Development• Photographic Developers are generally

Reducing agents. The silver ions are reduced to silver metal. The developer donates electrons to the positive silver ions.

• The greater the number of silver nuclei attracted to the sensitivity centers the faster the developer will reduce the silver ions to silver metal. So the more light a crystal is exposed to the faster it will develop and the darker it will be.

• Developers need to be somewhat selective so as not to turn unexposed silver dark. A process known as fogging.

• Photographic developers contain carefully balanced levels of the developing agents, “accelerators” such as Sodium or Potassium Hydroxide, and Sodium or Potassium Carbonate. There are also restraining agents built in such as Potassium Bromide. These restrainers slow down development in areas that received less exposure.

Conditions effecting rate of development

• User Controlled Dilution Temperature pH

• Non User Controlled

Diffusion rate of developer solution in gelatin Adsorption of developing agent Oxidation products of developing agents Accumulation of by products Purity of manufacturing chemicals

Dealing with impurities in raw materials …. cont

• Potassium Carbonate “Potash”

Manufacturers can remove most of the impurities found in the raw mined “Potash” leaving the fine white powder which contain primarily Potassium Carbonate. K2CO3

However, small amounts of impurities remain.

These include:Potassium Hydroxide (KOH)Potassium Chloride (KCl)

Potassium Nitrate (KNO3)

Potassium Oxide (K2O)

Dealing with impurities in raw materials …. cont

• Potassium Carbonate “Potash”

Even in trace amounts some of these impurities can have an impact on the performance of a Photographic developer.

Examples:

KCl – chemical restrainer

KOH – Chemical Accelerator

To ensure repeatable performance of their products photographic chemical manufacturers establish specific criteria for the raw materials they purchase. These criteria establish maximum concentrations of impurities.

Quality Control – raw materials

• Quality Control

All incoming shipments of raw materials are analyzed to ensure they meet the standards established by the company.

However…. The purer the incoming raw material is expected to be the more steps the company supplying it needs to go through to ensure it meets the buyers standards.

The additional purification steps add cost to the price of a raw material.

In-situ manufacture of raw materials

• In-situ: definition – in place, on site

• In the case of Potassium Carbonate it can be made by combining liquid (aqueous) Potassium Hydroxide KOH and Carbon Dioxide CO2 gas.

• KOH + CO2 K2CO3 + H2O

• Potassium Hydroxide formed this way contains much less in the way of impurities, AND is often less expensive than purchasing raw materials of the same grade.

Balancing the equation

KOH + CO2 K2CO3 + H2O

2KOH + CO2 K2CO3 + H2O

•Let’s calculate the amount of materials needed to produce 1 mole of Potassium Carbonate

Step 1 – determining amount of aqueous Potassium Hydroxide needed

2KOH + CO2 K2CO3 + H2O

Potassium Hydroxide, KOH, is easily purchased as a 45% by weight aqueous solution.

In a 45% by weight solution for each 100 grams of solution 45 grams will be KOH

MW KOH = 56.11

MW CO2 = 44.01

MW K2CO3 = 138.21

MW H2O = 18.02

To produce 1 mole of potassium carbonate we need 2 moles of KOH. Given a molecular weight of 56.11 grams/mole we can calculate the weight of 2 moles

56.11 x 2 = 112.22 grams

Step 1 – determining amount of aqueous Potassium Hydroxide needed - continued

2KOH + CO2 K2CO3 + H2O

Required KOH = 112.22 grams

Required 45% by weight aqueous KOH solution?

45/100 = 112.22/X

X = ?

Step 1 – determining amount of aqueous Potassium Hydroxide needed - continued

2KOH + CO2 K2CO3 + H2O

Required KOH = 112.22 grams

Required 45% by weight aqueous KOH solution?

45/100 = 112.22/X

X = 249.38 grams

112.22 grams KOH + 137.16 grams H2O

Step 2 – determining amount of aqueous Carbon Dioxide gas needed

2KOH + CO2 K2CO3 + H2O

Required CO2 = 44.01 grams (1 mole)

Potassium Carbonate produced K2CO3 = 138.21 grams (1 mole)

Additional water produced H2O = 18.02 grams (1 mole)

Step 3 – Confirm conservation of mass

2KOH + CO2 K2CO3 + H2O

112.22 + 44.01 = 138.21 + 18.02

156.23 156.23

Step 4 – Prepare bench sample

Step 5 – Analyze bench sample to confirm purity

Scale up to production level

• Things to consider:

Safe handling of liquid Potassium Hydroxide Safe handling of tank car quantities of liquid carbon dioxide gas. Jacketing mixing tank to remove heat