The study of how the properties of matter arise from its structure at all scales and of how processing can be used to modify those properties (often in pursuit of a specific application).

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3
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1answer
1k views

Is it possible to increase refractive index at lower densities?

Are there any materials for which the refractive index decreases with density? It seems that for most materials we would expect there to be a positive correlation between density and refractive index, ...
0
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1answer
42 views

What metal (or any other material) is a good thermal coductor but a bad conductor of electricity?

Also, this material needs to be easily manageable and accessible. So, I am trying to make a DIY soldering iron and I need to insulate the part that makes the heat and the part that transfers the ...
6
votes
1answer
538 views

Semiconductor problem: how much Boron is required to establish a certain amount of charge carrier density

The problem description is as follows: Boron is used to dope 1 kg of germanium (Ge). How much boron (B) is required to establish a charge carrier density of 3.091 x 10^17 / cm^3. One mole of ...
1
vote
2answers
238 views

What is the physical significance of the Curie constant?

What is the physical significance of the Curie constant? I understand it depends on the effective moment of the ion and hence must be some measure of it, but what is it exactly? Like some average ...
1
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0answers
18 views

Frequency range possible from a mechanical music box [on hold]

Here is a small mechanical music box. The tines of a metal comb are tuned to emit a particular frequency when plucked. The material and structural characteristics of the comb, plucking cylinder, ...
0
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0answers
13 views

Interpretation of Evanescent Elastic Waves for Material Damage

In elastodynamic theory, when the slowness vector is imaginary, the resulting elastic waves are called evanescent. I have read that this corresponds to exponential decay. I have also read that complex ...
-1
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2answers
66 views

What happens to gold under immense pressure? [closed]

What would happen to gold if you put it under immense atmospheric pressures? For example 2M atmospheres.
-1
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1answer
30 views

How is the formula for percent ionic character derived? [closed]

How do the "-(0.25)" and the exponential come into play? Formula: Ionic Character = $100(1 - e^{-0.25(X_C - X_H)^2})$
0
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1answer
416 views

Fundamental frequency of a material and its Young's modulus

I wonder if there is a connection between fundamental frequency and Young's modulus of a material. For example, how to calculate the Young's modulus of a glass bar by knowing its frequency spectrum?
0
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0answers
15 views

Question about a particular thermal shock scenario

I watched this video https://www.youtube.com/watch?v=xbuvcQrAOSk Where they heat up a pyrex pot and then add a few drops of cold water to see how the pot will react (while shooting the scene with a ...
-1
votes
1answer
54 views

How much approximately the pressure would drop?

A container made from from aluminium ($0.5~\mathrm{mm}$ thickness $10^3~\mathrm{cm^3}$) closed system , it has 50 psi (nitrogen) pressure inside at temperature $80^\circ~\mathrm C.$ Approximately : ...
1
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0answers
12 views

Total energy in tight binding methods

How to calculate total energy in tight binding methods? The total energy is calculated as the sum of the eigenvalues of the occupied state?
1
vote
1answer
122 views

Why does the bulk modulus of water have a maximum at around 60-70ºC

So I'm doing some water hammer analysis and was calculating bulk modulus of water as a function of temperature. I took the speed of sound and density of water as functions of temperature and ...
1
vote
0answers
40 views

Is Gas flow rate or Volumertric flow rate right one to use for thick wall?

I will make container from steel or aluminium ( 0.5 mm thickness ) and fill it with air (2 bar) and I want to know how much pressure would the container loose overtime (20 years) ? I have asked this ...
6
votes
1answer
288 views

Force problem related to adhesive and bonding

I have two PCBs (printed circuit board), and they are glued by adhesives, as show in the pictures. And the location of the adhesives are indicated on the picture (please notice that NO adhesive is ...
8
votes
1answer
1k views

Inflating a balloon (expansion resistance)

I am doing a quick calculation on how to calculate the pressure needed to inflate a perfectly spherical balloon to a certain volume, however I have difficulties with the fact that the balloon (rubber) ...
2
votes
3answers
51 views

Why alloy have more resistance?

