Vicente-M. Vizcay Castro (mapa@bitmailer.net)
Mon, 04 Oct 1999 07:44:16 +0200
H E L L O TO A L L :
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This procedure is published in interest of alt-photo-process-l community.
The most tedious phases are those whose purpose is to remove the water and nitric acid
from the precipitate. Please communicate to alt-photo-process-l community yours tests,
procedure variations, results and suggestions.
-------------------------------------IMPORTANT-----------------------------------------
The instructions are only for personal use. No commercial or another advantage
destination of then are permitted. No express or implied license for use exists.
No part of this instructions may be distributed, reproduced, republished, or stored in
a retrieval systems, or transmitted in any form or by any means (electronic, mechanical
, photocopying, recording or otherwise) without the express written permission of the
author.
If you quote any of this instructions, please acknowledge the source.
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The procedure is in WEB pages and Word Perfect format at:
"Guide to Platinum Palladium Photographic Printmaking"
by Jeffrey D. Mathias
http://home.att.net/~jeffrey.d.mathias/guide/title_page.htm
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Follow plain text of procedure:
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PREPARING FERRIC OXALATE POWDER
(by Vicente-M. Vizcay Castro, August/1999)
(English revision and adaptation by Jeffrey D. Mathias)
INTRODUCTION
The procedure of preparing ferric oxalate powder is believed to be of great interest to
alt-photo community. We consider that knowledge must be shared, not hidden, not used to
one's own advantage or in oneïs own interest.
Ferric oxalate (CAS number: 19469-07-9) is a sensitizer for some of the iron based
photographic processes. The dry powder form is desired because of its superior storage
characteristics. It is therefore an advantage for one using such a material to be able
to make it themselves from readily available materials and commonly available low-cost
equipment. Taking as reference the August/1999 prices of Alfa-Aesar for the reagents
(grade ACS and 1000g size), a derived price for the ferric oxalate of about $0.13/g
(only considering the reagents, no other cost considered).
The "modus operandi" has been adapted so as not to require specific laboratory
equipment and to allow for the use of low-cost elements. Efforts have been made to
illustrate and to maximize the details of the evolution of the reaction and the
subsequent processes. The most tedious phases are those with the purpose of removing
the water and nitric acid from the precipitate.
These instructions are only for personal use. No commercial or any derived advantage
of them are permitted. No express or implied license for use exists. No part of these
instructions may be distributed, reproduced, republished, or stored in a retrieval
system, or transmitted in any form or by any means (electronic, mechanical,
photocopying, recording or otherwise) without the express written permission of the
author.
THE PROCESS REACTION
2Fe(NO3)3.9H2O + 3H2C2O4.2H2O = Fe2(C2O4)3.6H2O + 6HNO3 + 18H2O
Fw: 403.99734 126.06604 483.84048 63.01288 18.01528
Eq: 807.9947 378.1981 483.8405 378.0773 324.2750
Grams: 250.0 120.0 149.7 116.9 100.3
NOTE: The theoretical amount of oxalic acid has been increased in a 2.5% to achieve
that all ferric nitrate react.
REAGENTS:
The quality of the ferric oxalate obtained depends on the quality on the reagents
(ferric nitrate and oxalic acid) used.
Ferric nitrate nonahydrate: (Fe(NO3)3.9H2O). Pale-rose-violet deliquesc small
crystals. Turns brown in air contact.
Dangers: Fire risk. Dangers in contact with organic materials.
Strong oxidizer. Irritant.
Oxalic acid dihydrate: (H2C2O4.2H2O). Transparent acicular small crystals.
Dangers: Toxic by inhalation and ingestion. Irritant.
PRODUCTS:
Ferric oxalate hexahydrate: (Fe2(C2O4)3.6H2O). Amorphous powder pale-yellow.
Dangers: Flammable. Corrosive. Toxic by ingestion and
inhalation.
Nitric acid: (HNO3). Diluted in the reaction water. The resulting
liquid of the reaction has a concentration of the
40-50% of nitric acid.
Dangers: Toxic by inhalation. Erodes the skin and the mucous
membranes. Corrosive. Strong oxidizing agent.
Water: (H2O).
All chemicals involved in procedure are common in alt-photo processes, with the
exception of nitric acid (40-50% concentration). Take care and consult : MSDS (Material
Safety Data Sheets), RTECS (Registry of Toxic Effects of Chemical Substance), LCSS
(Lab Chemical Safety Summaries) and "Prudent Practices in the Laboratory: Handling and
Disposal of Chemicals." by National Academy of Sciences.
