Steel
Stainless steels are generically defined as ferrous alloys containing chromium, generally in quantities between 11 and 30%. Chromium gives the steel a protective anti-corrosion film. Other binders can be nickel, copper, titanium, molybdenum and niobium. The variation of each individual binder affects the structural, mechanical and corrosion characteristics of the steel.
Based on the crystalline structure, steels are divided into:
Based on the crystalline structure, steels are divided into:
- martensitic: are chromium alloys in the percentage range of 11% – 18% with a significant quantity of carbon containing other elements such as manganese, silicon, chromium and molybdenum
- ferritics: i.e. stainless steels containing only chromium in the range percentage of 12% – 17%
- austenitic: i.e. stainless steels containing nickel (8% -14%), chromium (17% -19%) and a possible small quantity of molybdenum (2% -3%)
- austeno-ferritic (or duplex) i.e. stainless steels containing Chromium (18% – 26%), Ni (4.5%-6.5%), and a possible small quantity of molybdenum (2.5% -3
The acronyms AISI 304 and AISI 316 indicate a high quality austenitic stainless steel containing Chromium (18%) and Nickel (10%). In fact, AISI 304 stainless steel is also defined by the acronym 18/10 precisely in reference to the quantity of Chromium and Nickel. AISI 304 is the steel generally most used for cutlery, hoods, kitchens, sinks etc.
For other types of use and especially for difficult environments (ports, industrial areas, very polluted environments) AISI 316 certified steel is more suitable, which contains a percentage of approximately 3% Molybdenum which ensures better resistance to corrosion of chlorides. For this reason it is the first choice steel used in naval carpentry.
Aramid
Aramid or Aramid fibers are polymer fibers with very high mechanical performance obtained by processing Aromatic Polyamides. Polyamides are a family of polymeric materials obtained by polycondensation of diamines and dicarboxylic acid; they can be characterized by a "linear" structure or contain aromatic groups.
We talk about polyamides with a linear structure or chain when the bonds between the carbon atoms and the various functional groups develop predominantly along a line. Among the polyamides with a linear structure it is worth mentioning Nylon.
Nylon, being characterized by a linear structure, is very deformable. In fact, it is characterized by an elastic modulus E of around 5 GPa and has a relatively low mechanical tensile strength compared to that of other polymeric materials; Due to its low rigidity and toughness, Nylon is not used in the structural sector.
The presence of aromatic rings in the molecule of a polyamide leads to an increase in mechanical performance compared to those of linear polyamides, in particular, in the modulus of elasticity. If the content of aromatic rings is greater than 85%, it is called aromatic polyamides and, more specifically, ARAMIDS.
Aramid fibers are characterized by a mechanical tensile strength comparable to that of the most common carbon fibers but by an elastic modulus that is on average lower. On the other hand, due to their lower specific weight (1.4 g/cm3 versus 1.8 g/cm3 for carbon) aramid fibers are characterized by a higher specific resistance understood as mechanical tensile strength compared to the specific weight of the material.
The use of aramid fibers is mostly indicated in the reinforcement of masonry structures where a high elastic modulus is not necessary and can often constitute a problem.
Furthermore, they stand out for having high cut and abrasion resistance, good heat stability (it decomposes at around 500°C), and is a non-conducting material. In the presence of UV radiation, degradation phenomena are generated.
We talk about polyamides with a linear structure or chain when the bonds between the carbon atoms and the various functional groups develop predominantly along a line. Among the polyamides with a linear structure it is worth mentioning Nylon.
Nylon, being characterized by a linear structure, is very deformable. In fact, it is characterized by an elastic modulus E of around 5 GPa and has a relatively low mechanical tensile strength compared to that of other polymeric materials; Due to its low rigidity and toughness, Nylon is not used in the structural sector.
The presence of aromatic rings in the molecule of a polyamide leads to an increase in mechanical performance compared to those of linear polyamides, in particular, in the modulus of elasticity. If the content of aromatic rings is greater than 85%, it is called aromatic polyamides and, more specifically, ARAMIDS.
Aramid fibers are characterized by a mechanical tensile strength comparable to that of the most common carbon fibers but by an elastic modulus that is on average lower. On the other hand, due to their lower specific weight (1.4 g/cm3 versus 1.8 g/cm3 for carbon) aramid fibers are characterized by a higher specific resistance understood as mechanical tensile strength compared to the specific weight of the material.
The use of aramid fibers is mostly indicated in the reinforcement of masonry structures where a high elastic modulus is not necessary and can often constitute a problem.
