Dimitrios Tsipas - Academia.edu (original) (raw)

Papers by Dimitrios Tsipas

In the present paper, a selj~evaluation model on a spec(fic Postgraduate course in a critical tec... more In the present paper, a selj~evaluation model on a spec(fic Postgraduate course in a critical technological area, such as Advanced Materials is presented. The model developed is based on Total Quality Management methodologies which have been introduced in Higher Education sector.

Solid State Phenomena, 2005

Tin dioxide is a wide band semiconductor, with interesting chemical physical and mechanical prope... more Tin dioxide is a wide band semiconductor, with interesting chemical physical and mechanical properties, used in a variety of industrial, domestic, medical and agricultural applications, including gas detectors, transparent conductors, solar cells, anti-static films, nanoelectronic devices etc. The variety of nanosized SnO2 production methods in the form of powders or layers (e.g. solid state, sol-gel, sputtering, laser ablation, template, solution precipitation, precursor oxidation, CVD, PVD, etc) are discussed.

Surface and Coatings Technology, 2006

The corrosion behavior of borided hot work steel H13 (AISI) in specific acid solutions (HCl 5 vol... more The corrosion behavior of borided hot work steel H13 (AISI) in specific acid solutions (HCl 5 vol.%, H 2 SO 4 5 vol.%, H 3 PO 4 30 vol.%) was studied. Boriding was done by pack cementation. The corrosion behavior was evaluated by potentiodynamic polarization experiments and immersion corrosion tests. The borided steel showed a better corrosion behavior in H 2 SO 4 and H 3 PO 4 environments for short exposure periods, up to about 100 h, when compared to H13 steel. On the contrary H13 steel presented a better corrosion resistance in HCl acid environment in comparison to the borided H13 steel. The main corrosion mechanisms in order of appearance were crevice corrosion observed in the coating, galvanic corrosion between coating and H13 steel substrate and pitting corrosion of the substrate.

Materials and Corrosion, 2005

Eventhough 9-12% Cr steels are mechanically designed for power plant applications up to 650 C, th... more Eventhough 9-12% Cr steels are mechanically designed for power plant applications up to 650 C, their effective use is limited by the corrosion resistance at this temperature. Therefore, the present paper addresses the development of diffusion coatings on 9% Cr ferritic-martensitic steels. The difficulty of coating these materials with conventional diffusion processes arises from the temperature limit above which the conversion of the martensite is accelerated and the mechanical properties would be deteriorated. Aluminide coatings consisting of Fe 2 Al 5 or FeAl phases were thus developed for deposition temperatures between 650 and 715 C by the conventional pack cementation technique. As the addition of boron was expected to improve the oxidation properties of the coating, the influence of B on the aluminide coating was investigated. The precedent diffusion of Cr as an interdiffusion barrier before switching to the Al diffusion step was also investigated. As a further technique, the fluidised bed chemical vapour deposition (FBCVD) method allowed the development of Fe 2 Al 5 coatings at 550 C. Furthermore, Si or codiffusion Al-Si coatings were developed at temperatures as low as 550 C.

Ceramics International, 2009

Cr 2 O 3 -nucleated fine grained mono-mineral glass-ceramics of augite were produced from low-sil... more Cr 2 O 3 -nucleated fine grained mono-mineral glass-ceramics of augite were produced from low-silica fly ash and additives of SiO 2 , Al 2 O 3 and MgCO 3 , via two steps of heat treatment for nucleation and crystal growth. The starting glass approached the composition of CaMg ...

Advances in Science and Technology, 2006

In order to manufacture products of acceptable quality within predetermined specification limits,... more In order to manufacture products of acceptable quality within predetermined specification limits, an evaluation of the manufacturing process through the use of capability indices is necessary. Capability indices are used in order to evaluate a process and to monitor the product characteristics and the results of quality improvement cycles. The three point bending strength of kaolin ceramic specimens produced by two different production processes (slip casting and hydroplastic extrusion) were investigated. It was found that under statistical control and normal distribution of strength values, the process capability indices Cp, Cpk, regardless of any disadvantages and the fact that they have limitations, can be combined with other techniques in the field of statistical process control and become valuable tools in process evaluation of ceramic products.

