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NNadir

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A critical issue of critical materials; my holiday science reading list.

I have 10 glorious days off from paid work this holiday, and plan to catch up on some reading for which I've had little time.

One important task will be to write to an on line friend about what I've learned about her great niece's diffuse intrinsic pontine glioma, a very dangerous (and rare) pediatric brain cancer which has been the subject of considerable research.

It's frightening, but I believe I'm an old Obama boy; I believe in hope. I'll do what I can to be of any help.

Another is to catch up on some reading about the broader challenges to humanity beyond any individual beautiful and threatened child.

Tonight in my files, I came across a highly cited paper which I have not read; it's on my holiday reading list, this one:

What Do We Know About Metal Recycling Rates? (Graedel et al, Journal of Industrial Ecology Volume 15, Issue 3 June 2011 Pages 355–366)

A few years back, around this time of year, I came across an interesting (if unappreciated) book in the New Books rack in Princeton University's Engineering Library, a sort of shrine that I visit often on my path to peace. It's this one: Thanatia

The above cited paper was in fact a reference from this book.

Thanatia s a little rapped up in this Gaia/not Gaia sort of touchy feely stuff, but I think a somewhat poetic description of a critical issue about which too little public discussion takes place.

The preface of the book, which is now in my files, states issue it addresses quite well:

The extraction of fossil fuels and mineral resources has grown exponentially since the early 20th century and far from decelerating, it is expected to increase in the coming decades. "The Limits to Growth" (Meadows et al., 1972) already alerted that if demand of metals and fossil fuels maintained the same trend, mankind would sooner or later be close to collapse. The book provoked a strong controversy between those that considered that the Earth was plentiful of non-renewable resources (technooptimists) and those who believed in the need for a rational management of the planetary mineral endowment.

Forty years on society has experienced an unparalleled economic optimism (especially in the nineties and the first few years of the 21st century) and also the biggest economic crisis since the Wall Street crash in 1929. At the same time, computers, smartphones, the electric car, renewable energies, new materials and electronic appliances are renovating the optimism for a brighter future. Yet all these technoartifacts are deeply connected to the mineral endowment of the Earth. Elements like indium, gallium, germanium, rare earths, tantalum, zirconium, cobalt, tin, precious and platinum group metals, lithium, tellurium, phosphorous, etc, are profusely used without or with only minor recycling.

How long can society survive without a rational management of these scarce resources? Today, technology is employing all elements of the periodic table and their use is growing exponentially.-Yet this fact is barely discussed in conventional ecological discourse that preferably focuses on climate change, loss of biodiversity, deforestation or ecosystems destruction.


I am, even if I believe that the popular beliefs about sustainability are actually dangerously wrong headed - as much on the left as on the right - still a kind of "techno-optimist." I once spent an afternoon chatting with Freeman Dyson after all.

But as much as in my techno-optimism I believe that dire and extreme problems can be solved, I'm less and less inclined to have faith that they will be solved.

The Christmas season in the United States is a party time: I will participate. But there is some place in it as well, for me if not for everyone, for some sobriety.

Have happy holidays and if you can squeeze in some time, read some science. It's good for you, far better than egg nog.


A Nice Discussion of the Use of Desalination Brines for the Production of Caustic Soda (NaOH).

Many years ago, in this space, back when I was still a fan of so called "renewable energy," I wrote a brief discussion of the potential use of California's Salton Sea as a tool for energy recovery and desalination.

That post is here: I offer a crazy energy idea about which I've fantasized: The Salton Sea.

Many of my energy ideas have changed since I wrote that piece 12 years ago. This was, for example, before the planetary community invested trillions of dollars in so called "renewable energy," dominated by the useless solar and wind industries.

In November of 2005, the mean concentration of the dangerous fossil fuel waste as reported at the Mauna Loa carbon dioxide observatory was 378.29 ppm. In November of 2016, the most recent posted monthly mean posted there, the concentration was 405.14 ppm.

The average for all year to year monthly comparison figures recorded as increases in the 20th century was 1.30 ppm/year. Since November of 2005 to November of 2017, the same type of average is 2.24 ppm/year.

So called "renewable energy" is a grotesque failure. It has not worked; it is not working; it will not work, if the goal is to address climate change rather than to post "feel good" stuff on the internet about how wonderful solar and wind are and how wonderful it is to subsidize the billionaire Elon Musk to the tune of billions of dollars because he's so, um, "green."

However this may be, and however much I may have changed my mind about so called "renewable energy" since 2005, I am still very concerned about our absolute indifference on this planet to address climate change. Now, as the end of my life approaches filled with existential guilt about what my generation is leaving for future generations, I am very much trying to spend some portion of my time to thinking about ways to remove carbon dioxide from the atmosphere, in other words, how future generations might, to whatever extent possible, clean up the planetary superfund site with which we've left them.

Once consequence of climate change will almost certainly involve access to clean and fresh water. We have seen this in many places on this planet, most graphically and recently for those Americans who give a shit - this would leave out anyone involved with the Trump crime family - in California, where I used to live decades ago, and where I used to think all the time about water.

It does seem to me that the only approach to addressing this issue in places like California, and for that matter in places where water supplies depend on glaciers, which they do for billions of people will involve seawater desalination.

Desalination is not, in any way, environmentally benign, however. One of the most important issues involved is of course, energy. Unless clean carbon free sustainable energy is available - I never tire of pointing out that in my opinion only nuclear energy meets this criteria - all desalination schemes will be counter productive.

The other problem with desalination concerns the resulting brine. Most schemes for desalination return the concentrated brine directly to local waters. On a grand scale this has the potential for further environmental destruction not only because of the impact on local ecosystems, but also on the further destabilization of oceanic salt gradients, which in turn further destabilize climatic and temporal weather.

Although I still favor, for certain reasons, the same thing I proposed in 2005 for the Salton Sea, formally reduced pressure distillation, over all in the scientific literature, at least in my overall impression, much of the discussion has focused on membrane separation.

A very nice overview of a potential solution for the brine problem (with some impact on the energy problem as well) was recently published in the wonderful scientific journal ACS Sustainable Chemistry and Engineering by scientists out of MIT.

The paper is here: Utilization of Desalination Brine for Sodium Hydroxide Production: Technologies, Engineering Principles, Recovery Limits, and Future Directions (John Leinhard V, et al, ACS Sustainable Chem. Eng., 2017, 5 (12), pp 11147–11162)

All of the energy ideas I've had in my lifetime involve the utilization of by products of processes - often referred to as "waste" in our common parlance - as starting materials or tools to accomplish other tasks. (Mostly this involves material by products but also can include heat.) This is why this paper so pleases me. It proposes to use a waste product (brine) to make another value added product (caustic soda, NaOH).

