Category Archives: Chemistry

Gravity Anomaly Along the Colorado Mineral Belt

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The Colorado mineral belt (CMB) is a swath of metalliferous mineral veins and faults spanning 15 to 30 miles in width and running ~250 miles in length between Dolores and Jamestown, Colorado. This NE trending zone encloses most, but not all, of the significant occurrences of gold and silver deposits found to date in Colorado.

Significant finds like the Cripple Creek district have been found outside the CMB, but these are exceptions to the trend. The large gold/silver/tellurium lode in the Cripple Creek diatreme is the result of a volcanic past that stands somewhat apart from the vein deposition processes that produced the CMB lodes.

What is especially intriguing about the CMB is that it is coincident with a significant gravity anomaly. It turns out that a particularly deep negative gravity anomaly exists in the Colorado Rocky Mountains. A few papers on this effect can be found on the web. In particular, a paper (ref 1) by Mousumi Roy at the University of New Mexico offers some details on the  extent of the gravity anomaly and some possible reasons for the effect.

At first blush it might seem odd that a negative gravity anomaly should coincide with a region known for heavy metal deposits. After all, dense matter has greater mass per unit volume, and if there is a lot of volume, then one might expect the acceleration of gravity to be a tiny bit greater than some reference value.

While this line of reasoning has merit, it turns out that despite the presence of thin metalliferous veins in the region, the overall density of rock below the CMB formation is somewhat low. A density contrast exists in the CMB formation and the surrounding rock. A large, low density formation in the crust and/or upper mantle would cause the local acceleration of gravity to be slightly below that of the reference geoid value.  The structure of the density contrast is the subject of some scrutiny and has been addressed by Roy and others.

A large low density mass below the surface is expected to have some buoyancy. A buoyant mass is one that would exert an upward distortion on the crust. The Colorado Rocky Mountains are part of a region characterized by numerous past episodes of mountain building. Whether mountain building was the result of large scale tectonic interactions or more localized effects of density contrasts, the fact remains that a gravity anomaly exists coincident with the CMB.

The mechanical effect of the upthrust of the lower members of the crust to form the Colorado Rocky Mountains has been that a series of faults and fractures have formed. These void spaces have provided networks for the flow of mineral rich hydrothermal fluids over geological time.

High pressure, high temperature aqueous fluids are prone to cooling and depressuriation as they work their way upwards into cooler and less constricted formations. At some point these fluids throw down their solutes and suspensions in the form of solids that occupy the void network. Eventually the flows become self-sealing and circulation halts leaving veins filled with chemical species that were selectively extracted and transported from other formations.

The earths hydrothermal fluid system is continuously extracting soluble components and transporting them to distant locations where solubility properties force their deposition. But this process does not always produce solid, compacted veins. Void spaces can be left behind at all scales, from microscopic size to large chambers. These spaces are called “vugs”. Rock with a large fraction of void spaces is referred to as “vuggy”. It is possible to walk up to a mine dump in the CMB and find hand samples of vuggy rock. It is not unusual to find crystals of pyrite or other minerals lining the internal spaces of the vugs.

1.  McCoy, A., Roy, M., L. Trevino and R. Keller, Gravity models of the Colorado Mineral Belt, in The Rocky Mountain Region – An Evolving Lithosphere: Tectonics, Geochemistry, and Geophysics: American Geophysical Union Geophysical Monograph 154 (eds. Karlstrom, K.E. and Keller, G.R.), 2005.

[Note to the reader: Th’ Gaussling is just a chemist, not a geophysicist. But like many others, I have the ability to read and learn. When I learn something new and interesting, I like to write about it. It reinforces the learning.]

SF ACS Meeting, Not

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It has been 4 or 5 years since I have given a talk at a national ACS meeting. It was with great enthusiasm then that I registered and submitted my abstract last fall. There is not a lot we industrial guys can get up and talk about.  A few weeks ago I confidently decided to follow up on the disposition of my talk and was dismayed to learn that it was declined.

D’oh!!!

I am very disappointed. To my knowledge I followed all of the rules and chose a section that fit the topic.  While the ACS registration website does a good job of collecting your information, it is rather lacking in providing a means of feedback or status to speakers.

