Grammar: The verbs “to be”, “to have”. Modal Verbs

Word List:

1. membrane surface	поверхность мембраны
2. adhesion	слипание, прилипание, сцепление
3. biofouling	биозагрязнение
4. hydrophobic material	гидрофобный материал
5. to exceed	превышать
6. at the expense of	за счёт
7. ubiquitons	вездесущий, повсеместный
8. nutrient concentration	концентрация питательных веществ
9. tolerance level	допустимый уровень
10. regardless of	независимо от, несмотря на

 

Membranes and Microorganisms

The treatment of water by membrane technology intrinsically implies the contact of very large quantities of water with the membrane surfaces. This water is not sterile. In drinking water, the numbers of cells actually present as demonstrated by microscopic quantification usually range between 10⁴ and 10⁶ cells/ml. These cells have a tendency to adhere to surfaces; in oligotrophic systems, this is considered a survival strategy. There is virtually no surface material which cannot be colonized, even under extreme conditions; regardless of hydrophobicity or hydrophilicity, smoothness or chemical composition - surface conditions and materials will simply select for colonizing species among the spectrum of organisms in a given water volume. In a membrane system, adhesion to the membrane surface is facilitated by the vertical transport vector which is given by the water flow through the membrane - this can be described metaphorically as “love at first sight”, because there will always be some organisms which prefer to settle on the given membrane material, be it hydrophobic or hydrophilic. Once the organisms colonize the surface, they will inevitably multiply and form biofilms. All membrane systems which are not operated under absolutely sterile conditions will carry biofilms.

Not all of the systems carrying biofilms suffer from bio-fouling – “biofouling” is an operational term, applied when the effects of biofilms exceed a certain threshold, or tolerance level, which is individually set for different systems.

In membrane systems, however, biofouling is the “Achilles heel” of the process, because all other fouling components, such as organic and inorganic dissolved substances and particles can mostly be removed by efficient pretreatment; however, microorganisms are particles which can multiply. Thus, if they are removed to 99.99 %, there are still enough cells left which will grow at the expense of biodegradable substances in the water. Microorganisms are ubiquitous in any technical system unless it is kept sterile by enormous and continuous effort. The biofouling potential is represented by the types of microorganisms and the nutrient concentration.

Focused Practice

I. Answer the following questions:

1. What does the treatment of water by membrane technology imply?

2. What is a survival strategy in oligotrophic systems?

3. What will the organisms do when they colonize the surface?

4. When is the term “biofouling” applied?

5. Why if biofouling the “Achilles heel” of the process in membrane systems?

6. How is the biofouling potential represented?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: The vertical transport vector.

Unit 16

Grammar: Modal Verbs

Word List:

1. compatibility	совместимость
2. host	первичный материал, минерал-«хозяин»
3. a solid-state battery	твердотельная батарея
4. a voltage window (a voltage range)	диапазон напряжений
5. overcharge	избыточный заряд
6. availability	наличие
7. unstrained bonds	недеформированные связи (соединения)
8. both....and	как...так и; и...и
9. primarily	в первую очередь
10. until recently	до недавнего времени

What Materials Are Suitable as Polymer Electrolytes?

As the electrolyte must function as both a separator and an electrolyte in a solid-state battery (still seen as the major application for these materials), then a number of properties are critical for its success. The electrolyte must satisfy a minimum of requirements from an electrochemical point of view:

· Conductivity: the electrolyte must have sufficient ionic conductivity to allow a reasonable current density; 10 S/cm would be ideal at room temperature although a lower value may be acceptable (Armand originally quoted 10 S/cm minimum practical value).

· Electrochemical stability: the electrolyte should be electrochemically stable in a voltage window that is at least as wide as the voltage window defined by the electrode reactions (it should preferably be wider, to accommodate overcharge and discharge reactions).

· Compatibility: they must be chemically and electrochemically compatible with electrode materials.

· Thermal stability: electrolytes must have good thermal stability, especially in contact with a lithium electrode.

· Mechanical stability: the mechanical stability becomes important as battery technology moves from laboratory into process development, pilot production and, finally, full, production.

· Availability: raw materials must be readily available and inexpensive. Exotic materials have many uses as model compounds but may be impractical at a production level.

While many electrochemists throughout the 1980s preferred to study simple PEO-based polymer electrolyte systems using phase diagrams as a guide to suitable salt concentrations and temperature ranges, polymer chemists began to design more appropriate electrolyte constituents, primarily polymer hosts. The lain advantage of PEO as a host is it is chemically and electrochemically stable, since it contains only strong unstrained C-О, C-C, and C-H bonds. It is not surprising therefore that alternative host polymers have tended to incorporate ether units. It has perhaps been unfortunate that, with the bulk conductivity as the prime motivator of polymer electrolyte design, the other five factors listed above have not, until relatively recently, had the attention they deserve. As a result, the vast majority of alternative polymer hosts synthesized will have little practical application.

Focused Practice

I. Answer the following questions:

1. What requirements must the electrolyte satisfy from an electrochemical point of view?

2. What must the electrolyte have sufficient ionic conductivity for?

3. Where should the electrolyte be electrochemically stable?

4. Why did polymer chemists begin to design polymer hosts?

5. What tendency do alternative host polymers have?

6. What practical application will alternative polymer hosts synthesized have?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: Thermal and mechanical stability of electrolytes.

SECTION II

ELECTRICAL  ENGINEERING
AND  ELECTROMECHANICS

Unit 17