The introduction to the paper addresses this nicely:

Environmental and economic factors have long motivated interest in reducing the amount of brine discharged back into the ocean by seawater desalination plants. Modern designs for brine outfalls can limit adverse environmental impacts to “tens of meters” from the discharge source(1, 2) but are high cost.(3) An emerging class of solutions, broadly titled waste-to-resource, aim to reduce brine discharge by transforming it into useful compounds.(4-7)

Many previous such studies focus on recovering salts, of which the largest by mass is sodium chloride. But in many countries, NaCl exists in abundant, cheap supply as rock salt or brine, meaning any competing source must be extremely low cost. [The US Geological Survey reports average US rock salt and brine prices ranging from 38–50 USD/ton and 8–9 USD/ton, respectively, from 2011–2015.(8)] Its chemical derivatives, primarily soda ash, caustic soda (“caustic”), and chlorine, however, may be much higher value. Nearly 30% of NaCl sold in the US(8) is used as a feedstock in the chlor-alkali process to manufacture the most common of these at large scale: NaOH and Cl2. Also, NaOH is frequently used within the desalination plant itself.

Consequently, producing NaOH from seawater reverse osmosis (SWRO) brine for reuse within the SWRO facility has the potential to benefit environment and plant economics. By replacing NaOH manufactured off-site using chlor-alkali by an on-site, lower-energy process (e.g., one producing HCl as a byproduct instead of Cl2), the environmental and economic footprints of NaOH generation and transport are reduced. By diverting a portion of the brine discharge, less salt flows into the ocean, resulting in lower salt concentrations around brine discharge ports, which lessen the plant’s impact on marine life. Further, since both benefits scale with the amount of NaOH produced, any other nearby consumers of the NaOH produced would serve to increase the positive environmental and economic impacts of this technology.


In the following text, the authors point to the use of NaOH within a desalination plant, albeit in this case of a "SWRO" plant (Seawater Reverse Osmosis) plant.

They write:

Caustic soda has myriad uses both internal and external to the desalination plant. Internally, treating seawater feed with caustic soda increases the pH. At higher pH, several compounds are better rejected by the RO membrane. Around pH 9, the better-rejected borate anion B(OH)4– supplants boric acid as the dominant aqueous boron species.(11) The dissolved silica system behaves similarly, with the dominant SiO(OH)3– and SiO2(OH)22– species above pH 9 yielding better silica rejection,(12) and above pH 8, dissolved inorganic carbon exists as bicarbonate and free carbonate, which are better rejected than aqueous carbon dioxide.(13) Evidence also shows reduced organic fouling at high pH.(14) Finally, caustic soda is an ingredient in cleaning solutions to remove organic, biological, and organic/inorganic colloidal foulants and silica scale.(15)

For internal reuse, caustic soda purity requirements are moderate. Membrane manufacturers manuals for reverse osmosis(16) rate technical grade as sufficient purity for membrane and system compatibility.


I should point out at this point that while this situation applies to SWRO plants, NaOH would be useful in brine resulting from other processes. In particular it might prove of great utility in the recovery of certain metals from seawater, notably magnesium and calcium (but also including others) and another constituent of prime importance which is much more concentrated in seawater than it is in the atmosphere, carbon dioxide, along with certain carbon compounds. This would, however, probably involve a huge scale up of NaOH production, although there are some very cool approaches to in situ partitioning of seawater into HCl and NaOH fractions which I have no time to discuss here.

The authors further discuss the economic importance and current production methods for the production of sodium hydroxide:

n addition to its use in controlling pH and neutralizing acids, caustic soda is used as a reagent in the production of many chemicals. About 59% of NaOH in the EU and North America is used in the pulp and paper, inorganic, and organic chemical industries.(19) Soaps and detergent manufacture also account for significant demand. For external reuse, quality requirements are application specific, and some commercially produced caustic soda is of insufficient purity for certain industries. For example, caustic soda produced using the diaphragm process is not suitable for manufacturing viscose, also known as rayon.(20, 21)

Industrial production of caustic soda is massive. Global manufacture exceeded 59 million tons in 2004,(19) with significant growth in demand and capacity expected in Asia.(20) Production is also scalable, with plant capacities ranging from about 4.4 kt/yr (Kapachim, Inofita Viotias, Greece) to 1744 kt/yr (Dow, Stade, Germany) in the EU(22) and about 2 to 3333 kt/yr (Olin, Freeport, TX) in the US(20, 23) on a dry basis. [Estimated from chlorine capacity at 1.1 kt NaOH/kt chlorine,(18) which is slightly less than stoichiometric.] On the small end, ThyssenKrupp Uhde GmbH offers standardized skid-mounted plants at up to 17 kt/yr, and AVS Technology AG offers plants as small as 1.1 t/d.

About 99.5% of global caustic soda production is by the chlor-alkali process.(24) Briefly, the process produces caustic soda and chlorine gas in equimolar amounts by electrolysis of aqueous sodium chloride. Direct synthesis of process products can also produce hydrochloric acid, though less than 10% of HCl is manufactured this way.(25) (Technical aspects of the chlor-alkali process and other methods are discussed in-depth below.) Three variants of the process exist in widespread commercial use, generally distinguished by how catholyte and anolyte are separated. The variants are known as the membrane, diaphragm, and mercury processes.


The authors then discuss that the chlor-alkali process produces equal molar amounts of chlorine gas and NaOH and that the demand for these two commodities is not always matched, even if some of the chlorine is diverted to make another commodity, HCl, hydrochloric acid. (Hydrochloric acid is often a waste product needing disposal. There are huge waste disposal issues with it, and one dubious approach to dealing with it has been deep welling it.)

This mismatch has lead to wide fluctuations in the price of NaOH, as a graph from the paper shows:



It is worth noting that the "mercury process" - which is happily being phased out - has resulted in a large contribution to the widespread contamination of the environment with mercury. Although the amount of mercury from this source is definitely dwarfed by mercury contamination deriving from coal exhaust, fly ash and ash, it is still significant.

(Sometimes I think the whole world is developing "mad hatter disease." How else can we account for the placement of incredible fools like the orange nightmare in the White House, and his foreign equivalents, Kim Jung Un, Rodrigo Duarte, Recip Erdoğan, to name just a few.)

The authors graphically show the current chlor-alkali processes industrially in use:



The rest of the article is involved with thermodynamic and the always related economic issues, along with some technical arguments connected with membrane technology (which is the focus of the paper.)

Also discussed is heat, which is also an issue in the reduced pressure schemes about which I often privately muse.

Overall, I like these kinds of papers and I thought I'd share this one for anyone who may find it interesting. Interested readers who can manage access, are invited to look the paper up.

Esoteric I know, but important.

Enjoy the coming work week.


Substitution of Glycerol for Methanol For Denitrifying Sewage Sludge.

