Material Structure of Alumina

Structure of material focuses more on relationships between physical and chemical properties of certain material. Material is a physical substance that things can be made from. It can be any equipment or physical substance that need in daily life. (Cambridge University Press, 2012) Structure is a construction or framework of identifiable elements includes components, entities, factors, members, parts, steps and more which gives form and stability, and resists stresses and strains. Structures have defined boundaries within each element is physically or functionally connected to the other elements, the elements themselves and their interrelationships are taken to be either fixed or changing only occasionally or slowly. (Business Dictionary, 2016)

The structure of materials can be classified by the general magnitude of various features. There are three most common major classifications that listed generally in increasing size. Atomic structure has special features of cannot be seen, for example the bonding types between the atoms and its arrangement. Microstructure has features that can be seen easily using a microscope while macrostructure can be seen with the naked eye. The atomic structure primarily affects the chemical, physical, thermal, electrical, magnetic, and optical properties. The microstructure and macrostructure can also affect these properties but they generally have a larger effect on mechanical properties and on the rate of chemical reaction.

Alumina(Al2O3) normally appear to be white, is the chemicals composition of aluminium and oxygen. It is the main component in production of aluminium metal also serves as the raw material in making ceramics and an active agent in chemical processing. (Encyclopaedia Britannica, 2016) Alumina, the white crystalline powder, is made of bauxite which is naturally occur in various amount of hydrous aluminium oxides as the mineral corundum and some of it form the precious gemstones ruby and sapphire. Corundum is a rock-forming mineral appears as solid crystalline form of aluminium oxide containing traces of iron, titanium, vanadium and chromium.

Rubies and sapphires are gem forms of corundum, which has special characteristic in colour to trace impurities. Rubies are given their characteristic deep red colour and their laser qualities by traces of chromium. Sapphires come in different colours given by various other impurities, such as iron and titanium. (Wikipedia, 2016) Alumina has advantages such as its thermal, chemical, and physical properties when compared with several ceramics materials, and is widely used for firebricks, abrasives and integrated circuit (IC) packages.

Alumina is widely used compare to other materials in ceramic production. This is because it has very good electrical insulation, mechanical strength from moderate to extremely high also very high compressive strength which is basically from 2,000 to 4,000 MPa. Other than that, it is naturally hard and has moderate thermal conductivity. Alumina also can stand high resistance and less corrosive. Besides, it has good gliding properties, low density, bio-inert and food compatible.


Figure above shows a photograph of three thin disk specimens of alumina which have been placed over a printed page in order to demonstrate their differences in light-transmittance characteristics. The disk on the left is transparent, whereas the one in the middle is translucent and, the disk on the right is opaque. All the light that reflected from the printed page is passes through the transparent disk which are made of monocrystalline.

Polycrystalline materials, are solids that are comprised of a collection of crystallites, separated from one another by areas of relative disorder known as grain boundaries. Translucent disk has the structure of numerous and very small single crystals that are all connected. The boundaries between these small crystals scatter a portion of the light reflected from the printed page. Thus, some of the light reflected from the printed page is transmitted through the disk. The grain boundaries of high purity of alumina disks are very clean. Exceptional for the opaque disk, none of the light passes through it. 

Opaque disk composed of amorphous structure not only of many small, interconnected crystals, but also of a large number of very small pores or void spaces. These pores also effectively scatter the reflected light and render this material opaque. These differences in optical properties are a consequence of differences in structure of these materials, which have resulted from the way the materials were processed. (Specimen preparation, P.A. Lessing; photography by S. Tanner.) (William D. Callister, Jr., 2007)

Both monocrystalline and polycrystalline are crystalline solid. Monocrystalline structure shows periodic across the whole volume and perfect repeated arrangement of atoms that extends throughout the entirety of the specimen without interruption. All unit cells have the same orientation and interlock in the same way. It has crystal a regular geometric shape with flat faces. This transparent material is highly used in semiconductor industries, optics, material engineering and electrical conductors, refractories, insulators and heat radiation plates, metal matrix composites, high temperature materials and heat sinks, integrated circuit packages and substrate. (G.P. Thomas, 2016)

Polycrystalline composed of a collection of many small crystals or grains. It has small crystals or nuclei form at various positions. These have random crystallographic orientations. There is some atomic mismatch between the grains within the region called grain boundary. Grain boundaries disrupt the motion of dislocations through a material. Dislocation propagation is impeded because of the stress field of the grain boundary defect region and the lack of slip planes and slip directions and overall alignment across the boundaries. Reducing grain size is therefore a common way to improve strength. Translucent material usually used in potteries and porcelains. Amorphous is a type of non-crystalline solid that is less systematic and has irregular arrangement of atoms over relatively large atomic distances. Amorphous materials are characterized by atomic or molecular structures that are relatively complex and become ordered only with some difficulty. (William D. Callister, Jr., 2007)

