Ethyl Silicate Binder Research Articles

ВЗАИМОДЕЙСТВИЕ ХИМИЧЕСКИ АКТИВНЫХ РАСПЛАВОВ С МАТЕРИАЛАМИ КЕРАМИЧЕСКИХ ФОРМ В ВАКУУМЕ

To obtain precise castings from chemically active melts, a special method of precision cas¬ting according to removable models is traditionally used, consisting in the manufacture of ceramic molds on an ethyl silicate binder and further filling with melt in vacuum. At the same time, when forming castings of a responsible purpose by pouring titanium and heat-resistant nickel alloys in a vacuum, the current technology causes a high defect due to the identification of various surface casting defects that are unacceptable when working parts under the action of repeatedly repeated temperature changes and alternating mechanical loads. The analysis showed that the main reason for this defect is the lack of thermochemical resistance of ceramic corundum molds on an ethyl silicate binder to interaction with poured titanium and heat-resistant nickel al-loys in vacuum. The possibility of obtaining high-quality castings from chemically active alloys is reduced to the use as a binder of ceramic forms of materials that are resistant to thermal dissociation in vacuum at heating temperatures of 1913–1973 K. For this purpose, it is proposed to use a silica-free binder – an aqueous solution of aluminum phosphate concentrate. The composition of the mold made according to the proposed technology, in which there is no silica, excluded the harmful effect of oxidation processes in vacuum on the quality of castings from chemically active alloys. Ceramic electrocorundum molds based on aluminum phosphate concentrate are resistant to thermal dissociation and interaction with chemically active metals poured in vacuum. This will reduce defects in non-metallic inclusions and improve the quality of precision castings made of titanium and heat-resistant nickel alloys.

Manufacture of Ceramic Molds and Cores from Inorganic Materials Using Permanent

The paper describes the technology for the manufacture of ceramic molds and cores from inorganic materials using permanent masters. A technique for reinforcing molds and cores using ceramic tubes is proposed. The effect of pulse currents of different power on the slurry has been studied. In the experimental part, the performed experiments and the data obtained are described. In contrast to the conventional Show-process based on ethyl silicate binder (basic option), the technology developed for the manufacture of ceramic molds from inorganic materials ensures improving the quality and economic and environmental efficiency of investment castings. The quality improvement is determined by improved physical and mechanical characteristics of ceramic molds and the stable ceramic cracking. The improvement in environmental indicators is ensured by using safe inorganic molding materials and eliminating the solvent burning. Improving economic indicators is determined by reducing power consumption for calcining ceramic molds, casting defects, and molding material costs. Thus, the technology developed allows improving the quality of investment castings manufactured for the country’s oil and gas complex.

Producing alumosilicate heat insulation components with ethyl silicate binder

The company has developed a technology for making alumosilicate heat insulating components (lightweight) with ethyl silicate binder. Industrial tests have been performed and regular production has been initiated.

Effect of the type and quality of antioxidant additions on properties of materials of the system Al2O3-SiC-C

Results are presented for a study of the apparent density and ultimate strength in compression of developed materials of the system Al2O3-SiC-C, modified by introduction of phosphate addition and complex antioxidant (Al + Si + phosphate addition). It is established that introduction of a phosphate addition together with a complex antioxidant (Al + Si) to the composition of corundum-graphite SiC-containing refractory based on an ethyl silicate binder leads to compaction of the structure and formation of materials of prescribed phase composition with increased oxidation resistance.

Properties of materials of the system Al2O3-SiC-C after firing in a reducing atmosphere

A set of studies is presented for the physicomechanical properties of corundum-graphite carbide-containing refractories. The efficiency of introducing silicon carbide as an antioxidant addition to Al2O3-SiC2-C-materials is established. The structure and phase composition of corundum-graphite silicon carbide-containing refractories based on an ethyl silicate binder fired in a reducing atmosphere are studied.

Burning-out process of ceramic moulds

Burning-out is an important step in mould fabrication for the ceramic mould casting process to remove alcohol in the gelled ethyl silicate binder. It affects both the accuracy and stability of the ceramic mould dimensions. In this paper, results are described for length changes of ceramic mould specimens during the burning-out process after alcohol immersion or drying in air for various lengths of time. It is shown that preventing rapid evaporation/removal of alcohol from the ceramic mould specimen before burning-out by immersing the specimen in alcohol generally produces less overall length change compared to leaving the specimen to dry in air. The immersion time for the specimen in alcohol or drying in air before burning-out has a significant effect on the overall length changes in the specimen and on the characteristics of the burning-out curves. Under the conditions investigated, immersing in alcohol for 5–10 h followed by burning-out produced near zero overall length change in the specimen.