One of the real big environmental problems which gets less attention than maybe it used to, is involved with nitrogen chemistry.

In my view the most serious environmental impact may be the accumulation of nitrous oxide in the atmosphere, but the issue has very, very, very serious implications for both fresh and saline bodies of water.

Fixed nitrogen, along with phosphorous, was responsible for one of the most famous events related to the environmental impact of fixed nitrogen nutrients, the 2014 toxic algae bloom that shut the water supply to Toledo, Ohio because the particular species of algae produced a very potent biological toxic cyclic peptide, microcystin:



These outbreaks are now known all over the world. They are largely involved with agricultural practices.

Even where the output does not contain directly toxic compounds, these blooms can and do destroy major ecosystems. The "renewable" energy scheme to add ethanol to motor fuels, for example, has completely destroyed the ecosystem of the Mississippi Delta, because of nutrient run-off both nitrogen and phosphorous.

Although agriculture is a major cause, another is the treatment of sewage sludge.

In some, perhaps not enough, sewage plants, denitrification is accomplished using methanol as a carbon source. Although methanol can be made either by the hydrogenation of carbon dioxide or carbon monoxide, the source for the industrial quantities of all three of these starting materials is currently dangerous natural gas.

The waste product of this dangerous natural gas is directly dumped, without reserve directly into the planetary atmosphere, which it is destroying.

I'm generally an opponent of all forms of so called "renewable energy" at this point in my life, having decided in the last decade that they will never be as safe, as clean nor as reliable as nuclear energy, but a caveat is to note that one thing that living systems do better than nuclear energy will ever do is to collect carbon dioxide from the atmosphere, because biological systems, being self replicating, can cover huge amounts of surface area at almost no cost.

Algae, both deliberately grown and grown in uncontrolled conditions (such as occurred in Lake Erie) has often been studied as a source of fats, esters of fatty acids and the triol glycerol, which can be used to make biodiesel, a decent substitute for petroleum diesel, at least with some modifications.

The side product of biodiesel production is glycerol which is generally dumped as a waste product, not because it's entirely useless, but because there is much more produced by the biodiesel and soap industries than can be profitably utilized.

So I came across an old paper in my files that offered an interesting potential use for glycerol, which is to substitute for methanol as a carbon source in the denitrification of sewage sludge.

The paper is here:

Diagnosis and Quantification of Glycerol Assimilating Denitrifying Bacteria in an Integrated Fixed-Film Activated Sludge Reactor via 13C DNA Stable-Isotope Probing (Chandran and Lu, Environ. Sci. Technol., 2010, 44 (23), pp 8943–8949)

Some excerpts from the text, first the introduction, which I rehashed briefly above:

Methanol is one of the most widely used external organic carbon sources for enhancing denitrification at wastewater treatment plants (1-3). Of late, glycerol has emerged as an alternative to methanol due to three factors. First, the price of methanol, which is tied to the natural gas price, has been increasing (4). Second, the dramatic increase in biodiesel production as a means of moving away from petroleum as an energy source has given rise to significant quantities of glycerol as a waste product (5). Third, glycerol has been previouslyshownto foster higher denitrification kinetics than those of methanol (6, 7). Consequently, wastewater treatment plants today are intently considering glycerol as a supplement or replacement for methanol.

From the perspective of wastewater treatment process design, it is essential to determine the fraction of activated sludge bacteria assimilating any given carbon source...


Bacteria were isolated from sewage sludge treatment plants and then placed in a growth medium that was spiked with glycerol labeled with the heavy stable isotope of carbon, C-13.

They then looked for the fate of C-13 and noted the following:

The 13CDNAsequences of the biofilm samples were more diverse and dominated by Comamonasbadia(5/21),Bradyrhizobium sp. 1 (4/21), and Tessaracoccus bendigoensis (4/21) related bacteria. Bradyrhizobia and Tessaracocci belong to the family of Rhizobiales in R-proteobacteria (35) and Propionibacteriaceae in Actinobacteria (36), respectively. Very little is known about the denitrification capability of these bacteria and or their ability to use glycerol as an electron donor. It is notable that the glycerol assimilating bacteria diagnosed and quantified in this study have not been implicated in glycerol metabolism before (as reviewed by ref 5). A possible explanation for this discrepancy is that the previous studies selected their strains a priori for examining glycerol metabolism.


They find that the presence and distribution of organisms in denitrifying biofilms utilizing glycerol are considerably different than those in methanolic systems, and that the glycerol based systems seem to function better.

There's a lot of cool molecular biology in this paper, much of which is not really my bailiwick, but it's worth perusing just for general knowledge.

I personally feel that linear saturated and unsaturated fatty acids and products made by chemically modifying them might well be important tools in a putative post-petroleum age, should we ever have one before petroleum waste, along with coal and gas waste kills us. Since glycerol is a necessary byproduct of access to such materials of biological origin - ideally from microorganisms utilized in phosphorous and nitrogen contaminated waste waters - this interesting approach to denitrification seems quite interesting.

I'm not sure how much came of it - the paper is seven years old - but it's worth keeping in the back of one's mind.

I wish you a pleasant Sunday.



Now, THIS is a very cool Ph.D thesis: Francesco Ricci and the origins of chirality.

Life is asymmetric, and why this is so is one of the greatest mysteries of the universe. By asymmetric we are referring to the property that your hands have, they are mirror images of one another, but cannot be superimposed upon one another.

We refer to this property as chirality.

Here is a picture of the two forms of the simple amino acid alanine, with, by convention, the black wedge being representative of coming out of the plane of the page, the dashed wedge representative of being representative of going back behind the plane of the page:



In the laboratory, one can easily make alanine by the hydrogenation, in the presence of ammonia of the symmetric molecule pyruvic acid, with, say for example, a nickel or platinum catalyst. When one does this however, one will get a 50:50 mixture (exactly) of the two molecules above. We refer to such a 50:50 mixture as "racemic."

In living systems, by contrast, which also synthesize alanine from pyruvic acid, one will only get one of these isomers, the S isomer, 100%, exactly.

In fact, one can only synthesize pure chiral molecules in the laboratory (and this has been a subject of vast amounts of research over the last century or so) if one conducts the reaction in the presence of molecules that are also chiral. This is, in fact, what happens in living systems; the vast majority of molecules in living things (other than water) are chiral. But where did it come from? What was the first chiral molecule to exist in the absence of its mirror image, which we call its "enantiomer?"

I have wondered about this a lot while daydreaming over several decades; I've generally assumed with a vague sense, that it somehow resulted from certain types of chiral radiation associated with nuclear decay in cataclysmic stellar events. (Yes, light can be, and often is, chiral.) Here and there, I've pulled some papers down, but none were very satisfactory.

