RUBBER
The rubber industry, in its
development over the past one hundred years, has utilized an increasing number of the many
optical, physical and chemical properties of Zinc Oxide. Zinc Oxide proved the most
effective activator to speed up the rate of cure with the new accelerators.
Heavy-duty pneumatic tires carry high
loadings of Zinc Oxide for heat conductivity as well as reinforcement since heat-buildup
is critical at their higher operating speeds compared with their solid-rubber
counterparts.
Activation
In the curing process for natural
rubber and most types of synthetic rubbers, the chemical reactivity of Zinc Oxide
is utilized to activate the organic accelerator.
The unreacted portion of the Zinc Oxide
remains available as a basic reserve to neutralize the sulfur-bearing acidic decomposition
products formed during vulcanization. Adequate levels of Zinc Oxide contribute markedly to
chemical reinforcement, scorch control, and resistance to heat-aging and compression
fatigue.
Acceleration
Zinc Oxide serves as the accelerator
with some types of elastomer and the crosslinking, which it induces, takes several forms.
With some systems, Zinc Oxide is an effective co-accelerator in the vulcanization process.
Biochemical Activity
Zinc Oxide is useful in the
preservation of plantation latex as it reacts with the enzyme responsible for the
decomposition. The oxide is also a fungistat, inhibiting the growth of such fungi as mold
and mildew.
Dielectric Strength
In high-voltage wire and cable
insulation, Zinc Oxide improves the resistance to corona effects by its dielectric
strength, and at elevated operating temperatures it contributes to maintenance of the
physical properties of the rubber compound by neutralization of Acidic decomposition
product.
Heat Stabilization
Zinc Oxide similarly retards
devulcanization of many types of rubber compounds operating at elevated temperatures.
Latex Gelation
In the production of latex foam
rubber products, Zinc Oxide is particularly effective in gelation of the foam with
sufficient stability.
Light Stabilization
Zinc Oxide is outstanding among white
pigments and extenders for its absorption of ultraviolet rays. Thus, it serves as an
effective stabilizer of white and tinted rubber compounds under prolonged exposure to the
destructive rays of the sun.
Pigmentation
Through its high brightness,
refractive index, and optimum particle size, Zinc Oxide provides a high degree of
whiteness and tinting strength for such rubber products as tire sidewalls, sheeting and
surgical gloves.
Reinforcement
Zinc Oxide provides reinforcement in
natural rubber, and in some synthetic elastomers such as polysulfides and chloroprenes.
The degree of reinforcement appears to depend upon a combination of the particle size of
the oxide, the finest size being the most effective, and the reactivity of the oxide with
the rubber.
Under such service condition involving
rapid flexing or compression, Zinc Oxide also provides heat conduction to more rapidly
dissipate the heat and thereby provides lower operating temperatures. In addition, it
imparts heat stabilization by reacting with acidic decomposition products.
Rubber - Metal Bonding
In the bonding of rubber to brass,
Zinc Oxide reacts with copper oxide on the brass surface to form a tightly adhering
Zinc-copper salt.
Tack Retention
One of the unique properties of Zinc
Oxide is its ability to retain over many months of shelf –storage the tack of uncured
rubber compounds for adhesive tapes.
French process Zinc Oxides impart
heat-aging resistance superior to that of American-process Zinc Oxides. The former type,
being sulfur-free, has a higher pH and, thus, can neutralize more effectively the acidic
decomposition products formed during aging. Moreover, the finer French-process Zinc Oxides
prove superior to coarser grades in heat-aging resistance.
PLASTICS
Zinc compounds can provide a variety of
properties in the plastics field. Heat resistance and mechanical strength are imparted to
acrylic composites by Zinc Oxide. Zinc Oxide contributes to the formation and cure of
epoxide resin. Addition of Zinc Oxide to epoxy resins cured with aliphatic polyamines
imparts higher tensile strength and water resistance. Zinc Oxide imparts fire-resistant
properties to nylon fibers and moldings. Zinc Oxide is also useful in the preparation of
nylon polymers and in increasing their resistance. The formation of polyesters in the
presence of Zinc Oxide imparts higher viscosity and other improvements. ZnO reacts with
unsaturated polyesters to form higher viscosity and a thixotropic body. The dyeability of
polyester fibers is improved by Zinc Oxide. Zinc Oxide mixtures stabilize polyethylene
against aging and ultraviolet radiation. Zinc Oxide increases the transparency of
poly(chlorofluoroethylene) molding resin. Polyolefin's are improved in color, tensile
strength, and vulcanization properties by addition of Zinc Oxide. Thermal stabilization of
PVC is effected by Zinc Oxide. Antistatic, fungistatic and emulsion stability are
additional properties imparted to vinyl polymers by Zinc Oxide.