Since I have not yet been contacted by a human being, or an automated notification for that matter, I can only surmise that the theme of the section was a mismatch with my topic. Oh yes, I received a limp email “sorry” from somebody at the online help desk.

I wanted to talk about the unexpected energetic decomposition of a class of compounds and some DSC and TGA studies I have done.

Okay, I’m dismayed with certain organs of the Nat’l ACS and their inscrutable ways. But I am willing to admit that I missed some cue or other stagegate that kept me off the boat. But for cryin’ out loud! What was it?? Whose shoes do you have to shine to get an answer?

So, I’ll use the time to get more data and aim for the Boston meeting. A friend was helping with some Hartree-Fock calculations. I was able to correlate onset temperatures with certain periodic trends experimentally. Perhaps we’ll have a better theoretical understanding of the bonding issues by the next meeting.

Update.  Made contact with a person. The sections website is a bit lacking in detail, but with persistant surfing names and email addresses can be found elsewhere.

Antimatter Storage

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We had an ACS local section meeting recently in the clubhouse of the Air Force Academy golf course.  The featured speaker, a DoD chemist, gave an interesting talk on his work on some of the basic issues relating to the storage of positrons or anti-electrons. In the interest of fairness, since I am writing under a pseudonym, I’ll not wave his name about.

The speakers background is P-Chem and in particular, spectroscopy of isolated species in cryogenic matrices. He pointed out that an atom or molecule or cluster in an inert cryogenic matrix is in a dissipative environment and thus isolated from solvent interactions that might otherwise mask other kinds of phenomena.  So it is possible to spectroscopically examine the solid phase environment of the cryo matrix. In other words, an imbedded subject  molecule might find itself in an isotropic or ansiotropic environment, depending on the matrix. Infrared spectroscopy could give clues as to the symmetry of the local environment.

It turns out that ortho-hydrogen is an interesting matrix in which to study an important aspect of antimatter storage technology.  In order to collect positrons, one has to first find a source of them. While they can be supplied by some kind of nucleosynthesis, an easier route experimentally is to find a radioisotope that emits positrons.

It does not take too long for the would-be keeper of antimatter to move to the problem of storage. If you’re going to have anti-matter, you must think carefully about where you’re going to store it.  But there is another issue.  The challenge in collecting positrons from nuclear decay begins with slowing them down. As they are emitted they are travelling at relativistic velocities. Positrons, like “regular” beta particles are emitted in a fairly broad band of energies, so slowing them down via some kind of electromagnetic trap would result in very high losses. Instead, a moderator is envisioned to bleed off speed.

Positrons do not automatically annhilate with the first electron cloud they encounter. In fact, positrons were observed early on by the tracks of ionization they left in bubble and cloud chambers. So positrons can move through matter some distance without annhilation.

Electrons and positrons can pair up to give a transient neutral form of matter called positronium. There are two forms of positronium- singlet and triplet- with the difference being the relative alignment of their spins in either a parallel (triplet) or an antiparallel (singlet) arrangement.  Singlet positronium has the shortest lifetime at 125 picoseconds and triplet at a relatively long lived 145 nanoseconds.

Back to ortho-hydrogen. Positrons can interact with lattice defects in a solid, resulting in early annhilation losses. It turns out that ortho-hydrogen at 2.3 K can be warmed to 5 K and be annealed to a single crystal structure, largely free of defects. Therefore it is possible to prepare a solid moderator free of positron quenching defects.

This is where the speakers research stands at present. The have uncovered a potential positron moderator that would be part of a collection and storage system.  The speaker freely admitted that practical antimatter storage in a container is 100 years in the future. But given the high energy densities available from antimatter, the Air Force is committing modest funds to exploring the issues.

There is work being done to study the positronium Bose-Einstein condensate. It is complicated by the short lifetime of positronium. But fortunately there are ways of storing positrons in storage rings. The annhilation of positronium as a BE condensate would afford coherent 511 keV gamma rays. This would be the basis of a gamma ray laser.

