Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~
BACKGROUND OF THE INVENTION
This invention relates in general to electrophotography,
and more particularly, to a process for preparing carrier materials
useful in the magnetic-brush type development of electrostatic
latent images.
The formation and development of images on the surface
of photoconductive materials by electrostatic means is well known.
The basic electrostatographic process, as taught by C. F. Carlson
in U. S. Patent 2,297,691, involves placing a uniform electrostatic
charge on a photoconductive insulating layer, exposing the layer
to a light and shadow image to dissipate the charge on the areas
of the layer exposed to the light and developing the resulting
electrostatic latent image by depositing on the image a finely-
divided electroscopic material referred to in the art as "toner".
The toner will normally be attracted to those areas of the layer
which retain a charge, thereby forming a toner image corresponding
to the electrostatic latent image. This powder image may then be
transferred to a support surface such as paper. The transferred
image may subsequently be permanently affixed to the support
surface as by heat. Instead of latent image formation by uniformly
charging the photoconductive layer and then exposing the layer to
a light and shadow image, one may form the latent image by
directly charging the layer in image configuration. The powder
image may be fixed to the photoconductive layer if elimination
of the powder image transfer step is desired. Other suitable
fixing means such as solvent or overcoating treatment may be
substituted for the foregoing heat fixing step.
Many methods are known for applying the electroscopic
particles to the eIectrostatic latent image to be developed. One
development method, as disclosed by E. N. Wise in U. S. Patent
2,618,522 is known as "cascade" development. In this method,
a developer material comprising relatively large carrier particles
having finely-divided toner particles electrostatically clinging
to the surface of the carrier particles is conveyed to and rolled
or cascaded across the electrostatic latent image-bearing surface.
The composition of the toner particles is so chosen as to have a
triboelectric polarity opposite that of carrier particles. As
the mixture cascades or rolls across the image-bearing surface,
the toner particles are electrostatically deposited and secured
to the charged portion of the latent image and are not deposited
on the uncharged or background portions of the image. Most of
the toner particles accidentally deposited in the background
are removed by the rolling carrier, due apparently, to the greater
electrostatic attraction between the toner and the carrier than
between the toner and the discharged background. The carrier
particles an unused toner particles are then recycled. This
technique is extremely good for the development of line copy images.
The cascade development process is the most widely used commercial
electrostatographic development technique. A general purpose
office copying maching incorporating this technique is described
in U. S. Patent 3,099,943.
Another technique for developing electrostatic latent
images is the "magnetic brush" process as disclosed, for example,
in U. S. Patent 2,874,063. In this method, a developer material
containing toner and magnetic carrier particles is carried by a
magnet. The magentic field of the magnet causes alignment of the
magnetic carriers in a brush-like configuration. This "magnetic
brush" is engaged with an electrostatic-image bearing surface
and the toner particles are. drawn from the brush to the electrostatic
image by electrostatic attracti.on.
In magnetic-brush development of electrostatic latent images,
the developer is commonly a triboelectric mixture of finely-divided
toner powder comprised of dyed or pigmented thermoplastic resin
mixed with coarser carrier particles of a soft magnetic material
such as "ground chemical iron" (iron filings), reduced iron oxide
particles or the like. The conductivity of the ferromagnetic
carrier particles which form the "bristles" of a magnetic brush
provides the effect of a development electrode having a very close
spacing to the surface of the electrophotographic element being
developed. By virtue of this development electrode effect, it is
possible to develop part of the toners in pictures and solid blacks
as well as line copy. Magnetic brush development sometimes makes
this mode of developing advantageous where it is desired to copy
materials other than simply line copy.