Advances in Science and Technology, 2006

Although structural kaolin based ceramics are attractive and useful materials, having good mechan... more Although structural kaolin based ceramics are attractive and useful materials, having good mechanical characteristics, low density, good corrosion and high temperature resistance, their use is restricted by their brittle behaviour. In order to improve their properties and mainly strength, toughness and high temperature performance, fibre composite ceramics have been developed. In the present work a series of kaolin-short random dispersed Grafil carbon fibre composites were produced and sintered in an inert atmosphere of Argon at 1000oC and 1300oC and characterised using various techniques. XRD analysis of the kaolin matrix at 1000oC showed that the crystalline phases were decomposed without the formation of mullite a fact which also reconfirmed by SEM examination. However at 1300oC mullite formation was well evidenced. XRD analysis of the fibres in “as received” showed that they have graphite structure which was also retained, as SEM examination revealed, after sintering. Examinatio...

Advances in Applied Ceramics, 2009

The study concerns the recycling of the fly ash (FA) derived from the thermal power stations of P... more The study concerns the recycling of the fly ash (FA) derived from the thermal power stations of Ptolemaida (Greece) and its potential use of this FA as precursor in production of bulk nucleated GCs. The first attempt was addressed to produce a glass from the fine powder of as received FA without any additives. To overcome some drawbacks such as spontaneous crystallisation upon cooling of FA based glass and to improve its working properties, production of pyroxene based glasses from FA was undertaken. The parent glass approached the composition of CaMg 0?75 Al 0?4 Fe 0?1 Si 1?75 O 6 , derived from CaMg 0?75 Al 0?5 Si 1?75 O 6 , which belongs to diopside-Ca-Tschermak solid solutions. Cr 2 O 3 nucleated fine grained mono mineral glass ceramics of augite were produced from the glasses comprising FA and additives of SiO 2 , Al 2 O 3 and MgCO 3. The influence of Cr 2 O 3 content on the development of crystalline phases, the properties and the microstructure of the resultant glass ceramics crystallised at different temperatures was investigated.

Materials Chemistry and Physics, 1987

In this paper we present the results of corrosion resistance of boronized 1020 steel in naphtheni... more In this paper we present the results of corrosion resistance of boronized 1020 steel in naphthenic acid and during high temperature oxidation. The boride layer, consisting of FeB in the outer region and Fe2B in the inner zone, was found to be extremely resistant to naphthenic acid containing media, both in the liquid and vapour phase. During high temperature oxidation in air at 65@C a very thin, 10~ protective oxide layer was formed on the boronized steel, indicating that the boride layer acts as a barrier to oxygen and/or Fe diffusion. Finally both the morphology and distribution of FeB/F?B layers changed during high temperature oxidation.

Journal of Materials Science Letters, 1985

Journal of Materials Science Letters, 1987

Etude de la boruration par cementation en caisse d'aciers commerciaux allies et non allies. I... more Etude de la boruration par cementation en caisse d'aciers commerciaux allies et non allies. Influence des elements d'alliages sur la boruration. Profondeurs, structures et compositions des couches de borures formees

Key Engineering Materials, 2019

Boride coatings on steels have an excellent combination of properties. They can significantly imp... more Boride coatings on steels have an excellent combination of properties. They can significantly improve the hardness, the wear and corrosion resistance of steels. Boronizing of steels has been achieved using different methods such as pack cementation and paste boriding. On the other hand, fluidized bed technology has been successfully used in many surface engineering applications in the deposition of hard and / or corrosion resistant layers e.g. carburizing, aluminizing and chromizing. This method is simple, efficient and environmental friendly and is characterized by excellent heat and mass transfer, which results to improve quality of the as-produced coatings. As a result, fluidized bed technology can be considered as a useful alternative method for the production of boride coatings on steel substrates. In the present paper we used this method to deposit boride coatings on steels. The as-produced coatings were examined by means of optical microscopy, X-Rays diffraction, Vickers micr...

