Morphology and structure of bright electrodeposited metal coatings

The properties which determine whether the metal surface is mirror bright are precisely determined by scanning electron microscopy (SEM), atomic forces microscopy (AFM), scanning tunneling microscopy (STM) and reflectance spectrophotometry investigations. Mirror brightness of metal surfaces can be associated with the high degree of mirror reflection which approaches very nearly the ideal reflectance of the same metal with the lowest degree of diffuse reflection. Mirror brightness of the copper coatings and the copper surfaces polished both mechanically and electrochemically was determined by fiat and mutually parallel parts of the surface, which are smooth on the atomic level and which point out towards layer structure of these surfaces. Mirror bright metal surfaces can be obtained only by electrochemical polishing or electrochemical deposition in the presence of brightening addition agents

Quantitative Formulation of Mechanism of Sintering Process during Creep Deformation of Refractory Concretes

This paper is concerned with quantitative formulation of the mechanism of the sintering process during secondary state creep deformation of refractory concretes. Investigated concretes varied in, both, chemical and mineralogical compositions. The sintering process during secondary state creep within refractory concrete has an isothermal character. Thus, an attempt was made to describe the mentioned process quantitatively. Creep was investigated at three different temperatures: 1200, 1300 and 1400 degrees C. Variations of the microstructure of concrete samples, exposed to constant static pressure and constant temperature during certain time-intervals, were investigated using a scanning electron microscope. Obtained results of the investigation proved that creep resistance is an irreplaceable method when the decision about the best possible type of refractory concrete for application in metallurgical furnaces is required

Morphology and structure of bright electrodeposited metal coatings

The properties which determine whether the metal surface is mirror bright are precisely determined by scanning electron microscopy (SEM), atomic forces microscopy (AFM), scanning tunneling microscopy (STM) and reflectance spectrophotometry investigations. Mirror brightness of metal surfaces can be associated with the high degree of mirror reflection which approaches very nearly the ideal reflectance of the same metal with the lowest degree of diffuse reflection. Mirror brightness of the copper coatings and the copper surfaces polished both mechanically and electrochemically was determined by fiat and mutually parallel parts of the surface, which are smooth on the atomic level and which point out towards layer structure of these surfaces. Mirror bright metal surfaces can be obtained only by electrochemical polishing or electrochemical deposition in the presence of brightening addition agents

Microstructural changes initiated by sintering of refractory concrete based on recycled bauxite aggregate

Concretes whose structure and final properties are shaped during thermal pre-treatment or during life-service at elevated temperatures can be applied as construction material for thermal insulation and/or refractory linings in high-temperatureoperating plants. Refractory concretes designed with waste raw materials show satisfying performances in comparison with standard concretes. Sintering initiates microstructural changes within concrete. Concrete microstructure further develops with increasing temperature. Change progression can be monitored by means of destructive and non-destructive tests: either by investigating change of compressive strength or apparent porosity of concrete samples. Destructive tests, in this study, were applied in compressive strength investigation, while non-destructive tests were performed for results comparison. Experiment has been conducted on corundum (standard) concrete and recycled bauxite (experimental) concrete. Samples underwent thermal treatment from 110 to 1500°C. Macroperformance of the final refractory concrete was correlated to the microstructural change detected by means of XRD and SEM analysis. Creep testing was conducted to prove sintering process. Results showed that recycled concrete has equal if not better properties in comparison with standard refractory concrete and can be used as thermoinsulation or refractory material. The results presented in this paper contribute to the idea of including other testing methods (i.e. nondestructive methods) in investigation of microstructural changes and sintering process of refractory concrete. At the same time results of this investigation highlight advantages of application of secondary raw materials in design of refractory materials. Although recycled aggregate concrete showed lower compressive strength and higher porosity than commercial concrete it should be noted that both porosity and compressive strength are within satisfying value range for high-temperature application, i.e. these concretes will not be used as structural materials but as thermal insulation linings. In such application refractoriness is the property which is more important than strength. Considering the fact that compressive strength is above 50 MPa (and above 20 MPa at 1500°c) these concretes should be able to withstand load induced by other constructive parts of furnace and slag. Refractoriness test showed that bauxite-based recycled concrete is highly resistible on increasing temperatures and creep test showed initiation of sintering process. Corundum concrete can be used for temperature above 1500°c. Due to the satisfying performances it is concluded that recycled concrete can be equally used as standard concrete. Even though it has slightly lower properties, accent should be on the financial and ecological benefit found in using of recycled material and savings of energy and natural resources