~ hile ordinarily capable of producing good quality images,
conventional developing materials suffer serious deficiencies in
certain areas. Some developer materials, though possessing
desirable properties such as proper triboelectric characteristics,
are. unsuitable because they tend to cake, bridge and agglomerate
during handling and storage. Furthermore, with some polymer coated
carrier materials flaking of the carrier surface will cause the
carrier to have nonuniform triboelectric properties when the
carrier core is composed of a material different from the surface
coating thereon. In addition, the coatings of most carrier
particles deteriorate rapidly when employed in continuous
processes which re~uire the recycling of carrier particles by
bucket conveyors partially submerged in the devel~per supply such
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as disclosed in U. S. Patent 3,099,943. Deterioration occurs when
portions of or the entire coating separates from the carrier core.
The separation may be in the form of chips, flakes or enti.re
layers and is primarily caused by fragile, poorly adhering
coating material which fails. upon impact and abrasive contact
with machines parts and other carrier particles. Carriers having
coatings which tend to chip and otherwise separate from the carrier
core or substrate must be frequently replaced thereby increasing
expense and loss of productive time. Print deletion and poor
print quality occur when carriers having damaged coatings are not
replaced. Fines and grit formed from carrier dislntegration tend
to drift to and form undesirable and damaging deposits on critical
machine parts.
Another factor affecting the stability of the tribo-
electric properties of carrier particles is the susceptibility
of carrier coatings to "toner impaction". When carrier particles
are employed in automatic machines and recycled through many
cycles, the many collisions which occur between the carrier
particles and other surfaces in the machine cause the toner
particles carried on the surface to the carrier particles to
be welded or otherwise forced onto the carrier surfaces. The
gradual accumulation of impacted toner material on the surface
of the carrier causes a change in the triboelectric value of the
carrier and directly contributes to the degradation of copy
quality by eventual destruction of the toner carrying capacity
of the carrierO This problem is especially aggravated when the
carrier partic:Les, and parti.cularly the carrier cores, are prepared
from materials such as iron or steel having a high specific
gravity or density since during mixing and the development process
the toner particles are exposed to extremely high impact forces
from contact with the carrier particles. It is apparent from the
descriptions presented above as well as in other development
techniques, that tne toner is subjected to severe physical forces
which tend to break down the particles into undesirable dust fines
which become impacted onto carrier particles. Various attempts
have been made to decrease the density or the carrier particles
and reduce the concentration of the magnetic component by admixture
of a lighter material, such as a resin, either in the form of a
coating or as a uniform dispersion throughout the body of the
carrier granule. This approach is useful in some instances but
the amount of such lighter material sufficient to produce a sub-
stantial decrease in density has been indicated as seriously
diminishing the magnetic response of the carrier particles as to
cause a deterioration in the properties of a ~agnetic brush
formed therefrom. One such attempt is disclosed in Belgian
Patent 726,806, wherein the carrier particles
comprise a low density, non-magnetic core such as a resin, glass,
or the like having coated thereon a thin, continuous layer of a
ferromagnetic material. It is therein indicated that a coating
of finely powdered iron or other subdivided ferromagnetic material
does not show the high response to a magnetic field which is
displayed by the continuous layers of the invention. ~nother
earlier attempt at low density carrier materials is disclosed in
U. S. 2,880,696 wherein the carrier material is composed of particles
having a magnetic portion. The core therein may consist entirely
of a magnetic material, or it may be formed of solid insulatins
beads such as glass or ?lastic having a magnetic coating thereon,
or the core may consis~ of a hollow magnetic ball. However, 'or
f~
unknown reasons, the recited materials have apparently never been
commercially successful. Thus, there is a continuing need for a
better developer material for developing electrostatic latent
images.
Now, and in accordance with the present invention,
there is provided a magnetically responsive low density electro-
statographic composite carrier particle whlch has an average
particle diameter of from between about 10 microns to about 850
microns, the carrier particle comprising a porous silicaceous
material having an average bulk density of between about 0.2
and about 3.0 grams/cm3. The silicaceous material is micro-
reticulated and has pores with an average pore size of from
about 10 to about 500 Angstroms and is impregnated with a
magnetic or magnetically-attractable transition metal or metal
oxide.
