1、 The influence of temperature
Temperature is the most direct environmental factor affecting the electrical resistivity of carbon brush leads. For metal material leads, as the temperature increases, the thermal motion of metal atoms intensifies, and the probability of collision between free electrons and atoms increases during directional movement, resulting in an increase in resistance, that is, the electrical resistivity increases with increasing temperature. For example, the resistivity of copper leads at room temperature is about 1.7 × 10 ⁻⁸Ω· m, and when the temperature rises to 100 ℃, the resistivity increases to about 2.2 × 10 ⁻⁸Ω· m. Conversely, in low-temperature environments, atomic thermal motion weakens, electron collisions decrease, and resistivity decreases accordingly. However, within the conventional operating temperature range of carbon brush leads (-40 ℃ to 120 ℃), this change shows a clear linear pattern.
2、 The influence of humidity
Humidity mainly changes the resistivity by affecting the surface state of the leads. In high humidity environments, the surface of the lead is prone to adsorbing water vapor. If there are small oxide layers or impurities on the surface, water vapor will dissolve or ionize these substances, forming a conductive path that may reduce surface contact resistance to some extent; But when the humidity is extremely high (such as in a condensed state), water vapor will combine with pollutants in the air to form an electrolyte, accelerate the electrochemical corrosion of the lead, cause the surface oxide layer to thicken, and instead increase the electrical resistivity. For example, copper leads that are exposed to a humid environment for a long time will generate green copper rust (alkaline copper carbonate) on the surface, which has poor conductivity and significantly increases the contact resistance of the lead.
3、 The impact of corrosive substances
Corrosive gases (such as sulfur dioxide, hydrogen sulfide, chlorine gas, etc.) or liquids (such as acid-base solutions) in the environment can react chemically with the lead, causing surface corrosion or internal structural damage, thereby changing the electrical resistivity. For example, in a sulfur-containing environment, copper sulfide is generated on the surface of copper leads, which is a high resistance substance that reduces the effective conductive cross-sectional area of the lead and increases its resistivity; If corrosion penetrates deep into the interior, it may also cause local breakage of the lead, forming a "breakpoint resistance" and causing a sharp increase in overall resistivity. In addition, salt spray environments near the seaside or industrial areas can accelerate the oxidation and corrosion of leads, which can also lead to an increase in electrical resistivity.
4、 The impact of dust and pollutants
When pollutants such as dust and oil in the air adhere to the surface of the lead, they can form an insulation layer or increase contact resistance. For example, if metal dust covers the connection between the lead and carbon brush in an industrial workshop, it will hinder current conduction and increase contact resistivity; Organic pollutants such as oil stains will isolate the conductive contact between the leads and external circuits, resulting in an overall increase in resistivity. If pollutants accumulate for a long time and are not cleaned up in a timely manner, they may also absorb moisture, accelerate the corrosion of the leads, and further deteriorate the electrical resistivity performance.
In summary, environmental factors directly or indirectly affect the electrical resistivity of carbon brush leads through temperature effects, surface state changes, chemical corrosion, and pollutant adhesion. In practical applications, it is necessary to select appropriate lead materials and protective measures (such as coating, sealing protection, etc.) based on specific environmental characteristics (such as high temperature, humidity, dust, corrosiveness, etc.) to stabilize their electrical resistivity and ensure the normal operation of the carbon brush system.
