Pow­ders are a form of mat­ter that prove use­ful for stor­ing, pre­serv­ing and pack­ag­ing numer­ous sub­stances, but they also car­ry some risks, in terms of hygiene and safe­ty, plus some phys­i­cal and mechan­i­cal prop­er­ties that are not well under­stood. In order to assist the pro­fes­sion­als who make and/or use pow­ders, some UTC spe­cial­ists offer train­ing pack­ages to teach the basics of pow­der char­ac­ter­i­za­tion and their properties. 

“Today, close on 80% of exist­ing prod­ucts have at some time a pow­der-based exis­tence”, says Khasha­yar Saleh, Direc­tor of the UTC Indus­tri­al Process Engi­neer­ing Depart­ment (UTC-GPI), a spe­cial­ist in the physics and chem­istry of ‘gran­u­lar’ mat­ter. We find such pow­dered mat­ter in many areas, rang­ing from food­stuffs, cos­met­ics, chem­istry and phar­ma­ceu­ti­cals or even to nuclear pow­er fuels. They can be com­pact­ed in tablet form, or ‘raw’ (unprocessed) and present many advan­tages but con­trol­ling their uses calls for spe­cial exper­tise. The first advan­tage when mat­ter is trans­formed into a pow­der lies in improved stor­age and preservation. 

Advantages: dry, concentrate and separate

“Pow­dered milk, for exam­ple, los­es 94% of its mass in dry­ing out the water con­tent” empha­sis­es Khasha­yar Saleh. This is a com­mon­place prod­uct that clear­ly shows the advan­tage of the pow­der form: easy to store, easy to pre­serve. Cos­met­ics also make use of the fine grain of pow­ders and the soft touch obtained. Pow­ders also allow for con­cen­tra­tions of sub­stances that can be very con­cen­trat­ed indeed, such as in the case of colour pig­ments. Pow­ders are also used in phar­ma­ceu­ti­cals to pro­duce the coat­ings of so-called smart pills that will dis­solve or release their active prin­ci­ples only under cer­tain con­di­tions (milieu or time). The release process is selec­tive and increas­es the action and also allows you to decrease the amount of the dos­es admin­is­tered. Anoth­er advan­tage of pow­ders is that two antag­o­nis­tic mat­ters can be asso­ci­at­ed in a sin­gle prod­uct. “Deter­gents often mix acids and alka­lis and hair creams can mix col­orants and decol­orants” adds Khasha­yar Saleh. The pow­der for­mat allows indus­tri­al­ists to pack­age dif­fer­ent mat­ters and prod­ucts with per­fect­ly con­trolled contents. 

Risks: an explosive nature

Pow­ders also pos­sess a few dis­ad­van­tages! In terms of hygiene and safe­ty, those that come from organ­ic prod­ucts call for a degree of spe­cial care. It is nec­es­sary to char­ac­ter­ize the way these bio-mate­ri­als degrade so as to avoid putting unsafe prod­ucts on the shop-shelves, and on top of that, organ­ic pow­ders have a propen­si­ty … to explode! Sug­ar, flour and oth­er pow­ders can lead to explo­sive mix­es (det­o­nat­ing chem­i­cal reac­tions) because of the fine grain and the high sur­face exposed to oxy­gen. “In sug­ar and flour fac­to­ries, safe­ty mech­a­nisms are installed, capa­ble of detect­ing when a too high con­cen­tra­tion of pow­der is in the ambi­ent air”, con­firm the UTC pow­der spe­cial­ist but who imme­di­ate­ly adds that these ques­tions are dealt with very seri­ous­ly by the indus­tri­al­ists in the rel­e­vant sectors. 

Heterogeneous systems that resist modelling

“Anoth­er dif­fi­cul­ty relates to pow­der flow and rhe­ol­o­gy. The way pow­ders flow and how they behave under stress are fea­tures that have not as yet been stud­ied thor­ough­ly”, stress­es Khasha­yar Saleh. For exam­ple, a defect in the flow line of enriched nuclear fuel could lead to pos­si­bly very dis­as­trous results. Less dan­ger­ous, but still expen­sive, the unfore­seen behav­iour­al modes of the way pow­dered paint in pro­ject­ed on car bod­ies in the auto­mo­bile indus­try can lead to major paint fin­ish faults and there­fore incur seri­ous expens­es for the car-mak­ers. “Pow­ders, by essence, are het­ero­ge­neous sys­tems that do not read­i­ly lend them­selves to mod­el­ling equa­tions – indeed no such equa­tions exists as is the case for flu­ids and gas­es with well-mod­elled mechan­i­cal prop­er­ties”, under­lines Khasha­yar Saleh, who adds that these issues are often under-esti­mat­ed giv­en that engi­neers are not often trained in the appro­pri­ate tech­niques and approaches. 

Training courses offered at UTC

In the absence of a gen­er­al phys­i­cal mod­el that can rep­re­sent pow­dered sys­tems and the wide range of prob­lems asso­ci­at­ed have forced engi­neers to analyse sit­u­a­tions on a case-by-case basis. In this per­spec­tive, UTC offers train­ing pack­ages to as to make the indus­tri­al actors more aware of the issues when making/using pow­dered mat­ter. The cours­es are mod­u­lar and lec­tur­ers are invit­ed as per the spe­cial­ties cov­ered so as to detail how pow­ders are char­ac­ter­is­tic and to con­vey infor­ma­tion and data as to the phys­i­cal and chem­i­cal pro­pri­eties. The over­all objec­tive is to sup­ply infor­ma­tion that will prove use­ful for ques­tions of analy­sis, con­trol and improve­ment of process­es and products.

Where­as Khasha­yar Saleh is very hap­py to be able to organ­ise these twice year­ly sem­i­nars, for pro­fes­sion­als who come from many dif­fer­ing hori­zons, he also finds his own per­son­al inter­est here. In many instances, the trainees come with their ques­tions but also pro­vide valu­able expe­ri­ence and case-stud­ies that enrich the knowl­edge base of the sci­en­tists and the class lecturers.