In addition, there is also provided a process for
preparing a magnetically-responsive low density electrostato-
graphic composite carrier particle which comprises placing in a
suitable vessel particles of a porous silicaceous material having
a bulk density of between about 0.2 and about 3.0 grams/cm3
and an average particle diameter of from between about 10 microns
to about 850 microns. The silicaceous material is micro-
reticulated and has pores with an average pore size of from
between about 10 to about 500 Angstroms. A transition metal
carbonyl and a suspending medium is added to the vessel
and the mixture heated, in the substantial absence of air and
moisture, with agitation to reflux
temperature for about 24 hours at a temperature of the
suspending medium to thermally decompose the transition metal
carbonyl whereby the silicaceous material is impregnated with
the magnetic elemental metal or metal oxide of the transition
metal carbonyl. The mixture is cooled, the silicaceous material
washed with fresh suspending medium and subsequently dried.
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other features may be accomplished in accordance with
this invention, generally speaking, by encasing low density
silicaceous particles in a sheath of a high purity magnetic or
magnetically-attractable metal or metal oxide thereof to provide
electrostatographic carrier particles^having a low bulk density
and a high magnetic permeability. More specifically, low density
magnetic composite electrostatographic carrier particles are pre-
pared by the solution phase thermal decomposition of transition
metal carbonyls onto low density silicaceous substrates.
Magnetically, these composite structures respond like a
collection of solid, fine iron particles but, when employed
in electrostatographic magnetic brush
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development systems, form more uniform and "softer" magnetic
brushes due to their very low bulk densities which in some cases
are more than an order to magnitude less than the density of iron.
In accordance with this invention, transition metal
carbonyls are thermo-chemically deposited
into the pores of sllicaceous low density substra.es to provide low
density magnetic composite carrier particles. `~agnetic measurements
have indicated that the composites are magnetic equivalents to their
magnetic constituent, taking into account the significant difference
in density between the composite and that of its constituent.
Generally speaking, the low density magnetic composite
carrier particles are prepared by applying the me-tal deposit to
the silicaceous beads by the thermal decomposition of a
transi~ion metal carbonyl to the elemental metal in the presence
of the beads with a suitable suspending medium. For example,
glass beads may be covered with magnetic iron by placing them in
a suitable vessel with iron pentacarbonyl and a suspending
medium such a n-octane. Air and moisture are excluded by displace-
ment with a dry inert gas such as nitrogen, and the contents are
~.. _ . _ . . _ _,
heated and stirred so that the iron pentacarbonyl boils, and the
mixture is refluxed until the temperature rises to that of the
suspending medium whereupon deposition of iron on the beads is
complete. The mixture is then cooled, the beads are washed with
fresh suspending medium, air dried, and the beads recovered. The
magnetic low density spheres obtained typically are highly lustrous.
Thus, the thermal decomposition of typical transition
metal carbonyls may be exemplified by the following equations
for (1) iron pentacarbonyl, and (2) dicobalt octacarbonyl;
Fe(C05) ~ ~ Fe + 5CO (1)
C2~cQ)-8 - _ _ 2Co-~ 8CO (2).
The decomposition of the transition metals is performed in the
presence of porous silicaceous substrates and utilized to
prepare composite materials havin~ both chemical and mechanical
stability and which display gross magnetic behavior. Substrate
configuration is essentially retained throughout the coating
process. The bulk ma~netic response of the composite materials
may be controlled by varying the mass of the magnetic metal in
proportion to the coated particle mass.
Any suitable ma~netic or magnetically-attractable
transition metal or metal oxide thereof may be employed to cover
or impregnate the sllicaceous substrates of the low density
magnetic composite carrier particles of this invention. Typical
such transition metals may be provided from iron pentacarbonyl,
di-iron nonacarbonyl, tri-iron dodecacarbonyl, iron carbonyl
cluster compounds; dicobalt octacarbonyl, nickel tetracarbonyl,
any other thermally extrudable compound of such transition
metals, and mixtures thereof. Oxides may be provided by sub-
sequent oxidation of these transition metals.
