tomwalz
Materials
- May 29, 2002
- 947
Sorry the description of the situation should have been clearer.
Question
In order to protect the brazing operator we need to filter out Cadmium particles. What size filter and kind of filter is needed?
Background
Some braze alloys contain Cadmium. Cadmium boils at 1409F and fumes at lower temperatures. Some of these braze alloys need 1300 F to 1350 F to reach full flow. When brazing is done with a torch, often oxy-acetylene, the torch temperature can reach 5,000 F. The boiling Cadmium atomizes then cools and coalesces into droplets. (1) Both the fumes and the dust are dangerous. (2)
Particles as small as 0.5 microns are possible (3) Perhaps particles as small as 0.1 microns need to be considered as well (4) Obviously particles of a size seen in material available for sale are possible (5)
Notes
1. Atomization technology
Reade
Atomization - In this process molten metal is broken up into small droplets and rapidly frozen before the drops come into contact with each other or with a solid surface. The principal method is to disintegrate a thin stream of molten metal by subjecting it to the impact of high energy jets of gas or liquid. Air, nitrogen and argon are commonly used gases, and water is the liquid most widely used. A commercial scale plant was set up in Japan to produce iron powder using paraffin as the atomizing liquid the object being to keep the surface oxygen content as low a possible. The process was technically successful, but the advantages did not justify, in commercial terms, the extra cost involved. However, interest has not entirely evaporated and work is going on elsewhere. By varying the several parameters: design and configurations of the jets, pressure and volume of the atomizing fluid, thickness of the stream of metal etc. - it is possible to control the particle size distribution over a wide range. The particle shape is determined largely by the rate of solidification and varies from spherical, if a low heat capacity gas is employed, to highly irregular if water is used. In principle the technique is applicable to all metals that can be melted, and is commercially used for the production of iron, copper, including tool steels, alloy steels, brass, bronze and the low-melting-point metals, such as aluminum, tin, lead, zinc, cadmium. The readily oxidisable metals, for example chromium-bearing alloys, are being atomized on an increasing scale by means of inert gas, specially argon.
2. Health considerations
A. Metal fume fever Symptoms: flu-like illness with a metallic taste in the mouth, throat irritation, and dry cough;
Signs: leucocytosis (high white blood cell count) is common; normal chest x-ray;
Onset after exposure: 3-10 hours;
Heavy exposure to: zinc oxide fume or dust, e.g., after welding or flame cutting of galvanized steel, high temperature zinc coating processes, or metal pouring in brass foundries; (Brass is an alloy of copper and zinc.)
Resolution: spontaneously within 48 hours;
Comments: After an episode, there is a temporary period of tolerance for a day or two afterwards. Copper and magnesium fume can also cause metal fume fever. It is important to distinguish metal fume fever from cadmium pneumonitis.
B. Cadmium oxide fume is a severe pulmonary irritant; cadmium dust is a less potent irritant than cadmium fume because it has a larger particle size. Chronic exposure is associated with nephrotoxicity. Several inorganic cadmium compounds cause malignant tumors in animals.
SECTION 11. TOXICOLOGICAL INFORMATIONGeneral:Cadmium dust and fume are both pulmonary irritants, but freshly generated cadmium fume is an intense irritant and its small particle size allows it to reach into the lung more readily.
C.
Respirable Particulates: Dust particles having a 50% cut point of 4 m m (ACGIH) or 5 m m (BMRC). These particles may be hazardous when deposited in the gas exchange region of the lungs.
Smoke: Smoke consists of carbon or soot particles or tarry droplets less than 0.1 micrometer in size, and suspended in air. Smoke results from the incomplete combustion of carbonaceous materials such as coal, oil, or wood.
Inspirable Particulate: Only part of the total quantity of dust that is present in the worker's breathing zone is inhaled. This part is designated as the `inspirable fraction' of dust and is governed by the flow rates in the nose and mouth areas, as well as the airflow around the head. 'Inspirable' dust, as measured by the method described in AS3640-1989, derives from inspirability and `inspirable mass fraction' as defined by ISO or from inspirable particulate mass fraction as formerly used by ACGIH. Some authorities, such as the ACGIH, now use the terms `inhalable' or `total inhalable'.
Respirable Particulates: Dust particles having a 50% cut point of 4 m m (ACGIH) or 5 m m (BMRC). These particles may be hazardous when deposited in the gas exchange region of the lungs.
Key Point: Inhalable dust is dust that is hazardous when deposited anywhere in the respiratory tree. Particles in the region of 7 - 20 microns will penetrate to the bronchioles and are inspirable, while particles in the size range 0.5 - 7 microns are respirable.
Absorption
Absorption of cadmium is dependent upon the particle size and water solubility of the compound. Absorption may be increased in iron deficiency.
