Skip to main content

Manufacturing technique for layered carbon /ceramic composite for use in high temperature oxidative environment

We previously described a layered carbon glass material system that is different from c/sic , c/sio2 matrix composites in that it consists of a distinct C/C phase which is coated by an sio2 layer. 


https://akshatjiwannotes.blogspot.com/2024/12/low-energy-fabrication-of-high-strength.html


This material system presents a distinct advantage in a high temperature oxidative atmosphere as the C/C matrix is protected by the oxidation resistant glass shield.


Such a material can supposedly be synthesized in an open oxidative atmosphere. In this short note we will answer some questions such as 


What manufacturing technique will be used? 


How can silica particles be sintered on the substrate?


How can adhesion between sintered particles and carbon substrate be ensured?


What, if any ,sintering aids will be used?


What would be the mechanical properties of the composite so formed? 


What level of heat treatment will be required?


To make the composite only the minimum amount of heat that will fuse together the silica particles is required. Further heat treatment will carbonize the internal underlying substrate and convert some of the coating from sio2/c system to sic/c system. 

.


For manufacturing of the ceramics we will use laser sintering technique because it allows us to use lasers as well as focused sunlight in case of solar sinterer to manufacture the composite.


[Can concentrated solar energy be used in materials manufacturing? How?


https://akshatjiwannotes.blogspot.com/2024/10/can-concentrated-solar-energy-be-used.html]


Because the substrate used would be a lignocellulosic biomass, binders will be needed to aggregate the sand particles and to serve as an intermediary layer between carbon substrate and the glass coating after carbonisation. The interface will probably be sic after heat treatment. 


For sintering aid we need to use liquid phase carbon compound: vegetable oils would work well. 


When heat is applied to sio2 oil paste spread on the lignocellulosic substrate complex reactions start occurring 


The carbon on the surface that is exposed to Oxygen will immediately burnout increasing the surface temperature. Underlying carbon will not have access to oxygen and will undergo pyrolysis instead forming pitch /tar like substance. 


This pitch-like substance will be in a molten , low viscosity state due to high temperature of the laser beam and will lead to coalescence of sand particles due to capillary pressure. 


The laser striking the sand particles on the surface will locally melt them and fuse the particles along the boundaries decreasing the porosity of the structure after solidification.


Further heat will be transferred to the carbon intermediate compounds and pyrolize them(to a glassy or graphtic state depending upon the precursor used). At elevated temperatures carbothermal reduction of Sio2 to sic will occur via the formation of silicon monoxide gas. 


Because the laser will only work on the surface, the two faces of the substrate will have to be treated one by one. 


Ultimately all carbon precursors when they are pyrolyzed convert to graphtic or amorphous forms however in the intermediate stage polymeric carbon forms and diamond like carbon forms can be obtained. 


These polymeric carbon forms will act as a layer to hold the silica particles. As silica absorbs most of the heat it will melt on the surface and solidify on cooling. 


Thus a c/sio2 layer composite will be formed ,further heat treatment will slowly graphitise the underlying structure. The silica coating will prevent oxidation of carbon. 


By leaving the carbon in an unfinished state we can preserve energy while still maintaining strength. As long as carbon is not exposed to oxygen any heat addition will only drive it towards graphitization.



The strength of the underlying carbon will be determined by the strength of the original LC biomas. 


Soaking the biomass in oil will help decrease its porosity. Some of the oil will vaporize during heat treatment. 


The adhesion to the LC biomas will be provided by the pitch that is created during the pyrolysis phase that will act as a glue between silica and LC biomas.


The total strength of the composite will be limited by the intermediate layer that holds the substrate and silica particles. 


