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1

Surface Treatments Of Natural Fibres In Fibre Reinforced Composites: A Review

Seisa Keolebogile, Chinnasamy Vivekanandhan, Ude Albert U.

Fibres & Textiles in Eastern Europe

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2022

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Vol. 30, no. 2

82--89

EN

The use of natural fibres in fibre-reinforced composites comes with drawbacks. They are highly hydrophilic, leading to high moisture absorption and poor interfacial adhesion in matrix-reinforcement bonds. This affects the fibres’ thermal stability as well as mechanical properties, hence limiting their wider application. This paper reviewed different ways in which natural fibres have been treated to improve hydrophobicity, reinforcement-matrix interfacial adhesion and thermal stability. It will investigate. among others, treatments like alkali, acetylation, bleaching, silane, benzoylation and plasma, which have been found to improve fibre hydrophobicity. The literature reviewed showed that these methods work to improve mechanical, chemical, and morphological properties of natural fibres by removing the amorphous surface, thus allowing for more efficient load transfer on the fibre-matrix surface. Studies in the literature found alkali treatment to be the most common surface modification treatment due to its simplicity and effectiveness. However, plasma treatment has emerged due to its lower processing time and chemical consumption. A comparative analysis of other improved properties was also investigated.

2

Corrosion Behavior of Amorphous-Nanocrystalline Ni50Ti50 Shape Memory Alloy

Aghabeygzadeh H., Mohammad Sharifi E., Tavoosi M.

Archives of Metallurgy and Materials

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2021

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Vol. 66, iss. 1

267--272

EN

In the present study, the corrosion behaviors of amorphous-nanocrystalline Ni50Ti50 shape memory alloy with different crystallite sizes were investigated. The Ni50Ti50 homogenized specimens were hot rolled and annealed at 950°C. Thereafter, the nanocrystalline Ni50Ti50 specimens with different crystalline sizes in the range of 40-350 nm were prepared by cold rolling and annealing at temperature range of 400 to 900°C. The corrosion resistance of Ni50Ti50 specimen with coarse grain size has significantly increased after cold rolling as a result of the formation of amorphous-nanocrystalline structure. The amorphous and nanocrystalline (with the crystallite size of about 40 nm) Ni50Ti50 samples exhibited the best corrosion resistance in the 5% HCl electrolyte with the corrosion potential and corrosion current density of about –197 mV and 2.34×10-6 A/cm2, respectively. This effect can be attributed to the higher density of crystalline defects in amorphous and nanocrystalline structures to quickly form protective films on the surface.

3

Crystallization Behavior of Zr62Al8Ni13Cu17 Metallic Glass

Jo M. S., Lee J. K.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2B

1023--1026

EN

The crystallization behavior has been studied in Zr62Al8Ni13Cu17 metallic glass alloy. The Zr62Al8Ni13Cu17 metallic glass crystallized through two steps. The fcc Zr2Ni phase transformed from the amorphous matrix during first crystallization and then the Zr2Ni and residual amorphous matrix transformed into a mixture of tetragonal Zr2Cu and hexagonal Zr6Al2Ni phases. Johnson- Mehl-Avrami analysis of isothermal transformation data suggested that the formation of crystalline phase is primary crystallization by diffusion-controlled growth.

4

Mg-Phosphate Ceramics Produced from the Product of Thermal Transformation of Cement-Asbestos

Perez-Estebanez M., Macova P., Sasek P., Viani A., Gualtieri A.

