Remanence, Saturantion and Coercivity study of several ferrites

First the teory (from wikipedia.org):

Remanence:

Remanence or remanent magnetization is the magnetization left behind in a permanent magnet after an external magnetic field is removed. It is also the measure of that magnetization. Colloquially, when a magnet is "magnetized" it has remanence. It is also the magnetic memory in magnetic storage and the source of information on the past Earth's field in paleomagnetism.

The equivalent term residual magnetization is generally used in engineering applications. In transformers, electric motors and generators a large residual magnetization is desirable (see also electrical steel). In many other applications it is an unwanted contamination, for example a magnetization remaining in an electromagnet after the current in the coil is turned off. Where it is unwanted, it can be removed by degaussing.

Sometimes the term retentivity is used for remanence measured in units of magnetic flux density.

Saturation remanence:

The default definition for remanence is the magnetization remaining in zero field after a large magnetic field is applied (enough to achieve saturation). A magnetic hysteresis loop is measured using instruments such as a vibrating sample magnetometer and the zero-field intercept is a measure of the remanence. In physics this measure is converted to an average magnetization (the total magnetic moment divided by the volume of the sample) and denoted in equations as Mr. If it must be distinguished from other kinds of remanence it is called the saturation remanence or saturation isothermal remanence (SIRM) and denoted by Mrs.

In engineering applications the residual magnetization is often measured using a B-H Analyzer, which measures the response to an AC magnetic field. This is represented by a flux density BR. This value of remanence is one of the most important parameters characterizing permanent magnets; it measures the strongest magnetic field they can produce. Neodymium magnets, for example, have a remanence approximately equal to 1.3 teslas.

Magnetic saturation:

Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetizing field H cannot increase the magnetization of the material further, so the total magnetic field B levels off. It is a characteristic particularly of ferromagnetic materials, such as iron, nickel, cobalt and their alloys.

Coercivity:

In materials science, the coercivity, also called the coercive field or coercive force, of a ferromagnetic material is the intensity of the applied magnetic field required to reduce the magnetization of that material to zero after the magnetization of the sample has been driven to saturation. Coercivity is usually measured in oersted or ampere/meter units and is denoted HC.

Coercivity measures the resistance of a ferromagnetic material to becoming demagnetized. Coercivity can be measured using a B-H Analyzer or magnetometer.

Materials with high coercivity are called hard ferromagnetic materials, and are used to make permanent magnets. Permanent magnets find application in electric motors, magnetic recording media (e.g. hard drives, floppy disks, or magnetic tape) and magnetic separation.

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For a development, we did make a lot of magnetic measurements with a lot of differents ferrites:

Regards,

Tarik Della Santina Mohallem

R&D Director

Nanum Nanotecnologia SA

http://www.nanum.com.br

tarik@nanum.com.br

Inkjet MICR ink technology and production

MICR  (From Wikipedia):

Magnetic Ink Character Recognition, or MICR, is a character recognition technology used primarily by the banking industry to facilitate the processing of cheques. The technology allows computers to read information (such as account numbers) off printed documents. Unlike barcodes or similar technologies, however, MICR codes can be easily read by humans.

MICR characters are printed in special typefaces with a magnetic ink or toner, usually containing iron oxide. As a machine decodes the MICR text, it first magnetizes the characters in the plane of the paper. Then the characters are passed over a MICR read head, a device similar to the playback head of a tape recorder. As each character passes over the head it produces a unique waveform that can be easily identified by the system.

The use of magnetic printing allows the characters to be read reliably even if they have been overprinted or obscured by other marks, such as cancellation stamps and signature. The error rate for the magnetic scanning of a typical check is smaller than with optical character recognition systems. For well printed MICR documents, the "can't read" rate is usually less than 1% while the substitution rate (misread rate) is in the order of 1 per 100,000 characters.

______________________

In 2011, 98% of the MICR impression are made from laser printer. There is a tendency for cost, environmental, energy and logistics reasons to replace the laser printer technology to inkjet.

For this R&D challenge, we must:

1. Have a high density of solids dispersion of ferrimagnetic material.
2. A low viscosity.
3. A strong magnetic remanence. 
4. A dispersion with a very small particle size.

So, we did it!

Now we have a very stable inkjet MICR ink, with magnetic signal above 110%.

Regards,

Tarik Della Santina Mohallem

R&D Director

Nanum Nanotecnologia SA

http://www.nanum.com.br

tarik@nanum.com.br

Dispersion of agglomerated nanoparticles

Journal of the society of powder technology Japan

"

At dispersion of agglomerated nanoparticles to mono particles by a bead mill, large-sized beads give excess impact power to the agglomerated nanoparticles, resulting in crushing and re-agglomeration of the particles. Recentely a new process have been developed (new bead mill), capable of using microbeads (down to 0.03mm), and its dispersion performance for agglomerated ferrite nanoparticles to get the monodispersed nanoparticles was investigated under varios operating conditions in this study. Ut is shown that the impact force generated by the beads during the dispersion can be controlled by varying the bead size and that hence the adverse effect of impact force on the crystallinity and the surface of particles can be prevented. As a result, ferrite nanoparticles with diameter down to 50nm (close to the diameter of primary particles) and sharp size distributions were obtained. The present study of dispersion operation by microbeads is expected to be directly applicable to the development of nano-dispersion of novel materials.