Today, while going through files I collected but never actually read, I came across a recent Ph.D. thesis at Princeton University, written by a young scientist named Francesco Ricci. It's entitled "Theoretical and Computational Studies of Condensed-Phase Phenomena: The Origin of Biological Homochirality, and the Liquid-Liquid Phase Transition in Network-Forming Fluids."

The thesis can be accessed here: Ricci, Ph.D Thesis, Princeton

Very early in the text I came across a concept of which I'd never ever heard, "Viedma ripening" involving homochiral molecules.

Viedma ripening...

Never heard of it.

It doesn't get any better than this, being old and fairly broadly exposed and then run across something from some very charming young guy talking about something about which you know nothing.

I'm going to be pulling up this kid's papers and his references in the next several weeks. Beautiful, very, very, beautiful.

It's going to be a fun Christmas break!

The Remarkable Thermal Stability of the MAX Phase Zr2Al4C5

There are many thermochemical cycles known for the decomposition of water into hydrogen and oxygen (in separate compartments) as well as thermochemical cycles for the decomposition of carbon dioxide into carbon monoxide and oxygen, again in separate compartments.

Carbon monoxide can also be disproportionated to give elemental carbon and carbon dioxide; this is known as the Bouardard reaction. Thus it is theoretically possible given a source of high temperatures to reverse coal combustion.

Carbon monoxide can - and industrially is - used to make hydrogen: This is known as the "water gas reaction:" CO + H2O <-> H2 + CO2. Industrially this important reaction, which is used to make 99% of the hydrogen on earth, is driven by the partial combustion of dangerous natural gas, a fuel that like oil and coal is destroying the planetary atmosphere.

However, if carbon monoxide were made instead from carbon dioxide of course, this would have possibly the effect of reversing the effects of combustion dangerous fossil fuels and directly dumping dangerous fossil fuel waste, chiefly (but not limited to) carbon dioxide.

These cycles have been broadly studied and are fairly well known.

Examples of thermochemical water splitting cycles are the "sulfur iodine" cycle, the UT-3 (CaBr2) cycle, the copper chloride cycle, and others.

Examples of thermochemical carbon dioxide splitting cycles are the tin oxide carbon dioxide and water splitting cycle, the cerium dioxide carbon dioxide splitting cycle, and one of my absolute favorites, the zinc oxide cycle, among others.

In order to get grants one must appeal to the useless fantasy about solar energy, in particular thermal solar energy plants, which have not worked, are not working and will not work, which is why in some cases they are described as "solar thermochemical cycles" but there is no practical reason that they would not work with cleaner, safer, and more practical and sustainable energy, nuclear energy.

The basic problem with many of these cycles - most of these cycles - is that they require fairly high temperatures in corrosive environments. The most famous of these cycles, the sulfur iodine cycle involves the thermal decomposition of two strong acids, sulfuric acid into sulfur dioxide, oxygen and water and the thermal splitting of hydroiodic acid, HI, into hydrogen and elemental iodine.

This is a serious materials science problem.

The extremely important reason that it would be worth solving this materials science problem is that the use of such cycles, coupled with heat transfer to thermoelectric devices or brayton/rankine combined cycle devices, would be extremely efficient overall. In general the greater the heat difference involved in a thermal process, the more work or exergy can be derived from it.

It is regrettable that research into high temperature refractory materials in many materials science departments that I toured with my son while we were researching universities for him to attend seems to have been deprioritized with the major aerospace problems having been more or less solved, but that said, there is yet still some that is of interest.

Egyptian-American scientist, Michel Barsoum at Drexel University has been a world leader in the development of the MAX phases (My son actually met him during one of the tours; he was admitted there but chose to go elsewhere.)

There are many different MAX phases, and I came across an interesting one that I encountered in a paper I came across tonight in my unexplored files is the one described in the title of this post, Zr2Al4C5 a ternary compound of the elements zirconium, aluminum, and carbon, all earth abundant elements. (Zirconium is also a prominent fission product.) The paper is this one:

Thermal stability of bulk Zr2Al4C5 ceramic at elevated temperatures (Zhang et al, Int. Journal of Refractory Metals and Hard Materials 30 (2012) 102–106)

The authors succinctly and accurately describe what the MAX phases are and why they are interesting:

MAX phases are nano layered ceramics with the general formula MAX, where M is an early transition metal, A is a Group A element, and X is either carbon or nitrogen. These materials exhibit a unique combination of the characteristics of both ceramics and metals [1–4]. The domain of layered ternary transition-metal carbide extends beyond the MAX phases to a new family...


They go on to describe a relatively new class of these compounds which are, again, ternary composites of zirconium (or its cogener hafnium) aluminum and carbon.

Here is what they say about the compound described in the title:

Among these compounds, Zr2Al4C5 ceramics exhibit perfect high-temperature mechanical properties. Young's modulus decreases slowly with increasing temperature. At 1580 °C, Young's modulus is 293 GPa, which is approximately 81% of that at room temperature. Simultaneously, the strength at 1400 °C is 371 MPa, which is approximately 10% higher than that at room temperature [9,10]. Zr/Hf–Al–C compounds demonstrate excellent elastic stiffness and strengths of up to the temperature range for ultrahigh-temperature applications.


Wow.

The research in this paper involves finding out how high temperatures can go before the MAX phase decomposes. (The authors note that these temperatures, the decomposition temperature of the various MAX phases - there are a lot of them - vary with the conditions to which they are exposed; they differ in the presence of vacuums, under various gases, inert and otherwise, and other chemical environments.)

Here are what they find out and conclude.

The high-temperature thermal stability of Zr2Al4C5 under Ar atmosphere has been studied by thermal expansion analysis. The presented thermal expansion analysis result is in good agreement with the XRD and SEM results. Zr2Al4C5 was susceptible to decomposition at temperatures above 1900 °C through sublimation of high vapor pressure of Al, which resulted in the formation of a little amount of Al and Zr2Al3C5 on the surface layer. Ternary-phase Zr2Al4C5 and/or Zr3Al4C6 decomposed to ZrC and Al4C3 above 1900 °C due to weaker covalent bonds between ZrC slabs and Al4C3-type layers. Zr2Al3C5 further decomposed to ZrC1−x and Al4C3 at 2000 °C, and the amount of decomposing phase was found to slowly increase. The dissociation of Zr2Al4C5 was not complete at the end of the experiment, implying that the process never reached completion because of very slow kinetics. The present study clearly indicates that thermal expansion analysis, when combined with XRD and SEM, can provide a practical way for studying the thermal stability of ultra-high temperature materials.


High temperature refractory materials can often be protected beyond their melting (or in this case decomposition) point by coating with thermal barrier coatings, the most widely used one being zirconium oxide. To the extent that this type of coating would be useful in extreme environments is questionable. It would certainly not be stable in the presence of decomposing sulfuric acid or hydroiodic acid, but it would be interesting to understand the stability of the MAX phase or modified version in question under these conditions.