3. Substantiation of the possibility of half-micron size particles
US4396420: Process for making Ag powder with oxides
Country: US United States of America
Abstract: This invention relates to a silver powder of Ag/CdO composition for use in electrical contacts comprising particles in the size range of about 1 to 10 microns and containing cadmium oxide in the form of a precipitate with a grain size less than about 0.5 micron.
4. Size of particles in smoke
Smoke: Smoke consists of carbon or soot particles or tarry droplets less than 0.1 micrometer in size, and suspended in air. Smoke results from the incomplete combustion of carbonaceous materials such as coal, oil, or wood.
Inspirable Particulate: Only part of the total quantity of dust that is present in the worker's breathing zone is inhaled. This part is designated as the `inspirable fraction' of dust and is governed by the flow rates in the nose and mouth areas, as well as the airflow around the head. 'Inspirable' dust, as measured by the method described in AS3640-1989, derives from inspirability and `inspirable mass fraction' as defined by ISO or from inspirable particulate mass fraction as formerly used by ACGIH. Some authorities, such as the ACGIH, now use the terms `inhalable' or `total inhalable'.
Respirable Particulates: Dust particles having a 50% cut point of 4 m m (ACGIH) or 5 m m (BMRC). These particles may be hazardous when deposited in the gas exchange region of the lungs.
Key Point: Inhalable dust is dust that is hazardous when deposited anywhere in the respiratory tree. Particles in the region of 7 - 20 microns will penetrate to the bronchioles and are inspirable, while particles in the size range 0.5 - 7 microns are respirable.
5. Particle sizes in powders for sales
A. Merck Cadmium coarse powder, GR for analysis and for filling reductors particle size about 0.3-1.6 mm (300 – 1,600 microns)
B. Merck Cadmium granular, GR for analysis particle size about 3-6 mm (3,000 – 6,000 microns)
C. Goodfellow Cadmium Metal
Powder CD006010 Cadmium
Max. Particle size: 53micron, Purity: 99.5+%
D. Goodfellow Cadmium Metal
Powder CD006020 Cadmium
Max. Particle size: 60micron, Purity: 99.9%
ODD NOTE:
Merck offer for sale
CADMIUM POWDER GR PARTICLE SIZE < 60 MYM (> 230 ME
Product Number CAS# UN# Chemical Formula Package & Price
102000.0100
1 myriameter = 10 kilometers
Apparently the Merck catalog offers a Cadmium powder with a particle size less than 10 kilometers
Question
In order to protect the brazing operator we need to filter out Cadmium particles. What size filter and kind of filter is needed?
Background
Some braze alloys contain Cadmium. Cadmium boils at 1409F and fumes at lower temperatures. Some of these braze alloys need 1300 F to 1350 F to reach full flow. When brazing is done with a torch, often oxy-acetylene, the torch temperature can reach 5,000 F. The boiling Cadmium atomizes then cools and coalesces into droplets. (1) Both the fumes and the dust are dangerous. (2)
Particles as small as 0.5 microns are possible (3) Perhaps particles as small as 0.1 microns need to be considered as well (4) Obviously particles of a size seen in material available for sale are possible (5)
Notes
1. Atomization technology
Reade
Atomization - In this process molten metal is broken up into small droplets and rapidly frozen before the drops come into contact with each other or with a solid surface. The principal method is to disintegrate a thin stream of molten metal by subjecting it to the impact of high energy jets of gas or liquid. Air, nitrogen and argon are commonly used gases, and water is the liquid most widely used. A commercial scale plant was set up in Japan to produce iron powder using paraffin as the atomizing liquid the object being to keep the surface oxygen content as low a possible. The process was technically successful, but the advantages did not justify, in commercial terms, the extra cost involved. However, interest has not entirely evaporated and work is going on elsewhere. By varying the several parameters: design and configurations of the jets, pressure and volume of the atomizing fluid, thickness of the stream of metal etc. - it is possible to control the particle size distribution over a wide range. The particle shape is determined largely by the rate of solidification and varies from spherical, if a low heat capacity gas is employed, to highly irregular if water is used. In principle the technique is applicable to all metals that can be melted, and is commercially used for the production of iron, copper, including tool steels, alloy steels, brass, bronze and the low-melting-point metals, such as aluminum, tin, lead, zinc, cadmium. The readily oxidisable metals, for example chromium-bearing alloys, are being atomized on an increasing scale by means of inert gas, specially argon.
2. Health considerations
A. Metal fume fever Symptoms: flu-like illness with a metallic taste in the mouth, throat irritation, and dry cough;
Signs: leucocytosis (high white blood cell count) is common; normal chest x-ray;
Onset after exposure: 3-10 hours;
Heavy exposure to: zinc oxide fume or dust, e.g., after welding or flame cutting of galvanized steel, high temperature zinc coating processes, or metal pouring in brass foundries; (Brass is an alloy of copper and zinc.)
