Silicate Binder Research Articles

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 multiple-scattering model analysis of zinc oxide pigment for spacecraft thermal control coatings

Space assets inhabit a harsh thermal environment in which the high intensity of direct solar radiation can potentially raise temperatures to harmful levels. Thermal management is obtained through the use of radiators coated with thermal control coatings (TCCs) that diffusely reflect the sun’s high energy visible (VIS) and near infrared (NIR) radiation, while emitting infrared (IR) energy as a method of radiatively cooling. The current state-of-the-art TCC system utilizes a potassium silicate binder and zinc oxide (ZnO) pigment to maintain solar reflectance over a long exposure time. We are investigating improvements to TCCs that will have greater initial performance and significantly better end-of-life properties. We have utilized modeling techniques based upon Mie scattering to determine the theoretical scattering efficiency limits of the currently used materials. An optimized TCC would attain maximum diffuse solar reflectance at a lower film thickness and reduce the pigment volume concentration (PVC) required. These factors would contribute to a reduction in overall weight and possibly extend the durability of the system to longer time scales. Our results of modeling ZnO pigment embedded in a matrix similar to that of potassium silicate under solar irradiance conditions indicate that a narrow particle size distribution centered at 0.35 μm would provide the highest overall scattering coefficients, ranging from 0.75 μm −1 at 1000 nm to 5.0 μm −1 at 380 nm wavelengths. These results indicated that a significant improvement, 2–10 times dependent upon wavelength, in the scattering efficiency of ZnO-based TCCs can be realized by utilizing an optimized particle size distribution rather than the currently used size distribution.

Influence of zirconia raw materials on the development of DeNOx monolithic catalysts

Pd-zirconia-based monolithic catalysts were prepared with various commercial zirconia raw materials and a natural magnesium silicate binder, sepiolite, for the selective catalytic reduction (SCR) of NO with CH4 in oxygen excess. The different textural properties, metastable tetragonal zirconia phase stability, surface acidity, Pd dispersion and catalytic properties of these monoliths were compared to select the most suitable structured catalyst for NOx control in natural gas-fired power plants. The influence of operating temperature in the two reactions, NO reduction and CH4 combustion, with the monolithic catalysts was determined. A 0.4wt.% Pd-zirconia catalyst, manufactured from a sulphated zirconium hydroxide raw material, was selected as the most appropriate in the reaction under study, reaching a maximum NO conversion at 400°C.

Structural and Mechanical Properties of Silicon Carbide Mixtures Based on Boroethyl Silicate Binders

The rheologic properties of silicon carbide plastic mixtures with varying contents, in both concentration and type, of molding binders are analyzed. Ranges of binder concentrations, optimum for semi-dry pressing technology, are specified.

Solid Lubrication of Silicon Nitride with Cesium-Based Compounds: Part II — Surface Analysis

Energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) were used to characterize the wear surfaces of selected samples from Part 1 of the authors study. Results are presented for films generated on silicon nitride (Si3N4) originally coated with cesium oxytrithiotungstate (Cs2WOS3), cesium sulfate (Cs2SO4), and a hydrated cesium silicate (Cs2O·3SiO2·nH2O), all applied in a sodium silicate binder (Na2SiO3). Results show the presence of mostly Si, O, and Cs within the wear tracks of post-tested specimens. In some cases, W and S were not detected on samples that originally contained these elements, suggesting that decomposition had taken place. To simulate the reactions that might occur in a tribo-contact, mixtures of Si3N4 and Cs2WOS3 powders were heated in air to 700°C and analyzed using XPS and Bremsstrahlung-excited AES. It was found that Cs2WOS3 accelerates the formation ofSiO2 on Si3N4 under static conditions. These results support our hypothesis that high temperature chemical reactions between the cesium-containing compounds and the Si3N4 surface form a lubricious cesium silicate film. A mechanism is proposed based on the glass-modifying tendency of alkali metals and the hot-corrosion of Si3N4 Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

Influencia de distintos medios agresivos en la acción protectora de las pinturas ricas en zinc

The aim of the present work is to determine the influence that different atmospheric agents have in steel protection by zinc rich paints based on inorganic silicate binder. The presence of pollutants in the atmosphere has been simulated by periodical deposition of sulphate and/or chloride solutions on the surface of the samples. With the aim of determining the validity of immersion tests, usually used in these types studies, the samples were kept in a controlled atmosphere at 20°C and 60% RH. These exposition conditions could represent a relative dry atmosphere allowing the zinc corrosion. Electrochemical impedance spectroscopy was employed to follow the time evolution of the studied paints. The corresponding impedance spectra were modeled using an electrical equivalent circuit approach. This methodology allows establishing that pollutants as well as weathering conditions define the protecting mechanism of these zinc rich paints. The results show a fast evolution towards a barrier-type protecting mechanism.