It is interesting to note that zirconium, aluminum, and carbon are all fairly transparent to neutrons, and the stability of MAX phases in neutron fluxes is an active area of research. I personally believe that these phases might do remarkable things, should the world survive puerile orange fools and his traitorous apologists and fellow nut cases.

This is esoteric, I know, but interesting.

Self Medication by Orangatans Using Bioactive Plants.

The following paper is in Nature's open sourced journal Scientific Reports: Self-medication by orang-utans (Pongo pygmaeus) using bioactive properties of Dracaena cantleyi (I. Foitová et al, Scientific Reports 7, Article number: 16653 (2017))

This apparently is not the first instance among primates of this type of behavior, but it is only one of two examples of such a behavior of apes not originating in Africa. (As we originated in Africa, our particular species of ape does not qualify.)

According to this paper, orangatans have been observed to process (by chewing) this plant and then rubbing the resulting lather on their fur. Biological assays of the pulp of the plant showed, using cellular assays, that the plant had pronounced anti-inflammatory properties.

The paper is, again, open sourced, so there is no reason to excerpt it.

It's interesting, especially for the description of other species that self medicate.

Fascinating, I think.

Have a nice Friday tomorrow.

Monitoring the Burn Up History of Used Nuclear Fuels by Monitoring Ruthenium-106.

In the fast fission of plutonium, as one can learn by accessing the Brookhaven National Laboratory Data pages, fission products with a mass number 106 occur about 4.3% of the time.

After many years of thought and reading, I have convinced myself (irreversibly I believe) that the last best hope for this planet is, in fact, the fast fission of plutonium, irrespective of common public fantasies to the contrary.

The stable isotope at this mass number, 106, is palladium, but stable palladium-106 occurs in direct fission only about one in every 30 billionth fission. Before significant and salable quantities of palladium-106 can accumulate and be recovered, radioactive precursors with smaller atomic numbers with this mass number must be allowed to decay into it. The elements involved are yttrium, zirconium, molybdenum, and technetium. All of the nuclides with this mass number other than ruthenium have very short half-lives and mostly decay within the reactor, generating heat that helps drive turbines. Technetium-106, for example, ruthenium-106’s immediate precursor has a half-life of just 36 seconds. Ru-106 has a half-life of 367.6 days, short enough that it is possible to "milk" significant quantities of it's decay product, palladium-106 from it, but long enough that significant quantities remain in the used nuclear fuel after shut down of a nuclear reactor. (An intermediate in the decay of ruthenium 106 to stable palladium-106 is rhodium-106, but this has a half life of only 30 seconds and therefore exists in secular equilibrium with its parent until all of the ruthenium has decayed.)

The relatively long half-life of ruthenium-106 allows for the facile separation of the stable isotope of palladium from all other isotopes of palladium - a valuable metal, at least in the case of fast or continuous reprocessing of used nuclear fuels, something I personally favor. The way this would work would be to separate the 106 isotope as ruthenium and then to let the ruthenium decay into isotopically pure non-radioactive palladium-106 away from all other isotopes of palladium.

(Currently the only use for ruthenium-106 is in cancer treatment.)

Palladium accumulating in a reactor as palladium will invariably include the long lived radioactive isotope palladium-107, both from fissions occurring at mass number 107 and from neutron capture in palladium-106 resulting from that portion of the ruthenium-106 that decays within the reactor.

Because palladium-107 has a long half-life, 6.5 million years, the radioactivity of the pure isotope is rather low, about 0.5 millicuries per gram, activity which would be further diluted by the presence of the stable palladium isotopes also resulting as fission products, palladium-104, palladium-105 the aforementioned palladium-106, palladium-108 and palladium-110.

Still, it is likely that under most circumstances this radioactivity limit its use to closed system catalytic roles, a significant role, but of less utility than open systems. A common example of an open use of a palldium catalyst would be an automotive catalytic converter; common closed systems would be as a catalyst would be the arylation of ammonia, Suzuki couplings to form carbon carbon bonds on an industrial scale, water electrolysis, or the Fischer Tropsch synthesis of motor fuels from carbon dioxide and hydrogen.

The separation of ruthenium from the bulk of other fission products is somewhat simplified by the fact that ruthenium forms a volatile oxide, RuO4 that is a powerful oxidizing agent and is therefore easily reduced by relatively mild means. Very simple and clean chemistry can reduce it all the way to the metal. (Ruthenium oxide can be used in organic synthesis to form 1,2 diols from alkenes by oxidation, although generally its cogener's tetraoxide - also volatile - osmium tetraoxide is used for this purpose.)

In this process utilizing the volatile oxide of ruthenium to separate it from other constituents of used nuclear fuel, known as voloxidation, generally as part of an overall processing step with reduced use of solvents, the used nuclear fuel is treated with ozone to distill off the volatile oxide fission products, ruthenium, molybdenum, rhodium, technetium, tellurium and tritium, a facile and relatively simple separation. All six elements are therefore recovered for use.

(Other fission products that can be easily recovered by distillation are iodine, cesium and rubidium. Uranium, neptunium, and plutonium can all be recovered as volatile fluorides, and in principle, so can the aforementioned ruthenium and technetium be recovered as fluorides as well as oxides.)

But as I was reminded while going through my files last night, ruthenium-106, has another use, even before it is removed from used nuclear fuel, and this is to allow for understanding the operating history of a nuclear fuel rod.

I came across this paper in my files: Feasibility of 106Ru peak measurement for MOX fuel burnup analysis (Usman and Dennis, Nuclear Engineering and Design Volume 240, Issue 10, October 2010, Pages 3687-3696).

Some excerpts from the paper follow. First from the introduction:

To validate the initial computer simulation (Dennis and Usman, 2006), preliminary experimental data were collected for gamma emission from LEU test reactor fuel at Missouri University of Science and Technology (Missouri S&T). The primary goal of this effort is to determine if online burnup analysis of plutonium based mixed oxide (MOX) fuel is feasible using non-destructive gamma spectroscopy. Initial results are very encouraging and it seems feasible to develop techniques for determination of MOX fuel burnup, as well as for discrimination between MOX and uranium oxide (UO2) fuel assemblies. However, for commercial applications online,gamma spectroscopy immediately following shutdown/fuel discharge will be complicated by the extremely high activity of the irradiated fuel...


