS) is the idea, developed by the school of head correspondent of the Russian Academy of Sciences, V. B. Aleskovskii [1] in the field of chemical supramolecular bonding. In the fifties and sixties, based on the ‘spanning hypothesis’ of V. B. Aleskovskii and his students [1], a precision chemical method of synthesis of solids was developed which was given the general name of ‘chemical assembly method’.

The transformation of supra-molecular substances by means of the interaction of functional groups laid the foundation for the forming of the precision method of synthesis of solid materials – the molecular stratification method. The principles of the MS method were the first to be proposed by him together with S. I. Kolstov at the beginning of the sixties [2]. In ensuing publications (between the sixties and the eighties) a more in-depth consideration of the chemical basis for the new method of synthesis of solids was shown by authors and their students such as A. N. Volkovii, R. R. Rachkovskii, V. M. Smirnov, A. A. Maligin and others [3].

The basic idea of the MS method which is used for the precision synthesis of solid bodies with a regular construction is the sequential building up of single layer structures of the said chemical composition on the surface of solid phase matrices.

The outline of the process of the chemical assembly of nano-structures on the surface of solid bodies using the MS method, as well as the analysis of existing experimental data, confirms the fact that the MS method can be used to synthesise nanostructures with various chemical compositions (mono layer, including multi-component) on the surface of solid phase matrices, as well as to carry out atomic chemical assembly on the surface of nano-, micro- and macro- structures by means of multiple alternation of chemical reactions of the said programme. It should be noted that the MS method guarantees the formation of layers on the surface of solid to an accuracy of within one single molecular layer.

At the present time, a significant number of chemical transformations using centres on the surface of silicon have been carried out. As a result of chemical modification it has been possible to form new practically important, high specification adsorbents, selective catalysts, active polymer fillers and efficient viscosifiers for dispersants.

Very frequently one type of chemical reaction using particular centres of surfaces is carried out in totally different conditions. This can be related to the particularities of the electrical and geometric construction of the modifying agents present in the reaction volume of electron and proton molecules, and the gradual reduction and hydroxylation of the surface of the original silicon, diffusion and other factors.

It has been shown that all chlorides, with the exception of CCl₄, when heated to a temperature of about 180^oC, begin a condensation reaction with polysilic acid, in the process losing at least one chlorine atom [3].

Molecular stratification is known as one of the synthesis methods for solids by means of assembly on a matrix of structural units. By this means it is possible to derive multi-zone solids, regulating the order of the layers which are placed, as well as the thickness of the layer to one monolayer that is within the achievable accuracy.

Among the reactions which have been already studied, with the participation of functional groups on the surface of silicons, it has been possible to separate out neutrophylic and electrophylic displacement (S_N, S_E), neutrophylic and electrophylic bonding (Ad_N, Ad_E, Ad_N,E), as well as elimination processes (E) [3].

Possible types of heterolytic transformation with the participation of centres on the surface of the original silicon can be shown by the diagram in figure 1 [3].

Figure 1 – A diagram of the heterolytic transformation using centres on the surface of the silicon.

First of all, it is possible to separate a large group of reactions, in which the attack is made by electrophylic agents on oxygen atoms with a silanol group surface structure. This is a reaction of electrophylic displacement of a proton with the interaction of various chlorine and alkoxysilane, organosilazanes and other elementary organic compounds, for example isocyanates [4].

For the reaction of electrophylic displacement of a proton on silanol group surfaces it is postulated that four-centred transitional compounds are formed. In this case, the degree of nucleophylic action on the part of the one being substituted out (X) is very important. The depth of such interaction must be determined by the proton acceptor composition X [4].

The synthesis of multi-component mono-layer oxides can be carried out as follows [6]:

- The sequential treatment of matrices with chloride gases;

- The substitution on the surface of elements of the oxochloride group in reaction with chlorides of another chemical nature;

- The treatment of the substrate mixture of chlorides with other elements;

In the literature, a description is given of a significant number of processes for inorganic sulphurous compounds from solutions. In order to regulate the composition of the materials which are derived from the sulphurous liquids, modifying agents are used, in the form of various organic and inorganic compounds. The use of modifying agents is one of the best known methods of managing the production of sulphurous construction materials.

In the production of sulphur containing materials in the form of fillers for a wide range of uses, various silicon modifiers are used: sand (a-quartz) and rich specific surfaces of amorphous silicon (silicon gel, aerosil). In the literature of the USSR, the technology for deriving compounds using vibration with preloading, analogous with factory technologies for cement concrete [5] has been developed. The filler is mixed with ground sulphur, and then formation is carried out, using vibration under conditions of pre-loading of 50-500g/cm², after which the product is heated for 1-3 hours. The solidity achieved under pressure using a granite filler and ground quartz sand is 50-80MPa [5].

