properties of specific chemicals

R. B. Darling / EE-527 / Winter 2013

EE-527: MicroFabrication

Properties of Specific Chemicals


Be Careful and Know Some Chemistry

– “On April 16, 1947, 2200 tons of ammonium nitrate [fertilizer] was stored on board the S. S. Grandcamp along with 1500 tons of fuel oil. While docked at Texas City, Texas, a fire was detected in the hold. An order was given to close hatches and to apply steam throughout the hold. Under these conditions, the fire could not extinguish. Instead, the internal pressure built up at an uncontrollable rate, causing the cargo vessel to explode. Six hundred people were killed and another 3500 were injured. The property damage was comparable to that experienced during a major wartime bombing incident. The total property loss was estimated as $33 million based upon 1947 costs.”

– Eugene Meyer, The Chemistry of Hazardous Materials, 2nd ed.


The Texas City Disaster of 1947

(Images from Wikipedia)


The Texas City Disaster of 1947• This is usually cited as the deadliest industrial accident in U.S. history. • Witnesses compared the damage to Texas City as roughly equivalent to that

produced by the atomic bomb dropped on Nagasaki, Japan, during WW-II. • The official death toll was 581. • The true death toll has been estimated as high as 750. • The entire city was leveled. • 1,100 automobiles were destroyed. 1,000 homes were destroyed. • 5,000 people were injured, with 1,800 admitted into hospitals. • 2,000 people were left homeless. • Over 6,000 tons of the ship’s steel was thrown into the air at supersonic

speeds. One of the ship’s 2-ton anchors was thrown almost 2 miles away. • The blast created a 15 ft. high wave that affected 160 miles of Texas coastline. • The blast shock was felt over 100 miles away in Louisiana, and windows were

shattered over 40 miles away. • This also triggered the historically significant first class action lawsuit against

the U.S. government on behalf of 8,485 victims and resulted in the Federal Tort Claims Act (FTCA).


Chemistry of the 1947 Texas City Disaster

• This accident gravely illustrates: – The high density of chemical energy, – The explosive power of high pressure detonations in confined spaces, – The hazards of storing incompatible chemicals in adjacent locations

(e.g. fuel oil and ammonium nitrate), – The consequences of improperly dealing with a fire, and – Why knowing some fundamental chemistry of the materials you are

using is extremely important!

• Have we learned anything? The most recent ammonium nitrate fire and explosion was in Bryan, TX, on July 30, 2009. – Over 80,000 residents were evacuated and moved to Texas A&M

University at College Station, TX.


Sulfuric Acid (H2SO4) - 1

– most commonly used industrial chemical– also called oil of vitriol– colorless, oily, syrupy liquid, specific gravity = 1.84– standard reagent concentration is 98%, yellow bottle cap– NFPA704M code = 3-0-2-W; CAS # [7664-93-9]– “fuming sulfuric acid” or “oleum” has additional SO3 dissolved

into solution; which creates H2S2O7, disulfuric acid

• primary hazards:– when dissolved into water, H2SO4 liberates considerable heat

• 20 kcal/mol = 1570.9 J/cm3

– H2SO4 is a strong acid, but only the first proton dissociates completely; second proton has Ki = 10-2

– always add acid to water to avoid spattering

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Sulfuric Acid (H2SO4) - 2

• primary hazards:– concentrated H2SO4 has a great affinity for H2O: hygroscopic– concentrated H2SO4 will dehydrate sugars, starches, and cellulose– acid burns to skin dehydrate the tissue with localized evolution of

heat. skin becomes charred, like burnt wood– concentrated H2SO4 dehydrates concentrated HClO4 (perchloric

acid). The two can explosively decompose and must be stored in separate cabinets.

– concentrated H2SO4 can react to form hazardous compounds• chlorine containing oxidizers will react explosively• will decompose salts into other acids

– 2NaF + H2SO4 Na2SO4 + 2HF• may produce toxic gases, e.g. Br2, I2, SO2, CO, COS, H2S• concentrated H2SO4 will oxidize carbon, lead, and copper


Nitric Acid (HNO3) - 1

– second most commonly used industrial chemical– NFPA704M code = 4-0-0-OXY; CAS # [7697-37-2]– colorless liquid, often reddish-brown from dissolved NO2