Is there any simple way to understand why alloy have more resistance than metals? My teacher ask this, I answer that, there might be more free electrons in metals than an alloy, but she said you are ...
0
votes
1answer
55 views

Cardboard allows AM/FM waves but NOT light - Why?

I am going through Electromagnetic waves. In footnote, the author was giving illustration on transparency of materials. Was going through some references here as well as in Google. Many people ...
4
votes
2answers
294 views

Is it possible for an object to have low specific heat capacity and low thermal conductivity?

As I see, there are many examples of object with low specific heat capacity and high thermal conductivity and vice versa. Since they are different properties of matter and their definitions are not ...
13
votes
3answers
1k views

Can the speed of light become complex inside a metamaterial?

The speed of light in a material is defined as $c = \frac{1}{\sqrt{\epsilon \mu}}$. There are metamaterials with negative permittivity $\epsilon < 0$ and permeability $\mu < 0$ at the same time. ...
5
votes
5answers
5k views

Why does grinding steel create sparks but aluminium doesn't?

Grinding steel produces sparks. Grinding aluminium does not. Why? I found this article about why grinding steel produces sparks but would like to confirm if it is true. I would also like to know why ...
0
votes
0answers
13 views

Fracture Mechanics: Relation between delamination and incident pressure

I am working with thin film self replicating cracks wherein a film is placed on a substrate, and the delamination and crack propagation occur simultaneously. I intend to map out the force vector field ...
0
votes
1answer
30 views

atomic concentration by lattice constant [closed]

How to determind the atomic concentration by lattice constant? As a example Crystalline germanium has the diamond lattice structure with a lattice constant $5.66*10^{-10}$ at 300K how to find the ...
0
votes
0answers
46 views

Why are the $d$- or $f$-orbitals considered localised?

Why is it said that the $d$ and $f$ orbitals are localized and the on-site electron correlations could be important? How should one understand this in the context of solid-state physics?
0
votes
0answers
45 views

Bandgap calculation in MQW structure

In advance I want to apologize for my bad english. My question is about the calculation of a Bandgap of a multiple structure crystal. In this case: AlGaInAs. Lets assume that the distribution is: Al ...
2
votes
3answers
211 views

What can justify the decrease of the electrical conductivity with the increase of light intensity?

I have currently been working with a sample that "appears to" decrease its resistance when I cover it and protect it from light. Basically it presents the opposite behaviour of a photoresistor. What ...
17
votes
1answer
295 views

Third-order susceptibilities of metals?

Can anyone point me to a source for measurements of the third-order nonlinear electric susceptibilities $\chi^{(3)}$ of various metals? Specifically in relation to the AC Kerr effect, so measurements ...
0
votes
2answers
70 views

Estimating Young's Modulus

In order to measure the Young's modulus of a rectangular sample of elastic material I subject it to a vertical load along its major axis using weights of gradually increasing importance and measure ...
0
votes
2answers
69 views

How much pressure would I lose on one side?

The equation for the gas flow rate (in pressure*volume/time units) $$ Q = {kA\over d} (p_1-p_2) $$ where $A$ is the surface area, $d$ the wall thickness, $p_{1,2}$ the pressures on either side of the ...
3
votes
4answers
344 views

Surface area of glass (or general material) and strength

How does the surface area of a piece of glass (or any general material; sapphire isn't technically glass) correlate with strength? Strength as in resistance to pressure concentrated at a small point? ...
0
votes
3answers
66 views

the poisson ratio and conservation of volume

In order to measure the Poisson ratio of a rectangular sample of elastic material I subject it to a vertical load along its major axis using weights of gradually increasing importance and measure the ...
2
votes
4answers
15k views

Why don't FCC metals have a brittle-to-ductile temperature transition?