As follows from above, the range of contemporary sulphur compounds based on low molecular crystallised and polymerous sulphur is significant, and of various quality and purpose. In all publications shown the technological processes and the composition of the materials derived are shown. However, there is a practical lack of information on the mechanism of the interaction of components in these processes and there is no information on the chemistry of the processes. The ecological aspects of such have also not been considered. Meanwhile, it is well-known that the heating of sulphurous compounds to temperatures of melting always lead to the formation of sulphur dioxides. The sublimation of sulphur takes place at a temperature of 7^oC and its oxidisation begins at a temperature of around 100 ^oC.

An analysis of literature sources shows that the majority of research has been dedicated to the study of the influence of modifying additives on the composition of the sulphurous compounds, including sulphur, fillers and aggregates and very little work has been done on the study of the composition sulphur in the presence of various active agents. This makes it difficult to make an informed choice of the most effective modifiers in each specific instance. Thereby, research into the influence of various modifiers on the composition of derivatives and the stud of ecological aspects of processes involving non-organic sulphides and materials is a pressing task.

2. Results of molecular chemical calculations.

In order to explain the possibility of deriving nano-structures on the surface of silicon gel with modification using aluminium chloride, molecular chemical research was first carried out.

An important pre-condition for successful molecular chemical research is the correct choice of a calculation method, first of all the means of calculation of electronic correlation and the foundation used. The first test which various molecular chemical methods undergo is the accuracy of the communication of the character of the energy change in the event of the disruption of links between various molecules. The second is the determination of the accuracy of the transmission of geometric structures. The results of the tests and their comparison with experimental evaluations are shown in Table 1.

Table 1. Dissociation energy (D) and length of connections (r) of various compounds

Compound	Data from literature		Calculated data in RMZ		Calculated data in B3LYP/6-31G(d)		Calculated data in Priroda
	g, PM	D, kJ/mole	g, PM	D, kJ/mole	g, PM	D, kJ/mole	g, PM	D, kJ/mole
S2	188.9	412, 14+-2.54 05.85+-21	185.3	439.32	192.7	400.64	193.2	467.48
SH	134.1	340.6+-12	129.7	331.79	135.5	341.5	136.1	363.63
SO	148.09+-0.00001	516.20+-0.13516.72	145.8	469.03	151.2	487.56	152.4	566.93
SiS	192.93	619+-12.6	179.1	581.99	195.17	572.29	196.3	614.55
Si2	225.2	309.6+-21 288.7+-21	182.2	307.94	217.14	283.47	218.0	324.47
SiH	152.1	309.6+-25	195.5	270.7	153.9	197.82	155.1	297.06
SiO	150.9	803.24+-21.34	146.6	808.77	152.4	751.45	154.0	803.24
AlCl	212.98	482.79+-7.12	204.9	374.89	211.04	441.22	212.19	496.13

*Molecular permanent inorganic compounds: Reference book by K. S. Krasnov, N. V. Philipenko, V. A. Bokova, et al., one of the official journals of chemistry of K.S. Krasnov, Chemistryh 1979, page 448.

The thermodynamic character of the compound which we have determined shows that the calculation which gives the nearest value to the experimental value is the calculation of the Priroda programme (3z.bas) and B3LYP 6-31G(d).

According to the results of bonding, the formation of one or two sulphur atoms is much more long-lasting. Further, with an increase in the sulphur atoms in the chain, the energy of bonds (Si—S, O—S) is reduced and stabilises. More stable bonds are formed by the joining of sulphur to silicon atoms (substitution of hydroxyl group).

Priroda makes it possible to reliably evaluate the mechanism for the bonding in the sulphur system ie silica gel. This depends on the quality of the method and basis of the programme, taking into account the d-orbit of atoms. Reactions involving functional groups on the surface of silica gel, can be divided into those with nucleophyilic displacement and bonding. This reaction is with the attack of a nucleophylic agent (sulphur radicals) and nucleophylic displacement of OH^- groups or nucleophylic bonding (introduction of oxygen.

Reactions of bonding of sulphur to silicon atoms with the displacement of OH groups occur endothermically (104.14 kJ/mol). In the transitional stage Si–O bonds are lengthen to 236.5 pm, and O–S and Si–S bonds shrink to 227.7 pm and 229.5 pm, accordingly. The activation energy for nucleophylic displacement is 120.16 kJ/mol. Reactions for the introduction of diatomic sulphur (singlets) to oxygen atoms take place endothermically (9.21 kJ/mol). In the transitional stage the O–H bonds lengthen to 123.8 pm, and the O–S and S–H shrink to 188.7 and 176.0 pm accordingly. The activation energy is equivalent to 139.56 kJ/mol. The introduction of sulphur triplets takes place endothermically (143.13 kJ/mol). The activation energy is equivalent toа 169.95 kJ/mol. The process of bonding of diatomic sulphur (triplets) to silicon atoms with the displacement of the OH group takes place endothermically (266.96 kJ/mol). In the transitional stage the Si–O bonds lengthen to 224.9 pm, and the Si–S bonds shorten to 224.0 pm. The activation energy for nucleophylic displacement is 264.39 kJ/mol.