Reflecting a strong demand for nanoparticle materials dispersed down to several tens of nano meters in the field of eletronic materials, dispersion process for nanoparticle agglomerate using a bead mill has become an important issue. In addition, it is frequently demanded that nanoparticle agglomerate be dispersed down to the mono particles without damaging them.

However, the two technical requirements conflict, therefore, it has become necessary to determine optimum dispersion power that will satisfy the both requirements as much as practicable. Although varios attemps for optimum dispersion power were made eith convencional continuous bead-mills, it was difficult to reduce the diameter of a vead used in the processing. Large beads which generate large bead impact energy tended to cause a problem of re-agglomeration due to particle destruction and damages. In such circumstances, it was an important challenge to develop a new technology to disperse nanoaprticle down to the mono particle.

Meanwhile, a new system has developed a new bead mill, capable of using 0.3mm beads which were never usable in the conventional bead mills. In the present research, we also used 0.05mm and 0.1mm beads to make a comparative study betwee these and 0.03mm beads, Furthermore, the experimentation was conducted under different rotor speeds for bead agitation to investigate and empirically determine optimun operating conditions in which dispersion down to the primary particles with minimum influence on the particle´s crystaline properties and surface properties is possible. In the analysis of the results, we focused on impact energy applied to particles by the beads to evaluate the minimum impact energy required for agglomerates dispersion as well as the relationship between said impact energy and optimum operating conditions. 

"

Regards,

Tarik Della Santina Mohallem

R&D Director

Nanum Nanotecnologia SA

http://www.nanum.com.br

tarik@nanum.com.br

Zeta Potential

A value that can be related to the stability of a colloidal suspencion:

Zeta potential [mV]	Stability behavior of the colloid
from 0 to ±5,	Rapid coagulation or flocculation
from ±10 to ±30	Incipient instability
from ±30 to ±40	Moderate stability
from ±40 to ±60	Good stability
more than ±61	Excellent stability

The Zeta potential is related to the density of electrical charges present at the surface of dispersed materials (ionisable groups chemically bonded or physically adsorbed). The surface charge generate a potential around the particles which decays exponentially with distance into the surrounding medium. 



When the particles are subjected to an electric field, they will drift at a define and characteristic velocity, µ. This parameter per unit field strength is the electrophoretic mobility. 


The Zeta potential will influence the stability of colloids, especially in aqueous systems. A high value will be in favour of the electrostatic repulsion between particles of the same charge.

What is zeta potential?

Most particles dispersed in an aqueous system will acquire a surface charge, principally either by ionization of surface groups, or adsorption of charged species. These surface charges modify the distribution of the surrounding ions, resulting in a layer around the particle that is different to the bulk solution. If the particle moves, under Brownian motion for example, this layer moves as part of the particle. The zeta potential is the potential at the point in this layer where it moves past the bulk solution. This is usually called the slipping plane. The charge at this plane will be very sensitive to the concentration and type of ions in solution.

Zeta potential is one of the main forces that mediate interparticle interactions. Particles with a high zeta potential of the same charge sign, either positive or negative, will repel each other. Conventionally a high zeta potential can be high in a positive or negative sense, i.e. <-30mV and >+30mV would both be considered as high zeta potentials. For molecules and particles that are small enough, and of low enough density to remain in suspension, a high zeta potential will confer stability, i.e. the solution or dispersion will resist aggregation. The Faraday gold sol made in the 1850’s now in the science museum in London, is still a stable dispersion, particle aggregation being slowed to an imperceptible rate due to it’s high zeta potential. 

Applications

Typical applications are in the formulation of particulate dispersions. Zeta potential can be used to assess the effect of each additive in the formulation. Additives can have surprising effects; some materials sold as dispersion agents have been known to reduce the zeta potential in particular formulations. It is not always possible to predict the effect or the magnitude of the effect of an additive. The Zeta potential can also be used to increase shelf life by assessing the impact of product changes during storage, e.g. hydrolysis or gas ingress.

Principle of zeta potential measurement

Zeta potential is measured by applying an electric field across the dispersion. Particles within the dispersion with a zeta potential will migrate toward the electrode of opposite charge with a velocity proportional to the magnitude of the zeta potential.