Any suitable porous silicaceous material may be
employed as the substrate for the composite low density magnetic
carrier particles of this invention. Typical suitable porous
silicaceous materials include glass particles in various micro-
reticulated foxms. In addition, suitable porous vitreous
materials may also be used. Thus, a wide variety of particulate
micro-reticulated low density materials the pores of which can
be impregnated ~ith a ma~netic or magnetically-attractable
transition metal or metal oxide thereof may be employed in
accordance with this invention. As indicated, the particles
of the composite low density magnetic
carrier material of this invention may vary in size and shape.
~owever, it is preferred that the carrier particles have a
spherical shape as to avoid rough edges or protrusions which have
a tendency to abrade more easily. Particularly useful results
are obtained when the carrier material has an average particle
size from about 50 microns to about 300 microns, although
satisfactory results may be obtained when the composite material
has an average particle size of from between about 10 microns
and about ~50 microns. The size of the carrier particles employed
will, of course, depend upon several factors, such as the type of
images ultimately developed, the machine confisuration, and so forth.
The low density silicaceous ~aterial employed as the sub-
strate for the composite magnetic carrier particles of this invention
may have any suitable bulk density. Satisfactory results may be
obtained when the silicaceous material has an average bulk density
of between about 0.2 and about 3.0 grams/cm3. However, it is pre-
ferred tr:-t the silicaceous material have an average bulk density of
less than about 2.5 grams/cm3 because stress levels are sub-
stantially reduced thereby reducing toner impaction and
developer degradation.
The low density porous, micro-reticulated silicaceous
material employed as the substrate or matrix for the composite
carrier particles of this invention may have an average pore size
O O . :
of from between about 10 A and about 500 A. The low density
silicaceous material may have a surface area of up to about
250 M /gram. The magnetic metal may be deposited within
the pores of the carr:ier beads in the form of continuous
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threads or networks which provides a practical advantage in that
the magentic metal is well protected against abrasion. A ran~e
of volume ratios of silicaceo~s material to magnetic elemental
metal that will provide satisfactory magnetically-responsive
composite carrier particles is from between about 5:1 to 20:1.
To achieve further variation in the properties of the low
density magnetic composite carrier particles of this invention, ~ell~
known insulating polymeric resin coating materials may be applied
thereto. That is, lt may be desirable for some applications to alter
and control the conductivity or triboelectric properties of the mag-
netic composite carrier particles of this invention. Thus, this may
be accomplished by applying thereto typical insulating carrier
coating materials as described by L. E. Walkup in U. S. Patent
2,618,551; B. B. Jacknow et al in U. S. Patent 3,526,533; and
R. J. Hagenbach et al in U. S. Patents 3,533,835 and 3,658,500. ~-
Typical electrostatographic carrier particle coating materials
include vinyl chloride-vinyl acetate copolymers, poly-p-xylylene
polymers, styrene-acrylate-organosilicon terpolymers, natural
resins such as caoutchouc, colophony, copal, dammar, Dragon's
Blood, jalap, storax; thermoplastic resins includins the polyole~ins
such as polyethylene, polvpropylene, chlorinatec polye~hylene, anc
chlorosulfonated polyethylene; polyvinyls and polyvinylicenes
such as polystyrene, polymethylstyrene, polymethyl meth~cryl2te,
:, , - - -., ~ . . ... , , , ; : ~: -
2,rb
polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl
butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ethers,
and polyvinyl ketones; fluorocarbons such as polytetrafluoroethylene,
polyvinyl fluoride, polyvinylidene fluoride; and polychlorotri-
fluoroethylene; polyamides such as polycaprolactam and
polyhexamethylene adipamide; po]yesters such as polyethylene
terephthalate; polyurethanes; polysulfides, polycarbonates;
thermosetting resins including phenolic resins such as phenol-
formaldehyde, phenol-furfural and resorcinol formaldehyde; amino
resins such as urea-formaldehyde and melamineformaldehyde;
polyester resins; epoxy resins; and the like.