Thermodynamic benefits, from the point of view of activation energy and more stable bonding are generated in the reaction of the introduction of oxygen radicals of sulphur in the singlet form (Е_акт=134.82 kJ/mol), as well as the introduction of sulphur radicals in the singlet form to the silicon atom (Е_акт=146.35 kJ/mol). The products of these reactions form stable valent bonds of sulphur with oxygen atoms (282.8 kJ/mol) and atoms of silicon (309.9 kJ/mol), determining the formation of other sulphurous compounds.

The modification of silica gel by aluminium chloride facilitates an increase in the active centres on the surface of the silica geland the forming of sulphurous rings.

3. Experimental results.

Laboratory tests to derive sulphurous compound specimens based on silica gel, sulphur and aluminium chloride were carried out in order to confirm the theoretical quantum-chemical estimates. The strengthening of the behaviour of the derived compounds, has been verified by a hydraulic laboratory using a PGL-5 press, as shown in figure 2.

The preparation of specimens of sulphurous compounds using aluminium chloride was carried out in two stages. Firstly, the silica gel was modified using aluminium chloride mixed with reagents with heating to a temperature of 200 – 500^оС, then the modified silica gel was introduced to liquid sulphur. As can be seen from the figure, the dependency of solidity of the sample on the amount of modifying reagent AlCl₃ is very high. The specimen, after preliminary ignition at 500⁰С and with an aluminium chloride content of 5% mass has the optimal value of solidity under pressure. The solidity of such a sample is equal to 70 МPа.

Figure 2. The dependence of the solidity on the pressure of the formation of sulphurous sompounds from aluminium chloride containing compounds with a correlation of 1:1 or 1:1,5 at a temperature of initial thermal treatment of 500 ^оС.

Table 1 shows the results of the physical-mechanical testing of compounds, derived under optimal conditions, containing aluminium chloride of 5% mass.

Table 2 The physical-mechanical and operational indices of sulphurous materials (AlCl₃ – 5% mass)

Relationship of binding to the filling mass	Temperature of the reagent in ^оС	Density of the sample, g/сm^3	Frost resistance of the cycles	Water absorption % mass	Shock resistance, МPa	Resistance coefficient
						5% HCl	5% H2SO4	5% CaCl2	5% NaCl	5% MgSO4
1:1	400	1.796	228	2.94	34	0.989	0.949	0.959	0.977	0.963
1:1.5	400	1.684	188	4.06	21	0.928	0.920	0.928	0.933	0.929
1:1	500	1.804	239	2.46	48	0.966	0.957	0.964	0.979	0.965
1:1.5	500	1.811	202	3.74	23	0.924	0.924	0.931	0.936	0.933

As can be seen from the table and diagram, compounds produced by the suggested formulation with an optimal ration of components, have a high resistance coefficient to the solutions HCl, H₂SO₄, CaCl₂ , NaCl, MgSO₄, a high shock resistance (48 МPа), frost resistance (239 cycles) and density (1.804 g/cm³).

Physical-chemical research was carried out in order to explain the reasons for an improvement in the physical-mechanical behaviour of the composition of the optimal structure as a result of possible chemical interaction with the formation of silicon sulphides.

Results of IR spectroscopy are shown in Figure 3.

Figure 3. IR-spectrum of aluminium chloride (1), silica gel (2), silica gel specimens modified by 5% AlCl₃, under various thermo-treatment temperatures: 3 – 200⁰С; 4 – 500⁰С; and sulphur composition based on silica gel from 5% AlCl₃ (500⁰С) (5).

In the case of aluminium chloride modified by silica gel, triplets can be seem with an area of 2850-2950 cm^-1, which indicates the appearance of new chemical bonds in the system and the formation of active centres with temperatures raised to 400-500^oС.

4. Discussion and conclusions

The results of physical-chemical research suggest that the high physical-chemical behaviour of the compounds formed, depend on the chemical interaction of sulphur with aluminium, secured on the surface of the silica gel, as well as with oxygen and silicon itself in the form of silica gel by the donor-aceptor mechanism.

5. Bibliography:

1. V. B. Aleskovskii, The Chemistry of sub-molecular compounds: Text book, St. P: Publisher. St. Petersburg University, 1996. p.256

2. S. I. Koltsov, Chemical Construction of Solids, Lensovet Press, 1990, p.48.

3. А.А. Malygin, Chemical assemblage of materials with the set properties: The text of lections. L.: LTI, 1986. p. 51

4. А.А. Malygin, U.K. Ezhovsky, The equipment of process of chemical assemblage of materials: The manual. L.: LTI, 1987. p. 96
5. Ph.D. Minerbaeva, M.Sh. Ospanova, Building composition: the invention Description to the copyright certificate of the USSR 1265175: the opening Bulletin. Inventions. - 1986.- № 14.