• light exposure produces: 4HNO3 4NO2 + 2H2O + O2

– also called aqua fortis in art engraving– excess dissolved NO2 produces fuming nitric acid– standard reagent concentration is 68-70%, red bottle cap– while fundamentally a strong mineral acid, it is also considered to

be a strong oxidizer

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Nitric Acid (HNO3) - 2

• primary hazards:– reacts with metals and nonmetals, releases NO and/or NO2

– concentrated HNO3 will spontaneously ignite wood, cellulose products, and many organic materials such as turpentine, acetic acid, acetone, ethyl alcohol, nitrobenzene, and aniline

– concentrated HNO3 oxidizes proteins• produces xanthoproteic acid (yellow colored, slow-healing wound)

– concentrated HNO3 acts as both an acid and an oxidizer!!


Hydrochloric Acid (HCl)

– pure HCl is a strong-smelling, colorless gas• TLV = 5 ppm, exposure to > 1500 ppm is usually fatal• extremely soluble in H2O

– NFPA704M code = 3-0-0; CAS # [7647-01-0]– technical grade HCl is slightly yellow due to Fe++ impurities– also know as muriatic acid– standard reagent concentration is 37%, blue bottle cap

• primary hazards:– corrosive effect on metals– vapor toxicity:

• 1-5 ppm = limit of odor• 35 ppm = irritation of throat• 50 ppm = barely tolerable• 1000 ppm = fatal via lung edema

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Aqua Regia

– mixture of 3 parts conc. HCl and 1 part conc. HNO3

– also called nitrohydrochloric acid– very potent oxidizing agent– useful for dissolving Au and Pt


Perchloric Acid (HClO4)

– strongest of all of the common acids– NFPA704M code = 3-0-3-OXY; CAS # [7601-90-3]– anhydrous form is unstable– standard reagent concentration is 72%– must be used and stored in specially designed facilities

• primary hazards:– concentrated HClO4 when heated to 92°C explodes

• 4HClO4 2Cl2 + 7O2 + 2H2O– concentrated HClO4 ignites or explodes with cellulose materials

and most organic compounds– treated differently following the 1940’s Los Angeles explosion

caused by its reaction with aniline

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Hydrofluoric Acid (HF) - 1

– pure HF is a colorless gas above 20C, TLV = 2.5 ppm– NFPA704M code = 4-0-1; CAS # [7664-39-3]– similar in reactivity to H2SO4

– a strong dehydrating agent– has a high affinity for water (hygroscopic)– dissolved in H2O it becomes a weak acid (it partially dissociates)

• BUT IT IS STILL EXTREMELY DANGEROUS!!– standard reagent concentration is 49%, white bottle cap– HF dissolves glasses:

• CaSiO3 + 6HF CaF2 + SiF4 + 3H2O• SiO2 + 4HF SiF4 + 2H2O

– concentrated HF must be stored in polypropylene containers!!– commercially used for etching glass

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Hydrofluoric Acid (HF) - 2• primary hazards:

– HF vapor produces edema of the lungs and can permanently damage the cornea.

– HF is extremely dangerous to skin contact, the worst of all acids in terms of damage to tissue, can produce very severe, painful burns.

– HF has a slight anesthetizing effect, pain is often not noticed until the acid has penetrated a large distance into tissue, often down into bone material where it reacts with Ca and Mg to form fluorides.

– Because of small size of molecule, HF dissolves easily though pores of skin and cell membranes, and also through many plastics.

– Use Trionic or heavy neoprene gloves when dealing with HF!!– At present there exists no effective remedy for HF burns

• Some suggest an ointment of 3 oz. magnesium oxide, 4 oz. heavy mineral oil, and 11 oz. white vaseline is helpful.

• Commercially available calcium gluconate cream is commonly suggested to treat HF burns or exposures.


Buffered Oxide Etch (BOE)

– a solution of (40%) NH4F and (49%) HF• 6:1 is the fastest etching (~2 nm/sec grown SiO2 at 25°C)• 10:1 is common• 25:1 is also used for slower etches

– NFPA704M code = 4-0-1– industry standard solution for etching SiO2

– NH4F is a solid crystal, but dissolved in H2O, it produces some HF and fluorine ion; NH4F is normally used at 40% concentration.

– NH4F provides buffering of the fluoride ion. As SiO2 etching proceeds, the NH4F replenishes the fluoride ion that is consumed in the creation of SiF4. This keeps the etch rate more constant.