Focusing on optical properties of Alumina, will explain more on its light transmittance based on three principle effects which are Reflection (R), Absorption (A) and Transmittance (T). Reflection defined as the portion of light that bounces-off an alumina surface. Absorption means light that is captured-by and dissipated as heat within a material as it passes through while transmittance is a measure of light transmitted through alumina without being absorbed or reflected but only scattered. (Dow Corning, 2012)

Optical property means a material’s response to exposure to electromagnetic radiation and visible light. When light travels from one medium into another, several things happen. Some of the light radiation may be transmitted through the medium, some will be absorbed, and some might be reflected at the interface between the two medias. (William D. Callister, Jr., 2007) Lord Rayleigh, a British physicist has been developed a theory of light scattering to describe the light transmission properties on materials’ surface. It defines as elastic scattering of light or other electromagnetic radiation by particles that is smaller than the wavelength of the radiation. Rayleigh scattering does not change the state of material hence it is a parametric process. The particles may be individual atoms or molecules. It can occur when light travels through transparent solids and liquids. The transmission is varied due to the presence of grain boundaries, pores and type of surfaces. (Wikipedia, 2016)

A transmitted light beam is deflected in direction and appears diffuse as a result of multiple scattering events. Opacity results when the scattering is so extensive that virtually none of the incident beam is transmitted, not deflected, to the back surface. The index of refraction for polycrystalline material normally appeared translucent. Both reflection and refraction occur at grain boundaries, which causes a diversion in the incident beam.

This results from a slight difference in index of refraction between adjacent grains that do not have the same crystallographic orientation. Scattering of light also occurs in two-phase materials in which one phase is finely dispersed within the other. The beam dispersion occurs across phase boundaries when there is a difference in the refractive index for the two phases. The greater its difference, the more efficient is the scattering. Monocrystalline material will appear highly transparent.

The sizes of the crystallites are smaller than the wavelength of visible light, and the indices of refraction of the two phases are nearly identical. As a consequence of fabrication or processing, many ceramic pieces contain some residual porosity in the form of finely dispersed pores. These pores also effectively scatter light radiation. The single crystal is totally transparent, polycrystalline and porous materials are respectively, translucent and opaque. Some scattering of visible light occurs at the boundaries between crystalline and amorphous regions, again as a result of different indices of refraction. For highly crystalline specimens, this degree of scattering is extensive, which leads to translucency, and even opacity. Highly amorphous polymers are completely transparent. (William D. Callister, Jr., 2007)

Besides the variety on optical properties, these disks material were produced with different processing technique. Processing of materials and manufacturing can take place in open atmosphere, ovens, high temperature furnaces or in specifically designed reactors. Monocrystalline material of optical sapphire is known to possess highly desirable optical and physical characteristics, such as high strength, high density and a high degree of transparency, as well as the ability to retain these properties, to a large degree, at elevated temperatures. In recent years, many advances have been made in production of transparent ceramics by various processing and sintering strategies. Powder granulation and dry pressing for transparent ceramic applications has been demonstrated. (Michael Stuer, Zhe Zhao, Paul Bowen, 2012)

The polycrystalline translucent ceramic material is formed by pressing a powder material, such as high purity alumina, into a desired shape, sintering the shaped material to provide closed porosity, and subjecting the sintered material to hot isostatic pressing to yield a single phase material having substantially zero porosity and an average grain size of no greater than 1.0 micrometre. This small grain size contributes to a stronger material than conventional ceramic materials without detrimentally effecting translucency. This is surprising as small grain size is often considered to prevent relatively high translucency. Preferably, the material has a flexure strength of at least about 400 MPa. (Sumitomo Chemical, 1993)

In order for these amorphous powders of alumina to be made into bulk samples, it is necessary to develop new compositions that will require a much lower critical cooling rate and high thermal stability. To achieve this, amorphous powders can be produce by radiant heating. The radiation sources can be either electric or gas fired. Amorphous alumina coatings were processed by metalorganic chemical vapour deposition (MOCVD) with certain chemical properties. The processing temperature should be in the range of 350 oC–700 oC at low pressure of 5 Torr. The surface of low temperature processed amorphous films is hydrophobic where water contact angled 106 degrees. It is concluded that amorphous alumina coatings can be used as oxidation and corrosion barriers at ambient or moderate temperature. The process involves nitrogen as a carrier of dilution gas. (J. Nanosci. Nanotechnol, 2011)

In conclusion, the transparent disk of alumina absorbs, reflects and transmits large amount of light compare to translucent and opaque disk. This is due to the difference in structure of monocrystalline structure in the transparent disk which helps to reduce the scattering of lights. Monocrystalline structure is well arranged without any grain boundaries, no spaces between the crystalline that form good surface of alumina. Thus, the printed page placed under the transparent alumina disk can be seen clearly.