Applications in development for Zinc
Oxide-stabilized polypropylene and high-density polyethylene include safety helmets,
stadium seating, insulation, pallets, bags, fiber and filament, agricultural and
recreational equipment.
CERAMICS
The properties imparted by Zinc Oxide to
some of the newer applications are as electronic glass, low-melting glass for
metal-to-glass seals, thermistors for use as lighting arresters and devitrified glasses of
low thermal expansion.
Zinc Oxide imparts a unique combination
of properties when used in glass. Zinc Oxide reduces the coefficient of thermal expansion,
imparts high brilliance and luster and high stability against deformation under stress. As
a replacement flux for the more soluble constituents, it provides a viscosity curve of
lower slope. The specific heat is decreased and the conductivity increased by the
substitution of Zinc Oxide for BaO and PbO.
PHARMACEUTICAL
INDUSTRY
Zinc Oxide is mainly used in Zinc soap,
ointment, dental inlays, food powders etc. Zinc Oxide forms an indispensable element of
the production process of this industry.
COSMETICS
The optical and biochemical properties of
Zinc Oxide and its derivatives impart special features to a variety of cosmetic
preparations for care of the hair and skin. In powders and creams it protects the skin by
absorbing the ultraviolet sunburn rays; in burn ointments it aids healing.
Simple salts of Zinc provide astringent
and skin-conditioning properties to creams, while more complex salts furnish fungistatic
properties which contribute to the effectiveness of deodorants, soaps, and antidandruff
preparations.
ADHESIVES, MASTICS,
SEALANTS
Zinc Oxide has long been a major
constituent of surgical and industrial tapes based on natural or synthetic rubber as it is
outstanding in retention of tack during shelf–aging.
Neoprene adhesives are improved by the
addition of both Phenolic resins and Zinc compounds (including Zinc Oxide), the reaction
products imparting special properties such as high heat resistance, high bond strength,
improved peel and shear – stress resistance, and stability to settling of Neoprene
solution adhesives.
PHOTOCOPYING
Some of the unique electronic properties
of Zinc Oxide are distinctively utilized in the photocopying process. For use in that
process, Zinc Oxide is increased in photoconductivity and semiconductor properties by
special heat and/or doping treatments (addition of foreign elements). Also, Zinc Oxide is
greatly modified in optical properties to increase its absorption of light rays in the
visible region. This process known as sensitization, is generally carried out by addition
to certain dyes, which are absorbed on the surface of the Zinc Oxide.
Commercial Zinc Oxide for photocopying is
generally produced from metallic zinc, rather than ore, to obtain a product of higher
purity.
LUBRICANTS
In the research and development of
improved lubricants over the past two decades, Zinc Oxide and its derivatives have been
intently studied. Zinc Dithiophosphates which are prepared by reacting Zinc Oxide with
organic Phosphates, are used in substantial quantities as additives to lubricating oils
for automotive engines, to reduce oxidation corrosion and wear. Zinc Oxide has been found
to contribute special properties in many types of lubricants, such as extreme-pressure
lubricants, seizure-resistant lubricants, and greases. Improved adhesion is another
feature which Zinc Oxide contributes.
Zinc Oxide imparts special properties to
greases and other variety of lubricants. Such greases are useful in the lubrication of
food–processing equipment.
PAINTS
Zinc Oxide in organic coatings
provides a broad spectrum of properties: optical, chemical, biochemical and physical. Over
the past century the paint industry, in its constant development of improved products, has
utilized various aspects of those properties to high degree.
Manufacturers discovered that they could
produce coatings of brushing consistency and good suspension properties by incorporation
of Zinc Oxide into their pastes. Painters noted that they furnished better hiding power,
whiteness, cleaner tints, tint retention, and durability as well as nondarkening in the
presence of sulfur fumes. French-process Zinc Oxide has been proved superior to
American-process type in fungus resistance and less sulfide staining.
Metal –
Protective Coatings
Zinc metal powder (zinc dust) and
zinc compounds have long been utilized for their anticorrosive properties in
metal-protective coatings, and today they are the basis of such important specially metal
primers as Zinc Chromate primers.