As a consequence of the compounds involved in this reaction and during all the phases
of this process, it is recommended that the following are employed:
- well-ventilated work place.
- protective gloves, preferably nitrile or polypropylene.
- safety goggles or glasses.
- activated charcoal respirator or mask.
- rubber or polypropylene apron, lab coat or old clothes
- labware of Pyrex glass or similar, polypropylene, etc.
- stainless steel or plastic implements (spatulas, spoons and knife).
- plastic bucket for neutralizing waste
PROCEDURE
Remember to neutralize used utensils and waste liquids and papers prior to disposal.
WEIGHING:
The following amounts of reactants, with this procedure, should produce 125-149
grams of ferric oxalate dry powder. Proceed as follows:
1: In a "high sided" precipitates beaker of 500 ml. weigh 250 grams (g.) of
ferric nitrate (Fe(NO3)3.9H2O). Break up any lumps that exist.
2: On a paper weigh 120 g. of oxalic acid (H2C2O4.2H2O). Preferably in powder
or small crystals form.
3: Distribute the oxalic acid into 3 or 5 portions of approximately equivalent
size, each one on a different paper.
[Step3.jpg]
MIXING AND REACTING:
From this point, the process must be carried out in a well-ventilated area and
with safe light (normal ambient light may be OK). Avoid direct sunlight, high
intensity light or fluorescent light.
4: The following procedure is designed to mix, as uniformly as possible, the
oxalic acid and the ferric nitrate. To do this:
a) Take one of the portions established in step 3 and pour it in the beaker
that contains the ferric nitrate.
b) With a strong glass or plastic rod stir for 1 or 2 minutes.
This will mix the oxalic acid and the ferric nitrate more uniformly in
the beaker. The reaction (endothermic, the beaker cools) begins at the
moment of contact between the oxalic acid and the ferric nitrate. In
the contact zones, between both reactants, colors appear that change
from green to yellow (ferric oxalate). Since the reaction produces water
, the mixture is humidified and liquefied during the process which in
turn facilitates the mixing process.
c) Repeat a) and b) until all the oxalic acid established in step 3 has
been mixed with the ferric nitrate in the beaker.
At the completion of this step, the temperature of the mixture can go
down to 8-9 ºC (for an ambient room temperature of 25-28 ºC)
[Step4.jpg]
5: Cover the beaker with a piece of plastic kitchen film and let it rest.
To help homogenize the reactants and products, during the next 2 or 3 hours
and each half an hour, stir the contents of the beaker with the rod. This has
to be done gently to avoid splashes, since the content of the beaker already
contains nitric acid. Take care to always replace the cover with a new piece
of plastic film.
[Step5-cover.jpg]
If mixture is uniform the following is observed:
15 minutes after step 4 was ended (S4E), the mixture has been
liquefied enough, displaying a yellowish brown green
coloration. The mixture is quite fluid with bubbles (air)
, easily moves when inclining the beaker, and has a
temperature of 8,5ºC. The part of the beaker's wall over
the mixture, appears partially covered with dry yellow
particles of FO.
30 minutes after S4E, the green tonality of the mixture has
disappeared and has become a yellowish brown color.
60 minutes after S4E, the ferric oxalate begins to precipitate
(slowly). The mixture color is very similar to coffee
with very little milk. The mixture temperature has risen
to 11ºC.
It is observed throughout next the 2-3 hours, that the
coffee color disperses (as if adding milk to coffee drop
by drop).
150 minutes after S4E, the color is pale-yellow, somewhat brown. The
mixture temperature is 13ºC.
180 minutes after S4E, the color is more yellowish than above. The
mixture temperature is 14ºC.
If mixture isn't uniform the following is observed:
The mixture displays a yellowish coloration in the lower part and brown-
yellowish in the upper part. At the bottom of the beaker some zones
appears that are opened in fan-form of a yellow-greenish color. This
type of structure is a consequence of the fact that the reaction speed
is not homogeneous due to the heterogeneous nature of the mixture (the
reactants and products concentrations are different at various points
of the mixture). The occurrence of the yellow color indicates that, in
the points where this colo r appears, the concentration gradient of
ferric oxalate is so high that it supercedes the solubility product of
the oxalate and precipitates.