Inżynieria Mineralna

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2014

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R. 15, nr 2

187--192

EN

According to recent European directives, the need for environmentally friendly alternative solutions to landfill disposal of hazardous wastes, such as asbestos-containing materials, prompts their recycling as secondary raw materials. In this work, magnesium phosphate ceramics were prepared using the product of inertization of cement-asbestos. Magnesium phosphate ceramics show interesting properties like good water resistance and high strength that make them attractive materials for several applications. Asbestos containing materials were mixed with magnesium carbonate and annealed at two different temperatures (1100 and 1300 ºC). During thermal treatment complete destruction of asbestos minerals with their transformation into new phases, and crystallization of MgO from magnesium carbonate decomposition, occurs. Upon addition of potassium di-hydrogen phosphate and water, the magnesium oxide in the product of thermal treatment, contributes to the onset of a setting reaction whose product is magnesium potassium phosphate hydrate. The reactivity of periclase was found to be dependent on the calcination temperature. Lower reaction rates were observed for the MgO obtained at lower temperature. The setting reaction of the magnesium phosphate ceramic has been followed in time up to 6 months by means of the X-rays powder diffraction trechnique. Quantitative phase analysis was performed using the Rietveld method and both crystalline and amorphous phases were quantified. The amount of magnesium potassium phosphate was found to increase with time, and was accompained by a decrease in the amount of the amorphous fraction. This fact supports the hypothesis of the formation of an amorphous precursor of the crystalline MKP during the hydration reaction. SEM images showing elongated magnesium potassium phosphate hydrate crystals emerging from what appears as an amorphous matrix, further confirms this view. Since the mechanical properties of magnesium phosphate ceramics are known to increase with time, we can conclude that the main contribution to the development of strenght comes from the crystalline magnesium potassium phosphate hydrate. In this work, we describe a procedure for simultaneous destruction of asbestos minerals and formation of cementitious compounds, which represents a recycling opportunity for this class of hazardous wastes, bringing benefits in terms of energy requirements and preservation of natural resources in cement manufacturing.

PL

Zgodnie z niedawnymi dyrektywami europejskimi, potrzeba przyjaznego dla środowiska alternatywnego rozwiązania usuwania odpadów niebezpiecznych, takich jak materiałów zawierających azbest, pobudza ich ponowne wykorzystanie jako surowców wtórnych. W tej pracy, magnezowo fosforanowe wyroby ceramiczne zostały wytworzone z użyciem produktów inertyzacji cementu – azbestu. Magnezowo fosforanowe wyroby ceramiczne wykazują interesujące właściwości takie jak dobry opór wodny oraz duża wytrzymałość, co sprawia, że są atrakcyjnym materiałem dla wielu aplikacji. Materiały zawierające azbest zostały zmieszanie w węglanem magnezu i wyżarzone w dwóch różnych temperaturach (1100°C i 1300°C). Podczas obróbki cieplnej następuje całkowite zniszczenie minerałów azbestu wraz z ich transformacją w nowe fazy, oraz krystalizacja MgO z rozpadu węglanu magnezu. Podczas dodawania diwodorofosforanu magnezu do wody, tlenek magnezu jako produkt obróbki cieplnej, przyczynia się do rozpoczęcia reakcji wiązania, której produktem jest hydrat fosforanu magnezu i potasu. Odkryto, że reaktywność peryklazu zależy od temperatury kalcynacji. Niższa szybkość reakcji została zaobserwowana dla MgO uzyskanego w niższej temperaturze. Reakcja wiązania wyrobów ceramicznych magnezowo fosforanowych została przeprowadzona w czasie do 6 miesięcy za pomocą techniki rentgenowskiej dyfrakcji proszkowej. Ilościowe analizy fazowe zostały wykonane z użyciem metody Rietvelda i obliczono zarówno fazę krystaliczną jak i amorficzną. Zauważono, że ilość fosforanu magnezowo potasowego zwiększa się w czasie, i że towarzyszy jej spadek ilości części amorficznej. Fakt ten potwierdza hipotezę powstawania amorficznego prekursora krystalicznego fosforanu magnezowo potasowego podczas reakcji hydracji. Obrazy SEM przedstawiają wydłużone kryształy hydratu fosforanu magnezowo potasowego wyłaniające się, z wyglądającej na amorficzną, macierzy, następnie ten wygląd się potwierdza. Ponieważ wiadomo, że właściwości mechaniczne fosforanu magnezu zwiększają się z czasem, możemy wnioskować, że główny wpływ na zwiększenie się wytrzymałości ma krystaliczny hydrat fosforanu magnezowo potasowego. W pracy tej opisano procedurę jednoczesnego rozpadu minerałów azbestu i tworzenia się związków cementytowych, co wskazuje na możliwość powtórnego przetworzenia tego rodzaju odpadów niebezpiecznych, co przynosi korzyści w kategoriach zapotrzebowania energetycznego i ochrony zasobów naturalnych w przetwórstwie cementu.