A nice description of the history and procedure of using plutonium in commercial thermal reactors is included:

While the U.S. has not reprocessed and researched MOX fuel since the mid-70s, other countries have proceeded with extensive research and deployment efforts. European nations including France, Germany, and the United Kingdom have found that only replacing a fraction of a light water reactor (LWR) core with MOX provides the best neutronics and safety characteristics. In fact, France limits its cores to 30% MOX and different plutonium enrichments within a given assembly to flatten power peaking (Cochran and Tsoulfanidis, 1990b). Ultimately, the MOX fuel behaves differently based on multiple fissile plutonium isotopes, varying concentrations based on the level of recycling, how long the plutonium has been stored allowing the 241Pu decay product and poison 241Amto build-in, and neutron parameters such as absorption cross sections (Cochran and Tsoulfanidis, 1990b). As a result, along with limiting the amount of MOX in a LWR core, it is prudent to locate MOXaway from boron control rods due to reduced reactivity worth concerns and using the fuel as soon as possible to limit growth of 241Am.


The paper's stated purpose however, is to evaluate "NDA," Non-Destructive Analysis of MOX fuel, by using gamma spectroscopy to detect the "burn-up" of commercial MOX fuel. In general, "burn up," usually measured in terms like GWd/THM (gigawatt-day per ton of heavy metal) is a measure of mass to energy fuel efficiency, very much like "miles per gallon" in the automotive parlance. The higher the burn-up, the less fuel that has to be handled and the longer a reactor can run without refueling. MOX fuel is particularly desirable because it utilizes the mass more efficiently, requiring less mining and processing of uranium, although it can be shown that uranium supplies are inexhaustible, particularly in the case of the widespread use of fast fission of plutonium.

As the authors plainly confess, their research reactor at the Missouri University of Science and Technology does not produce fuel that is radioactive enough to properly evaluate the utility of the detecting of Ru-106 gamma radiation peaks to determine the burn up of commercial MOX fuel, which will be, especially on high burn up, far more radioactive than a research reactor can possibly provide.

Nevertheless the paper is an interesting read on some fairly technical grounds, in particular describing the criteria by which fission product spectra can differentiate in situ the fission totals of differing fissionable and fertile actinide nuclides. I will not go into these technical details any further; they're not appropriate for such a post.

After decades of studying nuclear technology, I have convinced myself that nuclear fuels having a mixture of actinides with a wide distribution of isotopes as is possible for each of them is the ideal approach to utilizing nuclear energy. The modeling of such use is highly complex of course, and perhaps at the dawn of the nuclear energy age would have been prohibitive, but now, at the end of 2017, with our great advances in both computational and materials science as well as in the science of thermodynamics, much more is possible than was ever possible before.

From my perspective, over the long term, I believe non-destructive testing may not be necessary. I favor liquid phase nuclear fuels, not necessary those diluted with salts such as FLIBE (to which I've learned to have certain objections) nor FLINAK. I suspect liquid metals will prove superior, if only for their tendency to offer spontaneous separations of particular use, both in phase separation and high temperature distillation. Liquid phases provide for facile removal and chemical separations in fuel, and to the extent one needed access to palladium that was non-radioactive, voloxidation to separate radioactive ruthenium-106 for decay into stable palladium-106 would be an option.

I do not know however, about the distribution coefficients of palladium and ruthenium in, for example, liquid plutonium or liquid neptunium relative to a barium/strontium/rubidium/cesium phase.

I do know that in the oxide fuels now utilized in most of the world's 400+ operating nuclear reactors, the solid metals plate out as what is know as ε-metal, an alloy of the metals palladium, rhodium, ruthenium, technetium, and molybdenum. They are typically resistant to attack by the nitric acid used in the old but still utilized PUREX process, making their separation somewhat easier than other separations, but unfortunately, the idea of what to do with them is still to throw them away, bury them.

This is absurd.

As I pointed out above, palladium that is obtained from used nuclear fuels - except for that which is obtained by separating ruthenium from palladium and allowing the Ru-106 in it to decay - will be radioactive, but as only one of the isotopes is radioactive and because it has a fairly long half life, such radioactivity is hardly unmanageable.

In ores on the planet, palladium is relatively rare and expensive. The price found on the internet today is a little higher than $900/troy ounce or around $28,000/kg.

Besides its use as a catalytst in closed systems, where low levels of radioactivity would not matter, it might also be possible to use this slightly radioactive palladium as a constituent of certain alloys that might be used in reactors, superalloys that in silico modeling suggests might well prove superior to the widely used nickel based superalloys of the Inconel and Hastelloy types. While much of the world's technology from jet engines to combined cycle power plants to certain kinds of chemical reactors depend on the utilization of nickel based superalloys, one has to very careful to prevent them from melting by utilizing, for example, zirconium or hafnium based ceramic oxides as thermal barrier coatings. The failure of these coatings can be catastrophic, and one of the interesting things found in the following paper is that palladium based superalloys, were they available have considerably higher melting points.

Effects of alloying elements such as Ti, Zr and Hf on the mechanical and thermodynamic properties of Pd-Base superalloy (Feng et al, Journal of Alloys and Compounds Volume 710, 5 July 2017, Pages 589-599)

It can be shown that in a theoretical and cleaner world where all of humanity's energy was derived from the fast fission of plutonium, say on a scale of 600 exajoules of energy per year, that the accumulation of palladium would annually be about 500 to 600 metric tons per year, certainly enough material to construct superalloy based industrial sized devices such as dual pyroprocessing/reactors that would operate at very high temperatures, be highly thermally efficient, and be suitable for the preparation of liquid fuels for use in devices where they might always be required, such as farm machinery or remote generators. It would not matter if the alloys in such pyroprocessing/reactors were radioactive, and in fact, the neutron fluxes might well prove to reduce their radioactivity over the long term.

But that particular technology is for discussion another day.

Being a little ill on a Sunday afternoon, I'm rambling a bit.

Anyway.

Have a nice Sunday evening.

Titanocene Electrocatalysts for Ammonia Synthesis.

One of the most intriguing stories in history - possibly the most Faustian story in science other than that of Robert Oppenheimer - is the tale of Fritz Haber, the Nobel Laureate who developed the Haber-Bosch process for nitrogen fixation to make ammonia. (Bosch was the chemical engineer who was able to design and build the high temperature/high pressure reactors in which the reaction, the reaction of 3 moles of hydrogen gas with one mole of nitrogen gas to make two moles of ammonia.

If you have food on your table, it's because of the Haber-Bosch process, the only real "green revolution" was the one that took place in the 1950's, the industrialization of fertilizers containing ammonium nitrate and ammonium hydrogen phosphates.

Haber was an interesting person because not only did he make food readily available for the masses (for the first time by the way), he also made it possible for the German War machine to fight World War I, since before World War I, all of the world's gunpowder manufacture depended on the importation of salt peter, potassium nitrate, which was mined in Chile. (Ammonia can be oxidized readily to nitrate.) Denying access to salt peter and not food (although food shortages, and not gunpowder shortages were the result) was a primary motivation for the British blockade of Germany. Haber, a fervent German nationalist almost to the point of fascism although he was, in fact, purely descended from Jews, also drove the introduction of gas warfare in the First World War, and after that war, the allies couldn't decide whether to celebrate his Nobel Prize or to try him as a war criminal.