I initially thought that it had something to do with the number of slip systems in FCC vs. BCC, but they're both the same.
0
votes
1answer
14 views

Material emissivity coefficient

If I have a coated material (e.g. oxidized steel painted with white paint) which emissivity coefficient do I use ? The one of the paint (0.3-0.5) or the one of the base material (0.8) ? Many collegues ...
0
votes
0answers
10 views

Advantage of magnetic material as film?

what is the advantage of depositing Neodymium magnetic film in the form of thin or thick film when compared to sintered neodymium magnets? Is there any difference in using magnetic material in the ...
0
votes
1answer
27 views

Can a decompressed airplane cargo hold cause packaging air pads to burst / deflate?

I received a parcel from Germany to Chile recently. The contents were severely bruised due to a lack of packaging material. On second inspection I found a bunch of deflated air pads. It was a ...
5
votes
1answer
411 views

What factors cause the velocity saturation to occur at different electric fields for different materials?

In semiconductors the velocity of carriers gets saturated after a certain value of electric field. In silicon it occurs at around $10^4 kV/cm$ and in GaAs at some other value. What factors are ...
0
votes
1answer
37 views

Dyson Sphere Structures [closed]

In a type II civilization we may need to harvest the energy of neighboring stars. Freeman Dyson gave an interesting point of view that we could invent a megastructure to harvest this type of energy. ...
20
votes
2answers
3k views

Melting diamond and cool down as diamond

Is it possible to melt diamond? And if possible while let it cool will it became diamond again?
1
vote
1answer
148 views

Energy conservation of permanent magnets engine

How to explain the fact that magnet can attract an object (apply a work W) without losing a (significant) part of its internal energy? How to apply the energy conservation principle? Please think to ...
49
votes
2answers
4k views

Why does sound absorption in oceans depend on the pH?

I was reading "The Sixth Extinction: An Unnatural History", by Elizabeth Kolbert, and there she comments that high level of $CO_{2}$ in the atmosphere lowers the pH of oceans (which makes sense) and, ...
0
votes
1answer
34 views

Composite materials [closed]

I'm reading about brake pad material. The paper said ...according to original equipment manufacturer (OEM) the pads are made by combining five types of materials: binders, abrasive, performance, ...
-1
votes
0answers
12 views

Chromatic confocal microscopy (CCM) and stylus probe

I read research that compared between chromatic confocal microscopy (CCM) and stylus probe in wear test but the research didn't clearfield what is chromatic confocal microscopy and what is the stylus ...
2
votes
1answer
109 views

Mathematical expression of energy storage

I'm trying to develop an idea which is as follows. Put simply, imagine a flat sheet of material which, when distorted (I.e. curved in the third dimension) stores energy. Now, by calculating the ...
0
votes
0answers
45 views

Speed of sound in solid — temperature dependence

Let $v$ denote the speed of sound in a fixed solid, at a fixed temperature $T$. This will depend on properties of the solid (such as the bulk modulus and density). Given an increase in $T$, does $v$ ...
5
votes
2answers
5k views

Penetration of armor plate

Is there a simple mathematical expression for the stopping power of a given thickness of armor, given the thickness of armor plate, the radius of a cannon ball, the density of the cannonball and the ...
6
votes
0answers
47 views

Crack pattern of safety glass - what gives rise to spider web-like shape

When (laminated) security or shatter-proof glass fractures, the ensuing crack-pattern is often resembling a spider web, with radial and concentric cracks, see e.g. (Source: http://essentialhommemag....
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votes
2answers
73 views

How do signals go through solid objects? [closed]

So many types of signals pass, or seem to pass I don't know, through solid objects. How do they do this?
2
votes
1answer
58 views

Why does wood go straight into ignition, while other materials melt first?

Background: I was cooking eggs (very difficult) with a plastic spatula which was not very good, so when I set it on the border of the pan it began melting. In order to keep cooking, I reached for a ...
8
votes
2answers
148 views

Why do headphones tangle themselves whereas shoe laces untie themselves?

Why do headphones tangle themselves whereas shoe laces untangle or untie themselves? Why aren't we using the phenomenon to create headphones that tangle less and shoe laces that untie less?
22
votes
3answers
2k views

Why are ceramics good electric insulators?

I know it depends a lot on the composition, so not all are great electric insulators. So what makes it good or bad? And is it different from what makes them good thermal insulators? Power line ...