Resolution: spontaneously within 48 hours;
Comments: After an episode, there is a temporary period of tolerance for a day or two afterwards. Copper and magnesium fume can also cause metal fume fever. It is important to distinguish metal fume fever from cadmium pneumonitis.
B. Cadmium oxide fume is a severe pulmonary irritant; cadmium dust is a less potent irritant than cadmium fume because it has a larger particle size. Chronic exposure is associated with nephrotoxicity. Several inorganic cadmium compounds cause malignant tumors in animals.
SECTION 11. TOXICOLOGICAL INFORMATIONGeneral:Cadmium dust and fume are both pulmonary irritants, but freshly generated cadmium fume is an intense irritant and its small particle size allows it to reach into the lung more readily.
C.
Respirable Particulates: Dust particles having a 50% cut point of 4 m m (ACGIH) or 5 m m (BMRC). These particles may be hazardous when deposited in the gas exchange region of the lungs.
Smoke: Smoke consists of carbon or soot particles or tarry droplets less than 0.1 micrometer in size, and suspended in air. Smoke results from the incomplete combustion of carbonaceous materials such as coal, oil, or wood.
Inspirable Particulate: Only part of the total quantity of dust that is present in the worker's breathing zone is inhaled. This part is designated as the `inspirable fraction' of dust and is governed by the flow rates in the nose and mouth areas, as well as the airflow around the head. 'Inspirable' dust, as measured by the method described in AS3640-1989, derives from inspirability and `inspirable mass fraction' as defined by ISO or from inspirable particulate mass fraction as formerly used by ACGIH. Some authorities, such as the ACGIH, now use the terms `inhalable' or `total inhalable'.
Respirable Particulates: Dust particles having a 50% cut point of 4 m m (ACGIH) or 5 m m (BMRC). These particles may be hazardous when deposited in the gas exchange region of the lungs.
Key Point: Inhalable dust is dust that is hazardous when deposited anywhere in the respiratory tree. Particles in the region of 7 - 20 microns will penetrate to the bronchioles and are inspirable, while particles in the size range 0.5 - 7 microns are respirable.
Absorption
Absorption of cadmium is dependent upon the particle size and water solubility of the compound. Absorption may be increased in iron deficiency.
3. Substantiation of the possibility of half-micron size particles
US4396420: Process for making Ag powder with oxides
Country: US United States of America
Abstract: This invention relates to a silver powder of Ag/CdO composition for use in electrical contacts comprising particles in the size range of about 1 to 10 microns and containing cadmium oxide in the form of a precipitate with a grain size less than about 0.5 micron.
4. Size of particles in smoke
Smoke: Smoke consists of carbon or soot particles or tarry droplets less than 0.1 micrometer in size, and suspended in air. Smoke results from the incomplete combustion of carbonaceous materials such as coal, oil, or wood.
Inspirable Particulate: Only part of the total quantity of dust that is present in the worker's breathing zone is inhaled. This part is designated as the `inspirable fraction' of dust and is governed by the flow rates in the nose and mouth areas, as well as the airflow around the head. 'Inspirable' dust, as measured by the method described in AS3640-1989, derives from inspirability and `inspirable mass fraction' as defined by ISO or from inspirable particulate mass fraction as formerly used by ACGIH. Some authorities, such as the ACGIH, now use the terms `inhalable' or `total inhalable'.
Respirable Particulates: Dust particles having a 50% cut point of 4 m m (ACGIH) or 5 m m (BMRC). These particles may be hazardous when deposited in the gas exchange region of the lungs.
Key Point: Inhalable dust is dust that is hazardous when deposited anywhere in the respiratory tree. Particles in the region of 7 - 20 microns will penetrate to the bronchioles and are inspirable, while particles in the size range 0.5 - 7 microns are respirable.
5. Particle sizes in powders for sales
A. Merck Cadmium coarse powder, GR for analysis and for filling reductors particle size about 0.3-1.6 mm (300 – 1,600 microns)
B. Merck Cadmium granular, GR for analysis particle size about 3-6 mm (3,000 – 6,000 microns)
C. Goodfellow Cadmium Metal
Powder CD006010 Cadmium
Max. Particle size: 53micron, Purity: 99.5+%
D. Goodfellow Cadmium Metal
Powder CD006020 Cadmium
Max. Particle size: 60micron, Purity: 99.9%
ODD NOTE:
Merck offer for sale
CADMIUM POWDER GR PARTICLE SIZE < 60 MYM (> 230 ME
Product Number CAS# UN# Chemical Formula Package & Price
102000.0100
1 myriameter = 10 kilometers
Apparently the Merck catalog offers a Cadmium powder with a particle size less than 10 kilometers