Prevention of electrofilter ash toxic leaching by embedding in composite materials

Disposal of the fly ash may pose a significant risk to the environment due to the leaching of hazardous pollutants. The only sustainable solution for the pollution-prevention is the reapplication of fly ash as one of the components in construction material composites. There is a risk of leaching even when fly ash is built-in the construction composites and the goal of this investigation was to prove that leaching concentrations of toxic elements is in range assigned by actual regulations. Fly ash was applied in several composits: mortar, concrete and asphalt. The leachability of the potentially toxic elements from the fly ash based products was investigated. The leaching behavior and potential environmental impact of the 11 potentially hazardous elements was tracked: Pb, Cd, Zn, Cu, Ni, Cr, Hg, As, Ba, Sb and Se. A detailed study of physico-chemical characteristics of the fly ash is included. The overall results showed that most of the elements are more readily leachable from the fly ash in comparison with the fly ash based composites

Correlation between mechanical properties and microstructure of refractory composites determined using non-destructive testing method

Cilj ovog rada je da se utvrdi veza između važnih mehaničkih svojstava i karakteristika mikrostrukture pomoću nedestruktivne ispitne metode - metode merenja berzine ultrazvuka, na uzorcima korundnih i boksitnih vatrostalnih betona. Ispitivani betoni se razlikuju po hemijskom i mineraloškom sastavu. Standardnom destruktivnom laboratorijskom metodom je određena mehanička čvrstoća pri pritisku na uzorcima koji su bili prethodno izloženi termičkom tretmanu na temperaturama: 110, 800, 1000, 1300 i 1500°C. Kada je uzorak vatrostalnog betona izložen uticaju povišene temperature i statičkog opterećenja dolazi do smanjenja pritisne čvrstoće i do sveukupne degradacije materijala (gustina i elastčna svojstva se smanjuju). Određivanjem mehaničkih svojstava betona može se ukazati ili se mogu pratiti promene koje se dešavaju unutar mikrostrukture materijala. Nivo površinske degradacije uzorka, nakon termičkih tretmana, je utvrđen pomoću optičkog mikroskopa i Image Pro Plus - kompjuterskog programa za analizu slike. Nedestuktivna metoda merenja brzine ultrazvuka je primenjena pri praćenju promene poroznosti unutar uzoraka vatrostalnog betona. Ultrazvučna metoda i analiza slike su pouzdane metode za karakterizaciju mikrostukturnih promena i defekata i veoma su korisne kada je potrebno utvrditi koji je tip vatrostalnog betona najpogodniji za određenu primenu.Aim of this paper is to establish the correlation between important mechanical properties and characteristics of microstructure using non-destructive testing method, i.e. ultrasonic pulse velocity, on the example of corundum and bauxite based refractory concretes. Investigated concretes are varying in chemical and mineralogical composition. Mechanical compressive strength of concrete samples after thermal treatment at various temperatures (110, 800, 1000, 1300 and 1500°C) was investigated using standard laboratory procedure. When refractory concrete sample is subjected to increased temperature and compressive load loss of strength and material degradation occurs (density and elastic properties of material are decreasing). Measurement of mechanical properties can indicate and monitor the changes in the microstructure. Level of surface deterioration after thermal treatment was determined using optical microscope and Image Pro Plus - program for image analysis. Nondestructive ultrasonic measurement was used as a means of monitoring of increasing porosity in refractory specimens. Ultrasonic pulse velocity technique and image analysis are reliable non-destructive methods for characterization of micro-structural defects and can be useful when type of refractory concrete is to be chosen for an application

