Difference between heartwood and sapwood
Forest Products Laboratory (U.S.)
1919
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Interfaces metal/cerâmico estão presentes em alguns sistemas de
restauração dentária, tais como coroas, pontes e implantes. Os fenómenos de
molhabilidade, espalhamento e adesão têm um papel importante nestes sistemas,
os quais muitas vezes exibem falhas e rupturas, tendo como consequências o
sofrimento e custos de substituição para o paciente. As falhas acima mencionadas
devem-se sobretudo a uma fraca adesão, diferenças acentuadas no coeficiente de
expansão térmica entre os materiais e a mudanças bruscas das propriedades
mecânicas na região interfacial. Uma tentativa de eliminar ou reduzir esses
problemas, poderá ser a introdução de um outro material para reagir e criar novas
interfaces entre a liga dentária e a porcelana.
A utilização de ligas de brasagem activas é uma da técnica comum para a
ligação metal-cerâmico. Normalmente envolv...
Nos últimos anos, o titânio tem sido utilizado em aplicações dentárias, devido às
suas óptimas propriedades mecânicas, resistência à corrosão e biocompatibilidade.
Contudo a falha do componente metálico do implante e o desgaste dos materiais
dentários continuam a ser um motivo de preocupação. Quando o implante dentário é
colocado na cavidade oral, este é sujeito a solicitações mecânicas como resultado de
micro-movimentos cíclicos na interface osso/implante ou implante/abutment ou mesmo
abutment/porcelana e também solicitações químicas como consequência do contacto do
implante com a saliva ou substâncias orgânicas. Podemos afirmar então que o implante
está inserido num sistema de tribo-corrosão, consistindo este numa degradação do
material devido a interacções mecânicas e corrosivas. Como consequência a
investigação dos mecanismos de tr...
The use of dental implants has been increasing exponentially over the last few decades, making it essential to understand their degradation behaviour in the oral environment. Dental implants are generally made out of titanium (Ti) because of its outstanding biocompability and high corrosion resistance. Even though the degradation of Ti, in vivo, is minimal due to its ability to develop a highly stable passive oxide layer (TiO2); Ti is not inert to corrosive attack and presents poor wear resistance.
Several studies have already been done on the corrosion and wear behaviour of titanium in artificial saliva and fluoride solutions. However, the microbial effect on the corrosion and wear of metallic biomaterials still remains unknown.
The major novelty of this work relies on the first ever evaluation of the combined behaviour of wear and co...
The objective of this research work was to study the degradation (corrosion and tribocorrosion) resulting from mechanical (wear) and electrochemistry (corrosion)
interactions in Al/Al3Ti and Al/Al3Zr functionally graded materials (FGMs). The
influence of the spatial distribution of the platelets on the corrosion and tribocorrosion
behaviour was evaluated. The Al/Al3Ti and Al/Al3Zr FGMs were produced by centrifugal casting, originating samples in the form of rings that presented radial gradients of the reinforcements.
The corrosion resistance of Al/Al3Ti and Al/Al3Zr FGMs was studied using
electrochemical techniques namely, open circuit potential (OCP), potenciodynamic
polarization and electrochemical impedance spectroscopy (EIS). Additionally, the
tribocorrosion behaviour was evaluated in a pin-on-plate configuration, under reciprocati...
Degradation of Ti dental implants is a common process usually caused by mechanical stress and/or by the physiological environment (human saliva) that surround the implant. These types of implant are most of the time subjected to micro-movements at the contact region with bone or at the implant/porcelain interface (due to the transmitted mastication loads) and chemical solicitations (oral environment). Such implant becomes part of a tribocorrosion system, which may undergo a complex degradation process that can lead to implant failure. Additionally, the passive film,
which naturally grows on the metallic implant surface, can be scratched or destroyed
during the insertion and implantation into the hard tissue by abrasion with bone and
other materials.
In this work, two different tribological arrangmets were studied. Fretting-corrosion
an...
The use of dental implants nowadays has become a regular method to replace missing or
awfully damaged teeth.
Titanium is a well known metal used for the construction of orthopedic implants due to its
biocompatible characteristics and ability to maintain those while playing the desirable functions. It
has the capacity of forming an appealing interface with bone, promoting its growth.
While overcoming some problems related to the functional part of the device, there are still
some biological interactions to be studied. By studying the effect of two titanium topographies on
the formation of protein layers (mixed layers containing mucin and albumin) as well as the
influence of these layers on the corrosion behavior of the surfaces it is expected to get a step
forward to understand the interaction between these biologic elements and a denta...
Dental implants have become increasingly common for the management of tooth loss.
Meanwhile, several implants still fail as a permanent solution despite the intense research on this
subject. Failures on these implants are usually related to the loosening of the implant, causing
inflammations, infections, decrease in bone density and release of toxic agents to the human body. On
the bases of these problems are phenomena like corrosion and wear of the material composing the
dental implant.
In this way, it becomes necessary to better understand the mechanisms of corrosion and wear
behind dental implants. The present work will increase the knowledge on the tribocorrosion
mechanisms of titanium as well it will study the influence of a new surface treatment by anodization.
Experimental tests will resemble the conditions presented on the oral...
We present an analysis of leaf shapes and venation patterns based on a new assumption of the way how water flows in plants, together with the assumption that leaf shapes and leaf venation patterns have evolved in time such as to provide easier and easier access to its internal currents (Constructal Law). Then, by minimizing the global resistance to flow we anticipate the number of veins in relation to leaf shape (slenderness and vein insertion angle) and prevalent environmental conditions (represented by the potential for leaf water intake from the atmosphere). We also anticipate that leaves in dry climates will be slender and shorter, and with more veins as compared with those of plants adapted to wet environments. We finish by showing some cases in which the theory describes the characteristic of real leaves closely.
The oral cavity is a complex environment where corrosive substances
from dietary, human saliva and oral biofilms may accumulate in retentive areas
of dental implant systems and prostheses promoting corrosion at their surfaces.
Additionally, during mastication, micro-movements may occur in artificial
joints causing a relative motion between contacting surfaces, leading to wear.
Both processes (wear and corrosion) result in a biotribocorrosion system.
Previous studies have reported the corrosion of titanium in fluoride solutions.
Nevertheless, the biotribocorrosion of titanium in fluoride solutions and in the
presence of biofilms has not yet been reported to the authors’ best knowledge.
Thus, the novelty of this work is to investigate the in-vitro corrosion and wear
behavior of titanium in fluorinated artificial saliva solutions, and in ...
The Al–Mg–Si–Cu family of alloys have been widely used in the automotive industry
due to the high castability (excellent foundry characteristics) promoted by Si presence.
The high strength to weight ratio and the good corrosion resistance are also important
properties normally associated to Al alloys. Nevertheless, in general they possess low
wear resistance. Typically, either age-hardening heat treatments or the addition of SiC
ceramic particles to Al matrix are used to improve the mechanical properties of Al
alloys. Further, by using centrifugal casting technique, the creation of a gradual
decrease of the reinforcing particles volume fraction from the surface to the bulk,
allows the conception of materials with high surface hardness and bulk toughness, this
is functionally graded materials – FGM. Although the presence of SiCp can cha...