When the magnetic composite carrier particles of this
invention are overcoated with an insulating resinous material any
suitable electrostatographic carrier coating thickness may be
employed. ~owever, a polymeric coating having a thickness at least
sufficient to form a thin continuous film on the carrier particle
is preferred because the carrier coating will then possess
sufficient thickness to resist abrasion and prevent pinholes which
adversely affect the triboelectric properties of the coating carrier
particles. Generally, for cascade and magnetic brush development,
the carrier coating may comprise from about 0.1 percent to about 30.0
percent by weight based on the weight of the coated composite
carrier particles. Preferably, the carrier coating should comprise
from about 0.2 percent to about 2.0 percent by weight based on the
weight of the coated carrier particles because maximum durability,
toner impaction resistance, and copy quality are achieved.
Any suitable solvent or suspending medium may be employed
in the thermal decomposition process of preparing the low density
magnetic composite carrier particles of this invention. Typical
solvents and suspend~n~ medlu~s~ ma~ be hydrocarbon solvents
with boiling points p~:eferably aboYe that of the transition
metal compound employed. Satis~actory results have been
obtained with n-octane.
~ n addition to preparln~ the low density magnetic
composite electrostatographic carrier particles of this inven-
tion by solution phase thermal decomposition of transition
metal carbonyls, it is also possible to prepare them via
chemical vapor deposition usin~ fluidized bed techniques. Thus,
magnetic nickel deposits, for example, may be placed in the
pores of a low density silicaceous substrate by thermal decom-
position of nickel tetracarbonyl in a fluidizing bed apparatus.
Typically, such a reactor has a cone-shaped bottom with propor-
tionately-sized capiIlary tube gas inlets at the apex. To avoid
plugging of the apparatus by premature decomposition of the
car-bonyl, the capillary zone and about one-half of the cone
height is usually cooled by heat transfer means. In addition,
the top half of the cone and a portion of the reactor is heated
to provide the desired temperature to the substrate. In opera-
tion, nickel carbonyl vapor is supplied by bubbling a fluidizing
gas such as hydrogen through the liquid at room temperature to
provide the desired volume percent vapor in the reactant stream.
~here desired, carbon monoxide may be added to the reactant
stream to suppress gas phase decomposition of the carbonyl.
The gas stream from the reactor is then passed through an oil
bubbler and burned in a hood to oxidize poisonous carbon mon-
oxide and any unreacted carbonyl vapors as well as to avoid
accumulation of explosive mixtures of hydrogen. Preferably,
the apparatus is located in a well-ventilated area or in a fume
hood to preclude accidental exposure to noxious fumes.
~ibrators are preferably attached to -the reactor to promo-te
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X
uniformity of coating deposition and aid in returning -to the
fluidized bed those particles which may adhere to reactor walls
above the active bed.
Any suitable well known toner material may be employed
with the low density composite carriers of this invention. Typical
toner materials include sum copal, gum sandarac, rosin, cumaroneincene
resin, asphaltum, gilsonite, phenolformaldehyde resins, rosin
modified phenolormaldehyde resins, methacrylic resins, polystyrene
resins, polypropylene resins, epoxy resins, polyethylene resins,
polyester resins, and mixtures thereof. The particular toner
material to be employed obviously depends upon the separation of
the toner particles from the magnetic carrier in the triboelectric
series and the separation should be sufficient to cause the toner
particles to electrostatically cling to the carrier surface. Among
the patents describing electroscopic toner compositions are U. S.
Patent 2,659,670 to Copley; U. S. Patent 2,753,308 to Landrigan;
U. S. Patent 3,079,342 to Insalaco; U. S. Patent Reis5ue 25,136
to Carlson and U. S. Patent 2,788,288 to Rheinfrank et al. These
toners generally have an average particle diameter between about
l and 30 microns.