Agilentus, Angry God of the Quadrupole

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I’m going home now.  Just spent a few hours trying to make a parameter change its state on the GC side of  my spiffy new Agilent GC/MS.  Modern instruments are a confederation of subsystems that must give a thumbs up before a software magistrate will allow the instrument to initiate a run. If it is a hyphenated instrument, then all the more so.  All of the flow rates and temperatures and dozens of software settings must be in the proper state before the method can be executed. 

One of the first things you learn after acquiring a complex piece of apparatus is that the help menu is limited in scope.  The mere definition of a mode or a key or a parameter is hardly enough when an annunciator declares that the boat won’t move because the flippin’ gas saver mode is on. The gas saver feature is meant to reduce helium losses from the splitter when the instrument is idle.  What is especially irksome is when an obscure  feature declares that it suddenly can’t  play ball on the (N+1)th run.

My assistant is a truly gifted chromatographer.  She learned analytical lab management in pharmaceutical cGMP and EPA lab settings. What she can do with GC or HPLC is a thing of beauty.  I, on the other hand, have become a grumpy instrument Luddite. It’s not that I don’t like chromatography. In fact I really dig it.  What I get grumpy and dispeptic about is having to claw up the learning curve of yet another software package and then use it enough to retain some kind of fluency.

So, in order to save face with my staff, I have to figure this thing out myself.  Modern chromatographic instrumentation is now configured around the needs of documentation requirements. Creeping featurism. Long gone are the days of sauntering up to the instrument and jamming a sample in it without having to answer a lot of irksome questions about method names and directory gymnastics. Software packages are designed to provide a robust paper trail on the results of all samples injected. It’s all gotten very “Old Testament”.

What is needed is a simplified mode of operation for boneheads like myself. For my process development work I just want resolved peaks, a peak report, and – please god- mass spectra of the components. I do not need a fancy schmancy report. I just need some numbers to scribble in my notebook and report in order to understand what happened in the reactor.

So there it is. A lamentation on chemistry.

Amine Question of the Day

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Here is an interesting question. What fraction of the organic nitrogen in your body is ultimately from the Haber-Bosch Process?  Any guesses?  This question arose during dinner discussion following a rousing seminar on frustrated Lewis pairs. There is no connection to frustrated Lewis pairs, but the speaker raised the question.

Oh, I don’t have an answer. This happens in science.  I’m guessing ~50 %, depending on the extent of protein containing corn products consumed. Any meat science people out there?

Thorium

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A short drive from my office is the Fort St Vrain power plant. The present electrical generating facility is powered by natural gas. But a generation ago it was a nuclear plant powered by a high temperature gas cooled reactor (HTGR). What’s more, the reactor used fissile uranium with fertile thorium.  The output of the plant was ca 330 MW electric and it operated from 1976 to 1989.

The utility eventually decommissioned the helium cooled reactor and converted to natural gas. Today, as before, the plant looks like a planetary humidifier, billowing great clouds of steam condensate into the thin dessicated air of the high plains. The link above outlines the trials and tribulations the utility experienced with some of the auxillary hardware. They had to learn the principle of KISS the hard way.

A thorium-based nuclear reactor uses a fissile element like U-235 to provide a source of neutron flux from which to jumpstart in-situ breeding of U-233. The absorption of a neutron by Th-232 gives Th-233 which beta decays to Pa-233 which decays again to U-233.  Remember, beta decay causes the atomic number to increase by one, but the atomic weight stays the same.  The resulting U-233 is fissile and serves as a fuel.

Thorium as a fuel has pluses and minuses. On the plus side, thorium is more abundant than uranium. And Th-232, the predominant isotope, is the desired fertile material. This is in contrast to natural uranium which offers less than 1 % abundance of fissile isotope U-235. A large part of our nuclear infrastructure involves separation of this isotope to a more concentrated form. After isotopic separation the uranium must then be converted to a suitable chemical form.

The refractory nature of thorium oxide reportedly makes fuel element manufacture somewhat problematic. Interestingly, it is the refractory nature of thorium oxide that makes it valuable for use in thoria lantern mantles. The high melting point of thoria allows a gossamer web of glowing thoria (and ceria) to sit in place in the lantern burner and radiate bright white light.