• primary hazards:– the same as for hydrofluoric acid, HF– Use Trionic or heavy neoprene gloves when dealing with BOE!!

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Phosphoric Acid (H3PO4)

– clear, odorless, sparkling liquid or transparent solid– NFPA704M code = 3-0-0; CAS # [7664-38-2]– used in several food products, e.g. Coca-Cola– phosphorous forms 8 different acids; H3PO4 is the most common– phosphorous anhydride is a strong dehydrator and has a great

affinity for water. Dissolved in water it produces phosphoric acid:• P4O10 + 6H2O 4H3PO4

– standard reagent concentration is 85%, white bottle cap

• primary hazards:– concentrated H3PO4 liberates considerable heat when diluted with

water; always add the acid to the water to avoid spattering– concentrated H3PO4 can cause severe skin burns, but it is generally

the least hazardous of the strong mineral acids

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Acetic Acid (CH3COOH)

– most common organic acid– NFPA704M code = 3-2-1; CAS # [64-19-7]– causes the sour taste and odor of vinegar (typ. 3-6% acetic acid)– “glacial” acetic acid is about 99.5% acetic acid, derived from the

decomposition of acetylene, used in photography– standard reagent concentration is 99%, brown bottle cap

• primary hazards:– highly corrosive– vapors are harmful, TLV = 10 ppm– CH3COOH freezes at 17°C, and like water, expands upon freezing

• Glass bottles must be protected against temperatures below 17°C. – CH3COOH will burn, but the autoignition temperature is 426°C

and is generally unlikely without the presence of an ignition source

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Sodium Hydroxide (NaOH) - 1

– It is the most common alkali. – NFPA704M code = 3-0-1; CAS # [1310-73-2]– also called lye or caustic soda– It is produced by electrolysis of brine:

• 2NaCl + 2H2O 2NaOH + H2 + Cl2

– At room temp., NaOH is a white solid, usually pellets or powder. – It is very hygroscopic. – Dry pellets will burn skin after absorbing moisture from the tissue. – Weak solutions have a bitter or caustic taste, and a slippery or

soapy feeling, typical of all alkalis. – Like all alkalis, it can destroy or burn tissues, leaving serious

wounds that heal very slowly. – The standard reagent concentration is 97%.

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Sodium Hydroxide (NaOH) - 2

• primary hazards:– can cause extremely severe burns to the skin

• treat with 1% acetic acid solution or common household vinegar• tissues have no natural defense to strong bases, so tissue damage can

be greater than that of a strong acid– strong acids create impermeable damage zone which limits the spread– strong bases do not create this reaction and can diffuse much farther

– can cause extremely severe burns to the cornea• treat with 1% boric acid to neutralize after several minutes of

irrigation with water– nonflammable by itself, but can trigger the ignition of other

materials– very exothermic upon dissolving in H2O

• 10 kcal/mole• hot enough to ignite or melt some materials


Potassium Hydroxide (KOH)

– also called potash or caustic potash– NFPA704M code = 3-0-1; CAS # [1310-58-3]– very similar to NaOH– considered a slightly stronger base– at room temp., NaOH is a white solid, usually pellets or powder– very hygroscopic – standard reagent concentration is 97%

• primary hazards:– very similar to NaOH

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Ammonium Hydroxide (NH4OH)

– created by dissolving NH3 into H2O– NFPA704M code = 3-1-0; CAS # [1336-21-6]– NH3 is very soluble in H2O – forms a weak base (partially ionizes)– neutralizes acids, but is generally unreactive with most metals– standard reagent concentration is 30%, green bottle cap

• primary hazards:– concentrated NH4OH will burn skin– NH3 vapors are harmful

• TLV = 50 ppm• moderately toxic, strong irritant to skin, eyes, and mucus membranes

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Hydrogen Peroxide (H2O2)– resembles water, but with a slightly sharp odor– a very strong oxidizer– NFPA704M code = 3-0-2-OXY; CAS # [7722-84-1]– inherently unstable, decomposes from sunlight, UV radiation, or heat

• 2H2O2 2H2O + O2

• typically lasts only a few months under refrigeration (~5°C)– standard reagent concentration is 30%, white bottle cap

• primary hazards:– decomposes violently at 144°C– readily provides oxygen in redox reactions

• can cause spontaneous ignition of combustible materials when > 50 %• greatly speeds up many reactions, turning some into explosions

– can cause severe skin burns or bleaching• drug store hydrogen peroxide is only 1-3 %

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Methanol (CH3OH) (MeOH)– also known as methyl alcohol or wood alcohol– NFPA704M code = 1-3-0; CAS # [67-56-1]– clear, colorless liquid, completely miscible with water– ρ = 0.792 g/cm3; the vapor is heavier than air. – Because it is non-polar, it is a very good solvent for removing oils,

greases, waxes, gums, and resins. – It is commonly used for cleaning in microfabrication because it can

be easily washed away with DI water. – It is fairly volatile: BP = 65°C.