Maternity Leave (Women’s Health)

Maternity leave refers to the temporary period of absence from employment granted to expectant, that a new mother takes off from work during the months immediately before and after childbirth. Maternity leave is usually created from a variety of benefits that include sick leave, vacation, holiday time, personal days, short-term disability and unpaid family leave time. These policies are important in supporting the mother’s full recovery from childbirth and enhancing a stronger bond between mother and child. (American Pregnancy Association, 2016)

There are two most notable laws protecting pregnant women are the Pregnancy Discrimination Act and the Family and Medical Leave Act. The Pregnancy Discrimination Act has been introduced in 1978 by United States federal statute to give opportunity to pregnant women for same rights as others with “medical conditions” by prohibiting job discrimination. The Act covers discrimination “on the basis of pregnancy, childbirth, or related medical conditions.” Furthermore, it only applies to employers with 15 or more employees.

With this act, employer cannot fire and force the pregnant women to take mandatory maternity leave. The employee also allowed to work as long as she can perform the job. During the leave, the employee will continue to accrue seniority and remain eligible for pay increases and benefits. This is a discrimination law that protects women from being treated differently than other employees which is good. Depending on the company, some employers will provide maternity leaves with paid but some will not. For instance, in the United States, only 11% of Americans employed by private industry have access to paid family leave. (Family Education, 2000)

The Family and Medical Leave Act (FMLA) was introduced in 1993. This Act applies to companies that employ 50 or more people within a 120 kilometre radius of the workplace. If they have been employed for at least one year by the company they work for, and work at least 25 hours a week, they can take up to 12 weeks of unpaid, job-protected leave in any 12-month period for the birth of their baby. All 12 weeks of maternity leave can be taken at the same time or they can be broken up over the course of the year before or after the birth of their baby. The laws regarding work and pregnancy have been written in response to a strong need for fairness. (Family Education, 2000) Having a baby, or caring for an adopted child, also falls under this category.

There are two types of maternity leave which are Ordinary Maternity Leave (OML) and Additional Maternity Leave (AML). OML available for 26 weeks leave for all employees and have rights to return to the same job with correct regulations. All women employees are entitled to OML from day one of their employment. It does not depend on how long they have worked for the employer. If they work under an agency or do casual work, they can still get maternity pay.

The earliest ordinary maternity leave is 11 weeks before the expected week of childbirth which is about 29 weeks pregnant. They can decide the date when to stop and start working after the baby is born. Secondly, the additional maternity leave which lasts for 26 weeks and starts on the day after the end of OML with correct notice to the employer. Up to 13 weeks of this leave will be paid, however the final 13 weeks of AML will remain unpaid. (Ask Baby, 2016)

In Malaysia, the paid maternity leave is available within 14 weeks compare to United States which have unpaid maternity leave. Under the 1955 Malaysia Employment Act, the pregnant women entitled to at least 60 consecutive days of maternity leave at full pay as long as they have been worked for at least 90 days in the four months before starting maternity leave. Additionally, the Act is applied to Peninsular Malaysia and Labuan only. For Sabah and Sarawak, they are governed by their respective Labour Ordinance. (Smart Investor, 2016)

Maternity leaves can be classified with paid and unpaid by the employers. Most of the countries will pay and give consideration for the maternity leave but the periods of leave given are different. Focusing on United States regarding the maternity leave that is never paid, there are several impacts that bring advantages to the pregnant employee.

After childbirth, the women employee that could not stay on leave longer and have to continue their profession will affect their child’s health and development. Maternity leaves help the mothers to care and allow them to better monitor the health of their child. Without it, they become attuned to their child’s health needs and are more effectively able to respond to any medical circumstances. Studies have shown that an additional week of maternity leave among industrialized countries reduces infant mortality rates by 0.5 deaths per 1,000 live births. (Wikipedia, 2016)

There is also a positive correlation between maternal leave and the duration of breast-feeding. Breast-feeding is good to practice by the mothers within 6 months after the childbirth which means mothers who are not involved in employment are more regularly able to participate in breast-feeding. Breast-feeding is vital to yield substantial health improvements in disease prevention and immune system build-up of the child. Besides, unemployed mothers are able to allocate substantially more time towards the educational and cognitive development of their child.