Any suitable colorant such as a pigment or dye may be
employed to color the toner particles. Toner colorants are well
known and include, for example, carbon black, nigrosine dye,
aniline blue, Calco Oil Blue, chrome yellow, ultramarine blue,
Quinoline Yellow, methylene blue chloride, ~onastral Blue,
~alachite Green Ozalate, lampblack, Rose Bengal, l`lonastral Red,
Sudan Black ~, and mixtures ~hereof. The pigment or dye snould
be present in a quality sufricient to rencer it hishly colored
so that it will form a clearly visible image on a recording member.
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Preferably, the pigment is employed in an amount from about 3
percent to about 20 percent by ~eight based on the total weight
of the colored toner because high quality images are obtained.
If the toner colorant employed is a dye, substantially smaller
quantitites of colorant may be used.
Any suitable conventional toner concentration may be
employed with the low density magnetic carriers of this invention.
Typical toner concentrations for development systems include about
1 part toner with about 10 to about 200 parts by weight of carrier.
When employing the low density magnetic carriers of this invention
for development of electrostatic latent images, the amount of
toner material present should be from between about 10 percent to
about 100 percent of the surface area of the carrier particles.
The carrier materials of the instant invention may be
mixed with finely-divided toner particles and employed to develop
electrostatic latent images on any suitable electrostatic latent
image-bearing surface including conventional photoconductive sur-
faces. Typical inorganic photoconductor materials include:
sulfur, selenium, zinc sulfide, zinc oxide, zinc cadmium sulfide,
zinc magnesium oxide, cadmium selenide, zinc silicate~ calcium
strontium sulfide, cadmium sulfide, mercuric iodide, mercuric
oxide, mercuric sulfide, indium tri-sulfide, gallium selenide
arsenic disulfide, arsenic trisulfide, arsenic triselenide,
antimony trisulfide, cadmium sulfoselenide, and mixtures thereof.
Typical organic photoconductors include: quinacridone pigments,
phthalocyanine pigments, triphenylamine, 2,4-bis(4,4'-diethylamino-
phenol~-1,3,4-oxadiazol, N-isopropylcarbazole, triphenylpyrrole,
4,5~-diphenylimidazolidinone, 4,5-diphenylimidazolidinethione,
4,5-bis-(4'amino-phenyl)-imidazolidinone, 1,4-dicyanonaphthalene,
1,4-dicyanonaphthalene, aminophthalocinitrile, ni~rophthalo-
dinitrile, 12,3,5,5-tetra-azacyclooctatetraene-(2,4,6,8),
2-mercaptobenzothiazole-2-phenyl-4-diphenylidene-oxazolone,
6-hydroxy-2,3-di(p-methoxvphenyl)-benzofurane, 4-dimethylamino-
benzylidene-benzhydrazide, 3-benzylidene-aminocarbazole,
polyvinyl carbazole, (2-nitrobenzylidene)-p-bromoaniline,
2,4-diphenyl-quinazoline, 1,2,4-triazine, 1,3-diphenyl-3-
methyl-pyrazoline, 2-(4'-dimethylamino phenyl)-benzoxazole,
3-amine-carbazole, and mixtures thereof. Representative patents
in which photoconductive materials are disclosed include U. S.
Patents 2,803,542 to Ullrich, U. S. Patent 3,121,007 to Middleton,
and U. S. Patent 3,151,982 to Corrsin.
The low density magnetic carrier materials produced by the
process of this invention provide numerous advantages when employed
to develop electrostatic latent images. For example, it has been
found that carrier of reduced density reduces levels of mechanical
stress in xerographic developer compositions, the reduction
resulting in lower toner impaction levels.
In the following e~amples, iron pentacarbonyl (99.5
percent purity) was obtained from Ventron Corporation, Danvers,
Mass. and filtered before use to remove iron oxides. N-octane
(practical) was obtained from Eastman-Kodak Company, Rochester,
N.Y. and refluxed over sodium for at least 24 hours and distilled
before use. Dicobalt octacarbonyl was obtained from Strem
Chemical Company, Andover, Mass. Porous glass beads were
obtained from PPG Industries, Pittsburg, Pa. and were used as
received. Similar porous glass particles were obtained from
.