Silicon Nitride Ceramics Prepared by Vibratory Casting of Self-Reinforced Mixtures: Testing for Crack Resistance

Technological factors capable of influencing the structure, physicomechanical properties, and crack resistance of silicon nitride ceramics intended for fabrication of component of complex shape are considered. The effect of a composite sintering aid Al2O3 + Y2O3 and an ethyl silicate binder on strength and crack resistance of raw and sintered ceramics subjected to hydrostatic compression is discussed. It is shown that the ceramics in question can be tested for crack resistance by the indentation method.

A new direction in the creation of ceramic materials with a specified composition and structure. Part 1. Manufacturing binders for the ceramic industry by the solgel method. 5. Preparation and physicochemical properties of ethylsilicate binders for ceramic and refractory production

Compositions and methods for preparing various ethylsilicate binders for the production of ceramics and refractories are presented. The physicochemical features of the transformations of the created binders recommended for cast and pressed articles, unshaped mixtures, and coats and adhesives are considered. It is shown that for each filler and design of the material the binder should be chosen so as to provide the specified phase composition and structure

A new direction in the creation of ceramic materials with a specified phase composition and structure. Part I. Preparation of binders for ceramic production by the sol-gel method. 3. Hydrolysis and gel formation in ethylsilicate binders without organic solvents

Results of a physicochemical study of hydrolysis and gel formation in ethylsilicate binders without organic solvents are presented. The effects of the kind and amount of acid catalyst and the proportion of water to ethylsilicate on the thermal effect of the hydrolysis reaction, the sol-gel transformation, and the properties of the binder are investigated. IR spectra of gels of hydrolysates prepared by rapid and slow hydrolysis are presented. The technological aspects of production of binders are considered.

A new direction in the creation of ceramic materials with a specified phase composition and structure. Part I. Preparation of binders for ceramics production by the sol-gel method. 2. Preparation of ethylsilicate binders and their modification1

The problem of obtaining ethylsilicate binders by hydrolysis of ethylsilicate in an acid medium with various amounts of water is considered. The difference in the polycondensation of different hydrolysis products is discussed. It is suggested that the silica binder be carbonized by introducing a water-soluble substance into the hydrolyzate.

1. Physicochemical aspects of the choice of silicon-bearing binders for production of refractories

The principles for selecting a silicon-bearing binder for refractory production are considered. The effect of the heat treatment temperature on the crystallization of SiO2 gels with various prehistories is considered. It is shown that ethyl silicate binders have an advantage over other silicon-bearing binders that consists in that SiO2 gel obtained from ethyl silicate eTS-32 can retain the amorphous state upon heating to over 1273 K.

Physicochemical aspects of graphite protection from oxidation in heat treatment of mixtures on ethyl silicate binder

Results of a study of the physicochemical processes that occur in heat treatment of graphite — ethyl silicate binder mixtures are presented. Diffusion “bridges” in plane 0001 of graphite between the latter and SiO2 gel confirm diffusion matching of the ≡ Si — O — Si ≡ and ≡ C — C ≡ bonds in heat treatment of the mixtures at 1223 K with the formation of β-SiC, which diminishes the oxidation of graphite.

Increase in cast density in production of silicon nitride articles of irregular shape

The effect of modifying organic additives on the tenacity of ethyl silicate binders and the strength of castings based on Si2N3 ultradisperse powder is studied. The effect of the modified Si3N4 powder together with the combined sol-gel composition on the density and strength of the castings is demonstrated.

Self-hardening coatings for protection of graphite products from oxidation

Results of testing coatings for silicided graphite that are based on a self-hardening mixture (Al2O3 powder modified with silicon alkoxide and ethyl silicate binder) are presented. The dense intermediate layer created, reinforced with mullite and SiC inclusions that resulted from mechanochemical reactions and firing, is shown to provide high resistance to oxidation for graphite up to 2003 K.

