SHS is known as a fast and potentially economical process for materials synthesis due to the self-propagation of exothermic synthesis reaction. If some of industrial wastes could be recycled to useful materials by SHS, the cost effective processes can be developed. We are investigating to develop such processes for silicon sludge produced in semiconductor industries and for aluminum dross in aluminum foundries both to sialon based ceramics by using nitriding combustion of SHS. These ceramics can be used for refractories, abrasives, and wear resistant materials. More than 60% of silicon single crystals used for production of silicon wafers in semiconductor industry is scrapped during the process of cutting and polishing. This silicon sludge contains alumina and zircon particles for polishing agents, and iron oxide and calcia used to deposite in the sewage process. Though the silicon sludge is used for a material of cement or reclamation land, if it is left outside, a serious environmental problem may occur because it changes to fine particles when dries and scatters in the wind. Silicon powders burns with pressurized nitrogen and convert to silicon nitride ceramic powders. Due to the low content of silicon in the silicon sludge, some combustion agents such as reclaimed silicon and aluminum powders were blended as much as 30wt.%. The nitriding combustion could be sustained at 1MPa of nitrogen pressure. The product consisted of mainly sialon ceramics with zirconia and iron silicide phases. The sintered product showed the flexural strength of 150 MPa. The iron oxide and calcia in the silicon waste were easily leached out with HCl solution. In this case, the combustion synthesis took place at 4 MPa nitrogen pressure. The product consisted of sialon and zirconia phases. The sintered body showed the flexural strength of 270MPa and a good oxidation resistance at 1200⁰С. The problem of the aluminum dross is an emergent issue because of gas generation with ammonia, methane and chlorine. It contains much aluminum nitride and alumina. This aluminum dross could be burned with the combustion agent of reclaimed silicon in an 1MPa nitrogen pressure and converted to sialon.
 
 

O-5-02: Treatment and Recycling of Zinc Hydrometallurgical

O-5-03: SHS of Mineral-Like Ceramics for Consolidation of Radioactive Wastes

In general, the perovskite synthesis can be presented by the following scheme:

where the oxidizer is Ca (NO₃)₂ and / or Fe₂O₃. The regulating additives as oxides of Al, Si, Zr, Ti were entered also in the initial green mixture.

Optimum composition of green mixture and main parameters of consolidation were determined for reception of ceramics with the given structure and properties. Samples with dense structure in general consisted of perovskite phase with a pseudo-cubic type of a crystal lattice are obtained as a result. Tests of the obtained samples for its mechanical and chemical stability have shown, that they have good mechanical stability on compression (not less than 300MPa) and stability to leaching of Cs and Sr ions into distilled water (R_n^Sr = 1.0 10^-7 g/sm² day, R_n^Cs = 2.5 10^-7g/sm²day, 20^oC, 14 days).

It was shown, that under optimum conditions of burning, Sr and Cs ions are allocated proportionally on the all volume of a sample, and there are no losses of these elements at synthesis.
 
 

O-5-04: SHS of Matrix Materials for Immobilization of PuO₂

and Other Radionuclides

A.N. Avramchik¹, V.G. Balahonov², A.N. Katushonok², V.D.,Kitler¹

Referense:

1. Patent 2065216 RF, MPK6 G21F 9/16.
 
 

O-5-05: Ceramic SHS Filters with Graded Porosity and Pore Size

I.P. Borovinskaya, A.G. Merzhanov, V.I. Uvarov

By using SHS technique, a number of unique porous structures can be produced. Due to low coefficient of pore tortuosity (characteristic for these materials), efficiency of gas and liquid ultrafiltration through the surface unit remarkably increases. SHS method is also advantageous due to possibility of one-step production of a graded filter (selective layer strongly adhering with the substrate).

Dependence of the SHS product porosity on that of the initial green mixture pellets at varying particle size of nonmelting green mixture component was studied. Optimum green mixture compositions for producing porous structures which can be used as a membrane selective layer and a strong substrate were found.

The data given in the table below prove that the characteristics of SHS filters are similar to those for the best ceramic filters.
 