,
. .
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- ,
Corning Glass Wor'cs, Corning, N.Y. as 7930 slass in the form of
chips and were used as received. ~aterial transfers from
the pretreatment stages to suspension in a solvent was effected in
an inert atmosphere o~ dry nitrogen.
Thermal decompositions of ~he carbonyls were carriec
out in solution in round-bottom flasXs with reflux condensor and
heating mantle under dry nitrogen at approxima-tely one atmospnere
pressure. All decompositions were carried out in vented hoods and
in some cases CO effluent was passed through solutions of phos-
phomolybdic acid in the presence of palladium chloride to afford
molybdenum blue and carbon dioxide..
The following examples, other than the control example,
further define, describe, and compare preferred methods of pre-
paring and utilizing the low density magnetic composite carriers
of the present invention in electrostatographic applications.
Parts and percentages are by weight unless otherwise indicated.
' ' .
~$~P~
EXP~5PLE I
-
A mixture of about 10 grams of porous glass beads
(XO-l, PPG) having an average particle diameter of between about
80 and 150 microns, about 10 ml of Fe(CO)5, and about 50 ml of
n-octane was refluxed for about 24 hours in a 300 ml flask. No
stirring was provided. Coated bead clumping within the flask
was noted and about 5 grams of material was isolated by
collecting the suspended solids, after cooling, by filtration,
washing it with octane, acetone and ethyl ether, and then
drying it. The beads had a brilliant luster.
EXA~5PLE II
A mixture of about 20 grams of porous glass beads
(XO-l, PPG) having an average particle diameter of between about
80 and 150 microns, about 40 ml of Fe(C~)5, and about 200 ml of
n-octane was refluxed in a 500 ml flask for about 24 hours with
gentle stirring. Approximately 30 grams of shiny black beads
were isolated as in Example I. The beads appeared to be
impregnated with iron or an iron oxide.
EXP~5PLE III
,,
; A mixture of about 1 gram of glass chips (Corning 7930)
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.
t~
having an average particle diameter of between about 90 and
140 microns, about 2 ml of Fe(Co)5~ and about 10 ml of n-octane
was refluxed in a 50 ml flask for about 2 hours. The contents
were filtered after cooling and about 1.2 grams of material was
recovered which had a bulk density of about 1 g/cm3. Micro-
scopic examination of the chips at 70X showed a reflective
iron coat on the chips. The bulk material appeared black,
probably due to high absorption by the multi-reflective chips.
Magnetic measurements were made wi-th a Princeton Applied
Research Vibrating Sample Magnetometer, which measures magnetization
M, at fields from 0 to 7,000 gauss. The instrument has a sensitivity
of better than 1 x 104 emu/gauss and the accuracy and resettability
of the applied field is within 1 gauss. The system was calibrated
with a Ni standard (55.0 emu/gm~ in a saturation field of 7 kilogauss.
The magnetization, M, is read out digitally, directly in emu's.
Mass magnetization, o, was obtained by dividing M by the sample
mass in grams. The samples were contained in cylindrical Kel-F
holders approximately 1/4 inch in diameter and height. The amount
of material used, 25 to 35 mg, was varied so that the volume of
the sample would remain approximately the same. In the values
reported, no attempt was made to account for the bulk shape
demagnetization effects of the samples. The magnetization values
obtained below the saturation region are the effective values for
the above sample configuration. Packing density of the material
was assumed to be the same in the hand tamped holder and in an
uncompressed but tamped container. The ma-terials of the examples
can be efficiently collected into magnetic brushes and manipulated
magnetically with a bar magnet or in laboratory magnetic brush
fixtures. The magnetic properties of the materials of the examples
were characterized as follows.