Zinc dust-Zinc Oxide paints are
especially useful as primers for new or weathered galvanised Iron. Such surfaces are
difficult to protect because their reactivity with organic coatings leads to brittleness
and lack of adhesion. Zinc dust-Zinc Oxide paints however, retain their flexibility and
adherence on such surfaces for many years. Zinc dust-Zinc Oxide paints also provide
excellent protection to steel structures under normal atmospheric conditions, as well as
to steel surfaces in such under-water conditions as dam faces and the interior of fresh
water tanks.
CIGARETTE FILTERS
Zinc Oxide as a constituent of cigarette
filters is effective in removal of selected ingredients from tobacco smoke. A filter
consisting of charcoal impregnated with Zinc Oxide and Iron Oxide removes significant
amounts of HCN and H2S from tobacco smoke without affecting its flavour.
SULFUR REMOVAL
Zinc Oxide is effective in removal of Sulfur
and Sulfur compounds from a variety of fluids and gases, particularly industrial flue
gases. Zinc is also effective in removal of H2S from hydrocarbon gases and for
desulfurization of H2S and certain other sulfur-containing compounds.
FOODS AND
FOOD-PACKAGING MATERIALS
Zinc Oxide and its derivatives
contributing special fungi-static and chemical properties to the processing and packaging
of various animal and vegetable products.
In the packaging of meat, fish, corn and
peas, for examples, Zinc Oxide has long been incorporated into the varnish linings of
the metal containers to prevent formation of black Sulfides which discolor the food.
FIRE RETARDANTS
Zinc Oxide and its derivatives were used
extensively in fire retardants for the military in World War II and those Zinc compounds
have since been the subject of extensive research and development for preparation of
fire-retardant compositions for a variety of substances.
Solutions for fireproofing textiles contain ZnO, Boric
Acid, and Ammonia in various proportions. It deposits water-insoluble Zn Borate on the
fibers.
FERRITES
Zinc Oxide continues as an essential
ingredient in the "soft" type of ferromagnetic materials for television, radio,
and tele-communication applications. In these fields ferrites based on Magnetite, Nickel
Oxide and Zinc Oxide are used as elements in many types of electronic devices.
Numerous electronic instruments for the
consumer market utilize ferrites to impart specific functions. In portable and car radios,
the antenna cores are ferrites designed to provide highly selective tuning. Television
picture tubes constitute a major market for ferrites, particularly for use in flyback
transformers and deflection yokes. In the communications area, ferrites are extensively
used in the filter inductors of telephone circuits to permit precise inductance adjustment
for the purpose of separating channels. Magnetic tape for recorders is improved by use of
a Magnetite precipitated in the presence of ZnO.
BATTERIES, FUEL CELLS,
PHOTOCELLS
Zinc Oxide is used in Zinc-Carbon dry cells,
Zinc-Silver Oxide batteries, Nickel Oxide-Cadmium batteries and even in secondary
batteries. In Fuel cells, Zinc Oxide is used as electrode material, cathodic material and
as a fuel element. And in Solar Energy Cells, it can act as a photocatalyst. Purification
of motorcar exhaust gases is currently the subject of extensive research, and Zinc Oxide
is already demonstrating its catalytic properties in some of those programs.
THERMOELEMENTS
Zinc Oxide plays an important role in
semiconductor ceramic elements for operation at elevated temperatures or High Voltages.
Such Thermoelements can be produced to cover a broad range of thermal and electrical
properties.
Varistors are composed of semiconductor
ZnO modified by other Oxides. Developed for use as lightning arrestors and high-voltage
surge arrestors in electric transmission lines, they are based on a unique electronic
property of semiconductor ZnO, nonlinear resistance. ZnO varistors have high-temperature
stability and resistance to humidity, electrical load, and current shocks.
SILICATE COMPOSITIONS
Zinc Oxide reacts with aqueous solutions
of Silicates, such as Sodium Silicate solutions (commonly known as water glass) to form
Zinc Silicate, a waterproof, fireproof refractory material, which is useful as a binder in
paints. Such refractory adhesives are used in bonding Asbestos-cement molded products to
building structures.
FUNGICIDES
Zinc Oxide and its derivatives contribute
effectively to the control of fungi in many different types of applications. Zinc Oxide
per se is not a fungicide; rather it is a fungistat, that is, it inhibits the growth of
fungi, such as mildew on the surface of exterior house paints. This property is also used
to particular advantage in the fortifying of fungicides; Zinc Oxide is added to fungicides
to increase their effectiveness in specific applications.
PORTLAND CEMENT
The beneficial effects of Zinc Oxide
additions to Portland cement have long been known -retardation of setting and hardening
(to reduce the rate of heat evolution), improvement in whiteness and final strength.
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