 

Characteristics of SHS membrane filters compared with those of conventionally produced filters
 

Company	MilliporeU.S.A.	Sartorius Germany	Seitz, Germany	Whatman U.K.	Mendeleev Chem. Tech University  Russia	ISMAN Russia
pore size,m m	0.22	0.45	0.2	0.19	0.5	0.1-0.5
D P mm H2O	160	100	125	184	250	100
g	0.033	0.053	0.048	0.028	0.012	0.06

where g is a filtration parameter depending only on the filter structure at filtration rate of 1cm/s.
 
 

Application of a block containing SHS filters for purification of drinking water proved that they are characterized by

- extremely low background of molecular-ion contaminations,

- high water consumption (2-10 l/cm²h at the pressure differential on the filter of 0.1 MPa),

- high gas consumption (35-40 l/cm²h at the pressure on the filter of 2 kPa),

- efficient purifying ability of drinking water from contaminations (Fe, Mn, Ba, Ce, Zn, Cu, Pb, U, etc.),

- ability to decrease content of dissolved carbon as well as acetone, atrazine, semizine, 2,4-dichlorphenoxyacetic acid, toluene, phenol, dibromchloromethane, tetrachloromethane, thrichloromethane, tetrachlorophenol, etc.
 
 

O-5-06: Production and Use of SHS Ceramic Filters

In the work the investigations of SHS technology of filtering materials with the use of natural minerals, i.e. ilmenite and quartz, as the initial components are being continued. The material production was carried out according to the SH synthesis scheme, combined with stage of recovering of starting oxides by aluminum, silicon and carbon where the end products are porous composite ceramics, consisting of Al oxide 40-60 mass.% and the spectrum of complex silicide, carbide, intermetallic compounds Ti, Fe and other metals.

The combustion mechanisms, formation of phase composition and material structure, depending on composition and structural parameters of the initial charge were investigated.

New data on chemical and strength properties of synthesis products were obtained.

The results of filtering materials in laboratory and industrial devices for drinking water purification are presented.
 
 

O-5-07: A New Material for the Radiation Protection

A.N. Pityulin, I.P. Borovinskaya

A group of samples was produced that passed detailed tests in various organizations. The following results were obtained:

– when the samples were treated with rays up to fluences of 4ґ 10²⁰ neutron/cm² at E > 0,1 MeV and temperature in the center of 800⁰C, one watches a slight decrease in bending strength. However, the material density and porosity are unchangeable. There is also no gassing, breaks and deformation.

– vibration-survival test, resistance to seismic impulse and portability demonstrated that abrasion, coloring, increase in cracks and decrease in sample mass were not exhibited. Portability of the samples is allowed with all means of transport provided that there are no longitudinal impacts above 40 g and side impacts above 70g at impulse duration up to 40 m s.

– Heating of samples in helium medium up to 600⁰C for 1000 hr demonstrated that long-term contact of the steel shell with TiB – B – Ni material results in alteration of the content and properties neither the material of biological shielding nor steel, as well as it does not influence the strength of adhesion between the material and the steel shell.

The conclusion is that the produced material can find application for biological shielding up to fluences of 4ґ 10²⁰ neutron/cm² at E > 0,1 MeV. Basis for the material operation under the harder radiation needs some additional research.
 
 

O-5-08: The Self-Propagating Degradation of Chloro-organic Compounds:

We report on the highly exothermic solid state reaction between hexachlorobenzene and calcium hydride. We showed the possibility to ignite compacted mixtures of the reactants through the use of a thermal spike. The self-sustaining character of the reaction was proven. The combustion wave was found to propagate at a rate between about 0.5 – 1.0 cm/s. A combustion composition range was established extending from a CaH₂/C₆Cl₆ molar ratio of 3 to 18. It was also found that the temperature of the combustion front approaches the adiabatic temperature of the reaction which, in the stoichiometric interval, ranges between about 2900-2550 K. These high temperatures ensure a complete breakdown of the aromatic molecule and of undesired chloro-organic congeners, only inorganic halide salts being found among the end-products.

Combustive-like reactions also observed when reactant powders were subjected to intensive mechanical treatment by ball milling. The combustive range of mechanically driven processes falls within the one found in the true self-sustaining regime even if the activation and the extinction of the reaction were ruled by completely different mechanisms. A neat correlation was worked out relating the temperatures at the combustion front to the total heat evolved in the reaction carried out in the mechanochemical mode. The same end-products were also found. It suggests that the same chemistry determines the transformation paths.

The practical exploitation of a self-sustaining methodology for the disposal of hazardous organochlorine compounds seems feasible.