Nanomaterials (Basel, Switzerland), Jan 10, 2017

Silver nanoparticles (AgNPs) have been demonstrated to restrain bacterial growth, while maintaini... more Silver nanoparticles (AgNPs) have been demonstrated to restrain bacterial growth, while maintaining minimal risk in development of bacterial resistance and human cell toxicity that conventional silver compounds exhibit. Several physical and chemical methods have been reported to synthesize AgNPs. However, these methods are expensive and involve heavy chemical reduction agents. An alternative approach to produce AgNPs in a cost-effective and environmentally friendly way employs a biological pathway using various plant extracts to reduce metal ions. The size control issue, and the stability of nanoparticles, remain some of the latest challenges in such methods. In this study, we used two different concentrations of fresh leaf extract of the plant Arbutus unedo (LEA) as a reducing and stabilizing agent to produce two size variations of AgNPs. UV-Vis spectroscopy, Dynamic Light Scattering, Transmission Electron Microscopy, and zeta potential were applied for the characterization of AgNP...

Solid State Phenomena, 2016

Heat treatments of alloys in fluidized bed reactors have been carried out for more than twenty-fi... more Heat treatments of alloys in fluidized bed reactors have been carried out for more than twenty-five years. Recently this technology has been used for surface engineering applications in the deposition of hard and/or corrosion resistant layers e.g. aluminizing, chromizing, nitriding, carburizing, boronizing. The fluidized bed method is simple, efficient, environmentally friendly and capable of immediate adjusting the furnace atmosphere for specific requirements e.g. production of multielement coatings. The boride coatings on steel have an excellent combination of properties e.g. high fatigue strength and wear resistance. On the other hand silicide coatings are well known for their excellent corrosion resistance. Boron-siliconizing in fluidized beds is a promising method to improve both the wear and corrosion properties of steels. In the present paper fluidized bed technology (FBT) was used to deposit boride and boron-silicide coatings on steels. The coatings were examined by means of...

Journal of Materials Science Letters, 2001

Journal of Biomedical Materials Research Part B Applied Biomaterials, 2009

Journal of Materials Science

Heat treatments of alloys in fluidized bed reactors have been carried out for more than twentyfiv... more Heat treatments of alloys in fluidized bed reactors have been carried out for more than twentyfive years. More recently this technology has been used for carrying out nitriding, carburizing and similar surface treatments. This technology offers certain advantages over other traditional methods for Surface Engineering. These advantages include a more precise process control, greater flexibility and more efficient mass and heat transfer control during the process. In this paper we present a design of a fluidized bed reactor capable for carrying out single, and multilayer surface coatings.

Materials Letters, 2002

A simultaneous one-step boroaluminizing process has been performed on a 2.25Cr-Mo steel by means ... more A simultaneous one-step boroaluminizing process has been performed on a 2.25Cr-Mo steel by means of pack cementation method using a B/Al boriding powder. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al and Fe and an inner layer containing mostly B and Fe. The layers were characterized by means of optical and scanning electron microscopy (SEM) in terms of coatings morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coating due to the boroaluminizing process.

Key Engineering Materials, 2011

Chromium coatings have been used for the protection of gas turbine blades in power plants during ... more Chromium coatings have been used for the protection of gas turbine blades in power plants during the last years due to their very good resistance against steam corrosion. Microhardness, scratch, adhesion and pin-on-disk sliding tests are commonly used for rapid evaluation of the mechanical properties of these coatings [1,2]. However, very limited information exists on their fatigue resistance. In this paper we present the experimental results of the impact testing examination of the above coatings. This experimental method is capable to assess the fatigue and the impact wear resistance of coatings working under cyclic impact loading conditions. From the experimental results it was concluded that the slurry Cr, Zr coatings deposited on P91 steel showed adequate fatigue strength for the above-mentioned kind of use.

