material news

What materials are named ‘high entropy alloys’, explain the origin this name and indicate their specific properties basing on a selected example.

High-entropy alloys (HEAs) are substances that are constructed with equal or nearly equal quantities of five or more metals. These alloys are currently the focus of significant attention in materials science and engineering because they have potentially desirable properties.

Furthermore, research indicates that some HEAs have considerably better strength-to-weight ratios, with a higher degree of fracture resistance, tensile strength, as well as corrosion and oxidation resistance than conventional alloys.

Indicate differences in properties between graphene and silicene.

Contrary to graphene, silicene is not flat, but has a periodically buckled topology; the coupling between layers in silicene is much stronger than in multilayered graphene; and the oxidized form of silicene, 2D silica, has a very different chemical structure from graphene oxide.

Silicene’s hydrogenation reaction is more exothermic than graphene’s. Another difference is that since silicon’s covalent bonds do not have pi-stacking, silicene does not cluster into a graphite-like form.

Compared with graphene, silicene has several prominent advantages: (1) a much stronger spin–orbit coupling, which may lead to a realization of quantum spin Hall effect in the experimentally accessible temperature, (2) a better tunability of the band gap, which is necessary for an effective field effect transistor (FET) operating at room temperature, (3) an easier valley polarization and more suitability for valleytronics study.

Give three examples of graphene-like materials.

The highlighted graphene-like structures include layered van der Waals (vdW) materials (h-BN, MoS2, α-MoO3, and V2O5), graphitic-like ZnO, MXenes (metal carbides or carbonitrides), the not-yet-synthesized B2C, SiC2, BSi3, arsenene and antimonene, and single-layer coordination polymers ([Cu2Br(IN)2]n (IN = isonicotinato), Fe-phthalocyanine, and nickel bis(dithiolene)).

What are major applications of graphene-like materials?

Solar energy cells, electrical batteries, medical aplications(corporal scanning,bionic), LEDS, electronical industry.

What properties are required for a material to be named biodegradable?

All biodegradable polymers should be stable and durable enough for use in their particular application, but upon disposal they should easily break down.non-toxic, capable of maintaining good mechanical integrity until degraded, and capable of controlled rates of degradation.

What are the factors controlling the rate of degradation?

Percent crystallinity, Molecular weight, Hydrophobicity

What two chemical reactions take place during biodegradation?

Those based on oxidation and those based on hydrolysis.

What takes more time, composting or biodegradation?

Biodegradation may take longer than required in composting

What are types of thermal based biodegradable films and their properties?

Biodegradable polythene film, Starch based or biobased (hydrodegradable) film, Additive based, Oxodegradable, Enhancing Hydrophilicity of the Polymer

What is the structure of graphene?

Graphene is a 2-dimensional, crystalline allotrope of carbon. Single layer of graphite Honeycomb (hexagonal) lattice.

Mention the known allotropic forms of carbon.

Diamond – Graphite – Graphene – Nanotube – Fullerene

What are the main properties of graphene?

Electrical Properties:Electrical conductivity 200 times faster than silicon.

• Dissipates heat 10 times better than copper.

Mechanical Properties:Strongest material ever discovered

• Ultimate tensile strength of 130 GPa compared to 400 MPa for structural steel,   it is very flexible

Optical Properties:Can transform light into electricity with a 82% of greater efficiency than the actual industrial technology.

• Only absorbs 2.3% of white light, very transparent.

How many times is graphene stronger than steel theoretically?

It is hundreds of times stronger than most steels by weight.

What is the main difference between metallic glasses and other metals?

Most metals are crystalline in their solid state, which means they have a highly ordered arrangement of atoms. Amorphous metals are non-crystalline, and have a glass-like structure.

What is the main advantage of metallic glasses?

Non-crystalline, and have a glass-like structure. Amorphous metals have good electrical conductivity.

The material structure also results in low shrinkage during cooling, and resistance to plastic deformation. The absence of grain boundaries, the weak spots of crystalline materials, leads to better resistance to wear and corrosion.

How many types of metallic glasses do we have depending on composition and what are they?

1. Metal – metal metallic glasses 2. Metal – metalloid metallic glasses.

Give three applications of metallic glasses in industry.

The low magnetization loss is used in high efficiency transformers (amorphous metal transformer) at line frequency and some higher frequency transformers.

Also electronic article surveillance (such as theft control passive ID tags,) often uses metallic glasses because of these magnetic properties.

Amorphous metals exhibit unique softening behaviour above their glass transition and this softening has been increasingly explored for thermoplastic forming of metallic glasses.