After birth, maternity leave may affect the amount of time a child spends with his mother rather than in non-maternal care. Maternity leave will also affect the quality of time the child spends with the mother, depending on changes to her stress level and her satisfaction with the trajectory of her career. The quantity and quality of time a mother spends with her child in his first year of life matter for the child’s well-being. (Maya Rossin, 2011) The mother and child can spend more time together in generating intellectual environments. The longer the maternal care of the mother, the lessen the problematic behaviors during child growth. Reports have indicated mothers’ ability to foster a more stable and nurturing home environment than their non-maternal care-taking counterparts. (Wikipedia, 2016)

Other than that, maternity leave may reduce maternal health during pregnancy and increases their risk in getting postpartum depression. If a woman is forced to work more hours during pregnancy would heightened her stress level. The stress of maintaining this balance has also been shown to weaken their immune systems and interact poorly with their psychological state.

The unpaid maternity leave may exert an effect on the mother’s income and therefore the family’s material resources available for child rearing. Not all new mothers may be able to take advantage of unpaid leave, and it may have different implications for the welfare of children depending on whether they grow up in low-income and low-educated one-parent households or high-income and high-educated two-parent households, as these families likely face different constraints. (Maya Rossin, 2011)

This will result in many low-income women who have a baby to choose either to sacrifice their health to maintain their family’s economic security or to risk their economic security for the sake of their family’s health. When women don’t receive paid maternity leave, research has shown that they are more likely to drop out of the workforce, therefore losing income for themselves and their families. About 43% of women with children leave work voluntarily at some point in their careers. Non-working adults aged 25 to 54 in the United States showed that 61% of women said family responsibilities were why they weren’t working, compared to 37% of men. (Lyndsey Gilpin, 2015)

Countries such as Russia, Mongolia and Uzbekistan are the longest maternity leave provided with paid. Paid maternity leave is beneficial too in economics also health effects to both mothers and children. When it comes to the economic benefit of paid leave, researchers have found it benefits women economically because they tend to go back to work and stay with the same employer, which means their wages grow at a faster rate afterward.

There are also savings when it comes to turnover and training costs for businesses. It can reduce infant mortality and increases the likelihood of infants getting well-baby care visits and vaccinations, with one study finding that children were 25.3% and 22.2% more likely to get their measles and polio vaccines, respectively, when their mother had access to paid maternity leave. Without paid leave, there was no increase in immunizations. (Kelly Wallace and Jen Christensen, 2015) The rate of duration of breast-feeding can be lengthen and babies are less likely to get a variety of infections and are also at lower risk for asthma, obesity and sudden infant death syndrome. There are advantages to the mothers too, as women who breast-feed are less likely to get breast cancer, ovarian cancer, type 2 diabetes and heart disease.

To overcome those problems, the responsible agencies should pay attention and provide support for the enactment and continuation of maternity leave policies in their country. Unlike men, women who have children must take at least some time off from working during childbirth. Hence policies that ensure their job security during this time period are crucial for women’s careers, health, and overall well-being. The incidence of poor birth outcomes and infant mortality is higher among women from lower socio-economic backgrounds, maternity leave policies that cover mothers and children from all backgrounds may result in much greater benefits that could outweigh the extra costs from covering more working women. Children of poor, single and low-educated working mothers are a key vulnerable population that was not reached by the FMLA.

As the conclusion, maternity leave brings a lot of advantages especially to the mothers that are working as well as their children. However, these children and their families may benefit the most from policies that enable their mothers to take time off work during their early life without substantial losses in income. These mothers are often forced to work immediately after childbirth, and their new born children are then placed in low-quality childcare. Their children already stand at a disadvantage for their later-life opportunities as they are born into low socio-economic status families, and lack of maternal time during their first few months of life may exacerbate this disadvantage. (Maya Rossin, 2011)

Thus, if policymakers are concerned with decreasing disparities in child health and well-being between children of different backgrounds, they need to consider the fact that an unpaid maternity leave policy may actually increase disparities because it only benefits those mothers who can afford to take it. On the other hand, paid maternity leave policies may allow poor, single and working mothers to care for their new born children at home, to seek prompt medical care when needed, and to develop a closer bond with them, thereby saving their lives and improving their life chances from the start.