In the present paper, a selj~evaluation model on a spec(fic Postgraduate course in a critical tec... more In the present paper, a selj~evaluation model on a spec(fic Postgraduate course in a critical technological area, such as Advanced Materials is presented. The model developed is based on Total Quality Management methodologies which have been introduced in Higher Education sector.

Solid State Phenomena, 2005

Tin dioxide is a wide band semiconductor, with interesting chemical physical and mechanical prope... more Tin dioxide is a wide band semiconductor, with interesting chemical physical and mechanical properties, used in a variety of industrial, domestic, medical and agricultural applications, including gas detectors, transparent conductors, solar cells, anti-static films, nanoelectronic devices etc. The variety of nanosized SnO2 production methods in the form of powders or layers (e.g. solid state, sol-gel, sputtering, laser ablation, template, solution precipitation, precursor oxidation, CVD, PVD, etc) are discussed.

Surface and Coatings Technology, 2006

The corrosion behavior of borided hot work steel H13 (AISI) in specific acid solutions (HCl 5 vol... more The corrosion behavior of borided hot work steel H13 (AISI) in specific acid solutions (HCl 5 vol.%, H 2 SO 4 5 vol.%, H 3 PO 4 30 vol.%) was studied. Boriding was done by pack cementation. The corrosion behavior was evaluated by potentiodynamic polarization experiments and immersion corrosion tests. The borided steel showed a better corrosion behavior in H 2 SO 4 and H 3 PO 4 environments for short exposure periods, up to about 100 h, when compared to H13 steel. On the contrary H13 steel presented a better corrosion resistance in HCl acid environment in comparison to the borided H13 steel. The main corrosion mechanisms in order of appearance were crevice corrosion observed in the coating, galvanic corrosion between coating and H13 steel substrate and pitting corrosion of the substrate.

Materials and Corrosion, 2005

Eventhough 9-12% Cr steels are mechanically designed for power plant applications up to 650 C, th... more Eventhough 9-12% Cr steels are mechanically designed for power plant applications up to 650 C, their effective use is limited by the corrosion resistance at this temperature. Therefore, the present paper addresses the development of diffusion coatings on 9% Cr ferritic-martensitic steels. The difficulty of coating these materials with conventional diffusion processes arises from the temperature limit above which the conversion of the martensite is accelerated and the mechanical properties would be deteriorated. Aluminide coatings consisting of Fe 2 Al 5 or FeAl phases were thus developed for deposition temperatures between 650 and 715 C by the conventional pack cementation technique. As the addition of boron was expected to improve the oxidation properties of the coating, the influence of B on the aluminide coating was investigated. The precedent diffusion of Cr as an interdiffusion barrier before switching to the Al diffusion step was also investigated. As a further technique, the fluidised bed chemical vapour deposition (FBCVD) method allowed the development of Fe 2 Al 5 coatings at 550 C. Furthermore, Si or codiffusion Al-Si coatings were developed at temperatures as low as 550 C.

Ceramics International, 2009

Cr 2 O 3 -nucleated fine grained mono-mineral glass-ceramics of augite were produced from low-sil... more Cr 2 O 3 -nucleated fine grained mono-mineral glass-ceramics of augite were produced from low-silica fly ash and additives of SiO 2 , Al 2 O 3 and MgCO 3 , via two steps of heat treatment for nucleation and crystal growth. The starting glass approached the composition of CaMg ...

Advances in Science and Technology, 2006

In order to manufacture products of acceptable quality within predetermined specification limits,... more In order to manufacture products of acceptable quality within predetermined specification limits, an evaluation of the manufacturing process through the use of capability indices is necessary. Capability indices are used in order to evaluate a process and to monitor the product characteristics and the results of quality improvement cycles. The three point bending strength of kaolin ceramic specimens produced by two different production processes (slip casting and hydroplastic extrusion) were investigated. It was found that under statistical control and normal distribution of strength values, the process capability indices Cp, Cpk, regardless of any disadvantages and the fact that they have limitations, can be combined with other techniques in the field of statistical process control and become valuable tools in process evaluation of ceramic products.