On the minus side, there is no established fuel supply infrastructure to provide thorium oxide to industry. In fact, there is virtually no thorium trade in the United States today, with the latest annual US sales volume amounting to a paultry $350,000 according to the USGS. Some of the nuclear chemistry is of the thorium cycle is problematic as well.

The natural history of thorium mineral placement is rather different than that of uranium. Uranium migrates fairly readily, depending on its oxidation state and pH of mobilized hydrothermal fluids. As a result, uranium can be found in porous or fractured formations that have a history of water migration.  From what I can tell in the geological literature, thorium concentration results largely from magmatic differentiation in the distant past. There is considerable diversity in the details of each occurrence of thorium, so one should be careful of generalizations.

There is a notable monazite (a common thorium mineral) placer district across the central North and South Carolina border region. These monazite placer deposits sit in ancient stream channels and are the result of alluvial dispersion.

Colorado has two notable thorium mineral deposits. The Wet Mountains SW of Canon City and the Powderhorn district near Gunnison have substantial deposits of thorium as well as lanthanide elements. In fact, rare earths are commonly associated in monazite. Monazite is a phosphate mineral with a variety of thorium and lanthanide cations present. It is useful to recall that the rare earth elements include Sc, Y, the lanthanides, and the actinides. In Colorado, the significant uranium deposits are not coincident with thorium deposits. Uranium is found in sedimentary deposits of the Colorado Plateau, in the tuffaceous sediments of the Thirty-Nine Mile volcanic field, and in vein lodes along parts of the Colorado mineral belt.

There is considerable variability in the elemental associations found in rare earth deposits. Monazite seems to be fairly consistant in regard to the presence of Th and lanthanides. Scandium, however, is often absent or quite scarce in monazites from the assays I have seen in the literature. 

Perhaps the richest thorium district in the lower 48 states is in the Lemhi Pass district along the lower Idaho-Montana border. A company called Thorium Energy reportedly holds substantial claims of thorium rich deposits at Lemhi.

The Passive Aggressive Opera. Act I. Reverse Delegation.

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Supervision of people is one of the things that a chemist can look forward to on the way up the ladder. The people who report to you may be called staff or report-to’s. The term “my employee” should be reserved for use by those who sign paychecks. What ever you call them, they’re your group.

I’m not going to write about how to manage people. After many years of doing it I’m not sure I really understand it yet. All I can say is that every day some people show up and expect you to keep them busy.

Okay, I’m just kidding. But I am serious about the mysteries of management of people. I think most would agree that the best way to lead people- the way most of us would prefer to be lead- is by setting a good example. It’s pulling instead of pushing. Inspired leadership by a charismatic and talented individual is preferable but, unfortunately, rather unusual. 

There are many theories of management and more management consultants than you can count out there urgently interested in telling you how to manage your staff.  All you have to do to sample the many management theories is to stroll through the business section of the local bokstore. Every one of the authors will trot out a set of polished anecdotes that outline the path to their own professional enlightenment.

Chemists on the  management track may move in many directions in a business organization. Most obvious is management of a technical activity like R&D. But there is also management opportunity in scale-up, pilot plant, production, QA/QC, and analytical services activity. Management of the production side is sure to include inventory and warehouse control, regulatory affairs, personnel issues, engineering, and maintenance. Itis not uncommon for engineers to head the production unit.

On the less technical side is sales, procurement management, and business development.  While perhaps less technical, the chemical industry needs (requires, really) chemically savvy people to handle purchasing and sales activity. It is not uncommon for sales oriented people to ascend into the upper reaches of management generally and the chemical industry is no different.

What is perhaps different in the chemical industry is that chemists are often disfavored in the track to the CEO’s office by their lack of economic training. The ability to deliver big projects on time and on budget is a key attribute and engineers are especially well positioned to do this very thing. The bigger the scale of operations the greater the likelihood that an engineer will be in charge. Or so my experience has been.

Among those I have observed, managers who have exemplary experience in controlling the big money are often the ones groomed for executive leadership. And the big money is in big projects with lots of sales volume. It is the source of life giving cash. That which makes the corporate world go ’round. The elusive spondulix.

But back to management. One of the most vexing aspects of managing people is that you have to manage people. People are complex and prone to nonlinear behavior. Everybody knows this. But the manager is tasked with using human resources to provide some kind of work product on time and on spec. How do you compel people to do this every day?

