What can "pressure cooker" do besides stewing meat?

Tech 2023-05-05 14:12:09 Source: Network

it is said that,People walk higher, water flows lower.since ancient times,People have endless longing for high places

it is said that,

People walk higher, water flows lower.

since ancient times,

People have endless longing for high places.

For physicists,

Besides being able to climb geographical peaks,

We also need to constantly climb the pinnacle of science,

This means that it is necessary to continuously create more extreme experimental environments.

Part I is afraid of Qionglou Yuyu, high and cold

As is well known, people living in plains or low altitude areas, after entering the plateauReduced air pressureThe oxygen content decreases and may be affected by factors such as ultraviolet radiation and low temperature, which can easily lead to altitude reactions.

But you know what? In addition to people, the daily necessities we use in our daily lives can also experience high reflexes~

For example, items such as toothpaste and facial cleansers will gush out on their own, and bags of puffed foods such as potato chips will swell and burst open.

Image source: Weibo

Reduced air pressureofAir pressure differenceCaused by.

So, the first question, of course, isWhy is the higher the altitude, the lower the air pressure

Let's first consider a small layer at a certain heightA thin atmosphereIts thickness is dz. Middle school physics tells us, what do we do to an object first when we see it?

Of course, it's done firstforce analysisThat's it!

This layer of atmosphere is affected by its owngravityPressure of gas on the upper and lower surfacesWe can assume that the pressure on the lower surface is p, and since atmospheric pressure definitely varies with height, we can set the pressure on the upper surface to p+dp.

according toForce balanceThere can be a formula (where A is the bottom area of the gas column, (z) Is the atmospheric density [1]:

Simplify it into:

Here we can temporarilyAssuming that the temperature of the atmosphere does not vary with altitudeAlthough this assumption is rough, it can be considered to be approximately valid at an altitude of 11-12km [2].

Bring inEquation of state for ideal gaspV=nRTI.e. pM= (z) RT, where M is the molar mass of atmospheric molecules.

And by integrating, the variation of atmospheric pressure p with altitude z can be obtained:

This model is also known asIsothermal atmospheric model

Of course, our daily experience is that temperature often decreases with increasing altitude.

Due to the complex relationship between pressure and temperature changes, we can useMultiparty state processTo describe:

among It's atmosphericSpecific heat ratiopAnd T0It is the atmospheric pressure and temperature on the surface of the earth.

By substituting the above formula and integrating it, a more accurate variation of atmospheric pressure p with altitude z can be obtained:

By calculating the numerical value, it can be known that when The variation of atmospheric pressure with altitude obtained at 1.235 is relatively accurate.

The variation curve of atmospheric pressure with altitude (source: Atmospheric pressure Wikipedia)

Part II wants to reach a thousand miles and take it to the next level

From the above discussion, we can know that in plateau areas, many objects' "high reflection phenomena" come from low pressure.

In other words, the expansion of potato chips and toothpaste comes from a relatively "high" pressure inside compared to the outside world. In addition, we all know that in the plateau area, the low air pressure leads to the low boiling point of water, which leads to inexperience in cooking, and pressure cooker can solve this problem.

In addition to the pressure cooker used in our daily life, in fact, in the laboratory, we can also make someHigh pressure environmentBy subjecting various materials to high pressure, many interesting phenomena can be discovered.

The simplest way to achieve high voltage isCompressing gas or liquidsuch asaccording toofofstate equation pV=nRT

From this, it can be seen that,The isothermal compression process compresses the volume of gas to achieve an increase in pressure

So, the earliest high-pressure scientific devices were created by British physicistsParsonsDesigned and processed in the late 19th centuryPiston Cylinder

Piston Cylinder [3]

Due to the large volume of the pressurized chamber and material limitations, this device cannot apply high pressure. Nowadays, it is often used to generate5GPaThe following pressure environment (approximately 50000 atmospheres).

Piston Cylinder

Later in the mid-20th century, American physicistsBridgmanIntroducing aAnvil pressThe device (pronounced duck gizzard) achieves higher pressure, which is calledBridgman press

Anvil press[3]

ofBridgman pressofAnvil pressofAnvil pressofAnvil pressHard alloy

Bridgman press[3]

Piston Cylinder ofAnvil press

In order to improve the shortcomings of both,Drickamar and BalchanAnvil pressDrickamar deviceAnvil pressofof

Drickamar device[3]

In order to apply a uniform pressure in the cavity, people have developedAnvil pressDesign the high-pressure chamber into a regular polyhedral shape to achieve a relatively uniform static pressure environment within the chamber.

such asofAnvil press[3]

as everyone knows,Diamond is the hardest known substanceAnvil pressofDiamond anvil

Diamond anvilofstayofextrusionThe sealing material in the middle generates high pressure. The small hole of the sealing material is filled with liquid or solid statePressure mediumTo expose the sample in the sealing material toHydrostatic or quasi hydrostatic pressure

Schematic diagram of diamond pressure chamber [3]

To be more specific, a diamond pressure chamber typically consists of theCavity body(Including base, piston, cap with screws to increase pressure and control separation)Anvil baseAnvil baseWashersThe diamond structure and gasket are the most important parts in the composition.