5

(Bi,Pb)-Sr-Ca-Cu-O glass-ceramics - superconductor and granular metal

Gazda M., Kusz B., Murawski L., Stizza S., Natali R.

Optica Applicata

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2008

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Vol. 38, nr 1

153-161

EN

In the (Bi,Pb)-Sr-Ca-Cu-O system, materials of various electrical and superconducting properties may be produced by a glass-ceramic method. As a result of heat treatment, amorphous material partially crystallizes. It causes an increase in the size and/or the number of conducting grains and a decrease in the width of the insulating barriers between them. The resistivity of the samples containing small, weakly coupled grains in the normal state follows the exponential temperature dependence of resistivity, while in the samples with larger intergrain conductivities the dependence is logarithmic. Still stronger connections between the grains lead to linear or almost linear ?(T). The granular character of the (Bi,Pb)4Sr3Ca3Cu4Ox materials also influences their superconducting properties.

6

Comparison of electrical characteristics of silicon solar cells

Dobrzański L. A., Wosińska L., Dołżańska B., Drygała A.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

215--218

EN

Purpose: The aim of this work is comparison of the operational characteristics of photovoltaic silicon cells: monocrystalline silicon, polycrystalline silicon and amorphous silicon. Design/methodology/approach: The notion of fill factor (FF), which is characteristic for Photovoltaic quality, has been introduced to compare properties of different silicon solar cells. Basing on the indicated characteristic the analysis of cell power efficiency has been carried out and the maximum power points PMM have been determined. Findings: It has been pointed out that crystal structure and surface texture affect utility properties of the investigated Photovoltaic Silicon Cells. Moreover, it has been stated that along with the radiation intensity growth the maximum cell power increases accompanied by its efficiency deterioration and simultaneous change of the maximum power point position, what causes and short-circuit current increase. Research limitations/implications: It has been found that the cell surface texture has an important influence on utility properties of the photovoltaic cells, which is connected with the high refractivity of silicon. Therefore, development of the cell surface forming methods is of a significant influence on improvement of the photovoltaic cells properties. Practical implications: Currently the photovoltaic industry is based mostly on the crystalline and polycrystalline silicon. Limitations of the utility properties resulting from the relationships presented in this paper accompany the advantages of cells fabricated from the amorphous and polycrystalline silicon, like the low manufacturing costs and no geometrical limitations. Analysis of the discussed relationships makes optimization of the cel parameters possible, depending on the service requirements. Originality/value: Known cells were compared as regards their conversion efficiency in various lighting conditions, depending on their design and material properties.

7

First principles molecular dynamics simulations for amorphous HfO2 and Hf1-xSixO2 systems

Ikeda M., Kresse G., Nabatame T., Toriumi A.

Materials Science Poland

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2005

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Vol. 23, No. 2

401--406

EN

Amorphous phases of HfO2 and Hf1-xSixO2 were obtained using the Projector Augmented Plane Wave method through the melt and quench technique. For the pure HfO2 system, several pore channels appear in the structures. Changes to x in the Hf1-xSixO2 were also studied. As the concentration of Si increases, the size of the pore channels increases, much space appears and two- fold oxygen atoms increase. By calculating the heat of formation energy, it was found that phase separation between amorphous HfO2 and SiO2 occurs at x> 0.1.

8

Thermal Stabilizing Effect of Amorphous Matrices of Sugars on Freeze-dried Proteins

Suzuki T., Okazaki M.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2000

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Vol. 48, nr 3

415-427

EN

Thermal stabilizing effect of sugars on freeze-dried proteins is studied remarking the reaction between the stabilizing effect and the degree of crystallinity of sugars. It is found that thermal stabilizing effect is higher when sugar is amorphous than crystalline. This thermal stabilizing effect is closely related to hydrogen bond between sugar molecules and proteins. It is also found that except the case of low moisture content protein can stabilize amorphous matrix of sugar and prevent its crystallization. Thus, we can deduce that sugars and proteins work together to maintain protein activities.