The threat of termination is a good though heavy handed tool to compel folks to do their job. But this is a tool that can also backfire. Frequent termination of people is stressful and puts the manager in the position of having to be in a more or less constant training mode. Best to hire hard working people who are self-starters.

I have not found a simple formula for management. All I can do is to support down and fight up. I fight for resources and reasonable expectations. I treat people in the most hospitable manner I can muster and in return I expect the same.

One of the most annoying behaviors is the phenomenon of “reverse delegation”. You ask your report-to to do a particular thing. In reply you are told that they can only do the thing if you first make some arrangements. You have to get this or that ready, or perhaps you have to write an SOP or work instruction, or maybe even they will need to fly to a hotel in Vegas or Orlando to take some training course. It is all push-back: a kind of passive aggressive behavior meant to deflect your attention.

What I have found is that these reverse delegators may be very concrete in their approach to the unfamiliar. They will assert that they must possess a good deal of skill to even begin some new task. Sometimes this is true. But often it is only a matter of time on task to make some good progress.  The hard part for some of us is dealing with the simple truth of the matter. Not everyone desires being collegial and operating on the give and take level of colleague. A lot of folks only respect the brusque barking of orders by a Captain Bly figure and the sight of a**holes and elbows hustling in the plant. I would have been Captain Kangaroo, not Bly. It’s just a fact.

Old Knowledge and New Problems in Chemistry

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I’ll admit to having a bit of a book fetish. I love everything about books except moving them. I collect new and old books. I have a professional chemistry library that is consuming quite a bit of wall space. And that doesn’t include the boxes of JOC, Organometallics, and JACS. It’s getting out of control.

My amateur geology library has gone from one book last summer to about 50 books and USGS circulars today, and more are enroute this very minute thanks to Amazon.com, Paleopublications, and many more booksellers.

What I’m beginning to see is that university libraries across the country are withdrawing older chemistry books from their shelves. I do not refer to textbooks. I am referring to the valuable secondary literature that has accumulated descriptive chemistry knowledge.  These books are snatched up by specialty book sellers and are placed on the internets for sale where odd characters such as myself will gratefully buy them.

Recently my fetish for old books is helping me solve a thorny contemporary inorganic analysis/synthesis problem. You see, the older texts are rich in wet chemical methods. While a book like Chemistry of the Elements by Greenwood and Earnshaw is fantastically broad in its scope, it is not meant to transfer the pargmatics of procedure. The older chemistry and ore refining texts are full of practical information that seems to be fading away. While the primary literature may be available on SciFinder, books that cover accumulated descriptive chemistries are becoming scarce.

I can’t reveal the details of my revelation. But I can say that a process development person can learn quite a bit about materials processing from the late 19th and early 20th century literature. Our predecessors couldn’t depend on ICP or GDMS or XRD to help them follow the process. The wet chemical methods they developed also give us insights into the transformations necessary to produce purified products.

The unit operations of calcining, comminution, reduction, oxidation, flotation, dissolution, drying, etc., have not changed much in a fundamental way since the days of Agricola. But they are better quantified by virtue of a century of research.

Our collective drift from wet chemical methods to instrumental and computational approaches to analysis are also taking many of us away from the pragmatics of chemistry. The hyphenated instruments of today are leading large numbers of chemists away from the art of chemical transformation and isolation in favor of chemist-as-software-expert. Certainly this computational intensive investigation is not lost in our university curricula. Our hypnotic embrace of technological triumphalism meshes with the perceived need to minimize hazardous material inventories in the chemistry department stockroom. And with the perceived need to minimize chemistry students to exposure to chemicals.

Chemical industry is centered on the art of making things. In the end, somebody has to figure out how to make chemical substances and somebody else has to do the actual work. We chemists have to make sure that university curricula meets the needs of society and that the librarians of the world understand the importance of older chemistry books.