During this step two layers are observed, one more fluid and light (superior)
and the other more compact and granular or earthy texture (inferior).
It is observed that the beaker externally presents a strong condensation
motivated by the low temperature of the beaker.
At an ambient temperature of 24-28ºC the beaker temperature can go down to 8-
12ºC.
After these 3 hours, observe that the content of the beaker, when stirred, is
a yellow mixture of earthy texture due to the initial reactants that didn't
react. The external condensation may continue.
[Step5-resto.jpg]
6: After 6-8 hours, since the initial mixing process was ended (step 4), observe
that the contents of the beaker is of a pale yellow color and has curdled.
That is to say, it resembles cement and is solid so that it does not fall out
of the beaker when inverted and presents resistance to the penetration of
the glass rod. With care (applying gentle force to avoid that the beaker will
be broken), penetrate this mass with the glass rod in several points and
observe that it is liquefied. Repeat several times in order to liquefy the
contents of the beaker as much as possible. Once liquefied, try to dissociate
with the rod or spatula, the lumps that exist in order to obtain the most
homogeneous fluid that is possible. Stir with the glass rod until the content
acquires the appearance of smoothly beaten yogurt or yellow-greenish cream.
[Step6.jpg]
The mixture is a finely divided precipitate of micro crystals which tends to
be colloidal and to aggregate with itself, and as a consequence can be
separated by decantation (rest). The color it becomes is dependent on the
size of the groupings: small (pale-yellow-greenish) or large (pale-green).
The size of the groupings is dependent on the temperature which the reaction
is carried out (>temperature = >size).
The reaction can be considered finished when the temperature of the contents of
the beaker is equal to the room temperature.
DECANTING:
7: Since the product obtained will be a fine powder (particle size of 5-15
microns), indicative of small groupings of particles, let the beaker rest,
covered by the plastic film, during 1-2-3-4..... days (the longer, the better
) in order to achieve a certain separation by gravity.
The separation process by normal gravity (not forced sedimentation) is very
slow, due to the small size of the groupings of particles. An approximated
estimation of the settling (sedimentation) time can be calculated. First
establish the following hypothesis:
- Solid density = 2,5 g/ml
- Liquid density = 1 g/ml
- Solid particle size = 10**(- 5) m
- Temperature = 20§C
- Dynamic viscosity = 10**(- 2) g/cm/s
- Acceleration due to gravity = 980 cm/s**2
then obtain:
- Terminal settling Stokes velocity:
v = 8,17x10**(- 7) cm/s
- Time for settling (for 8,17 cm):
t = 340 hours.
These results are for an isolated particle. The interactions between
particles, the density of the fluid and the real dynamic viscosity (variables
in the time) might cause the time to be multiplied by 100 or 1000.
The sedimentation speed can increase by:
increasing acceleration (centrifugation).
increasing of the solid particl e size (adding 0,5g of aluminum
sulphate (it reduces the repulsion forces between
particles facilitating flocculation), with further
mixing to homogenize its distribution in the mixture).
increasing of the solid particle size and temperature, and reducing
liquid density and dynamic viscosity (by heating the
suspension, this causes it to coagulate and facilitates
separating the precipitate from the solution (temperature
at least 40ºC but not >50ºC).
8: Every day change the plastic film since it becomes etched by the nitric acid.
Observe that floating on the yellow phase appears a liquid phase, almost
colorless, that will increase with time. It will reach a thickness of several
millimeters (it depends of ferric nitrate humidity), which represents
something less than 10-15% of the H2O and HNO3 formed in the reaction).
Increasing the days that it rests will facilitate the deposit compaction of
the suspension making easier to eliminate the liquid by pouring off (this
liquid has a nitric acid concentration of 40-50%).
9: The liquid that floats above the yellow precipitate (ferric oxalate) should
be withdrawn as thoroughly as possible and neutralized.
[Step9.jpg]
DRYING PHASE I:
The purpose of this phase is to remove the maximum amount of acid and water
mixture from the precipitate. This is achieved by capillary action by application
of absorbent paper (this paper can be: napkins, white kitchen paper towels, etc).
ATTENTION: the following steps should be carried out with wearing gloves (always),
goggles, mask and in a well-ventilated place with normal illumination
(as in step 4). Drying is considered to be eliminating, as thoroughly
as possible, a nitric acid solution with a concentration of the order
of 40-50%, that impregnates the ferric oxalate. Avoid more than 3-4
hours of contact of the oxalate with the absorbent papers since these
are etched by nitric acid and become fragile.