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The magnetic parameters of the. various transition metal
coated materials are listed in Table I and the actual magnetization
curves obtained with the vibrating sample magnetometer are shown
in Figures 1 and 2. The field limit of the magnet used was 7
kilogauss and this was taken as the saturation f~eld, although as
can be seen in Figure 1, sa.turation for some of the samples has
still not been attained. Table I is as follows:
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~:;
Ths material of Example I consists of elemental iron
on a pure (99.5 percent) SiO2 substrate (IV). This material
has basically the same magnetic characteristics; that is, high
saturation magnetization and initial susceptibility, small
remanence and coercive force. Furthermore, the magnetic
behavior displayed by these materials is consistent with that
of magnetically so~t iron.
The effective permeability,~eff, for the materials
of the Examples, may be obtained from the initial susceptibility
data ~~and the measured bulk density (calculated within 5
percent) p of the materials by the following relation:
~ eff = 1 + 4 (M/H) = 1 + 4 ~ (~ p/~)
where magnetization, M, is in emu/cm3. Since these magnetically
coated materials are spherical, the initial permeability of the
individual bead is dependent upon shape demagnetization effects
and in this case is limited to a value of 3. However, in the
compacted "powder" form in which the beads are measured, particle-
particle interacticns and the shape demagnetization o the bulk
- 22 -
::~$~
sample can also introduce changes in the effective demagneti~a-
tion effects. The values listed in Table I fall within the
expected range.
The materials of Examples II and III show a distinct
departure in the magnetic parameters (Figure 2) Xi,
~at~ ~-R and Hc from those of Example I . The initial
susceptibility is now quite small and the magnetization shows a
very flat approach to saturation at high fields (Figure 1). In
all cases the coercive force Hc has increased significantly.
These changes in Xi and Hc for the present Examples reflect
the morphological changes in the coating where we are no longer -
dealing with pure elemental iron. Optical examination of the
material of Example III (glass chips) showed a wide varia-tion
in the coating of this material. The material of Example II
differed entirely from the preceding iron coated porous
bead material, i.e., Example I, in that no surface coat of
elemental iron appeared; rather, the beads appeared impregnated, ';~
possibly with black iron oxides. The reason for this change in
final material as compared with that of Example I is not clear.
Reaction mixture contamination or reaction time may be responsible.
The magnetic changes observed in the materials o~ ExamplesII and III
are believed to De due to the different sur ace compositions, --
resulting from the formation oî discontinuous coa.ing regions
of isolated iron or iron oxide particles on the surface of the
materials.
, ~
:;
Prom these observations, i~ may be concluded that the
thermal decompositon of transition metal carbonyls such as iron
pentacarbonyl onto low densi~y silicaceous substrates produces
mechanically and chemically stable composites t~hich have the
original substrate configuration, and which, addi.ionally,
display gross masnetism~ The magne~lc behavior obser-v-ed '~or tnese
low density magnetic composites ranges from that typical of
magnetically soft iron to that -typical of magnetically hard
cobalt. The composites are, therefore, magnetic equivalents ;-
to their magnetic constituent ye-t afrord a drastic reduction in
density. The composites show good initial magnetic res?onse
(indicated by a relatively high u) indicating the use of these
materials as low density magnetic carrier particles. Further,
the various magnetic parameters, Ms, Hc~ ~eff of the low density .
magnetic materials can be controlled by varying the prepara-tion
and starting components of the materials. This type of control
offers a wide lattitude in design parameters not earily achieved
with solid or high density magnetic carriers. In addition, there
is a direct relationship between the magnetic characteristics
of the low density composites and their surface composition and
morphology as reflected in the relative values of Xi, 1~1S and Hc
for the materials of the various Examples.
EXAMPLES IV - IX
- : .
Six lots of spherical particles coated with chemical
vapor deposited iron from 0.9 to 1.5 microns thick on solid and
porous glass beds were prepared. Coatings and impregnations
were prepared by thermal decomposition of the respective carbonyls
-
-2~-
2~
using fluidized bed techniques. The materials were characterized
with respect to coating thickness. Table II summarizes these
results.
-25-
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Other modifications of the present inven-tion will occur
; to those skilled in the art upon a reading of the present dis-
closure. These are intended to be included within the scope
of this invention.
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