On the pitfalls of process intensification

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As any process development chemist knows, there is motivation to optimize a chemical process to produce maximum output in the minimum of reaction space. In the context of this essay, I’m referring to batch or semi-batch processes. Most multipurpose fine chemical production batch reactors have a capacity somewhere between 25 and 5000 gallons. These reactors are connected to utilities that supply heat transfer fluids for heating and cooling. These vessels are connected to inerting gases- nitrogen is typical- and to vacuum systems as well.

Maximum reactor pressure can be set as a matter of policy or by the vessel rating. Organizations can, as a matter of policy, set the maximum vessel pressure by the selection of the appropriate rupture disk rating. Vessel pressure rating and emergency venting considerations are a specialist art best left to chemical engineers.

Reactor temperatures are determined by the limits of the vessel materials and by the heat/chiller source. Batch reactors are typically heated or chilled with a heat transfer fluid. On heating, pressurized steam may be applied to the vessel jacket to provide even and controlled heating.  Or a heat transfer fluid like Dowtherm may be used in a heating or chilling circuit.

Process intensification is about getting the maximum space yield (kg product per liter of reaction volume) and involves several parameters in process design. Concentration, temperature, and pressure are three of the handles the process chemist can pull to increase the reaction velocity generally, but concentration is the important variable in high space yield processes.  Increasing reaction temperatures or pressures might increase the number of batches per week, but if more product per batch is desired and reactor choices are limited, then eventually the matter of higher concentration must be addressed.

The principle of the economy of scale says that on scale-up of a process, not all costs scale continuously or at the same rate. That is, if you double the scale, you double the raw material costs but not necessarily the labor costs. While there may be some beneficial economy of scale in the raw materials, most of the economy will be had in the labor component of the process cost. The labor and overhead costs in operating a full reactor are only slightly greater than a quarter full reactor. So, the labor component is diluted over a greater number of kg of product in a full reactor.

The same effect operates in higher space yield processes. The labor cost dilution effect can be considerable. This is especially important for the profitable production of commoditized products where there are many competitors and the customer makes the decision solely on price and delivery. Low margin products where raw material costs are large and relatively fixed and labor is the only cost that can be shaved are good candiates for larger scale and higher space yield.

But the chemist must be wary of certain effects when attempting process intensification. In general, process intensification involves increasing some kind of energy in the vessel. Process intensification through increased concentration will have the effect of increasing the amount of energy evolution per kilogram of reaction mixture.

Energy accumulation in a reactor is one of the most important things to consider when attempting to increase space yield. It is crucial to assure that process changes do not result in the accumulation of hazardous energy.

Energy accumulation in a reactor occurs in several ways. The accumulation of unreacted reagents is a form of stored energy. The danger here is in the potential for a runaway reaction. Accumulated reagents can react to evolve heat leading to an accelerated rates and eventually may open further exothermic pathways of decomposition. As the event ensues, the temperature rises, overwhelming the cooling capacity of the reactor. The reactor pressure rises, accelerating the event further. At some point the rupture disk bursts venting some of the reactor contents. Hopefully the pressure venting will result in cooling of the vessel contents and depressurizing the vessel. But it may not. If the pressure acceleration is greater than the deceleration afforded by the vent system, then the reactor pressure will continue to a pressure spike. This is where the weak components may fail. Hopefully, nobody is standing nearby. Survivors will report a bang followed by a rushing sound followed by a bigger bang and BLEVE-type flare if the system suffers a structural failure.

Energy accumulation can manifest in less obvious ways. Here is an example. Assume a spherical reaction volume. As the radius of the sphere increases, the surface area of the sphere increases as the square of the radius. The volume increases as the cube of the radius. So, on scale-up the volume of reaction mixture (and heat generation potential) will increase faster than the heat transfer surface area. The ratios are different for cylindrical volumes, but the principle is the same. Generally the adjustment of feed rates will take care of this matter in semi-batch reactions. Batch reactions where all of the reagents are added at once are where the unwary and unlucky can get into big trouble.

Process intensification via increased concentration may have deleterious effects on viscosity and mixing. This is especially true if slurries are produced and is even worse if a low boiling solvent is used. Slurries result in poor mixing and poor heat transfer. Low boiling solvents may be prone to cavitation with strong agitation, exacerbating the heat transfer problem. Slurry solids provide nucleation sites for the initiation of cavitation.  Cavitation is difficult to detect as well. The instinct to increase agitator speed to “help” the mixing may only make matters worse by increasing the shear and thus the onset of cavitation.