Advances in Science and Technology, 2006

Although structural kaolin based ceramics are attractive and useful materials, having good mechan... more Although structural kaolin based ceramics are attractive and useful materials, having good mechanical characteristics, low density, good corrosion and high temperature resistance, their use is restricted by their brittle behaviour. In order to improve their properties and mainly strength, toughness and high temperature performance, fibre composite ceramics have been developed. In the present work a series of kaolin-short random dispersed Grafil carbon fibre composites were produced and sintered in an inert atmosphere of Argon at 1000oC and 1300oC and characterised using various techniques. XRD analysis of the kaolin matrix at 1000oC showed that the crystalline phases were decomposed without the formation of mullite a fact which also reconfirmed by SEM examination. However at 1300oC mullite formation was well evidenced. XRD analysis of the fibres in “as received” showed that they have graphite structure which was also retained, as SEM examination revealed, after sintering. Examinatio...

Advances in Applied Ceramics, 2009

The study concerns the recycling of the fly ash (FA) derived from the thermal power stations of P... more The study concerns the recycling of the fly ash (FA) derived from the thermal power stations of Ptolemaida (Greece) and its potential use of this FA as precursor in production of bulk nucleated GCs. The first attempt was addressed to produce a glass from the fine powder of as received FA without any additives. To overcome some drawbacks such as spontaneous crystallisation upon cooling of FA based glass and to improve its working properties, production of pyroxene based glasses from FA was undertaken. The parent glass approached the composition of CaMg 0?75 Al 0?4 Fe 0?1 Si 1?75 O 6 , derived from CaMg 0?75 Al 0?5 Si 1?75 O 6 , which belongs to diopside-Ca-Tschermak solid solutions. Cr 2 O 3 nucleated fine grained mono mineral glass ceramics of augite were produced from the glasses comprising FA and additives of SiO 2 , Al 2 O 3 and MgCO 3. The influence of Cr 2 O 3 content on the development of crystalline phases, the properties and the microstructure of the resultant glass ceramics crystallised at different temperatures was investigated.

Materials Chemistry and Physics, 1987

In this paper we present the results of corrosion resistance of boronized 1020 steel in naphtheni... more In this paper we present the results of corrosion resistance of boronized 1020 steel in naphthenic acid and during high temperature oxidation. The boride layer, consisting of FeB in the outer region and Fe2B in the inner zone, was found to be extremely resistant to naphthenic acid containing media, both in the liquid and vapour phase. During high temperature oxidation in air at 65@C a very thin, 10~ protective oxide layer was formed on the boronized steel, indicating that the boride layer acts as a barrier to oxygen and/or Fe diffusion. Finally both the morphology and distribution of FeB/F?B layers changed during high temperature oxidation.

Journal of Materials Science Letters, 1985

Journal of Materials Science Letters, 1987

Etude de la boruration par cementation en caisse d'aciers commerciaux allies et non allies. I... more Etude de la boruration par cementation en caisse d'aciers commerciaux allies et non allies. Influence des elements d'alliages sur la boruration. Profondeurs, structures et compositions des couches de borures formees

Key Engineering Materials, 2019

Boride coatings on steels have an excellent combination of properties. They can significantly imp... more Boride coatings on steels have an excellent combination of properties. They can significantly improve the hardness, the wear and corrosion resistance of steels. Boronizing of steels has been achieved using different methods such as pack cementation and paste boriding. On the other hand, fluidized bed technology has been successfully used in many surface engineering applications in the deposition of hard and / or corrosion resistant layers e.g. carburizing, aluminizing and chromizing. This method is simple, efficient and environmental friendly and is characterized by excellent heat and mass transfer, which results to improve quality of the as-produced coatings. As a result, fluidized bed technology can be considered as a useful alternative method for the production of boride coatings on steel substrates. In the present paper we used this method to deposit boride coatings on steels. The as-produced coatings were examined by means of optical microscopy, X-Rays diffraction, Vickers micr...