Synthesizing a new type of mullite lining

Various possibilities for developing new mullite-based refractory linings that can be applied in a casting process were investigated and are presented in this paper. An optimization of the refractory-lining composition design with the controlled rheological properties was achieved by applying different lining components and altering the lining-production procedure. Mullite was used as a high-temperature filler. A mullite sample was tested with the following methods: X-ray diffraction analysis, differential thermal analysis and scanning-electron microscopy. The particle shape and particle size were analyzed with the program package for an image analysis called OZARIA 2.5. It was proved that an application of this type of lining has a positive effect on the surface quality, structural and mechanical properties of the castings of Fe-C alloys obtained by casting into sand molds, according to the method of expandable patterns (the EPC casting process)

Uticaj strukture čestica na nasipnu masu elektrolitički dobijenog bakarnog praha

The quantitative microstructural analysis and the sieve analysis of copper powder as well as the scanning electron microscopy analysis of the copper powders particles were performed. It was found that the structure of the copper powder particles determines the apparent density of copper powder. The powder particles from the same fractions of different powders occupy approximately the same volume, but the structure of metallic copper is very different. This causes the difference in apparent densities of copper powder obtained under different conditions. The more dendritic is the structure of powder particles the smaller is the apparent density of copper powder.Izvršena je kvalitativna mikrostrukturna i granulometrijska analiza bakarnih prahova kao i analiza morfologije i strukture čestica praha pomoću skenirajuće elektronske mikroskopije (SEM). Ustanovljeno je da struktura čestica praha određuje nasipnu masu bakarnog praha. Čestice iste frakcije različitih prahova zauzimaju otprilike istu zapreminu, ali je struktura metalnog bakra različita. Ovo uzrokuje razlike u nasipnoj masi bakarnog praha dobijenog pod različitim uslovima. Što je struktura čestica više dendritična to je manja nasipna masa bakarnog praha

Influence of the phase composition of refractory materials on creep

In this paper, the relationship between the creeping effect and mineralogical characteristics of the applied binding phase for various refractory materials (high-alumina materials, with high or low impurity content, tar bonded either magnesite or dolomite materials and silicate bonded chrom-magnesite materials) is presented. The mechanism of creeping is analyzed and the activation energy for creep for each investigated material is obtained and discussed. All investigated materials are creep sensitive under investigated conditions and have similar activation energies for creep except high-alumina refractories with a low impurity content

Lightweight construction ceramic composites based of pelletized fly ash aggregate

As coal combustion byproduct fly ash represents a risk for environment: direct ash emission from open land-fills causes pollution of air, soil and water. The solution for this severe pollution problem is fly ash reapplication in various construction ceramic composite materials. Although pelletization of waste powdery material is a known technique in the production of artificial aggregates, it still has not been widely used in construction sector. Here investigated cold-bonded fly ash aggregate was produced in semi-industrial pelletizing device. The fly ash particles were bonded with water-glass (Sodium silicate - Na2SiO3) and used as substitution for aggregate in Portland cement based composite. Half of the produced lightweight aggregate was submitted to thermal treatment and afterwards applied in the construction composite in the same ration as in the case of cold-bonded pellets. The performance characteristics of two types of lightweight composites were mutually compared and afterwards correlated with characteristics of normal-weight concrete. Compressive strength, modulus of elasticity and tensile strength were used as represents of the composites mechanical behavior. Mineral constituents of fly ash pellets were analyzed by means of X-ray diffraction analysis, differential thermal analysis was applied in crystalline phase investigation, and scanning electron microscopy in microstructural analysis. The leaching behavior and environmental impact of hazardous elements were also analyzed. It was concluded that content of potentially toxic elements found in leachate of fly-ash based composites was far below tolerance limit proposed by actual standards for the building materials, characterizing the fly ash non-harmful secondary raw material and enabling its reapplication in building materials industry. Utilizing fly ash to produce quality aggregates should yield significant environmental benefits