Materials Science Forum Vol. 1089

Abstract: The possibility of anodic oxidation of SiC surfaces by a strong, local electric field applied during Atomic Force Microscopy (AFM) under ambient conditions is an interesting method to achieve nanopatterning of SiC, but is also a side-effect to be well characterized and controlled during this kind of AFM measurements if used to determine the local electric properties. In this contribution, we will analyze the local electric fields by finite element simulations in order to quantify the effect of the presence of a water meniscus and of an oxide layer on the SiC surface. Furthermore, we will experimentally highlight the strong influence of the local doping on the anodization, leading to the formation of thicker oxide layers at the location of highly doped SiC. Therefore, the location of these areas can be determined by a simple AFM topography scan after the application of a high field, allowing to detect highly doped SiC areas in complex structures as for example SiC MOSFETs.

Abstract: The Smart CutTM process offers an advantageous opportunity to provide a large number of performance-improved SiC substrates for power electronics. The crystalline quality and the electrical activation of the 4H-SiC transferred layer are then at stake when it comes to the power device reliability. In this study, we find that the H⁺ ion implantation used for the Smart CutTM process leads to electrical deactivation of dopants and partially disorders the material. The transferred layer fully recovers its initial crystalline quality after a 1300°C anneal, with no further evolution beyond this temperature. At this point however, the n-type dopants are still inactive. The dopant reactivation occurs in the same temperature range than that of implanted nitrogen: between 1400°C and 1700°C. After 1700°C, the initial doping level of bulk SiC is recovered.

Abstract: The growing interest for the use of 4H-SiC in photonics is triggering the interest for more accurate characterizations of this semiconductor from the optical and opto-electronic point of view. In this work we report about new measurements run on an undoped 4H-SiC substrate, finalized at determining the precise dependence of its refractive index on temperature in the visible spectrum, and precisely at the wavelength of λ=632.8 nm, in a temperature range from room temperature (RT) to 400K. Measurements are performed by exploiting the properties of a Fabry-Perot cavity interrogated with a laser beam. It is known that the transmitted radiation intensity shows fringes that shift with temperature and the refractive index. By precisely monitoring the transmitted signal, the thermo-optic coefficient dn/dT can be determined with a resolution that approaches 10^-6 K^-1.

Abstract: Due to their properties, potential for demonstrating shape memory behavior, and cheaper cost, copper-based SMA materials hold great promise for use in a variety of industrial and medical applications. This work used powder metallurgy to create Cu-based SMA using Cu-25Zn-4Al as the master alloy. The master alloy having Beryllium additions of (0.4, 0.8, and 1.2%wt.) was studied. After combining the powders, all samples were compacted using compaction stresses of (800 MPa). Then, the process of sintering in a tube furnace using argon gas has been accomplished in three stages, the first stage lasting two hours at 350°C, the second lasting two hours at 550°C, and the third lasting three hours at 900°C. All samples are treated with a solution heat treatment that involves heating them to 850 °C for an hour, quenching them quickly in saline ice water, and then aging them at 450 °C for 180 minutes. According to linear polarization tests the adding 1.2 weight percent of the Be to the base alloy (Cu-25Zn-4Al alloy) decreased corrosion rate by (95%) as compared to the base sample in a 3.5 weight percent NaCl solution. Keywords-Cu-Zn-Al shape memory alloys, corrosion behavior, shape memory properties, Beryllium, microstructure

Abstract: Study wear resistance for heat treatment of Ni-B-CNT electroless coatings. Different concentrations for CNT (0 ,0.35 and 0.7 g/l Ni-B-CNT composite coatings deposition on 4340 steel. After the procedure of coating, all samples were heat treatment. The test wear of a coating was valued with pin on disk technique. Preparation of Ni–B–CNT electroless coatings are with using nickel chloride in alkaline bath, borohydride and Multi walled carbon nanotubes. characterization with FESEM, micro hardness, XRD and surface roughness. Study for surfaces of worn with EDS and FESEM. Micro hardness results are show that the larger hardness1010 HV is gained by heat treatment for coating (Ni-B- 0.35 g/L CNT) because of concentration CNT caused structure conversion for coating Ni-B from amorphous to crystalline. Also, CNT prevent maximum heat production and decrease of the friction coefficient during test wear. CNT aggregation was noted result the presence for more particles (Ni-B - 0.7g/l CNT) that occur create roughness and also lead to increase in rate of wear because of big particles with weakly joined in matrix of Ni.

