Implementation Of Triboelectric Charging On Chalkboard For Reduction Of Chalk Dust

Abstract - The primary issue with employing chalkboard is adverse consequences of chalk-dust particles causing health complications like Asthma, Dermatitis including Inflammation in eyes. The contact-electrification serves as basis. Air-ionizer is utilized for electrifying chalkboard surface on which chalk dust particles adheres to. The chalk-dust particle size targeted are in the range of PM2. 5 to PM10. In this paper, distinct types of chalk board surfaces are reviewed on the basis of their position in triboelectric series and dielectric constant of the material. After each trial the chalkboard surface was cleaned with mixture of distilled water and 70% isopropyl alcohol for deionization of the board. The findings would be helpful for creating revolutionary device to make any chalkboard dust less.

Index Terms— Air Ionizer, Chalk Dust, Contact Electrification, Deionization, Dielectric Constant, Negative Ion Generator, Static Charge, Tribo-Charging, Triboelectric Effect

Introduction

The domain of topic is the reduction of the amount of chalk-dust particles suspended in the classroom environment while writing. The competitiveness in selection between chalkboard and whiteboard was stagnant prior to two major events made it biased to whiteboard, the invention of Dry Erase markers in the 1980’s and the report from American Academy of Allergy, Asthma and Immunology (AAAAI) linking the chalk-dust to be a cause of asthma and other respiratory system related issues. Our skin might feel like an impervious, but substances in contact with skin are absorbed and ends up in the blood in long run. Also, the chalk contains native hydrous magnesium silicate with small proportion of aluminum silicate (Al2SiO5) or calcium carbonate.

Which is having similar chemical composition as of asbestos, a cancer causing agent. Still, chalkboard adheres to its place when it comes to designing and arts, chalkboards are way to go for shading and coloring. Also, they have better contrast ratio with crispier writing. Chalk is generally economical and has no shelf life unlike whiteboard markers. The only major disadvantage of chalkboard is chalk itself, while writing with chalk on chalkboard the chalk-dust particles are suspended in air. High number of Total Suspended Particles (TSP) of the chalk-dust can be lethal for teachers and students also. Today, blackboard chalks has Lime Stone or calcium carbonate (CaCO₃) as the chief component in chalks. Yet, some of the low quality yet cheap chalks are made from calcium sulfate di-hydrate (CaSO∙2H₂O) commonly known as Gypsum. The core idea of the research paper is to yield the mathematical approach to the calculation of the force excreted between particles and chalkboard followed by performing a practical experiment in which electrostatic force collects particles of chalk-dust. Because of triboelectric effect, static charge is generated. Here, we have used Air-Ionizer for generation of static electricity and the charge is transferred to the surface of the chalk board which collects dust particles reducing number of suspended dust particles and creating a healthy classroom environment.

Technical Work Preparation

Let’s start from the chalk board itself, there are two types of chalk board, Porous and Non-porous chalkboards,

Type of Chalkboards

1. Porous chalkboards are usually having porous bases like wood, coated with chalkboard finish, as wood being porous a lot of paint ends up getting soaked in the wooden base. Porous chalk board are more likely to be susceptible to faint “Ghosting” marks and are heavier in weight compared to non-porous ones.
2. Non-porous chalkboards are having solid base usually metal coated with non-porous surfaces like laminate, metal, porcelain, vinyl are some widely used surface finish for chalkboards. These chalkboards are immune to the “Ghosting” marks. Now-a-days, most of the chalkboards used are the non- porous ones as apart from them being light in weight and their immunity to “Ghosting” marks, they also give superior surface to write upon.

Static Charge Generation

The static charge generation is one of the primary need of the system. The static charge is generated by the Negative Ion generator (Fig. 1), which is a common component used in Air-Ionizer, It pumps the low voltage level electrons to the higher voltage potential generating negative charge. The internal circuitry is voltage multiplier circuit enclosed in general epoxy resin potting compound.

The Black and Red wires are the input which are rated for 3 to 6v DC, and current consumption is of 133mA at 5v DC, yielding power consumption (W).‘W’ is power consumption in watt, ‘I’ is the current supply and ‘V’ is the voltage of the supply. Still, current might go up TO 250mA while initial charging of the chalkboard surface. Thus, the static charge has been transferred to the chalkboard surface through contact electrification. Chalk-dust suspended by writing with normal quality gypsum chalk is attracter towards the electrostatic field of the electrons (Negative Ions). Calcium Carbonate (CaCO) and calcium sulfate di-hydrate (CaSO∙2HO) both are polar molecules, as all polar molecules are soluble in polar solvent (like HO). As shown in Fig. 2, the normal chalkboard without any static charge present to attract or collect the chalk-dust particles will have hoard of Total Suspended Particles (TSP) than the statically charged chalkboard.

Mathematical approach to calculating force excreted

We can measure the force of attraction between chalk-dust particles and the chalkboard with the help of a point charge and an infinite conductive surface theory. In theory if a +Q charge is placed at D distance perpendicular to the axis of the surface and the surface is negatively charged, then instead of using complex task of calculating force excreted between charge and the surface. We can put a charge –Q (notice the polarity is altered) on the mirror side of the charge resent, which is same axis as of the particle charge but opposite in the direction and polarity, thus the polarity can be calculated easily with the following equation, where ‘Q’ stands for the charge of the particle, ‘ε’ is the permittivity of the material and the distance between particles is denoted by letter ‘D’.