Synthesis of β-SiC and α-Si3N4 whiskers by the sol-gel process

A study is reported on a synthesis of α-Si3N4 whiskers from a modified ethyl silicate binder. It is noted that crystal growth induces thermal stresses. it is confirmed that such crystals are formed by a dislocation diffusion mechanism.

Physicochemical processes accompanying the heating of pitch and pitch—ethyl silicate mixtures

The problem of intensification of the synthesis of silicon carbide from pitch—ethyl silicate mixtures is considered. The physicochemical processes occurring in mixtures of pitch with nonhydrolyzed ethyl silicate and ethylsilicate binder thermally treated in air were studied by methods of differential thermal analysis and x-ray diffraction. The onset of SiC synthesis was observed at 1273 K. The yield of SiC increased upon formation of a silicon melt providing the maximum area of contact between carbon particles and ultradisperse silica. A self-organization takes place in the system that favors the formation of a layered material with SiC occurring predominantly in the form of whiskers.

The application of electrochemical measurements to the study and behaviour of zinc-rich coatings

Three zinc-rich coatings, two with polyamide cured epoxy binders and one with an ethyl silicate binder applied to grit blasted mild steel were chosen for examination. The two epoxy coatings differed in terms of their particle size distribution, but were similar in all other respects. The silicate system was chosen to be very similar to one of the epoxy systems except for the chemical nature of the binder. Techniques chosen to study these coatings included impedance, potential vs time for a fully coated and partially coated system, exterior exposure under marine conditions and SEM on film sections during exposure. The electrochemical response of each system was found to be highly dependent on the particle size distribution of the zinc rich pigment. Where pigment particles were comparable in size with the film thickness, the electrochemical behaviour could be modelled in terms of simple charge transfer processes. With smaller zinc particles, a diffuse time constant model is more appropriate. In the silicate system, a porous silicate layer is formed above the zinc-rich layer and the electrochemical response is determined by the nature of this porous layer.

スラリーキャスティングによる多孔質焼結体の製造 ＩＩ 静電植毛を利用した表面多孔質材の開発

Porous metal which has one directional porosity perpendicular to the surface, can be produced by the combination of slurry casting and fiber planting. First, fine short metal fiber is planted on the surface by electrostatic fiber planting, i.e.flocking and secondly metal powder slurry including ethyl silicate binder is casted on the fiber planted surface. At the subsequent sintering, metal powder is melted and infiltrated into metal powder matrix, which yieds long and one directional pores. Here, Cu fiber and Fe powder are used and electric coinductive vacuum chuck for grinding was experimentally producted.

Effects of tetraethyl orthosilicate binder on the characteristics of AN SnO 2 ceramic-type semiconductor gas sensor

As part of the research to improve the long-term stability of sintered SnO 2 semiconductor gas sensors, we examined the effect of the degree of polymerization (referred to as DP) of ethyl silicate binders added to the sensors on their characteristics. DPs in the range one to four were investigated. By using a binder with a large DP gas sensibility is increased and the sensor resistance is decreased. Humidity dependency and long-term stability are improved by using a binder with a smaller DP. A binder whose DP is more than 2.0 is needed in order to obtain the necessary mechanical strength of the sensor. We concluded that the binder's DP should be 2.5 for the sensor to be stable during long-term operation. Through measurements of H 2 oxidation activity and temperature-programmed desorption for H 2O and O 2, we concluded that the long-term change in the sensor sensitivity is based on the change in its catalytic activity caused by the increase or decrease of the amount of the hydroxyls on its surface.

Some features of the production of thermal-shock-resistant cast corundum materials in ethyl silicate binders

The use of ethyl silicate binders of an optimal composition makes it possible to produce cast corundum articles with a mullite-corundum binder with excellent characteristics. The best combination of properties is found in the articles when binders of optimal composition, close to stoichiometric, are used in the hydrolysis reaction of the ethyl silicate. The destruction and sintering processes in the corundum casts in an ethyl silicate binder during heat treatment are produced by the destruction kinetics of the hydrolysis products of the ethyl silicate and by the presence in them of active SiO2. The sintering of articles of such a composition begins at ∼ 1100°C. The excellent thermal-shock resistance of the ceramic made from masses with ethyl silicate binders and the slower destruction of these ceramics result from the rational phase composition and structure of the material.