Denser slurries resulting from process intensification are more problematic to transfer and filter as well. Ground gained from higher concentrations may be lost in subsequent materials handling problems. Filtration is where the whole thing can hang up. It is important for the process development chemist to pay attention to materials handling issues before commiting to increased slurry densities. Crow is best eaten while it is still warm.

PETN in his BVD’s

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History will record an underwear bomber and a shoe bomber. Luckily for the passengers of one transatlantic flight, the anonymous martyr on board was incompetent. Like the shoe bomber before him, this murderous buffoon failed to plan for a reliable means of triggering his bomb.

PETN, or pentaerythritoltetranitrate, was found to be the explosive agent used in the attempted inflight bombing of  Northwest Flight 253. This is a relatively common and powerful explosive in the category of aliphatic nitrate esters. It is a colorless powder that can be used in mixed and cast explosives or as the pure material. Like many detonable materials, it does not need to be placed in confinement to produce an explosion. PETN becomes unstable above 71 C, a fact that limits its suitability for some applications. My references do not clarify what is meant by unstable, but the material could be prone to chemical degradation above this temperature which would adversely affect its quality.

Other aliphatic nitrate esters include nitroglycerin, BTTN or 1,2,4-butanetriol trinitrate, EGDN or ethylene glycol dinitrate, and PETRIN, the trinitrate analog of PETN. A nitrate ester has a C-O-NO2 linkage and differs from aliphatic or aromatic nitro compounds which have C-NO2 linkages instead.

Nitrate esters are made from an alcohol or polyol and nitric acid. Nitro aromatics like TNT are made by acid catalyzed nitration of reasonably electron rich aromatic compounds like toluene or phenolics. The oxygen in the C-O-NO2 ester linkage confers some extra measure of instability to the molecule.

PETN is commonly used in Primacord, an explosive cord comprised of a PETN core inside a thin fabric or plastic sleeve. Primacord can be used as a blasting agent itself or it can be used as a fuse or delay line to trigger other explosives from a central point.

PETN is an explosive with a high brisance value. That is, it produces a shock that has a shattering effect on materials. In fact, brisance is quantified by the “sand test” which measures the production of fines from the shattering of 200 g of 30 mesh Ottawa sand. After the test, the sand is re-screened and the finer material that later passes through the screen is weighed. The greater the mass of fines, the greater the brisance.

Explosive         Sand Crush (g)   Heat of Explosion (cal/g) 
Black powder         8                                    684
Lead Azide            19                                  367
Comp C-4             55.7                            1590
TNT                      48                                1080
RDX                  60.2                        1280
Nitroglycerin         51.5                           1600
AN                               nil                                346
Picric Acid              48.5                           1000
PETN                         62.7                            1385
Source:  Cooper & Kurowski, Introduction to the Technology of Explosives, 1996, Wiley-VCH, p76-77. ISBN 0-471-18635-X

Pentolite is a composition prepared from a 50/50 blend of trinitrotoluene (TNT) and PETN with wax as a bonding agent and plasticizer. There are many blends of explosive materials. The composition is adjusted for the application.

The job of an explosive is to do PV work on objects. It does this by generating an abrupt pulse of heat and a large number of small gas molecules like N2 and CO2. The detonation velocity of PETN is ~ 8 km/s, so that a relatively small number of PETN molecules in a small volume are converted rapidly into a larger number of  gas phase molecules, all seeking to occupy the molar volume of 22.4 L/mol. 

The prompt generation of many moles of hot, small molecules results in the expansion of decomposition gases which forcefully press against the surroundings. The gases resulting from the 8 km/s detonation wave in the bulk solid explosive expand and compress the nearby air into a shock front that expands approximately spherically. As it does this the gases cool and the shock dissipates.

Explosive Power is a measure of an explosives ability to do work. Explosive power = Q x V,  Q = heat of explosion and V = volume of gas generated. The Power Index of a material is the ratio of explosive power to that of picric acid times 100 %. The power index of PETN is 167, TNT is 119, and RDX is 169.