10: Prepare a plastic container (at least 30x30 cm square) with a hermetic cover,
such as those which are used to preserve nutritional products in a
refrigerator (Tupperware, Rubbermaid, Curve, etc) by lining its bottom with
10 or 20 absorbent papers, over these papers place a piece of 25x25cm plastic
or glass fiber mesh, e.g. mosquito netting or fiberglass screen.
[Step10.jpg]
11: Liquefy the contents of the beaker (as described in step 6). With the aid of
plastic or stainless steel spoons, spatulas or knives, the precipitate is
removed by loosening it, little by little, and placing it onto the mesh and
spreading it, leaving an edge of 1,5-2 cm free. Next, cover the container
with its lid.
[Step11.jpg]
12: After 3-4 hours open the container and observe where moisture has penetrated
the papers.
a) Remove the moist papers and replace with new ones.
b) The consistency of the precipitate at this time will be quite firm.
Place 3 or 4 papers on top of the mass and strike on top with the fist
several times (this is to seat and loosen the mass and at the same time
to extract more liquid from the upper part of the mass)
c) Repeat a) and b), at intervals of several hours (2-3h), until it is
observed that the moisture that impregnates the papers is insignificant,
indicating that this phase of drying has ended.
Dispose of papers by diluting in a bucket of water and neutralizing to pH 7,
then pouring liquid down the drain with water and placing fully neutralized
papers with other trash.
DRYING PHASE II:
13: Move the precipitate along with the mesh onto new absorbent papers (5 or 10
layers) which are placed into the container (the mesh can be removed after
the third or fourth change which will be made in this phase, leaving the
precipitate directly on the absorbent papers).
The container should be left open to facilitate the drying and elimination of
the nitric acid and water. The container should be located in a place without
light which is well ventilated. The air can be forced to circulate over the
container as a soft current (that does not blow away the oxalate powder).
Take into account that the gases eliminated in the process of drying are very
corrosive and strong oxidizers. Any iron or steel present will be oxidized.
With the spatula or knife, break up, as much as practical, the precipitate
chunks that have been deposited on the absorbent paper. Spread it uniformly
over the mesh-paper.
With each paper change, reduce the size of the chunks with the aid of a
spatula or knife.
[Step13.jpg]
14: Repeat step 13, 5-8 times each 2 or 3 hours. When nearly all that is on the
paper is a pale-yellow powder and small chunks, this phase can be considered
as ended.
[Step14.jpg]
Dispose of papers by diluting in a bucket of water and neutralizing to pH 7,
then pouring liquid down the drain with water and placing fully neutralized
papers with other trash.
DRYING PHASE III:
To dry further, the ferric oxalate is moved to a plastic or glass container with
hermetical cover ( which will have conditioned so that these can contain a drying
agent (dry calcium oxide or hydroxide, zinc oxide, etc) which is not in direct
contact with the oxalate).
Keep the oxalate in the container until it is considered sufficiently dry, then
move it to the final container, an amber glass bottle with hermetical cap.
[Dry-Ph III.jpg]
OPTIONS
Steps 4 to 9 can be accelerated by using a magnetic stirrer. If the stirrer is a
hotplate stirrer, it is possible to heat and stir the mix (temperature not >50ºC).
If one is impatient they can skip the decanting steps and directly go from end of step
6 to DRYING PHASE I.
Some of the drying steps can be obviated or simplified if the liquefied precipitate
obtained at end of step 6 is submitted to filtration (vacuum filtration better). For
this use filters type Watman 50 or Millipore 4.
CONCLUSION
The theoretical weight of the ferric oxalate obtained in this reaction is about 149.7
grams. There are losses as a consequence of the numerous raking of the oxalate, as well
as the portion dissolved in the eliminated liquid. With care, somewhat more than 125g
of dry ferric oxalate is obtainable.
The obtained ferric oxalate contains some residual oxalic acid and nitric acid, witch
prevents ferric oxalate reduction with time.
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All the [xxxxx.jpg] images that illustrate the procedure are in Jeffrey's HTML Guide.
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Vicente-M. Vizcay Castro
SPAIN
This archive was generated by hypermail 2.0b3 on Fri Nov 05 1999 - 21:26:27