• primary hazards: – It is extremely flammable: FP = 12°C. – It is quite toxic! Poisoning can occur through mere skin contact.

• It is a small molecule that can easily be absorbed through the skin. • Lethal dose by ingestion is about 30-100 mL. It is a CNS depressant

and it metabolizes into formic acid.

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Green Wash Bottle

Blue Wash Bottle


Ethanol (CH3CH2OH) (EtOH)– also known as ethyl alcohol– NFPA704M code = 2-3-0; CAS # [64-17-5]– clear, colorless liquid, completely miscible with water– ρ = 0.789 g/cm3; the vapor is heavier than air. – It is another good non-polar solvent for removing oils, greases,

waxes, gums, and resins, although generally not as effective as methanol. It is also a good antiseptic for bacteria.

– It is less commonly used in microfabrication, but it is sometimes added to aqueous solutions to reduce the surface tension of water and improve wetting.

– It is fairly volatile: BP = 78.4°C.

• primary hazards: – It is very flammable: FP = 16.6°C. – It is a CNS depressant and is usually fatal at blood alcohol levels

of > 0.5% or > 5.0 g/L.

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Orange Wash Bottle


Isopropanol (CH3CHOHCH3) (IsOH, IPA) .– also known as rubbing alcohol or 2-propanol– clear, colorless liquid– NFPA704M code = 2-3-1; CAS # [67-63-0]– ρ = 0.786 g/cm3; the vapor is heavier than air– It is very miscible in water, but quite immiscible in salt water. – It is a non-polar solvent and can remove some oils, greases and

resins, but it is the weakest of all the common solvents. For the same reason, it is also the least damaging to plastics.

– It is used commonly as a sterilizing agent in cleaning pads, usually at 60-75% in water. A common drugstore item.

– It is fairly volatile: BP = 82.5°C.

• primary hazards: – high flammability; FP = 12°C; LEL = 2.0%; UEL = 12.7%– moderate toxicity; LD50 = 3600 mg/kg (oral, rat); TWA-TLV =

980 mg/m3

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Yellow Wash Bottle


Acetone (CH3COCH3)– also known as dimethyl ketone– NFPA704M code = 1-3-0; CAS # [67-64-1]– clear, colorless liquid, somewhat miscible in water– It is a much stronger solvent than most alcohols, and it is capable

of removing difficult oil, wax, and resin stains. It will also soften or dissolve most hard plastics like ABS, styrene, or polycarbonate.

– It has a slightly sweet odor. – ρ = 0.791 g/cm3; the vapor is heavier than air. – It is used in nail polish removers and oil-based paint thinners. – It is highly volatile and evaporates very quickly: BP = 56°C. – It has low toxicity: TWA-TLV = 1000 ppm for worker exposure.

• primary hazards: – It is extremely flammable and a serious fire and explosion risk! – FP = −17°C; LEL = 2.6%; UEL = 12.8%.

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Red Wash Bottle


1,1,1-Trichloroethane (CH3CCl3) (TCA)– also known as methyl chloroform– NFPA704M code = 3-1-1; CAS # [71-55-6]– clear, colorless liquid, completely immiscible in water– It is a much stronger solvent than most alcohols, and it is capable

of removing difficult oil, wax, and resin stains. It will also soften or dissolve some hard plastics. It is a very good cleaning solvent!

– It has a slightly sweet odor. – It is fairly volatile and evaporates rapidly: BP = 74°C. – ρ = 1.32 g/cm3; the vapor is heavier than air. – It is one of the least toxic of the chlorinated hydrocarbon solvents.

• It has generally been considered a much safer alternative to TCE. – It is an ozone depleting substance and its use is being phased out.

• primary hazards: – It is only mildly flammable. – It is a slight CNS depressant.

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properties of specific chemicals

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