Abstract: Our research novel Ti-22Nb biomedical alloys made by powder metallurgy and analyze the effect of adding silicon at various weight ratios to the base alloy (0.4, 0.8, and 1.2 %at Si). In this work, the wear characteristics of Ti-Nb-Si alloys in dry conditions are examined, as well as the wear process. To measure the wear rate, a pin-on-disc wear testing apparatus was employed. The optical microstructure analysis showed that the microstructure had a mixture-like appearance and included only a small quantity of another phase. XRD results showed that the stability of the β phase increased with silicon concentration. The (Ti-22Nb) alloy's hardness and compressive strength both increased once silicon is added. Hardness also rises as the amount of silicon additions increases, with the maximum percentage (1.2 percent Si) resulting in the highest hardness and compressive strength

Abstract: This paper presents the results of a study on one-component dry mix used for the preparation of silicate-based facade paint with self-cleaning properties. The advantages of the developed composition include the ease of the mix preparation and application, increased adhesion of the coating to the base, and improved aesthetic qualities of the coating provided by its ability to self-clean due to the addition of nanotitanium dioxide, which enhances photocatalysis. In the course of the research work, the optimal quantitative content of the main components and functional additives was established. Studies of the facade paint microstructure were carried out. Infrared spectral and differential thermal analysis of the composition confirmed the significant weather resistance of the facade paint, which is ensured by deep carbonization of the constituent components with their transformation into calcium carbonates, characterized by increased water resistance and chemical stability. Key words: facade coating, silicate paint, self-cleaning, photocatalysis, microstructure

Abstract: Concrete is most widely used as an essential building material in the construction industry all over the globe. Concrete deteriorates over time, and cracks eventually form on its surface for many reasons, such as environmental surroundings and extra. This deterioration and cracks might lead to the ingress of water and chemicals that susceptible steel bars or reinforcements to corrosion. Since this deterioration is inevitable, maintenance and repair are also necessary. This process requires skilled labor and is cost-effective. Thus, researchers suggested alternative techniques to enhance concrete's mechanical properties and search for treatments to be applied to concrete's surface for healing and sealing the cracks by producing calcium carbonate precipitation. Therefore, self-healing concrete was introduced; this method is significant as it's proven environmentally friendly. This research aims to investigate the use of liquid bacteria incorporated in concrete mix and assess whether there would be improvements in the mechanical properties of the bacterial concrete compared to the conventional mix and an autogenous self-healing mix. Two different concentrations of an alkaliphile bacterium called Bacillus Subtilis were incorporated into the concrete mixes to test their ability to repair cracks by producing calcium carbonate and sealing them. This experiment showed a remarkable increase in bacterial concrete's compressive and tensile strengths. A visible partial crack sealing was also observed in specimens containing different concentrations of Bacillus Subtilis. Results also indicate that optimum results were obtained when the bacterial solution of concentration 10⁸ cells/ml was incorporated, especially at early ages.

Abstract: The objective of this research is to study and analyse the properties of a cement-based composite modified with nickel/carbon nanocomposite (Ni/C NC). According to previous studies carried out by scientists in the field of nanostructures, it was assumed that metal/carbon nanostructures can increase the strength and impart electrically conductive properties to composite materials [9,12]. To confirm this hypothesis, in this research, mechanical strength tests and measurements of the electrical resistance of the modified samples were carried out. It was found that the addition of nickel/carbon nanocomposite in the amount of 0.05% increases the compressive strength of silicate composites by 35%. Moreover, by measuring the electrical conductivity of the samples, it was established that with the introduction of additives in the amount of 0.01-0.05% in relation to Portland cement, the resistance decreases by 80-84%. Further, the structural effect of Ni/C NC on the cement matrix was studied by the methods of IR spectral, differential thermal analyses, X-ray microanalysis. As a result of the analysis, it was revealed that the dispersions are crystallization centers during cement hydration and create chemical bonds with silicon oxide in the composition of the silicate composite. Ni/C NC has a structuring effect on the silicate binder matrix through the formation of a denser packing, which affects the mechanical properties and electrical conductivity of the material. The results of the study can be used to obtain electrically conductive materials with desired properties that can perform the functions of heating, monitoring the state of structures during operation, and protecting against an electromagnetic pulse.

Abstract: Concrete structure especially that exposed to aggressive environment is deteriorated leading to damage of concrete buildings. Concrete coating is one of the most effective methods used for concrete protection. In this work epoxy was modified with nanosilica (NS) with different loadings. Epoxy nanosilica (EP-NS) composite was formulated and used as concrete protective coating after evaluate its properties regarding drying time, dry film thickness (DFT), adhesion strength. The coated concretes ware tested as; water absorption, contact angle (hydrophobicity) and chloride diffusion resistance by ion exchange method. Although, durability of coated concretes were examined by determining change in weight and change in compressive strength after immersion in both sulfuric acid and sodium chloride solution separately. The study revealed that, the optimum NS content is 3 % by total weight of coating. The prepared EP-NS coatings have significant protection mechanism for enhancing concrete performance against the postulated aggressive attack. Keywords: protective coating, polymer nanocomposite coating