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Can a spectrogram for a composite material, ie a rock, be derived from chemical, crystallographic, and other data?

I'm a first year part-time engineering student at the University of South Australia, involved in a global citizen science project, Space Decentral Project Coral, headquartered in San Francisco, CA. Our team is designing a mission to demonstrate the production of a building material article, ie a brick or paver, by microwave sintering of lunar regolith.

I have a background in electronics, and in geology. My task is to find the optimum microwave frequency/s for sintering lunar regolith. This has implications for C-SWAP (cost, size, weight, and output power level) on our lunar lander.

Microwave sintering and/or melting of lunar rock and regolith has been demonstrated in the literature, but in virtually all cases, the investigators are using a domestic microwave oven and unlimited power from the electricity grid. Our lander will be mobile and quite small, and there is a limit to how many photovoltaic solar cells we can attach to the vehicle, and thus, how much power we can generate. In addition, we need to budget our generated power to other functions on the lander as well. So, our maximum generated power is 0.5-1 kW, and may be less.

I'm pretty sure for our purposes, access to lunar material for analysis isn't an option, so I've been working on another way to get my result, and I wish to ask someone here for a reality check.

Spectrographic data for the lunar material in the microwave frequency region doesn't exist. Believe me, I've looked pretty hard. There are some spectra in the low radio frequency (0.5 - 10 MHz), and plenty in the FIR to VIS region.

I have collected, or have access to, the published chemical, mineralogical, crystallographic data for lunar material. In addition, there are plenty of analyses for terrestrial constituent analogues of lunar rock (basalts). I also am reading the papers for all the past lunar mission microwave remote sensing experiments and data.

My plan is to use this data to forward model, ie derive or synthesise, the microwave absorption spectrum of lunar rock and regolith material, from 1 to, say, 150-200GHz. I realise some of the data has been derived from spectrographic techniques, but for reasons I've outlined above, that option isn't isn't available to me. I presume the principal of reciprocal action applies here.

The maxima should tell me which frequencies are being absorbed the most, and hence presumably heating the material. The higher the frequency my model is valid to, the better, since the microwave source generator, whichever one, would be smaller and lighter, and also the most energetic (Е = hν). In addition, at the high end, I'm starting to get into the Terahertz region, and there are currently some interesting technological developments happening in this region, with higher power level output devices becoming available.

I would test my model from existing analyses of terrestrial basalts, backed up with 2-3(?5) laboratory analyses to validate my method, depending on lab access, and what I can afford.

My current approach is to understand the interaction of matter with microwave radiation. I started from the Wikipedia articles, and have gone on to read about dielectric materials, and relaxation and dispersion mechanisms - Cole-Cole, Cole–Davidson, and Havriliak–Negami. Along the way I have strayed into fractional calculus. My next step would be to start connecting chemical and structural composition with dielectric constant, and to learn how the microwave spectral response is affected by multiple dielectric compositions.

Concurrently, I've identified some gaps in my knowledge, and I'm reading up on quantum mechanics, and the attendant mathematics and physics.

Is there any way I can use spectra or their information in other regions of the EM spectrum for any purpose in the microwave region?

Am I barking up the wrong tree?

Thanks in advance.

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Contributor III

Re: Can a spectrogram for a composite material, ie a rock, be derived from chemical, crystallographic, and other data?

Dear Julian,

The short answer is “no”. The more important question is what do you really want to know? Chemical composition, melting points, physical structure? We unfortunately have not yet discovered the low-power universal analyzer. MANY different chemical and physico-chemical methods are used for all kinds of different analyses. They exist because nothing works well for everything! Even within particular disciplines, like spectroscopy, the effects and observations of molecular and elemental interactions with electromagnetic radiation are quite different for all kinds of materials.

From your project description, I would suggest that better solutions will be obtained by defining exactly what you need to know about a sample (and why). THEN you may have a better perspective on possible solutions to the assays required. Using microwaves for reaction energy sources or for analytical references (not applicable to many materials, anyway) are two very different things.

The characteristics of EM interaction with elements and molecules are such that you cannot make inferences between different methods. That is, I cannot use an infrared spectrum to infer what a microwave spectrum would look like. With what we know about the interactions, we may be able to deduce the most probable sets of interactions – e.g. which electromagnetic frequencies would be most likely to induce an observable change in a compound (if at all).

There are published tables and books of tables for many spectrographic interactions. While we are happy that there seems to be no bound for the expansion of science, in most of these cases, if there are no published data it usually means that the particular sample-method combination does not work.

Best regards,

Steven