Furthermore, they stand out for having high cut and abrasion resistance, good heat stability (it decomposes at around 500°C), and is a non-conducting material. In the presence of UV radiation, degradation phenomena are generated.
Basalt
Basalt has always been used since ancient times for its hardness to pave roads and, as fill, in buildings. More recently it has also been used in the production of anti-abrasive coatings and flooring tiles using melt moulding. In fact, in recent decades, it has been discovered that basaltic rocks are not all identical chemically
The technological process for the production of basalt fiber is based on four fundamental steps:
▪ an initial pre-treatment of the basalt rock
▪ a furnace melting process to obtain continuous fibres
▪ a continuous "spinning" treatment
▪ "weaving" or other, more particular, processes to obtain other final shapes for specific applications
The technological process for the production of basalt fiber is based on four fundamental steps:
▪ an initial pre-treatment of the basalt rock
▪ a furnace melting process to obtain continuous fibres
▪ a continuous "spinning" treatment
▪ "weaving" or other, more particular, processes to obtain other final shapes for specific applications
To produce basalt fiber it is necessary to bring the rock beyond the melting temperature (around 1400 °C) in order to guarantee an adequate viscosity for spinning. To do this, a furnace made of refractory material is used. The melt is then extruded through a matrix containing multiple bushings to produce continuous basalt strands. These threads are wound on a spool, an operation which also has the task of stretching the fibers in order to reduce their diameter and increase their mechanical properties. Although quite similar to glass fibres, basalt fibers have superior mechanical properties but require a higher temperature to be spun, making the production process more energy-intensive. The Parisian Paul Dhé was the first to obtain a patent for the production of basalt filaments in 1923; after the Second World War researchers from France, Germany, Great Britain, Italy and mainly the USA continued with the first attempts to extrude basalt. Only in the 1950s and 1960s did the first significant results occur in Moscow and Prague and in the following decade interest, also motivated by the extensive existing deposits, also resumed in the north-west of the United States. In the same years, the Soviet Ministry of Defense also demonstrated interest in the potential of this technology for military and aerospace applications. The research was thus centered in the important center of Kiev: the development was successful but the technology was kept secret except for a few short, small publications. Research institutes and manufacturing facilities were clearly off limits. Only in the 1990s was this technology declassified and this allowed its use for civilian use to begin.
Carbon
Carbon fiber is a polymer consisting only of carbon atoms, characterized by:
• diameters between 5 and 15 µm;
• high electrical and thermal conductivity;
• chemical inertness (except for oxidation);
• high mechanical characteristics (flexibility, elastic modulus and resistance).
Carbon fibers can be produced from two precursors:
• diameters between 5 and 15 µm;
• high electrical and thermal conductivity;
• chemical inertness (except for oxidation);
• high mechanical characteristics (flexibility, elastic modulus and resistance).
Carbon fibers can be produced from two precursors:
- PAN
- PITCH (pitch)
Depending on the precursor used, fibers with different mechanical characteristics are obtained.
CARBON FIBERS FROM PADS
The process is divided into three phases:
CARBON FIBERS FROM PADS
The process is divided into three phases:
- heating to 300 - 400°C
- oxidation at approximately 700°C
- carbonization, in an inert atmosphere up to temperatures of 1300°C
The final result is the formation of polymers with an almost pure, continuous and regular graphitic structure along the entire fiber.
The carbon fibers obtained from PAN have a turbostratic structure, that is, with a crystalline structure formed by planes each deviated laterally compared to the other, the sheets of carbon atoms are joined randomly or folded together; these fibers tend to have a higher tensile strength
PITCH CARBON FIBERS
Pitch, pitch or tarry residue, is the residue of the distillation of tar or oil which, with a heat treatment between 400 and 450°C, forms a mesophase, i.e. liquid crystals having an intermediate molecular order between that of crystals and that of a liquid; subsequently, during extrusion from a capillary, the mesophase molecules are oriented along the fiber axis. Finally, heat setting (300 °C) and carbonization (1500-3000 °C) follow.
Increasing the final treatment temperature improves the degree of preferential orientation within the fiber and therefore the modulus of pitch-based fibers.
The carbon fibers obtained from PAN have a turbostratic structure, that is, with a crystalline structure formed by planes each deviated laterally compared to the other, the sheets of carbon atoms are joined randomly or folded together; these fibers tend to have a higher tensile strength
PITCH CARBON FIBERS
Pitch, pitch or tarry residue, is the residue of the distillation of tar or oil which, with a heat treatment between 400 and 450°C, forms a mesophase, i.e. liquid crystals having an intermediate molecular order between that of crystals and that of a liquid; subsequently, during extrusion from a capillary, the mesophase molecules are oriented along the fiber axis. Finally, heat setting (300 °C) and carbonization (1500-3000 °C) follow.