Amélioration De L'aptitude Au Décochage Et Au Débourrage: Des Sables Liés Au selicate De Soude Et Durcis: Par Le Gaz Carbonique

Improvement In the aptitude to discharge and to unstop of sands binded with sodium silicate and hardened by carbon dioxide. Chemically hardened sands offer a large choice of moulding and coring processes by the use of organic and mineral compounds. The use of these binders requires a knowledge of associated risks, to obtain a reduced residual resistance (in order to facilitate the discharging and the unstopping of the parts) and for the success of the products. The aim of this study was to rationalise the utilisation conditions of sodium silicate moulded sands, with additives, hardened by carbon dioxide. This should minimize the eventual defects in the cast parts. Sand resistance is very important right after the casting; it makes more difficult the tasks of discharging and unstopping. The need to incorporate organic matter to the sands becomes a necessity. The role of the organic matter is to reduce the sand resistance. The use of silicate binder requires the identification of the mechanism of the mixture hardening by carbon dioxide. It also calls for a knowledge of the gel structure formation, and of the influence of certain parameters on the properties. The experimental part is concerned with a comparative study of the behaviour of these sands in the foundry. The factors influencing this behaviour are: grain size, carbon dioxide blowing-in time, binder rates, adjuvant ratios and mixing time, etc… A thermographie study was carried out in order to perform the experimental work in real conditions. The obtained results have led to the determination of the optimal values of the above-mentionned parameters. This allows to obtain the smallest residual resistance, hence to improve the discharging and unstopping processes. This approach is clearly exhaustive and shows all possible interactions of the adjuvants with sodium silicate and the considered sands.

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.

One-component silicate binder systems for coatings

By observing the appropriate conditions relating to formulation, production, substrate examination and pretreatment and application, by using a dual system of potassium silicate binders and low amounts of organic polymer dispersions silicate emulsion paints and plasters constitute systems of essentially mineral character with application properties that, in many respects, have approached those of pure organic emulsion paints or polymer improved plasters without losing the major advantages of the traditional mineral binder systems.

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.

A study of thermodynamic stability of oxide phases in heating multicomponent ceramic binders

A computer simulation of the thermodynamic stability of phases in firing ceramic silicate binders in the SiO2-A12O3-B2O3-K2O-Na2O system for abrasive tools based on grained normal electrocorundum is described. The thermodynamic data for the computation are chosen from the HSC 203 data base of the Outokumpu concern and TAPP of the E. S. Microwave Inc. It is established that when the binder (67.73% SiO2,20.0% A12O3,5.47% B2O3, 5.78% K2O,2.84% Na2O with CaO, MgO and Fe2O3 impurity oxides, the remainder TiO2) is fired at 1250°C, the most stable phases bear potassium (KAlSi3O3 and KAlSi2O6), the amount of the sodium-bearing phases diminishes substantially after 900–1100°C with only the Na2O · A12O3 · 2SiO2 phase remaining stable. This seems to explain the fact that the proportion of K2O to Na2O in feldspar pegmatites and ceramic binders for abrasion tools is regulated by standards.

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.

Photocatalytic Degradation of Chlorinated Phenoxyacetic Acids by a New Buoyant Titania-Exfoliated Graphite Composite Photocatalyst

A new class of floating composite photocatalysts for water purification is introduced. The composite material is comprised of exfoliated graphite support, titania photocatalyst, and sol−gel-derived methyl silicate binder. The catalyst composition was optimized for the degradation of rhodamine B dye. The photodegradation performance of the optimized catalyst was compared with supported titania film and P-25 titania suspension for the degradation of chlorophenoxyacetic acids. The photodegradation of the coated catalyst was between 50% and 95% of the activity of supported photocatalyst film.

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.

Preparation of fly ash monoliths consolidated with a sodium silicate binder at ambient temperature

Sodium silicate binder prepared by diluting a commercially available sodium silicate having 2.1 SiO 2 Na 2O molar ratio with water has been applied for the consolidation of fly ash. Two kinds of fly ash, ordinary and ultrafine, were mixed to enrich fine particles of 1.2 μm in diameter. Granulated blast furnace slag was added as a hardener as much as 10 percent of the solid. The, fly ash monoliths were prepared by casting slurries having 0.50 binder-liquor to solid ratio. After demolding at 1 d samples were kept in air for 28 d with subsequent water soaking for 3 d and finally air-dried for 7 d. This successive process was all carried out at ambient temperature and humidity. Strength tests revealed that blending the ultrafine fly ash and the slag are effective to obtain high strength materials in addition to the soak-dry process. A monolith, for instance, having flexural and compressive strengths of 9.6 and 25.1 MPa, respectively, was obtained.

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.

Alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR) in activated blast furnace slag cement (ABFSC) concrete

This paper examines the dimensional change of concrete prisms that were fabricated using concrete made with either sodium silicate or sodium carbonate ABFSC binder incorporating either an innocuous control aggregate, an aggregate that is known to be reactive by way of ASR or ACR in ordinary Portland cement (OPC) concrete or an aggregate that contains reactive silica although a good service record has been exhibited. The concrete prism test procedures detailed in the Canadian Standards Association (CSA A23.2-14A-94) specifications were used. The results of a parallel study of the early dimensional stability of ABFSC concrete which involved petrographic examination of concrete thin sections are discussed. It was found that, although ABFSC concrete is more vulnerable to ACR, it is less susceptible to expansion due to ASR than OPC concrete, however, expansions after one year can still be unacceptable. Unlike OPC, many large cavities form within the paste structure of ABFSC mixtures at early ages which is accompanied by shrinkage. This behaviour must be considered in the analysis.

Materials

Borchibond 145 is a new water‐based silicate binder from Borchers AG, formulated for use as a resin, or with other resins, in waterborne paint systems.

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.