Practical Work Preparation

The practical work preparation consists of all the parameters that are affecting the practical of experiment with the practical setup.

Sample Selection

The samples are the prime factor for variation of the measured readings. Here in case of chalk-dust particles, we have used the cheap chalk made from composition of gypsum (calcium sulfate di-hydrate, CaSO∙2H₂O) and limestone (calcium carbonate, CaCO₃).

The chalk was manufactured by Xiamen Haochen Star Ltd. at Fujian, China. The chalk is SGS certified with US $0. 195 per 100 Pcs of chalk sticks. The chalk was rubbed against 8000 grit dry sandpaper and suspending chalk-dust particles were collected in a closed container with silica gel. For the sake of accurate results, the sample was same for each material.

Polarity of sample

First of all we have to check is the chalk-dust is polar or not as only polar molecules can exhibit this property of induced static electricity, so to check that we have to dissolve it in polar solvent which here is water and since it dissolves in water its polar molecule. The polarity can be checked by charging an air filled balloon with triboelectric effect, i. e. rubbing it with hair. Since, it will charge the balloon negatively. Then the negatively charged balloon is taken in proximity to the chalk-dust and if the chalk-dust adheres to the surface of balloon then the chalk-dust is having tendency of getting positively charged and is in the positively charging elements class of the triboelectric series. Both gypsum and limestone type chalk-dust are positively charging with triboelectric effect. Thus, they have the same setup for practical implementation.

Humidity

Humidity is affecting the static charge holding capability of the material. As the humidity level rises the static charge easily ionizes the water particles in the air, discharging the charged object and reducing the effectiveness of the system.

The chalk-dust is a desiccant, which means it will absorb the moisture in the air and thus becomes less active in terms of induced charge also demolishing the effect of the system. Also, we have taken the same samples for each of the testing of material, thus we must have to take care of moisture level of the chalk-dust as it increase constantly up till saturation, by absorbing moisture from environment. While, the chalkboard material would not be much affected from moisture since it is constantly electrified with the ionizer. So, Ionizer would be pumping charge faster than it discharges into the environment. Humidity of the experiment location was 58%, and the humidity of the chalk-dust after the oven treatment (i. e. dehumidification) is taken as a constant. Moisture levels of the chalk-dust is taken care by heating the sample in an oven for 1 minute after each trial. The oven is a good choice since it will not charge the chalk-dust particles giving false results, while Micro Wave oven might charge them slightly causing variation in results.

Temperature

Temperature is still a parameter that matters in terms of static charge as it changes the dielectric constant of the materials, changing static charge holding capabilities, while the temperature changes the moisture content of the atmosphere, causing change in humidity. The experiment was performed at room temperature at about 27. 5℃. A practical example of temperature affecting static charge related properties is the in winter we get more static shocks compared to summer and monsoon as in winter moisture content (humidity) and temperature both are lower than summer and monsoon, which in turn increases the static charge holding capabilities of body.

Residual Charge

The residual charge on the base material and sample also causes the variation in results, Thus after each experiments of a material both the material and sample should be discharged and should have zero charge left on them.

To come over this problem we cleaned the surface of material with mixture of distilled water and 70% isopropyl alcohol for deionization of the board. While, the humidity deionizes the chalk-dust and dehumidification reduces the humidity levels.

Material

Tested material are Aluminum, Acrylic and Porcelain. Each material was cleaned after each test with mixture of distilled water and 70% isopropyl alcohol for deionization of the board as described in the residual charge removal section.

Cautions

While dealing with high voltages you must be careful. Here are the cautions that should be taken while performing experiment.

Make sure you have touched the common ground before turning the supply ON. Common ground terminal must be connected to your body as it will ground any charge in your body that might have been induced in your body in case of contact with excitation wire or coming in proxy to the white wire.

In case, you lose contact with ground wire, do not touch it again, instead turn OFF the supply and leave the set up as it is, for a minute or two, because if you touch ground after it you will be shocked as static charge discharges with arc. By a minute or two you would be discharged on your own to the environment. It is recommended to not to touch the material while experimenting as most of the charge discharges from the touch point to the ground. Yet, it will not give a high voltage shock as it will not produce that much charge constantly that can be lethal, but it will give poor results as it will not put sufficient charge on material to electrify it properly and produces poor results.

Practical Setup

The setup is shown in Fig. 4, with ionizer pin connection. Fig. 4. Practical Setup. Air Ionizer used here is having three leads out of two are power supply and the third one is excited ion lead, which charges the material of chalkboard. The white wire from Fig. 1 is connected to the material, the supply is connected to the red and black wire with keeping in mind the polarity, power supply used here is a 5v DC with 2Amp. Current capability to avoid variation of supply voltage. The excitation lead is connected with board as it will be constantly generating the negative charge and charging the material negatively. The common ground terminal will be the reference to the 1. 2Kv DC static charge. The chalk-dust is sprinkled from the distance of about 2 cm while holding the ground terminal with the other hand. Which will attract the fine dust and it adheres to surface.

Future Scope

For better performance we can use higher voltage as well as charge outputting capacity Ionizers. Readings would be taken before and after the implementation of the concept, with the use of Particle analyzers.

Acknowledgement

I gratefully acknowledge the contributions my parents for their support and financial support for the research.