Some references of experiments that report wetting of carbon with silica 


Fabrication of silica-coated carbon fiber ultramicroelectrodes by 

chemical vapor deposition


https://www.sciencedirect.com/science/article/abs/pii/0022072894871760


A strong carbon-coated silica fibre


https://link.springer.com/article/10.1007/BF00555375


Chemical vapor deposition fabrication and

characterization of silica-coated carbon fiber

ultramicroelectrodes


https://pubs.acs.org/doi/abs/10.1021/ac00111a016


Wetting of carbon nanotubes by aluminum oxide –This result is extremely important because it opens up the possibility of aluminosilicate coating on carbons. Pure sio2 is not needed. Common sand will wo

rk. 


https://iopscience.iop.org/article/10.1088/0957-4484/19/16/165701










Labels:

Comments

Post a Comment

Popular posts from this blog

Low energy fabrication of a high strength layered ceramic composite for high temperature oxidative environments

High temperature materials are required in various applications: in metallurgy, for making combustion chambers of internal combustion engines ,for the body of Stirling engines, for wall material of nuclear fusion reactors, for the body of Jet engines among a few.  For such applications we need materials that can retain their strengths at elevated temperatures and can survive in an oxidative environment  It is the second requirement which is more stringent. Although numerous metallic alloys have been synthesized that can sustain both high temperatures and oxygen attack they require complex processing steps  On the other hand ceramics are good at resisting both oxygen attacks and high temperatures and are relatively simpler to fabricate but are limited by massive amounts of energy required. For example c/sic composites will perform well in demanding high temperature oxidative environments but require vacuum to be manufactured. The acheson process for the formation of sic is...
Post a Comment
Read more

Force calculations on electron in vacuum tubes

ABSTRACT A claim was made in the paper titled “Do electrons really flow as a beam in cathode ray tubes? ” where we asserted that electrons remain near the cathode surface during the operation of CRT. Here we do force calculations on electrons by estimating the debye length of electrons emitted after thermionic emission and show that under given applied voltages if electrons are placed at debye length they are sufficiently far away from the cathode surface to be accelerated towards it.  Debye length, while typically used to measure charge screening distance in plasmas and electrolytes, can also be used to estimate the distance of emitted electrons from the cathode surface.  In the same way debye length is used to calculate the thickness of an electrical double layer in which the surface charge and charge on inner helmholtz plane are immobile & the charges on outer helmholtz plane are mobile we can model emitted electrons as mobile charges & image charges distribute...
Post a Comment
Read more

Do electrons really flow as a beam in cathode ray tubes?

  Abstract: It is generally well accepted that a beam of electrons flow from cathode to anode in a cathode ray tube. Taking pressure  data from a variety of sources from CRT manufacturers’  data sheets to engineering documents of large hadron colliders we show through calculations that there is enough residual gas in these devices to form a conducting path from anode to cathode due to plasma formation. When high voltages are applied at the anode the gas is ionized and becomes a plasma forming a ‘wire’ between the two electrodes that causes conduction of energy.  The objective of this brief note is to encourage scientists and engineers to re-investigate commonly accepted beliefs about vacuum tubes and develop new knowledge that can revitalize the field especially at a time when nano scaled vacuum channel transistors are being envisioned.  Most vacuum tubes have  operating pressures in the ultra high vacuum range. This is true for cathode ray tubes, vacuum tu...
Post a Comment
Read more

Unlocking the Potential of Carbon for Long-Distance Electrical Transmission

ABSTRACT: We present a technique to manufacture large scale carbon based conductors for transmission of electrical energy over continental scale distances. We start by identifying precursors that could be used for production processes.We review the current manufacturing techniques of producing carbon based fibers and explain why certain precursors have dominated carbon materials industry. We identify methods that can be used to increase the yield through alternative precursors.We put forward a theory of why carbon conductors have less conductivity than metals and what can be done to improve it. Finally we postulate that with cheaper production methods even if carbon based conductors are 10 times less effective than poor metallic conductors like steel, they can still outperform them in High Voltage transmission lines if cheap manufacturing techniques could be developed.  INTRODUCTION: Copper and in certain very specific applications aluminium & silicon steels dominate when it co...
Post a Comment
Read more

What's with all the H1B ruckus?