Nanomaterials (Basel, Switzerland), Jan 10, 2017

Silver nanoparticles (AgNPs) have been demonstrated to restrain bacterial growth, while maintaini... more Silver nanoparticles (AgNPs) have been demonstrated to restrain bacterial growth, while maintaining minimal risk in development of bacterial resistance and human cell toxicity that conventional silver compounds exhibit. Several physical and chemical methods have been reported to synthesize AgNPs. However, these methods are expensive and involve heavy chemical reduction agents. An alternative approach to produce AgNPs in a cost-effective and environmentally friendly way employs a biological pathway using various plant extracts to reduce metal ions. The size control issue, and the stability of nanoparticles, remain some of the latest challenges in such methods. In this study, we used two different concentrations of fresh leaf extract of the plant Arbutus unedo (LEA) as a reducing and stabilizing agent to produce two size variations of AgNPs. UV-Vis spectroscopy, Dynamic Light Scattering, Transmission Electron Microscopy, and zeta potential were applied for the characterization of AgNP...

Solid State Phenomena, 2016

Heat treatments of alloys in fluidized bed reactors have been carried out for more than twenty-fi... more Heat treatments of alloys in fluidized bed reactors have been carried out for more than twenty-five years. Recently this technology has been used for surface engineering applications in the deposition of hard and/or corrosion resistant layers e.g. aluminizing, chromizing, nitriding, carburizing, boronizing. The fluidized bed method is simple, efficient, environmentally friendly and capable of immediate adjusting the furnace atmosphere for specific requirements e.g. production of multielement coatings. The boride coatings on steel have an excellent combination of properties e.g. high fatigue strength and wear resistance. On the other hand silicide coatings are well known for their excellent corrosion resistance. Boron-siliconizing in fluidized beds is a promising method to improve both the wear and corrosion properties of steels. In the present paper fluidized bed technology (FBT) was used to deposit boride and boron-silicide coatings on steels. The coatings were examined by means of...

Journal of Materials Science Letters, 2001

Journal of Biomedical Materials Research Part B Applied Biomaterials, 2009

Journal of Materials Science

Heat treatments of alloys in fluidized bed reactors have been carried out for more than twentyfiv... more Heat treatments of alloys in fluidized bed reactors have been carried out for more than twentyfive years. More recently this technology has been used for carrying out nitriding, carburizing and similar surface treatments. This technology offers certain advantages over other traditional methods for Surface Engineering. These advantages include a more precise process control, greater flexibility and more efficient mass and heat transfer control during the process. In this paper we present a design of a fluidized bed reactor capable for carrying out single, and multilayer surface coatings.

Materials Letters, 2002

A simultaneous one-step boroaluminizing process has been performed on a 2.25Cr-Mo steel by means ... more A simultaneous one-step boroaluminizing process has been performed on a 2.25Cr-Mo steel by means of pack cementation method using a B/Al boriding powder. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al and Fe and an inner layer containing mostly B and Fe. The layers were characterized by means of optical and scanning electron microscopy (SEM) in terms of coatings morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coating due to the boroaluminizing process.

Key Engineering Materials, 2011

Chromium coatings have been used for the protection of gas turbine blades in power plants during ... more Chromium coatings have been used for the protection of gas turbine blades in power plants during the last years due to their very good resistance against steam corrosion. Microhardness, scratch, adhesion and pin-on-disk sliding tests are commonly used for rapid evaluation of the mechanical properties of these coatings [1,2]. However, very limited information exists on their fatigue resistance. In this paper we present the experimental results of the impact testing examination of the above coatings. This experimental method is capable to assess the fatigue and the impact wear resistance of coatings working under cyclic impact loading conditions. From the experimental results it was concluded that the slurry Cr, Zr coatings deposited on P91 steel showed adequate fatigue strength for the above-mentioned kind of use.