Because of his Jewish heritage, he was expelled from Germany in 1938 and died shortly thereafter in Swiss exile.

The Haber Bosch process is still practiced today, although in most places the dangerous coal that was used to generate hydrogen has been displaced by dangerous natural gas reformation.

The story is ably told in great detail by Vaclav Smil - anyone who wants to know about energy should read the delightfully sarcastic Smil - in his important scientific and engineering book, Enriching the Earth.

(Smil is at his most amusing when he makes fun of the anti-nuke idiot Amory Lovins.)

The Haber-Bosch process is still being practiced today, albeit more efficiently, with profound environmental consequences, but is highly energy intensive, consuming something in the neighborhood of 3% of the world's energy. Were it abandoned, we would require about half of the world's current population to starve to death as a result.

Because the reaction requires such extreme conditions, it would be nice to have a milder reaction to make ammonia, and I came across a possible one in a recent issue of ACS Sustainable Chemistry and Engineering, this paper: Electrochemical Ammonia Synthesis Mediated by Titanocene Dichloride in Aqueous Electrolytes under Ambient Conditions (ACS Sustainable Chemistry & Engineering 2017 5 (11), 9662-9666)

Some excerpts from the introduction:

Renewable energy production and supply rates are rising worldwide as serious attempts to combat greenhouse gas emissions caused by the depletion of fossil fuels are pursued to mitigate catastrophic climate change; concomitantly, relevant research and development are actively being explored.1 Renewable energy requires energy carriers or storage systems because of regional and temporal variabilities. Recently, the use of ammonia (17.6 wt % H2) as a renewable-energy carrier has drawn considerable research interest in terms of storing and converting renewable energy, the so-called “power-to-gas technology”.2 As a hydrogen reservoir containing 17.6 wt % H2, ammonia is a noncarbon fuel that releases only water and nitrogen during combustion. Ammonia has a higher energy density per volume (NH3 HHV: 13.6 GJ·m−3) than that of hydrogen and is much easier to store and transport than hydrogen3,4 because it is liquid below 10 bar at room temperature. Furthermore, more than 150 million tons per year of ammonia are currently consumed globally;5 thus, infrastructure to support ammonia based technologies...


I don't agree with very much of what's been written here, particularly the idea of ammonia fuel, but no matter. What is important is the conditions under the reaction takes place at ambient conditions. Some comments by the authors:

Transition metals with strong reducing abilities for nitrogen are located in groups 4−6 of the periodic table, and the ammonia yield decreases in moving from the left to right in each row (e.g., Ti > V > Cr; Zr > Nb > Mo). Among them, Ti exhibits high activity for nitrogen.18 Judicious choice of coordinating ligand in these catalysts can lead to enhanced capacity of the metal to bind to nitrogen, thereby affecting the activity the metal toward nitrogen. These ligands include cyclopentadienyl,20 acetylacetonates,21 and phosphine complexes. 19 Bayer and Schurig studied the chemical synthesis of ammonia using titanium compounds such as titanocene dichloride (Cp2TiCl2), cyclopentadienyltitanium(IV) trichloride (Cp2TiCl3), zirconocene dichloride (Cp2ZnCl2), and titanium tetrachloride (TiCl4), as well as various alkali and alkaline earth metals (Li, Na, K, Mg, Ca, La, Cs, and Na).


The authors state:

in this study, experiments were conducted into the chemical and electrochemical synthesis of ammonia in the 0 to −2 V applied voltage range using various organic solvents with Li electrolytes and the Cp2TiCl2 catalyst, which has a high nitrogen-activation capacity. Furthermore, the ammonia synthesis rates and faradaic e_ciencies were compared in terms of the applied voltage. In addition, the rate-limiting step in the proposed ammonia-synthesis mechanism using Cp2TiCl2 was examined by density functional theory (DFT) calculations


There's a lot of discussion of the experiments conducted but what is relevant here is the conclusion:

We theoretically and experimentally demonstrated that chemical and electrochemical ammonia synthesis in Li-based aqueous electrolytes containing Cp2TiCl2 is feasible using various solvents including water, methanol, and THF. In the theoretical study, DFT calculations reveal that the nitrogenreduction reaction in a Li-based aqueous electrolyte containing the Cp2TiCl2 catalyst prefers to occur via the Cp2TiClN2 intermediate due to its relatively low _G, rather than the Cp2TiN2N2 intermediate. According to the DFT calculations, the activation barrier for the electrochemical ammoniasynthesis reaction is about 0.7 eV, which is lower than the Tafel-type reaction barrier (*H + *NHx _ *NHx+1, 1 eV) of most transition metal catalysts in the literature.28−30 Hence, the DFT results in this study suggest that Cp2TiCl2 significantly lowers the activation barrier for the protonation


Good news, if true and scalable, since it makes it simpler to utilize the only truly sustainable form of carbon free energy, nuclear energy, to displace the role of dangerous natural gas in this important, if problematic, industrial chemistry. (THF can be obtained from corn cobs, and methanol is accessible by the direct hydrogenation of carbon dioxide and, indeed, the electrochemical reduction of carbon dioxide.)

Have a nice afternoon.

Ancient German Forest Being Razed for Coal Mines.

As Germany hosts green summit, an energy firm is razing a nearby forest

From CNN:

This week, the German city of Bonn is the venue for hundreds of diplomats who are busy hammering out a road map to save the planet from climate change.

The country would seem an ideal host, with its sterling reputation for driving an ambitious green agenda centered around "energiewende," or transition to renewable energy.

Yet less than an hour's drive away from the COP23 summit lies an example of Germany's dirty environmental secret: A 12-thousand-year-old forest that has been almost completely consumed by the country's ravenous addiction to coal power.

Germany's biggest electricity provider, RWE, runs the vast open-pit mine that encroaches on Hambach Forest. Giant steel excavators grind away at the 33-square mile hole, leaving a scar on the green landscape but producing 40 million metric tons of coal annually.

Every year since 1978, the mine has been allowed to fell a section of forest to access the lignite, or "brown coal," beneath. As a result, the Hambach woodland has now shrunk to less than 10% of its original size, according to estimates by RWE and environmental activists...

...Almost 40% of Germany's electricity comes from coal-powered plants -- nearly a quarter from brown coal -- making it Europe's biggest polluter, spewing out more than 20% of the greenhouse gas emissions from the European Union, according to Eurostat.
"We need lignite. Lignite is not subsidized and we have a good supply in Germany. It makes us less dependent on imported natural gas, oil or other fossil fuels," Guido Steffen, a representative for RWE, told CNN.