The US policy makers are facing some tough choices as there's now an increased competition for talent from places like Europe,Australia,canada and even from asian nations like south korea , singapore ,saudi arabia ,UAE etc.  While I'm all for protecting domestic jobs there's the danger that USA may face significant competition in the coming decades from the nations that are eager to hire talented immigrants to build their industry.  The solution I think is to take lead in key industries to continue the growth. US did well initially with electric vehicles but it lost advantage. It has a lot going for it in AI and Google's quantum supremacy is promising for US deep tech. In semiconductors the chips and science act did well to promote local industries.  US still has one of the largest fiber optic cable manufacturers. It's telecom industry is doing reasonably well. Boeing  suffered some setbacks but other aviation components manufacturers like GE  are doing well. Th...
Post a Comment
Read more

Doping strategy for all carbon materials

The challange 1. Carbon is a very small atom. With an atomic number of 6, there are only 5 other atoms that are smaller than carbon. Compared to silicon with an atomic number of 14 the doping choices are minimal. Unlike silicon, elemental carbon can't be melt processed so existing tools & understanding about dopants (or more generally alloying) are out.  2. Carbon has a very rich chemistry. Elements like hydrogen & nitrogen that would become good candidates for doping actually form covalent bonds with carbon[1]. And instead of providing electron-hole pairs, the band gap continuously. Compare this with boron & phosphorus in silicon where they act more or less in their free atomic state. Sure with careful engineering maybe hydrogen & nitrogen can be made to fit inside carbon lattice (nitrogen happily sits inside diamond for example & it would be expected that it would act as a dopant in diamond like carbon as well)  3. The crystal arrangements of carbon that ...
Post a Comment
Read more

Powerful permanent magnets with easily available materials

  #engineering #magnets Magnets are critical to energy infrastructure today. They are used in generators (coal,hydroelectric,wind) ,motors in electric vehicles,mechanical pumps etc. Most magnets today use nickel,cobalt,neodymium, Strontium etc. These materials are hard to find, extract & purify. For a renewable energy future it is extremely important to make magnets from easily available materials. Latest research has shown that permanent magnets can be made from abundant materials : iron,carbon,silicon & nitrogen Iron nitride has already been demonstrated as the most powerful magnet ever synthesized but nitriding can be a little complicated. https://phys.org/news/2010-03-iron-nitrogen-compound-strongest-magnet.html https://magnairon.com/technology/niron-2/ Reasonably powerful magntes can be created with composites of iron,carbon and silicon. These elements are much easier to work with. https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.15.024012 https://www...
Post a Comment
Read more

Optical properties of carbon allotropes

   1. Single atom spectrum If we consider carbon as a single atom then it emits all over the visible light spectrum. There are emission lines in red,yellow,green,blue indigo & violet colors. With carbon there's a complete rainbow of colors. By applying corresponding energies(electrical,heat,mechanical it doesn't really matter what kind of energy)specific color lines would be obtainable in carbon.  2. Graphite vs diamond vs diamond like carbon Practically speaking however we don't really find one atom of carbon floating around displaying its vivid colors. Carbon atoms arrange themselves into a dark black graphitic form or a transparent diamond form. Already we have two extremes of optical properties in a single element.  But there's also diamond like carbon. In this form due to functionalization the bond angles of hetero atom-decorated carbon starts to look like that of sp3 diamond. Consequently its properties tend to shift towards diamond as well. It becomes opti...
Post a Comment
Read more

Which book will help me to make my own wireless network?

  Wireless networking is one of those things that is easier to do in practice than it is to learn in theory. You will learn more by jumping in right ahead rather than poring through the books. But if you’re an absolute beginner you need to start somewhere. So I’ll give an overview of the practical aspects of wireless networks first and towards the end of my answer I’ll give suggestions from where you can learn the theory. All wireless networks have three basic components Antennas that send out wireless signals A hardware that provides input signal to the antennas which it sends out wirelessly An operating system that controls the hardware, which sends the input signals to antennas, which then sends it out wirelessly. Now if you look at something as basic as a wifi router you’ll note that it has Antennas (either external or on chip) A chip to which those antennas are connected An OS (that is accessible through the web admin panel) that controls the chip So as a start you should try ...
Post a Comment
Read more