It is worth noting that due to the extremely brittle texture of diamonds, a huge force (about 10000 N) needs to be applied to the diamonds during compression. Therefore, to avoid direct contact between two diamonds, extremely precise mechanical control is required, and precise control must be achievedMicrometer scale[4]

Anvil baseOften made of durable materials (such as tungsten carbide) to withstand the enormous forces that need to be applied.WashersIt is a metal plate with holes used to carry the sample, and its function is to better control the sample in a small area to ensure that the applied pressurePressure gradientIt is uniform and can protect the diamond from direct contact leading to fracture.

Diamond anvil550GPaHigh pressure (5.5 million times atmospheric pressure).

As diamond is a transparent material, it can penetrateElectromagnetic radiation such as visible light, near-infrared light, and X-raysSo it can be widely applied in high-pressure science.

Diamond anvil[6]

After completing the implementation of high voltage, the next step to consider is how to calibrate the high voltage, that is to say,What is the method to know the value of the applied pressure

The most reliable method for measuring ultra-high pressure is to use known materialsstate equation

ofstayofstate equation Shock wave experimentGet. But the biggest drawback of this method is that it requires the use ofX-rayMeasurement is not easy to achieve [4].

Schematic diagram of plane shock wave generated by light bubbles [3]

stayAnvil pressofFormanFor the first time, others proposed usingSpectral methodsPerform pressure calibration [5]. The most commonly used pressure calibration materials areRuby

RubyofdopingCrIonic alumina, its internalCrIons have a series of energy levels, and electrons, after absorbing a certain amount of energy, willJump to a higher energy level firstAnd thenSpontaneous transition to another lower energy level, thereby radiating outfluorescence

Rubyof[3]

RadiativefluorescenceofRubyfluorescenceofof

Ruby[3]

Rubyofofof

Part III will climb to the top and take a look at the small mountains

When substances are in a high-pressure environment, they also exhibit some properties that are different from those under normal pressure. We can refer to them as having undergone high-pressure reactions (or referred to as high reactions).

The most common function of high pressure is pressure cooker. pressure cooker can make food more easily cooked, such as stewing meat more soft and rotten. that is becauseUnder high pressure, the boiling point of water increases When water boils, the temperature is higher, and using the higher temperature to cook food is certainly twice the result with half the effort.

The most direct effect of high pressure on matter isCompressing the volume of an objectThat is, to make the interior of the materialThe spacing between atoms has decreased Thus, the gas becomes a liquid, the liquid becomes a solid, and the density of the solid increases.

For example, under higher pressure, water not only turns into ice, but as the pressure continues to rise, people find thatThe properties of ice are also changing At 0.2GPa, water will form at atmospheric pressureUnstable ice structureThis is actually a new ice structure. At higher pressures, water also has over a dozen different structures [3].

Phase diagram of water [3]

In addition, changes in atomic spacing may cause changes in atomic arrangement.

For example, an atom can interact with a previously distant atom, thereby increasingCoordination number Or the interaction between atoms changes, thereby affectingChemical bondThe strength of. in other wordsPressure causes the structural phase transition of the crystal For example, graphite can be transformed into diamond under high temperature and pressure [6].

Furthermore, due to the reduction in atomic spacing, theEnergy levels are easier to overlapIt is manifested in the crystal as pressureThe force causes a change in the crystal band

For semiconductors or insulators, high voltage can induce the overlap of conduction and valence bands, thereby turning semiconductors or insulators into conductors.

such asIThe transition from insulating state to metallic state occurs at a pressure of 16GPa [6].NaYbSeTransforming from an insulator to a metal under a pressure of 50GPa [7].

How to realize high temperature superconductivity is known as the pearl on the crown of condensed matter physics, and high pressure science provides a means to win this pearl.

stayConventional superconductorofBCS theoryofofof

This means thatofofofSuperconducting transition temperature

ofofofSuperconducting transition temperature

ofstayGPaofofHydrogen rich compoundSH(203K) andLaH250KofSuperconducting transition temperature[4]

Conventional superconductorstayHigh-temperature copper oxide superconductorofSuperconducting transition temperaturestay1.4GPaLanthanum barium copper oxygen systemofSuperconducting transition temperature35K52KofYttrium elementTo replacelanthanide Superconducting transition temperature93KmercuryBarium copper oxygenstay164K[3]

Development History of High Voltage and High Temperature Superconductors [4]

ofof

reference:

[1] Qin Yunhao, Thermology, Higher Education Press, the third edition in 2011

[2] of. 2004233

[3] Liu Zhiguo, Qian Zheng, Male, High Voltage Technology. Harbin Institute of Technology Press, 2012

[4]J.A.Flores-Livas,M.Eremetsetc.Aperspectiveonconventionalhigh-temperaturesuperconductorsathighpressure:Methodsandmaterials,Phys.Rep.856,1(2020)

[5]FormanRA,PiermariniGJ,DeanBarnettJ,BlockS.Pressuremeasurementmadebytheutilizationofrubysharp-lineluminescence.Science.1972; 176(4032):284-5.

[6] , of. 2021

[7]Ya-TingJiaetc.MottTransitionandSuperconductivityinQuantumSpinLiquidCandidateNaYbSe2.Chin.Phys.Lett,37,097404(2020)

Editor: Garrett

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