Don't worry, be happy.

I'm sure that some of that coal will be used to make steel for wind turbines and redundant dangerous natural gas plants.

(If the wind industry were to become a significant forom of energy- it never has been, it isn't, and it won't be - it would require a huge scale up of the steel and aluminum industries.)

Have a nice day.

Formation of Hydroxyapatite on the Surface of Portland Cement in the Built Environment.

This week, in California, I had the distinct pleasure of attending a lecture by the Materials Science Engineer/Orthopedic Surgeon/Professor Cato T. Laurencin, M.D., Ph.D, a child of the inner city schools who grew up to study Chemical Engineering at Princeton, and to attend Harvard Medical School while simultaneously obtaining a Ph.D at MIT in biochemical engineering.

Here is a photograph of Dr. Laurencin receiving the National Medal of Technology and Innovation from his friend, Barack Obama, who he mentioned during his talk while speaking volumes in omission of the mention of the orange idiot:



(I also had the great privilege of speaking alone briefly to Dr. Laurentin, and even had the opportunity of telling him about my son, who is studying materials science engineering, whereupon the great man gave me his card and told me to be sure to have my son look him up when applying to graduate school...swoon...something that is several years off.)

Anyway.

Dr. Laurentin is an advocate, given his unique polymathic expertise of "convergent science" whereby physicians, chemists, physicists, mathematicians and engineers work together to solve important problems.

Dr. Laurentin's lecture concerned his development of stem cells supported in biopolymers and or synthetic matrices in order to grow new bone where it has been lost by trauma or disease - his discoveries are now commercially available to patients - as well as his current efforts to grow new connective tissue, tendons and ligaments in damaged knees and shoulders, thereby reducing the need for artificial (and somewhat problematic) implants. His long term goal, which he discussed at some length is develop a means by which people might regrow limbs and organs that they have lost, again, either to trauma or disease.

A remarkable man.

From a materials science perspective, part of his discussion involved the chemistry of hydroxyapatite, a calcium hydroxyphosphate mineral which in slightly modified form represents the bulk of bones and teeth.

Here is one structure of hydroxyapatite:



The lecture, particularly with the reference to convergent science reminded me of a paper I stumbled across recently on the protection and restoration of portland cement by use of biologically deposited hydroxyapatite surfaces, this one: Biogenic Hydroxyapatite: A New Material for the Preservation and Restoration of the Built Environment (Ronald J. Turner, Joanna C. Renshaw, and Andrea Hamilton, ACS Appl. Mater. Interfaces, 2017, 9 (37), pp 31401–31410)

(By the way, the abstract of the paper refers to the use of hydroxyapatite as a "waste form" for so called "nuclear waste," and before someone points it out, I'd like to state that I oppose the "disposal" of so called "nuclear waste" on the grounds that every single constituent of used nuclear fuel is extremely valuable and worthy of use for things that no other materials can do as well.)

Anyway. As mentioned in the abstract, portland cement is the single most produced material in the world, and its manufacture is responsible for a huge releases of the dangerous fossil fuel waste carbon dioxide. Because of the acidification of the planetary atmosphere and hydrosphere by the aforementioned carbon dioxide as well as the dangerous fossil fuel wastes sulfur dioxide, sulfur trioxide, sulfuric acid, nitrogen dioxide and nitric acid, portland cement has a tendency to degrade significantly, requiring its replacement.

This paper proposes to prevent or slow this degradation via the deposition on cement surfaces a thin layer or coating of hydroxyapatide, as it less susceptible to acid degradation than the mixed calcium carbonate and silicate comprising Portland cement.

An excerpt from the introductory text of the paper.:

Hydroxyapatite (HAP) is a calcium phosphate mineral with the general chemical formula Ca10(PO4)6(OH)2.1 HAP is an example of a bioceramic,2 a novel class of materials with potential applications such as bone implants3 and drug delivery.4 Hydroxyapatite coatings have been used to reinforce bone cements, enhancing load-bearing capacity5 and promoting proliferation and differentiation of human osteoblast-like cells.6,7 In addition, there is an emerging interest in the use of hydroxyapatite coatings for the consolidation and preservation of marble and limestone buildings and sculptures.8−12

Cement and concrete have been commonly used building materials throughout the 20th century, and there is significant interest in repairing concrete structures to reduce the amount of cement consumed worldwide. Cement is also used as an encapsulant for radioactive waste storage, which links with research on the use of hydroxyapatites for the remediation of radionuclide13,14 and heavy metal15 contaminants from the environment.

The crystal structure of naturally occurring HAP is too complex to be accurately mimicked by synthetic crystalline apatites and the use of synthetic apatites has been observed to result in poor adhesion and low mechanical strength in the field of dental treatments...

...Hydroxyapatite produced through the direct actions of a living organism (termed biogenic hydroxyapatite) may offer a solution to these limitations via intrinsic properties such as reduced solubility and comparable particle size to natural hydroxyapatites. 16−18

Here, we identify and describe a new method for deposition of a biogenic hydroxyapatite onto the surface of OPC using the Gram negative bacterium Pseudomonas fluorescens.


The authors utilize a common bacteria growth medium, LB (Lysogeny) Broth in a phosphate buffer to form the hydroxyapatite layer in an in situ bioreactor that utilizes free calcium from the cement to reform as the apatite layer.

The rest of the paper is rather technical, and probably would not be meaningful for readers here, referring to the structural characterization of the apatite layers by XRD, XRF and FT-IR, as well as a cool discussion of the mechanism of the deposition and the interactions of various constituents of the growth media, phosphate and carbon dioxide.

They remark that what they call "OPC" (Ordinary Portland Cement) is actually a superior material on which to grow biological hydroxyapatite than other more elaborate efforts to do pretty much the same thing.

Pseudomonas and other bacteria are capable of producing nanohydroxyapatite with physico-chemical properties very similar to those of natural bone material.31 Research on the bacterial production of hydroxyapatite has generally required immobilization of the bacteria on a matrix such as sol−gels or alginate beads prior to mineral formation31 and the addition of a specific calcium source to stimulate hydroxyapatite production.32 It is significant that these steps are not necessary when biohydroxyapatite is generated on an OPC substrate material, as shown in this study. OPC has several properties which may have contributed to this. The OPC block provides a fixed substrate for hydroxyapatite deposition, negating the requirement for a sol−gel or similar matrix.

In previous studies, calcium phosphate loading was found to be necessary when generating biohydroxyapatite on polyurethane or titanium,31 and the addition of calcium and phosphorus donors was also necessary when using sol−gel or alginate substrates.32 In the case of OPC, calcium is present in sufficient quantities (Table 1) both on the OPC surface and in the surrounding solution.



Cool, I think.

I wish you a very pleasant Friday.








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