Increasing the final treatment temperature improves the degree of preferential orientation within the fiber and therefore the modulus of pitch-based fibers.
Glass
Common experience teaches that monolithic glass is a fragile material. If, however, it is spun at diameters of less than a tenth of a millimetre, it loses its characteristic fragility to become a material with high mechanical resistance and resilience. The fragility of common glass is due to the large number of crystallization defects that act as microfractures and areas of stress concentration, on the contrary, glass fiber does not have many defects, so it reaches considerable mechanical resistance.
The main technology used today to form glass fibers is the direct fusion method; this method uses furnaces divided into three sections:
The main technology used today to form glass fibers is the direct fusion method; this method uses furnaces divided into three sections:
- in the first part the molten glass arrives, which is homogenized and from which gaseous inclusions are removed;
- a second refinement section, where the temperature decreases (from 1370 to 1200°C) to increase the melt density
- finally the section located directly above the stations for fibre production.
The glass is then passed through platinum-iridium dies which are also heated, which contain from 400 to 8000 holes. The amount of glass above the orifices, the viscosity of the melt, the number and size of the orifices, and the speed at which the wires are drawn affect the diameter of the filaments produced.
During the fibering phase, at the exit of the spinneret, each yarn is treated with sizing; the primer is made up of organic materials dispersed in water and is designed to give the glass thread the characteristics necessary for the final processing. The sizing treatment helps to improve the mechanical properties of composite materials and their resistance to ageing. Subsequently, the fibers, collected in spools, are placed in an oven to eliminate solvents and water associated with the sizing application.
A completely similar technique uses glass marbles with a diameter of ¾ inch which are heated and
brought almost to melting point to be drawn into the dies.
Among the main characteristics of glass fibers are:
During the fibering phase, at the exit of the spinneret, each yarn is treated with sizing; the primer is made up of organic materials dispersed in water and is designed to give the glass thread the characteristics necessary for the final processing. The sizing treatment helps to improve the mechanical properties of composite materials and their resistance to ageing. Subsequently, the fibers, collected in spools, are placed in an oven to eliminate solvents and water associated with the sizing application.
A completely similar technique uses glass marbles with a diameter of ¾ inch which are heated and
brought almost to melting point to be drawn into the dies.
Among the main characteristics of glass fibers are:
- Good stability at high temperatures
- Excellent resistance to thermal shock
- Good dimensional stability
- Good mechanical resistance (The glass maintains its mechanical properties up to 50% of its resistance capacity at 375°C and up to 25% at 538°C)
- Low thermal conductivity
- Incombustible
- Excellent flexibility
- Good chemical resistance
Depending on their composition, a distinction is made between: E Glass and AR Glass - E glass
- Since 1930, glass yarn has been considered one of the materials of the future thanks to its dielectric characteristics (it is used to insulate electrical conductors at high temperatures); these characteristics have determined the large-scale industrial use of type E glass yarn, alone or in combination with synthetic or painted resins. E glass is the most used, both in the textile industry and in composite materials, where it represents 90% of the reinforced materials used.
- AR glass(alkali resistant)
AR glass was conceived as a reinforcing material for concrete; contains a lot of zirconium oxide which gives it excellent resistance to the alkaline compounds generated by drying operations. AR glass yarns improve the load resistance and durability of the concrete, and furthermore, glass yarn reinforced concrete castings are consequently lighter.
Zylon Pbo
A few years ago, a new synthetic fiber, PBO (Polyparaphenylenebenzobisoxazole), produced by the Japanese company "TOYOBO", called ZYLON, began to be introduced in Europe.
Zylon® (PBO) is a fiber with very high modulus and tensile strength values, approximately double compared to an aramid fibre; excellent creep resistance and resists heat very well, with a decomposition temperature of 650°C.
In the presence of UV radiation, oxidation phenomena are activated leading to a decline in mechanical performance.
The main characteristics of PBO are:
Zylon® (PBO) is a fiber with very high modulus and tensile strength values, approximately double compared to an aramid fibre; excellent creep resistance and resists heat very well, with a decomposition temperature of 650°C.
In the presence of UV radiation, oxidation phenomena are activated leading to a decline in mechanical performance.
The main characteristics of PBO are:
- Very high elastic modulus and tensile strength
- excellent creep resistance
- excellent heat and flame resistance
- decomposition temperature of 650°C
- loss of mechanical performance in the presence of UV radiation
- chemically stable with most organic substances
- in the presence of strong acids there is a decrease in mechanical properties