This velocity is measured using the technique of laser Doppler anemometry. The frequency shift or phase shift of an incident laser beam caused by these moving particles is measured as the particle mobility, and this mobility is converted to the zeta potential by inputting the dispersant viscosity, and the application of the Smoluchowski or Huckel theories. These theories are approximations useful for most applications. More recent models are available which can give a more exact conversion, but require more knowledge of the chemistry of the dispersion.

Advantages of recent technology introductions

One of the biggest practical issues when making zeta potential measurements is that of contamination. If any part of the system has been in contact with a previous sample then the zeta potential, being so sensitive to small changes in the environment can be affected.
The disposable capillary cell available for the Zetasizer Nano series is the only cell with entirely disposable cuvette and electrodes, that will therefore eliminate this problem.

The Zetasizer Nano series uses second generation PALS (Phase Analysis Light Scattering), called M3PALS to measure the particle velocity. Using phase analysis rather than frequency analysis is up to 1000 times as sensitive to changes in particle mobility. This is particularly important when measuring samples at high ionic concentration, e.g. isotonic saline, or in low dielectric constant dispersants such as hexane.

Regards,

Tarik Della Santina Mohallem

R&D Director

Nanum Nanotecnologia SA

http://www.nanum.com.br
tarik@nanum.com.br

Inkjet Printing Technologies - brief

1. Flexography - is a form of printing process which utilizes two flexible relief plate.
2. Lithography - no flexible
3. 
   

Inkjet

Continuous Inkjet (CIJ)

 

Amateur technology - 50KHz to 175KHz

Piezo Crystal

25m/s

Drop on Demand Inkjet (DOD)

Pressure pulse most used

350° - 400°C

1. Thermal                    |  MEMS (Micro Eletronic Mechanical Systems)
2. Piezo                        |         lead zirconium titanate
3. Eletrostatic

Inkjet types:

1. phase-change
2. solvent-based
3. water-based
4. uv-curable
5. oil-based
6. liquid toner

Color combinations:

1. cyan
2. magenta
3. yelow
4. black

CMYK color model

Trends

3553 US and Europe patents (2006)

300 per month

Hewlett-Packard, Canon, Seiko, Epson and Silverbrook

Challenges

1. aplication performance (functional)
2. print quality (bleed, surface wetting)
3. compatibility
4. drying/curing time (relating to speed)
5. adhesion
6. jetting characteristics (viscosity, dynamic surface tension, etc.)
7. reability
8. easy of manufacturing
9. regulatory

Regards,

Tarik Della Santina Mohallem

R&D Director

Nanum Nanotecnologia SA

http://www.nanum.com.br
tarik@nanum.com.br

Utilization of nanoparticulate oxides in the general industry (I).

Dispersion.

A little of history:

When I had started my company, we had a small production line with same nanoparticulate oxides as dry powders. We knew that these oxides had a lot of application in various industries. But, It was not so simple.

When you take a little of nanoparticulate Alumina (Al2O3), with a DLS like Mv=80, and a surface area = 400 m²/g and try to disperse in water, what happen? The same think when you put chocolate milk in cold milk: Big agglomeration and sedimentation. This occurs because we have a lot of surface force attracting the particles each other.

So, we sell a couple of kilos of alumina alpha to a refractory company. They made refractory bricks with an aqueous slurry. Our nanoparticles had aggregated and sedimented at the bottom of the mold and the brick had cracked at the furnace.

So we had learned that we cannot sell simple nanoparticles to this kind of company. We developed a process that creates organic “hair” in our particle, like picture below. This organics structures have the job to prevent aggregation and sedimentation.

functionalized particle 

Now we sell functionalized alumina alpha to the same company. Could be powder or a water dispersion. A little of this material can reduce the sintering temperature, increase the density of the ceramic brick and increase the mechanical resistance.

Now, 99% of our sales are functionalized particles, as powder or colloidal suspensions. This eneabled our business model.

Regards,

Tarik Della Santina Mohallem

R&D Director

Nanum Nanotecnologia SA

http://www.nanum.com.br
tarik@nanum.com.br

How to make a good DLS analysis of ferrite

Question: Is a cobalt ferrite a transparent or absorbent particle?

I am talking about a water dispersion of a Cobalt Ferrite ( #ferrofluid  ). An industrial product of Nanum. The ink industrial pattern use as standard this statment:

• Black ink with carbon black is absorbent.
• Another ink could be transparent or absorbent.

So they rated our dispersion as absorbent, but, using a  UV espectroscopy we saw that our ferrite is fifty to fifty transparent in 770nm (wavelength). We have a Malvern Zetatrac and we set ours samples as transparent and they (a big buyer) set as absorvent.

The results are incredibly diferrent as below:

transparent - sperical

absorsorvent - irregular

 Another thing: Should I consider this particles sphericals or irregulars?:

AFM print sample

TEM

I certainly believe in a spherical aproximation.

Regards,

Tarik Della Santina Mohallem

R&D Director

Nanum Nanotecnologia SA

http://www.nanum.com.br
tarik@nanum.com.br